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Application notes
(see key)
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Recommended dilutions
ELISA: Use at a concentration of 0.5 - 1.0 µg/ml.
IHC-P: Use at a concentration of 15 µg/ml.
Neut: Used at a concentration of 1 - 3 µg/ml, the antibody will block 50 % of the binding of 30 ng/ml recombinant human activin A to immobilized recombinant human activin receptor type II/Fc chimera (100 µl of a 0.5 µg/ml solution coating each well) in a functional ELISA assay.
WB: Use at a concentration of 0.1 - 0.2 µg/ml. Detects human Activin Receptor type II at approximately 5 ng/lane under reducing and non-reducing conditions. Predicted molecular weight: 58 kDa.
Not tested in other applications.
Optimal dilutions/concentrations should be determined by the end user.
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Relevance
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Activins are dimeric growth and differentiation factors which belong to the transforming growth factor-beta (TGF-beta) superfamily of structurally related signaling proteins. Activins signal through a heteromeric complex of receptor serine kinases which include at least two type I (I and IB) and two type II (II and IIB) receptors. These receptors are all transmembrane proteins, composed of a ligand-binding extracellular domain with cysteine-rich region, a transmembrane domain, and a cytoplasmic domain with predicted serine/threonine specificity. Type I receptors are essential for signaling; and type II receptors are required for binding ligands and for expression of type I receptors. Type I and II receptors form a stable complex after ligand binding, resulting in phosphorylation of type I receptors by type II receptors. Type II receptors are considered to be constitutively active kinases. Activin has been suggested to be an autocrine/paracrine regulator in the human placenta. The presence of ACVR2 mRNA has been deomnstrated in human trophoblast cells and there is also evidence of expression of the gene in human brain and ovary.
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.
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