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Key Points In many biological situations in vivo , including tissue shaping during morphogenesis, tissue repair and cancer invasion, cells do not move as single bodies but as a collective. Two main mechanisms support collective dynamics: polarized collective cell migration and coordinated contractile processes of cell groups that involve multicellular actomyosin-based structures. In vitro wound-healing assays exploiting microfabricated devices have been models of choice to study collective cell behaviours. Such in vitro approaches are the most important methods to achieve multiscale analysis from the molecular to the multicellular level. In contrast to a single cell, collective cell migration relies not only on the interactions with the extracellular matrix but also with neighbouring cells. Coordinated movements strongly depend on intercellular interactions via mechanosensitive cadherin-based adhesions. Cellular coordination is a mechanoregulated multiscale process integrating events at the molecular, cellular and multicellular scales, and it occurs at a wide range of timescales, from milliseconds to minutes to days. Coordinated movements of cell collectives are important for morphogenesis, tissue regeneration and cancer cell dissemination. Recent studies, mainly using novel in vitro approaches, have provided new insights into the mechanisms governing this multicellular coordination, highlighting the key role of the mechanosensitivity of adherens junctions and mechanical cell–cell coupling in collective cell behaviours. The way in which cells coordinate their behaviours during various biological processes, including morphogenesis, cancer progression and tissue remodelling, largely depends on the mechanical properties of the external environment. In contrast to single cells, collective cell behaviours rely on the cellular interactions not only with the surrounding extracellular matrix but also with neighbouring cells. Collective dynamics is not simply the result of many individually moving blocks. Instead, cells coordinate their movements by actively interacting with each other. These mechanisms are governed by mechanosensitive adhesion complexes at the cell–substrate interface and cell–cell junctions, which respond to but also further transmit physical signals. The mechanosensitivity and mechanotransduction at adhesion complexes are important for regulating tissue cohesiveness and thus are important for collective cell behaviours. Recent studies have shown that the physical properties of the cellular environment, which include matrix stiffness, topography, geometry and the application of external forces, can alter collective cell behaviours, tissue organization and cell-generated forces. On the basis of these findings, we can now start building our understanding of the mechanobiology of collective cell movements that span over multiple length scales from the molecular to the tissue level.

E-cadherin is a key component of the adherens junctions that are integral in cell adhesion and maintaining epithelial phenotype of cells. Homophilic E-cadherin binding between cells is important in mediating contact inhibition of proliferation when cells reach confluence. Loss of E-cadherin expression results in loss of contact inhibition and is associated with increased cell motility and advanced stages of cancer. In this review we discuss the role of E-cadherin and its downstream signaling in regulation of contact inhibition and the development and progression of cancer.

Cell adhesion molecules are ubiquitous in multicellular organisms, specifying precise cell–cell interactions in processes as diverse as tissue development, immune cell trafficking and the wiring of the nervous system 1 – 4 . Here we show that a wide array of synthetic cell adhesion molecules can be generated by combining orthogonal extracellular interactions with intracellular domains from native adhesion molecules, such as cadherins and integrins. The resulting molecules yield customized cell–cell interactions with adhesion properties that are similar to native interactions. The identity of the intracellular domain of the synthetic cell adhesion molecules specifies interface morphology and mechanics, whereas diverse homotypic or heterotypic extracellular interaction domains independently specify the connectivity between cells. This toolkit of orthogonal adhesion molecules enables the rationally programmed assembly of multicellular architectures, as well as systematic remodelling of native tissues. The modularity of synthetic cell adhesion molecules provides fundamental insights into how distinct classes of cell–cell interfaces may have evolved. Overall, these tools offer powerful abilities for cell and tissue engineering and for systematically studying multicellular organization. Synthetic cell adhesion molecules yield customized cell–cell interactions with adhesion properties that are similar to native interactions, and offer abilities for cell and tissue engineering and for systematically studying multicellular organization.

