Maternally transmitted microbes that infect host germ cells are perfectly poised to influence animal genome evolution, either directly through horizontal gene transfer or indirectly through selection for host genetic variants that control symbiont proliferation. In this dissertation, both of these scenarios are examined using the obligate, intracellular bacteria Wolbachia as a model for maternally-transmitted bacteria because of its widespread distribution across 40-50% of all arthropod species and its localization to the maternal germ line cells. In the first project, whole-genome sequencing of uninfected Chorthippus parallelus grasshoppers revealed that large regions of DNA from two different supergroups of Wolbachia had horizontally transferred into the grasshopper genome. While horizontal gene transfer of Wolbachia DNA to a eukaryotic host is common given Wolbachia?s proximity to the germ line genome, this is the first known example of two divergent Wolbachia strains contributing DNA to the same host genome. Furthermore, Wolbachia inserts were present in almost all of the grasshopper chromosomes and often differed between closely-related C. parallelus subspecies, indicating that horizontal gene transfer from Wolbachia is an unusually dynamic process in grasshoppers.
In the second project, a forward genetic screen was conducted to find host genomic regions responsible for regulating an 80-fold difference in Wolbachia titers between two closely-related species of Nasonia parasitoid wasps (N. vitripennis and N. giraulti). Quantitative trait loci analyses and hybrid introgressions identified two genomic regions, one each on chromosomes 2 and 3, that act additively through a maternal effect to suppress Wolbachia titers in N. vitripennis. Thirty-three significantly differentially expressed genes are present in these regions, several of which function in pathways important for host control of intracellular bacteria including immunity, autophagy, and cell-to-cell trafficking. Additionally, staining of Nasonia ovaries with a nucleic acid dye revealed that N. vitripennis may keep Wolbachia out of developing oocytes by sequestering them in the neighboring nurse cells. Candidate genes that are overexpressed in N. vitripennis, such as trichohyalin, or those involved in Wolbachia trafficking, such as kinesin, are currently being evaluated using RNAi for their role in host regulation of Wolbachia titers and transmission.
| Identifer | oai:union.ndltd.org:VANDERBILT/oai:VANDERBILTETD:etd-02292016-094819 |
| Date | 29 February 2016 |
| Creators | Funkhouser-Jones, Lisa Jean |
| Contributors | Katherine Friedman, Seth Bordenstein, Julian Hillyer, Antonis Rokas, Timothy Cover |
| Publisher | VANDERBILT |
| Source Sets | Vanderbilt University Theses |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.vanderbilt.edu/available/etd-02292016-094819/ |
| Rights | restrictone, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Vanderbilt University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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