Genregulatorische und funktionelle Analysen des differentiell exprimierten rolling pebbles Transkriptes rols6 zeigen, dass das Rols6 Protein für die vollständige Differenzierung der Malpighischen Gefäße in Drosophila melanogaster notwendig ist.

Cell-cell communication, -migration and -adhesion are essentiell biological processes in Drosophila melanogaster Malpighian tubule (MpT) differentiation as well as in myoblast fusion. Several different protein families are involved in these processes, e.g. IgG-like proteins (Hibris), SH3-domain containing proteins (Myoblast city) and multidomain proteins such as Rolling pebbles (Rols). rolling pebbles encodes two transcripts (rols6 and rols7). These transcripts are regulated by distinct transcription initiation sites, of which only rols7 is transcribed within mesodermal derivates. Rols7 gives rise to the Rols7 protein, which is known to be an essential factor during myoblast fusion. Concerning rols6 transcription in the endoderm, in the head region and in the MpTs less is known about. The aim of this work was to clearify the relevance of the Rols6 protein during Malpighian tubule development. Phenotypic analyses of rolling pebbles alleles turned out that these alleles exhibit a phenotype in late MpT differentiation. As only rols6 is transcribed in MpT cells these differentiation defects might be caused by the deletion of rols6 within rols mutant embryos. This hypothesis could be verified by rols6 directed P-element excision mutagenesis. From this the excision strain EP(3)3330*5a resulted and exhibited the characteristical MpT differentiation defects previously seen in rols mutant embryos. Initial genregulatory analyses were made by lacZ-reportergene expression assays in transgenic flies. These revealed that the essential regulating regions are located within a 1100 bp genomic fragment upstream of the rols6 specific exon 1 (5ŽUTR) that includes the rols6 transcription initiation start site. This 1,1 kb fragment is sufficient to drive b-Galactosidase expression in a rols6 like pattern. Transcriptional activators (TAs) are unknown so far. In situ hybridizations with a rols6 specific probe on mutants of putative TAs revealed that early determinants such as Krüppel, Decapentaplegic, GATA-factors (Serpent; Grain) or the Drosophila GAGA-factor are not required for rols6 transcription. In this work first evidence for a role of the Rols6 protein in cell-reorganisation during late differentiation steps of the MpTs in Drosophila is presented. Phenotypic analysis of mutants for Rols7 interaction partners known from myogenesis, such as Myoblast city (Mbc) and Rac, support the hypothesis that Rols6, Mbc and Rac might act in a common signaling cascade during differentiation of MpTs. Finally in this work it is shown by generation of a rols6 specific deletion that Rols6 has a biological function in MpT development, whereas Rols7 is of essential function in myoblast fusion, and that both transcripts are regulated tissue specific by distinct promoter elements.