FIGURE 7.

BMP signaling pathway in mouse and zebrafish. BMP proteins bind as dimers to a transmembrane receptor complex, formed by BMPR-I and BMPR-II. Through this binding, which can be blocked by extracellular inhibitors like Noggin, a phosphorylation cascade is initiated leading to the phosphorylation of the Smad1/5/8 proteins. The activated Smad1/5/8 forms a complex with Smad4 which interacts in the nucleus with specific co-factors to bind to the regulatory sequences of downstream genes, such as id1. BMP, bone morphogenetic protein; BMPR, BMP receptor; id1, inhibitor of DNA binding 1.