Le principal système d’invasion chez Salmonella requiert un système de sécrétion de type III(T3SS-1) qui induit un mécanisme d’entrée de type Trigger. Cependant, d’autres invasine sont été décrites chez Salmonella mais leurs rôles dans la virulence restent peu connus. Nous avons ainsi caractérisé le rôle de Rck en tant qu’invasine chez Salmonella Enteritidis, et démontré par différentes approches que Rck induit un mécanisme d’invasion de type Zipper.L'étude de la cascade de signalisation cellulaire induite par Rck a permis de suggérer un modèle d'internalisation impliquant l’actine, le complexe Arp2/3, les GTPases Rac et Cdc42,Akt, la PI3K de classe I et Src. L'analyse du pouvoir d'invasion d'un mutant de S. Enteritidis cultivé dans des conditions où il est incapable d'exprimer les facteurs d'invasion connus : T3SS-1, Rck et PagN montre l’existence d'autre facteurs d’entrée encore non identifiés chez Salmonella qui semblent induire une invasion de type Zipper et de type Trigger. L’ensemble de ces données font de Salmonella, la première bactérie capable d’envahir les cellules soit via un mécanisme de type Trigger, dépendant au moins du T3SS-1, soit via un mécanisme de type Zipper, dépendant au moins de Rck et révèlent la complexité des mécanismes d’invasion de Salmonella. / The main invasion system of Salmonella requires a type III secretion system (T3SS-1) which promotes a Trigger entry mechanism. However, other invasins were described in Salmonella but their roles in virulence remain unclear. We have shown that Salmonella Enteritidis caninvade cells via the Rck outer membrane protein and we have demonstrated by different approaches that Rck mediates a Zipper entry process. Characterisation of the cellular transduction pathway induced by Rck enable us to propose a model of internalisation involving actin, Arp2/3, Rac and Cdc42, Akt, class I PI3K and Src. Finally, the invasion ability of a S. Enteritidis mutant grown under culture conditions that did not allow the expression of any identified invasion factors (T3SS-1, Rck and PagN) provides evidences for still non-characterised Salmonella invasion factors which seem to induce both Zipper and Trigger mechanisms. Overall, our data indicate that Salmonella is the first bacterium found tobe able to invade cells by both a Trigger mechanism at least mediated by the T3SS-1 and a Zipper entry process at least mediated by Rck. Study of the T3SS-1-independent invasion systems could bring to a better understanding of Salmonella pathogenicity, particularly in regard to the different diseases induced by Salmonella and to its great diversity of hosts.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Australian Acacia species are an important group of invaders and are known to form dense monospecific cultures in invaded habitats. Despite the ecological and economic importance of invasive acacias, little is known about their invasive biology both from an ecological and evolutionary perspective. Molecular genetic methods have increasingly become important in identifying source populations for invasive species and determining the population genetic structure of these populations. This thesis applied molecular tools to understand the invasion ecology of Acacia pycnantha and its rhizobial symbionts as a model system of Australian Acacia introductions. Specific objectives were to: reconstruct the molecular phylogeny of invasive and native populations of populations of Acacia pycnantha and identify the native provenance of A. pycnantha; identify microsatellite markers for Acacia pycnantha and other invasive Australian acacias based on transferring microsatellite markers developed for A. mangium, A. saligna, Paraserianthes lophantha and universal chloroplast microsatellites developed from tobacco; assess the introduction dynamics of Acacia pycnantha in South Africa and identify the source populations in the species’ native range ; and determine which nitrogen fixing symbionts nodulate A. pycnantha and determine whether A. pycnantha brought its symbionts along from its native range or acquired them in the invasive range. Nuclear and chloroplast DNA sequence data were used to reconstruct phylogeographic relationships between native and invasive A. pycnantha populations. The chloroplast phylogeny showed that Australian populations of A. pycnantha are geographically structured into two previously informally recognized lineages (representing wetland and dry land forms). Habitat fragmentation is probably the result of cycles of aridity and abundant rainfall during the Pleistocene0. The invasive population in Portugal was found to be the wetland form while South African populations were found to be predominantly wetland form although some dryland forms were identified. Thirty microsatellites out of the forty nine tested microsatellites successfully amplified across all species tested (A. implexa, A. longifolia, A. melanoxylon, A. pycnantha and A. podalyriifolia). High Transfer rates varied between 85% for microsatellites developed for A. mangium to 50% for those developed in A. saligna. Although transfer rates were high only twelve microsatellites (24%) out of the fifty tested were polymorphic while the chloroplast microsatellites showed no polymorphism. The low level of polymorphic loci calls for development of more microsatellites in this genus especially for species that have high commodity value. Nuclear microsatellites revealed three genetic groupings with substantial admixture in the native range (1. wetland Victoria and South Australia populations; 2. dryland Victoria and Flinders Range population; and 3. New South Wales). Admixture in the native range may have occurred as a result of reforestation exercises. Acacia pycnantha has been widely used in rea forestation projects in Australia because of its fast growth rate and ease of germination. Admixed populations were most - likely introduced to South Africa thus establishment of A. pycnantha may have been facilitated by already admixed propagules in the invasive range. Extensive admixture in the native range made it difficult to identify source populations of invasive A. pycnantha found in South Africa. The rhizobial symbionts of A. pycnantha were identified, showing that this species utilizes a wider suite of symbionts in its invasive range than its native range and there is support for both the co-introduction and host jumping hypotheses. This creates substantial opportunities for horizontal gene transfer between previously allopatric bacterial lineages, with as yet unknown consequences for plant and bacterial invasions.

