UMR168 – Laboratoire Physico-Chimie Curie

Publications de l’UMR 168

Année de publication : 2014

Volker Bormuth, Jérémie Barral, Jean-François Joanny, Frank Jülicher, Pascal Martin (2014 May 5)

Transduction channels’ gating can control friction on vibrating hair-cell bundles in the ear.

Proceedings of the National Academy of Sciences of the United States of America : 7185-90 : DOI : 10.1073/pnas.1402556111 En savoir plus
Résumé

Hearing starts when sound-evoked mechanical vibrations of the hair-cell bundle activate mechanosensitive ion channels, giving birth to an electrical signal. As for any mechanical system, friction impedes movements of the hair bundle and thus constrains the sensitivity and frequency selectivity of auditory transduction. Friction is generally thought to result mainly from viscous drag by the surrounding fluid. We demonstrate here that the opening and closing of the transduction channels produce internal frictional forces that can dominate viscous drag on the micrometer-sized hair bundle. We characterized friction by analyzing hysteresis in the force-displacement relation of single hair-cell bundles in response to periodic triangular stimuli. For bundle velocities high enough to outrun adaptation, we found that frictional forces were maximal within the narrow region of deflections that elicited significant channel gating, plummeted upon application of a channel blocker, and displayed a sublinear growth for increasing bundle velocity. At low velocity, the slope of the relation between the frictional force and velocity was nearly fivefold larger than the hydrodynamic friction coefficient that was measured when the transduction machinery was decoupled from bundle motion by severing tip links. A theoretical analysis reveals that channel friction arises from coupling the dynamics of the conformational change associated with channel gating to tip-link tension. Varying channel properties affects friction, with faster channels producing smaller friction. We propose that this intrinsic source of friction may contribute to the process that sets the hair cell’s characteristic frequency of responsiveness.

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Philippe Marcq (2014 Apr 29)

Spatio-temporal dynamics of an active, polar, viscoelastic ring.

The European physical journal. E, Soft matter : 29 : DOI : 10.1140/epje/i2014-14029-x En savoir plus
Résumé

Constitutive equations for a one-dimensional, active, polar, viscoelastic liquid are derived by treating the strain field as a slow hydrodynamic variable. Taking into account the couplings between strain and polarity allowed by symmetry, the hydrodynamics of an active, polar, viscoelastic body include an evolution equation for the polarity field that generalizes the damped Kuramoto-Sivashinsky equation. Beyond thresholds of the active coupling coefficients between the polarity and the stress or the strain rate, bifurcations of the homogeneous state lead first to stationary waves, then to propagating waves of the strain, stress and polarity fields. I argue that these results are relevant to living matter, and may explain rotating actomyosin rings in cells and mechanical waves in epithelial cell monolayers.

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Reffay M, Parrini MC, Cochet-Escartin O, Ladoux B, Buguin A, Coscoy S, Amblard F, Camonis J, Silberzan P (2014 Apr 16)

Interplay of RhoA and mechanical forces in collective cell migration driven by leader cells

Nat Cell Biol16(4):382 : DOI : 10.1038/ncb2917 En savoir plus
Résumé

The leading front of a collectively migrating epithelium often destabilizes into multicellular migration fingers where a cell initially similar to the others becomes a leader cell while its neighbours do not alter. The determinants of these leader cells include mechanical and biochemical cues, often under the control of small GTPases. However, an accurate dynamic cartography of both mechanical and biochemical activities remains to be established. Here, by mapping the mechanical traction forces exerted on the surface by MDCK migration fingers, we show that these structures are mechanical global entities with the leader cells exerting a large traction force. Moreover, the spatial distribution of RhoA differential activity at the basal plane strikingly mirrors this force cartography. We propose that RhoA controls the development of these fingers through mechanical cues: the leader cell drags the structure and the peripheral pluricellular acto-myosin cable prevents the initiation of new leader cells.

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Shalin H Naik, Ton N Schumacher, Leïla Perié (2014 Apr 15)

Cellular barcoding: a technical appraisal.

Experimental hematology : 598-608 : DOI : 10.1016/j.exphem.2014.05.003 En savoir plus
Résumé

Cellular barcoding involves the tagging of individual cells of interest with unique genetic heritable identifiers or barcodes and is emerging as a powerful tool to address individual cell fates on a large scale. However, as with many new technologies, diverse technical and analytical challenges have emerged. Here, we review those challenges and highlight both the power and limitations of cellular barcoding. We then illustrate the contribution of cellular barcoding to the understanding of hematopoiesis and outline the future potential of this technology.

