UMR168 – Laboratoire Physico-Chimie Curie

Publications de l’UMR 168

Année de publication : 2014

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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Pedro Campinho, Martin Behrndt, Jonas Ranft, Thomas Risler, Nicolas Minc, Carl-Philipp Heisenberg (2013 Nov 12)

Tension-oriented cell divisions limit anisotropic tissue tension in epithelial spreading during zebrafish epiboly.

Nature cell biology : 1405-14 : DOI : 10.1038/ncb2869 En savoir plus
Résumé

Epithelial spreading is a common and fundamental aspect of various developmental and disease-related processes such as epithelial closure and wound healing. A key challenge for epithelial tissues undergoing spreading is to increase their surface area without disrupting epithelial integrity. Here we show that orienting cell divisions by tension constitutes an efficient mechanism by which the enveloping cell layer (EVL) releases anisotropic tension while undergoing spreading during zebrafish epiboly. The control of EVL cell-division orientation by tension involves cell elongation and requires myosin II activity to align the mitotic spindle with the main tension axis. We also found that in the absence of tension-oriented cell divisions and in the presence of increased tissue tension, EVL cells undergo ectopic fusions, suggesting that the reduction of tension anisotropy by oriented cell divisions is required to prevent EVL cells from fusing. We conclude that cell-division orientation by tension constitutes a key mechanism for limiting tension anisotropy and thus promoting tissue spreading during EVL epiboly.

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Thomas Bornschlögl, Stéphane Romero, Christian L Vestergaard, Jean-François Joanny, Guy Tran Van Nhieu, Patricia Bassereau (2013 Nov 6)

Filopodial retraction force is generated by cortical actin dynamics and controlled by reversible tethering at the tip.

Proceedings of the National Academy of Sciences of the United States of America : 18928-33 : DOI : 10.1073/pnas.1316572110 En savoir plus
Résumé

Filopodia are dynamic, plasma finger-like membrane protrusions That sense the mechanical and chemical surroundings of the cell. Here, we show in epithelial cells que la filopodial dynamics of extension and retraction are Determined by the difference entre les actin polymerization rate at the tip and the retrograde flow at the base of the filopodium. Adhesion of a bead to the tip filopodial locally Reduces actin polymerization and leads to retraction via retrograde flow, reminiscent of a process used by pathogens to invade cells. Using optical tweezers, we show That filopodial retraction OCCURS at a constant speed contre counteracting force up to 50 pN. Our measurements Point Toward retrograde flow in the cortex together with frictional coupling entre les filopodial and cortical actin networks as the hand retraction force generator for filopodia. The forces exerted by filopodial retraction, HOWEVER, is limited by the connection entre filopodial actin filaments and the membrane at the tip. Upon mechanical breakage of the tip connection, filopodia Exert a passive retraction strength of 15 pN via Their plasma membrane. Transient reconnection at the tip allows filopodia to probe Continuously Their surroundings in a load-and-fail Manner Within a well-defined power range.

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Anthony Bruchet, Vélan Taniga, Stéphanie Descroix, Laurent Malaquin, Florence Goutelard, Clarisse Mariet (2013 Oct 24)

Centrifugal microfluidic platform for radiochemistry: potentialities for the chemical analysis of nuclear spent fuels.

Talanta : 488-94 : DOI : 10.1016/j.talanta.2013.06.064 En savoir plus
Résumé

The use of a centrifugal microfluidic platform is for the first time reported as an alternative to classical chromatographic procedures for radiochemistry. The original design of the microfluidic platform has been thought to fasten and simplify the prototyping process with the use of a circular platform integrating four rectangular microchips made of thermoplastic. The microchips, dedicated to anion-exchange chromatographic separations, integrate a localized monolithic stationary phase as well as injection and collection reservoirs. The results presented here were obtained with a simplified simulated nuclear spent fuel sample composed of non-radioactive isotopes of Europium and Uranium, in proportion usually found for uranium oxide nuclear spent fuel. While keeping the analytical results consistent with the conventional procedure (extraction yield for Europium of ≈97%), the use of the centrifugal microfluidic platform allowed to reduce the volume of liquid needed by a factor of ≈250. Thanks to their unique « easy-to-use » features, centrifugal microfluidic platforms are potential successful candidates for the downscaling of chromatographic separation of radioactive samples (automation, multiplexing, easy integration in glove-boxes environment and low cost of maintenance).

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Leïla Perié, Philip D Hodgkin, Shalin H Naik, Ton N Schumacher, Rob J de Boer, Ken R Duffy (2013 Oct 14)

Determining lineage pathways from cellular barcoding experiments.

Cell reports : 617-24 : DOI : 10.1016/j.celrep.2014.01.016 En savoir plus
Résumé

Cellular barcoding and other single-cell lineage-tracing strategies form experimental methodologies for analysis of in vivo cell fate that have been instrumental in several significant recent discoveries. Due to the highly nonlinear nature of proliferation and differentiation, interrogation of the resulting data for evaluation of potential lineage pathways requires a new quantitative framework complete with appropriate statistical tests. Here, we develop such a framework, illustrating its utility by analyzing data from barcoded multipotent cells of the blood system. This application demonstrates that the data require additional paths beyond those found in the classical model, which leads us to propose that hematopoietic differentiation follows a loss of potential mechanism and to suggest further experiments to test this deduction. Our quantitative framework can evaluate the compatibility of lineage trees with barcoded data from any proliferating and differentiating cell system.

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Kaoru Sugimura, Yohanns Bellaïche, François Graner, Philippe Marcq, Shuji Ishihara (2013 Oct 11)

Robustness of force and stress inference in an epithelial tissue.

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference : 2712-5 : DOI : 10.1109/EMBC.2013.6610100 En savoir plus
Résumé

During morphogenesis, the shape of a tissue emerges from collective cellular behaviors, which are in part regulated by mechanical and biochemical interactions between cells. Quantification of force and stress is therefore necessary to analyze the mechanisms controlling tissue morphogenesis. Recently, a mechanical measurement method based on force inference from cell shapes and connectivity has been developed. It is non-invasive, and can provide space-time maps of force and stress within an epithelial tissue, up to prefactors. We previously performed a comparative study of three force-inference methods, which differ in their approach of treating indefiniteness in an inverse problem between cell shapes and forces. In the present study, to further validate and compare the three force inference methods, we tested their robustness by measuring temporal fluctuation of estimated forces. Quantitative data of cell-level dynamics in a developing tissue suggests that variation of forces and stress will remain small within a short period of time (~minutes). Here, we showed that cell-junction tensions and global stress inferred by the Bayesian force inference method varied less with time than those inferred by the method that estimates only tension. In contrast, the amplitude of temporal fluctuations of estimated cell pressures differs less between different methods. Altogether, the present study strengthens the validity and robustness of the Bayesian force-inference method.

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