Search

The intricate interplay between cancer cells and their surrounding microenvironment has emerged as a critical factor driving the aggressive progression of various malignancies, including gliomas. Among the various components of this dynamic microenvironment, the extracellular matrix (ECM) holds particular significance. Gliomas, intrinsic brain tumors that originate from neuroglial progenitor cells, have the remarkable ability to actively reform the ECM, reshaping the structural and biochemical landscape to their advantage. This phenomenon underscores the adaptability and aggressiveness of gliomas, and highlights the intricate crosstalk between tumor cells and their surrounding matrix.In this review, we delve into how glioma actively regulates glioma ECM to organize a favorable microenvironment for its survival, invasion, progression and therapy resistance. By unraveling the intricacies of glioma-induced ECM remodeling, we gain valuable insights into potential therapeutic strategies aimed at disrupting this symbiotic relationship and curbing the relentless advance of gliomas within the brain., (© 2024. The Author(s).)

From the blood brain barrier to the synaptic space, astrocytes provide structural, metabolic, ionic, and extracellular matrix (ECM) support across the brain. Astrocytes include a vast array of subtypes, their phenotypes and functions varying both regionally and temporally. Astrocytes' metabolic and regulatory functions poise them to be quick and sensitive responders to injury and disease in the brain as revealed by single cell sequencing. Far less is known about the influence of the local healthy and aging microenvironments on these astrocyte activation states. In this forward-looking review, we describe the known relationship between astrocytes and their local microenvironment, the remodeling of the microenvironment during disease and injury, and postulate how they may drive astrocyte activation. We suggest technology development to better understand the dynamic diversity of astrocyte activation states, and how basal and activation states depend on the ECM microenvironment. A deeper understanding of astrocyte response to stimuli in ECM-specific contexts (brain region, age, and sex of individual), paves the way to revolutionize how the field considers astrocyte-ECM interactions in brain injury and disease and opens routes to return astrocytes to a healthy quiescent state., (© 2024 Wiley Periodicals LLC.)

Radial neuronal migration is a key neurodevelopmental event for proper cortical laminar organization. The multipolar-to-bipolar transition, a critical step in establishing neuronal polarity during radial migration, occurs in the subplate/intermediate zone (SP/IZ), a distinct region of the embryonic cerebral cortex. It has been known that the extracellular matrix (ECM) molecules are enriched in the SP/IZ. However, the molecular constitution and functions of the ECM formed in this region remain poorly understood. Here, we identified neurocan (NCAN) as a major chondroitin sulfate proteoglycan in the mouse SP/IZ. NCAN binds to both radial glial-cell-derived tenascin-C (TNC) and hyaluronan (HA), a large linear polysaccharide, forming a ternary complex of NCAN, TNC, and HA in the SP/IZ. Developing cortical neurons make contact with the ternary complex during migration. The enzymatic or genetic disruption of the ternary complex impairs radial migration by suppressing the multipolar-to-bipolar transition. Furthermore, both TNC and NCAN promoted the morphological maturation of cortical neurons in vitro. The present results provide evidence for the cooperative role of neuron- and radial glial-cell-derived ECM molecules in cortical development., Competing Interests: AM, MT, SN, TM, YI, CS, KK, HK, SM No competing interests declared, (© 2023, Mubuchi et al.)

Background: To which extent atrial remodeling occurs before atrial fibrillation (AF) is unknown., Objective: The PREventive left atrial appenDage resection for the predICtion of fuTure Atrial Fibrillation (PREDICT-AF) study investigated such subclinical remodeling, which may be used for risk stratification and AF prevention., Methods: Patients (N = 150) without a history of AF with a CHA 2 DS 2 -VASc score of ≥2 at an increased risk of developing AF were included. The left atrial appendage was excised and blood samples were collected during elective cardiothoracic surgery for biomarker discovery. Participants were followed for 2 years with Holter monitoring to determine any atrial tachyarrhythmia after a 50-day blanking period., Results: Eighteen patients (12%) developed incident AF, which was associated with increased tissue gene expression of collagen I (COL1A1), collagen III (COL3A1), and collagen VIII (COL8A2), tenascin-C (TNC), thrombospondin-2 (THBS2), and biglycan (BGN). Furthermore, the fibroblast activating endothelin-1 (EDN1) and sodium voltage-gated channel β subunit 2 (SCN2B) were associated with incident AF whereas the Kir2.1 channel (KCNJ2) tended to downregulate. The plasma levels of COL8A2 and TNC correlated with tissue expression and predicted incident AF. A gene panel including tissue KCNJ2, COL1A1, COL8A2, and EDN1 outperformed clinical prediction models in discriminating incident AF., Conclusion: The PREDICT-AF study demonstrates that atrial remodeling occurs long before incident AF and implies future potential for early patient identification and therapies to prevent AF (ClinicalTrials.gov identifier NCT03130985)., (Copyright © 2021 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Perineuronal nets (PNNs) are conspicuous neuron-specific substructures within the extracellular matrix of the central nervous system that have generated an explosion of interest over the last decade. These reticulated structures appear to surround synapses on the cell bodies of a subset of the neurons in the central nervous system and play key roles in both developmental and adult-brain plasticity. Despite the interest in these structures and compelling demonstrations of their importance in regulating plasticity, their precise functional mechanisms remain elusive. The limited mechanistic understanding of PNNs is primarily because of an incomplete knowledge of their molecular composition and structure and a failure to identify PNN-specific targets. Thus, it has been challenging to precisely manipulate PNNs to rigorously investigate their function. Here, using mouse models and neuronal cultures, we demonstrate a role of receptor protein tyrosine phosphatase zeta (RPTPζ) in PNN structure. We found that in the absence of RPTPζ, the reticular structure of PNNs is lost and phenocopies the PNN structural abnormalities observed in tenascin-R knockout brains. Furthermore, we biochemically analyzed the contribution of RPTPζ to PNN formation and structure, which enabled us to generate a more detailed model for PNNs. We provide evidence for two distinct kinds of interactions of PNN components with the neuronal surface, one dependent on RPTPζ and the other requiring the glycosaminoglycan hyaluronan. We propose that these findings offer important insight into PNN structure and lay important groundwork for future strategies to specifically disrupt PNNs to precisely dissect their function., (© 2020 Eill et al.)

The brain extracellular matrix (ECM) plays a crucial role in both the developing and adult brain by providing structural support and mediating cell-cell interactions. In this review, we focus on the major constituents of the ECM and how they function in both normal and injured brain, and summarize the changes in the composition of the ECM as well as how these changes either promote or inhibit recovery of function following traumatic brain injury (TBI). Modulation of ECM composition to facilitates neuronal survival, regeneration and axonal outgrowth is a potential therapeutic target for TBI treatment., (Published 2018. This article is a U.S. Government work and is in the public domain in the USA.)

The development of the spinal cord represents one of the most complex structure developments of the central nervous system (CNS) as it has to unfold along the longitudinal axis and within segmental cues. There it has to cope with on the one hand connection to the periphery (skeletal muscle, dermomyotome, smooth muscles) and connect it to the higher midbrain and cortical regions of the CNS. Major studies have been performed to analyze the specific subset of transcription factors of the different types of cells within the different segments of the spinal cord. But transcription factor expression is always a result of cellular positioning as the environment defines the intracellular changes during differentiation and in adulthood. The surrounding composed of mainly extracellular matrix does not only provide a "glue" to attach cells to each other but also provides signals with special domains docking to cell surface receptors and presents soluble molecules such as basic fibroblast growth factors (bFGFs) or Wnt-proteins. The availability of these molecules depends on the matrix composition and influences the transcription factor code of each cell. Recent research has also provided strong evidence that depletion of single matrix molecules like Tenascin C (TnC) can lead to developmental changes within the progenitor pools. Therefore beyond the transcription factor code that defines cellular properties we want to focus on the role of the extracellular matrix in the development of the spinal cord., (Copyright © 2015. Published by Elsevier Inc.)

