Overexpression of Xgsk-3 disrupts anterior ectodermal patterning in Xenopus

The Xenopus homolog of glycogen synthase kinase-3, Xgsk-3, plays a major role in regulating the formation of the dorsal-ventral axis, most likely through effects on the mesoderm. To determine whether Xgsk-3 is involved in ectodermal patterning, Xgsk-3 was ectopically overexpressed in the presumptive ectoderm. This approach resulted in a dramatically expanded cement gland, which is due to early changes in cement gland specification at the anterior end of the embryo. Explant experiments were used to show that Xgsk-3 overexpression enhances the response of ectoderm to cement-gland-inducing signals from the mesoderm and to the intercellular signaling factor noggin. Expression of two other noggin-inducible genes, Xotx2 and XANF-2, was also expanded in whole embryos, while the expression of the epidermal marker, Xgbx-2, was eliminated. These results suggest that Xgsk-3 may play a role in anterior ectodermal patterning as a component of an intracellular pathway that regulates the ectodermal responsiveness to endogenous inducing signals.