Follistatin

Its primary function is the binding and bioneutralization of members of the TGF-β superfamily, with a particular focus on activin, a paracrine hormone. An earlier name for the same protein was FSH-suppressing protein (FSP). At the time of its initial isolation from follicular fluid, it was found to inhibit the anterior pituitary's secretion of follicle-stimulating hormone (FSH). Three isoforms, FS-288, FS-300, and FS-315 have been reported. Two, FS-288 and FS-315, are created by alternative splicing of the primary mRNA transcript. FS-300 (porcine follistatin) is thought to be the product of posttranslational modification via truncation of the C-terminal domain from the primary amino-acid chain. Although FS is ubiquitous, its highest concentration is in the female ovary, followed by the skin. Follistatin is produced by folliculostellate (FS) cells of the anterior pituitary.