Behavior of a GPI-anchored protein in phospholipid monolayers at the air–water interface

AbstractThe interaction between alkaline phosphatase (AP), a glycosylphosphatidylinositol (GPI)-anchored protein (AP-GPI), and phospholipids was monitored using Langmuir isotherms and PM-IRRAS spectroscopy. AP-GPI was injected under C16 phospholipid monolayers with either a neutral polar head (1,2-dipalmitoyl-sn-glycero-3-phosphocholine monohydrate (DPPC)) or an anionic polar head (1,2-dipalmitoyl-sn-glycero-3-phospho-L-serine (DPPS)). The increase in molecular area due to the injection of protein depended on the surface pressure and the type of phospholipid. At all surface pressures, it was highest in the case of DPPS monolayers. The surface elasticity coefficient E, determined from the π–A diagrams, allowed to deduct that the AP-GPI–phospholipid mixtures presented a molecular arrangement less condensed than the corresponding pure phospholipid films. PM-IRRAS spectra suggested different protein–lipid interactions as a function of the nature of the lipids. AP-GPI modified the organization of the DPPS deuterated chains whereas AP-GPI affected only the polar group of DPPC at low surface pressure (8 mN/m). Different protein hydration layers between the DPPC and DPPS monolayers were suggested to explain these results. PM-IRRAS spectra of AP-GPI in the presence of lipids showed a shape similar to those collected for pure AP-GPI, indicating a similar orientation of AP-GPI in the presence or absence of phospholipids, where the active sites of the enzyme are turned outside of the membrane

Les méthodes d'évaluation de l'âge physiologique des moustiques (Dipt. Culicidae)

La détermination de l'âge physiologique des moustiques peut apporter une réponse à de nombreux problèmes d'échantillonnage des populations culicidiennes et permet d'apprécier rationnellement les répercussions des campagnes insecticides sur la longévité des moustiques vecteurs et sur leur potentialité de transmission. Les auteurs passent en revue les différentes méthodes permettant de reconnaître, parmi les femelles de moustiques, les nullipares, qui n'ont jamais pondu, des pares, qui ont pondu une ou plusieurs fois. Parmi les différentes techniques existantes, les principales sont celle de Polovodova (1941), basée sur les changements qualitatifs des oviductes pairs et des ampoules, applicable aux seuls anophèles, et celles basées sur les modifications irréversibles des trachéoles des ovaires (Detinova, 1945), et sur la présence de dilatations résiduelles de ponte sur les funicules des ovarioles (Polovodova, 1947), qui sont applicables à tous les moustiques. Cette dernière technique peut permettre, dans certaines conditions, de déterminer le nombre exact de pontes déposé par chaque femelle. Des méthodes mathématiques, dérivées des travaux de Davidson (1953 et 1955) et de Macdonald (1952 et 1957) permettent d'estimer, à partir des indices sporozoïtiques et oocystiques, ou à partir de la proportion de femelles pares, le taux quotidien moyen de mortalité et le pourcentage de femelles d'âge épidémiologiquement dangereux. L'emploi combiné de plusieurs de ces méthodes permet l'étude de l'âge physiologique des moustiques dans là plupart des conditions susceptibles de se rencontrer au cours d'enquêtes sur le terrain.Hamon J., Grjébine Alexis, Adam Jean-Paul, Chauvet G., Coz J., Gruchet H. Les méthodes d'évaluation de l'âge physiologique des moustiques [Dipt. Culicidae]. In: Bulletin de la Société entomologique de France, volume 66 (5-6), Mai-juin 1961. pp. 137-161

Litter Decomposition as an Indicator of Stream Ecosystem Functioning at Local-to-Continental Scales

RivFunction is a pan-European initiative that started in 2002 and was aimed at esta- blishing a novel functional-based approach to assessing the ecological status of rivers. Litter decomposition was chosen as the focal process because it plays a central role in stream ecosystems and is easy to study in the field. Impacts of two stressors that occur across the continent, nutrient pollution and modified riparian vegetation, were exam- ined at >200 paired sites in nine European ecoregions. In response to the former, decomposition was dramatically slowed at both extremes of a 1000-fold nutrient gra- dient, indicating nutrient limitation in unpolluted sites, highly variable responses across Europe in moderately impacted streams, and inhibition via associated toxic and addi- tional stressors in highly polluted streams. Riparian forest modification by clear cutting or replacement of natural vegetation by plantations (e.g. conifers, eucalyptus) or pasture produced similarly complex responses. Clear effects caused by specific riparian distur- bances were observed in regionally focused studies, but general trends across different types of riparian modifications were not apparent, in part possibly because of important indirect effects. Complementary field and laboratory experiments were undertaken to tease apart the mechanistic drivers of the continental scale field bioassays by addressing the influence of litter, fungal and detritivore diversity. These revealed generally weak and context-dependent effects on decomposition, suggesting high levels of redundancy (and hence potential insurance mechanisms that can mitigate a degree of species loss) within the food web. Reduced species richness consistently increased decomposition variability, if not the absolute rate. Further field studies were aimed at identifying impor- tant sources of this variability (e.g. litter quality, temporal variability) to help constrain ranges of predicted decomposition rates in different field situations. Thus, although many details still need to be resolved, litter decomposition holds considerable potential in some circumstances to capture impairment of stream ecosystem functioning. For instance, species traits associated with the body size and metabolic capacity of the con- sumers were often the main driver at local scales, and these were often translated into important determinants of otherwise apparently contingent effects at larger scales. Key insights gained from conducting continental scale studies included resolving the appar- ent paradox of inconsistent relationships between nutrients and decomposition rates, as the full complex multidimensional picture emerged from the large-scale dataset, of which only seemingly contradictory fragments had been seen previously

