TRUNCATED TYPE-II RECEPTOR FOR BMP-4 INDUCES SECONDARY AXIAL STRUCTURES IN XENOPUS EMBRYOS

BRK-3 is a vertebrate type II receptor for BMP-4 distantly related to invertebrate type II receptors for BMP-2/BMP-4/dpp, such as daf-d, and punt. BRK-3 has a long carboxy-terminal sequence following intracellu lar kinase domain and is capable of forming a high-affinity complex wi th a type I receptor, BRK-2. To examine the role of BRK-2 + BRK-3 rece ptor complex in BMP signaling during early embryogenesis, the dominant -negative form of BRK-3 was ectopically expressed in the Xenopus embry os. A secondary body axis expressing the Sonic hedgehog and N-CAM gene s is induced by injecting mRNA encoding truncated form of BRK-3 into v entral marginal region, implicating the BMP signaling in axial mesoder m induction. Formation of the secondary axis depends on whether the de letion extends into the kinase domain, not into the carboxy-terminal t ail, suggesting that the kinase domain, but not the tail region, is es sential for BMP signaling. (C) 1995 Academic Press, Inc.