Basal Cell-Extracellular Matrix Adhesion Regulates Force Transmission during Tissue Morphogenesis

Shaping epithelial tissues by stem cell mechanics in development and cancer

Adult stem cells balance self-renewal and differentiation to build, maintain and repair tissues. The role of signalling pathways and transcriptional networks in controlling stem cell function has been extensively studied, but there is increasing appreciation that mechanical forces also have a crucial regulatory role. Mechanical forces, signalling pathways and transcriptional networks must be coordinated across diverse length and timescales to maintain tissue homeostasis and function. Such coordination between stem cells and neighbouring cells dictates when cells divide, migrate and differentiate. Recent advances in measuring and manipulating the mechanical forces that act upon and are produced by stem cells are providing new insights into development and disease. In this Review, we discuss the mechanical forces involved when epithelial stem cells construct their microenvironment and what happens in cancer when stem cell niche mechanics are disrupted or dysregulated. As the skin has evolved to withstand the harsh mechanical pressures from the outside environment, we often use the stem cells of mammalian skin epithelium as a paradigm for adult stem cells shaping their surrounding tissues.

Cell position-based evaluation of mechanical features of cells in multicellular systems

Measurement of mechanical forces of cell-cell interactions is important for studying the emergence of diverse three-dimensional morphologies of multicellular organisms. We previously reported an image-based statistical method for inferring effective pairwise forces of cell-cell interactions (i.e., attractive/repulsive forces), where a cell particle model was fitted to cell tracking data acquired by live imaging. However, because the particle model is a coarse-grained model, it remains unclear how the pairwise forces relates to sub-cellular mechanical components including cell-cell adhesive forces. Here we applied our inference method to cell tracking data generated by vertex models that assumed sub-cellular components. Through this approach, we investigated the relationship between the effective pairwise forces and various sub-cellular components: cell-cell adhesion forces, cell surface tensions, cell-extracellular matrix (ECM) adhesion, traction forces between cells and ECM, cell growth, etc. We found that the cell-cell adhesion forces were attractive, and both the cell surface tensions and cell-ECM adhesive forces were repulsive, etc. These results indicate that sub-cellular mechanical components can contribute to the effective attractive/repulsive forces of cell-cell interactions. This comprehensive analysis provides theoretical bases for linking the pairwise forces to the sub-cellular mechanical components: this showcase is useful for speculating the sub-cellular mechanical components from the information of cell positions, and for interpreting simulation results based on particle models.

Finite element analysis in the Dental Sciences: A Bibliometric and a Visual Study

INTRODUCTION AND AIMS

Finite element analysis (FEA) is an incrementally practical and precise tool for the prediction of stress effects on different tissue structures and has therefore interested dental researchers for decades. This bibliometric and visualized study was aimed to assess the research progress related to FEA in the dental sciences in terms of research trends and frontiers.

METHODS

The articles about FEA studies in this field during 1999 to 2024 were obtained from Web of Science Core Collection. Then, these results were analysed and plotted using Microsoft Excel, VOSviewer, and CiteSpace in order to find out the historical evolution, current hotspots, and future directions.

RESULTS

Total 2838 literature records related to the topic were retrieved from Web of Science Core Collection. The most active country and institution were USA (538 documents) and Universidade Estadual Paulista (140 documents), respectively. Baggi et al from University of Naples Federico II was the author with the most highly cited article (352 citations), which was published on the Journal of Prosthetic Dentistry in 2008. Dental Materials ranked first (231 documents) among the 10 journals with the greatest numbers of relevant publications. The top three trending keywords were 'dental implant', 'stress distribution', and 'fracture'. The endocrown, clear aligner, and posterior edentulism were scientific frontiers in this field.

CONCLUSION

The present study provides a comprehensive bibliometric analysis of research in the dental science by FEA approaches, which will identify active hotspots of scientific interest to guide further research endeavours.

Activation of a Src-JNK pathway in unscheduled endocycling cells of the Drosophila wing disc induces a chronic wounding response

The endocycle is a specialized cell cycle during which cells undergo repeated G / S phases to replicate DNA without division, leading to large polyploid cells. The transition from a mitotic cycle to an endocycle can be triggered by various stresses, which results in unscheduled, or induced endocycling cells (iECs). While iECs can be beneficial for wound healing, they can also be detrimental by impairing tissue growth or promoting cancer. However, the regulation of endocycling and its role in tissue growth remain poorly understood. Using the Drosophila wing disc as a model, we previously demonstrated that iEC growth is arrested through a Jun N-Terminal Kinase (JNK)-dependent, reversible senescence-like response. However, it remains unclear how JNK is activated in iECs and how iECs impact overall tissue structure. In this study, we performed a genetic screen and identified the Src42A-Shark-Slpr pathway as an upstream regulator of JNK in iECs, leading to their senescence-like arrest. We found that tissues recognize iECs as wounds, releasing wound-related signals that induce a JNK-dependent developmental delay. Similar to wound closure, this response triggers Src-JNK-mediated actomyosin remodeling, yet iECs persist rather than being eliminated. Our findings suggest that the tissue response to iECs shares key signaling and cytoskeletal regulatory mechanisms with wound healing and dorsal closure, a developmental process during Drosophila embryogenesis. However, because iECs are retained within the tissue, they create a unique system that may serve as a model for studying chronic wounds and tumor progression.

Single nuclear RNA sequencing and analysis of basal cells in pulmonary acute respiratory distress syndrome

OBJECTIVE

This study aims to find the gene expression profile specifically in basal cells from pulmonary acute respiratory distress syndrome (ARDSp) patients using single-cell level analysis.

METHODS

Single nuclear RNA sequencing (snRNA-seq) data of lung samples, including 18 ARDSp participants and 7 healthy participants, were sourced from the GEO database (GSE171524). The differentially expressed genes (DEGs) were screened by | log2FC | >1 and P < 0.05. Functional enrichment was constructed via Gene Ontology (GO) analysis. Pathway enrichment was conducted via Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. The protein-protein interaction (PPI) network of the DEGs was performed via the STRING database. Cytoscape software was employed to find hub genes. The hub genes were sequenced and validated via data set after constructing the rat model of ARDSp.

RESULTS

Using DESeq2 package, 299 genes were disclosed to be downregulated, while 228 were upregulated in ARDSp participants. GO analysis disclosed DEGs were enriched in processes like actin filament organization, regulation of small GTPase-mediated signal transduction, response to unfolded protein, wound healing, and response to oxygen levels. Meanwhile, KEGG analysis disclosed DEGs were involved in protein digestion and absorption, Th17 cell differentiation, iron death, and other biological effects. Ten hub genes, including FN1, HIF1A, HSP90AA1, SMAD3, FOS, CDKN2A, COL1A1, HSPA8, FLNA, and NFKBIA were highlighted based on their network centrality and biological significance. HIF1A, HSPA8, NFKBIA, and CDKN2A were differentially expressed in the validation dataset.

