Cell adhesion and migration in the early vertebrate embryo: location and possible role of the putative fibronectin receptor complex

A machine learning pipeline revealing heterogeneous responses to drug perturbations on vascular smooth muscle cell spheroid morphology and formation

Machine learning approaches have shown great promise in biology and medicine discovering hidden information to further understand complex biological and pathological processes. In this study, we developed a deep learning-based machine learning algorithm to meaningfully process image data and facilitate studies in vascular biology and pathology. Vascular injury and atherosclerosis are characterized by neointima formation caused by the aberrant accumulation and proliferation of vascular smooth muscle cells (VSMCs) within the vessel wall. Understanding how to control VSMC behaviors would promote the development of therapeutic targets to treat vascular diseases. However, the response to drug treatments among VSMCs with the same diseased vascular condition is often heterogeneous. Here, to identify the heterogeneous responses of drug treatments, we created an in vitro experimental model system using VSMC spheroids and developed a machine learning-based computational method called HETEROID (heterogeneous spheroid). First, we established a VSMC spheroid model that mimics neointima-like formation and the structure of arteries. Then, to identify the morphological subpopulations of drug-treated VSMC spheroids, we used a machine learning framework that combines deep learning-based spheroid segmentation and morphological clustering analysis. Our machine learning approach successfully showed that FAK, Rac, Rho, and Cdc42 inhibitors differentially affect spheroid morphology, suggesting that multiple drug responses of VSMC spheroid formation exist. Overall, our HETEROID pipeline enables detailed quantitative drug characterization of morphological changes in neointima formation, that occurs in vivo, by single-spheroid analysis.

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.

Role of the lysyl oxidase family in organ development (Review)

Lysyl oxidase proteins (LOXs) are amine oxidases, which are mainly located in smooth muscle cells and fibroblasts and serve an important role in the formation of the extracellular matrix (ECM) in a copper-dependent manner. Owing to the ability of LOX proteins to modulate crosslinking between collagens and to promote the deposition of other fibers, they serve crucially in organogenesis and the subsequent organ development, as well as disease initiation and progression. In addition, ECM formation significantly influences organ morphological formation in both cancer- and non-tumor-related diseases, in addition to cellular epigenetic transformation and migration, under the influence of LOXs. A number of different signaling pathways regulate the LOXs expression and their enzymatic activation. The tissue remodeling and transformation process shares some resemblance between oncogenesis and embryogenesis. Additionally the roles that LOXs serve appeared to be stressed during oncogenesis and tumor metastasis. It has also been indicated LOXs have a noteworthy role in non-tumor diseases. Nonetheless, the role of LOXs in systemic or local organ development and disease control remains unknown. In the present study, the essential roles that LOXs play in embryogenesis were unveiled partially, whereas the role of LOXs in organ or systematic development requires further investigations. The present review aimed to discuss the roles of members of the LOX family in the context of the remodeling of organogenesis and organ development. In addition, the consequences of the malfunction of these proteins related to the development of abnormalities and resulting diseases is discussed.

Fibronectin assembly during early embryo development: A versatile communication system between cells and tissues

BACKGROUND

Fibronectin extracellular matrix is essential for embryogenesis. Its assembly is a cell-mediated process where secreted fibronectin dimers bind to integrin receptors on receiving cells, which actively assemble fibronectin into a fibrillar matrix. During development, paracrine communication between tissues is crucial for coordinating morphogenesis, typically being mediated by growth factors and their receptors. Recent reports of situations where fibronectin is produced by one tissue and assembled by another, with implications on tissue morphogenesis, suggest that fibronectin assembly may also be a paracrine communication event in certain contexts.

RESULTS

Here we addressed which tissues express fibronectin (Fn1) while also localizing assembled fibronectin matrix and determining the mRNA expression and/or protein distribution pattern of integrins α5 and αV, α chains of the major fibronectin assembly receptors, during early chick and mouse development. We found evidence supporting a paracrine system in fibronectin matrix assembly in several tissues, including immature mesenchymal tissues, components of central and peripheral nervous system and developing muscle.

CONCLUSIONS

Thus, similarly to growth factor signaling, fibronectin matrix assembly during early development can be both autocrine and paracrine. We therefore propose that it be considered a cell-cell communication event at the same level and significance as growth factor signaling during embryogenesis.

Cloning and characterization of chicken α5 integrin: endogenous and experimental expression in early chicken embryos

Key roles for fibronectin and its integrin receptors have been postulated in the multiple cell-matrix interactions essential for chick embryo morphogenesis. However, mechanistic studies of these processes have been hampered by the current absence of sequence data and chicken cDNA clones for the major fibronectin receptor subunit, integrin α5 (ITGA5). We report here the sequence, endogenous expression pattern, and transfection of full-length chicken integrin α5. During early chicken embryonic development, α5 is highly expressed in cranial neural folds and migrating neural crest cells, suggesting potential roles in neural crest formation and migration. In fact, over-expression of this integrin in early neural tube selectively induces BMP5, a growth factor recently implicated in neural crest formation. Availability of these α5 integrin tools should facilitate studies of its functions in early embryonic development.

Lessons from the embryonic neural stem cell niche for neural lineage differentiation of pluripotent stem cells

Pluripotent stem cells offer an abundant and malleable source for the generation of differentiated cells for transplantation as well as for in vitro screens. Patterning and differentiation protocols have been developed to generate neural progeny from human embryonic or induced pluripotent stem cells. However, continued refinement is required to enhance efficiency and to prevent the generation of unwanted cell types. We summarize and interpret insights gained from studies of embryonic neuroepithelium. A multitude of factors including soluble molecules, interactions with the extracellular matrix and neighboring cells cooperate to control neural stem cell self-renewal versus differentiation. Applying these findings and concepts to human stem cell systems in vitro may yield more appropriately patterned cell types for biomedical applications.

Expression and function of cell adhesion molecules during neural crest migration

Neural crest cells are highly migratory cells that give rise to many derivatives including peripheral ganglia, craniofacial structures and melanocytes. Neural crest cells migrate along defined pathways to their target sites, interacting with each other and their environment as they migrate. Cell adhesion molecules are critical during this process. In this review we discuss the expression and function of cell adhesion molecules during the process of neural crest migration, in particular cadherins, integrins, members of the immunoglobulin superfamily of cell adhesion molecules, and the proteolytic enzymes that cleave these cell adhesion molecules. The expression and function of these cell adhesion molecules and proteases are compared across neural crest emigrating from different axial levels, and across different species of vertebrates.

Integrins stimulate E-cadherin-mediated intercellular adhesion by regulating Src-kinase activation and actomyosin contractility

Cadherins and integrins are major adhesion molecules regulating cell-cell and cell-matrix interactions. In vitro and in vivo studies have demonstrated the existence of crosstalk between integrins and cadherins in cell adhesion and motility. We used a dual pipette assay to measure the force required to separate E-cadherin-producing cell doublets and to investigate the role of integrin in regulating the strength of intercellular adhesion. A greater force was required to separate cell doublets bound to fibronectin or vitronectin-coated beads than for doublets bound to polylysine-coated beads. This effect depended on cell spreading and the duration of stimulation. Cells expressing type II cadherin-7 also responded to fibronectin stimulation to produce a higher intercellular adhesion. Establishment of cadherin-mediated adhesion needed ROCK, MLCK and myosin ATPase II activity. The regulation of intercellular adhesion strength by integrin stimulation required activation of Src family kinases, ROCK and actomyosin contractility. These findings highlight the importance and mechanisms of molecular crosstalk between cadherins and integrins in the control of cell plasticity during histogenesis and morphogenesis.

Spatio-temporal control of neural epithelial cell migration and epithelium-to-mesenchyme transition during avian neural tube development

As opposed to the neural crest, the neural epithelium is generally viewed as a static and cohesive structure. Here, using an ex vivo system free of the environmental influences and physical constraints encountered in the embryo, we show that neural epithelial cells are on the contrary intrinsically motile, although they do not undergo spontaneous epithelium-to-mesenchyme transition and display molecular and cellular characteristics distinct from those of neural crest cells. However, they can be instructed to undergo epithelium-to-mesenchyme conversion independently of the acquisition of neural crest traits. Migration potentialities of neural epithelial cells are transient and are progressively restricted during neural tube development. Restriction of cell migration is irreversible and can be in part accounted for by increase in N-cadherin in cellular junctions and in cell polarity. In conclusion, our study reveals that the neural epithelium is a highly flexible tissue in which cells are maintained cohesive under the control of a combination of extrinsic factors and physical constraints.

