UMR168 – Laboratoire Physico-Chimie Curie

Publications de l’UMR 168

Année de publication : 2015

Vincent Nier, Maxime Deforet, Guillaume Duclos, Hannah G Yevick, Olivier Cochet-Escartin, Philippe Marcq, Pascal Silberzan (2015 Jul 21)

Tissue fusion over nonadhering surfaces.

Proceedings of the National Academy of Sciences of the United States of America : 9546-51 : DOI : 10.1073/pnas.1501278112 En savoir plus
Résumé

Tissue fusion eliminates physical voids in a tissue to form a continuous structure and is central to many processes in development and repair. Fusion events in vivo, particularly in embryonic development, often involve the purse-string contraction of a pluricellular actomyosin cable at the free edge. However, in vitro, adhesion of the cells to their substrate favors a closure mechanism mediated by lamellipodial protrusions, which has prevented a systematic study of the purse-string mechanism. Here, we show that monolayers can cover well-controlled mesoscopic nonadherent areas much larger than a cell size by purse-string closure and that active epithelial fluctuations are required for this process. We have formulated a simple stochastic model that includes purse-string contractility, tissue fluctuations, and effective friction to qualitatively and quantitatively account for the dynamics of closure. Our data suggest that, in vivo, tissue fusion adapts to the local environment by coordinating lamellipodial protrusions and purse-string contractions.

Replier
Leïla Perié, Ken R Duffy, Lianne Kok, Rob J de Boer, Ton N Schumacher (2015 Jul 20)

The Branching Point in Erythro-Myeloid Differentiation.

Cell : 1655-62 : DOI : 10.1016/j.cell.2015.11.059 En savoir plus
Résumé

Development of mature blood cell progenies from hematopoietic stem cells involves the transition through lineage-restricted progenitors. The first branching point along this developmental process is thought to separate the erythro-myeloid and lymphoid lineage fate by yielding two intermediate progenitors, the common myeloid and the common lymphoid progenitors (CMPs and CLPs). Here, we use single-cell lineage tracing to demonstrate that so-called CMPs are highly heterogeneous with respect to cellular output, with most individual CMPs yielding either only erythrocytes or only myeloid cells after transplantation. Furthermore, based on the labeling of earlier progenitors, we show that the divergence between the myeloid and erythroid lineage develops within multipotent progenitors (MPP). These data provide evidence for a model of hematopoietic branching in which multiple distinct lineage commitments occur in parallel within the MPP pool.

Replier
Sens P, Plastino J (2015 Jul 15)

Membrane tension and cytoskeleton organization in cell motility

Journal of Physics: Condensed Matter : 27 : 273103 : DOI : 10.1088/0953-8984/27/27/273103 En savoir plus
Résumé

Cell membrane shape changes are important for many aspects of normal biological function, such as tissue development, wound healing and cell division and motility. Various disease states are associated with deregulation of how cells move and change shape, including notably tumor initiation and cancer cell metastasis. Cell motility is powered, in large part, by the controlled assembly and disassembly of the actin cytoskeleton. Much of this dynamic happens in close proximity to the plasma membrane due to the fact that actin assembly factors are membrane-bound, and thus actin filaments are generally oriented such that their growth occurs against or near the membrane. For a long time, the membrane was viewed as a relatively passive scaffold for signaling. However, results from the last five years show that this is not the whole picture, and that the dynamics of the actin cytoskeleton are intimately linked to the mechanics of the cell membrane. In this review, we summarize recent findings concerning the role of plasma membrane mechanics in cell cytoskeleton dynamics and architecture, showing that the cell membrane is not just an envelope or a barrier for actin assembly, but is a master regulator controlling cytoskeleton dynamics and cell polarity.

Replier
María Elena Fernández-Sánchez, Sandrine Barbier, Joanne Whitehead, Gaëlle Béalle, Aude Michel, Heldmuth Latorre-Ossa, Colette Rey, Laura Fouassier, Audrey Claperon, Laura Brullé, Elodie Girard, Nicolas Servant, Thomas Rio-Frio, Hélène Marie, Sylviane Lesieur, Chantal Housset, Jean-Luc Gennisson, Mickaël Tanter, Christine Ménager, Silvia Fre, Sylvie Robine, Emmanuel Farge (2015 Jul 2)

Mechanical induction of the tumorigenic β-catenin pathway by tumour growth pressure.

