ASSAY FOR IDENTIFYING GENES CAUSING CHROMOSOME NON-DISJUNCTION

Abstract: Disclosed is a method of identifying genes whose gene products cause chromosome missegregation. The method involves transfecting a mammalian gene being assessed into a cell and then assessing whether the progeny cells have increased aneuploidy or increased chromosome breaks or translocations compared with cells that have not been transfected with the gene. Genes identified in this manner are likely to be involved in causing diseases such as cancer and Alzheimer's Disease, which result from improper chromosome segregation. Also disclosed is a method of identifying agents which can be used in the treatment of diseases caused by improper chromosome segregation. The method involves treating cells that have been transfected with a gene whose gene product causes improper chromosome segregation with an agent being assessed. Cells showing less aneuploidy or less chromosomal breakage or translocation compared with untreated cells indicate that the agent is useful in the treatment of diseases caused by improper chromosome segregation.

Description: ASSAY FOR IDENTIFYING GENES CAUSING CHROMOSOME NON-DISJUNCTION Related Application This application claims priority to U.S. Serial No. 60/002,448, the entire teachings of which are hereby incorporated into this application by reference. Background of the Invention It has been appreciated for some time that Alzheimer's Disease has a complex etiology. At least 15 percent of the cases appear to be due to the inheritance of an autosomal-dominant mutation, but the majority are "sporadic", showing no clear association with any identifiable genetic or environmental factor. Feldman, R.G., et al., Neurology, 11:811-824 1963; Heston, L.L., et al. , Arch Gen. Psychiat. , J38.:1084-1090 (1981) ; Terry, R.D., Aging, : 11-1 (1978); Jarvik, L.F. and Matsuyama, S.S., "The Biological Substrates of Alzheimer's Disease", Academic Press, pp. 17-20 (1986) . Even identical twins can show a large discordance in the age of onset of the disease. Nee, L.E., et al. , Neurology, 3.7:359-363 (1987) . Yet despite this variation, Alzheimer's Disease shows a uniform set of clinical and pathological features - progressive loss of memory and other intellectual functions beginning in middle to late life, coupled with neuronal cell loss in the higher centers of the brain. Price, D.L., Ann. Rev. Neurosci.. 9.:489-512 (1986) . While much has been learned about the biochemistry and expression of the aberrant protein deposits that characterize Alzheimer's Disease, progress toward the development of methods for the diagnosis and treatment of the disease has been slow. This is due, at least in part, to the fact that the molecular basis for the disease pathology has remained obscure. Summary of the Invention The present invention relates to a method of identifying genes which encode gene products (e.g. proteins and RNA) which cause chromosome missegrega ion, genes identified by the method, proteins encoded by the genes, antibodies which bind the gene product, a method of identifying agents which reduce (partially or totally) chromosome missegregation in cells, constructs useful in the method of identifying agents which reduce chromosome missegregation in cells, agents identified by the method, methods of preventing chromosome missegregation in cells and agents (including antibodies, peptides, antisense and complementary oligonucleotides and small organic molecules) useful in preventing chromosome missegregation. Also included are genes which hybridize to polynucleotides whose sequences are disclosed herein and which encode proteins which cause chromosome missegregation. As described herein, Applicant has shown that the incidence of trisomy 21 is higher in fibroblasts from individuals with Alzheimer's Disease than in fibroblasts from individuals without Alzheimer's Disease. Based in part on this result, Alzheimer's Disease arises from an accumulation of trisomy 21 cells during the life of the individual, resulting from chromosomal missegregation. The present invention relates to an assay useful to identify genes whose expression causes chromosome missegregation. Twenty-two genes whose products promoted chromosome missegregation in the yeast assay were isolated from cells obtained from an individual with Alzheimer's Disease. These results provide evidence that genes which give rise to gene products which cause improper chromosome segregation play a role in causing Alzheimer's Disease by promoting the accumulation of trisomy 21 cells. Agents which reduce improper chromosome segregation will slow or inhibit the progression of Alzheimer's Disease. One embodiment of the present invention is a method of detecting a gene which encodes a gene product which causes chromosome missegregation, thereby resulting in a disease condition. As a result of chromosome missegregation, total chromosome number in the progeny may be greater than, less than or the same as the number of chromosomes in cells in which missegregation does not occur. "Chromosome missegregation" includes processes which result in aneuploid cells, which include cells with an abnormal number of chromosomes. Aneuploid cells include hyperploid cells, which are cells with a greater than normal number of chromosomes, or hypoploid cells, which are cells with a lower than normal number of chromosomes. "Chromosome missegregation" also includes processes which result in chromosomes having one or more breaks or one or more translocations. A chromosome with a translocation is a chromosome which has been broken and recombined with a fragment from a different chromosome. The method comprises providing cells, referred to as tester cells. Also provided is a plasmid suitable for growth and reproduction in the tester cells. The plasmid comprises 1) a gene obtained from an organism other than yeast, preferably a mammalian gene, referred to as a test gene, whose gene product is suspected of causing chromosome missegregation; and 2) control elements suitable for expressing or overexpressing the test gene in the tester cells. The plasmid is introduced or transfected into the tester cells, which are then exposed to conditions suitable for the tester cells to reproduce, thereby producing progeny cells. The number of aneuploid progeny cells, the number of progeny cells with a chromosome having a break(s) or the number of progeny cells with a chromosome having a translocation is assessed, directly or indirectly, and compared to a suitable control, e.g. progeny cells obtained from the tester cells transfected with a plasmid without the tester gene or having a non-functional tester gene. A greater number of aneuploid progeny cells or a greater number of progeny cells with a chromosome having a break or translocation compared with the control number is indicative that the test gene causes chromosome missegregation. In a preferred embodiment, the tester cells are yeast cells having one or more chromosomes (preferably one) with a mutated centromere and a marker gene. The mutation in the centromere makes the chromosome(s) prone to improper segregation. The marker gene encodes a detectable/identifiable marker gene product, which gives a quantifiable indication of the number of the mutated chromosome(s) present in the tester cell. The number of aneuploid progeny cells is determined by quantifying the indication given by the marker gene product. Another embodiment of the present invention is a method of screening for an agent which inhibits improper chromosome segregation. Such an agent is useful in treating a disease caused by a gene product which causes improper chromosome segregation. The method comprises providing tester cells, as described above, transformed with a plasmid suitable for growth and reproduction in the tester cells and comprising 1) a gene which encodes a gene product which causes a disease process as a consequence of improper chromosome segregation resulting in aneuploid cells or cells with one or more chromsomes having a break or a translocation and 2) the appropriate control elements for expressing or over-expressing the gene in the tester cells. The tester cells are exposed to an agent being tested for its ability to inhibit the disease process and to conditions suitable for the tester cells to grow and reproduce, thereby producing progeny cells. The number of aneuploid progeny cells or the number of progeny cells with a chromosome having a break or a translocation is then assessed, either directly or indirectly. A lesser number of aneuploid progeny cells or a lesser number of progeny cells with a chromosome having a break or translocation in the presence of the agent being tested than in the absence of the agent being tested is indicative that the agent inhibits chromosome missegregation. The present invention can be used to screen for genes which cause Alzheimer's Disease, cancer and aging by promoting improper chromosome segregation. The present invention can also be used to screen for agents which inhibit chromosome