Degeneration and Regeneration in the Vertebrate Retina

International audienceThe human retina is a complex, layered tissue responsible for the perception of the visual stimuli coming from the external environment. Since the visual inputs account for about 30% of our sensory stimulations, it is not surprising that partial or complete blindness results in a strong decrease of life quality. Several diseases affect the retina, often leading to degeneration of one or several cell types. The damage induced by these diseases is often irreversible, thus leading to a permanent loss of the visual ability. Over the last decades significant progress has been made to elucidate the molecular basis of retinal degenerative diseases. This knowledge is necessary in order to design valid approaches for the treatment of retinopathies

Ressources en Géologie Caribéenne : les apports de l’outil GPS pour l’étude des séismes et failles majeures de République Dominicaine

Cet article présente comment l’utilisation d’un outil moderne, le GPS (Global Positioning System) peut apporter des éléments significatifs dans la connaissance des failles actives et de leur cycle sismique. Nous nous intéressons ici à la frontière de plaque Nord-Caraibe, en République Dominicaine, et présentons des quantifications de vitesses de déplacement obtenues grâce à l’instrumentation de la zone depuis 1994 par un groupe de chercheurs français, états-uniens et dominicains. Les résultats sont ensuite discutés en termes d’aléas sismologiques des failles majeures.This paper aims to demonstrate that the use of a modern tool, the GPS (Global Positioning System), can significantly improve our understanding of active faults and their seismic cycle. We focus on the North-Caribbean plate boundary, specifically in the Dominican Republic, and present some quantifications of velocities that result from measurements that have been made possible by the instrumentation of the area by a consortium of researchers from France, the USA and the Dominican Republic, since 1994. Then, we discuss the velocities in terms of seismic potential of the regional major faults

Modélisation du mécanisme de coalescence des grains de polymère

Dans le procédé du rotomoulage, le phénomène physique majeur lors de l’écoulement des poudres est la coalescence et densification des grains. La coalescence est la formation d’une seule particule elliptique à partir de deux particules sous l’effet de la température et des forces de tension surfacique. Nous intéressons dans cette étude en particulier au mécanisme de coalescence des grains de poudre de PVDF. Les résultats de cette étude permettent de déterminer des paramètres tel que la vitesse de la coalescence pour l’optimisation du procédé

Etude de l'endommagement de structures composites à matrice thermoplastique : application aux réservoirs de stockage hyperbare de l'hydrogène = Study of damages on thermoplastic composite structures: application for hydrogen storage vessels under high pressure

National audienceLe stockage de l'hydrogène est un verrou technologique et scientifique majeur à son utilisation comme vecteur énergétique, en remplacement des sources d'énergie traditionnelles. En effet, aujourd'hui encore, aucune solution « Haute pression » ne satisfait pleinement l'ensemble des spécifications techniques et économiques des industriels. Des progrès sont donc encore nécessaires pour améliorer les performances et la durabilité des réservoirs. Depuis 1998, le CEA travaille sur le développement de réservoirs de stockage haute pression de type IV (liner polymère renforcé d'une structuration composite). L'identification des paramètres matériaux et procédé influents ainsi que des sollicitations susceptibles de modifier les performances et la durabilité des réservoirs doit être prise en compte. En ce sens, les composites à matrice thermoplastique apparaissent comme de bons candidats en terme de durabilité et sécurité (Projet Français HYPE). Cet article présente les premiers résultats de travaux visant à développer les connaissances sur les mécanismes d'endommagement de structures composites à matrice thermoplastique (polyamide) liés à leur procédé de mise en forme (enroulement filamentaire) et leur utilisation pour le stockage hyperbare. Cette étude vise notamment à optimiser les étapes de conception numérique et de fabrication grâce à la connaissance des lois de comportement et de la durabilité du matériau. Dans un premier temps, on s'intéresse à des endommagements sous sollicitations statiques avant de s'intéresser à des sollicitations dynamiques comme l'impact

De l’unicité des relations entre représentation et système de valeur dans l’enseignement des SVT

Une analyse croisée de la transposition interne des concepts d’agrosystème en première L et d’identité biologique en première S s’appuyant sur des analyses de programmes et de manuels scolaires est ici présentée. Les rapports entre l’enseignement de ces connaissances et certaines idéologies (productivisme, déterminisme) sont mis en évidence. Enfin, l’unicité des liens entre représentations, systèmes de valeurs et paradigmes scientifiques est discutée.A cross-analysis of the transposition (analysis of official instructions and textbooks) of the concepts of “agrosystem” and “biological identity” in French secondary school on is presented here. The relationship between the teaching of these knowledges and some ideologies (productivism, determinism) are highlighted. Finally, the uniqueness of the relationship between conceptions, value systems and scientific paradigms is discussed

Chemorheological study of DGEBA/IPD system for Reactive Rotational Molding (RRM)

The identification of kinetic parameters controlling the crosslinking of Diglycidyl ether of bisphenol/isophorone diamine reactive system was achieved via optimization program (Inverse method) based on Fourier transform near infrared spectroscopy results. The reactivity ratio (k2/k 1) was determined using a new method based on the variation of amine conversion ratio versus epoxy conversion ratio. Gelation and vitrification of the reactive system were also analyzed. Time, temperature, transformation diagram was established to assess the rotational molding of this reactive system