Neuroepithelial and radial GLIA stem cells generate the majority of the cellular constituents of the central nervous system. Following precisely timed phases of neurogenesis and gliogenesis the stem cells recede, with the exception of adult neural stem cells that persist in two generally accepted canonical neurogenic regions, the subventricular zone of the lateral ventricle and the subgranular zone in the dentate gyrus of the hippocampus. It is believed that adult stem cells reside in privileged stem cell niche environments that provide favorable conditions for self-renewal and maintenance of this cellular compartment. Factors such as morphogens, cytokines, and growth factors influence the developmental pathway of neural stem/progenitor cells. By comparison, less is known about the regulatory roles of glycoproteins and proteoglycans of the extracellular matrix (ECM) and their receptors, although they represent important constituents of the micromolecular environment of the niche. Here, we summarize studies that indicate pivotal roles of the ECM micromilieu for the biology and instrumental use of glial stem and progenitor cells of the CNS. Advancing our understanding of structure-function relationships, signaling motifs and complementary receptors and their signal transduction pathways will be of central importance for the application of these cell types in regenerative medicine., (© 2015 Wiley Periodicals, Inc.)

Purpose: To detect by immunohistochemical means the changes in bleb capsules at the cellular level between functioning and non-functioning glaucoma drainage implants (GDIs)., Methods: Three samples each of functioning (1 Baerveldt and 2 Molteno implants) and non-functioning filtration blebs (1 Molteno and 2 Ahmed implants) were studied. A non-functioning bleb was defined as an intra-ocular pressure (IOP) >21 mmHg or a <20% reduction in IOP from baseline on three consecutive follow-up visits with maximal tolerated medication. The capsules were obtained between 6 and 108 months after GDI insertion for medical reasons only. Primary antibodies were used to stain fibronectin, tenascin, laminin, collagen IV and smooth muscle actin (SMA). The samples were graded on the basis of the intensity and quantity of immunohistochemical staining into four categories as follows: no staining or a mild, moderate or marked staining., Results: The non-functioning blebs expressed more fibronectin, tenascin and SMA through the whole capsule wall than the functioning blebs. In the functioning blebs, tenascin was found mainly in the inner layer of the capsule. More type IV collagen and laminin were also found in the non-functioning bleb capsules than in the functioning blebs. No difference was found between the bleb capsules irrespective of whether they had been perfused with aqueous humour immediately after surgery (Ahmed) or after a delay (Molteno, Baerveldt)., Conclusion: Accumulation of extracellular matrix components and activated fibroblasts in the bleb capsules of non-functioning GDI indicates the presence of an active wound healing process, suggesting a possible reduction in filtration through the bleb wall., (© 2013 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.)

Throughout the body, the extracellular matrix (ECM) provides structure and organization to tissues and also helps regulate cell migration and intercellular communication. In the injured spinal cord (or brain), changes in the composition and structure of the ECM undoubtedly contribute to regeneration failure. Less appreciated is how the native and injured ECM influences intraspinal inflammation and, conversely, how neuroinflammation affects the synthesis and deposition of ECM after CNS injury. In all tissues, inflammation can be initiated and propagated by ECM disruption. Molecules of ECM newly liberated by injury or inflammation include hyaluronan fragments, tenascins, and sulfated proteoglycans. These act as "damage-associated molecular patterns" or "alarmins", i.e., endogenous proteins that trigger and subsequently amplify inflammation. Activated inflammatory cells, in turn, further damage the ECM by releasing degradative enzymes including matrix metalloproteinases (MMPs). After spinal cord injury (SCI), destabilization or alteration of the structural and chemical compositions of the ECM affects migration, communication, and survival of all cells - neural and non-neural - that are critical for spinal cord repair. By stabilizing ECM structure or modifying their ability to trigger the degradative effects of inflammation, it may be possible to create an environment that is more conducive to tissue repair and axon plasticity after SCI., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Neural extracellular matrix (ECM) molecules derived from neurons and glial cells accumulate in the extracellular space and regulate synaptic plasticity through modulation of perisomal GABAergic inhibition, intrinsic neuronal excitability, integrin signaling, and activities of L-type Ca(2+) channels, NMDA receptors, and Rho-associated kinase. Genetic or enzymatic targeting of ECM molecules proved to bidirectionally modulate acquisition of memories, depending on experimental conditions, and to promote cognitive flexibility and extinction of fear and drug memories. Furthermore, evidence is accumulating that dysregulation of ECM is linked to major psychiatric and neurodegenerative diseases and that targeting ECM molecules may rescue cognitive deficits in animal models of these diseases. Thus, the ECM emerged as a key component of synaptic plasticity, learning, and memory and as an attractive target for developing new generation of synapse plasticizing drugs.

Extracellular matrix (ECM) molecules, their receptors at the cell surface, and cell adhesion molecules (CAMs) involved in cell-cell or cell-ECM interactions are implicated in processes related to major diseases of the central nervous system including Alzheimer's disease (AD), epilepsy, schizophrenia, addiction, multiple sclerosis, Parkinson's disease, and cancer. There are multiple strategies for targeting the ECM molecules and their metabolizing enzymes and receptors with antibodies, peptides, glycosaminoglycans, and other natural and synthetic compounds. ECM-targeting treatments include chondroitinase ABC, heparin/heparan sulfate-mimicking oligosaccharides, ECM cross-linking antibodies, and drugs stimulating expression of ECM molecules. The amount or activity of ECM-degrading enzymes like matrix metalloproteinases can be modulated indirectly via the regulation of endogenous inhibitors like TIMPs and RECK or at the transcriptional and translational levels using, e.g., histone deacetylase inhibitors, synthetic inhibitors like Periostat, microRNA-interfering drugs like AC1MMYR2, and natural compounds like flavonoids, epigallocatechin-3-gallate, anacardic acid, and erythropoietin. Among drugs targeting the major ECM receptors, integrins, are the anticancer peptide cilengitide and anti-integrin antibodies, which have a potential for treatment of stroke, multiple sclerosis, and AD. The latter can be also potentially treated with modulators of CAMs, such as peptide mimetics derived from L1-CAM and NCAM1.

Neural stem cells (NSCs) derive from the neuroepithelium of the neural tube, develop into radial glial cells, and recede at later developmental stages. In the adult, late descendants of these embryonic NSCs reside in discretely confined areas of the central nervous system, the stem cell niches. The best accepted canonical niches are the subventricular zone of the lateral ventricle and the subgranular zone of the dentate gyrus of the hippocampus. Stem cell niches provide a privileged environment to NSCs that supports self-renewal and maintenance of this cellular compartment. While numerous studies have highlighted the importance of transcription factors, morphogens, cytokines, and growth factors as intrinsic and extrinsic factors of stem cell regulation, less attention has been paid to the molecular micromilieu that characterizes the stem cell niches. In this chapter, we summarize increasing evidence that the extracellular matrix (ECM) of the stem cell environment is of crucial importance for the biology of this cellular compartment. A deeper understanding of the molecular composition of the ECM, the complementary receptors, and the signal transduction pathways engaged may prove highly relevant for harnessing NSCs in the context of biotechnological applications.

