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Extracellular signal-regulated kinase (ERK) plays a crucial role in regulating collective cell behaviors observed in diverse biological phenomena. Emerging studies have shed light on the involvement of the ERK signaling pathway in the reception and generation of mechanical forces, thereby governing local mechanical interactions within multicellular tissues. Although limited in number, studies have provided insights into how ERK-mediated mechanical interactions contribute to multicellular organization. Here we explore the impact of ERK-mediated mechanical interactions on tissue morphogenesis, cell extrusion in homeostasis, and their interplay with the physical microenvironments of the extracellular matrix. We conclude that the coupling system of ERK activity with mechanical forces offers a promising avenue to unravel the emergent collective dynamics underlying tissue organization. [ABSTRACT FROM AUTHOR]

Cell extrusion is a universal mode of cell removal from tissues, and it plays an important role in regulating cell numbers and eliminating unwanted cells. However, the underlying mechanisms of cell delamination from the cell layer are unclear. Here, we report a conserved execution mechanism of apoptotic cell extrusion. We found extracellular vesicle (EV) formation in extruding mammalian and Drosophila cells at a site opposite to the extrusion direction. Lipid-scramblase-mediated local exposure of phosphatidylserine is responsible for EV formation and is crucial for executing cell extrusion. Inhibition of this process disrupts prompt cell delamination and tissue homeostasis. Although the EV has hallmarks of an apoptotic body, its formation is governed by the mechanism of microvesicle formation. Experimental and mathematical modeling analysis illustrated that EV formation promotes neighboring cells' invasion. This study showed that membrane dynamics play a crucial role in cell exit by connecting the actions of the extruding cell and neighboring cells. [Display omitted] • EV is formed in extruding cells with a spatiotemporally regulated manner • EV formation drives efficient extrusion by creating space for the nearby cell invasion • Localized phosphatidylserine exposure is involved in EV formation • EV has hallmarks of both apoptotic body and microvesicle Kira et al. show the mechanism underlying cell exit from a cell layer during cell extrusion, a conserved mode of demise in epithelial cells. Localized extracellular vesicle (EV) formation via phosphatidylserine exposure drives efficient cell extrusion by making space for neighboring cells' invasion. [ABSTRACT FROM AUTHOR]

Summary Cells dynamically interact throughout animal development to coordinate growth and deter disease. For example, cell-cell competition weeds out aberrant cells to enforce homeostasis. In Drosophila , tumorigenic cells mutant for the cell polarity gene scribble ( scrib ) are actively eliminated from epithelia when surrounded by wild-type cells. While scrib cell elimination depends critically on JNK signaling, JNK-dependent cell death cannot sufficiently explain scrib cell extirpation. Thus, how JNK executed cell elimination remained elusive. Here, we show that repulsive Slit-Robo2-Ena signaling exerts an extrusive force downstream of JNK to eliminate scrib cells from epithelia by disrupting E-cadherin. While loss of Slit-Robo2-Ena in scrib cells potentiates scrib tumor formation within the epithelium, Robo2-Ena hyperactivation surprisingly triggers luminal scrib tumor growth following excess extrusion. This extrusive signaling is amplified by a positive feedback loop between Slit-Robo2-Ena and JNK. Our observations provide a potential causal mechanism for Slit-Robo dysregulation in numerous human cancers. [ABSTRACT FROM AUTHOR]

Excessive shedding of apoptotic enterocytes into the intestinal lumen is observed in inflammatory bowel disease and is correlated with disease relapse. Based on their cytolytic capacity and surveillance behavior, we investigated whether intraepithelial lymphocytes expressing the γδ T cell receptor (γδ IELs) are actively involved in the shedding of enterocytes into the lumen. Intravital microscopy was performed on GFP γδ T cell reporter mice treated with intraperitoneal lipopolysaccharide (10 mg/kg) for 90 minutes to induce tumor necrosis factor–mediated apoptosis. Cell shedding in various knockout or transgenic mice in the presence or absence of blocking antibody was quantified by immunostaining for ZO-1 funnels and cleaved caspase-3 (CC3). Granzyme A and granzyme B release from ex vivo–stimulated γδ IELs was quantified by enzyme-linked immunosorbent assay. Immunostaining for γδ T cell receptor and CC3 was performed on duodenal and ileal biopsies from controls and patients with Crohn's disease. Intravital microscopy of lipopolysaccharide-treated mice revealed that γδ IELs make extended contact with shedding enterocytes. These prolonged interactions require CD103 engagement by E-cadherin, and CD103 knockout or blockade significantly reduced lipopolysaccharide-induced shedding. Furthermore, we found that granzymes A and B, but not perforin, are required for cell shedding. These extracellular granzymes are released by γδ IELs both constitutively and after CD103/E-cadherin ligation. Moreover, we found that the frequency of γδ IEL localization to CC3-positive enterocytes is increased in Crohn's disease biopsies compared with healthy controls. Our results uncover a previously unrecognized role for γδ IELs in facilitating tumor necrosis factor–mediated shedding of apoptotic enterocytes via CD103-mediated extracellular granzyme release. Sentinel tissue-resident T cells facilitate the extrusion of epithelial cells undergoing programmed cell death in response to proinflammatory signals via integrin-mediated extracellular serine protease release. [ABSTRACT FROM AUTHOR]

