Figure 1.

Molecular components and pathways of BMP signaling. The BMP signaling is initiated by the binding of BMP ligands to BMPR1 and BMPR2. In the canonical pathway, BMP receptors phosphorylate Smad1/5/8, which can bind to Co-Smad4 and are translocated to the nucleus to regulate the expression of target genes. In the non-canonical pathways, BMP receptors activate non-Smad pathways. Termination of BMP signaling is achieved by noggin, Smad6, and/or Smad7. BMP: bone morphogenic protein; BMPR: BMP receptor