(Directly taken from the application) The long-term objectives of this proposal are: 1) to identify by positional cloning the product of the murine autosomal recessive juvenile cystic kidney (jck) mutation, 2) to localize and analyze candidate gene corresponding to modifier loci which affect severity of polycystic kidney disease (PKD) in this mouse model, and 3) to identify genes whose expression is altered in cystic kidneys. A novel method of chromosomal exclusion was used to map jck to chromosome 11 using an intercross between (C57BL/6 X DBA/2)F1 jck/+ mice; this mutation has been further localized to an interval of <1 cM and found to be very tightly linked with a microsatellite marker (no recombinants in over 1000 mice tested). Direct selection and CpG-island PCR are being used to analyze YAC clones to identify candidate transcripts for jck. In addition, the severity of PKD in the F2 progeny was significantly more variable than that found in the parental C57BL/6 strain, suggesting that a modifier locus introduced from DBA/2 affects expression of jck. Two regions one from DBA/2 on chromosome 10 and a second from C57BL/6 on chromosome 1 - are associated with inheritance of a more severe PKD phenotype. The finding of a highly significant association of inheritance of a C57BL/6-related locus with disease severity (with a LOD score of 16.8) was unexpected (since the disease phenotype in this background is not severe), and our results that it is the combination of loci from different genetic backgrounds that results in the more severe phenotype, presumably as a consequence of an interaction between the protein products. Since a positional cloning strategy is less appropriate for the characterization of loci that affect quantitative traits, congenic strains are being generated to more specifically localize the modifying genes. Additional crosses are also being analyzed to test the generality of the effects of these modifying loci. We have also used a modified differential display PCR technique that targets the entire gene (and not just 3' UTR) to test for genes whose expression is altered in jck mutant mice. Our first experiments using this approach have served to identify a novel putative transporter gene that appears to be required for normal bone development, since its expression is absent in the osteosclerosis (oc) mutant mouse, which has osteopetrosis and rickets as part of its phenotype. We propose to use this approach at very early time points in order to identify genes whose expression is immediately affected by the absence of the jck product. Understanding the molecular basis of this mutation should provide insight into a fundamental mechanism of cystogenesis that may be relevant to human disease. In addition, the importance of characterizing the modifying loci should not be underestimated, since these genes may provide useful targets for therapeutic intervention that could significantly ameliorate disease-related morbidity. Finally, the characterization of genes whose expression is altered in these mutant mice should serve to identify pathways of gene interactions.
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