CONCLUSIONS

Basal cells in ARDSp exhibit significant changes in gene expression, with ten hub genes identified. Among them, four (HIF1A, HSPA8, NFKBIA, CDKN2A) were validated experimentally using RNA-Seq data from an ARDSp rat model. This study emphasizes the role of basal cells in ARDSp, highlighting the altered gene networks involved in repair and inflammatory responses, providing potential targets for further therapeutic exploration. These findings suggest that alterations in these hub genes may be crucial to basal cell-driven inflammatory and reparative responses in ARDSp.

Actin-driven nanotopography promotes stable integrin adhesion formation in developing tissue

Morphogenesis requires building stable macromolecular structures from highly dynamic proteins. Muscles are anchored by long-lasting integrin adhesions to resist contractile force. However, the mechanisms governing integrin diffusion, immobilization, and activation within developing tissues remain elusive. Here, we show that actin polymerization-driven membrane protrusions form nanotopographies that enable strong adhesion at Drosophila muscle attachment sites (MASs). Super-resolution microscopy reveals that integrins assemble adhesive belts around Arp2/3-dependent actin protrusions, forming invadosome-like structures with membrane nanotopographies. Single protein tracking shows that, during MAS development, integrins become immobile and confined within diffusion traps formed by the membrane nanotopographies. Actin filaments also display restricted motion and confinement, indicating strong mechanical connection with integrins. Using isolated muscle cells, we show that substrate nanotopography, rather than rigidity, drives adhesion maturation by regulating actin protrusion, integrin diffusion and immobilization. These results thus demonstrate that actin-polymerization-driven membrane protrusions are essential for the formation of strong integrin adhesions sites in the developing embryo, and highlight the important contribution of geometry to morphogenesis.

Integrin-based adhesions promote cell-cell junction and cytoskeletal remodelling to drive embryonic wound healing

Embryos repair wounds rapidly, with no inflammation or scarring. Embryonic wound healing is driven by the collective movement of the cells around the lesion. The cells adjacent to the wound polarize the cytoskeletal protein actin and the molecular motor non-muscle myosin II, which accumulate at the wound edge forming a supracellular cable around the wound. Adherens junction proteins, including E-cadherin, are internalized from the wound edge and localize to former tricellular junctions at the wound margin, in a process necessary for cytoskeletal polarity. We found that the cells adjacent to wounds in the Drosophila embryonic epidermis polarized Talin, a core component of cell-extracellular matrix (ECM) adhesions, which preferentially accumulated at the wound edge. Integrin knockdown and inhibition of integrin binding delayed wound closure and reduced actin polarization and dynamics around the wound. Additionally, disrupting integrins caused a defect in E-cadherin reinforcement at tricellular junctions along the wound edge, suggesting crosstalk between integrin-based and cadherin-based adhesions. Our results show that cell-ECM adhesion contributes to embryonic wound repair and reveal an interplay between cell-cell and cell-ECM adhesion in the collective cell movements that drive rapid wound healing.

JNK signaling and integrins cooperate to maintain cell adhesion during epithelial fusion in Drosophila

The fusion of epithelial sheets is an essential and conserved morphogenetic event that requires the maintenance of tissue continuity. This is secured by membrane-bound or diffusible signals that instruct the epithelial cells, in a coordinated fashion, to change shapes and adhesive properties and when, how and where to move. Here we show that during Dorsal Closure (DC) in Drosophila, the Jun kinase (JNK) signaling pathway modulates integrins expression and ensures tissue endurance. An excess of JNK activity, as an outcome of a failure in the negative feedback implemented by the dual-specificity phosphatase Puckered (Puc), promotes the loss of integrins [the ß-subunit Myospheroid (Mys)] and amnioserosa detachment. Likewise, integrins signal back to the pathway to regulate the duration and strength of JNK activity. Mys is necessary for the regulation of JNK activity levels and in its absence, puc expression is downregulated and JNK activity increases.

Assembly, dynamics and remodeling of epithelial cell junctions throughout development

Cell junctions play key roles in epithelial integrity. During development, when epithelia undergo extensive morphogenesis, these junctions must be remodeled in order to maintain mechanochemical barriers and ensure the cohesion of the tissue. In this Review, we present a comprehensive and integrated description of junctional remodeling mechanisms in epithelial cells during development, from embryonic to adult epithelia. We largely focus on Drosophila, as quantitative analyses in this organism have provided a detailed characterization of the molecular mechanisms governing cell topologies, and discuss the conservation of these mechanisms across metazoans. We consider how changes at the molecular level translate to tissue-scale irreversible deformations, exploring the composition and assembly of cellular interfaces to unveil how junctions are remodeled to preserve tissue homeostasis during cell division, intercalation, invagination, ingression and extrusion.

The Effect of Substrate Stiffness on Elastic Force Transmission in the Epithelial Monolayers over Short Timescales

Purpose

The importance of mechanical forces and microenvironment in guiding cellular behavior has been widely accepted. Together with the extracellular matrix (ECM), epithelial cells form a highly connected mechanical system subjected to various mechanical cues from their environment, such as ECM stiffness, and tensile and compressive forces. ECM stiffness has been linked to many pathologies, including tumor formation. However, our understanding of the effect of ECM stiffness and its heterogeneities on rapid force transduction in multicellular systems has not been fully addressed.

Methods

We used experimental and computational methods. Epithelial cells were cultured on elastic hydrogels with fluorescent nanoparticles. Single cells were moved by a micromanipulator, and epithelium and substrate deformation were recorded. We developed a computational model to replicate our experiments and quantify the force distribution in the epithelium. Our model further enabled simulations with local stiffness gradients.

Results

We found that substrate stiffness affects the force transduction and the cellular deformation following an external force. Also, our results indicate that the heterogeneities, e.g., gradients, in the stiffness can substantially influence the strain redistribution in the cell monolayers. Furthermore, we found that the cells' apico-basal elasticity provides a level of mechanical isolation between the apical cell-cell junctions and the basal focal adhesions.

Conclusions

Our simulation results show that increased ECM stiffness, e.g., due to a tumor, can mechanically isolate cells and modulate rapid mechanical signaling between cells over distances. Furthermore, the developed model has the potential to facilitate future studies on the interactions between epithelial monolayers and elastic substrates.

Supplementary Information

The online version of this article (10.1007/s12195-023-00772-0) contains supplementary material, which is available to authorized users.

