Boundaries and inhibitory molecules in developing neural tissues

Developmental expression of the tenascin-C is altered by hypothyroidism in the rat brain

Tenascin-C is an extracellular matrix glycoprotein involved in cell adhesion and migration, and neurite outgrowth. Since these processes have been found to be under thyroid control in the developing rat brain, we have investigated the effect of congenital hypothyroidism on tenascin-C expression. At birth, in situ hybridization studies in hypothyroid rats show an abnormal up-regulation of tenascin-C in some areas (caudate-putamen, geniculate nuclei, ependymal epithelium of the lateral ventricles, hippocampus) and down-regulation in others (occipital and retrosplenial cortex, subiculum). With subsequent development, hypothyroid animals show higher tenascin-C expression also in the upper layers of the cerebral cortex and subplate, and the Bergmann glia of the cerebellum. Significantly, thyroxine treatment of hypothyroid rats led to normalization of tenascin-C levels in most areas. In agreement with the messenger RNA data, hypothyroid rats contain an uniformly higher level of immunoreactive tenascin-C protein throughout the brain, particularly in the cerebellum. Suggesting a direct cellular effect, thyroid hormone also decreases tenascin-C expression in two glial cell lines (C6, B3.1) expressing thyroid receptors. Our results show that congenital hypothyroidism causes specific alterations in the pattern of tenascin-C expression in the rat brain which may at least partially be responsible for some of the developmental disturbances observed in this syndrome.

High affinity binding and overlapping localization of neurocan and phosphacan/protein-tyrosine phosphatase-zeta/beta with tenascin-R, amphoterin, and the heparin-binding growth-associated molecule

We have studied the interactions of the nervous tissue-specific chondroitin sulfate proteoglycans neurocan and phosphacan with the extracellular matrix protein tenascin-R and two heparin-binding proteins, amphoterin and the heparin-binding growth-associated molecule (HB-GAM), using a radioligand binding assay. Both proteoglycans show saturable, high affinity binding to tenascin-R with apparent dissociation constants in the 2-7 nM range. Binding is reversible, inhibited in the presence of unlabeled proteoglycan, and increased by approximately 60% following chondroitinase treatment of the proteoglycans, indicating that the interactions are mediated via the core (glyco)proteins rather than by the glycosaminoglycan chains, which may in fact partially shield the binding sites. In contrast to their interactions with tenascin-C, in which binding was decreased by approximately 75% in the absence of calcium, binding of phosphacan to tenascin-R was not affected by the absence of divalent cations in the binding buffer, although there was a small but significant decrease in the binding of neurocan. Neurocan and phosphacan are also high affinity ligands of amphoterin and HB-GAM (Kd = 0.3-8 nM), two heparin-binding proteins that are developmentally regulated in brain and functionally involved in neurite outgrowth. The chondroitin sulfate chains on neurocan and phosphacan account for at least 80% of their binding to amphoterin and HB-GAM. The presence of amphoterin also produces a 5-fold increase in phosphacan binding to the neural cell adhesion molecule contactin. Immunocytochemical studies showed an overlapping localization of the proteoglycans and their ligands in the embryonic and postnatal brain, retina, and spinal cord. These studies have therefore revealed differences in the interactions of neurocan and phosphacan with the two major members of the tenascin family of extracellular matrix proteins, and also suggest that chondroitin sulfate proteoglycans play an important role in the binding and/or presentation of differentiation factors in the developing central nervous system.

Mucosal tenascin C content in inflammatory and neoplastic diseases of the large bowel

PURPOSE

Tenascin C is a glycoprotein of the extracellular matrix. It is upregulated during embryologic development, wound healing, and under conditions of normal and neoplastic growth. Most available data on tenascin C expression in tissues is based on immunohistologic studies. The present study was designed to quantify tissue concentrations in patients with inflammatory and neoplastic diseases of the large bowel.

