Quantum Yield Calculations for Strongly Absorbing Chromophores

This article demonstrates that a commonly-made assumption in quantum yield calculations may produce errors of up to 25% in extreme cases and can be corrected by a simple modification to the analysis.Comment: 3 pages, 2 figures. Accepted by Journal of Fluorescenc

Rab27a and Rab27b control different steps of the exosome secretion pathway

Exosomes are secreted membrane vesicles that share structural and biochemical characteristics with intraluminal vesicles of multivesicular endosomes (MVEs). Exosomes could be involved in intercellular communication and in the pathogenesis of infectious and degenerative diseases. The molecular mechanisms of exosome biogenesis and secretion are, however, poorly understood. Using an RNA interference (RNAi) screen, we identified five Rab GTPases that promote exosome secretion in HeLa cells. Among these, Rab27a and Rab27b were found to function in MVE docking at the plasma membrane. The size of MVEs was strongly increased by Rab27a silencing, whereas MVEs were redistributed towards the perinuclear region upon Rab27b silencing. Thus, the two Rab27 isoforms have different roles in the exosomal pathway. In addition, silencing two known Rab27 effectors, Slp4 (also known as SYTL4, synaptotagmin-like 4) and Slac2b (also known as EXPH5, exophilin 5), inhibited exosome secretion and phenocopied silencing of Rab27a and Rab27b, respectively. Our results therefore strengthen the link between MVEs and exosomes, and introduce ways of manipulating exosome secretion in vivo

Mise en oeuvre expérimentale d’impacts basse vitesse sur matériau énergétique

Les matériaux énergétiques présentent un caractère sensible aux sollicitations mécaniques, chimiques ou thermiques « faibles », dont l’origine est probablement liée à un endommagement microstructural progressif du matériau. La butalite analysée dans le cadre de notre étude est un propergol composite, constitué de grains de perchlorate d’ammonium et d’une matrice polymérique de type PBHT. Pour décrire la réponse thermomécanique sous faible choc de ce matériau à l’échelle mésoscopique, nous réalisons des essais d’impacts basse vitesse à la tour de chute, sous différentes  configurations expérimentales, en couplant un enregistrement par caméra rapide à une analyse ante et post mortem de l’échantillon par microtomographie X..

Cdc42 controls the dilation of the exocytotic fusion pore by regulating membrane tension.

Membrane fusion underlies multiple processes, including exocytosis of hormones and neurotransmitters. Membrane fusion starts with the formation of a narrow fusion pore. Radial expansion of this pore completes the process and allows fast release of secretory compounds, but this step remains poorly understood. Here we show that inhibiting the expression of the small GTPase Cdc42 or preventing its activation with a dominant negative Cdc42 construct in human neuroendocrine cells impaired the release process by compromising fusion pore enlargement. Consequently the mode of vesicle exocytosis was shifted from full-collapse fusion to kiss-and-run. Remarkably, Cdc42-knockdown cells showed reduced membrane tension, and the artificial increase of membrane tension restored fusion pore enlargement. Moreover, inhibiting the motor protein myosin II by blebbistatin decreased membrane tension, as well as fusion pore dilation. We conclude that membrane tension is the driving force for fusion pore dilation and that Cdc42 is a key regulator of this force.journal articleresearch support, non-u.s. gov't2014 Oct 152014 08 20importe

IODP expedition 347: Baltic Sea basin paleoenvironment and biosphere

The Integrated Ocean Drilling Program (IODP) expedition 347 cored sediments from different settings of the Baltic Sea covering the last glacial-interglacial cycle. The main aim was to study the geological development of the Baltic Sea in relation to the extreme climate variability of the region with changing ice cover and major shifts in temperature, salinity, and biological communities. Using the Greatship Manisha as a European Consortium for Ocean Research Drilling (ECORD) mission-specific platform, we recovered 1.6 km of core from nine sites of which four were additionally cored for microbiology. The sites covered the gateway to the North Sea and Atlantic Ocean, several sub-basins in the southern Baltic Sea, a deep basin in the central Baltic Sea, and a river estuary in the north. The waxing and waning of the Scandinavian ice sheet has profoundly affected the Baltic Sea sediments. During theWeichselian, progressing glaciers reshaped the submarine landscape and displaced sedimentary deposits from earlier Quaternary time. As the glaciers retreated they left a complex pattern of till, sand, and lacustrine clay, which in the basins has since been covered by a thick deposit of Holocene, organic-rich clay. Due to the stratified water column of the brackish Baltic Sea and the recurrent and widespread anoxia, the deeper basins harbor laminated sediments that provide a unique opportunity for high-resolution chronological studies. The Baltic Sea is a eutrophic intra-continental sea that is strongly impacted by terrestrial runoff and nutrient fluxes. The Holocene deposits are recorded today to be up to 50m deep and geochemically affected by diagenetic alterations driven by organic matter degradation. Many of the cored sequences were highly supersaturated with respect to methane, which caused strong degassing upon core recovery. The depth distributions of conservative sea water ions still reflected the transition at the end of the last glaciation from fresh-water clays to Holocene brackish mud. High-resolution sampling and analyses of interstitial water chemistry revealed the intensive mineralization and zonation of the predominant biogeochemical processes. Quantification of microbial cells in the sediments yielded some of the highest cell densities yet recorded by scientific drilling

Photoreflectance on wide bandgap nitride semiconductors

International audienc

Epi-bathyal ostracod assemblage in Holocene Rhone deltaic sediments (Gulf of Lions, NW Mediterranean) and their palaeoecological implications

International audienceSince the Last Glacial Maximum, the Rhone River, which is the most important source of freshwater and sediment to the western Mediterranean Sea, migrated in a north-westward direction during the rapid Deglacial and Early Holocene sea-level rise. During the phase of global high sea-level (Middle and Late Holocene), an overall eastward migration of the Rhone outlet, under natural and/or human influence, is recorded through several sediment accumulations confined along the inner shelf in the form of deltaic lobes. These lobes that make up the whole Rhone subaqueous delta represent very expanded sedimentary archives of the Rhone Holocene history. In this paper, using three long piston cores retrieved from the most recent Bras de Fer (RHS-KS55) and Roustan (RHS-KS22 and RHS-KS57) deltaic lobes, at water depth ranging from 43 m to 79 m, we analyze the distribution of the Rhone ostracod assemblages during the Holocene. Our study highlighted the presence of epi-bathyal ostracods belonging to the genus Argilloecia, Cytheropteron and Krithe in shallow water deltaic sediments. Close to the Rhone River mouth, the presence of these full-marine ostracods is limited because of well-marked fluvial influence, whereas the occurrence of Argilloecia spp., C. rotundatum, K. compressa and K. pernoides increases with increasing distance from the river mouth. Thus, we hypothesize that C. rotundatum, K. compressa, and especially Argilloecia spp. might be more tolerant to higher fluvial influence than K. pernoides, which is only observed in the distal part of the Rhone River influence. Environment-related parameters (such as fresh-water and sediment input from the Rhone River, food supply, and dissolved oxygen) other than bathymetry are thought to have a major role in the development of these full-marine ostracods at the studied site

Modeling and Optimization of photocatytic degradation kinetic of monolinuron using experimental design

International audienc