Rap1 coordinates cell-cell adhesion and cytoskeletal reorganization to drive collective cell migration in vivo

Collective cell movements contribute to tissue development and repair and spread metastatic disease. In epithelia, cohesive cell movements require reorganization of adherens junctions and the actomyosin cytoskeleton. However, the mechanisms that coordinate cell-cell adhesion and cytoskeletal remodeling during collective cell migration in vivo are unclear. We investigated the mechanisms of collective cell migration during epidermal wound healing in Drosophila embryos. Upon wounding, the cells adjacent to the wound internalize cell-cell adhesion molecules and polarize actin and the motor protein non-muscle myosin II to form a supracellular cable around the wound that coordinates cell movements. The cable anchors at former tricellular junctions (TCJs) along the wound edge, and TCJs are reinforced during wound closure. We found that the small GTPase Rap1 was necessary and sufficient for rapid wound repair. Rap1 promoted myosin polarization to the wound edge and E-cadherin accumulation at TCJs. Using embryos expressing a mutant form of the Rap1 effector Canoe/Afadin that cannot bind Rap1, we found that Rap1 signals through Canoe for adherens junction remodeling, but not for actomyosin cable assembly. Instead, Rap1 was necessary and sufficient for RhoA/Rho1 activation at the wound edge. The RhoGEF Ephexin localized to the wound edge in a Rap1-dependent manner, and Ephexin was necessary for myosin polarization and rapid wound repair, but not for E-cadherin redistribution. Together, our data show that Rap1 coordinates the molecular rearrangements that drive embryonic wound healing, promoting actomyosin cable assembly through Ephexin-Rho1, and E-cadherin redistribution through Canoe, thus enabling rapid collective cell migration in vivo.

Lack of Paxillin phosphorylation promotes single-cell migration in vivo

Focal adhesions are structures that physically link the cell to the extracellular matrix for cell migration. Although cell culture studies have provided a wealth of information regarding focal adhesion biology, it is critical to understand how focal adhesions are dynamically regulated in their native environment. We developed a zebrafish system to visualize focal adhesion structures during single-cell migration in vivo. We find that a key site of phosphoregulation (Y118) on Paxillin exhibits reduced phosphorylation in migrating cells in vivo compared to in vitro. Furthermore, expression of a non-phosphorylatable version of Y118-Paxillin increases focal adhesion disassembly and promotes cell migration in vivo, despite inhibiting cell migration in vitro. Using a mouse model, we further find that the upstream kinase, focal adhesion kinase, is downregulated in cells in vivo, and cells expressing non-phosphorylatable Y118-Paxillin exhibit increased activation of the CRKII-DOCK180/RacGEF pathway. Our findings provide significant new insight into the intrinsic regulation of focal adhesions in cells migrating in their native environment.

The extended analogy of extraembryonic development in insects and amniotes

It is fascinating that the amnion and serosa/chorion, two extraembryonic (EE) tissues that are characteristic of the amniote vertebrates (mammals, birds and reptiles), have also independently evolved in insects. In this review, we offer the first detailed, macroevolutionary comparison of EE development and tissue biology across these animal groups. Some commonalities represent independent solutions to shared challenges for protecting the embryo (environmental assaults, risk of pathogens) and supporting its development, including clear links between cellular properties (e.g. polyploidy) and physiological function. Further parallels encompass developmental features such as the early segregation of the serosa/chorion compared to later, progressive differentiation of the amnion and formation of the amniotic cavity from serosal-amniotic folds as a widespread morphogenetic mode across species. We also discuss common developmental roles for orthologous transcription factors and BMP signalling in EE tissues of amniotes and insects, and between EE and cardiac tissues, supported by our exploration of new resources for global and tissue-specific gene expression. This highlights the degree to which general developmental principles and protective tissue features can be deduced from each of these animal groups, emphasizing the value of broad comparative studies to reveal subtle developmental strategies and answer questions that are common across species. This article is part of the theme issue 'Extraembryonic tissues: exploring concepts, definitions and functions across the animal kingdom'.

New insights into FAK structure and function in focal adhesions

Focal adhesion kinase (FAK; also known as PTK2) was discovered three decades ago and is now recognised as a key player in the regulation of cell-matrix adhesion and mesenchymal cell migration. Although it is essential during development, FAK also drives invasive cancer progression and metastasis. On a structural level, the basic building blocks of FAK have been described for some time. However, a picture of how FAK integrates into larger assemblies in various cellular environments, including one of its main cellular locations, the focal adhesion (FA) complex, is only beginning to emerge. Nano-resolution data from cellular studies, as well as atomic structures from reconstituted systems, have provided first insights, but also point to challenges that remain for obtaining a full structural understanding of how FAK is integrated in the FA complex and the structural changes occurring at different stages of FA maturation. In this Review, we discuss the known structural features of FAK, the interactions with its partners within the FA environment on the cell membrane and propose how its initial assembly in nascent FAs might change during FA maturation under force.

An evolutionary and physiological perspective on cell-substrate adhesion machinery for cell migration

Cell-substrate adhesion is a critical aspect of many forms of cell migration. Cell adhesion to an extracellular matrix (ECM) generates traction forces necessary for efficient migration. One of the most well-studied structures cells use to adhere to the ECM is focal adhesions, which are composed of a multilayered protein complex physically linking the ECM to the intracellular actin cytoskeleton. Much of our understanding of focal adhesions, however, is primarily derived from in vitro studies in Metazoan systems. Though these studies provide a valuable foundation to the cell-substrate adhesion field, the evolution of cell-substrate adhesion machinery across evolutionary space and the role of focal adhesions in vivo are largely understudied within the field. Furthering investigation in these areas is necessary to bolster our understanding of the role cell-substrate adhesion machinery across Eukaryotes plays during cell migration in physiological contexts such as cancer and pathogenesis. In this review, we review studies of cell-substrate adhesion machinery in organisms evolutionary distant from Metazoa and cover the current understanding and ongoing work on how focal adhesions function in single and collective cell migration in an in vivo environment, with an emphasis on work that directly visualizes cell-substrate adhesions. Finally, we discuss nuances that ought to be considered moving forward and the importance of future investigation in these emerging fields for application in other fields pertinent to adhesion-based processes.

Focal adhesion-mediated cell anchoring and migration: from in vitro to in vivo

Cell-extracellular matrix interactions have been studied extensively using cells cultured in vitro. These studies indicate that focal adhesion (FA)-based cell-extracellular matrix interactions are essential for cell anchoring and cell migration. Whether FAs play a similarly important role in vivo is less clear. Here, we summarize the formation and function of FAs in cultured cells and review how FAs transmit and sense force in vitro. Using examples from animal studies, we also describe the role of FAs in cell anchoring during morphogenetic movements and cell migration in vivo. Finally, we conclude by discussing similarities and differences in how FAs function in vitro and in vivo.

