Antagonistic regulation of convergent extension movements in Xenopus by Wnt/β-catenin and Wnt/Ca2+ signaling

Convergent extension movements are the main driving force of Xenopus gastrulation. A fine-tuned regulation of cadherin-mediated cell-cell adhesion is thought to be required for this process. Members of the Wnt family of extracellular glycoproteins have been shown to modulate cadherin-mediated cell-cell adhesion, convergent extension movements, and cell differentiation. Here we show that endogenous Wnt/beta -catenin signaling activity is essential for convergent extension movements due to its effect on gene expression rather than on cadherins. Our data also suggest that XLEF-1 rather than XTCF-3 is required for convergent extension movements and that XLEF-1 functions in this context in the Wnt/beta -catenin pathway to regulate Xnr-3. In contrast, activation of the Wnt/Ca2+, pathway blocks convergent extension movements, with potential regulation of the Wnt/beta -catenin pathway at two different levels. PKC, activated by the Wnt/Ca2+ pathway, blocks the Wnt/beta -catenin pathway upstream of beta -catenin and phosphorylates Dishevelled. CamKII, also activated by the Wnt/Ca2+ pathway, inhibits the Wnt/beta -catenin signaling cascade downstream of beta -catenin. Thus, an opposing cross-talk of two distinct Wnt signaling cascades regulates convergent extension movements in Xenopus. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.