Adhesion mechanisms in embryogenesis and in cancer invasion and metastasis

Cell-substratum and cell-cell adhesion mechanisms contribute to the development of animal form. The adhesive status of embryonic cells has been analysed during epithelial-mesenchymal cell interconversion and in cell migrations. Clear-cut examples of the modulation of cell adhesion molecules (CAMs) have been described at critical periods of morphogenesis. In chick embryos the three primary CAMs (N-CAM. L-CAM and N-cadherin) present early in embryogenesis are expressed later in a defined pattern during morphogenesis and histogenesis. The axial mesoderm derived from gastrulating cells expresses increasing amounts of N-cadherin and N-CAM. During metamerization these two adhesion molecules become abundant at somitic cell surfaces. Both CAMs are functional in an in vitro aggregation assay; however, the calcium-dependent adhesion molecule N-cadherin is more sensitive to perturbation by specific antibodies. Neural crest cells which separate from the neural epithelium lose their primary CAMs in a defined time-sequence. Adhesion to fibronectins via specific surface receptors becomes a predominant interaction during the migratory process, while some primary and secondary CAMs are expressed de novo during the ontogeny of the peripheral nervous system. In vitro, different fibronectin functional domains have been identified in the attachment, spreading and migration of neural crest cells. The fibronectin receptors which transduce the adhesive signals play a key role in the control of cell movement. All these results have prompted us to examine whether similar mechanisms operate in carcinoma cell invasion and metastasis. In vitro, rat bladder transitional carcinoma cells convert reversibly into invasive mesenchymal cells. A rapid modulation of adhesive properties is found during the epithelial-mesenchymal carcinoma cell interconversion. The different model systems analysed demonstrate that a limited repertoire of adhesion molecules, expressed in a well-defined spatiotemporal pattern, is involved in tissue formation and in key processes of tumour spread.

The cell interaction sites of fibronectin in tumour metastasis

Adhesion to specific extracellular matrix molecules appears to be an important prerequisite for successful target organ colonization by metastasizing tumour cells. Interference in the adhesive function of malignant cells with antiadhesive agents is therefore one potential approach for preventing metastasis. Recently, synthetic peptides taken from the cell interaction sites of fibronectin have been characterized as inhibitors of cellular adhesion in vitro. Using these antiadhesive probes we have examined the role of cell adhesion to fibronectin in tumour metastasis using the B16-F10 murine melanoma model system. Two sequences from the IIICS cell-binding domain, the 25-mer CS1 peptide and the tetrapeptide Arg-Glu-Asp-Val (REDV), had no detectable activity, but the pentapeptide Gly-Arg-Gly-Asp-Ser (GRGDS), an active sequence from the central cell-binding domain, exhibited potent, dose-dependent inhibition, indicating a role for this cell recognition determinant in tumour metastasis. Under appropriate conditions GRGDS treatment afforded remarkable protection to the host; mice injected with melanoma cells and peptide were still alive 15 months after injection whereas mice injected with melanoma cells alone died within six weeks. Kinetic analyses of the retention of tumour cells in the lungs and of the vascular clearance rate of labelled GRGDS predict an early time frame of activity for the peptide. From the results of a variety of in vitro invasion and migration assays it appears that GRGDS may interfere with multiple, fibronectin-mediated adhesive and migratory events at different points of the metastatic cascade. In preliminary studies designed to optimize the therapeutic usefulness of GRGDS-like agents, peptide conjugates have been found to possess enhanced antiadhesive activity as well as an extended vascular clearance rate. In the future, therefore, these or related peptide derivatives may be potentially useful agents for the prevention of tumour metastasis.

Redefining the role of ectoderm in somitogenesis: a player in the formation of the fibronectin matrix of presomitic mesoderm

The absence of ectoderm impairs somite formation in cultured presomitic mesoderm (PSM) explants, suggesting that an ectoderm-derived signal is essential for somitogenesis. Here we show in chick that the standard enzymatic treatments used for explant isolation destroy the fibronectin matrix surrounding the anterior PSM, which fails to form somites when cultured for 6 hours. By contrast, explants isolated with collagenase retain their fibronectin matrix and form somites under identical culture conditions. The additional presence of ectoderm enhances somite formation, whereas endoderm has no effect. Furthermore, we show that pancreatin-isolated PSM explants cultured in fibronectin-supplemented medium, form significantly more somites than control explants. Interestingly, ectoderm is the major producer of fibronectin (Fn1) transcripts, whereas all but the anterior-most region of the PSM expresses the fibronectin assembly receptor, integrin alpha5 (Itga5). We thus propose that the ectoderm-derived fibronectin is assembled by mesodermal alpha5beta1 integrin on the surface of the PSM. Finally, we demonstrate that inhibition of fibronectin fibrillogenesis in explants with ectoderm abrogates somitogenesis. We conclude that a fibronectin matrix is essential for morphological somite formation and that a major, previously unrecognised role of ectoderm in somitogenesis is the synthesis of fibronectin.

Abnormalities in neural crest cell migration in laminin alpha5 mutant mice

Although numerous in vitro experiments suggest that extracellular matrix molecules like laminin can influence neural crest migration, little is known about their function in the embryo. Here, we show that laminin alpha5, a gene up-regulated during neural crest induction, is localized in regions of newly formed cranial and trunk neural folds and adjacent neural crest migratory pathways in a manner largely conserved between chick and mouse. In laminin alpha5 mutant mice, neural crest migratory streams appear expanded in width compared to wild type. Conversely, neural folds exposed to laminin alpha5 in vitro show a reduction by half in the number of migratory neural crest cells. During gangliogenesis, laminin alpha5 mutants exhibit defects in condensing cranial sensory and trunk sympathetic ganglia. However, ganglia apparently recover at later stages. These data suggest that the laminin alpha5 subunit functions as a cue that restricts neural crest cells, focusing their migratory pathways and condensation into ganglia. Thus, it is required for proper migration and timely differentiation of some neural crest populations.

Deletion of Mouse Embryo Fibroblast N-Acetylglucosaminyltransferase V Stimulates α5β1 Integrin Expression Mediated by the Protein Kinase C Signaling Pathway

An N-linked glycan often increased during oncogenic transformation contains beta(1,6)-linked GlcNAc, synthesized by the N-acetylglucosaminyltransferase V (GnT-V). The progression of polyoma middle T-antigen oncoprotein-induced mammary carcinomas in GnT-V null mice was significantly retarded compared with that observed in wild-type mice. The matrix adhesion of mouse embryonic fibroblasts (MEF) from GnT-V null and wild-type mice was investigated to understand the mechanism by which deletion of GnT-V could retard tumor progression. GnT-V null MEF displayed enhanced adhesion to and spreading on fibronectin-coated plates with concomitant inhibition of cell migration. GnT-V null MEF also showed increased focal adhesion kinase tyrosine phosphorylation, consistent with decreased cell motility on fibronectin-coated plates. Expression of GnT-V cDNA in the null MEF reversed these abnormal characteristics, indicating the direct involvement of N-glycosylation events in these phenotypic changes. The alpha5beta1 fibronectin receptors exhibited increased clustering on the null MEF cell surfaces, consistent with previous studies that observed less integrin clustering in cells overexpressing GnT-V. Most surprisingly, GnT-V null MEF displayed increased expression levels of both alpha5 and beta1 subunits in lysates and on the cell surface. Increased alpha5beta1 expression in the null MEF was because of increased alpha5beta1 transcript levels that declined after re-expression of GnT-V cDNA, confirming that increased alpha5beta1 expression in null MEF was because of changes in GnT-V expression. The increased null MEF transcripts were shown to be caused at least in part by increased integrin promoter activity. Moreover, increased alpha5beta1 integrin transcripts in GnT-V null MEF were not due to a differential response to fibronectin; rather, they appeared to be mediated by activation of a protein kinase C signaling pathway. These results demonstrate that deletion of MEF GnT-V resulted in enhanced integrin clustering and activation of alpha5beta1 transcription by protein kinase C signaling, which in turn up-regulated levels of cell surface alpha5beta1 fibronectin receptors that resulted in increased matrix adhesion and inhibition of migration.