Differential Cellular Stiffness Contributes to Tissue Elongation on an Expanding Surface

Pattern formation and morphogenesis of cell populations is essential for successful embryogenesis. Steinberg proposed the differential adhesion hypothesis, and differences in cell–cell adhesion and interfacial tension have proven to be critical for cell sorting. Standard theoretical models such as the vertex model consider not only cell–cell adhesion/tension but also area elasticity of apical cell surfaces and viscous friction forces. However, the potential contributions of the latter two parameters to pattern formation and morphogenesis remain to be determined. In this theoretical study, we analyzed the effect of both area elasticity and the coefficient of friction on pattern formation and morphogenesis. We assumed the presence of two cell populations, one population of which is surrounded by the other. Both populations were placed on the surface of a uniformly expanding environment analogous to growing embryos, in which friction forces are exerted between cell populations and their expanding environment. When the area elasticity or friction coefficient in the cell cluster was increased relative to that of the surrounding cell population, the cell cluster was elongated. In comparison with experimental observations, elongation of the notochord in mice is consistent with the hypothesis based on the difference in area elasticity but not the difference in friction coefficient. Because area elasticity is an index of cellular stiffness, we propose that differential cellular stiffness may contribute to tissue elongation within an expanding environment.

Integrins and Epithelial-Mesenchymal Cooperation in the Tumor Microenvironment of Muscle-Invasive Lethal Cancers

Muscle-invasive lethal carcinomas traverse into and through this specialized biophysical and growth factor enriched microenvironment. We will highlight cancers that originate in organs surrounded by smooth muscle, which presents a barrier to dissemination, including prostate, bladder, esophageal, gastric, and colorectal cancers. We propose that the heterogeneity of cell-cell and cell-ECM adhesion receptors is an important driver of aggressive tumor networks with functional consequences for progression. Phenotype heterogeneity of the tumor provides a biophysical advantage for tumor network invasion through the tensile muscle and survival of the tumor network. We hypothesize that a functional epithelial-mesenchymal cooperation (EMC)exists within the tumor invasive network to facilitate tumor escape from the primary organ, invasion and traversing of muscle, and navigation to metastatic sites. Cooperation between specific epithelial cells within the tumor and stromal (mesenchymal) cells interacting with the tumor is illustrated using the examples of laminin-binding adhesion molecules—especially integrins—and their response to growth and inflammatory factors in the tumor microenvironment. The cooperation between cell-cell (E-cadherin, CDH1) and cell-ECM (α6 integrin, CD49f) expression and growth factor receptors is highlighted within poorly differentiated human tumors associated with aggressive disease. Cancer-associated fibroblasts are examined for their role in the tumor microenvironment in generating and organizing various growth factors. Cellular structural proteins are potential utility markers for future spatial profiling studies. We also examine the special characteristics of the smooth muscle microenvironment and how invasion by a primary tumor can alter this environment and contribute to tumor escape via cooperation between epithelial and stromal cells. This cooperative state allows the heterogenous tumor clusters to be shaped by various growth factors, co-opt or evade immune system response, adapt from hypoxic to normoxic conditions, adjust to varying energy sources, and survive radiation and chemotherapeutic interventions. Understanding the epithelial-mesenchymal cooperation in early tumor invasive networks holds potential for both identifying early biomarkers of the aggressive transition and identification of novel agents to prevent the epithelial-mesenchymal cooperation phenotype. Epithelial-mesenchymal cooperation is likely to unveil new tumor subtypes to aid in selection of appropriate therapeutic strategies.

Abnormal respiratory progenitors in fibrotic lung injury

Recent advances in single-cell RNA sequencing (scRNA-seq) and epithelium lineage labeling have yielded identification of multiple abnormal epithelial progenitor populations during alveolar type 2 (ATII) cell differentiation into alveolar type 1 (ATI) cells during regenerative lung post-fibrotic injury. These abnormal cells include basaloid/basal-like cells, ATII transition cells, and persistent epithelial progenitors (PEPs). These cells occurred and accumulated during the regeneration of distal airway and alveoli in response to both chronic and acute pulmonary injury. Among the alveolar epithelial progenitors, PEPs express a distinct Krt8+ phenotype that is rarely found in intact alveoli. However, post-injury, the Krt8+ phenotype is seen in dysplastic epithelial cells. Fully understanding the characteristics and functions of these newly found, injury-induced abnormal behavioral epithelial progenitors and the signaling pathways regulating their phenotype could potentially point the way to unique therapeutic targets for fibrosing lung diseases. This review summarizes recent advances in understanding these epithelial progenitors as they relate to uncovering regenerative mechanisms.

An endosome-associated actin network involved in directed apical plasma membrane growth

Membrane trafficking plays many roles in morphogenesis, from bulk membrane provision to targeted delivery of proteins and other cargos. In tracheal terminal cells of the Drosophila respiratory system, transport through late endosomes balances membrane delivery between the basal plasma membrane and the apical membrane, which forms a subcellular tube, but it has been unclear how the direction of growth of the subcellular tube with the overall cell growth is coordinated. We show here that endosomes also organize F-actin. Actin assembles around late endocytic vesicles in the growth cone of the cell, reaching from the tip of the subcellular tube to the leading filopodia of the basal membrane. Preventing nucleation of endosomal actin disturbs the directionality of tube growth, uncoupling it from the direction of cell elongation. Severing actin in this area affects tube integrity. Our findings show a new role for late endosomes in directing morphogenesis by organizing actin, in addition to their known role in membrane and protein trafficking.

Crosstalk between basal extracellular matrix adhesion and building of apical architecture during morphogenesis

Tissues build complex structures like lumens and microvilli to carry out their functions. Most of the mechanisms used to build these structures rely on cells remodelling their apical plasma membranes, which ultimately constitute the specialised compartments. In addition to apical remodelling, these shape changes also depend on the proper attachment of the basal plasma membrane to the extracellular matrix (ECM). The ECM provides cues to establish apicobasal polarity, and it also transduces forces that allow apical remodelling. However, physical crosstalk mechanisms between basal ECM attachment and the apical plasma membrane remain understudied, and the ones described so far are very diverse, which highlights the importance of identifying the general principles. Here, we review apicobasal crosstalk of two well-established models of membrane remodelling taking place during Drosophila melanogaster embryogenesis: amnioserosa cell shape oscillations during dorsal closure and subcellular tube formation in tracheal cells. We discuss how anchoring to the basal ECM affects apical architecture and the mechanisms that mediate these interactions. We analyse this knowledge under the scope of other morphogenetic processes and discuss what aspects of apicobasal crosstalk may represent widespread phenomena and which ones are used to build subsets of specialised compartments.

