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Follistatin: A broadly distributed protein that binds directly to ACTIVINS. It functions as an activin antagonist, inhibits FOLLICLE STIMULATING HORMONE secretion, regulates CELL DIFFERENTIATION, and plays an important role in embryogenesis. Follistatin is a single glycosylated polypeptide chain of approximately 37-kDa and is not a member of the inhibin family (INHIBINS). Follistatin also binds and neutralizes many members of the TRANSFORMING GROWTH FACTOR BETA family.Activins: Activins are produced in the pituitary, gonads, and other tissues. By acting locally, they stimulate pituitary FSH secretion and have diverse effects on cell differentiation and embryonic development. Activins are glycoproteins that are hetero- or homodimers of INHIBIN-BETA SUBUNITS.Inhibin-beta Subunits: They are glycopeptides and subunits in INHIBINS and ACTIVINS. Inhibins and activins belong to the transforming growth factor beta superfamily.Inhibins: Glycoproteins that inhibit pituitary FOLLICLE STIMULATING HORMONE secretion. Inhibins are secreted by the Sertoli cells of the testes, the granulosa cells of the ovarian follicles, the placenta, and other tissues. Inhibins and ACTIVINS are modulators of FOLLICLE STIMULATING HORMONE secretions; both groups belong to the TGF-beta superfamily, as the TRANSFORMING GROWTH FACTOR BETA. Inhibins consist of a disulfide-linked heterodimer with a unique alpha linked to either a beta A or a beta B subunit to form inhibin A or inhibin B, respectivelyFollistatin-Related Proteins: Broadly distributed glycoproteins that are homologous to the activin-binding protein, FOLLISTATIN. These follistatin-related proteins are encoded by a number of genes.Activin Receptors: Receptors for ACTIVINS are membrane protein kinases belonging to the family of PROTEIN-SERINE-THREONINE KINASES, thus also named activin receptor-like kinases (ALK's). Activin receptors also bind TRANSFORMING GROWTH FACTOR BETA. As those transmembrane receptors of the TGF-beta superfamily (RECEPTORS, TRANSFORMING GROWTH FACTOR BETA), ALK's consist of two different but related protein kinases, Type I and Type II. Activins initiate cellular signal transduction by first binding to the type II receptors (ACTIVIN RECEPTORS, TYPE II ) which then recruit and phosphorylate the type I receptors (ACTIVIN RECEPTORS, TYPE I ) with subsequent activation of the type I kinase activity.Myostatin: A growth differentiation factor that is a potent inhibitor of SKELETAL MUSCLE growth. It may play a role in the regulation of MYOGENESIS and in muscle maintenance during adulthood.Glycoproteins: Conjugated protein-carbohydrate compounds including mucins, mucoid, and amyloid glycoproteins.Activin Receptors, Type II: One of the two types of ACTIVIN RECEPTORS. They are membrane protein kinases belonging to the family of PROTEIN-SERINE-THREONINE KINASES. The major type II activin receptors are ActR-IIA and ActR-IIB.Bone Morphogenetic Proteins: Bone-growth regulatory factors that are members of the transforming growth factor-beta superfamily of proteins. They are synthesized as large precursor molecules which are cleaved by proteolytic enzymes. The active form can consist of a dimer of two identical proteins or a heterodimer of two related bone morphogenetic proteins.Yeast, Dried: The dry cells of any suitable strain of SACCHAROMYCES CEREVISIAE or CANDIDA. It can be obtained as a by-product from the brewing of beer or by growing on media not suitable for beer production. Dried yeast serves as a source of protein and VITAMIN B COMPLEX.Follicle Stimulating Hormone: A major gonadotropin secreted by the adenohypophysis (PITUITARY GLAND, ANTERIOR). Follicle-stimulating hormone stimulates GAMETOGENESIS and the supporting cells such as the ovarian GRANULOSA CELLS, the testicular SERTOLI CELLS, and LEYDIG CELLS. FSH consists of two noncovalently linked subunits, alpha and beta. Within a species, the alpha subunit is common in the three pituitary glycoprotein hormones (TSH, LH, and FSH), but the beta subunit is unique and confers its biological specificity.Growth Substances: Signal molecules that are involved in the control of cell growth and differentiation.Granulosa Cells: Supporting cells for the developing female gamete in the OVARY. They are derived from the coelomic epithelial cells of the gonadal ridge. Granulosa cells form a single layer around the OOCYTE in the primordial ovarian follicle and advance to form a multilayered cumulus oophorus surrounding the OVUM in the Graafian follicle. The major functions of granulosa cells include the production of steroids and LH receptors (RECEPTORS, LH).Bone Morphogenetic Protein 7: A bone morphogenetic protein that is widely expressed during EMBRYONIC DEVELOPMENT. It is both a potent osteogenic factor and a specific regulator of nephrogenesis.