Follistatin also known as activin-binding protein is a protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 that in humans is encoded by the FST gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

. Follistatin is an autocrine glycoprotein

Glycoprotein

Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...

 that is expressed in nearly all tissues of higher animals.

Its primary function is the binding and bioneutralization of members of the TGF-β superfamily

Transforming growth factor beta superfamily

The transforming growth factor beta superfamily is a large family of structurally related cell regulatory proteins that was named after its first member, TGF-β1, originally described in 1983....

, with a particular focus on activin

Activin and inhibin

Activin and inhibin are two closely related protein complexes that have almost directly opposite biological effects. Activin enhances FSH biosynthesis and secretion, and participates in the regulation of the menstrual cycle...

, a paracrine hormone.

An earlier name for the same protein was FSH-suppressing protein (FSP).