Gas1 is a general negative target of Hedgehog signaling that is expressed in the ventral CNS during early stages of neural tube patterning. Analysis of Gas1 expression in wild-type (A), Smo−/− (B), and Ptch1−/− (C) eight- to 10-somite mouse embryos. Black arrowheads highlight Gas1 expression in somites. Whole-mount LacZ stain of wild-type (D,L,T) and Gas1+/− (H,P,X) embryos at the indicated stages. Embryos were sectioned at the forelimb level (for E9.5 and E10.5) and stained with DAPI (E,I,M,Q,U,Y), anti-β-gal (F,J,N,R,V,Z), and anti-Nkx6.1 (G,K,O,S,W,AA). Dashed lines in R, S, Z and AA denote the ventral limit of Gas1 expression in adjacent sections following antibody staining for β-galactosidase. Arrows in F and J denote notochord. Arrowhead in Z indicates Gas1-expressing commissural axons. Bars: F,N,V, 50 μm.