Le cycle cellulaire est un processus finement régulé à différents niveaux. p27 est un inhibiteur des complexes cyclines/CDK et cette fonction lui confère un rôle antiprolifératif lorsqu'il est localisé dans le noyau. De nombreuses études ont montré que p27 se comporte comme un suppresseur de tumeur lorsqu'il est localisé dans le noyau des cellules via l'inhibition des cyclines/CDK. De manière surprenante, p27 a également des fonctions oncogéniques dans certaines situations, notamment lorsqu'il est présent dans le cytoplasme. Il s'avère qu'en plus de ses fonctions de régulateur du cycle cellulaire, p27 est également impliqué dans la régulation d'autres processus cellulaires, comme la migration, la cytocinèse, la transcription ou encore l'autophagie et la différenciation. Durant ma thèse, j'ai caractérisé deux de ces nouvelles fonctions en mettant en lumière un rôle de p27 dans la régula.on des invadopodes ainsi que dans l'oncogenèse pancréatique.Mon premier objectif a été de comprendre la fonction de l'interaction de p27 avec la protéine Cortactine, un nouveau partenaire de p27.Cette protéine joue un rôle important dans la régulation de l'invasion cellulaire. J'ai confirmé cette interaction dans différents types cellulaires et observé une colocalisation au niveau des invadopodes. J'ai également cartographié leurs domaines d'interaction respectifs et montré que l'interaction de p27 avec Cortactine était induite par une stimulation avec du sérum. L'interaction p27/Cortactine permet le recrutement de PAK1, une sérine/thréonine kinase impliqué dans l'invasion cellulaire et favorisant notamment le renouvellement des invadopodes, sur Cortactine. J'ai également observé que les cellules invalidées pour p27 présentent de nombreux invadopodes et dégradent la matrice extracellulaire de manière très importante par rapport aux cellules exprimant p27. Par des approches d'inhibiteurs et de siARN j'ai mis en évidence que ce phénotype implique la voie Rac1/PAK1/phospho-Ser113-Cortactine qui est sous-activée en l'absence de p27 à cause du défaut de recrutement de PAK1 sur Cortactine, stabilisant ainsi les invadopodes. Mon second objectif a été d'étudier les mécanismes par lesquels p27 régule l'oncogenèse pancréatique. En effet, différentes études cliniques ou chez la souris ont montré que la localisation nucléaire de p27 était requise pour son rôle de suppresseur de tumeur dans le pancréas. Or nous avons constaté dans un modèle murin génétique d'oncogenèse pancréatique induite par l'activation de K-Ras que p27 était exclu du noyau avant l'apparition des premières lésions, suggérant un rôle précoce dans l'oncogenèse de ce tissu. De manière surprenante, l'étude comparative par immunomarquage de pancréas de souris p27+/+, p27-/- et p27CK-/CK-, un modèle de souris knock-in où p27 n'est plus capable d'inhiber les cyclines/CDK, n'a pas montré d'effet de p27 sur la prolifération dans le pancréas exocrine. Par contre, ces études ont montré une localisation anormale de plusieurs marqueurs de polarité acinaire ainsi qu'une réexpression des facteurs de transcription Sox9 et Pdx1, impliqués dans le processus de transdifférenciation cellulaire à l'origine de l'oncogenèse pancréatique appelée métaplasie acino-canalaire. Nous avons montré que p27 régulait de manière directe la transcription de Sox9 en interagissant avec son promoteur, suggérant que p27 participe normalement à la répression transcriptionnelle de Sox9 dans le noyau, réprimant ainsi la métaplasie acino-canalaire.Ainsi, mes travaux de thèse ont permis l'identification de deux nouvelles fonctions de p27. Une fonction oncogénique, indépendante de son activité d'inhibiteur des CDK/cyclines, par laquelle p27 régule la protéine Cortactine, et par ce biais les invadopodes et l'invasion ainsi qu'une fonction de suppresseur de tumeur dépendante des cyclines/CDK via la répression de la transcription de Sox9 dans les cellules acinaires du pancréas. / Cell cycle is a tightly regulated process. One level of regulation is provided by p27, a cyclin/ CDK inhibitor and as such, p27 has an antiproliferative function. Several studies have shown that p27 is a tumor suppressor when it is located in the nucleus via the inhibition of cyclins/ CDKs. Surprisingly, p27 may also play oncogenic roles depending on the cellular context, especially when it is excluded from the nucleus. In fact, several lines of evidence indicate that p27 functions extend beyond cell cycle regulation and that p27 also regulates cell migration, cytokinesis, transcription, autophagy and stemness/differenciation. During my PhD, I have characterized two novel p27 functions, one in the regulation of invadopodia, and the second in pancreatic oncogenesis.My first aim was to investigate the function of the interaction between p27 and Cortactin, a new p27-interacting protein which is an important regulator of cell invasion. I confirmed this interaction in different cell lines and found that p27 and Cortactin colocalized in invadopodia. I have mapped the domains mediating the interaction in both proteins and found that this interaction is induced after serum stimulation. p27 allows the recruitment of PAK1, a serine/ threonine kinase involved in cell invasion which promotes invadopodia turnover, on Cortactin. I also found that p27 knock-out cells have an increased number of invadopodia and degrade extracellular matrix more efficiently than wild-type cells. Using inhibitors and siRNAs I have shown that this phenotype involves the Rac1/PAK1/phospho-Ser113-Cortac.n pathway, which is underactivated in absence of p27 due to the PAK1/Cortactin interaction defect, causing a stabilization of invadopodia.My second aim was to study the mechanism by which p27 regulates pancreatic oncogenesis. Severals studies in the clinic or in animal models have shown that nuclear localization of p27 is required for its tumor suppressor function in the pancreas. In a genetic mouse model of K- Ras driven pancreatic oncogenesis, I found that p27 was excluded from the nucleus before the apparition of lesions, suggesting an early function in oncogenesis in this tissue. Surprisingly, comparative studies of pancreas from p27+/+, p27-/- and p27CK-/CK- (a knock- in mouse model where p27 no longer binds cyclins/CDKs) mice by immunostaining did not show any difference in proliferation in the exocrine pancreas. However, these studies have shown the mislocalization of different acinar polarity markers and the re-expression of two transcription factors, Sox9 and Pdx1, which are involved in acinar-to-ductal metaplasia, a cell transdifferenciation process thought to be the underlying cause of pancreatic oncogenesis. I have found that p27 regulates Sox9 transcription and directly interacts with its promoter, suggesting that p27 participates in the transcriptionnal repression of Sox9 in normal conditions to prevent acinar-to-ductal metaplasia. Overall, my PhD work has allowed the identification of two novel roles of p27. An oncogenic function, independent of its cyclin/CDK inhibitory activity, by which p27 regulates Cortac.n, invadopodia and cell invasion and a tumor suppressor function dependent of cyclin/CDK via the repression of Sox9 transcription in pancreas acinar cells.

