POLYCYSTIC KIDNEY DISEASE GENE

Abstract: The human PKD1 gene, responsible for autosomal dominant polycystic kidney disease (APKD), or adult onset polycystic kidney disease, has been identified. The genomic and cDNA sequences of the 5' end of PKD1 are disclosed.

Description: POLYCYSTIC KIDNEY DISEASE GENE Field of the Invention The present invention pertains to the diagnosis and treatment of polycystic kidney disease in humans, using DNA sequences derived from the human PKDl gene and the protein or proteins encoded by that gene. Background of the Invention Autosomal dominant polycystic kidney disease (APKD), also called adult- onset polycystic kidney disease, is one of the most common hereditary disorders in humans, affecting approximately one individual in a thousand. The prevalence in the United States is greater than 500,000, with 6,000 to 7,000 new cases detected yearly (Striker et al., Am. J. Nephrol. , 6:161-164, 1986; Iglesias et al., Am. J. Kid. Dis. , 2:630- 639, 1983). The disease is considered to be a systemic disorder, characterized by cyst formation in the ductal organs such as kidney, liver, and pancreas, as well as by gastrointestinal, cardiovascular, and musculoskeletal abnormalities, including colonic diverticulitis, berry aneurysms, hernias, and mitral valve prolapse (Gabow et al., Adv. Nephrol, 18:19-32, 1989; Gabow, New Eng. J. Med. , 229:332-342, 1993). The most prevalent and obvious symptom of APKD, however, is the formation of kidney cysts, which result in grossly enlarged kidneys and a decrease in renal-concentrating ability. Hypertension and endocrine abnormalities are also common in APKD patients, appearing even before symptoms of renal insufficiency. In approximately half of APKD patients, the disease progresses to end-stage renal disease; accordingly, APKD is responsible for 4-8% of the renal dialysis and transplantation cases in the United States and Europe (Proc. European Dialysis and Transplant Assn. , Robinson and Hawkins, eds., 17: 20, 1981). Thus, there is a need in the art for diagnostic and therapeutic tools to reduce the incidence and severity of this disease. APKD exhibits a transmission pattern typical of autosomal dominant inheritance, i.e. each offspring of an affected individual has a 50% chance of inheriting the causative gene. Linkage studies indicated that a causative gene is present on the short arm of chromosome 16, near the αr-globin cluster; this locus was designated PKDl (Reeders et al., Nature, 317:542, 1985.) Though other PKD-associated genes exist, such as, for example, PKD2, PKDl defects appear to cause APKD in about 85-90% of affected families (Parfrey et al., New Eng. J. Med. , 323: 1085-1090, 1990; Peters et al., Contrib. Nephrol , 97:128-139, 1992). The PKDl gene has been localized to chromosomal position 16pl3.3. Using extensive linkage analysis, in conjunction with the identification of new markers and restriction enzyme analysis, the gene has been further localized to an interval of approximately 600 kb between the markers ATPL and CMM65 (D16S84). The region is rich in CpG islands that are thought to flank transcribed sequences, and it has been estimated that this interval contains at least 20 genes. The precise location of the PKDl gene was pinpointed by the finding of a PKD family whose affected members carry a translocation that disrupts a 14 kb RNA transcript associated with this region, as reported in the European PKD Consortium, Cell, 77:881, 1994. This article describes approximately 5 kb of DNA sequence corresponding to the 3' end of the putative PKDl cDNA sequence. Notwithstanding knowlege of the partial PKDl 3' cDNA sequence, several significant impediments stand in the way of determining the complete sequence of the PKDl gene. For the most part, these impediments arise from the complex organization of the PKDl locus. One serious obstacle is that sequences related to the PKDl transcript are duplicated at least three times on chromosome 16 proximal to the PKDl locus, forming PKDl homologues. Another obstacle is that the PKDl genomic interval also contains repeat elements that are present in other genomic regions. Both of these types of sequence duplications interfere with "chromosome walking" techniques that are widely used for identification of genomic DNA. This is because these techniques rely on hybridization to identify clones containing overlapping fragments of genomic DNA; thus, there is a high likelihood of "walking" into clones derived from PKDl homologues instead of clones derived from the authentic PKDl gene. In a similar manner, the PKDl duplications and chromosome 16- specific repeats also interfere with the unambiguous determination of a complete cDNA sequence that encodes the PKDl protein. Thus, there is a need in the art for genomic and cDNA sequences corresponding to the authentic PKDl gene. This includes identification of segments of these sequences that are unique to the expressed PKDl and not are present in the duplicated homologous sequences also present on chromosome 16. Summary of the Invention The present invention involves an isolated normal human PKDl gene having the sequence set forth in Figure 1, an isolated intronless nucleic acid having the PKDl cDNA sequence set forth in Figure 2, and sequences derived therefrom. The PKDl gene is a genomic DNA sequence whose altered, defective, or non-functional expression leads to adult-onset polycystic kidney disease. The invention also encompasses DNA vectors comprising these nucleic acids, cells transformed with the vectors, and methods for producing PKDl protein or fragments thereof. In another aspect, the invention involves isolated oligonucleotides that hybridize only to the authentic expressed PKDl gene, and not to PKDl homologues. In yet another aspect, the invention involves isolated mutant PKDl genes, and their cDNA cognates, which contain alterations in nucleotide sequence relative to the normal PKDl gene, and whose presence in one or more copies in the genome of a human individual is associated with adult-onset polycystic kidney disease. In still another aspect, the invention involves isolated oligonucleotides that discriminate between normal and mutant versions of the PKDl gene. In still another aspect, the invention involves methods for identifying a human subject carrying a mutant PKDl gene in a human subject, comprising: a) obtaining a sample of biological material from the subject, and b) detecting the presence of the mutant gene or its protein product. In still another aspect, the invention involves methods and compositions for treating APKD or disease conditions having the characteristics of APKD. Such methods encompass administering an isolated human PKDl gene, or fragments of the gene, under conditions that result in expression of therapeutically effective amounts of all, or part of, the PKDl protein. The invention also encompasses compositions for treating APKD that comprise all or part of the PKDl DNA of Figure 1, or the PKDl protein encoded by the DNA of Figure 1. Brief Description of the Drawings Figure 1 shows the DNA sequence of 53,577 bases comprising the normal human PKDl gene. Figure 2 shows the partial DNA sequence of 894 bases within the 5' region of normal human PKDl cDNA. Figure 3 A shows a comparison of the DNA sequence of the 5' region of cDNAs derived from the authentic PKDl gene and PKDl homologues. A 29-base pair gap must be introduced into the sequence of the authentic gene to align the two sequences. In addition, the authentic PKDl cDNA and the PKDl homologue cDNA differ at position 418 of this figure. Figure 3B shows the DNA sequence of an oligonucleotide that can be used to discriminate between the authentic PKDl sequence and PKDl homologues. The star denotes a polymerization-blocking modification. Figure 4 shows the region of chromosome 16 containing the PKDl locus. The upper panel shows Notl restriction sites, as well as previously identified genetic markers in this region. The bottom panel shows PI clones covering this region. Figure 5 shows a restriction map of a PI clone designated 91.8B, which contains the authentic PKDl gene. Figure 6 shows a comparison between a previously reported partial PKDl cDNA sequence and the sequence reported herein. The upper sequence is that reported for the cDNA, while the lower sequence is the genomic sequence of the present invention. Discrepancies are highlighted by lower case in the cDNA sequence and by boxes in the genomic sequence. Figure 7 shows an illustration of the PKDl genomic structure as predicted by GRAIL2. The predicted exons are represented as boxes along the genomic sequence. The reported cDNA is at the top right. The position of the 2.5 kb GC-rich region is indicated by the striped box at the bottom. Figure 8 shows regions of homology in the PKDl gene between sequences encoded by GRAIL2-predicted exons and proteins present in SwissProt and PIR databases. Positions where the PKDl sequence matches the consensus sequence are shaded. Figure 9 shows the results of exon trapping within the PKDl locus. Detailed Description of the Invention All patent applications, patents, and literature references cited in this specification are hereby incorporated by reference in their entirety. In case of conflict or inconsistency, the present description, including definitions, will control. Definitions: 1. "APKD" as used herein denotes adult-onset polycystic kidney disease, which is characterized by the development of renal cysts and, ultimately, renal failure, and may alternatively or in addition involve cysts in other organs including liver and spleen, as well as gastrointestinal, cardiovascular, and musculoskeletal abnormalities. 