Fig. 4. BMP, but not Wnt, signals play an instructive role in the specification of neural plate border cells. Consecutive sections showing expression of molecular markers in chick explants cultured for 28 hours. (A) Stage 2 M explants (n>30) generated Sox1⁺ and Sox2⁺ cells, but no Snail2⁺, HNK-1⁺ or Ker⁺ cells. (B) Stage 2 M explants cultured together with BMP4 (5 ng/ml) (n>30) generated Ker⁺ cells, but no, or only a few, Sox1⁺, Sox2⁺, Snail2⁺ or HNK-1⁺ cells. (C) Stage 2 M explants cultured together with Wnt3A (n>30) generated Snail2⁺ and HNK-1⁺ cells, but no, or only a few, Sox1⁺, Sox2⁺ or Ker⁺ cells. (D) Stage 2 M explants cultured together with Wnt3A and Noggin (n=23) generated Sox1⁺ and Sox2⁺ cells, but no Snail2⁺, HNK-1⁺ or Ker⁺ cells. (E) Stage 2 M explants cultured together with Wnt3A and BMP4 (5 ng/ml) (n=25) generated Ker⁺ cells, but no Sox1⁺, Sox2⁺, Snail2⁺ or HNK-1⁺ cells. (F) Stage 2 M explants cultured together with BMP4 (5 ng/ml) and mFrz8CRD (n=17) generated Sox2⁺ and Ker⁺ cells, but no Sox1⁺, Snail2⁺ or HNK-1⁺ cells. Data are represented as the mean ± s.e.m. Scale bar: 100 µm.