Integrin alpha5beta1 supports the migration of Xenopus cranial neural crest on fibronectin

Interaction of Gαi2 with EB1 controls microtubule dynamics and Rac1 activity in Xenopus neural crest cell migration

Cell migration is crucial in embryonic development, tissue repair and cancer metastasis, driven by the actin and tubulin cytoskeletons that control cell shape, polarity, adhesion and movement in response to various cues. Although heterotrimeric G proteins are known to be involved in cell migration, the specific mechanisms, especially during development, remain elusive. This study examines the role of Gαi2, a heterotrimeric G-protein subunit, in cranial neural crest (NC) cell migration during Xenopus embryonic development. Our research reveals that Gαi2 interacts directly with the microtubule-associated protein EB1, regulating microtubule dynamics. We show that Gαi2 knockdown stabilizes microtubules, disrupts cell polarity and morphology, increases Rac1-GTP at the leading edge and cell-cell contacts, and impairs actin localization and focal adhesion disassembly. Additionally, RhoA-GTP is reduced at cell-cell contacts and concentrated at the leading edge in Gαi2 knockdown cells, providing evidence of a role for Gαi2 in polarity. Treatment with nocodazole, a microtubule-depolymerizing agent, reduces Rac1 activity, restoring cranial NC cell morphology, actin distribution and overall migration. Our findings highlight a crucial role for Gαi2 in cranial NC cell migration by modulating microtubule dynamics through EB1 and Rac1 activity.

The novel ECM protein SNED1 mediates cell adhesion via the RGD-binding integrins α5β1 and αvβ3

The extracellular matrix (ECM) is a complex meshwork comprising over 100 proteins. It serves as an adhesive substrate for cells and, hence, plays crucial roles in health and disease. We have recently identified a novel ECM protein, SNED1, and have found that it is required for neural crest cell migration and craniofacial morphogenesis during development and in breast cancer, where it is necessary for the metastatic dissemination of tumor cells. Interestingly, both processes involve the dynamic remodeling of cell-ECM adhesions via cell surface receptors. Sequence analysis revealed that SNED1 contains two amino acid motifs, RGD and LDV, known to bind integrins, the largest class of ECM receptors. We thus sought to investigate the role of SNED1 in cell adhesion. Here, we report that SNED1 mediates breast cancer and neural crest cell adhesion via its RGD motif. We further demonstrate that cell adhesion to SNED1 is mediated by the RGD integrins α5β1 and αvβ3. These findings are a first step toward identifying the signaling pathways activated downstream of the SNED1-integrin interactions guiding craniofacial morphogenesis and breast cancer metastasis.

The novel ECM protein SNED1 mediates cell adhesion via the RGD-binding integrins α5β1 and αvβ3

The extracellular matrix (ECM) is a complex meshwork comprising over 100 proteins. It serves as an adhesive substrate for cells and, hence, plays critical roles in health and disease. We have recently identified a novel ECM protein, SNED1, and have found that it is required for neural crest cell migration and craniofacial morphogenesis during development and in breast cancer, where it is necessary for the metastatic dissemination of tumor cells. Interestingly, both processes involve the dynamic remodeling of cell-ECM adhesions via cell surface receptors. Sequence analysis revealed that SNED1 contains two amino acid motifs, RGD and LDV, known to bind integrins, the largest class of ECM receptors. We thus sought to investigate the role of SNED1 in cell adhesion. Here, we report that SNED1 mediates breast cancer and neural crest cell adhesion via its RGD motif. We further demonstrate that cell adhesion to SNED1 is mediated by the RGD integrins α5β1 and αvβ3. These findings are a first step toward identifying the signaling pathways activated downstream of the SNED1-integrin interactions guiding craniofacial morphogenesis and breast cancer metastasis.

ADAM interact with large protein complexes to regulate Histone modification, gene expression and splicing

Cranial neural crest (CNC) cells are key stem cells that contribute to most of the facial structures in vertebrates. ADAM ( A D isintegrin A nd M etalloprotease) proteins are essential for the induction and migration of the CNC. We have shown that Adam13 associates with the transcription factor Arid3a to regulate gene expression. Here we show that Adam13 modulates Histone modifications in the CNC. We show that Arid3a binding to the tfap2α promoter depends on the presence of Adam13. This association promotes the expression of one tfap2α variant expressed in the CNC that uniquely activates the expression of gene critical for CNC migration. We show that both Adam13 and human ADAM9 associate with proteins involved in histone modification and RNA splicing, a function critically affected by the loss of Adam13. We propose that ADAMs may act as extracellular sensors to modulate chromatin availability, leading to changes in gene expression and splicing.

Induction of periodontal ligament-derived mesenchymal stromal cell-like cells from human induced pluripotent stem cells

Introduction

Periodontal disease is a common oral infection which affects the tooth-supportive tissues directly. Considering the limitation of present regenerative treatments for severe periodontal cases, cytotherapies have been gradually introduced. Human periodontal ligament-derived mesenchymal stromal cells (hPDLMSCs), while identified as one of the promising cell sources for periodontal regenerative therapy, still hold some problems in the clinical application especially their limited life span. To solve the problems, human induced pluripotent stem cells (hiPSCs) are taken into consideration as a robust supply for hPDLMSCs.

Methods

The induction of hPDLMSCs was performed based on the generation of neural crest-like cells (NCLCs) from hiPSCs. Fibronectin and laminin were tested as coating materials for NCLCs differentiation when following previous protocol, and the characteristics of induced cells were identified by flow cytometry and RT-qPCR for evaluating the induction efficiency. Subsequently, selected dental ectoderm signaling-related cytokines were applied for hPDLMSCs induction for 14 days, and dental mesenchyme-related genes, dental follicle-related genes and hPDL-related genes were tested by RT-qPCR for the evaluation of differentiation.

Results

Compared to the 58% in laminin-coated condition, fibronectin-coated condition had a higher induction efficiency of CD271high cells as 86% after 8-day induction, while the mesenchymal potential of induced NCLCs was similar between two coating materials.It was shown that the gene expressions of dental mesenchyme, dental follicles and hPDL cells were significantly enhanced with the stimulation of the combination with fibroblast growth factor 8b (FGF8b), FGF2, and bone morphogenetic protein 4 (BMP4).

Conclusion

FN coating was more effective in NCLCs induction, and the FGF8b+FGF2+BMP4 growth factor cocktail was effective in hPDLMSC-like cell generation. These findings underscored the likely regenerative potential of hiPSCs as an applicable and promising curative strategy for periodontal diseases.