2. The term "PKDl gene" refers to a genomic DNA sequence which maps to chromosomal position 16pl3.3 and gives rise to a messenger RNA molecule encoding the PKDl protein. The PKDl gene encompasses the sequence shown in Figure 1, which includes introns and putative regulatory sequences. The term "authentic" is used herein to denote the genomic sequence at this location, as well as sequences derived therefrom, and serves to distinguish these authentic sequences from "PKDl homologues" (see below.) 3. "PKDl complementary DNA (cDNA)" is defined herein as a single- stranded or double-stranded intronless DNA molecule that is derived from the authentic PKDl gene and whose sequence, or complement thereof, encodes the PKDl protein. 4. A "normal" PKDl gene is defined herein as a PKDl gene whose altered, defective, or non-functional expression leads to adult-onset polycystic kidney disease. A normal PKDl gene is not associated with disease and thus is considered to be a wild-type version of the gene. Included in this category are allelic variants in the PKDl gene, also denoted allelic polymorphisms, i.e. alternate versions of the PKDl gene, not associated with disease, that may be represented at any frequency in the population. Also included are alterations in DNA sequence, whether recombinant or naturally occurring, that have no apparent effect on expression or function of the PKDl gene product. 5. A "mutant" PKDl gene is defined herein as a PKDl gene whose sequence has been modified by transitions, transversions, deletions, insertions, or other modifications relative to the normal PKDl gene, which modifications cause detectable changes in the expression or function of the PKDl gene product, including causing disease. The modifications may involve from one to as many as several thousand nucleotides, and result in one or more of a variety of changes in PKDl gene expression, such as, for example, decreased or increased rates of expression, or expression of a defective RNA transcript or protein product. Mutant PKDl genes encompass those genes whose presence in one or more copies in the genome of a human individual is associated with APKD. 6. A "PKDl homologue" is a sequence which is closely related to PKDl, but which does not encode the authentic expressed PKDl gene product. Several examples of such homologues that map to chromosomal location 16pl3.1 have been identified and sequenced by the present inventors. 7. A "PKDl carrier" is defined herein as an individual who carries at least one copy of a disease-producing mutant PKDl gene. Since the disease generally exhibits an autosomal dominant pattern of transmission, PKDl carriers have a high probability of developing some symptom of PKD. Thus, a PKDl carrier is likely to be a "PKD patient. " 8. As referred to herein, a "contig" is a continuous stretch of DNA or DNA sequence, which may be represented by multiple, overlapping, clones or sequences. 9. As referred to herein, a "cosmid" is a DNA plasmid that can replicate in bacterial cells and that accomodates large DNA inserts from about 30 to about 45 kb in length. 10. The term "PI clones" refers to genomic DNAs cloned into vectors based on the PI phage replication mechanisms. These vectors generally accomodate inserts of about 70 to about 105 kb (Pierce et al. , Proc. Natl. Acad. Sci. , USA, 89:2056- 2060, 1992). 11. As used herein, the term "exon trapping" refers to a method for isolating genomic DNA sequences that are flanked by donor and acceptor splice sites for RNA processing. 12. The term "single-strand conformational polymorphism analysis" (SSCP) refers to a method for detecting sequence differences between two DNAs, comprising hybridization of the two species with subsequent mismatch detection by gel electrophoresis. (Ravnik-Glavac et al., Hum. Mol. Genet. , 2:801, 1994.) 13. "HOT cleavage" is defined herein as a method for detecting sequence differences between two DNAs, comprising hybridization of the two species with subsequent mismatch detection by chemical cleavage (Cotton, et al., Proc. Natl. Acad. Sci., USA, 85:4397, 1988). 14. "Denaturing gradient gel electrophoresis" (DDGE) refers to a method for resolving two DNA fragments of identical length on the basis of sequence differences as small as a single base pair change, using electrophoresis through a gel containing varying concentrations of denaturant (Guldberg et al., Nuc. Acids Res. , 22:880, 1994.) 15. As used herein, "sequence-specific oligonucleotides" refers to related sets of oligonucleotides that can be used to detect allelic variations or mutations in the PKDl gene. 16. As used herein, "PKDl-specific oligonucleotides" refers to ohgonucleotides that hybridize to sequences present in the authentic expressed PKDl gene and not to PKDl homologues or other sequences. 17. "Amplification" of DNA as used herein denotes a reaction that serves to increase the concentration of a particular DNA sequence within a mixture of DNA sequences. Amplification may be carried out using polymerase chain reaction (PCR; Saiki et al., Science, 229:487, 1988), ligase chain reaction (LCR), nucleic acid-specific based amplification (NSBA), or any method known in the art. 18. "RT-PCR" as used herein refers to coupled reverse transcription and polymerase chain reaction. This method of amplification uses an initial step in which a specific oligonucleotide, oligo dT, or a mixture of random primers is used to prime reverse transcription of RNA into single-stranded cDNA; this cDNA is then amplified using standard amplification techniques e.g. PCR. 19. A PKDl gene or PKDl cDNA, whether normal or mutant, corresponding to a particular sequence is understood to include alterations in the particular sequence that do not change the inherent properties of the sequence. It will be understood that additional nucleotides may be added to the 5' and/or 3' terminus of the PKDl gene shown in Figure 1 , or the PKDl cDNA shown in Figure 2, as part of routine recombinant DNA manipulations. Furthermore, conservative DNA substitutions, i.e. changes in the sequence of the protein-coding region that do not change the encoded amino acid sequence, may also be accommodated. The present invention encompasses the human gene for PKDl. Mutations in this gene are associated with the occurrence of adult-onset polycystic kidney disease. A "normal" version of the genomic sequence, corresponding to 53,577 bases of the 5' end of the PKDl gene is shown in Figure 1. The PKDl gene sequence was determined using the strategy described in Example 1. Briefly, a series of cosmid and PI DNA clones was assembled containing overlapping human genomic DNA sequences that collectively cover a 750 kilobase segment of chromosome 16 known to contain the PKDl locus. To identify transcribed sequences within this 750 kb segment, including those sequences encoding PKDl, both exon trapping and cDNA selection techniques were employed. At the same time, direct DNA sequencing of the human DNA sequences contained in the genomic clones was performed, using techniques that are well-known in the art. These included the isolation of subclones from particular cosmid or PI clones. Nested deletions were created from selected subclones, and the nested deletions were then subjected to direct DNA sequencing using the ALF™ automated sequencer (Pharmacia, Uppsala, Sweden). A partial sequence of PKDl cDNA is shown in Figure 2. This 5' cDNA fragment, comprising 894 bases, spans nucleotides 4378 to 5271 of the sequence shown in Figure 1. The present invention encompasses isolated oligonucleotides corresponding to sequences within the PKDl gene, or within PKDl cDNA, which, alone or together, can be used to discriminate between the authentic expressed PKDl gene and PKDl homologues or other repeated sequences. These oligonucleotides may be from about 12 to about 60 nucleotides in