Vangl2-dependent regulation of membrane protrusions and directed migration requires a fibronectin extracellular matrix

During zebrafish gastrulation the planar cell polarity (PCP) protein Vang-like 2 (Vangl2) regulates the polarization of cells that are engaged in directed migration. However, it is unclear whether Vangl2 influences membrane-protrusive activities in migrating gastrula cells and whether these processes require the fibronectin extracellular matrix. Here, we report that Vangl2 modulates the formation and polarization of actin- rich filopodia-like and large lamellipodia-like protrusions in ectodermal cells. By contrast, disrupted Glypican4/PCP signaling affects protrusion polarity but not protrusion number or directed migration. Analysis of fluorescent fusion protein expression suggests that there is widespread Vangl2 symmetry in migrating cells, but there is enrichment at membrane domains that are developing large protrusions compared with non-protrusive domains. We show that the fibronectin extracellular matrix is essential for cell-surface Vangl2 expression, membrane-protrusive activity and directed migration. Manipulation of fibronectin protein levels rescues protrusion and directed migration phenotypes in vangl2 mutant embryos, but it is not sufficient to restore either PCP, or convergence and extension movements. Together, our findings identify distinct roles for Vangl2 and Glypican4/PCP signaling during membrane protrusion formation and demonstrate that cell-matrix interactions underlie Vangl2-dependent regulation of protrusive activities in migrating gastrula cells.