The pathogen Campylobacter fetus (CF) is classified into two subspecies, Campylobacter fetus subspecies fetus (CFF) and Campylobacter fetus subspecies venerealis (CFV). Even though CFF and CFV are genetically closely related, they exhibit differences in their host adaptation; CFF inhabits the gastrointestinal tract of both humans and several animal species, while classical CFV is specific to the bovine genital tract and is of particular concern with respect to international bovine trade regulation. Traditionally, differentiation between the two subspecies has been achieved using a limited number of biochemical tests but more rapid and definitive genetic methods of discrimination are desired. A recent study suggested that the presence of a genomic island only in CFV could discriminate between the two sub- species but this hypothesis could not be confirmed on a collection of isolates originating in Canada. To identify alternative gene targets that would support accurate subspecies discrimination, this study has applied several approaches including suppression subtractive hybridization and whole genome sequencing supplemented with optical mapping. A subtractive hybridization screen, using a well-characterized CFV isolate recovered during routine screening of bulls in an Artificial Insemination center in western Canada and that lacked much of the genomic island and a typical Canadian CFF isolate, yielded 50 clones; characterization of these clones by hybridization screening against selected CF isolates and by nucleotide sequence BLAST analysis identified three potentially CFV-specific clones that contained inserts originating from a second genomic island. Further screening using a larger CF sample set found that only Clone #35 was truly CFV-specific. Optical maps (NcoI digest) of the Canadian CFF and CFV isolates used for the subtractive hybridization showed that certain regions of these genomes were quite distinct from those of two reference strains. Whole genome sequencing of these two isolates identified two target genes (PICFV5_ORF548 and CFF_Feature #3) that appear to be selectively retained in the two subspecies. Screening of a collection of CF isolates by PCRs targeting these three loci (SSH_Clone #35, PICFV5_ORF548 and CFF_Feature #3) supported their use for subspecies discrimination. This work demonstrates the complex genomic diversity associated with these CF subtypes and the challenge posed by their discrimination using limited genetic loci.