Parallel analysis of multiple surface markers expressed on rat neural stem cells using antibody microarrays

Neural stem cells are the attractive cell source for functional regeneration of damaged central nervous tissues by means of cell transplantation or in situ induction of differentiated neural cells. Such stem cell therapies require the prospective identification and isolation of neural stem cells. However they are difficult due to limited information on surface markers. This study aimed at developing an antibody microarray that permits parallel analysis of multiple surface antigens expressed on neural stem cells present in a neurosphere-forming cell population. A microarray was prepared by micro-spotting antibodies directed to surface antigens and ligands for membrane-associated receptors onto the patterned monolayer of alkanethiols self-assembled on a gold-evaporated glass plate. Neurosphere-forming cells were subjected to a cell-binding assay on the microarray followed by immunofluorescent staining of nestin, an intracellular marker of neural stem cells. It was demonstrated that such a cell based assay facilitated to examine the specificity of surface antigens for nestin-positive neural stem cells. Furthermore, the microarray could also be used to assess proliferation capability of cells bound to individual spots. These results suggest that the microarray-based strategy will provide a useful tool for the parallel analysis of surface markers expressed on a specific cell type in a heterogeneous population.

A dual role for Sonic hedgehog in regulating adhesion and differentiation of neuroepithelial cells

In vertebrates, the nervous system arises from a flat sheet of epithelial cells, the neural plate, that gradually transforms into a hollow neural tube. This process, called neurulation, involves sequential changes in cellular interactions that are precisely coordinated both spatially and temporally by the combined actions of morphogens. To gain further insight into the molecular events regulating cell adhesion during neurulation, we investigated whether the adhesive and migratory capacities of neuroepithelial cells might be modulated by Sonic hedgehog (Shh), a signaling molecule involved in the control of cell differentiation in the ventral neural tube. When deposited onto extracellular matrix components in vitro, neural plates explanted from avian embryos at early neurulation readily dispersed into monolayers of spread cells, thereby revealing their intrinsic ability to migrate. In the presence of Shh added in solution to the culture medium, the explants still exhibited the same propensity to disperse. In contrast, when Shh was immobilized to the substrate or produced by neuroepithelial cells themselves after transfection, neural plate explants failed to disperse and instead formed compact structures. Changes in the adhesive capacities of neuroepithelial cells caused by Shh could be accounted for by inactivation of surface beta1-integrins combined with an increase in N-cadherin-mediated cell adhesion. Furthermore, immobilized Shh promoted differentiation of neuroepithelial cells into motor neurons and floor plate cells with the same potency as soluble Shh. However, the effect of Shh on the neuroepithelial cell adhesion was discernible and apparently independent from its differentiation effect and was not mediated by the signaling cascade elicited by the Patched-Smoothened receptor and involving the Gli transcription factors. Thus, our experiments indicate that Shh is able to control sequentially adhesion and differentiation of neuroepithelial cells through different mechanisms, leading to a coordinated regulation of the various cell interactions essential for neural tube morphogenesis.

Temporal restriction of migratory and lineage potential in rhombomere 1 and 2 neural crest

Migratory cranial neural crest cells differentiate into a wide range of cell types, such as ectomesenchymal tissue (bone and connective tissues) ventrally in the branchial arches and neural tissue (neurons and glia) dorsally. We investigated spatial and temporal changes of migration and differentiation potential in neural crest populations derived from caudal midbrain and rhombomeres 1 and 2 by back-transplanting cells destined for the first branchial arch and trigeminal ganglion from HH8-HH19 quail into HH7-HH11 chicks. Branchial arch cells differentiated down ectomesenchymal lineages but largely lost both the ability to localize to the trigeminal position and neurogenic differentiation capacity by HH12-HH13, even before the arch is visible, and lost long distance migratory ability around HH17. In contrast, neural crest-derived cells from trigeminal ganglia lost ectomesechymal differentiation potential by HH17. Despite this, they retain the ability to migrate into the branchial arches until at least HH19. However, many of the neural crest-derived trigeminal ganglia cells in the branchial arch localized to the non-neural crest core of the arch from HH13 and older donors. These results suggest that long distance migration ability, finer scale localization, and lineage restriction may not be coordinately regulated in the cranial neural crest population.

Synthetic matrix metalloproteinase inhibitor decreases early cardiac neural crest migration in chicken embryos

During early embryonic development, cardiac neural crest (NC) cells emerge from the forming neural tube, migrate beneath the ectoderm, enter the pharyngeal arches, and subsequently participate in the septation of the heart. Like tumor cells, NC cells penetrate through basement membranes and invade extracellular matrix during their emigration and migration and, therefore, are liable to use similar invasive mechanisms. Matrix metalloproteinases (MMPs) are a family of zinc proteolytic enzymes known to be important in cell migration and invasion of normal and metastatic cells. In an earlier study, we found that the spatial and temporal distribution pattern of MMP-2 positively correlates with cardiac NC migration, suggesting MMP enzymatic activity may be important in mediating cardiac cell NC migration. To test this hypothesis, a synthetic MMP inhibitor, KB8301, was used to block MMP enzymatic activity during in vitro and in vivo cardiac NC cell migration in chick embryos. Injection of KB8301 into the cell-free space adjacent to the neural tube at the level of the second somite before the NC cells emigrated caused major morphologic anomalies in embryos and disrupted cardiac NC morphogenesis. Unilateral injection of KB8301 at lower concentrations, significantly decreased cardiac NC migration on the injected side compared with the noninjected side and compared with that of the injected controls. This decrease correlated with a decrease in MMP activity in the embryos and was not attributable to differences in embryo size or rate of embryonic development after injection. KB8301 also significantly decreased the rate of NC cell motility and distance NC cells migrated from explanted neural tubes and increased cell area and perimeter. These data suggest that MMP enzymatic activity is an important mediator of early cardiac NC migration and that perturbation of endogenous MMP activity may lead to NC-related congenital defects.

Differences in sensitivity of biological functions mediated by epidermal growth factor receptor activation with respect to endogenous and exogenous ligands

Despite constitutive expression of autocrine transforming growth factor-alpha (TGF-alpha) in growth factor-independent colon carcinoma cells, the epidermal growth factor receptor (EGFr) is not saturated and can be further activated by exogenous EGFr ligand. Given that the activation of EGFr by exogenous growth factor has no further effect on DNA synthesis, the question arises as to what function this additional EGFr activation might have. We report that EGF induces integrin alpha2 expression, integrin-mediated adhesion, and micromotility of HCT116 cells. The stimulatory effect of ligand on these biological functions is abrogated by treatment with AG1478- and EGFr-blocking monoclonal antibody. This provides evidence that the biological responses are EGFr-mediated and EGFr is located upstream of integrin alpha2 expression. Therefore, although exogenous EGF has no effect on DNA synthesis beyond that induced by autocrine TGF-alpha (at subsaturating levels of EGFr occupation) exogenous growth factor does induce integrin alpha2 expression, cell adhesion, and micromotion. An important finding revealed by this study is the documentation of biological responses of EGFr-mediated functions, including DNA synthesis, cell adhesion, and micromotion, which differ in sensitivity with respect to different degrees of EGFr activation at the basal state and in response to exogenous ligand.

Central role of the alpha4beta1 integrin in the coordination of avian truncal neural crest cell adhesion, migration, and survival

Based on functional and histological studies, the fibronectin receptor of the integrin family alpha4beta1 has been ascribed a critical role during neural crest cell migration in the vertebrate embryo. In the present study, because integrins have been shown to participate in multiple basic cellular processes, including cell adhesion, migration, survival, proliferation, and differentiation, we have reexamined in detail the role of alpha4beta1 during avian truncal neural crest cell migration. RT-PCR and immunocytochemical studies revealed that migrating neural crest cells but not premigratory cells explanted in vitro expressed detectable levels of alpha4 messengers and proteins suggesting that alpha4beta1 expression was induced at the time of the initiation of the migration phase. In agreement with this observation, antibody inhibition of alpha4beta1 activity in vitro resulted in a strong, immediate and sustained reduction of neural crest cell motion on fibronectin, as judged on videomicroscopy analyses, but apparently did not prevent their delamination from the neural tube. However, alpha4beta1 appeared to exhibit a broader role in the control of cell migration on a variety of extracellular matrix molecules, presumably by regulating cellular events downstream from integrins. Moreover, blocking alpha4beta1 function caused a severe increase in apoptotic cell death among the neural crest population without influencing notably cell proliferation. Collectively, these results indicate that, notwithstanding its critical implication in cell motion, alpha4beta1 integrin could play a central role in neural crest cell development by coordinating multiple cellular events, such as cell adhesion, locomotion, and survival.

