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- All Subjects: Evolution
- All Subjects: Immunology
- Creators: School of Life Sciences
Description
Many factors are at play within the genome of an organism, contributing to much of the diversity and variation across the tree of life. While the genome is generally encoded by four nucleotides, A, C, T, and G, this code can be expanded. One particular mechanism that we examine in this thesis is modification of bases—more specifically, methylation of Adenine (m6A) within the GATC motif of Escherichia coli. These methylated adenines are especially important in a process called methyl-directed mismatch repair (MMR), a pathway responsible for repairing errors in the DNA sequence produced by replication. In this pathway, methylated adenines identify the parent strand and direct the repair proteins to correct the erroneous base in the daughter strand. While the primary role of methylated adenines at GATC sites is to direct the MMR pathway, this methylation has also been found to affect other processes, such as gene expression, the activity of transposable elements, and the timing of DNA replication. However, in the absence of MMR, the ability of these other processes to maintain adenine methylation and its targets is unknown.
To determine if the disruption of the MMR pathway results in the reduced conservation of methylated adenines as well as an increased tolerance for mutations that result in the loss or gain of new GATC sites, we surveyed individual clones isolated from experimentally evolving wild-type and MMR-deficient (mutL- ;conferring an 150x increase in mutation rate) populations of E. coli with whole-genome sequencing. Initial analysis revealed a lack of mutations affecting methylation sites (GATC tetranucleotides) in wild-type clones. However, the inherent low mutation rates conferred by the wild-type background render this result inconclusive, due to a lack of statistical power, and reveal a need for a more direct measure of changes in methylation status. Thus as a first step to comparative methylomics, we benchmarked four different methylation-calling pipelines on three biological replicates of the wildtype progenitor strain for our evolved populations.
While it is understood that these methylated sites play a role in the MMR pathway, it is not fully understood the full extent of their effect on the genome. Thus the goal of this thesis was to better understand the forces which maintain the genome, specifically concerning m6A within the GATC motif.
To determine if the disruption of the MMR pathway results in the reduced conservation of methylated adenines as well as an increased tolerance for mutations that result in the loss or gain of new GATC sites, we surveyed individual clones isolated from experimentally evolving wild-type and MMR-deficient (mutL- ;conferring an 150x increase in mutation rate) populations of E. coli with whole-genome sequencing. Initial analysis revealed a lack of mutations affecting methylation sites (GATC tetranucleotides) in wild-type clones. However, the inherent low mutation rates conferred by the wild-type background render this result inconclusive, due to a lack of statistical power, and reveal a need for a more direct measure of changes in methylation status. Thus as a first step to comparative methylomics, we benchmarked four different methylation-calling pipelines on three biological replicates of the wildtype progenitor strain for our evolved populations.
While it is understood that these methylated sites play a role in the MMR pathway, it is not fully understood the full extent of their effect on the genome. Thus the goal of this thesis was to better understand the forces which maintain the genome, specifically concerning m6A within the GATC motif.
ContributorsBoyer, Gwyneth (Author) / Lynch, Michael (Thesis director) / Behringer, Megan (Committee member) / Geiler-Samerotte, Kerry (Committee member) / School of Life Sciences (Contributor) / Department of Psychology (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
Description
Many bacteria actively import environmental DNA and incorporate it into their genomes. This behavior, referred to as transformation, has been described in many species from diverse taxonomic backgrounds. Transformation is expected to carry some selective advantages similar to those postulated for meiotic sex in eukaryotes. However, the accumulation of loss-of-function alleles at transformation loci and an increased mutational load from recombining with DNA from dead cells create additional costs to transformation. These costs have been shown to outweigh many of the benefits of recombination under a variety of likely parameters. We investigate an additional proposed benefit of sexual recombination, the Red Queen hypothesis, as it relates to bacterial transformation. Here we describe a computational model showing that host-pathogen coevolution may provide a large selective benefit to transformation and allow transforming cells to invade an environment dominated by otherwise equal non-transformers. Furthermore, we observe that host-pathogen dynamics cause the selection pressure on transformation to vary extensively in time, explaining the tight regulation and wide variety of rates observed in naturally competent bacteria. Host-pathogen dynamics may explain the evolution and maintenance of natural competence despite its associated costs.
ContributorsPalmer, Nathan David (Author) / Cartwright, Reed (Thesis director) / Wang, Xuan (Committee member) / Sievert, Chris (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Introduction: Human papillomavirus (HPV) infection is seen in up to 90% of cases of cervical cancer, the third leading cancer cause of death in women. Current HPV screening focuses on only two HPV types and covers roughly 75% of HPV-associated cervical cancers. A protein based assay to test for antibody biomarkers against 98 HPV antigens from both high and low risk types could provide an inexpensive and reliable method to screen for patients at risk of developing invasive cervical cancer. Methods: 98 codon optimized, commercially produced HPV genes were cloned into the pANT7_cGST vector, amplified in a bacterial host, and purified for mammalian expression using in vitro transcription/translation (IVTT) in a luminescence-based RAPID ELISA (RELISA) assay. Monoclonal antibodies were used to determine immune cross-reactivity between phylogenetically similar antigens. Lastly, several protein characteristics were examined to determine if they correlated with protein expression. Results: All genes were successfully moved into the destination vector and 86 of the 98 genes (88%) expressed protein at an adequate level. A difference was noted in expression by gene across HPV types but no correlation was found between protein size, pI, or aliphatic index and expression. Discussion: Further testing is needed to express the remaining 12 HPV genes. Once all genes have been successfully expressed and purified at high concentrations, DNA will be printed on microscope slides to create a protein microarray. This microarray will be used to screen HPV-positive patient sera for antibody biomarkers that may be indicative of cervical cancer and precancerous cervical neoplasias.
