A protein first isolated from the culture fluid of Xenopus cell lines. Activin is a member of the transforming growth factor-β (q.v.) family of intercellular signaling molecules. It acts as a diffusible morphogen for mesodermal structures, and the type of differentiation is determined by the concentration of actin (i.e., high concentrations produce head structures, low concentrations tail structures).
Subjects: Medicine and health