Collective cell migration in development

Lamin A/C and Vimentin as a Coordinated Regulator during Amoeboid Migration in Microscale Confined Microenvironments

Cell migration occurs in confined microenvironments, which plays a vital role in the process of tumor metastasis. However, it is challenging to study their behaviors in vivo. Here we developed a cell squeeze system that can be scaled down to micrometers to mimic native physical confined microenvironments, wherein degrees of surface adhesion and mechanical constraints could be manipulated in order to investigate cell-migrating behaviors. Based on the microscale cell squeeze system, we found the synergistic role of lamin A/C and vimentin in cell transition and migration under strong confinement. The dynamic variations in lamin A/C and vimentin expression establish a positive feedback loop in response to confinement, effectively promoting amoeboid migration by modulating nuclear deformability while ensuring cell viability. This work shed light on modulating cell response to microenvironments by altering the expression of lamin A/C and/or vimentin, which may be a more efficient way of inhibiting cancer metastasis.

Optogenetic control of Wnt signaling models cell-intrinsic embryogenic patterning using 2D human pluripotent stem cell culture

In embryonic stem cell (ESC) models for early development, spatially and temporally varying patterns of signaling and cell types emerge spontaneously. However, mechanistic insight into this dynamic self-organization is limited by a lack of methods for spatiotemporal control of signaling, and the relevance of signal dynamics and cell-to-cell variability to pattern emergence remains unknown. Here, we combine optogenetic stimulation, imaging and transcriptomic approaches to study self-organization of human ESCs (hESC) in two-dimensional (2D) culture. Morphogen dynamics were controlled via optogenetic activation of canonical Wnt/β-catenin signaling (optoWnt), which drove broad transcriptional changes and mesendoderm differentiation at high efficiency (>99% cells). When activated within cell subpopulations, optoWnt induced cell self-organization into distinct epithelial and mesenchymal domains, mediated by changes in cell migration, an epithelial to mesenchymal-like transition and TGFβ signaling. Furthermore, we demonstrate that such optogenetic control of cell subpopulations can be used to uncover signaling feedback mechanisms between neighboring cell types. These findings reveal that cell-to-cell variability in Wnt signaling is sufficient to generate tissue-scale patterning and establish a hESC model system for investigating feedback mechanisms relevant to early human embryogenesis.

Cells collectively migrate during ammonium chemotaxis in Chlamydomonas reinhardtii

The mechanisms governing chemotaxis in Chlamydomonas reinhardtii are largely unknown compared to those regulating phototaxis despite equal importance on the migratory response in the ciliated microalga. To study chemotaxis, we made a simple modification to a conventional Petri dish assay. Using the assay, a novel mechanism governing Chlamydomonas ammonium chemotaxis was revealed. First, we found that light exposure enhances the chemotactic response of wild-type Chlamydomonas strains, yet phototaxis-incompetent mutant strains, eye3-2 and ptx1, exhibit normal chemotaxis. This suggests that Chlamydomonas transduces the light signal pathway in chemotaxis differently from that in phototaxis. Second, we found that Chlamydomonas collectively migrate during chemotaxis but not phototaxis. Collective migration during chemotaxis is not clearly observed when the assay is conducted in the dark. Third, the Chlamydomonas strain CC-124 carrying agg1^-, the AGGREGATE1 gene (AGG1) null mutation, exhibited a more robust collective migratory response than strains carrying the wild-type AGG1 gene. The expression of a recombinant AGG1 protein in the CC-124 strain suppressed this collective migration during chemotaxis. Altogether, these findings suggest a unique mechanism; ammonium chemotaxis in Chlamydomonas is mainly driven by collective cell migration. Furthermore, it is proposed that collective migration is enhanced by light and suppressed by the AGG1 protein.

Fasciclin 2 plays multiple roles in promoting cell migration within the developing nervous system of Manduca sexta

The coordination of neuronal and glial migration is essential to the formation of most nervous systems, requiring a complex interplay of cell-intrinsic responses and intercellular guidance cues. During the development of the enteric nervous system (ENS) in Manduca sexta (tobacco hornworm), the IgCAM Fasciclin 2 (Fas2) serves several distinct functions to regulate these processes. As the ENS forms, a population of 300 neurons (EP cells) undergoes sequential phases of migration along well-defined muscle pathways on the visceral mesoderm to form a branching Enteric Plexus, closely followed by a trailing wave of proliferating glial cells that enwrap the neurons. Initially, both the neurons and glial cells express a GPI-linked form of Fas2 (GPI-Fas2), which helps maintain cell-cell contact among the pre-migratory neurons and later promotes glial ensheathment. The neurons then switch isoforms, predominantly expressing a combination of transmembrane isoforms lacking an intracellular PEST domain (TM-Fas2 PEST-), while their muscle band pathways on the midgut transiently express transmembrane isoforms containing this domain (TM-Fas2 PEST+). Using intracellular injection protocols to manipulate Fas2 expression in cultured embryos, we found that TM-Fas2 promotes the directed migration and outgrowth of individual neurons in the developing ENS. Concurrently, TM-Fas2 expression by the underlying muscle bands is also required as a substrate cue to support normal migration, while glial expression of GPI-Fas2 helps support their ensheathment of the migratory neurons. These results demonstrate how a specific IgCAM can play multiple roles that help coordinate neuronal and glial migration in the developing nervous system.

The multifaceted role of aquaporins in physiological cell migration

Cell migration is an essential process that underlies many physiological processes, including the immune response, organogenesis in the embryo, and angiogenesis, as well as pathological processes such as cancer metastasis. Cells have at their disposal a variety of migratory behaviors and mechanisms that seem to be specific to cell type and the microenvironment. Research over the past two decades has elucidated the water channel protein family of aquaporins (AQPs) as a regulator of many cell migration-related processes, from physical phenomena to biological signaling pathways. The roles that AQPs play in cell migration are both cell type- and isoform-specific; thus, a large swath of information has accumulated as researchers seek to identify the responses across these distinct variables. There does not seem to be a universal role that AQPs play in cell migration; the complex interplay between AQPs and cell volume management, signaling pathway activation, and in a few identified circumstances, gene expression regulation, has shown the intricate, and perhaps paradoxical, role of AQPs in cell migration. The objective of this review is to provide an organized and integrated collection of recent work that has elucidated the many mechanisms by which AQPs regulate cell migration.NEW & NOTEWORTHY Research has elucidated the water channel protein family of aquaporins (AQPs) as a regulator of many cell migration-related processes, from physical phenomena to biological signaling pathways. The roles that AQPs play in cell migration are both cell type- and isoform-specific; thus, a large swath of information has accumulated as researchers seek to identify the responses across these distinct variables. This review compiles insights into the recent findings linking AQPs to physiological cell migration.

Specific prostaglandins are produced in the migratory cells and the surrounding substrate to promote Drosophila border cell migration

A key regulator of collective cell migration is prostaglandin (PG) signaling. However, it remains largely unclear whether PGs act within the migratory cells or their microenvironment to promote migration. Here we use Drosophila border cell migration as a model to uncover the cell-specific roles of two PGs in collective migration. Prior work shows PG signaling is required for on-time migration and cluster cohesion. We find that the PGE2 synthase cPGES is required in the substrate, while the PGF2α synthase Akr1B is required in the border cells for on-time migration. Akr1B acts in both the border cells and their substrate to regulate cluster cohesion. One means by which Akr1B regulates border cell migration is by promoting integrin-based adhesions. Additionally, Akr1B limits myosin activity, and thereby cellular stiffness, in the border cells, whereas cPGES limits myosin activity in both the border cells and their substrate. Together these data reveal that two PGs, PGE2 and PGF2α, produced in different locations, play key roles in promoting border cell migration. These PGs likely have similar migratory versus microenvironment roles in other collective cell migrations.