Inhibition of the serine protease HtrA1 by SerpinE2 suggests an extracellular proteolytic pathway in the control of neural crest migration

We previously showed that SerpinE2 and the serine protease HtrA1 modulate fibroblast growth factor (FGF) signaling in germ layer specification and head-to-tail development of Xenopus embryos. Here, we present an extracellular proteolytic mechanism involving this serpin-protease system in the developing neural crest (NC). Knockdown of SerpinE2 by injected antisense morpholino oligonucleotides did not affect the specification of NC progenitors but instead inhibited the migration of NC cells, causing defects in dorsal fin, melanocyte, and craniofacial cartilage formation. Similarly, overexpression of the HtrA1 protease impaired NC cell migration and the formation of NC-derived structures. The phenotype of SerpinE2 knockdown was overcome by concomitant downregulation of HtrA1, indicating that SerpinE2 stimulates NC migration by inhibiting endogenous HtrA1 activity. SerpinE2 binds to HtrA1, and the HtrA1 protease triggers degradation of the cell surface proteoglycan Syndecan-4 (Sdc4). Microinjection of Sdc4 mRNA partially rescued NC migration defects induced by both HtrA1 upregulation and SerpinE2 downregulation. These epistatic experiments suggest a proteolytic pathway by a double inhibition mechanism.

SerpinE2 ┤HtrA1 protease ┤Syndecan-4 → NC cell migration.

ADAM11 a novel regulator of Wnt and BMP4 signaling in neural crest and cancer

Introduction: Cranial neural crest (CNC) cells are induced at the border of the neural plate by a combination of FGF, Wnt, and BMP4 signaling. CNC then migrate ventrally and invade ventral structures where they contribute to craniofacial development. Methods: We used loss and gain of function experiments to determine phenotypes associated with the perturbation of Adam11 expression in Xenopus Laevis. Mass spectrometry to identify partners of Adam11 and changes in protein expression in CNC lacking Adam11. We used mouse B16 melanoma to test the function of Adam11 in cancer cells, and published database analysis to study the expression of ADAM11 in human tumors. Results: Here we show that a non-proteolytic ADAM, Adam11, originally identified as a putative tumor suppressor binds to proteins of the Wnt and BMP4 signaling pathway. Mechanistic studies concerning these non-proteolytic ADAM lack almost entirely. We show that Adam11 positively regulates BMP4 signaling while negatively regulating β-catenin activity. In vivo, we show that Adam11 influences the timing of neural tube closure and the proliferation and migration of CNC. Using both human tumor data and mouse B16 melanoma cells, we further show that ADAM11 levels similarly correlate with Wnt or BMP4 activation levels. Discussion: We propose that ADAM11 preserves naïve cells by maintaining low Sox3 and Snail/Slug levels through stimulation of BMP4 and repression of Wnt signaling, while loss of ADAM11 results in increased Wnt signaling, increased proliferation and early epithelium to mesenchyme transition.

Paracrine regulation of neural crest EMT by placodal MMP28

Epithelial-mesenchymal transition (EMT) is an early event in cell dissemination from epithelial tissues. EMT endows cells with migratory, and sometimes invasive, capabilities and is thus a key process in embryo morphogenesis and cancer progression. So far, matrix metalloproteinases (MMPs) have not been considered as key players in EMT but rather studied for their role in matrix remodelling in later events such as cell migration per se. Here, we used Xenopus neural crest cells to assess the role of MMP28 in EMT and migration in vivo. We show that a catalytically active MMP28, expressed by neighbouring placodal cells, is required for neural crest EMT and cell migration. We provide strong evidence indicating that MMP28 is imported in the nucleus of neural crest cells where it is required for normal Twist expression. Our data demonstrate that MMP28 can act as an upstream regulator of EMT in vivo raising the possibility that other MMPs might have similar early roles in various EMT-related contexts such as cancer, fibrosis, and wound healing.

Cas phosphorylation regulates focal adhesion assembly

Integrin-mediated cell attachment rapidly induces tyrosine kinase signaling. Despite years of research, the role of this signaling in integrin activation and focal adhesion assembly is unclear. We provide evidence that the Src-family kinase (SFK) substrate Cas (Crk-associated substrate, p130Cas, BCAR1) is phosphorylated and associated with its Crk/CrkL effectors in clusters that are precursors of focal adhesions. The initial phospho-Cas clusters contain integrin β1 in its inactive, bent closed, conformation. Later, phospho-Cas and total Cas levels decrease as integrin β1 is activated and core focal adhesion proteins including vinculin, talin, kindlin, and paxillin are recruited. Cas is required for cell spreading and focal adhesion assembly in epithelial and fibroblast cells on collagen and fibronectin. Cas cluster formation requires Cas, Crk/CrkL, SFKs, and Rac1 but not vinculin. Rac1 provides positive feedback onto Cas through reactive oxygen, opposed by negative feedback from the ubiquitin proteasome system. The results suggest a two-step model for focal adhesion assembly in which clusters of phospho-Cas, effectors and inactive integrin β1 grow through positive feedback prior to integrin activation and recruitment of core focal adhesion proteins.

ADAM11 a novel regulator of Wnt and BMP4 signaling in neural crest and cancer

Cranial neural crest (CNC) cells are induced at the border of the neural plate by a combination of FGF, Wnt, and BMP4 signaling. CNC then migrate ventrally and invade ventral structures where they contribute to craniofacial development. Here we show that a non-proteolytic ADAM, Adam11, originally identified as a putative tumor suppressor binds to proteins of the Wnt and BMP4 signaling pathway. Mechanistic studies concerning these non-proteolytic ADAM lack almost entirely. We show that Adam11 positively regulates BMP4 signaling while negatively regulating β-catenin activity. By modulating these pathways, Adam11 controls the timing of neural tube closure and the proliferation and migration of CNC. Using both human tumor data and mouse B16 melanoma cells, we further show that ADAM11 levels similarly correlate with Wnt or BMP4 activation levels. We propose that ADAM11 preserve naïve cells by maintaining low Sox3 and Snail/Slug levels through stimulation of BMP4 and repression of Wnt signaling, while loss of ADAM11 results in increased Wnt signaling, increased proliferation and early epithelium to mesenchyme transition.

Coordinated regulation of Cdc42ep1, actin, and septin filaments during neural crest cell migration

The septin cytoskeleton has been demonstrated to interact with other cytoskeletal components to regulate various cellular processes, including cell migration. However, the mechanisms of how septin regulates cell migration are not fully understood. In this study, we use the highly migratory neural crest cells of frog embryos to examine the role of septin filaments in cell migration. We found that septin filaments are required for the proper migration of neural crest cells by controlling both the speed and the direction of cell migration. We further determined that septin filaments regulate these features of cell migration by interacting with actin stress fibers. In neural crest cells, septin filaments co-align with actin stress fibers, and the loss of septin filaments leads to impaired stability and contractility of actin stress fibers. In addition, we showed that a partial loss of septin filaments leads to drastic changes in the orientations of newly formed actin stress fibers, suggesting that septin filaments help maintain the persistent orientation of actin stress fibers during directed cell migration. Lastly, our study revealed that these activities of septin filaments depend on Cdc42ep1, which colocalizes with septin filaments in the center of neural crest cells. Cdc42ep1 interacts with septin filaments in a reciprocal manner, with septin filaments recruiting Cdc42ep1 to the cell center and Cdc42ep1 supporting the formation of septin filaments.