Com o aumento progressivo do número de casos de infecção por diferentes arbovírus, por exemplo, dengue, zica e chikungunya, faz-se necessário o desenvolvimento de novas técnicas para o combate a esses arbovírus. A manipulação genética possibilitou a obtenção de mosquitos geneticamente modificados que sejam capazes de suprimir a população selvagem ou impedir a transmissão de agentes etiológicos gerando doenças. O estudo teve como objetivo o estabelecimento de linhagens para supressão populacional de Aedes aegypti. Esta construção apresenta esterilidade condicionada à presença ou ausência de antibiótico no meio em que esses mosquitos se desenvolvem durante a fase larval. Dessa forma, sem a necessidade de se utilizar radiação para obter insetos estéreis, é possível melhorar a qualidade dos machos adultos liberados e aumentar a competitividade dos mesmos em competir por fêmeas selvagens e adicionalmente gerar o desejado quadro de supressão populacional. / The increasing number of infection cases by arboviruses, for instance Dengue, Zika and Chikungunya, it is necessary to develop new techniques to fight against these arboviruses. Genetic manipulation allowed the production of genetically modified mosquitoes that are capable of suppressing the wild population or prevent pathogens transmission and avoid disease development. The project proposes to establish lines for population suppression of Aedes aegypti, one of the main vectors of those diseases. This construction presents the conditional sterility due to the presence or absence of antibiotics in the environment where these mosquitoes are developed during the larval stage. Thus, without the need to use radiation for sterile insects, it is possible to improve the quality of the released adult males and enhance the competitiveness thereof in competing with wild females and additionally generate population suppression.

O esquecimento intencional pode cumprir uma função estratégica no sistema cognitivo, que permite aos indivíduos não pensar sobre acontecimentos indesejados do passado, tais como eventos traumáticos, dolorosos e violentos, dos quais se prefere não recordar. Enquanto esquecer involuntariamente é uma falha da lembrança, por outro lado, esquecer intencionalmente parece ser uma função estratégica da memória. A presente dissertação teve por objetivo investigar os mecanismos neurocognitivos que contribuem para o esquecimento de memórias. A dissertação se organizou em dois estudos. O primeiro estudo consiste em uma revisão sistemática de artigos empíricos publicados nos últimos dez anos sobre a supressão de memórias indesejadas. O segundo estudo é um ensaio empírico, no qual foi executado um experimento adaptado do paradigma Think/No-Think com a utilização de marcadores eletrofisiológicos de eletroencefalograma. Participaram do experimento 22 sujeitos, alocados aleatoriamente em dois grupos com estratégias distintas de esquecimento: Supressão de memória e substituição de pensamentos. Durante toda a tarefa experimental, os participantes tiveram dados de EEG continuamente gravados. Os resultados decorrentes do ensaio empírico estão de acordo com os achados da literatura, indicando que a positividade parietal em torno de 400-800ms após a apresentação do estímulo é um marcador de lembrança consciente durante a recuperação de memória. Apenas na estratégia de supressão de memória houve uma redução da positividade centro-parietal durante o esquecimento, entre 450 e 700ms após apresentação do estímulo. Além disso, uma maior deflexão no componente N2 durante a supressão é um preditor de esquecimento induzido. Os achados indicam que é possível mapear o sistema neurocognitivo subjacente à supressão de memórias. / Intentional forgetting can be characterized as a strategic function of the cognitive system that allows us not to think about unwanted memories from our past, as for example emotional events or traumatic experiences that we would prefer not to remember. While forgetting involuntarily is a failure of recollection, on the other hand, forgetting intentionally seems to be a strategic function of memory. The aim of this dissertation was to investigate the neurocognitive mechanisms that contribute to forgetting memories. The dissertation was organized in two studies. The first study consists of a systematic review of empirical articles published in the last ten years on the suppression of unwanted memories. The second study is an empirical essay, in which an experiment adapted from the Think/No-Think paradigm was performed, with the use of electrophysiological markers of electroencephalogram. Twenty-two subjects participated in the experiment, randomly assigned to two groups with distinct strategies of forgetting: Memory suppression and thought substitution. Throughout the experimental task, participants had continuously recorded EEG data. The results of the empirical essay are in agreement with the literature findings, indicating that the parietal positivity around 400-800 ms after the presentation of the stimulus is a marker of conscious memory during memory recovery. Only direct memory suppression reduced centro-parietal positivity during forgetting, between 450 and 700 ms post-stimulus. Also, a greater deflection in the N2 component during suppression is an induced forgetting predictor. The findings indicate that it is possible to map the neurocognitive system underlying memory suppression.

