Follistatin/FST Protein, Mouse (HEK293, His)

Follistatin is first described as a follicle-stimulating hormone inhibiting substance present in ovarian follicular fluid. Follistatin binds activin A and myostatin with low nanomolar (nM) affinity, completely surrounds the ligand occluding all of the receptor binding sites and binds to the ligand^[1][2].
Mature human Follistatin shares 97% amino acid sequence identity with mouse and rat Follistatin.
Follistatin is a 32-35-kDa glycoprotein composed of four domains including an N-terminal domain (ND) followed by three Follistatin domains (FSD1, FSD2, and FSD3). C-terminal splicing of Follistatin can occur to generate various isoforms including FS288 and FS315. Follistatin neutralizes the TGFβ ligands, myostatin and activin A, by forming a nearly irreversible non-signaling complex by surrounding the ligand and preventing interaction with TGFβ receptors. In humans, the gene encoding Follistatin is located on chromosome 5q11.2. The Follistatin protein contains a TGF-β binding site where activins, bone morphonegic proteins (BMPs) and growth differentiation factors (GDFs) are bound with high affinity and thereby neutralised. The ligand binding site for Follistatin overlaps with the type I and type II receptor binding sites for these ligands. Follistatin also contains a heparin binding site where proteoglycans in the extracellular matrix can bind, and therefore Follistatin is believed to bind the extracellular matrix. There are two major isoforms of Follistatin, FST288, which is anchored to the cell surface by interactions with heparin sulfate proteoglycans, and FST315, which is the predominant form found in circulation. The two isoforms arise from alternative splicing; the 315 isoform includes a 27 amino acid acidic C-terminal tail, which Follistatin 288 does not have. The acidic tail on Follistatin 315 neutralises the heparin binding site, thereby inhibiting the binding of Follistatin 315 to the extracellular matrix^[1][2][3].
Follistatin as a liver-derived protein under the regulation of glucagon-to-insulin ratio suggests a relation to energy metabolism. In humans, aberrant expression of FST and activins are implicated in infertility. Follistatin is a potent tissue regulator in the gonad, pituitary gland, pregnancy membranes, vasculature, and liver^[1][3].

Recombinant mouse Follistatin (.2 μg/mL; 1-48 hours) significantly inhibits P21 mRNA expression, and increases Pcna and Cyclin D2 mRNA expression in CD49f positive cells (CD49f⁺ cells) isolated from male murine salivary glands^[4].

Recombinant mouse Follistatin (.5-1 μg; four does) is administered intranasally (5 μL) 1 h before each challenge in ovalbumin-sensitized BALB/c mice. Follistatin inhibits the allergen-specific Th2 immune response in mediastinal lymph nodes and mucus production in the lung^[5].