UMR168 – Laboratoire Physico-Chimie Curie

Publications de l’UMR 168

Année de publication : 2018

Patricia Bassereau, Rui Jin, Tobias Baumgart, Markus Deserno, Rumiana Dimova, Vadim A. Frolov, Pavel V. Bashkirov, Helmut Grubmüller, Reinhard Jahn, H. Jelger Risselada, Ludger Johannes, Michael M. Kozlov, Reinhard Lipowsky, Thomas J. Pucadyil, Wade F. Zeno, Jeanne C. Stachowiak, Dimitrios Stamou, Artù Breuer, Line Lauritsen, Camille Simon, Cécile Sykes, Gregory A. Voth, Thomas R Weikl (2018 Jul 20)

The 2018 biomembrane curvature and remodeling roadmap.

Journal of Physics D: Applied Physics : 51 : 343001 : DOI : 10.1088/1361-6463/aacb98 En savoir plus
Résumé

The importance of curvature as a structural feature of biological membranes has been recognized for many years and has fascinated scientists from a wide range of different backgrounds. On the one hand, changes in membrane morphology are involved in a plethora of phenomena involving the plasma membrane of eukaryotic cells, including endo- and exocytosis, phagocytosis and filopodia formation. On the other hand, a multitude of intracellular processes at the level of organelles rely on generation, modulation, and maintenance of membrane curvature to maintain the organelle shape and functionality. The contribution of biophysicists and biologists is essential for shedding light on the mechanistic understanding and quantification of these processes.

Given the vast complexity of phenomena and mechanisms involved in the coupling between membrane shape and function, it is not always clear in what direction to advance to eventually arrive at an exhaustive understanding of this important research area. The 2018 Biomembrane Curvature and Remodeling Roadmap of Journal of Physics D: Applied Physics addresses this need for clarity and is intended to provide guidance both for students who have just entered the field as well as established scientists who would like to improve their orientation within this fascinating area.

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Röper Jens-Christian, Mitrossilis Démosthène, Stirnemann Guillaume, Waharte François, Brito Isabel, Fernandez-Sanchez Maria-Elena, Baaden Marc, Salamero Jean, Farge Emmanuel (2018 Jul 19)

The major β-catenin/E-cadherin junctional binding site is a primary molecular mechano-transductor of differentiation in vivo

eLIFE : 7:e33381. DOI: https://doi.org/10.7554/eLife.33381 : DOI : DOI: https://doi.org/10.7554/eLife.33381 En savoir plus
Résumé

In vivo, the primary molecular mechanotransductive events mechanically initiating cell differentiation remain unknown. Here we find the molecular stretching of the highly conserved Y654-beta-catenin-D665-E-cadherin binding site as mechanically induced by tissue strain. It triggers the increase of accessibility of the Y654 site, target of the Src42A kinase phosphorylation leading to irreversible unbinding. Molecular dynamics simulations of the beta-catenin/E-cadherin complex under a force mimicking a 6 pN physiological mechanical strain predict a local 45% stretching between the two a-helices linked by the site and a 15% increase in accessibility of the phosphorylation site. Both are quantitatively observed using FRET lifetime imaging and non-phospho Y654 specific antibody labelling, in response to the mechanical strains developed by endogenous and magnetically mimicked early mesoderm invagination of gastrulating Drosophila embryos. This is followed by the predicted release of 16% of beta-catenin from junctions, observed in FRAP, which initiates the mechanical activation of the b-catenin pathway process.

