STUDIES WITH A XENOPUS BMP RECEPTOR SUGGEST THAT VENTRAL MESODERM-INDUCING SIGNALS OVERRIDE DORSAL SIGNALS IN-VIVO

We report the isolation of a Xenopus BMP receptor that is expressed ma ternally in the appropriate location to play a role in mesoderm induct ion. This receptor binds both BMP-2 and BMP-4 with high affinity. A tr uncated form of this BMP receptor specifically blocks BMP-4 signaling. Expression of this truncated BMP receptor during embryogenesis conver ts ventral mesoderm to dorsal mesoderm. Contrary to the popularly held view that ventral is the ground state for all mesoderm, our results s uggest that formation of ventral mesoderm requires an active signal an d that, in the absence of this ventral signal, dorsal mesoderm is form ed.