Intensity Correlation between Observations at Differrent Wavelengths for Mkn 501 in 1997

The CAT imaging telescope on the site of the former solar plant Th'emis in southern France observed gamma-rays from the BL Lac object Mkn501 above 250 GeV for more than 60 usable hours on-source from March to October 1997. This source was in a state of high activity during all this period. By studying the correlation between the photons of different energies detected by the CAT imaging telescope and by the ASM/RXTE experiment (1.3-12.0 keV) on board the Rossi X-Ray Timing Explorer, we may constrain the mechanisms which could lead to the emission of these photons.Comment: Proceedings of the 19th Texas Symposium. 8 pages, 7 figure

Metabolic profiling of Lolium perenne shows functional integration of metabolic responses to diverse subtoxic conditions of chemical stress

International audiencePlant communities are confronted with a great variety of environmental chemical stresses. Characterization of chemical stress in higher plants has often been focused on single or closely related stressors under acute exposure, or restricted to a selective number of molecular targets. In order to understand plant functioning under chemical stress conditions close to environmental pollution conditions, the C3 grass Lolium perenne was subjected to a panel of different chemical stressors (pesticide, pesticide degradation compound, polycyclic aromatic hydrocarbon, and heavy metal) under conditions of seed-level or root-level subtoxic exposure. Physiological and metabolic profiling analysis on roots and shoots revealed that all of these subtoxic chemical stresses resulted in discrete physiological perturbations and complex metabolic shifts. These metabolic shifts involved stressor-specific effects, indicating multilevel mechanisms of action, such as the effects of glyphosate and its degradation product aminomethylphosphonic acid on quinate levels. They also involved major generic effects that linked all of the subtoxic chemical stresses with major modifications of nitrogen metabolism, especially affecting asparagine, and of photorespiration, especially affecting alanine and glycerate. Stress-related physiological effects and metabolic adjustments were shown to be integrated through a complex network of metabolic correlations converging on Asn, Leu, Ser, and glucose-6-phosphate, which could potentially be modulated by differential dynamics and interconversion of soluble sugars (sucrose, trehalose, fructose, and glucose). Underlying metabolic, regulatory, and signalling mechanisms linking these subtoxic chemical stresses with a generic impact on nitrogen metabolism and photorespiration are discussed in relation to carbohydrate and low-energy sensing

Sex makes them sleepy: host reproductive status induces diapause in a parasitoid population experiencing harsh winters

When organisms coevolve, any change in one species can induce phenotypic changes in traits and ecology of the other species. The role such interactions play in ecosystems is central, but their mechanistic bases remain underexplored. Upper trophic level species have to synchronize their life-cycle to both abiotic conditions and to lower trophic level species’ phenology and phenotypic variations. We tested the effect of host seasonal strategy on parasitoid diapause induction by using a holocyclic clone of the pea aphid Acyrthosiphon pisum producing asexual and sexual morphs that are viviparous females (i.e. laying embryos) and oviparous females (laying eggs), respectively, the latter being only present at the end of the growing season. Aphidius ervi parasitoids from populations of contrasted climatic origin (harsh vs. mild winter areas) were allowed to parasitize each morph in a split-brood design and developing parasitoids were next reared under either fall-like or summer-like temperature-photoperiod conditions. We next examined aspects of the host physiological state by comparing the relative proportion of forty-seven metabolites and lipid reserves in both morphs produced under the same conditions. We found that oviparous morphs are cues per se for diapause induction; parasitoids entered diapause at higher levels when developing in oviparous hosts (19.4 ± 3.0%) than in viviparous ones (3.6 ± 1.3%), under summer-like conditions (i.e., when oviparous aphids appear in the fields). This pattern was only observed in parasitoids from the harsh winter area since low diapause levels were observed in the other population, suggesting local adaptations to overwintering cues. Metabolomics analyses show parasitoids’ response to be mainly influenced by the host’s physiology, with higher proportion of polyols and sugars, and more fat reserves being found in oviparous morphs. Host quality thus varies across the seasons and represents one of the multiple environmental parameters affecting parasitoid diapause. Our results underline strong coevolutionary processes between hosts and parasitoids in their area of origin, likely leading to phenological synchronization, and we point out the importance of such bottom-up effects for trait expression, and for the provision of ecosystem services such as biological control in the context of climate change

Moderate conformational impact of citrate on ovotransferrin considerably increases its capacity to self-assemble at the interface

