Mechanobiology of collective cell behaviours

Label-free optical mapping for large-area biomechanical dynamics of multicellular systems

Mapping cellular activities over large areas is crucial for understanding the collective behaviors of multicellular systems. Biomechanical properties, such as cellular traction forces, serve as critical regulators of physiological states and molecular configurations. However, existing technologies for mapping large-area biomechanical dynamics, which arise from changes in cellular traction forces, are limited by their small field of view and scanning-based nature. To address these limitations, we propose a novel platform that utilizes a vast number of optical diffractive elements to profile large-area biomechanical dynamics. This platform achieves a field of view of 10.6 mm × 10.6 mm, a three-order-of-magnitude improvement over traditional traction force microscopy. Transient mechanical waves generated by monolayer neonatal rat ventricular myocytes were captured with high spatiotemporal resolution (130 fps and 20 μm for temporal and spatial resolution, respectively). Furthermore, its label-free nature allows for long-term observations extended to a week, with minimal disruption to cellular functions. Finally, simultaneous measurements of calcium ion concentrations and biomechanical dynamics are demonstrated.

High-LET Proton Irradiation Significantly Alters the Clonogenic and Tumorigenic Potential of Human Breast Cancer Cell Lines In Vitro and In Vivo

BACKGROUND

The implementation of proton beam irradiation (PBI) for breast cancer (BC) treatment is rapidly advancing due to its enhanced target coverage and reduced toxicities to organs at risk. However, the effects of PBI can vary depending on the cell type. This study aimed to explore the effects of PBI on two BC cell lines, MCF7 and MDA-MB-231.

METHODS

The relative biological effectiveness (RBE) of PBI was assessed using a clonogenic assay. DNA double-strand break (DSB) repair, epithelial-mesenchymal transition (EMT), and filamentous actin (F-actin) were evaluated using immunofluorescence analysis. The extent of entosis and the senescence-associated β-galactosidase (SA-β-gal) activity were estimated by cytochemistry analysis. The influence of the extracellular matrix was evaluated by cultivating cells in both adherent two-dimensional (2D) environments and within 3D fibrin gels of varying stiffness. The metastatic propensity of cells was investigated using migration tests and the cell encapsulation of carboxylate-modified fluorescent nanoparticles. The comparative tumorigenic potential of cells was investigated using an in vivo model of the chick embryo chorioallantoic membrane (CAM).

RESULTS

PBI demonstrated superior efficacy in eliminating MCF7 and MDA-MB-231 cells with RBE 1.7 and 1.75, respectively. Following PBI, MDA-MB-231 cells exhibited significantly lower clonogenic survival compared to MCF7, which was accompanied by the accumulation of phosphorylated histone H2AX (γH2AX), p53-binding protein 1 (53BP1) and Rad51 foci of DNA DSBs repair proteins. After surviving 7 days post-PBI, MCF7 cells exhibited 2.5-fold higher levels of the senescence phenotype and entosis compared to the MDA-MB-231 offspring. Both PBI-survived cell lines had greater capability for 2D collective migration, but their metastatic potential was significantly reduced. A significant influence of extracellular matrix stiffness on the correlation between F-actin expression in PBI-survived cells-an indicator of cell stiffness-and their ability to uptake nanoparticles, a trait associated with metastatic potential, was observed. PBI-survived MDA-MB-231RP subline exhibited a hybrid EMT phenotype and a 70% reduction in tumor growth in the in vivo model of the chick embryo CAM. In contrast, PBI-survived MCF7RP cells exhibit mesenchymal-to-epithelial transition (MET)-like features, and their in vivo tumor growth increased by 66% compared to parental cells.

CONCLUSIONS

PBI triggers various cellular responses in different BC cell lines, influencing tumor growth through mechanisms like DNA damage repair, stress-induced premature senescence (SIPS), and alterations in the stiffness of tumor cell membranes. Our insights into entosis and the effect of extracellular matrix stiffness on metastatic propensity (nanoparticle uptake) enhance the understanding of the role of PBI in BC cells, emphasizing the need for more research to optimize its therapeutic application.

Flocking and giant fluctuations in epithelial active solids

The collective motion of epithelial cells is a fundamental biological process which plays a significant role in embryogenesis, wound healing, and tumor metastasis. While it has been broadly investigated for over a decade both in vivo and in vitro, large-scale coherent flocking phases remain underexplored and have so far been mostly described as fluid. In this work, we report an additional mode of large-scale collective motion for different epithelial cell types in vitro with distinctive features. By tracking individual cells, we show that cells move over long time scales coherently not as a fluid, but as a polar elastic solid with negligible cell rearrangements. Our analysis reveals that this solid flocking phase exhibits signatures of long-range polar order, accompanying with scale-free correlations of the transverse component of velocity fluctuations, anomalously large density fluctuations, and shear waves. Based on a general theory of active polar solids, we argue that these features result from massless orientational Goldstone mode, which, in contrast to polar fluids where they are generic, require the decoupling of global rotations of the polarity and in-plane elastic deformations in polar solids. We theoretically show and consistently observe in experiments that the fluctuations of elastic deformations diverge for large system sizes in such polar active solid phases, leading eventually to rupture and thus potentially loss of tissue integrity at large scales.

Substrate stress relaxation regulates monolayer fluidity and leader cell formation for collectively migrating epithelia

Collective migration of epithelial tissues is a critical feature of developmental morphogenesis and tissue homeostasis. Coherent motion of cell collectives requires large-scale coordination of motion and force generation and is influenced by mechanical properties of the underlying substrate. While tissue viscoelasticity is a ubiquitous feature of biological tissues, its role in mediating collective cell migration is unclear. Here, we have investigated the impact of substrate stress relaxation on the migration of micropatterned epithelial monolayers. Epithelial monolayers exhibit faster collective migration on viscoelastic alginate substrates with slower relaxation timescales, which are more elastic, relative to substrates with faster stress relaxation, which exhibit more viscous loss. Faster migration on slow-relaxing substrates is associated with reduced substrate deformation, greater monolayer fluidity, and enhanced leader cell formation. In contrast, monolayers on fast-relaxing substrates generate substantial substrate deformations and are more jammed within the bulk, with reduced formation of transient lamellipodial protrusions past the monolayer edge leading to slower overall expansion. This work reveals features of collective epithelial dynamics on soft, viscoelastic materials and adds to our understanding of cell-substrate interactions at the tissue scale.

Interface morphodynamics in living tissues

Interfaces between distinct tissues or between tissues and environments are common in multicellular organisms. The evolution and stability of these interfaces are essential for tissue development, and their dysfunction can lead to diseases such as cancer. Mounting efforts, either theoretical or experimental, have been devoted to uncovering the morphodynamics of tissue interfaces. Here, we review the recent progress of studies on interface morphodynamics. The regulatory mechanisms governing interface evolution are dissected, with a focus on adhesion, cortical tension, cell activity, extracellular matrix, and microenvironment. We examine the methodologies used to study morphodynamics, emphasizing the characteristics of experimental techniques and theoretical models. Finally, we explore the broader implications of interface morphodynamics in tissue morphogenesis and diseases, offering a comprehensive perspective on this rapidly developing field.

