Cadherin Switch during EMT in Neural Crest Cells Leads to Contact Inhibition of Locomotion via Repolarization of Forces

Collective cell migration driven by filopodia-New insights from the social behavior of myotubes

Collective migration is a key process that is critical during development, as well as in physiological and pathophysiological processes including tissue repair, wound healing and cancer. Studies in genetic model organisms have made important contributions to our current understanding of the mechanisms that shape cells into different tissues during morphogenesis. Recent advances in high-resolution and live-cell-imaging techniques provided new insights into the social behavior of cells based on careful visual observations within the context of a living tissue. In this review, we will compare Drosophila testis nascent myotube migration with established in vivo model systems, elucidate similarities, new features and principles in collective cell migration.

Epithelial plasticity, epithelial-mesenchymal transition, and the TGF-β family

Epithelial cells repress epithelial characteristics and elaborate mesenchymal characteristics to migrate to other locations and acquire new properties. Epithelial plasticity responses are directed through cooperation of signaling pathways, with TGF-β and TGF-β-related proteins playing prominent instructive roles. Epithelial-mesenchymal transitions (EMTs) directed by activin-like molecules, bone morphogenetic proteins, or TGF-β regulate metazoan development and wound healing and drive fibrosis and cancer progression. In carcinomas, diverse EMTs enable stem cell generation, anti-cancer drug resistance, genomic instability, and localized immunosuppression. This review discusses roles of TGF-β and TGF-β-related proteins, and underlying molecular mechanisms, in epithelial plasticity in development and wound healing, fibrosis, and cancer.

Ptk7 Is Dynamically Localized at Neural Crest Cell-Cell Contact Sites and Functions in Contact Inhibition of Locomotion

Neural crest (NC) cells are highly migratory cells that contribute to various vertebrate tissues, and whose migratory behaviors resemble cancer cell migration and invasion. Information exchange via dynamic NC cell-cell contact is one mechanism by which the directionality of migrating NC cells is controlled. One transmembrane protein that is most likely involved in this process is protein tyrosine kinase 7 (PTK7), an evolutionary conserved Wnt co-receptor that is expressed in cranial NC cells and several tumor cells. In Xenopus, Ptk7 is required for NC migration. In this study, we show that the Ptk7 protein is dynamically localized at cell-cell contact zones of migrating Xenopus NC cells and required for contact inhibition of locomotion (CIL). Using deletion constructs of Ptk7, we determined that the extracellular immunoglobulin domains of Ptk7 are important for its transient accumulation and that they mediate homophilic binding. Conversely, we found that ectopic expression of Ptk7 in non-NC cells was able to prevent NC cell invasion. However, deletion of the extracellular domains of Ptk7 abolished this effect. Thus, Ptk7 is sufficient at protecting non-NC tissue from NC cell invasion, suggesting a common role of PTK7 in contact inhibition, cell invasion, and tissue integrity.

Neutrophil motion in numbers: How to analyse complex migration patterns

In vivo imaging has revolutionised the study of leukocyte trafficking and revealed many insights on the dynamic behaviour of immune cells in their native environment. Neutrophil migration represents a prominent example whereby live imaging led to discovery of unanticipated cell migration patterns. These cells are the first to enter inflammatory sites and their recruitment had once been thought to be driven primarily by extrinsic signals and resolved by apoptosis in these lesions. However, in vivo imaging in zebrafish and mice indicated that neutrophils are also able to self-organise their migration to a large extent, through collective generation of gradients, in a process referred to as 'swarming', and that they can leave sites of inflammation, in a process referred to as 'reverse migration'. An important step in understanding these newly defined behaviours is the ability to detect and quantify them through statistical analysis. Here we provide a summary of considerations and recommendations for quantitative analysis of neutrophil swarming and reverse migration, with the purpose of introducing relevant analysis tools to new researchers in the field and establishing common frameworks and standards.

Mechanisms involved in selecting and maintaining neuroblastoma cancer stem cell populations, and perspectives for therapeutic targeting

Pediatric neuroblastomas (NBs) are heterogeneous, aggressive, therapy-resistant embryonal tumours that originate from cells of neural crest (NC) origin and in particular neuroblasts committed to the sympathoadrenal progenitor cell lineage. Therapeutic resistance, post-therapeutic relapse and subsequent metastatic NB progression are driven primarily by cancer stem cell (CSC)-like subpopulations, which through their self-renewing capacity, intermittent and slow cell cycles, drug-resistant and reversibly adaptive plastic phenotypes, represent the most important obstacle to improving therapeutic outcomes in unfavourable NBs. In this review, dedicated to NB CSCs and the prospects for their therapeutic eradication, we initiate with brief descriptions of the unique transient vertebrate embryonic NC structure and salient molecular protagonists involved NC induction, specification, epithelial to mesenchymal transition and migratory behaviour, in order to familiarise the reader with the embryonic cellular and molecular origins and background to NB. We follow this by introducing NB and the potential NC-derived stem/progenitor cell origins of NBs, before providing a comprehensive review of the salient molecules, signalling pathways, mechanisms, tumour microenvironmental and therapeutic conditions involved in promoting, selecting and maintaining NB CSC subpopulations, and that underpin their therapy-resistant, self-renewing metastatic behaviour. Finally, we review potential therapeutic strategies and future prospects for targeting and eradication of these bastions of NB therapeutic resistance, post-therapeutic relapse and metastatic progression.

Mechanics of developmental migration

The ability to migrate is a fundamental property of animal cells which is essential for development, homeostasis and disease progression. Migrating cells sense and respond to biochemical and mechanical cues by rapidly modifying their intrinsic repertoire of signalling molecules and by altering their force generating and transducing machinery. We have a wealth of information about the chemical cues and signalling responses that cells use during migration. Our understanding of the role of forces in cell migration is rapidly evolving but is still best understood in the context of cells migrating in 2D and 3D environments in vitro. Advances in live imaging of developing embryos combined with the use of experimental and theoretical tools to quantify and analyse forces in vivo, has begun to shed light on the role of mechanics in driving embryonic cell migration. In this review, we focus on the recent studies uncovering the physical basis of embryonic cell migration in vivo. We look at the physical basis of the classical steps of cell migration such as protrusion formation and cell body translocation and review the recent research on how these processes work in the complex 3D microenvironment of a developing organism.

Advanced mechanotherapy: Biotensegrity for governing metastatic tumor cell fate via modulating the extracellular matrix

Mechano-transduction is the procedure of mechanical stimulus translation via cells, among substrate shear flow, topography, and stiffness into a biochemical answer. TAZ and YAP are transcriptional coactivators which are recognized as relay proteins that promote mechano-transduction within the Hippo pathway. With regard to healthy cells in homeostasis, mechano-transduction regularly restricts proliferation, and TAZ and YAP are totally inactive. During cancer development a YAP/TAZ - stimulating positive response loop is formed between the growing tumor and the stiffening ECM. As tumor developments, local stromal and cancerous cells take advantage of mechanotransduction to enhance proliferation, induce their migratory into remote tissues, and promote chemotherapeutic resistance. As a newly progresses paradigm, nanoparticle-conjunctions (such as magnetic nanoparticles, and graphene derivatives nanoparticles) hold significant promises for remote regulation of cells and their relevant events at molecular scale. Despite outstanding developments in employing nanoparticles for drug targeting studies, the role of nanoparticles on cellular behaviors (proliferation, migration, and differentiation) has still required more evaluations in the field of mechanotherapy. In this paper, the in-depth contribution of mechano-transduction is discussed during tumor progression, and how these consequences can be evaluated in vitro.