missegregation and inhibit disease processes caused by genes encoding gene products which promote chromosome missegregation. Brief Description of the Figures Figure 1 shows the polynucleotide sequence (SEQ ID NO: 1) of AD3 (top line) , the amino acid sequence of AD3 (second line) (SEQ ID NO: 2) , the partial polynucleotide sequence of AD4/AD3LP (bottom line) (SEQ ID NO: 3), the partial amino acid sequence from one reading frame of AD4/AD3LP (third line) (SEQ ID NO: 4) and the sites of mutation in AD3 (indicated by bold letters immediately below the bottom line) . Also shown are the cdc2 kinase motifs of the AD3 and AD4/AD3LP proteins, indicated by boxes. Figure 2 is a graph showing the percentage of trisomy 21 cells in cultured fibroblasts from Alzheimer's Disease (AD) and unaffected individuals, as determined by fluorescence in si tu hybridization. The greater frequency of trisomy 21 in the Alzheimer fibroblasts is significant at p=.005. Figure 3 is a graph showing the percentage of trisomy 21 cells in cultured fibroblasts, as determined by fluorescence in si tu hybridization, for individuals with early onset of Alzheimer's Disease (before age 65 n=7) , late onset of Alzheimer's Disease (after age 65 n=5) , chromosome 14 linked Alzheimer's Disease (n=12) , chromosome 21 linked Alzheimer's Disease (n=2) and unaffected individuals (n=13) . Figure 4 shows the polydeoxynucleotide sequence of an expressed sequence tag of human mitochondrial tRNA gene (SEQ ID NO: 5) from an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 5 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 6) from chromosome 11 of an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 6 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 7) from chromosome 12 of an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 7 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 8) from chromosome 12 of an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 8 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 9) from human laminin receptor on chromosome 3 of an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 9 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 10) from chromosome 17 of an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 10 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 11) from human HLABS1 surface antigen on chromosome 6 of an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 11 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 12) from an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 12 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 13) from human H + ATPase subunit B on chromosome 18 of an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 13 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 14) from an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 14 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 15) from chromosome 17 of an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 15 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 16) from chromosome 17 of an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 16 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 17) from chromosome 10 of an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 17 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 18) from human protein kinase C, δ subunit on chromosome 5 of an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 18 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 19) from an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 19 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 20) from an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 20 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 21) from human histidine tRNA synthase gene on chromosome 9 from an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 21 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 22) on chromosome 9 from an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 22 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 23) on chromosome 15 from an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 23 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 24) from an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 24 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 25) from an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 25 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 26) from an individual with Alzheimer's Disease. The expressed gene containing the tag was shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 26 shows the polydeoxynucleotide sequence of an expressed sequence tag (SEQ ID NO: 27) for human elongation factor lα, shown to cause improper chromosome segregation in the yeast assay of the present invention. Figure 27 is a map showing the localization of AD4/AD3LP on chromsome 1 and the yeast artifical chromsomes containing AD4/AD3LP used in the localization. Figures 28A-B show the complete polydeoxynucleotide sequence for AD4/ADLP3 (SEQ ID NO: 28) . Figure 29 shows the complete amino acid sequence for AD4/AD P3 (SEQ ID NO: 29) . Detailed Description of the Invention Chromosome missegregation is associated with numerous human disorders. For example, individuals with Down syndrome have an extra chromosome 21, a condition which is referred to as trisomy 21. Alzheimer's Disease is a mosaic form of Down syndrome in which trisomy 21 cells accumulate over life time of the individual. As described herein, fibroblasts from individuals with Alzheimer's Disease show a statistically significant higher percentage of trisomy 21 than fibroblasts from individuals without the disease. The fibroblasts were derived from individuals with chromosome 14-linked, chromosome 21-linked, early onset, or late onset disease. Increased trisomy 21 was found in all categories of individuals with Alzheimer's Disease examined (see Example 1) . Additional support for the trisomy 21 model of Alzheimer's Disease comes from the observation that individuals with Down syndrome and Alzheimer's Disease have many of the same symptoms. For example, Down syndrome individuals develop the neuropathology associated with Alzheimer's Disease by the fourth decade of life. In addition, Down syndrome individuals are hypersensitive to cholinergic antagonists such as atropine (Sacks and Smith, J. Neurol . Neurosur. and Psych. 52:1294 (1989) and Potter, Am. J. Hum. Genet . 48 : 1192 (1991) . Specifically, when Down syndrome individuals are administered atropine or tropicamide in the eye, their pupils dilate at a lower concentration than is required to dilate the pupil of a normal individual. Alzheimer's individuals are highly sensitive to tropicamide and can be distinguished with 95% confidence from normal individuals or individuals with other neurodegenerative diseases (Scinto et al . , Science 266 : 1051 (1994) ) . This model of Alzheimer's Disease supports the conclusion that accumulation of cells with an extra chromosome 21 is caused by a mutated or overexpressed gene or genes which promote chromosome missegregation. "Chromosome non-disjunction," "chromosome missegregation" and "improper chromosome segregation" refer to processes which result in abnormal numbers of chromosomes in at least some members of a cell population. Such a cell is said to be "aneuploid." Cells with greater than normal numbers of chromosomes are "hyperploid" , while cells with fewer than normal numbers of chromosomes are "hypoploid" . "Chromosome non-disjunction," "chromosome missegregation" and "improper chromosome segregation" also refer to chromosomes with one or more breaks or which have been broken and then recombined with one or more fragments from another chromosome, i.e. the resulting chromosome comprises fragments from one or more fragmented chromosomes. Different genes may be involved in the chromosome missegregation that gives rise to different forms of Alzheimer's Disease, e.g. early onset versus late onset Alzheimer's Disease. Chromosome missegregation is associated with numerous other human disorders besides Alzheimer's Disease and Down syndrome. Many cancer cells are hyperploid, sometimes at very early stages in the transformation process. Highly aneuploid tumor cells are especially prone to metastasis. Therefore, it is important to identify members of a potential new class of oncogene which, when overexpressed or mutant, causes chromosome missegregation and aneuploidy. Such genes are likely to be oncogenes. Hypoploid cells are also likely to be associated with cancerous tumors. Elongation factor lα (EFlα) has been identified as causing chromosome missegregation, using a yeast screen described below. A number of studies have shown the EFlα is overexpressed in many tumors and in cells able to divide in culture, but not in normal tissues of a living organism (Pencil and Nicolson, Breast Cancer Research and Treatments 25:165 (1993)). It has also been shown that overexpression of EFlα makes cells more prone to further transformation by chemical or physical carcinogens such as 3-methyl- cholanthrene or