BMP-3, also known as Osteogenin, is a homodimeric cytokine and the most abundant bone morphogenetic protein in adult bone. The role of BMP-3 in bone is complex. It inhibits alkaline phosphatase production and induction of osteoblastic target genes in undifferentiated mesenchymal and osteogenic cell lines that have been treated with BMP-2. BMP-3 also induces the expression of TGF-beta/Activin responsive genes but not BMP-responsive genes. Since the inhibitory effect is not due to direct competition with osteogenic BMPs, BMP-3 may activate signaling through an Activin pathway, resulting in antagonism of osteogenesis induced by other BMPs. In addition, BMP-3 dorsalizes Xenopus embryos, the opposite effect of BMP-2 or 4, which cause ventralization.