Neuromorphic algorithms for brain implants: a review

Neuromorphic computing technologies are about to change modern computing, yet most work thus far has emphasized hardware development. This review focuses on the latest progress in algorithmic advances specifically for potential use in brain implants. We discuss current algorithms and emerging neurocomputational models that, when implemented on neuromorphic hardware, could match or surpass traditional methods in efficiency. Our aim is to inspire the creation and deployment of models that not only enhance computational performance for implants but also serve broader fields like medical diagnostics and robotics inspiring next generations of neural implants.

Hierarchically porous 3D-printed ceramic scaffolds for bone tissue engineering

Sacrificial templating offers the ability to create interconnected pores within 3D printed filaments and to control pore morphology. Beta-tricalcium phosphate (TCP) bone tissue engineering (BTE) scaffolds were fabricated with multiscale porosity: (i) macropores from direct ink writing (DIW, a material extrusion 3D printing technique), (ii) micropores from oil templating, and (iii) smaller micropores from partial sintering. The hierarchically porous scaffolds possessed a total porosity of 58-70 %, comprising 54-63 % interconnected open pores. The in vitro results demonstrated that scaffolds with macroporosity promoted human osteoblast growth more than scaffolds with only microporosity. The elongated pores from the capillary suspension filament microstructure induced greater cell spreading than the sphere-like pores from the emulsion. Overall, the hierarchically porous scaffold with capillary suspension TCP filaments provided a superior microenvironment for significantly higher cell viability and proliferation than the other scaffolds, including a poly(ε-caprolactone) (PCL) control, a material currently used clinically as porous BTE scaffolds. The cellular response was further enhanced when macropore size was in the range of 570-590 μm. Therefore, the hierarchically porous scaffolds in this study are promising as BTE scaffolds, and the reported process of DIW of oil-templated colloidal pastes is a feasible strategy with potential for further customization.

Regulation of cell migration by extracellular matrix mechanics at a glance

Cell migration occurs throughout development, tissue homeostasis and regeneration, as well as in diseases such as cancer. Cells migrate along two-dimensional (2D) surfaces or interfaces, within microtracks, or in confining three-dimensional (3D) extracellular matrices. Although the basic mechanisms of 2D migration are known, recent studies have elucidated unexpected migration behaviors associated with more complex substrates and have provided insights into their underlying molecular mechanisms. Studies using engineered biomaterials for 3D culture and microfabricated channels to replicate cell confinement observed in vivo have revealed distinct modes of migration. Across these contexts, the mechanical features of the surrounding microenvironment have emerged as major regulators of migration. In this Cell Science at a Glance article and the accompanying poster, we describe physiological contexts wherein 2D and 3D cell migration are essential, report how mechanical properties of the microenvironment regulate individual and collective cell migration, and review the mechanisms mediating these diverse modes of cell migration.

Tissue Active Matter: Integrating Mechanics and Signaling into Dynamical Models

The importance of physical forces in the morphogenesis, homeostatic function, and pathological dysfunction of multicellular tissues is being increasingly characterized, both theoretically and experimentally. Analogies between biological systems and inert materials such as foams, gels, and liquid crystals have provided striking insights into the core design principles underlying multicellular organization. However, these connections can seem surprising given that a key feature of multicellular systems is their ability to constantly consume energy, providing an active origin for the forces that they produce. Key emerging questions are, therefore, to understand whether and how this activity grants tissues novel properties that do not have counterparts in classical materials, as well as their consequences for biological function. Here, we review recent discoveries at the intersection of active matter and tissue biology, with an emphasis on how modeling and experiments can be combined to understand the dynamics of multicellular systems. These approaches suggest that a number of key biological tissue-scale phenomena, such as morphogenetic shape changes, collective migration, or fate decisions, share unifying design principles that can be described by physical models of tissue active matter.

BMP-dependent patterning of ectoderm tissue material properties modulates lateral mesendoderm cell migration during early zebrafish gastrulation

Cell migration is a fundamental process during embryonic development. Most studies in vivo have focused on the migration of cells using the extracellular matrix (ECM) as their substrate for migration. In contrast, much less is known about how cells migrate on other cells, as found in early embryos when the ECM has not yet formed. Here, we show that lateral mesendoderm (LME) cells in the early zebrafish gastrula use the ectoderm as their substrate for migration. We show that the lateral ectoderm is permissive for the animal-pole-directed migration of LME cells, while the ectoderm at the animal pole halts it. These differences in permissiveness depend on the lateral ectoderm being more cohesive than the animal ectoderm, a property controlled by bone morphogenetic protein (BMP) signaling within the ectoderm. Collectively, these findings identify ectoderm tissue cohesion as one critical factor in regulating LME migration during zebrafish gastrulation.

Force transmission is a master regulator of mechanical cell competition

Cell competition is a tissue surveillance mechanism for eliminating unwanted cells, being indispensable in development, infection and tumourigenesis. Although studies have established the role of biochemical mechanisms in this process, due to challenges in measuring forces in these systems, how mechanical forces determine the competition outcome remains unclear. Here we report a form of cell competition that is regulated by differences in force transmission capabilities, selecting for cell types with stronger intercellular adhesion. Direct force measurements in ex vivo tissues and different cell lines reveal that there is an increased mechanical activity at the interface between two competing cell types, which can lead to large stress fluctuations resulting in upward forces and cell elimination. We show how a winning cell type endowed with a stronger intercellular adhesion exhibits higher resistance to elimination and benefiting from efficient force transmission to the neighbouring cells. This cell elimination mechanism could have broad implications for keeping the strong force transmission ability for maintaining tissue boundaries and cell invasion pathology.

Evidence of universal conformal invariance in living biological matter

The emergent dynamics of collective cellular movement are typically thought to depend on how cells interact with one another and the mechanisms used to drive motility, both of which exhibit remarkable diversity across different biological systems. Here we report experimental evidence of a universal feature in the patterns of flow that spontaneously emerge in groups of collectively moving cells. Specifically, we demonstrate that the flows generated by collectively moving dog kidney cells, human breast cancer cells and two different strains of pathogenic bacteria exhibit robust conformal invariance. We also show that the precise form of invariance in all four systems is described by the Schramm-Loewner evolution-a family of planar curves defined by a single parameter-and belongs to the percolation universality class. The presence of universal conformal invariance reveals that the macroscopic features of living biological matter exhibit universal translational, rotational and scale symmetries that are independent of the microscopic properties of its constituents. Our results show that flow patterns generated by different systems are highly conserved and that biological systems can be used to experimentally test predictions from the theories for conformally invariant structures.

Metareview: a survey of active matter reviews

In the past years, the amount of research on active matter has grown extremely rapidly, a fact that is reflected in particular by the existence of more than 1000 reviews on this topic. Moreover, the field has become very diverse, ranging from theoretical studies of the statistical mechanics of active particles to applied work on medical applications of microrobots and from biological systems to artificial swimmers. This makes it very difficult to get an overview over the field as a whole. Here, we provide such an overview in the form of a metareview article that surveys the existing review articles and books on active matter. Thereby, this article provides a useful starting point for finding literature about a specific topic.