Nature : 92-5 : DOI : 10.1038/nature14329 En savoir plus
Résumé

The tumour microenvironment may contribute to tumorigenesis owing to mechanical forces such as fibrotic stiffness or mechanical pressure caused by the expansion of hyper-proliferative cells. Here we explore the contribution of the mechanical pressure exerted by tumour growth onto non-tumorous adjacent epithelium. In the early stage of mouse colon tumour development in the Notch(+)Apc(+/1638N) mouse model, we observed mechanistic pressure stress in the non-tumorous epithelial cells caused by hyper-proliferative adjacent crypts overexpressing active Notch, which is associated with increased Ret and β-catenin signalling. We thus developed a method that allows the delivery of a defined mechanical pressure in vivo, by subcutaneously inserting a magnet close to the mouse colon. The implanted magnet generated a magnetic force on ultra-magnetic liposomes, stabilized in the mesenchymal cells of the connective tissue surrounding colonic crypts after intravenous injection. The magnetically induced pressure quantitatively mimicked the endogenous early tumour growth stress in the order of 1,200 Pa, without affecting tissue stiffness, as monitored by ultrasound strain imaging and shear wave elastography. The exertion of pressure mimicking that of tumour growth led to rapid Ret activation and downstream phosphorylation of β-catenin on Tyr654, imparing its interaction with the E-cadherin in adherens junctions, and which was followed by β-catenin nuclear translocation after 15 days. As a consequence, increased expression of β-catenin-target genes was observed at 1 month, together with crypt enlargement accompanying the formation of early tumorous aberrant crypt foci. Mechanical activation of the tumorigenic β-catenin pathway suggests unexplored modes of tumour propagation based on mechanical signalling pathways in healthy epithelial cells surrounding the tumour, which may contribute to tumour heterogeneity.

Replier
Edouard Hannezo, Bo Dong, Pierre Recho, Jean-François Joanny, Shigeo Hayashi (2015 Jun 17)

Cortical instability drives periodic supracellular actin pattern formation in epithelial tubes.

Proceedings of the National Academy of Sciences of the United States of America : 8620-5 : DOI : 10.1073/pnas.1504762112 En savoir plus
Résumé

An essential question of morphogenesis is how patterns arise without preexisting positional information, as inspired by Turing. In the past few years, cytoskeletal flows in the cell cortex have been identified as a key mechanism of molecular patterning at the subcellular level. Theoretical and in vitro studies have suggested that biological polymers such as actomyosin gels have the property to self-organize, but the applicability of this concept in an in vivo setting remains unclear. Here, we report that the regular spacing pattern of supracellular actin rings in the Drosophila tracheal tubule is governed by a self-organizing principle. We propose a simple biophysical model where pattern formation arises from the interplay of myosin contractility and actin turnover. We validate the hypotheses of the model using photobleaching experiments and report that the formation of actin rings is contractility dependent. Moreover, genetic and pharmacological perturbations of the physical properties of the actomyosin gel modify the spacing of the pattern, as the model predicted. In addition, our model posited a role of cortical friction in stabilizing the spacing pattern of actin rings. Consistently, genetic depletion of apical extracellular matrix caused strikingly dynamic movements of actin rings, mirroring our model prediction of a transition from steady to chaotic actin patterns at low cortical friction. Our results therefore demonstrate quantitatively that a hydrodynamical instability of the actin cortex can trigger regular pattern formation and drive morphogenesis in an in vivo setting.

Replier
Pierre Sens, Julie Plastino (2015 Jun 11)

Membrane tension and cytoskeleton organization in cell motility.

