Biology subjects

Ladoux, B.

Publications and source records attributed to Ladoux, B..

At least 19 recordsLinked to original sources

bioRxiv2026

Local mechanical heterogeneity drives epidermal cell delamination

Delamination within stratified epithelia like the skin epidermis describes the detachment and upward motion of cells originating from the basal layer. Despite its fundamental importance for tissue development, homeostatic regeneration and repair, the mechanisms that drive delamination remain a longstanding open question. Upward motion follows cell shape changes, which are inherently driven by physical forces, but their role is elusive. Here, we investigate delamination in stratifying keratinocytes by combining imaging, force measurements and theoretical modeling. We identify a local change in force balance between differentiating cells and their environment as the key step initiating delamination. Within a homogeneous cell layer with apically polarized contractility, differentiation leads to actomyosin remodeling, redistributing cellular force exertion to the basal side. Such mechanical heterogeneity then results in differentiating cells experiencing and inward basal and outward apical forces that manifest in the formation of a +1 force defect and promote shape changes culminating in upward motion. Simultaneously, delaminating cells actively pull on their underlying neighbors, generating convergent tissue flows which close the basal layer below. Together, we propose a general physical description of delamination initiation, which may act across various multilayered epithelia.

biophysics↗

bioRxiv2026

Curvature-guided chiral collective organization of myoblast tissues

Surface curvature is a fundamental geometric cue in tissue morphogenesis, yet its role in guiding collective cell organization has remained elusive. Here, we show that curvature acts as a geometric control parameter that shapes supracellular alignment and chirality while modulating myogenic differentiation in myoblast tissues. Cells cultured on curved substrates self-organize into robust helical assemblies whose handedness is set, and can be reversed, by the sign of curvature: convex fibers produce right-handed helices, whereas concave channels invert the chirality. We identify a previously hidden clockwise bias in single-cell motion associated with the helical actin cytoskeleton. A minimal continuum theory coupling an effective chiral drive to curvature quantitatively captures the emergence and reversal of tissue-scale chiral alignment. On substrates with spatially varying curvature, local curvature gradients organize patterned multicellular architectures while preserving a global handedness. Curvature is also associated with myogenic state, with higher curvature linked to reduced or delayed differentiation. Together, these findings reveal how complex geometries shape the alignment, symmetry, and cellular state of living tissues.

biophysics↗

bioRxiv2026

A principal-stress rule for cell division in epithelia

Dense active materials, from cellular tissues to jammed and glassy systems, must continuously relieve internal mechanical stress to remain structurally stable as they are driven far from equilibrium. In epithelial tissues, this relief occurs through cell division, yet what sets the geometry of this structural remodeling event has, for over a century, been attributed to a purely geometric principle: Hertwigs rule, whereby cells divide along their long axis. We show that as epithelial tissues densify and cell shape anisotropy collapses, this geometric rule is superseded by a mechanical one in which dense epithelia relieve anisotropic stress by cells dividing along their principal axis, independent of the tissues isotropic stress state. Using direct force measurement and stress inference, we show that stress orientation, rather than cell shape, governs the axis of cell division across mechanically distinct systems, from fluid-like to jammed monolayers and structurally heterogeneous organoids, remaining predictive precisely where the classical geometric rule fails. This stress-oriented remodeling is reciprocally coupled to the materials mechanical state: anisotropic stress accelerates the underlying remodeling rate, while each remodeling event locally dissipates the stress that triggered it, closing a negative feedback loop. This "principal-stress rule" recasts epithelial cell division as a stress-relief mechanism intrinsic to dense active matter, providing a general mechanical framework linking internal stress, structural remodeling, and homeostasis in living materials.

