HOXD9 and Renal cyst: In all the Hox mutant cystic kidneys examined (Hoxa9,10,11−/− Hoxc,10,11+/−, Hoxa9,10,11+/− Hoxc,10,11−/−, Hoxc9,10,11−/− Hoxd,10,11+/−, and Hoxa9,10,11+/− Hoxc,10,11+/− Hoxd9,10,11+/−), we consistently observed cells with brush-border like microvilli characteristic of proximal tubules (i) interspersed among distal tubule/collecting duct cells with distinctive short, sparse37 microvilli (Fig. 6,C’, higher magnification in C”).