UMR168 – Laboratoire Physico-Chimie Curie

Publications de l’UMR 168

Année de publication : 2012

J Ranft, J Prost, F Jülicher, J-F Joanny (2012 Jun 16)

Tissue dynamics with permeation.

The European physical journal. E, Soft matter : 46 : DOI : 10.1140/epje/i2012-12046-5 En savoir plus
Résumé

Animal tissues are complex assemblies of cells, extracellular matrix (ECM), and permeating interstitial fluid. Whereas key aspects of the multicellular dynamics can be captured by a one-component continuum description, cell division and apoptosis imply material turnover between different components that can lead to additional mechanical conditions on the tissue dynamics. We extend our previous description of tissues in order to account for a cell/ECM phase and the permeating interstitial fluid independently. In line with our earlier work, we consider the cell/ECM phase to behave as an elastic solid in the absence of cell division and apoptosis. In addition, we consider the interstitial fluid as ideal on the relevant length scales, i.e., we ignore viscous stresses in the interstitial fluid. Friction between the fluid and the cell/ECM phase leads to a Darcy-like relation for the interstitial fluid velocity and introduces a new characteristic length scale. We discuss the dynamics of a tissue confined in a chamber with a permeable piston close to the homeostatic state where cell division and apoptosis balance, and we calculate the rescaled effective diffusion coefficient for cells. For different mass densities of the cell/ECM component and the interstitial fluid, a treadmilling steady state due to gravitational forces can be found.

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Isabelle Bonnet, Philippe Marcq, Floris Bosveld, Luc Fetler, Yohanns Bellaïche, François Graner (2012 May 26)

Mechanical state, material properties and continuous description of an epithelial tissue.

Journal of the Royal Society, Interface / the Royal Society : 2614-23 : DOI : 10.1098/rsif.2012.0263 En savoir plus
Résumé

During development, epithelial tissues undergo extensive morphogenesis based on coordinated changes of cell shape and position over time. Continuum mechanics describes tissue mechanical state and shape changes in terms of strain and stress. It accounts for individual cell properties using only a few spatially averaged material parameters. To determine the mechanical state and parameters in the Drosophila pupa dorsal thorax epithelium, we severed in vivo the adherens junctions around a disc-shaped domain comprising typically a hundred cells. This enabled a direct measurement of the strain along different orientations at once. The amplitude and the anisotropy of the strain increased during development. We also measured the stress-to-viscosity ratio and similarly found an increase in amplitude and anisotropy. The relaxation time was of the order of 10 s. We propose a space-time, continuous model of the relaxation. Good agreement with experimental data validates the description of the epithelial domain as a continuous, linear, visco-elastic material. We discuss the relevant time and length scales. Another material parameter, the ratio of external friction to internal viscosity, is estimated by fitting the initial velocity profile. Together, our results contribute to quantify forces and displacements, and their time evolution, during morphogenesis.

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Alice Berthaud, John Manzi, Javier Pérez, Stéphanie Mangenot (2012 May 25)

Modeling detergent organization around aquaporin-0 using small-angle X-ray scattering.

Journal of the American Chemical Society : 10080-8 : DOI : 10.1021/ja301667n En savoir plus
Résumé

Solubilization of integral membrane proteins in aqueous solutions requires the presence of amphiphilic molecules like detergents. The area of ​​the transmembrane proteins is Then Surrounded by a corona FORMED thesis by molecules, Ensuring a hydrophilic outer surface. The presence of this corona HAS Strongly hampered structural studies of membrane proteins solubilized by small-angle X-ray scattering (SAXS), a technology frequently used to monitor conformational exchange of soluble proteins. Through the online combination of size exclusion chromatography, SAXS, and refractometry, we-have a Determined precise geometrical model of the n-dodecyl β-d-corona surrounding maltopyranoside aquaporin-0, The Most abundant membrane protein of the eye lens. The SAXS data Were well-fitted by a corona detergent shaped in an elliptical toroid around the crystal structure of the protein, similar to the elliptical shape Recently Reported for nanodiscs (Skar-Gislinge et al. J. Am. Chem. Soc. 2010, 132, 13713-13722). The torus thickness Determined from the curve-fitting protocol is in excellent agreement with the thickness of a lipid bilayer, while the number of detergent molecules deduced from the volume of the torus Compares well with Those therefor obtained on the Sami sample from refractometry and mass analysis based SAXS is forward scattering. For the first time, the partial specific volume of the detergent surrounding a protein Was Measured. The present protocol is a crucial step Toward future conformational studies of membrane proteins in solution.