KSR1- and ERK-dependent translational regulation of the epithelial-to-mesenchymal transition

The epithelial-to-mesenchymal transition (EMT) is considered a transcriptional process that induces a switch in cells from a polarized state to a migratory phenotype. Here, we show that KSR1 and ERK promote EMT-like phenotype through the preferential translation of Epithelial-Stromal Interaction 1 (EPSTI1), which is required to induce the switch from E- to N-cadherin and coordinate migratory and invasive behavior. EPSTI1 is overexpressed in human colorectal cancer (CRC) cells. Disruption of KSR1 or EPSTI1 significantly impairs cell migration and invasion in vitro, and reverses EMT-like phenotype, in part, by decreasing the expression of N-cadherin and the transcriptional repressors of E-cadherin expression, ZEB1 and Slug. In CRC cells lacking KSR1, ectopic EPSTI1 expression restored the E- to N-cadherin switch, migration, invasion, and anchorage-independent growth. KSR1-dependent induction of EMT-like phenotype via selective translation of mRNAs reveals its underappreciated role in remodeling the translational landscape of CRC cells to promote their migratory and invasive behavior.

N-cadherin mediates the migration of bone marrow-derived mesenchymal stem cells toward breast tumor cells

Rationale: Bone marrow-derived mesenchymal stem cells (BM-MSCs) recruited into breast tumors regulate the behavior of tumor cells via various mechanisms and affect clinical outcomes. Although signaling molecules, such as transforming growth factor β (TGF-β), are known to transmit signals between BM-MSCs and breast tumor cells for recruiting BM-MSCs, it is unclear which specific intrinsic molecules involved in cell motility mediate the migration of BM-MSCs into breast tumor. It is also unclear as to how specific intrinsic molecules contribute to the migration. Methods: Conditioned medium (CM) from breast tumor cells (MCF-7 and MDA-MB-231) that simulates breast tumor secreting TGF-β was used to examine the migration of BM-MSCs into breast tumors. A three-dimensional migration assay was performed to investigate the collective migration of BM-MSCs, maintaining cell-cell adhesion, toward breast tumor cells. Results: N-cadherin formed adherens junction-like structures on the intercellular borders of BM-MSCs, and TGF-β increased the expression of N-cadherin on these borders. Knockdown of Smad4 impaired the TGF-β-mediated increase in N-cadherin expression in BM-MSCs, but inhibitors of non-canonical TGF-β pathways, such as extracellular signal-regulated kinases, Akt, and p38, did not affect it. siRNA-mediated knockdown of N-cadherin and Smad4 impaired the migration of BM-MSCs in response to TGF-β. Conditioned medium from breast tumor cells also enhanced the expression of N-cadherin in BM-MSCs, but inactivation of TGF-β type 1 receptor (TGFBR1) with SB505124 and TGFBR1 knockdown abolished the increase in N-cadherin expression. BM-MSCs collectively migrated toward CM from MDA-MB-231 in vitro while maintaining cell-cell adhesion through N-cadherin. Knockdown of N-cadherin abolished the migration of BM-MSCs toward the CM from breast tumor cells. Conclusion: In the present study, we identified N-cadherin, an intrinsic transmembrane molecule in adherens junction-like structures, on BM-MSCs as a mediator for the migration of these cells toward breast tumor. The expression of N-cadherin increases on the intercellular borders of BM-MSCs through the TGF-β canonical signaling and they collectively migrate in response to breast tumor cells expressing TGF-β via N-cadherin-dependent cell-cell adhesion. We, herein, introduce a novel promising strategy for controlling and re-engineering the breast tumor microenvironment.

Inhibition of Cyclooxygenase-2 Alters Craniofacial Patterning during Early Embryonic Development of Chick

A recent study from our lab revealed that the inhibition of cyclooxygenase-2 (COX-2) exclusively reduces the level of PGE2 (Prostaglandin E2) among prostanoids and hampers the normal development of several structures, strikingly the cranial vault, in chick embryos. In order to unearth the mechanism behind the deviant development of cranial features, the expression pattern of various factors that are known to influence cranial neural crest cell (CNCC) migration was checked in chick embryos after inhibiting COX-2 activity using etoricoxib. The compromised level of cell adhesion molecules and their upstream regulators, namely CDH1 (E-cadherin), CDH2 (N-cadherin), MSX1 (Msh homeobox 1), and TGF-β (Transforming growth factor beta), observed in the etoricoxib-treated embryos indicate that COX-2, through its downstream effector PGE2, regulates the expression of these factors perhaps to aid the migration of CNCCs. The histological features and levels of FoxD3 (Forkhead box D3), as well as PCNA (Proliferating cell nuclear antigen), further consolidate the role of COX-2 in the migration and survival of CNCCs in developing embryos. The results of the current study indicate that COX-2 plays a pivotal role in orchestrating craniofacial structures perhaps by modulating CNCC proliferation and migration during the embryonic development of chicks.

Contextual cues from cancer cells govern cancer-associated fibroblast heterogeneity

Cancer cells function as primary architects of the tumor microenvironment. However, the molecular features of cancer cells that govern stromal cell phenotypes remain unclear. Here, we show that cancer-associated fibroblast (CAF) heterogeneity is driven by lung adenocarcinoma (LUAD) cells at either end of the epithelial-to-mesenchymal transition (EMT) spectrum. LUAD cells that have high expression of the EMT-activating transcription factor ZEB1 reprogram CAFs through a ZEB1-dependent secretory program and direct CAFs to the tips of invasive projections through a ZEB1-driven CAF repulsion process. The EMT, in turn, sensitizes LUAD cells to pro-metastatic signals from CAFs. Thus, CAFs respond to contextual cues from LUAD cells to promote metastasis.

