Interaction between Wnt and TGF-β signalling pathways during formation of Spemann's organizer

Abstract

Members of the Wnt and TGF-β superfamilies regulate both cell fate and proliferation during development and tissue maintenance^1,2,3. In the early amphibian embryo, the Wnt and TGF-β superfamily signalling cascades are required for the establishment of a dorsal signalling centre, Spemann's organizer^4,5,6,7,8. Intracellular proteins of both pathways, upon activation, translocate to the nucleus to participate in transcription. Here we show that β-catenin and Lef1/Tcf, which are downstream components of the Wnt signalling cascade, form a complex with Smad4, an essential mediator of signals initiated by members of the TGF-β growth factor superfamily. In Xenopus, this interaction directly and synergistically affects expression of the twin (Xtwn) gene during formation of the organizer. This is, to our knowledge, the first demonstration of a physical interaction between TGF-β and Wnt signalling components in vivo.