Functional conservation of the Wnt signaling pathway revealed by ectopic expression of Drosophila dishevelled in Xenopus.

Wnt genes encode secreted growth factors that exhibit potent effects on both embryonic and postembryonic development in vertebrates and invertebrates. Recently, the dishevelled (dsh), shaggy/zeste-white 3, and armadillo genes have been shown to participate in Wnt (wingless; wg) signaling in Drosophila. Vertebrate genes that have sequence similarities to all of these Drosophila genes have been identified. To determine whether these structurally conserved components of insect wg signaling represent a functionally conserved Wnt signaling pathway in vertebrates, we investigated the role of Drosophila dsh in Xenopus Wnt signaling. Xenopus embryos ectopically injected with Drosophila dsh mRNA developed duplicated axes similar to those seen in embryos injected with Wnt mRNAs. The involvement of dsh function in the Wnt signaling pathway in Xenopus was demonstrated using two assays which are specifically sensitive to Wnt signaling: synergistic induction of dorsal mesoderm with bFGF and the specific induction of a Wnt-responsive reporter gene. These findings support the notion that the intracellular response to the Wnt signal has been conserved during evolution to such an extent that its components may be interchanged between distantly related species.