ultraviolet light (Shina et al . Science, 226:282 (1994) and Ghislain et al Nature 366:358 (1993)). Several observed functions of EFlα are consistent with EFlα causing chromosome missegregation. EFlα is an essential component of 26S protease complex, which is necessary for transition into anaphase. In addition, EFlα binds actin filaments and microtubules. It can also nucleate the polymerization of microtubules and has been reported to induce the severing of microtubules both in cell extracts and living cells when present at a high concentration. The latter activity is particularly likely to disrupt the microtubule apparatus of the spindle and lead to chromosome non-disjunction. Thus, it is likely that overexpression of certain genes, e.g. EFlα, or the expression of certain mutated genes cause aneuploidy and provide a necessary oncogenic event in the multistep process of carcinogenesis. Normal aging also likely involves an increase in chromosome missegregation and the development of aneuploid cells. Therefore, genes identified as causing improper chromosome segregation as a result of mutation or overexpression may underlie the various symptoms of normal aging, in addition to Alzheimer's Disease and cancer. The present invention is also based on the discovery that a cellular assay system can be used in a method of identifying mammalian genes which cause disease processes by promoting chromosome missegregation. A "disease process" includes a symptom or pathological consequence of a disease. Examples include memory loss and amyloid deposition in Alzheimer's Disease and tumor growth and metastasis in cancer. A gene which "promotes chromosome missegregation" results in significantly more chromosome missegregation when the gene is expressed than when it is not expressed. Such a gene can be a mutated gene which is expressed or wild type gene which is overexpressed. A gene which is "overexpressed" is expressed in amounts sufficiently greater than which normally occurs in the cell such that changes occur in the cell. The method of the present invention comprises providing tester cells, for example yeast cells, mammalian cells such as human, rat, mouse cells and hamster cells and insect cells. Suitable mammalian cells include lymphoblasts and fibroblast cells. In one embodiment the tester cells, preferably yeast cells, have a chromosome with a mutant centromere that makes the chromosome prone to improper chromosome segregation (a mutated chromosome) and a first marker gene on the mutated chromosome. A marker gene results in a marker gene product whose concentration is readily determined, either directly or indirectly (e.g. its concentration is proportional to the concentration of another gene product) . The concentration of the marker gene product gives an indication of the number of mutant chromosomes; non-disjunctive events which give rise to hyperploidy of the chromosome with the mutated centromere result in increases in the number of marker genes, thereby resulting in increases in the concentration of the marker gene product. Non-disjunctive events which give rise to hypoploidy of the chromosome with the mutated centromere result in a decrease in the number of marker genes, thereby resulting in decreases in the concentration of the marker gene product . The concentration of the marker gene product is directly proportional to the number of chromosomes encoding the marker gene. The assay system can be pre- calibrated, e.g. the concentration of the marker gene product for one, two, three or more copies of the chromosome can be predetermined. In one example, the first marker gene can give rise to a gene product which enhances or suppresses the expression of a second marker gene. The concentration of the gene product of the second marker gene is therefore proportional (directly or indirectly) to the concentration of the first marker gene product, and therefore proportional to the degree of aneuploidy, e.g. the number of extra chromosomes coding for the first marker gene. Preferably, the concentration of either marker can be assessed by a physical phenomenon which can be readily measured, e.g. color, enzyme assay or antibody detection (e.g. ELISA) . The concentration of either marker gene thus indicates the degree of aneuploidy. In another example, the first marker gene product forms a complex with the second marker gene or marker gene product. In this case, the concentration of the complex is an indication of the degree of aneuploidy. In the assay of the present invention, the tester cells are further modified to screen for mammalian genes which cause chromosome missegregation. Specifically, a mammalian gene, referred to as a test gene, suspected of encoding a product which causes chromosome missegregation, is introduced into the tester cells using an appropriate plasma vector; the resulting tester cells, which contain the test gene, are maintained under conditions suitable for the gene to be expressed and reproduced by the tester cells. Suitable plasmid vectors typically contain an origin of replication (e.g. an autonomously replicating sequence when the plasmid is transformed into yeast) , a yeast centromere and a growth origin suitable for growth and replication in the tester cells being transformed. The plasmid vector also contains a gene allowing for selection in the tester cells being transformed, e.g. a gene conferring resistance to an antibiotic provided in the growth medium (for example amp) or a gene allowing the tester cells to metabolize an essential nutrient supplied in the growth medium (for example trp) . Typically, the plasmid also comprises genes suitable for selection and growth in an amplifying organism such as E. Coli , as discussed below. Optionally, the plasmid can contain one or more polycloning sites and/or a gene (e.g. lacz gene) which indicates incorporation of the transforming DNA into the plasmid. Suitable tester cells include yeast, mammalian cells (e.g. human and rodent cells) , and insect cells. Plasmids are introduced into the tester cells by methods known in the art, for example electroporation, lithium chloride and by molecules that assist in the introduction of DNA into mammalian cells, such as Transfectam. Suitable plasmids also have promoter sites which allow the gene being assessed to be expressed in the tester cells. (e.g. SV40, gal 10 or other viral promoters) . In some cases, it may be desirable to determine whether overexpression of the gene being assessed increases the rate of chromosome missegregation. In these cases, enhancer sites which increase the expression of the gene in the tester cells are also included in the plasmid. The degree of expression can also be increased or decreased by changing the sequence of the promoter site, according to methods known in the art. In certain applications it may be advantageous to amplify the gene being screened before transforming the tester cells. In this case, the plasmid vector containing the gene is first introduced into an organism (referred to as an "amplifying organism") suitable for amplifying the plasmid. Suitable amplifying organisms include E. coli , gram negative organisms such as He ophilus influenzae and K. pneumoniae, gram positive organisms such as Bacillus subtilis and eukaryotes such as yeast. The plasmid vector contains a gene suitable for selection in the amplifying organism. The amplifying organism is exposed to suitable growth conditions, thereby allowing the organism to reproduce and amplify the vector. The amplified plasmid vector can then be isolated from the culture and used to transform the tester cells. After being transformed, the modified tester cells are exposed to conditions suitable for growth and reproduction, thereby producing progeny cells. Typically, a plasmid is used which allows selection of cells into which the plasmid has been incorporated, for example which confers resistance to an antibiotic. The cells are then generally allowed to grow for at least two to three cycles of reproduction before being selected. Cells grown for two to three cycles of reproduction can be analyzed for aneuploidy or chromosomes with breaks or translations, even though the plasmid has not been incorporated into the genome. Alternatively, the selected cells can be treated so that the plasmid is incorporated into the cellular genome, for example, by allowing the selected cells to grow for about 10-20 cycles of reproduction before being analyzed for aneuploid cells or cells with broken or translocated cbromosomes. The degree of aneuploidy in the progeny cells and the number of progeny cells having chromosomes with translocations can be determined by methods known in the art, for example by staining the cells and counting the number of abnormal cells. Methods for staining and determining the number of abnormal cells are disclosed, for example, in Sanchez et al . , Lancet 1973 : 11 : 269 (1973), the teachings of which are hereby incorporated herein by reference. When the tester cells contain a marker gene the degree of aneuploidy is assessed by