No description available.

No description available.

Approved for public release; distribution is unlimited. / The USS Winston S. Churchill (DDG-81) shock trial was conducted in May and June of 2001 off the coast of Naval Station Mayport, Florida. Because the USS Winston S. Churchill best represented the new line of Flight II-A Arleigh Burkes, it was chosen to undergo ship shock trials for its class. These trials are necessary in order to evaluate the vulnerability and survivability of the hull and the mission essential equipment in a "combat shock environment". However, shock trials are very expensive, require extensive planning and coordination, and represent a potential hazard to the marine environment and its mammals. Computer modeling and simulation are showing themselves to be a plausible alternative in investigating the dynamic response of a ship under these shock trials conditions. This thesis investigates the use of computer ship and fluid modeling, coupled with underwater explosion simulation and compares it to actual shock trial data from the USS Winston S. Churchill. Of particular concern in this study is the amount of fluid that must be modeled to accurately capture the structural response of a full ship finite element model. Four fluid meshes were constructed and used to study the ship's response to an underwater explosion. Each simulation data was analyzed to determine which mesh best represented the actual ship shock trial results. / Lieutenant, United States Navy

Mycobacterium tuberculosis is an exquisitely adapted intracellular pathogen that encounters hostile, host-derived reactive nitrogen and oxygen intermediates during the course of infection of its human host. These radicals cause DNA damage, which is repaired through various pathways to allow for the continued survival of the organism. Base excision repair (BER) is one such pathway, which depends on DNA glycosylases to identify and excise damaged DNA bases. Formamidopyrimidine DNA glycosylase (Fpg/ MutM/ FAPY) and Endonuclease VIII (Nei) are such enzymes, which both target oxidatively damaged DNA and together, form the Fpg family of DNA glycosylases. Bioinformatic analyses identified two copies each of Fpg and Nei-encoding genes in M. tuberculosis as well as in its non-pathogenic relative, Mycobacterium smegmatis. To understand the role of these multiple glycosylases in the maintenance of genomic integrity and survival of mycobacteria, the genes encoding the four Fpg/Nei glycosylases were individually deleted in M. smegmatis strain mc2155 by homologous recombination. In addition to the four single mutants, double and triple Fpg and Nei glycosylase knockout mutants were generated by sequential gene knockout. When compared to the parental strain, the single and double mutants showed no variation in growth kinetics, no increased sensitivity to hydrogen peroxide and no increase in spontaneous mutation rates. However, a slight increase in frequency of spontaneous C T transition mutations was observed in double knockout mutants compared to the wild type and single mutant strains. These results suggest that these enzymes may be part of an extensive network of enzymes which collectively work to enhance the overall survival of M. smegmatis through the repair of oxidatively damaged DNA.

Maintenance of genomic stability is paramount for survival of an organism; failure to repair DNA damage ultimately leads to the accumulation of genetically unstable cells and the onset of different human diseases including cancer. DNA single strand breaks and base oxidation/alkylation are among the most frequent types of DNA damage occurring spontaneously in cells. Base excision repair (BER), which copes with the majority of these lesions, is therefore a fundamental DNA repair system. Accordingly, it is important to understand how BER is regulated, and particularly, how and if BER is affected by the cellular load of DNA damage. Although functions of key BER proteins are well-defined, regulation of their expression is poorly understood. During BER, the protein XRCC1 is particularly important. It functions as a scaffold, stabilising repair complexes at sites of DNA damage thereby promoting efficient DNA repair. As a central coordinator in BER, it is therefore of great interest to understand how expression of XRCC1 is controlled. In this thesis I demonstrate that modulation of XRCC1 expression is mediated by transcription factor Sp1. Importantly, Sp1 is also affected during the DNA damage response, suggesting an indirect mechanism promoting BER modulation in response to the cellular DNA damage load. In fact, I show that, in response to persistent DNA strand breaks, the key DNA damage signalling factor ATM phosphorylates Sp1. This initiates Sp1 degradation, negatively affecting BER. Therefore, this thesis identifies a mechanism involving signalling from ATM that regulates BER in response to persistent DNA damage, which I link to susceptibility to apoptosis and cell elimination. I hypothesise that regulation of DNA repair in response to persistent DNA damage constitutes a mechanism to promote the elimination of potentially pre-cancerous cells that accumulate unrepairable levels of DNA lesions.