METHODS

Fifty patients with ulcerative colitis, 19 patients suffering from familiar adenomatous polyposis without malignant transformation, and 69 patients with colorectal carcinoma were investigated. Tenascin C concentrations in tissue extracts were determined by semiquantitative Western blotting.

RESULTS

The tenascin C tissue concentration of normal mucosa was 2.6 +/- 3.4 microg/mg (n = 55), 2.9 +/- 2.1 microg/mg in colorectal adenomas (n = 19), 7.5 +/- 4.7 microg/mg in ulcerative colitis (n = 50), and 18 +/- 15 microg/mg in colorectal carcinomas (n = 69; mean +/- standard deviation). In ulcerative colitis, the mucosal tenascin C content correlated with histopathologic disease activity. No differences were found between subgroups of adenomas or carcinomas.

CONCLUSIONS

Tenascin C tissue concentrations were not altered in adenomas, slightly elevated in ulcerative colitis, and substantially increased in colorectal carcinomas. Although less useful as a diagnostic parameter, tenascin C tissue levels serve as an instrument for assessing the activity of stromal remodeling in large-bowel diseases generally. Specifically, they may reflect disease activity in ulcerative colitis.

A nestin-negative precursor cell from the adult mouse brain gives rise to neurons and glia

Using a novel suspension culture approach, previously undescribed populations of neural precursor cells have been isolated from the adult mouse brain. Recent studies have shown that neuronal and glial precursor cells proliferate within the subependymal zone of the lateral ventricle throughout life, and a persistent expression of developmentally regulated surface and extracellular matrix molecules implicates cell-cell and cell-substrate interactions in the proliferation, migration, and differentiation of these cells. By using reagents that may affect cell-cell interactions, dissociated adult brain yields two types of cell aggregates, type I and type II spheres. Both sphere types are proliferative, and type I spheres evolve into type II spheres. Neurons and glia arise from presumptive stem cells of type II spheres, and they can survive transplantation to the adult brain.

Up-regulation of astrocyte-derived tenascin-C correlates with neurite outgrowth in the rat dentate gyrus after unilateral entorhinal cortex lesion

The extracellular matrix protein tenascin-C has been implicated in the regulation of axonal growth. Using unilateral entorhinal cortex lesions, which induce a massive sprouting response in the denervated outer molecular layer of the rat fascia dentata, the role of tenascin-C for axonal growth was investigated in vivo. Monoclonal antibodies against the neurite outgrowth and anti-adhesive domains of the molecule were employed. Immunostaining was increased throughout the denervated outer molecular layer by day 2, reached a maximum around day 10, and was back to control levels by four weeks post lesion. Growth cone deflecting as well as neurite outgrowth promoting isoforms of tenascin-C were up-regulated after the lesion. Using electron microscopy, single intensely tenascin-C immunoreactive cells were identified as reactive astrocytes that phagocytose degenerated terminals. In situ hybridization histochemistry for tenascin-C messenger RNA revealed numerous cellular profiles in the denervated outer molecular layer of the ipsilateral and contralateral dentate gyrus two days post lesion. Tenascin-C messenger RNA-positive cells in the outer molecular layer were identified as astrocytes using double-labelling for tenascin-C messenger RNA and glial fibrillary acidic protein immunohistochemistry. Thus, a tenascin-C-rich substrate is present in the outer molecular layer during the time of sprouting and a sharp boundary is formed against the inner molecular layer. This pattern may contribute to the layer-specific sprouting response of surviving afferents after entorhinal lesion. Neurite outgrowth may be promoted within the denervated zone, whereas axons trying to grow into the denervated outer molecular layer, for example from the inner molecular layer, would be deflected by a tenascin-C-rich barrier.