A cell membrane model that reproduces cortical flow-driven cell migration and collective movement

Many fundamental biological processes are dependent on cellular migration. Although the mechanical mechanisms of single-cell migration are relatively well understood, those underlying migration of multiple cells adhered to each other in a cluster, referred to as cluster migration, are poorly understood. A key reason for this knowledge gap is that many forces-including contraction forces from actomyosin networks, hydrostatic pressure from the cytosol, frictional forces from the substrate, and forces from adjacent cells-contribute to cell cluster movement, making it challenging to model, and ultimately elucidate, the final result of these forces. This paper describes a two-dimensional cell membrane model that represents cells on a substrate with polygons and expresses various mechanical forces on the cell surface, keeping these forces balanced at all times by neglecting cell inertia. The model is discrete but equivalent to a continuous model if appropriate replacement rules for cell surface segments are chosen. When cells are given a polarity, expressed by a direction-dependent surface tension reflecting the location dependence of contraction and adhesion on a cell boundary, the cell surface begins to flow from front to rear as a result of force balance. This flow produces unidirectional cell movement, not only for a single cell but also for multiple cells in a cluster, with migration speeds that coincide with analytical results from a continuous model. Further, if the direction of cell polarity is tilted with respect to the cluster center, surface flow induces cell cluster rotation. The reason why this model moves while keeping force balance on cell surface (i.e., under no net forces from outside) is because of the implicit inflow and outflow of cell surface components through the inside of the cell. An analytical formula connecting cell migration speed and turnover rate of cell surface components is presented.

What are the key mechanical mechanisms governing integrin-mediated cell migration in three-dimensional fiber networks?

Cell migration plays a vital role in numerous processes such as development, wound healing, or cancer. It is well known that numerous complex mechanisms are involved in cell migration. However, so far it remains poorly understood what are the key mechanisms required to produce the main characteristics of this behavior. The reason is a methodological one. In experimental studies, specific factors and mechanisms can be promoted or inhibited. However, while doing so, there can always be others in the background which play key roles but which have simply remained unattended so far. This makes it very difficult to validate any hypothesis about a minimal set of factors and mechanisms required to produce cell migration. To overcome this natural limitation of experimental studies, we developed a computational model where cells and extracellular matrix fibers are represented by discrete mechanical objects on the micrometer scale. In this model, we had exact control of the mechanisms by which cells and matrix fibers interacted with each other. This enabled us to identify the key mechanisms required to produce physiologically realistic cell migration (including advanced phenomena such as durotaxis and a biphasic relation between migration efficiency and matrix stiffness). We found that two main mechanisms are required to this end: a catch-slip bond of individual integrins and cytoskeletal actin-myosin contraction. Notably, more advanced phenomena such as cell polarization or details of mechanosensing were not necessary to qualitatively reproduce the main characteristics of cell migration observed in experiments.

Joint representation: Modeling a phenomenon with multiple biological systems

Biologists often study particular biological systems as models of a phenomenon of interest even if they already know that the phenomenon is produced by diverse mechanisms and hence none of those systems alone can sufficiently represent it. To understand this modeling practice, the present paper provides an account of how multiple model systems can be used to study a phenomenon that is produced by diverse mechanisms. Even if generalizability of results from a single model system is significantly limited, generalizations concerning specific aspects of mechanisms often hold across certain ranges of biological systems, which enables multiple model systems to jointly represent such a phenomenon. Comparing mechanisms that operate in different biological systems as examples of the same phenomenon also facilitates characterization and investigation of individual mechanisms. I also compare my account with two existing accounts of the use of multiple model systems and argue that my account is distinct from and complementary to them.

Excitable dynamics in a molecularly-explicit model of cell motility: Mixed-mode oscillations and beyond

Mesenchymal cell motility is mainly regulated by two members of the Rho-family of GTPases, called Rac and Rho. The mutual inhibition exerted by these two proteins on each other's activation and the promotion of Rac activation by an adaptor protein called paxillin have been implicated in driving cellular polarization comprised of front (high active Rac) and back (high active Rho) during cell migration. Mathematical modeling of this regulatory network has previously shown that bistability is responsible for generating a spatiotemporal pattern underscoring cellular polarity called wave-pinning when diffusion is included. We previously developed a 6V reaction-diffusion model of this network to decipher the role of Rac, Rho and paxillin (along with other auxiliary proteins) in generating wave-pinning. In this study, we simplify this model through a series of steps into an excitable 3V ODE model comprised of one fast variable (the scaled concentration of active Rac), one slow variable (the maximum paxillin phosphorylation rate - turned into a variable) and a very slow variable (a recovery rate - also turned into a variable). We then explore, through slow-fast analysis, how excitability is manifested by showing that the model can exhibit relaxation oscillations (ROs) as well as mixed-mode oscillations (MMOs) whose underlying dynamics are consistent with a delayed Hopf bifurcation with a canard explosion. By reintroducing diffusion and the scaled concentration of inactive Rac into the model, we obtain a 4V PDE model that generates several unique spatiotemporal patterns that are relevant to cell motility. These patterns are then characterized and their impact on cell motility are explored by employing the cellular potts model (CPM). Our results reveal that wave pinning produces purely very directed motion in CPM, while MMOs allow for meandering and non-motile behaviors to occur. This highlights the role of MMOs as a potential mechanism for mesenchymal cell motility.

Microfluidic platform for the reproduction of hypoxic vascular microenvironments

Vascular endothelial cells (ECs) respond to mechanical stimuli caused by blood flow to maintain vascular homeostasis. Although the oxygen level in vascular microenvironment is lower than the atmospheric one, the cellular dynamics of ECs under hypoxic and flow exposure are not fully understood. Here, we describe a microfluidic platform for the reproduction hypoxic vascular microenvironments. Simultaneous application of hypoxic stress and fluid shear stress to the cultured cells was achieved by integrating a microfluidic device and a flow channel that adjusted the initial oxygen concentration in a cell culture medium. An EC monolayer was then formed on the media channel in the device, and the ECs were observed after exposure to hypoxic and flow conditions. The migration velocity of the ECs immediately increased after flow exposure, especially in the direction opposite to the flow direction, and gradually decreased, resulting in the lowest value under the hypoxic and flow exposure condition. The ECs after 6-h simultaneous exposure to hypoxic stress and fluid shear stress were generally aligned and elongated in the flow direction, with enhanced VE-cadherin expression and actin filament assembly. Thus, the developed microfluidic platform is useful for investigating the dynamics of ECs in vascular microenvironments.