Chemical synapses allow neurons to perform complex computations and regulate other systems of the body. At a chemical synapse, pre- and postsynaptic sites are separated by a small space (the synaptic cleft) and surrounded by astrocytes. The basement membrane (BM), a sheetlike, specialized extracellular matrix (ECM), is found ubiquitously in the PNS. It has become clear that the ECMs not only play a structural role but also serve as barriers and filters in the PNS and CNS. Moreover, proteoglycans and tenascin family proteins in the ECM regulate synapse formation and synaptic plasticity. Although CNS synapses lack the BMs, recent results indicate that the BM-associated collagens are also present in the CNS synaptic cleft and affect synaptogenesis in both the CNS and the PNS. The C1q domain-containing family proteins are important components of the CNS synaptic cleft in regulating synapse formation, maintenance, and the pruning process. The ECM is regarded as a crucial component of the tetrapartite synapse, consisting of pre- and postsynaptic neurons, astrocyte, and ECM.

Currently, there are about 20 antiepileptic drugs on market. Still, seizures in about 30% of patients with epilepsy are not adequately controlled, or the drugs cause quality-of-life-compromising adverse events. Importantly, there are no treatments to combat epileptogenesis, a process that leads to the development of epilepsy and its progression. To fill the gaps in the treatment of epilepsy, there is an urgent need for identification of novel treatment targets. Data emerging over the recent years have shown that different components of the extracellular matrix (ECM) contribute to many components of tissue reorganization during epileptogenesis and the ECM is also a major regulator of synaptic excitability. Here, we review the role of urokinase-type plasminogen activator receptor interactome, matrix metalloproteinases, tenascin-R, and LGI1 in epileptogenesis and ictogenesis. Moreover, the role of the ECM in epilepsy-related comorbidities is reviewed. As there is active development of new imaging methods, we also summarize the data available on imaging of the ECM in epilepsy.

To investigate the molecular mechanisms involved in the outgrowth of retinal ganglion cell axons in the tectum, the expression of the extracellular matrix molecule tenascin was analysed in the tectum and retina of chickens by immunocytochemistry and in situ hybridization. Tissue was analysed between embryonic days 4 and 12, just before and during the period when retinal ganglion cell axons innervate their target region, the optic tectum. In the tectum, tenascin immunoreactivity becomes detectable at the anterior pole at embryonic day 4, 2 days before retinal ganglion cell axons arrive, and spreads caudally with increasing age. At early stages, tenascin is predominantly accumulated in the stratum opticum, the zone of ingrowing retinal ganglion cell axons, and along their prospective pathway. In the stratum opticum, the molecule is associated with radial glial fibres, glial endfeet and retinal ganglion cell axons located in the immediate neighbourhood of radial glial fibres. At all ages investigated, tenascin mRNA is mainly restricted to cells located in the periventricular region, suggesting that the molecule is synthesized by radial glial cells. In the retina, tenascin is expressed by amacrine, displaced amacrine and horizontal cells but not by retinal ganglion cells. To investigate whether the accumulation of tenascin in the developing and prospective pathway of retinal ganglion cell axons may affect their rate of growth we assayed the substrate properties of tenascin for retinal ganglion cell neurites in vitro. When retinal ganglion cell suspensions from 6-day-old chick embryos were maintained on homogeneous mouse or chick tenascin/polyornithine substrates, neurite length was significantly increased when compared to polyornithine substrates at coating concentrations of 10 or 20 micrograms/ml. Higher coating concentrations (35 or 70 micrograms/ml) resulted in neurite lengths comparable to control values. Together, these observations suggest that tenascin in the developing and prospective stratum opticum might serve as a performed pathway to support growth of retinal ganglion cell axons in the tectum.

Two major tenascin-C (TN-C) isoforms are generated by the alternative splicing of the pre-mRNA. The large isoform contains seven extra type three repeats that, by contrast, are omitted in the small TN-C isoform. The large TN-C isoform is mainly expressed at the onset of cellular processes that entail active cell migration, proliferation, or tissue remodeling such as occur in neoplasia, wound healing, and during development. Thus, the large TN-C isoform seems to be a specific component of the provisional extracellular matrix. Here we have studied the degradation of the large and small TN-C isoforms by matrix metalloproteinases (MMPs) 2, 3, 7, and 9. Among these proteolytic enzymes only MMP-7 can degrade the small TN-C isoform removing the NH2-terminal knob. The large TN-C isoform shows the same MMP-7-sensitive site adjacent to the NH2-terminal sequence, but is further degraded in the splicing area where three fibronectin-like type III repeats are completely digested. Moreover, the large TN-C isoform is degraded by MMP-2 and MMP-3 which completely digest a single type III repeat inside the splicing area. By contrast, the large TN-C isoform is resistant to MMP-9 digestion. The results show that the presence of the spliced sequence introduces new protease-sensitive sites in the large TN-C isoform.

The physiological role of tenascin in vivo has remained obscure. Although tenascin is regulated in a stage and tissue-dependent manner, knock-out mice appear normal. When tenascin expression was examined in the normal adult mouse mammary gland, little or none was present during lactation, when epithelial cells actively synthesize and secrete milk proteins in an extracellular matrix/lactogenic hormone-dependent manner. In contrast, tenascin was prominently expressed during involution, a stage characterized by the degradation of the extracellular matrix and the subsequent loss of milk production. Studies with mammary cell lines indicated that tenascin expression was high on plastic, but was suppressed in the presence of the laminin-rich, Engelbreth-Holm-Swarm (EHS) tumour biomatrix. When exogenous tenascin was added together with EHS to mammary epithelial cells, beta-casein protein synthesis and steady-state mRNA levels were inhibited in a concentration-dependent manner. Moreover, this inhibition by tenascin could be segregated from its effects on cell morphology. Using two beta-casein promoter constructs attached to the chloramphenicol acetyltransferase reporter gene we showed that tenascin selectively suppressed extracellular matrix/prolactin-dependent transcription of the beta-casein gene in three-dimensional cultures. Finally, we mapped the active regions within the fibronectin type III repeat region of the tenascin molecule that are capable of inhibiting beta-casein protein synthesis. Our data are consistent with a model where both the loss of a laminin-rich basement membrane by extracellular matrix-degrading enzymes and the induction of tenascin contribute to the loss of tissue-specific gene expression and thus the involuting process.

In order to elucidate the origin of the odontogenic myxoma, the composition and the structural organisation of the extracellular matrix (ECM) of this tumour were characterised. Collagen type I, VI, procollagen type III, undulin, tenascin and fibronectin were demonstrated in biopsy material of 4 cases by polyclonal antibodies. The tumour stroma showed a pronounced reaction for collagen type I. Fibroblasts displayed an intense intracytoplasmatic reaction for procollagen type III, and collagen type I was not found in the fibroblasts of the adjacent normal oral mucosa. In contrast to the surrounding connective tissue, label for collagen type VI was weak, as was the reaction for fibronectin and tenascin. Undulin was almost undetectable. The immunohistochemical results suggest that the odontogenic myxoma is characterised by an as yet unobserved structural organisation of ECM proteins, a secretion defect of fibrillar collagens type I and III with no resemblance to physiological tooth development.