Identification of Echovirus 1 and coxsackievirus A9 receptor molecules via a novel flow cytometric quantification method

BACKGROUND

Virus-receptor binding is an essential step in every virus infectious process. Many viruses employ more than one receptor molecule or even receptor complexes for attachment. In this study, we investigate the binding of Echovirus 1 (Echo1) and Coxsackievirus A9 (CAV-9) on cell surface molecules. CAV-9 has been reported to utilize integrin alpha v beta(3) in binding to cells, whereas Echo1 has been known to utilize integrin alpha 2 beta(1). METHODS AND RESULTS We directly test whether the presence of these molecules alone was sufficient for virus binding. We devised a novel flow cytometric binding assay that enables us to quantify virus particles bound on host cells and to further determine the extent to which viruses utilize specific receptors.

CONCLUSIONS

By quantifying virus particles and possible receptor molecules, we found that Echo1 utilizes mainly integrin alpha 2 beta(1). CAV-9 utilizes integrin alpha v beta(3) to a much lesser extent (40%), indicating that CAV-9 also utilizes other receptor(s).

Mechanisms of early neural crest development: from cell specification to migration

The neural crest is a group of embryonic progenitors that forms during the process of neurulation by interactions that take place between the prospective epidermis and the specified neuroectoderm. Although initially an integral part of the neuroepithelium, neural crest cells separate from the central nervous system primordium by a process of epitheliomesenchymal transition and become a motile cell population. These mesenchymal cells then migrate through stereotypic pathways, some of which are common and others unique to various vertebrate species. Furthermore, the availability of distinct migratory pathways also differs according to embryonic stage and axial level. Studies have begun to address the molecular basis of neural crest specification, delamination, and migration. The present review summarizes some major advances in our understanding of the nature of the intercellular interactions and the molecules that mediate them during early phases of neural crest ontogeny.

Human parechovirus 1 utilizes integrins alphavbeta3 and alphavbeta1 as receptors

Human parechovirus 1 (HPEV1) displays an arginine-glycine-aspartic acid (RGD) motif in the VP1 capsid protein, suggesting integrins as candidate receptors for HPEV1. A panel of monoclonal antibodies (MAbs) specific for integrins alphavbeta3, alphavbeta1, and alphavbeta5, which have the ability to recognize the RGD motif, and also a MAb specific for integrin alpha2beta1, an integrin that does not recognize the RGD motif, were tested on A549 cells. Our results showed that integrin alphav-specific MAb reduced infectivity by 85%. To specify which alphav integrins the virus utilizes, we tested MAbs specific to integrins alphavbeta3 and alphavbeta1 which reduced infectivity significantly, while a MAb specific for integrin alphavbeta5, as well as the MAb specific for alpha2beta1, showed no reduction. When a combination of MAbs specific for integrins alphavbeta3 and alphavbeta1 were used, virus infectivity was almost completely inhibited; this shows that integrins alphavbeta3 and alphavbeta1 are utilized by the virus. We therefore proceeded to test whether alphav integrins' natural ligands fibronectin and vitronectin had an effect on HPEV1 infectivity. We found that vitronectin reduced significantly HPEV1 infectivity, whereas a combination of vitronectin and fibronectin abolished infection. To verify the use of integrins alphavbeta3 and alphavbeta1 as HPEV1 receptors, CHO cells transfected and expressing either integrin alphavbeta3 or integrin alphavbeta1 were used. It was shown that the virus could successfully infect these cells. However, in immunoprecipitation experiments using HPEV1 virions and allowing the virus to bind to solubilized A549 cell extract, we isolated and confirmed by Western blotting the alphavbeta3 heterodimer. In conclusion, we found that HPEV1 utilises both integrin alphavbeta3 and alphavbeta1 as receptors; however, in cells that express both integrins, HPEV1 may preferentially bind integrin alphavbeta3.

Adhesion and migration of avian neural crest cells on fibronectin require the cooperating activities of multiple integrins of the (beta)1 and (beta)3 families

Based on genetic, functional and histological studies, the extracellular matrix molecule fibronectin has been proposed to play a key role in the migration of neural crest cells in the vertebrate embryo. In the present study, we have analyzed in vitro the repertoire and function of integrin receptors involved in the adhesive and locomotory responses of avian truncal neural crest cells to fibronectin. Immunoprecipitation experiments showed that neural crest cells express multiple integrins, namely (alpha)3(beta)1, (alpha)4(beta)1, (alpha)5(beta)1, (alpha)8(beta)1, (alpha)v(beta)1, (alpha)v(beta)3 and a (beta)8 integrin, as potential fibronectin receptors, and flow cytometry analyses revealed no major heterogeneity among the cell population for expression of integrin subunits. In addition, the integrin repertoire expressed by neural crest cells was found not to change dramatically during migration. At the cellular level, only (alpha)v(beta)1 and (alpha)v(beta)3 were concentrated in focal adhesion sites in connection with the actin microfilaments, whereas the other integrins were predominantly diffuse over the cell surface. In inhibition assays with function-perturbing antibodies, it appeared that complete abolition of cell spreading and migration could be achieved only by blocking multiple integrins of the (beta)1 and (beta)3 families, suggesting possible functional compensations between different integrins. In addition, these studies provided evidence for functional partitioning of integrins in cell adhesion and migration. While spreading was essentially mediated by (alpha)v(beta)1 and (alpha)8(beta)1, migration involved primarily (alpha)4(beta)1, (alpha)v(beta)3 and (alpha)8(beta)1 and, more indirectly, (alpha)3(beta)1. (alpha)5(beta)1 and the (beta)8 integrin were not found to play any major role in either adhesion or migration. Finally, consistent with the results of inhibition experiments, recruitment of (alpha)4(beta)1 and (alpha)v(beta)3, individually or in combination using antibodies or recombinant VCAM-1 and PECAM-1 molecules as a substratum, was required for migration but was not sufficient to produce migration of the cell population as efficiently as with fibronectin. In conclusion, our study indicates that neural crest cells express a multiplicity of fibronectin-binding integrins and suggests that dispersion of the cell population requires cooperation between distinct integrins regulating different events of cell adhesion, locomotion and, possibly, proliferation and survival.

A novel model to study the dorsolateral migration of melanoblasts

Melanocytes derived from pluripotent neural crest cells migrate initially in the dorsolateral pathway between the ectoderm and dermomyotome. To understand the role of specific proteins involved in this cell migration, we looked for a cellular model that mimics the in vivo behavior of melanoblasts, and that allows functional studies of their migration. We report here that wild-type embryonic stem (ES) cells are able to follow the ventral and dorsolateral neural crest pathways after being grafted into chicken embryos. By contrast, a mutant ES cell line deficient for beta1 integrin subunits, proteins involved in cell-extracellular interactions, had a severely impaired migratory behavior. Interestingly, ES cells deficient for Kit, the tyrosine kinase receptor for the stem cell factor (SCF), behaved similarly to wild-type ES cells. Thus, grafting mouse ES cells into chicken embryos provides a new cellular system that allows both in vitro and in vivo studies of the molecular mechanisms controlling dorsolateral migration.

Alteration of integrin expression in oral squamous cell carcinomas

OBJECTIVE

This study examines the intensity of expression of beta 1, alpha 2, alpha 3, alpha 5, alpha 6 integrin subunits in oral squamous cell carcinoma (SCC) as opposed to normal oral epithelium, and the intensity of expression and distribution pattern of the above subunits in relation to tumour differentiation grade.

MATERIALS AND METHODS

Cryostat sections of 25 cases of oral SCC and 15 cases of normal oral epithelium were studied by immunohistochemistry (APAAP method).