Who's really in charge: Diverse follower cell behaviors in collective cell migration

Collective cell migrations drive morphogenesis, wound healing, and cancer dissemination. Cells located at the front are considered leaders while those behind them are defined topologically as followers. Leader cell behaviors, including chemotaxis and their coupling to followers, have been well-studied and reviewed. However, the contributions of follower cells to collective cell migration represent an emerging area of interest. In this perspective, we highlight recent research into the broadening array of follower cell behaviors found in moving collectives. We describe examples of follower cells that possess cryptic leadership potential and followers that lack that potential but contribute in diverse and sometimes surprising ways to collective movement, even steering from behind. We highlight collectives in which all cells both lead and follow, and a few passive passengers. The molecular mechanisms controlling follower cell function and behavior are just emerging and represent an exciting frontier in collective cell migration research.

Rac1: A Regulator of Cell Migration and A Potential Target for Cancer Therapy

Cell migration is crucial for physiological and pathological processes such as morphogenesis, wound repair, immune response and cancer invasion/metastasis. There are many factors affecting cell migration, and the regulatory mechanisms are complex. Rac1 is a GTP-binding protein with small molecular weight belonging to the Rac subfamily of the Rho GTPase family. As a key molecule in regulating cell migration, Rac1 participates in signal transduction from the external cell to the actin cytoskeleton and promotes the establishment of cell polarity which plays an important role in cancer cell invasion/metastasis. In this review, we firstly introduce the molecular structure and activity regulation of Rac1, and then summarize the role of Rac1 in cancer invasion/metastasis and other physiological processes. We also discuss the regulatory mechanisms of Rac1 in cell migration and highlight it as a potential target in cancer therapy. Finally, the current state as well as the future challenges in this area are considered. Understanding the role and the regulatory mechanism of Rac1 in cell migration can provide fundamental insights into Rac1-related cancer progression and further help us to develop novel intervention strategies for cancer therapy in clinic.

Polarity and mixed-mode oscillations may underlie different patterns of cellular migration

In mesenchymal cell motility, several migration patterns have been observed, including directional, exploratory and stationary. Two key members of the Rho-family of GTPases, Rac and Rho, along with an adaptor protein called paxillin, have been particularly implicated in the formation of such migration patterns and in regulating adhesion dynamics. Together, they form a key regulatory network that involves the mutual inhibition exerted by Rac and Rho on each other and the promotion of Rac activation by phosphorylated paxillin. Although this interaction is sufficient in generating wave-pinning that underscores cellular polarization comprised of cellular front (high active Rac) and back (high active Rho), it remains unclear how they interact collectively to induce other modes of migration detected in Chinese hamster Ovary (CHO-K1) cells. We previously developed a six-variable (6V) reaction-diffusion model describing the interactions of these three proteins (in their active/phosphorylated and inactive/unphosphorylated forms) along with other auxiliary proteins, to decipher their role in generating wave-pinning. In this study, we explored, through computational modeling and image analysis, how differences in timescales within this molecular network can potentially produce the migration patterns in CHO-K1 cells and how switching between migration modes could occur. To do so, the 6V model was reduced to an excitable 4V spatiotemporal model possessing three different timescales. The model produced not only wave-pinning in the presence of diffusion, but also mixed-mode oscillations (MMOs) and relaxation oscillations (ROs). Implementing the model using the Cellular Potts Model (CPM) produced outcomes in which protrusions in the cell membrane changed Rac-Rho localization, resulting in membrane oscillations and fast directionality variations similar to those observed experimentally in CHO-K1 cells. The latter was assessed by comparing the migration patterns of experimental with CPM cells using four metrics: instantaneous cell speed, exponent of mean-square displacement ([Formula: see text]-value), directionality ratio and protrusion rate. Variations in migration patterns induced by mutating paxillin's serine 273 residue were also captured by the model and detected by a machine classifier, revealing that this mutation alters the dynamics of the system from MMOs to ROs or nonoscillatory behaviour through variation in the scaled concentration of an active form of an adhesion protein called p21-Activated Kinase 1 (PAK). These results thus suggest that MMOs and adhesion dynamics are the key mechanisms regulating CHO-K1 cell motility.

A mathematical model of wound healing in bovine corneal endothelium

We developed a mathematical model to describe healing processes in bovine corneal endothelial (BCE) cells in culture, triggered by mechanical wounds with parallel edges. Previous findings from our laboratory show that, in these cases, BCE monolayers exhibit an approximately constant healing velocity. Also, that caspase-dependent apoptosis occurs, with the fraction of apoptotic cells increasing with the distance traveled by the healing edge. In addition, in this study we report the novel findings that, for wound scratch assays performed preserving the basal extracellular matrix: i) the healing cells increase their en face surface area in a characteristic fashion, and ii) the average length of the segments of the cell columns actively participating in the healing process increases linearly with time. These latter observations preclude the utilization of standard traveling wave formalisms to model wound healing in BCE cells. Instead, we developed and studied a simple phenomenological model based on a plausible formula for the spreading dynamics of the individual healing cells, that incorporates original evidence about the process in BCE cells. The model can be simulated to: i) obtain an approximately constant healing velocity; ii) reproduce the profile of the healing cell areas, and iii) obtain approximately linear time dependences of the mean cell area and average length of the front active segments per column. In view of its accuracy to account for the experimental observations, the model can also be acceptably employed to quantify the appearance of apoptotic cells during BCE wound healing. The strategy utilized here could offer a novel formal framework to represent modifications undergone by some epithelial cell lines during wound healing.

Quantitative Image Analysis of Dynamic Cell Behaviors During Border Cell Migration

Drosophila border cells have emerged as a genetically tractable model to investigate dynamic collective cell migration within the context of a developing organ. Studies of live border cell cluster migration have revealed similarities with other migrating collectives, including formation and restriction of cellular protrusions to the front of the cluster, supracellular actomyosin contractility of the entire collective, and intra-collective cell motility. Here, we describe protocols to prepare ex vivo cultures of stage 9 egg chambers followed by live time-lapse imaging of fluorescently labeled border cells to image dynamic cell behaviors. We provide options to perform live imaging using either a widefield epifluorescent microscope or a confocal microscope. We further outline steps to quantify various cellular behaviors and protein dynamics of live migrating border cells using the Fiji image processing package of ImageJ. These methods can be adapted to other migrating cell collectives in cultured tissues and organs.

ARHGAP29 is required for keratinocyte proliferation and migration

BACKGROUND

RhoA GTPase plays critical roles in actin cytoskeletal remodeling required for controlling a diverse range of cellular functions including cell proliferation, cell adhesions, migration and changes in cell shape. RhoA cycles between an active GTP-bound and an inactive GDP-bound form, a process that is regulated by guanine nucleotide exchange factors (GEFs), and GTPase-activating proteins (GAPs). ARHGAP29 is a GAP expressed in keratinocytes of the skin and is decreased in the absence of Interferon Regulator Factor 6, a critical regulator of cell proliferation and migration. However, the role for ARHGAP29 in keratinocyte biology is unknown.

RESULTS

Novel ARHGAP29 knockdown keratinocyte cell lines were generated using both CRISPR/Cas9 and shRNA technologies. Knockdown cells exhibited significant reduction of ARHGAP29 protein (50-80%) and displayed increased filamentous actin (stress fibers), phospho-myosin light chain (contractility), cell area and population doubling time. Furthermore, we found that ARHGAP29 knockdown keratinocytes displayed significant delays in scratch wound closure in both single cell and collective cell migration conditions. Particularly, our results show a reduction in path lengths, speed, directionality and persistence in keratinocytes with reduced ARHGAP29. The delay in scratch closure was rescued by both adding back ARHGAP29 or adding a ROCK inhibitor to ARHGAP29 knockdown cells.

