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

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

3D MULTI-SCALE SEGMENTATION OF GRANULAR MATERIALS

On a microscopic scale, a pyrotechnic material is made of a polymer matrix containing grains with different sizes and shapes. Its physical behaviour can be predicted by homogenization. Information about the morphology of the grains can be obtained by different ways. One of these ways is 3D image processing. This has been made easier by the use of a new imaging technique, the microtomography, allowing fast threedimensional reconstruction and processing. In this paper images of two granular materials are segmented by means of 3D mathematical morphology algorithms, based on a multi-scale extraction of markers for watershed segmentation

Comparaison théorique et expérimentale de la pression générée par une matrice de haut-parleurs actionnés de façon analogique et digitale

ISBN 978-2-919340-02-6 - EAN 9782919340026National audienc

Design of thin-film AlN actuators for 4-inch transparent plates for haptic applications

International audienceNumerous applications require tactile interfaces today. In particular, many customers' applications such as Smartphone, tablet PC or touch pad can be concerned by high performances, low voltage haptic interfaces which allow the user to interact with its environment by the sense of touch. This technology is already used but with limitations such as high power consumption and limited feedback effect (simple vibration). We chose to work on the squeeze-film effect. It consists in changing the friction between the finger and a plate resonator. It provides high granularity level of haptic sensation. This paper deals with the design of high performances actuators in order to promote the squeeze-film effect on a 4-inch plate (diagonal of the plate). Using predictive models, we select the best design, able to generate the highest substrate displacement amplitude as possible. We built demonstrators using a generic technology based on thin-film AlN actuators. Electromechanical characterization is ongoing before the integration of the thin-film actuator plate in a haptic demonstrator in a close future

Design of thin-film AlN actuators for 4-inch transparent plates for haptic applications

International audienceNumerous applications require tactile interfaces today. In particular, many customers' applications such as Smartphone, tablet PC or touch pad can be concerned by high performances, low voltage haptic interfaces which allow the user to interact with its environment by the sense of touch. This technology is already used but with limitations such as high power consumption and limited feedback effect (simple vibration). We chose to work on the squeeze-film effect. It consists in changing the friction between the finger and a plate resonator. It provides high granularity level of haptic sensation. This paper deals with the design of high performances actuators in order to promote the squeeze-film effect on a 4-inch plate (diagonal of the plate). Using predictive models, we select the best design, able to generate the highest substrate displacement amplitude as possible. We built demonstrators using a generic technology based on thin-film AlN actuators. Electromechanical characterization is ongoing before the integration of the thin-film actuator plate in a haptic demonstrator in a close future

Meso-macro optical experimental analysis of woven composite reinforcements in plane shear during their forming

National audienc

Microstructure-aided digital volume correlation

International audienceno abstrac