CEREBELLUM-DERIVED GROWTH FACTORS, AND USES RELATED THERETO

Abstract: The present invention relates to erbB receptor ligands, referred to hereinafter as "cerebellum-derived growth factors" or "CDGFs", which proteins have apparently broad involvement in the formation and maintenance of ordered spatial arrangements of differentiated tissues in vertebrates, and can be used to generate and/or maintain an array of different vertebrate tissue both in vitro and in vivo.

Description: Cerebellum-derived Growth Factors, and Uses Related Thereto Government Funding Work described herein was supported by National Institutes of Health Grant NIH EY08397 and NIH NS14506. The United States Government has certain rights in the invention. Background ofthe Invention Pattern formation is the activity by which embryonic cells form ordered spatial arrangements of differentiated tissues. The physical complexity of higher organisms arises during embryogenesis through the interplay of cell-intrinsic lineage and cell-extrinsic signaling. Inductive interactions are essential to embryonic patterning in vertebrate development from the earliest establishment of the body plan, to the patterning of the organ systems, to the generation of diversive cell types during tissue differentiation (Davidson, E., (1990) Development 108: 365-389; Gurdon, J. B., (1992) Cell 68: 185-199; Jessell, T. M. et al., (1992) Cell 68: 257-270). The effects of developmental cell interactions are varied. Typically, responding cells are diverted from one route of cell differentiation to another by inducing cells that differ from both the uninduced and induced states of the responding cells (inductions). Sometimes cells induce their neighbors to differentiate like themselves (homoiogenetic induction); in other cases a cell inhibits its neighbors from differentiating like itself. Cell interactions in early development may be sequential, such that an initial induction between two cell types leads to a progressive amplification of diversity. Moreover, inductive interactions occur not only in embryos, but in adult cells as well, and can act to establish and maintain morphogenetic patterns as well as induce differentiation (J.B. Gurdon (1992) Cell 68:185-199). Many types of communication take place among animal cells during embryogenesis, as well as in the maintenance of tissue in adult animals. These vary from long-range effects, such as those of rather stable hormones circulating in the blood and acting on any cells in the body that possess the appropriate receptors, however distant they are, to the fleeting effects of very unstable neurotransmitters operating over distances of only a few microns. Of particular importance in development is the class of cell interactions referred to above as embryonic induction; this includes influences operating between adjacent cells or in some cases over greater than 10 cell diameters (Saxen et al. (1989) Int J Dev Biol 33:21-48; and Gurdon et al. (1987) Development 99:285-306). Embryonic induction is defined as in interaction between one (inducing) and another (responding) tissue or cell, as a result of which the responding cells undergo a change in the direction of differentiation. This interaction is often considered -* - one of the most important mechanism in vertebrate development leading to differences between cells and to the organization of cells into tissues and organs. Receptor tyrosine kinases are apparently involved in many different process including cellular differentiation, proliferation, embryonic development and, in some cases, neoplastic growth. High affinity binding of specfic soluble or matrix-associated growth factor ligands can cause the activated receptor to associate with a specific repertoire of cytoplasmic singnalling molecules that can lead to a cascade of intracellular signalling resulting in, for example, activation or inactivation of cellular gene programs involved in differentiation and/or growth. Accordingly, peptide growth factors that are ligands for such receptor tyrosine kinases are excellent candidates for intercellular signaling molecules with important developmental roles. Indeed, these ligands are known to have potent effects on a wide variety of cell activities in vitro, including survival, proliferation, differentiation, adhesion, migration and axon guidance. The powerful signaling effects of these molecules are further emphasized by the ability of both the ligands and the receptors, when activated by mutation or overexpression, to become potent oncogenes and cause drastic cellular transformation (reviewed by Cantley et al. (1991) Cell 64:281-302; Schlessinger and Ullrich (1992) Neuron 9:383-391; and Fantl et al. (1993) Annu Rev Biochem 62:453-481). To illustrate, specific developmental roles have been demonstrated for some growth factors or their tyrosine kinase receptors. For example, the c-kit receptor tyrosine kinase, encoded at the mouse W locus (Chabot et al. (1988) Nature 335:88-89; and Geissler et al. (1988) Cell 55:185-192) and its ligand KL, encoded at the mouse SI locus (Flanagan and Leder (1990) Cell 63:185-194; Copeland et al. (1990) Cell 63:175-183; Huang et al. (1990) Cell 63:225-233; and Zsebo et al. (1990) Cell 63:213-224), determine the proliferation, survival, and/or migration of primordial germ cells, hematopoietic stem cells, and neural crest progenitor cells. Other examples are the trk family ligands and receptors, with highly specific functions in the developing mammalian nervous system (Klein et al. (1993) Cell 75:113-122; and Jones et al. (1994) Cell 76:989-999) and the FGF receptor, implicated in Xenopus mesoderm induction (Amaya et al. (1991) Cell 66:251-210). In invertebrates, too, receptor tyrosine kinases and ligands such as sevenless, boss, torso, breathless and let-23 are known to play key roles in processes that range from setting up the primary embryonic axes to specifying the fate of a single cell in the ommatidium (Greenwald and Rubin (1992) Cell 68:271-281; Shilo (1992) Faseb J 6:2915-2922; and Zipursky et al. (1992) Cold Spring Harbor Symp Quant Biol 57:381-389). Taken together, the emerging picture of the developmental functions of receptor tyrosine kinases and their ligands is striking in that these molecules play key roles at all stages of embryonic development, and in a remarkable range of different types of patterning process. The receptor tyrosine kinases can be divided into families based on structural homology and, in at least some cases, obvious shared functional characteristics (Fantl et al. (1993) Annu Rev Biochem 62:453-481). Remarkably, despite a number of members in the erbB family, all of these molecules were initially identified as orphan receptors without known ligands. Summary ofthe Invention The present invention relates to the discovery of a family of novel erbB receptor ligands, referred to hereinafter as "cerebellum-derived growth factors" or "CDGFs", which proteins have apparently broad involvement in the formation and maintenance of ordered spatial arrangements of differentiated tissues in vertebrates, and can be used to generate and/or maintain an array of different vertebrate tissue both in vitro and in vivo. In general, the invention features CDGF polypeptides, e.g., preferably a substantially pure preparation of a CDGF polypeptide, or a recombinantly expressed CDGF polypeptide. In preferred embodiments the polypeptide has a biological activity associated with its binding to an erbB receptor, e.g., it retains the ability to bind to a erbB2, erbBS or erbB4 receptor, though it may be able to either agnoize or antagonize signal transduction by the erbB receptor. The polypeptide can include amino acid sequences be identical or homologous to the mammalian CDGF polypeptide (CDGF-1) shown in SEQ ID No: 2. Likewise, the polypeptide can include amino acid sequences identical or homologous to the mammalian CDGF polypeptides (CDGF-2) shown in SEQ ID No: 4 or 7. For instance, the polypeptide preferably has an amino acid sequence at least 70% homologous to the amino acid sequence in any of SEQ ID Nos: 2, 4 and 7, though higher sequence homologies of, for example, 80%, 85%, 90% or 95% are also contemplated. The polypeptide can comprise the full length protein represented in SEQ ID No: 2 or 4, or it can comprise a fragment of that protein, which fragment may be, for instance, at least 5, 10, 20, 50 or 100 amino acids in length. An exemplary fragments are shown in SEQ ID No. 5 or 7. A preferred CDGF polypeptide includes an EGF-like motif, such as an EGF-like motif represented in the general formula CNETAKSYCVNGGVCYYIEGINQLSCKCPXGXXGXRC, e.g., including Cys253 through Cys289 of SEQ ID Nos: 2 or 4, or Cysl01-Cysl37 of SEQ ID No. 1, or a sequence homologous thereto. An even more preferred EGF-like domain is represented by the general formula KCNETAKSYCVNGGVCYYIEGINQLSCKCPXGXXGXRCLEKLPLRL or KCNETAKSYCVNGGVCYYIEGINQLSCKCPXGXXGXRCQQFAMVNF. Yet another preferred CDGF polypeptide includes a core sequence motif, such as a polypeptide including amino acid residues corresponding to residues 143-314 of SEQ ID No. 2, or amino acid residues 143-330 of SEQ ID No. 4, or amino acid residues 1-182 of SEQ ID No. 7. Exemplary CDGF-1 polypeptides include: a membrane associated polypeptide having a core amino acid sequence with a molecular weight of about 78-83kD, e.g., about 82kD with a signal peptide, and about 79kD without a signal peptide; a soluble CDGF-1 polypeptide having a core amino acid sequence with a molecular weight of about 31-36kD, e.g., about 35kD with a signal peptide, and about 32kD without a signal peptide. Exemplary CDGF-2 polypeptides include a soluble CDGF-2 polypeptide having a core amino acid sequence with a molecular weight of about 32-38kD, e.g., about 36kD with a signal peptide, and about 34kD without a signal peptide. The polypeptide can be glycosylated, or, by virtue of the expression system in which it is produced, or by modification of the protein sequence to preclude glycosylation, reduced carbohydrate analogs can be provided. Likewise, CDGF polypeptides can be generated which lack an endogenous signal sequence (though this is typically cleaved off even if present in the pro-form of the protein), or which lack a transmembrane and cytoplasmic domain. In the instance ofthe latter, the removal of these C-terminal domains may result in a soluble form of the protein. In particular, polypeptides which lack amino acid residues C- terminal to Leu317 of SEQ ID No: 2 (the equivalent of CDGF-1 truncated at the transmembrane domain) are preferred, though polypeptides which are truncated anywhere between the equivalent of Cys289 and Thr318 of SEQ ID No: 2 are also contemplated. It is believed that the CDGF-2 mature amino acid sequence, which apparently lacks both a transmembrane domain and a cyctoplasmic domain, is soluble under certain conditions without further manipulation ofthe polypeptide sequence. Furthermore, the CDGF polypeptide can include a secretion signal sequence, though mature CDGF polypeptides may lack the secretion signal sequence by virtue of being expressed in a cell competent to remove the signal sequence. Exemplary mature forms ofthe subject CDGF poypeptides lack from 5 to 23 amino acid residues from the N-terminus ofthe polypeptide. In a preferred embodiment, a mature, soluble CDGF-1 polypeptide has an amino acid sequence corresponding to Ser24-Lys-314 of SEQ ID No. 2, and a mature, soluble CDGF-2 polypeptide has an amino acid sequence corresponding to Ser24-Asn330 of SEQ ID No. 4. Moreover, as described below, the polypeptide can be either an agonist (e.g. mimics), or alternatively, an antagonist of a biological activity of a naturally occuring form of the protein, e.g., the polypeptide is able to modulate growth and/or differentiation of a cell which expresses an erbB receptor. In a preferred embodiment, a peptide having at least one biological activity of the subject polypepide may differ in amino acid sequence from the sequence in SEQ ID No: 2, A, 5 or 7, but such differences result in a modified protein which functions in the same or similar manner as a native CDGF protein or which has the same or similar characteristics of a native CDGF protein. However, homologs of the naturally occuring protein are contemplated which are antagonistic of the normal physiological role of the naturally occurring protein. For example, the homolog may be capable of interfering with the ability of naturally-occurring forms of CDGF to modulate gene expression, e.g. of developmentally or growth regulated genes. In yet other preferred embodiments, the CDGF protein is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to CDGF, e.g. the second polypeptide portion is glutathione- S-transferase, e.g. the second polypeptide portion is an enzymatic activity such as alkaline phosphatase, and is a reagent for detecting CDGF receptors. In another embodiment, the second polypeptide sequence provides a cytotoxic or cytostatic protein which can be targeted to a cell by binding ofthe CDGF portion to its cognate receptors. Yet another aspect of the present invention concems an immunogen comprising a CDGF polypeptide in an immunogenic preparation, the immunogen being capable of eliciting an immune response specific for a CDGF polypeptide; e.g. a humoral response, e.g. an antibody response; e.g. a cellular response. In preferred embodiments, the immunogen comprising an antigenic determinant, e.g. a unique determinant, from a protein represented by SEQ ID No. 2 , SEQ ID No. 4 or SEQ ID No. 7. A still further aspect of the present invention features an antibody preparation specifically reactive with an epitope of the CDGF immunogen. Preferred antibodies can distinguish between CDGF proteins and neuregulins (e.g., with k a 's for CDGF proteins, relative to neuregulin proteins, of at least one, two or three orders of magnitude greater). Another aspect of the present invention provides an isolated nucleic acid having a nucleotide sequence which encodes a CDGF polypeptide. In preferred embodiments: the encoded polypeptide specifically binds an erbB receptor protein and/or is able to either agnoize or antagonize signal transduction events mediated by the erbB receptor. The coding sequence of the nucleic acid can comprise a sequence which can be identical to the coding sequence (or a portion thereof) ofthe cDNA shown in SEQ ID No: 1, 3 or 6, or it can merely be homologous to that sequence. For instance, the CDGF encoding sequence preferably has a sequence at least 70% homologous to a nucleotide sequence of any of SEQ ID Nos: 1, 3 and 6, though higher sequence homologies of, for example, 80%, 90% or 95% are also contemplated. The polypeptide encoded by the nucleic acid can comprise the amino acid sequence represented in SEQ ID No: 2, 4 or 7, which is the full length protein, or it can comprise a fragment of that nucleic acid, which fragment may be, for instance, at least 5, 10, 20, 50 or 100 amino acids in length (such as the CDGF-2 fragment of SEQ ID No. 5). A preferred CDGF polypeptide includes an EGF-like motif, such as an EGF-like motif represented in the general formula CNETAKSYCVNGGVCYYIEGINQLSCKCPXG- XXGXRC The polypeptide encoded by the nucleic acid can be either an agonist (e.g. mimics), or altematively, an antagonist of a biological activity of a naturally occuring form of the protein. - ά - Furthermore, in certain preferred embodiments, the subject CDGF nucleic acid will include a transcriptional regulatory sequence, e.g. at least one of a transcriptional promoter or transcriptional enhancer sequence, which regulatory sequence is operably linked to the CDGF gene sequence. Such regulatory sequences can be used in to render the CDGF gene sequence suitable for use as an expression vector. In a further preferred embodiment, the nucleic acid hybridizes under stringent conditions to a nucleic acid probe corresponding to at least 12 consecutive nucleotides of SEQ ID No: 1; preferably to at least 20 consecutive nucleotides of SEQ ID No: 1; more preferably to at least 40 consecutive nucleotides of SEQ ID No: 1. For instance, nucleic acid are provided which specifically hybridize to nucleotides 180-605 (corresponding to Spacer 1) and/or nucleotides 870-929 (corresponding to Spacer 2) of SEQ ID No. 1, or sequences complementary thereto. In yet a further preferred embodiment, the nucleic acid hybridizes under stringent conditions to a nucleic acid probe corresponding to at least 12 consecutive nucleotides of SEQ ID No: 3; preferably to at least 20 consecutive nucleotides of SEQ ID No: 3; more preferably to at least 40 consecutive nucleotides of SEQ ID No: 3. For instance, nucleic acid are provided which specifically hybridize to nucleotides 1-426 (corresponding to Spacer 1) and/or nucleotides 691-750 (corresponding to Spacer 2) of SEQ ID No. 1, or sequences complementary thereto. In still a further preferred embodiment, the nucleic acid hybridizes under stringent conditions to a nucleic acid probe corresponding to at least 12 consecutive nucleotides of SEQ ID No: 6; preferably to at least 20 consecutive nucleotides of SEQ ID No: 6; more preferably to at least 40 consecutive nucleotides of SEQ ID No: 6. For instance, nucleic acid are provided which specifically hybridize to nucleotides 1-100 (corresponding to a portion of Spacer 2) of SEQ ID No. 1, or sequences complementary thereto. The invention also features transgenic non-human animals, e.g. mice, rats, rabbits, chickens, frogs or pigs, having a transgene, e.g., animals which include (and preferably express) a heterologous form of a CDGF gene described herein, or which misexpress an endogenous CDGF gene, e.g., an animal in which expression ofthe subject CDGF protein is disrupted. Such a transgenic animal can serve as an animal model for studying cellular and tissue disorders comprising mutated or mis-expressed CDGF alleles or for use in drug screening. The invention also provides a probe/primer comprising a substantially purified oligonucleotide, wherein the oligonucleotide comprises a region of nucleotide sequence which hybridizes under stringent conditions to at least 10 consecutive nucleotides of sense or antisense sequence of SEQ ID No: 1, 3 and/or 6, or naturally occurring mutants thereof. In preferred embodiments, the probe/primer further includes a label group attached thereto and able to be detected. The label group can be selected, e.g., from a group consisting of radioisotopes, fluorescent compounds, enzymes, and enzyme co-factors. Probes of the invention can be used as a part of a diagnostic test kit for identifying transformed cells, such as for detecting in a sample of cells isolated from a patient, a level of a nucleic acid encoding the subject CDGF proteins; e.g. measuring the CDGF mRNA level in a cell, or determining whether the genomic CDGF gene has been mutated or deleted. Preferably, the oligonucleotide is at least 10 nucleotides in length, though primers of, for example, 20, 30, 50, 100, or 150 nucleotides in length are also contemplated. In yet another aspect, the invention provides an assay for screening test compounds for inhibitors, or altematively, potentiators, of an interaction between CDGF and an erbB receptor. An exemplary method includes the steps of (i) combining an erbB receptor, an CDGF polypeptide, and a test compound, e.g., under conditions wherein, but for the test compound, the CDGF protein and the erbB receptor are able to interact; and (ii) detecting the formation of a complex which includes the CDGF protein and the receptor. A statistically significant change, such as a decrease, in the formation of the complex in the presence of a test compound (relative to what is seen in the absence ofthe test compound) is indicative of a modulation, e.g., inhibition, ofthe interaction between CDGF and the receptor. For example, primary screens are provided in which the CDGF protein and the receptor protein are combined in a cell-free system and contacted with the test compound; i.e. the cell-free system is selected from a group consisting of a cell lysate and a reconstituted protein mixture. Another aspect of the present invention relates to a method of inducing and/or maintaining a differentiated state, causing proliferation, and/or enhancing survival of a cell responsive to a CDGF protein, by contacting the cells with a CDGF agonist or a CDGF antagonist. For example, the present method is applicable to cell culture technique, such as in the culturing of neuronal and other cells whose survival or differentiative state is dependent on CDGF function. Moreover, CDGF agonists and antagonists can be used for therapeutic intervention, such as to enhance survival and maintenance of neurons and other neural cells in both the central nervous system and the peripheral nervous system, as well as to influence other vertebrate organogenic pathways, such as other ectodermal patteming, as well as certain mesodermal and endodermal differentiation processes. Another aspect ofthe present invention provides a method of determining if a subject, e.g. a human patient, is at risk for a disorder characterized by unwanted cell proliferation or abherent control of differentiation. The method includes detecting, in a tissue of the subject, the presence or absence of a genetic lesion characterized by at least one of (i) a mutation of a gene encoding a CDGF protein, e.g. represented in SEQ ID No: 2, 4 or 7, or a homolog thereof; or (ii) the mis-expression of a CDGF gene. In preferred embodiments, detecting the genetic lesion includes ascertaining the existence of at least one of: a deletion of one or more nucleotides from a CDGF gene; an addition of one or more nucleotides to the gene, a substitution of one or more nucleotides of the gene, a gross chromosomal rearrangement of the gene; an alteration in the level of a messenger RNA transcript ofthe gene; the presence of a non-wild type splicing pattem of a messenger RNA transcript of the gene; or a non-wild type level ofthe protein. For example, detecting the genetic lesion can include (i) providing a probe/primer including an oligonucleotide containing a region of nucleotide sequence which hybridizes to a sense or antisense sequence of a CDGF gene, e.g. the nucleic acid represented in SEQ ID No: 1, 3, 5 or 7, or naturally occurring mutants thereof or 5 Or 3' flanking sequences naturally associated with the CDGF gene; (ii) exposing the probe/primer to nucleic acid of the tissue; and (iii) detecting, by hybridization of the probe/primer to the nucleic acid, the presence or absence of the genetic lesion; e.g. wherein detecting the lesion comprises utilizing the probe/primer to determine the nucleotide sequence of the CDGF gene and, optionally, of the flanking nucleic acid sequences. For instance, the probe/primer can be employed in a polymerase chain reaction (PCR) or in a ligation chain reaction (LCR). In altemate embodiments, the level of CDGF protein is detected in an immunoassay using an antibody which is specifically immunoreactive with a CDGF protein. The practice of the present invention will employ, unless otherwise indicated, conventional techniques of cell biology, cell culture, molecular biology, transgenic biology, microbiology, recombinant DNA, and immunology, which are within the skill of the art. Such techniques are explained fully in the literature. See, for example, Molecular Cloning A Laboratory Manual, 2nd Ed., ed. by Sambrook, Fritsch and Maniatis (Cold Spring Harbor Laboratory Press: 1989); DNA Cloning, Volumes I and II (D. N. Glover ed., 1985); Oligonucleotide Synthesis (M. J. Gait ed., 1984); Mullis et al. U.S. Patent No: 4,683,195; Nucleic Acid Hybridization (B. D. Hames & S. J. Higgins eds. 1984); Transcription And Translation (B. D. Hames & S. J. Higgins eds. 1984); Culture Of Animal Cells (R. I. Freshney, Alan R. Liss, Inc., 1987); Immobilized CeUs And Enzymes (IRL Press, 1986); B. Perbal, A Practical Guide To Molecular Cloning (1984); the treatise, Methods In Enzymology (Academic Press, Inc., N.Y.); Gene Transfer Vectors For Mammalian Cells (J. H. Miller and M. P. Calos eds., 1987, Cold Spring Harbor Laboratory); Methods In Enzymology, Vols. 154 and 155 (Wu et al. eds.), Immunochemical Methods In Cell And Molecular Biology (Mayer and Walker, eds., Academic Press, London, 1987); Handbook Of Experimental Immunology, Volumes I-IV (D. M. Weir and C. C. Blackwell, eds., 1986); Manipulating the Mouse Embryo, (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1986). Other features and advantages of the invention will be apparent from the following detailed description, and from the claims. Description ofthe Drawings Figure IA illustrates the sequences of rat CDGF cDNAs; in particular, the deduced amino acid sequence of rat CDGF-1 and the EGF-like domain of CDGF-2. For CDGF-1, arrowed underline marks the putative signal sequence; The immunoglobulin-like domain is outlined by a dashed box; Solid box indicates the EGF-like domain, the six characteristic cysteines of EGF-like domain are shown with asterisks; Potential N-glycosylation sites are indicated with arrowheads; The putative transmembrane region is underlined. An arrow points to the potential proteolytic site. For CDGF-2, the additional exon of 77 nucleotides is underlined between arrows; The EGF-like domain is outlined with a solid box. Figure IB is an amino acid sequence alignment between portions of CDGF-1 and CDGF-2, illustrating the splicing variation between the two transcriptional products. Figure IC is a schematic representation of the structural domains and motifs of CDGF-1. Figures 2A and 2B illustrate the sequence similarity between CDGFs and related proteins. Figure 2a: Amino acid sequences alignment of CDGF-1, heregulinβl (human), and the N-terminus of GGFII (human). Dots indicate gaps in sequence alignment. The Ig-like domains are marked by a box. Heavy black box indicates the EGF-like domains. The putative transmembrane domains are underlined. Identical amino acid residues are highlighted with black background and similar amino acid residues are shaded in gray. Figure 2B: Sequence comparison of the EGF-like domains of CDGFs, selected members of neuregulins (HRGαl, human heregulinαl; HRGβl, human heregulinβl; ARIA, chicken.), and rat epidermal growth factor. Amino acid residues common to two or more genes are highlighted by black background. The six characteristic cysteine residues are marked by asterisks. Figures 3 A and 3B illustrate the expression of CDGF transcripts in rat tissues. Figure 3 A: Northern blot analysis with poly(A)+ RNA samples, approximately 2 μg of poly(A)+ RNA were loaded to each lane. Three detected bands (3, 3.8, 6 kb) are marked on the side. Lv, liver; L, lung; M, skeletal muscle; B, brain; Sc, spinal cord; Figure 3B: RT-PCR analysis of CDGF mRNAs expression in rat tissues. Figures 4A and 4B demonstrate that recombinant CDGF-1 protein induces tyrosine phosphorylation of erbB family receptors through erbB4. Figure 4 A: CDGF-1 induces tyrosine phosphorylation of erbB2, erbB3, and erbB4 in MB-MDA453 and T47D cell lines. Figure 4B: CDGF-1 signaling through erbB4 receptors. CDGF-1 were tested on cell lines transfected with defined members of erbB receptors. Only cells with erbB4 receptors were activated. El, EGF receptor; E2, erbB2; E3, erbB3; E4, erbB4. Immunoprecipiting antibodies (IP Ab): al, anti-EGF receptor; a2, anti-erbB2; a3, anti-erbB3; a4, anti-erbB4. B, betacellulin; Hrg, Heregulinβl EGF-like domain; TGFα; TGFα; CM, CDGF-1 conditioned medium; - , negative control medium. Detailed Description ofthe Invention Growth factors that are ligands for receptor tyrosine kinases control a wide variety of cellular activities. Virtually all of these ligands that have been characterized are known to have important functions in development and/or physiology and, in at least some cases, to be useful clinically. The existence of many additional, hitherto unidentified ligands is implied by the discovery over the last few years of a large number of tyrosine kinases that appear by their stracture to be cell surface receptors, yet have no known ligand. The rapid discovery of these orphan receptors has been possible mostly through the application of techniques such as polymerase chain reaction that take advantage of the strong sequence conservation of the kinase catalytic domain. However, in contrast, identification of the ligands