Effects of rat axin domains on axis formation in Xenopus embryos

摘要

Wnt signaling plays an important role in axis formation in early vertebrate development. Axin is one Wnt signaling regulator that inhibits this pathway. The effects of the injection of mRNA of several rat Axin (rAxin) mutants on axis formation in Xenopus embryos were examined. It was found that rAxin mutants containing only a regulation of G-protein signaling (RGS) domain fragment or with deletion of the RGS domain induced axis formation. Because the RGS domain is a major adenomatous polyposis coligene product (APC)-binding domain, APC association with glycogen synthase kinase 3#beta# (GSK3#beta#) on the Axin molecule may be mportant in inhibition of axis formation. The ventralizing activities of wild-type rAxin and a mutant in which the Dishevelled and Axin (DIX) domain was deleted (#DELTA#DIX mutant) were examined. Histological examination and gene expression revealed that the ventralizing activity of the #DELTA#DIX mutant was weaker than that of wild-type rAxin. This finding suggests that theC-terminus of rAxin contributes to the inhibition of Wnt signaling in Xenopus embryos. Furthermore, an rAxin mutant that contained both the RGS and GSK3#beta#-binding domains affected both the dorsal and ventral sides of blastomeres, mediated ectodermalfate and induced expansion of notochord and/or endoderm, but did not induce axis formation.