Laminin a5 is a component of essentially all basement membranes in the kidney. It is particularly important in the glomerular basement membrane (GBM), where we have shown that it is necessary for maintenance of GBM integrity, for vascularization of glomeruli, and for mesangial cell organization of glomerular capillary loops. During the course of generating a conditional, floxed LamaS allele, we have serendipitously created a new mouse model for autosomal recessive polycystic kidney disease. This stems from the insertion of a FRT-flanked PGKneo selectable marker into an intron of LamaS, thus generating a hypomorphic LamaS allele, which we call LamaSneo. Preliminary studies show that LamaSneo/neo mice die at ~23 days of age with multiple large cysts, proteinuria, hematuria, and reduced levels of laminin a5 in most kidney basement membranes. Evidence that cysts are forming can be detected as early as the time of birth. The purpose of this limited two year Pilot and Feasibility Study is to segregate the putative epithelial cell/matrix defects in the tubular compartment of the nephron that result in cystogenesis, from the GBM defects that likely exacerbate kidney damage and speed the onset of renal failure in LamaSneo/neo mice. This will allow for a more meaningful analysis of cystogenesis and testing of hypotheses as to its origin. We will accomplish this by generating new transgenic mice that express the enhanced FLP recombinase specifically in podocytes, using the 2.5 kilobase podocin promoter. The FRT sites flanking the PGKneo are substrates for FLP recombinase, which will splice them together and delete the intervening PGKneo insertion specifically; in podocytes, thus restoring normal levels of laminin alphas in the GBM. We hypothesize this will also restore the integrity of the glomerular filtration barrier and allow a focused study of tubule defects that result in cystogenesis. In addition, the transgenic mice we will generate will serve as a useful resource to the nephrology research community, as they will provide a unique additional tool for manipulating podocyte gene expression. ? ? ?
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