Biology subjects

THERY, M.

Publications and source records attributed to THERY, M..

6 recordsLinked to original sources

bioRxiv2026

Uncoupling microtubule lifetime, stability and post-translational modifications.

Microtubules (MTs) undergo continuous cycles of growth and disassembly. Because the transitions between these states are stochastic, MT age varies widely within a population. As MTs age, they are thought to accumulate post-translational modifications (PTMs) that, directly or indirectly, enhance their stability and thereby extend their lifetime. The rare MTs that withstand prolonged exposure to destabilizing drugs such as nocodazole (NZ) are indeed enriched in PTMs; yet the relationships between MT age, PTMs and stability remain unclear. Using microinjection of labelled tubulin, we measured microtubule network turnover in immortalized mouse embryonic fibroblasts. Half of the network was renewed within 3 minutes and 80% within 10 minutes, while approximately 5% of microtubules persisted for more than 20 minutes. These dynamics were comparable in quiescent and senescent cells, although the fraction of slowly renewing or non-renewing microtubules rose to 20% in senescent cells. Unexpectedly, neither the amount of PTMs (acetylation and detyrosination) nor resistance to NZ increased with MT age, and resistance to NZ was independent of these PTMs. Degrees of acetylation and detyrosination should therefore not be taken as readouts of MT age or stability. Because these PTMs do not accumulate on MTs over time, the chemical modification of polymerized tubulin is likely more reversible and dynamic than previously assumed.

cell biology↗

bioRxiv2024

Disentangling the contributions of stress fibres and the unbundled actin meshwork to the anisotropy of cortical tension in response to cell shape

Many fundamental biological processes, in particular development and morphogenetic movements, involve tissue and cell deformation, as well as the generation of anisotropic mechanical stresses. They are often accompanied by the appearance of oriented contractile actomyosin structures resembling the stress fibres (SF) observed in vitro. Here, we investigate, at the single cell level, how cell shape -- by itself -- could control the structure and tension of the actomyosin cortex. Using a unique combination of 3D micropatterning, single peripheral SF (PSF) tension measurement, laser ablation and image analysis, we show that cell shape anisotropy, e.g. its 2D aspect ratio, is indeed sufficient to induce anisotropy of the cortical structure and tension. In particular, taking into account the experimentally measured anisotropy of the cortical meshwork, we could quantify cortical tension and decouple the contribution originating from bundled actin (oriented cortical stress fibres, CSF) and the contribution of the unbundled actin meshwork (UAM). We show that the increase of cortical tension anisotropy with the cells aspect ratio depends on the CSF alignment and orientation, the contribution of the isotropic mesh being independent of cell shape. Remarkably, while experimental data from single stress fibre measurements and laser ablation were analysed through different theoretical frameworks, namely that of negative pressure in nematics and hole drilling in prestressed materials, we found quantitatively the same composite material behaviour. In sum, we decipher here the very material properties of the actomyosin cortex, and its sensitivity to cell shape which is at the root of many mechanobiological processes, in particular morphogenesis.

biophysics↗

bioRxiv2024

Contractile forces direct the chiral swirling of minimal cell collectives

Chirality is a conserved biological feature with critical implications in tissue morphogenesis and embryonic development. In culture, large multicellular groups exhibit spontaneous chiral symmetry break when moving collectively on micropatterned surfaces. Although several studies have shown that actin network integrity and acto-myosin network contractility participate to the establishment of the chirality of the movement, the exact contribution of contractile forces to the directionality of the chiral bias in collectives remains to be elucidated. Here we studied the contractile forces produced by a minimal collective constituted of a pair of endothelial cells. We first show that cell doublets confined on disk-shaped micropatterns undergo spontaneous and persistent chiral swirling, displaying a mild but robust clockwise (CW) bias, as the one observed in bigger collectives. This bias could be amplified or reversed by modulating contractile forces. Traction force measurements revealed that large forces tend to drive counter-clockwise (CCW) rotation whereas low forces rather favor a CW rotation. Furthermore, the study of heterotypic doublets indicates that the speed and direction of the rotation is determined by the more contractile cells within the doublets. These results thus revealed that contractile leader cells could drive the chiral motion of minimal collectives. Significance StatementChirality, which represents a fundamental property of living systems, manifests in cell collectives by their persistent biased directional swirling. Despite the clear identification of the implication of actomyosin cytoskeleton in driving the internal chiral symmetry break occurring in cells, little is known about the actual role of cellular forces produced by this network in the development of handedness in collectives. Our findings establish that the level of mechanical energy developed by pairs of confined endothelial cells regulates the strength and direction of their rotation. Our results also identify the more contractile cell of the doublet as the cell driving the direction and speed of rotation of the pair. This study thus sheds new light on the importance of the generation and integration of mechanical forces within a small collective in the determination of its chiral rotation.

