Dissertations / Theses on the topic 'Chromosomes'
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Morroll, Shaun Michael. "Mapping of yeast artificial chromosomes from Arabidopsis chromosome 5." Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308922.
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Downie, Sarah Elizabeth. "Detection of chromosomes and chromosomal abnormalities in human sperm." Title page, contents and overview only, 1999. http://web4.library.adelaide.edu.au/theses/09PH/09phd751.pdf.
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Bibliography: leaves 135-151. A study of chromosomal abnormalities and the localisation of chromosomes in human sperm, especially from men with TSD, using fluorescence in situ hybridization (FISH). The project entailed: 1. development of reliable FISH protocols, 2. determination of basline frequencies of aneuploidy, 3. analysis of chromosomal abnormalities in men with severe TSD and 4. assessment of the localisation of individual chromosomes within the sperm head.
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Morey, Céline. "Caractérisation du rôle de la région en aval du gène Xist lors de l'inactivation du chromosome X murin par mutagenèse ciblée dans les cellules ES." Paris 5, 2004. http://www.theses.fr/2004PA05N040.
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Chez les mammifères, la compensation de dose des gènes liés à l' X entre les sexes est assurée par l' inactivation transcriptionnelle de l' un des deux chromosomes X, au hasard, chez la femelle. Ce processus dépend des fonctions de comptage et de choix et recquiert l' expression du gène Xist localisé sur le chromosome X. Ce gène produit un grand ARN non-codant qui recouvre le chromosome X inactif. La délétion de 65 kb en aval de Xist, incluant le minisatellite DXPas 34 et l' initiation d' une transcription antisens (Tsix), dans des cellules ES-cellules récapitulant l' inactivation lors de leur différenciation in vitro-induit l'altération du choix et du comptage. Par une stratégie de complémentation cre/oxP, nous avons montré que la restitution de Tsix au site de la délétion de 65 kb dans les cellules XX est insuffisante au rétablissement de l' inactivation aléatoire. . .In mammals, dosage compensation of X-linked genes is ensured by X-chromosome inactivation wherby one X chromosome in each female embryonic cell (ES) is chosen at random to become silenced. X-inactivation depends on the counting of X chromosomes and on the choice of the inactive X, It is mediated by the expression of the Xist non-coding RNA wich coats the inactive X and by the Tsix antisense transcipt, a Tsix antisense transcript, a Xist regulator. A 65 kb deletion extending 3' to Xist and including both Tsix and the DXPas34 minisatellite, disrupts choice and counting. Using a cre/loxP site-specific re-insertion strategy in XX deleted ES cells we showed that targeting back, at the 65 kb mutated locus, the Tsix antisense transcription fails to retore random X-inactivation. In contrast, normal counting can be restored in XO deleted ES cells. .
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Landmann, Cedric. "Rôles et régulations de Polo et BubR1 sur les cassures double-‐brin de l'ADN en mitose." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0852/document.
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La présence de cassures double-brin de l'ADN en mitose est problématique pour les cellules, car cette situation produit des fragments de chromosome ne possédant pas de centromères. En l'absence d'un mécanisme permettant leur prise en charge, ces fragments acentriques n'étant pas attachés au fuseau mitotique, pourraient être ségrégés aléatoirement dans les cellules filles, causant de l'instabilité génomique. Nous avons découvert un mécanisme permettant la transmission correcte des fragments acentriques dans les cellules filles via une structure faisant le lien entre les deux fragments cassés. Plusieurs protéines sont recrutées sur les cassures, comme les kinases mitotiques BubR1 et Polo, et favorisent la ségrégation correcte de ces chromosomes cassés. Cependant, les mécanismes permettant le recrutement de BubR1 et Polo sur les cassures d'ADN en mitose sont inconnus. De plus, les mécanismes moléculaires par lesquels BubR1 et Polo favorisent la ségrégation correcte des fragments acentriques restent à être identifiés. La première partie de mon projet a été d'étudier le rôle et la régulation de BubR1 sur les cassures d'ADN pendant la mitose. Nous avons montré que BubR1 requiert Bub3 pour se localiser sur les chromosomes cassés afin de favoriser leur ségrégation correcte. Nous avons également détecté l'accumulation de FizzyCDC20, un cofacteur de l'E3 ubiquitine ligase APC/C (Anaphase-Promoting- Complex/Cyclosome), sur les cassures d'ADN, et son recrutement dépend de son interaction avec la KEN Box de BubR1. De plus, l'utilisation d'un substrat synthétique de l'APC/C nous a permis de démontrer que la dégradation par l'APC/C est inhibée localement autour du chromosome cassé, de manière dépendante de BubR1. Ces résultats suggèrent fortement que le complexe BubR1/Bub3 recrut é sur les cassures d'ADN inhibe localement l'APC/C en séquestrant FizzyCDC20 et empêche ainsi la dégradation de substrats clefs impliqués dans la ségrégation correcte des chromosomes cassés. La seconde partie de mon projet a été d'étudier les relations d'interdépendance entre Polo et BubR1/Bub3/Fizzy sur les cassures d'ADN en mitose. Nous avons utilisé un laser UV pulsé pour induire des cassures dans un chromosome à un instant précis pendant la mitose, puis nous avons suivi le recrutement de protéines tagguées GFP sur les cassures de chromosome. Cette étude révèle que Polo est rapidement recrutée sur les cassures d'ADN et précède BubR1, Bub3 et Fizzy. De plus, la disparition de BubR1, Bub3 et Fizzy des cassures d'ADN coïncide avec la télophase alors que Polo disparait des cassures pendant l'interphase. Nous avons également montré que le recrutement de BubR1, Bub3 et Fizzy sur les cassures d'ADN est retardé dans les mutants polo, indiquant que Polo est requis pour un recrutement efficace de BubR1, Bub3 et Fizzy sur les cassures d'ADN. Pour finir, nous avons montré que l'accumulation de Polo et BubR1/Bub3/Fizzy sur les cassures d'ADN dépend de deux composants de la réponse aux dommages à l'ADN, le complexe MRN (Mre11-Rad50-Nbs1) et ATM (ataxia-telangiectasia mutated). Ce travail a permis d'avoir une meilleure compréhension sur la dynamique de recrutement de Polo et BubR1/Bub3/Fizzy sur les cassures d'ADN en mitose. De plus, le mécanisme moléculaire par lequel le complexe BubR1/Bub3 agit pour faciliter la ségrégation des chromosomes cassés a pu être en partie élucidéThe presence of DNA double strand breaks (DSB) during mitosis is challenging for the cell, as it produces fragments of chromosome lacking a centromere. If not processed, this situation can cause genomic instability resulting in improper segregation of the broken fragments into daughter cells. We uncovered a mechanism by which broken chromosomes are faithfully transmitted to daughter cells via the tethering of the two broken chromosome ends. Several proteins including the mitotic kinase BubR1 and Polo are recruited to the breaks and mediate the proper segregation of the broken fragments. However, the mechanism underlying Polo and BubR1 recruitment to DNA breaks is unknown. Moreover, the molecular mechanisms by which Polo and BubR1 mediate the proper segregation of the broken fragments remain to be elucidated. We first investigated the role and regulation of BubR1 on DNA breaks during mitosis. We show that BubR1 requires Bub3 to localize on the broken chromosome fragment and to mediate its proper segregation. We also find that FizzyCdc20, a co--‐factor of the E3 ubiquitin ligase Anaphase--‐Promoting--‐Complex/Cyclosome (APC/C), accumulates on DNA breaks in a BubR1 KEN box--‐dependent manner. A biosensor for APC/C activity demonstrates a BubR1--‐dependent local inhibition of APC/C around the segregating broken chromosome. These results are consistent with a model where Bub3/BubR1 complex on DNA breaks functions to inhibit the APC/C locally via the sequestration of FizzyCdc20, thus preserving key substrates from degradation, which promotes proper transmission of broken chromosomes. In a second study, we investigated the dependency relationship between Polo and BubR1/Bub3/Fizzy on DNA breaks in mitosis. We used a pulsed UV laser to break one chromosome at a define time during mitosis. We immediately follow the recruitment of GFP--‐tagged proteins to laser--‐induced DNA breaks. My study reveals that Polo is promptly recruited to DNA breaks and precedes BubR1, Bub3 and Fizzy. In addition, while BubR1, Bub3 and Fizzy dissociation from the breaks coincide with telophase and the nuclear envelope reformation, Polo remains on the breaks well into interphase. We further show that the appearance of BubR1, Bub3 and Fizzy on DNA breaks is delayed in polo mutant, indicating that Polo is required for the robust and efficient recruitment of BubR1, Bub3 and Fizzy to DNA breaks. Finally, the timely accumulation of Polo, BubR1 and Bub3 to DNA breaks depends on two components of the DNA Damage Response, the MRN complex (Mre11--‐Rad50--‐Nbs1) and ATM (ataxia--‐telangiectasia mutated). This work gives us a better understanding on how Polo and BubR1, Bub3 and FizzyCdc20 are recruited to DNA breaks in mitosis and how they promote broken chromosomes segregation
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Prades, Catherine. "Recherche de marqueurs polymorphes dans les régions centromériques des chromosomes humains." Montpellier 1, 1997. http://www.theses.fr/1997MON1T007.
