Intracellular rols7 mRNA localization and the importance of Barren for mitosis in the embryonic myogenesis of Drosophila melanogaster

The body wall musculature of the D. melanogaster larva is a highly ordered assembly of striated myotubes that are formed by fusion of myoblasts, much like the skeletal muscle fibres of vertebrates. In this study, the embryonic development of this musculature is used as a genetic model system for myo...

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Bibliographic Details
Main Author: Jacobs, Matthias P. F.
Contributors: Renkawitz-Pohl, Renate (Prof. Dr.) (Thesis advisor)
Format: Dissertation
Language:English
Published: Philipps-Universität Marburg 2018
Biologie
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Summary:The body wall musculature of the D. melanogaster larva is a highly ordered assembly of striated myotubes that are formed by fusion of myoblasts, much like the skeletal muscle fibres of vertebrates. In this study, the embryonic development of this musculature is used as a genetic model system for myogenesis, muscle regeneration and related processes. Rols7 is a crucial protein in the signal transduction chain that controls the Actin filament branching necessary for myoblast fusion. In somatic muscle founder cells, the rols7 mRNA shows intracellular localization into one or more patches near the cell surface. This thesis demonstrates that the rols7 transcript’s 3’ untranslated region is necessary for its localization. A reporter mRNA with this trailer region as well as the 5’ untranslated region gets intracellularly localized in a way seemingly identical to the wild type pattern, even in the absence of native rols transcripts. The rols7 mRNA is shown to be intracellularly localized in the circular and longitudinal visceral muscle founder cells as well; in the latter it forms spots close to the tips of the spindle-shaped cells, near the expected sites of cell-cell fusion. At least for this latter cell type it can be suspected that rols7 mRNA localisation facilitates protein localisation and eventually myoblast fusion by preforming the Rols7 protein’s distribution pattern. In search of previously unknown factors involved in myogenesis, the muscle phenotype of the EMS-induced mutant line E831 is analyzed. As the cause for the disturbed arrangement of the embryonic body wall musculature a nonsense mutation of the Condensin subunit barren is identified. Cap-G, another Condensin subunit, is found to show a phenotype very similar to that of barren. While in a barren mutant both muscle founder cells and fusion competent myoblasts seem to get specified, muscle identity genes are expressed irregularly in a manner that corresponds to the perturbation of the muscle pattern. In every cell, the Condensin complex fulfills a variety of essential functions. To help clarify whether the muscle phenotype is connected to Condensin’s regulatory role during interphase or its function in chromosome segregation during mitosis, the time point at which Barren is needed in the musculature has to be identified. To this end, the Gal4-UAS system is used to express a barren rescue construct. Gal4 drivers are found to rescue the phenotype only if they express Barren considerably before the final cell division that gives rise to the muscle founder cells. This finding suggests that the muscle phenotype is caused by a mitotic defect. The mechanism behind the loss of muscle identity appears to be a phenomenon related to the genomic instability of cancer cell lines.
Physical Description:174 Pages
DOI:https://doi.org/10.17192/z2018.0214