Fig. 2

The Extracellular Domain of Smo Is Required for High-Level Signaling

(A–L) Purmorphamine treatment of WT and smo^s294 mutant embryos. DMSO-treated WT (A, E, and I), DMSO-treated smo^s294 mutant (C, G, and K), purmorphamine-treated WT (B, F, and J), and purmorphamine-treated smo^s294 mutant (D, H, and L) embryos at 24 hpf are shown. Purmorphamine treatment did not significantly affect morphology (B) and caused only a modest increase in Prox1 (green) and sMHC staining (red) (F) but strongly induced ectopic Engrailed (Eng)-positive muscle pioneer cells (MPs) in WT embryos (J). Purmorphamine treatment of smo^s294 mutants resulted in significant rescue of the morphological phenotype (D) and restored Prox1 (green) and sMHC (red) expression (H), but not Eng expression (L).

(M–T) Injection of SmoΔCRD mRNA in WT and smo^hi1640 mutant embryos. Prox1 (green) and sMHC (red) staining (M–P) and Eng staining (Q–T) are shown. Injection of 250 pg SmoΔCRD mRNA caused a complete rescue of Prox1 and sMHC expression in smo^hi1640 mutants (P) compared to uninjected mutants (O) and a slight increase in Prox1 and sMHC expression in WT (N) compared to control (M). In contrast, injection of SmoΔCRD mRNA had no effect on Eng expression in WT (R) compared to control (Q) and did not rescue Eng expression in smo^hi1640 mutants (T). For quantification, see Tables S1 and S2.