Fig. 1. WNT signaling in the developing GT and tissue-specific Cre expression. (A-D) TOPGAL embryos stained with X-Gal at different stages. TOPGAL expression in the dUE persists from E10.5 to E14.5 (arrows, A-D). Preputial swellings (arrowheads, C) and labioscrotal swellings (arrowheads, D) are also positive for TOPGAL activity. (E,F) Coronal sections of E10.5 and E12.5 GTs showing distal urethral localization of TOPGAL positive cells (blue). (G,H) ³⁵S in situ hybridization on E12.5 GT sections (plane of section is shown in M) using probes indicated. (I-L) Coronal sections (plane of section is shown in N) of X-Gal-stained E10.5 embryos showing tissue-specific Cre-mediated recombination in the GTs. No endogenous X-Gal activity was detected at this stage (I). Scale bars: 100 µm in F-H; 50 µm in E,I-L.