Fig. 1.

The BMP signal is transduced through BMPRI and BMPRII receptors. These two receptors are combined into a functional complex, to initiate further signaling pathways. On the one hand, activated BMP type I receptor phosphorylates Smad-dependent signaling pathways. On the other hand, BMP receptors activate non-Smad-dependent signaling pathways, that is, activate p38 MAPK, JNK, and ERK signaling pathways. Then, BMP can stimulate the expression of three osteogenic main transcription factors Runx2, D1x5 and Osx. Reproduced from Ref. [65] with permission.