for the receptor tyrosine kinases has been more problematic. It is also generally accepted that intercellular signaling plays a key role throughout vertebrate development. A great deal of progress has been made in understanding signals that mediate some of the earliest patteming events. However, little is known about the signals that regulate many ofthe important events that unfold as gastrulation and early organogenesis proceed, particularly the cell-cell signaling molecules that control the expression of gene programs. Protein tyrosine kinase receptors, such as members ofthe erbB family of receptors (e.g., erbBl, erbB2, erbB3, erbB4, etc.) have been especially intriguing in this regard, particularly because the expression domains for several of these receptors include these stages of development. The expression pattems determined for some of the erbB family receptors have implied important roles for these molecules in early vertebrate development. In particular, the timing and pattem of expression the receptors during the phase of gastrulation and early organogenesis has suggested functions for these receptors in the important cellular interactions involved in patteming the embryo at this stage. Moreover, erbB receptors have been implicated, by their pattem of expression, in the development and maintenance of nearly every tissue in the embryonic and adult body. For instance, erbB receptors have been detected throughout the nervous system, the testes, the cartilaginous model of the skeleton, tooth primordia, the infundibular component of the pituitary, various epithelia tissues, lung, pancreas, liver and kidney tissues. Observations such as this have been indicative of important and unique roles for erbB family of receptor kinases in development and physiology, but further progress in understanding their action has been severely limited by the lack of information on their ligands. To date, only a few ligands have been identified. For instance, it has been recently reported that a 45kD protein heregulin-α (HRG-α) has been cloned from an mRNA-derived MDA-MB231 cell library. In addition, several complementary DNA clones encoding related HRGs were also identified, all the HRGs being similar to some extent to proteins in the epidermal growth factor (EGF) family (Holmes et al. 1992 Nature 256:1205). It has also v/- been reported that a 44kD glycoprotein secreted by transformed rat fibroblasts, termed Neu differentiation factor (NDF), has been cloned and expressed (Wen et al. 1992 Cell 69:559), and binds to an erbB receptor. Other molecules which have been identified as erbB ligands include the acetyichohne receptor inducing activity ("ARIA", Corfas et al. (1993) PNAS 90:1624-1628) and glial growth factor (GGF, Marchionni et al. (1993) Nature 362:312-328). As described in the appended examples, a gene encoding novel erbB receptor ligands has been identified, and various of the transcripts encoded by this gene have been cloned. The gene is termed herein "cerebellum-derived growth factor" (CDGF). The gene product of the CDGF gene, of which at least two isoforms exist, shares only about 50 percent homology with any of the ARIA, heregulin, NDF or GGF proteins. Based on the structure of the transcripts produced from the CDGF gene, a common feature among the various mammalian CDGF isoforms is the presence of an EGF-like domain, e.g., having a sequence identical or homologous to the EGF-like domain consensus sequence CNETAKSYCVNGGVCYYI- EGINQLSCKCPXGXXGXRC. Moveover, CDGF interacts with certain erbB receptors. For instance, recombinant forms of the CDGF-1 protein was produced, with the results indicate that the molecule can bind to, and induce tyrosine phosphorylation ofthe erbB4 protein. In addition to identifying this ligand and homologs thereof, the spatial distribution of expression of the protein in a number of different tissues has been carried out, and suggest that it that CDGF is of central importance in development and maintance of a variety of both neural and non-neural tissue. Given the apparent role of the CDGF proteins in mediating inductive signals between tissues, the present data suggests that this family of proteins are important therapeutic targets for modulating growth and developmental gene programs. For example, binding of a CDGF polypeptide of the present invention with an erbB receptor can be important for initiating and establishing diverse programs of growth or differentiation; as well as for providing a mechanism to ensure developmentally coordinated tissue patterning. Moreover, it is suggested that certain erbB receptors, e.g. the erbB2 and/or erbB4 receptors, may also play a role in tumorogenesis. Consequently, the interaction of an erbB receptor with certain of the subject CDGF polypeptides may be significant in the modulation of cellular homeostasis, in the control of organogenesis, or in the maintenance of differentiated tissues, as well as in the development of lymphocytic leukemias and other neoplastic disorders. Accordingly, certain aspects of the present invention relate to diagnostic and therapeutic assays and reagents for detecting and treating disorders involving abherent expression ofthe CDGF gene. Moreover, drug discovery assays are provided for identifying agents which can modulate the binding of a CDGF protein with an erbB receptor. Such agents can be useful therapeutically to alter the growth and/or differentiation of a cell. Other aspects ofthe invention are described below or will be apparent to those skilled in the art in light ofthe present disclosure. For convience, certain terms employed in the specfication, examples, and appended claims are collected here. The term "CDGF polypeptide" refers to a family of polypeptides characterized at least in part by being identical or sharing a degree of sequence homology with all or a portion of the polypeptides represented in SEQ ID Nos. 2, A, 5 and/or 7. The CDGF polypeptides can be cloned or purified from any of a number of eukaryotic organisms, especially vertebrates, and particularly mammals (including humans). Moreover, other CDGF polypeptides can be generated according to the present invention, which polypeptides do not ordinarily exist in nature, but rather are generated by non-natural mutagenic techniques. From analysis of various clones isolated by protocols described in the appended examples, the CDGF proteins are inclusive of at least two altemate splicing forms. The transcript corresponding to the "CDGF-1" form provides an open reading frame which encodes a protein (see Figure IC) having an extracellular domain (Metl-Lys314 of SEQ ID No. 2), a transmembrane domain (Thr318-Lys339 of SEQ ID No. 2), and a cytoplasmic domain (Thr340-Leu754 of SEQ ID No. 2). A dibasic sequence (K314/R315) is located adjacent to the transmembrane domain, indicating that proteolytic cleavage and release ofthe extracellular domain is likely. The open reading frame of the "CDGF-2" transcript, on the other hand, encodes a protein which is truncated shortly after the EGF-like motif in the extracellular domain, presumably producing a protein which, by lacking a transmembrane domain and a cytoplasmic domain, is likely a soluble form of the protein. It is noted in Figure IB that the insertion of a 77 nuclotide sequence gives rise to frame shift just 3' prime to the end of the EGF-like domain, with a stop codon occurring in-frame shortly thereafter. A number of features of this family of proteins can be observed from comparison of various CDGF polypeptides with each other and with other erbB receptor ligands. In particular, it is noted that the ectodomains ofthe CDGF proteins contain six cysteine residues which are apparently conserved with approximately the same characteristic spacing within the primary sequence of each of the known erbB receptor ligands. This "EGF-like" motif may represent a fragment which retains certain biological activities ofthe full length (mature) protein, such as, for example, the ability to bind an erbB receptor. In exemplary CDGF polypeptides, the EGF-like motif is represented by residues Cys253-Cys289 of SEQ ID No. 2 (rat CDGF-1) and SEQ ID No. 4 (rat CDGF-2), and Cysl01-Cysl37 of SEQ ID No. 7 (human CDGF-2). In addition to the EGF-like domain, both CDGF proteins identified contain an immunoglobulin-like domain (Thrl43-Val230), as well as two stretches of amino acid residues in the amino terminal half of the extracellular domain, referred to herein as - Ith ' "spacer-1", corresponding to Metl-Alal42 of SEQ ID Nos. 2 or 4, and "spacer-2", corresponding to Arg231-Arg251of SEQ ID Nos. 2 or 4 (see Figure IC). In addition to these features which characterize the extracellular domain of CDGF, the full length protein can also include a transmembrane domain and a cytoplasmic domain. The cysteinyl-bounded core amino acid sequence of the EGF family of mitogens has the consensus sequence CY1CY2CY3CY4CY5C, where C is a cysteine, Y | represents 7 amino acids which can be the same or different, Y2 represents 4 to 5 amino acids which can be the same or different, Y3 represents 10 to 13 amino acids which can be the same or different, Y4 represents any amino acid, and Y5 represents 8 amino acids which can be the same or different, and is generally 36-40 residues in length. Based on this general arrangement of cysteine residues, a closely related motif, termed EGF-like motif, has been identified in a number of proteins. As used herein, an "EGF-like" amino acid sequence is represented by the general formula CX1CX2CX3CX4CX5C, where C is a cysteine, X\ represents 4 to 14 amino acids which can be the same or different, X2 represents 3 to 8 amino acids which can be the same or different, X3 represents 4 to 14 amino acids which can be the same or different, X4 is any amino acid, and X5 represents 8 to 14 amino acids which can be the same or different. Finally, co- and post-translational modified forms of CDGF polypeptides are contemplated by the present invention. A "mature" CDGF polypeptide refers to a CDGF polypeptide which lacks a signal sequence (e.g., a peptidyl portion which causes extracellular secretion of at least a portion ofthe protein). A "glycosylated" CDGF polypeptide is a CDGF polypeptide having a covalent linkage with a glycosyl group (e.g. a derivatized with a carbohydrate). For instance, the exemplary CDGF-1 and CDGF-2 proteins contain potential Asn-linked glycosylation sites. To generate an unglycosylated CDGF polypeptide, the polypeptide can be expressed in a system which is defective for glycosylation, such as a bacterial cell. Altematively, an existing glycosylation site can be mutated to preclude carbohydrate attachment. Likewise, new glycosylation sites, such as for N-linked or O-linked glycosylation, can be added by recombinant techniques. As used herein, the terms "erbB receptor" or "erbB-type receptor" refer to a class of receptor tyrosine kinases, comprising at least three paralogous genes, though many more orthologs exist within this class, e.g. homologs from different species. The erbB receptors, in general, are a discrete group of receptors related by homology and easily reconizable, e.g., they are typically characterized by an extracellular domain containing a characteristic spacing of cysteine residues, a hydrophobic transmembrane domain, and an intracellular region containing a highly conserved tyrosine kinase domain. Exemplary erbB receptors include the erbB2, erbB3 and erbB4 receptors. The term "erbB receptor" refers to the membrane form of the receptor protein, as well as soluble extracellular fragments which retain the ability to bind the ligand(s) ofthe present invention. The term "ortholog" refers to genes or proteins which are homologs via speciation, e.g., closely related and assumed to have common descent based on structural and functional considerations. Orthologous proteins function as recognizably the same activity in different species. The term "paralog" refers to genes or proteins which are homologs via gene duplication, e.g., duplicated variants of a gene within a genome. See also, Fritch, WM (1970) Syst Zool 19:99-113. The phrases "modifies cellular activities" and "modulates cellular activities", with respect to the biological activity of the subject CDGF polypeptides, refers to changes which occur in a cell due to activation of intracellular signals, e.g., primary or secondary, by CDGF interaction with other cellular proteins. For example, such cellular activities which may be affected by CDGF include proliferation, differentiation or survival of a cell, as well as cell- cell adhesion and other alterations in phenotype. In one aspect, the cellular activities which can be modified by a CDGF polypeptide pertain to maintenance of neuronal connections. In general, the cellular modifications can be the relatively-direct biochemical consequence of signal transduction events, or can be caused more indirectly, such as CDGF dependent activation or inactivation of particular genes or gene programs. A CDGF polypeptide which "modifies" cellular activities can refer to homologs which either mimic (e.g., agonize) or inhibit (e.g., antagonize) the normal response of a cell to the wild-type form ofthe protein. As used herein, the term "nucleic acid" refers to polynucleotides such as deoxyribonucleic acid (DNA), and, where appropriate, ribonucleic acid (RNA). The term should also be understood to include, as equivalents, analogs of either RNA or DNA made from nucleotide analogs, and, as applicable to the embodiment being described, single (sense or antisense) and double-stranded polynucleotides. As used herein, the term "gene" or "recombinant gene" refers to a nucleic acid comprising an open reading frame encoding a CDGF polypeptide of the present invention, including both exon and (optionally) intron sequences. A "recombinant gene" refers to nucleic acid encoding a CDGF polypeptide and comprising CDGF-encoding exon sequences, though it may optionally include intron sequences which are either derived from a chromosomal CDGF gene or from an unrelated chromosomal gene. An exemplary recombinant gene encoding a subject CDGF polypeptide is represented by SEQ ID No: 1; yet another is represented by SEQ ID No: 3, still another is represented by SEQ ID No: 5. The term "intron" refers to a DNA sequence present in a given CDGF gene which is not translated into protein and is generally found between exons. -V5-- As used herein, the term "transfection" means the introduction of a nucleic acid, e.g., an expression vector, into a recipient cell by nucleic acid-mediated gene transfer. "Transformation", as used herein, refers to a process in which a cell's genotype is changed as a result of the cellular uptake of exogenous DNA or RNA, and, for example, the transformed cell expresses a recombinant form of a CDGF polypeptide or, where anti-sense expression occurs from the transferred gene, the expression of a naturally-occurring form of the CDGF protein is disrupted. As used herein, the term "vector" refers to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. One type of preferred vector is an episome, i.e., a nucleic acid capable of extra-chromosomal replication. Preferred vectors are those capable of autonomous replication and/expression of nucleic acids to which they are linked. Vectors capable of directing the expression of genes to which they are operatively linked are referred to herein as "expression vectors". In general, expression vectors of utility in recombinant DNA techniques are often in the form of "plasmids" which refer to circular double stranded DNA loops which, in their vector form are not bound to the chromosome. In the present specification, "plasmid" and "vector" are used interchangeably as the plasmid is the most commonly used form of vector. However, the invention is intended to include such other forms of expression vectors which serve equivalent functions and which become known in the art subsequently hereto. "Transcriptional regulatory sequence" is a generic term used throughout the specification to refer to DNA sequences, such as initiation signals, enhancers, and promoters, which induce or control transcription of protein coding sequences with which they are operably linked. In preferred embodiments, transcription of a recombinant CDGF gene is under the control of a promoter sequence (or other transcriptional regulatory sequence) which controls the expression of the recombinant gene in a cell-type in which expression is intended. It will also be understood that the recombinant gene can be under the control of transcriptional regulatory sequences which are the same or which are different from those sequences which control transcription ofthe naturally-occurring form ofthe CDGF protein. As used herein, the term "tissue-specific promoter" means a DNA sequence that serves as a promoter, i.e., regulates expression of a selected DNA sequence operably linked to the promoter, and which effects expression of the selected DNA sequence in specific cells of a tissue, such as cells of neural origin, e.g. neuronal cells. The term also covers so-called "leaky" promoters, which regulate expression of a selected DNA primarily in one tissue, but cause expression in other tissues as well. As used herein, a "transgenic animal" is any animal, preferably a non-human mammal, bird or an amphibian, in which one or more of the cells of the animal contain heterologous nucleic acid introduced by way of human intervention, such as by transgenic techniques well known in the art. The nucleic acid is introduced into the cell, directly or indirectly by introduction into a precursor of the cell, by way of deliberate genetic manipulation, such as by microinjection or by infection with a recombinant vims. The term genetic manipulation does not include classical cross-breeding, or in vitro fertilization, but rather is directed to the introduction of a recombinant DNA molecule. This molecule may be integrated within a chromosome, or it may be extrachromosomally replicating DNA. In the typical transgenic animals described herein, the transgene causes cells to express a recombinant form of the subject CDGF protein, e.g. either agonistic or antagonistic forms. However, transgenic animals in which the recombinant CDGF gene is silent are also contemplated, as for example, the FLP or CRE recombinase dependent constructs described below. The "non-human animals" of the invention include vertebrates such as rodents, non-human primates, sheep, dog, cow, chickens, amphibians, reptiles, etc. Preferred non-human animals are selected from the rodent family including rat and mouse, most preferably mouse, though transgenic amphibians, such as members ofthe Xenopus genus, and transgenic chickens can also provide important tools for understanding, for example, embryogenesis. The term "chimeric animal" is used herein to refer to animals in which the recombinant gene is found, or in which the recombinant is expressed in some but not all cells of the animal. The term "tissue-specific chimeric animal" indicates that the recombinant CDGF gene is present and/or expressed in some tissues but not others. As used herein, the term "transgene" means a nucleic acid sequence (encoding, e.g., a CDGF polypeptide), which is partly or entirely heterologous, i.e., foreign, to the transgenic animal or cell into which it is introduced, or, is homologous to an endogenous gene of the transgenic animal or cell into which it is introduced, but which is designed to be inserted, or is inserted, into the animal's genome in such a way as to alter the genome of the cell into which it is inserted (e.g., it is inserted at a location which differs from that ofthe natural gene or its insertion results in a knockout). A transgene can include one or more transcriptional regulatory sequences and any other nucleic acid, such as introns, that may be necessary for optimal expression of a selected nucleic acid. As is well known, genes for a particular polypeptide may exist in single or multiple copies within the genome of an individual. Such duplicate genes may be identical or may have certain modifications, including nucleotide substitutions, additions or deletions, which all still code for polypeptides having substantially the same activity. The term "DNA sequence encoding a CDGF polypeptide" may thus refer to one or more genes within a particular individual. Moreover, certain differences in nucleotide sequences may exist between individual organisms, which are called alleles. Such allelic differences may or may not result in differences in amino acid sequence ofthe encoded polypeptide yet still encode a protein with the same biological activity. "Homology" refers to sequence similarity between two peptides or between two nucleic acid molecules. Homology can be determined by comparing a position in each -/7 - sequence which may be aligned for purposes of comparison. When a position in the compared sequence is occupied by the same base or amino acid, then the molecules are homologous at that position. A degree of homology between sequences is a function of the number of matching or homologous positions shared by the sequences. An "unrelated" or "non-homologous" sequence shares less than 10 percent identity, though preferably less than 5 percent identity, with a CDGF sequence ofthe present invention. "Cells," "host cells" or "recombinant host cells" are terms used interchangeably herein. It is understood that such terms refer not only to the particular subject cell but to the progeny or potential progeny of such a cell. Because certain modifications may occur in succeeding generations due to either mutation or environmental influences, such progeny may not, in fact, be identical to the parent cell, but are still included within the scope of the term as used herein. A "chimeric protein" or "fusion protein" is a fusion of a first amino acid sequence encoding the subject CDGF polypeptide with a second amino acid sequence defining a domain foreign to and not substantially homologous with any domain of the CDGF protein. A chimeric protein may present a foreign domain which is found (albeit in a different protein) in an organism which also expresses the first protein, or it may be an "interspecies", "intergenic", etc. fusion of protein structures expressed by different kinds of organisms. In general, a fusion protein can be represented by the general formula X-GF-Y, wherein GF represents a portion of the protein which is derived from a CDGF protein, and X and Y are independently absent or represent amino acid sequences which are not related to a CDGF sequence. The term "evolutionarily related to", with respect to nucleic acid sequences encoding a CDGF polypeptide, refers to nucleic acid sequences which have arisen naturally in an organism, including naturally occurring mutants. The term also refers to nucleic acid sequences which, while derived from a naturally occurring CDGF gene, have been altered by mutagenesis, as for example, the combinatorial mutagenic technigques described below, yet still encode polypeptides which have at least one activity of a CDGF polypeptide. The term "isolated" as also used herein with respect to nucleic acids, such as DNA or RNA, refers to molecules separated from other DNAs, or RNAs, respectively, that are present in the natural source of the macromolecule. For example, an isolated nucleic acid encoding the subject CDGF polypeptides preferably includes no more than 10 kilobases (kb) of nucleic acid sequence which naturally immediately flanks the CDGF gene in genomic DNA, more preferably no more than 5kb of such naturally occurring flanking sequences, and most preferably less than 1.5kb of such naturally occurring flanking sequence. The term isolated as used herein also refers to a nucleic acid or peptide that is substantially free of cellular material, viral material, or culture medium when produced by recombinant DNA techniques, or chemical precursors or other chemicals when chemically synthesized. Moreover, an - #- "isolated nucleic acid" is meant to include nucleic acid fragments which are not naturally occurring as fragments and would not be found in the natural state. As described below, one aspect of the invention pertains to an isolated nucleic acid comprising the nucleotide sequence encoding a CDGF polypeptide, and/or equivalents of such nucleic acids. The term nucleic acid as used herein is intended to include fragments as equivalents. The term equivalent is understood to include nucleotide sequences encoding functionally equivalent CDGF polypeptides or functionally equivalent peptides which, for example, retain the ability to bind to an tyrosine kinase receptor of the erbB family, e.g. to the erbB 2 and/or erbB4 receptors. Equivalent nucleotide sequences will include sequences that differ by one or more nucleotide substitutions, additions or deletions, such as allelic variants; and will, therefore, include sequences that differ from the nucleotide sequence ofthe CDGF coding sequences shown in SEQ ID Nos: 1, 3 or 6 due to the degeneracy of the genetic code. Equivalents will also include nucleotide sequences that hybridize under stringent conditions (i.e., equivalent to about 20-27°C below the melting temperature (T m ) of the DNA duplex formed in about IM salt) to a nucleotide sequence represented by SEQ ID No: 1, 3 and/or 6. In preferred embodiments, equivalents includes nucleic acid sequences derived from and evolutionarily related to, a nucleotide sequences shown in any of SEQ ID No: 1, 3 or 6. Moreover, it will be generally appreciated that, under certain circumstances, it may be advantageous to provide, homologs of the subject CDGF polypeptides which function in a limited capacity as one of either a agonist or antagonist of a CDGF protein, in order to promote or inhibit only a subset ofthe biological activities ofthe naturally-occurring form of the protein. Thus, specific biological effects can be elicited by treatment with a homolog of limited function, and with fewer side effects relative to treatment with agonists or antagonists which are directed to all of the biological activities of naturally occuring forms ofthe CDGF protein. For instance, CDGF homologs can be generated which interfere with the ability of the wild-type protein in forming complexes with either the erbB2 and/or erbB4 receptor proteins, but which do not substantially interfere with the formation of complexes between the CDGF polypeptide and other members of the erbB receptor family, such as may be involved in other signal transduction mechanisms. Homologs ofthe subject CDGF protein can be generated by mutagenesis, such as by discrete point mutation(s), or by truncation. For instance, mutation can give rise to homologs which retain substantially the same, or merely a subset, of the biological activity of the CDGF polypeptide from which it was derived. Altematively, antagonistic forms of the protein can be generated which are able to inhibit the function ofthe naturally occurring form ofthe protein, such as by competitively binding to an erbB receptor. A protein has CDGF polypeptide biological activity if it has one or more of the following properties: the ability to modulate proliferation, survival and/or differentiation of a - A7- cell which expresses an erbB receptor, such as a erbB2 or erbB4 receptor; the ability to modulate proliferation, survival and/or differentiation of mesodermally-derived tissue, such as tissue derived from dorsal mesoderm; the ability to modulate proliferation, survival and/or differentiation of ectodermally-derived tissue, such as tissue derived from the neural tube, neural crest, or head mesenchyme; the ability to modulate proliferation, survival and/or differentiation of endodermally-derived tissue, such as tissue derived from the primitive gut. In general, the ability to bind an erbB receptor protein, e.g. erbB2 and/or erbB4, is sufficient to be characterized as having the biochemical activity of a CDGF polypeptide of the present invention. Thus, according to the present invention, a polypeptide has biological activity if it is a specific agonist or antagonist of a naturally-occurring form of a CDGF protein. Preferred nucleic acids encode a CDGF polypeptide comprising an amino acid sequence at least 75% homologous, more preferably 80% homologous and most preferably 85% homologous with an amino acid sequence shown in