Follistatin (FST) is a secreted, cysteine-rich glycoprotein that acts as a high-affinity ligand trap rather than a receptor antagonist. Two follistatin molecules wrap around a TGF-beta family ligand dimer and physically occlude both the type I and type II receptor interfaces, neutralising activin A, myostatin and several BMPs.
Isoforms and why they differ
Alternative splicing and proteolysis give three commonly cited forms. FST-288 carries a heparan-sulfate-binding motif and stays bound to the cell surface, so its action is local. FST-315 is the dominant circulating form. FST-344 is the primary translation product, processed to FST-315. A vendor listing of "follistatin-344" therefore describes the precursor construct, and the distinction matters for any experiment where tissue localisation is a variable.
Research context
Rodent work reported substantial increases in muscle mass with follistatin overexpression, and follistatin gene-transfer studies have been run in muscular dystrophy models and small human trials. As with direct myostatin blockade, lean-mass changes have been reported more consistently than functional gains. Follistatin proteins are supplied as recombinant research reagents; they are not stable to gastric passage and are not approved for any human use.
Related terms and material
activin receptor · recombinant · research use only. Reference material: Follistatin-344, IGF & muscle peptides. Further reading: what is follistatin-344.