Bone morphogenetic protein 4 (BMP-4) induces ventral mesoderm but represses dorsal mesoderm formation in Xenopus embryos. We show that BMP-4 inhibits two signaling pathways regulating dorsal mesoderm formation, the induction of dorsal mesoderm (Spemann organizer) and the dorsalization of ventral mesoderm. Ectopic expression of BMP-4 RNA reduces goosecoid and forkhead-l transcription in whole embryos and in activin-treated animal cap explants. Embryos and animal caps overexpressing BMP-4 transcribe high levels of genes expressed in ventral mesoderm (Xbra,

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