Investigating the role of gap junction protein and novel genes in renal function

Abstract

This thesis investigates the roles of genes with enriched expression in particular cells or regions of the Drosophila melanogaster Malpighian tubules in renal function and cellular homeostasis. Using reverse genetic, transcriptomic and metabolomic techniques, this study characterises the physiological role of Innexin 2, Innexin 7, the octopamine receptor Octα2R and the novel gene CG6602. These findings highlight the power of the Malpighian tubules as a model system for studying gene function in relation to osmoregulation, ion transport, and responses to stress. Initial studies characterised the gap junction proteins Innexin 2 and Innexin 7 to the principal cells of the tubules but found no strong impact of fluid secretion after RNAi knockdown. By contrast, Octα2R analysis revealed a specific role in secretion: reductions of Octα2R in stellate cells decreased the rate of secretion, and tubule secretion was found to be especially sensitive to octopamine compared with other biogenic amines. Further studies focused on CG6602, which is tubule-specific and might contribute to stress response pathways. Collectively, the knockdown of CG6602 resulted in altered expression of stress response genes, which implies possible involvement of CG6602 in pathways related to the maintenance of homeostasis of the cell. Metabolomic profiling confirmed this view, detecting changes in metabolites including those associated with oxidative stress defence, suggesting that CG6602's regulatory role in managing metabolic and environmental stress in the tubule cells. This study highlights the power of performing renal physiology studies in the fruit fly and begin to shed light on the molecular players responsible for maintaining tubule homeostasis. Due to the limitations of the analytical methods applied in this study, a more detailed exploration of the metabolomic data was not possible but the study provides a framework to connect state-of-the-art metabolomics with multi-omics approaches in future. It also adds to knowledge about the roles of gap junction proteins and the unique gene CG6602 in the renal system, and the genetic and metabolic networks involved in supporting renal function and stress responses