International audienceWe have compared the behavior of ovotransferrin at the air-solution interface in the presence of a monovalention (acetate), or a divalent ion (citrate), the latter being known to induce conformational changesof this protein upon interaction with its iron-binding sites. We have characterised the adsorption layer atthe air–water interface in terms of homogeneity, surface concentration excess and rheological propertiesat pH 4.0. Besides we have investigated the bulk conformation in the presence of the two anions. In thepresence of citrate only, interfacial layers display well-defined domains of higher overall surface concentrationsuggesting multilayers adsorption. Citrate also induces higher helical content and stabilizes theprotein against thermal denaturation. Hence we propose that these changes are involved in the propensityof ovotransferrin to self-assemble at the air–water interface resulting in thick and heterogeneousinterfacial layer

Vascular endothelial cell expression of JAK2V617F is sufficient to promote a pro-thrombotic state due to increased P-selectin expression

Thrombosis is the main cause of morbidity and mortality in patients with JAK2V617F myeloproliferative neoplasms. Recent studies have reported the presence of JAK2V617F in endothelial cells of some patients with myeloproliferative neoplasms. We investigated the role of endothelial cells that express JAK2V617F in thrombus formation using an in vitro model of human endothelial cells overexpressing JAK2V617F and an in vivo model of mice with endothelial-specific JAK2V617F expression. Interestingly, these mice displayed a higher propensity for thrombus. When deciphering the mechanisms by which JAK2V617F-expressing endothelial cells promote thrombosis, we observed that they have a pro-adhesive phenotype associated with increased endothelial P-selectin exposure, secondary to degranulation of Weibel-Palade bodies. We demonstrated that P-selectin blockade was sufficient to reduce the increased propensity of thrombosis. Moreover, treatment with hydroxyurea also reduced thrombosis and decreased the pathological interaction between leukocytes and JAK2V617F-expressing endothelial cells through direct reduction of endothelial P-selectin expression. Taken together, our data provide evidence that JAK2V617F-expressing endothelial cells promote thrombosis through induction of endothelial P-selectin expression, which can be reversed by hydroxyurea. Our findings increase our understanding of thrombosis in patients with myeloproliferative neoplasms, at least those with JAK2V617F-positive endothelial cells, and highlight a new role for hydroxyurea. This novel finding provides the proof of concept that an acquired genetic mutation can affect the pro-thrombotic nature of endothelial cells, suggesting that other mutations in endothelial cells could be causal in thrombotic disorders of unknown cause, which account for 50% of recurrent venous thromboses

CD133, CD15/SSEA-1, CD34 or side populations do not resume tumor-initiating properties of long-term cultured cancer stem cells from human malignant glio-neuronal tumors

<p>Abstract</p> <p>Background</p> <p>Tumor initiating cells (TICs) provide a new paradigm for developing original therapeutic strategies.</p> <p>Methods</p> <p>We screened for TICs in 47 human adult brain malignant tumors. Cells forming floating spheres in culture, and endowed with all of the features expected from tumor cells with stem-like properties were obtained from glioblastomas, medulloblastoma but not oligodendrogliomas.</p> <p>Results</p> <p>A long-term self-renewal capacity was particularly observed for cells of malignant glio-neuronal tumors (MGNTs). Cell sorting, karyotyping and proteomic analysis demonstrated cell stability throughout prolonged passages. Xenografts of fewer than 500 cells in Nude mouse brains induced a progressively growing tumor. CD133, CD15/LeX/Ssea-1, CD34 expressions, or exclusion of Hoechst dye occurred in subsets of cells forming spheres, but was not predictive of their capacity to form secondary spheres or tumors, or to resist high doses of temozolomide.</p> <p>Conclusions</p> <p>Our results further highlight the specificity of a subset of high-grade gliomas, MGNT. TICs derived from these tumors represent a new tool to screen for innovative therapies.</p

Etude de fonds diffus cosmologiques : Mesure indirecte du fond infra-rouge et mesure directe du fond millimétrique

