A proteoglycan with HNK-1 antigenic determinants is a neuron-associated ligand for cytotactin

Three Types of Demyelination, Perivenous, Confluent, and Perineuronal Nets-Rich in a COVID-19 Patient With Meningoencephalomyelitis

Neurologic symptoms are common in COVID-19, and a variety of neuropathological changes have been reported. One of the important neuropathological findings is demyelination. However, the underlying pathogenesis of demyelination remained poorly understood. We witnessed a case of COVID-19 with distinct types of demyelination in the cerebrum, medulla oblongata, and spinal canal, who died of sepsis. The postmortem examination showed the solitary massive demyelination in the medulla oblongata. The massive lesion was filled with components of perineuronal nets. In the spinal canal, confluent demyelination in bilateral lateral and dorsal funiculi was detected over the entire length from C1 to S5, which was maximum at the level of cervical spinal canal stenosis. Demyelination in the cerebrum was mainly perivenular, and augmented in the area of lacunar infarcts and dilated perivascular spaces. Considering the distribution patterns of the following three types of demyelination, the traces of viral spreading could be highlighted. Discontinuous perivenous demyelination in the cerebrum showed the result of hematogenous spreading. Longitudinal confluent demyelination of the spinal cord should be the picturesque of the trace of axonal spreading. The distribution of demyelination was possibly modified by the underlying diseases, diabetes mellitus, hypertension, and spinal canal stenosis.

Tenascin-C: Form versus function

Tenascin-C is a large, multimodular, extracellular matrix glycoprotein that exhibits a very restricted pattern of expression but an enormously diverse range of functions. Here, we discuss the importance of deciphering the expression pattern of, and effects mediated by, different forms of this molecule in order to fully understand tenascin-C biology. We focus on both post transcriptional and post translational events such as splicing, glycosylation, assembly into a 3D matrix and proteolytic cleavage, highlighting how these modifications are key to defining tenascin-C function.

The molecular basis of memory

We propose a tripartite biochemical mechanism for memory. Three physiologic components are involved, namely, the neuron (individual and circuit), the surrounding neural extracellular matrix, and the various trace metals distributed within the matrix. The binding of a metal cation affects a corresponding nanostructure (shrinking, twisting, expansion) and dielectric sensibility of the chelating node (address) within the matrix lattice, sensed by the neuron. The neural extracellular matrix serves as an electro-elastic lattice, wherein neurons manipulate multiple trace metals (n > 10) to encode, store, and decode coginive information. The proposed mechanism explains brains low energy requirements and high rates of storage capacity described in multiples of Avogadro number (N(A) = 6 × 10(23)). Supportive evidence correlates memory loss to trace metal toxicity or deficiency, or breakdown in the delivery/transport of metals to the matrix, or its degradation. Inherited diseases revolving around dysfunctional trace metal metabolism and memory dysfunction, include Alzheimer's disease (Al, Zn, Fe), Wilson's disease (Cu), thalassemia (Fe), and autism (metallothionein). The tripartite mechanism points to the electro-elastic interactions of neurons with trace metals distributed within the neural extracellular matrix, as the molecular underpinning of "synaptic plasticity" affecting short-term memory, long-term memory, and forgetting.

Identification of novel and distinct binding sites within tenascin-C for soluble and fibrillar fibronectin

Interactions between fibronectin and tenascin-C within the extracellular matrix provide specific environmental cues that dictate tissue structure and cell function. The major binding site for fibronectin lies within the fibronectin type III-like repeats (TNfn) of tenascin-C. Here, we systematically screened TNfn domains for their ability to bind to both soluble and fibrillar fibronectin. All TNfn domains containing the TNfn3 module interact with soluble fibronectin. However, TNfn domains bind differentially to fibrillar fibronectin. This distinct binding pattern is dictated by the fibrillar conformation of FN. TNfn1-3, but not TNfn3-5, binds to immature fibronectin fibrils, and additional TNfn domains are required for binding to mature fibrils. Multiple binding sites for distinct regions of fibronectin exist within tenascin-C. TNfn domains comprise a binding site for the N-terminal 70-kDa domain of fibronectin that is freely available and a binding site for the central binding domain of fibronectin that is cryptic in full-length tenascin-C. The 70-kDa and central binding domain regions are key for fibronectin matrix assembly; accordingly, binding of several TNfn domains to these regions inhibits fibronectin fibrillogenesis. These data highlight the complexity of protein-protein binding, the importance of protein conformation on these interactions, and the implications for the physiological assembly of complex three-dimensional matrices.

Structural and biological properties of the carbohydrate units of nervous tissue glycoproteins

We have identified structures in nervous tissue glycoproteins that are novel for glycoproteins in general or enriched in nervous tissue or cells of neural origin. These include: (alpha 2-8)-linked polysialic acid units, the linear form of poly-N-acetyllactosamine glycans, the sialylated X antigen determinant NeuAc(alpha 2-3)-Gal(beta 1-4) [Fuc(alpha 1-3)]GlcNAc, a series of Man-O-Ser(Thr)-linked glycans, and the O-glycosidically linked disaccharide unit Gal(alpha 1-3)GalNAc. The polysialic and poly-N-acetyllactosamine glycans are also developmentally regulated. The polysialic acid units in the cell adhesion molecule N-CAM. The poly-N-acetyllactosamine units occur in the adhesion molecule NILE (which is immunologically similar to Ng-CAM and L1) and in some other components revealed by a cell surface-labelling method specific for these glycans. The mannose-linked glycans occur in a chondroitin sulphate proteoglycan involved in neuron-glia interactions. Other biological interactions of the carbohydrates include their serving as bacterial receptors in meningitis, their serving as models for molecular mimicry by the capsules of meningitis-causing bacteria, and the role of some structures as antigens in autoimmune conditions. At the molecular level, two types of mechanisms are suggested for the glycans in molecular interactions: they may function either as mediators of interactions by serving as specific recognition ligands, or as modulators of the interactions determined by polypeptides or other molecules.

Families of neural adhesion molecules

The neural cell adhesion molecules L1 and N-CAM share a common carbohydrate epitope that is recognized by the monoclonal antibodies L2 and HNK-1. The L2/HNK-1 epitope is also present on the myelin-associated glycoprotein (MAG) and secreted J1 glycoprotein, both of which have been identified as cell adhesion molecules. Each of the four adhesion molecules is differentially expressed during development on distinct cell types. Expression of the L2/HNK-1 epitope is regulated independently of the protein backbone, is phylogenetically conserved, and plays a role in cell-cell and, particularly, cell-substrate interactions. Another set of glycoproteins shares a common carbohydrate epitope designated L3. This epitope is present on the novel adhesion molecule on glia (AMOG), L1 and MAG, but not on J1 and N-CAM. As in the L2/HNK-1 family, the number of glycoproteins expressing this epitope is not yet known. It is therefore possible that heterogeneities in carbohydrate structures are associated with different sets of adhesion molecules and may have functional implications.

DSD-1-Proteoglycan/Phosphacan and Receptor Protein Tyrosine Phosphatase-Beta Isoforms during Development and Regeneration of Neural Tissues

Interactions between neurons and glial cells play important roles in regulating key events of development and regeneration of the CNS. Thus, migrating neurons are partly guided by radial glia to their target, and glial scaffolds direct the growth and directional choice of advancing axons, e.g., at the midline. In the adult, reactive astrocytes and myelin components play a pivotal role in the inhibition of regeneration. The past years have shown that astrocytic functions are mediated on the molecular level by extracellular matrix components, which include various glycoproteins and proteoglycans. One important, developmentally regulated chondroitin sulfate proteoglycan is DSD-1-PG/phosphacan, a glial derived proteoglycan which represents a splice variant of the receptor protein tyrosine phosphatase (RPTP)-beta (also known as PTP-zeta). Current evidence suggests that this proteoglycan influences axon growth in development and regeneration, displaying inhibitory or stimulatory effects dependent on the mode of presentation, and the neuronal lineage. These effects seem to be mediated by neuronal receptors of the Ig-CAM superfamily.

