F'ollistatin is fascinating protein that can increase muscle mass beyond natural potential by suppressing myostatin. Scientists first identified f'ollistatin while examining porcine (re: pig) follicular fluid in the ovaries. F'ollistatin is naturally found in the skeletal muscle of almost all mammals with advanced or developed characteristics, such as humans, rodents, and cows. F'ollistatin is high in the non-essential amino acid cystine but unlike most proteins discussed in the fitness world, f'ollistatin has carbohydrates attached to it.

F'ollistatin, specifically F'ollistatin 344 (FS344), quickly gained popularity in the bodybuilding community as a potential supplement to rapidly increase lean tissue mass. Another protein, f'ollistatin-related gene (FLRG) acts on similar pathways as FS344 regarding its muscle building properties. Increased lean tissue mass could give a bodybuilder an advantage in a competitive setting and be the differentiating factor between first and second place.

F'ollistatin (FS) was initially identified as a follicle-stimulating hormone inhibiting substance found in ovarian follicular fluid. FS is a high-affinity activin-binding protein that can act as an activin antagonist. Two alternatively spliced f'ollistatin mRNAs exist, encoding mature FS with 288 amino acid (aa) residues (FS-288) and 315 aa residues (FS-315). Natural FS purified from porcine ovaries is primarily a carboxy-terminal truncated form of FS-315 composed of 300 aa residues.

F'ollistatin is a single-chain gonadal protein that specifically inhibits follicle-stimulating hormone release. The single FST gene encodes two isoforms, FST317 and FST344 containing 317 and 344 amino acids respectively, resulting from alternative splicing of the precursor mRNA. In a study in which 37 candidate genes were tested for linkage and association with polycystic ovary syndrome (PCOS) or hyperandrogenemia in 150 families, evidence was found for linkage between PCOS and f'ollistatin. F'ollistatin binds directly to activin and functions as an activin antagonist. specific inhibitor of the biosynthesis and secretion of pituitary follicle stimulating hormone (fsh).

F'ollistatin (FST) is a secreted glycoprotein that was first identified as a follicle?stimulating hormone inhibiting substance in ovarian follicular fluid (1, 2). Human F'ollistatin cDNA encodes a 344 amino acid (aa) protein with a 29 aa signal sequence, an N terminal atypical TGF binding domain, three F'ollistatin domains that contain EGF?like and kazal?like motifs, and a highly acidic Cterminal tail. F'ollistatin is a secreted protein that binds to ligands of the TGF-Beta family and regulates their activity by inhibiting their access to signaling receptors. It was originally discovered as activin antagonists whose activity suppresses expression and secretion of the pituitary hormone FSH (follicle stimulating hormone). In addition to being a natural antagonist, f'ollistatin can inhibit the activity of other TGF-Beta ligands including BMP-2,-4,-6,-7, Myostatin, GDF-11, and TGF-Beta1. F'ollistatin is expressed in the pituitary, ovaries, decidual cells of the endometrium, and in some other tissues. Recombinant human F'ollistatin 315 is a 34.7 kDa protein containing amino acids 30-344 of the FST-344 protein.