Sarcocystis neurona is an apicomplexan parasite that is a major cause of equine protozoal myeloencephalitis (EPM). During intracellular development of S. neurona, many genes are temporally regulated. To better understand gene regulation, it is important to identify and characterize regulatory elements controlling gene expression in S. neurona. To perform this study, it was essential to establish transfection system for this parasite. Hence, the 5 flanking region of the SnSAG1 gene was isolated from a genomic library and used to construct expression plasmids. In transient assays, the reporter molecules -galactosidase (-gal) and yellow fluorescent protein (YFP) were expressed by electroporated S. neurona, thereby confirming the feasibility of performing molecular genetic experiments in this organism. Stable transformation of S. neurona was achieved using a mutant dihydrofolate reductase thymidylate synthase (DHFR-TS) gene of T. gondii that confers resistance to pyrimethamine. This selection system was used to create transgenic S. neurona that stably express -gal and YFP. These transgenic clones were shown to be useful for analyzing growth rate of parasites in-vitro and for assessing drug sensitivities. To uncover possible sequence elements involved in promoter activity, the 5 flanking regions of five S. neurona genes were subjected to comparative analysis. This revealed the presence of a 7-base conserved motif GCGTCTC. Using a dual luciferase assay system, the SnSAG1 promoter was subjected to functional analysis. The motif GAGACGC located between -136 and -129 upstream of the transcription start site was found to be essential for SnSAG1 expression. This motif functions in an orientation dependent manner and was shown to play a role in binding nuclear proteins of S. neurona.

The fundamental physics and techniques employed in Laplace transform deep level transient spectroscopy (L-DLTS) are reviewed. A Laplace-DLTS system has been constructed. The high resolving power of this system has been demonstrated experimentally. The L-DLTS system was applied to characterize the defects in undoped n-type ZnO thin film grown by the pulsed laser deposition (PLD) method. A 0.3 eV deep trap has been identified. The formations of Ec-0.39eV and Ec-0.20eVcan be enhanced when the sample surface is seriously damaged by high temperature annealing.AnEc-0.25eV trap is identified in the freshly grown samples, but would disappear after the storage of 3 months. Copper doped n-type ZnO thin film samples with low carrier concentration (n~〖10〗^16 〖cm〗^(-3)) were investigated by using both conventional and Laplace DLTS techniques. Positive DLTS signal peaks were detected that are suspected to be contributed by the minority carrier (hole carrier) emission. A physics model involving the inversion layer of a metal-insulator-semiconductor contact has been invoked to interpret the hole carrier concentration existing near the metal-semiconductor interface. Expression for the defect concentration is determined as a function of the temperature of DLTS peaks. AnEv+0.6eV defect with high concentration (N_T~〖10〗^17 〖cm〗^(-3)) was detected. The concentration of Ev+0.6eVcan be enhanced when the annealing temperature was increased from 750 to 900 degree C. / published_or_final_version / Physics / Master / Master of Philosophy

In the context of sustainable development, steelmakers and automotive manufacturers decided for some years now to join their efforts to promote the development and use of advanced high strength steels such as the present TRIP steels in order to reduce the fuel consumption and emission of greenhouse gas. These multiphase steels contain some retained austenite, a ductile phase that can transform into hard and brittle martensite during a mechanical solicitation. One the one hand, this transformation improves the mechanical properties during plasticity by bringing about an additional work-hardening. On the other hand, the appearence of a hard and brittle phase can give rise to premature cracking after necking. Knowing the good influence of martensitic transformation on the work-hardening, this Thesis starts with the characterisation of the relationship between transformation rates and testing conditions. It appears that, for each testing condition, there is an optimum austenite stability that leads to a maximum uniform strain. After necking under monotonic loading conditions, the damage mechanisms that takes place in these steels has been characterised. It can be concluded that the TRIP-aided steels that present low or moderate austenite stability behave exactly like Dual-Phase steels, in which martensite replaces retained austenite. However, a very stable retained austenite brings about a significant toughness improvement by providing an additional work-hardening contribution in the necking zone. The mechanical behaviour of these steels has also been characterised under cyclic loading conditions. The results indicate that, for particular loading conditions (i.e. low load levels), the martensitic transformation improves the fatigue properties.