length, preferably about 18 nucleotides, may be single- or double-stranded, and may be labelled or modified as described below. An example of an oligonucleotide that can be used in this manner is shown in Figure 3B. The discrimination function of this oligonucleotide is based on a comparison of the sequence of the authentic PKDl gene with three cDNAs derived from the PKDl homologues, which revealed that homologue cDNAs contain a 29 bp insertion relative to the authentic PKDl sequence (Figure 3A). The oligonucleotide shown in Figure 3B is modified at its 3' terminus so that it does not support polymerization reactions, and is designed to hybridize specifically to the homologue sequence and not to the authentic PKDl sequence. When this oligonucleotide is included in amplification reactions, it selectively prevents the amplification of PKDl homologue sequences. In this manner, authentic PKDl sequences are selectively amplified and PKDl homologues are not. These oligonucleotides or their functional equivalents thus provide a basis for testing for the presence of mutations in the authentic PKDl gene in a human patient (see Example 3 below). The present invention encompasses isolated DNA and RNA sequences, including sense and antisense sequences, derived from the sequences shown in Figures 1 , 2, and 3. The particular sequences may represent "normal" alleles of PKDl, including allelic variants, or "mutant" alleles, which are associated with disease symptoms. PKD1- derived sequences may also be associated with heterologous sequences, including promoters, enhancers, response elements, signal sequences, polyadenylation sequences, and the like. Furthermore, the nucleic acids can be modified to alter stability, solubility, binding affinity, and specificity. For example, PKDl-derived sequences can be selectively methylated. The DNA may comprise antisense oligonucleotides, and may further include nuclease-resistant phosphorothioate, phosphoroamidate, and methylphosphonate derivatives, as well as "protein nucleic acid" (PNA) formed by conjugating bases to an amino acid backbone as described in Nielsen et al. , 1991, Science, 254: 1497. The DNA may be derivatized by linkage of the a-anomer nucleotide, or by formation of a methyl or ethyl phosphotriester or an alkyl phosphoramidate linkage. Furthermore, the nucleic acid sequences of the present invention may also be modified with a label capable of providing a detectable signal, either directly or indirectly. Exemplary labels include radioisotopes, fluorescent molecules, biotin, and the like. In general, nucleic acid manipulations according to the present invention use methods that are well known in the art, as disclosed in, for example, Molecular Cloning, A Laboratory Manual (2nd Ed. , Sambrook, Fritsch and Maniatis, Cold Spring Harbor), or Current Protocols in Molecular Biology (Eds. Aufubel, Brent, Kingston, More, Feidman, Smith and Stuhl, Greene Publ. Assoc, Wiley-Interscience, NY, NY, 1992). The invention also provides vectors comprising nucleic acids having PKDl or PKDl -related sequences. A large number of vectors, including plasmid and fungal vectors, have been described for expression in a variety of eukaryotic and prokaryotic hosts, and may be used for gene therapy as well as for simple protein expression. Advantageously, vectors may also include a promoter operably linked to the PKDl encoding portion, particularly when the PKDl -encoding portion comprises the cDNA shown in Figure 2 or derivatives or fragments thereof. The encoded PKDl may be expressed by using any suitable vectors, such as pREP4, pREP8, or pCEP4 (InVitrogen, San Diego, CA), and any suitable host cells, using methods disclosed or cited herein or otherwise known to those skilled in the relevant art. The particular choice of vector/host is not critical to the operation of the invention. Recombinant cloning vectors will often include one or more replication systems for cloning or expression, one or more markers for selection in the host, e.g. antibiotic resistance, and one or more expression cassettes. The inserted PKDl coding sequences may be synthesized, isolated from natural sources, or prepared as hybrids, for example. Ligation of the PKDl coding sequences to transcriptional regulatory elements and/or to other amino acid coding sequences may be achieved by known methods. Suitable host cells may be transformed/transfected/infected by any suitable method including electroporation, CaCl 2 mediated DNA uptake, fungal infection, microinjection, microprojectile, or other established methods. Appropriate host cells included bacteria, archebacteria, fungi, especially yeast, and plant and animal cells, especially mammalian cells. Of particular interest are E. coli, B. Subtilis, Saccharomvces cerevisiae, SF9 cells, C129 cells, 293 cells, Neurospora, and CHO cells, COS cells, HeLa cells, and immortalized mammalian myeloid and lymphoid cell lines. Preferred replication systems include M13, ColEl, SV40, baculovirus, lambda, adenovirus, artificial chromosomes, and the like. A large number of transcription initiation and termination regulatory regions have been isolated and shown to be effective in the transcription and translation of heterologous proteins in the various hosts. Examples of these regions, methods of isolation, manner of manipulation, and the like, are known in the art. Under appropriate expression conditions, host cells can be used as a source of recombinantly produced PKDl. This invention also contemplates the use of unicellular or multicellular organisms whose genome has been transfected or transformed by the introduction of PKDl coding sequences through any suitable method, in order to obtain recombinantly produced PKDl protein or peptides derived therefrom. Nucleic acids encoding PKDl polypeptides may also be incorporated into the genome of recipient cells by recombination events. For example, such a sequence can be microinjected into a cell, and thereby effect homologous recombination at the site of an endogenous gene encoding PKDl , an analog or pseudogene thereof, or a sequence with substantial identity to a PKDl -encoding gene. Other recombination-based methods such as nonhomologous recombinations or deletion of endogenous gene by homologous recombination, especially in pluripotent cells, may also be used. The present invention also encompasses an isolated polypeptide having a sequence encoded by the authentic PKDl gene, as well as peptides of six or more amino acids derived therefrom. The polypeptide(s) may be isolated from human tissues obtained by biopsy or autopsy, or may be produced in a heterologous cell by recombinant DNA methods as described above. Standard protein purification methods may be used to isolate PKDl-related polypeptides, including but not limited to detergent extraction, and chromatographic methods including molecular sieve, ion-exchange, and affinity chromatography using e.g. PKDl-specific antibodies or ligands. When the PKD1- polypeptide to be purified is produced in a recombinant system, the recombinant expression vector may comprise additional sequences that encode additional aminoterminal or carboxyterminal amino acids; these extra amino acids act as "tags" for immunoaffϊnity purification using immobilized antibodies or for affinity purification using immobilized ligands. Peptides comprising PKDl-specific sequences may be derived from isolated larger PKDl polypeptides described above, using proteolytic cleavages by e.g. proteases such as trypsin and chemical treatments such as cyanogen bromide that are well-known in the art. Alternatively, peptides up to 60 residues in length can be routinely synthesized in milligram quantities using commercially available peptide synthesizers. The present invention encompasses antibodies that specifically recognize the PKDl polypeptide(s) encoded by the gene shown in Figure 1 or the cDNA shown in Figure 2, and/or fragments or portions thereof. The antibodies may be polyclonal or monoclonal, may be produced in response to the native PKDl polypeptide or to synthetic peptides as described above. Such antibodies are conveniently made using the methods and compositions disclosed in Harlow and Lane, Antibodies, A Laboratory Manual, Cold Spring Harbor Laboratory, 1988, other references cited herein, as well as immunological and hybridoma technologies known to those in the art. Where natural or synthetic PKD1- derived peptides are used to induce a PKDl-specific immune response, the peptides may be conveniently coupled to an suitable carrier such as KLH and administered in a suitable adjuvant such as Freunds. Preferably, selected peptides are coupled to a lysine core carrier substantially according to the methods of Tarn, Proc. Natl. Acad. Sci, USA 8 :5409- 5413, 1988. The