Genetics Area Program electronic theses and dissertations (MU)
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The items in this collection are the theses and dissertations written by students of the Genetics Area Program. Some items may be viewed only by members of the University of Missouri System and/or University of Missouri-Columbia. Click on one of the browse buttons above for a complete listing of the works.
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Item Acetate mutants and obligate photoautotrophy in Chlamydomonas eugametos(University of Missouri--Columbia., 1971) Chu-Der, Orchid Ming-yu; Gowans, C. ShieldsIncorporation of C-14 labelled sodium acetate by three species of Chlamydomonas: C. eugametos, C. reinhardii and C. moewusii indicates that all three species assimilate and metabolize exogenous acetate. All three species have higher growth rate in the light with acetate than without. C. eugametos and C. moewusii, being obligate photoautotrophs, are not able to grow heterotrophically in the dark. C. reinhardii, a facultative photoautotroph, can grow heterotrophically. C. reinhardii has radioactive sodium acetate uptake over ten times greater than that of C. eugametos or C. moewusii. This suggests that the former assimilates and metabolizes acetate more efficiently than the latter two. Adaptation from autotrophic to mixotrophic growth is accompanied in C. eugametos and C. reinhardii by their individual characteristic and different patterns of radioactive sodium acetate uptake, indicating that the two species have different regulatory systems for acetate metabolism. Comparative intermediary carbohydrate metabolism in terms of enzyme activities in the tricarboxylic acid cycle was investigated in C. eugametos and C. reinhardii. All the expected enzyme activities of this cycle are present in both species grown either autotrophically or mixotrophically with acetate. The patterns of enzyme activities in each species differ with different growth conditions. In C. reinhardii, concomitant presence of light and acetate leads to higher activities of succinate dehydrogenase, fumarase and malic enzyme; while condensing enzyme, aconitase, NADP specific isocitrate dehydrogenase, NAD specific isocitrate dehydrogenase and [alpha]-ketoglutarate dehydrogenase are acetate inducible and light independent. The situation in C. reinhardii just mentioned indicates that succinate dehydrogenase, fumarase and malic enzyme may be closely associated with photosynthesis. Ten acetate mutants requiring both acetate and light to survive were recovered after ultraviolet treatment and are designated: R-l, R-2, R-3, R-4, R-5, R-6, R-7, R-8, R-9 and R-10. Mutants R-4, R-5, R-6, R-8 and R-9 have Mendelian segregation, and mutant R-l is most likely nontransmissible. Mutant R-3 has all the expected enzyme activities in the tricarboxylic acid cycle. Mutants R-l, R-5 and R-7 have no succinate dehydrogenase. In mutant R-4, activity of condensing enzyme cannot be demonstrated.Item Cytogenetic analysis of a knobbed chromosome 9 in maize(University of Missouri--Columbia., 1971) Chang, Chia-cheng; Kikudome, Gary Y.The K* knob of Mexican origin had a suppressive effect on recombination in the short arm of chromosome 9. It had the capacity to reduce recombination in both the distal and proximal regions or to reduce it only in the distal region (with a concomitant increase in recombination in the proximal region). The suppressive effect was stronger on the female-side than on the male-side. The suppressive effect of the K* knob was greatest when the chromosome containing it was opposed by a homologue which was knobless. This effect became less pronounced as the size of the opposing knob became larger. It appears that the total amount of knob material present in the bivalent was not a critical factor in this suppressive effect. In K*-containing heteromorphs, the effectiveness of the abnormal chromosome 10 in increasing recombination in the distal region was found to be progressively less as the amount of the K* knob not opposed by knob material in the homologue increased. It was also found that the greater the total amount of heterochromatin in the two knobs of the bivalent, the less effective was the abnormal chromosome 10 in increasing recombination in the proximal region. The K knob modified the B-chromosome effect on recombination. In megasporocytes of K /K heteromorphs, although total recombination in the short arm was enhanced in B-chromosome containing individuals over B-less plants, the K* knob's suppressive effect was still very much in evidence. In these heteromorphs containing the B-chromosomes, recombination was increased in both the proximal and the distal regions. In the K^S /K^S compounds the B-chromosomes did not increase total recombination in the short arm but only effected a shift in recombination from the distal to the proximal region. The K* knob did not influence the zig-zag effect on recombination induced by the odd-even number of B-chromosomes. Previous preferential segregation studies have indicated that it is the genes linked to the larger of the twoknobs of chromosome 9 bivalents which are preferentially recovered in the eggs. The K*/K^L study has provided the first exception : genes linked to the smaller K^L knob were preferentially recovered. No evidence was obtained to substantiate the possibility that the K*9 knob was functionally similar to the K10 chromosome although the K*9 and K10 knobs are morphologically quite similar. Thus it is not known whether the K*9 knob is a transposed K10 knob or not.Item The role of tumor-associated macrophages in pancreatic cancer(University of Missouri--Columbia, 2023) Zhou, Jing; Li, GuangfuDue to the lack of early diagnosis and efficient therapy, it is projected that