one of SEQ ID No: 2, 4 or 7. Nucleic acids which encode polypeptides having an activity of a CDGF polypeptide and having an amino acid sequence at least about 90%, more preferably at least about 95%, and most preferably at least about 98-99% homology with a sequence shown in one of SEQ ID No: 2, 4 or 7 are also within the scope ofthe invention. In one embodiment, the nucleic acid is a cDNA encoding a peptide having at least one activity of the subject CDGF polypeptide. Preferably, the nucleic acid is a cDNA molecule comprising at least a portion of the nucleotide sequence represented in SEQ ID No: 1, 3 or 6. A preferred portion of this cDNA molecules includes the coding region ofthe gene. Another aspect of the invention provides a nucleic acid which hybridizes under high or low stringency conditions to a nucleic acid which encodes a peptide having all or a portion of an amino acid sequence shown in SEQ ID No: 2, 4 or 7. Appropriate stringency conditions which promote DNA hybridization, for example, 6.0 x sodium chloride/sodium citrate (SSC) at about 45°C, followed by a wash of 2.0 x SSC at 50°C, are known to those skilled in the art or can be found in Current Protocols in Molecular Biology, John Wiley & Sons, N.Y. (1989), 6.3.1-6.3.6. For example, the salt concentration in the wash step can be selected from a low stringency of about 2.0 x SSC at 50°C to a high stringency of about 0.2 x SSC at 50°C. In addition, the temperature in the wash step can be increased from low stringency conditions at room temperature, about 22°C, to high stringency conditions at about 65°C. Nucleic acids, having a sequence that differs from the nucleotide sequence shown in SEQ ID No: 1, 3 or 6 due to degeneracy in the genetic code are also within the scope ofthe invention. Such nucleic acids encode functionally equivalent peptides (i.e., a peptide having a biological activity of a CDGF polypeptide) but differ in sequence from the sequence shown in the sequence listing due to degeneracy in the genetic code. For example, a number of amino acids are designated by more than one triplet. Codons that specify the same amino acid, or synonyms (for example, CAU and CAC each encode histidine) may result in "silent" mutations which do not affect the amino acid sequence ofthe CDGF polypeptide. However, it is expected that DNA sequence polymoφhisms that do lead to changes in the amino acid sequences ofthe subject CDGF polypeptides will exist among vertebrates. One skilled in the art will appreciate that these variations in one or more nucleotides (up to about 3-5% of the nucleotides) of the nucleic acids encoding polypeptides having an activity of a CDGF polypeptide may exist among individuals of a given species due to natural allelic variation. Any and all such nucleotide variations and resulting amino acid polymorphisms are within the scope of this invention. Fragments of the nucleic acids encoding an active portion of the CDGF protein are also within the scope of the invention. As used herein, a fragment of the nucleic acid encoding the active portion of a CDGF polypeptide refers to a nucleic acid having fewer nucleotides than the nucleotide sequence encoding the entire amino acid sequence of the CDGF protein represented in SEQ ID No: 2, 4 or 7, but which nevertheless encodes a peptide having a CDGF polypeptide biological activity, e.g. the fragment retains the ability to bind to an erbB receptor. For instance, CDGF-1 polypeptides can be provided which lack an endogenous signal sequence or a transmembrane/cytoplasmic domain. Nucleic acid fragments within the scope of the present invention include those capable of hybridizing under high or low stringency conditions with nucleic acids from other species for use in screening protocols to detect CDGF homologs, as well as those capable of hybridizing with nucleic acids from human specimens for use in detecting the presence of a nucleic acid encoding the subject CDGF protein, including altemate isoforms, e.g. mRNA splicing variants. Nucleic acids within the scope of the invention may also contain linker sequences, modified restriction endonuclease sites and other sequences useful for molecular cloning, expression or purification of recombinant forms ofthe subject CDGF polypeptides. As indicated by the examples set out below, a nucleic acid encoding a peptide having an activity of a CDGF polypeptide may be obtained from mRNA present in any of a number of eukaryotic cells. It should also be possible to obtain nucleic acids encoding CDGF polypeptides of the present invention from genomic DNA obtained from both adults and embryos. For example, a gene encoding a CDGF protein can be cloned from either a cDNA or a genomic library in accordance with protocols described herein, as well as those generally known to persons skilled in the art. A cDNA encoding a CDGF protein can be obtained by isolating total mRNA from a cell, e.g. a mammalian cell, e.g. a human cell, including embryonic cells. Double stranded cDNAs can then be prepared from the total mRNA, and subsequently inserted into a suitable plasmid or bacteriophage vector using any one of a number of known techniques. The gene encoding the CDGF protein can also be cloned using established polymerase chain reaction techniques in accordance with the nucleotide sequence information provided by the invention. The nucleic acid of the invention can be DNA or RNA. A preferred nucleic acid is a cDNA represented by a nucleotide sequence shown in SEQ ID No: 1, 3 or 6. Another aspect of the invention relates to the use of the isolated nucleic acid in "antisense" therapy. As used herein, "antisense" therapy refers to administration or in situ generation of oligonucleotide probes or their derivatives which specifically hybridizes (e.g. binds) under cellular conditions, with the cellular mRNA and/or genomic DNA encoding a CDGF protein so as to inhibit expression of that protein, e.g. by inhibiting transcription and/or translation. The binding may be by conventional base pair complementarity, or, for example, in the case of binding to DNA duplexes, through specific interactions in the major groove of the double helix. In general, "antisense" therapy refers to the range of techniques generally employed in the art, and includes any therapy which relies on specific binding to oligonucleotide sequences. An antisense construct of the present invention can be delivered, for example, as an expression plasmid which, when transcribed in the cell, produces RNA which is complementary to at least a unique portion of the cellular mRNA which encodes a CDGF protein. Altematively, the antisense construct is an oligonucleotide probe which is generated ex vivo and which, when introduced into the cell causes inhibition of expression by hybridizing with the mRNA and/or genomic sequences of a CDGF gene. Such oligonucleotide probes are preferably modified oligonucleotide which are resistant to endogenous nucleases, e.g. exonucleases and/or endonucleases, and is therefore stable in vivo. Exemplary nucleic acid molecules for use as antisense oligonucleotides are phosphoramidate, phosphothioate and methylphosphonate analogs of DNA (see also U.S. Patents 5,176,996; 5,264,564; and 5,256,775). Additionally, general approaches to constructing oligomers useful in antisense therapy have been reviewed, for example, by van der krol et al. (1988) Biotechniques 6:958-976; and Stein et al. (1988) Cancer Res 48:2659- 2668. Accordingly, the modified oligomers of the invention are useful in therapeutic, diagnostic, and research contexts. In therapeutic applications, the oligomers are utilized in a manner appropriate for antisense therapy in general. For such therapy, the oligomers of the invention can be formulated for a variety of loads of administration, including systemic and topical or localized administration. Techniques and formulations generally may be found in Remmington's Pharmaceutical Sciences. Meade Publishing Co., Easton, PA. For systemic administration, injection is preferred, including intramuscular, intravenous, intraperitoneal, and subcutaneuos for injection, the oligomers of the invention can be formulated in liquid solutions, preferably in physiologically compatible buffers such as Hank's solution or Ringer's solution. In addition, the oligomers may be formulated in solid form and redissolved or suspended immediately prior to use. Lyophilized forms are also included. Systemic administration can also be by transmucosal or transdermal means, or the compounds can be administered orally. For transmucosal or transdermal administration, penetrants appropriate to the barrier to be permeated are used in the formulation. Such penetrants are generally known in the art, and include, for example, for transmucosal administration bile salts and fusidic acid derivatives. In addition, detergents may be used to facilitate permeation. Transmucosal administration may be through nasal sprays or using suppositories. For oral administration, the oligomers are formulated into conventional oral administration forms such as capsules, tablets, and tonics. For topical administration, the oligomers ofthe invention are formulated into ointments, salves, gels, or creams as generally known in the art. In addition to use in therapy, the oligomers ofthe invention may be used as diagnostic reagents to detect the presence or absence of the target DNA or RNA sequences to which they specifically bind. Such diagnostic tests are described in further detail below. Likewise, the antisense constructs of the present invention, by antagonizing the normal biological activity of CDGF, can be used in the manipulation of tissue, e.g. tissue differentiation, both in vivo and in ex vivo tissue cultures. This invention also provides expression vectors containing a nucleic acid encoding a CDGF polypeptide, operably linked to at least one transcriptional regulatory sequence. Operably linked is intended to mean that the nucleotide sequence is linked to a regulatory sequence in a manner which allows expression of the nucleotide sequence. Regulatory sequences are art-recognized and are selected to direct expression of the subject CDGF proteins. Accordingly, the term transcriptional regulatory sequence includes promoters, enhancers and other expression control elements. Such regulatory sequences are described in Goeddel; Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, CA (1990). For instance, any of a wide variety of expression control sequences- sequences that control the expression of a DNA sequence when operatively linked to it may be used in these vectors to express DNA sequences encoding the CDGF polypeptides of this invention. Such useful expression control sequences, include, for example, a viral LTR, such as the LTR of the Moloney murine leukemia virus, the early and late promoters of SV40, adenovirus or cytomegalovirus immediate early promoter, the lac system, the trp system, the TAC or TRC system, T7 promoter whose expression is directed by T7 RNA polymerase, the major operator and promoter regions of phage λ , the control regions for fd coat protein, the promoter for 3-phosphoglycerate kinase or other glycolytic enzymes, the promoters of acid phosphatase, e.g., Pho5, the promoters of the yeast α-mating factors, the polyhedron promoter of the baculovirus system and other sequences known to control the expression of genes of prokaryotic or eukaryotic cells or their viruses, and various combinations thereof. It should be understood that the design ofthe expression vector may depend on such factors as the choice of the host cell to be transformed and/or the type of protein desired to be expressed. Moreover, the vector's copy number, the ability to control that copy number and the expression of any other proteins encoded by the vector, such as antibiotic markers, should also be considered. In one embodiment, the expression vector includes a recombinant gene encoding a peptide having an agonistic activity of a subject CDGF polypeptide, or altematively, encoding a peptide which is an antagonistic form of the CDGF protein. Such expression vectors can be used to transfect cells and thereby produce proteins or peptides, including fusion proteins or peptides, encoded by nucleic acids as described herein. Moreover, the gene constructs of the present invention can also be used as a part of a gene therapy protocol to deliver nucleic acids encoding either an agonistic or antagonistic form ofthe subject CDGF protein. Thus, another aspect ofthe invention features expression vectors for in vivo transfection and expression of a CDGF polypeptide in particular cell types so as to reconstitute the function of, or altematively, abrogate the function of CDGF in a tissue in which CDGF is misexpressed; or to deliver a form of the protein which alters differentiation of tissue, or which inhibits neoplastic transformation, by modulating the biological function of an erbB receptor. Expression constructs ofthe subject CDGF polypeptide, and mutants thereof, may be administered in any biologically effective carrier, e.g. any formulation or composition capable of effectively delivering the CDGF gene to cells in vivo. Approaches include insertion ofthe subject gene in viral vectors including recombinant retroviruses, adenovirus, adeno-associated virus, and herpes simplex virus- 1, or recombinant bacterial or eukaryotic plasmids. Viral vectors transfect cells directly; plasmid DNA can be delivered with the help of, for example, cationic liposomes (lipofectin) or derivatized (e.g. antibody conjugated), polylysine conjugates, gramacidin S, artificial viral envelopes or other such intracellular carriers, as well as direct injection ofthe gene construct or CaPO4 precipitation carried out in vivo. It will be appreciated that because transduction of appropriate target cells represents the critical first step in gene therapy, choice ofthe particular gene delivery system will depend on such factors as the phenotype of the intended target and the route of administration, e.g. locally or systemically. Furthermore, it will be recognized that the particular gene construct provided for in vivo transduction of CDGF expression are also useful for in vitro transduction of cells, such as for use in the ex vivo tissue culture systems described below. A preferred approach for in vivo introduction of nucleic acid into a cell is by use of a viral vector containing nucleic acid, e.g. a cDNA, encoding the particular form ofthe CDGF polypeptide desired. Infection of cells with a viral vector has the advantage that a large proportion ofthe targeted cells can receive the nucleic acid. Additionally, molecules encoded within the viral vector, e.g., by a cDNA contained in the viral vector, are expressed efficiently in cells which have taken up viral vector nucleic acid. Retrovirus vectors and adeno-associated virus vectors are generally understood to be the recombinant gene delivery system of choice for the transfer of exogenous genes in vivo, particularly into humans. These vectors provide efficient delivery of genes into cells, and the transferred nucleic acids are stably integrated into the chromosomal DNA of the host. A major prerequisite for the use of retrovimses is to ensure the safety of their use, particularly with regard to the possibility of the spread of wild-type virus in the cell population. The development of specialized cell lines (termed "packaging cells") which produce only replication-defective retroviruses has increased the utility of retroviruses for gene therapy, and defective retroviruses are well characterized for use in gene transfer for gene therapy purposes (for a review see Miller, A.D. (1990) Blood 76:271). Thus, recombinant retrovirus can be constructed in which part of the retroviral coding sequence (gag, pol, env) has been replaced by nucleic acid encoding one of the subject receptors rendering the retrovims replication defective. The replication defective retrovims is then packaged into virions which can be used to infect a target cell through the use of a helper virus by standard techniques. Protocols for producing recombinant retroviruses and for infecting cells in vitro or in vivo with such viruses can be found in Current Protocols in Molecular Biology. Ausubel, F.M. et al. (eds.) Greene Publishing Associates, (1989), Sections 9.10-9.14 and other standard laboratory manuals. Examples of suitable retroviruses include pLJ, pZIP, pWE and pEM which are well known to those skilled in the art. Examples of suitable packaging virus lines for preparing both ecotropic and amphotropic retroviral systems include ψCrip, ψCre, ψ2 and ψAm. Retroviruses have been used to introduce a variety of genes into many different cell types, including neuronal cells, in vitro and/or in vivo (see for example Eglitis, et al. (1985) Science 230:1395-1398; Danos and Mulligan (1988) Proc. Natl. Acad. Sci. USA 85:6460-6464; Wilson et al. (1988) Proc. Natl. Acad. Sci. USA 85:3014-3018; Armentano et al. (1990) Proc. Natl. Acad. Sci. USA 87:6141-6145; Huber et al. (1991) Proc. Natl. Acad. Sci. USA 88:8039-8043; Ferry et al. (1991) Proc. Natl. Acad. Sci. USA 88:8377-8381; Chowdhury et al. (1991) Science 254:1802-1805; van Beusechem et al. (1992) Proc. Natl. Acad. Sci. USA 89:7640-7644; Kay et al. (1992) Human Gene Therapy 3:641-647; Dai et al. (1992) Proc. Natl. Acad. Sci. USA 89:10892-10895; Hwu et al. (1993) J. Immunol. 150:4104- 4115; U.S. Patent No. 4,868,116; U.S. Patent No. 4,980,286; PCT Application WO 89/07136; PCT Application WO 89/02468; PCT Application WO 89/05345; and PCT Application WO 92/07573). Furthermore, it has been shown that it is possible to limit the infection spectrum of retrovimses and consequently of retroviral-based vectors, by modifying the viral packaging proteins on the surface ofthe viral particle (see, for example PCT publications WO93/25234 and WO94/06920). For instance, strategies for the modification ofthe infection spectrum of retroviral vectors include: coupling antibodies specific for cell surface antigens to the viral env protein (Roux et al. (1989) PNAS 86:9079-9083; Julan et al. (1992) J. Gen Virol 73:3251-3255; and Goud et al. (1983) Virology 163:251-254); or coupling cell surface receptor ligands to the viral env proteins (Neda et al. (1991) J Biol Chem 266:14143-14146). Coupling can be in the form ofthe chemical cross-linking with a protein or other variety (e.g. lactose to convert the env protein to an asialoglycoprotein), as well as by generating fusion proteins (e.g. single-chain antibody/env fusion proteins). This technique, while useful to limit or otherwise direct the infection to certain tissue types, can also be used to convert an ecotropic vector in to an amphotropic vector. Moreover, use of retroviral gene delivery can be further enhanced by the use of tissue- or cell-specific transcriptional regulatory sequences which control expression of the CDGF gene ofthe retroviral vector. Another viral gene delivery system useful in the present invention utilitizes adeno virus-derived vectors. The genome of an adenovirus can be manipulated such that it encodes and expresses a gene product of interest but is inactivated in terms of its ability to replicate in a normal lytic viral life cycle. See for example Berkner et al. (1988) BioTechniques 6:616; Rosenfeld et al. (1991) Science 252:431-434; and Rosenfeld et al. (1992) Cell 68:143-155. Suitable adenoviral vectors derived from the adenovirus strain Ad type 5 dl324 or other strains of adenovirus (e.g., Ad2, Ad3, Ad7 etc.) are well known to those skilled in the art. Recombinant adenoviruses can be advantageous in certain circumstances in that they are not capable of infecting nondividing cells and can be used to infect a wide variety of cell types, including epithelial cells (Rosenfeld et al. (1992) cited supra). Furthermore, the vims particle is relatively stable and amenable to purification and concentration, and as above, can be modified so as to affect the spectrum of infectivity. Additionally, introduced adenoviral DNA (and foreign DNA contained therein) is not integrated into the genome of a host cell but remains episomal, thereby avoiding potential problems that can occur as a result of insertional mutagenesis in situations where introduced DNA becomes integrated into the host genome (e.g., retroviral DNA). Moreover, the carrying capacity of the adenoviral genome for foreign DNA is large (up to 8 kilobases) relative to other gene delivery vectors (Berkner et al. cited supra; Haj-Ahmand and Graham (1986) J. Virol. 57:267). Most replication-defective adenoviral vectors currently in use and therefore favored by the present invention are deleted for all or parts of the viral El and E3 genes but retain as much as 80% of the adenoviral genetic material (see, e.g., Jones et al. (1979) Cell 16:683; Berkner et al., supra; and Graham et al. in Methods in Molecular Biology. E.J. Murray, Ed. (Humana, Clifton, NJ, 1991) vol. 7. pp. 109-127). Expression of the inserted CDGF gene can be under control of, for example, the El A promoter, the major late promoter (MLP) and associated leader sequences, the E3 promoter, or exogenously added promoter sequences. Yet another viral vector system useful for delivery of the subject CDGF gene is the adeno-associated virus (AAV). Adeno-associated vims is a naturally occurring defective virus that requires another vims, such as an adenovirus or a herpes vims, as a helper virus for efficient replication and a productive life cycle. (For a review see Muzyczka et al. Curr. Topics in Micro, and Immunol. (1992) 158:97-129). It is also one ofthe few vimses that may integrate its DNA into non-dividing cells, and exhibits a high frequency of stable integration (see for example Flotte et al. (1992) Am. J. Respir. Cell. Mol. Biol. 7:349-356; Samulski et al. (1989) J Virol. 63:3822-3828; and McLaughlin et al. (1989) J. Virol. 62:1963-1973). Vectors containing as little as 300 base pairs of AAV can be packaged and can integrate. Space for exogenous DNA is limited to about 4.5 kb. An AAV vector such as that described in Tratschin et al. (1985) Mol. Cell. Biol. 5:3251-3260 can be used to introduce DNA into cells. A variety of nucleic acids have been introduced into different cell types using AAV vectors (see for example Hermonat et al. (1984) Proc. Natl. Acad. Sci. USA 81 :6466-6470; Tratschin et al. (1985) Mol. Cell. Biol. 4:2072-2081; Wondisford et al. (1988) Mol. Endocrinol. 2:32-39; Tratschin et al. (1984) J. Virol. 51:611-619; and Flotte et al. (1993) J Biol. Chem. 268:3781-3790). In addition to viral transfer methods, such as those illustrated above, non-viral methods can also be employed to cause expression of a CDGF polypeptide in the tissue of an animal. Most nonviral methods of gene transfer rely on normal mechanisms used by mammalian cells for the uptake and intracellular transport of macromolecules. In preferred embodiments, non-viral gene delivery systems of the present invention rely on endocytic pathways for the uptake of the subject CDGF polypeptide gene by the targeted cell. Exemplary gene delivery systems of this type include liposomal derived systems, poly-lysine conjugates, and artificial viral envelopes. In a representative embodiment, a gene encoding one of the subject CDGF polypeptides can be entrapped in liposomes bearing positive charges on their surface (e.g., lipofectins) and (optionally) which are tagged with antibodies against cell surface antigens of the target tissue (Mizuno et al. (1992) No Shinkei Geka 20:547-551; PCT publication WO91/06309; Japanese patent application 1047381; and European patent publication EP-A- 43075). For example, lipofection of cells can be carried out using liposomes tagged with monoclonal antibodies against any cell surface antigen present on the tumor cells, as for example, the CD20 antigen which has been detected on the lymphoblastic cell line LK63/CD20+ which also expresses the hek receptor (Wicks et al. (1992) PNAS 89:1611- 1615). In clinical settings, the gene delivery systems for the therapeutic CDGF gene can be introduced into a patient by any of a number of methods, each of which is familiar in the art. For instance, a pharmaceutical preparation of the gene delivery system can be introduced systemically, e.g. by intravenous injection, and specific transduction of the protein in the target cells occurs predominantly from specificity of transfection provided by the gene delivery vehicle, cell-type or tissue-type expression due to the transcriptional regulatory sequences controlling expression of the receptor gene, or a combination thereof. In other embodiments, initial delivery of the recombinant gene is more limited with introduction into -Aη- the animal being quite localized. For example, the gene delivery vehicle can be introduced by catheter (see U.S. Patent 5,328,470) or by stereotactic injection (e.g. Chen et al. (1994) PNAS 91: 3054-3057). The pharmaceutical preparation of the gene therapy constmct can consist essentially ofthe gene delivery system in an acceptable diluent, or can comprise a slow release matrix in which the gene delivery vehicle is imbedded. Altematively, where the complete gene delivery system can be produced intact from recombinant cells, e.g. retroviral vectors, the pharmaceutical preparation can comprise one or more cells which produce the gene delivery system. Another aspect of the present invention concems recombinant forms of the subject CDGF protein which are encoded by genes derived from eukaryotic organisms such as mammals, e.g. humans. Recombinant proteins preferred by the present invention, in addition to native CDGF polypeptides, are at least 75% homologous, more preferably at least 80% homologous and most preferably at least 85% homologous with an amino acid sequence shown in any of SEQ ID No: 2, 4 or 7. Polypeptides having an activity ofthe subject CDGF polypeptides (i.e. either agonistic or antagonistic) and having at least about 90%, more preferably at least about 95%, and most preferably at least about 98-99% homology with a polypeptide sequence in SEQ ID No: 2, 4 or 7 are also within the scope ofthe invention. The term "recombinant protein" refers to a polypeptide ofthe present invention which is produced by recombinant DNA techniques, wherein generally DNA encoding a CDGF polypeptide is inserted into a suitable expression vector which is in turn used to transform a host cell to produce the heterologous protein. Moreover, the phrase "derived from", with respect to a recombinant CDGF gene, is meant to include within the meaning of "recombinant protein" those proteins having an amino acid sequence of a native CDGF polypeptide, or an amino acid sequence similar thereto which is generated by mutations including substitutions and deletions (including truncation) of a naturally occurring form of a CDGF protein. For instance, N-glycosylation sites in the CDGF protein can be modified (e.g. mutated) to preclude glycosylation, allowing expression of a more homogenous, reduced carbohydrate analog in mammalian, insect and yeast expression systems. Likewise, CDGF polypeptides can be generated which lack an endogenous signal sequence (though this is typically cleaved off even if present in the pro-form of the protein), or which lack a transmembrane domain/cytoplasmic domain. In the instance ofthe latter, the removal of the C-terminus may result in a soluble form of the protein. In particular, N- terminal fragments ofthe CDGF-1 polypeptides which are truncated at or before Leu317 are preferred as soluble forms ofthe protein. -AX- The present invention further pertains to recombinant forms of the subject CDGF polypeptides which are encoded by genes derived from a vertebrate organism, particularly a mammal (e.g. a human), and which have amino acid sequences evolutionarily related to the CDGF proteins represented in SEQ ID No: 2, A or 7. Such recombinant CDGF polypeptides are preferably capable of functioning in one of either role of an agonist or antagonist of at least one biochemical/biological activity of the CDGF polypeptide of the appended sequence listing. The term "evolutionarily related to", with respect to amino acid sequences of the present recombinant CDGF polypeptides, refers to CDGF polypeptides having amino acid sequences which have arisen naturally, and also to mutational variants of CDGF polypeptides which are derived, for example, by combinatorial