LOCALIZED BMP-4 MEDIATES DORSAL-VENTRAL PATTERNING IN THE EARLY XENOPUS EMBRYO

Mesoderm is initially induced in the amphibian embryo by events that o ccur in the early cleavage stage midblastula transition (MBT) and morp hogenesis. These inductive interactions establish the mesoderm at the equator and create a distinction between the dorsal and the ventral re gions. After the MBT, zygotic factors pattern the mesoderm and induce the neuroectoderm on the dorsal side of the embryo. Most previous stud ies have focused on the effects of signals originating in the dorsal m esoderm. We show that BMP-4 transcripts are localized to the ventral s ide of the gastrula embryo and provide evidence that localized express ion of BMP-4 is important for regulating the expression of mesodermal and neural genes. We show that ectopic expression of BMP-4 inhibits th e formation of dorsal and lateral mesoderm and reduces the size of the neural plate. Elimination of BMP-4 signaling with a dominant-negative BMP receptor expands the lateral mesoderm and neural plate without ex panding the expression of genes along the dorsal midline. These result s suggest that BMP-4 may act to oppose the action of dorsalizing signa ls and neural-inducing signals that originate in the dorsal organizer region. We suggest that BMP-4 may have an analogous role to the Drosop hila gene, dpp, in dorsal/ventral pattern formation. (C) 1995 Academic Press, Inc.