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Patricia Bassereau, Rob Phillips, Petra Schwille3 (2012 May 21)

Focus on the physics of the cell membrane.

New Journal of Physics : 14 : 055021 : DOI : 10.1088/1367-2630/14/5/055021 En savoir plus
Résumé

This focus issue on membrane biophysics presents a collection of papers illustrating new developments in modern biophysical research on cell membranes. The work described here addresses questions from a broad range of areas, including cell adhesion, membrane trafficking and activation of cells of the immune system. It also presents recent views on membrane mechanics, the effect of electric fields, as well as on the interplay of mechanics and chemistry and organization at many different scales.

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Anaïs Ali-Cherif, Stefano Begolo, Stéphanie Descroix, Jean-Louis Viovy, Laurent Malaquin (2012 May 18)

Programmable magnetic tweezers and droplet microfluidic device for high-throughput nanoliter multi-step assays.

Angewandte Chemie (International ed. in English) : 10765-9 : DOI : 10.1002/anie.201203862 En savoir plus
Résumé

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Mohamad Reza Mohamadi, Romain Verpillot, Myriam Taverna, Markus Otto, Jean-Louis Viovy (2012 May 16)

Microchip electrophoresis, with respect to « profiling of Aβ peptides in the cerebrospinal fluid of patients with Alzheimer’s disease ».

Methods in molecular biology (Clifton, N.J.) : 173-84 : DOI : 10.1007/978-1-61779-821-4_14 En savoir plus
Résumé

Aggregation of beta amyloid peptides especially Aβ1-42 in amyloid plaques is one of the major -neuropathological events in Alzheimer’s disease. This event is normally accompanied by a relative reduction of the concentration of Aβ1-42 in the cerebrospinal fluid (CSF) of patients developing the signs of Alzheimer’s disease. Here, we describe a microchip gel electrophoresis method in a polydimethylsiloxane (PDMS) chip that enables rapid profiling of major Aβ peptides. The method was applied to compare the relative concentration of Aβ1-42 with other Aβ peptides, for example, Aβ 1-40 in CSF. In order to increase the sensitivity of detection, Aβ peptides in the CSF samples were first captured and concentrated using magnetic beads coated with specific anti-Aβ antibodies.

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Jérémie Barral, Pascal Martin (2012 May 3)

Phantom tones and suppressive masking by active nonlinear oscillation of the hair-cell bundle.

Proceedings of the National Academy of Sciences of the United States of America : E1344-51 : DOI : 10.1073/pnas.1202426109 En savoir plus
Résumé

Processing of two-tone stimuli by the auditory system introduces prominent masking of one frequency component by the other as well as additional « phantom » tones that are absent in the sound input. Mechanical correlates of these psychophysical phenomena have been observed in sound-evoked mechanical vibrations of the mammalian cochlea and are thought to originate in sensory hair cells from the intrinsic nonlinearity associated with mechano-electrical transduction by ion channels. However, nonlinearity of the transducer is not sufficient to explain the rich phenomenology of two-tone interferences in hearing. Here we show that active oscillatory movements of single hair-cell bundles elicit two-tone suppression and distortions that are shaped by nonlinear amplification of periodic stimuli near the characteristic frequency of spontaneous oscillations. When both stimulus frequencies enter the bandwidth of the hair-bundle amplifier, two-tone interferences display level functions that are characteristic both of human psychoacoustics and of in vivo mechanical measurements in auditory organs. Our work distinguishes the frequency-dependent nonlinearity that emerges from the active process that drives the hair bundle into spontaneous oscillations from the passive nonlinear compliance associated with the direct gating of transduction channels by mechanical force. Numerical simulations based on a generic description of an active dynamical system poised near an oscillatory instability–a Hopf bifurcation–account quantitatively for our experimental observations. In return, we conclude that the properties of two-tone interferences in hearing betray the workings of self-sustained « critical » oscillators, which function as nonlinear amplifying elements in the inner ear.

