Human body is made up of various atoms and molecules, some of the molecules are very important in the process of development. Some of these development molecules include: activin, Cerberus, chordin, epimorphin, inhibin, notch, noggin, Indian hedgehog and hepatic growth factor among others. This paper is however aimed at describing activin and chordin technically as two important development molecules (Chang, p. 423).
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Activin is a TGF-beta family member and is a disulfide linked dimeric protein that is purified originally from the gonadal fluid as a protein stimulating the release of a pituitary follicle stimulating hormone. Activin has a vast range of activities termed biological. These include neural cell differentiation, mesoderm induction, hematopoiesis, bone remodeling and distinct roles in the reproductive physiology. This molecule exert its biological impacts through binding to the type 1 heteromeric complex and type 11 serine threonine kinase receptor. Both of these complexes are very essential in signal transduction (Browder, p. 98).
Activins are heterodimers and homodiners of different beta sub-units of isoforms. Its nomenclature has sub-units of protein composition reflected in it. They are represented as: Actvin AB, Activin B and Activin A. As member of TGF-beta family of molecules, activin is synthesized like a large precursor which has a pro-domain of the variable size, signal sequence and the mature C-terminal segment ranging from 110 to 140 in length of amino acids. The activin’s basic structure is a disulfide linked dimer which is composed of a beta chain and an alpha chain. The molecule is however described as a homodimer due to the fact that dimmers consist of two similar gene beta types of sub-units (Wittbrod, p. 241).
Activin, initially identified as a beta A beta A is potentiates the differentiation and proliferation of the erythroid progenitors. Recent studies show that the sub-units of beta A in Activin presence is confirmed via the bioassay with or without jamming antiserum against an activin binding protein. The activin production in the monocytes is actually stimulated by treatment more than nine fold with the granulocyte macrophage colony that is a stimulating factor. The activin expression in a marrow stromal cells is however regulated by the incubation with the necrosis factor of the tumor and the interleukin 1 alpha. I would therefore suggest that the production of activin locally within the bone marrow in the microenvironment may tune the regulation of the steady hematopoiesis state. Nevertherless, the factor may be produced at low levels though under specified situations which may be induced further to give vital biological functions (Carlson, p. 210).
Activins has vital biological functions, they are implicated in various processes. The processes include osteogenesis, embryogenesis, reproductive physiology and hematopoiesis. Despite the fact that activin induces the proliferation of the cells like fibroblasts and CFU-E, it induces in plasmacytoma cells the apoptosis and inhibits as well the proliferation of the hepatocytes. Activin is therefore a mesoderm inducing factor. Activin circulate freely in rare occasions. In both extra vascular fluid and blood, the dimer is complex to the binding proteins: 32-40kDa Follistatin and 725 kDa alpha2-macroglobulin (Slack, p. 335).
On the other hand, chordin is a secreted glycoprotein regulating dorsoventral patterning during the gastrulation. The molecule chordon functions like a bone morphogenetic protein that blocks the bone morphogenetic protein ventralizing activity via binding to the bone morphogenetic protein and inhibits their interaction with the receptors. The chordin molecule has a cysteine rich repeats that is composed of conserved domains that are present in the expanding family of the secreted molecules. The motifs directly mediate the bone morphogenetic protein antagonism signaling by the chordin molecule and play a vital role in the development. Chordin induces secondary axes after the mRNA injection in the Xenopus embryos. During late gastrulation, chordin presents contemporary and distinct patterns of expression in the mouse. Chordin expression is however restricted to the midline and node mesendoderm. Chordin was isolated by using immobilized monoclonal antibodies from cell extracts of the giant sturgeon notochord (Chang, p. 453).
The preparation of the purified chordin contains 60% of carbohydrates and 40% of protein. The predominant polar amino acids are serine, threonine, glycine, glutamine and asparagines. The treatment of the chordin with the enroglycosidases is hydrolyzing the chains of carbohydrate proteoglycans and this does not affect the antigenic chordin properties and it’s on gel filtration behavior. Chordin is related to glycoprotein that carries O-glycosidic carbohydrate peptide bonds that exists between the residues of beta-hydroxyamino acids and the N-acetyl-galactosamine. Chordin contains a N-glycosylamide carbohydrate peptide bond just as can be judged from the formation of the glucosaminite after the treatment of antigen with the alkaline LiHB4 (Carlson, p. 214).
Chordin is a molecule with a vital embryonic role of self regulation. It has a convoluted mechanism of the action. The molecule has four cysteine rich domain serving as the bone morphogenetic protein that binds various extracellular proteins. Chordin actually forms a diffusible ternary complex that may not bind all the bone morphogenetic proteins. The activities of the chordin are regulated by the tolloids. They regulate the molecule’s activity by cleaving them to two distinct sites. The factors originating from the Spemann’s organizer chordin is a bone morphogenic protein antagonist. Most of the chordin secreted antagonist work through binding to the growth factors within the extracellular space and this prevents them from binding to the receptors of the membrane (Slack, p. 342).
Chordin is a breast tumor novel factor just like CHL2. It is a glycoprotein that is secreted and has vital homology to the chordin and acts just like TGF-beta family antagonist. It also influences the type of the TGF-beta family bound member. The patterns in human tissue expression blots show different patterns of such expression than it is in mouse (Wittbrod, p. 234).
In summary, Activin is a TGF-beta family member and is a disulfide linked dimeric protein that is purified originally from the gonadal fluid as a protein stimulating the release of a pituitary follicle stimulating hormone. It has a vast range of activities termed biological. On the other hand, chordin is a secreted glycoprotein regulating dorsoventral patterning during the gastrulation. The molecule chordon functions like a bone morphogenetic protein that blocks the bone morphogenetic protein ventralizing activity via binding to the bone morphogenetic protein and inhibits their interaction with the receptors (Browder, p. 100).
- Browder, Levin. Embryonic Induction during Vertebrate Development: Boston, McGraw Hill 1997. Print.
- Carlson, Bob. Patten’s Foundations of Embryology (6th Edition). McGraw-Hill, Inc., New York. 1996. Print.
- Chang, Wilson. Xenopus type 1 activin receptor mediates mesodermal but not neural specification during embryogenesis: London, John Willey and Sons. 1997. Print.
- Slack, John. The nature of the mesoderm-inducing signal in Xenopus: New York, Springer. 1991. Print.
- Wittbrod, Rosa. Disruption of mesoderm and axis formation in fish by ectopic expression of activin variants: London, Elsevier. 1992. Print.