Atomic Force Microscopy: A Versatile Tool in Cancer Research

The implementation of novel analytic methodologies in cancer and biomedical research has enabled the quantification of parameters that were previously disregarded only a few decades ago. A notable example of this paradigm shift is the widespread integration of atomic force microscopy (AFM) into biomedical laboratories, significantly advancing our understanding of cancer cell biology and treatment response. AFM allows for the meticulous monitoring of different parameters at the molecular and nanoscale levels, encompassing critical aspects such as cell morphology, roughness, adhesion, stiffness, and elasticity. These parameters can be systematically investigated in correlation with specific cell treatment, providing important insights into morpho-mechanical properties during normal and treated conditions. The resolution of this system holds the potential for its systematic adoption in clinics; its application could produce useful diagnostic information regarding the aggressiveness of cancer and the efficacy of treatment. This review endeavors to analyze the current literature, underscoring the pivotal role of AFM in biomedical research, especially in cancer cases, while also contemplating its prospective application in a clinical context.

DNA-based Precision Tools to Probe and Program Mechanobiology and Organ Engineering

DNA nanotechnology represents an innovative discipline that combines nanotechnology with biotechnology. It exploits the distinctive characteristics of deoxyribonucleic acid (DNA) to create nanoscale structures and devices with remarkable accuracy and functionality. Researchers may create complex nanostructures with precision and specialized functions using DNA's innate stability, adaptability, and capacity to self-assemble through complementary base-pairing interactions. Integrating multiple disciplines, known as nanobiotechnology, allows the production of sophisticated nanodevices with a broad range of applications. These include precise drug delivery systems, extremely sensitive biosensors, and the construction of intricate tissue scaffolds for regenerative medicine. Moreover, combining DNA nanotechnology with mechanobiology provides a new understanding of how small-scale mechanical stresses and molecular interactions affect cellular activity and tissue development. DNA nanotechnology has the potential to revolutionize molecular diagnostics, tissue engineering, and organ regeneration. This could lead to enormous improvements in biomedicine. This review emphasizes the most recent developments in DNA nanotechnology, explicitly highlighting its significant influence on mechanobiology and its growing involvement in organ engineering. It provides an extensive overview of present trends, obstacles, and future prospects in this fast-progressing area.

Active Nematics Reinforce the Ratchet Flow in Dense Environments Without Jamming

The past decade witnessed a surge in discoveries where biological systems, such as bacteria or living cells, inherently portray active polar or nematic behavior: they prefer to align with each other and form local order during migration. Although the underlying mechanisms remain unclear, utilizing their physical properties to achieve controllable cell-layer transport will be of fundamental importance. In this study, the ratchet effect is harnessed to control the collective motion of neural progenitor cells (NPCs) in vitro. NPCs travel back-and-forth and do not specify head or tail, and therefore regarded as nematics alike liquid crystals. Ratchet and splay-shaped confinements are crafted to modulate collective cell dynamics in dense environments, while jamming is not explicitly spotted. The adaptation of an agent-based simulation further revealed how the ratchet's asymmetry and active forces from nematic order synergistically reinforce the directional cell flow. These findings provide insights into topotaxis in cell populations when restricted to crowded 2D ratchets and the mechanisms that regulate collective behavior of the cells.

In vitro regulation of collective cell migration: Understanding the role of physical and chemical microenvironments

Collective cell migration is the primary mode of cellular movement during embryonic morphogenesis, tissue repair and regeneration, and cancer invasion. Distinct from single-cell migration, collective cell migration involves complex intercellular signaling cascades and force transmission. Consequently, cell collectives exhibit intricate and diverse migration patterns under the influence of the microenvironment in vivo. Investigating the patterns and mechanisms of collective cell migration within complex environmental factors in vitro is essential for elucidating collective cell migration in vivo. This review elucidates the influence of physical and chemical factors in vitro microenvironment on the migration patterns and efficiency of cell collectives, thereby enhancing our comprehension of the phenomenon. Furthermore, we concisely present the effects of characteristic properties of common biomaterials on collective cell migration during tissue repair and regeneration, as well as the features and applications of tumor models of different dimensions (2D substrate or 3D substrate) in vitro. Finally, we highlight the challenges facing the research of collective cell migration behaviors in vitro microenvironment and propose that modulating collective cell migration may represent a potential strategy to promote tissue repair and regeneration and to control tumor invasion and metastasis.

Mechano-Responsive Biomaterials for Bone Organoid Construction

Mechanical force is essential for bone development, bone homeostasis, and bone fracture healing. In the past few decades, various biomaterials have been developed to provide mechanical signals that mimic the natural bone microenvironment, thereby promoting bone regeneration. Bone organoids, emerging as a novel research approach, are 3D micro-bone tissues that possess the ability to self-renew and self-organize, exhibiting biomimetic spatial characteristics. Incorporating mechano-responsive biomaterials in the construction of bone organoids presents a promising avenue for simulating the mechanical bone microenvironment. Therefore, this review commences by elucidating the impact of mechanical force on bone health, encompassing both cellular interactions and alterations in bone structure. Furthermore, the most recent applications of mechano-responsive biomaterials within the realm of bone tissue engineering are highlighted. Three different types of mechano-responsive biomaterials are introduced with a focus on their responsive mechanisms, construction strategies, and efficacy in facilitating bone regeneration. Based on a comprehensive overview, the prospective utilization and future challenges of mechano-responsive biomaterials in the construction of bone organoids are discussed. As bone organoid technology advances, these biomaterials are poised to become powerful tools in bone regeneration.

Wnt signaling modulates mechanotransduction in the epidermis to drive hair follicle regeneration

Most wounds form scars without hair follicles. However, in the wound-induced hair neogenesis (WIHN) model of skin regeneration, wounds regenerate hair follicles if tissue rigidity is optimal. Although WIHN depends on Wnt signaling, whether Wnt performs a mechanoregulatory role that contributes to regeneration remains uncharacterized. Here, we demonstrate that Wnt signaling affects mechanosensitivity at both cellular and tissue levels to drive WIHN. Atomic force microscopy revealed an attenuated substrate rigidity response in epidermal but not dermal cells of healing wounds. Super-resolution microscopy and nanoneedle probing of intracellular compartments in live human keratinocytes revealed that Wnt-induced chromatin remodeling triggers a 10-fold drop in nuclear rigidity without jeopardizing the nucleocytoskeletal mechanical coupling. Mechanistically, Wnt signaling orchestrated a massive reorganization of actin architecture and recruited adherens junctions to generate a mechanical syncytium-a cohesive contractile unit with superior capacity for force coordination and collective durotaxis. Collectively, our findings unveil Wnt signaling's mechanoregulatory role that manipulates the machinery of mechanotransduction to drive regeneration.

