Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item IDENTIFICATION AND CHARACTERIZATION OF REGULATORY MIRNAS AND MRNAS IN THE LONGITUDINAL HUMAN HOST RESPONSE TO VAGINAL MICROBIOTA(2017) Smith, Steven Bradley; Ravel, Jacques; El-Sayed, Najib; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The human vagina and the bacterial communities that reside therein exist in a finely balanced mutualistic association. Dysbiotic states of the vaginal microbiota, including bacterial vaginosis (BV), are characterized by a paucity of Lactobacillus spp., the presence of a wide array of strict and facultative anaerobes, and a pH >4.5. Symptoms such as odor and discharge can accompany these microbial dysbiotic states, however, epidemiologically, vaginal dysbioses have been associated with increased susceptibility to STIs, including chlamydia. The mechanisms by which vaginal microbiota protect or increase the risk to infections remain unknown. This thesis aimed to identify the molecular factors that control host cellular responses to Lactobacillus spp.-dominated and dysbiotic microbiota. Chapter 2 characterized the in vivo host microRNA (miRNA) response to different types of vaginal microbiota to gain insight into host functions that play a role in vaginal homeostasis. Leveraging daily collected vaginal samples in conjunction with a machine learning approach, eight miRNAs were discovered to be differently controlled by vaginal microbiota. Of these, expression of miR-193b, known to regulate host cell proliferation, was increased by Lactobacillus spp.-dominated microbiota. In vitro, vaginal epithelial cells exposed to Lactobacillus spp. culture supernatants exhibited reduced epithelial cell proliferation, high miRNA-193b expression and decreased abundance of cyclin D1. More importantly, epithelial cell proliferation was identified as a requirement for efficient Chlamydia trachomatis infection. Chapter 3 characterized the in vitro transcriptome of epithelial cells exposed to Lactobacillus spp. relative to Gardnerella vaginalis, a surrogate for dysbiotic vaginal microbiota. Immune response and cell cycle pathways were found to be among the most modulated by Lactobacillus spp. Longitudinal gene expression suggested a role of histone deacetylases (HDAC) as an intermediary between immune stimulation and cell proliferation. Additionally, the epidermal growth factor receptor (EGFR), required for C. trachomatis infection, was decreased when epithelial cells were exposed to Lactobacillus spp. These findings contribute to the fundamental understanding of the vaginal microbiota’s role in cellular homeostasis as a requirement for resistance to STI agents such as C. trachomatis, and ultimately will lead to improved preventive strategies against STIs through the modulation of vaginal microbiota composition and function.Item The PcG gene polyhomeotic controls cell proliferation autonomously and non-autonomously in Drosophila(2011) Feng, Siqian; Wang, Jian; Molecular and Cell Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polycomb group (PcG) proteins are conserved epigenetic regulators that maintain targets at a repressed transcription state. In my dissertation research, I generated phdel, the first real null allele of the Drosophila PcG gene polyhomeotic (ph). Using this allele, I found that loss of ph causes cell over-proliferation in mosaic tissues in a non-autonomous manner, meaning that the mutant cells induce over-proliferation of neighboring wild type cells. I further identified the underlying signaling pathways: Notch signaling is elevated autonomously in phdel cells, which causes the over-production of 3 Upd homologs. These ligands are then secreted and activate the JAK/STAT pathway in neighboring cells, which eventually causes cell over-proliferation. In addition, phdel cells maintain normal cell polarity but undergo invagination to form unique 3 dimensional structures. Such structures are morphologically and functionally similar to epithelia-derived endocrine glands. Interestingly, ph505, another ph allele that has long been considered null, causes both autonomous and non-autonomous cell proliferation in mosaic tissues. To explain the discrepancies between phdel and ph505, I characterized the nature of ph505. Data from embryonic lethal stage, rescue by ph-d, and exon sequencing all showed that ph505 is a hypomorph. Functional analysis then proved that the same signaling pathway also underlies non-autonomous proliferation in ph505 mosaic tissues. I then showed that ph505 cells still respond to the Upd ligands they secreted, but phdel cell are no longer responsive. This explains why ph505 cells still over-proliferate but phdel cell do not. Next, Real-Time PCR results demonstrated that the JAK/STAT pathway receptor domeless has a higher expression level in ph505 cells than in phdel cells, which may explain their different sensitivities to Upd ligands. Finally, genome wide ChIP data in public database suggest that Notch may be a direct target of Polycomb Repressive Complex 1, in which Ph is a core component. My dissertation established that loss of ph causes non-autonomous over-proliferation, and elucidated the underlying mechanism. My results also call for a reevaluation of the non-autonomous over-proliferation pathway in Drosophila. Finally, the fact that different alleles of the same gene cause tumors in very different ways have certain implications to cancer research and treatment.Item The Equilibrium Geometry Theory for Bone Fracture Healing(2008-04-29) Yew, Alvin Garwai; Hsieh, Adam H; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Models describing the impact of mechanical stimuli on bone fracture healing can be used to design improved fixation devices and optimize clinical treatment. Existing models however, are limited because they fail to consider the changing fracture callus morphology and probabilistic behavior of biological systems. To resolve these issues, the Equilibrium Geometry Theory (EGT) was conceptualized and when coupled with a mechanoregulation algorithm for differentiation, it provides a way to simulate cell processes at the fracture site. A three-dimensional, anisotropic random walk model with an adaptive finite element domain was developed for studying the entire course of fracture healing based on EGT fundamentals. Although a coarse cell dispersal lattice and finite element mesh were used for analyses, the computational platform provides exceptional latitude for visualizing the growth and remodeling of tissue. Preliminary parameter and sensitivity studies show that simulations can be fine-tuned for a wide variety of clinical and research applications.