Journal of physics. Condensed matter : an Institute of Physics journal : 273103 : DOI : 10.1088/0953-8984/27/27/273103 En savoir plus
Résumé

Cell membrane shape changes are important for many aspects of normal biological function, such as tissue development, wound healing and cell division and motility. Various disease states are associated with deregulation of how cells move and change shape, including notably tumor initiation and cancer cell metastasis. Cell motility is powered, in large part, by the controlled assembly and disassembly of the actin cytoskeleton. Much of this dynamic happens in close proximity to the plasma membrane due to the fact that actin assembly factors are membrane-bound, and thus actin filaments are generally oriented such that their growth occurs against or near the membrane. For a long time, the membrane was viewed as a relatively passive scaffold for signaling. However, results from the last five years show that this is not the whole picture, and that the dynamics of the actin cytoskeleton are intimately linked to the mechanics of the cell membrane. In this review, we summarize recent findings concerning the role of plasma membrane mechanics in cell cytoskeleton dynamics and architecture, showing that the cell membrane is not just an envelope or a barrier for actin assembly, but is a master regulator controlling cytoskeleton dynamics and cell polarity.

Replier
Mijo Simunovic, Ka Yee C Lee, Patricia Bassereau (2015 May 29)

Celebrating Soft Matter’s 10th anniversary: screening of the calcium-induced spontaneous curvature of lipid membranes.

Soft matter : 5030-6 : DOI : 10.1039/c5sm00104h En savoir plus
Résumé

Lipid membranes are key regulators of cellular function. An significant step in membrane-related phenomena is the reshaping of the lipid bilayer, Often induced by binding of macromolecules. Numerous experimental and simulation efforts-have Revealed That calcium, a ubiquitous cellular messenger: has a strong impact on the behavior stage, structural properties, and the stability of membranes. Yet, it is still unknown the way calcium and lipid interactions affect Their macroscopic mechanical properties. In this work, we Studied the interaction of calcium ions with membrane tethers pulled from giant unilamellar vesicles, QUANTIFY to the mechanical effect on the membrane. We found calcium That imposed a positive spontaneous curvature is Negatively charged membranes Contrary to predictions we made based on the Proposed atomic structure. Surprisingly, this effect vanishes in the presence of physiologically relevant concentrations of sodium chloride. Our work Implies That calcium May be a trigger for reshaping membrane only at high concentrations, in a process robustly That is screened by sodium ions.

Replier
Yevick HG, Duclos G, Bonnet I, Silberzan P. (2015 May 12)

Architecture and migration of an epithelium on a cylindrical wire

Proc Natl Acad Sci USA112(19):5944-9 : DOI : 10.1073/pnas.1418857112 En savoir plus
Résumé

In a wide range of epithelial tissues such as kidney tubules or breast acini, cells organize into bidimensional monolayers experiencing an out-of-plane curvature. Cancer cells can also migrate collectively from epithelial tumors by wrapping around vessels or muscle fibers. However, in vitro experiments dealing with epithelia are mostly performed on flat substrates, neglecting this out-of-plane component. In this paper, we study the development and migration of epithelial tissues on glass wires of well-defined radii varying from less than 1 µm up to 85 µm. To uncouple the effect of out-of-plane curvature from the lateral confinement experienced by the cells in these geometries, we compare our results to experiments performed on narrow adhesive tracks. Because of lateral confinement, the velocity of collective migration increases for radii smaller than typically 20 µm. The monolayer dynamics is then controlled by front-edge protrusions. Conversely, high curvature is identified as the inducer of frequent cell detachments at the front edge, a phenotype reminiscent of the Epithelial-Mesenchymal Transition. High curvature also induces a circumferential alignment of the actin cytoskeleton, stabilized by multiple focal adhesions. This organization of the cytoskeleton is reminiscent of in vivo situations such as the development of the trachea of the Drosophila embryo. Finally, submicron radii halt the monolayer, which then reconfigures into hollow cysts.

Replier
Sham Tlili, Cyprien Gay, François Graner, Philippe Marcq, François Molino, Pierre Saramito (2015 May 10)

Colloquium: Mechanical formalisms for tissue dynamics.

