Fig. 10

Sox3 can expand neural fate in the early ectoderm in the absence of Fgf signalling, but requires Fgf to maintain neural fate at later stages. (A–L) Lateral view of mid-gastrula stage embryos except for (K: Ventral view) and (L: Animal pole view). (A, G) Control embryos treated with DMSO only as a negative control for SU5402, showing expression of the prospective neural marker sox2 (A) and the prospective non-neural marker gata2 (G). Treatment with the Fgf inhibitor, SU5402, causes repression of sox2 (B, 37/37 embryos) and expansion of gata2 (H, 16/16). Injection of either DMSO treated (C, I) or SU5402 treated (D, J) embryos with sox3 mRNA at the 1–2 cell stage caused expansion of sox2 (C, 18/18; D, 14/19) and repression of gata2 (I, 7/17; J, 15/25). Injection of embryos with sox3 mRNA (and GFP mRNA lineage tracer) at the 16–32 cell stage caused ectopic expression of sox2 in a proportion of the sox3 over-expressing cells (E, 7/7; F, 21/25) and repression of gata2 (K, 5/5; L, 9/17) in embryos treated with either DMSO (E, K) or SU5402 (F, L). (E–F, K–L) Immunostaining of embryos for GFP (red colour) indicates the sox3 over-expressing region. (M–T) Embryos at the 3 somite stage viewed dorsally. (M, Q) DMSO treated control embryos showing expression of neural markers ncad (M) and sox2 (Q). (N, R) SU5402 treatment causes repression of neural markers leaving only a small rostral region of neural plate. Injection of sox3 mRNA (and GFP mRNA) at the 16–32 cell stage causes expansion of the neural plate (O, 19/20; S, 9/9) in DMSO treated embryos (bars in panels Q and S indicate the expansions of the neural plate), but by this stage has no effect on the expression of neural markers in SU5402 treated embryos (P, 25/25; T, 15/15). Arrows (P, T) indicate the region expression exogenous Sox3 (red), showing that the neural markers ncad and sox2 are absent from this region.