Fig. 1. FGF signalling is required to maintain Wnt8c expression. (A-C') Expression of Fgf8 (A,A'), Wnt8c (B,B') and Raldh2 (C,C') in HH10 chicken embryos and corresponding transverse sections (at position of white lines): arrowheads indicate the last somite formed. Diagram on the left defines the different regions of the caudal end of the embryos at stage HH10. (D,E) Wnt8c is downregulated 6 hours after presomitic mesoderm removal. (F-I) FGF4 beads beneath caudal neural plate (F) ectopically maintain Wnt8c 6 hours (G) and 18 hours (H) later, whereas control PBS beads do not (I). (J,K) Caudal Wnt3a (J) or Wnt5a (K) expression is not maintained rostrally by FGF4 beads (9 hours later). (L) Origin of explants used in M,M'. (M,M') Wnt8c loss in preneural tube explants (pNT) cultured 24 hours (M) is prevented by FGF4 (M'). (O) Origin of caudal neural plate (CNP) explants used in N,N',P,P' and caudal presomitic mesoderm (CPM) explants used in Q,Q'. (N,N') Wnt8c is still expressed in CNP explants after 8 hours in DMSO control media (N) but is downregulated by SU5402 (N'). Fgf8 transcripts are still detected in CNP with control cells after 24 hours (P) but not in CPM explants (Q). Explants (P-Q') are derived from the same embryo.Wnt8c cells do not alter Fgf8 expression (P',Q'). Scale bars: 100 µm in A for A-C and in E for E,G-K; 50 µm in M for M-N' and in P for P-Q'.