Figure 5. sox10 and islet1 lie downstream of prdm1a in neural crest cell and RB neuron fate specification.

Lateral views of wildtype and prdm1a mutant embryos at 25hpf. Crestin expression in a wild type embryo at 25 hpf (A). sox10 overexpression in a wild type embryo results in increased neural crest cell number as assessed by crestin expression (B). prdm1a mutant embryos have reduced crestin expression at 25hpf (C). sox10 overexpression in prdm1a mutant embryos rescues the neural crest cell defects but not the kinked tail or U-shaped somite phenotypes (D). Pigment is rescued following injection of sox10 mRNA. Low (E) and high (H) magnification of the same embryo showing wildtype pigment pattern (arrows point to pigment on yolk). Low (F) and high (I) magnification of the same prdm1a mutant embryo shows reduced pigment on the dorsal side and especially on the yolk (arrows). (G, J) Injection of sox10 mRNA partially rescues the prdm1a pigment phenotype, restoring pigment cells both on the dorsal side and yolk (arrows). (K) RB neurons stained with HNK-1 antibody within the dorsal trunk of a wild type embryo at 24 hpf. (L) prdm1a mutants lack RB neurons. (M.) islet1 overexpression within prdm1a mutant embryos results in partial rescue of RB neurons. (N,O) Quantification of sox10 and islet1 rescue of RB phenotype of prdm1a mutants. (N) Percentage of prdm1a mutants rescued after injection of either sox10 or islet1 RNA. Uninjected and GFP mRNA control injected prdm1a mutant embryos do not exhibit rescue, while on average, 58% of sox10 RNA injected (red) and 64% of islet1 RNA injected (orange) embryos display significant rescue. (O) Wild type embryos have an average of 100 RB sensory neurons (green) while prdm1a mutant embryos have an average of 12 RB neurons (blue) per embryo. islet1 mRNA injection partially rescues RB neurons, resulting in an average of 40.6 RB sensory neurons per embryo (red).