biophysics↗

bioRxiv2026

Mechanical Tension Actively Triggers RhoA-Mediated Cell Extrusion

Cell extrusion is a fundamental process in tissue homeostasis, morphogenesis, and cancer progression, facilitating the removal of cells either alive or through apoptosis. While biochemical signaling pathways are known to regulate extrusion, recent advances have underscored the importance of mechanical forces in this process. Here, using optogenetic control of RhoA activation in epithelial monolayers combined with Bayesian Inversion Stress Microscopy (BISM) and three-dimensional cell-based modeling, we uncover a counterintuitive mechanism whereby elevated tension, instead of stabilizing the monolayer, actively drives extrusion in highly contractile cells. We show that local RhoA activation enhances myosin II-dependent contractility and F-actin reorganization, which promotes cell stiffening, resulting in localized tension buildup. The ensuing tensile stress amplifies vertical mechanical fluctuations, which in turn trigger cell extrusion. Remarkably, these tension-induced extrusions occur both apically and basally. Furthermore, our findings show that RhoA-mediated contractility is not merely an effector of extrusion but also an active promoter of basal extrusion, independently of caspase activation. Our study demonstrates that tensile stress can directly initiate extrusion events and bias their outcome toward apical or basal fates. By identifying tension as a driver rather than a suppressor of extrusion, this work revises current models of epithelial homeostasis and highlights mechanical control as a targetable axis in disease and regeneration.

cell biology↗

bioRxiv2026

Vimentin bridges scales to convert polarized cell locomotion into coordinated collective migration

Collective cell migration is central in development and disease. Vimentin is an intermediate filament protein expressed by epithelial cells at the edge of wounds where collective cell migration is most efficient. Yet, its functional role in this context remains underexplored. Here, we show that vimentin, over-expressed in cells undergoing partial epithelial to mesenchymal transition at the edge of epithelial monolayers, has a multiscale impact on the whole monolayer mechano-dynamics. Vimentin knock-down delays wound closure, reduces cell coordination, while increasing traction forces exerted by cells on the substratum. It also disrupts the directionality of leader cells migration, as well as the cohesion and coordinated motion of cells deep in the monolayer. We further show that vimentin promotes the conversion of polarized cell locomotion into coordinate collective migration by polarizing actin, focal adhesions and traction forces, sustaining leader cells lamellipodium protrusive activity and directionality, while allowing mechanical coupling of leader with follower cells. Altogether, we show that vimentin is essential for bridging polarized single cell locomotion and coordinated collective migration to allow efficient collective migration. Significant statementEpithelial cells migrate coordinately to repair tissue. Vimentin, transiently enriched at the wound edge plays a key role in guiding this process by converting polarized cell locomotion into coordinate collective migration, enabling leader cells to polarize, form stable protrusions, and maintain directed migration, while allowing mechanical coupling of front cells with followers, necessary for efficient coordinated collective migration. These findings reveal vimentin, a known EMT marker, as a novel positive regulator of efficient wound healing.

cell biology↗

bioRxiv2025

Regulation of epithelial tissue homeostasis by active trans-epithelial transport

Epithelia are intricate tissues whose function is intimately linked to mechanics. While mechanobiology has primarily focused on factors such as cell-generated contractility and mechanical properties of extracellular matrix (ECM), a novel mechanobiological paradigm highlights the role of osmotic and mechanical pressures in shaping epithelial tissues. In our study, we developed an in vitro model of cell coated micro-sized hydrogel spheres (MHSs) which allows to decipher the interplay between cellular activities and tissue mechanics. Drastic, isotropic MHS compressions were observed once the epithelia reached confluence. Further studies revealed that the compression was a process independent of cell contractility but rather regulated by active transepithelial fluid flow. Compressive stresses of about 7 kPa are generated by such an active hydraulic mechanism. Tissue homeostasis is then maintained by a fine balance between cell proliferation and extrusion. Our findings demonstrate the critical role of fluid transport in generating mechanical forces within epithelial tissues. Supported by a theoretical mechano-hydraulic model, a mechanistic framework for understanding the intricate interplay between cellular processes and tissue mechanics was established. These results challenge traditional views of epithelial tissue mechanics, emphasizing the pivotal influence of osmotic and mechanical pressures in shaping tissues. We anticipate that this study will advance the understanding of epithelial tissue development, the maintenance of homeostasis, and the mechanisms underlying pathological conditions. Significance StatementEpithelial tissues are vital for many bodily functions, but their mechanics remain poorly understood. Our study uncovers a novel mechanism by which epithelial cells generate mechanical stress, not through traditional cell contractility, but by actively pumping ions and water across their membranes. Using a model of micro-sized hydrogel spheres (MHSs) coated with epithelial cells, we demonstrate that epithelial cells actively transport fluid across the tissue to compress the MHSs. This facilitates the establishment of tissue homeostasis, which is further maintained by a balanced cell proliferation and extrusion rate. Supported by a theoretical model, our findings highlight the overlooked role of fluid transport in tissue mechanics, offering new insights into how epithelial tissues develop, maintain stability, and respond to disease.