The European physical journal. E, Soft matter : 121 : DOI : 10.1140/epje/i2015-15033-4 En savoir plus
Résumé

The understanding of morphogenesis in living organisms has been renewed by tremendous progress in experimental techniques that provide access to cell scale, quantitative information both on the shapes of cells within tissues and on the genes being expressed. This information suggests that our understanding of the respective contributions of gene expression and mechanics, and of their crucial entanglement, will soon leap forward. Biomechanics increasingly benefits from models, which assist the design and interpretation of experiments, point out the main ingredients and assumptions, and ultimately lead to predictions. The newly accessible local information thus calls for a reflection on how to select suitable classes of mechanical models. We review both mechanical ingredients suggested by the current knowledge of tissue behaviour, and modelling methods that can help generate a rheological diagram or a constitutive equation. We distinguish cell scale (« intra-cell ») and tissue scale (« inter-cell ») contributions. We recall the mathematical framework developed for continuum materials and explain how to transform a constitutive equation into a set of partial differential equations amenable to numerical resolution. We show that when plastic behaviour is relevant, the dissipation function formalism appears appropriate to generate constitutive equations; its variational nature facilitates numerical implementation, and we discuss adaptations needed in the case of large deformations. The present article gathers theoretical methods that can readily enhance the significance of the data to be extracted from recent or future high throughput biomechanical experiments.

Replier
Renaud Renault, Nirit Sukenik, Stéphanie Descroix, Laurent Malaquin, Jean-Louis Viovy, Jean-Michel Peyrin, Samuel Bottani, Pascal Monceau, Elisha Moses, Maéva Vignes (2015 Apr 23)

Combining microfluidics, optogenetics and calcium imaging to study neuronal communication in vitro.

PloS one : e0120680 : DOI : 10.1371/journal.pone.0120680 En savoir plus
Résumé

In this paper we report the combination of microfluidics, optogenetics and calcium imaging as a cheap and convenient platform to study synaptic communication between neuronal populations in vitro. We first show that Calcium Orange indicator is compatible in vitro with a commonly used Channelrhodopsine-2 (ChR2) variant, as standard calcium imaging conditions did not alter significantly the activity of transduced cultures of rodent primary neurons. A fast, robust and scalable process for micro-chip fabrication was developed in parallel to build micro-compartmented cultures. Coupling optical fibers to each micro-compartment allowed for the independent control of ChR2 activation in the different populations without crosstalk. By analyzing the post-stimuli activity across the different populations, we finally show how this platform can be used to evaluate quantitatively the effective connectivity between connected neuronal populations.

Replier
Ricard Alert, Jaume Casademunt, Jan Brugués, Pierre Sens (2015 Apr 23)

Model for probing membrane-cortex adhesion by micropipette aspiration and fluctuation spectroscopy.

Biophysical journal : 1878-86 : DOI : 10.1016/j.bpj.2015.02.027 En savoir plus
Résumé

We propose a model for membrane-cortex adhesion that couples membrane deformations, hydrodynamics, and kinetics of membrane-cortex ligands. In its simplest form, the model gives explicit predictions for the critical pressure for membrane detachment and for the value of adhesion energy. We show that these quantities exhibit a significant dependence on the active acto-myosin stresses. The model provides a simple framework to access quantitative information on cortical activity by means of micropipette experiments. We also extend the model to incorporate fluctuations and show that detailed information on the stability of membrane-cortex coupling can be obtained by a combination of micropipette aspiration and fluctuation spectroscopy measurements.

Replier
Ludger Johannes, Robert G Parton, Patricia Bassereau, Satyajit Mayor (2015 Apr 11)

Building endocytic pits without clathrin.

Nature reviews. Molecular cell biology : 311-21 : DOI : 10.1038/nrm3968 En savoir plus
Résumé

How endocytic pits are built in clathrin- and caveolin-independent endocytosis still remains poorly Understood. Recent insight Suggests That different forms of clathrin-independent endocytosis might Involve the actin-driven focusing of membrane constituents, the lectin-glycosphingolipid-dependent endocytic nanoenvironments of building, and Bin-Amphiphysin-Rvs (BAR) domain proteins serving as scaffolding modules. We need the Chat for the different kinds of internalization processes in the context of diverse cellular functions, the existence of clathrin-independent Mechanisms of cargo recruitment and membrane bending from a physical and biological perspective, and finally propose a generic scheme for the formation of clathrin- independent endocytic pits.