Cancer-associated fibroblasts (CAFs) promote tumour invasion and metastasis. We show that CAFs exert a physical force on cancer cells that enables their collective invasion. Force transmission is mediated by a heterophilic adhesion involving N-cadherin at the CAF membrane and E-cadherin at the cancer cell membrane. This adhesion is mechanically active; when subjected to force it triggers β-catenin recruitment and adhesion reinforcement dependent on α-catenin/vinculin interaction. Impairment of E-cadherin/N-cadherin adhesion abrogates the ability of CAFs to guide collective cell migration and blocks cancer cell invasion. N-cadherin also mediates repolarization of the CAFs away from the cancer cells. In parallel, nectins and afadin are recruited to the cancer cell/CAF interface and CAF repolarization is afadin dependent. Heterotypic junctions between CAFs and cancer cells are observed in patient-derived material. Together, our findings show that a mechanically active heterophilic adhesion between CAFs and cancer cells enables cooperative tumour invasion. Cancer-associated fibroblasts (CAFs) promote metastasis by creating tracks for cancer cell migration. Labernadie  et al.  now show that heterotypic adhesions between E-cadherin on cancer cells and N-cadherin on CAFs transmit forces to drive invasion.

The transmembrane domain of NOTCH1 plays a key role in the assembly of adherens junctions and the non-transcriptional regulation of vascular permeability that links transcriptional programs with adhesive and cytoskeletal remodelling. Vascular barrier formation The interaction between the Notch receptor and its ligands causes proteolysis of the receptor's intracellular domain, which then relocates to the nucleus and regulates transcription of a battery of genes. William Polacheck et al . show that ligand binding to the Notch receptor in the endothelium—the layer of cells that line the interior of blood and lymphatic vessels—triggers a non-canonical signalling cascade that is mediated by the receptor's transmembrane domain. This domain catalyses the formation of a complex composed of vascular endothelial cadherin, the transmembrane protein tyrosine phosphatase LAR, and the RAC1 guanidine-exchange factor TRIO. This complex drives the assembly of adherens junctions and is crucial for the establishment and maintenance of the endothelial barrier, which is essential to vascular health. The vascular barrier that separates blood from tissues is actively regulated by the endothelium and is essential for transport, inflammation, and haemostasis 1 . Haemodynamic shear stress plays a critical role in maintaining endothelial barrier function 2 , but how this occurs remains unknown. Here we use an engineered organotypic model of perfused microvessels to show that activation of the transmembrane receptor NOTCH1 directly regulates vascular barrier function through a non-canonical, transcription-independent signalling mechanism that drives assembly of adherens junctions, and confirm these findings in mouse models. Shear stress triggers DLL4-dependent proteolytic activation of NOTCH1 to expose the transmembrane domain of NOTCH1. This domain mediates establishment of the endothelial barrier; expression of the transmembrane domain of NOTCH1 is sufficient to rescue defects in barrier function induced by knockout of NOTCH1 . The transmembrane domain restores barrier function by catalysing the formation of a receptor complex in the plasma membrane consisting of vascular endothelial cadherin, the transmembrane protein tyrosine phosphatase LAR, and the RAC1 guanidine-exchange factor TRIO. This complex activates RAC1 to drive assembly of adherens junctions and establish barrier function. Canonical transcriptional signalling via Notch is highly conserved in metazoans and is required for many processes in vascular development, including arterial–venous differentiation 3 , angiogenesis 4 and remodelling 5 . We establish the existence of a non-canonical cortical NOTCH1 signalling pathway that regulates vascular barrier function, and thus provide a mechanism by which a single receptor might link transcriptional programs with adhesive and cytoskeletal remodelling.

Yap and Lecuit review the interplay of E-cadherin-mediated adhesion and actomyosin-based contractility, and discuss the functional effects of their crosstalk at the cellular and tissue level. During epithelial morphogenesis, E-cadherin adhesive junctions play an important part in mechanically coupling the contractile cortices of cells together, thereby distributing the stresses that drive cell rearrangements at both local and tissue levels. Here we discuss the concept that cellular contractility and E-cadherin-based adhesion are functionally integrated by biomechanical feedback pathways that operate on molecular, cellular and tissue scales.