Microheterogeneity of anti-myelin-associated glycoprotein antibodies

Antibodies to the myelin-associated glycoprotein (MAG) are implicated in the pathogenesis of an acquired demyelinating polyneuropathy. We studied IgM affinity to MAG in 18 patients with anti-MAG antibodies. Binding of sera was tested for anti-MAG immunoreactivity in central nervous system (CNS) by ELISA and in CNS and peripheral nervous system (PNS) by Western blot analysis. Furthermore, immunohistochemical characterization of IgM binding on sural nerve tissue was investigated using the indirect peroxidase method. Western blot analysis revealed that all sera detected MAG in central myelin, but only eight in peripheral myelin. Anti-MAG-IgM-ELISA-titers correlated significantly (p<0.0001) with PNS-Western blot results. By indirect immunoperoxidase immunohistochemistry, 12 sera stained myelin sheaths, while 6 sera showed no staining. These results demonstrate considerable variations in antibody binding strength to MAG between PNS myelin and CNS myelin. The relevance of these differences for the pathogenesis of the neuropathy and clinical impairment remains to be demonstrated.

Tenascin expression in normal, hyperplastic, dysplastic and neoplastic canine mammary tissues

Mammary tumours are the most common neoplasias of female dogs and may have a complex histological pattern with both epithelial and spindle cells participating in the transformation process. A frequent feature of these tumours is chondroid or bone metaplasia of the extracellular matrix, which mainly occurs in areas of proliferated spindle-shaped cells, probably of myoepithelial origin. The present study evaluates immunohistochemically the expression of tenascin in 186 surgical samples of canine mammary tissues, ranging from normality to neoplasia. Tenascin was present in all mammary tissues studied, with an increased expression in remodelling situations and in neoplastic lesions. Basement membrane was the most frequently labelled structure, but stromal tissue was more often and widely labelled in neoplastic lesions. The extracellular matrix was positive in solid and anaplastic carcinomas as well as in spindle cell proliferation areas. Tenascin expression in extracellular matrix was also abundant in areas of initial chondroid metaplasia and, with variable extension, in almost all cartilage islands of mixed tumours. In well differentiated secretory areas only apical granules of luminal cells were positive, suggesting a different pattern of tenascin expression during secretory differentiation. The digestion of chondroitin sulphate significantly improved the labelling for tenascin when a co-expression of these two molecules was present. Although our results suggest that tenascin cannot be used as a marker of transformation or of malignancy in canine mammary oncology, it is clear that this molecule plays an important role in proliferation and differentiation processes in the canine mammary gland.

Identification and characterization of a conformational heparin-binding site involving two fibronectin type III modules of bovine tenascin-X

Tenascin-X is known as a heparin-binding molecule, but the localization of the heparin-binding site has not been investigated until now. We show here that, unlike tenascin-C, the recombinant fibrinogen-like domain of tenascin-X is not involved in heparin binding. On the other hand, the two contiguous fibronectin type III repeats b10 and b11 have a predicted positive charge at physiological pH, hence a set of recombinant proteins comprising these domains was tested for interaction with heparin. Using solid phase assays and affinity chromatography, we found that interaction with heparin was conformational and involved both domains 10 and 11. Construction of a three-dimensional model of domains 10 and 11 led us to predict exposed residues that were then submitted to site-directed mutagenesis. In this way, we identified the basic residues within each domain that are crucial for this interaction. Blocking experiments using antibodies against domain 10 were performed to test the efficiency of this site within intact tenascin-X. Binding was significantly reduced, arguing for the activity of a heparin-binding site involving domains 10 and 11 in the whole molecule. Finally, the biological significance of this site was tested by cell adhesion studies. Heparan sulfate cell surface receptors are able to interact with proteins bearing domains 10 and 11, suggesting that tenascin-X may activate different signals to regulate cell behavior.

The HNK-1 carbohydrate epitope in the eye: basic science and functional implications

The HNK-1 carbohydrate epitope is part of many cell membrane and extracellular matrix molecules. It has been implicated in cell to cell and cell to extracellular matrix adhesion, and antibodies to the HNK-1 epitope are emerging as a versatile tool in eye research. They have been used to identify a novel cell type in the human eye, the subepithelial matrix cells that reside in the inner connective tissue layer (ICTL) of the ciliary body. Although these cells resemble fibroblasts in ultrastructure, they form a distinct cell population that differs in its antigenic profile from fibroblasts of other tissues. These cells are associated with the elastic fiber system of the ICTL. Other structures in the human eye that harbor the HNK-1 epitope in a nonrandom pattern are the ciliary and iris epithelia, the zonular lamella, the lens capsule, the retina, glial cells of the optic and ciliary nerves, and scleral fibroblasts. The HNK-1 epitope in the eye appears early during embryonic development and is phylogenetically conserved, but many interspecies differences exist in its distribution. The role of the HNK-1 epitope may be to structurally stabilize the ciliary body and the retina, and to participate in zonular attachments. The HNK-1 epitope has been linked with many common eye diseases. The subepithelial matrix cells seem to be susceptible to undergo irreversible damage as a result of glaucoma, thermal injury, and tissue compression. This epitope has proved to be useful in identifying intraocular deposits of exfoliation syndrome. It can explain the adhesiveness of exfoliation material. Intraocular exfoliation material differs in HNK-1 immunoreactivity from the extraocular fibrillopathy of exfoliation syndrome and its presence in fellow eyes also argues against the concept of unilateral exfoliation syndrome. The HNK-1 epitope is found in the extracellular matrix of secondary cataract and anterior subcapsular cataract, and it may contribute to their pathogenesis. Finally, the HNK-1 epitope can be used to trace neuroepithelial derivatives of the optic vesicle in developmental anomalies and in tumors of the eye. Eventual identification of molecules that bear the HNK-1 epitope in the eye will likely shed light on many aspects of ocular physiology and pathobiology

Cell specific-chondroitin sulfate proteoglycan expression during CNS morphogenesis in the chick embryo

There is increasing evidence that proteoglycans, particularly chondroitin sulfate proteoglycans (CSPGs), are integral components in the assembly of the extracellular matrix during early stages of histogenesis. The differential expression of several CSPGs in the developing CNS has raised questions on their origin, phenotype (chemical and structural characteristics), regulation of expression and function. The S103L monoclonal antibody has been an invaluable specific reagent to identify and study a large and abundant CSPG in embryonic chick brain. In the present study we demonstrate that during embryogenesis of the chick CNS, the S103L CSPG (B-aggrecan) is synthesized by neurons of all major neuronal cell types but not by astrocytes, is developmentally regulated, and is associated predominantly with neuronal somata, suggesting that neuronal-specific regulatory mechanisms control the expression of the S103L CSPG in culture. Neurons also exhibit differential expression of glycosaminoglycan type (i.e., KS) and sulfation patterns on different CSPGs when compared to astrocytes, meningial cells or chondrocytes, implying the existence of additional, cell type-specific modes of regulation of the final CSPG phenotype (chemical and structural posttranslational characteristics). A specific temporal pattern of expression of the S103L-CSPG was observed which may contribute to conditions that induce or stabilize specific cell phenotypes during CNS development. In contrast, the other major CSPG in the CNS recognized by the HNK-1 antibody, is synthesized by all cell types of different cell lineages over the entire embryonic period, suggesting a more global cell maintenance function for this CSPG.

