TSC1 and cystic kidney disease: To better understand cross-talk between the TSC and PKD genes in renal cyst formation, we intercrossed mice harbouring either Pkd1 (ref. 24) or Tsc1 (ref. 25) floxable alleles with an identical Cre line (KspCre)26, which is active in the distal tubules and collecting ducts starting at E14.5, both on the same genetic background (C57Bl/6).