Fruit fly (Drosophila melanogaster) ovaries contains two set of germline stem cells surrounded by a group of highly differentiated somatic cells that express genes for two phenotypes (hedgehog & wingless). The TGF beta super family member, decpentaplegic (dpp) or its homologue BMP2/4 is specifically required for maintenance and promote its cell division in the female germline (1, 2). The Signaling by TGF beta-related factors requires ligand-induced association between type I and type II transmembrane receptors that have endogenous serine/threonine kinases activity. In Drosophila, thickveins (tkv) and saxophone (sax) genes encode type I receptors that mediate signaling by decapentaplegic (dpp), a member of the bone morphogenetic protein (BMP) subgroup of TGF beta-type factors. Patterning the dorsal surface of fruitfly blastoderm embryo requires Decapentaplegic (Dpp) and Screw (Scw), two BMP family members. The signaling by these ligands is mediated by Bone morphogenentic protein (BMP) binding proteins Sog and Tsg. It is demonstrated that Tsg and Sog play essential role in transport of heterodimer Dpp/Sog signaling through the two type I BMP receptors Tkv and SAX (3). Over expression or mutation in dpp suppress germline stem cell differentiation. Dpp actions are mediated by its receptor Saxophone. The Saxophone gene is expressed ubiquitously. The Saxophone gene also gives two products Brk43E and Berk25 and both gene products inter acts with TGF super family peptide ligands Dpp. Mutations that completely abolish Saxophone activity causes phenotype that are similar to partial or complete loss of activity of the dpp ligand. The saxophone products are also have serine threonine kinase activity responsible for phsosphorylation and activation of the ligands including pMAD, Screw (Scw), and short gastrulation protein (Sog).
|