Evidence for a frizzled-mediated wnt pathway required for zebrafish dorsalmesoderm formation

We have used zebrafish as a model system for the study of vertebrate dorsov entral patterning. We isolated a maternally expressed and dorsal organizer localized member of the frizzled family of wnt receptors. Wild-type and dom inant, loss-of-function molecules in misexpression studies demonstrate friz zled function is necessary and sufficient for dorsal mesoderm specification . frizzled activity is antagonized by the action of GSK-3, and we show GSK- 3 is also required for zebrafish dorsal mesoderm formation. frizzled cooper atively interacts with the maternally encoded zebrafish wnt8 protein in dor sal mesodermal fate determination. This frizzled-mediated wnt pathway for d orsal mesoderm specification provides the first evidence for the requiremen t of a wnt-like signal in vertebrate axis determination.