Figure 1. Temporal inactivation of Shh signalling in the external genitalia.

(a) Lateral view of X-gal-stained Shh^GFPcre; R26R mouse embryo at E12.5 showing position of LacZ expression in Shh^GFPcre descendent cells. Image captured using optical projection tomography. Red box shows schematic of a transverse section through the external genitalia at the level of the hindlimbs and depicts the position of Shh-producing cells at the posterior end of the embryo. (b) LacZ expression (red arrows) in Shh^creERT2;R26R embryos collected 6 and 9 h after injection of pregnant dams with tamoxifen. (c) Comparison of Ptch1 expression in Shh^creERT2/C and Shh^+/C embryos 24 and 48 h after tamoxifen injection. (d) Range of anogenital phenotypes produced by loss of Shh function at different developmental stages. All mice are males. Left panel shows complete agenesis of external genitalia and persistence of cloaca in Shh^−/− mutant. Middle panels show anogenital regions of Shh^creERT2/C mice, in which Shh was inactivated at E11.5 and E13.5 (tamoxifen injection at E10.5 and E12.5, respectively). Right panel shows normal genitalia of wild-type mouse with normal Shh activity.