<p>Topoisomerase 1 (Top1), a Type IB topoisomerase, functions to relieve transcription- and replication-associated torsional stress in DNA. Top1 cleaves one strand of DNA, covalently associates with the 3’ end of the nick to form a Top1-cleavage complex (Top1cc), passes the intact strand through the nick and finally re-ligates the broken strand. The chemotherapeutic drug, Camptothecin, intercalates at a Top1cc and prevents the crucial re-ligation reaction that is mediated by Top1, resulting in the conversion of a nick to a toxic double-strand break during DNA replication or the accumulation of Top1cc. This mechanism of action preferentially targets rapidly dividing tumor cells, but can also affect non-tumor cells when patients undergo treatment. Additionally, Top1 is found to be elevated in numerous tumor tissues making it an attractive target for anticancer therapies. We investigated the effects of Top1 on genome stability, effects of persistent Top1-cleavage complexes and elevated Top1 levels, in Saccharomyces cerevisiae. We found that increased levels of the Top1cc resulted in a five- to ten-fold increase in reciprocal crossovers, three- to fifteen fold increase in mutagenesis and greatly increased instability within the rDNA and CUP1 tandem arrays. Increased Top1 levels resulted in a fifteen- to twenty-two fold increase in mutagenesis and increased instability in rDNA locus. These results have important implications for understanding the effects of CPT and elevated Top1 levels as a chemotherapeutic agent.</p> / Dissertation

Il a été montré récemment que l'instabilité génétique joue un rôle central dans les étapes précoces de la tumorigenèse. Celle-ci provoquerait une activation chronique des voies ATR/CHK1 et ATM/CHK2 dans les cellules précancéreuses, entrainant l'apoptose ou la sénescence des cellules concernées. Les mécanismes de checkpoint constituant une barrière contre la progression tumorale, toute mutation affectant ce checkpoint serait ainsi sélectionnée très tôt dans le processu s de tumorigenèse et faciliterait ensuite la progression tumorale. Ce modèle met en évidence le rôle central de l'instabilité génomique et du checkpoint dans la progression tumorale.Au cours de ma thèse, je me suis intéressé au complexe Claspine / Timeless / Tipin, initialement identifié comme médiateur de la voie ATR/CHK1 et qui est donc considéré comme ayant une fonction suppresseur de tumeur. Cependant, Claspine présente aussi des propriétés oncogéniques, puisque qu'elle est surexprimée dans de nombreuses lignées tumorales et cette surexpression est importante pour la prolifération cellulaire. Nous nous sommes donc demandé comment cette protéine pouvait être à la fois un oncogène et un suppresseur de tumeur. Chez la levure, l'homologue de Claspine est impliqué dans le maintien de la stabilité des fourches de réplication, indépendamment de sa fonction dans le checkpoint. Nous proposons que dans les cellules cancéreuses cette surexpression permette une meilleure stabilité des fourches, ce qui serait très important pour répliquer efficacement un génome soumis à un stress réplicatif constant. Au cours de ma thèse, nous avons construit et caractérisé un modèle de cellulescancéreuses HCT116 dans lesquelles nous avons diminué le niveau de Claspine ou deTimeless grâce à des shRNA, sans que cela n'affecte l'efficacité du checkpoint de réplication. Nous avons pu observer dans ces cellules un ralentissement de la progression des fourches de réplication et l'apparition d'une instabilité génétique. Il semblerait que spécifiquement dans le cas de Timeless, le ralentissement de la fourche de réplication et l'instabilité génomique se manifeste surtout dans les régions du génome répliquées tardivement. / The correct execution of the replication program is essential for the maintenance of genome integrity during S phase. Indeed, replication fork progression is frequently challenged by DNA lesions and by a variety of natural pause sites. Arrested forks are unstable structures, which represent a major threat for the genome integrity if they are not promptly stabilized and restarted. In response to replicative stress, cells activated the replication checkpoint to prevent collapse of stalled forks and promote fork recovery. Recent evidence indicates that spontaneous replication stress occurs in precancerous lesions and promotes the development of cancer. Identifying the origin of this replication stress would represent a better understanding of the early stages of tumorigenesis. We study the function of Claspin, a mediator of the replication checkpoint, which plays a key role in the response to replication stress. It is therefore acting as a tumor suppressor, preventing genomic instability during DNA replication. Intriguingly, recent evidence indicates that Claspin is overexpressed in different cancers and can also acts as an oncoprotein. Studies on Mrc1p, the yeast homologue of Claspin, have shown that Mrc1 is permanently associated to forks, where it forms a complex with two partners called Tof1p and Csm3p (homologues of human Tim and Tipin respectively). We have shown by DNA combing that the replicative function of Mrc1p, is critical for viability in the presence of a replication stress. In l ight of our results in yeast, we propose that the Claspin/Tim/Tipin complex may also play a direct role for the replication of human cells. If confirmed, this replication function may account for the role of this complex in the cancer process and tumor resistance to genotoxic agents commonly used in anticancer therapy.