resulting antibodies may be modified to a monovalent form, such as, for example, Fab, Fa^, FAB', or FV. Anti-idiotypic antibodies may also be prepared using known methods. In one embodiment, normal or mutant PKDl polypeptides are used to immunize mice, after which their spleens are removed, and splenocytes used to form cell hybrids with myeloma cells and obtain clones of antibody-secreted cells according to techniques that are standard in the art. The resulting monoclonal antibodies are screened for specific binding to PKDl proteins or PKDl -related peptides. In another embodiment, antibodies are screened for selective binding to normal or mutant PKDl sequences. Antibodies that distinguish between normal and mutant forms of PKDl may be used in diagnostic tests (see below) employing ELISA, EMIT, CEDIA, SUFA, and the like. Anti-PKDl antibodies may also be used to perform subcellular and histochemical localization studies. Finally, antibodies may be used to block the function of the PKDl polypeptide, whether normal or mutant, or to perform rational drug design studies to identify and test inhibitors of the function (e.g., using an anti-idiotypic antibody approach.) Identification of Disease-Causing Mutations in PKDl In one mode of practice of the present invention, the isolated and sequenced PKDl gene is utilized to identify previously unknown or mutant versions of the PKDl gene. First, human subjects with inherited polycystic kidney disease are identified by clinical testing, pedigree analysis, and linkage analysis, using standard diagnostic criteria and interview procedures, and DNA or RNA samples are obtained from the subjects (see below). A variety of techniques are then employed to pinpoint new mutant sequences. First, PKDl DNA may be subjected to direct DNA sequencing, using methods that are standard in the art. Furthermore, deletions may be detected using a PCR-based assay, in which pairs of olignucleotides are used to prime amplification reactions and the sizes of the amplification products are compared with those of control products. Other useful techniques include Single-Strand Conformation Polymorphism analysis (SSCP), HOT cleavage, denaturing gradient gel electrophoresis, and two- dimensional gel electrophoresis. A confounding and complicating factor in the detection of a PKDl mutation is the presence of PKDl homologues at several sites on chromosome 16 proximal to the transcribed gene. In analysis of mutations in PKDl, it is critical to distinguish between sequences derived from the authentic PKDl gene and sequences derived from any of the homologues. Thus, an important feature of the present invention is the provision of oligonucleotide primers that discriminate between authentic PKDl and the homologues. A detailed comparison of the sequences of the authentic PKDl gene and the homologues enables the design of primers that discriminate between the authentic PKDl gene or cDNA and the homologues. Primers that conform to this criterion, such as those disclosed in Figure 3B, may be used in conjunction with any of the analytical methods described below. For SSCP, primers are designed that amplify DNA products of about 250- 300 bp in length across non-duplicated segments of the PKDl gene. For each amplification product, one gel system and two running conditions are used. Each amplification product is applied to a 10% polyacrylamide gel containing 10% glycerol. Separate aliquots of each amplimer are subjected to electrophoresis at 8W at room temperature for 16 hours and at 30W at 4°C for 5.4 hours. These conditions were previously shown to identify 98 % of the known mutations in the CFTR gene (Ravnik- Glavac et al., Hum. Mol. Genet. , 2:801, 1994.) For "HOT" cleavage, amplification reactions are performed using radiolabelled PKDl-specific primers. Each radiolabelled amplification product is then mixed with a 10-fold to 100-fold molar excess of unlabelled amplification products produced using the identical primers and DNA from APKD-affected or -unaffected subjects. Heteroduplex formation, chemical cleavage, and gel analysis are then performed as described (Cotton, et al., Proc. Natl. Acad. Sci., USA, 8 :4397, 1988). Bands on the gel that are smaller than the homoduplex result from chemical cleavage of heteroduplexes at base pair mismatches involving cytidine or thymidine. Once a mutation has been identified by this procedure, the exact location of the mismatch(es) is determined by direct DNA sequencing. Mutations are also identified by "broad range" DDGE (Guldberg et al., Nuc. Acids Res. , 22:880, 1994.) The use of GC-clamped PCR primers and a very broad denaturant gradient enables the efficient detection of mutant sequences. This method can also be combined with non-denaturing size fractionation in a two-dimensional system. An apparatus is used that permits automated two-dimensional electrophoresis, and the second dimension considerably increases the resolution of mutations. After the presence of a mutation is detected by any of the above techniques, the specific nucleic acid alteration comprising the mutation is identified by direct DNA sequence analysis. In this manner, previously unidentified PKDl mutations may be defined. Once a previously unidentified PKDl mutation is defined, methods for detecting the particular mutation in other affected individuals can be devised, using a variety of methods that are standard in the art. For example, oligonucleotide probes may be prepared that allow the detection and discrimination of the particular mutation. It will be understood that such probes may comprise either the mutant sequence itself, or, alternatively, may flank the mutant sequence. Furthermore, the oligonucleotide sequence can be used to design a peptide immunogen comprising the mutant amino acid sequence. These peptides are then used to elicit antibodies that distinguish between noimal and mutant PKDl polypeptides. Diagnostic Tests for PKDl Mutations Mutant PKDl genes, whether identified by the methods described above or by other means, find use in the design and operation of diagnostic tests. Tests that detect the presence of mutant PKDl genes, including those described below and in Example 3, can be applied in the following ways: (T) To determine donor suitability for kidney transplants. In general, it is desirable to use a close relative of the transplant receipient. When the recipient is a patient suffering from familial APKD, it is important to ascertain that the donor relative does not also carry the familial mutant PKDl gene. (2) To screen for at-risk individuals in APKD-affected families. Presymptomatic individuals who have a high probability of developing APKD can be identified, allowing them to be monitored and to avail themselves of preventive therapies. (3) To target hypertensive patients for antϊhypertensive treatment. Hypertension is also linked to APKD. Screening of hypertensive patients for the presence of mutant PKDl genes can be used to identify patients for pre-emptive regulation of blood pressure to prevent later kidney damage. (4) To perform prenatal screening. Most PKDl -linked PKD is of the adult-onset type. In a small subset of families carrying a mutation in PKDl genes, however, juvenile onset is common and signifies a more severe form of the disease. In these families, prenatal screening can be useful for genetic counselling purposes. In general, the diagnostic tests according to the present invention involve obtaining a biological sample from a subject, and screening the sample, using all or part of the PKDl gene of this invention, for the presence of one or more mutant versions of the PKDl gene or its protein product. The subject may be a fetus in utero, or a human patient of any age. In one embodiment, a sample of genomic DNA is obtained from a human subject and assayed for the presence of one or more disease-associated PKDl mutations. This DNA may be obtained from any cell source or body fluid. Non-limiting examples of cell sources available in clinical practice include blood cells, buccal cells, cervicovaginal cells, epithelial cells from urine, fetal cells, or any cells present in tissue obtained by biopsy. Body fluids include blood, urine, cerebrospinal fluid, ammotic fluid, and tissue exudates at the site of infection or inflammation. DNA is extracted from the cell source or body fluid using any of the numerous methods that are standard in the art. It will be understood that the particular method used to extract DNA will depend on the nature of the source. The minimum amount of DNA to be extracted for use in the present invention is about 25 pg (corresponding to about 5 cell equivalents of a genome size of 4 x 10 9 base pairs). In this embodiment, the assay used to detect the presence of mutations