The tenascin family of ECM glycoproteins: structure, function, and regulation during embryonic development and tissue remodeling

The determination of animal form depends on the coordination of events that lead to the morphological patterning of cells. This epigenetic view of development suggests that embryonic structures arise as a consequence of environmental influences acting on the properties of cells, rather than an unfolding of a completely genetically specified and preexisting invisible pattern. Specialized cells of developing multicellular organisms are surrounded by a complex extracellular matrix (ECM), comprised largely of different collagens, proteoglycans, and glycoproteins. This ECM is a substrate for tissue morphogenesis, lends support and flexibility to mature tissues, and acts as an epigenetic informational entity in the sense that it transduces and integrates intracellular signals via distinct cell surface receptors. Consequently, ECM-receptor interactions have a profound influence on major cellular programs including growth, differentiation, migration, and survival. In contrast to many other ECM proteins, the tenascin (TN) family of glycoproteins (TN-C, TN-R, TN-W, TN-X, and TN-Y) display highly restricted and dynamic patterns of expression in the embryo, particularly during neural development, skeletogenesis, and vasculogenesis. These molecules are reexpressed in the adult during normal processes such as wound healing, nerve regeneration, and tissue involution, and in pathological states including vascular disease, tumorigenesis, and metastasis. In concert with a multitude of associated ECM proteins and cell surface receptors that include members of the integrin family, TN proteins impart contrary cellular functions, depending on their mode of presentation (i.e., soluble or substrate-bound) and the cell types and differentiation states of the target tissues. Expression of tenascins is regulated by a variety of growth factors, cytokines, vasoactive peptides, ECM proteins, and biomechanical factors. The signals generated by these factors converge on particular combinations of cis-regulatory elements within the recently identified TN gene promoters via specific transcriptional activators or repressors. Additional complexity in regulating TN gene expression is achieved through alternative splicing, resulting in variants of TN polypeptides that exhibit different combinations of functional protein domains. In this review, we discuss some of the recent advances in TN biology that provide insights into the complex way in which the ECM is regulated and how it functions to regulate tissue morphogenesis and gene expression.

Mechanical modulation of tenascin-C and collagen-XII expression during avian synovial joint formation

The objective of this study was to investigate how temporal and spatial patterns of characteristic extracellular matrix molecules are altered in the absence of normal functional skeletal muscle contractions during avian synovial joint development. By using in situ detection of protein and mRNA expression in developing avian feet and femorotibial joints from a wide range of developmental stages, we demonstrate that the morphological abnormalities that result from embryonic immobilization are associated with altered patterns of tenascin-C and collagen-XII expression within developing joint structures. As the joints fuse in immobilized embryos, the cells of the presumptive articular surface differentiate from flattened fibroblasts to more rounded chondrocytes and collagens XII and I are no longer detected at sites of complete joint fusion. Although the expression of collagen XII persists at normal levels elsewhere within the immobilized joint, tenascin-C expression is diminished within the chondroepiphysis, synovium, and tendons, as well as within the remains of the fibrous articular surface. This effect is most notable for the shortest tenascin variant (Tn190) within the chondroepiphysis and the largest variant (Tn230) within tendons, synovium, and the fibrous surface layer of the joint. This study thus provides in vivo support of previous in vitro work that suggests that tenascin expression is sensitive to external changes in mechanical loading environment. However, these data do not support a similar conclusion for collagen XII during early development.

Anti-MAG IgM penetration into myelinated fibers correlates with the extent of myelin widening

The purpose of this study was to evaluate the relationship between immunoglobulin M (IgM) antibodies penetration into myelinated peripheral nerve fibers and the widening of the peripheral myelin sheaths in anti-myelin-associated glycoprotein (anti-MAG) demyelinating IgM monoclonal polyneuropathy. Demyelinating polyneuropathy with monoclonal IgM is often associated with anti-MAG autoantibodies, which are thought to initiate the disease with IgM deposits usually present on the myelin sheaths. We analyzed nerve biopsies from 12 patients with an anti-MAG demyelinating neuropathy by confocal and electron microscopy. The total number of nerve fibers and the proportion of IgM-associated fibers were quantified after immunohistochemical staining. The affinities of IgM were examined by analyzing the binding pattern of serum IgM on normal peripheral nerve sections. Ultrastructural examinations of the biopsies showed a good correlation between in situ widened myelin sheaths and the IgM penetration level into myelinated fibers. The terminal complement complex appears not be involved in the penetration of IgM into the myelinated fibers. Our findings suggest a causative role of the IgM anti-MAG antibodies in the ultrastructural modifications of the myelin sheaths. The basement membrane and myelin components appear to be the major targets of the IgM monoclonal antibodies. However, the pathogenic mechanism whereby IgM antibodies reach their targets and induce nerve damage are still unclear.

Extracellular matrix molecules play diverse roles in the growth and guidance of central nervous system axons

Axon growth and guidance represent complex biological processes in which probably intervene diverse sets of molecular cues that allow for the appropriate wiring of the central nervous system (CNS). The extracellular matrix (ECM) represents a major contributor of molecular signals either diffusible or membrane-bound that may regulate different stages of neural development. Some of the brain ECM molecules form tridimensional structures (tunnels and boundaries) that appear during time- and space-regulated events, possibly playing relevant roles in the control of axon elongation and pathfinding. This short review focuses mainly on the recognized roles played by proteoglycans, laminin, fibronectin and tenascin in axonal development during ontogenesis.

Tenascin-C in the cochlea of the developing mouse

Tenascin-C is a glycoprotein of the extracellular matrix that acts in vitro as both a permissive and a nonpermissive substrate for neurite growth. We analyzed, by immunocytochemistry, the distribution of tenascin-C along neural growth pathways in the developing mouse cochlea. In the spiral lamina, tenascin-C coexists in a region where nerve bundles arborize. In the organ of Corti, tenascin-C lines the neural pathways along pillar and Deiters' cells before and during the time of nerve fiber ingrowth. By embryonic day 16, tenascin-C is abundant on the pillar side of the inner hair cell but does not accumulate on the modiolar side until about birth, a time after the arrival of afferent fibers. The synaptic zones beneath outer hair cells are strongly labeled during the time when early events in afferent synaptogenesis are progressing but not during the time of efferent synaptogenesis. At the age when most neural growth ceases, tenascin-C immunoreactivity disappears. Faint tenascin-C immunolabeling of normal hair cells, strong tenascin immunolabeling in pathological hair cells of Bronx waltzer (bv/bv) mice, and staining for beta-galactosidase, whose gene replaces tenascin in a "knockout" mouse, indicate that hair cells supply at least part of the tenascin-C. The changing composition of the extracellular matrix in the synaptic region during afferent and efferent synaptogenesis is consistent with a role for tenascin in synaptogenesis. The presence of tenascin-C along the growth routes of nerve fibers, particularly toward the outer hair cells, raises the possibility that growth cone interactions with tenascin-C helps to guide nerve fibers in the cochlea.

Expanded T cell populations in patients with Wegener's granulomatosis: characteristics and correlates with disease activity

Patients with Wegener's granulomatosis have a high prevalence of expanded populations of CD4+ and CD8+ T cells bearing different alpha/beta T cell receptors. To elucidate the role of these populations, we studied the phenotypic and functional characteristics of 13 expanded T cell populations in four patients for a period of 35-51 months. The expanded populations generally showed a persistently high expression of the activation markers HLA-DR and CD25. This expression was independent of the activity of the disease. The expanded populations also expressed CD45RO and/or CD45RA and most of them expressed CD57 but not CD28. Analysis of intracellular presence and secretion of IFN-gamma, IL-2, and IL-4 showed that most of the expanded cell populations contained and/or secreted more of these cytokines than the nonexpanded populations, with an especially high expression/secretion of IFN-gamma and IL-2. The expanded populations showed little proliferative response to Con A and OKT3. The proliferative response of the cells was partly restored after preincubation in medium alone. Some of the expanded populations were associated with disease activity, thus suggesting a link between expanded T cells and the disease. The activated status of the expanded populations and the tendency for certain populations to correlate in magnitude with disease activity suggest their involvement in the disease process. The relative stability of these cell populations indicates that the stimulus driving them is persistent, in agreement with the chronicity of the disease.

