Die Entwicklung der mehrkernigen, glatten Muskeln von Drosophila melanogaster - Die Fusion der Testes-relevanten Myoblasten ist abhängig von Arp2/3-gesteuerter Aktin-Polymerisation

The five inner male reproductive organs are surrounded by muscle sheaths. There are three different types of muscles, two of which are multinuclear. The formation of the multinuclear, smooth muscles of the testes is mediated by fusion of FC- and FCM-like cells and requires the function of members of the immunglobulin family. In this study, further proteins that could be involved in the development of this muscle sheath were investigated. The myoblasts on the genital disc are precursors of the different muscle sheaths and can be isolated specifically to obtain RNA. RT-PCR results revealed genes to be transcribed in those myoblasts that could be involved in the differentiation of the muscle precursor cells. Additionally, transcripts of regulators of the branched F-actin polymerisation were detectable. RNAi-mediated knock-down revealed that those regulators are required for fusion of myoblasts but not for the migration of myotubes onto the testes. In contrast, knock-down of non-muscle myosin II or two cadherins resulted in defective myotube migration. In addition, loss of cadherins appears to prevent theattachment of muscles to each other to form a continuous muscle sheath. Another focus of this study was the identification of further components that regulate fusion of myoblasts in time and space. Transcripts of Notch and several target genes were detectable in testes myoblasts. Notch, Delta and Cut, as a marker for active Notch-signalling could be visualized in situ. The activity of the Notch pathway is required for efficient fusion. The presented data led to the hypothesis, that the activity of the Notch pathway regulates fusion and cooperation with the Wnt pathway can be postulated.