OVEREXPRESSION OF XGSK-3 DISRUPTS ANTERIOR ECTODERMAL PATTERNING IN XENOPUS

The Xenopus homolog of glycogen synthase kinase-3, Xgsk-3, plays a maj or role in regulating the formation of the dorsal-ventral axis, most l ikely through effects on the mesoderm. To determine whether Xgsk-3 is involved in ectodermal patterning, Xgsk-3 was ectopically overexpresse d in the presumptive ectoderm. This approach resulted in a dramaticall y 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 ectoder mal patterning as a component of an intracellular pathway that regulat es the ectodermal responsiveness to endogenous inducing signals. (C) 1 996 Academic Press, Inc.