The objective of this study was to determine the perceptions of the impact of political instability on Foreign Direct Investment (FDI) in Nigeria. In conducting this research, 350 questionnaires were distributed to some selected Foreign Direct Investors, Nigerians, and chief executive officers (CEOs) of indigenous companies. Out of the 350, 280 questionnaires were completed, returned and analyzed for this research. Chi-square statistics and frequency distribution were used for the evaluation of the perceptions of the impact of political instability on foreign direct investment in Nigeria. Two hypotheses were also developed on the same subject. The results of the tests conducted showed that fo reign investment is negatively affected by political instability in Nigeria. The results of the study suggest that it would be good public policy for the Nigerian Government to strike a balance between the nation's developmental objectives and the interest of foreign investors. The study makes some recommendations to help improve the climate for foreign investments.

It is known that age-related changes impacting multiple organ systems occur earlier in people with Down syndrome (Ds), but the biological basis underlying this trisomy 21-associated propensity for premature aging is poorly understood. Given that the trisomic/normal cells from people with mosaic Ds (mDs) are identical with regards to environmental exposures and genes (except for chromosome 21 copy number), comparisons of these isogenic trisomic/disomic cells allow one to “unmask” the cellular consequences of trisomy 21 by removing extraneous factors. The primary aim of this study was to determine if trisomy 21 results in an increase in the acquisition of age-related somatic chromosomal changes. To meet this aim, chromosome-specific telomere lengths, senescence-associated distension of satellites (SADS), and chromosomal instability frequencies were compared between the isogenic trisomic/disomic cells of people with mDs ranging from 1 to 44 years of age. Chromosome-specific telomere lengths were quantified using a Q-FISH (pantelomeric probe) method. The average trisomic cell telomere length (3.609 mean, +/- 0.082 SE) was significantly less than the average disomic cell telomere length (3.888 +/- 0.083) (n=28; p

United States intelligence officers and policymakers need reliable forecasts of country, regional, and global stability or instability. Such forecasts require a methodology for identifying and analyzing factors that contribute to stability. The anticipation of this stability level can facilitate crisis warning and diplomatic strategies for various timelines, including five, ten, and twenty year forecasts. While the problem of forecasting can be tackled in various ways, in the interest of time and space, I will only go into a few of them. The approach I will use is multiple linear regression to generate a short-term forecast for the stability levels of the countries of the Former Soviet Union (FSU). This model could ultimately be used to help formulate policies that enhance stability in developing or transitioning countries.

Ce manuscrit aborde le problème de l'atomisation de films liquides à travers diverses expériences portant sur leur formation, déstabilisation et fragmentation. Une première partie identifie et décrit deux mécanismes de désintégration à l'œuvre lors de la rétractation d'un film de savon. Lorsque le film se détache sur une frontière, le bord de Plateau est entrainé et son accélération explique la déstabilisation. Lorsque le perçage a lieu au centre, le battement du film résulte de l'interaction avec l'atmosphère au repos, ce qui conduit à sa fragmentation. Une seconde étude explique le plissement singulier de certaines cloches liquides par un ressaut hydraulique à interfaces libres assurant la transition d'un écoulement supercritique vis-à-vis des ondes capillaires à un écoulement subcritique. La courbure marquée associée à cette transition conduit à une accélération centripète du liquide susceptible de déstabiliser la cloche en aval. La formation des embruns par l'intermédiaire de l'éclatement des bulles de surface est abordée dans une troisième partie. La géométrie des bulles, le mécanisme de drainage de leurs films et les événements de perçage sont étudiés afin de rendre compte de l'épaisseur de la bulle au début de l'éclatement. La dynamique ultérieure de fragmentation est détaillée conduisant à une caractérisation du spray produit. Une dernière partie étudie l'atomisation dite effervescente sur une expérience modèle : une nappe liquide plane ensemencée en fines bulles d'air favorisant la nucléation de trous. Sur la base de mesures des taux de nucléation et croissance des trous, un modèle statistique du réseau de ligaments liquides formés par la réunion des bourrelets ceinturant les trous permet un description du spray issu de la fragmentation du réseau. / This thesis tackles the problem of liquid films atomization through various experimental configurations dealing with their formation, destabilization and fragmentation. In a first part, two mechanisms of receding soap film disintegration are identified and described. When the film is released from a border, the acceleration sustained by the Plateau border explains the destabilization. When puncture occurs in the center, the film flapping is promoted by the interaction with the surrounding atmosphere which leads to its fragmentation. In a second study, the singular folding of liquid bells is explained by an original free surfaces hydraulic jump insuring transition from a subcritical to a supercritical flow with respect to capillary waves. The strong curvatures associated with this transition, also implying strong centripetal acceleration of the flowing liquid, may induce the downstream sheet destabilization. The question of marine aerosols formation via surface bubble bursting is investigated in a third part. Bubbles geometry, their film drainage mechanism and puncture events are studied in order to account for the film thickness at the onset of bursting. The subsequent bursting dynamics is detailed to characterize the spray production. In a last part, effervescent atomization is studied on a model experimental set up: a flat liquid sheet seeded with small air bubbles acting as heterogeneous hole nuclei. On the basis of holes nucleation and growth measurements, a statistical model of the liquid ligament red resulting from the holes rims combination offers a description of the spray generated by the red fragmentation.