Mazabraud's Syndrome Coexisting with a Uterine Tumor Resembling an Ovarian Sex Cord Tumor (UTROSCT): a Case Report

The association of intramuscular myxoma and fibrous dysplasia is a rare disease known as Mazabraud's syndrome. We present a case of Mazabraud's syndrome coexisting with a uterine tumor and resembling an ovarian sex cord tumor (UTROSCT). This uterine tumor showed a high mitotic index and cytological atypia. To the best of our knowledge, the coexistence of the two different entities has not been reported in the literature

Exploring nervous system transcriptomes during embryogenesis and metamorphosis in Xenopus tropicalis using EST analysis

<p>Abstract</p> <p>Background</p> <p>The western African clawed frog <it>Xenopus tropicalis </it>is an anuran amphibian species now used as model in vertebrate comparative genomics. It provides the same advantages as <it>Xenopus laevis </it>but is diploid and has a smaller genome of 1.7 Gbp. Therefore <it>X. tropicalis </it>is more amenable to systematic transcriptome surveys. We initiated a large-scale partial cDNA sequencing project to provide a functional genomics resource on genes expressed in the nervous system during early embryogenesis and metamorphosis in <it>X. tropicalis</it>.</p> <p>Results</p> <p>A gene index was defined and analysed after the collection of over 48,785 high quality sequences. These partial cDNA sequences were obtained from an embryonic head and retina library (30,272 sequences) and from a metamorphic brain and spinal cord library (27,602 sequences). These ESTs are estimated to represent 9,693 transcripts derived from an estimated 6,000 genes. Comparison of these cDNA sequences with protein databases indicates that 46% contain their start codon. Further annotation included Gene Ontology functional classification, InterPro domain analysis, alternative splicing and non-coding RNA identification. Gene expression profiles were derived from EST counts and used to define transcripts specific to metamorphic stages of development. Moreover, these ESTs allowed identification of a set of 225 polymorphic microsatellites that can be used as genetic markers.</p> <p>Conclusion</p> <p>These cDNA sequences permit <it>in silico </it>cloning of numerous genes and will facilitate studies aimed at deciphering the roles of cognate genes expressed in the nervous system during neural development and metamorphosis. The genomic resources developed to study <it>X. tropicalis </it>biology will accelerate exploration of amphibian physiology and genetics. In particular, the model will facilitate analysis of key questions related to anuran embryogenesis and metamorphosis and its associated regulatory processes.</p

Live imaging of targeted cell ablation in Xenopus:a new model to study demyelination and repair

Live imaging studies of the processes of demyelination and remyelination have so far been technically limited in mammals. We have thus generated a Xenopus laevis transgenic line allowing live imaging and conditional ablation of myelinating oligodendrocytes throughout the central nervous system (CNS). In these transgenic pMBP-eGFP-NTR tadpoles the myelin basic protein (MBP) regulatory sequences, specific to mature oligodendrocytes, are used to drive expression of an eGFP (enhanced green fluorescent protein) reporter fused to the E. coli nitroreductase (NTR) selection enzyme. This enzyme converts the innocuous pro-drug metronidazole (MTZ) to a cytotoxin. Using two-photon imaging in vivo, we show that pMBP-eGFP-NTR tadpoles display a graded oligodendrocyte ablation in response to MTZ, which depends on the exposure time to MTZ. MTZ-induced cell death was restricted to oligodendrocytes, without detectable axonal damage. After cessation of MTZ treatment, remyelination proceeded spontaneously, but was strongly accelerated by retinoic acid. Altogether, these features establish the Xenopus pMBP-eGFP-NTR line as a novel in vivo model for the study of demyelination/remyelination processes and for large-scale screens of therapeutic agents promoting myelin repair

Widespread occurrence of non-canonical transcription termination by human RNA polymerase III

Human RNA polymerase (Pol) III-transcribed genes are thought to share a simple termination signal constituted by four or more consecutive thymidine residues in the coding DNA strand, just downstream of the RNA 3′-end sequence. We found that a large set of human tRNA genes (tDNAs) do not display any T≥4 stretch within 50 bp of 3′-flanking region. In vitro analysis of tDNAs with a distanced T≥4 revealed the existence of non-canonical terminators resembling degenerate T≥5 elements, which ensure significant termination but at the same time allow for the production of Pol III read-through pre-tRNAs with unusually long 3′ trailers. A panel of such non-canonical signals was found to direct transcription termination of unusual Pol III-synthesized viral pre-miRNA transcripts in gammaherpesvirus 68-infected cells. Genome-wide location analysis revealed that human Pol III tends to trespass into the 3′-flanking regions of tDNAs, as expected from extensive terminator read-through. The widespread occurrence of partial termination suggests that the Pol III primary transcriptome in mammals is unexpectedly enriched in 3′-trailer sequences with the potential to contribute novel functional ncRNAs