Les premiers photons libérés par la matière constituent le fond diffus cosmologique (CMB) observé aujourd'hui à T=2.725K. C'est l'image électro-magnétique de notre Univers la plus lointaine qui nous soit accessible. L'étude statistique des minuscules inhomogéités du CMB devrait permettre pratiquement à elle seule la détermination du contenu et de la geométrie de l'Univers. Toutefois d'autres photons émis ultérieurement par les premiers astres de l'Univers sont également massivement présents. En particulier les galaxies avec leurs étoiles et leurs nuages de poussière ont émis des rayonnements constituant un fond diffus infra-rouge (CIB). Ce fond est très difficile à détecter en raison de la pollution lumineuse du Système Solaire et de la Galaxie, en particulier dans l'infra-rouge moyen. On peut cependant tirer partie de l'interaction de ces photons avec d'autres plus énergétiques rencontrés en chemin pour contraindre leur densité en fonction de leur energie. Ce manuscrit indique par quels moyens directs (expériences CMB ballon Archeops ou satellite Planck) ou indirects (expériences gamma au sol CAT et HEGRA) ces fonds diffus peuvent être mis en évidence et conduire à une description de l'Univers cohérente et - peut-être - juste. The first photons decoupled from the matter constitute the Cosmic Microwave Background (CMB) observed today at T=2.725 K. They form the oldest electromagnetic picture of our Universe. The statistical study of the tiny inhomogeneities of the CMB should allow, almost only by themselves, to determine the content and the geometry of the Universe. Nevertheless other photons are numerous. In particular star and dust radiations form the Cosmic Infrared Background (CIB). This background is very difficult to detect due to the Solar and Galactic light pollution, in particular in the mid-infrared. But it is possible to take benefit of the interaction of the CIB photons with other energetic enough ones to constrain their density in function of their wavelengths.This report shows how directely (Archeops balloon or Planck satellite CMB experiments) or indirectely (CAT and HEGRA ground based gamma experiments), these backgrounds can be detected and lead to a coherent and - maybe - true description of the Universe.NI

Impact de perturbations sporadique et constante de matière organique sur l'écosystème benthique

RÉSUMÉ: La communauté macrofaunique benthique est étroitement liée aux apports de matière organique sur le fond et subit des pressions environnementales d'origine naturelle ou anthropique de plus en plus fortes. L'étude de l'impact des perturbations sur l' écosystème benthique devient essentielle afin d'évaluer les changements potentiels des communautés benthiques pour une meilleure gestion et préservation des ressources naturelle du St-Laurent. L'impact de deux fréquences de perturbations de matière organique, constante et sporadique, a été évalué sur une communauté benthique du Chenal Laurentien (Québec, Canada). L'expérience a été menée en laboratoire sur deux séries de 4 benthocosmes (une série pour chaque fréquence de perturbation) provenant de l'estuaire maritime du Saint-Laurent. La perturbation constante a consisté en un ajout quotidien de matière organique, tandis que pour la perturbation sporadique, toute la matière organique a été ajoutée en une fois au début de l'expérience. La quantité de matière organique totale ajoutée dans chaque perturbation équivaut à l'apport d'une floraison phytoplanctonique. L'expérience a durée 21 jours, un benthocosme de chaque série a été échantillonné avant, puis à 3, 6, 15 et 21 jours après le début des ajouts. L'utilisation des isotopes stables du carbone et de l'azote a permis le suivi de la matière organique ajouté dans les benthocosmes. Les résultats montrent que l'ajout de matière organique (300 mg.C.m-2.j ou(1) n'a pas d'influence sur la composition du sédiment qui est déjà un réservoir naturel de carbone organique. La composition en espèces de la communauté benthique reste similaire quelle que soit la fréquence de la perturbation. Les analyses isotopiques révèlent que l'assimilation par la macrofaune de la matière ajoutée reste faible dans les deux cas. Cette étude montre que la communauté benthique du Chenal Laurentien est capable de supporter un apport de matière organique bien plus important que celui expérimenté avant que celui ci ne vienne véritablement perturber la communauté macrofaunique benthique. -- Mots clés : Perturbation constante ; Perturbation sporadique ; Matière organique ; Communauté benthique ; Benthocosme ; Analyses isotopiques. --ABSTRACT: On the sea floor, benthic community is closely linked to the input of organic matter and is exposed to increasing environmental pressure. Influence of disturbance need to be studied for a better understanding of sea floor systems, in future. Two types of organic matter perturbation, press and pulse, were evaluated for the benthic community of the Laurentian Chanel (Quebec, Canada). The experiment was donc on two series of 4 benthocosms (one for each type of disturbance): coming from the St. Lawrence Lower Estuary. Concerning the press disturbance, organic matter was added every day on the first serie of benthocosms. In the second serie of benthocosm experiments the total amount of organic matter was added at once as a pulse disturbance in the beginning of the experiment. Organic matter amount added in each benthocosm is equivalent to phytoplanctonic bloom input. In each series, a benthocosm was sampled before the disturbances, then at 3, 6, 15, and 21 days . The use of stable isotopes of carbon and nitrogen has all owed the monitoring of the organic matter added in the benthocosm. Results showed that organic matter added (300 mg.c.m-2.jour-1) did not alter the composition of the sediment, because it already contained significant amount of natural organic matter. Species composition of the benthic community is similar regardless of the frequency of the disturbance. Isotopic analysis revealed low organic matter assimilation by macrofauna in both cases. Th is study highlights the capacity of the Laurentian Chanel benthic community to support higher organic matter inputs than those used in the experiment. -- Key words: Press disturbance; Pulse disturbance ; Organic matter; Benthic community; Benthocosm ; Isotopie analysis