Cell clusters softening triggers collective cell migration in vivo

Embryogenesis, tissue repair and cancer metastasis rely on collective cell migration. In vitro studies propose that cells are stiffer while migrating in stiff substrates, but softer when plated in compliant surfaces which are typically considered as non-permissive for migration. Here we show that cells within clusters from embryonic tissue dynamically decrease their stiffness in response to the temporal stiffening of their native substrate to initiate collective cell migration. Molecular and mechanical perturbations of embryonic tissues reveal that this unexpected mechanical response involves a mechanosensitive pathway relying on Piezo1-mediated microtubule deacetylation. We further show that decreasing microtubule acetylation and consequently cluster stiffness is sufficient to trigger collective cell migration in soft non-permissive substrates. This suggests that reaching an optimal cluster-to-substrate stiffness ratio is essential to trigger the onset of this collective process. Overall, these in vivo findings challenge the current understanding of collective cell migration and its physiological and pathological roles.

Noncanonical Wnt/Ror2 signaling regulates cell-matrix adhesion to prompt directional tumor cell invasion in breast cancer

Cell-extracellular matrix (ECM) interactions represent fundamental exchanges during tumor progression, yet how particular signal-transduction factors prompt the conversion of tumor cells into migratory populations capable of systemic spread during metastasis remains elusive. We demonstrate that the noncanonical Wnt receptor, Ror2, regulates tumor cell-driven matrix remodeling and invasion in breast cancer. Ror2 loss-of-function (LOF) triggers the disruption of E-cadherin within tumor cells, accompanied by an increase in tumor cell invasion and collagen realignment in three-dimensional cultures. RNA sequencing of Ror2-deficient organoids further uncovered alterations in actin cytoskeleton, cell adhesion, and collagen cross-linking gene expression programs. Spatially, we pinpoint the up-regulation and redistribution of α5 and β3 integrins together with the production of fibronectin in areas of invasion downstream of Ror2 loss. Wnt/β-catenin-dependent and Wnt/Ror2 alternative Wnt signaling appear to regulate distinct functions for tumor cells regarding their ability to modify cell-ECM exchanges during invasion. Furthermore, blocking either integrin or focal adhesion kinase (FAK), a downstream mediator of integrin-mediated signal transduction, abrogates the enhanced migration observed upon Ror2 loss. These results reveal a critical function for the alternative Wnt receptor, Ror2, as a determinant of tumor cell-driven ECM exchanges during cancer invasion and metastasis.

Nephronectin-Integrin α8 signaling is required for proper migration of periocular neural crest cells during chick corneal development

During development, cells aggregate at tissue boundaries to form normal tissue architecture of organs. However, how cells are segregated into tissue precursors remains largely unknown. Cornea development is a perfect example of this process whereby neural crest cells aggregate in the periocular region prior to their migration and differentiation into corneal cells. Our recent RNA-seq analysis identified upregulation of nephronectin (Npnt) transcripts during early stages of corneal development where its function has not been investigated. We found that Npnt mRNA and protein are expressed by various ocular tissues, including the migratory periocular neural crest (pNC), which also express the integrin alpha 8 (Itgα8) receptor. Knockdown of either Npnt or Itgα8 attenuated cornea development, whereas overexpression of Npnt resulted in cornea thickening. Moreover, overexpression of Npnt variants lacking RGD-binding sites did not affect corneal thickness. Neither the knockdown nor augmentation of Npnt caused significant changes in cell proliferation, suggesting that Npnt directs pNC migration into the cornea. In vitro analyses showed that Npnt promotes pNC migration from explanted periocular mesenchyme, which requires Itgα8, focal adhesion kinase, and Rho kinase. Combined, these data suggest that Npnt augments cell migration into the presumptive cornea extracellular matrix by functioning as a substrate for Itgα8-positive pNC cells.

Collective durotaxis along a self-generated stiffness gradient in vivo

Collective cell migration underlies morphogenesis, wound healing and cancer invasion^1,2. Most directed migration in vivo has been attributed to chemotaxis, whereby cells follow a chemical gradient^3-5. Cells can also follow a stiffness gradient in vitro, a process called durotaxis^3,4,6-8, but evidence for durotaxis in vivo is lacking⁶. Here we show that in Xenopus laevis the neural crest-an embryonic cell population-self-generates a stiffness gradient in the adjacent placodal tissue, and follows this gradient by durotaxis. The gradient moves with the neural crest, which is continually pursuing a retreating region of high substrate stiffness. Mechanistically, the neural crest induces the gradient due to N-cadherin interactions with the placodes and senses the gradient through cell-matrix adhesions, resulting in polarized Rac activity and actomyosin contractility, which coordinates durotaxis. Durotaxis synergizes with chemotaxis, cooperatively polarizing actomyosin machinery of the cell group to prompt efficient directional collective cell migration in vivo. These results show that durotaxis and dynamic stiffness gradients exist in vivo, and gradients of chemical and mechanical signals cooperate to achieve efficient directional cell migration.

Contact inhibition of locomotion generates collective cell migration without chemoattractants in an open domain

Neural crest cells are embryonic stem cells that migrate throughout embryos and, at different target locations, give rise to the formation of a variety of tissues and organs. The directional migration of the neural crest cells is experimentally described using a process referred to as contact inhibition of locomotion, by which cells redirect their movement upon the cell-cell contacts. However, it is unclear how the migration alignment is affected by the motility properties of the cells. Here, we theoretically model the migration alignment as a function of the motility dynamics and interaction of the cells in an open domain with a channel geometry. The results indicate that by increasing the influx rate of the cells into the domain a transition takes place from random movement to an organized collective migration, where the migration alignment is maximized and the migration time is minimized. This phase transition demonstrates that the cells can migrate efficiently over long distances without any external chemoattractant information about the direction of migration just based on local interactions with each other. The analysis of the dependence of this transition on the characteristic properties of cellular motility shows that the cell density determines the coordination of collective migration whether the migration domain is open or closed. In the open domain, this density is determined by a feedback mechanism between the flux and order parameter, which characterises the alignment of collective migration. The model also demonstrates that the coattraction mechanism proposed earlier is not necessary for collective migration and a constant flux of cells moving into the channel is sufficient to produce directed movement over arbitrary long distances.