Abnormal T cell receptor V gene usage in myasthenia gravis: prevalence and characterization of expanded T cell populations

The usage of T cell receptor (TCR) Valpha/Vbeta chains on cells from 38 patients with myasthenia gravis (MG) was determined by flow cytometry. There was a decreased number of cells expressing Vbeta2 in CD8+ and Vbeta3 in CD4+ cells in patients compared with healthy individuals. Abnormal expansions of T cells using particular TCR Valpha/Vbeta gene products were found in 18/38 patients. A significantly higher usage of Vbeta13 was observed but there was no restriction with regard to other TCR Valpha/Vbeta. Expanded cells belonging to both CD4+ and CD8+ were present in MG patients while restricted to the CD8+ population in healthy individuals. To elucidate the role of the expanded populations, we studied characteristics of the expanded and non-expanded T cells from MG patients who had persistent T cell expansions over more than 2 years. The cells were analysed with regard to phenotype, cytokine secretion, cytokine mRNA expression and reactivity with the autoantigen, the acetylcholine receptor. The characteristics of the expanded populations in MG clearly differed from those found in healthy individuals. More cells in the CD4+ expanded populations expressed HLA-DR and there was also a tendency for higher expression of CD25, CD28 and CD57. The number of cells spontaneously secreting cytokines was higher in the expanded populations. A dominant Th1-type cytokine secretion and mRNA expression was noted. Autoantigen-reactive CD4+ T cells were largely restricted to the expanded populations.

Double staining of proteoglycans and the HNK-1 carbohydrate epitope in pseudoexfoliation material

PURPOSE

We combined the techniques of both immunogold and cupromeronic-blue staining with electron microscopy to investigate the possible relationship between proteoglycans and the HNK-1 carbohydrate epitope in pseudoexfoliation material.

METHODS

The anterior segment was obtained from an enucleated eye with pseudoexfoliation syndrome. After cupromeronic-blue staining, following the method of Scott, specimens were embedded in L. R. White resin. Ultrathin sections were incubated successively in primary monoclonal antibodies, and 10 nm gold-conjugated secondary antibody.

RESULTS

The present study showed simultaneous presence of the HNK-1 epitope and proteoglycans associated with zonular fibrils and pseudoexfoliation material on the posterior surface of the iris. The HNK-1 epitope was immunolocalized to the periphery of the pseudoexfoliation fibers, while cupromeronic blue-positive filaments bridged adjacent pseudoexfoliation fibers.

CONCLUSIONS

Proteoglycans and the HNK-1 epitope might play a substantial role in the formation of pseudoexfoliation material via their adhesive function. Proteoglycans probably do not directly bear the HNK-1 epitope in pseudoexfoliation material.

Isolation of a tenascin-R binding protein from mouse brain membranes. A phosphacan-related chondroitin sulfate proteoglycan

We have isolated a chondroitin sulfate proteoglycan from mouse brain by affinity chromatography with a fragment of the extracellular matrix glycoprotein tenascin-R (TN-R) that comprises the amino-terminal cysteine-rich stretch and the 4.5 epidermal growth factor-like repeats. The isolated chondroitin sulfate proteoglycan has a molecular mass of 500-600 kDa and carries the HNK-1 carbohydrate epitope. Treatment with chondroitinase ABC reveals a major band of approximately 400 kDa and two minor bands at 200 and 150 kDa. Immunoblot analysis relates the molecule to phosphacan but not to the chondroitin sulfate proteoglycans neurocan and versican. Binding of the phosphacan-related molecule to the epidermal growth factor-like repeats of TN-R is Ca2+-dependent. Co-localization of the molecule with TN-R in the retina and optic nerve by immunocytochemistry suggests a functional relationship between the two molecules in vivo. Inhibition of neurite outgrowth from hippocampal neurons by the phosphacan-related molecule in vitro is neutralized by TN-R when coated as a uniform substrate. Furthermore, the phosphacan-related molecule neutralizes growth cone repulsion induced by TN-R coated as a sharp substrate boundary with or without prior treatment with chondroitinase ABC. These observations indicate that TN-R can interact with a phosphacan-related molecule and thereby modulate its inhibitory influence on neuritogenesis.

Insulin-like growth factor binding protein-2 binds to cell surface proteoglycans in the rat brain olfactory bulb

A family of six insulin-like growth factor binding proteins (IGFBPs) bind IGF-I and modulate its biological activity. IGFBPs may bind to macromolecules on the cell surface or pericellular extracellular matrix, and this interaction may modulate their effect on IGF activity. To date, little is known about the specificity of IGFBPs in the regulation of IGF action in the brain. We therefore explored whether IGFBPs were associated with cell membrane or extracellular matrix components in the rat brain. IGF-I binding sites with the characteristics of an IGFBP were found in the olfactory bulb mitral cell layer. This IGFBP was identified as IGFBP-2 by immunoprecipitation of both solubilized membrane preparations and cross-linked 125I-IGF: IGFBP complexes. While binding of IGFBP-2 to cell membranes was unaffected by RGD-containing peptide, it was inhibited by high salt concentration, suggesting interaction with proteoglycans. IGFBP-2 bound in vitro to the glycosaminoglycans chondroitin-4 and -6-sulfate, keratan sulfate, and heparin. IGFBP-2 also bound the proteoglycan aggrecan, an effect reduced by digestion of its glycosaminoglycans. Binding of IGFBP-2 to chondroitin-6-sulfate decreased the binding affinity of IGFBP-2 for IGF-I approximately 3-fold. Finally, an IGFBP-2 antibody coimmunoprecipitated IGFBP-2 and an approximately 200 kDa proteoglycan containing chondroitin-sulfate side chains from the rat olfactory bulb, providing definitive evidence for IGFBP-2 binding to olfactory bulb proteoglycans. These findings indicate that IGFBP-2 binds to proteoglycans in cell membranes of the rat olfactory bulb. Because we have previously shown that IGFs are highly expressed in the rat olfactory bulb, cell associated IGFBP-2 may have an important role in directing IGFs to specific sites in this brain region.

Changing activation sequence in the embryonic chick heart. Implications for the development of the His-Purkinje system

In the mature heart, impulse propagation through the His-Purkinje system (HPS) is required for efficient ventricular contraction in an apex-to-base direction. However, the embryonic heart begins to contract as a myocardial tube without a specialized conduction system. To identify the developmental stage when the HPS begins to function, we mapped the ventricular depolarization sequence from microvolt-level electrograms recorded from embryonic myocardium using 50-micron extracellular electrodes, high-gain amplification, and signal-processing techniques. Analysis of left ventricular activation in 99 embryonic hearts revealed a transition in the activation sequence that was dependent on developmental stage. As the heart develops, a transition in the activation sequence occurred from the primitive base-to-apex pattern (in 20 of 33 hearts) at early stages (Hamburger-Hamilton stages 25 to 28) to the HPS-like apex-to-base pattern (12 of 17 hearts) late in development (stages 33 to 36). Immunohistological experiments (n = 10) also confirm that the expression pattern of two biochemical HPS markers changes in parallel with the change to the mature ventricular activation pattern. These data indicate that the ventricular activation sequence in the chick heart develops to a mature pattern at stages 29 to 31, suggesting that preferential conduction through the HPS begins shortly after ventricular septation is complete.