Geometrically constrained cytoskeletal reorganisation modulates DNA nanostructures uptake

DNA nanostructures (DNs) have gained popularity in various biomedical applications due to their unique properties, including structural programmability, ease of synthesis and functionalization, and low cytotoxicity. Effective utilization of DNs in biomedical applications requires a fundamental understanding of their interactions with living cells and the mechanics of cellular uptake. Current knowledge primarily focuses on how the physicochemical properties of DNs, such as mass, shape, size, and surface functionalization, affect uptake efficacy. However, the role of cellular mechanics and morphology in DN uptake remains largely unexplored. In this work, we show that cells subjected to geometric constraints remodel their actin cytoskeleton, resulting in differential mechanical force generation that facilitates DN uptake. The length, number, and orientation of F-actin fibers are influenced by these constraints, leading to distinct mechanophenotypes. Overall, DN uptake is governed by F-actin forces arising from filament reorganisation under geometric constraints. These results underscore the importance of actin dynamics in the cellular uptake of DNs and suggest that leveraging geometric constraints to induce specific cell morphology adaptations could enhance the uptake of therapeutically designed DNs.

Co-zorbs: Motile, multispecies biofilms aid transport of diverse bacterial species

Biofilms are three-dimensional structures containing one or more bacterial species embedded in extracellular polymeric substances. Although most biofilms are stationary, Flavobacterium johnsoniae forms a motile spherical biofilm called a zorb, which is propelled by its base cells and contains a polysaccharide core. Here, we report the formation of spatially organized, motile, multispecies biofilms, designated "co-zorbs," that are distinguished by a core-shell structure. F. johnsoniae forms zorbs whose cells collect other bacterial species and transport them to the zorb core, forming a co-zorb. Live imaging revealed that co-zorbs also form in zebrafish, thereby demonstrating a different type of bacterial movement in vivo. This finding opens different avenues for understanding community behaviors, the role of biofilms in bulk bacterial transport, and collective strategies for microbial success in various environments.

Spatiotemporal dissection of collective cell migration and tissue morphogenesis during development by optogenetics

Collective cell migration and tissue morphogenesis play a variety of important roles in the development of many species. Tissue morphogenesis often generates mechanical forces that alter cell shapes and arrangements, resembling collective cell migration-like behaviors. Genetic methods have been widely used to study collective cell migration and its like behavior, advancing our understanding of these processes during development. However, a growing body of research shows that collective cell migration during development is not a simple behavior but is often combined with other cellular and tissue processes. In addition, different surrounding environments can also influence migrating cells, further complicating collective cell migration during development. Due to the complexity of developmental processes and tissues, traditional genetic approaches often encounter challenges and limitations. Thus, some methods with spatiotemporal control become urgent in dissecting collective cell migration and tissue morphogenesis during development. Optogenetics is a method that combines optics and genetics, providing a perfect strategy for spatiotemporally controlling corresponding protein activity in subcellular, cellular or tissue levels. In this review, we introduce the basic mechanisms underlying different optogenetic tools. Then, we demonstrate how optogenetic methods have been applied in vivo to dissect collective cell migration and tissue morphogenesis during development. Additionally, we describe some promising optogenetic approaches for advancing this field. Together, this review will guide and facilitate future studies of collective cell migration in vivo and tissue morphogenesis by optogenetics.

Advancements in Microphysiological systems: Exploring organoids and organ-on-a-chip technologies in drug development -focus on pharmacokinetics related organs

This study explored the evolving landscape of Microphysiological Systems (MPS), with a focus on organoids and organ-on-a-chip (OoC) technologies, which are promising alternatives to animal testing in drug discovery. MPS technology offers in vitro models with high physiological relevance, simulating organ function for pharmacokinetic studies. Organoids composed of 3D cell aggregates and OoCs mimicking in vivo environments based on microfluidic platforms represent the forefront of MPS. This paper provides a comprehensive overview of their application in studying the gut, liver, and kidney and their challenges in becoming reliable alternatives to in vivo models. Although MPS technology is not yet fully comparable to in vivo systems, its continued development, aided by in silico, automation, and AI approaches, is anticipated to bring about further advancements. Collaboration across multiple disciplines and ongoing regulatory discussions will be crucial in driving MPS toward practical and ethical applications in biomedical research and drug development.

A Microfluidic-Based Cell-Stretching Culture Device That Allows for Easy Preparation of Slides for Observation with High-Magnification Objective Lenses

Microfluidic-based cell-stretching devices are vital for studying the molecular pathways involved in cellular responses to mechanobiological processes. Accurate evaluation of these responses requires detailed observation of cells cultured in this cell-stretching device. This study aimed to develop a method for preparing microscope slides to enable high-magnification imaging of cells in these devices. The key innovation is creating a peelable bond between the cell culture membrane and the upper channel, allowing for easy removal of the upper layer and precise cutting of the membrane for high-magnification microscopy. Using the fabricated device, OP9 cells (15,000 cells/channel) were stretched, and the effects of focal adhesion proteins and the intracellular distribution of YAP1 were examined under a fluorescence microscope with 100× and 60× objectives. Stretch stimulation increased integrinβ1 expression and promoted integrin-vinculin complex formation by approximately 1.4-fold in OP9 cells. Furthermore, YAP1 nuclear localization was significantly enhanced (approximately 1.3-fold) during stretching. This method offers a valuable tool for researchers using microfluidic-based cell-stretching devices. The advancement of imaging techniques in microdevice research is expected to further drive progress in mechanobiology research.

Vertex model with internal dissipation enables sustained flows

Complex tissue flows in epithelia are driven by intra- and inter-cellular processes that generate, maintain, and coordinate mechanical forces. There has been growing evidence that cell shape anisotropy, manifested as nematic order, plays an important role in this process. Here we extend an active nematic vertex model by replacing substrate friction with internal viscous dissipation, dominant in epithelia not supported by a substrate or the extracellular matrix, which are found in many early-stage embryos. When coupled to cell shape anisotropy, the internal viscous dissipation allows for long-range velocity correlations and thus enables the spontaneous emergence of flows with a large degree of spatiotemporal organisation. We demonstrate sustained flow in epithelial sheets confined to a channel, providing a link between the cell-level vertex model of tissue dynamics and continuum active nematics, whose behaviour in a channel is theoretically understood and experimentally realisable. Our findings also show a simple mechanism that could account for collective cell migration correlated over distances large compared to the cell size, as observed during morphogenesis.

Mechanical Cell Interactions on Curved Interfaces

We propose a simple mathematical model to describe the mechanical relaxation of cells within a curved epithelial tissue layer represented by an arbitrary curve in two-dimensional space. This model generalises previous one-dimensional models of flat epithelia to investigate the influence of curvature for mechanical relaxation. We represent the mechanics of a cell body either by straight springs, or by curved springs that follow the curve's shape. To understand the collective dynamics of the cells, we devise an appropriate continuum limit in which the number of cells and the length of the substrate are constant but the number of springs tends to infinity. In this limit, cell density is governed by a diffusion equation in arc length coordinates, where diffusion may be linear or nonlinear depending on the choice of the spring restoring force law. Our results have important implications about modelling cells on curved geometries: (i) curved and straight springs can lead to different dynamics when there is a finite number of springs, but they both converge quadratically to the dynamics governed by the diffusion equation; (ii) in the continuum limit, the curvature of the tissue does not affect the mechanical relaxation of cells within the layer nor their tangential stress; (iii) a cell's normal stress depends on curvature due to surface tension induced by the tangential forces. Normal stress enables cells to sense substrate curvature at length scales much larger than their cell body, and could induce curvature dependences in experiments.