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Imakaev, Maksim (Maksim Viktorovich). "Polymer models of chromosomes." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103234.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 203-215).
Studies of chromosomes have a long history. Since late XIX century, microscopy studies have revealed that chromosomal organization as seen by light microscopy is different among organisms, cell types, or stages of the cell cycle. However, the internal organization of chromosomes at scales below the diffraction limit largely remained unexplored. Recently, genomic techniques to measure contacts between genomic regions were developed; the most advanced of them, Hi-C, measures probabilities of contact between all pairs of genomic regions. Throughout my Ph.D, we have been developing methods to analyze Hi-C data, and to infer principles of chromosomal organization from the contact map provided by Hi-C. As a first step, we developed a toolset to map, analyze, and correct the Hi-C data. We then we performed polymer simulations that implement hypothetical principles of chromosomal organization and compared them to the Hi-C data. We showed that mitotic chromosomes in humans are not organized hierarchically, as thought previously, and are likely folded as an array of consecutive chromosomal loops. In the bacterium Caulobacter Crescentus, we showed that the chromosome is organized as a dense array of supercoiled plectonemes interspersed by highly transcribed regions free of plectonemes. Finally, for human interphase chromosomes, we showed that the equilibrium state of a long unknoted polymer chain is inconsistent with the observed properties of chromosomes.
by Maksim Imakaev.
Ph. D.
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Mascarenhas, Judita. "Chromosome dynamics in Bacillus subtilis characterization of the structural maintenance of chromosomes (SMC) complex /." [S.l. : s.n.], 2004. http://archiv.ub.uni-marburg.de/diss/z2004/0125/.
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Kulharya, Anita S. (Anita Singh). "Cytogenetics of chromosome 22 and its clinical relevance." Thesis, University of North Texas, 1990. https://digital.library.unt.edu/ark:/67531/metadc798385/.
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This investigation reorganizes and identifies chromosomal anomalies and delineates the associated clinical findings. The present investigation involved 37 individuals with anomalies of chromosome 22. The clinical profile with the corresponding cytogenetic anomalies was studied.
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Coultas, Susan L. (Susan Lynette). "A comparison of straight-stained, Q-stained, and reverse flourescent-stained cell lines for detection of fragile sites on the human X chromosome." Thesis, North Texas State University, 1985. https://digital.library.unt.edu/ark:/67531/metadc798127/.
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Cell cultures were examined for percentage of fragile sites seen in straight-stained, Q-stained and reverse fluorescent-stained preparations. In all cases, percentage of fragile site expression was decreased when compared to straight-stained preparations. However, fragile sites seen in Q- and RF-stain could be identified as on X chromosomes.
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Khalil, Ahmad M. "Histone modifications and chromatin dynamics of the mammalian inactive sex chromosomes title." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0008329.
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Thesis (Ph.D.)--University of Florida, 2004.Typescript. Title from title page of source document. Document formatted into pages; contains 102 pages. Includes Vita. Includes bibliographical references.
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Novak, Ivana. "Molecular architecture of meiotic chromosomes /." Stockholm, 2006. http://diss.kib.ki.se/2006/91-7140-959-9/.
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Tannier, Eric. "Evolution Combinatoire, Algorithmique des Chromosomes." Habilitation à diriger des recherches, Université Claude Bernard - Lyon I, 2011. http://tel.archives-ouvertes.fr/tel-00750199.
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Ce mémoire est une présentation de certains de mes travaux de recherches effectués en bioinformatique au laboratoire de Biométrie et Biologie Evolutive de l'université de Lyon 1 depuis 2003, date de mon arrivée en post-doctorat à l'INRIA, suivie de la stabilisation de mon poste un an après.
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Vásárhelyi, Krisztina. "Statistical study of human constitutional chromosome rearrangement breakpoint distributions." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29201.
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In this study the question of nonrandomness in the distribution of human constitutional rearrangements was evaluated. The distribution of breakpoints were analysed in three groups of reciprocal translocations and three groups of inversions, subdivided according to method of ascertainment of cases for study. In addition, one data set of structural aberrations obtained from sperm chromosomes was also analysed.
The method of statistical analysis, based on the binomial distribution, was developed specifically to allow testing distributions in chromosome segments as small as chromosome bands. The distribution of breakpoints was analysed in all data sets using this method, in addition to testing for overall nonrandomness using goodness of fit statistics.
Nonrandomness in breakpoint distributions was found in reciprocal translocations (rcp) and inversions ascertained through abnormalities and through incidental events. However, random distribution was observed in incidentally ascertained de novo rearrangements
as well as in sperm chromosome aberrations.
The nonrandomness in the distribution of rcp breakpoints can be largely attributed to a bias in ascertainment of cases based on the phenotypic manifestations of chromosomal imbalance resulting from a rearrangement. A dependence of the probability of producing specific types of balanced or unbalanced progeny on the position of breakpoints is a likely explanation for the nonrandomness produced in breakpoint distributions. However, some bands including, 5q35, 7p22, 9p22, 13ql4, and 17q25, were observed in different ascertainment groups, excluding selection bias as a likely explanation for this observation. These bands may represent true sites of nonrandom rearrangement due to some factor associated with an underlying DNA sequence or structural characteristic of chromatin
that predisposes to rearrangement at specific sites.
The nonrandomness observed in the distribution of inversion breakpoints is most likely the product of a founder effect. Many identical inversions in apparently unrelated individuals have been found suggesting that a few ancestral mutations have become widespread in the population. A large data set of incidentally ascertained de novo inversions
is required to distinguish between sites of frequent breakage and nonrandomness produced by the ascertainment of related cases.
All evidence considered together, indisputable predisposition to rearrangement at specific sites was not found in this study. Furthermore, an overall random association of constitutional rearrangement breakpoints in bands with known oncogenes and fragile sites was observed. However, the possibility of oncogenes and fragile sites as factors involved in constitutional rearrangements in a few isolated cases cannot be excluded. Nonrandomness was found when distribution of breakpoints in light and dark G bands was compared. An excess of breakpoints in some light G bands was observed even after a conservative correction for a possible pattern recognition bias which may lead to the overascertainment of breakpoints in light G bands.Medicine, Faculty of
Medical Genetics, Department of
Graduate
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He, Bin. "Mitotic Dynamics of Normally and Mis-attached Chromosomes and Post-mitotic Behavior of Missegregated Chromosomes." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/73495.
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Equal segregation of the replicated genomic content to the two daughter cells is the major task of mitotic cells. The segregation is controlled by a complex system in the cell and relies mainly on the interaction between microtubules (MTs) of the mitotic spindle and kinetochores (KTs), specialized protein structures that assemble on each chromatid of each mitotic chromosome. By combining computational modeling and quantitative light microscopy, we established a quantitative model of the forces and regulators controlling metaphase chromosome movement in the mammalian cell line derived from Potorous tridactylis kidney epithelial cells (PtK1) (Chapter 2). This model can explain key features of metaphase chromosome dynamics and related chromosome structural changes experimentally observed. Moreover, the model made predictions, which we tested experimentally, on how changes in spindle dynamics affect certain aspects of chromosome structure. This quantitative model was next used to study the metaphase dynamics of chromosomes with erroneous KT-MT attachments (Chapter 3). Once again, the model predictions were tested experimentally and showed that erroneous KT-MT attachment alters the dynamics not only of the mis-attached KT, but also of its sister KT. Even more strikingly, experimental data showed that the presence of a single mis-attached KT could perturb the dynamics of all other, normally attached, KTs in anaphase. Chapter 3 also describe how MT poleward flux ensures correct KT-MT attachment and correct chromosome segregation. Indeed, reduced flux is associated with an increase in merotelically attached anaphase lagging chromosomes (LCs). These LCs form micronuclei (MNi) upon mitotic exit. The final effort of this work focused on the fate of MNi and micronuclated (MNed) cells (Chapter 4). Experimental observations showed that most of the chromosomes in MNi missegregated at the cell division following MN formation and that frequently the chromatin in the MN displayed delayed condensation. This work, thus, established a direct link between LCs and aneuploidy through the MN cell cycle.Ph. D.
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Conia, Jérôme. "Analyse des chromosomes de plantes en cytométrie en flux : purification d'un chromosome de Petunia hybrida (Hort.)." Paris 11, 1988. http://www.theses.fr/1988PA112372.
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This work is devoted to Petunia hybrida (2n=14) and Nicotiana plumhaginifolia (2n=20) plant chromosome classification by flow cytometry. Chromosome suspensions for flow analysis were prepared from mesophyll protoplast cultures which exibited substantial synchrony during the early days of culture, giving easily disrupted cell walls. Metaphase chromosomes were dispersed breaking the protoplasts-derived cells into a suspension buffer elaborated in order to stabilize both the chromosome structure and DNA content. Chromosomes were stained with Hocchst 33342 dy (HO) or with both HO and ethidium bromide (Bet), and classified according to their relative fluorescence intensities. The Petunia hybrida and Nicotiana plumbaginifolia flow karyotypes are in good correlation with their theoretical distribution generated on the basis of the relative chromosome lengths. A simple device useful to obtain local concentrations of sorted chromosomes further morphological analysis is described. Using a two colour methodology (HO+Bet) it was shown that the longest chromosome from petunia corresponded to a well isolated peak and could be purified, the purity of the sorted fraction being higher than 96%. Modeling of flow cytometric karyotypes was realized in order to determine whether the chromosomes of a given species can be accurately classified using flow cytometry. Moreover, if the aim is to sort one chromosome type, models will indicate the feasible targets and predict interactions between purity and yield. Theoretical flow karyotypes show that it should be possible to separate chromosomes from Zea mays (2n=20) and Arabidopsis thaliana (2n=10).
