The RNA-binding protein XSeb4R: a positive regulator of VegT mRNA stability and translation that is required for germ layer formation in Xenopus

VegT represents a localized maternal determinant essentially required for endoderm formation in Xenopus. Here, we report on the identification of the RNA-binding protein XSeb4R as a positive regulator of VegT. XSeb4R interacts directly with the 3'-untranslated region of VegT mRNA, stabilizes it, and stimulates translation. Ablation of XSeb4R activity results in impairment of endoderm and mesoderm formation, while ectopic expression of XSeb4R in ectodermal cells induces endodermal and mesodermal gene expression. These observations unravel a novel mode of VegT regulation at the post-transcriptional level that is essential for germ layer formation in Xenopus.