Continental-Scale Effects of Nutrient Pollution on Stream Ecosystem Functioning

Excessive nutrient loading is a major threat to aquatic ecosystems worldwide that leads to profound changes in aquatic biodiversity and biogeochemical processes. Systematic quantitative assessment of functional ecosystem measures for river networks is, however, lacking, especially at continental scales. Here, we narrow this gap by means of a pan-European field experiment on a fundamental ecosystem process—leaf-litter breakdown—in 100 streams across a greater than 1000-fold nutrient gradient. Dramatically slowed breakdown at both extremes of the gradient indicated strong nutrient limitation in unaffected systems, potential for strong stimulation in moderately altered systems, and inhibition in highly polluted streams. This large-scale response pattern emphasizes the need to complement established structural approaches (such as water chemistry, hydrogeomorphology, and biological diversity metrics) with functional measures (such as litter-breakdown rate, whole-system metabolism, and nutrient spiraling) for assessing ecosystem health

Transient Neuronal Populations Are Required to Guide Callosal Axons: A Role for Semaphorin 3C

Neurons, glia, and callosal axons operate as a “ménage à trois” in the development of the corpus callosum

La Chine, nouvel investisseur et créancier du tiers-monde – Le cas de l'Afrique

National audienc

Synthesis and interfacial properties of amphiphatic cryptophanes

International audienc

Simulation numérique et analyse physique d'un jet propulsif contrôlé par des injections radiales

A cause de sa température élevée, le jet propulsif d'un avion de combat est une source de rayonnement infrarouge qui rend l'appareil très vulnérable. Ce rayonnement peut toutefois être réduit en accélérant le mélange du jet avec l'atmosphère. Cette thèse est consacrée à la simulation numérique d'un jet propulsif réaliste contrôlé par des injections radiales et à l'analyse physique des mécanismes d'augmentation de son mélange. Deux types de simulations, RANS et ZDES, ont été réalisés sur la base du modèle de Spalart-Allmaras. Dans le modèle ZDES, une nouvelle longueur caractéristique de maille est formulée et améliore sensiblement la prévision de la région initiale du jet. Globalement, les simulations ZDES restituent fidèlement le champ moyen du jet supersonique sans et avec contrôle, aussi bien les cellules de détente/compression que la diffusion turbulente. L'analyse physique est dédiée à la compréhension d'une part des mécanismes compressibles concentrées au coeur du jet et d'autre part des mécanismes tourbillonnaires périphériques ainsi qu'à l'évaluation de leurs rôles respectifs dans l'augmentation du mélange. Il en ressort que l'augmentation du mélange est exclusivement due aux mécanismes tourbillonnaires. Une étude paramétrique fournit des indications pour concevoir un mélangeur efficace. L'analyse des tourbillons focalisée sur le régime lointain quasi-bidimensionnel souligne leur dynamique moyenne et fait apparaître l'action des fluctuations turbulentes sur leur taux de dégénérescence. Enfin, deux régimes de contrôle sont identifiés et associés aux pénétrations respectivement quasi-stationnaire et intermittente des jets secondaires.Because of its high temperature, a propulsive jet is a source of infrared radiation which makes combat aircraft vulnerable. However, radiation can be alleviated by an enhancement of the mixing between the jet and the ambient air. This thesis is dedicated to the numerical simulation of a real-life propulsive jet controlled by radial injections and to the physical investigation of the mixing enhancement mechanisms. As for the simulations, RANS and ZDES based upon the Spalart-Allmaras model are used. In the ZDES model, a new mesh cutoff size is proposed and is shown to improve the prediction of the jet near-field. On the whole, the results provided by ZDES are in fair agreement with the mean flow fields of the supersonic jets without and with control, as well for the expansion/compression cells as for the turbulent diffusion. The physical analysis deals with both the compressible and the vortical mechanisms. It is proved that mixing enhancement is only due to the action of vortices. A parametric study gives some information to design an efficient mixer. The analysis of the vortices is focused on the quasi-bidimensional regime of the far-field. Their mean longitudinal evolution is highlighted and the action of the turbulent fluctuations on their decay rate is shown. Finally, two control regimes are identified and respectively associated to a quasi-steady penetration and to an intermittent penetration of the secondary jets.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Étude cinétique de la photooxydation de la chlorophylle α dans les mélanges binaires triton X100-eau

L’oxydation photochimique de la chlorophylle par l’oxygène dissous dans les mélanges binaires Triton X 100-eau est assimilable à une réaction globale d’ordre un pour le pigment. Elle est limitée dans les milieux riches en détergent et sa vitesse est proportionnelle à l’intensité d’irradiation. L’étude par photolyse éclair et l’évolution de la vitesse en présence d’eau lourde ou d’azoture de sodium permettent d’envisager pour l’oxydation du pigment la formation d’un complexe intermédiaire chlorophylle-oxygène