Immunohistochemical studies to localise collagen IV, laminin, fibronectin and tenascin were undertaken in 59 bladder biopsies. These were non-neoplastic or contained foci of flat dysplasia or of transitional cell neoplasia. Collagen IV and laminin were reliably demonstrated in basement membranes but focal loss of reactivity for collagen IV was found in the urothelial basement membrane in some cases of inflammation, dysplasia, and non-invasive papillary transitional cell tumour. Basement membranes were rarely demonstrated around invasive transitional cell carcinomas. Fibronectin and tenascin were found in the sub-urothelial lamina propria and in some urothelial basement membranes. The stroma of invasive tumours reacted strongly for both. Increased numbers of sub-urothelial capillaries were present in association with some cases of cystitis, flat dysplasia or non-invasive transitional cell neoplasia suggesting an angiogenic stimulus in these circumstances. Immunohistochemical staining of basement membrane components is unlikely to be of value in the routine histopathological assessment of transitional cell neoplasms of the bladder.

Transforming growth factor beta (TGF-beta) comprises a group of multifunctional regulatory proteins, whose effects include stimulation of extracellular matrix formation and modification of immune function. The presence of TGF-beta 1 and TGF-beta 2 in invasive breast carcinomas has been determined and related to pathological features, the presence of fibronectin and tenascin and lymphocyte/macrophage infiltration, using immunohistochemistry. Differences were observed in the extent of reactivity within the same carcinoma and between tumours stained with an antibody detecting TGF-beta 1 ane one detecting TGF-beta plus TGF-beta 2, the latter having a higher level of reactivity. Prominent reactivity for TGF-beta 1 was associated with lymph node metastasis, (0.02 > P > 0.01), increased detection of cellular fibronectin, fine stromal fibronectin staining, more prominent reactivity for tenascin (0.02 > P > 0.01), the presence of tumour-associated macrophage infiltration and altered ratios of CD4 and CD8 lymphocyte populations, with CD8 lymphocytes predominating. These associations were not observed for carcinomas showing prominent staining with antibody detecting TGF-beta 2 as well as TGF-beta 1. The findings indicate that TGF-beta 1 may have a role in invasion and metastasis of breast carcinomas.

The extracellular domain of receptor type protein tyrosine phosphatase beta (RPTP beta) exhibits striking sequence similarity with a soluble, rat brain chondroitin sulfate proteoglycan (3F8 PG). Immunoprecipitation experiments of cells transfected with RPTP beta expression vector and metabolically labeled with [35S]sulfate and [35S]methionine indicate that the transmembrane form of RPTP beta is indeed a chondroitin sulfate proteoglycan. The 3F8 PG is therefore a variant form composed of the entire extracellular domain of RPTP beta probably generated by alternative RNA splicing. Previous immunohistochemical studies indicated that both RPTP beta and the extracellular matrix protein tenascin are localized in similar regions of the central nervous system. We have performed co-aggregation assays with red and green Co-vaspheres coated with tenascin and 3F8 PG, respectively, showing that the extracellular domain of RPTP beta (3F8 PG) binds specifically to tenascin. The interaction between a receptor tyrosine phosphatase and an extracellular matrix protein may have a role in development of the mammalian central nervous system.

The distribution of three (recently discovered) extracellular matrix components (tenascin, biglycan and decorin) was studied in normal adult human skin and in a number of monogenic disorders of keratinization, using immunohistology. The expression of tenascin, which is sparsely distributed in normal human dermis, was found to be grossly increased in epidermolytic hyperkeratoses and in Darier's disease. Tenascin expression in three types of ichthyosis (X-linked recessive ichthyosis, autosomal dominant ichthyosis vulgaris, non-erythrodermic lamellar ichthyosis) was similar to that of normal skin. The presence of biglycan and decorin did not show a marked variation between the different disorders studied, suggesting that their expression is subject to regulatory mechanisms distinct from those of tenascin. The increased expression of tenascin in two disorders of keratinization with a hyperproliferative phenotype, lends further support to the hypothesis that dermal tenascin expression is increased as a result of epidermal hyperproliferation.

Tenascin (TN) is a large oligomeric protein recently described as a component of the extracellular matrix. The distribution of TN in adult kidney tissue has not been adequately evaluated, but preliminary data have suggested that TN is variably seen in rare mesangial areas and in stroma surrounding some tubules. The enlargement of the mesangial matrix (mesangial sclerosis) is a common feature of many renal diseases and is thought to be partially related to oversynthesis of the normal components of the mesangial matrix (collagen type IV, laminin, fibronectin, and heparan sulfate proteoglycans) by mesangial cells. However, the possibility that mesangial cells are also the source of other extracellular matrix proteins that participate in the process of mesangial sclerosis has not been explored. In this study, the synthesis of TN by cultured rat mesangial cells was documented by the following observations: (1) Northern hybridization of total RNA extracted from mesangial cells showed two distinct species of TN mRNA; (2) immunoblotting of the protein extracted from the conditioned medium demonstrated four TN protein bands; (3) immunoblotting of the protein extracted from the mesangial cell lysate demonstrated at least four TN protein bands; and (4) immunohistochemical techniques identified TN within the cytoplasm of mesangial cells and in the surrounding extracellular matrix.(ABSTRACT TRUNCATED AT 250 WORDS)

Little attention has been paid to the composition of the extracellular matrix in synovial sarcoma, a tumour showing both epithelial and mesenchymal phenotypes. As extracellular matrix participates actively in interactions between epithelial and mesenchymal tissues, further knowledge of the pathogenesis of this tumour may be provided by the study of extracellular matrix components. Therefore, we have analysed the immunohistochemical distribution of type I, III, and IV collagen, fibronectin, laminin and tenascin in four cases of synovial sarcoma. The pattern of immunoreactivity for these molecules varied according to the tissue phenotype of the tumour. Mesenchymal tissue labelled mainly for type I and III interstitial collagen and fibronectin. The epithelial component was surrounded by a laminin and type IV collagen-positive basement membrane, but punctate pericellular reactivity for laminin and type IV collagen was also detected among some mesenchymal cells. Tenascin was strongly expressed in the mesenchymal tissue immediately around epithelial structures and weakly or not at all expressed in the monophasic tumours and in mesenchymal tissue distant from epithelial elements in the biphasic tumours. These results suggest some resemblances between synovial sarcoma and the embryonic development of epithelia from mesenchymal cells, providing further support for the concept of an epitheliogenesis from the mesenchyme in these tumours.

Expression of tenascin, an extracellular matrix protein associated with morphogenetic events and altered states of cellular adhesion, was examined in mouse uterus during the peri-implantation period. A uniform low level expression of tenascin was detected in stromal extracellular matrix during the estrous cycle and days 1 through 4 of early pregnancy. During the period of blastocyst attachment (day 4.5), an intense deposition of tenascin fibrils was located in the extracellular matrix of stroma immediately subjacent to the uterine epithelium surrounding the attaching blastocyst. This localized intensity of tenascin expression was both spatially and temporally restricted. By day 5.5, differentiation of stroma in the immediate area around the embryo to form the primary decidual zone was accompanied by a reduced amount of tenascin expression in the form of fragmented fibrils. Tenascin also could be induced by an artificial stimulus in uterine stroma of mice that had been hormonally prepared for implantation. The ability of artificial stimuli to induce tenascin expression suggested that the tenascin-inducing signals were derived from uterine cells, presumably lumenal epithelium, rather than embryonic cells. Consistent with this, conditioned medium from primary cultures of uterine epithelium was found to induce tenascin expression (2- to 4-fold) in isolated uterine stroma. Artificial stimuli generated a temporal pattern of tenascin expression similar to that observed during early pregnancy; however, in the artificially induced model, tenascin was induced in stroma immediately subjacent to lumenal epithelium along the entire length of the uterus. Purified tenascin and a recombinant tenascin fragment consisting of alternatively spliced fibronectin type III repeats, interfered with maintenance of uterine epithelial cell adhesion to Matrigel. In contrast, other recombinant tenascin fragments or fibronectin had no effect in this regard. Tenascin had no effect on adhesion of uterine stroma. Collectively, these results suggest that stimulation of TN expression in stromal extracellular matrix in vivo occurs via hormonally regulated, epithelial-mesenchymal interactions and serves as an early marker for uterine receptivity and the attachment phase of implantation. Furthermore, tenascin may facilitate embryo penetration by disrupting uterine epithelial cell adhesion to underlying basal lamina.

