The high-molecular-weight J1 glycoproteins are immunochemically related to tenascin

Demystifying the extracellular matrix and its proteolytic remodeling in the brain: structural and functional insights

The extracellular matrix (ECM) plays diverse roles in several physiological and pathological conditions. In the brain, the ECM is unique both in its composition and in functions. Furthermore, almost all the cells in the central nervous system contribute to different aspects of this intricate structure. Brain ECM, enriched with proteoglycans and other small proteins, aggregate into distinct structures around neurons and oligodendrocytes. These special structures have cardinal functions in the normal functioning of the brain, such as learning, memory, and synapse regulation. In this review, we have compiled the current knowledge about the structure and function of important ECM molecules in the brain and their proteolytic remodeling by matrix metalloproteinases and other enzymes, highlighting the special structures they form. In particular, the proteoglycans in brain ECM, which are essential for several vital functions, are emphasized in detail.

Putative Inhibitory Extracellular Matrix Molecules Do Not Prevent Dorsal Root Regeneration into Fetal Spinal Cord Transplants

We examined the distribution of several extracellular matrix molecules (ECM) and their relationship to regenerating axons in embryonic day 14 spinal cord transplants 1 to 12 weeks after transplantation into adult rats. We used immunocytochemical tech niques to label chondroitin sulfate proteoglycans (CSPGs) and tenascin-C in adjacent sections. Synthesis of these molecules by astrocytes is thought to be one mechanism by which astrocytes inhibit regeneration in the central nervous system (CNS); glial fibrillary acidic protein antibody was used to label astrocytes and examine their rela tionship to both the ECM molecules and regenerating calcitonin gene-related pep tide (CORP)-contammg dorsal roots. We also compared the expression and distribu tion of these five markers in transplants with normal spinal cord development.

Review : Glial Boundaries and Scars: Programs for Normal Development and Wound Healing in the Brain

Early studies of glial boundaries, which are composed of immature astrocytes and extracellular matrix mol ecules (which they express), initially offered insight into the partitioning that occurs in the developing nervous system. More recently, however, it has been suggested that similar "boundaries" may have important roles in other processes occurring in the brain, including repair after traumatic brain injury. As more is understood about the expression and function of boundary molecules and glia, their potential importance is becoming apparent in numerous neuropathological conditions, including neurodegeneration and neuroregeneration in Alzheimer's and Huntington's diseases as well as in brain neoplasms. Furthermore, before we can hope to fully understand and facilitate regeneration in the compromised brain, our knowledge of the glial boundary, both during development and in the adult, must be more complete. The Neuroscientist 1:142-154, 1995

Chondroitin sulphate proteoglycans: preventing plasticity or protecting the CNS?

It is well established that axonal regeneration in the adult CNS is largely unsuccessful. Numerous axon-inhibitory molecules are now known to be present in the injured CNS, and various strategies for overcoming these obstacles and enhancing CNS regeneration have been experimentally developed. Recently, the use of chondroitinase-ABC to treat models of CNS injury in vivo has proven to be highly beneficial towards regenerating axons, by degrading the axon-inhibitory chondroitin sulphate glycosaminoglycan chains found on many proteoglycans in the astroglial scar. This enzyme has now been shown to restore synaptic plasticity in the visual cortex of adult rats by disrupting perineuronal nets, which contain high levels of chondroitin sulphate proteoglycans (CS-PGs) and are expressed postnatally around groups of certain neurons in the normal CNS. The findings suggest exciting prospects for enhancing growth and plasticity in the adult CNS; however, some protective roles of CS-PGs in the CNS have also been demonstrated. Clearly many questions concerning the mechanisms regulating expression of extracellular matrix molecules in CNS pathology remain to be answered.

Immunohistological Localization of Tenascin in the Developing and Lesioned Adult Mouse Optic Nerve

To gain insight into the morphogenetic functions of the recognition molecule tenascin in the central nervous system, we have studied its localization in the developing and lesioned adult mouse optic nerve using light and electron microscopic immunocytochemistry. Since tenascin is a secreted molecule, we have analysed the tenascin-synthesizing cells in tissue sections of retinae and optic nerves by in situ hybridization. A weak and homogeneous tenascin immunoreactivity was detectable in the developing retinal nerve fibre layer and optic nerve of 14-day-old mouse embryos, the earliest developmental age investigated. In the optic nerve of neonatal and 1-week-old animals, a high number of tenascin messenger RNA (mRNA)-containing cells were present, and antibodies to tenascin labelled the surfaces of astrocytes and unmyelinated retinal ganglion cell axons. With increasing age, expression of tenascin in the optic nerve was down-regulated at the mRNA and protein levels. At the fourth postnatal week, blood vessels in the optic nerve and collagen fibrils in the vicinity of meningeal fibroblast-like cells still showed significant immunoreactivity, but the optic nerve tissue proper no longer did so. In adult animals, tenascin was no longer detectable in association with blood vessels located in the myelinated part of the optic nerve, and meninges were only weakly immunoreactive. Also, tenascin mRNA-containing cells were no longer detectable in the myelinated part of the adult mouse optic nerve and few labelled cells were found in the meninges. In the retina, ganglion cells contained no detectable levels of tenascin mRNA at any of the developmental ages analysed. No significant up-regulation of tenascin expression was seen in the nerve tissue proper of transected proximal (i.e. retinal) and distal (i.e. cranial) optic nerve stumps of adult mice during the first 4 weeks after lesioning, the time period studied. However, collagen fibrils associated with meningeal fibroblast-like cells and located near the lesion site became strongly tenascin-immunoreactive 2 days after lesioning. Also, some blood vessels at the lesion site became immunoreactive. We conclude that tenascin in the optic nerve is synthesized by glial cells and not by retinal ganglion cells. The detectability of tenascin at embryonic ages suggests that it may mediate neurite growth in vivo. The absence of a strong, lesion-induced up-regulation of tenascin expression in the regeneration-prohibitive mouse optic nerve contrasts with the lesion-induced pronounced up-regulation in the regeneration-permissive peripheral nervous system, and may indicate a functional involvement of tenascin in regenerative processes. The high tenascin positivity of collagen fibrils at early postnatal ages and after lesioning suggests that tenascin expression may be correlated with mitotic activity of the associated meningeal fibroblast-like cells. Finally, tenascin may be involved in the process of vascularization, since the molecule is associated with blood vessels in developing and adult lesioned, but not intact adult, optic nerves.

