Proteolysis-free amoeboid migration of melanoma cells through crowded environments via bleb-driven worrying.

In crowded microenvironments, migrating cells must find or make a path. Amoeboid cells are thought to find a path by deforming their bodies to squeeze through tight spaces. Yet, some amoeboid cells seem to maintain a near-spherical morphology as they move. To examine how they do so, we visualized amoeboid human melanoma cells in dense environments and found that they carve tunnels via bleb-driven degradation of extracellular matrix components without the need for proteolytic degradation. Interactions between adhesions and collagen at the cell front induce a signaling cascade that promotes bleb enlargement via branched actin polymerization. Large blebs abrade collagen, creating feedback between extracellular matrix structure, cell morphology, and polarization that enables both path generation and persistent movement.

Blebology: principles of bleb-based migration.

Bleb-based migration, a conserved cell motility mode, has a crucial role in both physiological and pathological processes. Unlike the well-elucidated mechanisms of lamellipodium-based mesenchymal migration, the dynamics of bleb-based migration remain less understood. In this review, we highlight in a systematic way the establishment of front-rear polarity, bleb formation and extension, and the distinct regimes of bleb dynamics. We emphasize new evidence proposing a regulatory role of plasma membrane-cortex interactions in blebbing behavior and discuss the generation of force and its transmission during migration. Our analysis aims to deepen the understanding of the physical and molecular mechanisms of bleb-based migration, shedding light on its implications and significance for health and disease.

Cell migration in dense microenvironments.

The nucleus has been viewed as a passenger during cell migration that functions merely to protect the genome. However, increasing evidence shows that the nucleus is an active organelle, constantly sensing the surrounding environment and translating extracellular mechanical inputs into intracellular signaling. The nuclear envelope has a large membrane reservoir which serves as a buffer for mechanical inputs as it unfolds without increasing its tension. In contrast, when cells cope with mechanical strain, such as migration through solid tumors or dense interstitial spaces, the nuclear envelope folds stretch, increasing nuclear envelope tension and sometimes causing rupture. Different degrees of nuclear envelope tension regulate cellular behaviors and functions, especially in cells that move and grow within dense matrices. The crosstalk between extracellular mechanical inputs and the cell nucleus is a critical component in the modulation of cell function of cells that navigate within packed microenvironments. Moreover, there is a link between regimes of nuclear envelope unfolding and different cellular behaviors, from orchestrated signaling cascades to cellular perturbations and damage.

Le noyau a longtemps été considéré comme un passager lors de la migration cellulaire, servant simplement à protéger le génome. Cependant, de plus en plus de preuves montrent que le noyau est un organite actif, qui sonde le milieu environnant et traduit les entrées mécaniques extracellulaires en signalisation intracellulaire. L'enveloppe nucléaire possède un grand réservoir membranaire qui sert de tampon face aux entrées mécaniques en se dépliant sans augmenter sa tension. En revanche, lorsque les cellules font face à des contraintes mécaniques, telles que la migration au travers de tumeurs solides ou despaces interstitiels denses, les plis de l'enveloppe nucléaire s'étirent, augmentant sa tension et provoquant parfois sa rupture. Différents degrés de tension de l'enveloppe nucléaire régulent les comportements et les fonctions cellulaires, en particulier des cellules qui se déplacent et se développent dans des matrices denses. La signalisation croisée entre les entrées mécaniques extracellulaires et le noyau cellulaire sont des composants essentiels dans la modulation de la fonction des cellules qui naviguent dans des microenvironnements encombrés. De plus, il existe un lien entre les régimes de déploiement de l'enveloppe nucléaire et les différents comportements cellulaires, allant des cascades de signalisation jusquaux perturbations et dommages cellulaires.

Fluorogenic In Situ Thioacetalization: Expanding the Chemical Space of Fluorescent Probes, Including Unorthodox, Bifurcated, and Mechanosensitive Chalcogen Bonds.

