Requirement of FoxD3-class signaling for neural crest determination in Xenopus

Fox factors twinged-helix transcription factors) play important roles in ea rly embryonic patterning, We show here that FoxD3 (Forkhead 6) regulates ne ural crest determination in Xenopus embryos. Expression of FoxD3 in the pre sumptive neural crest region starts at the late gastrula stage in a manner similar to that of Sing, and overlaps with that of Zic-r1. When overexpress ed in the embryo and in ectodermal explants, FoxD3 induces expression of ne ural crest markers. Attenuation of FoxD3-related signaling by a dominant-ne gative FoxD3 construct (FoxD3delN) inhibits neural crest differentiation in vivo without suppressing the CNS marker Sox2, Interestingly, these loss-of -function phenotypes are reversed by coinjecting Slug, In animal cap explan ts, neural crest differentiation induced by Slug and Wnt3a is also inhibite d by FoxD3delN but not by a dominant-negative form of XBF2. Loss-of-functio n studies using dominant-negative forms of FoxD3 and Slug indicate that Slu g induction by Zic factors requires FoxD3-related signaling, and that FoxD3 and Slug have different requirements in inducing downstream neural crest m arkers. These data demonstrate that FoxD3 (or its closely related factor) i s an essential upstream regulator of neural crest determination.