Die Myoblastenfusion zur Entstehung der glatten Testismuskulatur ist abhängig von Duf und Rst wobei die embryonale Myogenese unabhängig von Argininkinase abläuft

The larval musculature of Drosophila arises by heterotypic fusion of myoblasts. A signaling cascade is activated by adhesion of fusing cells and leads to actin rearrangements as well as membrane break down. For this process, an extensive amount of energy must be provided in a short time. It was assumed that arginine kinase (Argk) supports the energy supply of myoblast fusion. It was demonstrated in the course of this thesis that Argk is expressed in embryonic musculature during myoblast fusion and colocalizes partially with mitochondria. Yet, analyses of deletion lines, ectopically expressed protein variants as well as localization studies indicate that Argk does not fulfill an essential function in embryonic myoblast fusion. During metamorphosis, further processes of myogenesis occur. The larval musculature is replaced by adult muscles e.g. leg and flight muscles. The musculature of the female and male reproductive tract is newly formed. In the course of this thesis, the musculature of the male reproductive tract was analyzed particularly with regard to the development of the testis musculature. The inner organs of the male reproductive tract are encircled by muscle sheaths with different properties. The muscle sheaths of the testes differ from all other muscles previously described in Drosophila: smooth, multinuclear muscle fibers enclose the organ entirely. It was demonstrated that the testis myoblasts are located on the genital disc at the beginning of metamorphosis, amplify and fuse before migrating as multinuclear nascent myotubes onto the testes. The adhesion molecules Dumbfounded (Duf) and Roughest (Rst), assuring adhesion of myoblasts in embryonic myogenesis, are involved in fusion of the testis myoblasts as well. In a knock-down of duf, rst and duf + rst together mediated by RNA interference, testis muscles with fewer nuclei than the wild type are developing. Filament arrangement and migration of the nascent myotubes from genital disc onto the testes are not affected. Despite reduced fusion efficiency, the adult male reproductive tracts do not differ from the wild type. Therefore, it is postulated that reduced fusion rates are compensated specifically in the testis muscles.