Replier
Lemière J, Carvalho K, Sykes C (2015 Apr 8)

Cell-sized liposomes that mimic cell motility and the cell cortex

Methods in Cell Biology : 128 : 271-85 : DOI : 10.1016/bs.mcb.2015.01.013 En savoir plus
Résumé

Cells move and change shape by dynamically reorganizing their cytoskeleton next to the plasma membrane. In particular, actin assembly generates forces and stresses that deform the cell membrane. Cell-sized liposomes are designed to mimic this function. The activation of actin polymerization at their membrane is able to push the membrane forward, thus reproducing the mechanism of lamellipodium extension at the cell front. Moreover, the cell cortex, a submicrometer-thick actin shell right beneath the cell membrane can be reproduced; it contributes to cell tension with the action of molecular motors. We will describe experimental methods to prepare liposomes that mimic the inside geometry of a cell, and that reproduce actin-based propulsion of the liposome using an outside geometry. Such systems allow to study how actin-related proteins control and affect actin cortex assembly and can produce forces that drive cell shape changes.

Replier
Matthias Garten, Coline Prévost, Clotilde Cadart, Romain Gautier, Luc Bousset, Ronald Melki, Patricia Bassereau, Stefano Vanni (2015 Apr 1)

Methyl-branched lipids promote the membrane adsorption of α-synuclein by enhancing shallow lipid-packing defects.

Physical chemistry chemical physics : PCCP : 15589-97 : DOI : 10.1039/c5cp00244c En savoir plus
Résumé

Alpha-synuclein (AS) is a synaptic protein That Is Directly Involved in Parkinson’s disease due to ict tendency to form protein aggregates. Since AS aggregation can be dependent on the interactions entre les protein and the cell plasma membrane, elucidating the membrane binding properties of AS is of crucial importance to the suit les molecular basis of AS aggregation into toxic fibrils. Using a combination of in vitro reconstitution experiments based on Giant Unilamellar Vesicles (GUVs), confocal microscopy and all-atom molecular dynamics simulations, we-have Investigated the membrane binding properties of AS, with a focus on the relative contribution of hydrophobic versus electrostatic interactions. In contrast with previous observations, We Did not observed Any binding of AS to membranes Containing the ganglioside GM1, GM1-even at high Relatively happy. AS we Reviews the other hand, Showed a stronger affinity for neutral flat membranes consistant en methyl-branched lipids. To rationalize thesis results, we used all-atom molecular dynamics simulations to Investigate the effect of methyl-branched lipids is membrane interfacial properties. We found That methyl-branched lipids Promote the membrane adsorption of AS by Creating shallow lipid-packing defects to a larger extent than polyunsaturated and monounsaturated lipids. Our Findings suggest methyl-branched lipids That May Constitute a substrate for adhesive Remarkably peripheral proteins adsorbed That is hydrophobic membranes via inserts.

Replier
Almonacid M, Ahmed WW, Bussonnier M, Mailly P, Betz T, Voituriez R, Gov NS, Verlhac MH (2015 Apr 1)

Active diffusion positions the nucleus in mouse oocytes

Nature Cell Biology : 17 : 470-9 : DOI : 10.1038/ncb3131 En savoir plus
Résumé

In somatic cells, the position of the cell centroid is dictated by the centrosome. The centrosome is instrumental in nucleus positioning, the two structures being physically connected. Mouse oocytes have no centrosomes, yet harbour centrally located nuclei. We demonstrate how oocytes define their geometric centre in the absence of centrosomes. Using live imaging of oocytes, knockout for the formin 2 actin nucleator, with off-centred nuclei, together with optical trapping and modelling, we discover an unprecedented mode of nucleus positioning. We document how active diffusion of actin-coated vesicles, driven by myosin Vb, generates a pressure gradient and a propulsion force sufficient to move the oocyte nucleus. It promotes fluidization of the cytoplasm, contributing to nucleus directional movement towards the centre. Our results highlight the potential of active diffusion, a prominent source of intracellular transport, able to move large organelles such as nuclei, providing in vivo evidence of its biological function.

Replier