Fig. 2

Fig. 2 you-too/gli2 embryos lack adaxial cells and display pathfinding defects. Cross-section of wild-type (A) and you-too/gli2 (B) embryos at 28 hpf stained for pax9a expression. In wild-type and you-too/gli2 mutants, pax9a-positive sclerotome cells migrate dorsally, between the notochord and the myotome, encircling the notochord (arrow) and the spinal cord (arrowhead). Note that the horizontal myoseptum is missing in you-too/gli2 embryos, and the somites therefore appear wider. (C, D) Cross-section of a 24-hpf wild-type sibling and you-too/gli2 mutant embryos stained with F59 (red) and F310 (green) antibody. (A) In wild-type siblings F310 (green) stains the fast-twitch muscle cells, while F59 (red) stains the lateral adaxial cell derived slow-twitch muscle cells. (B) In you-too/gli2 mutant embryos, fast-twitch muscle is present (green), while adaxial cell derived slow-twitch muscle is absent. Lateral views of wild-type (E) and you-too/gli2 (F) embryos at 52 hpf stained with zn-5 antibody. Note the expression of zn-5 in the somata of secondary motor neurons (asterisks). In wild-type embryos, (E) secondary motor axons have completed migration along the common path (between red and white line), and extend along their cell-type-specific paths into the dorsal (white arrowhead), medial (yellow arrowhead), and ventral myotome (red arrowhead), respectively. In you-too/gli2 mutant embryos (F), secondary motor axons extend normally inside the spinal cord (white arrows) but often stall at the segmental exit point, where their growth cones accumulated (red arrows), instead of exiting into the periphery.