Craniofacial and Long Bone Development in the Context of Distraction Osteogenesis

BACKGROUND

Bone retains regenerative potential into adulthood, and surgeons harness this plasticity during distraction osteogenesis. The underlying biology governing bone development, repair, and regeneration is divergent between the craniofacial and appendicular skeleton. Each type of bone formation is characterized by unique molecular signaling and cellular behavior. Recent discoveries have elucidated the cellular and genetic processes underlying skeletal development and regeneration, providing an opportunity to couple biological and clinical knowledge to improve patient care.

METHODS

A comprehensive literature review of basic and clinical literature regarding craniofacial and long bone development, regeneration, and distraction osteogenesis was performed.

RESULTS

The current understanding in craniofacial and long bone development and regeneration is discussed, and clinical considerations for the respective distraction osteogenesis procedures are presented.

CONCLUSIONS

Distraction osteogenesis is a powerful tool to regenerate bone and thus address a number of craniofacial and appendicular skeletal deficiencies. The molecular mechanisms underlying bone regeneration, however, remain elusive. Recent work has determined that embryologic morphogen gradients constitute important signals during regeneration. In addition, striking discoveries have illuminated the cellular processes underlying mandibular regeneration during distraction osteogenesis, showing that skeletal stem cells reactivate embryologic neural crest transcriptomic processes to carry out bone formation during regeneration. Furthermore, innovative adjuvant therapies to complement distraction osteogenesis use biological processes active in embryogenesis and regeneration. Additional research is needed to further characterize the underlying cellular mechanisms responsible for improved bone formation through adjuvant therapies and the role skeletal stem cells play during regeneration.

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.

Reciprocal integrin/integrin antagonism through kindlin-2 and Rho GTPases regulates cell cohesion and collective migration

Collective cell behaviour during embryogenesis and tissue repair requires the coordination of intercellular junctions, cytoskeleton-dependent shape changes controlled by Rho GTPases, and integrin-dependent cell-matrix adhesion. Many different integrins are simultaneously expressed during wound healing, embryonic development, and sprouting angiogenesis, suggesting that there is extensive integrin/integrin cross-talk to regulate cell behaviour. Here, we show that fibronectin-binding β1 and β3 integrins do not act synergistically, but rather antagonize each other during collective cell processes in neuro-epithelial cells, placental trophoblasts, and endothelial cells. Reciprocal β1/β3 antagonism controls RhoA activity in a kindlin-2-dependent manner, balancing cell spreading, contractility, and intercellular adhesion. In this way, reciprocal β1/β3 antagonism controls cell cohesion and cellular plasticity to switch between extreme and opposing states, including epithelial versus mesenchymal-like phenotypes and collective versus individual cell migration. We propose that integrin/integrin antagonism is a universal mechanism to effectuate social cellular interactions, important for tissue morphogenesis, endothelial barrier function, trophoblast invasion, and sprouting angiogenesis.

Integrating chemical and mechanical signals in neural crest cell migration

Neural crest cells are a multipotent embryonic stem cell population that migrate large distances to contribute a variety of tissues. The cranial neural crest, which contribute to tissues of the face and skull, undergo collective migration whose movement has been likened to cancer metastasis. Over the last few years, a variety of mechanisms for the guidance of collective cranial neural crest cell migration have been described: mostly chemical, but more recently mechanical. Here we review these different mechanisms and attempt to integrate them to provide a unified model of collective cranial neural crest cell migration.

Mechanisms of Neural Crest Migration

Neural crest cells are a transient embryonic cell population that migrate collectively to various locations throughout the embryo to contribute a number of cell types to several organs. After induction, the neural crest delaminates and undergoes an epithelial-to-mesenchymal transition before migrating through intricate yet characteristic paths. The neural crest exhibits a variety of migratory behaviors ranging from sheet-like mass migration in the cephalic regions to chain migration in the trunk. During their journey, neural crest cells rely on a range of signals both from their environment and within the migrating population for navigating through the embryo as a collective. Here we review these interactions and mechanisms, including chemotactic cues of neural crest cells' migration.

In vivo topology converts competition for cell-matrix adhesion into directional migration

When migrating in vivo, cells are exposed to numerous conflicting signals: chemokines, repellents, extracellular matrix, growth factors. The roles of several of these molecules have been studied individually in vitro or in vivo, but we have yet to understand how cells integrate them. To start addressing this question, we used the cephalic neural crest as a model system and looked at the roles of its best examples of positive and negative signals: stromal-cell derived factor 1 (Sdf1/Cxcl12) and class3-Semaphorins. Here we show that Sdf1 and Sema3A antagonistically control cell-matrix adhesion via opposite effects on Rac1 activity at the single cell level. Directional migration at the population level emerges as a result of global Semaphorin-dependent confinement and broad activation of adhesion by Sdf1 in the context of a biased Fibronectin distribution. These results indicate that uneven in vivo topology renders the need for precise distribution of secreted signals mostly dispensable.

The Ric-8A/Gα13/FAK signalling cascade controls focal adhesion formation during neural crest cell migration in Xenopus

Ric-8A is a pleiotropic guanine nucleotide exchange factor involved in the activation of various heterotrimeric G-protein pathways during adulthood and early development. Here, we sought to determine the downstream effectors of Ric-8A during the migration of the vertebrate cranial neural crest (NC) cells. We show that the Gα13 knockdown phenocopies the Ric-8A morphant condition, causing actin cytoskeleton alteration, protrusion instability, and a strong reduction in the number and dynamics of focal adhesions. In addition, the overexpression of Gα13 is sufficient to rescue Ric-8A-depleted cells. Ric-8A and Gα13 physically interact and colocalize in protrusions of the cells leading edge. The focal adhesion kinase FAK colocalizes and interacts with the endogenous Gα13, and a constitutively active form of Src efficiently rescues the Gα13 morphant phenotype in NC cells. We propose that Ric-8A-mediated Gα13 signalling is required for proper cranial NC cell migration by regulating focal adhesion dynamics and protrusion formation.

Gap junction protein Connexin-43 is a direct transcriptional regulator of N-cadherin in vivo

Connexins are the primary components of gap junctions, providing direct links between cells under many physiological processes. Here, we demonstrate that in addition to this canonical role, Connexins act as transcriptional regulators. We show that Connexin 43 (Cx43) controls neural crest cell migration in vivo by directly regulating N-cadherin transcription. This activity requires interaction between Cx43 carboxy tail and the basic transcription factor-3, which drives the translocation of Cx43 tail to the nucleus. Once in the nucleus they form a complex with PolII which directly binds to the N-cadherin promoter. We found that this mechanism is conserved between amphibian and mammalian cells. Given the strong evolutionary conservation of connexins across vertebrates, this may reflect a common mechanism of gene regulation by a protein whose function was previously ascribed only to gap junctional communication.