cell biology↗

bioRxiv2025

The complex microscopic dynamics of cells in high-density epithelial tissues

Epithelial tissues line the surfaces of vital organs and are often densely packed in a disordered, mechanically arrested state, referred to as jammed or glassy state. While collective migration at low-density regimes has been extensively studied, the microscopic dynamics within such jammed epithelia remains poorly understood. Here, we reveal that contrary to expectations from thermal systems with glassy dynamics, jammed epithelial monolayers do not exhibit cage effects that reflect the temporary spatial trapping of the particles. Instead, cells display sub-diffusive creep and Fickian yet non-Gaussian dynamics, accompanied by compressed exponential relaxation, features that reveal stress-driven fluidity. We show that cell divisions and extrusions transiently do enhance local motion, they are insufficient to fluidize the tissue globally. Fast-moving cells form collective, anisotropic clusters, and these dynamic heterogeneities correlate with local structural entropy and low-frequency vibrational modes. These findings challenge the conventional view that jammed tissues are static and inert structures, uncovering a hidden fluidity that can be expected to play a critical role in morphogenesis, wound healing, and early tumor progression.

biophysics↗

bioRxiv2025

Cytoplasmic crowding acts as a porous medium reducing macromolecule diffusion

Intracellular transport of macromolecules is crucial for the proper functioning of most cellular processes. Although intracellular crowding is known to strongly alter macromolecule mobility, how cytoplasmic structures physically modulate diffusion remains largely unexplored. Here we investigated the mechanisms by which cytoplasmic crowding controls diffusivity using live-cell experiments and porous media modeling approaches. Confocal microscopy combined with fluorescence recovery after photobleaching (FRAP) and fluorescence correlation spectroscopy (FCS) measurements revealed an anti-correlation between free-GFP diffusivity and the heterogeneous cytoplasmic structure abundance in live mammalian cells. This motivated the development of a multiscale model, where the cytoplasm is treated as a hierarchical porous medium with nanometric and micrometric obstacles. Numerically solving the model allowed us to predict the effective cytoplasmic diffusion coefficient for various obstacle volume fractions, and to identify tortuous and porous hydrodynamic hindrances as key diffusion reduction mechanisms. Comparison with our experimental results highlighted the importance of hydrodynamic interactions between diffusing molecules and nanometric obstacles. Importantly, we found that the effective cytoplasmic diffusivity was not dependent on specific intracellular regions but rather on the local intracellular obstacle volume fraction. Finally, the model was extended to predict the diffusivity of larger macromolecules, showing excellent agreement with literature data for several macromolecules and cell lines. This study provides new insights into the physical mechanisms impeding intracellular diffusion, demonstrating the potential of porous media modeling approaches to predict transport mechanisms in dynamic or heterogeneous intracellular structures, as in cell motility, blebbing, and apoptosis.

biophysics↗

bioRxiv2024

Force transmission is a master regulator of mechanical cell competition

Cell competition is a tissue surveillance mechanism for eliminating unwanted cells and as such is indispensable in development, infection and tumorigenesis. Although different biochemical mechanisms are proposed, due to the dearth of direct force measurements, how mechanical forces determine the competition outcome remains unclear. Here, using ex vivo tissues and different cell lines, we have discovered an unknown form of cell competition that is regulated by differences in force transmission capabilities, favoring cell types with stronger intercellular adhesion. Direct force measurements reveal increased mechanical activity at the interface of the two competing cell types in the form of large stress fluctuations which can lead to upward forces and cell elimination. We show how a winning cell type endowed with a stronger intercellular adhesion exhibits a higher resistance to elimination while benefiting from efficient force transmission to neighboring cells. This cell elimination mechanism could have broad implications of keeping strong force transmission ability for maintaining tissue boundaries and cell invasion pathology.

