BMP4 is a secreted ligand of the TGF-beta (transforming growth factor-beta) superfamily of proteins. BMP4 plays a crucial role in regulating bone and cartilage development. BMP4 is primarily located in the extracellular matrix and is secreted by various cell types, where BMP4 interacts with specific receptors to initiate signaling pathways that lead to cellular differentiation and tissue formation. BMP4 is involved in activating the Smad signaling pathway, which is essential for mediating BMP effects on gene expression. BMP4′s ability to induce cartilage and bone formation highlights BMP4′s importance in developmental biology and regenerative medicine, making BMP4 a significant target for research into skeletal disorders and tissue engineering applications.