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Alexandre Beber, Maryam Alqabandi, Coline Prevost, Fanny Viars, Daniel Levy, Patricia Bassereau, Aurélie Bertin*, Stéphanie Mangenot* (2018 Jul 16)

Septin-based readout of PI(4,5)P2 incorporation into membranes of giant unilamellar vesicles

Cytoskeleton : DOI : 10.1002/cm.21480 En savoir plus
Résumé

Septins constitute a novel class of cytoskeletal proteins. Budding yeast septins self-assemble into non-polar filaments bound to the inner plasma membrane through specific interactions with L- α-phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2). Biomimetic in vitro assays using Giant Unilamellar Vesicles (GUVs) are relevant tools to dissect and reveal insights in proteins-lipids interactions, membrane mechanics and curvature sensitivity. GUVs doped with PI(4,5)P2 are challenging to prepare. This report is dedicated to optimize the incorporation of PI(4,5)P2 lipids into GUVs by probing the proteins-PI(4,5)P2 GUVs interactions. We show that the interaction between budding yeast septins and PI(4,5)P2 is more specific than using usual reporters (phospholipase  Cd1). Septins have thus been chosen as reporters to probe the proper incorporation of PI(4,5)P2 into giant vesicles. We have shown that electro-formation on platinum wires is the most appropriate method to achieve an optimal septin-lipid interaction resulting from an optimal PI(4,5)P2 incorporation for which, we have optimized the growth conditions. Finally, we have shown that PI(4,5)P2 GUVs have to be used within a few hours after their preparation. Indeed, over time, PI(4,5)P2 is expelled from he GUV membrane and the PI(4,5)P2 concentration in the bilayer decreases .

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Duclos G., Deforet M., Yevick H.G., Cochet-Escartin O., Ascione F., Moitrier S., Sarkar T., Yashunsky V., Bonnet I., Buguin A., Silberzan P. (2018 Jun 11)

Controlling confinement and topology to study collective cell behaviors

Methods in Molecular Biology“Cell Migration: Methods and Protocols” : 1749 : 387-399 : DOI : 10.1007/978-1-4939-7701-7_28 En savoir plus
Résumé

Confinement and substrate topology strongly affect the behavior of cell populations and, in particular, their collective migration. In vitro experiments dealing with these aspects require strategies of surface patterning that remain effective over long times (typically several days) and ways to control the surface topology in three dimensions. Here, we describe protocols addressing these two aspects. High-resolution patterning of a robust cell-repellent coating is achieved by etching the coating through a photoresist mask patterned directly on the coated surface. Out-of-plane curvature can be controlled using glass wires or corrugated « wavy » surfaces.

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Broders-Bondon Florence, Nguyen Ho-Bouldoires Thanh, Fernandez-Sanchez Maria Elena-Farge Emmanuel (2018 May 17)

Mechanotransduction in tumor progression: The dark side of the force.

Journal of Cell Biology : 217(5):1571-1587 : DOI : 10.1083/jcb.201701039 En savoir plus
Résumé

Cancer has been characterized as a genetic disease, associated with mutations that cause pathological alterations of the cell cycle, adhesion, or invasive motility. Recently, the importance of the anomalous mechanical properties of tumor tissues, which activate tumorigenic biochemical pathways, has become apparent. This mechanical induction in tumors appears to consist of the destabilization of adult tissue homeostasis as a result of the reactivation of embryonic developmental mechanosensitive pathways in response to pathological mechanical strains. These strains occur in many forms, for example, hypervascularization in late tumors leads to high static hydrodynamic pressure that can promote malignant progression through hypoxia or anomalous interstitial liquid and blood flow. The high stiffness of tumors directly induces the mechanical activation of biochemical pathways enhancing the cell cycle, epithelial–mesenchymal transition, and cell motility. Furthermore, increases in solid-stress pressure associated with cell hyperproliferation activate tumorigenic pathways in the healthy epithelial cells compressed by the neighboring tumor. The underlying molecular mechanisms of the translation of a mechanical signal into a tumor inducing biochemical signal are based on mechanically induced protein conformational changes that activate classical tumorigenic signaling pathways. Understanding these mechanisms will be important for the development of innovative treatments to target such mechanical anomalies in cancer.

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Begoña Ugarte-Uribe, Coline Prévost, Kushal Kumar Das, Patricia Bassereau, Ana J. García-Sáez (2018 Apr 19)

Drp1 polymerization stabilizes curved tubular membranes similar to those of constricted mitochondria.