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Chan, David Yiu Leung. "Analysis of artificial chromosomes and factors affecting stability in murine and human cultured and embryonic stem cells." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.568074.
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Human Artificial Chromosomes (HAC) are fascinating extrachromosomal molecules that stay independently from the host genome and are capable of segregating as efficiently as endogenous chromosomes. It has been proven that HAC are potential tools for both basic chromosome behavioural research and agents for gene therapy purposes. My DPhil project is divided into two main themes. The first theme was to develop a novel artificial chromosome in mouse embryonic stem cells. The second theme was to understand the factors affecting chromosome stability which may also affect the efficiency of artificial chromosome formation. so that our protocol for better HAC preparation can be refined. There are six results chapters in my thesis. The first three chapters described how I developed human artificial chromosomes in mouse embryonic stem cells. Initially, vectors containing a long stretch of human alphoid DNA were delivered to mouse cells using the Herpes Simplex Virus-I (HSV-l) amplicon system but the efficiency was low. Next, mouse pericentromeric and centromeric DNAs were employed for mouse artificial chromosome (MAC) via HSV-l system. However, the efficiency remained the same. Finally, I used the Microcell-Mediated Chromosome Transfer (MMCT) system to transfer HAC from HTl 080 cells into mouse ES cells and successfully established HAC in ES which were highly stable. The results obtained in this first part of my thesis suggested that to increase HAC formation efficiency it would be necessary to improve the techniques of HSV-I delivery and MMCT. Moreover, it would also be important to better characterize factors affecting chromosome behaviour. The last three results chapters focus on factors affecting chromosomes stability and improving the HSV -1 delivery system and MMCT. I undertook an in vivo study of whole cell fusion experiments with the aid of live cell irnaging system, and found that histone H2B proteins underwent a dynamic assembly/disassembly processes. Live cell imaging of MMCT suggested that the microcell delivery is a very slow process and the results may lead to a refinement of the MMCT protocol. I found it is possible to generate a single HAC using two HSV-l amplicons containing two different constructs, potentially doubling the HSV-l HAC capacity from 150 kb to 300 kb. The last chapter illustrated how the expression of non- coding centromeric satellites impaired chromosome stability in both human cultured and human embryonic stem cells. The findings revealed that non-coding centromeric RNA plays an important role on chromosome stability that might be important for artificial chromosome development.
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Kaszás, Étienne. "Molecular and genetic analyses of the maize B chromosome centromere /." free to MU campus, to others for purchase, 1997. http://wwwlib.umi.com/cr/mo/fullcit?p9841157.
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Minnen, Anita [Verfasser], and Thorsten [Akademischer Betreuer] Mascher. "Structural Maintenance of Chromosomes (SMC) localization on the Bacillus subtilis chromosome / Anita Minnen. Betreuer: Thorsten Mascher." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2015. http://d-nb.info/1101344172/34.
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Conia, Jérôme. "Analyse des chromosomes de plantes en cytométrie en flux purification du chromosome I de Petunia hybrida /." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37612978g.
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Majed, Zeina. "Elaboration d'un nouveau modèle pour la caractérisation de nouveaux gènes impliqués dans la stabilité des sites fragiles." Montpellier 1, 2009. http://www.theses.fr/2009MON1T022.
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Les sites fragiles sont des sites récurrents de cassures, favorisant l'apparition de remaniements chromosomiques et participant ainsi à la progression tumorale. Les mécanismes et les gènes impliqués dans cette fragilité chromosomique sont actuellement peu connus. Afin de mieux comprendre ces mécanismes, nous avons établis un nouveau modèle d'étude. Ce modèle est constitué de clones cellulaires issus de la lignée HCT116 MMR déficiente, pour lesquels un ou plusieurs gènes cibles, potentiellement impliqués dans la stabilité des sites fragiles, possèdent une mutation l'inactivant partiellement. Nous avons sélectionné et analysé 20 gènes codant pour des protéines impliquées dans les voies de signalisation de la réponse aux dommages de l'ADN, au stress réplicatif et à la condensation des chromosomes. Nous avons ainsi établi une collection de 200 clones cellulaires qui portent des mutations dans 13 gènes étudiés. Nous avons ensuite mis en évidence le rôle de la mutation obtenue dans le gène ATR dans l'inactivation de ce dernier en favorisant l'accumulation des cassures au niveau des sites fragiles. Ces résultats nous ont permis de proposer un système modèle constituant un outil de choix pour l'étude des sites fragiles. Dans une étude menée en parallèle, nous nous sommes intéressés au gène MCPH1/BRIT1 codant pour une protéine impliquée dans plusieurs processus cellulaires. Nous avons pu mettre en évidence qu'une dérégulation du gène MCPH1/BRIT1 engendre une instabilité chromosomique et une accumulation des cassures au niveau des sites fragilesCommon fragile sites are chomosomal regions involved in recurrent breaks, which are "expressed" under various physiological stresses, most of them are known to disturb DNA replication. A direct link between fragile sites and emergence of various types of chromosomal rearrangement has been established, even in early stages of tumorigenesis. However, only few genes involved in genome stability at fragile sites have been identified. The aim of this study is to identify new genes involved in the expression of fragile sites and to elucidate molecular processes that affect their stability. We established a cell based system on a mismatch repair deficient background. 20 candidate genes were targeted in this study. We examined the incidence of frameshift mutations in 32 mononucleotide repeats of these genes. 17 frameshift mutations were found. We demonstrate that frameshift mutations affecting coding mononucleotide repeat of ATR, inactivate one of the two alleles leading to formation of breaks at fragile sites. This collection of clones gives us a unique cellular model to study precisely the maintenance of genome stability at fragile sites. Furthermore, we have investigated the effects of the deregulation of the expression of MCPH1/BRIT1 on common fragile site stability. MCPH1/BRIT1 acts as a regulator of both the intra-S and G2/M keckpoints. We show that deregulation of the expression of MCPH1/BRIT1 increase H2AX phosphorylation suggesting the accumulation of DNA double-strand breaks. This leads to formation of breaks at fragile sites. These findings demonstrate a critical role for the MCPH1/BRIT1 in regulating chromosome stability, and in particular, common fragile site
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Edwards, Frances. "Mécanismes d’alignement et de ségrégation des chromosomes lors de la mitose dans les zygotes de Caenorhabditis elegans." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC110.
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La mitose permet la multiplication des cellules, contribuant ainsi à générer de nouveaux organismes unicellulaires, ou à construire des organismes multicellulaires. Pendant la mitose, le génome répliqué de la cellule mère est réparti entre les deux cellules filles. Les erreurs survenant lors de la répartition peuvent mener à l’aneuploïdie, une caractéristique de certaines maladies développementales dont les cancers. La fidélité de la répartition des chromatides sœurs dépend du fuseau mitotique, un réseau bipolaire de microtubules qui dirigent les chromosomes via leurs interactions avec les kinétochores assembles sur les chromatides sœurs. Ces interactions mènent à l’alignement des chromosomes, et à leur biorientation. Les chromatides sœurs sont alors attachés à des microtubules .manant des pôles opposés du fuseau. La ségrégation des chromatides sœurs a alors lieu en anaphase, et simultanément le fuseau central est assemblé entre les deux jeux de chromosomes. Cette structure composée de microtubules contribue à la ségrégation des chromatides sœurs en spécifiant la localisation et en favorisant l’ingression du sillon de division cellulaire. Pendant ma thèse, j’ai étudié les fonctions d’un ensemble de protéines du kinétochore, BUB-1, HCP-1/2CENP-F et CLS-2CLASP, lors de la mitose dans les zygotes de C. elegans. En combinant des approches de génétique et de vidéo-microscopie, j’ai montré que ces protéines participent à l’alignement et à la ségrégation des chromosomes. En particulier, BUB-1 contribue à l’alignement des chromosomes en accélérant l’attachement des microtubules aux kinétochores, tout en contrôlant la conformation et la maturation de ces attachements. Ces activités dépendent du recrutement de HCP-1/2 et CLS-2 par BUB-1, mais aussi du complexe RZZ et de la dynéine, ainsi que d’une activité de BUB-1 inhibant le recrutement du complexe SKA aux kinétochores. De plus, j’ai montré que BUB-1, HCP-1/2 and CLS-2 contribuent à l’assemblage des microtubules du fuseau central via l’activité polymérase de CLS-2. Cette fonction dépend du pré-recrutement de ces protéines aux kinétochores en métaphase, en aval de KNL-1, révélant une nouvelle fonction pour les kinétochores dans l’assemblage du fuseau central. Ce travail identifie donc des fonctions versatiles pour ces protéines, les plaçant comme des gardiennes majeures de l’intégrité génétiqueMitosis is a process by which cells multiply, contributing to the generation of new unicellular organisms, or the construction of multicellular organisms. During mitosis, the daughter cells inherit an identical copy of the mother cell’s replicated genome. Errors in genetic material distribution can lead to aneuploidy, a hallmark of developmental diseases including cancer. The accurate segregation of sister chromatids relies on the mitotic spindle, a bipolar network of microtubules that governs chromosome movements by interacting with the kinetochores assembled on sister chromatids. This drives chromosome alignment at the spindle equator, and chromosome bi-orientation meaning that sister kinetochores are connected to opposite spindle poles, laying the ground for sister chromatid segregation during anaphase. Once segregation has initiated, the microtubule-based central spindle is assembled between the two sets of chromosomes. This structure contributes to sister chromatid segregation, by specifying the location and favoring the ingression of the cytokinesis furrow. During my thesis, I have studied the functions of a subset of conserved kinetochore proteins called BUB-1, HCP-1/2CENP-F and CLS-2CLASP, during mitosis in C. elegans zygotes. By combining genetics and live imaging, I have shown that these proteins are involved both in chromosome alignment and segregation. In particular, I have shown that BUB-1 contributes to chromosome alignment by accelerating the establishment of end-on kinetochore-microtubule attachments, while controlling the conformation and maturation of these attachments. These activities rely on BUB-1’s downstream partners HCP-1/2CENP-F and CLS-2CLASP, but also on the RZZ complex and dynein, as well as an activity for BUB-1 in inhibiting the recruitment of the SKA complex. Additionally, I have shown that BUB-1, HCP-1/2CENP-F and CLS-2CLASP contribute to central spindle microtubule assembly, via CLS-2CLASP’s polymerase activity. This function relies on the prior kinetochore recruitment of these proteins during metaphase by the kinetochore scaffold protein KNL-1, revealing a new function for the kinetochore in central spindle assembly. Together, this work identifies versatile functions for this subset of conserved kinetochore proteins, making them major safe-keepers of genomic integrity
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Almagro, Sébastien. "Organisation structurale et fonctionnelle des chromosomes." Phd thesis, Université Joseph Fourier (Grenoble), 2003. http://tel.archives-ouvertes.fr/tel-00003099.