Connexins are components of gap junctions that link cells and allow intercellular communication. Here, the authors show that the Connexin 43 carboxy tail interacts with basic transcription factor-3, leading to nuclear translocation and direct regulation of N-cadherin expression and neural crest migration.

MMP14 Regulates Cranial Neural Crest Epithelial-to-Mesenchymal Transition and Migration

BACKGROUND

Neural crest is a vertebrate specific cell population. Induced at lateral borders of the neural plate, neural crest cells (NCCs) subsequently undergo epithelial-to-mesenchymal transition (EMT) to detach from the neuroepithelium before migrating into various locations in the embryo. Despite the wealth of knowledge of transcription factors involved in this process, little is known about the effectors that directly regulate neural crest EMT and migration.

RESULTS

Here, we examined the activity of matrix metalloproteinase MMP14 in NCCs and found that MMP14 is expressed in both premigratory and migrating NCCs. Overexpression of MMP14 led to premature migration of NCCs, while down-regulation of MMP14 resulted in reduced neural crest migration. Transplantation experiment further showed that MMP14 is required in NCCs, whereas MMP2, which can be activated by MMP14, is required in the surrounding mesenchyme. in vitro explant culture showed that MMP14 is required for neural crest EMT but not for spreading. This is possibly mediated by the changes in cadherin levels, as decreasing MMP14 level led to increased cadherin expression and increasing MMP14 level led to reduced cadherin expression.

CONCLUSIONS

The results demonstrate that MMP14 is critical for neural crest EMT and migration, partially through regulating the levels of cadherins. Developmental Dynamics 247:1083-1092, 2018. © 2018 Wiley Periodicals, Inc.

Using Zebrafish to Study Collective Cell Migration in Development and Disease

Cellular migration is necessary for proper embryonic development as well as maintenance of adult health. Cells can migrate individually or in groups in a process known as collective cell migration. Collectively migrating cohorts maintain cell-cell contacts, group polarization, and exhibit coordinated behavior. This mode of migration is important during numerous developmental processes including tracheal branching, blood vessel sprouting, neural crest cell migration and others. In the adult, collective cell migration is important for proper wound healing and is often misappropriated during cancer cell invasion. A variety of genetic model systems are used to examine and define the cellular and molecular mechanisms behind collective cell migration including border cell migration and tracheal branching in Drosophila melanogaster, neural crest cell migration in chick and Xenopus embryos, and posterior lateral line primordium (pLLP) migration in zebrafish. The pLLP is a group of about 100 cells that begins migrating around 22 hours post-fertilization along the lateral aspect of the trunk of the developing embryo. During migration, clusters of cells are deposited from the trailing end of the pLLP; these ultimately differentiate into mechanosensory organs of the lateral line system. As zebrafish embryos are transparent during early development and the pLLP migrates close to the surface of the skin, this system can be easily visualized and manipulated in vivo. These advantages together with the amenity to advance genetic methods make the zebrafish pLLP one of the premier model systems for studying collective cell migration. This review will describe the cellular behaviors and signaling mechanisms of the pLLP and compare the pLLP to collective cell migration in other popular model systems. In addition, we will examine how this type of migration is hijacked by collectively invading cancer cells.

Redistribution of Adhesive Forces through Src/FAK Drives Contact Inhibition of Locomotion in Neural Crest

Contact inhibition of locomotion is defined as the behavior of cells to cease migrating in their former direction after colliding with another cell. It has been implicated in multiple developmental processes and its absence has been linked to cancer invasion. Cellular forces are thought to govern this process; however, the exact role of traction through cell-matrix adhesions and tension through cell-cell adhesions during contact inhibition of locomotion remains unknown. Here we use neural crest cells to address this and show that cell-matrix adhesions are rapidly disassembled at the contact between two cells upon collision. This disassembly is dependent upon the formation of N-cadherin-based cell-cell adhesions and driven by Src and FAK activity. We demonstrate that the loss of cell-matrix adhesions near the contact leads to a buildup of tension across the cell-cell contact, a step that is essential to drive cell-cell separation after collision.

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Focal adhesions disassemble at cell-cell contacts in contact inhibition of locomotion

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FA disassembly at the cell contact during CIL requires N-cadherin/Src/FAK signaling

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Cell separation during CIL involves a buildup of tension across the cell contact

Cut loose and run: The complex role of ADAM proteases during neural crest cell development

ADAM metalloproteases have been shown to play critical roles during development. In this review, we will describe functional evidence that implicates ADAM proteins during the genesis, migration and differentiation of neural crest cells. We will restrict our analysis to the transmembrane ADAMs as other reviews have addressed the role of extracellular metalloproteases (Christian et al. [2013] Critical Reviews in Biochemistry and Molecular Biology 48:544-560). This review will describe advances that have been obtained mainly through the use of two vertebrate model systems, the frog, and avian embryos. The role of the principal substrates of ADAMs, the cadherins, has been extensively described in other reviews, most recently in (Cousin [1997] Mechanisms of Development 148:79-88; Taneyhill and Schiffmacher [2017] Genesis, 55). The function of ADAMs in the migration of other cell types, including the immune system, wound healing and cancer has been described previously in (Dreymueller et al. [2017] Mediators of Inflammation 2017: 9621724). Our goal is to illustrate both the importance of ADAMs in controlling neural crest behavior and how neural crest cells have helped us understand the molecular interactions, substrates, and functions of ADAM proteins in vivo.

The Physical and Biochemical Properties of the Extracellular Matrix Regulate Cell Fate

The extracellular matrix is a complex network of hydrated macromolecular proteins and sugars that, in concert with bound soluble factors, comprise the acellular stromal microenvironment of tissues. Rather than merely providing structural information to cells, the extracellular matrix plays an instructive role in development and is critical for the maintenance of tissue homeostasis. In this chapter, we review the composition of the extracellular matrix and summarize data illustrating its importance in embryogenesis, tissue-specific development, and stem cell differentiation. We discuss how the biophysical and biochemical properties of the extracellular matrix ligate specific transmembrane receptors to activate intracellular signaling that alter cell shape and cytoskeletal dynamics to modulate cell growth and viability, and direct cell migration and cell fate. We present examples describing how the extracellular matrix functions as a highly complex physical and chemical entity that regulates tissue organization and cell behavior through a dynamic and reciprocal dialogue with the cellular constituents of the tissue. We suggest that the extracellular matrix not only transmits cellular and tissue-level force to shape development and tune cellular activities that are key for coordinated tissue behavior, but that it is itself remodeled such that it temporally evolves to maintain the integrated function of the tissue. Accordingly, we argue that perturbations in extracellular matrix composition and structure compromise key developmental events and tissue homeostasis, and promote disease.