<p>Case hardening distortions are a major problem for gear manufacturers. The aim of the current work is to create a simulation model, able to predict how and when case hardening distortions arise. The results presented in this thesis form a basis for such a model.</p><p>Two case hardening steels, with base carbon contents of 0.20 and 0.21 % C were studied using dilatometer experiments. One of them was carburized to 0.36, 0.52 and 0.65 % C in order to investigate the influence of carbon content. Experiments were performed during both isothermal and continuous heating and cooling conditions. The results were used to evaluate phase transformations, heat expansion behaviors and phase transformation strains. The expansion behavior of the material was modeled as a function of temperature, carbon content and phase fractions. The phase transformations to martensite and bainite were modeled, using the Koistinen-Marburger equation and a transformation rate equation based on Austin-Rickett kinetics, respectively. Experiments were simulated using the COMSOL Multiphysics software, to verify the model with respect to martensite and bainite transformations, heat expansion behavior and phase transformation strains.</p>

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<p>Trichome formation in Arabidopsis lyrata is a naturally occurring trait with phenotypic polymorphisms within wild populations. In Swedish accessions of A. lyrata, three genetic polymorphisms situated in the coding region of GL1, an important transcription factor in trichome production, have been identified, and these are candidates for being the cause of a glabrous phenotype. In this study a complementation test has been performed to clarify which mutation/mutations that are detrimental for trichome formation. A set of constructs has been transformed into A. thaliana, a close relative to A. lyrata, and subsequent generations of plants were examined for phenotype, genotype and gene expression. A SNP (Single Nucleotide Polymorphism) in the R3 MYB domain of GL1, resulting in a change of an alanine to aspartic acid, was identified as the critical polymorphism. The other two mutations, two indels, were harmless to protein function. The inserted constructs were under control of the native GL1 promoter. Plants that, because of the SNP, lacked trichome production, became totally glabrous.</p>

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Vitamin A is known to have an important role in cellular differentiation and proliferation. In addition to regulating normal cellular processes vitamin A has also been shown to possess potent antineoplastic activity. The work in this dissertation characterizes the role of retinoic acid (RA) in cellular transformation and tumorigenesis with known oncogene involvement. These studies were initiated by examining the effects of RA on human carcinoma cell lines which express an activated c-ras gene. The bladder carcinoma, EJ/T24 (c-rasᴴ) and the two lung carcinoma cell lines, LXl (c-rasᴷ) and A2182 (c-rasᴷ), were not sensitive to RA. No inhibition of anchorage- or density-dependent growth was observed. Therefore, since these in vitro markers of transformation indicated a lack of effectiveness of RA on carcinomas containing a c-ras gene, retrovirally transformed cells were tested for RA sensitivity. Kirsten murine sarcoma, Balb/c murine sarcoma virus, and Simian sarcoma virus transformed NIH/3T3 and NRK cells were used in these studies. In contrast to the human carcinoma cell lines, anchorage-independent growth of some of the virally transformed cells was very sensitive to inhibition by RA. Anchorage-independent growth of KNRK and SSVNRK cells was sensitive to high concentrations (5 μM) of RA; whereas, Balb/cMSV3T3 and SSV3T3 were sensitive to 1-20 nM RA. BALB/cMSVNRK anchorage-independent growth was stimulated 3.5 fold by 1 μM RA. KNRK displayed a 60% reduction in anchorage-dependent growth at 10 μM RA while little inhibition was observed with the other retrovirally transformed cells. A high level of sensitivity to RA inhibition of anchorage-independent growth was correlated with the presence of cytoplasmic retinoic acid binding protein (CRABP). This indicated that CRABP may have some role in the inhibition of retrovirally induced cellular transformation. RA was shown to significantly reduce the incidence and size of Balb/cMSV3T3 cell tumors in nude mice. The inhibition of tumorigenesis in vivo therefore confirmed the results observed in vitro. To investigate the mechanism by which RA was acting to inhibit retroviral transformation, v-onc mRNA levels were examined. RA had no effect on v-onc mRNA levels in cell lines sensitive to the inhibition of transformation. The effect of RA on the relative rate of synthesis of p21, the transforming protein of KMSV and Balb/cMSV, was investigated. No effect of RA was observed in any of the cell lines. Also, GDP binding by p21 in KNRK cell was unchanged by RA treatment indicating that the functional activity of this transforming protein was not modified. RA does appear to be effective in inhibiting retrovirally induced cellular transformation and tumorigenesis. Evidence presented here indicates that this inhibition is not due to a direct effect of RA on the expression of the v-onc gene and/or gene product. Therefore, some other essential cooperating event(s) occurring within the cell are being acted upon by RA.

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No description available.