Glycosaminoglycans modulate fibronectin matrix assembly and are essential for matrix incorporation of tenascin-C

We have investigated the role of glycosaminoglycans in fibronectin matrix assembly and the incorporation of tenascin-C into matrix fibrils. Chinese hamster ovary cell mutants with a total block in heparan and chondroitin sulfate production failed to assemble a fibronectin matrix, and incorporated no tenascin-C. Another mutant with reduced heparan sulfate produced a normal fibronectin matrix but failed to incorporate tenascin-C. Excess soluble glycosaminoglycans inhibited the binding of tenascin-C to purified fibronectin in ELISA, and completely blocked incorporation into matrix fibrils. Treating cultured cells with xyloside, which interferes with glycosaminoglycan attachment to proteoglycans, also completely blocked their ability to incorporate tenascin-C into matrix fibrils. We conclude that proteoglycans bound to fibronectin fibrils play a major role in binding tenascin-C to these fibrils. We examined more closely the large heparan sulfate proteoglycan, perlecan, and found that it co-localizes with tenascin-C and fibronectin in the matrix. The perlecan binding site in tenascin-C was mapped to the fibronectin type III domains 3–5, but this binding was strongly enhanced for the small splice variant, which is the major form incorporated into the matrix. Apparently when the alternative splice segment is inserted after domain 5 it inhibits perlecan binding. Thus heparan sulfate glycosaminoglycans, and perlecan in particular, may play a role in incorporation of the small splice variant of tenascin-C into fibronectin matrix fibrils.

Differential expression of PSA-NCAM and HNK-1 epitopes in the developing cardiac conduction system of the chick

Although the critical role of the His-Purkinje system (HPS) in the propagation of cardiac action potentials from the atria to the ventricular myocardium in the mature heart is well appreciated, its functional and anatomical development are not well understood. The embryonic heart begins beating early in development devoid of a mature conduction system, and the HPS cannot be identified by conventional histochemical analysis until the seventh embryonic day of chicken development. Although many biochemical markers have been found that apparently identify HPS precursors, little is known about how these biochemical markers function in the maturation of the cardiac conduction system. Using immunohistological techniques, we demonstrated that the maturation of the HPS may be observed by the expression of two distinct populations of conduction system precursors, identified by the expression of cell surface carbohydrates PSA-NCAM (PSA) and HNK-1, both of which are known to participate in cell-cell and cell-substrate interactions in the development of the nervous system. By stage 25, PSA was detected in ventricular trabeculae and the interventricular septum (IVS) in a pattern that resembles bundle branches and Purkinje fibers. Beginning at stage 28, HNK-1 epitope expression in the IVS was observed in myocardium just superior to the PSA-positive bundles in a pattern that resembles the common His bundle. This junctional region was also positive for atrial myosin heavy chain (alpha MHC), another marker for the HPS. These data suggest that a complex, coordinated process of biochemical and morphological change governs the development of the cardiac conduction system.

Chondroitin sulfate proteoglycan and tenascin in the wounded adult mouse neostriatum in vitro: dopamine neuron attachment and process outgrowth

Extracellular matrix (ECM) molecules, including chondroitin-4 or chondroitin-6 sulfate proteoglycans (CSPGs) and tenascin, are upregulated in and around wounds and transplants to the adult CNS. In the present study, striatal wounds from adult mice were used in a novel in vitro paradigm to assess the effects of these wound-associated molecules on embryonic dopamine cell attachment and neurite outgrowth. Light and electron microscopic immunocytochemistry studies have shown that astroglial scar constituents persist in cultured explants for at least 1 week in vitro, and despite the loss of neurons from adult striatal explants, there is a retention of certain structural features suggesting that the wound explant-neuron coplant is a viable model for analysis of graft-scar interactions. Explants from the wounded striatum taken at different times after a penetrating injury in vivo were used as substrates for embryonic ventral mesencephalon neurons that were plated on their surfaces. Dopamine cell attachment is increased significantly in relation to the expression of both CSPG and tenascin. The increase in neuronal attachment in this paradigm, however, is accompanied by a postlesion survival time-dependent significant decrease in neuritic growth from these cells. In vitro ECM antibody treatment suggests that CSPG may be responsible for heightened dopamine cell attachment and that tenascin simultaneously may support cell attachment while inhibiting neurite growth. The present study offers a new approach for the in vitro analysis of cell and molecular interactions after brain injury and brain grafting, in essence acting as a nigrostriatal transplant-in-a-dish.

CD8high+ (CD57+) T cells in patients with rheumatoid arthritis

OBJECTIVE

To investigate the development and T cell receptor (TCR) usage of CD8+, CD57+ T cells in rheumatoid arthritis (RA) patients.

METHODS

Three-color flow cytometry using monoclonal antibodies (MAb) to CD8, CD57 and different TCR V beta gene products.

RESULTS

The proportion of CD8+ T cells expressing CD57 (CD57/CD8) was significantly higher in RA patients compared with age-matched controls. Expanded TCR V beta populations were more frequent, and were found in both RA patient-derived CD8high+ (CD57+) and CD8+, CD57- populations. TCR V beta 5+ and TCR V beta 13+ expansions were present at high frequency (5 of 26 and 7 of 26, respectively). TCR V beta expansions in CD8high+ (CD57+) lymphocytes from RA patients were significantly larger than those in age-matched controls (expansion index 2.38 +/- 0.28, n = 41 and 1.63 +/- 0.09, n = 32, respectively), and were stable over time.

CONCLUSION

RA leads to an increase in the frequency of expanded CD8+ T cell subsets expressing selected TCR, due to expansion of TCR V beta + populations in CD8high+ (CD57+) T cells. Their restricted TCR usage suggests potential specificity for RA antigens and, therefore, a potential role in the pathogenesis of RA.

Chondroitin sulfate proteoglycan and tenascin in the wounded adult mouse neostriatum in vitro: dopamine neuron attachment and process outgrowth

Extracellular matrix (ECM) molecules, including chondroitin-4 or chondroitin-6 sulfate proteoglycans (CSPGs) and tenascin, are upregulated in and around wounds and transplants to the adult CNS. In the present study, striatal wounds from adult mice were used in a novel in vitro paradigm to assess the effects of these wound-associated molecules on embryonic dopamine cell attachment and neurite outgrowth. Light and electron microscopic immunocytochemistry studies have shown that astroglial scar constituents persist in cultured explants for at least 1 week in vitro, and despite the loss of neurons from adult striatal explants, there is a retention of certain structural features suggesting that the wound explant-neuron coplant is a viable model for analysis of graft-scar interactions. Explants from the wounded striatum taken at different times after a penetrating injury in vivo were used as substrates for embryonic ventral mesencephalon neurons that were plated on their surfaces. Dopamine cell attachment is increased significantly in relation to the expression of both CSPG and tenascin. The increase in neuronal attachment in this paradigm, however, is accompanied by a postlesion survival time-dependent significant decrease in neuritic growth from these cells. In vitro ECM antibody treatment suggests that CSPG may be responsible for heightened dopamine cell attachment and that tenascin simultaneously may support cell attachment while inhibiting neurite growth. The present study offers a new approach for the in vitro analysis of cell and molecular interactions after brain injury and brain grafting, in essence acting as a nigrostriatal transplant-in-a-dish.

