Author ORCID Identifier
Semester
Fall
Date of Graduation
2024
Document Type
Dissertation
Degree Type
PhD
College
Eberly College of Arts and Sciences
Department
Biology
Committee Chair
Rita V.M. Rio
Committee Co-Chair
Timothy Driscoll
Committee Member
Jennifer E.G. Gallagher
Committee Member
Dana Huebert Lima
Committee Member
Joshua B. Benoit
Abstract
Microbial symbioses are ubiquitous across all kingdoms of life with broad and diverse impacts on the evolution of species. The sum of all microbes living in, on, or otherwise in close association with a host form the microbiota. In some cases, the development of a stable microbial association seems to have been necessary for the specialization of diet, as can be observed in numerous insect species, especially wood-eating, sap-feeding, and blood-feeding organisms. For the medically and economically tsetse fly (family Glossinidae), the mutualistic bacteria Wigglesworthia glossinidia is required for proper reproduction and supplementation of nutrients that the fly does not receive from its strict blood-feeding diet. This symbiosis is ancient, dating back at least 50 million years, with extreme genome reduction occurring in Wigglesworthia, whose ~0.7 kb genome is specifically adapted to survival in the host environment. Unlike other hematophagous Dipterans such as mosquitoes, tsetse flies feed solely on blood, a diet low in essential B-vitamins such as thiamine (B1), pyridoxine (B6), and folate (B9), which Wigglesworthia retains the capacity to synthesize and can be supplemented to symbiont-free flies for partial phenotypic recovery. This essential nature of the Wigglesworthia-tsetse symbiosis to the survival and reproduction of the fly has necessitated extensive evolutionary change in the tsetse fly to promote the survival and perfect vertical transfer of the bacteria. This includes the evolution of adenotrophic viviparity, a metabolically costly reproductive strategy in which the flies give birth to a single, well-developed larvae per gonotrophic cycle that is sustained by specialized milk glands in utero. These milk secretions serve to infect the progeny with Wigglesworthia, which colonizes the milk glands as free-living organisms, while another population resides in a specialized region of the gut known as the bacteriome. The bacteriome contains specialized bacteriocyte cells that host an intracellular Wigglesworthia population responsible for nutrient provisioning. While these physiological adaptations for the symbiosis are well understood, the dynamics of a fly’s lifecycle and various events such as feeding or mating, are likely to significantly impact the symbiosis, necessitating the evolution of complex mechanisms for preventing dysbiosis, the disruption of the microbiota’s homeostasis. One factor that has been demonstrated to play a role in similar nutritional symbioses of other insects is host-generated microRNAs (miRNAs). By binding to mRNAs, primarily at the 3’ UTR of the host organism, these small, noncoding, RNAs prevent the translation of mRNAs to proteins which may be essential to the symbiosis. My dissertation sought to uncover the potential of microRNAs to contribute to tsetse-Wigglesworthia symbiosis. In Chapter 1, significant background information is provided in host-microbe symbiosis, the tsetse fly and its symbionts, and miRNAs in general, in comparison to small interfering RNAs (siRNAs), and in symbiosis. In Chapter 2, RNAseq data from two evolutionary distant species (G. morsitans and G. brevipalpis) of tsetse flies is explored. Aposymbiotic crop and proventriculus tissues were compared to the symbiont containing bacteriome organs, and genes showing conserved differential expression between species and tissues identified by known homology and functional characterization based on clusters of orthologous groups (COGs) and phylogenetic reconstruction. A small number of genes were differentially expressed between aposymbiotic and bacteriome tissues and found to have consistent expression patterns between both species, of which a subset shows different expression between mated and virgin flies of G. morsitans and was targeted by miRNAs found to have a comparable level of expression in both species. A single miRNA::mRNA interaction (miR-31a::fatty acyl-CoA reductase) within bacteriomes was identified as being of further interest after further phylogenetic analysis. Finally, the fatty acyl-CoA reductase gene family in Glossina is characterized with a prediction for a role in the structural maintenance of the bacteriome. Ultimately, no impact on the host could be determined by the disruption of the fatty acyl-CoA reductase, however, disruption of the functionally identical miR-31 with antagomirs showed an impact on bacteriome development suggesting other targets may be essential to the symbiosis.
Recommended Citation
Lee, Mason Hubbard, "A Balancing Act: MicroRNA Mediated Insect-Bacterial Homeostasis and the Tsetse Fly" (2024). Graduate Theses, Dissertations, and Problem Reports. 12685.
https://researchrepository.wvu.edu/etd/12685
Included in
Entomology Commons, Evolution Commons, Molecular Genetics Commons, Other Ecology and Evolutionary Biology Commons
