Activin A signaling directly activates Xenopus winged helix factors XFD-4/4', the orthologues to mammalian MFH-1.

We investigated the Xenopus winged helix gene XFD-4, its cDNA, and a pseudoallelic cDNA, termed XFD-4', representing Xenopus orthologues to chicken CWH-2 and mammalian MFH-1. XFD-4/4' genes are activated after midblastula transition in dorsolateral mesoderm but not within the dorsal lip. Later, expression is found in two segmented lines of cells bordering the somites, in head mesenchyme, in ventral abdominal muscle, and in the tail tip. Smad2 RNA injection leads to ectopic expression of XFD-4'. Since activation is also observed in activin A treated animal cap explants in the presence of cycloheximide, XFD-4/4' genes represent direct targets of activin signaling. Note that the future nomenclature for XFD-4 will be FoxC2a and for XFD-4' will be FoxC2b (Fox Nomenclature Committee).