Fig. 7. The central role of Xbra in convergence extension and somite formation. FGF activates pathways through FGFR1 and Xbra, leading to convergence extension movements and myogenic specification. Xnr3 also activates FGFR-dependent Xbra expression, but only in the embryonic dorsal area. Xbra causes convergence extension movements by activating the expression of zygotic Wnt11. Wnt11 signaling causes convergence extension in a dishevelled-dependent manner that does not involve ß-catenin, the so-called `non-canonical Wnt pathway'. A separate pathway regulating convergence extension involves the activation of paraxial protocadherin downstream of Xlim1. The cytoplasmic kinase regulator genes sprouty and spred regulate whether cells undergo convergence extension or somite formation in response to FGFR stimulation (see text for details).