In der Myogenese von Drosophila melanogaster interagiert Rolling pebbles 7 in den Z-Scheiben der Sarkomere mit α-Aktinin und D-Titin/Kettin/Zormin, in der terminalen Z-Scheibe kolokalisiert es zudem mit Dumbfounded/Kirre

The Rols7 protein has an essential function for myoblast fusion during the embryonic development of Drosophila melanogaster. One aim of this work was to analyse the relevance of the protein-protein-interaction domains RING-finger and ankyrin repeats for the subcellular localisation of Rols7, which is detectable at the plasma membrane during myoblast fusion. Therefore, the RING-finger domain as well as three of the nine ankyrin repeats were expressed together with the first 20, respectively 309 aminoacids of Rols7 and one, respectively six Myc-tags as a fusion protein in the mesoderm of Drosophila using the UAS-GAL4-system. However, the fusion proteins can be detected only in an incorrect manner at, respectively around the nucleus. A dependence of this mislocalisation on a nuclear localisation signal, which is predicted in the region of the first 309 amino acids, could not be confirmed. Additionally, the expression of the fusion proteins in the mesoderm did not cause a dominant-negative effect, whereas an expression in the eye imaginal discs leads to a reduced number of ommatidia. A further aim was to clarify if Rols7 has an additional function during the later stages of myogenesis. Rols7 is expressed anew from stage 16/17 onwards and is localised to the muscle attachment sites in the embryo. There, a transient expression of Dumbfounded/ Kin of irregular chiasm-C (Duf/Kirre), whose intracellular domain interacts with Rols7, is also detectable. Thus it can be postulated that Duf/Kirre mediates the first contact of the outgrowing myofiber to the epidermal tendon cell via an interaction with Roughest/Irregular-chiasm-C (Rst/IrreC). During this process, Rols7 interacts with Duf/Kirre on the site of the muscle and takes part in the assembly of the terminal Z-discs together with D-Titin/Kettin and α-Actinin. These three proteins are also involved in the assembly of the sarcomeres, which are built shortly after the terminal Z-discs. Rols7 could be detected in colocalisation with D-Titin/Kettin and α-Actinin in the terminal Z-discs as well as in the Z-discs of the sarcomeres. In yeast interaction assays the R1-fragment of Rols7, which contains the RING-finger, interacts with the N-terminus of Zormin, an isoform that is derived from the sls gene, as well as with α-Actinin. In combination with results from Menon et al., 2005, a certain function for the R1-fragment of Rols7 for the assembly of the terminal Z-disc and the Z-discs of the sarcomeres could be proposed, whereas the ankyrin repeats and the TPR-repeats seem to have a function during myoblast fusion.