Follistatin-344 Follistatin (also known as activin-binding protein) is an autocrine glycoprotein encoded by the FST gene that is expressed in nearly all tissues. Its primary function in the body is bioneutralization of members of the TGF-β superfamily, with a particular focus on activin and paracrine hormones. Follistatin is a potent Moystatin inhibitor. An original Follistatin acted also as an activin inhibitor, which on the other hand stimulates the secretion of follicle-stimulating hormone – FSH (activin regulates the growth and differentiation of all cell types, including cells within sexual glands, pituitary gland and skeletal muscles). Therefore, scientists developed a particular Follistatin (Follisttain-344) that is derived from the original one and that is capable of blocking preferentially Moystatin activity.