determining the concentration of one of the marker gene products. This concentration is compared with the concentration of the marker gene product in a suitable control, for example the concentration of the marker gene product in the progeny of tester cells that have been transformed with a plasmid that does not contain the gene being tested for its ability to cause chromosome missegregation. The control can be predetermined, or can be performed simultaneously with or subsequent to the assay which tests the mammalian gene for its ability to cause chromosome missegregation. A concentration of one of the marker gene products in the progeny cells that differs from the concentration of one of the marker gene products in the control such that there is a greater degree of aneuploidy in the progeny cells than in the control cells indicates that the gene being tested causes chromosome missegregation. Typically, the concentration of one of the marker gene products is determined within subpopulations of progeny cells. A non- disjunction event in a cell will result in aneuploidy being passed on to the progeny of that cell alone. A non- disjunctive event can give rise to hypoploid progeny, hyperploid progeny or both. Consequently, the concentration of the marker gene product will be not be uniform throughout the colonies, but will differ from the control levels only in subpopulations, referred to as "sectors", which are progeny of a cell having undergone chromosome missegregation. Typically, the degree of aneuploidy is assessed by determining the number of sectors throughout the test colony, wherein a larger number of sectors is indicative of a higher degree of aneuploidy. The concentration of marker gene product within the sector and the overall concentration of the marker gene product throughout the test colonies are also indications of the ability of the gene to cause chromosome missegregation. In a preferred embodiment more than one gene is introduced into the tester cells. It is more preferred that a cDNA library be used to transform the tester cells. The cDNA library is typically obtained from a cell or cells of an individual who has a disease which is believed to arise, at least in part, from a gene causing chromosome non-disjunction. Thus, this preferred embodiment is a method of identifying genes which are involved in disease processes resulting from improper chromosome segregation caused by the genes or their gene products. The cells are grown at low density to keep the progeny of individual clones from overlapping (e.g. about 200 original cells/100 mm plate with augar containing growth medium) . Plasmids are recovered from sectors showing marker gene product concentrations which differ from control levels and sequenced. The resulting sequences are from genes which cause chromosome missegregation and are likely involved in the etiology of the disease. In one example of a suitable assay system, a diploid yeast strain is constructed carrying an ochre mutation in the ade2 gene which determines the color of the yeast colonies grown on plates containing a limited (6 μg/ml ) concentration of adenine. This yeast strain is described in Hieter, et al . , Cell 40 : 381 (1985); McGrew, et al . , Yeast, 5:271 (1989) ; Stoler, et al . , Genes Dev. , 9 : 573 (1995) , the teachings of which are incorporated herein by reference. Cells homozygous for the ochre mutant ade2 gene (ade2-101) are red on these plates. The colonies are changed to pink or white by the presence of either one or two copies respectively of the supll gene . Supll encodes a suppressor tRNA molecule that can suppress the ochre mutation in the ade2-101 gene and allow production of the ade2 protein product, 5AIR carboxylase, an enzyme involved in purine biosynthesis. The supll gene in turn is placed on one specially altered yeast chromosome III that has a mutant centromere (cenl30-3) that makes the chromosome prone (100-fold more than normal) to improper chromosome segregation. As a result, this yeast strain shows a high level of variable colored colonies and also colonies in which several colors occur at once to form "sectors." Sectored colonies indicate that during the growth of the colony from a single cell, the instability of the chromosome carrying the supll gene results in subclones containing zero, one, or two copies of that chromosome and thus cells which are either red, pink, or white respectively. As these cells divide, their progeny form the multi-colored sectors visible to the naked eye. Under normal conditions, the yeast strain so constructed shows a frequency of chromosome missegregation of about IO "5 as detected by the color assay (Stoler et al . ) . However, if a gene encoding a protein that increases chromosome missegregation is introduced into the tester strain, then the frequency of sectored colonies increases. One yeast gene involved in chromosome segregation have been identified in this manner (Stoler et al . ) . The above assay was modified to screen for mammalian genes that cause chromosome missegregation, including mutant familial Alzheimer's Disease (FAD) genes. Specifically, a cDNA library was constructed from a human lymphoblastoid cell from a patient with chromosome 14- 1inked FAD using a plasmid vector that can grow in either E. coli or yeast (pRS314 . gall -10) . This plasmid contains the CEN6 yeast centromere, the ARSH4 yeast replication origin, a pBR322 origin for growth in E. coli , a trp gene for selection in yeast, an amp gene for selection in E. coli , and a poly-cloning site in the lacz gene. Library DNA was prepared and used to transform E. coli by electroporation (Potter, "Methods in Enzymology: Recombinant DNA Technology," Wu ed. Orlando, FL, Academic Press, 1993) . Cells that received a plasmid were selected by virtue of the ability of the plasmid to provide the trp gene (which is mutant in the yeast strain) and allow the cells to grow in the absence of tryptophan. Transformed cells were plated at relatively low density and the resulting colonies examined for multi-colored sectoring. Sectored colonies were recovered, desegregated into single cells and replated to confirm the cells' high sectoring phenotype. Plasmids were then recovered from the yeast clones showing high sectoring frequency and retransformed into the parent yeast strain to retest the specific cDNA's ability to induce increased chromosome segregation as revealed by sectored colonies. Following several such sequential screening steps, twenty-two candidate genes were identified. Each gene caused increased levels of chromosome missegregation when expressed in the tester yeast strain and are therefore involved in one way or another in chromosome segregation. The increased chromosome missegregation may be due to overexpression in the target yeast cells of a normal gene involved in chromosome segregation, or to the presence of a mutation in a gene that yields an aberrant protein product that increases chromosome missegregation. Either of these two possibilities may cause the chromosome missegregation observed in the Alzheimer's cells from which the gene's cDNA was derived, and thus all of these twenty-two genes are potential candidates for being a causative agent in the development of Alzheimer's Disease. Partial sequences of these genes are given in Figures 4-25. As described previously, missegregation of chromosomes is involved in the development of a number of different diseases. The assay described above identifies the genes which cause the improper chromosome segregation and, more specifically, genes which cause disease processes as a result of chromosome missegregation. Agents which prevent these genes from causing chromosome missegregation in the assay described above are likely prevent chromosome missegregation in vivo and theerfore be useful in treating the disease caused by the aberrant gene. Tester cells containing a chromosome with a mutated centromere, as described above, are particularly useful for identifying agents which inhibit chromosome missegregation. The effect of genes which cause chromosomal missegregation is amplified in these cells and therefore readily detectable. The chromosome with the mutated centromere is more prone to improper segregation than normal yeast chromosomes. When transformed into the tester cells as part of a suitable plasmid, genes which cause chromosomal missegregation cause a detectable change in the concentration of a marker gene product, indicative of a detectable increase in the rate of chromosome non- disjunction. This assay therefore provides a convenient medium to test agents which inhibit chromosomal missegregation. Agents which decrease the rate of missegregation in tester cells transformed with a gene causing missegregation compared with untransformed tester cells are likely to slow the development of the disease caused by the gene and be useful in the treatment and/or development of treatments of the disease. Another embodiment of the present invention is a method of identifying an agent which is an inhibitor of a disease process