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Evolution and gene expression of Wolbachia in D. melanogaster.

Gutzwiller, Florence

[Thesis]. Manchester, UK: The University of Manchester; 2016.

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Abstract

Wolbachia is a facultative endosymbiont infecting D. melanogaster, among many other arthropod species. In D. melanogaster, Wolbachia is a reproductive manipulator, but also gives some benefits to its host, such as protection against viruses. We used open access libraries of D. melanogaster resequencing data and yet unpublished sequences from our lab, to study the phylogenomics and geographical diversity of Wolbachia in D. melanogaster from five continents. We confirmed the clade structure of Wolbachia infecting D. melanogaster and the vertical transmission of Wolbachia from a single ancestral infection in D. melanogaster for almost all samples as shown in previous studies. However, for the first time, we found some discrepancies between Wolbachia and mitochondrial clades, indicating potential horizontal transfers. The geographical distribution of the clades, and the variation in proportion of uninfected flies between clades suggest that the clade composition and infection rate in different populations is the result of trade-off between local adaptations and Wolbachia transmission efficiency. After confirming the tight coevolution between Wolbachia and D. melanogaster, and the existence of diversity in Wolbachia strains, we analysed the gene expression of Wolbachia in different clades and host backgrounds. We first looked at the variations in gene expression of Wolbachia w Mel across the developmental life cycle of the ISO1 line of D. melanogaster. We found 93 Wolbachia genes differentially expressed across the D. melanogaster life cycle and/or between adult males and females. Most of the stage-specific genes follow a similar pattern of expression with up-regulation after embryonic stages and stronger up-regulation in early larvae and late pupae, and most of sex-specific genes were up-regulated in males. Then, we analyzed Wolbachia w MelCS gene expression in a nos-gal4, UAS-DCR2 driver mutant line of D. melanogaster (DCR2), in embryo, ovaries and ovarectomized carcasses. We found 118 genes differentially expressed between embryo and female carcasses, a lot of them (46) being also differentially expressed between embryo and ovaries, and up-regulated in embryo. A small number of the genes differentially expressed between embryo and female carcasses are up-regulated in female carcasses and are, for most of them, also found differentially expressed between ovaries and carcasses in the same dataset, and between embryo and female adult in Wolbachia wMel infecting the ISO1 line of D. melanogaster. Both RNAseq analyses showed that most of the Wolbachia genes were expressed and that the expression level of most of the genes was relatively constant across the life cycle stages, sex and tissues tested.