Growth factor of the TGF-beta superfamily that plays important role in various biological processes, including embryogenesis, hematopoiesis, neurogenesis and skeletal morphogenesis. Initiates the canonical BMP signaling cascade by associating with type I receptor ACVR1 and type II receptor ACVR2A. Once all three components are bound together in a complex at the cell surface, ACVR2A phosphorylates and activates ACVR1. In turn, ACVR1 propagates signal by phosphorylating SMAD1/5/8 that travel to the nucleus and act as activators and repressors of transcription of target genes. Homodimer; disulfide-linked. Interacts with twsg1. Belongs to the TGF-beta family.