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. 2019 Aug 2;39(8):BSR20190377. doi: 10.1042/BSR20190377

Figure 1. Schematic diagram of the BMP/Activin A signaling network in normal and FOP patients.

Figure 1

BMP signals via the BMP type I receptor ALK2, inducing phosphorylation of Smad1/5, whereas Activin A induces the phosphorylation of Smad2/3 via ALK4/7. It also binds to ALK2, but it does not activate Smad1/5 phosphorylation and inhibits BMP signaling. BMP and Activin A share type II receptors (ACVR2A, ACVR2B). However, in FOP, Activin A leads to activation of Smad1/5 phosphorylation via mutant ALK2 and triggers HO formation. The star: classic mutation site of ALK2 R206H. Abbreviation: P, phosphorylation.