Negative regulation of axis formation and Wnt signaling in Xenopus embryosby the F-box/WD40 protein beta TrCP

Screening a maternal Xenopus expression library for activities that synergi ze with low levels of injected beta-catenin, we have isolated a clone encod ing the C-terminal end of x-beta TrCP-2, a highly conserved protein belongi ng to the F-box/WD40 family of ubiquitin-ligase specificity factors. We sho w that x-beta TrCP-2 expression reduces dorsal axis formation in Xenopus em bryos. A dominant negative mutant lacking the F-box triggers the opposite e ffect, inducing secondary axes and activating the expression of Wnt respons ive genes in ectodermal explants. In light of the existence of beta TrCP tr anscripts associated with the vegetal cortex, we propose that beta TrCP pla ys a fundamental role in the establishment of the dorsal determinants durin g cortical rotation in Xenopus. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.