Cranial Neural Crest Explants

The cranial neural crest (CNC) explant assay was originally designed to assess the basic requirements for CNC migration in vitro. This protocol describes the key parameters of CNC explants in Xenopus laevis, with a focus on how to extirpate CNC cells and assay their migration in vitro. The protocol can be adapted according to the needs of the experimenter, some examples of which are discussed here.

Tissue stiffening coordinates morphogenesis by triggering collective cell migration in vivo

Collective cell migration (CCM) is essential for morphogenesis, tissue remodelling, and cancer invasion1,2. In vivo, groups of cells move in an orchestrated way through tissues. This movement requires forces and involves mechanical as well as molecular interactions between cells and their environment. While the role of molecular signals in CCM is comparatively well understood1,2, how tissue mechanics influence CCM in vivo remains unknown. Here we investigated the importance of mechanical cues in the collective migration of the Xenopus laevis neural crest cells, an embryonic cell population whose migratory behaviour has been likened to cancer invasion3. We found that, during morphogenesis, the head mesoderm underlying the cephalic neural crest stiffens. This stiffening initiated an epithelial-to-mesenchymal transition (EMT) in neural crest cells and triggered their collective migration. To detect changes in their mechanical environment, neural crest use integrin/vinculin/talin-mediated mechanosensing. By performing mechanical and molecular manipulations, we showed that mesoderm stiffening is necessary and sufficient to trigger neural crest migration. Finally, we demonstrated that convergent extension of the mesoderm, which starts during gastrulation, leads to increased mesoderm stiffness by increasing the cell density underneath the neural crest. These results unveil a novel role for mesodermal convergent extension as a mechanical coordinator of morphogenesis, and thus reveal a new link between two apparently unconnected processes, gastrulation and neural crest migration, via changes in tissue mechanics. Overall, we provide the first demonstration that changes in substrate stiffness can trigger CCM by promoting EMT in vivo. More broadly, our results raise the exciting idea that tissue mechanics combines with molecular effectors to coordinate morphogenesis4.

Cadherins function during the collective cell migration of Xenopus Cranial Neural Crest cells: revisiting the role of E-cadherin

Collective cell migration is a process whereby cells move while keeping contact with other cells. The Xenopus Cranial Neural Crest (CNC) is a population of cells that emerge during early embryogenesis and undergo extensive migration from the dorsal to ventral part of the embryo's head. These cells migrate collectively and require cadherin mediated cell-cell contact. In this review, we will describe the key features of Xenopus CNC migration including the key molecules driving their migration. We will also review the role of the various cadherins during Xenopus CNC emergence and migration. Lastly, we will discuss the recent and seemingly controversial findings showing that E-cadherin presence is essential for CNC migration.

The ectodomain of cadherin-11 binds to erbB2 and stimulates Akt phosphorylation to promote cranial neural crest cell migration

During development, a multi-potent group of cells known as the cranial neural crest (CNC) migrate to form craniofacial structures. Proper migration of these cells requires proteolysis of cell adhesion molecules, such as cadherins. In Xenopus laevis, preventing extracellular cleavage of cadherin-11 impairs CNC migration. However, overexpression of the soluble cleavage product (EC1-3) is capable of rescuing this phenotype. The mechanism by which EC1-3 promotes CNC migration has not been investigated until now. Here we show that EC1-3 stimulates phosphorylation of Akt, a target of PI3K, in X.laevis CNC. Through immunoprecipitation experiments, we determined that EC1-3 interacts with all ErbB receptors, PDGFRα, and FGFR1. Of these receptors, only ErbB2 was able to produce an increase in Akt phosphorylation upon treatment with a recombinant EC1-3. This increase was abrogated by mubritinib, an inhibitor of ErbB2. We were able to recapitulate this decrease in Akt phosphorylation in vivo by knocking down ErbB2 in CNC cells. Knockdown of the receptor also significantly reduced CNC migration in vivo. We confirmed the importance of ErbB2 and ErbB receptor signaling in CNC migration using mubritinib and canertinib, respectively. Mubritinib and the PI3K inhibitor LY294002 significantly decreased cell migration while canertinib nearly prevented it altogether. These data show that ErbB2 and Akt are important for CNC migration and implicate other ErbB receptors and Akt-independent signaling pathways. Our findings provide the first example of a functional interaction between the extracellular domain of a type II classical cadherin and growth factor receptors.

Multidisciplinary approaches to understanding collective cell migration in developmental biology

Mathematical models are becoming increasingly integrated with experimental efforts in the study of biological systems. Collective cell migration in developmental biology is a particularly fruitful application area for the development of theoretical models to predict the behaviour of complex multicellular systems with many interacting parts. In this context, mathematical models provide a tool to assess the consistency of experimental observations with testable mechanistic hypotheses. In this review, we showcase examples from recent years of multidisciplinary investigations of neural crest cell migration. The neural crest model system has been used to study how collective migration of cell populations is shaped by cell–cell interactions, cell–environmental interactions and heterogeneity between cells. The wide range of emergent behaviours exhibited by neural crest cells in different embryonal locations and in different organisms helps us chart out the spectrum of collective cell migration. At the same time, this diversity in migratory characteristics highlights the need to reconcile or unify the array of currently hypothesized mechanisms through the next generation of experimental data and generalized theoretical descriptions.

Cdc42 regulates the cellular localization of Cdc42ep1 in controlling neural crest cell migration

The member of Rho family of small GTPases Cdc42 plays important and conserved roles in cell polarity and motility. The Cdc42ep family proteins have been identified to bind to Cdc42, yet how they interact with Cdc42 to regulate cell migration remains to be elucidated. In this study, we focus on Cdc42ep1, which is expressed predominantly in the highly migratory neural crest cells in frog embryos. Through morpholino-mediated knockdown, we show that Cdc42ep1 is required for the migration of cranial neural crest cells. Loss of Cdc42ep1 leads to rounder cell shapes and the formation of membrane blebs, consistent with the observed disruption in actin organization and focal adhesion alignment. As a result, Cdc42ep1 is critical for neural crest cells to apply traction forces at the correct place to migrate efficiently. We further show that Cdc42ep1 is localized to two areas in neural crest cells: in membrane protrusions together with Cdc42 and in perinuclear patches where Cdc42 is absent. Cdc42 directly interacts with Cdc42ep1 (through the CRIB domain) and changes in Cdc42 level shift the distribution of Cdc42ep1 between these two subcellular locations, controlling the formation of membrane protrusions and directionality of migration as a consequence. These results suggest that Cdc42ep1 elaborates Cdc42 activity in neural crest cells to promote their efficient migration.

