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Fig. 3 Shh overexpression in smu-/- and forskolin-treated embryos does not rescue slow muscle development. (A-C) shh mRNA injected embryos were fixed at 12h and labeled by in situ hybridization for myoD; dorsal views are shown. In 3/4 of the embryos from a cross of 2 smu heterozygotes (60/86), myoD expression is expanded into the segmental plate as a result of Shh overexpression (A). In 1/4 of the embryos (26/86), myoD expression is not affected by Shh overexpression (B). 100% of the forskolin-treated embryos failed to respond to Shh overexpression (C). (D-F) shh mRNA injected embryos were fixed at 30h and transverse sections were labeled for S58 (green) and zm4 (red). In wild-type embryos (D), most of the zm4-labeled fast muscle (red) is replaced by S58-labeled slow muscle (green), compare to Fig. 2J. Slow muscle is not rescued by Shh overexpression in smu-/- (E) or in forskolin-treated (F) embryos; compare to Fig. 2K,L. See also Fig. 4. Bars, 100 μm (A-C); 50 μm (D-F).