may comprise restriction enzyme digestion, direct DNA sequencing, hybridization with sequence-specific oligonucleotides, amplification by PCR, single-stranded conformational polymorphism analysis, denaturating gradient gel electrophoresis (DDGE), two- dimensional gel electrophoresis, in situ hybridization, and combinations thereof. In a preferred embodiment, RNA is isolated from a PKDl -expressing cell or tissue, preferably lymphocytes, using standard techniques including automated systems such as that marketed by Applied Biosystems, Inc. (Foster City, CA). The RNA is then subjected to coupled reverse-transcription and PCR amplification (RT-PCR). The resulting DNA may then be screened for the presence of mutant sequences by any of the methods outlined above (see Example 3 below). As discussed above, any nucleic-acid-based screening method for PKDl mutations must be able to discriminate between the authentic PKDl gene present at chromosome location 16pl3.3 and PKDl homologues present at 16pl3.1 and other locations. The oligonucleotides shown in Figure 3 are examples of primers that discriminate between the authentic and homologue sequences, and these oligonucleotides or their equivalents form an important part of any such diagnostic test. Furthermore, nucleotides 43,818 through 52,882 of the PKDl sequence of Figure 1 represent a sequence that is unique to the authentic PKDl gene and is not present in the homologues. Thus, oligonucleotides derived from this region can be used in a screening method to insure that the authentic PKDl gene, and not the homologues, are detected. In another embodiment, the assay used to detect the presence of a mutant PKDl gene involves testing for mutant gene products by an immunological assay, using one of many methods known in the art, such as, for example, radioimmunoassay, ELISA, immunfluorescence, and the like. In this embodiment, the biological sample is preferably derived from a PKDl -expressing tissue such as kidney. The PKDl polypeptide may be extracted from the sample. Alternatively, the sample may be treated to allow detection or visualization of specifically bound antibodies in situ as occurs in, for example, cryosectioning followed by immunofluorescent staining. The antibodies may be monoclonal or polyclonal, may be raised against intact PKDl protein, or natural or synthetic peptides derived from PKDl. In a preferred embodiment, the antibodies discriminate between "normal" and "mutant" PKDl sequences, and possess a sufficiently high affinity for PKDl polypeptides so that they can be used in routine assays. It will be understood that the particular method or combination of methods used will depend on the particular application. For example, high-throughput screening methods preferably involve extraction of DNA or RNA from an easily available tissue, followed by amplification of particular PKDl sequences and hybridization of the amplification products with a panel of specific oligonucleotides. Therapeutic Applications The present invention encompasses the treatment of PKD using the methods and compositions disclosed herein. All or part of the normal PKDl gene disclosed above can be delivered to kidney cells or other affected cells using a variety of known methods, including e.g. liposomes, viral vectors, recombinant viruses, and the like. The gene can be incorporated into DNA vectors that additionally comprise tissue-specific regulatory elements, allowing PKDl expression in a tissue-specific manner. This approach is feasible if a particular mutant PKDl allele, when present in a single copy, merely causes the level of the PKDl protein to diminish below a threshold level necessary for normal function; in this case, increasing the gene dosage by supplementing with additional normal copies of the PKDl gene should correct the functional defect. In another embodiment, a mixture of isolated nucleic acids, such as that set forth in Figure 2 and at least a portion of the normal PKDl gene, may be delivered to kidney or other affected cells in order to treat APKD. Alternatively, it may be desired to limit the expression of a mutant PKDl gene, using, for example, antisense sequences. In this embodiment, antisense oligonucleotides may be delivered to kidney or other cells. For therapeutic uses, PKDl -related DNA may be administered in any convenient way, for example, parenterally in a physiologically acceptable carrier such as phosphate buffered saline, saline, deionized water, or the like. Typically, the compositions are added to a retained physiological fluid such as blood or synovial fluid. The amount administered will be empirically determined using routine experimentation. Other additives, such as stabilizers, bactericides, and the like, may be included in conventional amounts. This invention also encompasses the treatment of APKD by protein replacement. In one embodiment, protein produced by host cells transformed or transfected with DNA encoding the PKDl polypeptide of the present invention is introduced into the cells of an individual suffering from altered, defective, or non¬ functional expression of the PKDl gene. This approach augments the absence of PKDl protein, or the presence of a defective PKDl protein, by adding functional PKDl protein. The PKDl protein used in augmentation may comprise a subcellular fragment or fraction, or may be partially or substantially purified. In any case, the PKDl protein is formulated in an appropriate vehicle, such as, for example, liposomes, that may additionally include conventional carriers, excipients, stabilizers, and the like. It will be understood that the therapeutic compositions of the present invention need not in themselves constitute an effective amount, since such effective amounts can be reached by administering a plurality of such therapeutic compositions. The following examples are intended to illustrate the invention without limiting its scope thereof. Example 1: Cloning and Sequencing of the Human PKDl gene A. Methods: Ordered restriction fragments were subcloned into either pBLUEscript (Stratagene, LaJolla, CA) or pGEM (Promega, Madison, WI). Plasmids were purified by CsCl density centrifugation in the presence of ethidium bromide. Nested deletions were generated from each plasmid using Exoiπ (Henikoff, S. , Methods Enzymol. 155: 156-165, 1987) and additional enzymatic reagents provided by the Erase- A-Base kit (Promega, Madison, WI). The resulting nested clones were analyzed electrophoretically after appropriate restriction enzyme digestion and were ordered into a nested set of templates for sequencing. A minimum tiling series of plasmids, each differing by approximately 250 op from flanking clones, were identified and used for sequencing. Plasmid DNAs were prepared for sequencing in one of two ways. Initially, all clones of interest were cultured in 2 mL of Super Broth (Tartof et al. , BRL Focus 9: 12, 1987) for 20 hours at 37°C. Sets of 12-24 were processed simultaneously using a modified alkaline SDS procedure followed by ion exchange chromatography as described by the manufacturer (Easy-Prep, Pharmacia, Piscataway, NJ). Plasmid DNA yields ranged from 2.5 to 25 μg. Poor growing clones, or those whose plasmids generated sequence of unacceptable quality, were recultured in 100 mL of Luria's Broth and the plasmid DNA isolated using Qiagen columns (Qiagen, San Diego, CA). Dideoxy sequencing reactions were performed on deletion clones using the Auto-Read Sequencing Kit (Pharmacia, Piscataway, NJ) and fluorescein-labeled vector primers (M13 universal, M13 reverse, T3, T7 and SP6). Reaction products were separated on 6% denaturing acrylamide gels using the ALF DNA Sequencer (Pharmacia, Piscataway, NJ). Second strand sequencing was performed using either an opposing set of nested deletions or primer walking. For primer walking, custom 17mers, staggered every 250 bp, were purchased from a commercial supplier (Protogene, Palo Alto, CA). Template DNAs prepared by Qiagen or CsCl density gradients were sequenced using the unlabeled 17mers by inclusion of fluor-dATP labeling mix in the sequencing reactions as described by the manufacturer (Pharmacia, Piscataway, NJ). In all cases, except the 2.5kb GC-rich region, single-stranded DNA was rescued from deletion clones using helper phage VCSM13 (Stratagene) essentially as described by the manufacturer. Single-stranded templates from the 2.5 kb GC-rich region were sequenced using fluorescein-labeled universal primer and the Sequitherm Long Read cycle sequencing kit (Epicentre Technologies, Madison, WI) (Zimmerman et al., Biotechnigues 17: 303-307, 1994). All processed sequencing data was transferred to a Quadra 700 Macintosh computer and assembled using the SEQUENCHER (Gene Codes, Ann Arbor, MI) sequencing