mutagenesis. Such evolutionarily derived CDGF polypeptides preferred by the present invention are at least 70% homologous, more preferably at least 80% homologous and most preferably at least 85% homologous with an amino acid sequence shown in SEQ ID No: 2, A, 5 and/or 7. Polypeptides having at least about 90%, more preferably at least about 95%, and most preferably at least about 98-99% homology with a sequence shown in SEQ ID No: 2, 4, 5 or 7 are also within the scope ofthe invention. The present invention further pertains to methods of producing the subject CDGF polypeptides. For example, a host cell transfected with a nucleic acid vector directing expression of a nucleotide sequence encoding the subject CDGF polypeptide can be cultured under appropriate conditions to allow expression ofthe peptide to occur. The peptide may be secreted and isolated from a mixture of cells and medium containing the recombinant CDGF polypeptide. Altematively, the peptide may be retained cytoplasmically by removing the signal peptide sequence from the recombinant CDGF gene and the cells harvested, lysed and the protein isolated. A cell culture includes host cells, media and other byproducts. Suitable media for cell culture are well known in the art. The recombinant CDGF polypeptide peptide can be isolated from cell culture medium, host cells, or both using techniques known in the art for purifying proteins including ion-exchange chromatography, gel filtration chromatography, ultrafiltration, electrophoresis, and immunoaffinity purification with antibodies specific for such peptide. In a preferred embodiment, the recombinant CDGF polypeptide is a fusion protein containing a domain which facilitates its purification, such as a CDGF/GST fusion protein or a poly(His) tagged CDGF protein. This invention also pertains to a host cell transfected to express a recombinant form of the subject CDGF polypeptides. The host cell may be any prokaryotic or eukaryotic cell, and the choice can be based at least in part on the desirablity of such post-translation modifications as glycosylation. Thus, a nucleotide sequence derived from the cloning of CDGF, encoding all or a selected portion of the full-length protein, can be used to produce a recombinant form of a CDGF polypeptide via microbial or eukaryotic cellular processes. Ligating the polynucleotide sequence into a gene construct, such as an expression vector, and transforming or transfecting into hosts, either eukaryotic (yeast, avian, insect or mammalian) or prokaryotic (bacterial cells), are standard procedures used in producing other well-known proteins, e.g. EGF, interferons, heregulins, neu differentiation factor and the like. Similar procedures, or modifications thereof, can be employed to prepare recombinant CDGF polypeptides by microbial means or tissue-culture technology in accord with the subject invention. The recombinant CDGF gene can be produced by Iigating nucleic acid encoding the subject CDGF protein, or a portion thereof, into a vector suitable for expression in either prokaryotic cells, eukaryotic cells, or both. Expression vectors for production of recombinant forms of the subject CDGF polypeptides include plasmids and other vectors. For instance, suitable vectors for the expression of a CDGF polypeptide include plasmids of the types: pBR322-derived plasmids, pEMBL-derived plasmids, pEX-derived plasmids, pBTac-derived plasmids and pUC-derived plasmids for expression in prokaryotic cells, such as E. coli. A number of vectors exist for the expression of recombinant proteins in yeast. For instance, YEP24, YIP5, YEP51, YEP52, pYES2, and YRP17 are cloning and expression vehicles useful in the introduction of genetic constmcts into S. cerevisiae (see, for example, Broach et al. (1983) in Experimental Manipulation of Gene Expression, ed. M. Inouye Academic Press, p. 83, incorporated by reference herein). These vectors can replicate in E. coli due the presence of the pBR322 ori, and in S. cerevisiae due to the replication determinant of the yeast 2 micron plasmid. In addition, drag resistance markers such as ampicillin can be used. In an illustrative embodiment, a CDGF polypeptide is produced recombinantly utilizing an expression vector generated by sub-cloning the coding sequence of a CDGF gene represented in SEQ ID NO. 1, 3, 5 or 7. The preferred mammalian expression vectors contain both prokaryotic sequences to facilitate the propagation of the vector in bacteria, and one or more eukaryotic transcription units that are expressed in eukaryotic cells. The pcDNAI/amp, pcDNAI/neo, pRc/CMV, pSV2gpt, pSV2neo, pSV2-dhfr, pTk2, pRSVneo, pMSG, pSVT7, pko-neo and pHyg derived vectors are examples of mammalian expression vectors suitable for transfection of eukaryotic cells. Some of these vectors are modified with sequences from bacterial plasmids, such as pBR322, to facilitate replication and dmg resistance selection in both prokaryotic and eukaryotic cells. Altematively, derivatives of vimses such as the bovine papillomavirus (BPV-1), or Epstein-Barr vims (pHEBo, pREP-derived and p205) can be used for transient expression of proteins in eukaryotic cells. The various methods employed in the preparation of the plasmids and transformation of host organisms are well known in the art. For other suitable expression systems for both prokaryotic and eukaryotic cells, as well as general recombinant procedures, see Molecular Cloning A Laboratory Manual, 2nd Ed., ed. by Sambrook, Fritsch and Maniatis (Cold Spring Harbor Laboratory Press: 1989) Chapters 16 and 17. In some instances, it may be desirable to express the recombinant CDGF polypeptide by the use of a baculovims expression system. Examples of such baculovims expression systems include pVL-derived vectors (such as pVL1392, pVL1393 and pVL941), pAcUW- derived vectors (such as pAcUWl), and pBlueBac-derived vectors (such as the β-gal containing pBlueBac III). When it is desirable to express only a portion of a CDGF protein, such as a form lacking a portion of the N-terminus, i.e. a tmnction mutant which lacks the signal peptide, it may be necessary to add a start codon (ATG) to the oligonucleotide fragment containing the desired sequence to be expressed. It is well known in the art that a methionine at the N- terminal position can be enzymatically cleaved by the use of the enzyme methionine aminopeptidase (MAP). MAP has been cloned from E. coli (Ben-Bassat et al. (1987) J Bacteriol. 169:751-757) and Salmonella typhimurium and its in vitro activity has been demonstrated on recombinant proteins (Miller et al. (1987) PNAS 84:2118-1122). Therefore, removal of an N-terminal methionine, if desired, can be achieved either in vivo by expressing CDGF-derived polypeptides in a host which produces MAP (e.g., E. coli or CM89 or S. cerevisiae), or in vitro by use of purified MAP (e.g., procedure of Miller et al., supra). Altematively, the coding sequences for the polypeptide can be incoφorated as a part of a fusion gene including a nucleotide sequence encoding a different polypeptide. This type of expression system can be useful under conditions where it is desirable to produce an immunogenic fragment of a CDGF protein. For example, the VP6 capsid protein of rotavirus can be used as an immunologic carrier protein for portions ofthe CDGF polypeptide, either in the monomeric form or in the form of a viral particle. The nucleic acid sequences corresponding to the portion of a subject CDGF protein to which antibodies are to be raised can be incoφorated into a fusion gene constmct which includes coding sequences for a late vaccinia vims structural protein to produce a set of recombinant vimses expressing fusion proteins comprising CDGF epitopes as part of the virion. It has been demonstrated with the use of immunogenic fusion proteins utilizing the Hepatitis B surface antigen fusion proteins that recombinant Hepatitis B virions can be utilized in this role as well. Similarly, chimeric constmcts coding for fusion proteins containing a portion of a CDGF protein and the poliovims capsid protein can be created to enhance immunogenicity of the set of polypeptide antigens (see, for example, EP Publication No: 0259149; and Evans et al. (1989) Nature 339:385; Huang et al. (1988) J. Virol. 62:3855; and Schlienger et al. (1992) J. Virol. 66:2). The Multiple Antigen Peptide system for peptide-based immunization can also be utilized to generate an immunogen, wherein a desired portion of a CDGF polypeptide is obtained directly from organo-chemical synthesis ofthe peptide onto an oligomeric branching lysine core (see, for example, Posnett et al. (1988) JBC 263:1719 and Nardelli et al. (1992) J. Immunol. 148:914). Antigenic determinants of CDGF proteins can also be expressed and presented by bacterial cells. -3/- In addition to utilizing fusion proteins to enhance immunogenicity, it is widely appreciated that fusion proteins can also facilitate the expression of proteins, including the CDGF polypeptides of the present invention. For example, a CDGF polypeptide can be generated as a glutathione-S-transferase (GST-fusion protein). Such GST-fusion proteins can enable easy purification of the CDGF polypeptide, as for example by the use of glutathione- derivatized matrices (see, for example, Current Protocols in Molecular Biology, eds. Ausubel et al. (N.Y.: John Wiley & Sons, 1991)). In another embodiment, a fusion gene coding for a purification leader sequence, such as a poly-(His)/enterokinase cleavage site sequence, can be used to replace the signal sequence which naturally occurs at N-terminus the CDGF protein, in order to permit purification of the poly(His)-CDGF protein by affinity chromatography using a Ni 2+ metal resin. The purification leader sequence can then be subsequently removed by treatment with enterokinase (e.g., see Hochuli et al. (1987) J. Chromatography 411 :177; and Janknecht et al. PNAS 88:8972). Furthermore, the generation of CDGF fusion proteins can be utilized as means for facilitating clustering, e.g., oligomerization, of CDGF proteins to enhance certain activities associated with, for example, receptor cross-linking. For example, a CDGF/alkaline phosphatase fusion protein may provide such a function, relying on the ability of alkaline phosphatase domains to promote complex formation between two or more CDGF/ AP proteins. Moreover, it may be desirable to provide multiple CDGF domains in the same molecule, rather than rely on intermolecular complementation for oligomerization. For instance, an unstmctured polypeptide linker region can be introduced between two CDGF portions of the fusion protein. This linker can facilitate enhanced flexibility of the fusion protein, allowing the CDGF domains to freely interact through intramolecular association, e.g., because of reduced steric hindrance between the two fragments, as well as permit appropriate folding of each fragment to occur. The linker can be of natural origin, such as a sequence determined to exist in random coil between two domains of a protein. Altematively, the linker can be of synthetic origin. For instance, the sequence (Gly4Ser)3 can be used as a synthetic unstmctured linker. Linkers of this type are described in Huston et al. (1988) PNAS 85:4879; and U.S. Patent No. 5,091,513, both incoφorated by reference herein. Techniques for making fusion genes are known to those skilled in the art. Essentially, the joining of various DNA fragments coding for different polypeptide sequences is performed in accordance with conventional techniques, employing blunt-ended or stagger- ended termini for ligation, restriction enzyme digestion to provide for appropriate termini, filling-in of cohesive ends as appropriate, alkaline phosphatase treatment to avoid undesirable joining, and enzymatic ligation. In another embodiment, the fusion gene can be synthesized by conventional techniques including automated DNA synthesizers. Altematively, PCR amplification of gene fragments can be carried out using anchor primers which give rise to complementary overhangs between two consecutive gene fragments which can subsequently be annealed to generate a chimeric gene sequence (see, for example, Current Protocols in Molecular Biology, eds. Ausubel et al. John Wiley & Sons: 1992). The CDGF polypeptide may also be chemically modified to create CDGF derivatives by forming covalent or aggregrative conjugates with other chemical moieties, such as glycosyl groups, lipids, phosphate, acetyl groups and the like. Covalent derivatives of CDGF can be prepared by linking the chemical moeities to functional groups on CDGF amino acid sidechains or at the N-terminus or at the C-terminus of the polypeptide. For instance, a CDGF protein can generated which includes a moiety, other than sequences naturally associated with the CDGF protein, that binds a component of the extracellular matrix and enhances localization of the CDGF analog to cell surfaces. For example, sequences derived from the fibronectin "type-Ill repeat", such as a tetrapeptide sequence R-G-D-S (Pierschbacher et al. (1984) Nature 309:30-3; and Kornblihtt et al. (1985) EMBO 4:1755-9) can be added to the CDGF polypepyide to support attachment of the chimeric molecule to a cell through binding ECM components (Ruoslahti et al. (1987) Science 238:491-497; Pierschbacheret al. (1987) J. Biol. Chem. 262:17294-8.; Hynes (1987) Cell 48:549-54; and Hynes (1992) Cell 69:11-25) particularly where the CDGF polypeptide lacks the C-terminal transmembrane and cytoplasmic domains. The present invention also makes available isolated CDGF polypeptides which are isolated from, or otherwise substantially free of other cellular and extracellular proteins, especially erbB receptor proteins or other extracellular factors, normally associated with the CDGF polypeptide. The term "substantially free of other cellular or extracellular proteins" (also referred to herein as "contaminating proteins") or "substantially pure or purified preparations" are defined as encompassing preparations of CDGF polypeptides having less than 20% (by dry weight) contaminating protein, and preferably having less than 5% contaminating protein. Functional forms ofthe subject CDGF polypeptides can be prepared, for the first time, as purified preparations by using a cloned gene as described herein. Altematively, the subject CDGF polypeptides can be isolated by affinity purification using, for example, matrix bound erbB receptor protein. By "purified", it is meant, when referring to a peptide or DNA or RNA sequence, that the indicated molecule is present in the substantial absence of other biological macromolecules, such as other proteins. The term "purified" as used herein preferably means at least 80% by dry weight, more preferably in the range of 95-99% by weight, and most preferably at least 99.8% by weight, of biological macromolecules of the same type present (but water, buffers, and other small molecules, especially molecules having a molecular weight of less than 5000, can be present). The term "pure" as used herein preferably has the same numerical limits as "purified" immediately above. "Isolated" and "purified" do not encompass either natural materials in their native state or natural materials that have been separated into components (e.g., in an acrylamide gel) but not obtained either as pure (e.g. lacking contaminating proteins, or chromatography reagents such as denaturing agents and polymers, e.g. acrylamide or agarose) substances or solutions. As described above for recombinant polypeptides, isolated CDGF polypeptides can include all or a portion of an amino acid sequence represented in SEQ ID No. 2, A, 5 or 7, or homologous sequence thereto. Exemplary derivatives of that sequence include proteins which lack glycosylation sites (e.g. to produce an unglycosylated protein), or which lack an N-terminus and or/C-terminus sequence, e.g. a CDGF polypeptide which consists essentially of (with respect to receptor binding) an EGF-like domain. Furthermore, isolated peptidyl portions of CDGF proteins can also be obtained by screening peptides recombinantly produced from the coπesponding fragment of the nucleic acid encoding such peptides. In addition, fragments can be chemically synthesized using techniques known in the art such as conventional Meπifield solid phase f-Moc or t-Boc chemistry. For example, a CDGF polypeptide of the present invention may be arbitrarily divided into fragments of desired length with no overlap of the fragments, or preferably divided into overlapping fragments of a desired length. The fragments can be produced (recombinantly or by chemical synthesis) and tested to identify those peptidyl fragments which can function as either agonists or antagonists of a CDGF polypeptide activity, such as by in vivo competition assays or in vitro protein binding assays with erbB receptors. It will also be possible to modify the stmcture of the subject CDGF polypeptides for such puφoses as enhancing therapeutic or prophylactic efficacy, or stability (e.g., ex vivo shelf life and resistance to proteolytic degradation in vivo). Such modified peptides, when designed to retain at least one activity of the naturally-occurring form of the protein, are considered functional equivalents of the CDGF polypeptide described in more detail herein. Such modified peptide can be produced, for instance, by amino acid substitution, deletion, or addition. For example, it is reasonable to expect that an isolated replacement of a leucine with an isoleucine or valine, an aspartate with a glutamate, a threonine with a serine, or a similar replacement of an amino acid with a structurally related amino acid (i.e. conservative mutations) will not have a major effect on the biological activity of the resulting molecule. Conservative replacements are those that take place within a family of amino acids that are related in their side chains. Genetically encoded amino acids are can be divided into four families: (1) acidic = aspartate, glutamate; (2) basic = lysine, arginine, histidine; (3) nonpolar = alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan; and (4) uncharged polar = glycine, asparagine, glutamine, cysteine, serine, threonine, tyrosine. Phenylalanine, tryptophan, and tyrosine are sometimes classified jointly as aromatic amino acids. In similar fashion, the amino acid repertoire can be grouped as (1) acidic = aspartate, glutamate; (2) basic = lysine, arginine histidine, (3) aliphatic = glycine, alanine, valine, leucine, isoleucine, serine, threonine, with serine and threonine optionally be grouped separately as aliphatic-hydroxyl; (4) aromatic = phenylalanine, tyrosine, tryptophan; (5) amide = asparagine, glutamine; and (6) sulfur -containing = cysteine and methionine. (see, for example, Biochemistry, 2nd ed., Ed. by L. Stryer, WH Freeman and Co.: 1981). Whether a change in the amino acid sequence of a peptide results in a functional CDGF homolog (e.g. functional in the sense that it acts to mimic or antagonize the wild-type form) can be readily determined by assessing the ability of the variant peptide to produce a response in cells in a fashion similar to the wild-type CDGF protein or competitively inhibit such a response. Peptides in which more than one replacement has taken place can readily be tested in the same manner. Accordingly, the present invention contemplates a method of generating sets of combinatorial mutants of the presently disclosed novel CDGF polypeptides, as well as truncation and fragmentation mutants, and is especially useful for identifying potential variant sequences which are functional in binding to an erbB receptor. One puφose for screening such combinatorial libraries is, for example, to isolate novel CDGF homologs which function as one of either an agonist or antagonist of the biological activities of the wild-type ("authentic") protein, or altematively, which possess novel activities all together. To illustrate, CDGF homologs can be engineered by the present method to provide proteins which bind an erbB receptor yet which block (antagonize) receptor-mediated gene transcription resulting from signal transduction pathways normally associated with activation of that receptor. Such proteins, when expressed from recombinant DNA constmcts, can be used in gene therapy protocols, or can be formulated as pharmaceutical preparations and delivered in such manner. Likewise, mutagenesis can give rise to CDGF homologs which have extracellular half-lives dramatically different than the coπesponding wild-type protein. For example, the altered protein can be rendered either more stable or less stable to proteolytic degradation or other extracellular process which result in destmction of, or otherwise inactivation of, a CDGF polypeptide. Such CDGF homologs can be utilized to alter the envelope of bioavailabilty for a recombinant CDGF protein by modulating, for example, the plasma half- life of the protein. For instance, a short half-life can give rise to more transient biological effects associated with a particular recombinant CDGF polypeptide and can therefore allow tighter control of protein levels within or around a particular tissue. As above, such proteins, and particularly their recombinant nucleic acid constmcts, can be used in gene therapy protocols as well as formulated into pharmaceutical preparations. In an illustrative embodiment of this method, the amino acid sequences for a population of CDGF homologs or other related proteins are aligned, preferably to promote the highest homology possible. Such a population of variants can include, for example, CDGF homologs from one or more species, e.g. various mammals, or CDGF homologs from the same species but which differ due to mutation. Amino acids which appear at each position of the aligned sequences are selected to create a degenerate set of combinatorial sequences. In a prefeπed embodiment, the variegated library of CDGF variants is generated by combinatorial mutagenesis at the nucleic acid level, and is encoded by a variegated gene library. For instance, a mixture of synthetic oligonucleotides can be enzymatically ligated into gene sequences such that the degenerate set of potential CDGF sequences are expressible as individual polypeptides, or altematively, as a set of larger fusion proteins (e.g. for phage display) containing the set of CDGF sequences therein. There are many ways by which the library of potential CDGF homologs can be generated from a degenerate oligonucleotide sequence. Chemical synthesis of a degenerate gene sequence can be carried out in an automatic DNA synthesizer, and the synthetic genes then ligated into an appropriate expression vector. The puφose of a degenerate set of genes is to provide, in one mixture, all ofthe sequences encoding the desired set of potential CDGF sequences. The synthesis of degenerate oligonucleotides is well known in the art (see for example, Narang, SA (1983) Tetrahedron 39:3; Itakura et al. (1981) Recombinant DNA, Proc 3rd Cleveland Sympos. Macromolecules, ed. AG Walton, Amsterdam: Elsevier pp273- 289; Itakura et al. (1984) Annu. Rev. Biochem. 53:323; Itakura et al. (1984) Science 198:1056; Ike et al. (1983) Nucleic Acid Res. 11:477. Such techniques have been employed in the directed evolution of other proteins (see, for example, Scott et al. (1990) Science 249:386-390; Roberts et al. (1992) PNAS 89:2429-2433; Devlin et al. (1990) Science 249: 404-406; Cwirla et al. (1990) PNAS 87: 6378-6382; as well as U.S. Patents Nos. 5,223,409, 5,198,346, and 5,096,815). Altematives to the above combinatorial mutagenesis also exist. For example, CDGF homologs (both agonist and antagonist forms) can be generated and isolated from a library by screening using, for example, alanine scanning mutagenesis and the like (Ruf et al. (1994) Biochemistry 33:1565-1572; Wang et al. (1994) J. Biol. Chem. 269:3095-3099; Balint et al. (1993) Gene 137:109-118; Grodberg et al. (1993) Eur. J. Biochem. 218:597-601; Nagashima et al. (1993) J. Biol. Chem. 268:2888-2892; Lowman et al. (1991) Biochemistry 30:10832- 10838; and Cunningham et al. (1989) Science 244:1081-1085), by linker scanning mutagenesis (Gustin et al. (1993) Virology 193:653-660; Brown et al. (1992) Mol. Cell Biol. 12:2644-2652; McKnight et al. (1982) Science 232:316); by saturation mutagenesis (Meyers et al. (1986) Science 232:613); by PCR mutagenesis (Leung et al. (1989) Method Cell Mol Biol 1 :11-19); or by random mutagenesis (Miller et al. (1992) A Short Course in Bacterial Genetics, CSHL Press, Cold Spring Harbor, NY; and Greener et al. (1994) Strategies in Mol Biol 7:32-34). A wide range of techniques are known in the art for screening gene products of combinatorial libraries, and for screening cDNA libraries for gene products having a certain property. Such techniques will be generally adaptable for rapid screening of the gene libraries generated by the combinatorial mutagenesis of CDGF homologs. The most widely used techniques for screening large gene libraries typically comprises cloning the gene library into replicable expression vectors, transforming appropriate cells with the resulting library of vectors, and expressing the combinatorial genes under conditions in which detection of a desired activity facilitates relatively easy isolation of the vector encoding the gene whose product was detected. Each of the illustrative assays described below are amenable to high through-put analysis as necessary to screen large numbers of degenerate CDGF sequences created by combinatorial mutagenesis techniques. In one screening assay, the candidate CDGF polypeptides are displayed on the surface of a cell or viral particle, and the ability of particular cells or viral particles to bind an erbB receptor protein via this gene product is detected in a "panning assay". For instance, the gene library can be cloned into the gene for a surface membrane protein of a bacterial cell, and the resulting fusion protein detected by panning (Ladner et al., WO 88/06630; Fuchs et al. (1991) Bio/Technology 9:1370-1371; and Goward et al. (1992) TIBS 18:136-140). In a similar fashion, a detectably labeled erbB receptor can be used to score for potentially functional CDGF polypeptide homologs. For example, the Alkaline Phosphatase-ert Z?2 or Ap-erbB4 fusion proteins, or the equivalent fluorescently labeled receptors, can be used to detect CDGF homologs which retain receptor-binding activity. In the application of fluorescently labeled receptor, cells can be visually inspected and separated under a fluorescence microscope, or, where the moφhology ofthe cell permits, separated by a fluorescence-activated cell sorter. In an altemate embodiment, the gene library is expressed as a fusion protein on the surface of a viral particle. For instance, in the filamentous phage system, foreign peptide sequences can be expressed on the surface of infectious phage, thereby conferring two significant benefits. First, since these phage can be applied to affinity matrices at very high concentrations, a large number of phage can be screened at one time. Second, since each infectious phage displays the combinatorial gene product on its surface, if a particular phage is recovered from an affinity matrix in low yield, the phage can be amplified by another round of infection. The group of almost identical E. coli filamentous phages Ml 3, fd., and fl are most often used in phage display libraries, as either of the phage gill or gVIII coat proteins can be used to generate fusion proteins without disrupting the ultimate packaging of the viral particle (Ladner et al. PCT publication WO 90/02909; Gaπard et al., PCT publication WO 92/09690; Marks et al. (1992) J Biol. Chem. 267:16007-16010; Griffiths et al. (1993) EMBO J 12:725-734; Clackson et al. (1991) Nature 352:624-628; and Barbas et al. (1992) PNAS 89:4457-4461). In an illustrative embodiment, the recombinant phage antibody system (RPAS, Pharamacia Catalog number 27-9400-01) can be easily modified for use in expressing and screening CDGF combinatorial libraries. For instance, the pCANTAB 5 phagemid of the RPAS kit contains the gene which encodes the phage gill coat protein. The CDGF combinatorial gene library can be cloned into the phagemid adjacent to the gill signal - 67- sequence such that it will be expressed as a gill fusion protein. After ligation, the phagemid is used to transform competent E. coli TGI cells. Transformed