RESULTS

The intensity of expression of beta 1, alpha 2 (Pearson chi 2 P < 0.001) and alpha 6 (Test for Trend P < 0.05) integrin subunits was reduced significantly in SCC compared to normal oral epithelium. All integrin subunits were mainly expressed in the peripheral cell layer of tumour islands. No correlation was found between the intensity of integrin expression and the degree of differentiation in SCC. The same applied to the distribution pattern of the integrin subunits. By means of cross examination of all integrins, the loss of intensity of alpha 2 beta 1 integrin expression was found to have the strongest correlation with oral SCC (Ordered Logistic Regression).

CONCLUSIONS

Reduced intensity of expression of all subunits was found in oral SCC compared to normal epithelium. Further investigation is needed to determine whether alpha 2 beta 1 integrin expression can be used as a prognostic evaluator for the behaviour of the disease.

Hirschsprung's disease: a search for etiology

In 1967, Okamoto et al suggested that the absence of ganglion cells in Hirschsprung's disease (HD) was attributable to failure of migration of neural crest cells. The earlier the arrest of migration, the longer the aganglionic segment. Since then, this hypothesis generally has been accepted. However, subsequent experiments using mouse models of intestinal aganglionosis indicate that nerve cells may reach the correct position but then fail to develop or survive. An alternative hypothesis has been proposed that the aganglionosis may be caused by failure of differentiation as a result of microenvironmental changes after the migration has occurred. Extracellular matrix proteins are recognized as important microenvironmental factors. It has been shown that enteric neurogenesis is dependent on extracellular matrices, which provide a migration pathway for neural crest-derived cells and promote the maturation of settled neural crest-derived cells. Altered distributions of extracellular matrices have been shown in human HD cases and murine HD models, suggesting the role of extracellular matrices in the pathogenesis of HD. Recent studies suggest that intestinal smooth muscle cells, target cells of enteric neurons, play an important role in guiding and influencing its own innervation. Normal maturation was inhibited in neurons cultured with smooth muscle cells of aganglionic colon in comparison to normal colon. Furthermore, it was demonstrated that levels of neurotrophic factors, crucial in the development and survival of enteric neurons, are decreased in circular muscle layers of aganglionic colon in comparison to normoganglionic colon. The smooth muscle cells of the aganglionic colon may represent an unfavorable microenvironment for neuronal development compared with the normally innervated region. Recently, markedly increased immunoreactivity of major histocompatibility complex (MHC) class II antigens and ICAM-1 was demonstrated in aganglionic bowel, suggesting the immunological mechanisms may be involved in the etiology of HD. Genetic factors have been implicated in the etiology of this condition because HD is known to occur in families and in association with some chromosomal abnormalities. Recent expansion of molecular genetics identified multiple susceptibility genes of HD, including the RET gene, the glial cell line-derived neurotrophic factor gene, the endothelin-B receptor gene, and endothelin-3 gene. Of these, inactivating mutations of the RET gene are the most frequent, occurring in 50% of familial and 15% to 20% of sporadic cases of HD. To date, despite extensive research, the exact etiology of this condition remains poorly understood. The present report describes the authors' current understanding of and recent progress in the etiology of HD.

Changes in the expression of extracellular matrix (ECM) and matrix metalloproteinases (MMP) of proliferating rat parotid acinar cells

Tissue morphogenesis, development, and maintenance of function are mediated by signals generated through the composition of the extracellular matrix. The regulation of the composition of matrix is determined by enzymes specific for their degradation, the matrix metalloproteinases. Chronic injections of the beta-adrenergic receptor agonist, isoproterenol, result in a non-neoplastic hypertrophy and hyperplasia of the rat parotid gland. The activity of matrix metalloproteinases, as measured by gelatin zymography and enzymatic digestion of Azocoll substrates by gland lysates, decreased significantly (P < 0.05) following 24 hrs of agonist treatment, and slowly recovered to control values by 6 days of treatment. Daily administration of the broad-spectrum matrix metalloproteinase inhibitor Galardin for 3 days in combination with isoproterenol resulted in enhanced gland hypertrophy compared with that produced by isoproterenol alone. Given alone, Galardin also caused hypertrophy. The relative abundance of mRNA for the extracellular matrix molecules, collagens I and III and fibronectin, declined rapidly following the initiation of beta-agonist treatment in vivo, while laminin B1 and B2 mRNA levels increased initially before declining below control levels. These changes in patterns of mRNA levels also were observed in the concentrations of glandular protein when Western dot blot analysis of collagens I and III and laminin, respectively, was used. The importance of laminin, in vivo, was demonstrated by coinjection of anti-laminin antibody along with isoproterenol, which resulted in the inhibition of beta-agonist-induced parotid gland hypertrophy and hyperplasia. These data suggest that modulation of the ECM is associated with isoproterenol-induced salivary gland hypertrophy and hyperplasia. It is likely that this modulation of the ECM takes place through transcriptional regulation of some ECM genes and regulation of matrix-degrading enzyme activity.

Entamoeba histolytica contains a beta 1 integrin-like molecule similar to fibronectin receptors from eukaryotic cells

Entamoeba histolytica trophozoites do interact with extracellular matrix components in order to invade and finally destroy tissue. An important step in this interaction involves the binding of a 140-kDa membrane protein that binds to fibronectin. The similarity of this amoebic receptor to fibronectin receptors from higher eukaryotic cells was defined by indirect immunofluorescence, western blot and immunohistochemistry, using polyclonal monospecific antibodies raised against the amoebic protein. These results suggest that lower eukaryotic cells have and use a beta 1 integrin-like molecule as well as mechanisms similar to those present in higher eukaryotic cells during interaction with extracellular matrix components.

Role of extracellular matrix in tumor invasion: migration of glioma cells along fibronectin-positive mesenchymal cell processes

OBJECTIVE

The major morbidity of glioma lies in its infiltrative growth. One of the major patterns of this invasive growth is the formation of Scherer's secondary structures associated with the blood vessels and the leptomeninges. To better understand the role of extracellular matrix (ECM) in glioma invasion, we investigated in vitro the interaction between glioma cells and the meningeal mesenchymal tissue from the brain. As an aid to this study, ECM in glioma cell line spheroids was compared with that in primary fetal brain aggregates.

METHODS

To study the expression of ECM, four glioma cell lines (U-87 MG, U-251 MG, AN1/lac-z, and HF-66) and primary cells from fetal rat brain were grown as spheroids and monolayers. To sudy the role of ECM in glioma invasion, spheroids from the glioma cell lines were grown over established cultures of fetal meningeal and mesenchymal tissue. Expression of fibronectin, laminin, tenascin, collagen VI, and chondroitin sulfate proteoglycan was studied by immunofluorescence.

RESULTS

Expression of ECM by the spheroids was variable. U-87 MG expressed most of the ECM components robustly, whereas AN1/lac-z expressed them all weakly. Fetal rat brain aggregates produced minimal ECM. In cocultures of glioma spheroids and fetal meningeal mesenchymal tissue, individual cells from the glioma spheroids that expressed least fibronectin (AN1/lac-z and U-251 MG) migrated along the fibronectin-positive mesenchymal cells in the culture dish. Cells from the other two lines (U-87 MG and HF-66) that expressed fibronectin strongly did not demonstrate such behavior. None of the other ECM components showed a similar association; mesenchymal cells did not express laminin as strongly as fibronectin, and glioma cells were not observed to align with the laminin-positive structures.

CONCLUSION

This study suggests that fibronectin may play a key role in intracerebral invasion of glioma cells.

Developmental changes in integrin beta-subunits in rat cerebral cortex

The present study was carried out to characterize the developmental expression of beta 1-, beta 5- and beta 6-integrin subunits in rat cerebral cortex. Using reverse transcriptase-polymerase chain reaction, mRNA of the three beta-subunits were shown to be present at all developmental stages. Based on immunoblots, beta 1-subunit expression was decreased during cortical development from embryonic stages to adults. beta 6-subunit expression appeared only in adult cortex. beta 5-subunit expression did not change during development. These beta-subunits were expressed in cortical embryonic cells as revealed by immunological studies in vitro. beta 5 and beta 6 were also present in neuronal cells and in oligodendrocytes in adult cortex. Altogether, these results demonstrate that rat cerebral cortex expresses distinct integrin beta-subunits with different developmental profiles. This switch of beta-subunits may be an important mechanism for the regulation of cell behaviour during development.