assembly program. For differences that would not be resolved by examining the chromatograms, templates were either resequenced or primers proximal to the ambiguity were designed and used for resolution of the sequence difference. Cycle sequencing was performed using the Sequitherm cycle sequencing kit as described by the manufacturer (Epicentre Technologies, Madison, WI). Reaction products were separated on denaturing acrylamide gels and subsequently detected by autoradiography. B. Sequencing Strategy: A 700 kbp region of chromosome 16 containing the PKDl locus is shown in Figure 4 (top panel). A contig covering this region was assembled from overlapping PI clones (shown in the middle panel). The contig was assembled by unidirectional chromosomal walking from the ends of the interval (ATPL and D16S84) and bidirectional walking from several internal loci (D16S139 and KG8). One of the clones, 91.8B, appears to span the entire PKDl interval and includes cosmids cDEBll, cGGG10.2, and substantial portions of cosmids 2H2 and 325A11 (S tailings, R.L. et al., Genomics 12: 1031, 1992). This PI clone (shown schematically in Figure 5) was used as a second genomic template to confirm discrepancies between the published cDNA sequence and the cosmid-derived genomic sequence. Preliminary experiments revealed the presence of multiple repetitive elements in the cGGG10.2 cosmid. Therefore, an ordered approach based on nested deletions, rather than random shotgun subcloning, was used to sequence the PKD l gene. Restriction fragments derived from the inserts of both cGGG10.2 and cDEBll were subcloned into high-copy number plasmids as a preliminary step to the generation of nested deletions. Unidirectional deletions were prepared and sequenced, using the the ALF™ automated sequencing system (Pharmacia, Uppsala, Sweden). Read lengths averaged 350 nucleotides, with runs greater than 500 nucleotides being common. This strategy allowed for the rapid and accurate sequencing of 53,577 nucleotides of linear gene sequence using 1,200 sequencing reactions. Based on this analysis, the cumulative fold-redundancy is approximately 7-fold. Intervals of minimum redundancy (3-fold) showed perfect sequence identity between overlapping templates. The only exception to complete double-stranded sequencing was the 2.5 kb GC-rich region in the 4 kb BamHl-SacI fragment, and an adjoining 150 bp GC-rich region in the adjacent Sacl-BamHl fragment. These segments were only sequenced on the non-coding strand due to complications arising from the repetitive nature of the sequences in this region. In this manner, the sequence of PKDl genomic DNA shown in Figure 1 was obtained. C. Primary Structure of the PKDl Locus: The primary sequence of the interval encompassing the PKDl gene is 53,577 bp in length. The locus is GC-rich (62.4%), with a CpG/GpC dinucleotide ratio of 0.485. Comparison of this sequence with the previously reported partial cDNA sequence revealed differences at three locations (Figure 6). The first and most significant difference is the presence of two additional cytosine residues on the plus strand at position 4566 of the reported sequence. This sequence difference was confirmed using sequence derived from cDNA originating from a different individual. In addition, allele-specific oligonucleotides (ASOs) homologous to either the reported sequence or the present sequence were hybridized to the genomic and cDNA clones. In all cases, dot-blot analysis using single-base discrimination conditions showed that only the ASO containing the additional cytosine residues hybridized to all cloned DNAs. The presence of these two cytosine residues results in a frame shift in the predicted protein coding sequence, leading to the replacement of 92 carboxy terminal amino acids with a novel 12-amino acid carboxy terminus. Seven of the the twelve amino acids of the new carboxy terminus are charged or polar. Additional sequence differences are located at positions 3639-3640 and 3708-3709 of the published sequence (Figure 6). A GC dinucleotide pair is present at each of these positions in the present sequence, while a CG pair is found in the reported sequence. In each case, histidine and valine residues would replace the previously predicted glutamine and leucine residues, respectively. It is unclear at present if these latter differences represent allelic variation or errors in the reported sequence. It is clear that the previously reported cDNA sequence provides an inaccurate sequence with an incorrect reading frame. Any proteins encoded by the prior partial sequence would thus be defective, and would in no way suggest proteins encoded by the sequence of the present invention, or indeed the sequence itself. It follows that employ of the prior sequence, or of proteins encoded thereby, in therapeutic or diagnostic uses would not be successful. The entire sequence was analyzed for transcriptional elements and CpG islands using GRAIL2 (Uberbacher, E.C. et al. , Proc. Natl. Acad. Sci. USA 88: 11261 , 1991) and XGrail client server (Shah et al. , User's Guide to GRAIL and GENQUEST, Client- Server Systems, available by anonymous ftp to arthur.epm.omi.gov (128.219.9.76) from directory pub/xgrail or pub/xgenquest, as file manual, grail-genquest, 1994). Ten CpG islands were identified (Figure 7). Forty-eight exons were predicted on the coding strand by the GRAIL program. The quality of 39 of the 48 exons was "excellent", six were considered "good", and three were deemed "marginal". These data were analyzed using the gene model feature of GRAIL2. The final gene model contained 46 exons. When the accuracy of the gene model was examined by comparison to the published cDNA, 22 of 23 exons in the published cDNA were predicted in the model. Of the 22 exons present in the gene model, 16 were correctly spliced, four were wholly contained in the model but used either an incorrect 5' or 3' splice site, and in one case two exons were combined into a single exon in the model (with the program failing to remove a small intron). Only one of the deduced exons in the published cDNA was absent from the gene model. D. Identification of Protein Coding Regions: Exons predicted by the GRAIL2 program with an "excellent" score were used to search the SwissProt and PIR databases using the BLASTP program. Exons 3 and 4 of the gene model were predicted to encode peptides with homology to a number of leucine-rich repeat (L Mt)-containing proteins involved in protein-protein interactions (Figure 8). In addition to the LRR itself, sequences amino- and caΛoxy-flanking to the LRR may also be conserved in proteins of the leucine-rich glycoprotein (LRG) family, either singly or together. Exon 3 encodes residues homologous to the LRR from leucine- rich α2 glycoprotein, members of the GPlb.IX complex which comprise the von Willebrand factor receptor, as well as to the Drosophila proteins chaoptin, toll, and slit. The latter are involved in adhesion, dorsal- ventral polarity, and morphogenesis, respectively. Sequences predicted by GRAIL2 to be encoded by exon 4 were found to have homology to the conserved region carboxy terminal to the LRR in all of the above proteins except chaoptin, which lacks this conserved region. Homology was also observed between the exon 4-encoded sequences and the trk proto-oncogene, which encodes a receptor for nerve growth factor. Further examination of the predicted PKDl peptide revealed additional regions of weaker homology with conserved regions of the trk tyrosine kinase domain. None of the more proximal exons in the gene model appear to encode a peptide with homology to the conserved ammo-flanking region seen in a subset of the LRR-containing proteins. Exon trapping, RT-PCR, and Northern blot analysis revealed that GRAIL2- predicted exons 3 and 4 are present in expressed sequences. During initial exon trapping experiments using genomic PI and cosmid clones from the PKDl locus, an exon trap was identified that contained both of these exons. In separate experiments, the presence of the 1,-RR-carboxy-flanking motif in transcribed sequences was confirmed by RT-PCR using as a template RNA from fetal kidney and from adult brain. On the Northern blot, an RT- PCR fragment containing this motif detected the 14kb PKDl transcript and several other transcripts of 21 kb, 17 kb, and 8.5 kb. A region of homology was also observed between the GRAIL2-predicted peptide and the human gpl00/Pmell7 gene products, as well as with bovine RPE1. The gplOO/Pmel 17 gene encodes two alternately spliced products (gplO and Pmell7) that differ by only 7 amino acids. Closer examination indicated that this region of homology was present in sequences encoded by three separate GRAIL-predicted exons; however, only the exon containing the first