CONCLUSIONS

These data demonstrate that ARHGAP29 is required for keratinocyte morphology, proliferation and migration mediated through the RhoA pathway.

Assessing cell migration in hydrogels: An overview of relevant materials and methods

Cell migration is essential in numerous living processes, including embryonic development, wound healing, immune responses, and cancer metastasis. From individual cells to collectively migrating epithelial sheets, the locomotion of cells is tightly regulated by multiple structural, chemical, and biological factors. However, the high complexity of this process limits the understanding of the influence of each factor. Recent advances in materials science, tissue engineering, and microtechnology have expanded the toolbox and allowed the development of biomimetic in vitro assays to investigate the mechanisms of cell migration. Particularly, three-dimensional (3D) hydrogels have demonstrated a superior ability to mimic the extracellular environment. They are therefore well suited to studying cell migration in a physiologically relevant and more straightforward manner than in vivo approaches. A myriad of synthetic and naturally derived hydrogels with heterogeneous characteristics and functional properties have been reported. The extensive portfolio of available hydrogels with different mechanical and biological properties can trigger distinct biological responses in cells affecting their locomotion dynamics in 3D. Herein, we describe the most relevant hydrogels and their associated physico-chemical characteristics typically employed to study cell migration, including established cell migration assays and tracking methods. We aim to give the reader insight into existing literature and practical details necessary for performing cell migration studies in 3D environments.

A planar-polarized MYO6-DOCK7-RAC1 axis promotes tissue fluidification in mammary epithelia

Tissue fluidification and collective motility are pivotal in regulating embryonic morphogenesis, wound healing and tumor metastasis. These processes frequently require that each cell constituent of a tissue coordinates its migration activity and directed motion through the oriented extension of lamellipodia cell protrusions, promoted by RAC1 activity. While the upstream RAC1 regulators in individual migratory cells or leader cells during invasion or wound healing are well characterized, how RAC1 is controlled in follower cells remains unknown. Here, we identify a novel MYO6-DOCK7 axis that is critical for spatially restriction of RAC1 activity in a planar polarized fashion in model tissue monolayers. The MYO6-DOCK7 axis specifically controls the extension of cryptic lamellipodia required to drive tissue fluidification and cooperative mode motion in otherwise solid and static carcinoma cell collectives.

Highlights

Collective motion of jammed epithelia requires myosin VI activityThe MYO6-DOCK7 axis is critical to restrict the activity of RAC1 in a planar polarized fashionMYO6-DOCK7-RAC1 activation ensures long-range coordination of movements by promoting orientation and persistence of cryptic lamellipodiaMyosin VI overexpression is exploited by infiltrating breast cancer cells.

Cell Migration in Three Dimensions

Cell migration plays an essential role in many pathophysiological processes, including embryonic development, wound healing, immunity, and cancer invasion, and is therefore a widely studied phenomenon in many different fields from basic cell biology to regenerative medicine. During the past decades, a multitude of increasingly complex methods have been developed to study cell migration. Here we compile a series of current state-of-the-art methods and protocols to investigate cell migration in a variety of model systems ranging from cells, organoids, tissue explants, and microfluidic systems to Drosophila, zebrafish, and mice. Together they cover processes as diverse as nuclear deformation, energy consumption, endocytic trafficking, and matrix degradation, as well as tumor vascularization and cancer cell invasion, sprouting angiogenesis, and leukocyte extravasation. Furthermore, methods to study developmental processes such as neural tube closure, germ layer specification, and branching morphogenesis are included, as well as scripts for the automated analysis of several aspects of cell migration. Together, this book constitutes a unique collection of methods of prime importance to those interested in the analysis of cell migration.

Coupling During Collective Cell Migration is Controlled by a Vinculin Mechanochemical Switch

Collective cell migration (CCM) plays important roles in development, physiological, and pathological processes. A key feature of CCM is the dynamic mechanical coupling between cells, which enables both long-range coordination and local rearrangements. This coupling requires the ability of cell adhesions to adapt to forces. Recent efforts have identified key proteins and implicated cellular-scale mechanical properties, but how key proteins give rise to these larger-scale mechanical processes is unclear. Using force-sensitive biosensors, cell migration assays, and molecular clutch models, we sought a molecular understanding of adhesion strengthening that could bridge this gap. We found that the mechanical linker protein vinculin bears substantial loads at AJs, FAs, and in the cytoplasm during epithelial sheet migration, and we identified a switch-like residue on vinculin that regulates its conformation and loading at the AJs during CCM. In vinculin KO-rescue, this switch jointly controlled the speed and coupling length-scale of CCM, which suggested changes in adhesion-based friction. To test this, we developed molecularly detailed friction clutch models of the FA and AJ. They show that open, loaded vinculin increases friction in adhesive structures, with larger affects observed in AJs. Thus, this work elucidates how load-bearing linker proteins can be regulated to alter mechanical properties of cells and enable rapid tuning of mechanical coupling in CCM.

Targeting integrin pathways: mechanisms and advances in therapy

Integrins are considered the main cell-adhesion transmembrane receptors that play multifaceted roles as extracellular matrix (ECM)-cytoskeletal linkers and transducers in biochemical and mechanical signals between cells and their environment in a wide range of states in health and diseases. Integrin functions are dependable on a delicate balance between active and inactive status via multiple mechanisms, including protein-protein interactions, conformational changes, and trafficking. Due to their exposure on the cell surface and sensitivity to the molecular blockade, integrins have been investigated as pharmacological targets for nearly 40 years, but given the complexity of integrins and sometimes opposite characteristics, targeting integrin therapeutics has been a challenge. To date, only seven drugs targeting integrins have been successfully marketed, including abciximab, eptifibatide, tirofiban, natalizumab, vedolizumab, lifitegrast, and carotegrast. Currently, there are approximately 90 kinds of integrin-based therapeutic drugs or imaging agents in clinical studies, including small molecules, antibodies, synthetic mimic peptides, antibody-drug conjugates (ADCs), chimeric antigen receptor (CAR) T-cell therapy, imaging agents, etc. A serious lesson from past integrin drug discovery and research efforts is that successes rely on both a deep understanding of integrin-regulatory mechanisms and unmet clinical needs. Herein, we provide a systematic and complete review of all integrin family members and integrin-mediated downstream signal transduction to highlight ongoing efforts to develop new therapies/diagnoses from bench to clinic. In addition, we further discuss the trend of drug development, how to improve the success rate of clinical trials targeting integrin therapies, and the key points for clinical research, basic research, and translational research.

Contractile and expansive actin networks in Drosophila: Developmental cell biology controlled by network polarization and higher-order interactions

Actin networks are central to shaping and moving cells during animal development. Various spatial cues activate conserved signal transduction pathways to polarize actin network assembly at sub-cellular locations and to elicit specific physical changes. Actomyosin networks contract and Arp2/3 networks expand, and to affect whole cells and tissues they do so within higher-order systems. At the scale of tissues, actomyosin networks of epithelial cells can be coupled via adherens junctions to form supracellular networks. Arp2/3 networks typically integrate with distinct actin assemblies, forming expansive composites which act in conjunction with contractile actomyosin networks for whole-cell effects. This review explores these concepts using examples from Drosophila development. First, we discuss the polarized assembly of supracellular actomyosin cables which constrict and reshape epithelial tissues during embryonic wound healing, germ band extension, and mesoderm invagination, but which also form physical borders between tissue compartments at parasegment boundaries and during dorsal closure. Second, we review how locally induced Arp2/3 networks act in opposition to actomyosin structures during myoblast cell-cell fusion and cortical compartmentalization of the syncytial embryo, and how Arp2/3 and actomyosin networks also cooperate for the single cell migration of hemocytes and the collective migration of border cells. Overall, these examples show how the polarized deployment and higher-order interactions of actin networks organize developmental cell biology.