Identification of a region in the integrin beta3 subunit that confers ligand binding specificity

Many integrin adhesion receptors bind ligands containing the Arg-Gly-Asp (RGD) peptide motif. Most integrins exhibit considerable specificity for particular ligands and can distinguish among the many conformations of RGD. In this study we identify the domain of the integrin beta subunit involved in determining ligand binding specificity. Chimeras of beta3 and beta5, the most homologous integrin beta subunits, were expressed with alphav on the surface of human 293 cells. The ligand binding phenotype of each chimera was assessed using the ligands Fab-9 and fibrinogen, both of which have a binding preference for alphavbeta3. The results of the study show that when exons C and D of the beta3 subunit (residues 95-233) are substituted into beta5, the chimera gained the ability to bind Fab-9 with an affinity close to that of wild-type alphavbeta3. This chimera was able to mediate cell adhesion to fibrinogen. Furthermore, the swap of only a 39-residue segment of this larger domain, beta3 residues 164-202, into the backbone of beta5 enabled the chimeric integrin to bind soluble Fab-9. This small domain is highly divergent among the integrin beta subunits, suggesting that it may play a role in determining ligand selection by all integrins.

Cross talk between adhesion molecules: control of N-cadherin activity by intracellular signals elicited by beta1 and beta3 integrins in migrating neural crest cells

During embryonic development, cell migration and cell differentiation are associated with dynamic modulations both in time and space of the repertoire and function of adhesion receptors, but the nature of the mechanisms responsible for their coordinated occurrence remains to be elucidated. Thus, migrating neural crest cells adhere to fibronectin in an integrin-dependent manner while maintaining reduced N-cadherin-mediated intercellular contacts. In the present study we provide evidence that, in these cells, the control of N-cadherin may rely directly on the activity of integrins involved in the process of cell motion. Prevention of neural crest cell migration using RGD peptides or antibodies to fibronectin and to beta1 and beta3 integrins caused rapid N-cadherin-mediated cell clustering. Restoration of stable intercellular contacts resulted essentially from the recruitment of an intracellular pool of N-cadherin molecules that accumulated into adherens junctions in tight association with the cytoskeleton and not from the redistribution of a preexisting pool of surface N-cadherin molecules. In addition, agents that cause elevation of intracellular Ca2+ after entry across the plasma membrane were potent inhibitors of cell aggregation and reduced the N-cadherin- mediated junctions in the cells. Finally, elevated serine/ threonine phosphorylation of catenins associated with N-cadherin accompanied the restoration of intercellular contacts. These results indicate that, in migrating neural crest cells, beta1 and beta3 integrins are at the origin of a cascade of signaling events that involve transmembrane Ca2+ fluxes, followed by activation of phosphatases and kinases, and that ultimately control the surface distribution and activity of N-cadherin. Such a direct coupling between adhesion receptors by means of intracellular signals may be significant for the coordinated interplay between cell-cell and cell-substratum adhesion that occurs during embryonic development, in wound healing, and during tumor invasion and metastasis.

Direct role of the carboxy-terminal cell-binding domain of fibronectin in neural crest cell motility

We have analyzed the interaction of neural crest cells with fragments of fibronectin corresponding to the different spliced variants of the COOH-terminal cell-binding domain (COOH-ter CBD). We have shown that this domain can support cell adhesion and migration and that both the IIICS and HepII regions are involved in these events. The rate of locomotion is high, although undirectional, compared to that of whole fibronectin. Interactions with the COOH-ter CBD are controlled by alpha4beta1 and maybe other beta1 integrins and cell-surface proteoglycans. These receptors act cooperatively to mediate attachment, spreading, and migration on fibronectin.

Changes in cell adhesion and extracellular matrix molecules in spontaneous spinal neural tube defects in avian embryos

Quail embryos (embryonic days 2-2.5) with spontaneous neural tube defects (NTDs), along with age-matched normal embryos, were examined immunocytochemically for the extracellular matrix (ECM) molecules laminin, fibronectin, and chondroitin sulfate proteoglycan, the cell adhesion molecules (CAMs) E- and N-cadherin and neural CAM (NCAM), and the neural crest marker HNK-1. The embryos with NTDs were at the lower limit of the normal stage range and the affected region was about 25% shorter than in normal embryos. Open NTDs occurred in cervical and upper thoracic level, although often the ventral neural tube was morphologically normal. Widened, irregular but closed neural tubes (lower thoracic to sacral levels) showed disorganized mesenchyme-like cells centrally and often multiple lumens. Finger-like tabs projecting from the ectoderm over the neural tube also occurred at lower thoracic to sacral levels. In open NTDs, the E-cadherin-labeled epidermis was incomplete dorsally, and was continuous with the N-cadherin-labeled neural tissue, with a sharp demarcation between E- and N-cadherin-expressing regions, as in the early stages of normal primary neurulation. A sharp inverted peak of epidermis extended ventrally, closely applied to the side of the neural tissue. The intervening matrix labeled less intensely for chondroitin sulfate proteoglycan relative to laminin and fibronectin, in comparison to control embryos. In closed NTDs, the dorsal superficial cell layer (i.e., positionally epidermis) was not separated from the underlying neural tissue by a band of matrix as in control embryos. In addition, this layer expressed E-cadherin (as in normal embryos), but coexpressed N-cadherin and NCAM, which are not normally found here at this stage. This overlap region resembled the mid-dorsal tissue at earlier stages in normal secondary neurulation in the tail-bud. The tabs of tissue appeared to be localized hypertrophy of the epidermal and neural ectoderm, and also showed codistribution of E- and N-cadherin. In all these defects, matrix molecules occurred within (rather than around) the neural and epidermal epithelia. HNK-1-labeled neural crest cells were frequently absent in regions of NTDs, in contrast to control embryos. These results show that matrix and cell adhesion molecules are disturbed in spontaneous NTDs at the time of neurulation, and therefore could be involved in the generation of the defects by altering cell adhesion-dependent morphogenetic events.

Expression of the mouse fibronectin gene and fibronectin-lacZ transgenes during somitogenesis

Fibronectins (FNs) are essential for the proper development of embryonic mesenchymal tissues. A lacZ reporter gene has been fused to 4.9 kbp of DNA from the rat FN gene 5' flanking region, and this construct has been microinjected into fertilized mouse embryos to investigate the cis elements needed for the temporal and spatial regulation of FN in vivo. Histochemical staining of embryos for beta-galactosidase activity demonstrated that four independent lines shared a specific pattern of lacZ expression, reflecting the activity of the fibronectin sequences contained within the transgene. Specifically, somites stained positively for lacZ, but expression was spatially and temporally non-uniform, with higher levels in more caudal somites after a total of ca. 13 somite pairs had formed. This rostral-caudal gradient of lacZ expression in somites of embryos beyond this stage resembled the distribution of endogenous FN mRNA, as detected by whole mount in situ hybridization. The transgene was not expressed in the developing heart where endogenous FN mRNA was detected. Unexpectedly, highly localized staining was observed within the neural tube beginning at ca. E10-10.5, and two of the lines exhibited additional areas of staining due to the individual integration sites. Thus, the 4.9 kbp FN fragment appears to recapitulate closely the complex pattern of FN expression observed during somitogenesis. A smaller fragment of 0.9 kbp also directed lacZ expression in caudal somites at E9.5, suggesting that these sequences are sufficient to establish the spatio-temporal pattern.

Altered cell-matrix contact: a prerequisite for breast cancer metastasis?

