Growth factor of the TGF-beta superfamily that plays essential roles in many developmental processes including cartilage and bone formation (By similarity). Also plays an important role in the regulation of iron metabolism by acting as a ligand for hemojuvelin/HJV (By similarity). Initiates the canonical BMP signaling cascade by associating with type I receptor ACVR1 and type II receptor ACVR2B. 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. Can also signal through non-canonical pathway such as TAZ-Hippo signaling cascade to modulate VEGF signaling by regulating VEGFR2 expression (By similarity). Interacts with SOSTDC1 (By similarity). Interacts (when glycosylated) with type I receptor ACVR1. Interacts with type II receptor ACVR2B (By similarity). Interacts with Hemojuvelin/HJV (By similarity). Belongs to the TGF-beta family.