Angiomotin cleavage promotes leader formation and collective cell migration

Collective cell migration (CCM) is involved in multiple biological processes, including embryonic morphogenesis, angiogenesis, and cancer invasion. However, the molecular mechanisms underlying CCM, especially leader cell formation, are poorly understood. Here, we show that a signaling pathway regulating angiomotin (AMOT) cleavage plays a role in CCM, using mammalian epithelial cells and mouse models. In a confluent epithelial monolayer, full-length AMOT localizes at cell-cell junctions and limits cell motility. After cleavage, the C-terminal fragment of AMOT (AMOT-CT) translocates to the cell-matrix interface to promote the maturation of focal adhesions (FAs), generate traction force, and induce leader cell formation. Meanwhile, decreased full-length AMOT at cell-cell junctions leads to tissue fluidization and coherent migration of cell collectives. Hence, the cleavage of AMOT serves as a molecular switch to generate polarized contraction, promoting leader cell formation and CCM.

Unjamming Transition as a Paradigm for Biomechanical Control of Cancer Metastasis

Tumor metastasis is a complex phenomenon that poses significant challenges to current cancer therapeutics. While the biochemical signaling involved in promoting motile phenotypes is well understood, the role of biomechanical interactions has recently begun to be incorporated into models of tumor cell migration. Specifically, we propose the unjamming transition, adapted from physical paradigms describing the behavior of granular materials, to better discern the transition toward an invasive phenotype. In this review, we introduce the jamming transition broadly and narrow our discussion to the different modes of 3D tumor cell migration that arise. Then we discuss the mechanical interactions between tumor cells and their neighbors, along with the interactions between tumor cells and the surrounding extracellular matrix. We center our discussion on the interactions that induce a motile state or unjamming transition in these contexts. By considering the interplay between biochemical and biomechanical signaling in tumor cell migration, we can advance our understanding of biomechanical control in cancer metastasis.

Regulation of epithelial cell jamming transition by cytoskeleton and cell-cell interactions

Multicellular systems, such as epithelial cell collectives, undergo transitions similar to those in inert physical systems like sand piles and foams. To remodel or maintain tissue organization during development or disease, these collectives transition between fluid-like and solid-like states, undergoing jamming or unjamming transitions. While these transitions share principles with physical systems, understanding their regulation and implications in cell biology is challenging. Although cell jamming and unjamming follow physics principles described by the jamming diagram, they are fundamentally biological processes. In this review, we explore how cellular processes and interactions regulate jamming and unjamming transitions. We begin with an overview of how these transitions control tissue remodeling in epithelial model systems and describe recent findings of the physical principles governing tissue solidification and fluidization. We then explore the mechanistic pathways that modulate the jamming phase diagram axes, focusing on the regulation of cell fluctuations and geometric compatibility. Drawing upon seminal works in cell biology, we discuss the roles of cytoskeleton and cell-cell adhesion in controlling cell motility and geometry. This comprehensive view illustrates the molecular control of cell jamming and unjamming, crucial for tissue remodeling in various biological contexts.

Intercellular junction-driven stromal cell stacking in a confined 3D microcavity

Understanding the detailed mechanisms driving fibroblast migration within native tissue settings during pathophysiological events presents a critical research challenge. In this study, we elucidate how stromal cells migrate and contribute to the development of three-dimensional (3D) cellular aggregates within confined microcavities. Integrin α5β1 and β-catenin (β-cat) are central in guiding this collective migration and achieving optimal filling of the microcavity. When β-cat is suppressed, cells tend to migrate more sporadically, leading to less efficient cellular organization. Furthermore, we also detail the pivotal roles of Cx43 and N-cadherin (N-cad) in orchestrating collective migration and in shaping efficient cellular stacking. Suppressing gap junctions, especially Cx43, significantly impacts the extracellular matrix expression, integrin α5 and β1, and other elements in the 3D construct, emphasizing the importance of physicochemical cell-cell interactions. The distribution patterns of N-cad and focal adhesion kinase (FAK) further corroborate the essential roles in forming cell-cell junctions and FAK in establishing the foundational layer that underpins the cell stacking within the microcavity. Interestingly, neither Rho-associated protein kinase (ROCK) nor RhoA significantly alter the cell migration pattern toward microcavity. These findings provide fresh perspectives on fibroblast activities in 3D space, enriching our understanding and offering implications for advancements in wound healing and tissue engineering.

Src kinase slows collective rotation of confined epithelial cell monolayers

Collective cell migration is key during development, wound healing, and metastasis and relies on coordinated cell behaviors at the group level. Src kinase is a key signalling protein for the physiological functions of epithelia, as it regulates many cellular processes, including adhesion, motility, and mechanotransduction. Its overactivation is associated with cancer aggressiveness. Here, we take advantage of optogenetics to precisely control Src activation in time and show that its pathological-like activation slows the collective rotation of epithelial cells confined into circular adhesive patches. We interpret velocity, force, and stress data during period of non-activation and period of activation of Src thanks to a hydrodynamic description of the cell assembly as a polar active fluid. Src activation leads to a 2-fold decrease in the ratio of polar angle to friction, which could result from increased adhesiveness at the cell-substrate interface. Measuring internal stress allows us to show that active stresses are subdominant compared to traction forces. Our work reveals the importance of fine-tuning the level of Src activity for coordinated collective behaviors.

Sound innovations for biofabrication and tissue engineering

Advanced biofabrication techniques can create tissue-like constructs that can be applied for reconstructive surgery or as in vitro three-dimensional (3D) models for disease modeling and drug screening. While various biofabrication techniques have recently been widely reviewed in the literature, acoustics-based technologies still need to be explored. The rapidly increasing number of publications in the past two decades exploring the application of acoustic technologies highlights the tremendous potential of these technologies. In this review, we contend that acoustics-based methods can address many limitations inherent in other biofabrication techniques due to their unique advantages: noncontact manipulation, biocompatibility, deep tissue penetrability, versatility, precision in-scaffold control, high-throughput capabilities, and the ability to assemble multilayered structures. We discuss the mechanisms by which acoustics directly dictate cell assembly across various biostructures and examine how the advent of novel acoustic technologies, along with their integration with traditional methods, offers innovative solutions for enhancing the functionality of organoids. Acoustic technologies are poised to address fundamental challenges in biofabrication and tissue engineering and show promise for advancing the field in the coming years.

Enhancing cell motility via non-contact capacitively coupled electrostatic field

Cellular motility is essential for making and maintaining multicellular organisms throughout their lifespan. Migrating cells can move either individually or collectively by a crawling movement that links the cytoskeletal activity to the adhesion surface. In vitro stimulation by electric fields can be achieved by direct, capacitive or inductive coupled setups. We tested the effects of electrical stimulation provided by capacitive coupling on glioma cells, using a capacitive-coupled system powered by a potential difference of 35 V between two electrodes placed outside the culture dish. Numerical dosimetry identified two different fields: (i) in the order of 103 V/m at the level of the dielectric substrates, with almost uniform distribution; (ii) in the order of 10-1 V/m at the level of the culture medium, with spatial and material-dependent distribution. The scratch assay and the tracking of single-cell movement showed a boosted motility when crawling occurs on polystyrene surfaces, demonstrating the feasibility of this peculiar exposure system to generate forces capable of influencing cell behavior.