Journal of Cell Science : 132 : jcs208603 : DOI : 10.1242/jcs.208603 En savoir plus
Résumé

Dynamin-related protein 1 (Drp1), an 80 kDa mechanochemical GTPase of the dynamin superfamily, is required for mitochondrial division in mammals. Despite the role of Drp1 dysfunction in human disease, its molecular mechanism remains poorly understood. Here, we examined the effect of Drp1 on membrane curvature using tubes pulled from giant unilamellar vesicles (GUVs). We found that GTP promoted rapid rearrangement of Drp1 from a uniform distribution to discrete foci, in line with the assembly of Drp1 scaffolds at multiple nucleation sites around the lipid tube. Polymerized Drp1 preserved the membrane tube below the protein coat, also in the absence of pulling forces, but did not induce spontaneous membrane fission. Strikingly, Drp1 polymers stabilized membrane curvatures similar to those of constricted mitochondria against pressure changes. Our findings support a new model for mitochondrial division whereby Drp1 mainly acts as a scaffold for membrane curvature stabilization, which sets it apart from other dynamin homologs.

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Mijo Simunovic, Patricia Bassereau, Gregory A. Voth (2018 Mar 30)

Organizing membrane-curving proteins: the emerging dynamical picture.

Current Opinion in Structural Biology : 51 : 99-105 : DOI : 10.1016/j.sbi.2018.03.018 En savoir plus
Résumé

Lipid membranes play key roles in cells, such as in trafficking, division, infection, remodeling of organelles, among others. The key step in all these processes is creating membrane curvature, typically under the control of many anchored, adhered or included proteins. However, it has become clear that the membrane itself can mediate the interactions among proteins to produce highly ordered assemblies. Computer simulations are ideally suited to investigate protein organization and the dynamics of membrane remodeling at near-micron scales, something that is extremely challenging to tackle experimentally. We review recent computational efforts in modeling protein-caused membrane deformation mechanisms, specifically focusing on coarse-grained simulations. We highlight work that exposed the membrane-mediated ordering of proteins into lines, meshwork, spirals and other assemblies, in what seems to be a very generic mechanism driven by a combination of short and long-ranged forces. Modulating the mechanical properties of membranes is an underexplored signaling mechanism in various processes deserving of more attention in the near future.

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Eran Agmon, Jérôme Solon, Patricia Bassereau, Brent R. Stockwell (2018 Mar 26)

Modeling the effects of lipid peroxidation during ferroptosis on membrane properties.

Scientific Reports : 8 : 5155 : DOI : 10.1038/s41598-018-23408-0 En savoir plus
Résumé

Ferroptosis is a form of regulated cell death characterized by the accumulation of lipid hydroperoxides. There has been significant research on the pathways leading to the accumulation of oxidized lipids, but the downstream effects and how lipid peroxides cause cell death during ferroptosis remain a major puzzle. We evaluated key features of ferroptosis in newly developed molecular dynamics models of lipid membranes to investigate the biophysical consequences of lipid peroxidation, and generated hypotheses about how lipid peroxides contribute to cell death during ferroptosis.

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Jérémie Barral, Frank Jülicher, Pascal Martin (2018 Feb 6)

Friction from Transduction Channels’ Gating Affects Spontaneous Hair-Bundle Oscillations.

Biophysical journal : 425-436 : DOI : S0006-3495(17)31251-1 En savoir plus
Résumé