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Ayako Yamada, Alexandre Mamane, Jonathan Lee-Tin-Wah, Aurélie Di Cicco, Coline Prévost, Daniel Lévy, Jean-François Joanny, Evelyne Coudrier*, Patricia Bassereau* (2014 Apr 7)

Catch-bond behaviour facilitates membrane tubulation by non-processive myosin 1b.

Nature communications : 3624 : DOI : 10.1038/ncomms4624 En savoir plus
Résumé

Myosin 1b is a single-headed membrane-associated motor actin filaments to That Bind with a catch-hop behavior in response to load. In vivo, myosin 1b is required to form membrane tubules at Both endosomes and the trans-Golgi network. To suit les the link entre thesis Fundamental two properties, here we Investigate the capacity of myosin 1b to extract membrane tubes along bundled actin filaments in a minimum reconstituted system. We that show single-headed non-processive myosin 1b can extract membrane tubes at biologically relevant low density. In contrast to kinesins we do not observe motor accumulation at the tip, Suggesting que la Underlying mechanism for tube formation is different. In our theoretical model, myosin 1b catch-bond properties Facilitate tube extraction under the conditions of membrane voltage by Increasing Reducing the density of myo1b required to pull tubes.

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Morgan Delarue, Fabien Montel, Danijela Vignjevic, Jacques Prost, Jean-François Joanny, Giovanni Cappello (2014 Apr 2)

Compressive stress inhibits proliferation in tumor spheroids through a volume limitation.

Biophysical journal : 1821-8 : DOI : 10.1016/j.bpj.2014.08.031 En savoir plus
Résumé

In most instances, the growth of solid tumors occurs in constrained environments and requires a competition for space. A mechanical crosstalk can arise from this competition. In this article, we dissect the biomechanical sequence caused by a controlled compressive stress on multicellular spheroids (MCSs) used as a tumor model system. On timescales of minutes, we show that a compressive stress causes a reduction of the MCS volume, linked to a reduction of the cell volume in the core of the MCS. On timescales of hours, we observe a reversible induction of the proliferation inhibitor, p27Kip1, from the center to the periphery of the spheroid. On timescales of days, we observe that cells are blocked in the cell cycle at the late G1 checkpoint, the restriction point. We show that the effect of pressure on the proliferation can be antagonized by silencing p27Kip1. Finally, we quantify a clear correlation between the pressure-induced volume change and the growth rate of the spheroid. The compression-induced proliferation arrest that we studied is conserved for five cell lines, and is completely reversible. It demonstrates a generic crosstalk between mechanical stresses and the key players of cell cycle regulation. Our results suggest a role of volume change in the sensitivity to pressure, and that p27Kip1 is strongly influenced by this change.

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François Quemeneur, Jon K Sigurdsson, Marianne Renner, Paul J Atzberger*, Patricia Bassereau*, David Lacoste* (2014 Mar 24)

Shape matters in protein mobility within membranes.

Proceedings of the National Academy of Sciences of the United States of America : 5083-7 : DOI : 10.1073/pnas.1321054111 En savoir plus
Résumé

The lateral mobility of proteins within cell membranes is usually thought to be dependent on their size and modulated by local heterogeneities of the membrane. Experiments using single-particle tracking on reconstituted membranes demonstrate that protein diffusion is significantly influenced by the interplay of membrane curvature, membrane tension, and protein shape. We find that the curvature-coupled voltage-gated potassium channel (KvAP) undergoes a significant increase in protein mobility under tension, whereas the mobility of the curvature-neutral water channel aquaporin 0 (AQP0) is insensitive to it. Such observations are well explained in terms of an effective friction coefficient of the protein induced by the local membrane deformation.

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Patricia Bassereau, Benoit Sorre, Aurore Lévy (2014 Mar 18)

Bending lipid membranes: experiments after W. Helfrich’s model.

Advances in colloid and interface science : 47-57 : DOI : 10.1016/j.cis.2014.02.002 En savoir plus
Résumé

Current description of biomembrane mechanics for a large part originates from W. Helfrich’s model. Based On His continuum theory, Many experiments-have-been Performed in the past four Decades membranes is simplified in order to Characterize the mechanical properties of lipid membranes and the contribution of polymers or proteins. The long-term goal Was to Develop a better understanding of the mechanical properties of cell membranes. In this paper, we will review experimental representative Approaches That Were Developed During this period and the hand results That Were therefor obtained.