ContributorsMeshay, Ian Matthew (Author) / Anderson, Karen (Thesis director) / Magee, Mitch (Committee member) / Katchman, Benjamin (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2015-05
Description
Efforts to quantify the diversity of the T cell repertoire have generally been unsuccessful because not all factors accounting for diversity have been considered. In order to get an accurate representation of the T cell repertoire, one must incorporate analysis of germline gene diversity, diversity from somatic recombination, joining diversity from N- and P- nucleotides, and TCR chain pairing diversity. Because of advances in high-throughput sequencing techniques, estimates have been able to account for diversity from TCR genes. However the ability to account for chain pairing diversity has been more difficult. In order to do so, single cell sorting techniques must be employed. These techniques, though effective, are time consuming and expensive. For this reason, no large-scale analyses have been done on the immune repertoires using these techniques. In this study, we propose a novel method for linking the two TCR chain sequences from an individual cell. DNA origami nanostructure technology is employed to capture and bind the TCRγ and TCRδ chain mRNA inside individual cells using probe strands complementary to the C-region of those sequences. We then use a dual-primer RT and ligation molecular strategy to link the two sequences together. The result is a single amplicon containing the CDR3 region of the TCRγ and TCRδ. This amplicon can then be easily PCR amplified using sequence specific primers, and sequenced. DNA origami nanostructures offer a rapid, cost-effective method alternative to conventional single cell sorting techniques, as both TCR mRNA can be captured on one origami molecule inside a single cell. At present, this study outlines a proof-of-principle analysis of the method to determine its functionality. Using known TCRγ and TCRδ sequences, the DNA origami and RT/PCR method was tested and resulting sequence data proved the effectiveness of the method. The original TCRγ and TCRδ sequences were linked together as a single amplicon containing both CDR3 regions of the genes. Thus, this method can be employed in further research to elucidate the γδ T cell repertoire. This technology is also easily adapted to any gene target or cell type and therefore presents a large opportunity to be used in other immune repertoire analysis and other immunological studies (such as the rapid identification and subsequent production of antibodies).
ContributorsPoindexter, Morgan Elizabeth (Author) / Blattman, Joseph (Thesis director) / Yan, Hao (Committee member) / Schoettle, Louis (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2015-05
Description
We examined the evolutionary morphological responses of Drosophila melanogaster that had evolved at constant cold (16°), constant hot (25°C), and fluctuating (16° and 25°C). Flies that were exposed to the constant low mean temperature developed larger thorax, wing, and cell sizes than those exposed to constant high mean temperatures. Males and females both responded similarly to thermal treatments in average wing and cell size. The resulting cell area for a given wing size in thermal fluctuating populations remains unclear and remains a subject for future research.
ContributorsAdrian, Gregory John (Author) / Angilletta, Michael (Thesis director) / Harrison, Jon (Committee member) / Rusch, Travis (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2015-05
Description
Cancer poses a significant burden on the global health system and represents a leading cause of death worldwide. For late-stage cancers, the traditional treatments of chemotherapy, radiation, and surgery are not always viable, and they can pose unnecessary health risks to the patients. New immunotherapies, such as adoptive cell transfer, are being developed and refined to treat such cancers. T cell immunotherapies in particular, where a patient’s T cell lymphocytes are isolated and amplified to be re-infused into the patient or where human cell lines are engineered to express T cell receptors for the recognition of common cancer antigens, are being expanded on because for some cancers, they could be the only option. Constructing an optimal pipeline for cloning and expression of antigen-specific TCRs has significant bearing on the efficacy of engineered cell lines for ACT. Adoptive T cell transfer, while making great strides, has to overcome a diverse T cell repertoire – cloning and expressing antigen-specific TCRs can mediate this understanding. Having identified the high frequency FluM1-specific TCR sequences in stimulated donor PBMCs, it was hypothesized that the antigen-specific TCR could be reconstructed via Gateway cloning methods and tested for expression and functionality. Establishing this pipeline would confirm an ability to properly pair and express the heterodimeric chains. In the context of downstream applications, neoantigens would be used to stimulate T cells, the α and β chains would be paired via single-cell or bulk methods, and instead of Gateway cloning, the CDR3 hypervariable regions α and β chains alone would be co-expressed using Golden Gate assembly methods.