resulting from a gene which causes chromosome missegregation. The method comprises providing tester cells, as described above, additionally comprising a plasmid suitable for growth and reproduction in the tester cells. The plasmid also comprises a gene whose gene product results in the disease process by causing chromosome missegregation resulting in either aneuploid cells or cells with translocated chromosomes. The plasmid also comprises control elements allowing the gene to be expressed in the tester cells. In those cases where overexpression of the gene results in improper chromosome segregation, the plasmid also contains control elements, e.g., an enhancer site, which increases the level of expression of the gene in the tester cells. The tester cells are exposed to an agent being tested for its ability to inhibit the disease process and then to conditions suitable for the cell to grow and reproduce, thereby producing progeny cells. The number of aneuploid progeny cells and the number of progeny cells having translocated chromosomes are then assessed. A lesser number of aneuploid progeny cells or progeny cells having translocated chromosomes in the presence of the agent than in its absence is indicative that the agent inhibits chromosome missegregation and therefore also inhibits the disease process. A suitable control is, for example, run by allowing tester cells which contain the gene which causes chromosome missegregation to grow and reproduce under the same conditions used in the test assay, but in the absence of the agent being assessed. The number of aneuploid progeny cells and the number of progeny cells with translocations are then assessed and compared to progeny cells grown in the presence of the agent, as described above. The control can be run prior to, simultaneously with or subsequent to the test assay. There are numerous genes which can be used in the screening assay of the present invention to identify agents which can be used for the treatment of Alzheimer's Disease. For example, locus AD3, associated with susceptibility to early onset of Alzheimer's Disease has recently been mapped to a specific region on human chromosome 14. Five different mis-sense mutations (Figure 1) have been found that cosegregate with early-onset familial Alzheimer's Disease (Sherrington et al . , Nature 375:754 (1995)). It is predicted that these mutations result in increased levels of cells with trisomy 21 in carriers of the mutation compared with non-carriers. As a result, increased levels of chromosome missegregation will be observed when these mutated genes are used in an appropriate plasmid to transform the tester cells used in the assay of the present invention compared with untransformed tester cells. Agents which, when exposed to tester cells, decrease the degree of aneuploidy arising as a result of the expression of these mutated genes are likely to be agents useful in the treatment of Alzheimer's Disease. It is reported herein that the translation product of the gene (SEQ ID NO: 3 shows a portion of AD4/AD3LP) containing the expressed sequence tag of Accession No. T03796 (Genbank) , referred to herein as "AD4/AD3LP" or "Presenilin 2" , is highly homologous to AD3 (also referred to as "Presenilin 1") (Sherrington et al . , 1995) . Confirmation that AD4/AD3LP encodes a novel protein related to AD3 was obtained by genomic mapping. Oligonucleotide primers corresponding to AD4/AD3LP were used for PCR localization of the gene to chromosome 1 rather than chromosome 14, where AD3 resides. Sublocalization using YAC libraries have placed the gene corresponding to AD4/AD3LP to the long arm of chromosome 1, 289 centamorgans from the centromere (see Figure 27) . The complete polynucleotide sequence (SEQ ID NO: 28) and amino acid sequence (SEQ ID NO: 29) of AD4/AD3LP was determined, as described in Example 4. AD4/AD3LP has four DNA binding motifs (S/T P X X) . AP3 also has DNA binding domains. Thus, AD4/AD3LP AD3 are likely involved in controlling gene expression or in the binding of chromatin to the nuclear membrane. Mutations in chromatin-binding proteins are known to cause chromosome missegregation. Therefore, the observation that AD4/AD3LP and AD3 have DNA binding motifs is consistent with AD4/AD3LP playing a role in causing familial and sporadic forms of Alzheimer's Disease The sites of mutation in AD3 leading to Alzheimer's Disease change amino acids that are identical between AD3 and AD4/AD3LP. For example, Figure 1 shows the amino acid sequence of AD3, the amino acid sequence from one reading frame of AD4/AD3LP and the amino acid mutations leading to Alzheimer's Disease. It can be seen that the amino acids at these mutated positions in AD3 and the corresponding positions in AD4/AD3LP are identical. This observation coupled with the similarity of AD3 and AD4/AD3LP indicates a similarity of function and is consistent with AD4/AD3LP playing a role in causing familial and sporadic forms of Alzheimer's Disease as a result of mutations similar to those found in AD3. Consequently, AD4/AD3LP can also be used in the screening assay to identify new agents for the treatment of Alzheimer's Disease. There are numerous genes which can be used in the screening assay of the present invention to identify agents which can be used for the treatment of cancer. For example, overexpression of EFlα, as described earlier, occurs in certain cancers and has been shown to result in highly aneuploid human cells in culture and increased susceptibility to transformation. Introduction of the EFlα gene into yeast and mammalian cells by a plasmid which results in its overexpression causes chromosome missegregation. Agents which reduce the level of chromosome missegregation in these transformed cells can be used in the treatment of cancer in which EFlα is overexpressed. The twenty-two genes identified in the cellular assay as causing chromosome missegregation are likely to be involved in the development of cancer and Alzheimer's Disease. Consequently, these genes can also be used in the assay described above to screen for agents useful for the treatment of cancer and Alzheimer's Disease. The sequence for the entire gene can be routinely obtained by sequencing the entire plasmid isolated from clones in which non- disjunction is observed. Other genes thought to be involved in the development of Alzheimer's disease such as Apolipoprotein E, for examploe E2, E3 and E4, can also be used in the assay described above to screen for agents useful for the treatment of Alzheimer's Disease. Another embodiment of the present invention is a polydeoxynucleotide having a sequence represented by SEQ ID NOS: 3, 6-8, 10, 12, 14-17, 19-20 and 22-26. These sequences represent novel polydeoxynucleotides (SEQ ID NOS: 6-8, 10, 12 and 25) or known polydeoxynucleotides with no known function SEQ ID NOS: 3, 14-17, 19-20, 22-24 and 26. Genes comprising these nucleic acids are useful in the assay described above in screening the agents for the treatment of Alzheimer's Disease and cancer and are included in the present invention. These polydeoxynucelotides have many other uses. One example is as a gene marker, i.e. determining the presence or absence in a sample of the gene to which the polydeoxynucleotide hybridizes. The polydeoxynucleotide is labeled, e.g. with a radioactive group or a biotinylated group, and combined with the sample or restricted sample under hybridizing conditions and then amplified by polymerase chain reaction. The presence of the gene is indicated by the presence of labeled, amplified product. Identifying the presence or absence of a gene is particularly useful when the gene or a mutated form of the gene is known to cause a disease. In this instance, identifying the presence or absence of the gene in a sample which contains the genetic material of an individual can be used as a method of diagnosis for the disease. The presence of the form of AD4/AD3LP causing chromosomal missegregation, as described above, is likely to be useful in diagnosing Alzheimer's Disease, both before and after the onset of symptoms typically associated with the disease. The polydeoxynucleotides of the present invention can also be used for chromosome walking and to assist in determining the nucleotide sequence in the vicinity of the gene, e.g. mapping a chromosome (Singer and Berg, Genes and Genomes, University Science Books, Mill Valley, CA (1991)). The chromosome or nucleic acids being mapped are divided into portions two of which are each digested with a different restriction enzyme. The polydexoynucleotide is used as a probe to identify a fragment from each portion which hybridizes to the probe. The fragments are each sequenced and compared. New non-overlapping sequences can thereby be identified as sequences in the vicinity of the probe. These polynucleotides are also useful in identifying polymorphic markers such as a sequence repeat. Polymorphic markers are identified by comparing the sequences from the genes of healthy individuals with those from individuals with a disease caused by a