pancreatic cancer (PaC) will become the second leading cause of cancer-related death in the U.S. by 2030. Conventional therapies provide very limited benefit to human patients. Surgery, as a potential cure, is only available for a small proportion of patients. PaC is resistant to most therapies and has a dense desmoplastic stroma, and most patients die of distant metastasis. Tumor-associated macrophages (TAMs) are essential components of the tumor microenvironment (TME) and play essential roles in the regulation of tumor progression and immunity. In recent years, macrophage-targeted monotherapy or integrated therapies have been investigated in pre-clinical models. However, only limited success was obtained when these drugs or ideals translated into clinic trials. PaC is resistant to immune checkpoint therapy, but the underlying mechanisms are largely unknown. In this study, comparative analysis of single-cell RNA sequencing (scRNA-Seq) data and validated experiments demonstrated that more exhausted effector CD8+ T cells and increased M2-like TAMs with a reduced capacity of antigen presentation are detected in resistant Panc02-formed tumors versus responsive Panc02-H7-formed tumors. Our data highlight the correlation of tumor-induced imbalance of macrophages with the fate of tumor-resident effector CD8+ T cells and PaC response to [alpha]PD-1 immunotherapy. TAMs as a critical regulator of tumor immunity and immunotherapy contribute to PaC resistance to immune checkpoint blockade. Using scRNA-Seq, we identified TAMs as the main cells producing transforming growth factor-beta-induced protein (TGFBI, also known as [beta]ig-H3). Further in vitro and in vivo studies demonstrate that TGFBI as a macrophage (M[phi])-intrinsic and secreted factor promotes PaC tumor growth, programs M[phi], and impacts T cell activation and exhaustion. These exciting findings inspire us to perform further mechanistic studies and the potential of TGFBI and M[phi] as PaC therapeutic targets.Item The identification of novel genes involved in copper and oxygen metabolism(University of Missouri--Columbia, 2020) Gudekar, Nikita S.; Petris, Michael J.Copper (Cu) is an essential trace dietary metal which is also potentially toxic. Cells have evolved an intricate system of transporters and chaperones to carefully regulate Cu homeostasis. Cu uptake is mediated by the Cu1+-specific permease, CTR1. Cytoplasmic Cu is delivered to specific compartments via a series of metallochaperones. In the trans-Golgi network (TGN), the ATP7A or ATP7B proteins are required to pump Cu into the secretory pathway to various cuproenzymes. ATP7A also plays a protective role against Cu toxicity by trafficking to the plasma membrane to export Cu from the cell. Metallothioneins (MTs) are another type of protein that plays a protective role against Cu toxicity by sequestering excess Cu in the cytoplasm. There are four isoforms of MT in mice of which MT I and MT II are ubiquitously expressed. Our preliminary data demonstrates the essentiality of ATP7A, MTI and MTII in copper tolerance. We generated a fibroblast cell line in which Atp7a, Mt-I, and Mt-II genes were deleted (Atp7a-/Mt-), which resulted in sensitivity of these cells to sub-micromolar levels of copper. Using a genome-wide CRISPR-Cas9 deletion screen, we identified a novel gene, VHL (von Hippel-Lindau), that when deleted confers Cu tolerance to Atp7a-/Mt- cells. The VHL protein is a ubiquitin-ligase responsible for the degradation of HIF transcription factors, which are the major regulators of gene expression in response to hypoxia. We show that VHL deletion confers Cu tolerance by stimulating the expression of the ATP7B copper transporter. Pharmacological inhibition of VHL-HIF1[alpha] by Roxadustat (a prolyl hydroxylase inhibitor), which is clinically used to treat anemia, conferred resistance to copper by upregulating ATP7B. Importantly, Roxadustat was found to increase hepatic ATP7B expression in vivo. These novel data identify a previously unknown link between copper homeostasis and oxygen sensing and have potential translational implications for the treatment of Wilson disease, a copper overload condition cause by insufficient expression of ATP7B.Item Leveraging large scale beef cattle genomic data to identify the architecture of polygenic selection and local adaptation(University of Missouri--Columbia, 2020) Rowan, Troy; Decker, Jared E.Since the invention of the first array-based genotyping assay for cattle in 2008, millions of animals have been genotyped worldwide. Leveraging these genotypes offers exciting opportunities to explore both basic and applied research questions. Commercial genotyping assays are of adequate variant density to perform well in prediction contexts but are not sufficient for mapping studies. Using reference panels made up of individuals genotyped at higher densities, we can statistically infer the missing variation of low-density assays through the process of imputation. Here, we explore the best practices for performing routine imputation in large commercially generated genomic datasets of U.S. beef cattle. We find that using a large multi-breed imputation reference maximizes accuracy, particularly for rare variants. Using three of these large, imputed datasets, we explore two major population genetics questions. First, we map polygenic selection in the bovine genome, using Generation Proxy Selection Mapping (GPSM). This identifies hundreds of regions of the genome actively under selection in cattle populations. Using a similar approach, we identify dozens of genomic variants associated with environments across the U.S., likely involved local adaptation. Understanding the genomic basis of local adaptation in cattle will enable select and breed cattle better suited to a changing climate.