biophysics↗

bioRxiv2024

Mechanical stresses govern myoblast fusion and myotube growth

Myoblast fusion into multinucleated myotubes is essential for skeletal muscle development and repair, yet how tissue-scale mechanics contributes to this process remains poorly understood. Here, we show that primary myoblasts behave as an evolving active nematic system in which actomyosin-dependent stresses, extracellular-matrix (ECM) remodeling and fusion-driven myotube growth are dynamically coupled. As myoblasts fuse into elongated myotubes, orientational order increases and the nematic field is progressively reshaped. We identify a strong coupling between cellular and ECM nematic organization, whereby cytoskeleton-dependent ECM remodeling stabilizes topological defects and reinforces their associated stress patterns. Fusion events preferentially accumulate near comet-shaped +1/2 defects, which correspond to regions of high compressive stress predicted by our theoretical model. Our findings support a model in which the intrinsic fusion machinery provides fusion competence, while ECM-stabilized nematic stress patterns spatially bias the localization of fusion events. Fusion-driven myotube growth then feeds back on the mechanical landscape, increasing nematogen length and stress magnitude. Together, these results reveal a self-reinforcing biomechanical mechanism that contributes to the organization of myoblast fusion and myotube growth, with potential relevance for developmental and regenerative morphogenesis.

biophysics↗

bioRxiv2024

Scale-free flocking and giant fluctuations in epithelial active solids

The collective motion of epithelial cells is a fundamental biological process which plays a significant role in embryogenesis, wound healing and tumor metastasis. While it has been broadly investigated for over a decade both in vivo and in vitro, large scale coherent flocking phases remain underexplored and have so far been mostly described as fluid. In this work, we report a mode of large-scale collective motion for different epithelial cell types in vitro with distinctive new features. By tracking individual cells, we show that cells move over long time scales coherently not as a fluid, but as a polar elastic solid with negligible cell rearrangements. Our analysis reveals that this solid flocking phase exhibits signatures of long-range polar order, unprecedented in cellular systems, with scale-free correlations, anomalously large density fluctuations, and shear waves. Based on a general theory of active polar solids, we argue that these features result from massless Goldstone modes, which, in contrast to polar fluids where they are generic, require the decoupling of global rotations of the polarity and in-plane elastic deformations in polar solids. We theoretically show and consistently observe in experiments that the fluctuations of elastic deformations diverge for large system size in such polar active solid phases, leading eventually to rupture and thus potentially loss of tissue integrity at large scales. Significance statementDuring embryonic development and wound healing, epithelial cells usually display in-plane polarity over large spatial scales and move coherently. However, over years, most in vitro studies have examined the fluid-like chaotic dynamics of epithelial cells, in which collective cellular flows self-organize into recurring transient vortices and jets similar to those observed in classical fluid turbulence. Little is known about the large-scale coherent dynamics of epithelial cells. We demonstrate that such coherent motions are not simply turbulent-like flows with larger correlation lengths, but a new mode of collective motion with a solid-like behavior, accompanied by an emergent global order, scale-free correlations, anomalous density fluctuations and propagating Goldstone modes. Our work suggests that such a collective motion of epithelial cells falls outside the scope of traditional active fluids, which may shed new light on the current studies of collective cell migration as well as active matter physics.

biophysics↗

bioRxiv2023

Aging and freezing of active nematic dynamics of cancer-associated fibroblasts by fibronectin matrix remodeling

Cancer-associated fibroblasts (CAFs) are one of the most abundant cell types in tumor stroma. Exhibiting an elongated morphology, CAFs align with each other, closely resembling nematic ordering in liquid crystal physics. CAFs play a pivotal role in the genesis and remodeling of the extracellular matrix (ECM), with ECM proteins, especially fibronectin, reciprocally modulating CAF alignment and coherence. Yet, the intricate feedback loops between fibronectin deposition and CAF structuring remain largely unexplored. Here, we combined CAF live imaging, traction force microscopy, ECM microfabrication, and theoretical modeling to assess how the ECM influences the dynamics of nematically ordered CAFs. We found that CAFs dynamically orchestrate a fibronectin network that mirrors their nematic ordering. Over time, this passive nematic ordering of fibronectin, in turn, steers CAF rearrangement. Contrary to most cellular systems, where defects remain dynamic at a steady state, the ECM/CAF interplay profoundly alters the behavior of both CAF and ECM nematics, leading to aging-massive slowdown, and even freezing of defect dynamics. This results in a CAFs capsule where aligned areas and defects are spatially and temporally fixed, yet active, exerting forces at the substate and transmitting forces between cells. Functionally, while defects may be permissive, it is the fibronectin loss-induced fluidization of the CAF capsule that critically undermines its barrier function.

