Fig. 4. Preaxial polydactyly and ectopic Shh expression induced by dHAND-VP16. F₀ transgenic mouse embryos were sacrificed at E16.5 and limbs were stained for bone and cartilage. (A) Limb from an embryo harboring the prx-dHAND-VP16 transgene. This construct induced severe preaxial polydactyly. Note the presense of four ectopic digits that have similar morphology. Ectopic digits are indicated with an asterisk. (B,C) Detection of Shh transcripts by whole-mount in situ hybridization to wild-type and prx-dHAND-VP16 transgenic embryos, respectively, at E11.5. In wild-type embryos, Shh transcripts are localized to the ZPA at the posterior of the limb bud. In prx-dHAND-VP16 embryos, Shh transcripts are seen throughout the peripheral region of the limb bud. Blue arrowheads indicate Shh expression domain. fl, forelimb bud; hl, hindlimb bud.