Ectodermal syndecan-2 mediates left-right axis formation in migrating mesoderm as a cell-nonautonomous Vg1 cofactor

Heparan sulfate proteoglycans expressed on the Xenopus animal cap ectoderm have been implicated in transmitting left-right information to heart and gut primordia. We report here that syndecan-2 functions in the ectoderm to mediate cardiac and visceral situs, upstream of known asymmetrically expressed genes but independently of its ability to mediate fibronectin fibrillogenesis. Left-right development is dependent on a distinct subset of glycosaminoglycan attachment sites on syndecan-2. A novel in vivo approach with enterokinase demonstrates that syndecan-2 functions in left-right patterning during early gastrulation. We describe a cell-nonautonomous role for ectodermal syndecan-2 in transmitting left-right information to migrating mesoderm. The results further suggest that this function may be related to the transduction of Vg1-related signals.