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Andrew Callan-Jones, Patricia Bassereau (2012 Apr 21)

Membrane fission: curvature-sensitive proteins cut it both ways.

Developmental cell : 691-2 : DOI : 10.1016/j.devcel.2012.04.001 En savoir plus
Résumé

Boucrot et al. (2012) demonstrate a membrane fission mechanism independent of nucleotide hydrolysis that is based on membrane insertion of amphipathic helices. They show that, for N-BAR domain proteins, which promote membrane curvature but also contain amphipathic helices, fission is opposed by the BAR domain that stabilizes tubular membrane structures.

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Sandrine Miserere, Guillaume Mottet, Velan Taniga, Stephanie Descroix, Jean-Louis Viovy, Laurent Malaquin (2012 Apr 11)

Fabrication of thermoplastics chips through lamination based techniques.

Lab on a chip : 1849-56 : DOI : 10.1039/c2lc21161k En savoir plus
Résumé

In this work, we propose a novel strategy for the fabrication of flexible thermoplastic microdevices entirely based on lamination processes. The same low-cost laminator apparatus can be used from master fabrication to microchannel sealing. This process is appropriate for rapid prototyping at laboratory scale, but it can also be easily upscaled to industrial manufacturing. For demonstration, we used here Cycloolefin Copolymer (COC), a thermoplastic polymer that is extensively used for microfluidic applications. COC is a thermoplastic polymer with good chemical resistance to common chemicals used in microfluidics such as acids, bases and most polar solvents. Its optical quality and mechanical resistance make this material suitable for a large range of applications in chemistry or biology. As an example, the electrokinetic separation of pollutants is proposed in the present study.

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Shalin H Naik, Leïla Perié, Erwin Swart, Carmen Gerlach, Nienke van Rooij, Rob J de Boer, Ton N Schumacher (2012 Apr 2)

Diverse and heritable lineage imprinting of early haematopoietic progenitors.

Nature : 229-32 : DOI : 10.1038/nature12013 En savoir plus
Résumé

Haematopoietic stem cells (HSCs) and their subsequent progenitors produce blood cells, but the precise nature and kinetics of this production is a contentious issue. In one model, lymphoid and myeloid production branch after the lymphoid-primed multipotent progenitor (LMPP), with both branches subsequently producing dendritic cells. However, this model is based mainly on in vitro clonal assays and population-based tracking in vivo, which could miss in vivo single-cell complexity. Here we avoid these issues by using a new quantitative version of ‘cellular barcoding’ to trace the in vivo fate of hundreds of LMPPs and HSCs at the single-cell level. These data demonstrate that LMPPs are highly heterogeneous in the cell types that they produce, separating into combinations of lymphoid-, myeloid- and dendritic-cell-biased producers. Conversely, although we observe a known lineage bias of some HSCs, most cellular output is derived from a small number of HSCs that each generates all cell types. Crucially, in vivo analysis of the output of sibling cells derived from single LMPPs shows that they often share a similar fate, suggesting that the fate of these progenitors was imprinted. Furthermore, as this imprinting is also observed for dendritic-cell-biased LMPPs, dendritic cells may be considered a distinct lineage on the basis of separate ancestry. These data suggest a ‘graded commitment’ model of haematopoiesis, in which heritable and diverse lineage imprinting occurs earlier than previously thought.

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Otger Campàs, L Mahadevan, Jean-François Joanny (2012 Mar 13)

Actin network growth under load.

Biophysical journal : 1049-58 : DOI : 10.1016/j.bpj.2012.01.030 En savoir plus
Résumé

Many processes in eukaryotic cells, including the crawling motion of the whole cell, rely on the growth of branched actin networks from surfaces. In addition to their well-known role in generating propulsive forces, actin networks can also sustain substantial pulling loads thanks to their persistent attachment to the surface from which they grow. The simultaneous network elongation and surface attachment inevitably generate a force that opposes network growth. Here, we study the local dynamics of a growing actin network, accounting for simultaneous network elongation and surface attachment, and show that there exist several dynamical regimes that depend on both network elasticity and the kinetic parameters of actin polymerization. We characterize this in terms of a phase diagram and provide a connection between mesoscopic theories and the microscopic dynamics of an actin network at a surface. Our framework predicts the onset of instabilities that lead to the local detachment of the network and translate to oscillatory behavior and waves, as observed in many cellular phenomena and in vitro systems involving actin network growth, such as the saltatory dynamics of actin-propelled oil drops.