Cohesive cancer invasion of the biophysical barrier of smooth muscle

Smooth muscle is found around organs in the digestive, respiratory, and reproductive tracts. Cancers arising in the bladder, prostate, stomach, colon, and other sites progress from low-risk disease to high-risk, lethal metastatic disease characterized by tumor invasion into, within, and through the biophysical barrier of smooth muscle. We consider here the unique biophysical properties of smooth muscle and how cohesive clusters of tumor use mechanosensing cell-cell and cell-ECM (extracellular matrix) adhesion receptors to move through a structured muscle and withstand the biophysical forces to reach distant sites. Understanding integrated mechanosensing features within tumor cluster and smooth muscle and potential triggers within adjacent adipose tissue, such as the unique damage-associated molecular pattern protein (DAMP), eNAMPT (extracellular nicotinamide phosphoribosyltransferase), or visfatin, offers an opportunity to prevent the first steps of invasion and metastasis through the structured muscle.

Orchestrating morphogenesis: building the body plan by cell shape changes and movements

During embryonic development, a simple ball of cells re-shapes itself into the elaborate body plan of an animal. This requires dramatic cell shape changes and cell movements, powered by the contractile force generated by actin and myosin linked to the plasma membrane at cell-cell and cell-matrix junctions. Here, we review three morphogenetic events common to most animals: apical constriction, convergent extension and collective cell migration. Using the fruit fly Drosophila as an example, we discuss recent work that has revealed exciting new insights into the molecular mechanisms that allow cells to change shape and move without tearing tissues apart. We also point out parallel events at work in other animals, which suggest that the mechanisms underlying these morphogenetic processes are conserved.

Collagen, stiffness, and adhesion: the evolutionary basis of vertebrate mechanobiology

The emergence of collagen I in vertebrates resulted in a dramatic increase in the stiffness of the extracellular environment, supporting long-range force propagation and the development of low-compliant tissues necessary for the development of vertebrate traits including pressurized circulation and renal filtration. Vertebrates have also evolved integrins that can bind to collagens, resulting in the generation of higher tension and more efficient force transmission in the extracellular matrix. The stiffer environment provides an opportunity for the vertebrates to create new structures such as the stress fibers, new cell types such as endothelial cells, new developmental processes such as neural crest delamination, and new tissue organizations such as the blood-brain barrier. Molecular players found only in vertebrates allow the modification of conserved mechanisms as well as the design of novel strategies that can better serve the physiological needs of the vertebrates. These innovations collectively contribute to novel morphogenetic behaviors and unprecedented increases in the complexities of tissue mechanics and functions.

Integrins Modulate Extracellular Matrix Organization to Control Cell Signaling during Hematopoiesis

During hematopoiesis, progenitor cells receive and interpret a diverse array of regulatory signals from their environment. These signals control the maintenance of the progenitors and regulate the production of mature blood cells. Integrins are well known in vertebrates for their roles in hematopoiesis, particularly in assisting in the migration to, as well as the physical attachment of, progenitors to the niche. However, whether and how integrins are also involved in the signaling mechanisms that control hematopoiesis remains to be resolved. Here, we show that integrins play a key role during fly hematopoiesis in regulating cell signals that control the behavior of hematopoietic progenitors. Integrins can regulate hematopoiesis directly, via focal adhesion kinase (FAK) signaling, and indirectly, by directing extracellular matrix (ECM) assembly and/or maintenance. ECM organization and density controls blood progenitor behavior by modulating multiple signaling pathways, including bone morphogenetic protein (BMP) and Hedgehog (Hh). Furthermore, we show that integrins and the ECM are reduced following infection, which may assist in activating the immune response. Our results provide mechanistic insight into how integrins can shape the signaling environment around hematopoietic progenitors.

Isotropic expansion of external environment induces tissue elongation and collective cell alignment

Cell movement is crucial for morphogenesis in multicellular organisms. Growing embryos or tissues often expand isotropically, i.e., uniformly, in all dimensions. On the surfaces of these expanding environments, which we call "fields," cells are subjected to frictional forces and move passively in response. However, the potential roles of isotropically expanding fields in morphogenetic events have not been investigated well. Our previous mathematical simulations showed that a tissue was elongated on an isotropically expanding field (Imuta et al., 2014). However, the underlying mechanism remains unclarified, and how cells behave during tissue elongation was not investigated. In this study, we mathematically analyzed the effect of isotropically expanding fields using a vertex model, a standard type of multi-cellular model. We found that cells located on fields were elongated along a similar direction each other and exhibited a columnar configuration with nearly single-cell width. Simultaneously, it was confirmed that the cell clusters were also elongated, even though field expansion was absolutely isotropic. We then investigated the mechanism underlying these counterintuitive phenomena. In particular, we asked whether the dynamics of elongation was predominantly determined by the properties of the field, the cell cluster, or both. Theoretical analyses involving simplification of the model revealed that cell clusters have an intrinsic ability to asymmetrically deform, leading to their elongation. Importantly, this ability is effective only under the non-equilibrium conditions provided by field expansion. This may explain the elongation of the notochord, located on the surface of the growing mouse embryo. We established the mechanism underlying tissue elongation induced by isotropically expanding external environments, and its involvement in collective cell alignment with cell elongation, providing key insight into morphogenesis involving multiple adjacent tissues.

The extracellular matrix in development

As the crucial non-cellular component of tissues, the extracellular matrix (ECM) provides both physical support and signaling regulation to cells. Some ECM molecules provide a fibrillar environment around cells, while others provide a sheet-like basement membrane scaffold beneath epithelial cells. In this Review, we focus on recent studies investigating the mechanical, biophysical and signaling cues provided to developing tissues by different types of ECM in a variety of developing organisms. In addition, we discuss how the ECM helps to regulate tissue morphology during embryonic development by governing key elements of cell shape, adhesion, migration and differentiation.

Summary: This Review discusses our current understanding of how the extracellular matrix helps guide developing tissues by influencing cell adhesion, migration, shape and differentiation, emphasizing the biophysical cues it provides.

New perspectives on integrin-dependent adhesions

Integrins are heterodimeric transmembrane receptors that connect the extracellular matrix environment to the actin cytoskeleton via adaptor molecules through assembly of a range of adhesion structures. Recent advances in biochemical, imaging and biophysical methods have enabled a deeper understanding of integrin signalling and their associated regulatory processes. The identification of the consensus integrin-based 'adhesomes' within the last 5 years has defined common core components of adhesion complexes and associated partners. These approaches have also uncovered unexpected adhesion protein behaviour and molecules recruited to adhesion sites that have expanded our understanding of the molecular and physical control of integrin signalling.

