Recherche avancée
Affichage des résultats 141 à 160 sur 1266 au total
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Reconstitutions du climat, des régimes alimentaires et de la thermophysiologie à partir des compositions isotopiques des fossiles
L'évolution du vivant peut être déduite du registre fossile qui en est de facto le référentiel temporel. Les compositions en isotopes stables de leurs restes biominéralisés permettent de quantifier aussi bien des paramètres extrinsèques comme le complexe climat-environnement qu'intrinsèques comme la place d'un organisme vivant dans une chaîne trophique ou encore sa thermophysiologie. Au cours de ce séminaire quelques exemples seront abordés tels que 1) le régime alimentaire de certains oiseaux fossiles qui ont vécu au Tertiaire, 2) le statut thermophysiologique des reptiles marins géants du Mésozoïque et 3) l'évolution de la température des océans au cours de la plus grande phase de biodiversification marine du Paléozoïque.
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Single-Cell-Based Analysis Highlights a Surge in Cell-to-Cell Molecular Variability Preceding Irreversible Commitment in a Differentiation Process
In some recent studies, a view emerged that stochastic dynamics governing the switching of cells from one differentiation state to another could be characterized by a peak in gene expression variability at the point of fate commitment. We have tested this hypothesis at the single-cell level by analyzing primary chicken erythroid progenitors through their differentiation process and measuring the expression of selected genes at six sequential time-points after induction of differentiation. In contrast to population-based expression data, single-cell gene expression data revealed a high cell-to-cell variability, which was masked by averaging. We were able to show that the correlation network was a very dynamical entity and that a subgroup of genes tend to follow the predictions from the dynamical network biomarker (DNB) theory. In addition, we also identified a small group of functionally related genes encoding proteins involved in sterol synthesis that could act as the initial drivers of the differentiation. In order to assess quantitatively the cell-to-cell variability in gene expression and its evolution in time, we used Shannon entropy as a measure of the heterogeneity. Entropy values showed a significant increase in the first 8 h of the differentiation process, reaching a peak between 8 and 24 h, before decreasing to significantly lower values. Moreover, we observed that the previous point of maximum entropy precedes two paramount key points: an irreversible commitment to differentiation between 24 and 48 h followed by a significant increase in cell size variability at 48 h. In conclusion, when analyzed at the single cell level, the differentiation process looks very different from its classical population average view. New observables (like entropy) can be computed, the behavior of which is fully compatible with the idea that differentiation is not a "simple" program that all cells execute identically but results from the dynamical behavior of the underlying molecular network.http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002585
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Équipe Biodémographie Évolutive et Équipe Baobab
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Experimental evolution of ageing
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deux équipes:
-Modélisation et Écotoxicologie Prédictives - Génétique et Évolution des Interactions Hôtes-Parasites
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Title to be announced
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Testing the invasive pathogen hypothesis of rapidly declining bumble bee populations in North America
Bumble bees are one of our most important wild pollinators, and populations are declining globally. Causes of decline appear to vary geographically. In Europe, for example, the proposed drivers are climate change, loss of floral resources and pesticides. In North America, however, a widely accepted hypothesis suggested that contact with an exotic European strain of fungal pathogen, Nosema bombi, was the sole cause of a precipitous decline. We have tested this exotic pathogen hypothesis using multiple genetic and genomic tools.
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Équipes Ecoépidémiologie Evolutionniste & Epigénétique et Formation du Zygote
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Génomique de la domestication des plantes
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Deux équipes du LBBE présentent leurs travaux:
- Évaluation et Modélisation des Effets Thérapeutiques - Bioinformatique, Phylogénie et Génomique Évolutive
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Comment évaluer la médecine personnalisée en cancérologie : Des études rétrospectives aux essais randomisés
Personalized medicine is defined by the National Cancer Institute as "a form of medicine that uses information about a person's genes, proteins, and environment to prevent, diagnose, and treat disease." In oncology, the term "personalized medicine" arose with the emergence of molecularly targeted agents. The prescription of approved molecularly targeted agents to cancer patients currently relies on the primary tumor location and histological subtype. Predictive biomarkers of efficacy of these modern agents have been exclusively validated in specific tumor types. A major concern today is to determine whether the prescription of molecularly targeted therapies based on tumor molecular abnormalities, independently of primary tumor location and histology, would improve the outcome of cancer patients. This new paradigm requires prospective validation before being implemented in clinical practice. In this communication, we will first review different designs, including observational cohorts, as well as nonrandomized and randomized clinical trials, that have been recently implemented to evaluate the relevance of this approach. We then focus on the SHIVA trial, a randomized proof-of-concept phase II trial comparing therapy based on tumL'inscription est gratuite mais obligatoire et doit se faire au plus tard le jeudi 28 septembre 2017 par courriel à stephanie.robert@chu-lyon.frecular profiling versus conventional therapy in patients with refractory cancer. We will present various aspects of implementation, underlying statistical and design questions, limits and strengths and review the results using this prism.