Previous studies have shown that several forms of the glycoprotein tenascin are present in the embryonic extracellular matrix. These forms are the result of alternative splicing, which generates tenascin variants with different numbers of fibronectin type III repeats. We have used degenerate primers and PCR to isolate a novel tenascin exon from an avian genomic library. Genomic clones contained a sequence encoding a fibronectin type III repeat that corresponds to repeat 'C' from the variable domain of human tenascin. To demonstrate that tenascin containing repeat 'C' is actually synthesized by avian cells, a monospecific antiserum was raised against a repeat 'C' fusion protein. This antiserum recognized a novel high-molecular-weight variant on immunoblots of tenascin isolated from chicken embryo fibroblast-conditioned medium, and stained tendons on frozen sections of chicken embryos. A cDNA probe specific for mRNA encoding repeat 'C' was used for in situ hybridization. This probe hybridized in a subset of the embryonic tissues labelled with a universal tenascin probe, including tendons, ligaments and mesenchyme at sites of epithelial-mesenchymal interactions. Finally, we provide evidence that additional fibronectin type III repeats, one corresponding to a recently discovered human repeat as well as one entirely novel sequence, also exists in chicken tenascin mRNA. These data indicate that tenascin is present in the embryonic matrix in a multitude of forms and that these forms have distinctive distributions that may reflect more than one function for tenascin in development.

Japanese quail embryos were used to examine paths of neural crest cell (NC) migration in relationship to the embryonic vasculature. Immunolabeling for NC, angioblasts and the extracellular matrix (ECM) glycoproteins fibronectin (FN), laminin (LN) and tenascin (TN) revealed several instances where spatiotemporal patterns of NC migration coincide with the embryonic vascular pattern and its associated ECM. An in vitro model for angiogenesis was modified to include NC, and associations with "capillary-like" endothelial cell structures were demonstrated. A working hypothesis is that the embryonic vasculature may, in specific instances, be used as a substratum for directed NC migration and that these interactions are mediated primarily through the adhesive interactions of FN. Some members of the TN family of glycoproteins, through their relatively non-adhesive properties, may act to help guide neural crest cells to the FN-rich blood vessel surface.

The proliferative nodules of Dupuytren's disease are electron microscopically characterized by the occurrence of myofibroblasts with a basal lamina-like material. As reported in the literature, immunohistochemical investigations showed a fibronectin matrix but failed to demonstrate laminin. This discrepancy between electron microscopic features and immunohistochemical findings prompted us to examine the composition of extracellular matrix (fibronectin, laminin, collagen type IV and tenascin) in relation to the myofibroblast phenotype in proliferative nodules from 13 native surgical specimens of nodular palmar fibromatosis (Dupuytren's disease). The immunohistochemical staining for fibronectin was positive within the whole palmar aponeurosis and was particularly intense in the proliferative areas, whereas laminin, collagen type IV and tenascin labelling was restricted to the alpha-smooth muscle actin-positive proliferative nodules. To exclude definitively an unspecific laminin labelling, SDS-PAGE and immunoblot were performed. The electrophoretic pattern of Dupuytren's disease tissue revealed laminin and was in congruence with human placental tissue used as positive control. The results substantiate an extracellular matrix formation by myofibroblasts with fibronectin, laminin, collagen type IV and tenascin as constituents. Therefore, laminin expression can no longer be considered to be a distinguishing feature between myofibroblasts and smooth muscle cells.

Tenascin (TN), a large oligomeric glycoprotein, is a recently described component of the extracellular matrix (ECM). Previous reports focusing largely on the role of TN in nephrogenesis have documented the strong expression of TN in embryonic kidney tissue and implied an important role for TN in nephrogenesis. However, the expression of TN in normal and pathologic kidneys in adults has not been systematically evaluated. In this study immunohistochemical staining for TN was applied to 184 renal specimens diagnosed as: normal kidney (23 cases); minimal change disease and its variants (8); mesangial proliferative glomerulonephritis (GN) including IgA nephropathy and mesangial proliferative lupus nephritis (9); endocapillary proliferative GN including membranoproliferative GN, lupus nephritis, and post-infectious GN (25); crescentic GN (11); membranous GN (19); focal segmental sclerosis (15); thrombotic microangiopathy (8); amyloidosis (5); diabetic nephropathy (9); primary tubulointerstitial nephritis (14); transplant rejection (14); and ischemia (24). It was found that: (a) there was unequivocal global diffuse staining limited to the mesangium in normal kidney; (b) regardless of the etiologies and the morphologic types of glomerular disease, whenever there was expansion of the ECM, whether in the mesangial, endocapillary, or extracapillary spaces, there was a concomitant and proportional in situ increase in the TN staining; (c) globally sclerotic glomeruli, regardless of causes, showed diffuse, strong staining, especially in the subcapsular fibrous deposition seen in ischemic sclerosis; (d) non-sclerotic glomeruli showing early ischemic change uniformly displayed a marked decrease or complete loss of staining; (e) in cases of thrombotic microangiopathy, there was segmental or global staining of the capillary wall, probably corresponding to the enlarged lamina rara interna; (f) all nodular lesions in diabetic glomerulosclerosis showed strong staining, but in several of them this staining was much more pronounced in the periphery than in the center of the lesion. Our study proves that TN is probably a component of the normal mesangial matrix, that TN is an ubiquitous component of the expanded glomerular ECM in pathologic conditions regardless of morphologic subtypes, and that further studies on the cell types and mechanisms responsible for TN synthesis may provide a new venue for the understanding of the process of glomerular sclerosis.

In recent years the interaction between tumour cells and the surrounding extracellular matrix in the process of tumour development, invasion and metastasis has been a focus of interest. We studied frozen sections of nine naevocellular naevi (junctional, compound and intradermal), 40 dysplastic naevi, six pagetoid in situ melanomas and 12 superficial spreading melanomas in order to determine the expression of: the basement membrane proteins collagen type IV and laminin, the interstitial collagen types I, III and VI, and fibronectin and tenascin. An indirect immunoperoxidase technique was used. In the various stages of melanocytic tumour progression we observed: 1 loss of type IV collagen and laminin within dermal melanocytic cell nests; 2 de novo expression of basement membrane type IV collagen and increased expression of the interstitial collagen types I, III and VI, as well as tenascin and fibronectin in the dermal stroma surrounding dysplastic naevus cells and melanoma cells; 3 presence of extracellular matrix components in close association with intra-epidermally located invading atypical melanocytes. These data demonstrate the complex alterations of the composition of the extracellular matrix from bland naevi through lesions with progressive atypia to invasive melanoma. The changes described result in a molecular environment which melanocytes with an altered adhesion molecule profile are able to invade.

