Fig. 6. Wnt-regulated temporal control of BMP exposure mediates the induction of neural plate border cells. Consecutive sections showing expression of molecular markers in chick explants cultured for 28 hours. The schematics to the left illustrate the periods of exposure to mFrz8CRD (Frz), Noggin and BMP4 during the culture. (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 together with mFrz8CRD for the first 10 hours of culture (n=29) generated Sox1⁺ and Sox2⁺ cells, but no Snail2⁺, HNK-1⁺ or Ker⁺ cells. (C) Stage 2 B explants cultured together with mFrz8CRD for the last 18 hours of culture (n>30) generated Sox2⁺ and Ker⁺ cells, but no Sox1⁺, Snail2⁺ or HNK-1⁺ cells. (D) Stage 2 B explants cultured together with Noggin for the first 10 hours of culture (n=17) generated Snail2⁺ and HNK-1⁺ cells, and a few Sox2⁺ and Ker⁺ cells, but no Sox1⁺ cells. (E) Stage 2 B explants cultured together with Noggin for the last 18 hours of culture (n=16) generated Sox1⁺ and Sox2⁺ cells, but no Snail2⁺, HNK-1⁺ or Ker⁺ cells. (F) Stage 2 B explants cultured together with BMP4 (5 ng/ml) for the entire culture period (n=27) generated Ker⁺ cells, but no Sox1⁺, Sox2⁺, Snail2⁺ or HNK-1⁺ cells. (G) Stage 2 B explants cultured together with BMP4 (5 ng/ml) for the last 18 hours of culture (n>30) generated Snail2⁺ and HNK-1⁺ cells, and a few Sox2⁺ and Ker⁺ cells, but no Sox1⁺ cells. Data are represented as the mean ± s.e.m. Scale bar: 100 µm.