Neural crest multipotency and specification: power and limits of single cell transcriptomic approaches

The neural crest is a unique population of multipotent cells forming in vertebrate embryos. Their vast cell fate potential enables the generation of a diverse array of differentiated cell types in vivo. These include, among others, connective tissue, cartilage and bone of the face and skull, neurons and glia of the peripheral nervous system (including enteric nervous system), and melanocytes. Following migration, these derivatives extensively populate multiple germ layers. Within the competent neural border ectoderm, an area located at the junction between the neural and non-neural ectoderm during embryonic development, neural crest cells form in response to a series of inductive secreted cues including BMP, Wnt, and FGF signals. As cells become progressively specified, they express transcriptional modules conducive with their stage of fate determination or cell state. Those sequential states include the neural border state, the premigratory neural crest state, the epithelium-to-mesenchyme transitional state, and the migratory state to end with post-migratory and differentiation states. However, despite the extensive knowledge accumulated over 150 years of neural crest biology, many key questions remain open, in particular the timing of neural crest lineage determination, the control of potency during early developmental stages, and the lineage relationships between different subpopulations of neural crest cells. In this review, we discuss the recent advances in understanding early neural crest formation using cutting-edge high-throughput single cell sequencing approaches. We will discuss how this new transcriptomic data, from 2017 to 2021, has advanced our knowledge of the steps in neural crest cell lineage commitment and specification, the mechanisms driving multipotency, and diversification. We will then discuss the questions that remain to be resolved and how these approaches may continue to unveil the biology of these fascinating cells.

Are You Interested or Afraid of Working on EMT?

When referring to the epithelial-to-mesenchymal transition (EMT), readers are familiar with sentences alluding to its pivotal role both in embryonic development and in disease. Following that argument, usually there is a point on the importance of studying the process and the impact it has on the design of therapeutic strategies. However, it is also very common to find arguments on how the EMT is very difficult to tackle, being a somehow obscure and complex process, where the field cannot reach universal conclusions, particularly in pathological contexts. Even worse, it is sometimes defined as a process that cannot be described with universal markers, making it therefore very difficult for cancer studies, where there is a need to use optimal animal models and stratify patients for differential therapeutic strategies. In the face of all this, the question is whether you have been frightened off working on pathological EMTs, or even if you are not interested anymore and would prefer waiting till the field reaches a steady state of robust knowledge. Do not be afraid and be interested now. It only involves being more plastic, like the EMT itself.

N-cadherin in osteolineage cells modulates stromal support of tumor growth

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N-cadherin in osteolineage, Osterix+ cells restrains extraskeletal tumor growth.

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Osterix+ cells are present in the stromal microenvironment of extraskeletal tumors.

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Osterix+ cells are present in normal tissues frequent sites of metastasis.

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N-cadherin modulates pro-tumorigenic signaling in tumor associated Osterix+ cells.

Tumor growth and metastases are dependent on interactions between cancer cells and the local environment. Expression of the cell–cell adhesion molecule N-cadherin (Ncad) is associated with highly aggressive cancers, and its expression by osteogenic cells has been proposed to provide a molecular “dock” for disseminated tumor cells to establish in pre-metastatic niches within the bone. To test this biologic model, we conditionally deleted the Ncad gene (Cdh2) in osteolineage cells using Osx-cre (cKO). Contrary to expectations, the metastatic breast cancer cell line PyMT-BO1 was able to form tumors in bone and to induce osteolysis in cKO as well as in control mice. Despite absence of Ncad, bone marrow stromal cells isolated from cKO mice were able to engage in direct cell–cell interactions with tumor cells expressing either N- or E-cadherin. However, subcutaneous PyMT-BO1 and B16F10 tumors grew larger in cKO relative to control littermates. Cell tracking experiments using the Ai9 reporter revealed the presence of Osx+ and Ncad+ cells in the stroma of extra-skeletal tumors and in a small population of lung cells. Gene expression analysis by RNAseq of Osx+ cells isolated from extra-skeletal tumors revealed alterations of pro-tumorigenic signaling pathways in cKO cells relative to control Osx+ cells. Thus, Ncad in Osx+ cells is not necessary for the establishment of bone metastases, but in extra-skeletal tumors it regulates pro-tumorigenic support by the microenvironment.

Localized EMT reprograms glial progenitors to promote spinal cord repair

Anti-regenerative scarring obstructs spinal cord repair in mammals and presents a major hurdle for regenerative medicine. In contrast, adult zebrafish possess specialized glial cells that spontaneously repair spinal cord injuries by forming a pro-regenerative bridge across the severed tissue. To identify the mechanisms that regulate differential regenerative capacity between mammals and zebrafish, we first defined the molecular identity of zebrafish bridging glia and then performed cross-species comparisons with mammalian glia. Our transcriptomics show that pro-regenerative zebrafish glia activate an epithelial-to-mesenchymal transition (EMT) gene program and that EMT gene expression is a major factor distinguishing mammalian and zebrafish glia. Functionally, we found that localized niches of glial progenitors undergo EMT after spinal cord injury in zebrafish and, using large-scale CRISPR-Cas9 mutagenesis, we identified the gene regulatory network that activates EMT and drives functional regeneration. Thus, non-regenerative mammalian glia lack an essential EMT-driving gene regulatory network that reprograms pro-regenerative zebrafish glia after injury.

Filopodia-based contact stimulation of cell migration drives tissue morphogenesis

Cells migrate collectively to form tissues and organs during morphogenesis. Contact inhibition of locomotion (CIL) drives collective migration by inhibiting lamellipodial protrusions at cell-cell contacts and promoting polarization at the leading edge. Here, we report a CIL-related collective cell behavior of myotubes that lack lamellipodial protrusions, but instead use filopodia to move as a cohesive cluster in a formin-dependent manner. We perform genetic, pharmacological and mechanical perturbation analyses to reveal the essential roles of Rac2, Cdc42 and Rho1 in myotube migration. These factors differentially control protrusion dynamics and cell-matrix adhesion formation. We also show that active Rho1 GTPase localizes at retracting free edge filopodia and that Rok-dependent actomyosin contractility does not mediate a contraction of protrusions at cell-cell contacts, but likely plays an important role in the constriction of supracellular actin cables. Based on these findings, we propose that contact-dependent asymmetry of cell-matrix adhesion drives directional movement, whereas contractile actin cables contribute to the integrity of the migrating cell cluster.

Ectoderm to mesoderm transition by down-regulation of actomyosin contractility

Collective migration of cohesive tissues is a fundamental process in morphogenesis and is particularly well illustrated during gastrulation by the rapid and massive internalization of the mesoderm, which contrasts with the much more modest movements of the ectoderm. In the Xenopus embryo, the differences in morphogenetic capabilities of ectoderm and mesoderm can be connected to the intrinsic motility of individual cells, very low for ectoderm, high for mesoderm. Surprisingly, we find that these seemingly deep differences can be accounted for simply by differences in Rho-kinases (Rock)-dependent actomyosin contractility. We show that Rock inhibition is sufficient to rapidly unleash motility in the ectoderm and confer it with mesoderm-like properties. In the mesoderm, this motility is dependent on two negative regulators of RhoA, the small GTPase Rnd1 and the RhoGAP Shirin/Dlc2/ArhGAP37. Both are absolutely essential for gastrulation. At the cellular and tissue level, the two regulators show overlapping yet distinct functions. They both contribute to decrease cortical tension and confer motility, but Shirin tends to increase tissue fluidity and stimulate dispersion, while Rnd1 tends to favor more compact collective migration. Thus, each is able to contribute to a specific property of the migratory behavior of the mesoderm. We propose that the "ectoderm to mesoderm transition" is a prototypic case of collective migration driven by a down-regulation of cellular tension, without the need for the complex changes traditionally associated with the epithelial-to-mesenchymal transition.