Vestigial-like 3 is a novel Ets1 interacting partner and regulates trigeminal nerve formation and cranial neural crest migration

Drosophila Vestigial is the founding member of a protein family containing a highly conserved domain, called Tondu, which mediates their interaction with members of the TEAD family of transcription factors (Scalloped in Drosophila). In Drosophila, the Vestigial/Scalloped complex controls wing development by regulating the expression of target genes through binding to MCAT sequences. In vertebrates, there are four Vestigial-like genes, the functions of which are still not well understood. Here, we describe the regulation and function of vestigial-like 3 (vgll3) during Xenopus early development. A combination of signals, including FGF8, Wnt8a, Hoxa2, Hoxb2 and retinoic acid, limits vgll3 expression to hindbrain rhombomere 2. We show that vgll3 regulates trigeminal placode and nerve formation and is required for normal neural crest development by affecting their migration and adhesion properties. At the molecular level, vgll3 is a potent activator of pax3, zic1, Wnt and FGF, which are important for brain patterning and neural crest cell formation. Vgll3 interacts in the embryo with Tead proteins but unexpectedly with Ets1, with which it is able to stimulate a MCAT driven luciferase reporter gene. Our findings highlight a critical function for vgll3 in vertebrate early development.

Cadherin-11 promotes neural crest cell spreading by reducing intracellular tension-Mapping adhesion and mechanics in neural crest explants by atomic force microscopy

During development cranial neural crest cells (NCCs) display a striking transition from collective to single-cell migration, but the mechanisms enabling individual NCCs to separate from the neural crest tissue are still incompletely understood. In this study we have employed atomic force microscopy (AFM) to investigate potential adhesive and mechanical changes associated with the dissociation of individual cells from cohesive Xenopus NCC explants at early stages of migration. AFM-based single-cell force spectroscopy (SCFS) revealed a uniform distribution of cell-cell adhesion forces within NCC explants, including semi-detached leader cells in the process of delaminating from the explant edge. This suggested that dissociation from the cell sheet may not require prior weakening of cell-cell contacts. However, mapping NCC sheet elasticity by AFM microbead indentation demonstrated strongly reduced cell stiffness in semi-detached leader cells compared to neighbouring cells in the NCC sheet periphery. Reduced leader cell stiffness coincided with enhanced cell spreading and high substrate traction, indicating a possible mechano-regulation of leader cell delamination. In support, AFM elasticity measurements of individual NCCs in optical side view mode demonstrated that reducing cell tension by inhibiting actomyosin contractility induces rapid spreading, possibly maximizing cell-substrate interactions as a result. Depletion of cadherin-11, a classical cadherin with an essential role in NCC migration and substrate adhesion, prevented the tension reduction necessary for NCC spreading, both in individual cells and at the edge of explanted sheets. In contrast, overexpression of cadherin-11 accelerated spreading of both individual cells and delaminating leader cells. As cadherin-11 expression increases strongly during NCC migration, this suggests an important role of cadherin-11 in regulating NCC elasticity and spreading at later stages of NCC migration. We therefore propose a model in which high tension at the NCC sheet periphery prevents premature NCC spreading and delamination during early stages of migration, while a cadherin-11-dependent local decrease in cell tension promotes leader cell spreading and delamination at later stages of migration.

Dual control of pcdh8l/PCNS expression and function in Xenopus laevis neural crest cells by adam13/33 via the transcription factors tfap2α and arid3a

Adam13/33 is a cell surface metalloprotease critical for cranial neural crest (CNC) cell migration. It can cleave multiple substrates including itself, fibronectin, ephrinB, cadherin-11, pcdh8 and pcdh8l (this work). Cleavage of cadherin-11 produces an extracellular fragment that promotes CNC migration. In addition, the adam13 cytoplasmic domain is cleaved by gamma secretase, translocates into the nucleus and regulates multiple genes. Here, we show that adam13 interacts with the arid3a/dril1/Bright transcription factor. This interaction promotes a proteolytic cleavage of arid3a and its translocation to the nucleus where it regulates another transcription factor: tfap2α. Tfap2α in turn activates multiple genes including the protocadherin pcdh8l (PCNS). The proteolytic activity of adam13 is critical for the release of arid3a from the plasma membrane while the cytoplasmic domain appears critical for the cleavage of arid3a. In addition to this transcriptional control of pcdh8l, adam13 cleaves pcdh8l generating an extracellular fragment that also regulates cell migration.

Mechanisms of collective cell movement lacking a leading or free front edge in vivo

Collective cell movement is one of the strategies for achieving the complex shapes of tissues and organs. In this process, multiple cells within a group held together by cell-cell adhesion acquire mobility and move together in the same direction. In some well-studied models of collective cell movement, the mobility depends strongly on traction generated at the leading edge by cells located at the front. However, recent advances in live-imaging techniques have led to the discovery of other types of collective cell movement lacking a leading edge or even a free edge at the front, in a diverse array of morphological events, including tubule elongation, epithelial sheet extension, and tissue rotation. We herein review some of the developmental events that are organized by collective cell movement and attempt to elucidate the underlying cellular and molecular mechanisms, which include membrane protrusions, guidance cues, cell intercalation, and planer cell polarity, or chirality pathways.

Xenopus as a model organism to study heterotrimeric G-protein pathway during collective cell migration of neural crest

Collective cell migration is essential in many fundamental aspects of normal development, like morphogenesis, organ formation, wound healing, and immune responses, as well as in the etiology of severe pathologies, like cancer metastasis. In spite of the huge amount of data accumulated on cell migration, such a complex process involves many molecular actors, some of which still remain to be functionally characterized. One of these signals is the heterotrimeric G-protein pathway that has been studied mainly in gastrulation movements. Recently we have reported that Ric-8A, a GEF for Gα proteins, plays an important role in neural crest migration in Xenopus development. Xenopus neural crest cells, a highly migratory embryonic cell population induced at the border of the neural plate that migrates extensively in order to differentiate in other tissues during development, have become a good model to understand the dynamics that regulate cell migration. In this review, we aim to provide sufficient evidence supporting how useful Xenopus model with its different tools, such as explants and transplants, paired with improved in vivo imaging techniques, will allow us to tackle the multiple signaling mechanisms involved in neural crest cell migration.

Modeling human craniofacial disorders in Xenopus

PURPOSE OF REVIEW

Craniofacial disorders are among the most common human birth defects and present an enormous health care and social burden. The development of animal models has been instrumental to investigate fundamental questions in craniofacial biology and this knowledge is critical to understand the etiology and pathogenesis of these disorders.

