Silberblick/Wnt11 mediates convergent extension movements during zebrafishgastrulation

Vertebrate gastrulation involves the specification and coordinated movement of large populations of cells that give rise to the ectodermal, mesodermal and endodermal germ layers. Although many of the genes involved in the spe cification of cell identity during this process have been identified, littl e is known of the genes that coordinate cell movement. Here we show that th e zebrafish silberblick (slb) locus(1) encodes Wnt11 and that Slb/Wnt11 act ivity is required for cells to undergo correct convergent extension movemen ts during gastrulation. In the absence of Slb/Wnt11 function, abnormal exte nsion of axial tissue results in cyclopia and other midline defects in the head(2). The requirement for Slb/Wnt11 is cell non-autonomous, and our resu lts indicate that the correct extension of axial tissue is at least partly dependent on medio-lateral cell intercalation in paraxial tissue. We also s how that the slb phenotype is rescued by a truncated form of Dishevelled th at does not signal through the canonical Wnt pathway(3), suggesting that, a s in flies(4), Wnt signalling might mediate morphogenetic events through a divergent signal transduction cascade. Our results provide genetic and expe rimental evidence that Wnt activity in lateral tissues has a crucial role i n driving the convergent extension movements underlying vertebrate gastrula tion.