Analysis of mRNA Subcellular Distribution in Collective Cell Migration

The movement of groups of cells by collective cell migration requires division of labor between group members. Therefore, distinct cell identities, unique cell behaviors, and specific cellular roles are acquired by cells undergoing collective movement. A key driving force behind the acquisition of discrete cell states is the precise control of where, when, and how genes are expressed, both at the subcellular and supracellular level. Unraveling the mechanisms underpinning the spatiotemporal control of gene expression in collective cell migration requires not only suitable experimental models but also high-resolution imaging of messenger RNA and protein localization during this process. In recent times, the highly stereotyped growth of new blood vessels by sprouting angiogenesis has become a paradigm for understanding collective cell migration, and consequently this has led to the development of numerous user-friendly in vitro models of angiogenesis. In parallel, single-molecule fluorescent in situ hybridization (smFISH) has come to the fore as a powerful technique that allows quantification of both RNA number and RNA spatial distribution in cells and tissues. Moreover, smFISH can be combined with immunofluorescence to understand the precise interrelationship between RNA and protein distribution. Here, we describe methods for use of smFISH and immunofluorescence microscopy in in vitro angiogenesis models to enable the investigation of RNA and protein expression and localization during endothelial collective cell migration.

The Concordance of Alveolar Bone Deficiency with Severity of Lip Deformity in Microform Cleft Lip

Background: We assessed the anthropometric measurements of bone defects in microform cleft lip. Methods: The external phenotypes of the nose and upper lip, and alveolar bone defects in microform cleft lip were measured anthropometrically using multimodal tools and clinical photographs. The height and thickness of the alveolar bone, paranasal hypoplasia, and alveolar volume were measured on CT. Results: Our study included 23 patients with unilateral microform cleft lip. The mean age of the patients was 13.84 ± 12.35 years (range: 1.25−50 years). Alveolar height (C1), thickness (C2), and paranasal hypoplasia (C3) were evaluated on 3D CT scans. The mean differences in C1, C2, and C3 between the cleft and normal sides were 5.52 ± 3.76 mm (p < 0.0001), 1.96 ± 2.8 mm (p < 0.0001), and 5.57 ± 9.72 mm (p < 0.0001), respectively. There was bony deficiency at the cleft side of the alveolar bone and paranasal area. In volumetric analysis, the means of the normal and cleft-side alveolar bone volumes were 6579 ± 2200 mm3 and 6528 ± 2255 mm3, respectively. The mean difference in alveolar bone volume between the cleft and normal sides was 51.05 ± 521 mm3 (p < 0.0001). C1 was positively correlated with lip height (F2; correlation coefficient (r) = 0.564, p = 0.0051) and dry vermilion thickness (F3; r = −0.543, p = 0.0074). The linear regression test revealed significant correlations between C1 and F2 (r2 = 0.318, p = 0.0051), and F3 (r2 = 0.295, p = 0.0074). However, there was no correlation between alveolar height and nasal anthropometric measurements. Conclusions: Alveolar bone deficiency was concordant with the severity of soft tissue in microform cleft lip.

Pattern formation of elliptic particles by two-body interactions: A model for dynamics of endothelial cells in angiogenesis

A two-dimensional mathematical model for dynamics of endothelial cells in angiogenesis is investigated. Angiogenesis is a morphogenic process in which new blood vessels emerge from an existing vascular network. Recently a one-dimensional discrete dynamical model has been proposed to reproduce elongation, bifurcation, and cell motility such as cell-mixing during angiogenesis on the assumption of a simple two-body interaction between endothelial cells. The present model is its two-dimensional extension, where endothelial cells are represented as the ellipses with the two-body interactions: repulsive interaction due to excluded volume effect, attractive interaction through pseudopodia and rotation by contact. We show that the oblateness of ellipses and the magnitude of contact rotation significantly affect the shape of created vascular patterns and elongation of branches.

Collective cell migration during human mammary gland organoid morphogenesis

Organ morphogenesis is driven by cellular migration patterns, which become accessible for observation in organoid cultures. We demonstrate here that mammary gland organoids cultured from human primary cells, exhibit oscillatory and collective migration patterns during their development into highly branched structures, as well as persistent rotational motion within the developed alveoli. Using high-resolution live-cell imaging, we observed cellular movement over the course of several days and subsequently characterized the underlying migration pattern by means of optical flow algorithms. Confined by the surrounding collagen matrix, characteristic correlated back-and-forth movements emerge due to a mismatch between branch invasion and cell migration speeds throughout the branch invasion phase. In contrast, alveolar cells exhibit continuous movement in the same direction. By modulating cell-cell adhesions, we identified collective migration as a prerequisite for sustaining these migration patterns both during the branching elongation process and after alveolus maturation.

Creating artificial signaling gradients to spatially pattern engineered tissues

Artificially constructing a fully-fledged tissue - comprising multiple cell types whose identities and spatial arrangements reflect those of a native tissue - remains daunting. There has been impressive progress in generating three-dimensional cell cultures (often dubbed 'organoids') from stem cells. However, it is critical to appreciate that not all such three-dimensional cultures will intrinsically self-organize to spontaneously recreate native tissue architecture. Instead, most tissues in vivo are exogenously patterned by extracellular signaling gradients emanating from organizer cells located outside the tissue. Innovations to impose artificial signaling gradients - using microfluidics, optogenetics, or introducing organizer cells - could thus prove decisive to create spatially patterned tissues in vitro. Additionally, unified terminology to describe these tissue-like simulacra as 'aggregates', 'spheroids', or 'organoids' will be critical for the field.

Epithelial morphogenesis in the Drosophila egg chamber requires Parvin and ILK

Integrins are the major family of transmembrane proteins that mediate cell-matrix adhesion and have a critical role in epithelial morphogenesis. Integrin function largely depends on the indirect connection of the integrin cytoplasmic tail to the actin cytoskeleton through an intracellular protein network, the integrin adhesome. What is currently unknown is the role of individual integrin adhesome components in epithelia dynamic reorganization. Drosophila egg chamber consists of the oocyte encircled by a monolayer of somatic follicle epithelial cells that undergo specific cell shape changes. Egg chamber morphogenesis depends on a developmental array of cell-cell and cell-matrix signalling events. Recent elegant work on the role of integrins in the Drosophila egg chamber has indicated their essential role in the early stages of oogenesis when the pre-follicle cells assemble into the follicle epithelium. Here, we have focused on the functional requirement of two key integrin adhesome components, Parvin and Integrin-Linked Kinase (ILK). Both proteins are expressed in the developing ovary from pupae to the adult stage and display enriched expression in terminal filament and stalk cells, while their genetic removal from early germaria results in severe disruption of the subsequent oogenesis, leading to female sterility. Combining genetic mosaic analysis of available null alleles for both Parvin and Ilk with conditional rescue utilizing the UAS/Gal4 system, we found that Parvin and ILK are required in pre-follicle cells for germline cyst encapsulation and stalk cell morphogenesis. Collectively, we have uncovered novel developmental functions for both Parvin and ILK, which closely synergize with integrins in epithelia.

