PKD1 and Renal cyst: In support of our data in cell culture, protein expression levels of p53 in lysates of P21 cystic kidneys of Ksp-CreERT2;Pkd1f/f and P16 or P21 Ubc-CreERT2;Pkd1f/f mice, induced by 4-OHT from P2-P6, were increased in mutant kidneys (Figs 4B–D and S3C–E), suggesting that deletion of Pkd1 either ubiquitously or specifically in kidney epithelial cells results in massive activation of p53 in cystic kidneys.