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Nous avons utilisé une technique récente de mesure d'élasticité de chromosomes mitotiques assemblés in vitro de Xénope et mis au point une technique de fonctionnalisation par anticorps de micropipettes. Nous avons confirmé que le chromosome mitotique n'était pas un objet homogène. Il est constitué de deux parties bien distinctes : une gaine molle de chromatine et une structure rigide. Nous avons identifié les protéines SMC comme actrices de ces structures rigides. Nous avons aussi montré que l'ADN et les protéines sont nécessaires au maintien de l'organisation des chromosomes alors que l'ARN ne l'est pas. Nous avons aussi étudié le paysage énergétique du chromosome, ce qui n'avait jamais été réalisé sur un objet aussi complexe. Nous proposons un modèle dynamique de formation des chromosomes dans lequel les protéines SMC agissent comme médiatrices de la forme en bâtonnet des chromosomes mitotiques et dans lequel les ions Mg++ et Ca++ jouent le rôle d'agents de
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Laval, S. H. "Molecular analysis of mammalian sex chromosomes." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302954.
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Heller, Raoul. "Engineering of human artificial mini-chromosomes." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360317.
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Barnett, Michael A. "Telomere directed breakage of mammalian chromosomes." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314882.
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Bellott, Daniel Winston. "Sequence of the chicken sex chromosomes." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/57992.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references.
In birds, as in mammals, the chromosome complement determines sex. Male birds are designated ZZ, female ZW. Mammals have the opposite system; males are XY and females XX. Both the avian ZW and mammalian XY pair are believed to have evolved from autosomes, with dramatic changes, both gene loss as well as gene acquisition and amplification occurring on the sex-specific W and Y chromosomes. In contrast, Z and X chromosomes are assumed to have diverged little from their autosomal progenitors. The Z and W sex chromosomes of the chicken provide a unique opportunity to study the evolution of sex chromosomes in a second lineage with an alternate system of heterogamety. We produced the finished sequence of the chicken Z chromosome and generated female-specific markers necessary to produce a complete sequence of the chicken W chromosome. Already our analysis of the Z chromosome has revealed that the sex chromosomes of birds evolved independently of the sex chromosomes of mammals. Despite this independence, the chicken Z chromosome converged on a suite of features analogous to those of the human X chromosome: low gene density, an enrichment for interspersed repeats, and large multi-copy gene families expressed in the testis. These features arose during the evolution of the Z and X chromosomes as sex chromosomes, overturning the notion that Z and X chromosomes are evolutionarily stable. Our preliminary efforts on the W chromosome have provided insights into its structure and underscore the ubiquity of gene acquisition and amplification on vertebrate sex chromosomes. As we accumulate genomic data from additional sex chromosomes, explaining the evolutionary forces that result in gene acquisition and amplification will remain a major challenge.
by Daniel Winston Bellott.
Ph.D.
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QIU, XIAOHUI. "Vers la classification automatique des chromosomes." Nantes, 1990. http://www.theses.fr/1990NANT2062.
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Les travaux effectues dans le cadre de cette these, s'inscrivent dans la perspective de la conception et la realisation d'un systeme de classification entierement automatique des chromosomes. Celui-ci doit a partir de l'image numerisee d'une metaphase, engendrer la reconnaissance et le classement de tous les chromosomes de cette metaphase (le caryotype). D'abord, avec l'aide des cytogeneticiens, nous avons recueilli et repertorie les connaissances humaines mises en jeu dans l'elaboration d'un caryotype, dans une forme adaptee a leur traduction sous forme de regles utilisables pour un systeme expert. Ces connaissances ont ete utilisees pour le developpement d'un ensemble de methodes d'extraction des caracteristiques chromosomiques et de reconnaissance des chromosomes. Des outils performants de segmentation ont ete concus et mis au point pour permettre de localiser de facon fiable les chromosomes et les extraire du fond metaphasique. Les procedures de reconnaissance de forme developpees incluent des methodes structurelles, statistiques et hierarchiques pour la classification des chromosomes. Une evaluation systematique des performances montre que les outils developpes se comparent tres favorablement a ceux developpes recemment par d'autres chercheurs
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Tapia, Páez Isabel. "Characterization of human chromosome 22 : cloning of breakpoints of the constitutional translocation t(11;22)(q23;q11) and detection of small constitutional deletions by microarray CGH /." Stockholm, 2003. http://diss.kib.ki.se/2003/91-7349-505-0.
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Lindow, Janet C. (Janet Christine) 1974. "A role for the Bacillus subtilis Structural Maintenance of Chromosomes (BsSMC) protein in chromosome organization and compaction." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8385.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Biology, 2002.Includes bibliographical references.
All cells must compact their chromosomes in order for the DNA to fit inside the cell or nucleus. In Bacillus subtilis, and other bacteria, replication occurs simultaneously with the organization, compaction and segregation of newly duplicated chromosomal regions. My work indicates that the B. subtilis Structural Maintenance of Chromosomes (BsSMC) protein is involved in compacting and organizing the chromosome. Increasing the amount of supercoiling of DNA is a means to compact the chromosome. This thesis describes a role for BsSMC in supercoiling. I determined that BsSMC can alter the DNA topology of plasmids in vivo. There is also genetic evidence that BsSMC is involved in supercoiling. An smc null mutant is hypersensitive to inhibitors of DNA gyrase, which reduce the level of negative supercoiling in the cell. Conversely, depletion of Topoisomerase I, which increases the amount of negative supercoiling of the chromosome, partially suppresses the phenotype of an smc null mutant. These data are consistent with the model that BsSMC affects chromosome compaction by constraining positive supercoils. Interestingly, SMC-containing complexes in eukaryotes are able to constrain positive supercoils in vitro and affect chromosome architecture suggesting that there is a conserved function for SMC proteins in chromosome structure. I also determined the subcellular localization of BsSMC. I found that BsSMC is a moderately abundant protein that can bind to many regions of the chromosome. A portion of BsSMC localizes in a pattern similar to the replication machinery.
(cont.) Simultaneous localization of BsSMC and a component of the replisome revealed that they are usually in the same region of the cell but are not always colocalized. Finally, the formation of BsSMC foci is dependent on the presence of the nucleoid but not ongoing replication. I propose that BsSMC is acting to compact newly replicated DNA by affecting DNA topology and is thereby facilitating the partitioning of sister chromosomes to opposite halves of the cell.
by Janet C. Lindow.
Ph.D.
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ROTOMONDO, FRANCOISE. "Caracterisation de la region pericentromerique du chromosome 19 murin, a l'aide de chromosomes artificiels de levures (yacs)." Nice, 1996. http://www.theses.fr/1996NICE5012.