A Scribble/Cdep/Rac pathway controls follower-cell crawling and cluster cohesion during collective border-cell migration

Collective cell movements drive normal development and metastasis. Drosophila border cells move as a cluster of 6-10 cells, where the role of the Rac GTPase in migration was first established. In border cells, as in most migratory cells, Rac stimulates leading-edge protrusion. Upstream Rac regulators in leaders have been identified; however, the regulation and function of Rac in follower border cells is unknown. Here, we show that all border cells require Rac, which promotes follower-cell motility and is important for cluster compactness and movement. We identify a Rac guanine nucleotide exchange factor, Cdep, which also regulates follower-cell movement and cluster cohesion. Scribble, Discs large, and Lethal giant larvae localize Cdep basolaterally and share phenotypes with Cdep. Relocalization of Cdep::GFP partially rescues Scribble knockdown, suggesting that Cdep is a major downstream effector of basolateral proteins. Thus, a Scrib/Cdep/Rac pathway promotes cell crawling and coordinated, collective migration in vivo.

A review on mechanobiology of cell adhesion networks in different stages of sporadic colorectal cancer to explain its tumorigenesis

Sporadic colorectal cancer (CRC) is strongly linked to extraneous factors, like poor diet and lifestyle, but not to inherent factors like familial genetics. The changes at the epigenomics and signalling pathways are known across the sporadic CRC stages. The catch is that temporal information of the onset, the feedback loop, and the crosstalk of signalling and noise are still unclear. This makes it challenging to diagnose and treat colon cancer effectively with no relapse. Various microbial cells and native cells of the colon, contribute to sporadic CRC development. These cells secrete autocrine and paracrine for their bioenergetics and communications with other cell types. Imbalances of the biochemicals affect the epithelial lining of colon. One side of this epithelial lining is interfacing the dense colon tissue, while the other side is exposed to microbiota and excrement from the lumen. Hence, the epithelial lining is prone to tumorigenesis due to the influence of both biochemical and mechanical cues from its complex surrounding. The role of physical transformations in tumorigenesis have been limitedly discussed. In this context, cellular and tissue structures, and force transductions are heavily regulated by cell adhesion networks. These networks include cell anchoring mechanism to the surrounding, cell structural integrity mechanism, and cell effector molecules. This review will focus on the progression of the sporadic CRC stages that are governed by the underlaying cell adhesion networks within the epithelial cells. Additionally, current and potential technologies and therapeutics that target cell adhesion networks for treatments of sporadic CRC will be incorporated.

FGF8 induces chemokinesis and regulates condensation of mouse nephron progenitor cells

Kidneys develop via iterative branching of the ureteric epithelial tree and subsequent nephrogenesis at the branch points. Nephrons form in the cap mesenchyme as the metanephric mesenchyme (MM) condenses around the epithelial ureteric buds (UBs). Previous work has demonstrated that FGF8 is important for the survival of nephron progenitor cells (NPCs), and early deletion of Fgf8 leads to the cessation of nephron formation, which results in post-natal lethality. We now reveal a previously unreported function of FGF8. By combining transgenic mouse models, quantitative imaging assays and data-driven computational modelling, we show that FGF8 has a strong chemokinetic effect and that this chemokinetic effect is important for the condensation of NPCs to the UB. The computational model shows that the motility must be lower close to the UB to achieve NPC attachment. We conclude that the FGF8 signalling pathway is crucial for the coordination of NPC condensation at the UB. Chemokinetic effects have also been described for other FGFs and may be generally important for the formation of mesenchymal condensates.

Picking winners in cell-cell collisions: Wetting, speed, and contact

Groups of eukaryotic cells can coordinate their crawling motion to follow cues more effectively, stay together, or invade new areas. This collective cell migration depends on cell-cell interactions, which are often studied by colliding pairs of cells together. Can the outcome of these collisions be predicted? Recent experiments on trains of colliding epithelial cells suggest that cells with a smaller contact angle to the surface or larger speeds are more likely to maintain their direction ("win") upon collision. When should we expect shape or speed to correlate with the outcome of a collision? To investigate this question, we build a model for two-cell collisions within the phase field framework, which allows for cell shape changes. We can reproduce the observation that cells with high speed and small contact angles are more likely to win with two different assumptions for how cells interact: (1) velocity aligning, in which we hypothesize that cells sense their own velocity and align to it over a finite timescale, and (2) front-front contact repolarization, where cells polarize away from cell-cell contact, akin to contact inhibition of locomotion. Surprisingly, though we simulate collisions between cells with widely varying properties, in each case, the probability of a cell winning is completely captured by a single summary variable: its relative speed (in the velocity-aligning model) or its relative contact angle (in the contact repolarization model). Both models are currently consistent with reported experimental results, but they can be distinguished by varying cell contact angle and speed through orthogonal perturbations.

Two Rac1 pools integrate the direction and coordination of collective cell migration

Integration of collective cell direction and coordination is believed to ensure collective guidance for efficient movement. Previous studies demonstrated that chemokine receptors PVR and EGFR govern a gradient of Rac1 activity essential for collective guidance of Drosophila border cells, whose mechanistic insight is unknown. By monitoring and manipulating subcellular Rac1 activity, here we reveal two switchable Rac1 pools at border cell protrusions and supracellular cables, two important structures responsible for direction and coordination. Rac1 and Rho1 form a positive feedback loop that guides mechanical coupling at cables to achieve migration coordination. Rac1 cooperates with Cdc42 to control protrusion growth for migration direction, as well as to regulate the protrusion-cable exchange, linking direction and coordination. PVR and EGFR guide correct Rac1 activity distribution at protrusions and cables. Therefore, our studies emphasize the existence of a balance between two Rac1 pools, rather than a Rac1 activity gradient, as an integrator for the direction and coordination of collective cell migration.

Previous studies suggested a chemokine receptor governed gradient of Rac1 activity is essential for collective guidance of Drosophila border cells. Here, Zhou et al. report that two distinct Rac1 pools at protrusions and cables, not Rac1 activity gradient, integrate the direction and coordination for collective guidance.

Pulsations and flows in tissues as two collective dynamics with simple cellular rules

Collective motions of epithelial cells are essential for morphogenesis. Tissues elongate, contract, flow, and oscillate, thus sculpting embryos. These tissue level dynamics are known, but the physical mechanisms at the cellular level are unclear. Here, we demonstrate that a single epithelial monolayer of MDCK cells can exhibit two types of local tissue kinematics, pulsations and long range coherent flows, characterized by using quantitative live imaging. We report that these motions can be controlled with internal and external cues such as specific inhibitors and substrate friction modulation. We demonstrate the associated mechanisms with a unified vertex model. When cell velocity alignment and random diffusion of cell polarization are comparable, a pulsatile flow emerges whereas tissue undergoes long-range flows when velocity alignment dominates which is consistent with cytoskeletal dynamics measurements. We propose that environmental friction, acto-myosin distributions, and cell polarization kinetics are important in regulating dynamics of tissue morphogenesis.