Divalent Cations Modulate the Inhibitory Substrate Properties of Murine Glia-derived J1-160 and J1-180 Extracellular Matrix Glycoproteins for Neuronal Adhesion

J1-160 and J1-180 are developmentally late appearing J1 extracellular matrix glycoproteins derived from oligodendrocytes. They prevent adhesion of neurons (but not of astrocytes or fibroblasts) when offered as a substrate in mixture with laminin (Pesheva et al., J. Cell Biol., 109, 1765 - 1778, 1989). In the present study we have examined the influence of divalent cations on the inhibitory substrate properties of J1-160/180 glycoproteins towards adhesion of neurons. By metal chelate affinity chromatography, we show that J1-180, but not J1-160, binds Ca2+, while both J1 components are capable of binding Zn2+ and other divalent metal ions. Divalent cation binding was observed by gel filtration, aggregation assays with coated latex beads and electron microscopic examination to elicit aggregation of the molecules. Divalent cation binding also affects their non-permissive substrate properties towards neurons from early postnatal mouse cerebellum. Without divalent cations, J1-160 and J1-180 are inhibitory for substrate adhesion of neurons independently of the adhesive substrate present (laminin or poly-l-lysine). This effect is neutralized when J1-180 is preincubated with Ca2+ or Zn2+ prior to coating as substrate. In contrast, preincubation with Ca2+ ions does not affect the inhibitory substrate properties of J1-160 under these conditions. These observations show that J1-160/180 molecules may undergo self-aggregation in a divalent cation-dependent mechanism, which correlates with the neutralization of their inhibitory effect on neuronal adhesion. The aggregation state of the molecules may thus influence the process of myelination by a homophilic binding mechanism and determine the effectiveness of neurite extension during central nervous system development and under traumatic conditions in the adult.

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

The yin and yang of tenascin-R in CNS development and pathology

An important biological consequence of the initial interactions between the cell surface and its extracellular environment is the diversity of cellular responses ranging from overt repulsion or avoidance reaction to stable adhesion or final positioning. It is now evident that positive and negative guiding mechanisms are equally relevant to normal pattern formation during development and decisive for the outcome of a regenerative process. In this context, the present review summarizes the knowledge about the extracellular matrix glycoprotein tenascin-R, a member of the tenascin gene family. In contrast to all other known family members, tenascin-R is exclusively expressed in the central nervous system of vertebrates by oligodendrocytes and neuronal subsets at later developmental stages and in adulthood. We focus on the glycoprotein's structure, tissue distribution and functional implications in the molecular control of axon targeting, neural cell adhesion, migration and differentiation during nervous system morphogenesis and pathology.

Heat shock produces periodic somitic disturbances in the zebrafish embryo

Environmental influences are known to produce segmental defects in a variety of organisms. In this paper we report upon segmental aberrations produced by brief heat shocks delivered to developing zebrafish embryos. The initial defects in the segmental pattern of somitic boundaries and motoneuron axon outgrowth were usually observed five somites caudal to the somite which was forming at the time of heat shock application. Segmental defects in zebrafish embryos exposed to a single heat shock treatment can occur in a periodic pattern similar to the multiple disturbances observed to occur in chick embryos. These data are discussed with regard to models involving cell cycle synchrony or 'clock and wavefront' schemes in the process of somitogenesis.

The expression of tenascin-C along the lamprey olfactory pathway during embryonic development and following axotomy-induced replacement of the olfactory receptor neurons

Extracellular guidance molecules affect the pathway of growing axons by both attractive and repulsive interactions. Tenascin-C, a glycoprotein of the extracellular matrix, is localized along developing axonal pathways where it may function by repulsion, restricting axons within specific boundaries. The lamprey olfactory pathway offers an advantageous model for studying the role of extracellular matrix proteins in axon guidance because the entire pathway is readily seen in horizontal sections and because lesioning the olfactory nerve will induce the system into a new phase of coordinated neurogenesis and axon outgrowth. Although tenascin-C expression was absent during embryonic development, olfactory nerve fascicles contained tenascin-C-immunoreactivity (IR) during the larval stage. During retrograde degeneration, the fascicles lost tenascin-C-IR. Diffuse unfasciculated axonal processes extending from the olfactory epithelium did not express tenascin-C-IR; however, acetylated tubulin and GAP-43-IR was present, indicating axonal outgrowth. When the newly extended axons of olfactory receptor neurons converged to form fascicles, tenascin-C-IR was evident within the fascicular boundaries. The absence of tenascin-C expression when axonal process were short and diffuse, and its return when axons coalesced within fascicles, supports the view that tenascin-C functions as a boundary molecule in the olfactory pathway.

Differential expression of tenascin by astrocytes associated with the supraoptic nucleus (SON) of hydrated and dehydrated adult rats

The present study evaluated the expression of tenascin by astrocytes in the supraoptic nucleus and associated ventral glial limitans (SON-VGL) under conditions that induce reversible changes in neuronal organization (dehydration and rehydration). Immunostaining of astroglia cultured from rat neonatal SON-VGL confirmed that these cells are capable of both expressing and secreting tenascin. Observations of immunostained tissue sections from adult rats revealed tenascin immunoreactivity primarily in the VGL and dendritic zone, subjacent to SON neuronal somata. Comparison of immunostained tissues from hydrated and dehydrated animals showed an apparent decrease in the intensity of immunostaining with dehydration. Subsequent Western blots of similar tissues confirmed the presence of the 210-220-kDa tenascin protein in the SON-VGL. SON-VGL tissues from control, dehydrated, and rehydrated rats were then studied by using SDS-PAGE and quantitative gel densitometry. A consistent decrease in tenascin concentration was observed by 6 days of dehydration that, with rehydration, reversed back toward or beyond control levels. Together, these observations indicate that SON-VGL astrocytes variably express tenascin and that this protein may play a role in adult SON plasticity.

Seizures induce tenascin-C mRNA expression in neurons

Tenascin-C, an extracellular matrix glycoprotein that exhibits both growth-promoting and growth-inhibiting properties, is produced in the CNS mainly by astrocytes. In the present study we show that kainate-induced seizures result in an increased expression of tenascin-C in rat brain. Tenascin-C mRNA was increased mainly in the granule cell layer of the hippocampal complex, but tenascin-C mRNA expression was also observed in the pyriform cortex and amygdalo-cortical nucleus. Double labelling experiments using tenascin-C probes and MAP2 (a neuronal microtubule associated protein) antibodies revealed many neurons in these layers that express tenascin-C mRNA. These results support our previous findings of an increased tenascin-C immunoreactivity associated with the axons of granule cells. Tenascin-C expression is rapidly induced by seizures (6 h), preceding any lesion and glial reaction. In this pathological condition tenascin-C appears to be produced by both glia and neurons. The functional repercussions on the scarring and remodelling processes are also discussed.