The endoplasmic reticulum (ER) facilitates the synthesis, assembly and quality control of all secretory, transmembrane, and resident proteins of the endomembrane system. An accumulation of unfolded proteins or a disruption in the specialized folding environment within the organelle causes ER stress, thus impairing the folding capacity of the ER. In response to this stress, the ER initiates a signaling cascade called the unfolded protein response (UPR) in an attempt to restore ER homeostasis. The vertebrate UPR is propagated by three ER-resident transmembrane proteins (i.e., PERK, IRE1α, and ATF6α), each initiating a signaling cascade that ultimately culminates in production of a transcriptional activator. The UPR was originally characterized as a pathway for the upregulation of ER chaperones, and a comprehensive body of subsequent work has shown that protein synthesis, folding, oxidation, trafficking, and degradation are all transcriptionally enhanced by the UPR. However, UPR activation is also accompanied by extensive mRNA suppression. The mechanisms responsible for this suppression and its consequences for physiological processes beyond the realm of ER protein folding and processing are only now beginning to be described. The overall goal of my thesis work was to explore this process of UPR-mediated gene suppression by identifying the mechanisms involved and the cellular processes affected. As a result, I characterized a novel mechanism of UPR-mediated transcriptional repression involving the translational regulation of the transcription factor C/EBPβ resulting in the suppression of the gene Il4ra, encoding an essential subunit of the IL-4/IL-13 receptor. As a consequence of this suppression, a novel effect of ER stress was identified in the impairment of IL-4/IL-13 signaling, a finding of potential significance in the study of inflammatory disease. In addition to this mechanism, I validated a novel approach to the identification of UPR-regulated transcription factors using publically available bioinformatic software. Through this analysis, I identified the transcription factor HNF4α as a novel post-translational UPR-regulated transcription factor, the regulation of which, resulted in the suppression of a number of lipid metabolic genes. This analysis not only identified a novel UPR-regulated transcription factor, but also presented a new tool for the characterization of UPR-mediated gene suppression. My work represents an independent and original investigation into the process of UPR-mediated gene suppression; and reveals that the UPR facilitates transcriptional suppression through the transcriptional, translational, and post-translational regulation of multiple transcription factors, resulting in the coordinated attenuation of physiological pathways. This function of the UPR is likely to contribute to metabolic, inflammatory, and other chronic disease states.

No description available.

Vegetable producers may benefit from integrating living mulches into their operations to manage weeds and improve soil quality. Living mulches, however, can reduce vegetable yield through competition. Here we investigate strip tilling into living mulches and then direct seeding a vegetable crop in the strip till zone as a production practice to limit competition. We further investigate the use of two surface-applied mulches, a newsprint hydromulch and a compost blanket, for weed control within the strip till zone. In field conditions, living mulches reduced vegetable yield by 49-84% and the use of the newsprint hydromulch and compost blanket reduced weed biomass by 84% and 85% respectively. In greenhouse conditions, a 50% reduction in the hydromulch application rate used in the field experiment achieved similar weed control, suggesting an application rate of 6.4 L m-2 or a mulch strength of 0.6 MPa may be sufficient for weed control with a hydromulch.