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Avec une longueur estimee genetiquement aux alentours de 55cm, le chromosome 19 est le plus petit des automes murins. La region pericentromerique, qui s'etend environ sur 15 cm, contient de nombreux genes impliques dans diverses pathologies murines. De plus, cette region est homologue a la bande q13 du chr11 humain, elle-meme siege de nombreuses alterations responsables de pathologies humaines variees. Nous avons entrepris, en etroite collaboration avec une autre equipe menant une etude cartographique approfondie sur 11q13, l'etablissement d'une carte physique hautement resolutive de la region pericentromerique du chr19 murin. Nous esperons ainsi definir avec plus de precision le degre d'homologie entre ces deux regions et, a plus long terme, exploiter cette conservation syntenique pour identifier de nouveaux genes aussi bien humains que murins. A l'aide de 17 microsattelites disponibles dans la region d'interet, nous avons isole 101 yacs que nous avons organises en 3 contigs de taille comprise entre 2 et 3 mb. Les liaisons entre ces trois contigs devraient etre rapidement etablies grace au nombre croissant de marqueurs et de yacs disponibles dans la region
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Szabo, Quentin. "Étude du repliement tridimensionnel de la chromatine en domaines topologiques." Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTT064.
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Mon projet de thèse a consisté à étudier les mécanismes du repliement tridimensionnel du génome dans les cellules eucaryotes. L’organisation des chromosomes est étroitement liée à la régulation de nombreuses fonctions biologiques, telles que le contrôle de l’expression génique, la réplication de l’ADN ou encore la stabilité génomique. La méthode de « chromosome conformation capture » Hi-C, qui permet la cartographie des interactions entre régions d’ADN, a révélé que chez de nombreuses espèces, le génome est organisé en domaines enrichis en interactions chromatiniennes, les « Topologically Associating Domains » (TADs). Les TADs sont apparus être des acteurs majeurs de la régulation du génome par leur capacité à définir spatialement des domaines fonctionnels. Cependant, les méthodes de chromosome conformation capture générèrent des profils d’interactions généralement moyennés à partir d’ensemble de cellules. Déterminer la nature du repliement des TADs en cellules individuelles est donc crucial pour comprendre la relation structure-fonction de ces domaines génomiques. Au cours de ma thèse, j’ai utilisé des techniques de marquage fluorescent d'ADN combinés à de la microscopie en super-résolution afin d’étudier l’organisation des chromosomes en cellules uniques. Chez la drosophile, les TADs coïncident avec le partitionnement de la chromatine en domaines épigénétiques distincts. Nous avons pu caractériser chez cette espèce que les chromosomes sont organisés en une série d’unités discrètes qui correspondent aux TADs, reflétant l’exclusion mutuelle de régions transcriptionnellement actives et inactives. Ces résultats indiquent que les TADs de drosophile forment des domaines physiques qui caractérisent un niveau d’organisation structurale des chromosomes en cellules uniques. Chez les mammifères, la majorité des TADs est formée grâce à l’action du complexe cohésine et à la présence de la protéine CCCTC-binding factor (CTCF) à leurs frontières. L'application de l'imagerie à super-résolution dans des cellules souches embryonnaires et des cellules progénitrices neuronales de souris nous a permis de caractériser l’hétérogénéité du repliement des TAD d’une cellule à l’autre. Nous avons notamment pu observer leur organisation en sous-domaines globulaires qui semblent représenter une propriété générale du repliement de la chromatine à l’échelle de la centaine de nanomètres. De plus, nos résultats indiquent que les interactions chromatiniennes sont fortement favorisées à l’intérieur des TADs dans la majorité des cellules. La déplétion de CTCF abolie l’organisation spatiale de la fibre de chromatine associée aux TAD, soulignant le rôle de cette protéine dans la génération de barrières physiques entre TAD adjacents. Ces données démontrent que le repliement dynamique des TAD est compatible avec l'établissement d'environnements chromosomiques dans lesquels les contacts sont privilégiés, et réconcilient ainsi la nature probabiliste du repliement de la chromatine avec le rôle proposé des TAD dans la définition spatiale d’unités génomiques fonctionnellesMy thesis project consisted in studying the mechanisms of the three-dimensional genome folding in eukaryotic cells. The organization of chromosomes is closely related to the regulation of many biological processes, such as gene expression control, DNA replication or genomic stability. The Hi-C "chromosome conformation capture" method, which allows the mapping of interactions between DNA regions, has revealed that the genome of many species is organized into domains enriched in chromatin interactions, the "Topologically Associating Domains" (TADs). TADs have emerged as major players of genome regulation by their ability to spatially define functional domains. However, chromosome conformation capture methods generate averaged interaction profiles that generally come from an ensemble of cells. Determining the nature and the folding of TADs in individual cells is therefore crucial to better understand the structure-function relationship of these domains. During my thesis, I used a combination of fluorescent DNA labeling and super-resolution microscopy to characterize the organization of chromosomes in single cells. In Drosophila, TADs coincide with the partitioning of the chromatin into distinct epigenetic domains. In this species, we could characterize the folding of the chromosomes into a series of discrete units that correspond to TADs, reflecting the mutual exclusion of transcriptionally active and inactive regions. These results indicate that Drosophila TADs form physical domains that characterize a higher-order layer of chromosome folding in individual cells. In mammals, the majority of TADs emerge through the action of the cohesin complex and the CCCTC-binding factor (CTCF) bound at their borders. The application of super-resolution imaging in mouse embryonic stem cells and neuronal progenitor cells revealed the high degree of cell-to-cell heterogeneity of TAD folding, ranging from condensed and globular objects to dispersed and stretched conformations. We were able to observe their organization into discrete subdomains which seem to represent a general property of the folding of the chromatin fiber at the nanoscale. Furthermore, our data indicate that the physical intermingling of the chromatin is highly favored within TADs in a large majority of cells. Depletion of CTCF abolishes the TAD-dependent spatial organization of the chromatin fiber, highlighting the role of this protein in generating physical barriers between adjacent TADs. Altogether, our results demonstrate that the dynamic folding of TAD is compatible with the establishment of chromosomal environments in which contacts are privileged, and thus reconcile the probabilistic nature of chromatin folding with the proposed role of TADs in the spatial definition of functional genomic units
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Muir, Kyle. "Caractérisation biochimique et biophysique du complexe cohésine." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAV005/document.
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L'appariement des chromatides sœurs est un prérequis fondamental pour la ségrégation fidèle du génome. Cet assemblage est précisément régulé par plusieurs facteurs modulant la solidarité entre le complexe formant la cohésine et les chromosomes. Un de ces facteurs, Pds5, engage la cohésine par le biais de SCC1 et participe à la fois au renforcement de la cohésion, et inversement à la libération de la cohésine de la chromatine. Dans cette thèse, la structure cristalline du complexe entre les protéines de levure Pds5 et SCC1 est présentée. Celle-ci permet la compréhension de la fonction moléculaire de Pds5. Pds5 forme un « heat-repeat » allongé qui se lie à SCC1 via une interface dont sa séquence reste conservée. Suite à la caractérisation biologique et biochimique de cette structure, cette thèse démontre que l'intégrité de l'interface entre Pds5 et SCC1 est indispensable pour le recrutement de Pds5 à la cohésine et que son abrogation conduit à la perte de la cohésion entre les chromatides sœurs ainsi que la perte de la viabilité cellulaire. Les résultats présentés dans cette thèse suggèrent donc que Pds5 est constitutivement lie au cœur de la sous-unité de la cohésineSister chromatid cohesion is a fundamental prerequisite to faithful genome segregation. Cohesion is precisely regulated by accessory factors that modulate the stability with which the cohesin complex embraces chromosomes. One of these factors, Pds5, engages cohesin through Scc1 and participates both in the enhancement of cohesion, and conversely in mediating the release of cohesin from chromatin. In this thesis the crystal structure of a complex between budding yeast Pds5 and Scc1 is presented, thus elucidating the molecular basis of Pds5 function. Pds5 forms an elongated HEAT repeat that binds to Scc1 via a conserved surface patch. Through complementary cell biological and biochemical characterisation of this structure, the thesis demonstrates that the integrity of the Pds5–Scc1 interface is indispensable for the recruitment of Pds5 to cohesin, and that its abrogation results in loss of sister chromatid cohesion and cell viability. The results presented in this thesis therefore suggest that Pds5 is a constitutively bound, core subunit of cohesin
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Bhatt, Samarth. "Segregation analysis of paracentric inversions in human sperm." Montpellier 1, 2008. http://www.theses.fr/2008MON1T002.
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Les inversions paracentriques sont des anomalies chromosomiques généralement considérées comme inoffensives. Toutefois, des cas de porteurs de chromosomes remaniés issus d'inversions paracentriques ont été rapportés, soulignant la nécessité d'étudier le comportement méiotique de ces anomalies. Seules quelques études ont été pratiquées, utilisant la technique de fécondation croisée Homme-Hamster, le typage génétique des spermatozoïdes (sperm typing) ou l'hybridation in situ fluorescente (FISH) par marquages centromériques ou télomériques. Afin d'améliorer l'efficacité de l'étude méiotique des inversions paracentriques, nous avons développé l'utilisation des sondes BAC qui permettent une localisation chromosomique précise des points de cassures chromosomiques et l'identification de tous les produits méiotiques des inversions dans le sperme humain. Les points de cassures et la ségrégation méiotique de 3 inversions paracentriques, inv(5)(q13. 2q33. 1), inv(9)(q21. 2q34. 13) et inv(14)(q23. 2q32. 13), ont ainsi été déterminés. Les taux de recombinants observés dans ces 3 inversions varient de 3,72% à12,55%. Cette localisation des points de cassures et l'analyse des séquences d'ADN adjacentes sont essentielles pour mettre en évidence la formation de boucles d'inversion, pour déterminer le risque de recombinaison à terme, ainsi que pour étudier les mécanismes méiotiques de formation des recombinaisons. Ainsi, la présence de régions d'ADN riches en recombinaisons et en duplications inter-chromosomiques a été mise en évidence, en complément de la formation de recombinants chromosomiques. Par ailleurs, une nouvelle technique de FISH multi-couleurs 3D (3D MCB FISH) a été adaptée aux spermatozoïdes humains pour l'analyse in situ des ségrégations. Cette approche permet de visualiser in situ les inversions paracentriques et d'estimer la fréquence de tous les types de recombinants issus de boucles d'inversion, de recombinaisons U-loop ou de processus de cassure/fusion des chromatides-soeurs.