cell biology↗

bioRxiv2023

Secreted footprints let cells switch between confined, oscillatory, and exploratory migration

For eukaryotic cells to heal wounds, respond to immune signals, or metastasize, they must migrate, often by adhering to extracellular matrix. Cells may also deposit extracellular matrix components, leaving behind a footprint that influences their crawling. Recent experiments showed that some epithelial cells on micropatterned adhesive stripes move persistently in regions they have previously crawled over, where footprints have been formed, but barely advance into unexplored regions, creating an oscillatory migration of increasing amplitude. Here, we explore through mathematical modeling how footprint deposition and cell responses to footprint combine to allow cells to develop oscillation and other complex migratory motions. We simulate cell crawling with a phase field model coupled to a biochemical model of cell polarity, assuming local contact with the deposited footprint activates Rac1, a protein that establishes the cells front. Depending on footprint deposition rate and response to the footprint, cells on micropatterned lines can display many types of motility, including confined, oscillatory, and persistent motion. On two-dimensional substrates, we predict a transition between cells undergoing circular motion and cells developing an exploratory phenotype. Small quantitative changes in a cells interaction with its footprint can completely alter exploration, allowing cells to tightly regulate their motion, leading to different motility phenotypes (confined vs exploratory) in different cells when deposition or sensing is variable from cell to cell. Consistent with our computational predictions, we find in earlier experimental data evidence of cells undergoing both circular and exploratory motion. Significance StatementRecent experiments showed that epithelial cells modify and sense their local environment, creating a footprint that guides their own motion. Here, we explore how these deposited footprints regulate cell motility. We can recapitulate earlier experimental results with a model that assumes the footprint activates proteins that establish the cell front. We find that cells can use their footprints to change how they explore their surroundings, and that small changes in sensing or depositing footprint can switch the cell from being trapped to being able to explore new environments easily. We find both behaviors in experimental data, suggesting that cells can exhibit multiple crawling behaviors depending on how they deposit and respond to their foot-print.

biophysics↗

bioRxiv2023

Polarization and motility of one-dimensional multi-cellular trains

Collective cell migration, whereby cells adhere to form multi-cellular clusters that move as a single entity, play an important role in numerous biological processes, such as during development and cancer progression. Recent experimental work focused on migration of one-dimensional cellular clusters, confined to move along adhesive lanes, as a simple geometry in which to systematically study this complex system. One-dimensional migration also arises in the body when cells migrate along blood vessels, axonal projections and narrow cavities between tissues. We explore here the modes of one-dimensional migration of cellular clusters ("trains"), by implementing cell-cell interactions in a model of cell migration that contains a mechanism for spontaneous cell polarization. We go beyond simple phenomenological models of the cells as self-propelled particles, by having the internal polarization of each cell depend on its interactions with the neighboring cells, that directly affect the actin polymerization activity at the cells leading edges. Both Contact Inhibition of Locomotion (CIL) and Cryptic Lamellipodia (CL) interactions between neighboring cells are introduced. We find that this model predicts multiple motility modes of the cell trains, that can have several different speeds for the same polarization pattern. Comparing to experimental data we find that MDCK cells are poised along the transition region where CIL and CL roughly balance each other, where collective migration speed is most sensitive to the values of the cell-cell interaction strength.

biophysics↗

bioRxiv2023

A minimal physical model for curvotaxis driven by curved protein complexes at the cell's leading edge