copy of the motif is fully contained within the final gene model. GRAH2-predicted exons 9, 22, and 28, upstream of the 3' cDNA, showed strong homology to EST T03080 (85%, 255 bp), EST T04943 (98%, 189 bp) and EST T05931 (94% , 233 bp). In addition, nucleotides 10378-10625 of GRAIL-predicted intron 1 showed strong homology to a region of the Apo CD. gene (81 %, 263 bp). E. Repeated Sequences: The PKDl locus was searched for known classes of repetitive DNA by FASTA comparison against the repeat database of Jurka et al. (J.Mol.Evol. 35:286-291, 1992). This search identified 23 Alu repeats but no other repetitive elements. The Alu repeats are organized into three clusters of four or more Alu repeats, three clusters of two Alu repeats, and two singlet Alu repeats (Figure 7). The average density of Alu repeats per kb is 0.4. The three clusters of four or more Alu repeats are positioned within the first 20,000 nucleotides (0.85 Alu per kb) and are predominantly on the reverse strand (15 of 17). Intervals 20,000-40,000 and 47,000-54,000 are devoid of Alu repeats. The sequence interval contained two dinucleotide repeats (> (TG)8) and a single tetranucleotide repeat ((TTTA)6). The TG dinucleotide repeats are present at positions 209-224 and 52,693-52,708. The tetranucleotide repeat is located at position 7795-7810. No trinucleotide repeats > 5 were identified. Only the TG8 repeat is known to be polymorphic. In addition to the more usual repetitive elements, the PKDl gene contains several types of repeated sequences that either do not appear in existing data bases, or do not appear in the extreme form seen at this locus. The most striking repeat is a 2.5 kb segment within the 4 kb BamHl-Sacl fragment. A significantly shorter C-T rich region is also found in the adjoining 1.8 kb Sacl-BamHl fragment. These regions proved very difficult to sequence unambiguously due to the high GC content (65 %), to the purine assymetry with respect to each strand and to the length of the repeat. The coding strand in this region has an extreme pyrimidine bias, being 96% C-T, and could not be sequenced using T7 DNA polymerase or Sequenase. This was true regardless of the template type (plasmid, single-stranded phage, or strand-separated single-stranded DNA). In both cases, the non-coding strand, which is G-A rich, was successfully sequenced with both T7 DNA polymerase and Sequenase, although run lengths were noticeably abbreviated compared to all other regions sequenced. Compressions on the non-coding strand were resolved by conventional and cycle sequencing using single-stranded template. The exteme purine assymetry of strands in this segment may promote localized triple strand conformation under the appropriate conditions (pH, divalent cations, supercoiling), and may be a major cause of the difficulty in sequencing this segment. The other unusual repeat was located in the 7.6 kb Xhol fragment. This repeat is 459 bp in length and consists of 17 tandem copies of a perfect 27 bp repeat. Example 2: PKDl cDNA Sequences Obtained Through Exon Trapping and cDNA Selection Techniques The 700 kbp interval of chromosome 16 that includes the PKDl gene appears to be particularly rich in CpG islands and, by association, is most likely rich in expressed sequences as well. To purify and sequence expressed PKDl sequences, an exon-rescue vector, pSPL3, was used to recover sequences from cosmids that contain both a splice acceptor and splice donor element; this method is designated "exon trapping." The application of this method, in conjunction with standard subcloning, amplification, and DNA sequencing methods, allowed the determination of PKDl cDNA sequence as shown in Figure 2. Exon trapping is a highly efficient method for isolating expressed sequences from genomic DNA. The procedure utilizes the pSPL3 plasmid, which contains rabbit β-globin coding sequences separated by a portion of the HTV-tat gene, or improved derivatives of SPL3 lacking cryptic (interfering) splice sites. Fragments of cloned PKDl genomic DNA were cloned into the intron of the tat gene, and the resulting subclones were transfected into COS-7 cells. SV40 sequences in the vector allow for both relaxed episomal replication of the transfected vectors, as well as transcription of the cloned genomic DNAS. Exons within the subcloned genomic DNAs spliced into the globinV tat transcript were recovered using RT-PCR, using primers containing tat splice donor and acceptor sequences. A major advantage of exon trapping is that expression of the cloned DNA is directed by a viral promoter; thus, developmental or tissue-specific expression of gene products is not a concern. PKDl -containing genomic clones, in the form of either cosmid or PI DNA, were either double digested with BamHT and Bgiπ or partially digested with Sau3A and shotgun cloned into BamHI-digested and dephosphorylated pSPL3 (GIBCO BRL, Bethesda, MD) or its derivatives. Plasmid minipreps were electroporated into COS-7 cells, and trapped exons were recovered by RT-PCR, followed by subcloning, using standard procedures. Trapped exons from the PKDl locus are shown in Figure 9 (bottom). The trapped exons were subjected to automated DNA sequencing as above, allowing their alignment with the genomic PKDl DNA. Example 3: Diagnostic Test for PKDl Mutations Whole blood samples collected in high glucose ACD VacutainersTM (yellow top) were centrifuged and the buffy coat collected. The white cells were lysed with two washed of a 10: 1 (v/v) mixture of 14mM NH 4 CI and ImM NaHCO 3 , their nuclei were resuspended in nuclei-lysis buffer (lOmM Tris, pH 8.0, 0.4M NaCl, 2mM EDTA, 0.5 % SDS, 500 ug/ml proteinase K) and incubated overnight at 37°C. Samples were then extracted with a one-fourth volume of saturated NaCl and the DNA was precipitated in ethanol. The DNA was then washed with 70% ethanol, dried, and dissolved in TE buffer (lOmM Tris-HCl, pH 7.5, ImM EDTA.) 0.2-1 μg of DNA (in 1-2 μl) was then added to a PCR reaction mixture containing the following components: 10X Taq buffer 8 μl dNTPS (2 mM each) 7 μ\ Forward primer (100 μM) 1.5 μl Reverse primer (100 μM) 1.5 μl Blocking oligo (2mM) 1.5 μl Taq DNA polymerase 1 μl water to 80 μ\ Thirty cycles of amplification are then performed, using a standard DNA thermal cycler the following protocol for each cycle: 94°C, 30 seconds; 55°C, 30 seconds; and 72 °C, 30 seconds. It will be understood that the enzymes and nucleotides used in the above reactions may be obtained from any manufacturer, such as GIBCO- BRL, Promega, New England Biolabs, and the like. The forward primer used in the reaction described above comprises an oligonucleotide that hybridizes to both authentic PKDl and PKDl homologue sequences. An example of such a primer is: 5'-CAGGACCTGTCCCAGGCAT-3'. The reverse primer comprises a sequence derived from a 3' region of the authentic PKDl gene, which may or may not be present in the PKDl homologues. Examples of suitable reverse primers are: 5'-CTGGCGGGCGAGGAGAT-3', 5'-CTTTGACAAGCACATCT-3\ and 5'- C AACTGGCTGG AC AAC A-3 ' . The blocking oligonucleotide comprises: 5 '-AGGACCTGTCC AGGC ATC- 3 ' . Importantly, this oligonucleotide must be incapable of supporting polymerization. One example is an oligonucleotide in which the 3' terminal nucleotide comprises a dideoxynucleotide. It will be understood that any modification that achieves this effect may be used in practicing the invention. Under appropriate conditions, the blocking oligonucleotide hybridizes efficiently to PKDl homologues but inefficiently to the authentic PKDl sequence. Thus, the amplification products in this diagnostic test are derived only from the authentic PKDl gene. The RT-PCR products obtained above are analyzed for the presence of specific PKDl mutations as follows: 8 μl of the amplified prepared as describe above are added to 50 μl of a denaturing solution (0.5mM NaOH, 2.0M NaCl, 25mM EDTA) and spotted onto nylon membrane filters (INC Biotrans). The DNA is then fixed to the membranes by baking the filters at 80°C for 15 minutes under vacuum. Oligonucleotides that detect PKDl mutations are chemically synthesized using an automated synthesizer and radiolabelled with 32 P with polynucleotide kinase, using methods that are standard in the art. Hybridizations are carried out in plastic bags containing the filters prepared as in Example ID above, to which one or more labelled oligonucleotides are added in a hybridization buffer (3.0M Tetramethylammonium chloride (TMAC), 0.6% SDS, ImM EDTA, lOmM sodium phosphate pH 6.8, 5X Denhardt's Solution, and 40 μg/ml yeast RNA). Oligonucleotide concentrations in the pools range from 0.03 to 0.15 pmol/ml hybridization solution. Hybridizations are allowed to proceed overnight at 52 °C, with agitation. The membranes are then removed from the bags and washed for 20 min at room temperature with wash buffer (3.0M TMAC, 0.6% SDS, ImM EDTA, lOmM sodium phosphate pH 6.8), followed by a second wash in the same buffer for 20 min at 52 °C. The membranes are then dried and exposed to Kodak X-OMAT film. While the present invention has been described with respect to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims: What is claimed: 1. An isolated human PKDl gene, comprising the DNA sequence set forth in Figure 1. 