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Two collective cell motions, pulsations and flows, coexist in MDCK monolayers

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Each collective movement is identified using divergence and velocity correlations

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Motion is controlled by the regulation of substrate friction and cytoskeleton

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A vertex model recapitulates the motion by tuning velocity and polarity alignment

Fat2 polarizes the WAVE complex in trans to align cell protrusions for collective migration

For a group of cells to migrate together, each cell must couple the polarity of its migratory machinery with that of the other cells in the cohort. Although collective cell migrations are common in animal development, little is known about how protrusions are coherently polarized among groups of migrating epithelial cells. We address this problem in the collective migration of the follicular epithelial cells in Drosophila melanogaster. In this epithelium, the cadherin Fat2 localizes to the trailing edge of each cell and promotes the formation of F-actin-rich protrusions at the leading edge of the cell behind. We show that Fat2 performs this function by acting in trans to concentrate the activity of the WASP family verprolin homolog regulatory complex (WAVE complex) at one long-lived region along each cell's leading edge. Without Fat2, the WAVE complex distribution expands around the cell perimeter and fluctuates over time, and protrusive activity is reduced and unpolarized. We further show that Fat2's influence is very local, with sub-micron-scale puncta of Fat2 enriching the WAVE complex in corresponding puncta just across the leading-trailing cell-cell interface. These findings demonstrate that a trans interaction between Fat2 and the WAVE complex creates stable regions of protrusive activity in each cell and aligns the cells' protrusions across the epithelium for directionally persistent collective migration.

Confined migration induces heterochromatin formation and alters chromatin accessibility

During migration, cells often squeeze through small constrictions, requiring extensive deformation. We hypothesized that nuclear deformation associated with such confined migration could alter chromatin organization and function. By studying cells migrating through microfluidic devices that mimic interstitial spaces in vivo, we found that confined migration results in increased H3K9me3 and H3K27me3 heterochromatin marks that persist for days. This "confined migration-induced heterochromatin" (CMiH) was distinct from heterochromatin formation during migration initiation. Confined migration decreased chromatin accessibility at intergenic regions near centromeres and telomeres, suggesting heterochromatin spreading from existing sites. Consistent with the overall decrease in accessibility, global transcription was decreased during confined migration. Intriguingly, we also identified increased accessibility at promoter regions of genes linked to chromatin silencing, tumor invasion, and DNA damage response. Inhibiting CMiH reduced migration speed, suggesting that CMiH promotes confined migration. Together, our findings indicate that confined migration induces chromatin changes that regulate cell migration and other functions.

Dominant geometrical factors of collective cell migration in flexible 3D gelatin tube structures

Collective cell migration is a dynamic and interactive behavior of cell cohorts essential for diverse physiological developments in living organisms. Recent studies have revealed the importance of three-dimensional (3D) topographical confinements to regulate the migration modes of cell cohorts in tubular confinement. However, conventional in vitro assays fail to observe cells' behavior in response to 3D structural changes, which is necessary for examining the geometric regulation factors of collective migration. Here, we introduce a newly developed assay for fabricating flexible 3D structures of capillary microtunnels to examine the behavior of vascular endothelial cells (ECs) as they progress through the successive transition across wide or narrow tube structures. The microtunnels with altered diameters were formed inside gelatin-gel blocks by photo-thermal etching with micrometer-sized spot heating of the focused infrared laser absorption. The ECs migrated and spread two-dimensionally on the inner surface of gelatin capillary microtunnels as a monolayer instead of filling the entire capillary. In the straight cylindrical topographical constraint, leading ECs exhibited no apparent diameter dependence for the maximum peak migration velocity. However, widening the diameter in the narrow-wide structures caused a decrease in migration velocity following in direct proportion to the diameter increase ratio, whereas narrowing the diameter in wide-narrow microtunnels increased the speed without obvious correlation between velocity change and diameter change. The results demonstrated the ability of the newly developed flexible 3D gelatin tube structures for collective cell migration, and the findings provide insights into the dominant geometric factor of the emerging migratory modes for endothelial migration as asymmetric fluid flow-like behavior in the borderless cylindrical cell sheets.

Signatures of directed and spontaneous flocking

Collective motion-or flocking-is an emergent phenomena that underlies many biological processes of relevance, from cellular migrations to animal group movements. In this work, we derive scaling relations for the fluctuations of the mean direction of motion and for the static density structure factor (which encodes static density fluctuations) in the presence of a homogeneous, small external field. This allows us to formulate two different and complementary criteria capable of detecting instances of directed motion exclusively from easily measurable dynamical and static signatures of the collective dynamics, without the need to detect correlations with environmental cues. The static one is informative in large enough systems, while the dynamical one requires large observation times to be effective. We believe these criteria may prove useful to detect or confirm the directed nature of collective motion in in vivo experimental observations, which are typically conducted in complex and not fully controlled environments.

Appropriate tension sensitivity of α-catenin ensures rounding morphogenesis of epithelial spheroids

The adherens junction (AJ) is an actin filament-anchoring junction. It plays a central role in epithelial morphogenesis through cadherin-based recognition and adhesion among cells. The stability and plasticity of AJs are required for the morphogenesis. An actin-binding α-catenin is an essential component of the cadherin-catenin complex and functions as a tension transducer that changes its conformation and induces AJ development in response to tension. Despite much progress in understanding molecular mechanisms of tension sensitivity of α-catenin, its significance on epithelial morphogenesis is still unknown. Here we show that the tension sensitivity of α-catenin is essential for epithelial cells to form round spheroids through proper multicellular rearrangement. Using a novel in vitro suspension culture model, we found that epithelial cells form round spheroids even from rectangular-shaped cell masses with high aspect ratios without using high tension and that increased tension sensitivity of α-catenin affected this morphogenesis. Analyses of AJ formation and cellular tracking during rounding morphogenesis showed cellular rearrangement, probably through AJ remodeling. The rearrangement occurs at the cell mass level, but not single-cell level. Hypersensitive α-catenin mutant-expressing cells did not show cellular rearrangement at the cell mass level, suggesting that the appropriate tension sensitivity of α-catenin is crucial for the coordinated round morphogenesis.Key words: α-catenin, vinculin, adherens junction, morphogenesis, mechanotransduction.

Force Estimation during Cell Migration Using Mathematical Modelling

Cell migration is essential for physiological, pathological and biomedical processes such as, in embryogenesis, wound healing, immune response, cancer metastasis, tumour invasion and inflammation. In light of this, quantifying mechanical properties during the process of cell migration is of great interest in experimental sciences, yet few theoretical approaches in this direction have been studied. In this work, we propose a theoretical and computational approach based on the optimal control of geometric partial differential equations to estimate cell membrane forces associated with cell polarisation during migration. Specifically, cell membrane forces are inferred or estimated by fitting a mathematical model to a sequence of images, allowing us to capture dynamics of the cell migration. Our approach offers a robust and accurate framework to compute geometric mechanical membrane forces associated with cell polarisation during migration and also yields geometric information of independent interest, we illustrate one such example that involves quantifying cell proliferation levels which are associated with cell division, cell fusion or cell death.