mutation in the gene being assessed. Genetic markers can also be identified by sequencing in the vicinity of the gene. Genetic markers can be used in genetic linkage studies, in the mapping of chromosomes and in determining the inheritance of human diseases, including cancer, developmental abnormalities and aging diseases. Another embodiment of the present invention is a gene which is hybridizable to a polydeoxynucleotide represented by SEQ ID NO: 3, 6-8, 10, 12, 14-17, 19-20 and 22-26. These genes can be obtained by sequencing the entire plasmid from which the polydeoxynucleotide was obtained. These genes have the same uses described above for the polydeoxynucleotides described above. They can also be used for obtaining the genomic gene. A polydeoxydeoxynucleotide comprising the gene is used as a probe to isolate the fragments from a restriction enzyme digest to which it can hybridize. These fragments are then sequenced, thereby identifying regions in the genomic gene, e.g. introns, which do not appear in the cDNA gene. The invention is further illustrated by the following examples, which are not intended to be limiting in any way. EXEMPLIFICATION Example 1 - Individuals with Alzheimer's Disease Have Higher Levels of Trisomy 21 in their Fibroblast Cells than Individuals Without Alzheimer's Disease Cell Lines - Human fibroblast cell lines were obtained primarily from the NIA Aging Cell Repository (Camden, NJ) . Cell lines containing a mutation in the amyloid precursor protein were obtained from cells from affected family members by skin biopsy and then grown in culture. Fluorescence in si tu Hybridization (FISH) - Fibroblast cells growing directly on clean, uncoated glass slides were washed with PBS and fixed in cold MeOH: acetic acid, 3:1 for ten minutes. Fixed cells were permeabilized for 15 minutes in 0.5% Triton X-100 and 0.5% saponin in PBS, washed and stored until use in PBS containing 0.2% NaN 3 . FISH was carried out according to a modification of the methods described by Lichter et al . , Proc. Natl . Acad. Sci . USA, 85:9664 (1988) . Slides were denatured in 70% formamide, 2X SSC (IX SSC is 0.15 M NaCl/0.015 M sodium citrate) pH 7.0 at 70°C for 2 minutes then dehydrated in a cold ethanol series. Denatured probe prepared by nick translation (approximately 10 μg) was applied to the slides in a solution containing 50% formamide, 10% dextran sulphate, 2X SSC, and sheared DNA (herring sperm and Cot I) to block non-specific hybridization (commercially supplied probes were applied in a pre-made solution) , cover-slipped, and sealed with rubber cement. Hybridizations were carried out overnight at 37°C in a humid chamber. Slides were then washed in either 50% formamide in 2X SSC, three times for two minutes each at 42°C followed by three washes in 0.1X SSC at 60°C, or for two minutes in 2X SSC at 72°C. Detection of Hybrids - Probes labeled with biotin or digoxigenin were detected using standard immunocytochemistry techniques. Hybridized and washed slides were rinsed in PN (0.1 M NaP0 4 , 0.1% Nonidet P40) , then incubated with FITC-conjugated avidin (Vector) or FITC-conjugated antidigoxigenin (Boehringer) . After washing three times for two minutes each in PN, mounting medium containing propidium iodide (a red fluorescing DNA dye) or DAPI (a blue fluorescing DNA dye) and an antifade reagent was applied and coverslips mounted. Identifying labels on the slides were replaced with anonymous codes before being given to an observer to count the number of chromosomes 21 per nucleus. Slides were evaluated using a Zeiss Axiophot equipped with a mercury lamp and a 63X objective. An average of 800 nuclei were analyzed per cell line. Hybridization Probes - Biotinylated or digoxigenin- labeled chromosome 21-specific probes were either commercially obtained (Oncor) or generated using a cosmid containing a 21-specific sequence. The cosmid was labeled by nick translation with biotinylated dATP. Calculation of Trisomy Percentages - Not all chromosomes hybridize in the FISH procedure. Therefore it was necessary to correct for the number of false trisomies caused by under-hybridization of cells that were in the G2 phase of the cell cycle and so were actually tetrasomic. The following formula was developed to estimate the real number of trisomies present in fibroblast cultures using only the assumptions that each chromosome in a nucleus hybridizes as an independent event and all observed monosomies are actually disomies in which one chromosome failed to hybridize. P = probabili ty of hybridization = m+2d 2 (m+d) (1-P 4 ) T = % real trisomies = tl-(l-P 4 )] [l-(l-P 3 )] 1-(1-P 3 ) Where M = observed % monosomies, d = observed % disomies, t = observed % trisomies, and q = observed % tetrasomies Results Table I and Figure 2 show the percent trisomy 21 observed by FISH in fibroblast cultures of 39 Alzheimer's Disease patients and unaffected individuals. The overall average amount of trisomy 21 was 5.5% in Alzheimer's Disease cultures and 2.5% in cultures from unaffected individuals. Using the same procedure, the number of trisomies in a Down syndrome culture was determined to be 98%. The greater frequency of trisomy 21 cells in Alzheimer's Disease patients is significant (p=0.005) and is not related to the age of the affected individuals. It is unlikely that there is a general influence of time in culture on the degree of aneuploidy as this is varied in both control and Alzheimer's Disease cultures, and it has been found that human fibroblasts remain largely euploid throughout their lifetime in culture (Hayflick and Moorehead, Exp. Cell . Res . 25:585 (1961)). The Alzheimer's Disease cultures were derived from individuals with chromosome 14-linked, chromosome 21- linked, early onset, or late onset disease. It is of interest to know whether the trisomies were confined only to individuals in specific categories. Figure 3 shows that there is increased trisomy 21 in all categories of Alzheimer's Disease cultures compared to cultures from unaffected individuals. The individuals with chromosome 14-linked Alzheimer's Disease were from the large Canadian, Italian, and German pedigrees and had an average trisomy 21 frequency of 3.7%. Only two individuals with chromosome 21 linked Alzheimer's Disease were examined and they exhibited 4% and 5% trisomy 21. Individuals with early- and late- onset disease had distinctly elevated levels of trisomy 21 compared to unaffected controls. Their average trisomy 21 frequencies were 8.5% and 5.8%, respectively as compared to the unaffected individuals (2.5%). In these latter groups, insufficient family data were available to determine whether they were familial or sporadic cases of Alzheimer's Disease. These results indicate that several different mechanisms causing Alzheimer's Disease, both familial and sporadic (which includes complex genetic and/or environmental effects) , may directly induce trisomy 21 via chromosome nondisjunction. The effect of nondisjunction could be restricted to chromosome 21 alone, but more likely involves other, perhaps all, chromosomes as well. The effect of non-disjunction on other chromosomes can be determined by using the procedures described above with probes specific for the other chromosomes. Table I # of Nuclei Culture Name AD Status Analyzed % Trisomy 0364D AD/early 195 18.9 4159 AD/chr. 14 505 2.2 4400A AD/early 1481 1.3 4402A AD/early 937 6.7 5770 AD/early 517 4.6 5809 AD/early 225 21 5810C AD/late 136 10.5 6840B AD/chr. 14 840 3.8 6844 AD/chr. 14 1144 3.6 6848B AD/chr. 14 1001 2.9 7375 AD/early 1115 4.9 7377A AD/early 502 2.2 7872 AD/chr. 14 1938 4.7 8110 AD/chr. 14 321 4.3 8170A AD/chr. 14 1026 1.9 8243 AD/late 500 6.9 8245 AD/late 719 6.9 8446 AD/chr. 14 1063 4.8 8523 AD/chr. 14 614 5.4 8527 AD/chr. 14 570 6.4 8563A AD/chr. 14 501 3.3 8597 AD/chr. 14 502 1.3 9908 AD/late 500 1.3 10788 AD/late 498 3.4 CG AD/chr. 21 481 3.7 H010 AD/chr. 21 479 5.2 Table I (Continued) # of Nuclei Culture Name AD Status Analyzed % Trisomy 8942 Down syndrome 1515 98.3 2602 Unaffected 853 3.9 4153 Unaffected 1017 2.9 7615 Unaffected 195 4.1 7865 Unaffected 1540 1.0 7871 Unaffected 336 2.1 8125 Unaffected 505 2.6 8379 Unaffected 508 3.8 8517 Unaffected 485 1.1 8620 Unaffected 1117 2.7 8701 Unaffected 509 3.9 8712 Unaffected 508 0.9 9173 Unaffected 612 0.5 Swedish 2 Unaffected 513 3.4 Culture names are those assigned by the Coriell Cell Repository with the exception of CG and DH, which are lines from M. Benson, and Swedish 2 which is an unaffected member of a Swedish family carrying an APP mutation. Lines identified as Chr. 21 and Chr. 14 are from individuals whose Alzheimer's Disease has been linked to those chromosomes. Early and late refer to the apparent early (before age 65) and late (after age 65) age of onset of Alzheimer's Disease in individuals whose disease is either familial with no specific chromosomal linkage identified or apparently sporadic. Example 2 - Assay for Identifying Genes Causing Chromosome Non-Disjunction SBD8 is a yeast strain of the genotype a/α, ade2- 101/ade2-101, HIS3+/-, leu2-/-, lys2-/-, trpl-/-, ura3+/-, CEN3SUPll:cenl30-3:URA3 (Stoler et al . ) PRS314.GAL1-10 is a TRP1 plasmid constructed from the original pRS314 of Hieter et al . , Cell , 40 : 381 (1985) . It contains the GA/10 UAS in the RI/BAM site of the polylinker and is induced on 2% nonautoclaved galactose. The GAll/lO UAS is repressed on 5-10% glucose. AG09371 (GU3908) is a lymphoblastoid cell line from an affected member of a familial Alzheimer's Disease pedigree (termed FAD3, in St. George-Hyslop et al . , Science, 235 : 885 (1987) , which incorrectly identified the family as harboring a mutant gene on chromosome 21. The family has subsequently been identified as a chromosome 14 familial Alzheimer's Disease family (Schellenberg, et al . , Science, 258 : 668 (1992); St. George-Hyslop et al . , Nature Genet . 