Recombinaison à haute fréquence induite par l'antigène grand T des papovavirus

Afin de définir les mécanismes par lesquels les antigènes grand T des papovavirus induisent la recombinaison dans les cellules de mammifère, nous avons construit deux lignées cellulaires permettant d'étudier la recombinaison homologue entre un tandem tête-à-queue de gènes T moyen du virus du polyome inactifs pour la transformation néoplasique. Ces lignées ont été nommées Hy2 et Hy5. Une recombinaison homologue entre les séquences répétées de T moyen devrait restaurer un gène intact capable de transformer la cellule. La reconstitution d'un gène T moyen fonctionnel par recombinaison spontanée se produit avec un taux qui se situe entre 10-7 et 10-5 événement par génération cellulaire. Dans la lignée Hy2, la recombinaison reconstitue un gène T moyen entre les deux copies défectueuses du gène. Dans la lignée Hy5, la recombinaison spontanée se produit surtout entre les séquences plasmidiques de l'insert viral provoquant ainsi l'inversion d'un des gènes T moyen inactifs. Cette inversion augmente l'expression du gène défectueux et la surproduction d'antigène T moyen mutant transforme la cellule. L'introduction de l'antigène grand T du virus du polyome augmente de 10 000 à 1 000 000 de fois le taux de recombinaison dans les lignées Hy2 et Hy5. L'antigène grand T de SV40 induit aussi une recombinaison à haute fréquence en dépit du fait qu'il ne puisse pas initier la synthèse de l'ADN à l'origine de réplication du virus du polyome. Des mutants de l'antigène grand T du virus du polyome inactifs pour l'initiation de la réplication virale provoquent également une recombinaison de l'insert viral dans les deux lignées. Mes résultats montrent que la recombinaison est indépendante des fonctions réplicatives de grand T et ne nécessite pas l'amplification des séquences virales. La restauration d'un gène T moyen n'est donc pas le résultat du modèle de la structure en pelure d'oignon. Dans la lignée Hy2, nous proposons que la recombinaison reconstitue un gène T moyen intact entre les deux copies défectueuses par des mécanismes de "slipped-strand mispairing" et d'échange inégal au niveau de l'insert. Dans la lignée Hy5, la restauration d'un gène T moyen intact est plutôt le résultat d'échange inégal entre chromatides-soeurs, de conversion génique et d'événements de recombinaison complexes. Un de ces événements mène à la perte d'un fragment acentrique et la formation d'un chromosome dicentrique. Mes résultats permettent de mieux comprendre comment l'antigène grand T induit la formation d'aberrations chromosomiques dans des cellules transformées. Finalement, je discute d'une relation possible entre le degré de méthylation d'une région d'ADN et son influence sur l'efficacité de recombinaison homologue dans les cellules de mammifère

Appariement de points caractéristiques trouvés à même les régions d'avant-plan de vidéos à spectres visible et infrarouge

Systèmes de caméras calibrés -- Extraction des points caractéristiques -- Appariement des points caractéristiques -- Filtrage des paires de points caractéristiques -- Filtrage des paires de points caractéristiques -- Le projet de référence -- Aperçu de la méthode -- Prétraitements -- La méthode du squelette -- Le processus DCE -- Filtrage par paires de blobs -- Filtrage par RANSAC -- Calcul des disparités -- Complexité des méthodes

RECTGAUSS-Tex : block-based background subtraction

This paper presents an approach to background subtraction based on rectangular regions (blocks). The general principle is to successively divide the image into blocks and detect foreground pixels based on the color histogram and the variance between pixels of the blocks. Then, the classic Gaussian Mixture background subtraction method is applied to refine the detected foreground. Results show that this approach reduces false positives by filtering noise coming from small motion as it is based on groups of pixels instead of on individual pixels

An articulated assistive robot for intuitive hands-on-payload manipulation

This paper presents an intelligent assistive robot designed to help operators in lifting and moving large payloads through direct physical contact (hands-on-payload mode). The mechanical design of the robot is first presented. Although its kinematics are similar to that of a cable-suspended system, the proposed mechanism is based on articulated linkages, thereby allowing the payload to be offset from the rail support on which it is suspended. A dynamic model of the robot is then developed. It is shown that a simplified dynamic model can be obtained using geometric assumptions. Based on the simplified dynamic model, a controller is then presented that handles the physical human-robot interaction and that provides the operator with an intuitive direct control of the payload. Experimental validation on a full-scale prototype is presented in order to demonstrate the effectiveness of the proposed robot and controller

The diabetes-linked transcription factor PAX4 promotes β-cell proliferation and survival in rat and human islets

The mechanism by which the β-cell transcription factor Pax4 influences cell function/mass was studied in rat and human islets of Langerhans. Pax4 transcripts were detected in adult rat islets, and levels were induced by the mitogens activin A and betacellulin. Wortmannin suppressed betacellulin-induced Pax4 expression, implicating the phosphatidylinositol 3-kinase signaling pathway. Adenoviral overexpression of Pax4 caused a 3.5-fold increase in β-cell proliferation with a concomitant 1.9-, 4-, and 5-fold increase in Bcl-xL (antiapoptotic), c-myc, and Id2 mRNA levels, respectively. Accordingly, Pax4 transactivated the Bcl-xL and c-myc promoters, whereas its diabetes-linked mutant was less efficient. Bcl-xL activity resulted in altered mitochondrial calcium levels and ATP production, explaining impaired glucose-induced insulin secretion in transduced islets. Infection of human islets with an inducible adenoviral Pax4 construct caused proliferation and protection against cytokine-evoked apoptosis, whereas the mutant was less effective. We propose that Pax4 is implicated in β-cell plasticity through the activation of c-myc and potentially protected from apoptosis through Bcl-xL gene expression

