During gastrulation, the blastula organises into three germ layers in a process that is dependent on the establishment of cell polarity and directed cell migration. Ulrich and co-workers use detailed confocal imaging of cell movement and morphology to show that Silberblick (Slb), the zebrafish orthologue of Wnt11, controls hypoblast morphogenesis and cell migration at the onset of zebrafish gastrulation (see ). In slb mutant embryos, hypoblast cells in the forming germ ring still move in the correct direction but move more hesitantly than cells in wild-type embryos. These aberrant cell movements are preceded by defects in the orientation of cellular processes. The Wnt signalling pathway is also important at later stages of gastrulation and, say the researchers, additional studies will show whether it acts through the same target processes in both early and late gastrulation.