Astrocytes and extracellular matrix following intracerebral transplantation of embryonic ventral mesencephalon or lateral ganglionic eminence

Transplantation of embryonic neurons to the adult mammalian central nervous system (CNS) offers the possibility of re-establishing neural functions lost after traumatic injuries or neurodegenerative disease. In the adult CNS, however, transplanted neurons and their growing neurites can become confined to the graft region, and there may also be a relative paucity of afferents innervating grafted neurons. Because glia may influence the development and regeneration of CNS neurons, the present study has characterized the distribution of astrocytes and developmentally regulated glycoconjugates (chondroitin-6-sulfate proteoglycan and tenascin) within regions of the embryonic mouse CNS used as donor tissues, and in and around these grafts to the adult striatum and substantia nigra. Both chondroitin-6-sulfate proteoglycan and tenascin are present in the embryonic ventral mesencephalon (in association with radial glia and their endfeet, and glial boundaries that cordon off the ventral mesencephalon dopamine neuron migratory zone) and lateral ganglionic eminence before transplantation, and they are conserved within grafts of these tissues to the adult mouse. Neostriatal grafts exhibit a heterogeneous pattern of astrocyte and extracellular matrix molecule distribution, unlike ventral mesencephalon grafts, which are rather homogeneous. There is evidence to suggest that, in addition to variation in astroglial/extracellular matrix immunostaining within different compartments in striatal grafts to either adult striatum or substantia nigra, there are also boundaries between these compartments that are rich in glial fibrillary acidic protein/extracellular matrix components. Substantia nigra grafts, with cells immunoreactive for tyrosine hydroxylase, are also rich in immature astroglia (RC-2-immunopositive), and as the astroglia mature (to glial fibrillary acidic protein-positive) over time the expression of chondroitin-6-sulfate proteoglycan and tenascin is also reduced. These same extracellular matrix constituents, however, are only slightly up-regulated in an area of the adult host which surrounds the grafted tissue. Glial scar components exhibit no obvious differences between grafts from different sources to homotopic (e.g., striatum to striatum) or heterotopic (e.g., substantia nigra to striatum) sites, and likewise grafts of non-synaptically associated structures (e.g., cerebellum to striatum), needle lesions or vehicle injections all yield astroglial/extracellular matrix scars in the host that are indistinguishable. Studies utilizing the ROSA-26 transgenic (beta-galactosidase-positive) mouse as a host for non-5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside-labeled grafts indicate that the early astroglial/extracellular matrix response to the graft is derived from the surrounding host structures. Furthermore, biochemical analysis of one of the "boundary molecules", tenascin, from the developing ventral mesencephalon versus adult striatal lesions, suggests that different forms of the molecule predominate in the embryonic versus lesioned adult brain. Such differences in the nature and distribution of astroglia and developmentally regulated extracellular matrix molecules between donor and host regions may affect the growth and differentiation of transplanted neurons. The present study suggests that transplanted neurons and their processes may flourish within graft versus host regions, in part due to a confining glial scar, but also because the extracellular milieu within the graft site remains more representative of the developmental environment from which the donor neurons were obtained [Gates M. A., et al. (1994) Soc. Neurosci. Abstr. 20, 471].

Human tenascin-R. Complete primary structure, pre-mRNA alternative splicing and gene localization on chromosome 1q23-q24

We have established the primary structure of human tenascin-R (TN-R), a component of the extracellular matrix of the central nervous system, by sequencing cDNA clones which cover its complete coding region. The deduced amino acid sequence of human TN-R (1358 amino acids) showed a homology to chicken and rat TN-R of 75 and 93%, respectively. By reverse transcriptase-polymerase chain reaction we have studied the existence of TN-R isoforms generated by pre-mRNA alternative splicing in various human astrocytomas and meningiomas. Our findings demonstrate the existence of a human isoform in which one fibronectin-like repeat is omitted. Northern blot analysis of the poly(A)-rich RNA from different tissues showed two mRNAs having sizes of about 10 and 11 kilobases. Using DNA from a panel of human-hamster and human-mouse somatic cell hybrids and by fluorescence in situ hybridization, we have assigned the gene for human TN-R to the region 1q23-q24. The mouse mutation loop-tail (Lp), which has been proposed as a model for human neural tube defects, maps to region of mouse chromosome 1 syntenic with human 1q23-q24.

Tenascin-C contains distinct adhesive, anti-adhesive, and neurite outgrowth promoting sites for neurons

The glia-derived extracellular matrix glycoprotein tenascin-C (TN-C) is transiently expressed in the developing CNS and may mediate neuron-glia interactions. Perturbation experiments with specific monoclonal antibodies suggested that TN-C functions for neural cells are encoded by distinct sites of the glycoprotein (Faissner, A., A. Scholze, and B. Götz. 1994. Tenascin glycoproteins in developing neural tissues--only decoration? Persp. Dev. Neurobiol. 2:53-66). To characterize these further, bacterially expressed recombinant domains were generated and used for functional studies. Several short-term-binding sites for mouse CNS neurons could be assigned to the fibronectin type III (FNIII) domains. Of these, the alternatively spliced insert TNfnA1,2,4,B,D supported initial attachment for both embryonic day 18 (E18) rat and postnatal day 6 (P6) mouse neurons. Only TNfn1-3 supported binding and growth of P6 mouse cerebellar neurons after 24 h, whereas attachment to the other domains proved reversible and resulted in cell detachment or aggregation. In choice assays on patterned substrates, repulsive properties could be attributed to the EGF-type repeats TNegf, and to TNfnA1,2,4. Finally, neurite outgrowth promoting properties for E18 rat hippocampal neurons and P0 mouse DRG explants could be assigned to TNfnB,D, TNfnD,6, and TNfn6. The epitope of mAb J1/tn2 which abolishes the neurite outgrowth inducing effect of intact TN-C could be allocated to TNfnD. These observations suggest that TN-C harbors distinct cell-binding, repulsive, and neurite outgrowth promoting sites for neurons. Furthermore, the properties of isoform-specific TN-C domains suggest functional significance of the alternative splicing of TN-C glycoproteins.

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.