Determining the factors affecting drizzle formation in marine boundary layer (MBL) clouds remains a challenge for both observation and modeling communities. To investigate the roles of vertical wind shear and buoyancy (static instability) in drizzle formation, ground-based observations from the Atmospheric Radiation Measurement Program at the Azores are analyzed for two types of conditions. The type I clouds should last for at least 5h and more than 90% time must be nondrizzling and then followed by at least 2h of drizzling periods, while the type II clouds are characterized by mesoscale convection cellular structures with drizzle occur every 2 to 4h. By analyzing the boundary layer wind profiles (direction and speed), it was found that either directional or speed shear is required to promote drizzle production in the type I clouds. Observations and a recent model study both suggest that vertical wind shear helps the production of turbulent kinetic energy (TKE), stimulates turbulence within cloud layer, and enhances drizzle formation near the cloud top. The type II clouds do not require strong wind shear to produce drizzle. The small values of lower tropospheric stability (LTS) and negative Richardson number (R-i) in the type II cases suggest that boundary layer instability plays an important role in TKE production and cloud-drizzle processes. By analyzing the relationships between LTS and wind shear for all cases and all time periods, a stronger connection was found between LTS and wind directional shear than that between LTS and wind speed shear.

No description available.

Recursive partitioning is embedded into the general and well-established class of parametric models that can be fitted using M-type estimators (including maximum likelihood). An algorithm for model-based recursive partitioning is suggested for which the basic steps are: (1) fit a parametric model to a data set, (2) test for parameter instability over a set of partitioning variables, (3) if there is some overall parameter instability, split the model with respect to the variable associated with the highest instability, (4) repeat the procedure in each of the daughter nodes. The algorithm yields a partitioned (or segmented) parametric model that can effectively be visualized and that subject-matter scientists are used to analyze and interpret. / Series: Research Report Series / Department of Statistics and Mathematics

Student Number : 9607275H - MSc dissertation - School of Electrical and Information Engineering - Faculty of Engineering and the Built Environment / Internet worms are capable of quickly propagating by exploiting vulnerabilities of hosts that have access to the Internet. Once a computer has been infected, the worms have access to sensitive information on the computer, and are able to corrupt or retransmit this information. This dissertation describes a method of predicting Internet instability due to the presence of a worm on the Internet, using data currently available from global Internet routers. The work is based on previous research which has indicated a link between the increase in the number of Border Gateway Protocol (BGP) routing messages and global Internet instability. The type of system used to provide the prediction is known as an autoencoder. This is a specialised type of neural network, which is able to provide a degree of novelty for inputs. The autoencoder is trained to recognise “normal” data, and therefore provides a high novelty output for inputs dissimilar to the normal data. The BGP Update routing messages sent between routers were used as the only inputs to the autoencoder. These intra-router messages provide route availability information, and inform neighbouring routers of any route changes. The outputs from the network were shown to help provide an early warning mechanism for the presence of a worm. An alternative method for detecting instability is a rule-based system, which generates alarms if the number of certain BGP routing messages exceeds a prespecified threshold. This project compared the autoencoder to a simple rule-based system. The results showed that the autoencoder provided a better prediction and was less complex for a network administrator to configure. Although the correlation between the number of BGP Updates and global Internet instability has been shown previously, this work presents the first known application of a neural network to predict the instability using this correlation. A system based on this strategy has the potential to reduce the damage done by a worm’s propagation and payload, by providing an automated means of detection that is faster than that of a human.