Hair cells of the inner ear can power spontaneous oscillations of their mechanosensory hair bundle, resulting in amplification of weak inputs near the characteristic frequency of oscillation. Recently, dynamic force measurements have revealed that delayed gating of the mechanosensitive ion channels responsible for mechanoelectrical transduction produces a friction force on the hair bundle. The significance of this intrinsic source of dissipation for the dynamical process underlying active hair-bundle motility has remained elusive. The aim of this work is to determine the role of friction in spontaneous hair-bundle oscillations. To this end, we characterized key oscillation properties over a large ensemble of individual hair cells and measured how viscosity of the endolymph that bathes the hair bundles affects these properties. We found that hair-bundle movements were too slow to be impeded by viscous drag only. Moreover, the oscillation frequency was only marginally affected by increasing endolymph viscosity by up to 30-fold. Stochastic simulations could capture the observed behaviors by adding a contribution to friction that was 3-8-fold larger than viscous drag. The extra friction could be attributed to delayed changes in tip-link tension as the result of the finite activation kinetics of the transduction channels. We exploited our analysis of hair-bundle dynamics to infer the channel activation time, which was ∼1 ms. This timescale was two orders-of-magnitude shorter than the oscillation period. However, because the channel activation time was significantly longer than the timescale of mechanical relaxation of the hair bundle, channel kinetics affected hair-bundle dynamics. Our results suggest that friction from channel gating affects the waveform of oscillation and that the channel activation time can tune the characteristic frequency of the hair cell. We conclude that the kinetics of transduction channels’ gating plays a fundamental role in the dynamic process that shapes spontaneous hair-bundle oscillations.

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Année de publication : 2017

Francesco Gianoli, Thomas Risler, Andrei S. Kozlov (2017 Dec 19)

Lipid bilayer mediates ion-channel cooperativity in a model of hair-cell mechanotransduction

Proceedings of the National Academy of Sciences of the United States of America : 114 : E11010-E11019 : DOI : 10.1073/pnas.1713135114 En savoir plus
Résumé

Mechanoelectrical transduction in the inner ear is a biophysical process underlying the senses of hearing and balance. The key players involved in this process are mechanosensitive ion channels. They are located in the stereocilia of hair cells and opened by the tension in specialized molecular springs, the tip links, connecting adjacent stereocilia. When channels open, the tip links relax, reducing the hair-bundle stiffness. This gating compliance makes hair cells especially sensitive to small stimuli. The classical explanation for the gating compliance is that the conformational rearrangement of a single channel directly shortens the tip link. However, to reconcile theoretical models based on this mechanism with experimental data, an unrealistically large structural change of the channel is required. Experimental evidence indicates that each tip link is a dimeric molecule, associated on average with two channels at its lower end. It also indicates that the lipid bilayer modulates channel gating, although it is not clear how. Here, we design and analyze a model of mechanotransduction where each tip link attaches to two channels, mobile within the membrane. Their states and positions are coupled by membrane-mediated elastic forces arising from the interaction between the channels’ hydrophobic cores and that of the lipid bilayer. This coupling induces cooperative opening and closing of the channels. The model reproduces the main properties of hair-cell mechanotransduction using only realistic parameters constrained by experimental evidence. This work provides an insight into the fundamental role that membrane-mediated ion-channel cooperativity can play in sensory physiology.

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Win Pin Ng, Kevin D. Webster, Caroline Stefani, Eva M. Schmid, Emmanuel Lemichez, Patricia Bassereau, Daniel A. Fletcher (2017 Oct 2)

Force-induced transcellular tunnel formation in endothelial cells

Molecular Biology of the Cell : 28 : 2650-2660 : DOI : 10.1091/mbc.E17-01-0080 En savoir plus
Résumé

The endothelium serves as a protective semipermeable barrier in blood vessels and lymphatic vessels. Leukocytes and pathogens can pass directly through the endothelium by opening holes in endothelial cells, known as transcellular tunnels, which are formed by contact and self-fusion of the apical and basal plasma membranes. Here we test the hypothesis that the actin cytoskeleton is the primary barrier to transcellular tunnel formation using a combination of atomic force microscopy and fluorescence microscopy of live cells. We find that localized mechanical forces are sufficient to induce the formation of transcellular tunnels in human umbilical vein endothelial cells (HUVECs). When HUVECs are exposed to the bacterial toxin called epidermal cell differentiation inhibitor (EDIN), which can induce spontaneous transcellular tunnels, less mechanical work is required to form tunnels due to the reduced cytoskeletal stiffness and thickness of these cells, similarly to the effects of a Rho-associated protein kinase (ROCK) inhibitor. We also observe actin enrichment in response to mechanical indentation that is reduced in cells exposed to the bacterial toxin. Our study shows that the actin cytoskeleton of endothelial cells provides both passive and active resistance against transcellular tunnel formation, serving as a mechanical barrier that can be overcome by mechanical force as well as disruption of the cytoskeleton.

