FGF signalling is required for the appropriate onset of krox20 expression. (A-D,F-I) Zebrafish embryos were incubated in either DMSO carrier or SU5402 from 50% epiboly to 10.25 hpf (A,B) or from 50% epiboly to the 1-somite stage (10.5 hpf) (C,D) or from 80% epiboly to the 4-somite stage (F-I) and analysed by in situ hybridisation for krox20 and ntl (A-D) or for krox20 alone (F-I). The insets in A-D show tailbud views of the corresponding embryos (see Fig. 3). Wild-type (WT) and krox20fh227/fh227 mutant embryos are compared in F-I. (E) Distribution of the embryos according to krox20 expression in r3 and r5 (see Fig. 3). **, P<0.0001; χ2-test.
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