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Title: The evolution and genetics of Drosophila melanogaster and the sigma virus
Author: Carpenter, Jennifer A.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2008
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I describe the isolation and characterisation of new sigma-viral isolates collected from Europe and North America. With these new isolates, I show that sigma virus has very low levels of viral genetic diversity across Europe and North America compared to other RNA viruses. I examine the susceptibility of Drosophila melanogaster to five of the viral isolates to investigate whether specificity exists in this system. The results suggest that there is little constraint on flies evolving resistance to all five viruses and that trade-offs between resistance against the five viruses are unlikely to explain why variation is susceptibility exists in wild populations of Drosophila melanogaster. Sigma-viruses increase the susceptibility of flies to the fungus Beauveria bassiana – that commonly infects insects in the wild. This could have profound effects in the wild where flies are constantly exposed to bacteria and fungus during feeding. One interpretation of the increased susceptibility of sigma-infected flies, is that the sigma virus is suppressing the Toll-pathway. However, I found no evidence for viral suppression of the Toll-pathway, nor did I find evidence that flies mount a Toll-dependent immune response against the sigma virus. This suggests that either Drosophila do not mount an immune response against the sigma virus, or that the immune response is controlled by other pathways. Finally, I describe the hypermutation of adenosines to guanosines in the genome of the sigma virus. The clustering of these mutations and the context in which thy occur indicates that they have been caused by ADAR–RNA editing enzymes that target double stranded RNA. This is the first evidence that ADARs target viruses outside of mammals, and it raises the possibility that ADARs could play a role in the antiviral defences of insects.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available