Differential expression of fibronectin, tenascin-C and NCAMs in cultured hippocampal astrocytes activated by kainate, bacterial lipopolysaccharide or basic fibroblast growth factor

Different reports demonstrated that reactive glial cells express increased amounts of adhesion and matrix molecules. Despite a wealth of information on the expression of these molecules during development and after lesion, very little is known of how this expression is regulated. In the present report we used Western blots and immunocytochemistry to investigate the expression of neural cell adhesion molecule (NCAM), fibronectin and tenascin-C in cultured astrocytes from rat hippocampus. The effects of three different extracellular signals were analyzed: the glutamatergic receptor agonist kainic acid, the basic fibroblast growth factor (bFGF) and the bacterial lipopolysaccharide. Each treatment had a specific pattern of glial activation and differentially modified the expression of these proteins. Treatment of astrocytes with kainic acid resulted in an increase of tenascin-C, a decrease of fibronectin and a shift of NCAMs isoforms: NCAM 140 and PSA-NCAM (polysialic acid-rich NCAMs) were increased while NCAM 120 was decreased, bFGF increased fibronectin, tenascin-C and NCAM 120, while decreasing PSA-NCAM. Finally, the treatment of astrocytes with lipopolysaccharide induced a significant increase of fibronectin, tenascin-C and NCAM 120 but did not modify the expression of NCAM 140 and PSA-NCAM. These data suggest different mechanisms for modulation of cell surface interactions. They suggest that glial activation by bFGF and lipopolysaccharide are associated with an increase of the adhesive properties, while kainate action is rather associated with a decrease of the adhesiveness of astrocytes.

Mapping of a defined neurocan binding site to distinct domains of tenascin-C

Neurocan is a member of the aggrecan family of proteoglycans which are characterized by NH2-terminal domains binding hyaluronan, and COOH-terminal domains containing C-type lectin-like modules. To detect and enhance the affinity for complementary ligands of neurocan, the COOH-terminal neurocan domain was fused with the NH2-terminal region of tenascin-C, which contains the hexamerization domain of this extracellular matrix glycoprotein. The fusion protein was designed to contain the last downstream glycosaminoglycan attachment site and was expressed as a proteoglycan. In ligand overlay blots carried out with brain extracts, it recognized tenascin-C. The interaction was abolished by the addition of EDTA, or TNfn4,5, a bacterially expressed tenascin-C fragment comprising the fourth and fifth fibronectin type III module. The fusion protein directly reacted with this fragment in ligand blot and enzyme-linked immunosorbent assay procedures. Both tenascin-C and TNfn4,5 were retained on Sepharose 4B-linked carboxyl-terminal neurocan domains, which in BIAcore binding studies yielded a KD value of 17 nM for purified tenascin-C. We conclude that a divalent cation-dependent interaction between the COOH-terminal domain of neurocan and those fibronectin type III repeats is substantially involved in the binding of neurocan to tenascin-C.

Neuronal differentiation in SH-SY5Y human neuroblastoma cells induces synthesis and secretion of tenascin and upregulation of alpha(v) integrin receptors

Human SH-SY5Y neuroblastoma cells were induced to neuronal differentiation by using 12-0-tetradecanoylphorbol-13-acetate (TPA) and retinoic acid (RA). Both treatments rapidly induced long neurites and increased the content of neurofilaments as shown by immunocytochemistry and immunoblotting. Immunoprecipitation and immunoblotting of the culture medium with monoclonal antibodies demonstrated a rapid onset of synthesis and secretion of Mr 280,000 tenascin (Tn) polypeptide with TPA and both Mr 280,000 and 190,000 Tn polypeptides with RA and an increased secretion of extradomain A cellular fibronectin (EDA-Fn) upon both treatments. Upon RA treatment both Tn polypeptides were also found in extracellular matrix preparations of the differentiated cells. A diffuse extracellular Tn immunoreactivity and a distinct cytoplasmic reaction were seen in differentiated cells especially after exposure to monensin to inhibit cellular secretion. Instead, immunoprecipitation experiments suggested that laminin was synthesized by the cells but was not upregulated upon differentiation. Experiments with purified Tn, used to coat the culture substratum, demonstrated that the undifferentiated cells were unable to adhere or spread on Tn but rapidly acquired the spreading capacity upon differentiation with the inducing agents. In immunofluorescence and immunoblotting the undifferentiated cells presented only a faint heterogenous reaction for beta1 integrin (Int) subunit, whereas cells exposed to RA presented a strong reaction for the Int alpha1 and beta1 subunits, hence suggestive of Int alpha1beta1, and for Int alpha(v) subunit. Cells exposed to TPA showed an enhanced immunoreaction for Int alpha2 and beta1 subunits, suggestive of Int alpha2beta1, and for Int alpha(v) subunit. Immunoreactivity for Int alpha(v) located to distinct punctate plaques in the differentiated cells after both inducing agents. The results suggest that Tn is produced by cultured neuronally differentiating cells, and it is accompanied by the acquitance of an adhesion receptor for Tn.