Using Xenopus to analyze neurocristopathies like Kabuki syndrome

Neurocristopathies are human congenital syndromes that arise from defects in neural crest (NC) development and are typically associated with malformations of the craniofacial skeleton. Genetic analyses have been very successful in identifying pathogenic mutations, however, model organisms are required to characterize how these mutations affect embryonic development thereby leading to complex clinical conditions. The African clawed frog Xenopus laevis provides a broad range of in vivo and in vitro tools allowing for a detailed characterization of NC development. Due to the conserved nature of craniofacial morphogenesis in vertebrates, Xenopus is an efficient and versatile system to dissect the morphological and cellular phenotypes as well as the signaling events leading to NC defects. Here, we review a set of techniques and resources how Xenopus can be used as a disease model to investigate the pathogenesis of Kabuki syndrome and neurocristopathies in a wider sense.

Tactics of cancer invasion: solitary and collective invasion

Much attention has been paid on the mechanism of cancer invasion from the viewpoint of the behaviour of individual cancer cells. On the other hand, histopathological analyses of specimens from cancer patients and of cancer invasion model animals have revealed that cancer cells often exhibit collective invasion, characterized by sustained cell-to-cell adhesion and polarized invasion as cell clusters. Interestingly, it has recently become evident that during collective invasion of cancer cells, the cells localized at invasion front (leader cells) and the cells following them (follower cells) exhibit distinct cellular characteristics, and that there exist the cells expressing representative proteins related to both epithelial and mesenchymal properties simultaneously, designated as hybrid epithelial-to-mesenchymal transition (EMT)-induced cells, in cancer tissue. Furthermore, the findings that cells adopted in hybrid EMT state form clusters and show collective invasion in vitro emphasize an importance of hybrid EMT-induced cells in collective cancer invasion. In this article, we overview recent findings of the mechanism underlying collective invasion of cancer cells and discuss the possibility of controlling cancer invasion and metastasis by targeting this process.

Insights Into the Complexity of Craniofacial Development From a Cellular Perspective

The head represents the most complex part of the body and a distinctive feature of the vertebrate body plan. This intricate structure is assembled during embryonic development in the four-dimensional process of morphogenesis. The head integrates components of the central and peripheral nervous system, sensory organs, muscles, joints, glands, and other specialized tissues in the framework of a complexly shaped skull. The anterior part of the head is referred to as the face, and a broad spectrum of facial shapes across vertebrate species enables different feeding strategies, communication styles, and diverse specialized functions. The face formation starts early during embryonic development and is an enormously complex, multi-step process regulated on a genomic, molecular, and cellular level. In this review, we will discuss recent discoveries that revealed new aspects of facial morphogenesis from the time of the neural crest cell emergence till the formation of the chondrocranium, the primary design of the individual facial shape. We will focus on molecular mechanisms of cell fate specification, the role of individual and collective cell migration, the importance of dynamic and continuous cellular interactions, responses of cells and tissues to generated physical forces, and their morphogenetic outcomes. In the end, we will examine the spatiotemporal activity of signaling centers tightly regulating the release of signals inducing the formation of craniofacial skeletal elements. The existence of these centers and their regulation by enhancers represent one of the core morphogenetic mechanisms and might lay the foundations for intra- and inter-species facial variability.

Cell Migration Guided by Cell-Cell Contacts in Innate Immunity

The directed migration of leukocytes to sites of damage or infection is necessary for a productive immune response. There is substantial evidence supporting a key role for chemoattractants in directed migration, however, less is known about how cell-cell contacts affect the migratory behavior of leukocytes in innate immunity. Here, we explore how cell-cell contacts can affect the directed migration of innate immune cells, including their role in attracting, repelling, or stopping cell motility. Further investigation of cell contact dynamics as guidance cues may yield new insights into the regulation of innate immunity.

FGF signaling regulates development by processes beyond canonical pathways

FGFs are key developmental regulators that engage a signal transduction cascade through receptor tyrosine kinases, prominently engaging ERK1/2 but also other pathways. However, it remains unknown whether all FGF activities depend on this canonical signal transduction cascade. To address this question, we generated allelic series of knock-in Fgfr1 and Fgfr2 mouse strains, carrying point mutations that disrupt binding of signaling effectors, and a kinase dead allele of Fgfr2 that broadly phenocopies the null mutant. When interrogated in cranial neural crest cells, we identified discrete functions for signaling pathways in specific craniofacial contexts, but point mutations, even when combined, failed to recapitulate the single or double null mutant phenotypes. Furthermore, the signaling mutations abrogated established FGF-induced signal transduction pathways, yet FGF functions such as cell-matrix and cell-cell adhesion remained unaffected, though these activities did require FGFR kinase activity. Our studies establish combinatorial roles of Fgfr1 and Fgfr2 in development and uncouple novel FGFR kinase-dependent cell adhesion properties from canonical intracellular signaling.

Using migrating cells as probes to illuminate features in live embryonic tissues

The biophysical and biochemical properties of live tissues are important in the context of development and disease. Methods for evaluating these properties typically involve destroying the tissue or require specialized technology and complicated analyses. Here, we present a novel, noninvasive methodology for determining the spatial distribution of tissue features within embryos, making use of nondirectionally migrating cells and software we termed "Landscape," which performs automatized high-throughput three-dimensional image registration. Using the live migrating cells as bioprobes, we identified structures within the zebrafish embryo that affect the distribution of the cells and studied one such structure constituting a physical barrier, which, in turn, influences amoeboid cell polarity. Overall, this work provides a unique approach for detecting tissue properties without interfering with animal's development. In addition, Landscape allows for integrating data from multiple samples, providing detailed and reliable quantitative evaluation of variable biological phenotypes in different organisms.

A hybrid model of intercellular tension and cell-matrix mechanical interactions in a multicellular geometry

Epithelial cells form continuous sheets of cells that exist in tensional homeostasis. Homeostasis is maintained through cell-to-cell junctions that distribute tension and balance forces between cells and their underlying matrix. Disruption of tensional homeostasis can lead to epithelial-mesenchymal transition (EMT), a transdifferentiation process in which epithelial cells adopt a mesenchymal phenotype, losing cell-cell adhesion and enhancing cellular motility. This process is critical during embryogenesis and wound healing, but is also dysregulated in many disease states. To further understand the role of intercellular tension in spatial patterning of epithelial cell monolayers, we developed a multicellular computational model of cell-cell and cell-substrate forces. This work builds on a hybrid cellular Potts model (CPM)-finite element model to evaluate cell-matrix mechanical feedback of an adherent multicellular cluster. Cellular movement is governed by thermodynamic constraints from cell volume, cell-cell and cell-matrix contacts, and durotaxis, which arises from cell-generated traction forces on a finite element substrate. Junction forces at cell-cell contacts balance these traction forces, thereby producing a mechanically stable epithelial monolayer. Simulations were compared to in vitro experiments using fluorescence-based junction force sensors in clusters of cells undergoing EMT. Results indicate that the multicellular CPM model can reproduce many aspects of EMT, including epithelial monolayer formation dynamics, changes in cell geometry, and spatial patterning of cell-cell forces in an epithelial tissue.