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Le séquençage et l'assemblage de génomes de référence à partir de données PacBio et Oxford Nanopore
Depuis 2015, les avancées des technologies de séquençage PacBio et Oxford Nanopore ont bouleversé les projets de séquençages génomiques. Les chromosomes bactériens et les bras chromosomiques des génomes eucaryotes peuvent être assemblés en une seule séquence. La qualité des assemblages atteint si ce n'est dépasse les assemblages de références Sanger des années 2000, les centromères et télomères alors souvent non résolus deviennent désormais analysables. Les résultats sur plusieurs espèces de bactéries, champignons et plantes seront présentés afin d'illustrer les réussites de cette rupture technologique mais aussi les cas qui restent encore non parfaitement résolus.
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Evolution des ornements colorés chez les oiseaux dans le temps et l'espace
Le séminaire présentera les trois axes de recherche en écologie évolutive et comportementale développés par Claire Doutrelant (CEFE, Montpellier). Le premier axe de recherche porte sur la variation spatio-temporelle et l'évolution des ornements colorés chez les oiseaux (en particulier chez les femelles). Le deuxième axe de recherche porte sur la coopération et la dynamique de populations d'une espèce d'oiseau à reproduction coopérative, le républicain social. Le 3ème axe porte sur l'évolution en milieu insulaire par des comparaisons de plusieurs espèces vivant en milieu insulaire et continental.
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Allocation au sexe chez les mammifères
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La Formule de Bayes : Exemples d'application au-delà de la démarche Diagnostiquen nL'inscription est gratuite mais obligatoire au plus tard le mardi 31 octobre 2017 par courriel à paola.damaso@chu-lyon.frn
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Immune function and the island syndrome
Life on isolated oceanic islands often means life in the absence of (or at least with fewer) top predators and large herbivores. Such a change in prey-predator and plant-herbivore interactions likely translates into slackened natural selection on the animals and plants that are normally being eaten. One consequence is high population densities on islands. Another is that over evolutionary time island organisms lose their defenses against predation and herbivory. The extent to which similar dynamics underlie changes in host defenses against parasites (i.e., immune function) is less clear. The host-parasite interaction can be seen as ecologically analogous to prey-predator and plant-herbivore interactions, and some instances of island animals being hard hit by infectious diseases have been described. If the selective pressures imposed by parasites are reduced on islands compared to on continents and if immune defenses incur costs, then the immune system architecture is expected to differ between animal hosts on living on islands and continents. In my presentation, I will explore this hypothesis by reviewing current literature and examining the breadth and consistency of results. If the hypothesis is well supported, then changes in the immune system might be appropriately recognized as a physiological aspect of the island syndrome. I will end by introducing plans for a new direction in this line of research: an examination of immunological and physiological changes associated with the reverse island syndrome. Under this scenario, low or fluctuating population densities on islands, for example due to severe environmental variation, appears to lead to a reverse set of life history changes in island animals. To date, however, little is known about the interaction between parasites and hosts defenses in this system.
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Fidelity of parent-offspring transmission and the evolution of social behaviour in structured populations
The theoretical investigation of how spatial structure affects the evolution of social behavior has mostly been done under the assumption that parent-offspring strategy transmission is perfect, i.e., for genetically transmitted traits, that mutation is very weak or absent. In this talk, we investigate the evolution of social behavior in structured populations under arbitrary mutation probabilities. We consider spatially structured populations of fixed size N, in which two types of individuals,A and B, corresponding to two types of social behavior, are competing. Under the assumption of small phenotypic differences (weak selection), we provide a formula for the expected frequency of type A individuals in the population, and deduce conditions for the long-term success of one strategy against another. We then illustrate this result with three common life-cycles (Wright-Fisher,Moran Birth-Death and Moran Death-Birth),and specific population structures. Qualitatively, we find that some life-cycles (Moran Birth-Death,Wright-Fisher, when social interactions affect fecundities) prevent the evolution of altruistic behavior, confirming previous results obtained with perfect strategy transmission. Imperfect strategy transmission also alters the balance between the benefits and costs of staying next to one's kin, leading to surprising results in subdivided populations, in that higher emigration probabilities can be favourable to the evolution of altruistic strategies.
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Genomic evidence for ameiotic evolution and genetic exchanges in the bdelloid rotifer Adineta vaga.
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Magnetic biomineralization: multi-faceted evolutionary history of a complex prokaryotic function
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Pathology 2.0 : how omics technologies and bioinformatics are changing the rules
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