Fig. 1. Shh^Cre was effective in removing Shh activity from all Shh-producing cells. (A,B) The distribution of Shh mRNA (A) and lacZ activated in compound heterozygous for the Shh^Cre and R26R reporter allele (B) are very similar. External morphology of E10.5 embryos (C-E). Shh-null embryo (D) is almost identical to Shh^Cre/C (E). In Shh^-/- mutants (G,J,M,P), the floorplate (G) and distinct ventral progenitors [Olig2⁺ (J), Nkx6.1⁺ (M) and Nkx2.2⁺ (P) cells] are absent. Furthermore, Pax7 (M) and Pax6 (P), negative targets of Hh signaling, move ventrally to occupy the entire ventral neural tube. In the Shh^Cre/C mutant, one or two Nkx6.1⁺ cells remain (arrow in N) in the ventral neural tube, which is indicative of some low level signaling prior to Cre activity.