In vivo Neural Crest Cell Migration Is Controlled by "Mixotaxis"

Directed cell migration is essential all along an individual's life, from embryogenesis to tissue repair and cancer metastasis. Thus, due to its biomedical relevance, directed cell migration is currently under intense research. Directed cell migration has been shown to be driven by an assortment of external biasing cues, ranging from gradients of soluble (chemotaxis) to bound (haptotaxis) molecules. In addition to molecular gradients, gradients of mechanical properties (duro/mechanotaxis), electric fields (electro/galvanotaxis) as well as iterative biases in the environment topology (ratchetaxis) have been shown to be able to direct cell migration. Since cells migrating in vivo are exposed to a challenging environment composed of a convolution of biochemical, biophysical, and topological cues, it is highly unlikely that cell migration would be guided by an individual type of "taxis." This is especially true since numerous molecular players involved in the cellular response to these biasing cues are often recycled, serving as sensor or transducer of both biochemical and biophysical signals. In this review, we confront literature on Xenopus cephalic neural crest cells with that of other cell types to discuss the relevance of the current categorization of cell guidance strategies. Furthermore, we emphasize that while studying individual biasing signals is informative, the hard truth is that cells migrate by performing a sort of "mixotaxis," where they integrate and coordinate multiple inputs through shared molecular effectors to ensure robustness of directed cell motion.

Genetics Underlying the Interactions between Neural Crest Cells and Eye Development

The neural crest is a unique, transient stem cell population that is critical for craniofacial and ocular development. Understanding the genetics underlying the steps of neural crest development is essential for gaining insight into the pathogenesis of congenital eye diseases. The neural crest cells play an under-appreciated key role in patterning the neural epithelial-derived optic cup. These interactions between neural crest cells within the periocular mesenchyme and the optic cup, while not well-studied, are critical for optic cup morphogenesis and ocular fissure closure. As a result, microphthalmia and coloboma are common phenotypes in human disease and animal models in which neural crest cell specification and early migration are disrupted. In addition, neural crest cells directly contribute to numerous ocular structures including the cornea, iris, sclera, ciliary body, trabecular meshwork, and aqueous outflow tracts. Defects in later neural crest cell migration and differentiation cause a constellation of well-recognized ocular anterior segment anomalies such as Axenfeld–Rieger Syndrome and Peters Anomaly. This review will focus on the genetics of the neural crest cells within the context of how these complex processes specifically affect overall ocular development and can lead to congenital eye diseases.

Cadherin-11 Is Required for Neural Crest Specification and Survival

Neural crest (NC) cells are multipotent embryonic cells that form melanocytes, craniofacial bone and cartilage, and the peripheral nervous system in vertebrates. NC cells express many cadherin proteins, which control their specification, epithelial to mesenchymal transition (EMT), migration, and mesenchymal to epithelial transition. Abnormal NC development leads to congenital defects including craniofacial clefts as well as NC-derived cancers. Here, we identify the role of the type II cadherin protein, Cadherin-11 (CDH11), in early chicken NC development. CDH11 is known to play a role in NC cell migration in amphibian embryos as well as cell survival, proliferation, and migration in cancer cells. It has also been linked to the complex neurocristopathy disorder, Elsahy-Waters Syndrome, in humans. In this study, we knocked down CDH11 translation at the onset of its expression in the NC domain during NC induction. Loss of CDH11 led to a reduction of bonafide NC cells in the dorsal neural tube combined with defects in cell survival and migration. Loss of CDH11 increased p53-mediated programmed-cell death, and blocking the p53 pathway rescued the NC phenotype. Our findings reveal an early requirement for CDH11 in NC development and demonstrated the complexity of the mechanisms that regulate NC development, where a single cell-cell adhesion protein simultaneous controls multiple essential cellular functions to ensure proper specification, survival, and transition to a migratory phase in the dorsal neural tube. Our findings may also increase our understanding of early cadherin-related NC developmental defects.

Somatic mutational landscapes of adherens junctions and their functional consequences in cutaneous melanoma development

Cell-cell interaction in skin homeostasis is tightly controlled by adherens junctions (AJs). Alterations in such regulation lead to melanoma development. However, mutations in AJs and their functional consequences are still largely unknown.

Methods: Cadherin mutations in skin cutaneous melanoma were identified using sequencing data from TCGA dataset, followed by cross-validation with data from non-TCGA cohorts. Mutations with significant occurrence were subjected to structural prediction using MODELLER and functional protein simulation using GROMACS software. Neo-antigen prediction was carried out using NetMHCpan tool. Cell-based fluorescence reporter assay was used to validate β-catenin activity in the presence of cadherin mutations. Clinical significance was analyzed using datasets from TCGA and other non-TCGA cohorts. Targeted gene exon sequencing and immunofluorescence staining on melanoma tissues were performed to confirm the in silico findings.

Results: Highly frequent mutations in type-II classical cadherins were found in melanoma with one unique recurrent mutation (S524L) in the fifth domain of CDH6, which potentially destabilizes Ca²⁺-binding and cell-cell contacts. Mutational co-occurrence and physical dynamics analyses placed CDH6 at the center of the top-four mutated cadherins (core CDHs; all type-II), suggesting altered heterophilic interactions in melanoma development. Mutations in the intracellular domains significantly disturbed CDH6/β-catenin complex formation, resulting in β-catenin translocation into cytosol or nucleus and dysregulation of canonical Wnt/β-catenin signaling. Although mutations in core CDH genes correlated with advanced cancer stages and lymph node invasion, the overall and disease-free survival times in those patients were longer in patients with wild-type. Peptide/MHC-I binding affinity predictions confirmed overall increased neo-antigen potentials of mutated cadherins, which associated with T-lymphocyte infiltration and better clinical outcomes after immunotherapy.

Conclusion: Changes in cell-cell communications by somatic mutations in AJ cadherins function as one of mechanisms to trigger melanoma development. Certain mutations in AJs may serve as potential neo-antigens which conversely benefit patients for longer survival times.

rad21 Is Involved in Corneal Stroma Development by Regulating Neural Crest Migration

Previously, we identified RAD21^R450C from a peripheral sclerocornea pedigree. Injection of this rad21 variant mRNA into Xenopus laevis embryos disrupted the organization of corneal stroma fibrils. To understand the mechanisms of RAD21-mediated corneal stroma defects, gene expression and chromosome conformation analysis were performed using cells from family members affected by peripheral sclerocornea. Both gene expression and chromosome conformation of cell adhesion genes were affected in cells carrying the heterozygous rad21 variant. Since cell migration is essential in early embryonic development and sclerocornea is a congenital disease, we studied neural crest migration during cornea development in X. laevis embryos. In X. laevis embryos injected with rad21 mutant mRNA, neural crest migration was disrupted, and the number of neural crest-derived periocular mesenchymes decreased significantly in the corneal stroma region. Our data indicate that the RAD21^R450C variant contributes to peripheral sclerocornea by modifying chromosome conformation and gene expression, therefore disturbing neural crest cell migration, which suggests RAD21 plays a key role in corneal stroma development.