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Shunsuke Yabunaka, Philippe Marcq (2017 Sep 28)

Cell growth, division, and death in cohesive tissues: A thermodynamic approach.

Physical review. E : 022406 : DOI : 10.1103/PhysRevE.96.022406 En savoir plus
Résumé

Cell growth, division, and death are defining features of biological tissues that contribute to morphogenesis. In hydrodynamic descriptions of cohesive tissues, their occurrence implies a nonzero rate of variation of cell density. We show how linear nonequilibrium thermodynamics allows us to express this rate as a combination of relevant thermodynamic forces: chemical potential, velocity divergence, and activity. We illustrate the resulting effects of the nonconservation of cell density on simple examples inspired by recent experiments on cell monolayers, considering first the velocity of a spreading front, and second an instability leading to mechanical waves.

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Shuji Ishihara, Philippe Marcq, Kaoru Sugimura (2017 Sep 28)

From cells to tissue: A continuum model of epithelial mechanics.

Physical review. E : 022418 : DOI : 10.1103/PhysRevE.96.022418 En savoir plus
Résumé

A two-dimensional continuum model of epithelial tissue mechanics was formulated using cellular-level mechanical ingredients and cell morphogenetic processes, including cellular shape changes and cellular rearrangements. This model incorporates stress and deformation tensors, which can be compared with experimental data. Focusing on the interplay between cell shape changes and cell rearrangements, we elucidated dynamical behavior underlying passive relaxation, active contraction-elongation, and tissue shear flow, including a mechanism for contraction-elongation, whereby tissue flows perpendicularly to the axis of cell elongation. This study provides an integrated scheme for the understanding of the orchestration of morphogenetic processes in individual cells to achieve epithelial tissue morphogenesis.

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Shunsuke Yabunaka, Philippe Marcq (2017 Aug 30)

Emergence of epithelial cell density waves.

Soft matter : DOI : 10.1039/c7sm01172e En savoir plus
Résumé

Epithelial cell monolayers exhibit traveling mechanical waves. We rationalize this observation thanks to a hydrodynamic description of the monolayer as a compressible, active and polar material. We show that propagating waves of the cell density, polarity, velocity and stress fields may be due to a Hopf bifurcation occurring above threshold values of active coupling coefficients.

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Breau M, Bonnet I, Stoufflet J, Xie J, De Castro S, Schneider-Maunoury S (2017 Aug 21)

Extrinsic mechanical forces mediate retrograde axon extension in a developing neuronal circuit

Nature Communications : 8 : 282 : DOI : 10.1038/s41467-017-00283-3 En savoir plus
Résumé

To form functional neural circuits, neurons migrate to their final destination and extend axons towards their targets. Whether and how these two processes are coordinated in vivo remains elusive. We use the zebrafish olfactory placode as a system to address the underlying mechanisms. Quantitative live imaging uncovers a choreography of directed cell movements that shapes the placode neuronal cluster: convergence of cells towards the centre of the placodal domain and lateral cell movements away from the brain. Axon formation is concomitant with lateral movements and occurs through an unexpected, retrograde mode of extension, where cell bodies move away from axon tips attached to the brain surface. Convergence movements are active, whereas cell body lateral displacements are of mainly passive nature, likely triggered by compression forces from converging neighbouring cells. These findings unravel a previously unknown mechanism of neuronal circuit formation, whereby extrinsic mechanical forces drive the retrograde extension of axons.

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