ContributorsHirneise, Gabrielle Rachel (Author) / Anderson, Karen (Thesis director) / Mason, Hugh (Committee member) / Hariadi, Hugh (Committee member) / School of Life Sciences (Contributor, Contributor) / School of Sustainability (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05
Description
Since its discovery in 1524, many people have characterized the vermiform appendix. Charles Darwin considered the human appendix to be a vestige and a useless structure. Others at the time opposed this hypothesis. However, Darwin's hypothesis became prevalent one until recently when there became a renewed interest in the appendix because of advancements in microscopes, knowledge of the immune system, and phylogenetics. In this review, I will argue that the vermiform appendix, although still not completely understood, has important functions. First, I will give the anatomy of the appendix. I will discuss the comparative anatomy between different animals and also primates. I will address the effects of appendicitis and appendectomy. I will give background on vestigial structures and will discuss if the appendix is a vestige. Following, I will review the evolution of the appendix. Finally, I will argue that the function of the appendix is as an immune organ, including discussion of gut-associated lymphoid tissue (GALT), development of lymphoid follicles in GALT and their comparison within different organs, Immunoglobulin A (IgA) function in the gut, biofilms as evidence that the appendix is a safe-house for beneficial bacteria, re-inoculation of the bowel, and protection against recurring infection. I will conclude with future studies that should be conducted to further our understanding of the vermiform appendix.
ContributorsPrestwich, Shelby Elizabeth (Author) / Cartwright, Reed (Thesis director) / Lynch, John (Committee member) / Furstenau, Tara (Committee member) / School of Geographical Sciences and Urban Planning (Contributor) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
The Cannabis plant has historical roots with human beings. The plant produces compounds called cannabinoids, which are responsible for the physiological affects of Cannabis and make it a research candidate for medicinal use. Analysis of the plant and its components will help build a better database that could be used to develop a complete roster of medicinal benefits. Research regarding the cellular protein receptors that bind the cannabinoids may not only help provide reasons explaining why the Cannabis plant could be medicinally relevant, but will also help explain how the receptors originated. The receptors may have been present in organisms before the present day Cannabis plant. So why would there be receptors that bind to cannabinoids? Searching for an endocannabinoid system could help explain the purpose of the cannabinoid receptors and their current structures in humans. Using genetic technologies we are able to take a closer look into the evolutionary history of cannabinoids and the receptors that bind them.
ContributorsSalasnek, Reed Samuel (Author) / Capco, David (Thesis director) / Mangone, Marco (Committee member) / Stump, Edmund (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2014-05
Description
The evolution of blindness in cave animals has been heavily studied; however, little research has been done on the interaction of migration and drift on the development of blindness in these populations. In this study, a model is used to compare the effect that genetic drift has on the fixation of a blindness allele for varying amounts of migration and selection. For populations where the initial frequency is quite low, genetic drift plays a much larger role in the fixation of blindness than populations where the initial frequency is high. In populations where the initial frequency is high, genetic drift plays almost no role in fixation. Our results suggest that migration plays a greater role in the fate of the blindness allele than selection.
ContributorsMerry, Alexandra Leigh (Author) / Cartwright, Reed (Thesis director) / Rosenberg, Michael (Committee member) / Schwartz, Rachel (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2014-05
Description
Viral infections are a significant cause of disease in humans. While some viral diseases have been eliminated, many more continue to infect millions. Viral infections are challenging to treat because viruses use host cell machinery to replicate, so it is difficult to develop drugs that can target viruses. Normally, the host’s immune system is capable of destroying the virus, but during chronic infections it becomes exhausted and T cells lose their effector functions necessary for the clearance of the virus. IL-2 can help relieve this exhaustion, but causes toxicity to the body. In mice infected with chronic LCMV, IL-2 administration causes death due to pulmonary hemorrhage. CD4 deficient mice were infected with chronic LCMV and then dosed with IL-2 and survived, but mice that were deficient for CD8 T cells died, indicating that toxicity was mediated by CD8 T cells. CD8 T cells can kill infected host cells directly by producing perforin, or can produce cytokines like IFN-γ and TNF to further activate the immune system and mediate killing. Mice that were deficient in perforin died after IL-2 administration, as well as mice that were deficient in IFN-γ. Mice deficient in TNF, however, survived, indicating that TNF was mediating the toxicity in response to IL-2. There are two different receptors for TNF, p55 and p75. p55 is known as TNFR1 and has been implicated in apoptosis of virally infected cells. P75 is known as TNFR2 and is associated more with inflammation in response to infection. My hypothesis was that if TNFR2 was knocked out, infected mice would survive IL-2 dosing. When single knockouts of TNFR1 and 2 were used in an experiment however, it was found that either receptor is capable of mediating toxicity, as both experimental groups failed to survive. This is relevant to current IL-2 therapies because there is no way to eliminate a single receptor in order to reduce toxicity. Further studies exploring the anti-viral capabilities of IFN-γ are suggested.
ContributorsJarvis, Jordan Alisa (Author) / Blattman, Joseph (Thesis director) / Denzler, Karen (Committee member) / McAfee, Megan (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2014-05