The heart of the neural crest: cardiac neural crest cells in development and regeneration

Cardiac neural crest cells (cNCCs) are a migratory cell population that stem from the cranial portion of the neural tube. They undergo epithelial-to-mesenchymal transition and migrate through the developing embryo to give rise to portions of the outflow tract, the valves and the arteries of the heart. Recent lineage-tracing experiments in chick and zebrafish embryos have shown that cNCCs can also give rise to mature cardiomyocytes. These cNCC-derived cardiomyocytes appear to be required for the successful repair and regeneration of injured zebrafish hearts. In addition, recent work examining the response to cardiac injury in the mammalian heart has suggested that cNCC-derived cardiomyocytes are involved in the repair/regeneration mechanism. However, the molecular signature of the adult cardiomyocytes involved in this repair is unclear. In this Review, we examine the origin, migration and fates of cNCCs. We also review the contribution of cNCCs to mature cardiomyocytes in fish, chick and mice, as well as their role in the regeneration of the adult heart.

Non-junctional role of Cadherin3 in cell migration and contact inhibition of locomotion via domain-dependent, opposing regulation of Rac1

Classical cadherins are well-known adhesion molecules responsible for physically connecting neighboring cells and signaling this cell-cell contact. Recent studies have suggested novel signaling roles for "non-junctional" cadherins (NJCads); however, the function of cadherin signaling independent of cell-cell contacts remains unknown. In this study, mesendodermal cells and tissues from gastrula stage Xenopus laevis embryos demonstrate that deletion of extracellular domains of Cadherin3 (Cdh3; formerly C-cadherin in Xenopus) disrupts contact inhibition of locomotion. In both bulk Rac1 activity assays and spatio-temporal FRET image analysis, the extracellular and cytoplasmic Cdh3 domains disrupt NJCad signaling and regulate Rac1 activity in opposing directions. Stabilization of the cytoskeleton counteracted this regulation in single cell migration assays. Our study provides novel insights into adhesion-independent signaling by Cadherin3 and its role in regulating single and collective cell migration.

Using Xenopus Neural Crest Explants to Study Epithelial-Mesenchymal Transition

The epithelial-mesenchymal transition (EMT) converts coherent epithelial structures into single cells. EMT is a dynamic cellular process that is not systematically completed (not all EMTs lead to single cells) and reversible (cells can re-epithelialize). EMT is orchestrated at multiple levels from transcription, to posttranslational modifications, to protein turnover. It involves remodeling of polarity and adhesion and enhances migratory capabilities. During physiological events such as embryogenesis or wound healing EMT is used to initiate cell migration, but EMT can also occur in pathological settings. In particular, EMT has been linked to fibrosis and cancer. Neural crest (NC) cells, an embryonic stem cell population whose behavior recapitulates the main steps of carcinoma progression, are a great model to study EMT. In this chapter, we provide a fully detailed protocol to extract NC cells from Xenopus embryos and culture them to study the dynamics of cell-cell adhesion, cell motility, and dispersion.

Epithelial-mesenchymal plasticity: emerging parallels between tissue morphogenesis and cancer metastasis

Many cells possess epithelial–mesenchymal plasticity (EMP), which allows them to shift reversibly between adherent, static and more detached, migratory states. These changes in cell behaviour are driven by the programmes of epithelial–mesenchymal transition (EMT) and mesenchymal–epithelial transition (MET), both of which play vital roles during normal development and tissue homeostasis. However, the aberrant activation of these processes can also drive distinct stages of cancer progression, including tumour invasiveness, cell dissemination and metastatic colonization and outgrowth. This review examines emerging common themes underlying EMP during tissue morphogenesis and malignant progression, such as the context dependence of EMT transcription factors, a central role for partial EMTs and the nonlinear relationship between EMT and MET.

This article is part of a discussion meeting issue ‘Contemporary morphogenesis'.

Rules of collective migration: from the wildebeest to the neural crest

Collective migration, the movement of groups in which individuals affect the behaviour of one another, occurs at practically every scale, from bacteria up to whole species' populations. Universal principles of collective movement can be applied at all levels. In this review, we will describe the rules governing collective motility, with a specific focus on the neural crest, an embryonic stem cell population that undergoes extensive collective migration during development. We will discuss how the underlying principles of individual cell behaviour, and those that emerge from a supracellular scale, can explain collective migration. This article is part of the theme issue 'Multi-scale analysis and modelling of collective migration in biological systems'.

Cadherin-Mediated Cell Coupling Coordinates Chemokine Sensing across Collectively Migrating Cells

The directed migration of cells sculpts the embryo, contributes to homeostasis in the adult, and, when dysregulated, underlies many diseases [1, 2]. During these processes, cells move singly or as a collective. In both cases, they follow guidance cues, which direct them to their destination [3-6]. In contrast to single cells, collectively migrating cells need to coordinate with their neighbors to move together in the same direction. Recent studies suggest that leader cells in the front sense the guidance cue, relay the directional information to the follower cells in the back, and can pull the follower cells along [7-19]. In this manner, leader cells steer the collective and set the collective's overall speed. However, whether follower cells also participate in steering and speed setting of the collective is largely unclear. Using chimeras, we analyzed the role of leader and follower cells in the collectively migrating zebrafish posterior lateral line primordium. This tissue expresses the chemokine receptor Cxcr4 and is guided by the chemokine Cxcl12a [20-23]. We find that leader and follower cells need to sense the attractant Cxcl12a for efficient migration, are coupled to each other through cadherins, and require coupling to pull Cxcl12a-insensitive cells along. Analysis of cell dynamics in chimeric and protein-depleted primordia shows that Cxcl12a-sensing and cadherin-mediated adhesion contribute jointly to direct migration at both single-cell and tissue levels. These results suggest that all cells in the primordium need to sense the attractant and adhere to each other to coordinate their movements and migrate with robust directionality.

Mechanobiology of neural development

As the brain develops, proliferating cells organize into structures, differentiate, migrate, extrude long processes, and connect with other cells. These biological processes produce mechanical forces that further shape cellular dynamics and organ patterning. A major unanswered question in developmental biology is how the mechanical forces produced during development are detected and transduced by cells to impact biochemical and genetic programs of development. This gap in knowledge stems from a lack of understanding of the molecular players of cellular mechanics and an absence of techniques for measuring and manipulating mechanical forces in tissue. In this review article, we examine recent advances that are beginning to clear these bottlenecks and highlight results from new approaches that reveal the role of mechanical forces in neurodevelopmental processes.