Progress with fluorescent flippers, small-molecule probes to image membrane tension in living systems, has been limited by the effort needed to synthesize the twisted push-pull mechanophore. Here, we move to a higher oxidation level to introduce a new design paradigm that allows the screening of flipper probes rapidly, at best in situ. Late-stage clicking of thioacetals and acetals allows simultaneous attachment of targeting units and interfacers and exploration of the critical chalcogen-bonding donor at the same time. Initial studies focus on plasma membrane targeting and develop the chemical space of acetals and thioacetals, from acyclic amino acids to cyclic 1,3-heterocycles covering dioxanes as well as dithiolanes, dithianes, and dithiepanes, derived also from classics in biology like cysteine, lipoic acid, asparagusic acid, DTT, and epidithiodiketopiperazines. From the functional point of view, the sensitivity of membrane tension imaging in living cells could be doubled, with lifetime differences in FLIM images increasing from 0.55 to 1.11 ns. From a theoretical point of view, the complexity of mechanically coupled chalcogen bonding is explored, revealing, among others, intriguing bifurcated chalcogen bonds.

A mechano-osmotic feedback couples cell volume to the rate of cell deformation.

Mechanics has been a central focus of physical biology in the past decade. In comparison, how cells manage their size is less understood. Here, we show that a parameter central to both the physics and the physiology of the cell, its volume, depends on a mechano-osmotic coupling. We found that cells change their volume depending on the rate at which they change shape, when they spontaneously spread or when they are externally deformed. Cells undergo slow deformation at constant volume, while fast deformation leads to volume loss. We propose a mechanosensitive pump and leak model to explain this phenomenon. Our model and experiments suggest that volume modulation depends on the state of the actin cortex and the coupling of ion fluxes to membrane tension. This mechano-osmotic coupling defines a membrane tension homeostasis module constantly at work in cells, causing volume fluctuations associated with fast cell shape changes, with potential consequences on cellular physiology.

Heterochromatin-Driven Nuclear Softening Protects the Genome against Mechanical Stress-Induced Damage.

Tissue homeostasis requires maintenance of functional integrity under stress. A central source of stress is mechanical force that acts on cells, their nuclei, and chromatin, but how the genome is protected against mechanical stress is unclear. We show that mechanical stretch deforms the nucleus, which cells initially counteract via a calcium-dependent nuclear softening driven by loss of H3K9me3-marked heterochromatin. The resulting changes in chromatin rheology and architecture are required to insulate genetic material from mechanical force. Failure to mount this nuclear mechanoresponse results in DNA damage. Persistent, high-amplitude stretch induces supracellular alignment of tissue to redistribute mechanical energy before it reaches the nucleus. This tissue-scale mechanoadaptation functions through a separate pathway mediated by cell-cell contacts and allows cells/tissues to switch off nuclear mechanotransduction to restore initial chromatin state. Our work identifies an unconventional role of chromatin in altering its own mechanical state to maintain genome integrity in response to deformation.

Reconstitution of cell migration at a glance.

Single cells migrate in a myriad of physiological contexts, such as tissue patrolling by immune cells, and during neurogenesis and tissue remodeling, as well as in metastasis, the spread of cancer cells. To understand the basic principles of single-cell migration, a reductionist approach can be taken. This aims to control and deconstruct the complexity of different cellular microenvironments into simpler elementary constrains that can be recombined together. This approach is the cell microenvironment equivalent of in vitro reconstituted systems that combine elementary molecular players to understand cellular functions. In this Cell Science at a Glance article and accompanying poster, we present selected experimental setups that mimic different events that cells undergo during migration in vivo These include polydimethylsiloxane (PDMS) devices to deform whole cells or organelles, micro patterning, nano-fabricated structures like grooves, and compartmentalized collagen chambers with chemical gradients. We also outline the main contribution of each technique to the understanding of different aspects of single-cell migration.