Cells and tissues can sense and react to the modifications of the physico-chemical properties of the extracellular environment (ECM) through integrin-based adhesion sites and adapt their physiological response in a process called mechanotransduction. Due to their critical localization at the cell-ECM interface, transmembrane integrins are mediators of bidirectional signaling, playing a key role in “outside-in” and “inside-out” signal transduction. After presenting the basic conceptual fundamentals related to cell mechanobiology, we review the current state-of-the-art technologies that facilitate the understanding of mechanotransduction signaling pathways. Finally, we highlight innovative technological developments that can help to advance our understanding of the mechanisms underlying nuclear mechanotransduction.

Collective cell migration is fundamental throughout development, wound healing and in many diseases. Although much effort has focused on cell-cell junctions, a role for physical confinement in collective cell migration remains unclear. Here we used adhesive microstripes of varying widths to mimic the spatial confinement experienced by follower cells within epithelial tissues. Our results reveal that the substrate area confinement is sufficient to modulate the three-dimensional (3D) cellular morphology without the need for intercellular adhesive cues. Our findings show a direct correlation between the migration velocity of confined cells and their cell-substrate adhesive area. Closer examination revealed that adhesive area confinement reduces lamellipodial protrusive forces, decreases the number of focal complexes at the leading edge and prevents the maturation of focal adhesions at the trailing edge, leading together to less effective

Skeletal muscle fibers are formed by the fusion of mononucleated myoblasts into long linear myotubes, which differentiate and reorganize into multinucleated myofibers that assemble in bundles to form skeletal muscles. This fundamental process requires the elongation of myoblasts into a bipolar shape, although a complete understanding of the mechanisms governing skeletal muscle fusion is lacking. To address this question, we consider cell aspect ratio, actomyosin contractility and the Hippo pathway member YAP as potential regulators of the fusion of myoblasts into myotubes. Using fibronectin micropatterns of different geometries and traction force microscopy, we investigated how myoblast elongation affects actomyosin contractility. Our findings indicate that cell elongation enhances actomyosin contractility in myoblasts, which regulate their actin network to their spreading area. Interestingly, we found that the contractility of cell pairs increased after their fusion and raise on elongated morphologies. Furthermore, our findings indicate that myoblast elongation modulates nuclear orientation and triggers cytoplasmic localization of YAP, increasing evidence that YAP is a key regulator of mechanotransduction in myoblasts. Taken together, our findings support a mechanical model where actomyosin contractility scales with myoblast elongation and enhances the differentiation of myoblasts into myotubes through YAP nuclear export.

The wide range of epithelial cell shapes reveals the complexity and diversity of the intracellular mechanisms that serve to construct their morphology and regulate their functions. Using mechanosensitive steps, epithelial cells can sense a variety of different mechanochemical stimuli and adapt their behavior by reshaping their morphology. These changes of cell shape rely on a structural reorganization in space and time that generates modifications of the tensional state and activates biochemical cascades. Recent studies have started to unveil how the cell shape maintenance is involved in mechanical homeostatic tasks to sustain epithelial tissue folding, identity, and self-renewal. Here, we review relevant works that integrated mechanobiology to elucidate some of the core principles of how cell shape may be conveyed into spatial information to guide collective processes such as epithelial morphogenesis. Among many other parameters, we show that the regulation of the cell shape can be understood as the result of the interplay between two counteracting mechanisms: actomyosin contractility and intercellular adhesions, and that both do not act independently but are functionally integrated to operate on molecular, cellular, and tissue scales. We highlight the role of cadherin-based adhesions in force-sensing and mechanotransduction, and we report recent developments that exploit physics of liquid crystals to connect cell shape changes to orientational order in cell aggregates. Finally, we emphasize that the further intermingling of different disciplines to develop new mechanobiology assays will lead the way toward a unified picture of the contribution of cell shape to the pathophysiological behavior of epithelial tissues.

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The directed migration of epithelial cell collectives through coordinated movements is key to many physiological and pathological processes and is increasingly well understood at the level of large confluent monolayers. Numerous migration processes rely on the migration of small groups of polarized epithelial clusters and their responses to external geometries. However, the interplay of cell-cell interactions and external boundaries in small cell clusters remain poorly understood. To tackle this, we used micropatterned stripes to investigate the migration of small epithelial clusters with well-defined geometries. Here we show that their migration efficiency is strongly dependent on the contact geometry, and in particular whether cell-cell contacts are parallel or perpendicular to the direction of migration. By systematically screening possible interaction mechanisms in a minimal active matter model, we show that a combination of velocity and polarity alignment with contact inhibition of locomotion captures the experimental data, which we then validated via force and intracellular stress measurements, as well as perturbations. Altogether, our results highlight the importance of geometry in defining the migration properties of cell clusters, providing a conceptual framework to extract interaction rules from how active systems interact with physical boundaries.

The ability of cells to respond to substrate-bound protein gradients is crucial for many physiological processes, such as immune response, neurogenesis and cancer cell migration. However, the difficulty to produce well-controlled protein gradients has long been a limitation to our understanding of collective cell migration in response to haptotaxis. Here we use a photopatterning technique to create circular, square and linear fibronectin (FN) gradients on two-dimensional (2D) culture substrates. We observed that epithelial cells spread preferentially on zones of higher FN density, creating rounded or elongated gaps within epithelial tissues over circular or linear FN gradients, respectively. Using time-lapse experiments, we demonstrated that the gap closure mechanism in a 2D haptotaxis model requires a significant increase of the leader cell area. In addition, we found that gap closures are slower on decreasing FN densities than on homogenous FN-coated substrate and that fresh closed gaps are characterized by a lower cell density. Interestingly, our results showed that cell proliferation increases in the closed gap region after maturation to restore the cell density, but that cell–cell adhesive junctions remain weaker in scarred epithelial zones. Taken together, our findings provide a better understanding of the wound healing process over protein gradients, which are reminiscent of haptotaxis.

The development of epithelial lumens in ducts is essential to the functioning of various organs and in organogenesis. Ductal elongation requires the collective migration of cell cohorts in three‐dimensional (3D) confined spaces, while maintaining their epithelial integrity. Epithelial lumens generally adopt circular morphologies, however abnormalities in complex physiological environments can lead to the narrowing of glandular spaces that adopt elongated and slit‐like morphologies. Here, we describe a simple method to form epithelial tissues in microchannels of various widths (100–300 µm) with a constant height of 25 µm that mimic elongated geometries of glandular spaces. The significance of this biomimetic platform has been evidenced by studying the migration of epithelial cell sheets inside these narrow slits of varying dimensions. We show that the growth of epithelial tissues in 3D‐confined slits leads to a gradient of cell density along the slit axis and that the migration cell velocity depends on the extent of the spatial confinement. Our findings indicate that nuclear orientation is higher for leader cells and depends on the slit width, whereas YAP protein was predominantly localized in the nucleus of leader cells. This method will pave the way to studies aiming at understanding how 3D‐confined spaces, which are reminiscent of in vivo pathological conditions, can affect the growth and the homeostasis of epithelial tissues.