Tenascins, a growing family of extracellular matrix proteins

The tenascins are a family of large multimeric extracellular matrix proteins consisting of repeated structural modules including heptad repeats, epidermal growth factor (EGF)-like repeats, fibronectin type III repeats, and a globular domain shared with the fibrinogens. The tenascins are believed to be involved in the morphogenesis of many organs and tissues. To date three members of the tenascin family have been described, tenascin-C, tenascin-R, and tenascin-X. Tenascin-R seems to be specific for the central and peripheral nervous system, tenascin-X is most prominent in skeletal and heart muscle, while tenascin-C is present in a large number of developing tissues including the nervous system, but is absent in skeletal and heart muscles. Tenascin-C was the original tenascin discovered, partly because of its overexpression in tumors. Inferring from cell biological studies, it has been proposed that tenascin-C is an adhesion-modulating protein.

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.

Tenascin-C expression by neurons and glial cells in the rat spinal cord: changes during postnatal development and after dorsal root or sciatic nerve injury

We have used in situ hybridization with a digoxigenin-labelled probe for tenascin-C mRNA and immunocytochemistry with antibodies against tenascin-C, glial fibrillary acidic protein, OX-42 and the 200 kDa neurofilament protein to study the expression, distribution and cellular relationships of tenascin-C mRNA and protein in the developing (postnatal) and adult spinal cord of rat, and the effects thereon of dorsal root, ventral root and sciatic nerve injuries. The most interesting finding was that on postnatal day 7 (P7), P14 and in the adult, but not on P0 or P3, a group of neurons in the lumbar ventral horn expressed the tenascin-C mRNA gene. They represented about 5% of ventral horn neurons in the adult and were among the smaller such neurons. Since 40-60% of such cells were lost at P13 following sciatic nerve crush on P0, some were almost certainly motor neurons. In addition, we found that at P0 and P3, mRNA-containing glial cells were widespread in grey and white matter but sparse in the developing dorsal columns; tenascin-C immunofluorescence showed a similar distribution. By P7 there were fewer mRNA-containing cells in the ventral horns and in the area of the dorsal columns containing the developing corticospinal tract where immunofluorescence was also weak. At P14 there were no glial-like mRNA-containing cells in the grey matter; such cells were confined to the periphery of the lateral and ventral white columns but were present throughout the dorsal columns where tenascin-C immunofluorescence was also strong. No glial-like mRNA-containing cells were present in the adult lumbar spinal cord and tenascin-C immunofluorescence was confirmed to irregular patches in the ventral horn, especially around immunonegative cell bodies of small neurons, a zone around the central canal, and a thin zone adjacent to the glia limitans. Thus the expression of tenascin-C is differentially developmentally regulated in the grey matter and in different parts of the white matter. Three days after injury of dorsal roots L4-6, many cells containing tenascin-C mRNA, some identified as glial fibrillary acidic protein-positive astrocytes, were present in the ipsilateral dorsal column, but were rare after longer survivals. Immunoreactivity, however, was elevated in the ipsilateral dorsal column at 3 days, remained high for several months and disappeared at 6.5 months. Dorsal root injury had no effect on tenascin-C mRNA or protein in the grey matter. Sciatic nerve or ventral root injury had no effect on these molecules in any part of the spinal cord.

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.

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.

Focal brain injury and upregulation of a developmentally regulated extracellular matrix protein

Tenascin is an extracellular matrix glycoprotein expressed during both normal development and neoplastic growth in both neural and nonneural tissues. During development of the central nervous system (CNS), tenascin is synthesized by glial cells, in particular by immature astrocytes, and is concentrated in transient boundaries around emerging groups of functionally distinct neurons. In the mature CNS, only low levels of the glycoprotein can be detected. The present study demonstrates that following trauma to the adult human cerebral cortex, discrete populations of reactive astrocytes upregulate their expression of tenascin and dramatically increase their transcription of the tenascin gene. The enhanced expression of tenascin may be involved in CNS wound healing, and may also affect neurite growth within and around a brain lesion.

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.

In vitro analyses of neurite outgrowth indicate a potential role for tenascin-like molecules in the development of insect olfactory glomeruli

Tenascin-like material is associated with glial cells that form borders around developing glomerular units in the olfactory (antennal) lobe of the moth Manduca sexta and is present at critical stages of glomerulus formation (Krull et al., 1994, J. Neurobiol. 25:515-534). Tenascin-like immunoreactivity declines in the mature lobe, coincident with a wave of synapse formation within the glomeruli and glomerulus stabilization. Tenascin-like molecules associated with neuropilar glia are in the correct position to influence the branching patterns of growing neurites by constraining them to glomeruli. In this study, we examine the growth of cultured moth antennal-lobe neurons in response to mouse CNS tenascin. Uniform tenascin provides a poor substrate for cell-body attachment and neurite outgrowth. Neuronal cell bodies provided with a striped substratum consisting of tenascin and concanavalin-A (con-A)/laminin attach preferentially to con-A/laminin lanes. Most neurons restrict their branching to con-A/laminin lanes both at early and later times in culture but others send processes across multiple tenascin and con-/laminin lanes in an apparently indiscriminate manner. Tenascin can inhibit the neuritic outgrowth of most antennal-lobe neurons, and this raises the possibility that the tenascin-like molecules associated with neuropilar glia in vivo act to constrain growing neurites to glomeruli. Thus, glial cells, acting in concert with olfactory axons, might act to promote glomerular patterns of branching by antennal-lobe neurons.

Isolation of a neural chondroitin sulfate proteoglycan with neurite outgrowth promoting properties

Proteoglycans are expressed in various tissues on cell surfaces and in the extracellular matrix and display substantial heterogeneity of both protein and carbohydrate constituents. The functions of individual proteoglycans of the nervous system are not well characterized, partly because specific reagents which would permit their isolation are missing. We report here that the monoclonal antibody 473HD, which binds to the surface of early differentiation stages of murine astrocytes and oligodendrocytes, reacts with the chondroitin sulfate/dermatan sulfate hybrid epitope DSD-1 expressed on a central nervous system chondroitin sulfate proteoglycan designated DSD-1-PG. When purified from detergent-free postnatal days 7 to 14 mouse brain extracts, DSD-1-PG displays an apparent molecular mass between 800-1,000 kD with a prominent core glycoprotein of 350-400 kD. Polyclonal anti-DSD-1-PG antibodies and monoclonal antibody 473HD react with the same molecular species as shown by immunocytochemistry and sequential immunoprecipitation performed on postnatal mouse cerebellar cultures, suggesting that the DSD-1 epitope is restricted to one proteoglycan. DSD-1-PG promotes neurite outgrowth of embryonic day 14 mesencephalic and embryonic day 18 hippocampal neurons from rat, a process which can be blocked by monoclonal antibody 473HD and by enzymatic removal of the DSD-1-epitope. These results show that the hybrid glycosaminoglycan structure DSD-1 supports the morphological differentiation of central nervous system neurons.