The nanomelic mutation in the aggrecan gene is expressed in chick chondrocytes and neurons

We have established the presence of at least two large chondroitin sulfate proteoglycans in the developing chick brain, one that reacts exclusively with HNK-1, a carbohydrate epitope found on several neural specific molecules, and one that reacts with S103L, a defined peptide epitope in the CS-2 domain of the cartilage-specific chondroitin sulfate proteoglycan (CSPG), aggrecan. In order to determine the relationships between the two distinct S103L-reactive CSPGs from cartilage (chondrocytes) and brain (neurons), as well as among the three large CSPGs expressed in brain, S103L, HNK-1 and versican, we studied the expression of these multiple proteoglycan species in the brain of nanomelic chicks. We have previously shown that homozygous embryos expressing the nanomelic phenotype exhibit a single point mutation in the aggrecan gene. In the present study, the S103L CSPG is not accumulated or synthesized by embryonic chick CNS tissue or E8CH neuronal cultures derived from nanomelic chick embryo cerebral hemispheres. In contrast, expression of both versican and the HNK-1 CSPG was normal in the mutant embryo CNS. Pulse chase experiments demonstrated the presence of the 380 kDa precursor in normal neurons and the 300 kDa truncated precursor in nanomelic neurons. Northern blot analysis revealed normal-sized mRNA but reduced levels of expression of the S103L CSPG message in nanomelic neurons, while expression of the versican message was comparable in normal and nanomelic neurons. Most conclusively, the point mutation previously identified in nanomelic cartilage mRNA was also identified in nanomelic brain mRNA. Together these results provide evidence that a single aggrecan gene is expressed in both cartilage and CNS tissue leading to the production of identical core proteins which then undergo differential and tissue-specific post-translation processing, resulting in the characteristic tissue-specific proteoglycans. Furthermore, versican and the HNK-1 CSPG, although structurally and chemically similar to the S103L CSPG, are the products of separate genes.

Distinct effects of recombinant tenascin-C domains on neuronal cell adhesion, growth cone guidance, and neuronal polarity

Using a set of recombinantly expressed proteins, distinct domains of the mouse extracellular matrix glycoprotein tenascin-C, hereafter called tenascin, have been identified to confer adhesion, anti-adhesion, and changes in morphology of neuronal cells. In short-term adhesion assays (1 hr), cerebellar and hippocampal neurons adhered to several domains, encompassing the fibronectin type III-like (FN III) repeats 1-2 and 6-8, as well as to the alternatively spliced FN III repeats and to tenascin itself. Although no short-term adhesion to the EGF repeats containing fragment could be detected under the conditions used, it was anti-adhesive for neuronal cell bodies and repellent for growth cone advance and neuritogenesis. FN III repeats 3-5 were repellent only for growth cones but not for neuronal cell bodies. Neurite outgrowth promoting activities at early stages and induction of a polarized neuronal morphology at later stages of differentiation were associated with the EGF repeats and the FN III repeats 6-8. These observations suggest differential effects of particular domains of the tenascin molecule on distinct cellular compartments, i.e., cell body, axon and dendrite, and existence of multiple neuronal receptors with distinct intracellular signaling features.

Differentiation of glycoconjugates localized to sensory terminals and selected sites in brain

Distribution of complex carbohydrates in the peripheral and central nervous systems was investigated cytochemically with a lectin that binds specifically to terminal alpha GalNAc and with monoclonal antibodies against carbohydrate epitopes, including glucuronic acid 3-SO4 and chondroitins 6-SO4 and 4-SO4. Comparative staining with these methods differentiated and partially characterized several glycoconjugates in various sites and allowed a comparison of chemical heterogeneity to neural specialization. Distal terminals of sensory neurons concerned with hearing, balance, taste, touch, and sight expressed glucuronyl 3-SO4, which apparently was present in an undefined glycoprotein. Some neurons in sensory nuclei of the brainstem exhibited a similar constituent on their surfaces. Retinal rod outer segments and the cerebellar granular layer possessed masked glucuronyl 3-SO4 that became immunopositive after digestion with chondroitinase ABC and that occurred in chondroitin 6-SO4 and chondroitin 4-SO4, respectively. The surface of neurons in the eighth nerve root and in neighboring nodes of Ranvier stained for unmasked glucuronic acid 3-SO4 and chondroitin 6-SO4. Some neurons of the cerebral cortex expressed unmasked glucuronyl 3-SO4, chondroitin 6-SO4, and terminal alpha GalNAc on their surfaces. Certain cortical neurons and nerve tracts with chondroitin 6-SO4 and terminal alpha GalNAc lacked glucuronyl 3-SO4, and other neurons possessing chondroitin 6-SO4 failed to express either glucuronyl 3-SO4 or terminal alpha GalNAc. Lability of lectin affinity to hyaluronidase suggested the presence of terminal alpha GalNAc in the chondroitin 6-SO4 on cortical neurons. The findings document further the heterogeneity of neural glycoconjugates, expand knowledge about the diversity of neurons with respect to their content of partially characterized glycoconjugates, and link glucuronyl 3-SO4 with or without chondroitin 6-SO4 spatially to sites of active Na+ transport in sensory nerves.

Transient increase of tenascin-C in immature hippocampus: astroglial and neuronal expression

In the present report we describe the anatomical localization of cells expressing tenascin-C, an extracellular matrix glycoprotein, in the hippocampal complex of developing rats. We report a development-dependent down regulation of both tenascin-C protein and mRNA. The highest levels of expression of tenascin-C was observed in rat pups from embryonic day 18 to postnatal day 7. Double labelling experiments performed with a tenascin-C antibody or tenascin-C probes combined with specific markers of astrocytes (GFAP) or neurons (MAP2 and Tau) allowed us to demonstrate that tenascin-C is expressed by both immature astrocytes and neurons in immature hippocampus. The temporal and topographic distribution of cells expressing tenascin-C (in the hilus and the stratum oriens of CA3) correlate with the localization and period of migration and maturation of post-mitotic cells. In view of these data we discuss the hypothesis that tenascin-C, as a mediator of neuron-glia interactions, may contribute to the development of hippocampal cells.

Receptor-mediated adhesive and anti-adhesive functions of chondroitin sulfate proteoglycan preparations from embryonic chicken brain

Chondroitin sulfate proteoglycans inhibit the adhesion of cells to extracellular matrix proteins that otherwise permit adhesion. Although proteoglycans are widely assumed to act by masking the other protein in a mixed substrate, recent studies suggest that proteoglycans inhibit adhesion through mechanisms initiated by their binding to specific cell surface receptors. To explore this issue, we developed a purification scheme to isolate proteoglycan aggregates, monomers, and core proteins. Two distinct adhesion assays were used to study the interaction of these proteoglycan preparations with human foreskin fibroblasts: the gravity assay in which cell attachment is stabilized by cell spreading, and the centrifugation assay in which spreading does not play a role. All proteoglycan preparations mediate adhesion in the centrifugation assay but not in the gravity assay. In the centrifugation assay, proteoglycan aggregates and monomers are considerably more active than other extracellular matrix proteins while proteoglycan core proteins are at least as active as other extracellular matrix proteins. Proteoglycan core proteins bind to cell-associated hyaluronic acid, but not to integrins. Using mixed substrates in the gravity assay, all proteoglycan preparations inhibited cell attachment to fibronectin and vitronectin but not to collagen I and laminin. Although proteoglycan aggregates and monomers are more active than core proteins in inhibiting adhesion in the gravity assay, core proteins are still clearly active. A variety of control experiments suggest that the inhibition of cell attachment by proteoglycans is mediated through the specific interactions of proteoglycans with cell surface receptors, resulting in the inhibition of cell spreading. These results suggest at least two molecular mechanisms for proteoglycan-fibroblast interactions, one involving the chondroitin sulfate on the proteoglycan and an as yet unidentified receptor, the other involving the proteoglycan core protein and cell-associated hyaluronic acid.

The versican C-type lectin domain recognizes the adhesion protein tenascin-R

The core proteins of large chondroitin sulfate proteoglycans contain a C-type lectin domain. The lectin domain of one of these proteoglycans, versican, was expressed as a recombinant 15-kDa protein and shown to bind to insolubilized fucose and GlcNAc. The lectin domain showed strong binding in a gel blotting assay to a glycoprotein doublet in rat brain extracts. The binding was calcium dependent and abolished by chemical deglycosylation treatment of the ligand glycoprotein. The versican-binding glycoprotein was identified as the cell adhesion protein tenascin-R, and versican and tenascin-R were both found to be localized in the granular layer of rat cerebellum. These results show that the versican lectin domain is a binding domain with a highly targeted specificity. It may allow versican to assemble complexes containing proteoglycan, an adhesion protein, and hyaluronan.