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Tomaszkiewicz, Marta. "Molecular characterization of the Y chromosome-linked sex-determining region of the platyfish Xiphophorus maculatus." Thesis, Lyon, École normale supérieure, 2012. http://www.theses.fr/2012ENSL0791.
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De par leur diversité de mécanismes de déterminisme du sexe et de chromosomes sexuels, les poissons téléostéens représentent d’excellents modèles pour mieux comprendre les bases moléculaires et évolutives du contrôle du développement sexuel chez les vertébrés. Grâce à l’analyse de chromosomes artificiels bactériens couvrant les chromosomes sexuels du platy Xiphophorus maculatus, trois copies d’un nouveau gène nommé teximY ont été découvertes dans la région de déterminisme du sexe du chromosome Y mais pas du chromosome X. Un gène texim1 très apparenté à teximY ainsi que trois gènes plus divergents ont été identifiés sur les autosomes. Les gènes teximY sont préférentiellement exprimés dans les testicules, au niveau des cellules germinales lors des étapes tardives de la spermatogénèse, alors que texim1 est également transcrit dans les gonades femelles. Des gènes texim ont été détectés chez d'autres poissons téléostéens mais pas chez le poisson-zèbre, ainsi que chez des céphalocordés, des urocordés et des échinodermes mais pas chez les tétrapodes. Les gènes texim codent pour des estérases putatives à domaine SGNH apparentées à des protéines cellulaires procaryotes et eucaryotes ou codées par des retrotransposons animaux. Les gènes texim sont associés à des transposons Helitron chez les poissons mais pas chez les autres animaux, suggérant capture et mobilisation du gène ancestral texim par un transposon à la base de la radiation des téléostéens. TeximY pourrait jouer un rôle dans la transposition du transposon Helitron dans la lignée germinale mâle, ou correspondre à un gène de spermatogenèse mobilisé par le transposon Helitron sur les nouveaux chromosomes sexuels de poissonsThe molecular and evolutionary basis of sex determination in vertebrates needs to be unveiled via comparison of different systems. Fish exhibit hypervariability of sex determination mechanisms. Thanks to the analysis of the Bacterial Artificial Chromosome (BAC) library covering the sex chromosomes of the platyfish Xiphophorus maculatus (Rio Jamapa population, XX /XY), three copies of a new gene have been identified in the sex-determining region of the Y but not the X chromosome, and named teximY. Four autosomal counterparts of teximY have been also detected in the genome of the platyfish with one of them, texim1 presenting 95% of cDNA sequence identity with the Y-linked copies. RT-qPCR expression analyses have been performed for each copy in male and female tissues. Two Y-linked teximY copies were preferentially expressed in testis, whereas the autosomal copy texim1 showed preferential expression in male and female gonads. In situ hybridizations with a teximY/1 probe revealed expression in late spermatids and spermatozeugmata. Texim sequences were detected in several fish species, but not in zebrafish, as well as in cephalochordates, urochordates and sea echinoderms but not in tetrapods. Predicted Texim proteins are related to proteins from different origins. Interestingly, texim genes are associated with a Helitron transposon in fish but neither in cephalochordates nor in echinoderms, suggesting capture and mobilization of an ancestral texim gene at the base of the bony fish lineage. TeximY proteins may play a role in Helitron transposition in the male germ line in fish, or texim genes are spermatogenesis genes mobilized and spread by transposable elements in fish genomes
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Sousa, dos Santos Aretuza. "Molecular cytogenetics and phylogenetic modeling to study chromosome evolution in the araceae and sex chromosomes in the cucurbitaceae." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-174017.
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This study involved the combination of molecular-cytogenetic data and phylogenetic approaches to infer pathways by which chromosome numbers and sizes may have changed during the course of evolution. The two systems for which I generated new data are the monocot plant family Araceae and Coccinia, a genus of Cucurbitaceae. Araceae have about 3800 species in 118 genera, and chromosome numbers range from 2n = 168 to 2n = 8, the latter the lowest number so far and newly reported in my study. The small genus Coccinia includes C. grandis, with the largest known Y chromosome in plants, as documented in my work. The thesis comprises four published or submitted papers.
The first paper reports the result of phylogenetic modeling of chromosome number change along a phylogeny for the Araceae with 113 genera represented. I used a maximum likelihood approach to find the most likely combination of events explaining today’s chromosome numbers in the 113 genera. The permitted events were chromosome gains (i.e. breaks), losses (i.e. fusions), doubling (polyploidization), or fusion of gametes with different ploidy. The best-fitting model inferred an ancestral haploid number of 16 or 18, higher than previously suggested numbers, a large role for chromosome fusion, and a limited role of polyploidization. The sparse taxon sampling and deep age (at least 120 Ma) of the events near the root of Araceae caution against placing too much weight on “ancestral” numbers, but inferred events in more closely related species can be tested with cytogenetic methods, which I did in two further studies (papers 2 and 3).
I selected Typhonium, with 50-60 species, a range of 2n = 8 to 2n = 65 chromosomes. The family-wide study had suggested a reduction from a = 14 to 13 by fusion in Typhonium, but had included relatively few of its species. I built a phylogeny that included 96 species and subspecies sequenced for a nuclear and two chloroplast markers, and then selected 10 species with 2n = 8 to 24 on which to perform fluorescence in situ hybridization (FISH) with three chromosomal probes (5S rDNA, 45S rDNA, and Arabidopsis-like telomeres; paper 2). The results supported chromosome fusion in two species where I found interstitially located telomere repeats (ITRs), which can be a signal of end-to-end fusions, and polyploidization in one species where I found multiple rDNA sites. I then extended my cytological work to other lineages of Araceae, selecting 14 species from 11 genera in key positions in the family phylogeny, which I enlarged to 174 species, adding new chromosome counts and FISH data for 14 species with 2n = 14 to 2n = 60 (paper 3). With the new data, I confirmed descending dysploidy as common in the Araceae, and I found no correlation between the number of rDNA sites and ploidy level (which would have pointed to recent polyploidy). I detected ITRs in three further species, all with 2n = 30. I also discovered gymnosperms-like massive repeat amplification in Anthurium. Similar ITRs are only known from Pinus species.
Paper 4 presents molecular-cytogenetic data for Coccinia grandis, one of a handful of angiosperms with heteromorphic sex chromosomes. The male/female C-value difference in this species is 0.09 pg or 10% of the total genome. My FISH and GISH results revealed that the Y chromosome is heterochromatic, similar to the Y chromosomes of Rumex acetosa, but different from the euchromatic Y chromosome of Silene latifolia; it is more than 2x larger than the largest other chromosome in the genome, making C. grandis an ideal system for sequencing and studying the molecular steps of sex chromosome differentiation in plants.
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Sundström, Hannah. "Mutation and Diversity in Avian Sex Chromosomes." Doctoral thesis, Uppsala University, Department of Evolutionary Biology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3732.
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Sex chromosomes are useful for the study of how factors such as mutation, selection, recombination and effective population size affect diversity and divergence.
A comparison of gametologous introns in seven different bird species revealed a complete lack of diversity on the female-specific W chromosome. In contrast, Z had at least one segregating site in all examined species. This can be explained by the lower mutation rate and lower effective population size of W but also suggests that selection affects diversity levels on the non-recombining W chromosome.
In a diverse set of chicken breeds, the Z chromosome showed reduced diversity compared to autosomes and significant heterogeneity in levels of variation. High variance in male reproductive success, leading to a reduced Z chromosome effective population size, can partly explain this observation. In addition, we suggest that selective sweeps frequently act on the Z chromosome and are responsible for a significant part of the observed Z reduction.
Differences in the mutation rate of Z and W chromosome sequences indicate that the time spent in male germ line is important for the mutation rate, but does not exclude a specifically reduced mutation rate on the Z chromosome. Estimates of mutation rate in autosomal, Z- and W-linked chicken and turkey sequences indicate a slight reduction in the rate on Z. However, due to rate heterogeneity among introns this reduction is not significant and we cannot exclude male biased mutation as the single cause of rate variation between the chromosomal classes.
Analysis of indel mutation rates in avian and mammalian gametologous introns show frequent occurrence of indels on both W and Y, excluding meiotic recombination as the only source of this type of mutation. The different indel rate patterns in birds (Z>W) and mammals (X=Y) suggest that indels are caused by both replication and recombination.
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Sundström, Hannah. "Mutation and diversity in avian sex chromosomes /." Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3732.
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Ross, Mark T. "Molecular studies of the human sex-chromosomes." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.258353.
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Harrison, Peter William. "Bacterial chromids are neither chromosomes nor plasmids." Thesis, University of York, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.556257.