cell biology↗

bioRxiv2024

Centrosome positioning independently of microtubule-based forces

The regulation of centrosome position is central to the establishment of polarized cell functions. This process is thought to rely on the generation of mechanical forces along microtubules, the balance of which determines centrosome position. By studying these forces in adherent cells in culture, we found that neither pushing nor pulling forces propagate along microtubules to the centrosome. Inhibiting dyneins or disassembling microtubules did not disrupt the maintenance of the centrosome at the center of the cell. In contrast, the actomyosin contractile network appears to be responsible for the generation of a centripetal flow that drives the centrosome towards the center of the cell independently of the microtubules. Furthermore, we found that centering of the centrosome depends more on the reorganization of cell shape around the centrosome than on an effective centrosome displacement throughout the cytoplasm. Interestingly, despite their lack of mechanical role, microtubules appear to direct this remodeling of cell shape. This revised view of centrosome positioning offers a new perspective for understanding the establishment of cell polarity.

cell biology↗

bioRxiv2023

Microtubules under mechanical pressure can breach dense actin networks

The crosstalk between actin network and microtubules is key to the establishment of cell polarity. It ensures that the asymmetry of actin architec ture along cell periphery directs the organization of microtubules in cell interior. In particular, the way the two networks are physically inter-twined regulates the spatial organization and the distribution of forces in the microtubule network. While their biochemical crosstalk is getting uncovered, their mechanical crosstalk is still poorly understood. Here we designed an in vitro reconstitution assay to study the physical interaction between dynamic microtubules with various structures made of actin fil aments. We found that microtubules can align and move by their polymerization force along linear bundles of actin filaments. But they cannot enter dense and branched actin meshworks, such as those found in the lamellipodium along cell periphery. However, when microtubules are immobilized, by their crosslinking with actin structures or others means, the force of polymerization builds up pressure in the microtubules that is sufficient to allow them to breach and penetrate these dense actin meshworks. This mechanism may explain the final progression of microtubules up to cell periphery through the denser parts of the actin network.

biophysics↗

bioRxiv2020

Stress fibers are embedded in a contractile cortical network.

Contractile actomyosin networks generate intracellular forces essential for the regulation of cell shape, migration, and cell-fate decisions, ultimately leading to the remodeling and patterning of tissues. Although actin filaments aligned in bundles represent the main source of traction-force production in adherent cells, there is increasing evidence that these bundles form interconnected and interconvertible structures with the rest of the intracellular actin network. In this study, we explored how these bundles are connected to the surrounding cortical network and the mechanical impact of these interconnected structures on the production and distribution of traction forces on the extracellular matrix and throughout the cell. By using a combination of hydrogel micropatterning, traction-force microscopy and laser photoablation, we measured the relaxation of the cellular traction field in response to local photoablations at various positions within the cell. Our experimental results and modeling of the mechanical response of the network revealed that bundles were fully embedded along their entire length in a continuous and contractile network of cortical filaments. Moreover, the propagation of the contraction of these bundles throughout the entire cell was dependent on this embedding. In addition, these bundles appeared to originate from the alignment and coalescence of thin and unattached cortical actin filaments from the surrounding mesh.

cell biology↗