Induction of FAM46C expression mediated by DNMT3A downregulation is involved in early-onset preeclampsia through gene body methylation

BACKGROUND

Aberrant methylation of genomic DNA has been found in preeclamptic placentas, which is characterized by elevated DNA methylation and hypermethylation of gene body regions, but the underlying mechanism is not yet fully understood.

METHODS

Global DNA methylation was assessed through ELISA and HPLC. The methylation sites were detected using the Illumina Human Methylation 450 K Microarray. The methylation level of FAM46C promoter and gene body was detected through the bisulfite sequencing. RNA-seq was utilized to investigate the mechanism by which DNMT3A and FAM46C mediate the migration and invasion of trophoblast cells.

RESULTS

We discovered that DNMT3A knockdown led to elevated levels of gene body methylation and FAM46C transcription. FAM46C downregulation completely rescued the suppressive effects caused by DNMT3A knockdown on the migration and invasion of trophoblast cells. Mechanistically, DNMT3A reduction led to an increase in the enrichment of DNMT3B and DNMT1 in the gene body region of FAM46C. The results of transcriptome sequencing showed that DNMT3A and FAM46C regulate the adhesion of trophoblast cells. Elevated expression of FAM46C and increased methylation levels within its gene body region were observed in extravillous trophoblast cells of early-onset preeclamptic placentas.

CONCLUSIONS

DNMT3A-mediated aberrant FAM46C gene body methylation is relevant to the development of early-onset preeclampsia.

Different Biomechanical Cell Behaviors in an Epithelium Drive Collective Epithelial Cell Extrusion

In vertebrates, many organs, such as the kidney and the mammary gland form ductal structures based on the folding of epithelial sheets. The development of these organs relies on coordinated sorting of different cell lineages in both time and space, through mechanisms that remain largely unclear. Tissues are composed of several cell types with distinct biomechanical properties, particularly at cell-cell and cell-substrate boundaries. One hypothesis is that adjacent epithelial layers work in a coordinated manner to shape the tissue. Using in vitro experiments on model epithelial cells, differential expression of atypical Protein Kinase C iota (aPKCi), a key junctional polarity protein, is shown to reinforce cell epithelialization and trigger sorting by tuning cell mechanical properties at the tissue level. In a broader perspective, it is shown that in a heterogeneous epithelial monolayer, in which cell sorting occurs, forces arising from epithelial cell growth under confinement by surrounding cells with different biomechanical properties are sufficient to promote collective cell extrusion and generate emerging 3D organization related to spheroids and buds. Overall, this research sheds light on the role of aPKCi and the biomechanical interplay between distinct epithelial cell lineages in shaping tissue organization, providing insights into the understanding of tissue and organ development.

Microfluidic Platform for Generating and Releasing Patient-Derived Cancer Organoids with Diverse Shapes: Insight into Shape-Dependent Tumor Growth

Multicellular spheroids and patient-derived organoids find many applications in fundamental research, drug discovery, and regenerative medicine. Advances in the understanding and recapitulation of organ functionality and disease development require the generation of complex organoid models, including organoids with diverse morphologies. Microfluidics-based cell culture platforms enable time-efficient confined organoid generation. However, the ability to form organoids with different shapes with a subsequent transfer from microfluidic devices to unconstrained environments for studies of morphology-dependent organoid growth is yet to be demonstrated. Here, a microfluidic platform is introduced that enables high-fidelity formation and addressable release of breast cancer organoids with diverse shapes. Using this platform, the impact of organoid morphology on their growth in unconstrained biomimetic hydrogel is explored. It is shown that proliferative cancer cells tend to localize in high positive curvature organoid regions, causing their faster growth, while the overall growth pattern of organoids with diverse shapes tends to reduce interfacial tension at the organoid-hydrogel interface. In addition to the formation of organoids with diverse morphologies, this platform can be integrated into multi-tissue micro-physiological systems.

Fabrication of micropatterned PCL-collagen nanofibrous scaffold for cellular confinement induced early osteogenesis

The intricate interaction of the scaffold's architecture/geometry and with the cells is essential for tissue engineering and regenerative medicine. Cells sense their surrounding dynamic cues such as biophysical, biomechanical, and biochemical, and respond to them differently. Numerous studies have recently explored and reported the effect of contact guidance by culturing various types of cells on different types of micropatterned substrates such as microgrooves, geometric (square and triangle) micropattern, microstrips, micropatterned nanofibers. Amongst all of these micropatterned polymeric substrates; electrospun nanofibers have been regarded as a suitable substrate as it mimics the native ECM architectures. Therefore, in the present study; stencil-assisted electrospun Grid-lined micropatterned PCL-Collagen nanofibers (GLMPCnfs) were fabricated and its influence on the alignment and differentiation of pre-osteoblast cells (MC3T3-E1) was investigated. The randomly orientated Non-patterned PCL-Collagen nanofibers (NPPCnfs) were used as control. The patterns were characterized for their geometrical features such as area and thickness of deposition using surface profiler and scanning electron microscopy. A 61 % decrease in the overall area of GLMPCnfs as compared to the stencil area demonstrated the potential of electrofocusing phenomenon in the process of patterning electrospun nanofibers into various micron-scale structures. The MC3T3-E1 cells were confined and aligned in the direction of GLMPCnfs as confirmed by a high cellular aspect ratio (AR = 5.41), lower cellular shape index (CSI = 0.243), and cytoskeletal reorganization assessed through the F-actin filament immunocytochemistry (ICC) imaging. The aligned cells along the GLMPCnfs exhibited elevated alkaline phosphatase activity and enhanced mineralization. Furthermore, the gene expression profiling revealed upregulation of key osteogenic markers, such as ALP, OCN, OPN, COL1A1, and osteocyte markers DMP1, and SOST. Consequently, the research highlights the impact of GLMPCnfs on the cellular behaviour that results to the pre-osteoblast differentiation and the potential for stimulant-free early osteogenesis. These results offer an extensive understanding and mechanistic insight into how scaffold topography can be modified to influence cellular responses for effective bone regeneration strategies.

The characterization of cell traction force on nonflat surfaces with different curvature by elastic hydrogel microspheres

It is of great importance to study the detachment/attachment behaviors of cells (cancer cell, immune cell, and epithelial cell), as they are closely related with tumor metastasis, immunoreaction, and tissue development at variety scales. To characterize the detachment/attachment during the interaction between cells and substrate, some researchers proposed using cell traction force (CTF) as the indicator. To date, various strategies have been developed to measure the CTF. However, these methods only realize the measurements of cell passive forces on flat cases. To quantify the active CTF on nonflat surfaces, which can better mimic the in vivo case, we employed elastic hydrogel microspheres as a force sensor. The microspheres were fabricated by microfluidic chips with controllable size and mechanical properties to mimic substrate. Cells were cultured on microsphere and the CTF led to the deformation of microsphere. By detecting the morphology information, the CTF exerted by attached cells can be calculated by the in-house numerical code. Using these microspheres, the CTF of various cells (including tumor cell, immunological cell, and epithelium cell) were successfully obtained on nonflat surfaces with different curvature radii. The proposed method provides a versatile platform to measure the CTF with high precision and to understand the detachment/attachment behaviors during physiology processes.