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In addition to the main chromosome, many bacterial genomes have a second element, often called a "second chromosome" or "megaplasmid". It has become clear that, while they carry some essential genes, these replicons do not have the properties normally expected of chromosomes. In this thesis a systematic analysis of all publicly available sequenced bacterial genomes demonstrates that these large secondary replicons represent a single class of elements with a distinct and consistent set of properties. The term 'chromid' is proposed to distinguish them from both chromosomes and plasmids. Chapter Two utilises compositional measures to demonstrate that chromids are present in approximately one in ten sequenced genomes, and found in many bacteria of medical, agricultural' and environmental importance. Moreover, the nucleotide composition and codon usage of chromids is very similar to that of the chromosomes they are associated with, despite possessing plasmid replication and partitioning systems. Chapter Three determines that chromids possess a number of orthologous genes held on chromosomes in other species, as well as being particularly rich in genus-specific genes. This, combined with chromids of different genera having unrelated replication and maintenance systems, suggests that the creation of a new chromid may be associated with the origin of a genus. Chapter Four demonstrates that only genes held on the chromosome maintain high levels of phylogenetic consistency, and Chapter Five highlights the complexity of the interaction between gene composition, expression and function, investigating differences between the three classes of replicon. No large-scale study incorporating all published data has previously been conducted. Yet the identification and characterisation of this component provides an important framework for understanding the evolution and organisation of bacterial genomes. By proposing a clear definition, this thesis seeks to encourage consistent annotation and discussion of the evolution and functional biology of this distinct and common type of replicon.
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Sun, Lawrence (Lawrence J. ). "Inference of 3D structure of diploid chromosomes." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119570.
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Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 61-62).
The spatial organization of DNA in the cell nucleus plays an important role for gene regulation, DNA replication, and genomic integrity. Through the development of chromosome capture experiments (such as 3C, 4C, Hi-C) it is now possible to obtain the contact frequencies of the DNA at the whole-genome level. In this thesis, we study the problem of reconstructing the 3D organization of the genome from whole-genome contact frequencies. A standard approach is to transform the contact frequencies into noisy distance measurements and then apply semidefinite programming (SDP) formulations to obtain the 3D configurations. However, neglected in such reconstructions is the fact that most eukaryotes including humans are diploid and therefore contain two (from the available data) indistinguishable copies of each genomic locus. Due to this, the standard approach performs very poorly on diploid organisms. We prove that the 3D organization of the DNA is not identifiable from exclusively chromosome capture data for diploid organisms. In fact, there are infinitely many solutions even in the noise-free setting. We then discuss various additional biologically relevant constraints (including distances between neighboring genomic loci and to the nucleus center or higher-order interactions). Under these conditions we prove there are finitely many solutions and conjecture we in fact have identifiability. Finally, we provide SDP formulations for computing the 3D embedding of the DNA with these additional constraints and show that we can recover the true 3D embedding with high accuracy even under noise.
by Lawrence Sun.
M. Eng.
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BOURSAUX, EUDE CAROLINE. "Chromosomes plastiques et lineaires chez les spirochetes." Paris 6, 1996. http://www.theses.fr/1996PA066496.
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L'absence de transfert genetique utilisable en routine chez les spirochetes a incite a approfondir l'analyse du genome de ces bacteries pathogenes pour l'homme et les animaux. La caracterisation de deux elements d'insertion de la famille des is3 de e. Coli, dont plus precisement is1500, a ete effectuee chez deux serovars de la meme espece pathogene : leptospira interrogans sensu stricto. La localisation de ces elements a permis de les associer a certains remaniements observes entre les deux serovars et de suggerer une explication a la grande fluidite de l'organisation genetique chez les leptospires. Ces resultats suggerent l'existence d'un troisieme element d'insertion de la famille des is3 chez certains serovars appartenant a l. Interrogans sensu lato. Je me suis ensuite interessee aux extremites du chromosome lineaire d'un autre spirochete, borrelia burgdorferi, constituees d'epingles a cheveux. J'ai determine la sequence de plus de 20kpb de la region telomerique gauche mettant en evidence au moins sept genes potentiels, trua, udk, pria, pfpb, quea, ruvb et ruva. De plus, j'ai determine pour certains leur appartenance a un operon. Le gene udk, codant pour l'uridine kinase, fait partie de la voie de recyclage des pyrimidines et a ete localise a cote de pria. La fonction de l'uridine kinase est liee a l'utilisation de l'uridine endogene, etant donne la resistance des spirochetes au 5-fluorouracile, caracteristique permettant de les selectionner parmi des contaminants. Ruvab et pria, codant pour des helicases, interviennent respectivement dans la resolution des jonctions holliday et dans l'assemblage du primosome. L'isolement et la caracterisation d'helicases intervenant dans la replication et la reparation permettent d'envisager des modeles de replication differents de la replication dependante d'oric, typique des chromosomes circulaires. La caracterisation des proteines pria, ruvab, dnaa ainsi que l'isolement des telomeres sensu stricto permettront de tester ces modeles.
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BARIL, CELINE. "Chromosomes circulaires et lineaires chez les spirochetes." Paris 7, 1991. http://www.theses.fr/1991PA077131.
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L'organisation des genomes de deux spirochetes infectant l'homme et l'animal, leptospira interrogans et borrelia burgdorferi, a ete analysee. Les resultats obtenus par la technique d'electrophorese en champ pulse montrent que le chromosome de l. Interrogans est circulaire (5000 kilopaires de base) tandis que celui de b. Burgdorferi est lineaire (1000 kilopaires de base). La carte circulaire pour l'enzyme de restriction noti a ete construite pour le chromosome de l. Interrogans. Les genes ribosomaux, organises en unites de transcriptions separees, ont ete localises sur le chromosome, fort loin les uns des autres. La construction de souches attenuees de l. Interrogans a ete envisagee dans le but d'obtenir un vaccin vivant. Comme premiere approche de ce nouveau vaccin, les genes asd, arod et dapd specifiant l'aspartate beta-semialdehyde dehydrogenase, 3-dehydroquinase, tetrahydrodipicolinate-n-succinyl transferase respectivement, ont ete clones par complementation de mutants d'escherichia coli correspondants. Ces genes clones ont ete inactives. Les essais d'introduction de ces genes inactives chez l. Interrogans par electroporation sont decrits. La comparaison de la sequence de l'aspartate semialdehyde, deduite de la sequence nucleotidique, avec celles elucidees pour d'autres bacteries revele un niveau eleve d'identite avec celle de saccharomyces cerevisiae
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Lee, Shane. "Genetic algorithms, orthognal arrays and diploid chromosomes." Thesis, University of Wales, Newport, 2002. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.761244.
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Donald, Tamzin. "Organisation and expression of plant B chromosomes /." Title page, table of contents and abstract only, 1999. http://web4.library.adelaide.edu.au/theses/09PH/09phd6758.pdf.
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NISKA, JOANNA. "TERMINATING REPLICATION AT TERS AT EUKARYOTIC CHROMOSOMES." Doctoral thesis, Università degli Studi di Milano, 2014. http://hdl.handle.net/2434/234148.
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Faithful transmission of genetic material is challenged by the presence of natural impediments affecting replication fork progression that jeopardize genome integrity. Transcription, which competes with DNA replication for the same template, is a common barrier to replication in both prokaryotes and higher eukaryotes. Multiple mechanisms minimize the consequences of DNA replication and transcription collisions in order to prevent torsional stress accumulation that occurs when replication fork encounters the transcription machinery. Defects in resolving topological problems during chromosome replication lead to fork reversal, R loop formation and recombination-induced genome rearrangements. Our interest is focused on the processes that coordinate replication with transcription at TERs (termination sites) and on the molecular pathways involved in termination of DNA replication. We investigated the roles of Rrm3, a DNA helicase that assists replication fork progression, and of Sen1, a DNA/RNA helicase that resolves the conflicts between replication and transcription. We found that Rrm3 and Sen1 mediate replication termination at specific TERs, preventing aberrant events ultimately leading to chromosome fragility. Our results contribute to the elucidation of mechanisms coordinating replication and transcription at TER zones in eukaryotes.
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Mercy, Guillaume. "L'organisation 3D des chromosomes synthétiques de levure." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS034/document.