This study describes the sequential changes in tenascin expression in hepatic fibrosis induced by bile duct ligation (BDL) in the rat. Two days after BDL, tenascin was strongly expressed in the matrix surrounding interlobular bile ducts and also between proliferating ductules. From day 7 onwards, its distribution was restricted to the connective tissue-parenchymal interfaces where ductular proliferation was still active. A markedly increased number of desmin- and alpha-smooth muscle actin (alpha-smA)-positive cells, considered myofibroblasts, was noted around interlobular bile ducts and between proliferating ductules during periductal fibrogenesis. Type IV collagen and laminin were strongly expressed on the basement membranes of proliferating ductules, and contributed to the development of newly formed fibrous septa. The transient expression of tenascin around interlobular bile ducts in the early phase of BDL may be related to the onset of periductal fibrosis or to the mitogenic response of the biliary epithelium. The expression of tenascin between 'proliferating' ductules in contrast to its absence from 'mature' fibrous areas suggests a transient role in early matrix organization. Furthermore, alpha-smA-positive cells may modulate the synthesis of extracellular matrix components.

The distribution of collagens type I, IV and VI, of procollagen type III, of undulin and of tenascin was studied in 10 lesions which were clinically and histologically diagnosed as localized oral fibrous hyperplasias. The immunohistochemical distribution of these proteins was similar to that observed for normal oral mucosa. Undulin showed a pattern of parallel fibers throughout. Collagen type VI was pronounced in the subepithelial connective tissue, whereas the collagen fiber bundles were equally reactive for collagens type I and III. Tenascin was observed close to the subepithelial basement membrane and in proximity to collagen fiber bundles in the upper connective tissue. The present findings indicate that oral fibrous hyperplasias that are probably caused by inflammation or chronic irritation show the differentiated and ordered pattern of extracellular matrix proteins characteristic of normal oral mucosa.

Tenascin is a large extracellular matrix (ECM) glycoprotein found in restricted tissue locations in the adult organism. It is copiously synthesized in regenerative organs or regenerating tissues and by certain tumors. We have analyzed the expression of tenascin in human long term bone marrow cultures as well as in cryostat sections of native bone marrow and found it strongly expressed by the stromal cells of the microenvironment. Two different protein subunits of 280 and 220 kD were detected by immunoblotting. These two forms are derived most likely from two different mRNA splice variants of 6 and 8 kb detected by Northern blotting. The in vivo analysis of cryostat sections showed a codistribution with other ECM molecules such as fibronectin and collagen type III in the microenvironment surrounding the maturing hematopoietic cells. Using two independent cell adhesion assays tenascin could be shown to function as a cytoadhesive molecule for hematopoietic cells. These data suggest a direct involvement of tenascin in the retention of hematopoietic progenitor cells in the stroma.

"Mice develop normally without tenascin", was a shock to biologists studying the extracellular matrix. Could tenascin be a useless protein? This seems most improbable, as it is conserved in every vertebrate species. Moreover, two new proteins have been discovered in the last year that are closely related to the original tenascin, providing evidence for a tenascin family. Speculations on functions are ripe for re-evaluation.

Expression and distribution of tenascin (TN) were immunohistochemically studied in the primary and metastatic sites of 90 cases of resected gastric cancer. TN was present in stromal cells surrounding cancer nests, but not in cancer cells. The overall incidence of TN-positive cases in the primary site was 70%, and the incidence in advanced cancer cases was significantly higher than that in early cancer cases. The incidence of TN-positive cases was significantly higher in the metastatic site than in the primary site. TN tended to be expressed intensively in the periphery of tumors. Coexpression of fibronectin (FN) and TN was observed in 50% of the TN-positive cases. However, the cases, in which TN was strongly positive in the periphery of tumors, were not reactive with anti-FN antibody. Ki-67 monoclonal antibody was also utilized to compare the number of proliferating cells in the TN-positive cases with that in the TN-negative cases. The number of Ki-67-positive cells was larger in the TN-positive cases than in the TN-negative cases. These results suggest that TN would be related to progression and metastasis of the gastric cancer, and that its biological function would be different from that of FN.

A loss in cell-cell adhesion and an increase in cell motility are clearly prerequisites for the development of invasive tumors and metastasis. Since disseminating tumor cells have to interact with and migrate through extracellular matrices it is of interest to compare the composition of extracellular matrix proteins in normal and tumor tissues, in order to determine whether the extracellular matrix could be critically involved in affecting tumor cell adhesion and migration. The question will be addressed whether tumor extracellular matrix contains increased amounts of potentially antiadhesive extracellular matrix components and whether cells behave differently depending on the extracellular matrix they encounter. The results reviewed support the hypothesis that changes in the extracellular matrix and the cellular receptors are indeed important in the process of tumorigenesis.

Janusin and tenascin are glia-derived, structurally related, extracellular matrix glycoproteins of the J1 family that are expressed in vivo at times and in locations where active neurite outgrowth occurs, but also when the formation or stabilization of cytoarchitectonic boundaries appears to be in operation. To resolve this apparent functional dichotomy, we have studied the behavioral response of growth cones, growing in culture on the permissive substrate laminin to janusin and tenascin, by video time lapse microscopy. When janusin and tenascin were offered as sharp substrate boundaries, dorsal root ganglion (DRG) and retinal ganglion neuron growth cones avoided growing on these molecules, but were not induced to collapse. On the other hand, when janusin and tenascin were offered, in a mixture with laminin, as uniform substrates, DRG growth cones displayed a collapsed morphology and were able to advance at a faster rate than on laminin alone. In contrast, the outgrowth of retinal ganglion neuron growth cones was completely inhibited under these conditions, underscoring a cell type specificity in the response of growth cones to these molecules. Using several monoclonal antibodies binding to distinct epitopes on the tenascin molecule, we have identified two domains responsible for growth cone repulsion, on epidermal growth factor (EGF)-like repeats 3-5 and fibronectin type III homologous repeats 4 and 5. These domains are different from the one previously recognized to be involved in neurite outgrowth on a uniform tenascin substrate. We conclude that both molecules may promote or retard growth cone advance, depending on the spatial expression pattern and the neuronal cell type.

The sequence of events and the distribution of extracellular matrix (ECM) components was examined during mouse secondary palatal shelf elevation in an in vitro model using standard roller tube culture methods developed for the culture of early embryos. In this culture system, the morphological changes associated with remodelling and reorientation of the palatal shelves of gestational day 13 mouse fetuses were similar to those observed in vivo. However, in specimens explanted 24-30 h prior to reorientation in vivo, remodelling began rapidly after explantation, and significant reorientation was accomplished within 4 h. Midline contact between the shelves did not occur until after 18 h in vitro, concomitant with shelf growth. Therefore, in this in vitro model, events related to palatal shelf remodelling and reorientation can be distinguished from those related to shelf growth. We used this in vitro model to characterize the transient changes in ECM distribution and accumulation that occur concomitant with events in shelf remodelling. Our results show that, during rapid remodelling in vitro, the relative distributions of collagen III, fibronectin and hyaluronate, as visualized by immunofluorescent staining, decreased within specific regions of the mesenchymal compartment. In contrast, the distribution of collagen I within the mesenchyme increased, and the distribution of tenascin did not change significantly. All molecules examined, except tenascin, showed changes in distribution within the basement membrane. These patterns of distribution are similar to those observed during more gradual remodelling in vivo. During remodelling in vitro, the deposition of [3H]-glucosamine- and [3H]-proline-labelled components of the ECM, as visualized by autoradiography, was greatest during the first 3 h of culture. During this period, labelled ECM accumulated within specific regions of the mesenchyme and palatal epithelial basement membrane. Uptake was reduced dramatically during the subsequent 3 h in culture and was restricted mainly to the palatal epithelium and its underlying basement membrane. The in vitro system permitted the characterization of early events in shelf remodelling leading to reorientation. Results suggest that remodelling is accompanied by rapid, local accumulation of ECM in specific regions of the palatal shelf previously thought to play a role in the process.