Spatiotemporal analysis of glioma heterogeneity reveals COL1A1 as an actionable target to disrupt tumor progression

Intra-tumoral heterogeneity is a hallmark of glioblastoma that challenges treatment efficacy. However, the mechanisms that set up tumor heterogeneity and tumor cell migration remain poorly understood. Herein, we present a comprehensive spatiotemporal study that aligns distinctive intra-tumoral histopathological structures, oncostreams, with dynamic properties and a specific, actionable, spatial transcriptomic signature. Oncostreams are dynamic multicellular fascicles of spindle-like and aligned cells with mesenchymal properties, detected using ex vivo explants and in vivo intravital imaging. Their density correlates with tumor aggressiveness in genetically engineered mouse glioma models, and high grade human gliomas. Oncostreams facilitate the intra-tumoral distribution of tumoral and non-tumoral cells, and potentially the collective invasion of the normal brain. These fascicles are defined by a specific molecular signature that regulates their organization and function. Oncostreams structure and function depend on overexpression of COL1A1. Col1a1 is a central gene in the dynamic organization of glioma mesenchymal transformation, and a powerful regulator of glioma malignant behavior. Inhibition of Col1a1 eliminates oncostreams, reprograms the malignant histopathological phenotype, reduces expression of the mesenchymal associated genes, induces changes in the tumor microenvironment and prolongs animal survival. Oncostreams represent a pathological marker of potential value for diagnosis, prognosis, and treatment.

It is essential to improve our understanding of the features that influence aggressiveness and invasion in high grade gliomas (HGG). Here, the authors characterize dynamic anatomical structures in HGG called oncostreams, which are associated with tumor growth and are regulated by COL1A1.

Crucial Convolution: Genetic and Molecular Mechanisms of Coiling during Epididymis Formation and Development in Embryogenesis

As embryonic development proceeds, numerous organs need to coil, bend or fold in order to establish their final shape. Generally, this occurs so as to maximise the surface area for absorption or secretory functions (e.g., in the small and large intestines, kidney or epididymis); however, mechanisms of bending and shaping also occur in other structures, notably the midbrain–hindbrain boundary in some teleost fish models such as zebrafish. In this review, we will examine known genetic and molecular factors that operate to pattern complex, coiled structures, with a primary focus on the epididymis as an excellent model organ to examine coiling. We will also discuss genetic mechanisms involving coiling in the seminiferous tubules and intestine to establish the final form and function of these coiled structures in the mature organism.

BMP-gated cell-cycle progression drives anoikis during mesenchymal collective migration

Tissue homeostasis involves the elimination of abnormal cells to avoid compromised patterning and function. Although quality control through cell competition is well studied in epithelial tissues, it is unknown if and how homeostasis is regulated in mesenchymal collectives. Here, we demonstrate that collectively migrating Drosophila muscle precursors utilize both fibroblast growth factor (FGF) and bone morphogenetic protein (BMP) signaling to promote homeostasis via anoikis, a form of cell death in response to substrate de-adhesion. Cell-cycle-regulated expression of the cell death gene head involution defective is responsible for caudal visceral mesoderm (CVM) anoikis. The secreted BMP ligand drives cell-cycle progression via a visceral mesoderm-specific cdc25/string enhancer to synchronize collective proliferation, as well as apoptosis of cells that have lost access to substrate-derived FGF. Perturbation of BMP-dependent cell-cycle progression is sufficient to confer anoikis resistance to mismigrating cells and thus facilitate invasion of other tissues. This BMP-gated cell-cycle checkpoint defines a quality control mechanism during mesenchymal collective migration.

Border cell polarity and collective migration require the spliceosome component Cactin

Border cells are an in vivo model for collective cell migration. Here, we identify the gene cactin as essential for border cell cluster organization, delamination, and migration. In Cactin-depleted cells, the apical proteins aPKC and Crumbs (Crb) become abnormally concentrated, and overall cluster polarity is lost. Apically tethering excess aPKC is sufficient to cause delamination defects, and relocalizing apical aPKC partially rescues delamination. Cactin is conserved from yeast to humans and has been implicated in diverse processes. In border cells, Cactin's evolutionarily conserved spliceosome function is required. Whole transcriptome analysis revealed alterations in isoform expression in Cactin-depleted cells. Mutations in two affected genes, Sec23 and Sec24CD, which traffic Crb to the apical cell surface, partially rescue border cell cluster organization and migration. Overexpression of Rab5 or Rab11, which promote Crb and aPKC recycling, similarly rescues. Thus, a general splicing factor is specifically required for coordination of cluster polarity and migration, and migrating border cells are particularly sensitive to splicing and cell polarity disruptions.

Leveraging the model-experiment loop: Examples from cellular slime mold chemotaxis

Interplay between models and experimental data advances discovery and understanding in biology, particularly when models generate predictions that allow well-designed experiments to distinguish between alternative mechanisms. To illustrate how this feedback between models and experiments can lead to key insights into biological mechanisms, we explore three examples from cellular slime mold chemotaxis. These examples include studies that identified chemotaxis as the primary mechanism behind slime mold aggregation, discovered that cells likely measure chemoattractant gradients by sensing concentration differences across cell length, and tested the role of cell-associated chemoattractant degradation in shaping chemotactic fields. Although each study used a different model class appropriate to their hypotheses - qualitative, mathematical, or simulation-based - these examples all highlight the utility of modeling to formalize assumptions and generate testable predictions. A central element of this framework is the iterative use of models and experiments, specifically: matching experimental designs to the models, revising models based on mismatches with experimental data, and validating critical model assumptions and predictions with experiments. We advocate for continued use of this interplay between models and experiments to advance biological discovery.

Guidance by followers ensures long-range coordination of cell migration through α-catenin mechanoperception

Morphogenesis, wound healing, and some cancer metastases depend upon the migration of cell collectives that need to be guided to their destination as well as coordinated with other cell movements. During zebrafish gastrulation, the extension of the embryonic axis is led by the mesendodermal polster that migrates toward the animal pole, followed by the axial mesoderm that undergoes convergence and extension. Here, we investigate how polster cells are guided toward the animal pole. Using a combination of precise laser ablations, advanced transplants, and functional as well as in silico approaches, we establish that each polster cell is oriented by its immediate follower cells. Each cell perceives the migration of followers, through E-cadherin/α-catenin mechanotransduction, and aligns with them. Therefore, directional information propagates from cell to cell over the whole tissue. Such guidance of migrating cells by followers ensures long-range coordination of movements and developmental robustness.

Cellular protrusions in 3D: Orchestrating early mouse embryogenesis

Cellular protrusions generated by the actin cytoskeleton are central to the process of building the body of the embryo. Problems with cellular protrusions underlie human diseases and syndromes, including implantation defects and pregnancy loss, congenital birth defects, and cancer. Cells use protrusive activity together with actin-myosin contractility to create an ordered body shape of the embryo. Here, I review how actin-rich protrusions are used by two major morphological cell types, epithelial and mesenchymal cells, during collective cell migration to sculpt the mouse embryo body. Pre-gastrulation epithelial collective migration of the anterior visceral endoderm is essential for establishing the anterior-posterior body axis. Gastrulation mesenchymal collective migration of the mesoderm wings is crucial for body elongation, and somite and heart formation. Analysis of mouse mutants with disrupted cellular protrusions revealed the key role of protrusions in embryonic morphogenesis and embryo survival. Recent technical approaches have allowed examination of the mechanisms that control cell and tissue movements in vivo in the complex 3D microenvironment of living mouse embryos. Advancing our understanding of protrusion-driven morphogenesis should provide novel insights into human developmental disorders and cancer metastasis.