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L'adénocarcinome canalaire pancréatique (ACP) est le type de cancer le plus fréquent touchant le pancréas exocrine. Il est caractérisé par un phénotype métastatique et chimio-résistant pour lequel il n'existe aucun marqueur diagnostic, ni de traitement efficace. Les projections pour 2030 montrent que ce cancer pourrait devenir la deuxième cause de mortalité. Il y a un besoin urgent de mieux comprendre comment progresse l'ACP. La dissémination métastatique dépend de plusieurs mécanismes cellulaires dont l'invasion du stroma par les cellules cancéreuses. Nous avons montré récemment que le canal transmembranaire TRPM7 est surexprimé dans l'ACP et régule la migration cellulaire. Le but de ce travail est d'évaluer le rôle de TRPM7 dans l'invasion et de mettre en évidence les mécanismes moléculaires impliqués dans les cellules cancéreuses d'ACP et également dans les cellules non-cancéreuses. TRPM7 régule l'invasion basale dans les cellules cancéreuses pancréatiques via l'entrée constitutive de magnésium et la régulation de la sécrétion de MMP-2, uPA et Hsp90α. TRPM7 interagit directement avec Hsp90α et sa kinase participe à la phosphorylation des résidus sérines. De plus, l'expression de TRPM7 dans les métastases est corrélée à celle dans la tumeur primaire. Dans les cellules non cancéreuses, TRPM7 n'est pas impliqué dans l'invasion basale mais sa surexpression (par transfections de plasmides ou induite par une exposition au cadmium, un polluant probablement carcinogène) entraine la transformation des cellules vers un phénotype invasif. TRPM7 est impliqué dans la modification de l'homéostasie magnésique majoritairement, dans la modification de morphologie cellulaire et la transition épithélio-mésenchymateuse. Pour conclure, nos résultats apportent de nouvelles connaissances sur le rôle TRPM7 en tant que régulateur de l'invasion basale dans l'ACP et initiateur dans l'acquisition du phénotype invasif des cellules non-cancéreuses / Pancreatic ductal adenocarcinoma (PDAC) is the most common form of pancreatic cancer. It is characterized by a metastatic and chemoresistant phenotype for which there is no diagnostic marker or effective treatment. It may become the second leading cause of cancer-related death by 2030. There is an urgent need to better understand PDAC progression. Metastatic spread depends on several cellular mechanisms, including the invasion of stroma by cancer cells. We have recently shown that the transmembrane channel TRPM7 (Transient Receptor Potential Melastatin related 7) is overexpressed in PDAC and regulates cell migration. The aim of this work is to evaluate TRPM7 implication in invasion and to highlight the molecular mechanisms in PDAC and non-cancer pancreatic cells. TRPM7 channel regulates basal cell invasion, MMP-2, uPA and Hsp90α secretion in human pancreatic cancer cell lines through constitutive magnesium entry. TRPM7 interacts directly with Hsp90α and it contributes to the phosphorylation of serine residues. Magnesium could participate by activating TRPM7 kinase or by modifying Hsp90α conformation. Moreover, TRPM7 expression in metastatic lymph nodes is correlated to its expressionin primary tumor. In non-cancer cells, TRPM7 is not implicated in basal cell invasion but its overexpression (through plasmid orchronic treatment with cadmium, known as probable carcinogen pollutant) induces invasive phenotype transition. TRPM7 is mainly involved in magnesium homeostasis variation, in cellular morphology modification and mesenchymal transition. In conclusion, our results provide new insights into the key role of TRPM7 in both regulation of basal cell invasion in ACP and initiation of invasive phenotype acquisition in non-cancer epithelial cells

We study the behavior of diffusive Lotka-Volterra systems in environments with spatially varying carrying capacities. In particular, we use numeric and analytic techniques to study two similar models for population growth, in order to determine their qualitative differences. Additionally, we investigate competition models in the presence of periodic disasters, in order to determine what factors affect competitive dominance. We found that under conditions of high spatial heterogeneity, the model for population growth was the main factor determining coexistence. Under low spatial heterogeneity, the effect of disturbance on the stronger competitor was the main factor determining coexistence.

Glioma is one of the most challenging types of brain tumors to be treated or controlled locally. One of the main problems is to determine which areas of the apparently normal brain contain glioma cells, as gliomas are known to infiltrate several centimetres beyond the clinically apparent lesion that is visualized on standard CT or MRI. To ensure that radiation treatment encompasses the whole tumor, including the cancerous cells not revealed by MRI, doctors treat the volume of brain that extends 2cm out from the margin of the visible tumor. This approach does not consider varying tumor-growth dynamics in different brain tissues, thus it may result in killing some healthy cells while leaving cancerous cells alive in other areas. These cells may cause recurrence of the tumor later in time which limits the effectiveness of the therapy. In this thesis, we propose two models to define the tumor invasion margin based on the fact that glioma cells preferentially spread along nerve fibers. The first model is an anisotropic reaction-diffusion type tumor growth model that prioritizes diffusion along nerve fibers, as given by DW-MRI data. The second proposed approach computes the tumor invasion margin using a geodesic distance defined on the Riemannian manifold of brain bers. Both mathematical models result in Partial Differential Equations (PDEs) that have to be numerically solved. Numerical methods used for solving differential equations should be chosen with great care. A part of this thesis is dedicated to discuss in detail, the numerical aspects such as stability and consistency of different finite difference methods used to solve these PDEs. We review the stability issues of several 2D methods that discretize the anisotropic diffusion equation and we propose an extension of one 2D stable method to 3D. We also analyze the stability issues of the geodesic model. In comparison, the geodesic model is numerically more stable than the anisotropic diffusion model since it results in a rst-order PDE. Finally, we evaluate both models on actual DTI data from patients with glioma by comparing our predicted growth with follow-up MRI scans. Results show improvement in predicting the invasion margin when using the geodesic distance model as opposed to the 2cm conventional Euclidean distance.