Fig. 3. BMP and Wnt signals are required for the generation of epidermal cells. (A-C) Consecutive sections showing expression of molecular markers in chick explants cultured for 28 hours. (A) Stage 2 L explants (n>30) generated Ker⁺ cells, but no, or only a few, Sox1⁺, Sox2⁺, Snail2⁺ or HNK-1⁺ cells. (B) Stage 2 L explants cultured in the presence of Noggin (n>30) generated Sox1⁺ and Sox2⁺ cells, but no Snail2⁺, HNK-1⁺ or Ker⁺ cells. (C) Stage 2 L explants cultured in the presence of mFrz8CRD (n>30) generated Sox2⁺ and Ker⁺ cells, but no Sox1⁺, Snail2⁺ or HNK-1⁺ cells. (D) Stage 2 L explants cultured in the presence of both Noggin and mFrz8CRD (n=18) generated Sox1⁺ and Sox2⁺ cells, but no Snail2⁺, HNK-1⁺ or Ker⁺ cells. Data are represented as the mean ± s.e.m. Scale bar: 100 µm. (E) Relative Sp5 and Dlx5 mRNA levels measured by quantitative real-time PCR. The mRNA expression of the Wnt target gene Sp5, but not of the BMP target gene Dlx5, is inhibited in stage 2 L explants cultured in the presence of mFrz8CRD. Bars represent mean ± s.e.m. of five independent experiments. ^*P<0.05, ^**P<0.01; two-sided, one-sample t-test.