Fig. 5. FGF8 induces neural crest in vivo and in vitro. (A-D) In vivo injections of FGF8 mRNA in one of two-cell stage embryos, analyzed by in situ hybridization for Slug (A,B) or MyoD (C,D) at stage 18-20. (A) Control embryos. (B) FGF8 mRNA unilateral injections result in a strong overexpression of Slug on the injected side (yellow arrows) and sometimes in the contralateral side and the anterior neural fold (red arrowheads). (C) Control embryos. (D) FGF8 mRNA injections (injected side indicated by yellow arrowheads) do not expand paraxial mesoderm, they even reduce it in some embryos (embryo on the right) (red arrowhead). (E) FGF8 mRNA is expressed as a ring around the blastopore at stage 11 (top), reinforced dorsally (red arrows). Later on, FGF8 is expressed in the DLMZ and downregulated in the midline (bottom, red arrow). (F) FGF8 mRNA injections induce neural crest markers in animal caps. RT-PCR analysis shows the induction of FoxD3 and Zic5 by 100 pg of FGF8 mRNA, but not of paraxial mesoderm formation. (G) When the caps are analyzed earlier (stage 15), increased doses of FGF8 induce strongly FoxD3, Sox9 and Zic5. By stage 19, FoxD3 and Zic5 expression was not maintained.