Spatiotemporal pattern of expression of tenascin-like molecules in a developing insect olfactory system

During the development of the olfactory (antennal) lobe of the moth Manduca sexta, olfactory sensory axons induce glomerular branching patterns in their target neurons. Glial cells, by surrounding the developing glomerular template, are thought to mediate the developmental influence of olfactory axons on these branching patterns. Previous studies have demonstrated that, in the absence of glia, neurons in the antennal lobe branch in an aglomerular fashion, even in the presence of competent antennal axons (Oland and Tolbert, 1988, J. Comp. Neurol. 278:377-387; Oland et al., 1988, J. Neurosci. 8:353-367). We have begun to explore the molecular basis by which glial cells could influence patterns of neurite branching. For this work, we have utilized immunocytochemical techniques and a partial biochemical analysis to demonstrate that molecules antigenically similar and comparable in size to mammalian tenascin are localized on the neuropil-associated glial cells that form borders around glomeruli in the developing antennal lobe. These tenascin-like molecules associated with neuropilar glia are present at critical stages of glomerulus development; tenascin-like immunoreactivity declines after glomeruli form and become stabilized. Neither the arrival nor the absence of antennal axons in the lobe induces changes in either the molecular forms or the amounts of tenascin-like molecules. The spatiotemporal pattern of expression of tenascin-like molecules suggests that they are in a position to participate in the formation of a glomerular neuropil and could form a molecular barrier that constrains neurite outgrowth strictly to glomeruli.

Identification of cDNA clones expressed selectively during the critical period for visual cortex development by subtractive hybridization

We have used the method of subtractive hybridization to isolate cDNA clones of mRNAs expressed in abundance in the visual cortex of 30-day-old kittens but absent or in lower abundance in the adult cat visual cortex. Of 12,000 colonies screened, 200 clones which hybridized to the subtracted probe were isolated and characterized. Northern blots confirmed the specificity of the vast majority of the isolated clones. 120 of the 200 clones were sequenced and the EMBL and GenBank (release 76) database were searched for known identities using FASTA and BLAST programs. Twenty-seven of these sequenced clones were identifiable. The identities showed that these sequences code for proteins involved in a variety of cellular processes. These include cell-cell interaction (TAPA-1, contactin, tachykinin receptor, phospholipase A2), cellular remodeling (C1q beta isoform, heat shock protein), neurofilament assembly (alpha tubulin and alpha internexin), neurotransmitter release (VAMP-2, amphiphysin, carboxypeptidase E, scg 10 and proton channel), energy metabolism (mitochondrial hinge protein, ADP/ATP transporter, cytochrome oxidase subunits), RNA processing (helix destabilizing protein, ribonucleoprotein) and protein synthesis (eIF-4A initiation factor, ribosomal protein S27). The results show that gene expression in the kitten visual cortex differs rather little from that of the adult visual cortex since over 98% of the sequences appear common. The relatively rare kitten-specific sequences are likely to form the basis for the critical period plasticity in this system.

Tenascin mRNA isoforms in the developing mouse brain

The extracellular matrix glycoprotein tenascin is expressed in the developing mouse cerebellum as a group of four protein species of different molecular weights. The difference is most likely due to alternative splicing which is known to occur in tenascin mRNA within the region of the fibronectin type III repeats. In order to systematically analyze tenascin mRNA isoforms that would account for this heterogeneity, tenascin splice variants were isolated from mouse brain by the polymerase chain reaction (PCR). In agreement with Northern blot analysis, amplification by PCR revealed a general decrease in tenascin mRNA expression during development from embryonic and early postnatal to adult stages. This decrease was more pronounced for isoforms of high molecular weight compared to those of low molecular weight. In accord with the observations at the protein level, four splice variants were found to be predominantly expressed, containing insertions of either six, five, or one fibronectin type III repeat, or comprising no insertion. In addition, a minor splice variant with an insertion of four fibronectin type III repeats was isolated. Three of the isolated mRNA splice variants have not yet been described for mouse tenascin. Among them, an isoform containing six alternatively spliced repeats was found to include a novel fibronectin type III repeat. The sequence of this repeat displays 96.7% similarity to a corresponding type III repeat in human tenascin, revealing a strict evolutionary conservation between tenascin molecules from different species in the region of alternative splicing. Southern blot analysis of the amplified mRNA isoforms showed that the novel mouse type III repeat is confined to splice variants with an insertion of six fibronectin type III repeats. Furthermore, in situ hybridization on sections from mouse embryos indicated that tenascin-specific mRNAs containing the novel type III repeat are predominantly expressed in the central nervous system.

Differential expression of tenascin after denervation, damage or paralysis of mouse soleus muscle

The expression of the extracellular matrix molecule tenascin was studied by immunocytochemistry and Western blotting in soleus muscles of adult mice after nerve damage (denervation), muscle injury (induced by enforced running or freezing) and functional block of synaptic transmission (botulinum toxin). Enhanced expression of tenascin in the extracellular spaces around focally damaged muscle fibres was found already 10 h after onset of running on a motor-driven treadmill which causes muscle injury in soleus muscle. Tenascin expression reached a peak at 2-3 days post-exercise, after which it declined gradually and became undetectable by two weeks after injury. Similarly, cryo-damage of soleus muscles in situ led to upregulation of tenascin. Chronic muscle denervation after sciatic nerve transection caused a persistent (studied up to 31 days) expression of tenascin at denervated endplates and in intramuscular nerve branches but not in other tissue compartments. Local application of botulinum toxin Type A, which results in muscle inactivity but not in tissue degeneration, however, did not induce tenascin expression 12 h to 12 days post-injection. Expression of tenascin after denervation and muscle damage, but its absence after paralysis, were verified by SDS-PAGE and Western blot analysis. Independent of the type of injury (muscle, nerve or both) the known major isoforms of mouse tenascin, as judged by M(r) comparison, were re-expressed, with no preponderance of individual M(r) forms. These results show that tenascin expression in adult muscles is induced by both axon and muscle fibre damage but not by muscle inactivity. In contrast, NCAM, in accordance with previous observations, showed enhanced expression both as a result of inactivity and in association with tissue repair.

Influence of janusin and tenascin on growth cone behavior in vitro

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.