Long range juxtacrine signalling through cadherin for collective cell orientation

Many life phenomena, such as development, morphogenesis, tissue remodelling, and wound healing, are often driven by orderly and directional migration of collective cells. However, when cells are randomly oriented or localized disorder exists in orderly oriented collective cells, cell migration cannot occur in an orderly manner although various motion modes such as global rotation and local swirling and/or various motion patterns such as radial pattern and chiral pattern often occur. Therefore, it is important to control cell orientation to ensure the orderly migration of collective cells. Here, we show that it is not force transmission, but juxtacrine signalling through cadherin that plays a critical role in the orientation of collective cells. Surprisingly, juxtacrine signalling for cell orientation reached cells on a plastic dish that were not directly subjected to mechanical stimulation, up to 7 mm away from the actuator. The present study suggests that even weak mechanical stimulation is transmitted in a long range without force transmission through juxtacrine signalling. The long range juxtacrine signalling might play an important role in various life phenomena. STATEMENT OF SIGNIFICANCE: Juxtacrine signalling is direct cell-cell contact-dependent signalling, which plays a crucial role in cell behaviors such as mechanosensing, mechanotransduction and collective cell behaviors, however, there is not enough understanding about juxtacrine signalling. The present study has demonstrated that juxtacrine signalling for collective cell orientation is transmitted over a long range through cadherin. To the best of our knowledge, this is the first report of long range juxtacrine signalling. This finding may lead to the elucidation of various life phenomena such as development, morphogenesis, tissue remodelling, and wound healing.

Cell-cell junctions in focus - imaging junctional architectures and dynamics at high resolution

Studies utilizing electron microscopy and live fluorescence microscopy have significantly enhanced our understanding of the molecular mechanisms that regulate junctional dynamics during homeostasis, development and disease. To fully grasp the enormous complexity of cell-cell adhesions, it is crucial to study the nanoscale architectures of tight junctions, adherens junctions and desmosomes. It is important to integrate these junctional architectures with the membrane morphology and cellular topography in which the junctions are embedded. In this Review, we explore new insights from studies using super-resolution and volume electron microscopy into the nanoscale organization of these junctional complexes as well as the roles of the junction-associated cytoskeleton, neighboring organelles and the plasma membrane. Furthermore, we provide an overview of junction- and cytoskeletal-related biosensors and optogenetic probes that have contributed to these advances and discuss how these microscopy tools enhance our understanding of junctional dynamics across cellular environments.

Recent advances in cancer detection using dynamic, stimuli-responsive supramolecular chemosensors. a focus review

In current chemistry, supramolecular materials that respond to a wide variety of external stimuli, such as solvents, temperature, light excitation, pH, and mechanical forces (pressure, stress, strain, and tension), have attracted considerable attention; for example, we have developed cyclodextrins, cucurbiturils, pillararenes, calixarenes, crown ether-based chemical sensors, or chemosensors. These supramolecular chemosensors have potential applications in imaging, probing, and cancer detection. Recently, we focused on pressure, particularly solution-state hydrostatic pressure, from the viewpoint of cancer therapy. This Mini Review summarizes (i) why hydrostatic pressure is important, particularly in biology, and (ii) what we can do using hydrostatic pressure stimulation.

Bioprinting of Cells, Organoids and Organs-on-a-Chip Together with Hydrogels Improves Structural and Mechanical Cues

The 3D bioprinting technique has made enormous progress in tissue engineering, regenerative medicine and research into diseases such as cancer. Apart from individual cells, a collection of cells, such as organoids, can be printed in combination with various hydrogels. It can be hypothesized that 3D bioprinting will even become a promising tool for mechanobiological analyses of cells, organoids and their matrix environments in highly defined and precisely structured 3D environments, in which the mechanical properties of the cell environment can be individually adjusted. Mechanical obstacles or bead markers can be integrated into bioprinted samples to analyze mechanical deformations and forces within these bioprinted constructs, such as 3D organoids, and to perform biophysical analysis in complex 3D systems, which are still not standard techniques. The review highlights the advances of 3D and 4D printing technologies in integrating mechanobiological cues so that the next step will be a detailed analysis of key future biophysical research directions in organoid generation for the development of disease model systems, tissue regeneration and drug testing from a biophysical perspective. Finally, the review highlights the combination of bioprinted hydrogels, such as pure natural or synthetic hydrogels and mixtures, with organoids, organoid-cell co-cultures, organ-on-a-chip systems and organoid-organ-on-a chip combinations and introduces the use of assembloids to determine the mutual interactions of different cell types and cell-matrix interferences in specific biological and mechanical environments.

Inferring cellular contractile forces and work using deep morphology traction microscopy

Traction-force microscopy (TFM) has emerged as a widely used standard methodology to measure cell-generated traction forces and determine their role in regulating cell behavior. While TFM platforms have enabled many discoveries, their implementation remains limited due to complex experimental procedures, specialized substrates, and the ill-posed inverse problem whereby low-magnitude high-frequency noise in the displacement field severely contaminates the resulting traction measurements. Here, we introduce deep morphology traction microscopy (DeepMorphoTM), a deep-learning alternative to conventional TFM approaches. DeepMorphoTM first infers cell-induced substrate displacement solely from a sequence of cell shapes and subsequently computes cellular traction forces, thus avoiding the requirement of a specialized fiduciarily marked deformable substrate or force-free reference image. Rather, this technique drastically simplifies the overall experimental methodology, imaging, and analysis needed to conduct cell-contractility measurements. We demonstrate that DeepMorphoTM quantitatively matches conventional TFM results while offering stability against the biological variability in cell contractility for a given cell shape. Without high-frequency noise in the inferred displacement, DeepMorphoTM also resolves the ill-posedness of traction computation, increasing the consistency and accuracy of traction analysis. We demonstrate the accurate extrapolation across several cell types and substrate materials, suggesting robustness of the methodology. Accordingly, we present DeepMorphoTM as a capable yet simpler alternative to conventional TFM for characterizing cellular contractility in two dimensions.

Ductile-to-brittle transition and yielding in soft amorphous materials: perspectives and open questions

Soft amorphous materials are viscoelastic solids ubiquitously found around us, from clays and cementitious pastes to emulsions and physical gels encountered in food or biomedical engineering. Under an external deformation, these materials undergo a noteworthy transition from a solid to a liquid state that reshapes the material microstructure. This yielding transition was the main theme of a workshop held from January 9 to 13, 2023 at the Lorentz Center in Leiden. The manuscript presented here offers a critical perspective on the subject, synthesizing insights from the various brainstorming sessions and informal discussions that unfolded during this week of vibrant exchange of ideas. The result of these exchanges takes the form of a series of open questions that represent outstanding experimental, numerical, and theoretical challenges to be tackled in the near future.