Tenascin-C mRNA is expressed in cranial neural crest cells, in some placodal derivatives, and in discrete domains of the embryonic zebrafish brain

A partial zebrafish tenascin-C cDNA clone was isolated from an embryonic zebrafish cDNA library on the basis of homology to mouse tenascin-C. The expression pattern in the head of embryonic zebrafish was analyzed by in situ hybridization. Tenascin-C mRNA was detected in neural crest cells during the period of their migration and differentiation. Expression also occurred in differentiating placodal tissues and in mesodermal cells. In the developing brain, tenascin-C mRNA was expressed in specific domains. In the hindbrain the pattern of the domains was dynamic. At 18 to 22 h postfertilization, expression was widespread in rhombomeres 3, 5, and 6, confined to periventricular cells in rhombomere 2, and not detectable in rhombomere 4. At 32 h postfertilization, tenascin-C was expressed at the rhombomere boundaries. In contrast to the hindbrain, the pattern in the forebrain and midbrain did not show any major changes between 22 and 32 h postfertilization. Domains expressing tenascin-C alternated with regions devoid of it. The most anterior domain of expression was observed at the telencephalic-diencephalic border, surrounding the optic recess. A second domain, at the border between the diencephalon and the midbrain, and a third domain, in the caudal midbrain tegmentum, appeared restricted to the basal plate. Additionally, expression of tenascin-C mRNA was detected in the hypothalamus and in the developing epiphysis. These expression patterns suggest that tenascin-C may play a role in neural crest cell migration and during the differentiation of neural crest, placodal, and mesodermal derivatives. In the developing brain, tenascin-C may be involved in the consolidation of different regional identities.

Gliosis and axonal sprouting in the hippocampus of epileptic rats are associated with an increase of tenascin-C immunoreactivity

Temporal lobe epilepsy is associated with neuronal death, gliosis and sprouting of mossy fibres in the hippocampus of human and rats. In the present study we show that immunoreactivity for tenascin-C (an extracellular matrix glycoprotein) increase in the hippocampus of epileptic rats. However, this increase was only observed in the cases displaying neuronal cell loss and glial reaction (i.e. after kainate treatment but not after kindling). Tenascin-C increase was particularly striking at Ammon's horn, where the antibody labelled both reactive astrocytes (confirmed by double-labelling experiments) and axonal plasma membranes. In the molecular layer tenascin-C immunoreactivity remained unchanged in both kindled or kainate treated rats. It is interesting that increased tenascin-C immunoreactivity was observed within zones in which axonal regeneration did not occur (the CA3 area in kainate-treated animals) whereas zones in which reactive synaptogenesis occurred (such as the CA3 area of kindled rats or the molecular layer of both kindled and kainate-treated rats) were devoid of tenascin-C immunoreactivity. We infer from these results that tenascin-C impedes the terminal sprouting of mossy fibres in CA3 of kainate-treated rats.

The interaction of the retina cell surface N-acetylgalactosaminylphosphotransferase with an endogenous proteoglycan ligand results in inhibition of cadherin-mediated adhesion

We have previously shown that the binding to cells of a monoclonal antibody directed against the chick neural retina N-acetylgalactosaminylphosphotransferase (GalNAcPTase) results in inhibition of cadherin-mediated adhesion and neurite outgrowth. We hypothesized that the antibody mimics the action of an endogenous ligand. Chondroitin sulfate proteoglycans (CSPGs) are potential ligands because they inhibit adhesion and neurite outgrowth and are present in situ at barriers to neuronal growth. We therefore assayed purified CSPGs for their ability to inhibit homophilic cadherin-mediated adhesion and neurite outgrowth, as well as their ability to bind directly to the GalNAcPTase. A proteoglycan with a 250-kD core protein following removal of chondroitin sulfate chains (250-kD PG) inhibits cadherin-mediated adhesion and neurite outgrowth whether presented as the core protein or as a proteoglycan monomer bearing chondroitin sulfate. A proteoglycan with a 400-kD core protein is not inhibitory in either core protein or monomer form. Treatment of cells with phosphatidylinositol-specific phospholipase C, which removes cell surface GalNAcPTase, abolishes this inhibitory effect. Binding of the 250-kD core protein to cells is competed by the anti-GalNAcPTase antibody 1B11, suggesting that 1B11 and the 250-kD core protein bind to the same site or in close proximity. Moreover, soluble GalNAcPTase binds to the immobilized 250-kD core protein but not to the immobilized 400-kD core protein. Concomitant with inhibition of cadherin mediated adhesion, binding of the 250-kD core protein to the GalNAcPTase on cells results in the enhanced tyrosine phosphorylation of beta-catenin and the uncoupling of N-cadherin from its association with the cytoskeleton. Moreover, the 250-kD PG is present in embryonic chick retina and brain and is associated with the GalNAcPTase in situ. We conclude that the 250-kD PG is an endogenous ligand for the GalNAcPTase. Binding of the 250-kD PG to the GalNAcPTase initiates a signal cascade, involving the tyrosine phosphorylation of beta-catenin, which alters the association of cadherin with the actin-containing cytoskeleton and thereby inhibits adhesion and neurite outgrowth. Regulation of the temporal and spatial expression patterns of each member of the GalNacPTase/250-kD PG interactive pair may create opportunities for interaction that influence the course of development through effects on cadherin-based morphogenetic processes.

Restricted appearance of tenascin and chondroitin sulphate proteoglycans after transection and sprouting of adult rat postcommissural fornix

Transected fibres of the adult rat postcommissural fornix sprout over short distances but fail to traverse the lesion site and terminate in close vicinity to the wound. As a step in defining the molecular environment responsible for regeneration failure at the lesion site, we have used immunocytochemistry to analyse the spatio-temporal expression pattern of two putative growth-inhibitory extracellular matrix components, tenascin and chondroitin sulphate proteoglycans and their topographical relationship to the sprouting axons. Both tenascin and chondroitin sulphate proteoglycan labelling appeared after fornix transection and were confined to the immediate vicinity of the lesion site. While tenascin-labelling was associated with astrocytes and microglia/macrophages, which accumulate preferentially at the tract borders, chondroitin sulphate proteoglycan labelling appeared as a homogeneous meshwork around the wound. Tenascin-like immunoreactivity disappeared between 17 days and 4 weeks, but chondroitin sulphate proteoglycan staining persisted at least up to 14 months after transection. Regrowing fornix fibres invaded and elongated within the chondroitin sulphate proteoglycan-immunopositive region up to the lesion site, where they terminated. This zone of axonal growth inhibition was neither characterized by an increase of chondroitin sulphate proteoglycan immunoreactivity nor by the presence of tenascin-immunopositive structures. The spatio-temporal distribution patterns of tenascin and chondroitin sulphate proteoglycan and the permeability of the chondroitin sulphate proteoglycan-immunopositive region for sprouting axons do not support the hypothesis that chondroitin sulphate proteoglycan alone and/or tenascin inhibit the advance of sprouting fornix fibres.

Oriented growth of regenerating axons in axolotl forelimbs is consistent with guidance by diffusible factors from distal nerve stumps

Previous studies have shown that when peripheral nerves in axolotl limbs are cut and surgically misdirected, regenerating axons grow back to the original pathways and innervate their correct muscles. In the present study however, we demonstrate that when given a choice between their correct nerve stump and an incorrect stump (forearm flexor nerve), regenerating extensor cranialis nerve axons grow towards both pathways. This result suggests that the directed growth of regenerating axons in the peripheral nervous system may be in response to factor(s) released from the distal nerve stumps, but that in this region of the limb, axons were unable to differentiate between correct and incorrect pathways. Growing axons appeared to be accompanied by neural sheath cells, whilst activated macrophages remained near the cut nerve stumps. Possible mechanisms by which regenerating axons may eventually innervate their correct targets are discussed.