In the present study, the pattern of some extracellular matrix glycoproteins was determined in traumatic anterior cruciate ligament ruptures (n = 17) and in normal ligaments (n = 11). 6 microns cryo-sections were incubated with monoclonal antibodies recognizing tenascin, laminin, and fibronectin, and FITC-labeled secondary antibodies. Immunohistochemistry revealed that tenascin, fibronectin and laminin are sparsely distributed in normal anterior cruciate ligaments, but strongly expressed in ruptured ligaments with a time-restricted pattern. The de novo-expression of tenascin appeared before laminin but later than fibronectin. The data suggest that fibronectin and tenascin are important, partially antagonistic components during healing processes after anterior cruciate ligament ruptures.

Aims: To determine the distribution of tenascin in normal and pathological bone marrow., Methods: 48 different bone marrow lesions were studied immunohistochemically using a monoclonal antibody to tenascin., Results: Tenascin immunoreactivity was found in lesions with increased fibrosis and high numbers of reticular fibres. The strongest immunoreactivity was found in myelofibrosis. Bone marrow from acute and chronic myeloid and lymphatic leukaemias showed weak or moderate immunoreactivity. In hyperplasias inconsistent reticular tenascin immunoreactivity was found; in normal bone marrow, only a few scattered positive fibres were occasionally seen., Conclusions: Tenascin was generally observed in conditions in which megakaryocytic hyperplasia was a feature. This is in line with the notion that tenascin synthesis in bone marrow fibroblasts is stimulated by TGF-beta which is synthesised by the megakaryocytic lineage. Tenascin also contains EGF-like repeats. It might therefore function as a growth promoter and in this way could also stimulate synthesis of other matrix components. On the other hand, tenascin could function as an adhesive molecule to some cells of the bone marrow. The presence of tenascin in many pathological states of the bone marrow suggests that it may have a role in their pathogenesis and that it also could be a potential marker of disease.

Monoclonal antibodies (MAb) were used to show that cultured human amnion epithelial (HuA) cells produce tenascins (Tn) and isoforms of cellular fibronectin (cFn). Tn polypeptides of M(r) 280,000 and 190,000, assembled into extracellular matrix (ECM) but not secreted into the culture medium by HuA cells, were electrophoretically similar to those produced by human fibroblasts as revealed with domain-specific MAbs. The results suggested that most Fn produced by HuA cells contained the extradomain (ED) A and an oncofetal domain but only a minor fraction EDB. In immunofluorescence Tn and Fn were seen in different cytoplasmic granules upon monensin-induced intracellular accumulation. Tn appeared to be deposited in the ECM in colocalization with Fn but distinctly slower. The present results show that cultured normal human epithelial cells synthesize Tn and three isoforms of cFn and secrete them by using different cytoplasmic pathways.

The glycoprotein tenascin is found in the extracellular matrix in regions of cell motility, cell proliferation, and tissue modelling. We have used novel tenascin cDNA probes to localize tenascin transcripts in the developing mouse and to study the regulation of tenascin expression by growth factors in vitro. At postnatal day 1 tenascin mRNAs are abundant in regions of bone and cartilage formation, as well as in the ependymal layer of the central nervous system. Previous studies have demonstrated that transforming growth factor-beta type 1 (TGF-beta 1) can induce tenascin expression in vitro. As TGF-beta 1 is absent or scarce in the developing brain, it is likely that other growth factors, alone or in addition to TGF-beta 1, may regulate tenascin expression during development. Therefore, we have compared the effects of TGF-beta 1 and a growth factor that is found in both developing connective tissue and the central nervous system, basic fibroblast growth factor (bFGF), on tenascin expression in a mouse embryo fibroblast cell line (Swiss 3T3 cells). Immuno-slot blot analysis of Swiss 3T3 cell-conditioned culture medium demonstrates that bFGF is a more potent inducer of tenascin expression than TGF-beta 1. Furthermore, bFGF and TGF-beta 1 have an additive effect on levels of tenascin, but not fibronectin, in the conditioned medium. Western blots revealed that different forms of tenascin are induced by bFGF and TGF-beta 1: the tenascin induced by the former has a molecular mass of approximately 250 kDa, the latter induces an approximately 200 kDa form of tenascin. The induction of large tenascin by bFGF was confirmed by northern blot analysis, which revealed increased levels of an 8 kb tenascin transcript after 24 h by as little as 4 ng/ml of bFGF in serum-free medium. Thus bFGF, alone or in combination with TGF-beta 1, is a potential regulator of tenascin expression in vitro. bFGF may alter not only the relative abundance of tenascin and fibronectin in the extracellular matrix, but also the splice variant of tenascin expressed by a given cell type.

Monoclonal antibodies (mAb) utilized in regeneration studies to date identify antigens that are up-regulated in the blastema. We obtained a monoclonal antibody, designated ST1 (Stump 1), that is reactive to an extracellular matrix (ECM) antigen exhibiting the opposite distribution; ST1 is an abundant antigen of the limb stump soft tissues but is absent from within the blastema. The border between abundance and absence of mAb ST1 reactivity was sharp and extended as a concavity into the stump. This distinct dichotomy led to further studies relevant to understanding how this extracellular matrix antigen is modulated during regeneration. mAb ST1 reactivity decreased in the internal tissues at the distal end of the limb prior to blastema formation and remained absent until the onset of differentiation. The initial decrease in mAb ST1 reactivity was dependent on the combined effects of injury and the wound epithelium but was nerve independent. At blastema stages of regeneration, the distribution of tenascin, ascertained by mAb MT1 reactivity, closely matched the area without reactivity to mAb ST1. The spatial and temporal distribution of the ST1 antigen in unamputated limbs and during regeneration did not correspond to any previously described ECM component.

A crucial part of secondary palate morphogenesis is the movement of the palatal shelves from an initial vertical position on either side of the tongue to a final horizontal one above it to achieve palate closure. The immunocytochemical localization of extracellular matrix (ECM) molecules in the palatal shelf during this remodelling and reorientation revealed the existence of an ECM infrastructure within the mesenchyme. The major components of this infrastructure were collagen III, fibronectin, and hyaluronate (HA). With remodelling, HA's domain within the mesenchyme was expanded, whereas those of fibronectin and collagen III became more circumscribed. The expansion of an HA-rich matrix within the mesenchyme is thought to be crucial for palatal reorientation. The results of this study suggest that, as this expansion occurs, it is modulated by collagen and fibronectin components of the ECM infrastructure. Prior to shelf remodelling, this infrastructure may be anchored by a specialized region of the midoral epithelial-mesenchymal interface and the subjacent mesenchyme which is characterized by the unique distribution of collagen III, fibronectin, and tenascin. The midoral palatal epithelium also may play a role in directing shelf expansion. This epithelial region undergoes changes in cell packing and epithelial cell layering that correlate with shelf remodelling. These changes occur concomitantly with changes in the expression of collagen III, collagen IV, and laminin within the underlying basement membrane. The localization and patterning of tenascin within the developing palate suggests that it not only contributes to the postulated anchoring structure of the midoral epithelial-mesenchymal region, but also plays a role in the determining the fate of the medial edge epithelial cells during the final stage of palate closure.

