Activin Receptor Type IB antibody

Activin, a disulfide-linked homodimeric protein is secreted by Sertoli cells in the testis and granulosa cells in the ovary. In early studies, this peptide was thought to be an inhibin and not recognized as a unique compound. Activins and inhibins are members of the TGF-beta superfamily due to amino acid homology with respect to the conservation of 7 of the 9 cysteine residues common to all TGF-beta forms. Activins are homodimers or heterodimers of the various beta subunit isoforms, while inhibins are heterodimers of a unique alpha subunit and one of the various beta subunits. Five beta subunits have been cloned (mammalian betaA, betaB, betaC, betaE, and Xenopus betaD). The activin/inhibin nomenclature reflects the subunit composition of the proteins: activin A (betaA-betaA), activin B (betaB-betaB), activin AB (betaB-betaA), inhibin A (alpha-betaA), and inhibin B (alpha- betaB). Activins have a wide range of biological activities including mesoderm induction, neural cell differentiation, bone remodeling, hematopoiesis, and reproductive physiology. Activins are also involved in growth and differentiation of several tissues from different species. This protein also plays a key role in the production and regulation of hormones such as FSH, LH, GnRH, and ACTH. Activin influences erythropoiesis and the potentiation of erythroid colony formation, oxytocin secretion, paracrine, and autocrine regulation. Similar to other TGF-beta family members, activins exert their biological activities through the effects ot the heterodimeric complex composed of two membrane spanning serine-threonine kinases designated type I and type receptors. Activin type I and type II receptors are distinguished by the level of sequence homology of their kinase domains and other structural and functional features. To date, seven type I and five type II activin receptors have been cloned from mammals, including activin receptor IA, activin receptor IIA, activin receptor IB, and activin receptor IIB. In addition, two splice variants of activin receptor IIA and five splice variants of activin receptor IIB have been reported. Type I activin receptors are highly conserved and do not bind directly to activin but will associate with the type II receptor-activin complex and initiate signal transduction. Type I activin receptors will also bind with the BMP-2/7-bound BMPR-II and form signaling complexes. Human, mouse, and bovine type IB activin receptors share greater than 98 % homology.