Macrophages, microglia, and astrocytes are rapidly activated after crush injury of the goldfish optic nerve: a light and electron microscopic analysis

Several matrix and adhesion molecules in fish optic nerve, which are constitutively expressed, are increased during axonal regeneration and are primarily associated with nonneuronal cells (W.P. Battisti, Y. Shinar, M. Schwartz, P. Levitt, and M. Murray [1992] J. Neurocytol. 21:557-573). The current study examines the reactions of specific cell types to optic nerve crush and axonal regeneration. The goldfish optic nerve contains macroglia and microglia as well as a population of monocyte-derived cells (granular macrophages) unique to goldfish. Two cell types were OX-42 positive (granular macrophages and microglia), indicating monocyte lineage, each with a distinct morphology and distribution within the nerve. Within hours of the optic nerve crush, the number of OX-42-labeled cell profiles increased near the crush site, remained elevated during the time axons were elongating, and then declined. Microglia, but not granular macrophages, were phagocytically active. Astrocytes are readily identified in the normal optic nerve, but they exhibited marked morphologic changes within hours of injury, which is consistent with the contribution these cells make to the altered environment. Oligodendroglia could not be reliably identified in regenerating optic nerves until myelin was formed. A comparison of the distribution of OX-42-labeled cells with that of transforming growth factor beta-1 (TGF-beta 1) and tenascin suggests that these molecules are expressed by granular macrophages. Tenascin staining may be additionally associated with astrocytes and/or microglia. The rapid response of these nonneuronal cells to injury, their rapid phagocytic activity, and the secretion of growth-promoting factors by these cells likely contributes to the environment that supports robust regeneration by optic axons in the goldfish.

Boundaries and inhibitory molecules in developing neural tissues

Numerous studies of the past decade have illuminated the importance of intercellular adhesion events for neural pattern formation. It has been documented that members of the Ig and cadherin gene superfamilies, that glycoproteins and, probably to some extent, proteoglycans of the extracellular matrix play a role in this context. Recent observations suggest that, in addition to adhesive interactions, repulsive and/or inhibitory phenoma are also of importance in regulating neural pattern formation. Several molecules are under study which are considered possible mediators of inhibitory interactions in the nervous system. The hypothesis has been advanced that some of these might be partially responsible for restrictive, boundary-like properties ascribed to glial cells in developing and regenerating tissues. The current review summarizes these studies and focusses on molecular aspects of boundary and compartmentation phenomena.

Tenascin-C binds heparin by its fibronectin type III domain five

Two sites on tenascin mediate interactions with glycosaminoglycan chains of proteoglycans. One is situated on the fibrinogen-like domain, whereas the other lies within the fibronectin type III homology region (Aukhil, I., Joshi, P., Yan, Y.Z., and Erickson, H.P. (1993) J. Biol. Chem. 268, 2542-2553.). We now characterize the latter binding site more closely by means of recombinant protein fragments derived from the type III homology region of tenascin. Using a heparin-Sepharose column, we localize the second heparin binding site to the fifth fibronectin type III domain. This is confirmed in solid phase assays by incubation of fusion proteins with biotin-labeled heparin. In addition, we demonstrate the binding of heparan sulfate and dermatan sulfate to domain five. Molecular modelling of this domain reveals a conserved heparin-binding motif that we propose as the putative binding site. The fact, that different glycosaminoglycans may bind to this domain, implies that different classes of proteoglycans may in vivo compete for the same site.

Further characterization of axonally transported proteoglycans

We report further analysis of axonally transported proteoglycans in soluble and membranous subfractions of goldfish optic tectum. Distribution of transported 35SO4 radioactivity was 35.2% soluble, 63.4% Triton-NaCl extractable and 1.4% unextracted. Proteoglycans isolated on DEAE cellulose were treated with chondroitinase AC or nitrous acid and remaining heparan sulfate proteoglycans (HSPGs) and chondroitin sulfate proteoglycans (CSPGs) were sized on Sepharose CL-6B. Kav values and estimated molecular weights were: Soluble CSPG-0.36 (160 kDa), Triton-NaCl extracted CSPG-.031 (200 kDa), Soluble HSPG-0.37 (150 kDa), Triton-NaCl extracted HSPG-0.37 (150 kDa). For constituent CS and HS chains the Kav values and estimated molecular weights on CL-6B were: Soluble CS-0.55 (15 kDa), Triton-NaCl extracted CS-0.55 (15 kDa), Soluble HS-0.59 (13 kDa) and Triton-NaCl extracted HS-0.65 (9 kDa). CS was shown to be sulfated exclusively at carbon 4 for both soluble and Triton NaCl extracted fractions.

Immunohistochemical localization of chondroitin sulfate proteoglycan and tenascin in the human eye compared with the HNK-1 epitope

BACKGROUND

A previous study revealed the HNK-1 epitope in the human ciliary body beneath the ciliary epithelium. The molecules bearing this 3-sulphoglucuronic acid-containing oligosaccharide epitope in the eye remain unknown. As chondroitin sulphate proteoglycan (CSPG) and tenascin are potential candidates as bearers of the HNK-1 epitope, their distribution in the human eye was compared with that of the HNK-1 epitope.

METHODS

Fifty-five formalin-fixed, paraffin-embedded human eyes, including 20 normal eyes and 35 eyes with exfoliation syndrome or glaucoma, were studied immunohistochemically with monoclonal antibody (MAb) CS-56 to CSPG, MAb TN2 to tenascin, and MAbs HNK-1 and VC1.1 to the HNK-1 epitope. Additionally, four frozen lens capsules with exfoliation material were studied by indirect immunofluorescence.

RESULTS

A population of dendritic cells in the inner connective tissue layer of the ciliary body and exfoliation material were immunoreactive with antibodies to the HNK-1 epitope, but no labelling for CSPG and tenascin was seen in them, including frozen sections. The inner surface of the nonpigmented ciliary epithelium was reactive for the HNK-1 epitope, and at the ora serrata also for CSPG. In some eyes with glaucoma, immunoreaction for CSPG and tenascin was seen beneath the epithelium and endothelium of the cornea. The nerve fibre layer of the retina was labelled for tenascin. In the sclera, all antibodies labelled the ground substance, and in some large blood vessels immunoreaction for CSPG and tenascin was seen subendothelially.

CONCLUSION

Apart from the sclera, the distribution of CSPG and tenascin was different form that of the HNK-1 epitope, suggesting that this carbohydrate epitope may not be borne by these molecules in the human ciliary body.

Polyclonal antibodies against NCAM and tenascin delay endplate reinnervation

Experiments were performed to block molecules with antibodies which are upregulated in nerve and muscle following denervation. The delay in endplate reinnervation was taken as a measure for their involvement in regeneration. Gluteus maximus muscles of 86 male CBA/J mice were hemidenervated by freezing the caudal gluteal nerve at a defined position. The degree of reinnervation was evaluated in identified endplates by repeated vital staining of ACh receptors with rhodaminated alpha-bungarotoxin and of axons with 4Di-2ASP. Normally, endplates were completely reinnervated by 13-14 days (108 endplates in seven muscles). After daily application of polyclonal antibodies against NCAM or tenascin, reinnervation was significantly delayed. Preimmune serum, rabbit immunoglobulins or saline did not show this effect. Several monoclonal antibodies against NCAM (H-28) and tenascin (576, 578, 630, 633) showed a tendency but no significant effect. It is concluded that both NCAM and tenascin, upregulated after denervation, are involved in axon guidance and/or endplate reinnervation.