FGF signaling induces neuron formation despite the presence of BMP signaling. (A) RT-PCR of embryos collected at the hpf indicated at the top. Primers are indicated on the left side of the panel. Ef1a was used as a loading control and samples without MMLV RTase added were used as RT- controls (far right). (B) RT-PCR of stage 17 ectodermal explants dissected from uninjected embryos (UI) or embryos injected with mRNA coding for Nog, FGF8a, or Nog+ FGF8a. WE is whole embryo control. Primers for markers of the neural plate border (slug, msx-1), epidermis (bmp4, vent2, vent1, epi-k) and mesoderm (xbra) and are shown on the left side of the panel. (C-I) WISH for (C) sox3, (D) foxd5α, (E) ngnr-1, (F) n-tub, (G, G') msx-1, (H) vent2 and (H) epi-k using embryos that were either uninjected (UI) or injected with either Nog, FGF8a or Nog+ FGF8a and lacZ mRNA. All stage 17 embryos are a dorsal view with anterior to the top (C-G, I) and G' embryos are a lateral view of embryos in G with anterior to the left. Embryos in H are stage 10.5 animal pole view with dorsal to the top. Asterisk indicates expansion in the deep layer of the ectoderm; white arrow indicates expansion in both the deep and superficial ectoderm and red arrow indicates expansion in the superficial layer only.