Fig. 1. Neural crest induction is dependent on canonical, but not non-canonical, Wnt signalling. (A) Several dishevelled (Dsh) mutants were used to distinguish between canonical (ß-cat) and non-canonical (PCP) Wnt signalling. DN, dominant negative; –, no effect; +, activation. (B-I) mRNA coding for each of these mutants was injected at the two-cell stage into the animal region fated to become ectoderm, the embryos were cultured until the equivalent of stage 17 and the expression of the neural crest marker Slug was analyzed. B,C,F and G are dorsal views; D,E,H and I are sections; anterior is to the top. The injected side (arrowhead) was identified by the lineage marker FDX (pale green). (B,D) Embryo injected with 1 ng of dd2 mRNA. Strong inhibition of the neural crest marker on the injected side is observed (35% of embryos showed inhibition of Slug expression, n=65; embryos with gastrulation defects were not included). (C,E) Embryo injected with 1 ng of dd1 mRNA. Strong inhibition of the neural crest marker on the injected side is observed (37% of embryos showed inhibition of Slug expression, n=85; embryos with gastrulation defects were not included). (F,H) Embryo injected with 1 ng of Dsh-N mRNA. Normal expression of the neural crest marker is observed on the injected side. Some embryos exhibited a weak inhibition of the expression of Slug (12% of embryos showed inhibited Slug expression, n=85). (G,I) Embryo injected with 1 ng of Dsh-DEP+ mRNA. No effect on the expression of the neural crest marker is observed (n=55).