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G Duclos, S Garcia, H G Yevick, P Silberzan (2014 Mar 14)

Perfect nematic order in confined monolayers of spindle-shaped cells.

Soft matter : 10 : 2346-53 : DOI : 10.1039/c3sm52323c En savoir plus
Résumé

Elongated, weakly interacting, apolar, fibroblast cells (mouse fibroblasts NIH-3T3) cultured at confluence align together, forming large domains (correlation length ∼ 500 μm) where they are perfectly ordered. We study the emergence of this mesoscopic nematic order by quantifying the ordering dynamics in a two-dimensional tissue. Cells are initially very motile and the monolayer is characterized by anomalous density fluctuations, a signature of far-from-equilibrium systems. As the cell density increases because of proliferation, the cells align with each other forming these large oriented domains while, at the same time, the cellular movements and the density fluctuations freeze. Topological defects that are characteristic of nematic phases remain trapped at long times thereby preventing the development of infinite domains. When confined within adhesive stripes of given widths (from 30 μm to 1.5 mm) cells spontaneously align with the domain edges. This orientation then propagates toward the pattern center. For widths smaller than the orientation correlation length, cells perfectly align in the direction of the stripe. Experiments performed in cross-shaped patterns show that in the situation of two competing populations, both the number of cells and the degree of alignment impact the final orientation.

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Mijo Simunovic, Patricia Bassereau (2014 Mar 1)

Reshaping biological membranes in endocytosis: crossing the configurational space of membrane-protein interactions.

Biological chemistry : 395 : 275-283 : DOI : 10.1515/hsz-2013-0242 En savoir plus
Résumé

Lipid membranes are highly dynamic. Over Several Decades, physicists and biologists-have uncovered a number of ways They Can change the shape of membranes or alter Their stage behavior. In cells, the intricate work of membrane proteins drives thesis processes. Considering the highly complex ways proteins interact with biological membranes, Molecular mechanisms of membrane remodeling REMAIN still unclear. When studying membrane remodeling phenomena, Researchers Often observed different results, leading to disparate conclusions em on the physiological race of Such processes. Here we how the Chat-combining research methodologies and various experimental requirements Contributes to the understanding of the Entire Phase space of membrane-protein interactions. Using the example of clathrin-mediated endocytosis we try to Distinguish the question « how can remodel the membrane proteins? ‘ from ‘how do proteins remodel the membrane in the cell?’ In Particular, we Consider how altering physical parameters affect the way May membrane is remodeled. Uncovering the full range of physical requirements under qui membrane phenomena take place is key in understanding the way cells take advantage of membrane properties in carrying out vital Their tasks.

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Sophie Aimon, Andrew Callan-Jones, Alice Berthaud, Mathieu Pinot, Gilman E S Toombes*, Patricia Bassereau* (2014 Jan 27)

Membrane shape modulates transmembrane protein distribution.

Developmental cell : 212-8 : DOI : 10.1016/j.devcel.2013.12.012 En savoir plus
Résumé

Although membrane shape varies greatly throughout the cell, the contribution of membrane curvature to transmembrane protein targeting is unknown because of the numerous sorting mechanisms that take place concurrently in cells. To isolate the effect of membrane shape, we used cell-sized giant unilamellar vesicles (GUVs) containing either the potassium channel KvAP or the water channel AQP0 to form membrane nanotubes with controlled radii. Whereas the AQP0 concentrations in flat and curved membranes were indistinguishable, KvAP was enriched in the tubes, with greater enrichment in more highly curved membranes. Fluorescence recovery after photobleaching measurements showed that both proteins could freely diffuse through the neck between the tube and GUV, and the effect of each protein on membrane shape and stiffness was characterized using a thermodynamic sorting model. This study establishes the importance of membrane shape for targeting transmembrane proteins and provides a method for determining the effective shape and flexibility of membrane proteins.

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Ludger Johannes, Christian Wunder, Patricia Bassereau (2014 Jan 4)

Bending « on the rocks »–a cocktail of biophysical modules to build endocytic pathways.

