kit mutant reveals critical period for ErbB activity during neural crest migration. Embryos were reared to juvenile stages after treatment with AG1478 as embryos. (A) Normal kit mutant pigment pattern after AG1478 treatment between 26 and 30 hpf (stripe break score=0; for details see Materials and methods). kit mutant adults exhibit about half as many stripe melanophores as wild-type fish and completely lack melanophores over the dorsum and on scales (Johnson et al., 1995). (B,C) Treatment with AG1478 between 14 and 18 hpf results in pattern defects that are moderate (B, stripe break score=3) to severe (C, stripe break score=4). (D) Distinct melanophore-free patches (arrows) in kit mutant treated between 8 and 11 hpf then again between 26 and 30 hpf. (E,F) Quantitation of stripe break defects in kit mutants treated with AG1478 in two separate experiments. Shown are median stripe break scores (red bars) and interquartile ranges (50% of scores, black vertical bars). Numbers above each treatment stage are sample sizes of adult fish analyzed. con, DMSO-treated controls. (E) Initial experiment reveals peak sensitivity between 16 and 22 hpf, with lesser defects extending between 8 and 36 hpf (test of differences in median locations across all treatments, Wilcoxon test χ2 approximation=38.6, d.f.=11, P<0.0001). (F) Second experiment confirms peak sensitivity between ∼14 and 22 hpf (χ2=115.6, d.f.=14, P<0.0001). More severe defects are generated with repeated treatments (right).
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