cells are subsequently infected with M13KO7 helper phage to rescue the phagemid and its candidate CDGF gene insert. The resulting recombinant phage contain phagemid DNA encoding a specific candidate CDGF, and display one or more copies of the coπesponding fusion coat protein. The phage-displayed candidate CDGF proteins which are capable of binding a CDGF receptor are selected or enriched by panning. For instance, the phage library can be on glutathione-immobilized erbB receptor/GST fusion proteins to enrich for CDGF homologs which retain an ability to bind an erbB receptor. The bound phage is then isolated, and ifthe recombinant phage express at least one copy ofthe wild type gill coat protein, they will retain their ability to infect E. coli. Thus, successive rounds of reinfection of E. coli, and panning will greatly enrich for CDGF homologs. Εach of these homologs can subsequently be screened for further biological activities in order to differentiate agonists and antagonists. For example, receptor-binding homologs isolated from the combinatorial library can be tested for their effect on cellular proliferation relative to the wild-type form of the protein. Altematively, one could screen the homologs for agonists by detecting autophosphorylation of an erbB receptor in response to treatment with the homolog (see, for example, Millauer et al. (1993) Cell 72:835-846). In similar fashion, antagonists can be identified from the enriched fraction based on their ability to inhibit autophosphorylationof the receptor by wild-type CDGF protein. In another embodiment, the combinatorial library is designed to be extracellularly presented (e.g. as it occurs naturally) and, though optionally, secreted (e.g. the polypeptides of the library all include a signal sequence but no transmembrane or cytoplasmic domains). The gene can be used to transfect a eukaryotic cell that can be co-cultured with cells which express an functional erbB receptor, e.g. a erbB2 or erbB4 receptor, and which are sensitive to treatement with the wild-type soluble form of CDGF. Functional CDGF homologs secreted by the cells expressing the combinatorial library will diffuse to neighboring erbB+ cells and induce a phenotypic change. Using, for example, antibodies directed to epitopes which are either created or destroyed in response to CDGF treatment, the pattem of detection of CDGF induction will resemble a gradient function, and will allow the isolation (generally after several repetitive rounds of selection) of cells producing active CDGF homologs. Likewise, CDGF antagonists can be selected in similar fashion by the ability of the cell producing a functional antagonist to protect neighboring cells from the effect of authentic CDGF added to the culture media. To illustrate, target cells are cultured in 24-well microtitre plates. The target cells can be, for instance, cells which naturally express erbB2 and/or erbB4 receptors, such as MDA- MB 453 cells, or cells which have been transfected with genes encoding such receptors. COS-7 cells are transfected with the combinatorial CDGF gene library and cultured (optionally) in a cell culture insert (e.g. Collaborative Biomedical Products, Catalog #40446) that are able to fit into the wells of the microtitre plate. The cell culture inserts are placed in the wells such that recombinant CDGF homologs secreted by the cells in the insert can diffuse through the porous bottom of the insert and contact the target cells in the microtitre plate wells. After a period of time sufficient for functional forms of CDGF to produce a measurable response in the target cells, the inserts are removed and the effect of any CDGF homologs on the target cells determined. Cells from the inserts coπesponding to wells which score positive for activity can be split and re-cultured on several inserts, the process being repeated until the active clones are identified. The invention also provides for reduction of the CDGF polypeptides to generate mimetics, e.g. peptide or non-peptide agents, which are able to dismpt binding of a CDGF polypeptide of the present invention with an erbB receptor. Accordingly, such mutagenic techniques as described above are also useful to map the determinants of the CDGF polypeptides which participate in protein-protein interactions involved in, for example, binding of the subject CDGF polypeptide to an erbB receptor or in causing oligomerization of receptors. To illustrate, the critical residues of a subject CDGF polypeptide which are involved in molecular recognition of an erbB receptor can be determined and used to generate CDGF polypeptide-derived peptidomimetics which competitively inhibit binding of the authentic CDGF protein with that receptor. By employing, for example, scanning mutagenesis to map the amino acid residues of the CDGF protein involved in binding the erbB receptor, peptidomimetic compounds can be generated which mimic those residues in binding to the receptor and which consequently can inhibit binding of CDGF to the receptor and interfere with its function. For instance, non-hydrolyzable peptide analogs of such residues can be generated using benzodiazepine (e.g., see Freidinger et al. in Peptides: Chemistry and Biology, G.R. Marshall ed., ESCOM Publisher: Leiden, Netherlands, 1988), azepine (e.g., see Huffman et al. in Peptides: Chemistry and Biology, G.R. Marshall ed., ESCOM Publisher: Leiden, Netherlands, 1988), substituted gama lactam rings (Garvey et al. in Peptides: Chemistry and Biology, G.R. Marshall ed., ESCOM Publisher: Leiden, Netherlands, 1988), keto-methylene pseudopeptides (Ewenson et al. (1986) J Med Chem 29:295; and Ewenson et al. in Peptides: Structure and Function (Proceedings of the 9th American Peptide Symposium) Pierce Chemical Co. Rockland, IL, 1985), β-turn dipeptide cores (Nagai et al. (1985) Tetrahedron Lett 26:647; and Sato et al. (1986) J Chem Soc Perkin Trans 1 :1231), and β-aminoalcohols (Gordon et al. (1985) Biochem Biophys Res Communl26:Al9; and Dann et al. (1986) Biochem Biophys Res Commun 134:71). Another aspect of the invention pertains to an antibody specifically reactive with a CDGF protein. For example, by using immunogens derived from a CDGF protein, e.g. based on the cDNA sequences, anti-protein/anti-peptide antisera or monoclonal antibodies can be made by standard protocols (See, or example, Antibodies: A Laboratory Manual ed. by Harlow and Lane (Cold Spring Harbor Press: 1988)). A mammal, such as a mouse, a hamster or rabbit can be immunized with an immunogenic form ofthe peptide (e.g., a CDGF polypeptide or an antigenic fragment which is capable of eliciting an antibody response). Techniques for confeπing immunogenicity on a protein or peptide include conjugation to carriers or other techniques well known in the art. An immunogenic portion of the CDGF protein can be administered in the presence of adjuvant. The progress of immunization can be monitored by detection of antibody titers in plasma or semm. Standard ELISA or other immunoassays can be used with the immunogen as antigen to assess the levels of antibodies. In a prefeπed embodiment, the subject antibodies are immunospecific for antigenic determinants of the CDGF protein of the present invention, e.g. antigenic determinants of a protein represented by SEQ ID No: 2, 4 or 7, or a closely related human or non-human mammalian homolog (e.g. atleast 85 percent homologous, preferably atleast 90 percent homologous, and more preferably at least 95 percent homologous). In yet a further prefeπed embodiment of the present invention, the anti-CDGF polypeptide antibodies do not substantially cross react (i.e. does not react specifically) with a protein which is, for example, less than 85 percent homologous to SEQ ID No: 2; e.g. less than 95 percent homologous with one of SEQ ID No: 2; e.g. less than 98-99 percent homologous with one of SEQ ID No: 2; less than 85 percent homologous to SEQ ID No: 4; e.g. less than 95 percent homologous with one of SEQ ID No: 4; e.g. less than 98-99 percent homologous with one of SEQ ID No: 4; less than 85 percent homologous to SEQ ID No: 7; e.g. less than 95 percent homologous with one of SEQ ID No: 7; e.g. less than 98-99 percent homologous with one of SEQ ID No: 7. By "not substantially cross react", it is meant that the antibody has a binding affinity for a non-homologous protein (e.g. heregulin, NDF, GGF or ARIA proteins) which is at least one order of magnitude, more preferably at least 2 orders of magnitude, and even more preferably at least 3 orders of magnitude less than the binding affinity of the antibody for the protein of SEQ ID No: 2, 4 and/or 7. Following immunization, anti-CDGF antisera can be obtained and, if desired, polyclonal anti-CDGF antibodies isolated from the serum. To produce monoclonal antibodies, antibody-producing cells (lymphocytes) can be harvested from an immunized animal and fused by standard somatic cell fusion procedures with immortalizing cells such as myeloma cells to yield hybridoma cells. Such techniques are well known in the art, an include, for example, the hybridoma technique (originally developed by Kohler and Milstein, (1975) Nature, 256: 495-497), the human B cell hybridoma technique (Kozbar et al., (1983) Immunology Today, A: 12), and the EBV-hybridoma technique to produce human monoclonal antibodies (Cole et al., (1985) Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc. pp. 77-96). Hybridoma cells can be screened immunochemically for production of antibodies specifically reactive with a CDGF polypeptide of the present invention and monoclonal antibodies isolated from a culture comprising such hybridoma cells. The term antibody as used herein is intended to include fragments thereof which are also specifically reactive with one of the subject CDGF polypeptide. Antibodies can be fragmented using conventional techniques and the fragments screened for utility in the same manner as described above for whole antibodies. For example, F(ab)2 fragments can be generated by treating antibody with pepsin. The resulting F(ab)2 fragment can be treated to reduce disulfide bridges to produce Fab fragments. The antibody of the present invention is further intended to include single chain, bispecific and chimeric molecules having a CDGF affinity confeπed by at least one CDR region ofthe antibody. Both monoclonal and polyclonal antibodies (Ab) directed against CDGF polypeptide or CDGF polypeptide variants, and antibody fragments such as Fab and F(ab)2, can be used to block the action of CDGF and allow the study of the role of CDGF in, for example, embryogenesis and/or tumorogenesis. For example, purified monoclonal Abs can be injected directly into the limb buds of chick or mouse embryos. Thus, the use of anti-CDGF Abs during this developmental stage can allow assessment of the effect of CDGF on the formation of limbs in vivo. In a similar approach, hybridomas producing anti-CDGF monoclonal Abs, or biodegradable gels in which anti-CDGF Abs are suspended, can be implanted at a site proximal or within the area at which CDGF action is intended to be blocked. Experiments of this nature can aid in deciphering the role of this and other factors that may be involved in limb patteming and tissue formation. Antibodies which specifically bind CDGF polypeptide epitopes can also be used in immunohistochemical staining of tissue samples in order to evaluate the abundance and pattem of expression of each ofthe subject CDGF polypeptides. Anti-CDGF antibodies can be used diagnostically in immuno-precipitation and immuno-blotting to detect and evaluate CDGF protein levels in tissue or bodily fluid as part of a clinical testing procedure. For instance, such measurements can be useful in predictive valuations of the onset or progression of neurological disorders, such as those marked by denervation-like or disuse¬ like symptoms. Likewise, the ability to monitor CDGF levels in an individual can allow determination of the efficacy of a given treatment regimen for an individual afflicted with such a disorder. The level of CDGF polypeptides can be measured in bodily fluid, such as in samples of cerebral spinal fluid, or can be measured in tissue, such as produced by biopsy. Diagnostic assays using anti-CDGF antibodies can include, for example, immunoassays designed to aid in early diagnosis of a neurodegenerative disorder, particularly ones which are manifest at birth. Diagnostic assays using anti-CDGF polypeptide antibodies can also include immunoassays designed to aid in early diagnosis and phenotyping of a neoplastic or hypeφlastic disorder. Another application of anti-CDGF antibodies of the present invention is in the immunological screening of cDNA libraries constmcted in expression vectors such as λgtll, λgtl8-23, λZAP, and λORF8. Messenger libraries of this type, having coding sequences inserted in the coπect reading frame and orientation, can produce fusion proteins. For instance, λgtl 1 will produce fusion proteins whose amino termini consist of β-galactosidase amino acid sequences and whose carboxy termini consist of a foreign polypeptide. Antigenic epitopes of a CDGF protein can then be detected with antibodies, as, for example, reacting nitrocellulose filters lifted from infected plates with anti-CDGF antibodies. Positive phage detected by this assay can then be isolated from the infected plate. Thus, the presence of CDGF homologs (orthologs) can be detected and cloned from other animals, as can altemate isoforms (including splicing variants). Moreover, the nucleotide sequence determined from the cloning of the CDGF gene will further allow for the generation of probes and primers designed for use in identifying and/or cloning CDGF homologs in other cell types, e.g. from other tissues, as well as CDGF homologs from other animals, e.g. humans. For instance, the present invention also provides a probe/primer comprising a substantially purified oligonucleotide, which oligonucleotide comprises a region of nucleotide sequence that hybridizes under stringent conditions to at least 10 consecutive nucleotides of sense or anti-sense sequence of SEQ ID No: 1, 3 and/or 6, or naturally occuning mutants thereof. For instance, primers based on the nucleic acids represented in SEQ ID No. 1, 3 or 6 can be used in PCR reactions to clone CDGF homologs. Likewise, probes based on the CDGF gene sequences of SEQ ID No. 1, 3 and 6 can be used to detect CDGF transcripts or genomic sequences. In prefeπed embodiments, the probe further comprises a label group attached thereto and able to be detected, e.g. the label group is selected from the group consisting of radioisotopes, fluorescent compounds, enzymes, and enzyme co-factors. Such probes can also be used as a part of a diagnostic test kit for identifying cells in which CDGF is misexpressed, such as by measuring a level of a CDGF encoding nucleic acid in a sample of cells from a patient; e.g. detecting CDGF mRNA levels or determining whether a genomic CDGF gene has been mutated or deleted. To illustrate, nucleotide probes can be generated from the CDGF gene which facilitate histological screening of intact tissue and tissue samples for the presence of a CDGF polypeptide mRNA. Similar to the diagnostic uses of anti-CDGF polypeptide antibodies, the use of probes directed to CDGF messages, or to genomic CDGF sequences, can be used for both predictive and therapeutic evaluation of allelic mutations which might be manifest in, for example, neoplastic or hypeφlastic disorders (e.g. unwanted cell growth) or abnormal differentiation of tissue. Used in conjunction with anti-CDGF immunoassays, the nucleotide probes can help facilitate the determination of the molecular basis for a developmental disorder which may involve some abnormality associated with expression (or lack thereof) of a CDGF polypeptide. For instance, variation in CDGF polypeptide synthesis can be differentiated from a mutation in the CDGF coding sequence. Accordingly, the present method provides a method for determining if a subject is at risk for a disorder characterized by unwanted cell proliferation or abherent control of differentiation. In prefeπed embodiments, the subject method can be generally characterized as comprising detecting, in a tissue sample of the subject (e.g. a human patient), the presence or absence of a genetic lesion characterized by at least one of (i) a mutation of a gene encoding a CDGF polypeptide or (ii) the mis-expression of a CDGF gene. To illustrate, such genetic lesions can be detected by ascertaining the existence of at least one of (i) a deletion of one or more nucleotides from a CDGF gene, (ii) an addition of one or more nucleotides to such a CDGF gene, (iii) a substitution of one or more nucleotides of a CDGF gene, (iv) a gross chromosomal reanangement of a CDGF genes, (v) a gross alteration in the level of a messenger RNA transcript of a CDGF gene, (vi) abeπant modification of a CDGF gene, such as ofthe methylation pattem ofthe genomic DNA, (vii) the presence of a non- wild type splicing pattem of a messenger RNA transcript of a CDGF gene, and (viii) a non- wild type level of a CDGF polypeptide. In one aspect ofthe invention there is provided a probe/primer comprising an oligonucleotide containing a region of nucleotide sequence which is capable of hybridizing to a sense or antisense sequence of SEQ ID Nos: 1, 3, 5 and or 7, or naturally occuning mutants thereof, or 5' or 3' flanking sequences or intronic sequences naturally associated with a CDGF gene. The probe is exposed to nucleic acid of a tissue sample; and the hybridization of the probe to the sample nucleic acid is detected. In certain embodiments, detection of the lesion comprises utilizing the probe/primer in a polymerase chain reaction (PCR) (see, e.g., U.S. Patent No: 4,683,195 and 4,683,202) or, altematively, in a ligation chain reaction (LCR) (see, e.g., Landegran et al. (1988) Science, 241:1077-1080; and NaKazawa et al. (1944) PNAS 91:360-364) the later of which can be particularly useful for detecting point mutations in the CDGF gene. Altematively, immunoassays can be employed to determine the level of CDGF protein, either soluble or membrane bound. Also, the use of anti-sense techniques (e.g. microinjection of antisense molecules, or transfection with plasmids whose transcripts are anti-sense with regard to a CDGF mRNA or gene sequence) can be used to investigate role of CDGF in developmental events, as well as the normal cellular function of CDGF in adult tissue. Such techniques can be utilized in cell culture, but can also be used in the creation of transgenic animals. Furthermore, by making available purified and recombinant CDGF polypeptides, the present invention facilitates the development of assays which can be used to screen for dmgs, or for CDGF homologs, which are either agonists or antagonists of the normal cellular function of the subject CDGF polypeptides, or of their role in the pathogenesis of cellular proliferation and/or differentiation and disorders related thereto. In one embodiment, the assay evaluates the ability of a compound to modulate binding between a CDGF polypeptide and an erbB receptor. A variety of assay formats will suffice and, in light of the present inventions, will be comprehended by skilled artisan. In many dmg screening programs which test libraries of compounds and natural extracts, high throughput assays are desirable in order to maximize the number of compounds surveyed in a given period of time. Assays which are performed in cell-free systems, such as may be derived with purified or semi-purified proteins, are often prefened as "primary" screens in that they can be generated to permit rapid development and relatively easy detection of an alteration in a molecular target which is mediated by a test compound. Moreover, the effects of cellular toxicity and/or bioavailability of the test compound can be generally ignored in the in vitro system, the assay instead being focused primarily on the effect of the drag on the molecular target as may be manifest in an alteration of binding affinity with receptor proteins. Accordingly, in an exemplary screening assay of the present invention, the compound of interest is contacted with an erbB receptor polypeptide which is ordinarily capable of binding a CDGF protein. To the mixture ofthe compound and receptor is then added a composition containing a CDGF polypeptide. Detection and quantification of receptor/CDGF complexes provides a means for determining the compound's efficacy at inhibiting (or potentiating) complex formation between the receptor protein and the CDGF polypeptide. The efficacy of the compound can be assessed by generating dose response curves from data obtained using various concentrations of the test compound. Moreover, a control assay can also be performed to provide a baseline for comparison. In the control assay, isolated and purified CDGF polypeptide is added to a composition containing the receptor protein, and the formation of receptor/CDGF complex is quantitated in the absence ofthe test compound. Complex formation between the CDGF polypeptide and an erbB receptor may be detected by a variety of techniques. For instance, modulation ofthe formation of complexes can be quantitated using, for example, detectably labelled proteins such as radiolabelled, fluorescently labelled, or enzymatically labelled CDGF polypeptides, by immunoassay, or by chromatographic detection. Typically, it will be desirable to immobilize either the erbB receptor or the CDGF polypeptide to facilitate separation of receptor/CDGF complexes from uncomplexed forms of one ofthe proteins, as well as to accomadate automation ofthe assay. In one embodiment, a fusion protein can be provided which adds a domain that allows the protein to be bound to a matrix. For example, glutathione-S-transferase/receptor (GST/receptor) fusion proteins can be adsorbed onto glutathione sepharose beads (Sigma Chemical, St. Louis, MO) or glutathione derivatized microtitre plates, which are then combined with the CDGF polypeptide, e.g. an 35 S-labeled CDGF polypeptide, and the test compound and incubated under conditions conducive to complex formation, e.g. at physiological conditions for salt and pH, though slightly more stringent conditions may be desired, e.g., at 4°C in a buffer containing 0.6M NaCl or a detergent such as 0.1% Triton X-l 00. Following incubation, the beads are washed to remove any unbound CDGF polypeptide, and the matrix bead-bound radiolabel determined directly (e.g. beads placed in scintilant), or in the superntantant after the receptor/CDGF complexes are dissociated. Altematively, the complexes can dissociated from the bead, separated by SDS-PAGE gel, and the level of CDGF polypeptide found in the bead fraction quantitated from the gel using standard electrophoretic techniques. Other techniques for immobilizing proteins on matrices are also available for use in the subject assay. For instance, the erbB receptor protein can be immobilized utilizing conjugation of biotin and streptavidin. For instance, biotinylated receptor molecules can be prepared from biotin-NHS (N-hydroxy-succinimide) using techniques well known in the art (e.g., biotinylation kit, Pierce Chemicals, Rockford, IL), and immobilized in the wells of streptavidin-coated 96 well plates (Pierce Chemical). Altematively, antibodies reactive with the erbB receptor but which do not interfere with CDGF binding can be derivatized to the wells of the plate, and the receptor trapped in the wells by antibody conjugation. As above, preparations of a CDGF polypeptide and a test compound are incubated in the receptor- presenting wells ofthe plate, and the amount of receptor/CDGF complex trapped in the well can be quantitated. Exemplary methods for detecting such complexes, in addition to those described above for the GST-immobilized complexes, include immunodetection of complexes using antibodies reactive with the CDGF polypeptide, or which are reactive with the receptor protein and compete for binding with the CDGF polypeptide; as well as enzyme- linked assays which rely on detecting an enzymatic activity associated with the CDGF polypeptide. In the instance of the latter, the enzyme can be chemically conjugated or provided as a fusion protein with the CDGF polypeptide. To illustrate, the CDGF polypeptide can be chemically cross-linked or genetically fused with alkaline phosphatase, and the amount of CDGF polypeptide trapped in the complex can be assessed with a chromogenic substrate of the enzyme, e.g. paranitrophenylphosphate. Likewise, a fusion protein comprising the CDGF polypeptide and glutathione-S-transferase can be provided, and complex formation quantitated by detecting the GST activity using l-chloro-2,4- dinitrobenzene (Habig et al (1974) JBiol Chem 249:7130). For processes which rely on immunodetection for quantitating one of the proteins trapped in the complex, antibodies against the protein, such as the anti-CDGF antibodies described herein, can be used. Altematively, the protein to be detected in the complex can be "epitope tagged" in the form of a fusion protein which includes, in addition to the CDGF polypeptide or erbB receptor sequence, a second polypeptide for which antibodies are readily available (e.g. from commercial sources). For instance, the GST fusion proteins described above can also be used for quantification of binding using antibodies against the GST moiety. Other useful epitope tags include myc-epitopes (e.g., see Ellison et al. (1991) J Biol Chem -VS- 266:21150-21157) which includes a 10-residue sequence from c-myc, as well as the pFLAG system (International Biotechnologies, Inc.) or the pEZZ-protein A system (Pharamacia, NJ). Another aspect of the present invention relates to a method of inducing and/or maintaining a differentiated state, enhancing survival, and/or promoting proliferation of a cell responsive to a CDGF protein, by contacting the cells with a CDGF agonist or a CDGF antagonist. For instance, it is contemplated by the invention that, in light of the present finding of an apparently broad involvement of CDGF proteins in the formation and maintanence of ordered spatial aπangements of differentiated tissues in vertebrates, the subject method could be used to generate and/or maintain an aπay of different vertebrate tissue both in vitro and in vivo. The CDGF agent can be, as appropriate, any of the preparations described above, including isolated polypeptides, gene therapy constructs, antisense molecules, peptidomimetics or agents identified in the drag assays provided herein. For example, the present method is applicable to cell culture technique. In vitro neuronal culture systems have proved to be fundamental and indispensable tools for the study of neural development, as well as the identification of neurotrophic factors such as nerve growth factor (NGF), ciliary trophic factors (CNTF), and brain derived neurotrophic factor (BDNF). Once a neuronal cell has become terminally-differentiated it typically will not change to another terminally differentiated cell-type. However, neuronal cells can nevertheless readily lose their differentiated state. This is commonly observed when they are grown in culture from adult tissue, and when they form a blastema during regeneration. The present method provides a means for ensuring an adequately restrictive environment in order to maintain neuronal cells at various stages of differentiation, and can be employed, for instance, in cell cultures designed to test the specific activities of other trophic factors. In such embodiments of the subject method, the cultured cells can be contacted with a CDGF polypeptide, or an agent identifed in the assays described above, in order to induce neuronal differentiation (e.g. of a stem cell), or to maintain the integrity of a culture of terminally- differentiated neuronal cells by preventing loss of differentiation. The source of CDGF in the culture can be derived from, for example, a purified or semi-purified protein composition added directly to the cell culture media, or altematively, released from a polymeric device which supports the growth of various neuronal cells and which has been doped with a CDGF protein. The source of the CDGF can also be a cell that is co-cultured with the intended neuronal cell and which produces either a recombinant or natural form of a CDGF protein. Altematively, the