Schematic of TGFβ family signaling. (a) TGFβ and Activin form one subfamily that have separate receptors and antagonists, but common 2nd messenger Smads. (b) BMPs form a second subfamily with their own receptors and antagonists, as well as a different set of 2nd messengers. All receptor Smads dimerize with the common Smad (Smad4) and the complex translocates to the nucleus to alter gene transcription. MSTN, myostatin; LAP, latency protein; FST, follistatin; FSTL3, follistatin like-3; ALK, activin like kinase.