Lectin-binding properties of oligodendrocyte lineage cells aid in defining functionally important surface proteins

Oligodendrocytes are the myelin-forming cells of the central nervous system. They develop from migratory and proliferative precursor cells, which differentiate to mature myelinating cells. As a first step toward investigating the expression of cell surface glycoproteins by oligodendrocyte lineage cells, we tested 14 different lectins for their binding to oligodendrocyte lineage cells. Peanut agglutinin (PNA) was the only lectin used that showed a differentiation stage-dependent binding to oligodendrocytes. PNA-binding molecules are specifically expressed by oligodendrocyte precursor cells, downregulated with differentiation, and reexpressed by mature oligodendrocytes. It was additionally observed that PNA stimulates the proliferation of oligodendrocyte precursor cells. PNA may therefore be a useful tool for isolating and characterizing important cell surface glycoproteins expressed by oligodendrocyte lineage cells.

Neuritic outgrowth associated with astroglial phenotypic changes induced by antisense glial fibrillary acidic protein (GFAP) mRNA in injured neuron-astrocyte cocultures

In the adult CNS, axons fail to regenerate after injury. Among the cell interactions that lead to this failure are those developed with astrocytes. In an effort to elucidate the mechanisms underlying these negative interactions, we have used astrocytes treated with antisense glial fibrillary acidic protein (GFAP) mRNA to inhibit the formation of gliofilaments, indispensable for the astroglial morphological response to injury, and have studied their permissivity for neuritic outgrowth. In a neuron-astrocyte coculture, a mechanical lesion led to hypertrophy of astrocytes neighboring the lesion. Neuronal cell bodies and neurites were absent both from the area of lesion and from its surroundings. Reactive astrocytes appeared, therefore, to be a nonpermissive substrate. Transfection that used antisense GFAP mRNA blocked astroglial morphological changes and was characterized by both a persistence of neuronal cell bodies in the vicinity of the lesion site and a growth of neurites into the same region. These morphological differences were associated with a 46% decrease in the GFAP translation capacity and a 50% increase in the concentration of GAP-43 in the treated cultures. Neurons were associated mainly with an extracellular laminin network, which was predominant at the lesion site in treated cocultures. In contrast, those astrocytes highly laminin-immunoreactive appeared to be a nonpermissive substrate for neurons. These results show that inhibition in GFAP synthesis, leading to a reduction of astroglial hypertrophy, relieves the blockade of neuritic outgrowth that normally is observed after a lesion. The mechanisms may involve changes in the secretion of extracellular matrix molecules by astrocytes.

Expression of high levels of the extracellular matrix glycoprotein, tenascin-C, in the normal adult hypothalamoneurohypophysial system