source can be the neuronal cell itself which as been engineered to produce a recombinant CDGF. In an exemplary embodiment, a naive neuronal cell (e.g. a stem cell) is treated with a CDGF agonist in order to induce differentiation of the cells into, for example, sensory neurons or, alternatively, motorneurons. Such neuronal cultures can be used as convenient assay systems as well as sources of implantable cells for therapeutic treatments. For example, CDGF polypeptides may be useful in establishing and maintaining the olfactory neuron cultures described U.S. Patent 5,318,907 and the like. To further illustrate potential uses, it is noted that intracerebral grafting has emerged as an additional approach to central nervous system therapies. For example, one approach to repairing damaged brain tissues involves the transplantation of cells from fetal or neonatal animals into the adult brain (Dunnett et al. (1987) J Exp Biol 123:265-289; and Freund et al. (1985) J Neurosci 5:603-616). Fetal neurons from a variety of brain regions can be successfully incoφorated into the adult brain, and such grafts can alleviate behavioral defects. For example, movement disorder induced by lesions of dopaminergic projections to the basal ganglia can be prevented by grafts of embryonic dopaminergic neurons. Complex cognitive functions that are impaired after lesions of the neocortex can also be partially restored by grafts of embryonic cortical cells. Thus, use of the present erbB receptor ligands for maintenance of neuronal cell cultures can help to provide a source of implantable neuronal tissue. The use of a CDGF polypeptide in the culture can be to prevent loss of differentiation, or where fetal tissue is used, especially neuronal stem cells, a CDGF polypeptide can be used to induce differentiation. Stem cells useful in the present invention are generally known. For example, several neural crest cells have been identified, some of which are multipotent and likely represent uncommitted neural crest cells, and others of which can generate only one type of cell, such as sensory neurons, and likely represent committed progenitor cells. The role of a CDGF protein employed in the present method to culture such stem cells can be to induce differentiation ofthe uncommitted progenitor and thereby give rise to a committed progenitor cell, or to cause further restriction of the developmental fate of a committed progenitor cell towards becoming a terminally-differentiated neuronal cell. For example, the present method can be used in vitro to induce and/or maintain the differentiation of neural crest cells into glial cells, schwann cells, chromaffin cells, cholinergic sympathetic or parasympathetic neurons, as well as peptidergic and serotonergic neurons. The CDGF polypeptide can be used alone, or can be used in combination with other neurotrophic factors which act to more particularly enhance a particular differentiation fate of the neuronal progenitor cell. In the later instance, the CDGF polypeptide might be viewed as ensuring that the treated cell has achieved a particular phenotypic state such that the cell is poised along a certain developmental pathway so as to be properly induced upon contact with a secondary neurotrophic factor. In similar fashion, even relatively undifferentiated stem cells or primative neuroblasts can be maintained in culture and caused to differentiate with treatment of CDGF polypeptides. Exemplary primative cell cultures comprise cells harvested from the nueral plate or neural tube of an embryo even before much overt differentiation has occuπed. In addition to the implantation of cells cultured in the presence of a functional CDGF activity, yet another objective ofthe present invention concems the therapeutic application of a CDGF polypeptide or mimetic to enhance survival of neurons and other neuronal cells in both the central nervous system and the peripheral nervous system. The ability of CDGF to regulate neuronal differentiation and survival during development of the nervous system and also presumably in the adult state indicates that CDGF can be reasonably expected to facilitate control of adult neurons with regard to maintenance, functional performance, and aging of normal cells; repair and regeneration processes in chemically or mechanically lesioned cells; and prevention of degeneration and premature death which result from loss of differentiation in certain pathological conditions. In light of this understanding, the present invention specifically contemplates applications of the subject proteins to the treatment of (prevention and/or reduction of the severity of) neurological conditions deriving from: (i) acute, subacute, or chronic injury to the nervous system, including traumatic injury, chemical injury, vasal injury and deficits (such as the ischemia resulting from stroke), together with infectious/inflammatory and tumor-induced injury; (ii) aging ofthe nervous system including Alzheimer's disease; (iii) chronic neurodegenerative diseases of the nervous system, including Parkinson's disease, Huntington's chorea, amylotrophic lateral sclerosis and the like, as well as spinocerebellar degenerations; (iv) chronic immunological diseases of the nervous system or affecting the nervous system, including multiple sclerosis; and (v) disorders of sensory neurons as well as degenerative diseases ofthe retina. Many neurological disorders are associated with degeneration of discrete populations of neuronal elements and may be treatable with a therapeutic regimen which includes a CDGF polypeptide (or equivalent thereof). For example, Alzheimer's disease is associated with deficits in several neurotransmitter systems, both those that project to the neocortex and those that reside with the cortex. For instance, the nucleus basalis in patients with Alzheimer's disease were observed to have a profound (75%) loss of neurons compared to age-matched controls. Although Alzheimer's disease is by far the most common form of dementia, several other disorders can produce dementia. Several of these are degenerative diseases characterized by the death of neurons in various parts ofthe central nervous system, especially the cerebral cortex. However, some forms of dementia are associated with degeneration of the thalmus or the white matter underlying the cerebral cortex. Here, the cognitive dysfunction results from the isolation of cortical areas by the degeneration of efferents and afferents. Huntington's disease involves the degeneration of intrastraital and cortical cholinergic neurons and GABAergic neurons. Pick's disease is a severe neuronal degeneration in the neocortex of the frontal and anterior temporal lobes, sometimes accompanied by death of neurons in the striatum. Treatment of patients suffering from such degenerative conditions can include the application of CDGF polypeptides, or agents which mimic their effects, in order to manipulate, for example, the de-differentiation and apoptosis of neurons which give rise to loss of neurons. In prefeπed embodiments, a source of a CDGF agent is stereotactically provided within or proximate the area of degeneration. In addition to degenerative-induced dementias, a pharmaceutical preparation of a CDGF homolog can be applied opportunely in the treatment of neurodegenerative disorders which have manifestations of tremors and involuntary movements. Parkinson's disease, for example, primarily affects subcortical structures and is characterized by degeneration of the nigrostriatal pathway, raphe nuclei, locus cereleus, and the motor nucleus of vagus. Ballism is typically associated with damage to the subthalmic nucleus, often due to acute vascular accident. Also included are neurogenic and myopathic diseases which ultimately affect the somatic division of the peripheral nervous system and are manifest as neuromuscular disorders. Examples include chronic atrophies such as amyotrophic lateral sclerosis, Guillain-Baπe syndrome and chronic peripheral neuropathy, as well as other diseases which can be manifest as progressive bulbar palsies or spinal muscular atrophies. The present method is ammenable to the treatment of disorders of the cerebellum which result in hypotonia or ataxia, such as those lesions in the cerebellum which produce disorders in the limbs ipsilateral to the lesion. For instance, a preparation of a CDGF homolog can be used to treat a restricted form of cerebellar corical degeneration involving the anterior lobes (vermis and leg areas) such as is common in alcoholic patients. In yet another embodiment, the subject method is used to treat amyotrophic lateral sclerosis. ALS is a name given to a complex of disorders that comprise upper and lower motor neurons. Patients may present with progressive spinal muscular atrophy, progressive bulbar palsy, primary lateral sclerosis, or a combination of these conditions. The major pathological adnomality is characterized by a selective and progressive degeneration of the lower motor neurons in the spinal cord and the upper motor neurons in the cerebral cortex. The therapeutic application of a CDGF therapeutic agent, such as a soluble form of a polypeptide represented in either of SEQ ID No: 2, 4 or 6, or a peptidomimetic thereof, can be used alone or in conjunction with other neurotrophic factors such as CNTF, BDNF, or NGF to prevent and/or reverse motor neuron degeneration in ALS patients. The CDGF polypeptides of the present invention can also be used in the treatment of autonomic disorders of the peripheral nervous system, which include disorders affecting the innervation of smooth muscle and endocrine tissue (such as glandular tissue). For instance, CDGF compositions may be useful to treat tachycardia or atrial cardiac arrythmias which may arise from a degenerative condition of the nerves innervating the striated muscle of the heart. Accordingly, compositions comprising CDGF homologs or other CDGF agents described herein may be employed to support, or altematively, antagonize the survival and reprojection of several types of central and peripheral ganglionic neurons, sympathetic and sensory neurons, as well as motor neurons. To illustrate, such therapeutic compositions may be useful in treatments designed to rescue, for example, retinal ganglia, inner ear and accoustical nerves, and motorneurons, from lesion-induced death as well as guiding reprojection of these neurons after such damage. Such diseases and conditions include but are not limited to CNS trauma, infarction, infection (such as viral infection with varicella- zoster), metabolic disease, nutritional deficiency, toxic agents (such as cisplatin treatment). Moreover, certain of the CDGF agents (probably antagonistic forms) may be useful in the selective ablation of sensory neurons, for example, in the treatment of chronic pain syndromes. CDGF can be used in nerve prostheses for the repair of central and peripheral nerve damage. In particular, where a crashed or severed axon is entubulated by use of a prosthetic device, CDGF polypeptides can be added to the prosthetic device to increase the rate of growth and regeneration of the dendritic processes. Exemplary nerve guidance channels are described in U.S. patents 5,092,871 and 4,955,892. Accordingly, a severed axonal process can be directed toward the nerve ending from which it was severed by a prosthesis nerve guide which contains, e.g. a semi-solid formulation containing a CDGF polypeptide or mimetic, or which is derivatized along the inner walls with a CDGF protein. In yet another embodiment, the subject CDGF polypeptides can be used in the treatment of neoplastic or hypeφlastic transformations, particulary of the central nervous system and lymphatic system. For instance, certain CDGF homologs are likely to be capable of inducing differentiation of transformed neuronal cells to become post-mitotic or possibly apoptotic. Treatment with other CDGF homologs may involve disruption of autocrine loops, such as TGF-β or PDGF autostimulatory loops, believed to be involved in the neoplastic transformation of several neuronal tumors. CDGF homologs may, therefore, be of use in the treatment of, for example, malignant gliomas, medulloblastomas, neuroectodermal tumors, and ependymonas. Yet another aspect of the present invention concems the application of the discovery that CDGF proteins are likely induction signals involved in other vertebrate organogenic pathways in addition to neuronal differentiation as described above, having potential roles in other ectodermal patteming, as well as both mesodermal and endodermal differentiation processes. Thus, it is contemplated by the invention that compositions comprising CDGF proteins can also be utilized for both cell culture and therapeutic methods involving generation and maintenance of non-neuronal tissue, such as in controlling the development and maintenance of tissue from the digestive tract, liver, lungs, and other organs which derive from the primitive gut, as well as dorsal mesoderm-derived stmctures including muscular- skeletal tissues and connective tissue of the skin; intermediate mesoderm-derived stmctures, such as the kidney and other renal and urogenital tissues; and head mesenchymal and neural crest-derived tissue, such as cephalic connective tissue and skull and branchial cartilage, occular tissue, muscle and cardiac tissue. This should not be constmed as a comprehensive list, and other tissues which may be affected by CDGF polypeptides are envisaged. -527 -- The CDGF polypeptides of the present invention, or pharmaceutically acceptable salts thereof, may be conveniently formulated for administration with a biologically acceptable medium, such as water, buffered saline, polyol (for example, glycerol, propylene glycol, liquid polyethylene glycol and the like) or suitable mixtures thereof. The optimum concentration of the active ingredient(s) in the chosen medium can be determined emperically, according to procedures well known to medicinal chemists. As used herein, "biologically acceptable medium" includes any and all solvents, dispersion media, and the like which may be appropriate for the desired route of administration of the pharmaceutical preparation. The use of such media for pharmaceutically active substances is known in the art. Except insofar as any conventional media or agent is incompatible with the activivity of the CDGF polypeptide, its use in the pharamceutical preparation of the invention is contemplated. Suitable vehicles and their formulation inclusive of other proteins are described, for example, in the book Remington's Pharmaceutical Sciences (Remington's Pharmaceutical Sciences. Mack Publishing Company, Easton, Pa., USA 1985). These vehicles include injectable "deposit formulations". Based on the above, such pharmaceutical formulations include, although not exclusively, solutions or freeze-dried powders of a CDGF polypeptide in association with one or more pharmaceutically acceptable vehicles or diluents, and contained in buffered media at a suitable pH and isosmotic with physiological fluids. For illustrative puφoses only and without being limited by the same, possible compositions or formulations which may be prepared in the form of solutions for the treatment of nervous sytem disorders with a CDGF polypeptide are given in U.S. Patent No. 5,218,094. In the case of freeze-dried preparations, supporting excipients such as, but not exclusively, mannitol or glycine may be used and appropriate buffered solutions of the desired volume will be provided so as to obtain adequate isotonic buffered solutions of the desired pH. Similar solutions may also be used for the pharmaceutical compositions of CDGF polypeptides in isotonic solutions ofthe desired volume and include, but not exclusively, the use of buffered saline solutions with phosphate or citrate at suitable concentrations so as to obtain at all times isotonic pharmaceutical preparations ofthe desired pH, (for example, neutral pH). Methods of introduction of exogenous CDGF polypeptides at the site of treatment include, but are not limited to, intradermal, intramuscular, intraperitoneal, intravenous, subcutaneous, oral, and intranasal. In addition, it may be desirable to introduce the pharmaceutical compositions ofthe invention into the central nervous system by any suitable route, including intraventricular and intrathecal injection. Intraventricular injection may be facilitated by an intraventricular catheter, for example, attached to a reservoir, such as an Ommaya reservoir. Methods of introduction may also be provided by rechargable or biodegradable devices, particularly where gradients of CDGF concentrations in a tissue is desired. Various slow release polymeric devices have been developed and tested in vivo in recent years for the controlled delivery of drags, including proteinacious biopharmaceuticals. A variety of biocompatible polymers (including hydrogels), including both biodegradable and non- degradable polymers, can be used to form an implant for the sustained release of a CDGF at a particular target site. Such embodiments ofthe present invention can be used for the delivery of an exogenously purified CDGF polypeptides, which has been incoφorated in the polymeric device, or for the delivery of CDGF polypeptides produced by a cell encapsulated in the polymeric device. The generation of such implants is generally known in the art. See, for example, Concise Encylopedia of Medical & Dental Materials, ed. by David Williams (MIT Press: Cambridge, MA, 1990); the Sabel et al. U.S. Patent No. 4,883,666; Aebischer et al. U.S. Patent No. 4,892,538; Aebischer et al. U.S. Patent No. 5,106,627; Lim U.S. Patent No. 4,391,909; and Sefton U.S. Patent No. 4,353,888. In yet another embodiment of the present invention, the pharmaceutical CDGF polypeptide can be administered as part of a combinatorial therapy with other agents. For example, the combinatorial therapy can include a CDGF protein with at least one trophic factor. Exemplary trophic factors include nerve growth factor, cilliary neurotrophic growth factor, schwanoma-derived growth factor, glial growth factor, stiatal-derived neuronotrophic factor, platelet-derived growth factor, and scatter factor (HGF-SF). Another aspect ofthe invention features transgenic non-human animals which express a heterologous CDGF gene ofthe present invention, or which have had one or more genomic CDGF gene(s) dismpted in at least one ofthe tissue or cell-types ofthe animal. Accordingly, the invention features an animal model for developmental diseases, which animal has a CDGF allele which is mis-expressed. For example, a mouse can be bred which has one or more CDGF alleles deleted or otherwise rendered inactive. Such a mouse model can then be used to study disorders arising from mis-expressed CDGF genes. Another aspect of the present invention concems transgenic animals which are comprised of cells (of that animal) which contain a transgene of the present invention and which preferably (though optionally) express an exogenous CDGF protein in one or more cells in the animal. The CDGF transgene can encode the wild-type form of the protein, or can encode homologs thereof, including both agonists and antagonists, as well as antisense constmcts. In prefeπed embodiments, the expression ofthe transgene is restricted to specific subsets of cells, tissues or developmental stages utilizing, for example, cis-acting sequences that control expression in the desired pattem. In the present invention, such mosiac expression ofthe subject polypeptide can be essential for many forms of lineage analysis and can additionally provide a means to assess the effects of, for example, lack of CDGF expression which might grossly alter development in small patches of tissue within an otherwise normal embryo. Toward this and, tissue-specific regulatory sequences and conditional regulatory sequences can be used to control expression ofthe transgene in certain spatial pattems. Moreover, temporal pattems of expression can be provided by, for example, conditional recombination systems or prokaryotic transcriptional regulatory sequences. Genetic techniques which allow for the expression of transgenes can be regulated via site-specific genetic manipulation in vivo are known to those skilled in the art. For instance, genetic systems are available which allow for the regulated expression of a recombinase that catalyzes the genetic recombination a target sequence. As used herein, the phrase "target sequence" refers to a nucleotide sequence that is genetically recombined by a recombinase. The target sequence is flanked by recombinase recognition sequences and is generally either excised or inverted in cells expressing recombinase activity. Recombinase catalyzed recombination events can be designed such that recombination of the target sequence results in either the activation or repression of expression of the subject CDGF polypeptide. For example, excision of a target sequence which interferes with the expression of a recombinent CDGF gene, such as one which encodes an antagonistic homolog, can be designed to activate expression of that gene. This interference with expression of the protein can result from a variety of mechanisms, such as spatial separation of the CDGF gene from the promoter element or an intemal stop codon. Moreover, the transgene can be made wherein the coding sequence ofthe gene is flanked recombinase recognition sequences and is initially transfected into cells in a 3' to 5' orientation with respect to the promoter element. In such an instance, inversion of the target sequence will reorient the subject gene by placing the 5' end of the coding sequence in an orientation with respect to the promoter element which allow for promoter driven transcriptional activation. In an illustrative embodiment, either the crelloxP recombinase system of bacteriophage Pl (Lakso et al. (1992) PNAS 89:6232-6236; Orban et al. (1992) PNAS 89:6861-6865) or the FLP recombinase system of Saccharomyces cerevisiae (O'Gorman et al. (1991) Science 251:1351-1355; PCT publication WO 92/15694) can be used to generate in vivo site-specific genetic recombination systems. Cre recombinase catalyzes the site-specific recombination of an intervening target sequence located between loxP sequences. loxP sequences are 34 base pair nucleotide repeat sequences to which the Cre recombinase binds and are required for Cre recombinase mediated genetic recombination. The orientation of loxP sequences determines whether the intervening target sequence is excised or inverted when Cre recombinase is present (Abremski et al. (1984) J. Biol. Chem. 259:1509-1514); catalyzing the excision of the target sequence when the loxP sequences are oriented as direct repeats and catalyzes inversion of the target sequence when loxP sequences are oriented as inverted repeats. Accordingly, genetic recombination ofthe target sequence is dependent on expression of the Cre recombinase. Expression of the recombinase can be regulated by promoter elements which are subject to regulatory control, e.g., tissue-specific, developmental stage-specific, inducible or repressible by extemally added agents. This regulated control will result in genetic recombination of the target sequence only in cells where recombinase expression is mediated by the promoter element. Thus, the activation expression of the receombinant CDGF protein can be regulated via control of recombinase expression. Use of the crelloxP recombinase system to regulate expression of a recombinant CDGF protein requires the constmction of a transgenic animal containing transgenes encoding both the Cre recombinase and the subject protein. Animals containing both the Cre recombinase and a recombinant CDGF gene can be provided through the constmction of "double" transgenic animals. A convenient method for providing such animals is to mate two transgenic animals each containing a transgene, e.g., a CDGF gene and recombinase gene. One advantage derived from initially constructing transgenic animals containing a CDGF transgene in a recombinase-mediated expressible format, particularly derives from the likelihood that the subject protein will be deleterious upon expression in the transgenic animal. In such an instance, a founder population, in which the subject transgene is silent in all tissues, can be propagated and maintained. Individuals of this founder population can be crossed with animals expressing the recombinase in, for example, one or more tissues. Thus, the creation of a founder population in which, for example, an antagonistic CDGF transgene is silent will allow the study of progeney from that founder in which dismption of CDGF mediated induction in a particular tissue or at developmental stages would result in, for example, a lethal phenotype. Similar conditional transgenes can be provided using prokaryotic promoter sequences which require prokaryotic proteins to be simultaneous expressed in order to facilitate expression of the transgene. Exemplary promoters and the coπesponding trans-activating prokaryotic proteins are given in U.S. Patent No. 4,833,080. Moreover, expression of the conditional transgenes can be induced by gene therapy-like methods wherein a gene encoding the trans-activating protein, e.g. a recombinase or a prokaryotic protein, is delivered to the tissue and caused to be expressed, such as in a cell-type specific manner. By this method, the CDGF transgene could remain silent into adulthood until "tumed on" by the introduction of the trans-activator. In an exemplary embodiment, the "transgenic non-human animals" of the invention are produced by introducing transgenes into the germline of the non-human animal. Embryonal target cells at various developmental stages can be used to introduce transgenes. Different methods are used depending on the stage of development of the embryonal target cell. The zygote is the best target for micro-injection. In the mouse, the male pronucleus reaches the size of approximately 20 micrometers in diameter which allows reproducible injection of l-2pl of DNA solution. The use of zygotes as a target for gene transfer has a major advantage in that in most cases the injected DNA will be incoφorated into the host gene before the first cleavage (Brinster et al. (1985) PNAS 82:4438-4442). As a consequence, all cells of the transgenic non-human animal will carry the incoφorated transgene. This will in general also be reflected in the efficient transmission of the transgene to offspring of the founder since 50% of the germ cells will harbor the transgene. Microinjection of zygotes is the prefeπed method for incoφorating transgenes in practicing the invention. Retroviral infection can also be used to introduce transgene into a non-human animal. The developing non-human embryo can be cultured in vitro to the blastocyst stage. During this time, the blastomeres can be targets for retroviral infection (Jaenich, R. (1976) PNAS 73:1260-1264). Efficient infection of the blastomeres is obtained by enzymatic treatment to remove the zona pellucida (Manipulating the Mouse Embryo, Hogan eds. (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, 1986). The viral vector system used to introduce the transgene is typically a replication-defective retrovims carrying the transgene (Jahner et al. (1985) PNAS 82:6927-6931; Van der Putten et al. (1985) PNAS 82:6148-6152). Transfection is easily and efficiently obtained by culturing the blastomeres on a monolayer of virus-producing cells (Van der Putten, supra; Stewart et al. (1987) EMBO J. 6:383-388). Altematively, infection can be performed at a later stage. Virus or virus-producing cells can be injected into the blastocoele (Jahner et al. (1982) Nature 298:623-628). Most of the founders will be mosaic for the transgene since incoφoration occurs only in a subset of the cells which formed the transgenic non-human animal. Further, the founder may contain various retroviral insertions of the transgene at different positions in the genome which generally will segregate in the offspring. In addition, it is also possible to introduce transgenes into the germ line by intrauterine retroviral infection of the midgestation embryo (Jahner et al. (1982) supra). A third type of target cell for transgene introduction is the embryonal stem cell (ES). ES cells are obtained from pre-implantation embryos cultured in vitro and fused with embryos (Evans et al. (1981) Nature 292:154-156; Bradley et al. (1984) Nature 309:255-258; Gossler et al. (1986) PNAS 83: 9065-9069; and Robertson et al. (1986) Nature 322:445-448). Transgenes can be efficiently introduced into the ES cells by DNA transfection or by retrovims-mediated transduction. Such transformed ES cells can thereafter be combined with blastocysts from a non-human animal. The ES cells thereafter colonize the embryo and contribute to the germ line of the resulting chimeric animal. For review see Jaenisch, R. (1988) Science 240:1468-1474. Methods of making knock-out or dismption transgenic animals are also generally known. See, for example, Manipulating the Mouse Embryo, (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1986). Recombinase dependent knockouts can also be generated, e.g. by homologous recombination to insert recombinase target sequences flanking portions of an endogenous CDGF gene, such that tissue specific and/or temporal control of inactivation of a CDGF allele can be controlled as above. The invention now being generally described, it will be more readily understood by reference to the following examples which are included merely for pmposes of illustration of certain aspects and embodiments of the p -re5sen5t in -vention, and are not intended to limit the invention. Exemplification The invention now being generally described, it will be more readily understood by reference to the following examples which are included merely for pmposes of illustration of certain aspects and embodiments of the present invention, and are not intended to limit the invention. Neuregulins (also called ARIA, GGF, Heregulin, and NDF; cf Falls et al. (1993) Cell 72:801-15; Marchionni, M.A., et al. (1993) Nature 362:312-8; Holmes, W.E., et al. (1992) Science 256:1205-10.; and Wen, D., et al. (1992) Cell 69:559-72) are a group of polypeptide factors that arise from altemative RNA splicing of a single gene. Through interaction with the erbB family receptors (erbB2, erbB3, and erbB4), neuregulins are thought to play important roles in the regulation of cell growth and differentiation in many tissues (Marchionni, M.A. (1995) Nature 378:334-5; Lemke, G. (1993) Nature 362:291-2; and Caπaway et al. (1995) Curr. Opin. Neurobiol. 