No description available.

acase@tulane.edu / Influenza is a highly contagious viral respiratory infection that occurs in annual outbreaks. Activity levels for the 2017-2018 influenza season reached heights not seen since the 2009 pandemic. This was partly due to the inefficiency of the vaccine (25% effective) against the predominant circulating strain, H3N2. To make matters worse, current antiviral therapies must be given within 48 hours of the onset of symptoms. This is often well outside the window of opportunity for hospitalized patients. Developing a therapy that promotes repair of the extensive damage that occurs in severely infected patients is vital for their recovery. Our lab focuses on the innate immune response, more specifically the IL-22 pathway, and the mechanisms involved in repair following pulmonary injury and infection. IL-22 is important in cell proliferation, wound healing, maintaining epithelial barriers and innate pathogen defense. In the lung, its receptor, IL-22Ra1, is only found on epithelial cells and is rapidly induced in response to damage of the lung epithelium. The central hypothesis of this dissertation is that IL-22Ra1 is induced during influenza infection on pulmonary epithelial and progenitor cells, allowing for enhanced sensitivity to IL-22. We have found this induction to be TLR3 and STAT1 dependent. In vivo, bronchial brushings from H1N1 infected mice (PR/8/34) mice demonstrate that Il-22ra1 is rapidly induced in the airways following infection. This occurs in a STAT1 dependent manner as upregulation does not occur in STAT1-/- mice in vivo or following STAT1 inhibition in vitro. This pathway is important as IL-22 treatment induces expression of tight junction transcripts both in vitro and in vivo. Moreover, we believe this induction of IL-22Ra1 is critical for the survival of lung progenitor cells as we have data showing that over 80% of basal cells express Il-22ra1 in the naïve lung. Furthermore, we have developed a lung organoid model and upon treatment with IL-22, organoid size was significantly increased after seven days as evidenced by measurement and BrdU incorporation. Overall, our data shows that IL-22Ra1 is highly induced after injury and subsequent treatment with IL-22 is essential for altering tight junctions and promoting lung repair. / 1 / Kelly Douglas Hebert II

No description available.

DNA repair mechanisms constitute an essential cellular response to DNA damage arising either from metabolic processes or from environmental sources such as ultraviolet radiation. Repair of these lesions may be via direct reversal, or by processes such as nucleotide excision repair (NER), a coordinated pathway in which lesions and the surrounding nucleotides are excised and replaced via DNA resynthesis. The importance of repair is illustrated by human disease states such as xeroderma pigmentosum and Cockayne's syndrome which result from defects in the NER system arising from mutations in XP- genes or XP- and CS- genes respectively Little detail is known of DNA damage repair processes in plants, despite the economic and ecological importance of these organisms. This study aimed to expand our knowledge of the process of NER in plants, largely via a polymerase chain reaction (PCR)-based approach involving amplification, cloning and characterisation of plant genomic DNA and cDNA. Homologues of the NER components XPF/RAD1 and XPD/RAD3 were isolated as both genomic and complete cDNA sequences from the model dicotyledonous plant Arabidopsis thaliana. The sequence of the 3'-untranslated region of atXPD was also determined. Comparison of genomic and cDNA sequences allowed a detailed analysis of gene structures, including details of intron/exon processing. Variable transcript processing to produce three distinct transcripts was found in the case of atXPF. In an attempt to validate the proposed homologous function of these cDNAs, assays to test complementation of resistance to ultraviolet radiation in the relevant yeast mutants were performed. Despite extensive amino acid sequence conservation, neither plant cDNA was able to restore UV-resistance. As the yeast RAD3 gene product is also involved in vivo in transcription, and so is required for viability, the atXPD cDNA was tested in a complementation assay for this function in an appropriate yeast mutant. The plant cDNA was found to substantially increase the viability of the yeast mutant. The structural and functional significance of these results is discussed comparatively with reference to yeast, human and other known homologues. Other putative NER homologues were identified in A. thaliana database sequences, including those of ERCC1/RAD10 and XPG/ERCC5/RAD2, and are now the subjects of ongoing investigations. This study also describes preliminary investigations of putative REVS and RAD30 translesion synthesis genes from A. thaliana.

Graduation date: 2003