Cells often migrate on curved surfaces inside the body, such as curved tissues, blood vessels or highly curved protrusions of other cells. Recent in-vitro experiments provide clear evidence that motile cells are affected by the curvature of the substrate on which they migrate, preferring certain curvatures to others, termed "curvotaxis". The origin and underlying mechanism that gives rise to this curvature sensitivity are not well understood. Here, we employ a "minimal cell" model which is composed of a vesicle that contains curved membrane protein complexes, that exert protrusive forces on the membrane (representing the pressure due to actin polymerization). This minimal-cell model gives rise to spontaneous emergence of a motile phenotype, driven by a lamellipodia-like leading edge. By systematically screening the behaviour of this model on different types of curved substrates (sinusoidal, cylinder and tube), we show that minimal ingredients and energy terms capture the experimental data. The model recovers the observed migration on the sinusoidal substrate, where cells move along the grooves (minima), while avoiding motion along the ridges. In addition, the model predicts the tendency of cells to migrate circumferentially on convex substrates and axially on concave ones. Both of these predictions are verified experimentally, on several cell types. Altogether, our results identify the minimization of membrane-substrate adhesion energy and binding energy between the membrane protein complexes as key players of curvotaxis in cell migration.

biophysics↗

bioRxiv2022

Hexanematic crossover in epithelial monolayers depends on cell adhesion and cell density

Changes in tissue geometry during developmental processes are associated with collective migration of cells. Recent experimental and numerical results suggest that these changes could leverage on the coexistence of nematic and hexatic orientational order at different length scales. How this multiscale organization is affected by the material properties of the cells and their substrate is presently unknown. In this study, we address these questions in monolayers of Madin-Darby canine kidney cells having various cell densities and molecular repertoires. At small length scales, confluent monolayers are characterized by a prominent hexatic order, independent of the presence of E-cadherin, monolayer density, and underlying substrate stiffness. However, all three properties affect the meso-scale tissue organization. The length scale at which hexatic order transits to nematic order, the "hexanematic" crossover scale, strongly depends on cell-cell adhesions and correlates with monolayer density. Our study demonstrates how epithelial organization is affected by mechanical properties, and provides a robust description of tissue organization during developmental processes.

biophysics↗

bioRxiv2022

Mechanical stress driven by rigidity sensing governs epithelial stability

Epithelia act as a barrier against environmental stress and abrasion and in vivo they are continuously exposed to environments of various mechanical properties. The impact of this environment on epithelial integrity remains elusive. By culturing epithelial cells on 2D hydrogels, we observe a loss of epithelial monolayer integrity through spontaneous hole formation when grown on soft substrates. Substrate stiffness triggers an unanticipated mechanical switch of epithelial monolayers from tensile on soft to compressive on stiff substrates. Through active nematic modelling, we find unique patterns of cell shape texture called nematic topological defects that underpin large isotropic stress fluctuations at certain locations thereby triggering mechanical failure of the monolayer and hole opening. Our results show that substrate stiffness provides feedback on monolayer mechanical state and that topological defects can trigger stochastic mechanical failure, with potential application towards a mechanistic understanding of compromised epithelial integrity in bacterial infection, tumor progression and morphogenesis.

biophysics↗

bioRxiv2021

Optineurin links Hace1-dependent Rac ubiquitylation to integrin-mediated mechanotransduction to control bacterial invasion and cell division

Extracellular matrix (ECM) elasticity is perceived by cells via focal adhesion structures, which transduce mechanical cues into chemical signalling to conform cell behaviour. Although the contribution of ECM compliance to the control of cell migration or division has been extensively studied, little has been reported regarding infectious processes. We have studied how mechanical properties of the ECM impact invasion of cells by the extraintestinal Escherichia coli pathogen UTI89. We show that UTI89 takes advantage, via its CNF1 toxin, of integrin mechanoactivation to trigger its invasion into cells. We identified OPTN as a protein regulated by ECM stiffness whose function is required for bacterial invasion and integrin mechanical coupling and for stimulation of HACE1 E3 ligase activity towards the Rac1 GTPase. We showed that OPTN knockdown cells display enhanced Rac1 activation, strong mechanochemical adhesion signalling and increased cyclin D1 translation, together with enhanced cell proliferation independent of ECM stiffness. Despite such features, OPTN knockdown cells displayed defective traction force buildup associated with limited cellular invasion by UTI89. Together, our data indicate that OPTN, through a new role in mechanobiology, supports CNF1-producing uropathogenic E. coli invasion and links HACE1-mediated ubiquitylation of Rac1 to ECM mechanical properties and integrin mechanotransduction.

cell biology↗