Single-molecule force spectroscopy reveals intra- and intermolecular interactions of Caenorhabditis elegans HMP-1 during mechanotransduction

The Caenorhabditis elegans HMP-2/HMP-1 complex, akin to the mammalian [Formula: see text]-catenin-[Formula: see text]-catenin complex, serves as a critical mechanosensor at cell-cell adherens junctions, transducing tension between HMR-1 (also known as cadherin in mammals) and the actin cytoskeleton. Essential for embryonic development and tissue integrity in C. elegans, this complex experiences tension from both internal actomyosin contractility and external mechanical microenvironmental perturbations. While offering a valuable evolutionary comparison to its mammalian counterpart, the impact of tension on the mechanical stability of HMP-1 and HMP-2/HMP-1 interactions remains unexplored. In this study, we directly quantified the mechanical stability of full-length HMP-1 and its force-bearing modulation domains (M1-M3), as well as the HMP-2/HMP-1 interface. Notably, the M1 domain in HMP-1 exhibits significantly higher mechanical stability than its mammalian analog, attributable to interdomain interactions with M2-M3. Introducing salt bridge mutations in the M3 domain weakens the mechanical stability of the M1 domain. Moreover, the intermolecular HMP-2/HMP-1 interface surpasses its mammalian counterpart in mechanical stability, enabling it to support the mechanical activation of the autoinhibited M1 domain for mechanotransduction. Additionally, the phosphomimetic mutation Y69E in HMP-2 weakens the mechanical stability of the HMP-2/HMP-1 interface, compromising the force-transmission molecular linkage and its associated mechanosensing functions. Collectively, these findings provide mechanobiological insights into the C. elegans HMP-2/HMP-1 complex, highlighting the impact of salt bridges on mechanical stability in [Formula: see text]-catenin and demonstrating the evolutionary conservation of the mechanical switch mechanism activating the HMP-1 modulation domain for protein binding at the single-molecule level.

Lost in Rotation: How TiO2 and ZnO Nanoparticles Disrupt Coordinated Epithelial Cell Rotation

Coordinated cell movement is a cardinal feature in tissue organization that highlights the importance of cells working together as a collective unit. Disruptions to this synchronization can have far-reaching pathological consequences, ranging from developmental disorders to tissue repair impairment. Herein, it is shown that metal oxide nanoparticles (NPs), even at low and non-toxic doses (1 and 10 µg mL-1), can perturb the coordinated epithelial cell rotation (CECR) in micropatterned human epithelial cell clusters via distinct nanoparticle-specific mechanisms. Zinc oxide (ZnO) NPs are found to induce significant levels of intracellular reactive oxygen species (ROS) to promote mitogenic activity. Generation of a new localized force field through changes in the cytoskeleton organization and an increase in cell density leads to the arrest of CECR. Conversely, epithelial cell clusters exposed to titanium dioxide (TiO2) NPs maintain their CECR directionality but display suppressed rotational speed in an autophagy-dependent manner. Thus, these findings reveal that nanoparticles can actively hijack the nano-adaptive responses of epithelial cells to disrupt the fundamental mechanics of cooperation and communication in a collective setting.

Compressible Hollow Microlasers in Organoids for High-Throughput and Real-Time Mechanical Screening

Mechanical stress within organoids is a pivotal indicator in disease modeling and pharmacokinetics, yet current tools lack the ability to rapidly and dynamically screen these mechanics. Here, we introduce biocompatible and compressible hollow microlasers that realize all-optical assessment of cellular stress within organoids. The laser spectroscopy yields identification of cellular deformation at the nanometer scale, corresponding to tens of pascals stress sensitivity. The compressibility enables the investigation of the isotropic component, which is the fundamental mechanics of multicellular models. By integrating with a microwell array, we demonstrate the high-throughput screening of mechanical cues in tumoroids, establishing a platform for mechano-responsive drug screening. Furthermore, we showcase the monitoring and mapping of dynamic contractile stress within human embryonic stem cell-derived cardiac organoids, revealing the internal mechanical inhomogeneity within a single organoid. This method eliminates time-consuming scanning and sample damage, providing insights into organoid mechanobiology.

Nuclease-Resistant L-DNA Tension Probes Enable Long-Term Force Mapping of Single Cells and Cell Consortia

DNA-based tension probes with precisely programmable force responses provide important insights into cellular mechanosensing. However, their degradability in cell culture limits their use for long-term imaging, for instance, when cells migrate, divide, and differentiate. This is a critical limitation for providing insights into mechanobiology for these longer-term processes. Here, we present DNA-based tension probes that are entirely designed based on the stereoisomer of biological D-DNA, i.e., L-DNA. We demonstrate that L-DNA tension probes are essentially indestructible by nucleases and provide days-long imaging without significant loss in image quality. We also show their superiority already for short imaging times commonly used for classical D-DNA tension probes. We showcase the potential of these resilient probes to image minute movements, and for generating long term force maps of single cells and of collectively migrating cell populations.

Non-Muscle Myosin II A: Friend or Foe in Cancer?

Non-muscle myosin IIA (NM IIA) is a motor protein that belongs to the myosin II family. The myosin heavy chain 9 (MYH9) gene encodes the heavy chain of NM IIA. NM IIA is a hexamer and contains three pairs of peptides, which include the dimer of heavy chains, essential light chains, and regulatory light chains. NM IIA is a part of the actomyosin complex that generates mechanical force and tension to carry out essential cellular functions, including adhesion, cytokinesis, migration, and the maintenance of cell shape and polarity. These functions are regulated via light and heavy chain phosphorylation at different amino acid residues. Apart from physiological functions, NM IIA is also linked to the development of cancer and genetic and neurological disorders. MYH9 gene mutations result in the development of several autosomal dominant disorders, such as May-Hegglin anomaly (MHA) and Epstein syndrome (EPS). Multiple studies have reported NM IIA as a tumor suppressor in melanoma and head and neck squamous cell carcinoma; however, studies also indicate that NM IIA is a critical player in promoting tumorigenesis, chemoradiotherapy resistance, and stemness. The ROCK-NM IIA pathway regulates cellular movement and shape via the control of cytoskeletal dynamics. In addition, the ROCK-NM IIA pathway is dysregulated in various solid tumors and leukemia. Currently, there are very few compounds targeting NM IIA, and most of these compounds are still being studied in preclinical models. This review provides comprehensive evidence highlighting the dual role of NM IIA in multiple cancer types and summarizes the signaling networks involved in tumorigenesis. Furthermore, we also discuss the role of NM IIA as a potential therapeutic target with a focus on the ROCK-NM IIA pathway.

Co-zorbs: Motile, multispecies biofilms aid transport of diverse bacterial species

Biofilms are three-dimensional structures containing one or more bacterial species embedded in extracellular polymeric substances. Although most biofilms are stationary, Flavobacterium johnsoniae forms a motile spherical biofilm called a zorb, which is propelled by its base cells and contains a polysaccharide core. Here, we report formation of spatially organized, motile, multispecies biofilms, designated "co-zorbs," that are distinguished by a core-shell structure. F. johnsoniae forms zorbs whose cells collect other bacterial species and transport them to the zorb core, forming a co-zorb. Live imaging revealed that co-zorbs also form in zebrafish, thereby demonstrating a new type of bacterial movement in vivo. This discovery opens new avenues for understanding community behaviors, the role of biofilms in bulk bacterial transport, and collective strategies for microbial success in various environments.