Fig. 5. FGF signalling represses neuronal differentiation and somites repress Fgf8, but attenuation of this pathway is not sufficient to elicit neuronal differentiation. (A) CNP explants cultured with PSM express NeuroM after 24 hours, but (B) only a few NeuroM-positive cells appear in the presence of FGF4. (C) CNP explants contain NeuroM-positive cells after 48 hours, but (D) fail to express this gene with FGF4. (E) Diagram to show the position of PNT and NT explants from a stage HH8 embryo. (F) PNT explants cultured for 24 hours contain NeuroM-positive cells but FGF4 treatment (G) inhibits NeuroM expression. (H) PNT explants cultured for 24 hours do not contain any bra-expressing cells but maintain some expression in the presence of FGF4 (I). (J) NT explants contain NeuroM +ve cells, while (K) FGF4 inhibits NeuroM expression. (L) CNP explants retain Fgf8 after 24 hours, but (M) Fgf8 is repressed when cultured with somites. (N) CNP explants cultured for 24 hours express bra but treatment with SU5402 down regulates bra (O) and maintains expression of Sox2 (P). (Q) CNP explants do not contain NeuroM-positive cells after 24 hours even following treatment with SU5402 (R). Scale bar: 100 µm.