Integrin-Mediated Focal Anchorage Drives Epithelial Zippering during Mouse Neural Tube Closure

Epithelial fusion is a key process of morphogenesis by which tissue connectivity is established between adjacent epithelial sheets. A striking and poorly understood feature of this process is "zippering," whereby a fusion point moves directionally along an organ rudiment. Here, we uncover the molecular mechanism underlying zippering during mouse spinal neural tube closure. Fusion is initiated via local activation of integrin β1 and focal anchorage of surface ectoderm cells to a shared point of fibronectin-rich basement membrane, where the neural folds first contact each other. Surface ectoderm cells undergo proximal junction shortening, establishing a transitory semi-rosette-like structure at the zippering point that promotes juxtaposition of cells across the midline enabling fusion propagation. Tissue-specific ablation of integrin β1 abolishes the semi-rosette formation, preventing zippering and causing spina bifida. We propose integrin-mediated anchorage as an evolutionarily conserved mechanism of general relevance for zippering closure of epithelial gaps whose disturbance can produce clinically important birth defects.

Talin Autoinhibition Regulates Cell-ECM Adhesion Dynamics and Wound Healing In Vivo

Cells in multicellular organisms are arranged in complex three-dimensional patterns. This requires both transient and stable adhesions with the extracellular matrix (ECM). Integrin adhesion receptors bind ECM ligands outside the cell and then, by binding the protein talin inside the cell, assemble an adhesion complex connecting to the cytoskeleton. The activity of talin is controlled by several mechanisms, but these have not been well studied in vivo. By generating mice containing the activating point mutation E1770A in talin (Tln1), which disrupts autoinhibition, we show that talin autoinhibition controls cell-ECM adhesion, cell migration, and wound healing in vivo. In particular, blocking autoinhibition gives rise to more mature, stable focal adhesions that exhibit increased integrin activation. Mutant cells also show stronger attachment to ECM and decreased traction force. Overall, these results demonstrate that modulating talin function via autoinhibition is an important mechanism for regulating multiple aspects of integrin-mediated cell-ECM adhesion in vivo.

Cell Adhesion by Integrins

Integrins are heterodimeric cell surface receptors ensuring the mechanical connection between cells and the extracellular matrix. In addition to the anchorage of cells to the extracellular matrix, these receptors have critical functions in intracellular signaling, but are also taking center stage in many physiological and pathological conditions. In this review, we provide some historical, structural, and physiological notes so that the diverse functions of these receptors can be appreciated and put into the context of the emerging field of mechanobiology. We propose that the exciting journey of the exploration of these receptors will continue for at least another new generation of researchers.

Topographic cues of a novel bilayered scaffold modulate dental pulp stem cells differentiation by regulating YAP signalling through cytoskeleton adjustments

Objectives

Topographic cues can modulate morphology and differentiation of mesenchymal stem cells. This study aimed to determine how topographic cues of a novel bilayered poly (lactic‐co‐glycolic acid) (PLGA) scaffold affect osteogenic/odontogenic differentiation of dental pulp stem cells (DPSCs).

Methods

The surface morphology of the scaffolds was visualized by scanning electron microscope, and the surface roughness was measured by profilometry. DPSCs were cultured on each side of the scaffolds. Cell morphology, expression of Yes‐associated protein (YAP) and osteogenic/odontogenic differentiation were analysed by immunohistochemistry, real‐time polymerase chain reaction, and Alizarin Red S staining. In addition, cytochalasin D (CytoD), an F‐actin disruptor, was used to examine the effects of F‐actin on intracellular YAP localisation. Verteporfin, a YAP transcriptional inhibitor, was used to explore the effects of YAP signalling on osteogenic/odontogenic differentiation of DPSCs.

Results

The closed side of our scaffold showed smaller pores and less roughness than the open side. On the closed side, DPSCs exhibited enhanced F‐actin stress fibre alignment, larger spreading area, more elongated appearance, predominant nuclear YAP localization and spontaneous osteogenic differentiation. Inhibition of F‐actin alignments was correlated with nuclear YAP exclusion of DPSCs. Verteporfin restricted YAP localisation to the cytoplasm, down‐regulated expression of early osteogenic/odontogenic markers and inhibited mineralization of DPSCs cultures.

Conclusions

The surface topographic cues changed F‐actin alignment and morphology of DPSCs, which in turn regulated YAP signalling to control osteogenic/odontogenic differentiation.

Extracellular Matrix (ECM) and the Sculpting of Embryonic Tissues

Extracellular matrices (ECMs) are structurally and compositionally diverse networks of collagenous and noncollagenous glycoproteins, glycosaminoglycans, proteoglycans, and associated molecules that together comprise the metazoan matrisome. Proper deposition and assembly of ECM is of profound importance to cell proliferation, survival, and differentiation, and the morphogenesis of tissues and organ systems that define sequential steps in the development of all animals. Importantly, it is now clear that the instructive influence of a particular ECM at various points in development reflects more than a simple summing of component parts; cellular responses also reflect the dynamic assembly and changing topology of embryonic ECM, which in turn affect its biomechanical properties. This review highlights recent advances in understanding how biophysical features attributed to ECM, such as stiffness and viscoelasticity, play important roles in the sculpting of embryonic tissues and the regulation of cell fates. Forces generated within cells and tissues are transmitted both through integrin-based adhesions to ECM, and through cadherin-dependent cell-cell adhesions; the resulting short- and long-range deformations of embryonic tissues drive morphogenesis. This coordinate regulation of cell-ECM and cell-cell adhesive machinery has emerged as a common theme in a variety of developmental processes. In this review we consider select examples in the embryo where ECM is implicated in setting up tissue barriers and boundaries, in resisting pushing or pulling forces, or in constraining or promoting cell and tissue movement. We reflect on how each of these processes contribute to morphogenesis.

Organization of Embryonic Morphogenesis via Mechanical Information

Embryonic organizers establish gradients of diffusible signaling molecules to pattern the surrounding cells. Here, we elucidate an additional mechanism of embryonic organizers that is a secondary consequence of morphogen signaling. Using pharmacological and localized transgenic perturbations, 4D imaging of the zebrafish embryo, systematic analysis of cell motion, and computational modeling, we find that the vertebrate tail organizer orchestrates morphogenesis over distances beyond the range of morphogen signaling. The organizer regulates the rate and coherence of cell motion in the elongating embryo using mechanical information that is transmitted via relay between neighboring cells. This mechanism is similar to a pressure front in granular media and other jammed systems, but in the embryo the mechanical information emerges from self-propelled cell movement and not force transfer between cells. The propagation likely relies upon local biochemical signaling that affects cell contractility, cell adhesion, and/or cell polarity but is independent of transcription and translation.