Establishing Primary Cultures of Trunk Neural Crest Cells

Neural crest cells constitute a unique population of progenitor cells with extensive stem cell capacities able to navigate throughout various environments in the embryo and are a source of multiple cell types, including neurons, glia, melanocytes, smooth muscles, endocrine cells, cardiac cells, and also skeletal and supportive tissues in the head. Neural crest cells are not restricted to the embryo but persist as well in adult tissues where they provide a reservoir of stem cells with great therapeutic promise. Many fundamental questions in cell, developmental, and stem cell biology can be addressed using this system. During the last decades there has been an increased availability of elaborated techniques, animal models, and molecular tools to tackle neural crest cell development. However, these approaches are often very challenging and difficult to establish and they are not adapted for rapid functional investigations of mechanisms driving cell migration and differentiation. In addition, they are not adequate for collecting pure populations of neural crest cells usable in large scale analyses and for stem cell studies. Transferring and adapting the neural crest system in tissue culture may then represent an attractive alternative, opening up numerous prospects. Here we describe a simple method for establishing primary cultures of neural crest cells derived from trunk neural tubes using the avian embryo as a source of cells. This protocol is suited for producing pure populations of neural crest cells that can be processed for cytological, cellular, and functional approaches aimed at characterizing their phenotype, behavior, and potential. © 2020 Wiley Periodicals LLC. Basic Protocol: Primary cultures of avian trunk neural crest cells Support Protocol: Adaptations for immunofluorescence labeling and videomicroscopy.

Epithelial-to-mesenchymal transition and different migration strategies as viewed from the neural crest

Epithelial-to-mesenchymal transition (EMT) is a dynamic process that produces migratory cells from epithelial precursors. However, EMT is not binary; rather it results in migratory cells which adopt diverse strategies including collective and individual cell migration to arrive at target destinations. Of the many embryonic cells that undergo EMT, the vertebrate neural crest is a particularly good example which has provided valuable insight into these processes. Neural crest cells from different species often adopt different migratory strategies with collective migration predominating in anamniotes, whereas individual cell migration is more prevalent in amniotes. Here, we will provide a perspective on recent work toward understanding the process of neural crest EMT focusing on how these cells undergo collective and individual cell migration.

Pcdh18a regulates endocytosis of E-cadherin during axial mesoderm development in zebrafish

The notochord defines the axial structure of all vertebrates during development. Notogenesis is a result of major cell reorganization in the mesoderm, the convergence and the extension of the axial cells. However, it is currently not fully understood how these processes act together in a coordinated way during notochord formation. The prechordal plate is an actively migrating cell population in the central mesoderm anterior to the trailing notochordal plate cells. We show that prechordal plate cells express Protocadherin 18a (Pcdh18a), a member of the cadherin superfamily. We find that Pcdh18a-mediated recycling of E-cadherin adhesion complexes transforms prechordal plate cells into a cohesive and fast migrating cell group. In turn, the prechordal plate cells subsequently instruct the trailing mesoderm. We simulated cell migration during early mesoderm formation using a lattice-based mathematical framework and predicted that the requirement for an anterior, local motile cell cluster could guide the intercalation and extension of the posterior, axial cells. Indeed, a grafting experiment validated the prediction and local Pcdh18a expression induced an ectopic prechordal plate-like cell group migrating towards the animal pole. Our findings indicate that the Pcdh18a is important for prechordal plate formation, which influences the trailing mesodermal cell sheet by orchestrating the morphogenesis of the notochord.

Control of cell colony growth by contact inhibition

Contact inhibition is a cell property that limits the migration and proliferation of cells in crowded environments. Here we investigate the growth dynamics of a cell colony composed of migrating and proliferating cells on a substrate using a minimal model that incorporates the mechanisms of contact inhibition of locomotion and proliferation. We find two distinct regimes. At early times, when contact inhibition is weak, the colony grows exponentially in time, fully characterised by the proliferation rate. At long times, the colony boundary moves at a constant speed, determined only by the migration speed of a single cell and independent of the proliferation rate. Further, the model demonstrates how cell-cell alignment speeds up colony growth. Our model illuminates how simple local mechanical interactions give rise to contact inhibition, and from this, how cell colony growth is self-organised and controlled on a local level.

WNT1, a target of miR-34a, promotes cervical squamous cell carcinoma proliferation and invasion by induction of an E-P cadherin switch via the WNT/β-catenin pathway

Purpose

Persistent infection with high-risk human papillomavirus (HR-HPV) is thought to play a prominent role in the initiation and progression of almost all cases of cervical cancer. Previously, we and others found that microRNA 34a (miR-34a) may be regulated by HR-HPV E6 to contribute to the development of cervical cancer. Here, we aimed to identify the oncogenic potential and clinical significance of a known miR-34a target, WNT1, in cervical squamous cell carcinoma (SCC) development and to investigate the associated mechanisms underlying cervical SCC cell proliferation and invasion.

Methods

WNT1 and miR-34a expression levels were assessed in primary cervical lesions using immunohistochemistry and qRT-PCR, respectively. The cellular effects and the expression of its associated genes were examined in cervical SCC-derived Siha and Caski cells after siRNA-WNT1 (downregulation) or miR-34a mimic (upregulation) treatment. A cervical SCC xenograft mouse model was used to investigate the in vivo effects of miR-34a overexpression. HPV-16 E6/E7 expression was inhibited by gene promoter siRNA targeting, after which the levels of miR-34a and WNT1 were examined.

Results

WNT1 protein upregulation was found to be associated with a poor prognosis in cervical SCC patients. In vitro assays in Siha and Caski cells revealed that WNT1 downregulation decreased cell proliferation and invasion, inhibited WNT/β-catenin activation and affected the expression of E-cadherin and P-cadherin. MiR-34a upregulation resulted in decreased WNT1 expression. An inverse correlation between miR-34a and WNT1 expression was also observed in primary cervical SCC tissues. In addition, we found that MiR-34a could regulate an E-cadherin to P-cadherin switch (E-P cadherin switch) to inhibit cell proliferation and tumorigenesis in vitro and in vivo via inactivation of the WNT1/β-catenin pathway. Finally, we found that decreased HPV-16 E6/E7 expression resulted in miR-34a upregulation and WNT1 downregulation in Siha and Caski cells.

Conclusions

From our results we conclude that WNT1, as a target of miR-34a, can promote cervical SCC cell proliferation and invasion by induction of an E-P cadherin switch via the WNT1/β-catenin pathway. Our results may provide new options for the treatment of patients with cervical SCC.

Electronic supplementary material

The online version of this article (10.1007/s13402-020-00506-8) contains supplementary material, which is available to authorized users.

Guidelines and definitions for research on epithelial-mesenchymal transition

Epithelial–mesenchymal transition (EMT) encompasses dynamic changes in cellular organization from epithelial to mesenchymal phenotypes, which leads to functional changes in cell migration and invasion. EMT occurs in a diverse range of physiological and pathological conditions and is driven by a conserved set of inducing signals, transcriptional regulators and downstream effectors. With over 5,700 publications indexed by Web of Science in 2019 alone, research on EMT is expanding rapidly. This growing interest warrants the need for a consensus among researchers when referring to and undertaking research on EMT. This Consensus Statement, mediated by ‘the EMT International Association’ (TEMTIA), is the outcome of a 2-year-long discussion among EMT researchers and aims to both clarify the nomenclature and provide definitions and guidelines for EMT research in future publications. We trust that these guidelines will help to reduce misunderstanding and misinterpretation of research data generated in various experimental models and to promote cross-disciplinary collaboration to identify and address key open questions in this research field. While recognizing the importance of maintaining diversity in experimental approaches and conceptual frameworks, we emphasize that lasting contributions of EMT research to increasing our understanding of developmental processes and combatting cancer and other diseases depend on the adoption of a unified terminology to describe EMT.