2:330 (1992)) . This is a Russian-Jewish pedigree containing 23 affected individuals. The cell line AG09371 is from the NIA aging cell repository sponsored by the National Institute on Aging and located at the Coriell Institute for Medical Research in Camden, New Jersey. GUS3908 is the Massachusetts General Hospital cell number. Library Construction PolyA+ mRNA was isolated from 2 x 10 8 cells of a lymphoblastoid line (AG09371) from a familial Alzheimer's Disease patient using the FASTTRACK kit (Pharmacia) . Full- length cDNA primed with oligoDT-containing primers was carried out using the SUPERSCRIPT cDNA library kit (Gibco¬ BRL) according to manufacturer's instructions. The resulting full-length cDNA (above 500 nucleotides in length) was ligated into the pRS314.gall-10 vector using the BamHl and NotI sites to ensure directional cloning. The resulting plasmids were used to transform K-12 E. coli strain by electroporation (Potter, 1993) and plated on large (150 mm) , amp-containing plates to amplify the library. DNA was prepared from the transformed bacteria by the Qiagen column method. Library DNA was used to transform SBD8 yeast cells by the lithium chloride method. Transformants were plated on plates lacking tryptophan and containing 6 μg/ml adenine at a concentration of about 500 cells/100 mm plate. Sectored colonies were visually screened by the method below, taken from Stoler et al . (1995) . Yeast Colony Screening The mitotic segregation of SUP11-marked chromosomes bearing cenl30-3 centromeres was monitored using the color colony assay on limiting adenine media (Hieter et al . , 1985) . SUP11 partially suppresses the red color phenotype of ade2-101 yeast cells. Hence, in a diploid yeast cell homozygous for the ade2-101 allele, one copy of SUP11 suppresses partially the red color to form homogeneous pink colonies. Two copies of SUP11 suppress fully this phenotype resulting in white colonies. Strains where SUP11 is linked genetically to a chromosome that is mitotically unstable form colonies that contain red, pink and white sectors. Red and pink sectors arise from chromosome loss (1:0) events and nondisjunction (2:0) events result in red/white sectors. Half-sectored colonies represent mis¬ segregation events that occurred at the first division after plating. The number of half-sectored colonies divided by the total number of mostly pink colonies plated represents the mis-segregation frequency of the SUP11- bearing chromosome. In addition, the number of red/pink and red/white half-sectored colonies is used to determine the frequency of chromosome loss or nondisjunction, respectively. The mis-segregation data from cenl30-3 chromosomes was collected as follows. In each assay, three mostly pink colonies were picked from color media plates and about 3000 cells were spread onto large (150 x 15 mm) color media plates, incubated for 4 days at 30°C and then overnight at 4°C. At least three independent assays were performed to monitor the segregation of cenl30-3 chromosomes in each wild-type and cse4-l strain. DNA Analysis Following multiple transformation and sector colony screening, twenty-two cDNAs were identified which continuously cause chromosome nondisjunction and sectored colonies in the transformed yeast cells. DNA prepared from twenty-two E. coli strains harboring the individual candidate human cDNA recombinant plasmids was then subjected to dideoxy sequencing analysis. Several known genes were among the candidates, including HLAB51, protein kinase C-δ, and elongation factor lα. In addition, a number of unknown genes were identified. All sequences were mapped to their respective human chromosomes by PCR analysis of mapped YAC libraries and/or human-rodent somatic cell hybrid lines. Partial sequences are shown in Figures 4-26. The plasmids isolated above containing polynucleotides corresponding to SEQ ID NOS: 6, 15, 19, 20 22, 24 and 26 were re-transfected into SBD8 yeast cells as described above. The nondisjunctive frequency for each transformation was then determined, as described above. Yeast transformed with genes corresponding to SEQ ID NOS: 6, 15, 19, 20 22, 24 and 26 showed an increase in the frequency of nondisjunction of 2.7 (standard deviation = 1.92) , 2.4 (standard deviation = 1.74), 3.1 (standard deviation = 3.17), 3.7 (standard deviation = 3.21) , 3.7 (standard deviation = 2.1) and 3.3 (standard deviation = 1.98) fold, respectively, compared with yeast transformed with the pRS314.gall-10 vector alone. Example 3 - AD3 and AD4/AD3LP Increase the Frequency of Chromosome Nondisjunction in cDNA Transfected Lvmphoblasts The AD3 gene was obtained as described in Sherrington et al . , Nature 375:754 (1995); the AD4/AD3LP gene obtained as described above. These genes were ligated into the pcDNA3 vector purchased from Invitrogen, Inc. according to procedures disclosed in "Current Protocols in Molecular Biology", John Wiley & Sons (1989) and transfected into lymphoblasts with normal karyotypes by electroporation techniques disclosed in Potter, "Methods in Enzymology: Recombinant DNA Technology," Wu ed. Orlando, FL, Academic Press, 1993) . Untransfected control cells and control cells transfected with unmodified pcDNA3 vector were also prepared. The cells were then allowed to grow for about sixty hours and the frequency of nondisjunction determined by methods disclosed in Sanchez et al . , Lancet 1973 : 11 : 269 (1973) . The results are shown in Table II below: Table II CHROMOSOME NONDISJUNCTION TEST IN cDNA TRANSFECTED LYMPHOBLAST Expt# H 2 0 Count* Total No. of Count/Tot Cells 1 2 20 0.10 2 0 17 0.00 3 4 25 0.16 pcDNA3 Count* Total No. Count/Tot Ratio to of Cells H2C 1 0 20 0.00 0.00 2 3 2 24 0.08 0.52 *Total number of aneuploid cells or cells with broken or translocated chromosomes. Table II CHROMOSOME NONDISJUNCTION TEST IN cDNA TRANSFECTED LYMPHOBLAST (Continued) AD4 Count* Total No. Count/Cell Ratio to H 2 0 of Cells 1 14 20 0.70 7.00 2 7 64 0.11 >7 3 10 25 0.40 2.50 AD3/AD4LP Count* Total No. Count/Cell Ratio to H 2 0 of Cells 1 2 4 54 0.07 >7 3 6 34 0.18 1.10 ♦ Total number of aneuploid cells or cells with broken or translocated chromosomes. Cells transfected with the AD3 gene or the AD4/AD3LP gene were found to have an increased frequency of nondisjunction compared with control cells. Example 4 - Determination of the Entire Polynucleotide and Amino Acid Sequence of AD4/AD3LP Identification of T03796 and Cloning of the Full- Length cDNA - All nucleotide sequences in the GenBank data base were translated into amino acid sequences in all six reading frames and then compared to the published protein sequence (24) of AD3 (S182) , by using TBLASTIN (National Center for Biotechnology Information server) . The expressed sequence tag (EST) sequence (T03796) whose encoded protein was most highly homologous to AD3 was thus identified, and the corresponding cDNA clone was obtained from the Lawrence Livermore National Laboratory (IMAGE Consortium) . After we had determined the full sequence of T03796 (see below) , additional EST sequences identical to T03796 (GenBank accession nos. R16831 and R05822) were also identified. Because all of these EST clones were partial, 5' rapid amplification of cDNA ends (RACE) was used to complete the full-length cDNA corresponding to T03796. Sequencing and Analysis of DNA and Encoded Proteins - The T03796 sequence in GenBank consists of 476 nt, with some errors. We resequenced the reported region and then sequenced the rest of T03796 and the 5' RACE clones for a total of 2.4 kb. DNA sequencing was carried out by the dideoxynucleotide china-terminating procedure with fluorescent-tag-labeled deoxynucleotides by the Biopolymer Laboratory, Harvard Medical School. Oligonucleotide primers used for sequencing were also synthesized by the Biopolymer Laboratory. Sequences were compared for homology to other sequences in the GenBank, GenEMBL, and dbest data bases, by using FASTA (GCG software package from the Wisconsin Genetics Computer Group) and by BLASTIN and BLASTIN (National Center for Biotechnology Information server) . Equivalents Those skilled in the art will know, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. These and all other equivalents are intended to be encompassed by the following claims.

