Activins are homodimers or heterodimers of the different B subunit isoforms， part of the TGFB family. Mature Activin A has two 116 amino acids residues BA subunits （BA-BA）. Activin displays an extensive variety of biological activities， including mesoderm induction， neural cell differentiation， bone remodelling， haematopoiesis， and reproductive physiology. Activins takes part in the production and regulation of hormones such as FSH， LH， GnRH and ACTH. Cells that are identified to express Activin A include fibroblasts， endothelial cells， hepatocytes， vascular smooth muscle cells， macrophages， keratinocytes， osteoclasts， bone marrow monocytes， prostatic epithelium， neurons， chondrocytes， osteoblasts， Leydig cells， Sertoli cells， and ovarian granulosa cells.
