FGF signaling is required for the induction of sox2 and foxd5α expression in the neural plate and the maintenance of other early neural genes. WISH for (A) sox2, (B) zicr1, (C) foxd5α, and (D) sox3 and gem of embryos that were either uninjected (UI) or injected with Noggin (Nog), dominant negative FGFR4a (Δ4a), or Nog + Δ4a and were collected at stages 10.5 and 11.5 (A-C) or 12.5 (D). All embryos are dorsal view with anterior to the top. The dashed line separates the domain of gem expression (right) from that inhibited by Δ4a (top left). (E) RT-PCR of ectodermal explants for genes indicated on the left side of panel. Explants were dissected from embryos that were either uninjected (UI) or injected with mRNA coding for Nog, Nog + dominant negative FGFR1 (XFD), Nog+Δ4a, or Nog+XFD+Δ4a.