The integrins are receptors that regulate interaction between epithelial cells and the extracellular matrix. Previous studies have shown that a reduction in the expression of the alpha2beta1, alpha3beta1, alpha6beta1, alpha(v)beta1 and alpha(v)beta5 integrins in primary breast cancer is associated with positive nodal status. In order to assess the functional significance of altered integrin expression, primary breast cancer cells were derived from individual patients with known tumour characteristics using immunomagnetic separation. Purified human fibronectin, vitronectin, laminin and type IV collagen were used to represent the principal extracellular matrix proteins in an in vitro adhesion assay. Primary breast cancer cells from lymph node-positive patients were significantly less adhesive to each of the matrix proteins studied (P<0.001, Mann-Whitney U-test). Matrix adhesion of primary breast cancer cells from node-negative patients was inhibited by appropriate integrin monoclonal antibodies (P<0.001, paired Wilcoxon test). Adhesion to fibronectin, vitronectin and laminin, but not type IV collagen, was influenced by the inhibitor arginine-glycine-aspartate, suggesting that breast cancer cell recognition of collagen IV is mediated through alternative epitopes. Weak matrix adhesion correlated with loss of integrin expression in tissue sections from corresponding patients assessed using immunohistochemistry. This study demonstrates a link between altered integrin expression and function in primary breast cancers predisposed to metastasize.

Response of human osteoblasts to implant materials: integrin-mediated adhesion

The initial interaction of the human osteoblast-like cell line Saos-2 with orthopaedic implant materials was analyzed to determine the mechanism by which these cells adhere to implant surfaces. Saos-2 cells were allowed to attach to disks composed of the orthopaedic implant materials Tivanium (Ti6A14V) and Zimaloy (CoCrMo) and to control disks of glass and plastic. Serum had no effect on the number of cells that attached to Tivanium and Zimaloy at 4 or 24 hours but did increase the number of cells that attached to glass at 24 hours. Collagen synthesis was determined by [3H]proline incorporation into collagenase-digestible protein and noncollagen protein. A significant increase of 19% was found for collagen synthesized in cells cultured on Zimaloy for 24 hours compared with glass, with no differences on Tivanium and plastic. However, collagenase-digestible protein and noncollagen protein were increased the most (204 and 198%, respectively) on Tivanium compared with glass. To determine if integrins were involved in cell attachment to implant materials, the peptide GRGDSP (Gly-Arg-Gly-Asp-Ser-Pro), which blocks integrin receptors through the Arg-Gly-Asp sequence, was added to the cells in serum-free medium. This peptide inhibited cell adhesion by 28% on Tivanium and 40% on Zimaloy but had no effect on glass and plastic. The control peptide GRADSP (Gly-Arg-Ala-Asp-Ser-Pro) had no effect on adhesion. Inhibition of protein synthesis and enzymatic removal of surface proteins did not affect the ability of Arg-Gly-Asp peptides to inhibit cell attachment to the implant materials. These results suggest that integrins are able to bind directly to Tivanium and Zimaloy. Western blot analysis of integrin protein demonstrated changes in many integrin subunits, depending on the substrate to which cells attached. In particular, the beta 1 integrin subunit was increased 3.8 to 9.5-fold at 24 hours. To determine specifically which integrins may be involved in adhesion, antibodies to integrins were added. An antibody to the fibronectin receptor, alpha 5 beta 1, significantly inhibited binding of cells to Tivanium by 63% and to Zimaloy by 49% and had no effect on glass. The vitronectin receptor antibody, alpha v beta 3/beta 5, did not alter cell adhesion. In conclusion, osteoblast-like cells appear to be capable of attaching directly to implant materials through integrins. The type of substrate determines which integrins and extracellular matrix proteins are expressed by osteoblasts. These data provide information on how implant materials may affect osteoblast differentiation and bone growth.

Urokinase-type plasminogen activator regulates cranial neural crest cell migration in vitro

Proper migration and differentiation of neural crest (NC) cells are required for normal development of craniofacial structures, heart and great vessels, sensory and autonomic nervous systems, and other organs with vertebrate embryos. Serine-protease inhibitors reduce NC cell migration in vitro, suggesting the extracellular proteases are important mediators of NC cell migration. While plasminogen activator activity levels are high in NC cells relative to other embryonic tissue, its ability to regulate NC cell migration has not been specifically tested in vivo or in vitro through its ability to convert plasminogen to plasmin. Using a transfilter migration assay, NC cell migration was measured in the presence or absence of plasminogen. Our results showed that plasminogen significantly enhanced NC cell migration. This increase could not be attributed to differences in initial NC cell attachment or cytotoxicity and did not require a chemotactic gradient. The plasminogen-enhanced NC cell migration was blocked by aprotinin (a plasmin inhibitor) and was mimicked by the direct addition of plasmin to the NC cells, indicating that the plasminogen effect was mediated through plasmin generation. Furthermore, anticatalytic-uPA antibody blocked the plasminogen-enhanced NC cell migration showing that NC cell-associated uPA activity was required for this effect. Finally, decreasing NC-uPA activity by treating cells with transforming growth factor-Beta, also blocked the plasminogen-dependent increase in cell migration. These data show that in vitro, NC cell migration is regulated by NC-associated uPA activity suggesting that growth factor-regulation of this activity may play a major role in regulating NC cell migratory capacity in vivo.

Immunolocalization of vinculin in the heart of the early developing rat embryo

BACKGROUND

The interaction of cells and extracellular matrix (ECM) components is important in the morphogenesis of the developing heart and is thought be mediated in part by adhesion plaques associated with vinculin, paxillin, talin, integrin, and other proteins. We investigated the patterns of expression of vinculin in the early embryonic rat heart to evaluate the role of vinculin in cardiac morphogenesis.

METHODS

Vinculin expression was studied immunohistochemically in developing Sprague-Dawley embryonic rat hearts between days 11.5 and 15.5.

RESULTS

Vinculin expression was transient and specific in the aorticopulmonary septum on day 13.5 and in the conal septum on day 14.5, when the respective septations were complete. Less vinculin immunoreactivity was detected in the atrioventricular cushion or ventricular septum, where obvious morphological alteration takes place.

CONCLUSIONS

Sites that were immunoreactive for vinculin in the present study are reportedly associated with the distribution of neural cell adhesion molecules (N-CAM) or of soluble tropoelastin. Thus vinculin appears to play a key role in aorticopulmonary septation, where neural crest cells are transformed into ectomesenchyme. Vinculin appears to be involved in elastogenesis and is contributed by ectomesenchyme derived from the neural crest cells.

Expression of the avian alpha 7-integrin in developing nervous system and myotome

Integrins are cell surface receptors for a variety of extracellular matrix molecules including fibronectin, laminin and collagens. Although their role in development is not completely understood, they are likely to have important functions in cell migration and axon guidance. To characterize the types of integrins expressed in the developing nervous system, we have used monoclonal antibodies against alpha 7- and alpha v-integrin subunits to examine the distribution of these subunits in the early chick embryo. Low levels of alpha 7 immunoreactivity were first observed in the neural tube and developing myotome of stage 17 embryos (E2.5). Although low levels of alpha 7 expression were associated with most neuroepithelial cells, distinct alpha 7 immunoreactivity was first detected in the ventrolateral portions of the neural tube at a stage corresponding to the time when the first neurons differentiate. Its distribution pattern overlapped with that of commissural neurons in the developing spinal cord. alpha 7 was also prominently localized to the motor neurons and their axons emanating from the neural tube. In addition, alpha 7 immunoreactivity was observed on a subpopulation of trunk neural crest cells migrating through the somitic sclerotome. At later stages, alpha 7 expression was observed in other nervous system structures such as the pigmented retinal epithelial cells. In addition to its distribution in the developing nervous system, alpha 7 immunoreactivity was associated with early myotomal cells shortly after myotome formation and its expression persisted throughout myotome development. In contrast to alpha 7, alpha v-integrin had a limited distribution in the nervous system, being expressed only at low levels in the neural tube. However, alpha v displayed prominent immunoreactivity in the myotome and in endothelial cells of the dorsal aorta. The results suggest that alpha 7-integrin is one of the prevalent integrin subunits on neurons and axons in the developing spinal cord.

