Investigating the role of copper homeostasis in the nervous system of drosophila melanogaster
thesisposted on 23.02.2017 by Hwang, Ern Ci Joab
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Copper is an essential trace metal required by multiple processes within the body, such as energy metabolism, neuropeptide maturation and pigmentation. However, excess copper is toxic to the body, and a homeostatic balance must be achieved using a set of copper homeostasis proteins which strictly control the concentration of copper in the body and in cells. While much research has been carried out into the general mechanisms of copper homeostasis, little is known about the specific roles of copper and copper homeostasis in various organs and tissues, such as the nervous system. This project has sought to use Drosophila melanogaster as an in vivo model to examine the role of copper homeostasis in the nervous system. I have found that pan-neuronal overexpression of the copper importer Ctr1B (resulting in cellular copper overload) causes lethality, while pan-neuronal overexpression of the copper exporter DmATP7 (resulting in cellular copper deficiency) causes both lethality and an unexpanded wing phenotype in surviving adults. I also have found that these phenotypes are sensitive to copper and BCS (a copper chelator) feeding. For example, feeding flies which overexpress Ctr1B pan-neuronally with BCS reduces cellular copper overload and rescues the lethality phenotype. I have found that copper overload causes damage to the cell, leading to cell death, and is the likely mechanism underlying the lethality phenotype observed. Further, I have found that copper deficiency in neuropeptidergic cells lead to failure of neuropeptide processing, resulting in the unexpanded wing defect. I have also used an in vivo system based on green fluorescent protein constructs to examine the effect of mutations on DmATP7 localization and function in different tissues, and have carried out a screen based on the pan-neuronal copper overload and deficiency phenotypes to screen for new players in copper homeostasis. Rab10 emerged as a candidate gene from this screen, and I have shown that Rab10 plays a role in copper homeostasis due to its requirement for proper localization of the copper transport proteins Ctr1A and DmATP7. Finally, this study provides evidence for cellular compartmentalization of the requirement for copper, that is, different pathways and compartments in the cell having different requirements for copper. For example, it is possible to generate situations where the lethality and the unexpanded wing phenotypes of flies overexpressing DmATP7 pan-neuronally respond differently to changes in copper homeostasis. Overall, this project has established Drosophila melanogaster as a valuable in vivo model for examining the role of copper in the nervous system.