In this Consensus Statement, the authors (on behalf of the EMT International Association) propose guidelines to define epithelial–mesenchymal transition, its phenotypic plasticity and the associated multiple intermediate epithelial–mesenchymal cell states. Clarification of nomenclature and definitions will help reduce misinterpretation of research data generated in different experimental model systems and promote cross-disciplinary collaboration.

In Vivo Quantitative Imaging Provides Insights into Trunk Neural Crest Migration

Neural crest (NC) cells undergo extensive migrations during development. Here, we couple in vivo live imaging at high resolution with custom software tools to reveal dynamic migratory behavior in chick embryos. Trunk NC cells migrate as individuals with both stochastic and biased features as they move dorsoventrally to form peripheral ganglia. Their leading edge displays a prominent fan-shaped lamellipodium that reorients upon cell-cell contact. Computational analysis reveals that when the lamellipodium of one cell touches the body of another, the two cells undergo "contact attraction," often moving together and then separating via a pulling force exerted by lamellipodium. Targeted optical manipulation shows that cell interactions coupled with cell density generate a long-range biased random walk behavior, such that cells move from high to low density. In contrast to chain migration noted at other axial levels, the results show that individual trunk NC cells navigate the complex environment without tight coordination between neighbors.

The road best traveled: Neural crest migration upon the extracellular matrix

Neural crest cells have the extraordinary task of building much of the vertebrate body plan, including the craniofacial cartilage and skeleton, melanocytes, portions of the heart, and the peripheral nervous system. To execute these developmental programs, stationary premigratory neural crest cells first acquire the capacity to migrate through an extensive process known as the epithelial-to-mesenchymal transition. Once motile, neural crest cells must traverse a complex environment consisting of other cells and the protein-rich extracellular matrix in order to get to their final destinations. Herein, we will highlight some of the main molecular machinery that allow neural crest cells to first exit the neuroepithelium and then later successfully navigate this intricate in vivo milieu. Collectively, these extracellular and intracellular factors mediate the appropriate migration of neural crest cells and allow for the proper development of the vertebrate embryo.

An electrochemical biosensor for the detection of epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is critically involved in a variety of biological processes. Electrochemical sensing offers potential to develop more effective technology for EMT detection. In this study, by using the unique performance of quantum dot (QD)-nanocomposite materials, we establish an electrochemical biosensor that can specifically detect the change of E-cadherin and analyze different stages of EMT. The signal for EMT is largely magnified due to the transmission of molecular information to the electronic device. In addition, differential pulse voltammetry reveals that the response of the electrochemical signals is rapid and sensitive, due to the synergistic effect of QDs and carbon nanotube-gold nanoparticles. Our study thus suggests that electrochemical sensing is an effective technology for detecting EMT and may have broad applications in analyzing various cell type transitions.

Cell interactions in collective cell migration

Collective cell migration is the coordinated movement of a physically connected group of cells and is a prominent driver of development and metastasis. Interactions between cells within migrating collectives, and between migrating cells and other cells in the environment, play key roles in stimulating motility, steering and sometimes promoting cell survival. Similarly, diverse heterotypic interactions and collective behaviors likely contribute to tumor metastasis. Here, we describe a sampling of cells that migrate collectively in vivo, including well-established and newer examples. We focus on the under-appreciated property that many - perhaps most - collectively migrating cells move as cooperating groups of distinct cell types.

Connecting gene expression to cellular movement: A transport model for cell migration

The adhesion properties and the mobility of biological cells play key roles in the propagation of cancer. These properties are expected to depend on intracellular processes and on the concentrations of chemicals inside the cell. While most existing reaction-diffusion models for cell migration consider that cell mobility and proliferation rate are constant or depend on an external diffusing species, they do not include the gene expression dynamics taking place in moving cells that affect cellular transport. In this work, we propose a multiscale model where mobility and proliferation depend explicitly on the cell's internal state. We focus more specifically on the case of cellular mobility in epithelial tissues. Wound-healing experiments have demonstrated that the loss of a key protein, E-cadherin, results in a significant increase in both mobility and invasiveness of epithelial cells, with dramatic consequences on cancer progression. We can reproduce the results of these experiments under various genetic conditions with a single set of parameters.

Neural crest development: insights from the zebrafish

Our understanding of the neural crest, a key vertebrate innovation, is built upon studies of multiple model organisms. Early research on neural crest cells (NCCs) was dominated by analyses of accessible amphibian and avian embryos, with mouse genetics providing complementary insights in more recent years. The zebrafish model is a relative newcomer to the field, yet it offers unparalleled advantages for the study of NCCs. Specifically, zebrafish provide powerful genetic and transgenic tools, coupled with rapidly developing transparent embryos that are ideal for high-resolution real-time imaging of the dynamic process of neural crest development. While the broad principles of neural crest development are largely conserved across vertebrate species, there are critical differences in anatomy, morphogenesis, and genetics that must be considered before information from one model is extrapolated to another. Here, our goal is to provide the reader with a helpful primer specific to neural crest development in the zebrafish model. We focus largely on the earliest events-specification, delamination, and migration-discussing what is known about zebrafish NCC development and how it differs from NCC development in non-teleost species, as well as highlighting current gaps in knowledge.

A cadherin switch marks germ layer formation in the diploblastic sea anemone Nematostella vectensis

Morphogenesis is a shape-building process during development of multicellular organisms. During this process, the establishment and modulation of cell-cell contacts play an important role. Cadherins, the major cell adhesion molecules, form adherens junctions connecting epithelial cells. Numerous studies of Bilateria have shown that cadherins are associated with the regulation of cell differentiation, cell shape changes, cell migration and tissue morphogenesis. To date, the role of cadherins in non-bilaterians is unknown. Here, we study the expression and function of two paralogous classical cadherins, Cadherin 1 and Cadherin 3, in a diploblastic animal, the sea anemone Nematostella vectensis We show that a cadherin switch accompanies the formation of germ layers. Using specific antibodies, we show that both cadherins are localized to adherens junctions at apical and basal positions in ectoderm and endoderm. During gastrulation, partial epithelial-to-mesenchymal transition of endodermal cells is marked by stepwise downregulation of Cadherin 3 and upregulation of Cadherin 1. Knockdown experiments show that both cadherins are required for maintenance of tissue integrity and tissue morphogenesis. Thus, both sea anemones and bilaterians use independently duplicated cadherins combinatorially for tissue morphogenesis and germ layer differentiation.