PKD1 and cyst: Thus, we collected Pkd1 HET (control) and Pkd1 HOMO kidneys at postnatal day 7 before cyst initiation (pre-cyst formation stage), at postnatal day 14 (critical time point/stage) and at postnatal day 21 when cysts are aggressively developing in Pkd1flox/flox:Pkhd1-Cre kidneys (late stage of cyst formation) [38].