Cold Spring Harbor perspectives in biology : DOI : 10.1101/cshperspect.a016741 En savoir plus
Résumé

Numerous biological processes Rely on endocytosis. The building is of endocytic pits Achieved by a bewildering complexity of factoring That biochemical function in clathrin-dependent and -independent pathways. In this review, we argue That this complexity can be conceptualized by a deceptively small number of physical principles That Fall into two broad categories: passive Mechanisms, Such As asymmetric transbilayer stress, scaffolding, line voltage, and crowding, and active Mechanisms driven by mechanochemical enzymes and / or cytoskeleton. We Illustrate how the functional identity of biochemical modules depends on system parameters Such As local protein density on membranes, THUS explaining Reviews some of the controversy in the field. Different modules frequently operate in parallel in the Sami Often step and are shared by divergent Apparently uptake processes. The emergence of a novel endocytic classification system THUS May be envisioned in qui functional modules are the elementary bricks.

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Blanchoin L, Boujemaa-Paterski R, Sykes C, Plastino J (2014 Jan 1)

Actin dynamics, architecture, and mechanics in cell motility

Physiological Reviews : 94 : 235-63 : DOI : 10.1152/physrev.00018.2013 En savoir plus
Résumé

Tight coupling between biochemical and mechanical properties of the actin cytoskeleton drives a large range of cellular processes including polarity establishment, morphogenesis, and motility. This is possible because actin filaments are semi-flexible polymers that, in conjunction with the molecular motor myosin, can act as biological active springs or « dashpots » (in laymen’s terms, shock absorbers or fluidizers) able to exert or resist against force in a cellular environment. To modulate their mechanical properties, actin filaments can organize into a variety of architectures generating a diversity of cellular organizations including branched or crosslinked networks in the lamellipodium, parallel bundles in filopodia, and antiparallel structures in contractile fibers. In this review we describe the feedback loop between biochemical and mechanical properties of actin organization at the molecular level in vitro, then we integrate this knowledge into our current understanding of cellular actin organization and its physiological roles.

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Année de publication : 2013

Edouard Hannezo, Jacques Prost, Jean-Francois Joanny (2013 Dec 23)

Theory of epithelial sheet morphology in three dimensions.

Proceedings of the National Academy of Sciences of the United States of America : 27-32 : DOI : 10.1073/pnas.1312076111 En savoir plus
Résumé

Morphogenesis during embryo development requires the coordination of mechanical forces to generate the macroscopic shapes of organs. We propose a minimal theoretical model, based on cell adhesion and actomyosin contractility, which describes the various shapes of epithelial cells and the bending and buckling of epithelial sheets, as well as the relative stability of cellular tubes and spheres. We show that, to understand these processes, a full 3D description of the cells is needed, but that simple scaling laws can still be derived. The morphologies observed in vivo can be understood as stable points of mechanical equations and the transitions between them are either continuous or discontinuous. We then focus on epithelial sheet bending, a ubiquitous morphogenetic process. We calculate the curvature of an epithelium as a function of actin belt tension as well as of cell-cell and and cell-substrate tension. The model allows for a comparison of the relative stabilities of spherical or cylindrical cellular structures (acini or tubes). Finally, we propose a unique type of buckling instability of epithelia, driven by a flattening of individual cell shapes, and discuss experimental tests to verify our predictions.

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Thomas Bornschlögl, Patricia Bassereau (2013 Dec 17)

The sense is in the fingertips: The distal end controls filopodial mechanics and dynamics in response to external stimuli.

Communicative & integrative biology : 6 : e27341 : DOI : 10.4161/cib.27341 En savoir plus
Résumé

Small hair-like cell protrusions, called filopodia, often establish adhesive contacts with the cellular surroundings with a subsequent build up of retraction force. This process seems to be important for cell migration, embryonic development, wound healing, and pathogenic infection pathways. We have shown that filopodial tips are able to sense adhesive contact and, as a consequence, locally reduce actin polymerization speed. This induces filopodial retraction via forces generated by the cell membrane tension and by the filopodial actin shaft that is constantly pulled rearwards via the retrograde flow of actin at the base. The tip is also the weakest point of actin-based force transduction. Forces higher than 15 pN can disconnect the actin shaft from the membrane, which increases actin polymerization at the tip. Together, this points toward the tip as a mechano-chemical sensing and steering unit for filopodia, and it calls for a better understanding of the molecular mechanisms involved.

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