Magister Public Health - MPH / Background: With the improvements in the effectiveness and availability of antiretroviral therapy (ART), perinatally infected children are surviving to adolescence and emerging as a significant sub-population living with HIV/AIDS in Zimbabwe. Adolescents, aged 10-19 years, face unique challenges related to adherence to chronic medication due to this period of vulnerability that is characterised by decreased parental support and supervision, decreased inhibition, increased risk-taking, and immature judgement. It is widely reported that poor adherence to ART leads to viral rebound, disease progression and drug resistance, in addition to increasing the risk of transmitting resistant strains of HIV to others. It is imperative to determine the factors that influence ART adherence among HIV positive adolescents so that effective interventions can be put in place. The current study described the factors that are associated with adherence to ART among HIV positive adolescents in Zimbabwe. Methodology: A cross-sectional survey of 136 randomly selected adolescents (10-19 years) who were receiving ART at two referral hospitals in Masvingo District in 2019 was undertaken. A questionnaire was administered to collect data on socio-demographic characteristics, adherence and factors related to adherence such as person/patient, health system, medication, disease characteristics and social factors. Clinical data were extracted from the Electronic Monitoring Patient System. SPSS v24 was used for descriptive and inferential analysis. Results: More than half of the participants (61%) had combined optimal adherence (dose adherence, schedule adherence and adhered to dietary instructions) in the previous three days. The most frequent reasons reported for missing HIV medications in the previous month was being away from home (50%); forgetfulness (25%); and having too many pills to take (25%). In bivariate analysis, only duration of time since HIV diagnosis was significantly associated with combined adherence to ART in the previous three days. Conclusion: Tailored interventions are recommended to address low adherence amongst adolescents. These interventions should include convenient clinic appointment schedules for adolescents to pick up medication, reminders to take medication, regimen change to a single dose, and peer education and adherence clubs to improve knowledge about HIV and treatment, and curb treatment fatigue.

Creativity is a complex construct that is conceptualized and measured in multiple ways. This study examined the relationship between creativity and personality taking this into account. It was hypothesized that applying different conceptions and measures would cause variation in the creativity-personality relationship. The participants (N = 224) were undergraduate students completed six creativity measures, a personality inventory, and a demographic questionnaire. Personality predicted more creative production (R2 = .277) than creative potential (R2 = .176) and more self-reported creativity (R2 = .348) than that which was externally-rated (R2 = .149). Personality predicted creativity beyond demographic and intellect variables, but the effects varied based on the creativity measure. Openness was most consistently and strongly related to creativity. Other personality factors demonstrated suppression effects in multiple models. Overall, the results suggest that despite relatively small effects of personality on creativity, it can help strengthen prediction in creativity models. Implications for educational settings and future research are discussed.

Inducer performance is investigated for a variety of inducer geometries operating at multiple flow conditions using computational fluid dynamics. Inducers are used as a first stage in turbopumps to minimize cavitation and allow the pump to operate at lower inlet head conditions. The formation of inlet flow recirculation or backflow in the inducer occurs at low flow conditions and can lead to instabilities and cavitation-induced head breakdown. Backflow formation is often attributed to tip leakage flow. The performance of an inducer with and without tip clearance is examined. Removing the tip clearance eliminates tip leakage flow; however, backflow is still observed. Analysis suggests that blade inlet diffusion, not tip leakage flow, is the fundamental mechanism leading to the formation of backflow. Performance improvements in turbopump systems pumping cold water have been obtained through implementation of a recirculation channel called a stability control device (SCD). However, many inducers actually pump cryogenic fluids, such as liquid hydrogen. To determine the real world effects of SCD implementation, inducer performance at on and off design flow coefficients with and without an SCD were modeled with liquid hydrogen as the working fluid. Relevant thermodynamic effects present in liquid hydrogen at cryogenic temperatures are considered. The results reveal that the SCD yields marginal changes in the head coefficient. However, a stabilizing effect occurs at all considered flow coefficients, where a reduction in backflow occurs over much of the pump operational range. This occurs due to the SCD maintaining consistent, low incidence angles at the inducer leading edge.The final consideration of this work is the acceleration of an inducer from rest to the operating rotational rate. Rapid acceleration of rocket engine turbopumps during start-up imparts significant transient effects to the resulting flow field, causing pump performance to vary widely when compared to quasi-steady operation. A method to simulate turbopump start-up using CFD is developed and presented. The defined outlet pressure is modified based on the difference between simulation inlet pressure and target inlet pressure of a previous simulation. This process is repeated until simulation inlet pressure is essentially constant during start-up. Using this novel simulation method, the performance of a centrifugal turbopump during start-up is simulated. Analysis suggests this simulation method provides a reasonable prediction of cavitation formation and inducer performance.