Failure of NC sublineage specification in foxd3zdf10;tfap2alow double mutants. (A-D) Lateral views with anterior to the left. (A) mitf expression at 24 hpf (arrowheads). foxd3zdf10;tfap2alow double mutant embryos completely lack NC-derived melanoblast mitf expression. (B) xanthine dehydrogenase (xdh), diagnostic of xanthophore precursors, at 30 hpf. (C) endothelin receptor B (ednrb1), presumed to be expressed by all chromatophore precursors, at 30 hpf and (D) leukocyte tyrosine kinase (ltk), reported to be expressed by iridophore precursors, at 30 hpf. (E) Dorsal views of dhand expression, anterior to left, ventral of the caudal hindbrain, at 48 hpf. Sympathetic neuron precursors are labeled in wild-type embryos (arrowheads), as are the more ventral and laterally localized enteric neuron precursors (arrows). In the majority of foxd3zdf10 embryos, both sympathetic and enteric neuron progenitors are absent (asterisk) (Stewart et al., 2006). In tfap2alow mutants, sympathetic neuron precursors are absent whereas a small number of enteric precursors are present (arrow) (Knight et al., 2003). In foxd3zdf10;tfap2alow double mutants, both sympathetic and enteric neuron precursors are absent (asterisk). (F-J) Lateral (F-I) and dorsolateral views (J), anterior to the left. (F) dlx2 expression at 24 hpf. dlx2 expression (arrowheads) is absent in the branchial arches of double mutant embryos, but is retained in the forebrain (arrows). (G) dlx3 expression at 30 hpf; (H) dhand expression at 30 hpf. NC expression of both genes is absent in double mutant embryos with dlx3 expression maintained in non-NC otic vesicle (asterisks). (I) tbx1 expression in the branchial arches (asterisk) at 30 hpf is diagnostic of the endodermal component of the arches. tbx1 expression is normal in all experimental embryos. (J) endothelin 1 (edn1) expression in the mesodermal component of the branchial arches at 30 hpf. Branchial mesoderm appears to develop normally in foxd3zdf10 and tfap2alow single mutants, as well as in foxd3zdf10;tfap2alow double mutant embryos.