Fig. 6

Exacerbation of slow muscle deficits in sonic you;cyclops double mutant. Schematic representation of hedgehog gene expression in wild-type and mutant zebrafish embryos (A). Slow MyHC-expressing muscle cells (B–E) in the yolk extension region of 24-hpf wild-type (B) and cyc (C) embryos are indistinguishable. syu embryos show slow muscle reduction (D). A syu;cyc double mutant embryo has only isolated residual slow muscle cells (E, arrow), yet expresses substantially normal fast muscle in an adjacent section (F). All panels show transverse sections, dorsal at top. Each of three syu;cyc mutants from 91 cross progeny, identified by lack of oorplate and U-shaped somites,were serially sectioned and individuals were found to contain two, five, and eight slow cells. Bar, 50 μm.