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Le projet international de synthèse des chromosomes de S. cerevisiae (projet Sc2.0) a débuté il y a une dizaine d'années en suivant des principes établis par le Pr. Jef Boeke. Les chromosomes synthétiques ont été conçus pour augmenter la stabilité du génome en supprimant toutes les séquences répétées (ARNt, éléments transposables...), tout en y ajoutant un système d'évolution inductible dépendant du système Cré/LoxP (système SCRaMbLE), permettant de générer rapidement des réarrangements chromosomiques. Bien que le design du projet Sc2.0 soit très conservateur en ce qui concerne le contenu des gènes, la suppression de plusieurs classes de séquences répétées peut affecter l'organisation du génome et potentiellement altérer les fonctions cellulaires. En utilisant la méthode de capture de conformation de chromosome couplée au séquençage de seconde génération (Hi-C), mon objectif a été de caractériser l'organisation 3D des génomes des souches synthétiques et évoluées. À ce jour, huit chromosomes (syn I, II, III, V, VI, IX-R, X et XII) ont été entièrement assemblés séparément. En utilisant les souches contenant un ou plusieurs de ces chromosomes, nous avons pu montrer que leur organisation génomique n'est globalement pas affectée par leur présence. Quelques exceptions subsistent, avec synIII dont les cassettes HML et HMR ont été retirées, et synXII d'où l'ADNr a été déplacé sur un autre chromosome. À ce stade, nous concluons que l'ADN répétitif dispersé ne conduit pas la conformation moyenne globale du génome de S. cerevisiae. Nous avons aussi exploité les cartes de contacts pour identifier les réarrangements dans les souches SCRaMbLEThe international project Sc2.0 started 10 years ago by the Pr. Jef Boeke aims to build a fully synthetic genome of S. cerevisiae which increases the genome stability by removing all repeated sequences (tRNA, transposable elements, etc.), and implements SCRaMbLE (for Synthetic Chromosome Rearrangement and Modification by LoxP-mediated Evolution), an inducible, high-throughput chromosome rearrangement system. This design is highly conservative with respect to gene content, the deletion of several classes of repeated sequences and the introduction of thousands of designer changes. However, it may affect genome organization and potentially alter cellular functions. To determine wether those modifications affected the three-dimensional conformation of synthetic chromosmes, we investigated it using chromosomes conformation capture coupled to second generation sequencing method (Hi-C). Currently, eight synthetic chromosomes (synI, synII, synIII, synV, synVI, synIX-R, synX et synXII) have been fully assembled. Using these strains we observed that the large-scale genomic organization is globally unaffected by the presence of synthetic chromosome(s). Two exceptions are synIII, which lacks the silent mating-type cassettes, and synXII, specifically when the ribosomal DNA is moved to another chromosome. We also exploited the contact maps to detect rearrangements induced in these SCRaMbLE strains
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Mercy, Guillaume. "L'organisation 3D des chromosomes synthétiques de levure." Electronic Thesis or Diss., Sorbonne université, 2018. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2018SORUS034.pdf.
Full textAbstract:
Le projet international de synthèse des chromosomes de S. cerevisiae (projet Sc2.0) a débuté il y a une dizaine d'années en suivant des principes établis par le Pr. Jef Boeke. Les chromosomes synthétiques ont été conçus pour augmenter la stabilité du génome en supprimant toutes les séquences répétées (ARNt, éléments transposables...), tout en y ajoutant un système d'évolution inductible dépendant du système Cré/LoxP (système SCRaMbLE), permettant de générer rapidement des réarrangements chromosomiques. Bien que le design du projet Sc2.0 soit très conservateur en ce qui concerne le contenu des gènes, la suppression de plusieurs classes de séquences répétées peut affecter l'organisation du génome et potentiellement altérer les fonctions cellulaires. En utilisant la méthode de capture de conformation de chromosome couplée au séquençage de seconde génération (Hi-C), mon objectif a été de caractériser l'organisation 3D des génomes des souches synthétiques et évoluées. À ce jour, huit chromosomes (syn I, II, III, V, VI, IX-R, X et XII) ont été entièrement assemblés séparément. En utilisant les souches contenant un ou plusieurs de ces chromosomes, nous avons pu montrer que leur organisation génomique n'est globalement pas affectée par leur présence. Quelques exceptions subsistent, avec synIII dont les cassettes HML et HMR ont été retirées, et synXII d'où l'ADNr a été déplacé sur un autre chromosome. À ce stade, nous concluons que l'ADN répétitif dispersé ne conduit pas la conformation moyenne globale du génome de S. cerevisiae. Nous avons aussi exploité les cartes de contacts pour identifier les réarrangements dans les souches SCRaMbLEThe international project Sc2.0 started 10 years ago by the Pr. Jef Boeke aims to build a fully synthetic genome of S. cerevisiae which increases the genome stability by removing all repeated sequences (tRNA, transposable elements, etc.), and implements SCRaMbLE (for Synthetic Chromosome Rearrangement and Modification by LoxP-mediated Evolution), an inducible, high-throughput chromosome rearrangement system. This design is highly conservative with respect to gene content, the deletion of several classes of repeated sequences and the introduction of thousands of designer changes. However, it may affect genome organization and potentially alter cellular functions. To determine wether those modifications affected the three-dimensional conformation of synthetic chromosmes, we investigated it using chromosomes conformation capture coupled to second generation sequencing method (Hi-C). Currently, eight synthetic chromosomes (synI, synII, synIII, synV, synVI, synIX-R, synX et synXII) have been fully assembled. Using these strains we observed that the large-scale genomic organization is globally unaffected by the presence of synthetic chromosome(s). Two exceptions are synIII, which lacks the silent mating-type cassettes, and synXII, specifically when the ribosomal DNA is moved to another chromosome. We also exploited the contact maps to detect rearrangements induced in these SCRaMbLE strains
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Martins, Francisco de Lemos. "Decrypting the Vibrio cholerae crtS site and its role on the coordinated replication of the two chromosomes." Electronic Thesis or Diss., Sorbonne université, 2018. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2018SORUS126.pdf.
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Les génomes bactériens sont composés de deux types de réplicons: les chromosomes, qui sont essentiels, et les plasmides. Bien que la plupart des bactéries n'aient qu'un seul chromosome, environ 10% des bactéries avec des chromosomes secondaires sont apparues indépendamment dans plusieurs taxa. Les chromosomes secondaires dérivent des plasmides et possèdent des systèmes de réplication plasmidiques. Les chromosomes se répliquent une fois et pendant une période définie du cycle cellulaire, tandis que les plasmides sont généralement répliqués de façon aléatoire. Vibrio cholerae a son génome divisé en deux chromosomes (Chr1 et Chr2) dont la réplication est contrôlée de manière distincte. La réplication du Chr1 dépend de DnaA, tandis que la réplication du Chr2 est initiée par un facteur spécifique à Vibrio, RctB. Malgré ses origines plasmidiques, la réplication du Chr2 est strictement contrôlée et s’effectue une fois par cycle cellulaire. Les deux chromosomes communiquent entre eux pour coordonner leur réplication via un locus du Chr1, crtS. Nous avons montré que la réplication de crtS est cruciale pour déclencher la réplication du Chr2. Toutefois, le mécanisme moléculaire par lequel crtS contrôle la réplication du Chr2 est encore flou. Ici, nous avons combiné des approches in vivo et in vitro pour éclairer cette questionBacterial genomes are mainly composed of two types of replicons: chromosomes, which are essential, and plasmids. Although most bacteria have only one chromosome, bacteria with secondary chromosomes have arisen independently in several taxa and represent approximately 10% of all bacterial species. Secondary chromosomes originate from plasmids and possess plasmid-type replication systems. While chromosomes replicate once and during a defined period of the cell cycle, plasmids generally replicate randomly. Vibrio cholerae has its genome divided in two chromosomes (Chr1 and Chr2) that use distinct initiators for replication. Chr1 replication depends on the ubiquitous initiator DnaA, while Chr2 replication is initiated by a Vibrio specific factor, RctB. Despite its plasmid origins, Chr2 replication is tightly controlled and occurs once per cell cycle. Both chromosomes communicate with each other to coordinate their replication through an RctB-binding locus on Chr1, called crtS. We have shown that crtS replication is crucial to trigger Chr2 replication initiation. However, the molecular mechanism by which crtS controls the initiation of Chr2 replication was still obscure. Here we combined in vivo and in vitro approaches to shed light on this question. We have shown that crtS activity is driven by RctB binding in a methylation-independent manner. This appears to be an effective way to integrate the Chr2 replication in the cell cycle
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Kayserili, Melek A., Dave T. Gerrard, Pavel Tomancak, and Alex T. Kalinka. "An Excess of Gene Expression Divergence on the X Chromosome in Drosophila Embryos: Implications for the Faster-X Hypothesis." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-180730.
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The X chromosome is present as a single copy in the heterogametic sex, and this hemizygosity is expected to drive unusual patterns of evolution on the X relative to the autosomes. For example, the hemizgosity of the X may lead to a lower chromosomal effective population size compared to the autosomes, suggesting that the X might be more strongly affected by genetic drift. However, the X may also experience stronger positive selection than the autosomes, because recessive beneficial mutations will be more visible to selection on the X where they will spend less time being masked by the dominant, less beneficial allele—a proposal known as the faster-X hypothesis. Thus, empirical studies demonstrating increased genetic divergence on the X chromosome could be indicative of either adaptive or non-adaptive evolution. We measured gene expression in Drosophila species and in D. melanogaster inbred strains for both embryos and adults. In the embryos we found that expression divergence is on average more than 20% higher for genes on the X chromosome relative to the autosomes; but in contrast, in the inbred strains, gene expression variation is significantly lower on the X chromosome. Furthermore, expression divergence of genes on Muller's D element is significantly greater along the branch leading to the obscura sub-group, in which this element segregates as a neo-X chromosome. In the adults, divergence is greatest on the X chromosome for males, but not for females, yet in both sexes inbred strains harbour the lowest level of gene expression variation on the X chromosome. We consider different explanations for our results and conclude that they are most consistent within the framework of the faster-X hypothesis.
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Stear, Jeffrey Hamilton. "Studies of chromosome structure and movement in C. elegans /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/5056.
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