5:606-612). As described herein, a second neuregulin-like gene, refered to as CDGF, has been cloned. Sequence analysis of CDGF cDNA clones indicates that they have a motif stracture similar to that of neuregulins, e.g., that differential splicing occurs to produce various transcripts. Northern blot analysis of adult tissues indicates that CDGF transcripts are detected mostly in neural tissues. An altemative splicing site in the EGF-like domain gives rise to two isoforms of CDGF (Type 1 and Type 2). Recombinant CDGF-1 induces the tyrosine phosphorylation of erbB2, erbB3 and erbB4 in cell lines expressing all of these erbB family receptors. However, in cell lines with defined combinations of erbBs, CDGF-1 only activates those with erbB4, suggesting that CDGF signaling is through erbB4 receptors. ErbB2, erbB3, and erbB4 (Plowman et al. (1993) PNAS 90:1746-50) are members of a subfamily of receptor tyrosine kinases that also includes the EGF receptor (EGFR). Although it has been demonstrated that neuregulins can activate erbB2/3/4 receptors through direct or indirect interaction (Sliwkowski et al. (1994) J Biol Chem 269:14661-5), recent experiments suggest that additional ligands may exist (Meyer et al. (1995) Nature 378:386- 90; Gassmann et al. (1995) Nature 378:390-4; and Lee et al. (1995) Nature 378:394-8). To clone CDGF cDNAs, a polymerase chain reaction (PCR) based strategy was employed to search for neuregulin-related sequences in an adult rat cerebellum cDNA library. The new gene, cerebellum derived growth factor (CDGF), is expressed in several tissues. Cloning of CDGF transcripts Two pools of degenerate oligonucleotides were synthesized based on two conserved regions ofthe neuregulin sequences, one in the immunoglobulin-like domain and the other in the EGF-like domain. Phages from an adult rat cerebellum cDNA library were used as templates for PCR. Two steps were used to reduce neuregulin sequences and select neuregulin-related sequences. First, PCR products were digested with Bcl-I and separated by agarose gel electrophoresis, since there is a Bcl-I site in the rat neuregulin cDNA. DNA of expected sizes were isolated from agarose gel and re-amplified with the same primers. Final PCR products were subcloned into pBlueScriptll vector (Stratagene). Second, individual clones were hybridized with a neuregulin probe under low stringency conditions, and only positive clones were sequenced. I identified one clone, n9, that shows significant homology to neuregulins. 3 P labeled probes from the n9 insert were used to screen the above cDNA library (-500,000 clones screened), and several positive clones were identified. The inserts of each clone was sequenced in both directions and analyzed. In particular, two partial, overlapping clones, designated clone 2b and 2d, were identified as encoding the CDGF-1 protein. Clone 2b corresponds to the nucleic acid sequence 1-1252 of SEQ ID No. 1. Clone 2d corresponds to nucleotides 592-3441 of SEQ ID No. 1. Another clone, designated clone 3, was a partial clone coπesponding to the C- terminal fragment of the CDGF protein (see SEQ ID No. 5), which fragment lacked the Spacer 1 sequence and the N-terminal half of the Ig-like domain. Moreover, the nucleic acid sequence revealed a 77 nucleotide insert (see Figure IB) at the 3' end ofthe EGF-like coding sequence which results in a frame shift and, consequently, a stop codon to form a tmncated protein lacking transmembrane and cytoplasmic domains. Each of the clones 2b, 2d and 3 were present as inserts in the pBluescript II phagemid vector (Stratagene, La Jolla, Ca) as EcorRI inserts. Both the CDGF-1 and CDGF- 2 proteins shares only about 50 percent homology with any of the ARIA, heregulin, NDF or GGF proteins. A deposit of a nucleic acid library containing the pBluescript clones 2b, 2d and 3 was made with the American Type Culture Collection (Rovkville, MD) on September, 8 1995, under the terms of the Budapest Treaty. ATCC Accession number 97274 has been assigned to the deposit. Each ofthe clones can be separately isolated from the ATCC deposit by, for example, PCR amplification using primers sets in which at least one primer anneals to a nucleic acid sequence unique to only one clone of the library. To illustrate, the primer set 5'-ATGCTCGCCTGCTACTCGCCC and 5'-GCCGGACACATGTTCTGCC can be used to amplify the coding sequence of clone 2b from the library. Likewise, the primer sets 5'- CACTGACTGCGCAAC-CCGG and 5*-GGCCTTAGAGGGGCCCGGA, and 5'- AAAGAACTCACGGCTACAGTTC and 5'-CCTTTAATTCAAATCCAAGGT can be used to amplify the coding sequences in clone 2d and clone 3, respectively. Moreover, it will be apparent that a full length construct can be generated for each of the CDGF-1 and CDGF-2 homologs by annealing a fragment from clone 2b with a fragment generated from clone 2d or clone 3, respectively. For example, the primers 5'- GAATTCGGCACGAGGGCAG and 5'-CTCATTGCACTTCCGGGCG can be used to provide a double stranded fragment of clone 2b coπesponding to Metl-Glu255, which is common to both CDGF-1 and CDGF-2. As above, the primer sets 5'- CACTGACTGCGCAAC-CCGG and 5'-GGCCTTAGAGGGGCCCGGA, and 5 * - AAAGAACTCACGGCTACAGTTC and 5'-CCTTTAATTCAAATCCAAGGT can be used to double stranded fragments of clone 2d and clone 3, respectively. The clone 2b PCR products are mixed with those of either clone 2d or clone 3 under denaturing conditions, and then renatured. Upon renaturation, the single-stranded regions are filled in by incubating with a DNA polymerase, dNTPs, and DNA ligase; and the resulting CDGF-encoding gene subsequently cloned into an expression vector to provide the proteins represented by either SEQ ID No. 2 or 4. Figure IA shows the deduced amino acid sequence of CDGF-1, derived from a composite of two overlapping cDNA clones. This composite contains an open reading frame (ORF) encoding a 754 amino acid protein. Sequence analysis revealed four structural motifs in the deduced amino acid sequence (see Figure IC). Near the N-terminal, a stretch of hydrophobic residues might serve as a signal sequence. Cysteine residues 165 and 219, and the suπounding sequences fit the definition of an C2-type immunoglobulin-like (Ig-like) domain (Williams et al. (1988) Annu Rev Immunol 6:381-405). Further downstream, an EGF- like domain (residues 252-297) contains six characteristic cysteines (Caφenter et al. (1990) J Biol Chem 265:7709-12). A second stretch of 23 hydrophobic amino acids qualifies as a transmembrane domain, separating the whole sequence into a 315 residue extracellular domain and a 414 residue cytoplasmic domain. Interestingly, another CDGF cDNA clone (CDGF-2) with an extra 77 base pair exon inserted (Figure IB) between the fourth and fifth cysteine residues of the EGF-like domain, encodes an altematively spliced variant of CDGF with a different EGF-like domain. The CDGF-2 isoform also lacks a transmembrane domain, since the insertion ofthe extra exon causes a frame shift in the downstream sequence and the termination of the ORF 33 amino acids downstream of the EGF-like domain. CDGFs with the two variant EGF-like domains are termed CDGF-1 and CDGF-2, respectively. The neuregulin gene also has a similar altemative splicing site that gives rise to the α and β subtypes of neuregulins, although CDGF-1 and CDGF-2 are about equally distant from neuregulin-α or from neuregulin-β. Moreover, another altemative splicing site in the cytoplasmic domain of CDGF was also observed in other CDGF cDNA clones (data not shown), coπesponding to the a/b/c tail splicing site in the neuregulin gene. Therefore, it seems that CDGF and neuregulin not only have similar sequences, they also have similar gene stmctures. A protein database search revealed that CDGFs are most similar to neuregulins (heregulinβl among isoforms of neuregulins). Overall CDGF-1 shares 45% identity with Heregulinβl and 40% with GGFII. The identities are about 38% in the Ig-like domain and about 50% in the EGF-like domain. Except for the N-terminus of CDGF-1, similarity between CDGF-1 and heregulinβl extends through entire sequences (Figure 2A). On the other hand, the N-terminus of CDGF-1 has significant identity to that of GGFII (43%) (Figure 2A). Interestingly, the most similar region between CDGF-1 and heregulinβl is the transmembrane domain (90% identity) and adjacent sequence. The putative proteolysis site (KR) is also conserved, suggesting that the extracellular portion of CDGF-1 may be released from its precursor as suggested for neuregulins. Highly conserved regions also exist in the cytoplasmic tails of CDGF-1 and heregulinβl, implying that the cytoplasmic domains have important biological functions. Relatively high conservation between neuregulin cytoplasmic tails from distant veterbrate species has been noted before. Since the EGF-like domain of neuregulins has been reported to be sufficient for receptor binding and stimulating cellular responses, I did a detailed comparison of the EGF-like domain of CDGFs with other EGF- like motifs (Figure 2B). Among all known EGF-like motifs, the EGF-like domain of CDGFs is most similar to that of neuregulins (48% identity between terminal cysteines in the case of heregulinβl). Second to neuregulins is the rat epidermal growth factor (EGF), with 43% identity between terminal cysteines. In order to clone human CDGF homologs, a human lung cDNA library (Clontech HL3002a) was screened with a probe from the EGF-like domain ofthe rat CDGF-2 clone. A 2.2kb insert was isolated, cut with EcoRI and subcloned into the pBlueScriptll SK vector (Stratagene). The sequence to the first 667 base pairs ofthe insert is provided in SEQ ID No. 6. The amino acid sequence of the EGF-like domain of the human clone (SEQ ID No. 7) is 100% conserved with rat CDGF-2. Over the span of the human CDGF-2 sequence obtained, the rat and human clones were 70.2 percent homologous. Expression pattern of CDGF To determine the size and tissue distribution of CDGF mRNAs, Northern blot hybridization experiments with ploy(A)+ RNA were caπied out using a probe spanning the EGF-like domain plus the Ig-like domain (Figure 3 A). Briefly, Poly(A)+ RNA were purified directly from tissues with a FastTrack kit (Invitrogen). RNA samples were separated on agarose gels and transfeπed to nylon filters by standard protocols. Filters were hybridized with 32 P-labeled probes under high stringency conditions. A probe was generated by random- priming of a fragment of CDGF cDNAs spanning the EGF-like plus the Ig-like domains. The highly conserved transmembrane domain and adjacent sequence were excluded. The probe would hybridize to both CDGFa and CDGF-2 transcripts. Among adult rat tissues examined, CDGF transcripts were most abundant in neural tissues (brain and spinal cord) and lung. A separate experiment with total RNA samples shows that the cerebellum has highest amount of CDGF transcripts, compare to brain minus cerebellum and other adult tissues (data not shown). Three bands were noted in brain samples -5f- (Figure 3A): a prominent band of 3 kb, and two additional bands of 3.8 and 6 kb. Only the 3 and 3.8 kb transcripts were detected in spinal cord and lung samples. The general pattem of three major transcripts has also been observed in the neuregulin gene. However, at the level detected by Northern blot, the tissue distribution of CDGF transcripts in adult rat seems to be more restrictive compared to that of neuregulins. I also used a more sensitive reverse-transcriptase coupled PCR (RT-PCR) technique to detect the presence of CDGF transcripts in different adult rat tissues. For RT-PCR experiments, total RNA from various tissues was isolated by guanidinium thiocyanate/acid phenol method, and poly(A)+ RNA was purified from total RNA with a MicroFastTrack kit (Invitrogen). cDNA was synthesized using a Stratagene kit (Stratagene). Primers were designed to amplify the EGF-like region of CDGF cDNA. PCR amplification was performed for 35 cycles at 94°C for 1 min, 55°C for 45 see, and 72°C for 1 min. PCR products were separated on an agarose gel and viewed by ethidium bromide staining. As shown in Figure 3B, CDGF-1 transcripts were detected in all tissues examined so far (liver, heart, kidney, spleen, skeletal muscle, lung, brain, spinal cord). CDGF-2 was detected in neural tissues, lung, and spleen. Both isoforms were detected in postnatal rat brain (P2 brain). Control samples without reverse transcriptase during cDNA synthesis showed no band (data not shown). Induction of autophosphorylation of erbB receptors by CDGFs The structural similarity between CDGFs and neuregulins suggests that CDGFs may also function as ligands for erbB family receptors. To test this possibility, I subcloned the insert of a clone which included all of the extracellular domain and part of cytoplasmic domain of CDGF-1 into a mammalian expression vector. Since the sequences around the putative proteolysis sites is highly conserved between CDGFs and neuregulins, a soluble form of CDGF-1 protein should be released from the membrane-bound precursors to the culture medium, as in the case of neuregulins. Briefly, a CDGF-1 sequence including the EGF-like domain was subcloned into the pRc/CMV expression vector (Invitrogen) and stably transfected into CHO cells. Semm-free conditioned medium was collected. Negative control media are conditioned medium from CHO cell, or from CHO cells transfected with a unrelated gene. With reference to Figure 4A, cells were starved in serum-free medium for 2-6 h before the addition of CDGF-1 conditioned medium, negative control medium, or heregulinβl (extracellular portion, 20 ng/ml, provided by Dr. Steven J. Burden). After 5-10 min incubation at room temperature, cells were lysed in RIPA buffer (50 mM Tris-HCl pH 7.5, 150 mM NaCl, 1% Triton X-l 00, 0.5% sodium deoxycholate, 0.1% SDS, 1 mM sodium orthovanadate, 50 μg/ml aprotinin, 0.5 mM PMSF), immunoprecipitated with rabbit antibodies (Santa Cruz Biotechnology) specific for erbB2(C18), erbB3(C17), or erbB4(C18). The immunoprecipitated proteins were collected on protein A-Sepharose beads, analyzed by western blotting with an anti- phosphotyrosine antibody 4G10 (Upstate Biotechnology). Antibody binding was detected by enhanced chemiluminescence (Amersham Life Science). With reference to Figure 4B, establishment of Ba/F3 and Ψ2 cell lines transfected with defined combination of erbB family receptors was described before (Riese et al. (1995) Mol. Cell Biol. 15:5770-5776). EGFR and erbB2 expression in Fischer rat 3T3 (F3T3) was described earlier (Dobashi et al. (1991) Oncogene 6:1151-1159). Human recombinant betacellulin (R&D Systems) was used at 200 ng/ml. Human recombinant TGF-α (Collaborative Biomedical Products) was used 100 ng/ml. Chemically synthesized heregulin¬ βl 65mer (Barbacci et al. (1995) J Biol. Chem. 270:9585-9589) was used at 94 ng/ml. Treatment of cells, immunoprecipitation, and western blotting were performed essentially the same as described (Riese et al., supra). Conditioned medium from stably transfected CHO cells were collected and used to treat cells expressing erbB family receptors (MDA-MB453 and T47D breast cancer cell lines). Individual erbB family receptors were immunoprecipitated from cells with antibodies against each erbB-receptors, and analyzed with anti-phosphotyrosine antibody. As shown in Figure 4A, erbB2, erbB3, and erbB4 receptors were activated by CDGF-1 conditioned medium. However, since erbB family receptors can form ligands induced heterodimers, and since these cell lines express all the erbB2/3/4 receptors, the activation of each type of erbB family receptors could be due to direct or indirect interaction with CDGF-1. To determine which of the erbB family receptors are involved in CDGF-1 signaling, I used cell lines expressing defined combinations of erbB receptors. I assayed tyrosine phosphorylation of EGF receptors in Ba/F3(EGFR) cell line, erbB2 and erbB3 receptors in Ba/F3(erbB2+erbB3) cell line, and erbB2 receptor in Fischer rat 3T3 cell line (Figure 4B). These cell lines, which do not express erbB4, did not exhibit CDGF-1 activation of EGFR, erbB2, and erbB3. Positive control factors (Betacellulin, TGFα, and heregulinβl) demonstrated that EGFR, erbB2, and erbB3 receptors in these cell lines are capable of being stimulated. On the other hand, erbB4 receptors are stimulated in erbB4 expressing cell lines, such as Ba/F3(erbB4) and Ψ2(erbB4) cell lines (Figure 4B). Taken together, the above experiments strongly suggest that CDGF-1 signaling is through direct interaction with erbB4 receptors. Preliminary results of an IL-3 independent growth assay (Riese et al. (1995) Mol. Cell Biol. 15:5770-5776), which show that CDGF-1 induces the IL-3 independence of Ba/F3(EGFR+erbB4) cells but not of Ba/F3(erbB2+erbB3) cells, are also consistent with the tyrosine phosphorylation assay (data not shown). In a related set of experiments, I expressed the EGF-like domain of CDGF-1 and CDGF-2 in E. coli. The expressed protein is insoluble. However, after solubilizing the protein pellet in denaturing solution (6M Guanidine HCl) and a refolding step, the refolded proteins were observed to activate erbB- receptors on MDA-MB453 cells (supra). In summary, I demonstrated that the CDGF gene, with stracture similarity to the neuregulin gene, encodes ligands for erbB4 receptors. A detailed comparison of CDGFs with neuregulins and other ligands for erbB family receptors, including the temporal and spatial regulation of their expression, will be crucial for understanding the biological functions of this multi-ligand/multi-receptor signaling network. All of the references and publications cited in the foregoing specification are hereby incoφorated by reference. Equivalents Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims. SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANT: (A) NAME: President and Fellows of Harvard College (B) STREET: 124 Mt . Auburn Street (C) CITY: Cambridge (D) STATE: MA (E) COUNTRY: USA (F) POSTAL CODE (ZIP) : 02138 (ii) TITLE OF INVENTION: Cerebellum-derived Growth Factors, and Uses related thereto (iii) NUMBER OF SEQUENCES: 7 (iv) COMPUTER READABLE FORM: (A) MEDIUM TYPE: Floppy disk (B) COMPUTER: IBM PC compatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: ASCII (text) (v) CURRENT APPLICATION DATA: (A) APPLICATION NUMBER: (B) FILING DATE: 9-SEP-1996 (vi) PRIOR APPLICATION DATA: (A) APPLICATION NUMBER: US 08/525,864 (B) FILING DATE: 08-SEP-1995 (viii) ATTORNEY/AGENT INFORMATION: (A) NAME: Vincent, Matthew P. (B) REGISTRATION NUMBER: 36,709 (C) REFERENCE/DOCKET NUMBER: HMI-017PC (ix) TELECOMMUNICATION INFORMATION: (A) TELEPHONE: (617) 227-7400 (B) TELEFAX: (617) 227-5941 (2) INFORMATION FOR SEQ ID NO:l: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 3441 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: both (D) TOPOLOGY: linear (ii) MOLECULE TYPE: cDNA (ix) FEATURE: (A) NAME/KEY: CDS (B) LOCATION: 180..2441 (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1: GAATTCGGCA CGAGGGCAGC ACCACCACCA CCAGCAGCAG CGAGAACAGC GGCAGCAACA 60 GCGGCAGCAT CTTCCGTCCC GCTGCGCCCC CAGAGCCGCG GCCGCAGCCA CAGCCGCAGC 120 CCCGCAGCCC CGCAGCCCGG AGAGCCGCCG CCCGCTCGCG AGCCGCAGCC GCCGGCGGC 179 ATG AGG CGC GAC CCG GCC CCC GGC TTC TCG ATG CTG CTC TTC GGT GTG 227 Met Arg Arg Asp Pro Ala Pro Gly Phe Ser Met Leu Leu Phe Gly Val 1 5 10 15 TCA CTC GCC TGC TAC TCG CCC AGC CTC AAG TCC GTG CAG GAC CAG GCG 275 Ser Leu Ala Cys Tyr Ser Pro Ser Leu Lys Ser Val Gin Asp Gin Ala 20 25 30 TAC AAG GCA CCC GTG GTG GTG GAG GGC AAG GTA CAG GGA CTG GCC CCG 323 Tyr Lys Ala Pro Val Val Val Glu Gly Lys Val Gin Gly Leu Ala Pro 35 40 45 GCA GGC GGT TCC AGC TCT AAC AGC ACC CGA GAG CCT CCC GCC TCG GGT 371 Ala Gly Gly Ser Ser Ser Asn Ser Thr Arg Glu Pro Pro Ala Ser Gly 50 55 60 CGG GTG GCG CTG GTG AAG GTG CTG GAC AAG TGG CCG CTC CGG AGC GGG 419 Arg Val Ala Leu Val Lys Val Leu Asp Lys Trp Pro Leu Arg Ser Gly 65 70 75 80 GGG CTG CAG CGC GAG CAG GTG ATC AGC GTG GGC TCC TGC GCG CCG CTC 467 Gly Leu Gin Arg Glu Gin Val Ile Ser Val Gly Ser Cys Ala Pro Leu 85 90 95 GAA AGG AAC CAG CGC TAC ATC TTT TTC CTG GAG CCC ACC GAG CAG CCC 515 Glu Arg Asn Gin Arg Tyr Ile Phe Phe Leu Glu Pro Thr Glu Gin Pro 100 105 110 TTA GTT TTT AAG ACA GCC TTT GCC CCG GTC GAC CCT AAC GGC AAA AAC 563 Leu Val Phe Lys Thr Ala Phe Ala Pro Val Asp Pro Asn Gly Lys Asn 115 120 125 ATC AAG AAA GAG GTG GGC AAG ATC CTG TGC ACT GAC TGC GCA ACC CGG 611 Ile Lys Lys Glu Val Gly Lys Ile Leu Cys Thr Asp Cys Ala Thr Arg 130 135 140 CCC AAG CTG AAG AAG ATG AAG AGT CAG ACA GGA GAG GTG GGC GAG AAG 659 Pro Lys Leu Lys Lys Met Lys Ser Gin Thr Gly Glu Val Gly Glu Lys 145 150 155 160 CAG TCG CTC AAG TGT GAG GCG GCG GCG GGG AAC CCC CAG CCC TCC TAT 707 Gin Ser Leu Lys Cys Glu Ala Ala Ala Gly Asn Pro Gin Pro Ser Tyr 165 170 175 CGA TGG TTC AAG GAC GGC AAG GAG CTC AAC CGG AGT CGT GAC ATT CGC 755 Arg Trp Phe Lys Asp Gly Lys Glu Leu Asn Arg Ser Arg Asp Ile Arg 180 185 190 ATC AAG TAT GGC AAC GGC AGA AAG AAC TCA CGG CTA CAG TTC AAC AAA 803 Ile Lys Tyr Gly Asn Gly Arg Lys Asn Ser Arg Leu Gin Phe Asn Lys 195 200 205 GTG AAG GTG GAG GAC GCT GGA GAG TAC GTC TGT GAG GCT GAG AAC ATC 851 Val Lys Val Glu Asp Ala Gly Glu Tyr Val Cys Glu Ala Glu Asn Ile 210 215 220 CTT GGG AAG GAC ACT GTG AGG GGC CGG CTC CAT GTC AAC AGT GTG AGC 899 Leu Gly Lys Asp Thr Val Arg Gly Arg Leu His Val Asn Ser Val Ser 225 230 235 240 ACC ACT CTG TCG TCC TGG TCG GGG CAC GCC CGG AAG TGC AAT GAG ACA 947 Thr Thr Leu Ser Ser Trp Ser Gly His Ala Arg Lys Cys Asn Glu Thr 245 250 255 GCC AAG TCC TAC TGT GTG AAT GGA GGC GTG TGC TAC TAC ATC GAA GGC 995 Ala Lys Ser Tyr Cys Val Asn Gly Gly Val Cys Tyr Tyr Ile Glu Gly 260 265 270 ATC AAC CAA CTC TCC TGC AAG TGT CCT GTG GGA TAC ACC GGG GAC AGG 1043 Ile Asn Gin Leu Ser Cys Lys Cys Pro Val Gly Tyr Thr Gly Asp Arg 275 280 285 TGT CAG CAG TTC GCA ATG GTC AAC TTC TCC AAG CAC CTT GGA TTT GAA 1091 Cys Gin Gin Phe Ala Met Val Asn Phe Ser Lys His Leu Gly Phe Glu 290 295 300 TTA AAG GAG GCT GAG GAG CTG TAC CAG AAG AGA GTC CTG ACA ATT ACC 1139 Leu Lys Glu Ala Glu Glu Leu Tyr Gin Lys Arg Val Leu Thr Ile Thr 305 310 315 320 GGC ATC TGT GTG GCT CTG CTG GTC GTG GGC ATC GTC TGT GTG GTC GCC 1187 Gly Ile Cys Val Ala Leu Leu Val Val Gly Ile Val Cys Val Val Ala 325 330 335 TAC TGC AAG ACT AAA AAA CAG AGG AGG CAA ATG CAT CAC CAT CTC CGG 1235 Tyr Cys Lys Thr Lys Lys Gin Arg Arg Gin Met His His His Leu Arg 340 345 350 CAG AAC ATG TGT CCG GCC CAC CAG AAC CGA AGC CTG GCC AAT GGG CCC 1283 Gin Asn Met Cys Pro Ala His Gin Asn Arg Ser Leu Ala Asn Gly Pro 355 360 365 AGC CAC CCT CGG CTG GAC CCT GAG GAG ATC CAG ATG GCA GAT TAC ATT 1331 Ser His Pro Arg Leu Asp Pro Glu Glu Ile Gin Met Ala Asp Tyr Ile 370 375 380 TCC AAA AAT GTG CCA GCT ACA GAC CAT GTG ATC CGG AGG GAA GCT GAG 1379 Ser Lys Asn Val Pro Ala Thr Asp His Val Ile Arg Arg Glu Ala Glu 385 390 395 400 ACC ACA TTT TCT GGG AGC CAC TCC TGT TCA CCC TCT CAC CAC TGT TCC 1427 Thr Thr Phe Ser Gly Ser His Ser Cys Ser Pro Ser His His Cys Ser 405 410 415 ACA GCC ACA CCC ACC TCC AGC CAC AGA CAT GAG AGC CAC ACG TGG AGC 1475 Thr Ala Thr Pro Thr Ser Ser His Arg His Glu Ser His Thr Trp Ser 420 425 430 TTG GAA CGT TCG GAG AGC CTG ACC TCG GAT TCC CAG TCA GGC ATC ATG 1523 Leu Glu Arg Ser Glu Ser Leu Thr Ser Asp Ser Gin Ser Gly Ile Met 435 440 445 CTA TCA TCA GTG GGC ACC AGC AAG TGC AAC AGC CCA GCA TGT GTG GAG 1571 Leu Ser Ser Val Gly Thr Ser Lys Cys Asn Ser Pro Ala Cys Val Glu 450 455 460 GCA CGG GCA CGG AGG GCA GCA GCC TAC AGC CAG GAG GAG CGA CGC AGG 1619 Ala Arg Ala Arg Arg Ala Ala Ala Tyr Ser Gin Glu Glu Arg Arg Arg 465 470 475 480 GCT GCC ATG CCA CCC TAC CAC GAC TCC ATA GAC TCG CTG CGT GAC TCC 1667 Ala Ala Met Pro Pro Tyr His Asp Ser Ile Asp Ser Leu Arg Asp Ser 485 490 495 CCA CAC AGT GAG AGG TAC GTG TCA GCC CTG ACC ACG CCC GCG CGC CTT 1715 Pro His Ser Glu Arg Tyr Val Ser Ala Leu Thr Thr Pro Ala Arg Leu 500 505 510 TCG CCC GTG GAC TTC CAC TAC TCG CTG GCC ACC CAG GTG CCG ACT TTC 1763 Ser Pro Val Asp Phe His Tyr Ser Leu Ala Thr Gin Val Pro Thr Phe 515 520 525 GAG ATC ACG TCG CCC AAC TCT GCC CAC GCC GTG TCG CTG CCA CCC GCA 1811 Glu Ile Thr Ser Pro Asn Ser Ala His Ala Val Ser Leu Pro Pro Ala 530 535 540 GCG CCC ATC AGC TAC CGC CTA GCG GAG CAG CAG CCG CTC CTG GGG CAC 1859 Ala Pro Ile Ser Tyr Arg Leu Ala Glu Gin Gin Pro Leu Leu Gly His 545 550 555 560 CCA GCG CCG CCC GGC CCG GGG CCA GGG CCC GGA GCG GAC ATG CAG CGC 1907 Pro Ala Pro Pro Gly Pro Gly Pro Gly Pro Gly Ala Asp Met Gin Arg 565 570 575 AGC TAC GAC AGC TAC TAC TAC CCG GCG GCG GGG CCC GGG CCG CGG CGG 1955 Ser Tyr Asp Ser Tyr Tyr Tyr Pro Ala Ala Gly Pro Gly Pro Arg Arg 580 585 590 GGC GCC TGC GCG CTG GGC GGC AGT TTG GGC AGC CTG CCC GCC AGC CCC 2003 Gly Ala Cys Ala Leu Gly Gly Ser Leu Gly Ser Leu Pro Ala Ser Pro 595 600 605 TTC CAC ATC CCG GAG GAC GAC GAG TAC GAG ACC ACG CAG GAG TGC GCG 2051 Phe His Ile Pro Glu Asp Asp Glu Tyr Glu Thr Thr Gin Glu Cys Ala 610 615 620 CCC CCG CCA CCG CCG CGG CCG CGC ACG CGC GGC GCG TCC CGC AGG ACG 2099 Pro Pro Pro Pro Pro Arg Pro Arg Thr Arg Gly Ala Ser Arg Arg Thr 625 630 635 640 TCG GCG GGG CCG CGG CGC TGG CGG CGC TCC CGC CTC AAC GGG TTG GCT 2147 Ser Ala Gly Pro Arg Arg Trp Arg Arg Ser Arg Leu Asn Gly Leu Ala 645 650 655 GCG CAG CGC GCA CGC GCA GCG CGG GAC TCG CTG TCG TTG AGC AGC GGT 2195 Ala Gin Arg Ala Arg Ala Ala Arg Asp Ser Leu Ser Leu Ser Ser Gly 660 665 670 TCG GGC TGC GGC TCG GCG TCG GCC TCG GAC GAC GAT GCG GAC GAC GCG 2243 Ser Gly Cys Gly Ser Ala Ser Ala Ser Asp Asp Asp Ala Asp Asp Ala 675 680 685 GAC GGG GCG CTG GCG GCC GAG AGC ACG CCT TTC CTC GGC CTG CGA GCG 2291 Asp Gly Ala Leu Ala Ala Glu Ser Thr Pro Phe Leu Gly Leu Arg Ala 690 695 700 GCG CAC GAC GCG CTG CGC TCG GAC TCG CCG CCG CTC TGC CCG GCG GCG 2339 Ala His Asp Ala Leu Arg Ser Asp Ser Pro Pro Leu Cys Pro Ala Ala 705 710 715 720 GAC AGC AGG ACT TAC TAC TCC CTG GAC AGC CAC AGC ACG CGC GCC AGC 2387 Asp Ser Arg Thr Tyr Tyr Ser Leu Asp Ser His Ser Thr Arg Ala Ser 725 730 735 AGC AGA CAC AGC CGG GGG CCG CCC ACG AGG GCA AAG CAG GAC TCC GGG 2435 Ser Arg His Ser Arg Gly Pro Pro Thr Arg Ala Lys Gin Asp Ser Gly 740 745 750 CCC CTC TAAGGCCTCC CGCCTCGCCC GCCTCACGTC TCCGAGGAGA GCGGAGACCA 2491 Pro Leu CCGACTGGAG AGGGAAAAAG GAGCGAACAA AGAAATAAAA ATATTTTTAT TTTCTATAAA 2551 