Insects are highly successful and their large numbers lead to economic loss through crop damage and disease transmission. Insecticides provide a valuable tool for control of insect populations. However, as resistance is increasing to existing products, new modes of action are required for the development of novel products. Understanding of the biological mechanisms underlying stress resistance in insects may provide insight into new potential insecticide targets. Malpighian tubules are critical for epithelial fluid transport and xenobiotic tolerance in insects. The function of Malpighian tubules in desiccation stress tolerance was explored by examining changes in gene expression, protein levels, fluid transport rates, and metabolism following stress exposure. The results indicate a reduction in secretion rate during desiccation that is reflected in accumulation of metabolites that are normally processed and excreted by the tubules. Moreover, the involvement of Drosophila melanogaster diuretic hormones corticotrophin releasing factor-like (DH44) and leucokinin (LK) were examined using genetic manipulations based on the GAL4-UAS system. Highly selective manipulation of the DH44-producing neurons via knockdown of DH44 and neuronal ablation indicates that suppression of DH44 signalling contributes to desiccation tolerance. This result is supported by the finding that knockdown of DH44 receptor 2 in the Malpighian tubule principal cells improves survival during desiccation stress. Previous work suggests the possibility of interaction between LK and DH44 signalling as LK receptor (LKR) is colocalised to the DH44 neurons. This hypothesis is supported by the results of this study as selective knockdown of LKR and DH44 in the DH44 neurons produced opposing effects on desiccation tolerance. Moreover, knockdown of DH44 in the DH44 neurons or ablation of these neurons resulted in significantly decreased LKR expression in the Malpighian tubules. Finally, a novel role for the Malpighian tubules in starvation tolerance was uncovered by the study, with LKR gene expression increasing significantly following starvation. Knockdowns of either DH44-R2 or LKR in the Malpighian tubules significantly impaired starvation tolerance. Here, a mechanism for this role of renal epithelia in starvation tolerance is proposed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:681848 |
| Date | January 2015 |
| Creators | Cannell, Elizabeth |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/7120/ |
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