PKD1 and polycystic kidney disease: In this model, exons 2 to 4 of the Pkd1 gene are floxed and recombinase expression is restricted to renal tubules via the Ksp-cadherin promotor [179], permitting kidney specific inactivation of Pkd1. Pkd1flox:Ksp-Cre animals show a rapid progression of polycystic kidney disease and die, between the postnatal days 14 and 17, presumably due to kidney failure.