Claims: CLAIMS What is claimed is: 1. A method of detecting a gene which causes chromosome missegregation resulting in a disease condition in a mammal, comprising the steps of: a) providing cells, referred to as tester cells; b) providing a plasmid suitable for growth and reproduction in the tester cells and comprising: i) a gene obtained from an organism other than yeast, referred to as a test gene, whose gene product is suspected of causing chromosome missegregation; and ii) control elements suitable for expressing or overexpressing the test gene in the tester cells; c) introducing the plasmid into the tester cells; d) exposing the tester cells to conditions suitable for the tester cells to reproduce, thereby producing progeny cells; e) assessing the number of aneuploid progeny cells or the number of progeny cells with a chromosome having a break or a translocation, wherein a greater number of aneuploid progeny cells or a greater number of progeny cells with a chromosome having a break or translocation compared with the number of the aneuploid progeny cells or progeny cells having a chromosome with a break or a translocation in a suitable control is indicative that the test gene causes chromosome missegregation. 2. The method of Claim 1 wherein the test gene is a mammalian gene. 3. The method of Claim 2 wherein the tester cells are mammalian cells. 4. The method of Claim 3 wherein the mammalian cells are human cells. 5. The method of Claim 2 wherein the tester cells are ' grown for a sufficient number of generations so that the plasmid is incorporated into the genome of the progeny cells. 6. The method of Claim 2 wherein: a) the tester cells comprise: i) a chromosome with a mutated centromere which makes the chromosome prone to improper segregation; and ii) a gene on the chromosome with the mutated centromere, referred to as a marker gene, whose gene product gives a quantifiable indication of the number of chromosomes with the mutated centromere present in the tester cell; and b) the number of aneuploid progeny cells is determined by quantifying the indication given by the marker gene product. 7. The method of Claim 1 wherein the tester cells are yeast cells. 8. The method of Claim 6 wherein the marker gene encodes a gene product which enhances or suppresses the expression of a second marker gene, wherein the second marker gene encodes a gene product which gives a quantifiable indication of the number of chromosomes with the mutated centromere present in the test cell . 9. The method of Claim 8 wherein the first marker gene supll and the second marker gene is ade2. 10. A method of identifying an agent which is an inhibitor of improper chromosome segregation comprising the steps of: a) providing cells, referred to as tester cells, transfected with a plasmid suitable for growth and reproduction in the tester cells, wherein the plasmid comprises a gene, referred to as a test gene, whose gene product causes chromosome missegregation and the appropriate control elements for expressing or overexpressing the gene; b) exposing the tester cells to an agent being tested as an inhibitor of chromosome missegregation; c) exposing the tester cells to conditions suitable for the tester cells to reproduce, thereby producing progeny cells; d) assessing the number of aneuploid progency cells or the number of progeny cells with a chromosome having a break or a translocation, wherein a lesser number of aneuploid progeny cells or a lesser number of progeny cells with a chromosome having a break or a translocation in the presence of the agent being tested than in the absence of the agent being tested is indicative that the agent is an inhibitor of improper chromosome segregation. 11. The method of Claim 10 wherein the tester cells are mammalian cells. 12. The method of Claim- 11 wherein the mammalian cells are human cells. 13. The method of Claim 10 wherein: a) the tester cells comprise: i) a chromosome with a mutated centromere which makes the chromosome prone to improper segregation; and ii) a gene on the chromosome with the mutated centromere, referred to as a marker gene, whose gene product gives a quantifiable indication of the number of chromosomes with the mutated centromere present in the tester cell; b) the number of aneuploid progeny cells is determined by quantifying the indication given by the marker gene product; and c) the tester cells are yeast cells. 14. The method of Claim 13 wherein the marker gene encodes a gene product which enhances or suppresses the expression of a second marker gene, wherein the second marker gene encodes a gene product which gives a quantifiable indication of the number of chromosomes with the mutated centromere present in the test cell. 15. The method of Claim 13 wherein the first marker gene supll and the second marker gene is ade2. 16. The method of Claim 11 wherein the test gene comprises a polynucleotide represented by SEQ ID NO: 1 17. The method of Claim 11 wherein the test gene comprises a polydeoxynucleotide represented by SEQ ID NO : 3. 18. The method of Claim 11 wherein the test gene comprises a polydeoxynucleotide represented by SEQ ID NO: 27. 19. The method of Claim 11 wherein the test gene is represented by a polydeoxynucleotide selected from the group consisting of a polynucleotide represented by SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 9, SEQ ID NO: 10, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24 and SEQ ID NO: 25. 20. The method of Claim 11 wherein the test gene encodes an Apolipoprotein E. 21. A polydeoxynucleotide represented by SEQ ID NO: 3. 22. A polydeoxynucleotide selected from the group consisting of a polynucleotide represented by SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12 and SEQ ID NO: 25. 23. A polydeoxynucleotide selected from the group consisting of a polydeoxynucleotide represented by SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24 and SEQ ID NO: 26. 24. A gene which hybridizes to a polydeoxynucleotide represented by SEQ ID NO: 3. 25. A gene which hybridizes to a polydeoxynucleotide selected from the group consisting of a polydeoxynucleotide represented by SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12 and SEQ ID NO: 25. 26. A gene which hybridizes to a polydeoxynucleotide selected from the group consisting of a polydeoxynucleotide represented by SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24 and SEQ ID NO: 26. 27. A method of identifying a gene which causes chromosome missegregation resulting in a disease condition in a mammal, comprising the steps of: a) providing cells, referred to as tester cells; b) introducing a library of DNA fragments into the tester cells, wherein each fragment of the DNA library is provided as a plasmid suitable for growth and reproduction in the tester cells and comprising: i) a DNA fragment; and ii) control elements suitable for expressing or overexpressing the DNA fragment in the tester cells; c) growing the tester cells at low density, thereby producing non-overlapping colonies of progeny cells; d) identifying colonies cells containing a greater number of aneuploid progeny cells or progeny cells with a chromosome having a break or translocation compared with progeny cells from a suitable control; and e) recovering and sequencing plasmids from progeny cells of the colonies identified in step d) , thereby identifying a gene which cause chromosome missegregation. 28. A polydeoxynucleotide represented by SEQ ID NO: 28. 29. A protein represented by SEQ ID NO: 29.

Inventors: LI JINHE, POTTER HUNTINGTON, LI, JINHE, POTTER, HUNTINGTON
Applicants: HARVARD COLLEGE, LI JINHE, POTTER HUNTINGTON, LI, JINHE, POTTER, HUNTINGTON, PRESIDENT AND FELLOWS OF HARVARD COLLEGE
Application year: 1996
Main classification: C12N15
IPC codes: A61K38, C07K14, C12N15, C12Q1, G01N33