Fig. 1. Ontogeny of p63 in urogenital sinus (UGS) and phenotype of p63^–/– UGS. (A-D) Ontogeny of p63 in embryonic UGS. CA, cloaca; HG, hind gut; MND, mesonephric duct; NT, neural tube. Cross section (A) and saggital section (B-D) of mouse embryos. Scale bar: 50 µm. (E-O) Marker expression was examined in male p63^+/+ UGS (E-H,M) and male (I-L,N) and female (O) p63^–/– UGSs at E17.5. MD, Müllerian duct; WD, Wolffian duct. Gross morphology of the p63^–/– UGS was normal and showed normal sexual dimorphism at E17.5 (compare O [female] with I-L [male]). p63^–/– urogenital sinus epithelium (UGE) expressed differentiation markers identical to that of p63^+/+ UGE [uroplakin (G,K), involucrin (H,L) and androgen receptor (AR) (M,N)] with the exception that p63 (E,I) and K14 (F,J) were absent in p63^–/– UGE. In both male p63^+/+ and p63^–/– UGSs, notice epithelial outgrowths into stroma in the area where prostates normally form (black and white arrows).