Decoupling from yolk sac is required for extraembryonic tissue spreading in the scuttle fly Megaselia abdita

Extraembryonic tissues contribute to animal development, which often entails spreading over embryo or yolk. Apart from changes in cell shape, the requirements for this tissue spreading are not well understood. Here, we analyze spreading of the extraembryonic serosa in the scuttle fly Megaselia abdita. The serosa forms from a columnar blastoderm anlage, becomes a squamous epithelium, and eventually spreads over the embryo proper. We describe the dynamics of this process in long-term, whole-embryo time-lapse recordings, demonstrating that free serosa spreading is preceded by a prolonged pause in tissue expansion. Closer examination of this pause reveals mechanical coupling to the underlying yolk sac, which is later released. We find mechanical coupling prolonged and serosa spreading impaired after knockdown of M. abdita Matrix metalloprotease 1. We conclude that tissue–tissue interactions provide a critical functional element to constrain spreading epithelia.

Principles of Actomyosin Regulation In Vivo

The actomyosin cytoskeleton is responsible for most force-driven processes in cells and tissues. How it assembles into the necessary structures at the right time and place is an important question. Here, we focus on molecular mechanisms of actomyosin regulation recently elucidated in animal models, and highlight several common principles that emerge. The architecture of the actomyosin network - an important determinant of its function - results from actin polymerization, crosslinking and turnover, localized myosin activation, and contractility-driven self-organization. Spatiotemporal regulation is achieved by tissue-specific expression and subcellular localization of Rho GTPase regulators. Subcellular anchor points of actomyosin structures control the outcome of their contraction, and molecular feedback mechanisms dictate whether they are transient, cyclic, or persistent.

Tissue mechanics regulates form, function, and dysfunction

Morphogenesis encompasses the developmental processes that reorganize groups of cells into functional tissues and organs. The spatiotemporal patterning of individual cell behaviors is influenced by how cells perceive and respond to mechanical forces, and determines final tissue architecture. Here, we review recent work examining the physical mechanisms of tissue morphogenesis in vertebrate and invertebrate models, discuss how epithelial cells employ contractility to induce global changes that lead to tissue folding, and describe how tissue form itself regulates cell behavior. We then highlight novel tools to recapitulate these processes in engineered tissues.

Three-dimensional forces beyond actomyosin contraction: lessons from fly epithelial deformation

Epithelium undergoes complex deformations during morphogenesis. Many of these deformations rely on the remodelling of apical cell junctions by actomyosin-based contractile force and this has been a major research interest for many years. Recent studies have shown that cells can use additional mechanisms that are not directly driven by actomyosin contractility to alter cell shape and movement, in three-dimensional (3D) space and time. In this review, we focus on a number of these mechanisms, including basolateral cellular protrusion, lateral shift of cell polarity, cytoplasmic flow, regulation of cell volume, and force transmission between cell-cell adhesion and cell-extracellular matrix adhesion, and describe how they underlie Drosophila epithelia deformations.

Cell Sheet Morphogenesis: Dorsal Closure in Drosophila melanogaster as a Model System

Dorsal closure is a key process during Drosophila morphogenesis that models cell sheet movements in chordates, including neural tube closure, palate formation, and wound healing. Closure occurs midway through embryogenesis and entails circumferential elongation of lateral epidermal cell sheets that close a dorsal hole filled with amnioserosa cells. Signaling pathways regulate the function of cellular structures and processes, including Actomyosin and microtubule cytoskeletons, cell-cell/cell-matrix adhesion complexes, and endocytosis/vesicle trafficking. These orchestrate complex shape changes and movements that entail interactions between five distinct cell types. Genetic and laser perturbation studies establish that closure is robust, resilient, and the consequence of redundancy that contributes to four distinct biophysical processes: contraction of the amnioserosa, contraction of supracellular Actomyosin cables, elongation (stretching?) of the lateral epidermis, and zipping together of two converging cell sheets. What triggers closure and what the emergent properties are that give rise to its extraordinary resilience and fidelity remain key, extant questions.

Vangl2 disruption alters the biomechanics of late spinal neurulation leading to spina bifida in mouse embryos

Human mutations in the planar cell polarity component VANGL2 are associated with the neural tube defect spina bifida. Homozygous Vangl2 mutation in mice prevents initiation of neural tube closure, precluding analysis of its subsequent roles in neurulation. Spinal neurulation involves rostral-to-caudal ‘zippering’ until completion of closure is imminent, when a caudal-to-rostral closure point, ‘Closure 5’, arises at the caudal-most extremity of the posterior neuropore (PNP). Here, we used Grhl3^Cre to delete Vangl2 in the surface ectoderm (SE) throughout neurulation and in an increasing proportion of PNP neuroepithelial cells at late neurulation stages. This deletion impaired PNP closure after the ∼25-somite stage and resulted in caudal spina bifida in 67% of Grhl3^Cre/+Vangl2^Fl/Fl embryos. In the dorsal SE, Vangl2 deletion diminished rostrocaudal cell body orientation, but not directional polarisation of cell divisions. In the PNP, Vangl2 disruption diminished mediolateral polarisation of apical neuroepithelial F-actin profiles and resulted in eversion of the caudal PNP. This eversion prevented elevation of the caudal PNP neural folds, which in control embryos is associated with formation of Closure 5 around the 25-somite stage. Closure 5 formation in control embryos is associated with a reduction in mechanical stress withstood at the main zippering point, as inferred from the magnitude of neural fold separation following zippering point laser ablation. This stress accommodation did not happen in Vangl2-disrupted embryos. Thus, disruption of Vangl2-dependent planar-polarised processes in the PNP neuroepithelium and SE preclude zippering point biomechanical accommodation associated with Closure 5 formation at the completion of PNP closure.

Summary: Disruption of Vangl2-dependent planar-polarised processes in the posterior neuropore (PNP) neuroepithelium and surface ectoderm preclude zippering point biomechanical accommodation associated with Closure 5 formation at the completion of PNP closure.

Predicting the Functional Impact of CDH1 Missense Mutations in Hereditary Diffuse Gastric Cancer

The role of E-cadherin in Hereditary Diffuse Gastric Cancer (HDGC) is unequivocal. Germline alterations in its encoding gene (CDH1) are causative of HDGC and occur in about 40% of patients. Importantly, while in most cases CDH1 alterations result in the complete loss of E-cadherin associated with a well-established clinical impact, in about 20% of cases the mutations are of the missense type. The latter are of particular concern in terms of genetic counselling and clinical management, as the effect of the sequence variants in E-cadherin function is not predictable. If a deleterious variant is identified, prophylactic surgery could be recommended. Therefore, over the last few years, intensive research has focused on evaluating the functional consequences of CDH1 missense variants and in assessing E-cadherin pathogenicity. In that context, our group has contributed to better characterize CDH1 germline missense variants and is now considered a worldwide reference centre. In this review, we highlight the state of the art methodologies to categorize CDH1 variants, as neutral or deleterious. This information is subsequently integrated with clinical data for genetic counseling and management of CDH1 variant carriers.