Localization of janusin mRNA in the central nervous system of the developing and adult mouse

Janusin (formerly termed J1-160/180) is an oligodendrocyte-derived extracellular matrix molecule which is restricted to the central nervous system and which is expressed late during development (Pesheva et al., J. Cell Biol., 1765-1778, 1989). To gain insights into the molecule's morphogenetic functions and to identify its cellular source in vivo, we have studied the localization of janusin messenger RNA in the optic nerve, retina and spinal cord and the expression of janusin protein in the spinal cord of developing and adult mice. Moreover, we have analysed optic nerve cell cultures and retinal cell suspensions in double-labelling experiments using a janusin-specific anti-sense complementary RNA probe and cell type-specific antibodies to identify the cell types containing janusin transcripts. In developing animals, oligodendrocytes were strongly labelled with the janusin anti-sense cRNA probe during the period of myelination. The number of labelled cells and intensity of the hybridization signal decreased significantly with increasing age. Interestingly, expression of janusin was not confined to oligodendrocytes. Some neuronal cell types and type-2 astrocytes present in optic nerve cell cultures also contained janusin transcripts. In contrast to oligodendrocytes, the number and labelling intensity of neurons containing janusin transcripts remained constant during postnatal development and into adulthood. Expression of janusin protein in the spinal cord was developmentally regulated, with a peak of expression in 2- or 3-week-old animals. The molecule was visible in the white and grey matter. In myelinated regions, it was associated with myelinated fibres and accumulated at nodes of Ranvier. These observations suggest that janusin may be of functional relevance for myelination.

Molecular characterization and in situ mRNA localization of the neural recognition molecule J1-160/180: a modular structure similar to tenascin

The oligodendrocyte-derived extracellular matrix glycoprotein J1-160/180 is a recognition molecule expressed exclusively in the central nervous system. J1-160/180 has been shown to be adhesive for astrocytes and repellent towards neurons and growth cones. We report here the complete nucleotide sequence of J1-160/180 in the rat. The predicted amino acid sequence showed a structural architecture very similar to tenascin: a cysteine-rich amino terminal region is followed by 4.5 epidermal growth factor-like repeats, 9 fibronectin type III homologous repeats and a domain homologous to fibrinogen. Sequence comparison analysis revealed highest homology of rat J1-160/180 to mouse tenascin and chicken restrictin with a similarity of 66% and 85%, respectively. The J1-160/180-coding mRNA is derived from a single copy gene. Using the polymerase chain reaction we could show that two J1-160/180 isoforms are generated by alternative splicing of the sixth fibronectin type III homologous repeat. Localization of J1-160/180 mRNA by in situ hybridization in the cerebellum, hippocampus and olfactory bulb confirmed the expression of J1-160/180 by oligodendrocytes with a peak of transcription at 7-14 d after birth, indicating a functional role during myelination. In addition, J1-160/180-specific RNA was found in a small subset of neurons in all three structures of the CNS analyzed. These neurons continue to express J1-160/180 in the adult.

The extracellular matrix glycoproteins BM-90 and tenascin are expressed in the mesenchyme at sites of endothelial-mesenchymal conversion in the embryonic mouse heart

BM-90 is a novel glycoprotein initially isolated from the extracellular matrix of a mouse tumor. We here studied the expression of BM-90 during embryonic development of the mouse heart and compared its expression pattern with that of tenascin and laminin. Distribution was studied by immunofluorescence using antibodies specifically raised against mouse BM-90, laminin and tenascin. Some expression of BM-90 was seen in myocardial basement membranes at early developmental stages, but expression abruptly decreased from these sites at day 12 of embryogenesis. Laminin B chains were also found in the muscle basement membranes early but did not decrease with advancing development. The most striking observation was the markedly enriched expression of BM-90 in the endocardial cushion tissue (ECT). The ECT is derived from mesenchymal cells converted from endothelium and they will form the cardiac valves and septa. In the ECT, BM-90 showed considerable co-distribution with tenascin, but tenascin expression was more focal and did not mark all areas of the ECT. Northern blot data show that BM-90 and tenascin were produced by the developing heart. With antibodies detecting A, B1 and B2 chains of mouse laminin, no immunoreactivity was seen in the ECT. Our data thus show clear-cut differences in the molecular composition of the ECT and muscle basement membranes in the developing heart. The focal expression of BM-90 in the ECT suggests that BM-90 could be involved in epithelial-mesenchymal transitions.

Interaction of astrochondrin with extracellular matrix components and its involvement in astrocyte process formation and cerebellar granule cell migration

We have recently characterized a chondroitin sulfate proteoglycan from the murine central nervous system which is expressed by astrocytes in vitro and carries the L2/HNK-1 and L5 carbohydrate structures. In the present study, we provide evidence that its three core proteins of different size are similar in their proteolytic peptide maps and thus designate this group of structurally related molecules astrochondrin. During development, astrochondrin and the L5 carbohydrate were hardly detectable in the brain of 14-d-old mouse embryos by Western blot analysis. Expression of astrochondrin and the L5 epitope was highest at postnatal day 8, the peak of cerebellar granule cell migration and Bergmann glial process formation, and decreased to weakly detectable levels in the adult. Immunocytochemical localization of astrochondrin in the cerebellar cortex of 6-d-old mice showed association of immunoreactivity with the cell surface of astrocytes, including Bergmann glial processes and astrocytes in the internal granular layer or prospective white matter. Endfeet of astrocytes contacting the basal lamina of endothelial and meningeal cells and contact sites between Bergmann glial processes and granule cells also showed detectable levels of astrochondrin. Furthermore, granule cell axons in the molecular layer were astrochondrin immunoreactive. In the adult, astrochondrin immunoreactivity was weakly present in the internal granular layer and white matter. Both Fab fragments of polyclonal antibodies to astrochondrin and monovalent fragments of the L5 monoclonal antibody reduced the formation of processes of mature GFAP-positive astrocytes on laminin and collagen type IV, but not on fibronectin as substrata. Interestingly, the initial attachment of astrocytic cell bodies was not disturbed by these antibodies. Antibodies to astrochondrin also reduced the migration of granule cells in the early postnatal mouse cerebellar cortex. In a solid phase radioligand binding assay, astrochondrin was shown to bind to the extracellular matrix components laminin and collagen type IV, being enhanced in the presence of Ca2+, but not to fibronectin, J1/tenascin or other neural recognition molecules. Furthermore, astrochondrin interacted with collagen types III and V, less strongly with collagen types I, II, and IX, but not with collagen type VI. The interaction of astrochondrin with collagen types III and V was saturable and susceptible to increasing ionic strength, and could be competed by chondroitin sulfate, heparin, and dextran sulfate, but not by hyaluronic acid, glucose-6-phosphate, or neuraminic acid.(ABSTRACT TRUNCATED AT 400 WORDS)

Tenascin: a modulator of cell growth

The large, multidomain extracellular matrix protein tenascin displays a markedly restricted tissue distribution during embryogenesis and remains present only in a few adult tissues. The protein is reexpressed, however, during wound healing and in the stroma of malignant tumours. While a variety of studies have dealt with the important role of tenascin in the development of neural and non-neural tissues, there is growing evidence that tenascin expression may be associated with proliferation of cells lining these tissues. The presence of repeating domains in tenascin similar to those in epidermal growth factor prompted us to investigate the ability of tenascin to modulate the growth of different cell types. Tenascin was actually found to be mitogenic for several cell types. This mitogenic activity, however, appears to be associated with a region in the fibronectin type III domains. The mitogenic mechanism is clearly distinct from pathways used by peptide growth factors such as epidermal growth factor and platelet-derived growth factor, which activate the intrinsic tyrosine kinase activity of their cell-surface receptors. However, we show that this large extracellular matrix molecule is efficiently internalised and may be processed by responding cells.