2. A purified RNA molecule comprising an RNA sequence corresponding to the DNA sequence of claim 1 or its complement. 3. A purified DNA molecule comprising an intronless sequence derived from the DNA sequence of claim 1. 4. A recombinant vector comprising the DNA sequence of claim 1. 5. The vector of claim 4 further comprising a transcriptional regulatory element operably linked to said PKDl DNA sequence, said element having the abihty to direct the expression of genes of prokaryotic or eukaryotic cells and their viruses or combinations thereof. 6. A cell comprising the vector of claim 4. 7. A method for producing PKDl protein, which comprises: (a) culturing the cell of claim 6 in a medium and under conditions suitable for expression of said protein, and (b) isolating said expressed protein. 8. An isolated mutant human PKDl gene, comprising a DNA sequence whose presence in one or more copies in the genome of a human individual is associated with adult-onset polycystic kidney disease in said individual. 9. The mutant gene of claim 8 wherein said DNA sequence encodes a protein whose expression is associated with adult-onset polycystic kidney disease. 10. An isolated mutant human PKDl gene, comprising the DNA sequence set forth in Figure 1 having modifications selected from the group consisting of: transitions, transversions, deletions, and insertions. 11. The mutant gene of claim 10, comprising a DNA sequence whose presence in one or more copies in the genome of a human individual is associated with adult-onset polycystic kidney disease in said individual. 12. A purified RNA molecule comprising an RNA sequence corresponding to the DNA sequence of claim 10 or its complement. 13. A purified DNA molecule comprising an intronless sequence derived from the DNA sequence of claim 10. 14. A recombinant vector comprising the DNA sequence of claim 13. 15. The vector of claim 14 further comprising a transcriptional regulatory element operably linked to said PKDl DNA sequence, said element having the abihty to direct the expression of genes of prokaryotic or eukaryotic cells and their viruses or combinations thereof. 16. A cell comprising the vector of claim 14. 17. A method for producing mutant PKDl protein, which comprises: (a) culturing the cell of claim 16 in a medium and under conditions suitable for expression of said protein, and (b) isolating said expressed protein. 18. An isolated nucleic acid comprising the sequence set forth in Figure 2. 19. An isolated nucleic acid comprising: 5'-AGGACCTGTCCAGGCATC-3\ 20. A diagnostic method for screening human subjects to identify PKDl carriers, which comprises the steps of: (1) obtairiing a sample of biological material from said subject; and (2) assaying for the presence of mutant PKDl genes or their protein products in said biological material. 21. The method of claim 20 wherein said biological material comprises nucleic acid, and said assaying comprises: (a) selectively amplifying the authentic PKDl gene, or fragments thereof, from said biological material; and (b) detecting the presence of normal and mutant PKDl genes using an analytical method selected from the group consisting of: restriction enzyme digestion, direct DNA sequencing, hybridization with sequence-specific oligonucleotides, single- stranded conformational polymorphism analysis, denaturating gradient gel electrophoresis (DDGE), two-dimensional gel electrophoresis, and combinations thereof. 22. The method of claim 21 wherein said amplifying is performed in the presence of an oligonucleotide comprising 5'-AGGACCTGTCCAGGCATC-3\ 23. The method of claim 21 wherein said nucleic acid comprises RNA, and said method further comprises selectively transcribing said PKDl RNA prior to said amplifying step. 24. The method of claim 23 wherein said said amplifying is performed in the presence of an oligonucleotide comprising: 5'-AGGACCTGTCCAGGCATC-3\ 25. The method of claim 20 wherein said mutant gene is predetermined. 26. The method of claim 20, wherein said assaying step comprises an immunoassay employing an antibody specific for said mutant PKDl gene product. 27. The method of claim 20, wherein said assaying step comprises measuring a predetermined biological or chemical function of said PKDl gene product in said sample. 28. The method of claim 20, wherein said subject is a fetus in utero. 29. An isolated antibody directed against a peptide comprising the sequence LRAKNKVHPSST, or immunogenic fragments thereof. 30. The antibody of claim 29 immunoreactive with a polypeptide encoded by the gene sequence set forth in Figure 1. 31. An isolated antibody immunoreactive with a polypeptide encoded by the gene sequence set forth in Figure 1. 32. An isolated antibody immunoreactive with the PKDl polypeptide. 33. An isolated human PKDl gene, consisting essentially of the DNA sequence set forth in Figure 1. 34. An isolated mutant human PKDl gene, consisting essentially of a DNA sequence whose presence in one or more copies in the genome of a human individual is associated with adult-onset polycystic kidney disease in said individual. 35. An isolated nucleic acid consisting essentially of the sequence set forth in Figure 2. 36. An isolated nucleic acid consisting essentially of: 5 '- AGGACCTGTCCAGGC ATC-3 ' . 37. A method for treating a disease condition having the characteristics of APKD, which comprises administering to cells having defective PKDl gene function a normal human PKDl gene or fragments thereof, wherein said administration results in expression of therapeutically effective amounts of normal PKDl protein or fragments thereof. 38. The method of claim 37, wherein said normal human PKDl gene comprises the DNA sequence of Figure 1. 39. The method of claim 37, wherein said normal human PKDl gene comprises the DNA sequence of Figure 2. 40. The method c claim 38, further comprising administering the DNA sequence of Figure 2 or fragments thereof. 41. A method for treating a disease condition having the characteristics of APKD, which comprises administering to cells having defective PKDl gene function therapeutically effective amounts of a normal PKDl protein or fragments thereof. 42. The method of claim 41, wherein said PKDl protein is encoded by the DNA sequence of Figure 1. 43. The method of claim 41 , wherein said PKDl protein is encoded by the DNA sequence of Figure 2. 44. The method of claim 42, further comprising administering a polypeptide encoded by the DNA sequence of Figure 2. 45. A composition for treating a disease condition having the characteristics of APKD, said composition comprising an isolated human PKDl gene having the DNA sequence of Figure 1, or fragments thereof, and a pharmaceutically acceptable carrier or diluent. 46. The composition of claim 45, comprising a vector into which said PKDl gene is incorporated. 47. The composition of claim 45, further comprising an isolated human PKDl gene having the DNA sequence of Figure 2 or fragments thereof. 48. A composition for treating a disease condition having the characteristics of APKD, said composition comprising a normal PKDl protein encoded by the DNA sequence of Figure 1, or fragments thereof, and a pharmaceutically acceptable carrier or diluent. 49. The composition of claim 48, further comprising a polypeptide encoded by the DNA sequence of Figure 2, or fragments thereof. 50. A unicellular or multicellular organism whose genome comprises a recombinant PKDl gene or fragments thereof. 51. The organism of claim 50, wherein said PKDl gene has the DNA sequence of Figure 1 or fragments thereof. 52. The organism of claim 50, wherein said PKDl gene has the sequence of Figure 2 or fragments thereof. 53. The organism of claim 51 whose genome further comprises the DNA sequence of Figure 2 or fragments thereof.

Inventors: BURN TIMOTHY C, CONNORS TIMOTHY D, DACKOWSKI WILLIAM, GERMINO GREGORY, KLINGER KATHERINE W, LANDES GREGORY M, QIAN FENG, BURN, TIMOTHY, C., CONNORS, TIMOTHY, D., DACKOWSKI, WILLIAM, GERMINO, GREGORY, KLINGER, KATHERINE, W., LANDES, GREGORY, M., QIAN, FENG
Applicants: IG LAB INC, UNIV JOHNS HOPKINS, IG LABORATORIES, INC., JOHNS HOPKINS UNIVERSITY
Application year: 1995
Main classification: C12P21
IPC codes: A01K67, A61K31, A61K38, A61K48, A61P13, C07K14, C07K16, C12N1, C12N5, C12N15, C12P21, C12Q1