Autosomal dominant polycystic kidney disease (ADPKD) is the most common lethal monogenic genetic diseases (ADPKD) of man, affecting ~1 in 1,000 individuals. ADPKD is characterized by focal dilatations of renal tubules that lead to cystic replacement of renal tissue and eventually renal failure, requiring renal replacement therapy in half of the cases by age 50. ADPKD is a systemic disease involving the kidney, liver, pancreas, arteries, and heart. Mutations in the PKD1 and PKD2 genes which encode polycystin-1 and -2 (PC1 and PC2), respectively, cause ADPKD. Mutations in the PKD1 gene alone are responsible for -85% cases of ADPKD. To study PKD7-disease, the principal investigator's group previously generated mice with two germline mutations (de!34 and null) targeted to the Pkd1 locus by homologous recombination in embryonic stem (ES) cells. Unfortunately, these mice, as well as all other Pkd1 mutants generated later, die between the 13th day of embryonic life and shortly after birth, which greatly limits the use of these animal models to answer a number of questions and prevented one from studying the role of PC1 in adult life. In the last funding period, the principal investigator developed a new line of germline Pkd1 mutant mice by creating an in-frame deletion (deletion of exon 2-6) in the extracellular domain of PC1 and a line of transgenic mice with exon 2-6 of Pkd1 flanked by loxP sites by homologous recombination in ES cells. The new germline Pkd1 mutant line differs from all existing Pkd1 mutant lines in not having an artificial insertion of a neomycin resistant cassette. Such an insertion has previously been reported to affect the expression of neighboring genes. In this proposal, the principal investigator aims to perform comparative studies of the phenotypes of the new germline mutant (cte/2-6) with existing Pkd1 mutants to determine the authentic phenotypes caused by Pkd1 mutations. She will use the newly developed Pkd1 floxed mice to generate tissue- and cell type-specific Pkd1 knockouts to provide a better animal model of the human disease, to study the role of PC1 in postnatal development and in adult life, and to test therapies that might palliate or cure PKDt-disease. She will test the "two-hit" hypothesis as a mechanism for cyst formation in ADPKD. The principal investigator's group has recently shown that PC1 and PC2 function as a mechanosensitive receptor-channel complex mediating Ca2+ signaling in cultured renal epithelia. In this proposal, she will test this hypothesis in vivo. These studies are likely to advance our knowledge on the molecular mechanisms of the disease and on the design of therapeutic strategies.