Immunocytochemical localization of cell adhesion molecules in the developing and mature olfactory system

The localization of Ca+(+)-independent cell adhesion molecules (CAMs) in the developing and mature olfactory epithelium and bulb is reviewed. The CAMs included in this article are the neural cell adhesion molecule (N-CAM), the 180 kD component of N-CAM (N-CAM 180), the embryonic form of N-CAM (E-N-CAM), L1 glycoproteins, J1 glycoproteins, and the adhesion molecule on glia (AMOG). In addition, the expression of the L2-HNK-1 carbohydrate epitope, shared by N-CAM, L1, J1 and myelin-associated glycoprotein (MAG) in the adult olfactory epithelium and bulb has also been documented. For the localization of these molecules at the light and electron microscopic levels, immunocytochemical techniques were used and are described in detail. During development and organogenesis, the olfactory system exhibits a pattern of CAM expression similar to the general pattern described for the developing nervous system. In the adult olfactory system, however, a significant retention of CAMs characteristic for developmental and morphogenetic processes, such as E-N-CAM, AMOG, as well as the high molecular weight components of J1 glycoproteins, can be observed. The retention of these embryonic features are most likely associated with the cell turnover and high plasticity of this system. Moreover, the predominance of N-CAM 180 with respect to other components of N-CAM, as well as the absence of the L2/HNK-1 carbohydrate epitope, are also particular traits of the primary olfactory system which could be associated with its exceptional properties.

Species diversity of neuronectin and cytotactin expression patterns in the vertebrate central nervous system

Two extracellular matrix proteins of brain tissue, neuronectin (NEC1) and cytotactin (CT), are disulfide-bonded multimers of M(r) 180,000-250,000 subunits. The previously known distribution of these molecules is, however, very different. Human NEC1 is found throughout the white matter of rostral segments of the adult central nervous system (CNS) but not in rostral gray matter or in caudal CNS segments, including the cerebellum. In contrast, CT is absent or expressed at a low level in the adult chicken cerebrum but highly expressed in the cerebellum. Despite these differences in distribution, results obtained with antibodies that recognize NEC1 and CT in several vertebrate species indicate that these molecules are identical or at least closely related: (1) alpha NEC1 antibodies recognize proteins affinity-purified with CT-binding proteoglycan; (2) proteins recognized by alpha NEC1 and alpha CT antibodies in cells constitutively expressing the molecules, cells in which expression is induced by growth factors and phorbol ester and cells treated with tunicamycin (to block glycosylation) are identical in subunit composition and mobility on SDS gels; (3) the removal of NEC1 from culture supernatants by immunoprecipitation removes all molecules reactive with alpha CT antibodies and vice versa; (4) immunoblots of brain extracts with alpha NEC1 and alpha CT antibodies yield identical results. Having demonstrated the structural similarity between NEC1 and CT, we reexamined their distribution in the CNS. Surprisingly, the temporal and spatial distribution pattern of NEC1/CT varied greatly among species. Immunohistochemical and immunoblot experiments with adult human CNS tissues revealed significant levels of NEC1/CT in rostral but not caudal segments. In contrast, in cows and pigs the molecule is found throughout the CNS. Adult rat and mouse brains show regionally restricted expression of NEC1/CT in several areas of the cerebrum--distinct from those showing NEC1/CT in the human--and in the molecular layer of the cerebellum. Tests with fetal and newborn tissues revealed that CNS development in humans, cows and pigs is not accompanied by the marked decline in NEC1/CT levels or the changes in subunit composition found in the chicken CNS. The marked species diversity in temporospatial expression patterns suggests that intrinsic and/or extrinsic elements controlling the expression of NEC1/CT have diverged during vertebrate evolution.

Altered content and distribution of tenascin in colitis, colon adenoma, and colorectal carcinoma

Tenascin is a fibroblast product and extracellular matrix protein probably excerting a fibronectin-antagonizing role. Tenascin is broadly distributed interstitially during embryogenesis but restricted to a small range of structures in normal adult tissues. Using tenascin antibodies and an indirect immunoperoxidase method, normal colon, colitis, colon adenomas, and colorectal carcinomas were examined for tissue distribution of tenascin. Normal mucosa displayed a sparce meshwork of microfibrillar tenascin in the lamina propria. The basement membrane was tenascin negative at the bottom of the crypt and developed into a positive band steadily broadening towards the mucosal surface. In colitis, this polarity was effaced; the basement membrane was a broad tenascin-positive band nearly throughout while interstitial tenascin was moderately increased. Loss of polarity in tenascin content of the basement membrane was a constant feature of adenomas, inconsistently paralleled by structural alterations in surface qualities and continuity of tenascin pattern of the basement membrane. These were most pronounced in carcinomas, where this interface was often discontinuous and had a rough surface; in addition, interstitial tenascin was considerably increased. In carcinomas, the rough surface aspect of the tenascin pattern of the basement membrane was correlated with presence of lymph node metastases (P = 0.04). It is concluded that alterations in tenascin pattern and content reflect complex disturbances in the interaction of inflamed/neoplastic colon epithelium and underlying matrix, leading to an organoid induction of tenascin in the inflammatory context and to induction together with structural abnormalities in neoplasia.