The cadherin superfamily includes many proteins other than E-cadherin. These cadherins are very diverse in both structure and function, and their mutual interactions seem to influence cancer development and progression in complex and versatile ways. Loss of cadherin 1 (CDH1; also known as epithelial cadherin (E-cadherin)) is used for the diagnosis and prognosis of epithelial cancers. However, it should not be ignored that the superfamily of transmembrane cadherin proteins encompasses more than 100 members in humans, including other classical cadherins, numerous protocadherins and cadherin-related proteins. Elucidation of their roles in suppression versus initiation or progression of various tumour types is a young but fascinating field of molecular cancer research. These cadherins are very diverse in both structure and function, and their mutual interactions seem to influence biological responses in complex and versatile ways.

The global-scale production of plastics has been instrumental in advancing modern society, while the rising accumulation of plastics in landfills, oceans, and anything in between has become a major stressor on environmental sustainability, climate, and, potentially, human health. While mechanical and chemical forces of man and nature can eventually break down or recycle plastics, our understanding of the biological fingerprints of plastics, especially of nanoplastics, remains poor. Here we report on a phenomenon associated with the nanoplastic forms of anionic polystyrene and poly(methyl methacrylate), where their introduction disrupted the vascular endothelial cadherin junctions in a dose-dependent manner, as revealed by confocal fluorescence microscopy, signaling pathways, molecular dynamics simulations, as well as ex vivo and in vivo assays with animal model systems. Collectively, our results implicated nanoplastics-induced vasculature permeability as primarily biophysical-biochemical in nature, uncorrelated with cytotoxic events such as reactive oxygen species production, autophagy, and apoptosis. This uncovered route of paracellular transport has opened up vast avenues for investigating the behaviour and biological effects of nanoplastics, which may offer crucial insights for guiding innovations towards a sustainable plastics industry and environmental remediation. In this study, the authors report that anionic nanoplastics can harness the paracellular space of endothelial cells and puncture blood vasculature ex vivo and in vivo, thereby entailing new environmental and health implications.

Scars are more severe when the subcutaneous fascia beneath the dermis is injured upon surgical or traumatic wounding. Here, we present a detailed analysis of fascia cell mobilisation by using deep tissue intravital live imaging of acute surgical wounds, fibroblast lineage-specific transgenic mice, and skin-fascia explants (scar-like tissue in a dish – SCAD). We observe that injury triggers a swarming-like collective cell migration of fascia fibroblasts that progressively contracts the skin and form scars. Swarming is exclusive to fascia fibroblasts, and requires the upregulation of N-cadherin. Both swarming and N-cadherin expression are absent from fibroblasts in the upper skin layers and the oral mucosa, tissues that repair wounds with minimal scar. Impeding N-cadherin binding inhibits swarming and skin contraction, and leads to reduced scarring in SCADs and in animals. Fibroblast swarming and N-cadherin thus provide therapeutic avenues to curtail fascia mobilisation and pathological fibrotic responses across a range of medical settings. Extensive scars develop in deep wounds as opposed to superficial wounds but it is unclear why. Here, the authors use live imaging of physiologic wounds and scars formed ex vivo to show that fascia fibroblasts upregulate N-cadherin allowing coordinated cell migration that drives extensive scar formation of deep wounds.

The development and maintenance of tissues requires collective cell movement, during which neighbouring cells coordinate the polarity of their migration machineries. Here, we ask how polarity signals are transmitted from one cell to another across symmetrical cadherin junctions, during collective migration. We demonstrate that collectively migrating endothelial cells have polarized VE-cadherin-rich membrane protrusions, ‘cadherin fingers’, which leading cells extend from their rear and follower cells engulf at their front, thereby generating opposite membrane curvatures and asymmetric recruitment of curvature-sensing proteins. In follower cells, engulfment of cadherin fingers occurs along with the formation of a lamellipodia-like zone with low actomyosin contractility, and requires VE-cadherin/catenin complexes and Arp2/3-driven actin polymerization. Lateral accumulation of cadherin fingers in follower cells precedes turning, and increased actomyosin contractility can initiate cadherin finger extension as well as engulfment by a neighbouring cell, to promote follower behaviour. We propose that cadherin fingers serve as guidance cues that direct collective cell migration. Hayer et al.  observe that collectively migrating endothelial cells extend rear VE-cadherin-rich membrane structures that are engulfed by follower cells, correlating spatially with the direction of movement.