The extracellular matrix molecule cytotactin is a multidomain protein that plays a role in cell migration, proliferation, and differentiation during development. To analyze the structure-function relationships of the different domains of this glycoprotein, we have prepared a series of fusion constructs in bacterial expression vectors. Results obtained using a number of adhesion assays suggest that at least four independent cell binding regions are distributed among the various cytotactin domains. Two of these are adhesive; two others appear to be counteradhesive in that they inhibit cell attachment to otherwise favorable substrates. The adhesive regions were mapped to the fibronectin type III repeats II-VI and the fibrinogen domain. The morphology of the cells plated onto these adhesive fragments differed; the cells spread on the fibronectin type III repeats as they do on fibronectin, but remained round on the fibrinogen domain. The counteradhesive properties of the molecule were mapped to the EGF-like repeats and the last two fibronectin type III repeats, VII-VIII. The latter region also contained a cell attachment activity that was observed only after proteolysis of the cells. Several cell types were used in these analyses, including fibroblasts, neurons, and glia, all of which are known to bind to cytotactin. The different domains exert their effects in a concentration-dependent manner and can be inhibited by an excess of the soluble molecule, consistent with the hypothesis that the observed properties are mediated by specific receptors. Moreover, it appears that some of these receptors are restricted to particular cell types. For example, glial cells bound better than neurons to the fibrinogen domain and fibroblasts bound better than glia and neurons to the EGF fragment. These results provide a basis for understanding the multiple activities of cytotactin and a framework for isolating different receptors that mediate the various cellular responses to this molecule.

As part of a major clinical trial, sequential biopsies were taken from the margins of venous leg ulcers during their healing. The changing patterns of tissue architecture and extracellular matrix synthesis during healing were documented histologically and immunocytochemically. Initial biopsies were similar in appearance: prominent fibrin cuffs, variable inflammation, hemosiderin, and red blood cell extravasation. So called "fibrin cuffs" were highly organized structures composed of laminin, fibronectin, tenascin, and collagen as well as trapped leukocytes and fibrin. Fibronectin was absent from the ulcer tissue although collagen was abundant. Major histologic changes were observed after 2 weeks' pressure bandage therapy; hemosiderin, acute inflammation, and granulation tissue with the deposition of fibronectin had all increased and epithelial migration had commenced. Complete epithelialization was frequent by the fourth week of treatment, but the basement membrane was incomplete. At this time, hemosiderin and red blood cell extravasation had decreased and "fibrin cuffs" were virtually absent although chronic inflammation remained. The complex organization of the so-called "fibrin cuffs" may inhibit angiogenesis (but offer protection against increased venous pressure) in addition to their previously ascribed role in causing tissue ischemia.

The expression of tenascin, a recently discovered extracellular matrix protein, was studied by immunohistochemical techniques in scleroderma skin and compared with its distribution in normal skin. In progressive systemic sclerosis, a marked increase in tenascin content was observed in the superficial reticular dermis. In localized scleroderma, the deposition of tenascin was increased both in the superficial and deep dermis of involved skin, whereas in clinically uninvolved skin the distribution of tenascin was the same as in normal control skin, i.e. the papillary dermis and peri-appendiceal zone. The distribution of tenascin did not strictly parallel that of fibronectin. These findings and the current knowledge of tenascin biology suggest that the overproduction of tenascin in scleroderma dermis could be secondary to stimulation of fibroblasts by immune cell-derived cytokines, or could be due to abnormal fibroblasts, or a subpopulation of fibroblasts, producing high levels of this extracellular matrix protein.

In Xenopus embryos, the extracellular matrix (ECM) protein tenascin (TN) is expressed dorsally in a very restricted pattern. We have studied the spatial and temporal expression of TN mRNA in tailbud-stage embryos by RNAase protection and in situ hybridization using a cDNA probe for Xenopus TN obtained by PCR amplification. We report that TN transcripts are principally expressed in cells dispersed around the neural tube and notochord as well as in myotome and sclerotome cells. No TN mRNA could be detected in lateral plate mesoderm, but expression was detectable beneath tail fin epidermis. In a second series of experiments, we studied the expression of TN mRNA and protein in combinations between animal and vegetal stage-6 blastomeres and in stage-8 blastula animal caps treated with activin A or basic fibroblastic growth factor (b-FGF). Isolated animal cap tissue cultured alone differentiates into epidermis, which expresses neither TN protein nor TN mRNA. TN expression is, however, elicited in response to isolated dorsal vegetal blastomeres and in response to high concentrations of activin, both of which treatments lead to formation of muscle and/or notochord. Low concentrations of activin, and ventral vegetal blastomeres, treatments that induce mesoderm of ventral character, are poor inducers of TN. However, b-FGF, which also induces ventral mesoderm, elicits strong expression. These results indicate that TN regionalization is a complex process, dependent both on the pattern of differentiation of mesodermal tissues and on the agent with which they are induced. The data further show that "ventral mesoderm" induced by low concentrations of activin is distinct from that induced by b-FGF, and imply that activin induces ventral mesoderm of the trunk while b-FGF induces posterior mesoderm of the tailbud.

Background: Acute and chronic renal allograft rejection injuries involve, albeit variably, all compartments of the organ and are associated with significant structural changes. We hoped to gain new insights into these phenomena by determining distribution of certain extracellular matrix proteins known to be involved in architectural remodeling processes., Experimental Design: Frozen tissue samples from biopsies of acute (n = 14) and chronic (n = 12) human renal allograft rejections were studied to compare distribution of tenascin, the extradomains A and B (EDA, EDB), and oncofetal (Onc) isoforms of cellular fibronectin (cFn). Normal kidneys (n = 4) served as controls. Cryosections were immunostained by the avidin-biotin-complex method with monoclonal antibodies specific for those molecules., Results: In acute rejection, reactivity for tenascin and EDA-cFn was increased slightly to moderately in glomerular mesangia and in most vessels while it was intensely and diffusely increased in the interstitium. Rarely were focal EDB-cFn and Onc-cFn reactions seen in lesions deemed to reflect acute injury. In chronic rejection, tenascin and EDA-cFn were strongly increased in most glomerular mesangia and in vascular walls but unevenly in the interstitium. In rare glomerular synechiae and vessels, enhanced staining for tenascin and EDA-cFn as well as EDB-cFn and Onc-cFn was noted while in obsolete glomeruli only EDB-cFn and Onc-cFn were detected. The enhanced distribution of tenascin and EDA-cFn partly reflected that noted during nephrogenesis, whereas staining patterns for EDB-cFn and Onc-cFn differed from their fetal counterparts., Conclusions: Tenascin and EDA-cFn are strongly and preferentially expressed in the interstitial and vascular compartments of acute and chronic renal rejection injury suggesting that, in these sites, active repair and remodeling occur during both phases of the rejection process irrespective of the changes seen by conventional microscopy. Tenascin, EDA-cFn as well as EDB-cFn and Onc-cFn are all involved, albeit variably, in the glomerular and vascular alterations of chronic rejection. The finding of tenascin and of the three isoforms of cFn in glomerular synechiae with actively proliferating epithelium suggests that certain epithelial cells might partake in the synthesis of these molecules.