mob;mos double mutant embryos exhibit complete absence of neural crest and its derivatives. (A–D) Lateral view of wild-type (WT) (A), mob (B), mos (C), and mob;mos (D) live embryos at 5 dpf. In mob and mos embryos the Meckel′s cartilage (m) is pointing ventrally (arrows in B,C). In mob;mos embryos, the ventral part of the head (arrow in D) is ventrally concave and skin pigmentation is absent. (E–H) Ventral view of Alcian blue-stained heads showing the craniofacial skeleton of WT (E), mob (F), mos (G), and mob;mos (H) embryos at 5 dpf. Pharyngeal cartilage elements corresponding to the second and posterior arches are reduced in mob and mos embryos; in mob;mos embryos, all pharyngeal cartilage is absent, and the neurocranium is deformed. bh, basihyal; cb 1–5, ceratobranchials 1–5; ch, ceratohyal; ep, ethmoid plate; hs, hyosymplectic; m, Meckel′s cartilage; pch, parachordal; pq, palatoquadrate; tr, trabecula. (I–L) Lateral view of trunk regions of WT (I), mob (J), mos (K), and mob;mos (L) embryos stained with anti-Hu antibody to label dorsal root ganglia (DRG) and enteric neurons (en) at 3 dpf. DRG and enteric neurons are reduced and scattered in mob and mos embryos (arrows in J,K) and absent in mob;mos embryos. In contrast, Rohon–Beard neurons are present in double mutants (arrow in L). (M–R) Migratory neural crest cells are absent in mob;mos embryos. In situ hybridization analysis for genes expressed in migratory neural crest cells in WT (M, O, Q) and mob;mos (N, P, R) embryos at 24 hpf. Embryos in (O, P) are flattened and shown in dorsal view, the rest in lateral views. crestin (M, N) expression in the migratory neural crest is completely absent in mob;mos embryos. dlx2a (O, P) is expressed in the telencephalon (tel), diencephalon, and migratory neural crest streams in the head of wild-type embryos, but absent in mob;mos embryos. sox10 (Q, R) is expressed in non-ectomesenchymal neural crest cells and otic vesicles (ov) of wild-type embryos, while in mob;mos embryos, sox10 is only expressed in otic vesicles. (S–V) Dorsal view of WT (S), mob (T), mos (U) and mob;mos (V) embryos showing expression of snail1b at 12 hpf in premigratory neural crest, which is completely absent in mob;mos embryos.