Innovation through Wearable Sensors to Collect Real-Life Data among Pediatric Patients with Cardiometabolic Risk Factors

Background. While increasing evidence links environments to health behavior, clinicians lack information about patients’ physical activity levels and lifestyle environments. We present mobile health tools to collect and use spatio-behavioural lifestyle data for personalized physical activity plans in clinical settings. Methods. The Dyn@mo lifestyle intervention was developed at the Sainte-Justine University Hospital Center to promote physical activity and reduce sedentary time among children with cardiometabolic risk factors. Mobility, physical activity, and heart rate were measured in free-living environments during seven days. Algorithms processed data to generate spatio-behavioural indicators that fed a web-based interactive mapping application for personalised counseling. Proof of concept and tools are presented using data collected among the first 37 participants recruited in 2011. Results. Valid accelerometer data was available for 5.6 (SD=1.62) days in average, heart rate data for 6.5 days, and GPS data was available for 6.1 (2.1) days. Spatio-behavioural indicators were shared between patients, parents, and practitioners to support counseling. Conclusion. Use of wearable sensors along with data treatment algorithms and visualisation tools allow to better measure and describe real-life environments, mobility, physical activity, and physiological responses. Increased specificity in lifestyle interventions opens new avenues for remote patient monitoring and intervention

Isolated virtualised clusters: testbeds for high-risk security experimentation and training

International audienceAdequate testbeds for conducting security experiments and test under controlled, safe, repeatable and asrealistic- as-possible conditions, are a key element for the research and development of adequate security solutions and the training of security personnel and researchers. In this paper, we report on the construction and operations of isolated virtualised testbeds used in two separate security research labs in Canada and France, as part of a joint collaborative effort. The main idea was to use mid- to large-scale isolated computing clusters to obtain high levels of scale, manageability and safety by heavily leveraging virtualisation technology, open-source cluster management tools and a network architecture separating experiment and control traffic. Both facilities have been used for conducting different types of security research experiments, including in-lab reconstructions of botnets, denial-of-service attacks, and virus detection experimentation. They have also been used for teaching and training students in experimental security methods. We describe these facilities and the criteria that we used to design them, the research and training activities that were conducted, and close by discussing the lessons learned and the pros and cons of this approach

The case for in-the-lab botnet experimentation: creating and taking down a 3000-node botnet

International audienceBotnets constitute a serious security problem. A lot of effort has been invested towards understanding them better, while developing and learning how to deploy effective counter-measures against them. Their study via various analysis, modelling and experimental methods are integral parts of the development cycle of any such botnet mitigation schemes. It also constitutes a vital part of the process of understanding present threats and predicting future ones. Currently, the most popular of these techniques are “in-the-wild” botnet studies, where researchers interact directly with real-world botnets. This approach is less than ideal, for many reasons that we discuss in this paper, including scientific validity, ethical and legal issues. Consequently, we present an alternative approach employing “in the lab” experiments involving at-scale emulated botnets. We discuss the advantages of such an approach over reverse engineering, analytical modelling, simulation and in-the-wild studies. Moreover, we discuss the requirements that facilities supporting them must have. We then describe an experiment in which we emulated a close to 3000-node, fully-featured version of the Waledac botnet, complete with a reproduced command and control (C&C) infrastructure. By observing the load characteristics and yield (rate of spamming) of such a botnet, we can draw interesting conclusions about its real-world operations and design decisions made by its creators. Furthermore, we conducted experiments where we launched sybil attacks against the botnet. We were able to verify that such an attack is, in the case of Waledac, viable. However, we were able to determine that mounting such an attack is not so simple: high resource consumption can cause havoc and partially neutralise the attack. Finally, we were able to repeat the attack with varying parameters, in an attempt to optimise it. The merits of this experimental approach is underlined by the fact that it is very difficult to obtain these results by employing other methods

The liver receptor homolog-1 (LRH-1) is expressed in human islets and protects β-cells against stress-induced apoptosis

Liver receptor homolog (LRH-1) is an orphan nuclear receptor (NR5A2) that regulates cholesterol homeostasis and cell plasticity in endodermal-derived tissues. Estrogen increases LRH-1 expression conveying cell protection and proliferation. Independently, estrogen also protects isolated human islets against cytokine-induced apoptosis. Herein, we demonstrate that LRH-1 is expressed in islets, including β-cells, and that transcript levels are modulated by 17β-estradiol through the estrogen receptor (ER)α but not ERβ signaling pathway. Repression of LRH-1 by siRNA abrogated the protective effect conveyed by estrogen on rat islets against cytokines. Adenoviral-mediated overexpression of LRH-1 in human islets did not alter proliferation but conferred protection against cytokines and streptozotocin-induced apoptosis. Expression levels of the cell cycle genes cyclin D1 and cyclin E1 as well as the antiapoptotic gene bcl-xl were unaltered in LRH-1 expressing islets. In contrast, the steroidogenic enzymes CYP11A1 and CYP11B1 involved in glucocorticoid biosynthesis were both stimulated in transduced islets. In parallel, graded overexpression of LRH-1 dose-dependently impaired glucose-induced insulin secretion. Our results demonstrate the crucial role of the estrogen target gene nr5a2 in protecting human islets against-stressed-induced apoptosis. We postulate that this effect is mediated through increased glucocorticoid production that blunts the pro-inflammatory response of islet