Dual specificity of activin type II receptor ActRIIb in dorso-ventral patterning during zebrafish embryogenesis

Members of the transforming growth factor-beta (TGF-beta) superfamily are t hought to regulate specification of a variety of tissue types in early embr yogenesis. These effects are mediated through a cell surface receptor compl ex, consisting of two classes of ser/thr kinase receptor, type I and type I I. In the present study, cDNA encoding zebrafish activin type II receptors, ActRIIa and ActRIIb was cloned and characterized. Overexpression of ActRII b in zebrafish embryos caused dorsalization of embryos, as observed in acti vin-overexpressing embryos. However, in blastula stage embryos, ActRllb ind uced formation of both dorsal and ventro-lateral mesoderm. It has been sugg ested that these inducing signals from ActRllb are mediated through each sp ecific type I receptor, TARAM-A and BMPRIA, depending on activin and bone m orphogenetic protein (BMP), respectively In addition, it was shown that a k inase-deleted form of ActRIIb (dnActRIIb) suppressed both activin- and BMP- like signaling pathways. These results suggest that ActRIIb at least has du al roles in both activin and BMP signaling pathways during zebrafish embryo genesis.