Fig. 2. BMP and Wnt signals are required for the specification of neural crest cells. (A-C) Consecutive sections showing expression of molecular markers in chick explants cultured for 28 hours. (A) Stage 2 B explants (n>30) generated Snail2⁺ and HNK-1⁺ cells, but no, or only a few Sox1⁺, Sox2⁺ or Ker⁺ cells. (B) Stage 2 B explants cultured in the presence of Noggin (n=26) generated Sox1⁺ and Sox2⁺ cells, but no Snail2⁺, HNK-1⁺ or Ker⁺ cells. (C) Stage 2 B explants cultured in the presence of mFrz8CRD (n>30) generated Sox1⁺ and Sox2⁺ cells, but no Snail2⁺, HNK-1⁺ or Ker⁺ cells. Data are represented as mean ± s.e.m. Scale bar: 100 µm. (D,E) Relative Dlx5 and Sp5 mRNA levels measured by quantitative real-time PCR. mRNA expression of the BMP target gene Dlx5 (D) and of the Wnt target gene Sp5 (E) is inhibited in stage 2 B explants cultured in the presence of Noggin (D) or mFrz8CRD (E). Bars represent mean ± s.e.m. of four (D) and five (E) independent experiments.