RECENT FINDINGS

The vast majority of craniofacial disorders arise from abnormal development of the neural crest, a multipotent and migratory cell population. Therefore, defining the pathogenesis of these conditions starts with a deep understanding of the mechanisms that preside over neural crest formation and its role in craniofacial development.

SUMMARY

This review discusses several studies using Xenopus embryos to model human craniofacial conditions, and emphasizes the strength of this system to inform important biological processes as they relate to human craniofacial development and disease.

Collective cell migration in development

During embryonic development, tissues undergo major rearrangements that lead to germ layer positioning, patterning, and organ morphogenesis. Often these morphogenetic movements are accomplished by the coordinated and cooperative migration of the constituent cells, referred to as collective cell migration. The molecular and biomechanical mechanisms underlying collective migration of developing tissues have been investigated in a variety of models, including border cell migration, tracheal branching, blood vessel sprouting, and the migration of the lateral line primordium, neural crest cells, or head mesendoderm. Here we review recent advances in understanding collective migration in these developmental models, focusing on the interaction between cells and guidance cues presented by the microenvironment and on the role of cell–cell adhesion in mechanical and behavioral coupling of cells within the collective.

In vivo confinement promotes collective migration of neural crest cells

Collective cell migration is fundamental throughout development and in many diseases. Spatial confinement using micropatterns has been shown to promote collective cell migration in vitro, but its effect in vivo remains unclear. Combining computational and experimental approaches, we show that the in vivo collective migration of neural crest cells (NCCs) depends on such confinement. We demonstrate that confinement may be imposed by the spatiotemporal distribution of a nonpermissive substrate provided by versican, an extracellular matrix molecule previously proposed to have contrasting roles: barrier or promoter of NCC migration. We resolve the controversy by demonstrating that versican works as an inhibitor of NCC migration and also acts as a guiding cue by forming exclusionary boundaries. Our model predicts an optimal number of cells in a given confinement width to allow for directional migration. This optimum coincides with the width of neural crest migratory streams analyzed across different species, proposing an explanation for the highly conserved nature of NCC streams during development.

Musculocontractural Ehlers-Danlos syndrome and neurocristopathies: dermatan sulfate is required for Xenopus neural crest cells to migrate and adhere to fibronectin

Of all live births with congenital anomalies, approximately one-third exhibit deformities of the head and face. Most craniofacial disorders are associated with defects in a migratory stem and progenitor cell population, which is designated the neural crest (NC). Musculocontractural Ehlers-Danlos syndrome (MCEDS) is a heritable connective tissue disorder with distinct craniofacial features; this syndrome comprises multiple congenital malformations that are caused by dysfunction of dermatan sulfate (DS) biosynthetic enzymes, including DS epimerase-1 (DS-epi1; also known as DSE). Studies in mice have extended our understanding of DS-epi1 in connective tissue maintenance; however, its role in fetal development is not understood. We demonstrate that DS-epi1 is important for the generation of isolated iduronic acid residues in chondroitin sulfate (CS)/DS proteoglycans in early Xenopus embryos. The knockdown of DS-epi1 does not affect the formation of early NC progenitors; however, it impairs the correct activation of transcription factors involved in the epithelial-mesenchymal transition (EMT) and reduces the extent of NC cell migration, which leads to a decrease in NC-derived craniofacial skeleton, melanocytes and dorsal fin structures. Transplantation experiments demonstrate a tissue-autonomous role for DS-epi1 in cranial NC cell migration in vivo Cranial NC explant and single-cell cultures indicate a requirement of DS-epi1 in cell adhesion, spreading and extension of polarized cell processes on fibronectin. Thus, our work indicates a functional link between DS and NC cell migration. We conclude that NC defects in the EMT and cell migration might account for the craniofacial anomalies and other congenital malformations in MCEDS, which might facilitate the diagnosis and development of therapies for this distressing condition. Moreover, the presented correlations between human DS-epi1 expression and gene sets of mesenchymal character, invasion and metastasis in neuroblastoma and malignant melanoma suggest an association between DS and NC-derived cancers.

Cadherin-11 localizes to focal adhesions and promotes cell-substrate adhesion

Cadherin receptors have a well-established role in cell–cell adhesion, cell polarization and differentiation. However, some cadherins also promote cell and tissue movement during embryonic development and tumour progression. In particular, cadherin-11 is upregulated during tumour and inflammatory cell invasion, but the mechanisms underlying cadherin-11 stimulated cell migration are still incompletely understood. Here, we show that cadherin-11 localizes to focal adhesions and promotes adhesion to fibronectin in Xenopus neural crest, a highly migratory embryonic cell population. Transfected cadherin-11 also localizes to focal adhesions in different mammalian cell lines, while endogenous cadherin-11 shows focal adhesion localization in primary human fibroblasts. In focal adhesions, cadherin-11 co-localizes with β1-integrin and paxillin and physically interacts with the fibronectin-binding proteoglycan syndecan-4. Adhesion to fibronectin mediated by cadherin-11/syndecan-4 complexes requires both the extracellular domain of syndecan-4, and the transmembrane and cytoplasmic domains of cadherin-11. These results reveal an unexpected role of a classical cadherin in cell–matrix adhesion during cell migration.

Cadherins are typically involved in cell-cell adhesion, however cadherin-11 promotes cell migration through an undefined mechanism. Langhe et al. show that cadherin-11 mediates adhesion to the cell matrix at focal adhesions through interaction with syndecan-4.

ADAM13 cleavage of cadherin-11 promotes CNC migration independently of the homophilic binding site

The cranial neural crest (CNC) is a highly motile population of cells that is responsible for forming the face and jaw in all vertebrates and perturbing their migration can lead to craniofacial birth defects. Cell motility requires a dynamic modification of cell-cell and cell-matrix adhesion. In the CNC, cleavage of the cell adhesion molecule cadherin-11 by ADAM13 is essential for cell migration. This cleavage generates a shed extracellular fragment of cadherin-11 (EC1-3) that possesses pro-migratory activity via an unknown mechanism. Cadherin-11 plays an important role in modulating contact inhibition of locomotion (CIL) in the CNC to regulate directional cell migration. Here, we show that while the integral cadherin-11 requires the homophilic binding site to promote CNC migration in vivo, the EC1-3 fragment does not. In addition, we show that increased ADAM13 activity or expression of the EC1-3 fragment increases CNC invasiveness in vitro and blocks the repulsive CIL response in colliding cells. This activity requires the presence of an intact homophilic binding site on the EC1-3 suggesting that the cleavage fragment may function as a competitive inhibitor of cadherin-11 adhesion in CIL but not to promote cell migration in vivo.