The role of matrix molecules in regeneration of leech CNS

Extracellular matrix (ECM) molecules extracted from the leech central nervous system (CNS) provide substrates that induce extensive growth of processes of identified leech nerve cells in culture. Two ECM molecules, laminin and tenascin, have been identified. The laminin-like molecule has been purified and shown to be a cross-shaped molecule similar to vertebrate laminin with subunits of 340, 220, 180, and 160 kD. Purified laminin as a substrate induces rapid outgrowth of Retzius (R) and Anterior Pagoda (AP) cells in culture. The tenascin molecule has been partially purified. In electronmicrographs, leech tenascin, like vertebrate tenascin, has six arms of equal size joined in a central globule. Highly enriched fractions of leech tenascin induce rapid and extensive outgrowth of Retzius and AP cells in culture. Substrate molecules not only induce outgrowth of processes but also affect the growth patterns of individual nerve cells. Neurites are straight with few branches in laminin, but curved with profuse branches on tenascin. During regeneration of the CNS in the animal, laminin appears at new sites associated with growth cones. The appearance of laminin correlates with the accumulation of microglial cells. Thus, ECM molecules with growth-promoting activity for leech nerve cells in vitro appear to be involved in inducing regeneration and allowing the neurites to reconnect with former targets.

Enhanced expression of the developmentally regulated extracellular matrix molecule tenascin following adult brain injury

Tenascin is an extracellular matrix molecule synthesized and released by young astrocytes during embryonic and early postnatal development of the nervous system, and it is concentrated in boundaries around emerging functional neuronal units. In the adult nervous system, tenascin can be detected only in very low levels. Distinct spatial and temporal distributions of tenascin during developmental events suggest a role in the guidance and/or segregation of neurons and their processes within incipient functional patterns. We show here, using in situ hybridization and immunocytochemistry, that stab wounds of the adult mouse cerebellar and cerebral cortices result in an enhanced expression of tenascin in a discrete region around the lesion site that is associated with a subset of glial fibrillary acidic protein-positive astrocytes. Tenascin up-regulation in the lesioned adult brain may be directly involved in failed regeneration or indirectly involved through its interactions with other glycoconjugates that either inhibit or facilitate neurite growth.

Localization and cellular source of the extracellular matrix protein tenascin in normal and fibrotic rat liver

The distribution and the cellular source of the novel extracellular matrix glycoprotein tenascin were studied in normal and fibrotic rat liver. Cryostat sections of normal rat livers, livers of rats treated with intraperitoneal injections of CCl4 and 4-day-old and 8-day-old primary fat-storing cell cultures were stained for tenascin and desmin using an immunoperoxidase procedure or a double-label immunofluorescence technique. Fat-storing cell cultures were metabolically labeled with 3H-proline. Radiolabeled proteins were immunoprecipitated from the supernatant with antitenascin antiserum and subjected to polyacrylamide gel electrophoresis. In normal rat livers, tenascin was detected discontinuously along the sinusoids, whereas portal tracts were devoid of staining. In fibrotic rat livers, tenascin was preferentially expressed in areas of cell damage, in slender septa or at connective tissue-parenchymal interfaces. The middle region of broad septa was negative. Desmin-positive fat-storing cells accumulated in areas strongly immunoreactive for tenascin, and double-label immunofluorescence showed cells positive for both tenascin and desmin. In fat-storing cell cultures, both intracellular positivity for tenascin and staining of extracellular fibers were seen. Gel electrophoresis of immunoprecipitated proteins revealed two major and three minor bands with molecular weights consistent with tenascin. We conclude that tenascin is a component of the extracellular matrix of both normal and fibrotic rat livers. The strong expression of tenascin in areas of cell damage, in "early" septa or at septal-parenchymal interfaces, in contrast to its absence from the middle region of mature septa, suggests a role in early matrix organization. Fat-storing cells synthesize and secrete tenascin.

Comparison of human tenascin expression in normal, simian-virus-40-transformed and tumor-derived cell lines

Tenascin is a polymorphic high-molecular-mass extracellular-matrix glycoprotein composed of six similar subunits. Using two-domain-specific anti-tenascin monoclonal antibodies, we have studied the expression and distribution of tenascin in four cultured normal human fibroblasts, two simian-virus-40-(SV40)-transformed and three tumor-derived (melanoma, rhabdomyosarcoma and fibrosarcoma) cell lines. We found that (a) cultured normal human fibroblasts accumulate considerable amounts of tenascin and retain 60-90% in the extracellular matrix, while they release the remainder into the tissue-culture medium; (b) of the two SV40-transformed counterparts we have tested, the AG-280 cell line accumulates no detectable amounts of tenascin and the WI-38-VA cell line accumulates about 10-times less tenascin than its normal counterpart and releases about 90% of it into the culture medium; (c) some tumor-derived cell lines accumulate considerable amounts of tenascin, but in these cases, more than 90% is released into the culture media; (d) in normal human fibroblasts, two major tenascin isoforms, generated by alternative splicing of the mRNA precursor, are detectable (280 kDa and 190 kDa, respectively) and the lower-molecular-mass tenascin isoform is accumulated preferentially in the extracellular matrix; (e) in SV40-transformed or tumor-derived cell lines, only the higher-molecular-mass isoform is detectable and it is more sialylated than the tenascin produced by the normal human fibroblast cell lines.

Tenascin promotes cerebellar granule cell migration and neurite outgrowth by different domains in the fibronectin type III repeats

The extracellular matrix molecule tenascin has been implicated in neuron-glia recognition in the developing central and peripheral nervous system and in regeneration. In this study, its role in Bergmann glial process-mediated neuronal migration was assayed in vitro using tissue explants of the early postnatal mouse cerebellar cortex. Of the five mAbs reacting with nonoverlapping epitopes on tenascin, mAbs J1/tn1, J1/tn4, and J1/tn5, but not mAbs J1/tn2 and J1/tn3 inhibited granule cell migration. Localization of the immunoreactive domains by EM of rotary shadowed tenascin molecules revealed that the mAbs J1/tn4 and J1/tn5, like the previously described J1/tn1 antibody, bound between the third and fifth fibronectin type III homologous repeats and mAb J1/tn3 bound between the third and fifth EGF-like repeats. mAb J1/tn2 had previously been found to react between fibronectin type III homologous repeats 10 and 11 of the mouse molecule (Lochter, A., L. Vaughan, A. Kaplony, A. Prochiantz, M. Schachner, and A. Faissner. 1991. J. Cell Biol. 113:1159-1171). When postnatal granule cell neurons were cultured on tenascin adsorbed to polyornithine, both the percentage of neurite-bearing cells and the length of outgrowing neurites were increased when compared to neurons growing on polyornithine alone. This neurite outgrowth promoting effect of tenascin was abolished only by mAb J1/tn2 or tenascin added to the culture medium in soluble form. The other antibodies did not modify the stimulatory or inhibitory effects of the molecule. These observations indicate that tenascin influences neurite outgrowth and migration of cerebellar granule cells by different domains in the fibronectin type III homologous repeats.