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Jonathan Saragosti, Pascal Silberzan, Axel Buguin (2012 Jan 30)

Modeling E. coli tumbles by rotational diffusion. Implications for chemotaxis.

PloS one : e35412 : DOI : 10.1371/journal.pone.0035412 En savoir plus
Résumé

The bacterium Escherichia coli in suspension in a liquid medium swims by a succession of runs and tumbles, effectively describing a random walk. The tumbles randomize incompletely, i.e. with a directional persistence, the orientation taken by the bacterium. Here, we model these tumbles by an active rotational diffusion process characterized by a diffusion coefficient and a diffusion time. In homogeneous media, this description accounts well for the experimental reorientations. In shallow gradients of nutrients, tumbles are still described by a unique rotational diffusion coefficient. Together with an increase in the run length, these tumbles significantly contribute to the net chemotactic drift via a modulation of their duration as a function of the direction of the preceding run. Finally, we discuss the limits of this model in propagating concentration waves characterized by steep gradients. In that case, the effective rotational diffusion coefficient itself varies with the direction of the preceding run. We propose that this effect is related to the number of flagella involved in the reorientation process.

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Maxime Deforet, Maria Carla Parrini, Laurence Petitjean, Marco Biondini, Axel Buguin, Jacques Camonis, Pascal Silberzan (2012 Jan 20)

Automated velocity mapping of migrating cell populations (AVeMap).

Nature methods : 1081-3 : DOI : 10.1038/nmeth.2209 En savoir plus
Résumé

Characterizing the migration of a population of cells remains laborious and somewhat subjective. Advances in genetics and robotics allow researchers to perform many experiments in parallel, but analyzing the large sets of data remains a bottleneck. Here we describe a rapid, fully automated correlation-based method for cell migration analysis, compatible with standard video microscopy. This method allows for the computation of quantitative migration parameters via an extensive dynamic mapping of cell displacements.

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Benoît Sorre, Andrew Callan-Jones, John Manzi, Bruno Goud, Jacques Prost, Patricia Bassereau*, Aurélien Roux* (2012 Jan 3)

Nature of curvature coupling of amphiphysin with membranes depends on its bound density.

Proceedings of the National Academy of Sciences of the United States of America : 109 : 173-178 : DOI : 10.1073/pnas.1103594108 En savoir plus
Résumé

Cells are populated by a vast array of membrane-binding proteins That execute critical functions. Functions, like signaling and intracellular transport require the abilities to bind to highly curved membranes and membrane deformation to trigger. Among proteins thesis is Amphiphysin 1 Implicated in clathrin mediated endocytosis. It contains a Bin-Amphiphysin Rvs-membrane-binding domain with an N-terminal amphipathic helix and senses That Generates membrane curvature. However, an understanding of the parameters distinguishing thesis two functions is missing. By pulling a highly curved nanotube radius of controlled from a giant vesicle in a solution Containing Amphiphysin, we Observed que la actions of the protein depends on icts Directly density on the membrane. At low densified of protein on the vesicle Nearly flat, the distribution of proteins and the mechanical effects are induced Described by a model based on spontaneous curvature induction. The tube radius and strength are modified by protein binding but still depends on membrane voltage. In the dilute limit, When Were Practically no proteins present on the vesicle, no mechanical effects Were detected, strong goal protein enrichment proportional to curvature Was seen on the tube. At high densified, the radius is independent of voltage and vesicle protein density, resulting and from the formation of a scaffold around the tube. As a result, the scaling of the power with voltage is modified. For the entire density range, protein enriched Was on the tube as Compared to the vesicle. Our approach shows que le strength of curvature sensing and mechanical effects on the tube depends on the protein density.

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Année de publication : 2011

Jacques Prost (2011 Dec 24)

[But where are the genes?].

Médecine sciences : M/S : 1043-4 : DOI : 10.1051/medsci/20112712001 En savoir plus
Résumé

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