Mice with principal cell-specific inactivation of TSC complex subunit (Tsc1), a modulator of mTOR kinase activity, develop renal cysts composed of hyperproliferative intercalated cells with robust expressions of Foxi1 and its downstream genes Ca2 and subunits of V-ATPase that are critical components of intercalated cells. This evidence concerns the gene FOXI1 and cystic kidney disease.