Epithelial rotation is preceded by planar symmetry breaking of actomyosin and protects epithelial tissue from cell deformations

Symmetry breaking is involved in many developmental processes that form bodies and organs. One of them is the epithelial rotation of developing tubular and acinar organs. However, how epithelial cells move, how they break symmetry to define their common direction, and what function rotational epithelial motions have remains elusive. Here, we identify a dynamic actomyosin network that breaks symmetry at the basal surface of the Drosophila follicle epithelium of acinar-like primitive organs, called egg chambers, and may represent a candidate force-generation mechanism that underlies the unidirectional motion of this epithelial tissue. We provide evidence that the atypical cadherin Fat2, a key planar cell polarity regulator in Drosophila oogenesis, directs and orchestrates transmission of the intracellular actomyosin asymmetry cue onto a tissue plane in order to break planar actomyosin symmetry, facilitate epithelial rotation in the opposite direction, and direct the elongation of follicle cells. In contrast, loss of this rotational motion results in anisotropic non-muscle Myosin II pulses that are disorganized in plane and causes cell deformations in the epithelial tissue of Drosophila eggs. Our work demonstrates that atypical cadherins play an important role in the control of symmetry breaking of cellular mechanics in order to facilitate tissue motion and model epithelial tissue. We propose that their functions may be evolutionarily conserved in tubular/acinar vertebrate organs.

Movement of epithelial tissues is essential for organ and body formation as well as function. To facilitate epithelial movements, cells need an internal or external source of mechanical force and a collective decision in which direction to move. However, little is known about the underlying mechanism of collective cell movement in living and moving epithelial tissues. Using high-speed confocal imaging of rotating follicle epithelia in acinar-like Drosophila egg chambers, we find that individual cells polarize their actomyosin network, a potent force-generating source, at their basal surface. We show that the atypical cadherin Fat2, a key regulator of planar cell polarity in Drosophila oogenesis, unifies and amplifies the polarized non-muscle Myosin II of individual follicle cells to break the symmetry of actomyosin contractility at the epithelial level. We propose that this is essential to facilitate epithelial rotation, and thereby directed cell elongation, at the basal surface of follicle cells. In contrast, a lack of unidirectional actomyosin contractility results in disrupted non-muscle Myosin II polarity within follicle cells and causes asynchronous Myosin II pulses that deform follicle cells. This demonstrates the critical function of Fat2, in the planar symmetry breaking of actomyosin, in epithelial motility, and potentially in organ development.

Sculpting epithelia with planar polarized actomyosin networks: Principles from Drosophila

Drosophila research has revealed how planar polarized actomyosin networks affect various types of tissue morphogenesis. The networks are positioned by both tissue-wide patterning factors (including Even-skipped, Runt, Engrailed, Invected, Hedgehog, Notch, Wingless, Epidermal Growth Factor, Jun N-terminal kinase, Sex combs reduced and Fork head) and local receptor complexes (including Echinoid, Crumbs and Toll receptors). Networks with differing super-structure and contractile output have been discovered. Their contractility can affect individual cells or can be coordinated across groups of cells, and such contractility can drive or resist physical change. For what seem to be simple tissue changes, multiple types of actomyosin networks can contribute, acting together as contractile elements or braces within the developing structure. This review discusses the positioning and effects of planar polarized actomyosin networks for a number of developmental events in Drosophila, including germband extension, dorsal closure, head involution, tracheal pit formation, salivary gland development, imaginal disc boundary formation, and tissue rotation of the male genitalia and the egg chamber.

Actomyosin contractility and collective migration: may the force be with you

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Collective migration relies on the ability of a multicellular co-ordinated unit to efficiently respond to physical changes in their surrounding matrix.

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Conversely, migrating cohorts physically alter their microenvironment using mechanical forces.

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During collective migration, actomyosin contractility acts as a central hub coordinating mechanosensing and mechanotransduction responses.

Collective cell migration is essential during physiological processes such as development or wound healing and in pathological conditions such as cancer dissemination. Cells migrating within multicellular tissues experiment different forces which play an intricate role during tissue formation, development and maintenance. How cells are able to respond to these forces depends largely on how they interact with the extracellular matrix. In this review, we focus on mechanics and mechanotransduction in collective migration. In particular, we discuss current knowledge on how cells integrate mechanical signals during collective migration and we highlight actomyosin contractility as a central hub coordinating mechanosensing and mechanotransduction responses.

Shape of my heart: Cell-cell adhesion and cytoskeletal dynamics during Drosophila cardiac morphogenesis

The fruit fly Drosophila melanogaster has recently emerged as an excellent system to investigate the genetics of cardiovascular development and disease. Drosophila provides an inexpensive and genetically-tractable in vivo system with a large number of conserved features. In addition, the Drosophila embryo is transparent, and thus amenable to time-lapse fluorescence microscopy, as well as biophysical and pharmacological manipulations. One of the conserved aspects of heart development from Drosophila to humans is the initial assembly of a tube. Here, we review the cellular behaviours and molecular dynamics important for the initial steps of heart morphogenesis in Drosophila, with particular emphasis on the cell-cell adhesion and cytoskeletal networks that cardiac precursors use to move, coordinate their migration, interact with other tissues and eventually sculpt a beating heart.

Cell-cell and cell-extracellular matrix adhesions cooperate to organize actomyosin networks and maintain force transmission during dorsal closure

Cell–extracellular matrix (ECM) and cell–cell adhesion are interdependent during dorsal closure in the fly. Cell–ECM adhesion is required for normal myosin dynamics and organization of both cell–cell adhesions and actin networks during dorsal closure. Loss of cell–cell adhesion affects cell–ECM adhesion and tissue biomechanics.

Tissue morphogenesis relies on the coordinated action of actin networks, cell–cell adhesions, and cell–extracellular matrix (ECM) adhesions. Such coordination can be achieved through cross-talk between cell–cell and cell–ECM adhesions. Drosophila dorsal closure (DC), a morphogenetic process in which an extraembryonic tissue called the amnioserosa contracts and ingresses to close a discontinuity in the dorsal epidermis of the embryo, requires both cell–cell and cell–ECM adhesions. However, whether the functions of these two types of adhesions are coordinated during DC is not known. Here we analyzed possible interdependence between cell–cell and cell–ECM adhesions during DC and its effect on the actomyosin network. We find that loss of cell–ECM adhesion results in aberrant distributions of cadherin-mediated adhesions and actin networks in the amnioserosa and subsequent disruption of myosin recruitment and dynamics. Moreover, loss of cell–cell adhesion caused up-regulation of cell–ECM adhesion, leading to reduced cell deformation and force transmission across amnioserosa cells. Our results show how interdependence between cell–cell and cell–ECM adhesions is important in regulating cell behaviors, force generation, and force transmission critical for tissue morphogenesis.