AGGAAAAAAG TATAACAAAA TGTTTTATTT TCATTTTAGC AAAAAAAATT GTCTTATAAT 2611 ACTAGCTAAC GGCAAAGACG TTTTTATAGG GAAACTATTT ATATGTAACA TCCTGATTTA 2671 CAGCTTCGGA AAAAAAAAAG AAACAACAAA AAAAAAAAAG AGAGATGGGC CAATTTTTTT 2731 GACTCTTTAA TAGAAACCTA TATTGTGGTG CCTTTTGCTG TACGCTAATC TGGGGCTCCT 2791 GGAGAGCCGT CTGGGGTGCA GTGTGGGGAT GGGCGCTTAT AGGATCCCAA ACTGGTGGGG 2851 GTGAGAAAAG GCAGGTAAAG AAGAGACTGT GAGGTTCGAA TGGTTCTGAG GGTAATGAAC 2911 AATGAGGAAG AAGATGAAGA TAAGACGAAA TTTTATCTTC CCCAGTCCAG ATCTGGAGTC 2971 CTGAACAGAG AGGGCAGGGA TCCTAGCCTT CGAGCTGGAA TTGAGATGGG GTTATTTCCA 3031 GGAGGAGACA CAGGCCTCCC GTTACAGCAA CTAGAATGGG GAAGGTCCTC CCCAGCCCTC 3091 ACAGCTGCTA AGGGAAAGAG GACAGAGAAG GCTGTCTCCC CACCAGCCCC CCCGCCTAGG 3151 GAGGGGGCAG CTCTACCAGG GGCCCAACCT TCATGGCTCC TCCTCCCTGC GGCCTCCAGG 3211 ATGTCCTCTG TCCTCTGCAG CACCTTCGTT TACAGGTCGT CTTTTCTATT TTACGCCTGC 3271 ATGTCCTTCG CATTTCAGAT TCTTTAGATT GAATGCATGG TCACGCTGGG ACCCGGAAGA 3331 GCCACTCCAA CAGTGTATTC GATTCCCCTT TTAGCAATAA AGTAACACCA TATCCTCACA 3391 GCCCAGCTCC CAACCCACCT ATGACTTTCA TCTTCCCTCT TGCCGAATTC 3441 (2) INFORMATION FOR SEQ ID NO:2: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 754 amino acids (B) TYPE: amino acid (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2: Met Arg Arg Asp Pro Ala Pro Gly Phe Ser Met Leu Leu Phe Gly Val 1 5 10 15 Ser Leu Ala Cys Tyr Ser Pro Ser Leu Lys Ser Val Gin Asp Gin Ala 20 25 30 Tyr Lys Ala Pro Val Val Val Glu Gly Lys Val Gin Gly Leu Ala Pro 35 40 45 Ala Gly Gly Ser Ser Ser Asn Ser Thr Arg Glu Pro Pro Ala Ser Gly 50 55 60 Arg Val Ala Leu Val Lys Val Leu Asp Lys Trp Pro Leu Arg Ser Gly 65 70 75 80 Gly Leu Gin Arg Glu Gin Val Ile Ser Val Gly Ser Cys Ala Pro Leu 85 90 95 Glu Arg Asn Gin Arg Tyr Ile Phe Phe Leu Glu Pro Thr Glu Gin Pro 100 105 110 Leu Val Phe Lys Thr Ala Phe Ala Pro Val Asp Pro Asn Gly Lys Asn 115 120 125 Ile Lys Lys Glu Val Gly Lys Ile Leu Cys Thr Asp Cys Ala Thr Arg 130 135 140 Pro Lys Leu Lys Lys Met Lys Ser Gin Thr Gly Glu Val Gly Glu Lys 145 150 155 160 Gin Ser Leu Lys Cys Glu Ala Ala Ala Gly Asn Pro Gin Pro Ser Tyr 165 170 175 Arg Trp Phe Lys Asp Gly Lys Glu Leu Asn Arg Ser Arg Asp Ile Arg 180 185 190 Ile Lys Tyr Gly Asn Gly Arg Lys Asn Ser Arg Leu Gin Phe Asn Lys 195 200 205 Val Lys Val Glu Asp Ala Gly Glu Tyr Val Cys Glu Ala Glu Asn Ile 210 215 220 Leu Gly Lys Asp Thr Val Arg Gly Arg Leu His Val Asn Ser Val Ser 225 230 235 240 Thr Thr Leu Ser Ser Trp Ser Gly His Ala Arg Lys Cys Asn Glu Thr 245 250 255 Ala Lys Ser Tyr Cys Val Asn Gly Gly Val Cys Tyr Tyr Ile Glu Gly 260 265 270 Ile Asn Gin Leu Ser Cys Lys Cys Pro Val Gly Tyr Thr Gly Asp Arg 275 280 285 Cys Gin Gin Phe Ala Met Val Asn Phe Ser Lys His Leu Gly Phe Glu 290 295 300 Leu Lys Glu Ala Glu Glu Leu Tyr Gin Lys Arg Val Leu Thr Ile Thr 305 310 315 320 Gly Ile Cys Val Ala Leu Leu Val Val Gly Ile Val Cys Val Val Ala 325 330 335 Tyr Cys Lys Thr Lys Lys Gin Arg Arg Gin Met His His His Leu Arg 340 345 350 Gin Asn Met Cys Pro Ala His Gin Asn Arg Ser Leu Ala Asn Gly Pro 355 360 365 Ser His Pro Arg Leu Asp Pro Glu Glu Ile Gin Met Ala Asp Tyr Ile 370 375 380 Ser Lys Asn Val Pro Ala Thr Asp His Val Ile Arg Arg Glu Ala Glu 385 390 395 400 Thr Thr Phe Ser Gly Ser His Ser Cys Ser Pro Ser His His Cys Ser 405 410 415 Thr Ala Thr Pro Thr Ser Ser His Arg His Glu Ser His Thr Trp Ser 420 425 430 Leu Glu Arg Ser Glu Ser Leu Thr Ser Asp Ser Gin Ser Gly Ile Met 435 440 445 Leu Ser Ser Val Gly Thr Ser Lys Cys Asn Ser Pro Ala Cys Val Glu 450 455 460 Ala Arg Ala Arg Arg Ala Ala Ala Tyr Ser Gin Glu Glu Arg Arg Arg 465 470 475 480 Ala Ala Met Pro Pro Tyr His Asp Ser Ile Asp Ser Leu Arg Asp Ser 485 490 495 Pro His Ser Glu Arg Tyr Val Ser Ala Leu Thr Thr Pro Ala Arg Leu 500 505 510 Ser Pro Val Asp Phe His Tyr Ser Leu Ala Thr Gin Val Pro Thr Phe 515 520 525 Glu Ile Thr Ser Pro Asn Ser Ala His Ala Val Ser Leu Pro Pro Ala 530 535 540 Ala Pro Ile Ser Tyr Arg Leu Ala Glu Gin Gin Pro Leu Leu Gly His 545 550 555 560 Pro Ala Pro Pro Gly Pro Gly Pro Gly Pro Gly Ala Asp Met Gin Arg 565 570 575 Ser Tyr Asp Ser Tyr Tyr Tyr Pro Ala Ala Gly Pro Gly Pro Arg Arg 580 585 590 Gly Ala Cys Ala Leu Gly Gly Ser Leu Gly Ser Leu Pro Ala Ser Pro 595 600 605 Phe His Ile Pro Glu Asp Asp Glu Tyr Glu Thr Thr Gin Glu Cys Ala 610 615 620 Pro Pro Pro Pro Pro Arg Pro Arg Thr Arg Gly Ala Ser Arg Arg Thr 625 630 635 640 Ser Ala Gly Pro Arg Arg Trp Arg Arg Ser Arg Leu Asn Gly Leu Ala 645 650 655 Ala Gin Arg Ala Arg Ala Ala Arg Asp Ser Leu Ser Leu Ser Ser Gly 660 665 670 Ser Gly Cys Gly Ser Ala Ser Ala Ser Asp Asp Asp Ala Asp Asp Ala 675 680 685 Asp Gly Ala Leu Ala Ala Glu Ser Thr Pro Phe Leu Gly Leu Arg Ala 690 695 700 Ala His Asp Ala Leu Arg Ser Asp Ser Pro Pro Leu Cys Pro Ala Ala 705 710 715 720 Asp Ser Arg Thr Tyr Tyr Ser Leu Asp Ser His Ser Thr Arg Ala Ser 725 730 735 Ser Arg His Ser Arg Gly Pro Pro Thr Arg Ala Lys Gin Asp Ser Gly 740 745 750 Pro Leu (2) INFORMATION FOR SEQ ID NO:3: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 993 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: both (D) TOPOLOGY: linear (ii) MOLECULE TYPE: CDNA (ix) FEATURE: (A) NAME/KEY: CDS (B) LOCATION: 1..990 ( i) SEQUENCE DESCRIPTION: SEQ ID NO:3: ATG AGG CGC GAC CCG GCC CCC GGC TTC TCG ATG CTG CTC TTC GGT GTG 48 Met Arg Arg Asp Pro Ala Pro Gly Phe Ser Met Leu Leu Phe Gly Val 1 5 10 15 TCA CTC GCC TGC TAC TCG CCC AGC CTC AAG TCC GTG CAG GAC CAG GCG 96 Ser Leu Ala Cys Tyr Ser Pro Ser Leu Lys Ser Val Gin Asp Gin Ala 20 25 30 TAC AAG GCA CCC GTG GTG GTG GAG GGC AAG GTA CAG GGA CTG GCC CCG 144 Tyr Lys Ala Pro Val Val Val Glu Gly Lys Val Gin Gly Leu Ala Pro 35 40 45 GCA GGC GGT TCC AGC TCT AAC AGC ACC CGA GAG CCT CCC GCC TCG GGT 192 Ala Gly Gly Ser Ser Ser Asn Ser Thr Arg Glu Pro Pro Ala Ser Gly 50 55 60 CGG GTG GCG CTG GTG AAG GTG CTG GAC AAG TGG CCG CTC CGG AGC GGG 240 Arg Val Ala Leu Val Lys Val Leu Asp Lys Trp Pro Leu Arg Ser Gly 65 70 75 80 GGG CTG CAG CGC GAG CAG GTG ATC AGC GTG GGC TCC TGC GCG CCG CTC 288 Gly Leu Gin Arg Glu Gin Val Ile Ser Val Gly Ser Cys Ala Pro Leu 85 90 95 GAA AGG AAC CAG CGC TAC ATC TTT TTC CTG GAG CCC ACC GAG CAG CCC 336 Glu Arg Asn Gin Arg Tyr Ile Phe Phe Leu Glu Pro Thr Glu Gin Pro 100 105 110 TTA GTT TTT AAG ACA GCC TTT GCC CCG GTC GAC CCT AAC GGC AAA AAC 384 Leu Val Phe Lys Thr Ala Phe Ala Pro Val Asp Pro Asn Gly Lys Asn 115 120 125 ATC AAG AAA GAG GTG GGC AAG ATC CTG TGC ACT GAC TGC GCA ACC CGG 432 Ile Lys Lys Glu Val Gly Lys Ile Leu Cys Thr Asp Cys Ala Thr Arg 130 135 140 CCC AAG CTG AAG AAG ATG AAG AGT CAG ACA GGA GAG GTG GGC GAG AAG 480 Pro Lys Leu Lys Lys Met Lys Ser Gin Thr Gly Glu Val Gly Glu Lys 145 150 155 160 CAG TCG CTC AAG TGT GAG GCG GCG GCG GGG AAC CCC CAG CCC TCC TAT 528 Gin Ser Leu Lys Cys Glu Ala Ala Ala Gly Asn Pro Gin Pro Ser Tyr 165 170 175 CGA TGG TTC AAG GAC GGC AAG GAG CTC AAC CGG AGT CGT GAC ATT CGC 576 Arg Trp Phe Lys Asp Gly Lys Glu Leu Asn Arg Ser Arg Asp Ile Arg 180 185 190 ATC AAG TAT GGC AAC GGC AGA AAG AAC TCA CGG CTA CAG TTC AAC AAA 624 Ile Lys Tyr Gly Asn Gly Arg Lys Asn Ser Arg Leu Gin Phe Asn Lys 195 200 205 GTG AAG GTG GAG GAC GCT GGA GAG TAC GTC TGT GAG GCT GAG AAC ATC 672 Val Lys Val Glu Asp Ala Gly Glu Tyr Val Cys Glu Ala Glu Asn Ile 210 215 220 CTT GGG AAG GAC ACT GTG AGG GGC CGG CTC CAT GTC AAC AGT GTG AGC 720 Leu Gly Lys Asp Thr Val Arg Gly Arg Leu His Val Asn Ser Val Ser -7/ - 225 230 235 240 ACC ACT CTG TCG TCC TGG TCG GGG CAC GCC CGG AAG TGC AAT GAG ACA 768 Thr Thr Leu Ser Ser Trp Ser Gly His Ala Arg Lys Cys Asn Glu Thr 245 250 255 GCC AAG TCC TAC TGT GTG AAT GGA GGC GTG TGC TAC TAC ATC GAA GGC 816 Ala Lys Ser Tyr Cys Val Asn Gly Gly Val Cys Tyr Tyr Ile Glu Gly 260 265 270 ATC AAC CAA CTC TCC TGC AAA TGT CCA AAC GGA TTC TTC GGA CAG AGA 864 lie Asn Gin Leu Ser Cys Lys Cys Pro Asn Gly Phe Phe Gly Gin Arg 275 280 285 TGT TTG GAG AAA CTG CCT TTG CGA TTG TAC ATG CCA GAT CCT AAG CAA 912 Cys Leu Glu Lys Leu Pro Leu Arg Leu Tyr Met Pro Asp Pro Lys Gin 290 295 300 AGT GTC CTG TGG GAT ACA CCG GGG ACA GGT GTC AGC AGT TCG CAA TGG 960 Ser Val Leu Trp Asp Thr Pro Gly Thr Gly Val Ser Ser Ser Gin Trp 305 310 315 320 TCA ACT TCT CCA AGC ACC TTG GAT TTG AAT TAA 993 Ser Thr Ser Pro Ser Thr Leu Asp Leu Asn 325 330 (2) INFORMATION FOR SEQ ID NO:4: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 330 amino acids (B) TYPE: amino acid (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein ( i) SEQUENCE DESCRIPTION: SEQ ID NO:4 : Met Arg Arg Asp Pro Ala Pro Gly Phe Ser Met Leu Leu Phe Gly Val 1 5 10 15 Ser Leu Ala Cys Tyr Ser Pro Ser Leu Lys Ser Val Gin Asp Gin Ala 20 25 30 Tyr Lys Ala Pro Val Val Val Glu Gly Lys Val Gin Gly Leu Ala Pro 35 40 45 Ala Gly Gly Ser Ser Ser Asn Ser Thr Arg Glu Pro Pro Ala Ser Gly 50 55 60 Arg Val Ala Leu Val Lys Val Leu Asp Lys Trp Pro Leu Arg Ser Gly 65 70 75 80 Gly Leu Gin Arg Glu Gin Val Ile Ser Val Gly Ser Cys Ala Pro Leu 85 90 95 Glu Arg Asn Gin Arg Tyr Ile Phe Phe Leu Glu Pro Thr Glu Gin Pro 100 105 110 -7a - Leu Val Phe Lys Thr Ala Phe Ala Pro Val Asp Pro Asn Gly Lys Asn 115 120 125 lie Lys Lys Glu Val Gly Lys Ile Leu Cys Thr Asp Cys Ala Thr Arg 130 135 140 Pro Lys Leu Lys Lys Met Lys Ser Gin Thr Gly Glu Val Gly Glu Lys 145 150 155 160 Gin Ser Leu Lys Cys Glu Ala Ala Ala Gly Asn Pro Gin Pro Ser Tyr 165 170 175 Arg Trp Phe Lys Asp Gly Lys Glu Leu Asn Arg Ser Arg Asp Ile Arg 180 185 190 Ile Lys Tyr Gly Asn Gly Arg Lys Asn Ser Arg Leu Gin Phe Asn Lys 195 200 205 Val Lys Val Glu Asp Ala Gly Glu Tyr Val Cys Glu Ala Glu Asn Ile 210 215 220 Leu Gly Lys Asp Thr Val Arg Gly Arg Leu His Val Asn Ser Val Ser 225 230 235 240 Thr Thr Leu Ser Ser Trp Ser Gly His Ala Arg Lys Cys Asn Glu Thr 245 250 255 Ala Lys Ser Tyr Cys Val Asn Gly Gly Val Cys Tyr Tyr Ile Glu Gly 260 265 270 Ile Asn Gin Leu Ser Cys Lys Cys Pro Asn Gly Phe Phe Gly Gin Arg 275 280 285 Cys Leu Glu Lys Leu Pro Leu Arg Leu Tyr Met Pro Asp Pro Lys Gin 290 295 300 Ser Val Leu Trp Asp Thr Pro Gly Thr Gly Val Ser Ser Ser Gin Trp 305 310 315 320 Ser Thr Ser Pro Ser Thr Leu Asp Leu Asn 325 330 (2) INFORMATION FOR SEQ ID NO:5: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 1207 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (ii) MOLECULE TYPE: cDNA (ix) FEATURE: (A) NAME/KEY: CDS (B) LOCATION: 2..394 (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5: A AAG AAC TCA CGG CTA CAG TTC AAC AAA GTG AAG GTG GAG GAC GCT 46 Lys Asn Ser Arg Leu Gin Phe Asn Lys Val Lys Val Glu Asp Ala 1 5 10 15 GGA GAG TAC GTC TGT GAG GCT GAG AAC ATC CTT GGG AAG GAC ACT GTG 94 Gly Glu Tyr Val Cys Glu Ala Glu Asn Ile Leu Gly Lys Asp Thr Val 20 25 30 AGG GGC CGG CTC CAT GTC AAC AGT GTG AGC ACC ACT CTG TCG TCC TGG 142 Arg Gly Arg Leu His Val Asn Ser Val Ser Thr Thr Leu Ser Ser Trp 35 40 45 TCG GGG CAC GCC CGG AAG TGC AAT GAG ACA GCC AAG TCC TAC TGT GTG 190 Ser Gly His Ala Arg Lys Cys Ash Glu Thr Ala Lys Ser Tyr Cys Val 50 55 60 AAT GGA GGC GTG TGC TAC TAC ATC GAA GGC ATC AAC CAA CTC TCC TGC 238 Asn Gly Gly Val Cys Tyr Tyr Ile Glu Gly Ile Asn Gin Leu Ser Cys 65 70 75 AAA TGT CCA AAC GGA TTC TTC GGA CAG AGA TGT TTG GAG AAA CTG CCT 286 Lys Cys Pro Asn Gly Phe Phe Gly Gin Arg Cys Leu Glu Lys Leu Pro 80 85 90 95 TTG CGA TTG TAC ATG CCA GAT CCT AAG CAA AGT GTC CTG TGG GAT ACA 334 Leu Arg Leu Tyr Met Pro Asp Pro Lys Gin Ser Val Leu Trp Asp Thr 100 105 110 CCG GGG ACA GGT GTC AGC AGT TCG CAA TGG TCA ACT TCT CCA AGC ACC 382 Pro Gly Thr Gly Val Ser Ser Ser Gin Trp Ser Thr Ser Pro Ser Thr 115 120 125 TTG GAT TTG AAT TAAAGGAGGC TGAGGAGCTG TACCAGAAGA GAGTCCTGAC 434 Leu Asp Leu Asn 130 AATTACCGGC ATCTGTGTGG CTCTGCTGGT CGTGGGCATC GTCTGTGTGG TCGCCTACTG 494 CAAGACTAAA AAACAGAGGA GGCAAATGCA TCACCATCTC CGGCAGAACA TGTGTCCGGC 554 CCACCAGAAC CGAAGCCTGG CCAATGGGCC CAGCCACCCT CGGCTGGACC CTGAGGAGAT 614 CCAGATGGCA GATTACATTT CCAAAAATGT GCCAGCTACA GACCATGTGA TCCGGAGGGA 674 AGCTGAGACC ACATTTTCTG GGAGCCACTC CTGTTCACCC TCTCACCACT GTTCCACAGC 734 CACACCCACC TCCAGCCACA GACATGAGAG CCACACGTGG AGCTTGGAAC GTTCGGAGAG 794 CCTGACCTCG GATTCCCAGT CAGGCATCAT GCTATCATCA GTGGGCACCA GCAAGTGCAA 854 CAGCCCAGCA TGTGTGGAGG CACGGGCACG GAGGGCAGCA GCCTACAGCC AGGAGGAGCG 914 ACGCAGGGCT GCCATGCCAC CCTACCACGA CTCCATAGAC TCGCTGCGTG ACTCCCCACA 974 CAGTGAGAGG TACGTGTCAG CCCTGACCAC GCCCGCGCGC CTTTCGCCCG TGGACTTCCA 1034 7≠ CTACTCGCTG GCCACCCAGG TGCCGACTTT CGAGATCACG TCGCCCAACT CTGCCCACGC 1094 CGTGTCGCTG CCACCCGCAG CGCCCATCAG CTACCGCCTA GCGGAGCAGC AGCCGCTCCT 1154 GGGGCACCCA GCGCCGCCCG GCCCGGGGCC AGGGCCCGGA GCGGACATGC AGC 1207 (2) INFORMATION FOR SEQ ID NO:6: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 667 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: both (D) TOPOLOGY: linear (ii) MOLECULE TYPE: cDNA (ix) FEATURE: (A) NAME/KEY: CDS (B) LOCATION: 1..546 (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6: CGG GGG GAG GGA ATC TCC TTC CCA TCT AAG CTG CAG GGC CAC TGT GGC 48 Arg Gly Glu Gly Ile Ser Phe Pro Ser Lys Leu Gin Gly His Cys Gly 1 5 10 15 TCT GTG GAG AGA GGC AAC CGC TGG GTG ACT GCT GGG GAG CCA CAG CCG 96 Ser Val Glu Arg Gly Asn Arg Trp Val Thr Ala Gly Glu Pro Gin Pro 20 25 30 GCC CTG GCT CAC GCC TCT CCC CCT TTT ATC CCC TCC CTA ACC AGA AAG 144 Ala Leu Ala His Ala Ser Pro Pro Phe Ile Pro Ser Leu Thr Arg Lys 35 40 45 AAC TCA CGA CTA CAG TTC AAC AAG GTG AAG GTG GAG GAC GCT GGG GAG 192 Asn Ser Arg Leu Gin Phe Asn Lys Val Lys Val Glu Asp Ala Gly Glu 50 55 60 TAT GTC TGC GAG GCC GAG AAC ATC CTG GGG AAG GAC ACC GTC CGG GGC 240 Tyr Val Cys Glu Ala Glu Asn Ile Leu Gly Lys Asp Thr Val Arg Gly 65 70 75 80 CGG CTT TAC GTC AAC AGC GTG AGC ACC ACC CTG TCA TCC TGG TCG GGG 288 Arg Leu Tyr Val Asn Ser Val Ser Thr Thr Leu Ser Ser Trp Ser Gly 85 90 95 CAC GCC CGG AAG TGC AAC GAG ACA GCC AAG TCC TAT TGC GTC AAT GGA 336 His Ala Arg Lys Cys Asn Glu Thr Ala Lys Ser Tyr Cys Val Asn Gly 100 105 110 GGC GTC TGC TAC TAC ATC GAG GGC ATC AAC CAG CTC TCC TGC AAA TGT 384 Gly Val Cys Tyr Tyr Ile Glu Gly Ile Asn Gin Leu Ser Cys Lys Cys 115 120 125 CCA AAT GGA TTC TTC GGA CAG AGA TGT TTG GAG AAA CTG CCT TTG CGA 432 Pro Asn Gly Phe Phe Gly Gin Arg Cys Leu Glu Lys Leu Pro Leu Arg 130 135 140 TTG TAC ATG CCA GAT CCT AAG CAA AGT GTC CTG TGG GAT ACA CCG GGG 480 Leu Tyr Met Pro Asp Pro Lys Gin Ser Val Leu Trp Asp Thr Pro Gly 145 150 155 160 ACA GGT GTC AGC AGT TCG CAA TGG TCA ACT TCT CCA AAG CCG AGG AGC 528 Thr Gly Val Ser Ser Ser Gin Trp Ser Thr Ser Pro Lys Pro Arg Ser 165 170 175 TGT ACC AGA AGA GGG TCC TGACCATCAC GGGCATCTGC GTGGCTCTGC 576 Cys Thr Arg Arg Gly Ser 180 TGGTCGTGGG CATCGTCTGT GTGGTGGCCT ACTGCAAGAC CAAAAAACAG CGGAAGCAGA 636 TGCACAACCA CCTCCGGCAG AACATGTGCC C 667 (2) INFORMATION FOR SEQ ID NO:7: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 182 amino acids (B) TYPE: amino acid (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7: Arg Gly Glu Gly Ile Ser Phe Pro Ser Lys Leu Gin Gly His Cys Gly 1 5 10 15 Ser Val Glu Arg Gly Asn Arg Trp Val Thr Ala Gly Glu Pro Gin Pro 20 25 30 Ala Leu Ala His Ala Ser Pro Pro Phe Ile Pro Ser Leu Thr Arg Lys 35 40 45 Asn Ser Arg Leu Gin Phe Asn Lys Val Lys Val Glu Asp Ala Gly Glu 50 55 60 Tyr Val Cys Glu Ala Glu Asn Ile Leu Gly Lys Asp Thr Val Arg Gly 65 70 75 80 Arg Leu Tyr Val Asn Ser Val Ser Thr Thr Leu Ser Ser Trp Ser Gly 85 90 95 His Ala Arg Lys Cys Asn Glu Thr Ala Lys Ser Tyr Cys Val Asn Gly 100 105 110 Gly Val Cys Tyr Tyr Ile Glu Gly Ile Asn Gin Leu Ser Cys Lys Cys 115 120 125 Pro Asn Gly Phe Phe Gly Gin Arg Cys Leu Glu Lys Leu Pro Leu Arg 130 135 140 -7 - Leu Tyr Met Pro Asp Pro Lys Gin Ser Val Leu Trp Asp Thr Pro Gly 145 150 155 160 Thr Gly Val Ser Ser Ser Gin Trp Ser Thr Ser Pro Lys Pro Arg Ser 165 170 175 Cys Thr Arg Arg Gly Ser 180

Claims: I claim: 1. An isolated and/or recombinant CDGF polypeptide. 2. The CDGF polypeptide of claim 1 , which polypeptide comprises a CDGF amino acid sequence at least 70 percent homologous to an amino acid sequence represented in any of SEQ ID Nos. 2, 4 and 7, or a portion thereof, which polypeptide specfically binds to an erbB-type receptor. 3. The CDGF polypeptide of claim 1, which polypeptide comprises an EGF-like domain coπesponding an EGF-like domain represented in any of SEQ ID Nos. 2, A and 7, which polypeptide specfically binds to an erbB-type receptor. 4. The CDGF polypeptide of claim 1, comprising an amino acid sequence encoded by a nucleic acid which hybridizes under stringent conditions to a mammalian CDGF gene. 5. The CDGF polypeptide of claim 1, comprising an amino acid sequence cross-reactive with an antibody specific for a CDGF protein designated any one in SEQ ID Nos. 2, 4 or 7, which polypeptide specfically binds to an erbB-type receptor. 6. The CDGF polypeptide of any of claims 1 or 4, which polypeptide specifically bind an erbB receptor. 7. The CDGF polypeptide of any of claims 2, 3, 5 or 6, which erbB receptor is erbB4. 8. The CDGF polypeptide of any of claims 2, 3, 5 or 6, which polypeptide modifies cellular activities of a cell which expresses the erbB-type receptor. 9. The CDGF polypeptide of claim 8, which polypeptide modifies at least one of proliferation, differentiation, cell-cell contact and survival ofthe cell. 10. The CDGF polypeptide of claim 8, which polypeptide stimulates intracellular signal transduction pathways mediated by the erbB-type receptor. 11. The CDGF polypeptide of claim 8, which polypeptide antagonizes intracellular signal transduction pathways mediated by the erbB-type receptor. 12. The CDGF polypeptide of any of claims 2, 3, 5 or 6, which induces phosphorylation ofthe erbB-type receptor. 13. The CDGF polypeptide of any of claims 1-5, which polypeptide is soluble and has a molecular weight of about 78-83kD. 14. The CDGF polypeptide any of claims 1-5, which polypeptide is soluble and has a molecular weight of about 3 l-36kD. 15. The CDGF polypeptide of claim A, wherein the CDGF gene is a human CDGF gene. 16. The CDGF polypeptide of claim 15, wherein the human CDGF gene includes a coding sequence designated in SEQ ID No. 6. 17. The CDGF polypeptide of claim A, which polypeptide is encoded by a nucleic acid which hybridizes under stringent conditions to a nucleic acid sequence represented in any of SEQ ID Nos. 1, 5 and 6. 18. The CDGF polypeptide of claim A, which polypeptide is encoded by a nucleic acid which hybridizes under stringent conditions to a nucleic acid sequence coπesponding to at least one of nucleotides 180-695 or nucleotides 870-929 in SEQ ID No. 1. 19. The CDGF polypeptide of claim 3, wherein the EGF-like domain is at least 70 percent homologous to an EGF-like domain represented in any of SEQ ID Nos. 2, 4 and 7. 20. The CDGF polypeptide of claim 3, wherein the EGF-like domain includes an amino acid sequence represented in the general formula CNETAKSYCVNGGVCYYIEGIN- QLSCKCPXGXXGXRC. 21. The CDGF polypeptide of claim 1, wherein the CDGF amino acid sequence includes a sequence coπesponding to amino acid residues 1-314 of SEQ ID No. 2, or the sequence thereof lacking a secretion signal peptide. - 7?- 22. The CDGF polypeptide of claim 1, wherein the CDGF amino acid sequence includes a sequence coπesponding to amino acid residues 1-330 of SEQ ID No. 4, or the sequence thereof lacking a secretion signal peptide. 23. The CDGF polypeptide of claim 1 , which polypeptide is post-translationally modified to include a carbohydrate moiety. 24. The CDGF polypeptide of claim 1, which polypeptide is a fusion protein further comprising, in addition to a CDGF polypeptide sequence, a second polypeptide sequence having an amino acid sequence unrelated to the CDGF polypeptide sequence. 25. The CDGF polypeptide of claim 24, wherein the fusion protein includes, as a second polypeptide sequence, a polypeptide which functions as a detectable label for detecting the presence of the fusion protein or as a matrix-binding domain for immobilizing the fusion protein. 26. The CDGF polypeptide of claim 1 , which polypeptide is substantially free of other cellular proteins with each it naturally associates. 27. The CDGF polypeptide of claim 1, which polypeptide is a recombinant polypeptide. 28. The CDGF polypeptide of claim 1, which polypeptide of mammalian origin. 29. The CDGF polypeptide of claim 1, which polypeptide of human origin. 30. An antibody preparation specifically reactive with an epitope of the CDGF polypeptide of any of claims 1-5. 31. A substantially pure nucleic acid comprising a polypeptide coding sequence encoding a recombinant CDGF polypeptide. - SO- 32. The nucleic acid of claim 31, wherein the CDGF polypeptide comprises a CDGF amino acid sequence at least 70 percent homologous to an amino acid sequence represented in any of SEQ ID Nos. 2, A and 1, or a portion thereof, and which CDGF polypeptide specfically binds to an erbB-type receptor. 33. The nucleic acid of claim 31, wherein the CDGF polypeptide comprises an EGF-like domain coπesponding an EGF-like domain represented in any of SEQ ID Nos. 2, 4 and 7, which polypeptide specfically binds to an erbB-type receptor. 34. The nucleic acid of claim 31 , wherein the polypeptide coding sequence comprises a CDGF coding sequence which hybridizes under stringent conditions to a mammalian CDGF gene. 35. The nucleic acid of claim 31, wherein the CDGF polypeptide comprises an amino acid sequence cross-reactive with an antibody specific for a CDGF protein designated any one in SEQ ID Nos. 2, 4 or 7, which polypeptide specfically binds to an erbB-type receptor. 36. The nucleic acid of any of claims 31 or 34, wherein the CDGF polypeptide specifically bind an erbB receptor. 37. The nucleic acid of any of claims 32, 33, 35 or 63, wherein the erbB receptor is erbB4. 38. The nucleic acid of claim 34, wherein the CDGF gene is a human CDGF gene. 39. The nucleic acid of claim 38, wherein the human CDGF gene includes a coding sequence designated in SEQ ID No. 6. 40. The nucleic acid of claim 34, wherein the CDGF coding sequence hybridizes under stringent conditions to a nucleic acid sequence represented in any of SEQ ID Nos. 1, 5 and 6. 41. The nucleic acid of claim 34, wherein the CDGF coding sequence hybridizes under stringent conditions to a nucleic acid sequence coπesponding to at least one of nucleotides 180-695 or nucleotides 870-929 in SEQ ID No. 1. 42. The nucleic acid of claim 33, wherein the EGF-like domain is at least 70 percent homologous to an EGF-like domain represented in any of SEQ ID Nos. 2, 4 and 7. 43. The nucleic acid of claim 33, wherein the EGF-like domain includes an amino acid sequence represented in the general formula CNETAKSYCVNGGVCYYIEGIN- QLSCKCPXGXXGXRC. 44. The nucleic acid of claim 31, wherein the CDGF polypeptide comprises a CDGF amino acid sequence conesponding to amino acid residues 1-314 of SEQ ID No. 2, or the sequence thereof lacking a secretion signal peptide. 45. The nucleic acid of claim 31, wherein the CDGF polypeptide comprises a CDGF amino acid sequence conesponding to amino acid residues 1-330 of SEQ ID No. 4, or the sequence thereof lacking a secretion signal peptide. 46. The nucleic acid of claim 31 , which nucleic acid hybridizes under stringent conditions to a nucleic acid probe having a sequence represented by at least 60 consecutive nucleotides of SEQ ID No. 1, 3 or 6. 47. The nucleic acid of claim 31, further comprising a transcriptional regulatory sequence operably linked to the polypeptide coding sequence so as to render the nucleic acid suitable for use as an expression vector for the recombinant CDGF polypeptide. 48. An expression vector, capable of replicating in at least one of a prokaryotic cell and eukaryotic cell, comprising the nucleic acid of claim 31. 49. A host cell transfected with the expression vector of claim 48 and expressing the recombinantCDGF polypeptide. 50. A method of producing a recombinant CDGF polypeptide comprising culturing the cell of claim 49 in a cell culture medium to express the recombinant CDGF polypeptide and isolating the recombinant CDGF polypeptide from the cell culture. 51. A transgenic animal comprising recombinantly engineered cells which harbor a transgene comprising the nucleic acid of claim 31, or in which one or more endogenous CDGF genes are disrupted. 52. A recombinant transfection system, comprising (i) a gene construct including the nucleic acid of claim 1317 and operably linked to a transcriptional regulatory sequence for causing expression of the recombinant CDGF polypeptide in eukaryotic cells, the recombinant CDGF polypeptide being characterized by an ability to bind to an erbB-type receptor, and (ii) a gene delivery composition for delivering the gene construct to a cell and causing the cell to be transfected with the gene construct. 53. The recombinant transfection system of claim 52, wherein the gene delivery composition is selected from a group consisting of a recombinant viral particle, a liposome, and a poly-cationic nucleic acid binding agent, 54. A probe/primer comprising a substantially purified oligonucleotide, the oligonucleotide containing a region of nucleotide sequence which hybridizes under stringent conditions to at least 20 consecutive nucleotides of sense or antisense sequence of SEQ ID No. 1, 3 or 6, or naturally occuring mutants thereof. 55. The probe/primer of claim 54, which probe/primer hybridizes under stringent conditions to at least 60 consecutive nucleotides of sense or antisense sequence of SEQ ID No. 1 , 3 or 6, or naturally occuring mutants thereof. 56. The probe/primer of claim 54, which probe/primer hybridizes under stringent conditions to a sense or anti-sense nucleic acid sequence coπesponding to at least one of nucleotides 180-695 or nucleotides 870-929 in SEQ ID No. 1. 57. The probe/primer of claim 54, which probe/primer further comprises a label group attached thereto and able to be detected. 58. A test kit for detecting cells which contain a CDGF mRNA transcript, comprising a probe/primer of claim 54 for measuring, in a sample of cells, a level of nucleic acid encoding a CDGF protein. 59. An assay for screening test compounds that modulate the binding of a CDGF polypeptide with an erbB-type receptor comprising: i. combining a CDGF polypeptide, an erbB receptor protein, and a test compound; and ii. detecting the formation of a complex comprising the CDGF polypeptide and the erbB receptor protein, wherein a change in the formation of the complex in the presence of the test compound is indicative of a modulator ofthe interaction between CDGF and an erbB receptor. 60. The assay of claim 59, wherein the erbB-type receptor is an erbB4 receptor. 61. A diagnostic assay for identifying a cell or cells at risk for a disorder characterized by unwanted cell proliferation or differentiation, comprising detecting, in a cell sample, the presence or absence of a genetic lesion characterized by at least one of (i) abenant modification or mutation of a gene encoding a CDGF protein, (ii) mis-expression of the gene (iii) abenant levels soluble CDGF protein. 62. The assay of claim 61 , wherein detecting the lesion includes: i. providing a diagnostic probe comprising a nucleic acid including a region of nucleotide sequence which hybridizes to a sense or antisense sequence of the gene, or naturally occuning mutants thereof, or 5' or 3' flanking sequences naturally associated with the CDGF gene; ii. combining the probe with nucleic acid ofthe cell sample; and iii. detecting, by hybridization of the probe to the cellular nucleic acid, the existence of at least one of a deletion of one or more nucleotides from the gene, an addition of one or more nucleotides to the gene, a substitution of one or more nucleotides of the gene, a gross chromosomal reaπangement of all or a portion of the gene, a gross alteration in the level of an mRNA transcript of the gene, or a non- wild type splicing pattem of an mRNA transcript of the gene. 63. The assay of claim 62, wherein hybridization of the probe further comprises subjecting the probe and cellular nucleic acid to a polymerase chain reaction (PCR) and detecting abnormalities in an amplified product. 6A. The assay of claim 62, wherein hybridization of the probe further comprises subjecting the probe and cellular nucleic acid to a ligation chain reaction (LCR) and detecting abnormalities in an amplified product. 65. The assay of claim 61, wherein detection of a genetic lesion comprises detecting the presence or absence of a CDGF protein, or portion thereof, associated with cells of a tissue sample and/or as soluble proteins in bodily fluid.

Inventors: CHANG HAN, CHANG, HAN
Applicants: CHANG HAN, HARVARD COLLEGE, TRUSTEES OF LELAND S STANFORD, CHANG, HAN, PRESIDENT AND FELLOWS OF HARVARD COLLEGE, TRUSTEES OF LELAND S. STANFORD UNIVERSITY
Application year: 1996
Main classification: C12N15
IPC codes: A61K48, C07K14, C07K16, C12N15, C12Q1