Cell injury poses a substantial challenge for epithelia homeostasis. Several cellular processes preserve epithelial barriers in response to apoptosis, but less is known about other forms of cell death, such as pyroptosis. Here we use an inducible caspase-1 system to analyze how colon epithelial monolayers respond to pyroptosis. We confirm that sporadic pyroptotic cells are physically eliminated from confluent monolayers by apical extrusion. This is accompanied by a transient defect in barrier function at the site of the pyroptotic cells. By visualizing cell shape changes and traction patterns in combination with cytoskeletal inhibitors, we show that rapid lamellipodial responses in the neighbor cells are responsible for correcting the leakage and resealing the barrier. Cell contractility is not required for this resealing response, in contrast to the response to apoptosis. Therefore, pyroptosis elicits a distinct homeostatic response from the epithelium that is driven by the stimulation of lamellipodia in neighbor cells. [Display omitted] • Caspase-1 activation induces lytic cell death and extrusion response in epithelia • Transient epithelial permeability occurs during extrusion of Casp-1-activated cells • Neighbor cells rapidly extend lamellipodia to re-establish epithelial homeostasis • Lamellipodia inhibition delays epithelial resealing during pyroptotic extrusion Bonfim-Melo et al. show that apical extrusion is the epithelial response to sporadic pyroptotic events. In contrast to apoptosis, pyroptosis causes a transient local increase in monolayer permeability that is corrected by rapid lamellipodial responses from the neighbors, rather than their contractility [ABSTRACT FROM AUTHOR]

What regulates the spatiotemporal distribution of cell elimination in tissues remains largely unknown. This is particularly relevant for epithelia with high rates of cell elimination where simultaneous death of neighboring cells could impair epithelial sealing. Here, using the Drosophila pupal notum (a single-layer epithelium) and a new optogenetic tool to trigger caspase activation and cell extrusion, we first showed that death of clusters of at least three cells impaired epithelial sealing; yet, such clusters were almost never observed in vivo. Accordingly, statistical analysis and simulations of cell death distribution highlighted a transient and local protective phase occurring near every cell death. This protection is driven by a transient activation of ERK in cells neighboring extruding cells, which inhibits caspase activation and prevents elimination of cells in clusters. This suggests that the robustness of epithelia with high rates of cell elimination is an emerging property of local ERK feedback. [Display omitted] • Simultaneous elimination of three neighboring cells is detrimental for epithelia • Biased cell-death distribution prevents the appearance of such clusters • This bias is driven by ERK pulses and caspase inhibition in the neighbors of dying cells • Clusters of elimination and transient sealing defects appear upon EGFR/ERK inhibition How epithelia fine-tune the spatiotemporal distribution of cell death and cope with high rates of elimination remains unclear. Valon et al. shows that pulses of ERK induced near every dying cell prevent the simultaneous elimination of neighboring cells, hence maintaining epithelial sealing despite the high rates of cell elimination. [ABSTRACT FROM AUTHOR]

Severe and often fatal opportunistic fungal infections arise frequently following mucosal damage caused by trauma or cytotoxic chemotherapy. Interaction of fungal pathogens with epithelial cells that comprise mucosae is a key early event associated with invasion, and, therefore, enhancing epithelial defense mechanisms may mitigate infection. Here, we establish a model of mold and yeast infection mediated by inducible epithelial cell loss in larval zebrafish. Epithelial cell loss by extrusion promotes exposure of laminin associated with increased fungal attachment, invasion, and larval lethality, whereas fungi defective in adherence or filamentation have reduced virulence. Transcriptional profiling identifies significant upregulation of the epidermal growth factor receptor ligand epigen (EPGN) upon mucosal damage. Treatment with recombinant human EPGN suppresses epithelial cell extrusion, leading to reduced fungal invasion and significantly enhanced survival. These data support the concept of augmenting epithelial restorative capacity to attenuate pathogenic invasion of fungi associated with human disease. [Display omitted] • Inducible epithelial cell loss allows modeling of fungal infection in zebrafish larvae • Extrusion of numerous cells exposes laminin and increases fungal adhesion and invasion • Cell extrusion stimulates epigen , mmp13a , and il1b expression and neutrophil recruitment • rhEPGN suppresses extrusion to provide protective effects against fungal invasion Wurster et al. show that extrusion of numerous epithelial cells from tissue can expose underlying extracellular matrix components to promote increased attachment and invasion of fungi associated with human disease. Treatment with recombinant human EPGN suppressed epithelial cell extrusion, leading to significantly reduced opportunistic fungal invasion. [ABSTRACT FROM AUTHOR]

Blood flow modulates endothelial cell (EC) response during angiogenesis. Shear stress is known to control gene expression related to the endothelial-mesenchymal transition and endothelial-hematopoietic transition. However, the impact of blood flow on the cellular processes associated with EC extrusion is less well understood. To address this question, we dynamically record EC movements and use 3D quantitative methods to segregate the contributions of various cellular processes to the cellular trajectories in the zebrafish dorsal aorta. We find that ECs spread toward the cell extrusion area following the tissue deformation direction dictated by flow-derived mechanical forces. Cell extrusion increases when blood flow is impaired. Similarly, the mechanosensor polycystic kidney disease 2 (pkd2) limits cell extrusion, suggesting that ECs actively sense mechanical forces in the process. These findings identify pkd2 and flow as critical regulators of EC extrusion and suggest that mechanical forces coordinate this process by maintaining ECs within the endothelium. • Endothelial cell (EC) nuclei are enriched in the ventral dorsal aorta (DA) during EC movement • DA wall deforms asymmetrically in response to pulsatile blood flow • Low blood flow or abnormal mechanosensing results in increased cell extrusion Campinho et al. show that cell extrusion associated with hematopoietic stem cell generation in the ventral dorsal aorta is under the control of blood flow-dependent tissue mechanics. The mechanosensitive channel trpp2 and blood flow limit endothelial cell extrusion originating from the endothelium during the process. [ABSTRACT FROM AUTHOR]