THE ROLE OF MATERNAL VEGT IN ESTABLISHING THE PRIMARY GERM LAYERS IN XENOPUS EMBRYOS

VegT is a T-box transcription factor whose mRNA is synthesized during oogenesis and localized in the vegetal hemisphere of the egg and early embryo. We show that maternally expressed VegT controls the pattern o f primary germ layer specification in Xenopus embryos. Reduction of th e maternal store completely alters the fates of different regions of t he blastula so that animal cell fate is changed from epidermis and ner vous system to epidermis only, equatorial cell fate is changed from me soderm to ectoderm, and vegetal cell fate is changed from endoderm to mesoderm and ectoderm. Vegetal cells lose their capacity both to form endoderm and to release mesoderm-inducing signals. These results show that a single maternally expressed gene controls the patterning of the Xenopus blastula.