Graded fibronectin receptor aggregation in migrating cells

We have examined the distribution of the integrin fibronectin receptor in migrating NIH 3T3 fibroblasts to test the hypothesis that cell locomotion involves regional differences of adhesive receptor aggregation. A distinct asymmetry of fibronectin receptor aggregation was observed on the surface of migrating NIH 3T3 fibroblasts. Direct current electric fields were used to stimulate directional cell migration and thus allow the quantitative correlation of receptor asymmetries to the direction of cell locomotion. Digital particle analysis of fluorescent confocal micrographs demonstrates that the leading half of cells has a higher proportion of receptors contained in small clusters than does the trailing half. Conversely, larger receptor aggregates are more prevalent in the rear of the cell than in the front. We have also observed a gradient of extracellular fibronectin fibril assembly, similar to that described for the fibronectin receptor. Extracellular fibronectin appears in progressively larger fibrils across the ventral cell surface from front to rear, with dense meshworks often deposited as a trail behind the cell. Large fibronectin receptor clusters toward the rear of the cell generally do not correlate with focal contacts, and are thus most likely aggregated by cell surface-bound fibronectin fibrils and not by adhesion to the substratum. These results suggest that spatial variations in the degree of adhesive receptor aggregation are created in fibroblasts during the processes of migration and matrix synthesis.

Expression of the antigen recognized by mAb GB36 in normal skin and in skin tumours

GB36, a mouse monoclonal antibody (mAb) raised against an epithelial antigen of the human trophoblast, reacts with the epithelial basement membrane of chorionic villi; it does not react with the invasive extravillous cytotrophoblast. Expression and characterization of the antigen of GB36 (designated GBA36) were investigated in normal keratinocytes by immunoprecipitation, immunofluorescence and immunoelectron microscopic studies. Immunoprecipitation experiments demonstrated that the proteins identified on keratinocytes by mAb GB36 and a rat mAb anti-integrin alpha 6 (GoH3) were the same. Using immunofluorescence and immunoelectron microscopic methods, GBA36 was localized on the cell membrane facing the epithelial basal lamina of basal keratinocytes. GBA36 distribution in benign and malignant skin tumours was evaluated by immunostaining methods (immunofluorescence and immunoperoxidase). Analysis of tumours revealed that whereas benign epithelial tumours and intradermal naevi displayed high levels of GBA36, the expression of this antigen decreased progressively in spinocellular and basal cell carcinomas, and in cutaneous melanomas in relation to invasiveness. During cell transformation, GBA36 undergoes quantitative alterations, and expression is down-regulated. Although the functional relevance of these changes remains unknown, the correlation of decreased GBA36 expression with tumour progression may indicate a role for altered integrin expression in tissue invasion by human skin carcinoma and melanoma.

Control of N-cadherin-mediated intercellular adhesion in migrating neural crest cells in vitro

Dispersion of neural crest cells and their ultimate regroupment into peripheral ganglia are associated with precisely coordinated regulations both in time and space of the expression and function of cell adhesion receptors. In particular, the disappearance of N-cadherin from the cell surface at the onset of migration and its reexpression during cell aggregation suggest that, during migration, N-cadherin expression is repressed in neural crest cells. In the present study, we have analyzed in vitro the mechanism of control of N-cadherin expression and function in migrating neural crest cells. Although these cells moved as a dense population, each individual did not establish extensive and permanent intercellular contacts with its neighbors. However, cells synthesized and expressed mature N-cadherin molecules at levels comparable to those found in cells that exhibit stable intercellular contacts, but in contrast to them, the bulk of N-cadherin molecules was not connected with the cytoskeleton. We next determined which intracellular events are responsible for the instability of the N-cadherin junctions in neural crest cells using various chemical agents known to affect signal transduction processes. Agents that block a broad spectrum of serine-threonine kinases (6-dimethylaminopurine, H7 and staurosporine) or that affect selectively protein kinases C (bisindolylmaleimide and sphingosine), inhibitors of protein tyrosine kinases (erbstatin, herbimycin A, and tyrphostins), and inhibitors of phosphatases (vanadate) all restored tight cell-cell associations among neural crest cells, accompanied by a slight increase in the overall cellular content of N-cadherin and its accumulation to the regions of intercellular contacts. The effect of the kinase and phosphatase blockers was inhibitable by agents known to affect protein synthesis (cycloheximide) and exportation (brefeldin A), indicating that the restored cell-cell contacts were mediated chiefly by an intracellular pool of N-cadherin molecules recruited to the membrane. Finally, N-cadherin molecules were constitutively phosphorylated in migrating neural crest cells, but their level and state of phosphorylation were apparently not modified in the presence of kinase and phosphatase inhibitors. These observations therefore suggest that N-cadherin-mediated cell-cell interactions are not stable in neural crest cells migrating in vitro, and that they are under the control of a complex cascade of intracellular signals involving kinases and phosphatases and probably elicited by surface receptors.

Differential mRNA regulation of integrin subunits alpha V, beta 1, beta 3, and beta 5 during mouse embryonic organogenesis

Cell interactions with extracellular matrices play important roles in morphogenetic processes during embryonic development. Extracellular matrix receptors of the integrin family have been implicated in these steps. Recent studies indicate that a variety of integrins can be differentially expressed during development, consistent with diverse roles for integrins in embryogenesis. The present study compares the expression patterns of several major members of the alpha V integrin subfamily, focusing on mRNA expression of alpha V, beta 1, beta 3, and beta 5 subunits during mouse embryonic organogenesis using Northern blot analysis and in situ hybridization. The alpha V and beta 1 subunits showed widespread tissue expression, although most tissues expressed alpha V at relatively low or basal levels. The mRNA for beta 5 was also expressed in a variety of embryonic organs and showed unusual localization patterns in certain organs. Striking, high-level expression of beta 5 transcripts was detected in the ependymal layer of the central nervous system, glomeruli of the kidney, epicardial region of the heart, and in the tooth germs, suggesting specific functions for this molecule during morphogenetic events in these organs. In contrast, few beta 3 transcripts were expressed during mid-gestation mouse embryogenesis except in megakaryocytes within the embryonic liver. These observations of differing expression spectra suggest that members of the alpha V integrin subfamily have distinct roles and also suggests that they have different transcriptional regulation. The beta 5 integrin is unique in its degree of tissue-specific mRNA regulation associated with morphogenesis of embryonic organs.

Expression of alpha 3 beta 1 integrin receptor and its ligands in human lung tumors

Increasing experimental evidence demonstrates that malignant transformation is associated with changes in the repertoire of expression of the integrin family of molecules, which mediate cell-matrix and cell-cell interactions. We have analyzed immunohistochemically and immunochemically the expression of VLA-3 integrin and its known ligands, namely, laminin (LM), fibronectin (FN), collagen type IV (Coll IV), nicein (NIC), and entactin/nidogen (ENT), in lung tumors of various histological types. alpha 3 beta 1 was detectable in normal bronchial epithelium and along basement membranes of alveolar walls. In non-small cell lung carcinomas (NSCLC) the integrin was expressed in 82% of the cases, independently of histological type and degree of differentiation of the tumors. On the other hand, only 13% of the small cell lung carcinomas (SCLC) displayed a weak and heterogeneous distribution of the alpha 3 beta 1 complex. Our findings were confirmed immunochemically using long-term tumor cell lines. While the expression of both alpha 3 beta 1 and ligands LM, FN, Coll IV, and Ent correlated in NSCLC with the presence of basement membranes, FN was the only ligand detectable in the stroma of SCLCs. A selective loss of nicein in basement membranes was demonstrated in NSCLC indicating an impairment of expression of this glycoprotein following malignant transformation.

Expression of ret proto-oncogene products in the hypoganglionic segment of the small intestine of congenital aganglionosis rats

The ret proto-oncogene (proto-ret) encodes a receptor tyrosine kinase that contains a cadherin-related sequence in the extracellular domain, which plays an important role in control of normal cell growth and differentiation. Recent studies have shown that familial Hirschsprung's disease is closely linked to the proto-ret locus. Immunohistologically studies on congenital aganglionosis rats were made using polyclonal antibody generated for the carboxy-terminal sequence of the proto-ret products. Immunoreactivity was investigated in the small and large intestines of mutant and control rats. It was increased in the ganglia of the hypoganglionic segment of the small intestine and was minimal in the normoganglionic small intestinal segment of congenital aganglionosis in rats. The reactivity was also strong in the ganglia of the large intestine of normal rats. Because the proto-ret is preferentially expressed in the neuronal tissue and plays a critical role in differentiation of apparently multipotential neural crest cells to enteric neurons, the results suggest that abnormal development of local vagal neural crest cells, which were influenced by spatially regulating factors, results in the hypoganglionic segment.