Fig. 1

you Mutants Exhibit Hedgehog-Associated Defects in Slow Muscle and Ventral Spinal Cord. (A and B) Lateral views of live zebrafish at 22 hpf. Wild-type embryos (A) have chevron-shaped somites and a clearly visible floor plate (arrowhead), while you mutants (B) exhibit U-shaped somites and an indistinct floor plate (arrowhead). (C and D) Lateral views of somites 8–13 in whole-mount embryos at 24 hpf. Wild-type embryos (C) show strong Engrailed expression in muscle pioneers (arrow), and weaker expression in multinucleate medial fast fibers (arrowheads). Engrailed expression in you mutants (D) is mostly absent, though very weak expression can occasionally be observed (arrowhead). (E and F) Dorsal views of posterior trunk and tail bud in 12-somite embryos. Wild-type embryos (E) exhibit adaxial myod expression throughout the somitic (arrowhead) and presomitic (arrow) mesoderm, while you mutants (F) lack expression in the somitic (arrowhead) and in parts of the presomitic (arrow) mesoderm. (G and H) Lateral view of somites 9–15 in whole-mount embryos at 22 hpf. Wild-type embryos (G) exhibit strong expression of ptc1, while you mutants (H) show weaker levels of ptc1 expression. (I and J) Lateral view of spinal cord in the posterior trunk of whole-mount embryos at 24 hpf. Wild-type embryos (I) show expression of nkx2.2 in the ventral spinal cord, while in you mutants (J) this expression is strongly reduced. (K–N) Dorsal views of whole-mount embryos at bud stage (10 hpf). Expression in you mutant embryos of both ehh (L) and shh (N) is similar to that observed wild-type embryos (K and M). Anterior is to the left in all images. Genotypes of all embryos were determined by PCR after photography.