Xenopus GDF6, a new antagonist of noggin and a partner of BMPs

In Xenopus, ectodermal cell fates are determined by antagonistic interactio n between the BMP subfamily of TGF-beta ligands and the organizer-specific secreted factors (e.g. noggin, chordin and follistatin), Inhibition of BMP function by these factors can convert cells from an epidermal to a neural c ell fate, In this study, we report that GDF6, a new member of the Xenopus T GF-beta family, can function in antagonistic interaction with neural induce rs. GDF6 induces epidermis and inhibits neural tissue in dissociated cells, and this activity is blocked by the presence of noggin, We demonstrate tha t GDF6 binds directly to the neural inducer noggin, Furthermore, we find th at GDF6 and BMP2 can form heterodimers and the process seems to require cot ranslation of the proteins in the same cells, In normal embryos, GDF6 and B MP2 are coexpressed in several places, including the edge of the neural pla te at early neurula stages, suggesting that GDF6 may synergize with BMPs to regulate patterning of the ectoderm, Our data show for the first time that noggin can bind directly to and inhibit another TGF-beta family member: GD F6, In addition, BMP and GDF6 heterodimers may play an important role in vi vo to regulate cell fate determination and patterning.