Glia and neurons of the hypothalamoneurohypophysial system (HNS) undergo reversible morphological changes, which are concomitant with the remodelling of afferents onto the neurons, under different conditions of neurohormone secretion. Here, we show that the adult rat HNS contains high levels of tenascin-C (TN-C), which is an extracellular matrix glycoprotein whose expression is usually associated with neuronal-glial interactions in the developing and lesioned central nervous system (CNS). By using light and electron microscopic immunocytochemical procedures, we visualized TN-C immunoreactivity in the hypothalamic supraoptic (SON) and paraventricular nuclei, where somata of the neurons are localized; in the median eminence, where their axons transit; and in the neurohypophysis, where they terminate. Hypothalamic areas adjacent to the magnocellular nuclei were devoid of immunoreactivity. Electron microscopy of the neurohypophysis showed immunolabelling of perivascular spaces, glial (pituicyte) and axonal surfaces, a type of labelling that also characterized the median eminence. In the hypothalamic nuclei, there was labelling of extracellular spaces and astrocytic surfaces. In normal animals, we detected no cytoplasmic reaction in glia somata, neurons, or endothelial cells. However, in animals treated with the intracellular transport blocker colchicine, there was intracytoplasmic labelling of all HNS glial cells, indicating a glial source for TN-C. Immunoblot analysis revealed TN-C isoforms of apparent high molecular weight (225, 240, and 260 kD) in the SON and median eminence, whereas lower MW forms (190/200 kD) predominated in the neurohypophysis. By using immunocytochemistry and immunoblot analysis, we found no visible differences in TN-C expression in relation to age, sex, or differing neurohypophysial secretion, which suggests that the expression of TN-C is a permanent feature of the HNS.

Tenascin-C synthesis and influence on axonal growth during rat cortical development

Several putative guidance molecules are restricted to the marginal and subplate zones, the major fibre tracts in the developing cortex. It is presently unknown how their distribution is achieved and how these molecules affect neurite extension. Tenascin-C is of particular interest in this context, because it may either promote or deflect growing axons depending on its mode of presentation. Therefore, the cellular origin of tenascin-C in the developing rat cortex and its effects on the extension of cortical afferents and efferents were examined. Tenascin-C protein is first restricted to the marginal and subplate zones and spreads later into the developing grey matter, in close correlation with afferent innervation. In situ hybridization showed that tenascin-C mRNA is first confined to the ventricular zone, at some distance from the location of the protein, while at later stages tenascin-C-synthesizing cells become scattered throughout the cortical thickness, concomitant with the spread of the protein. In order to assess its function, monoclonal antibodies directed against different domains of tenascin-C were used in a quantitative axonal outgrowth assay. These perturbation experiments suggested that distinct tenascin-C fibronectin type III repeats sustain the growth of thalamic and cortical axons on cortical membrane carpets, whereas the EGF-type repeats are not involved. The combination of different antibodies revealed that separate fibronectin-type III repeats exert cooperative effects. These results suggest that ventricular zone cells regulate the establishment of thalamic and cortical axonal projections through locally restricted deposition of tenascin-C.

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.

Isolation and culture of adult rat hippocampal neurons

Inability to culture adult central neurons and the failure of injured neurons to regenerate in the brain could be due to genetic controls or environmental inhibitors. We tested the environmental inhibitor hypothesis by attempting to regenerate adult rat neurons in B27/Neurobasal culture medium, a medium optimized for survival of embryonic neurons. To isolate neurons from their numerous connections, papain was the best of six different proteases screened on slices of hippocampus for survival of isolated cells after 4 days of culture. Use of a density gradient enabled separation of oligodendroglia and some enrichment of neurons and microglia from considerable debris which was inhibitory to sprouting and viability. With these techniques, about 900000 viable neurons were isolated from each hippocampus of any age rat from birth to 24-36 months, near the median mortality. FGF2 was found to enhance viability at least 3-fold to 40-80%, independent of age, without affecting the length of the processes. Neurons were cultured for more than 3 weeks. These methods demonstrate that hippocampal neurons can regenerate axons and dendrites if provided with adequate nutrition and if inhibitors are removed. They also will enable aging studies. Therefore, the concept of environmental growth restriction may be more appropriate for neurons in the brain than the concept of a genetic block that precludes regeneration of processes.

Inhibitors and promoters of thalamic neuron adhesion and outgrowth in embryonic neocortex: functional association with chondroitin sulfate

When embryonic thalamic neurons are plated onto living slices of mouse forebrain, cell attachment and neurite outgrowth on different layers of the developing cerebral cortex vary dramatically, in ways that correlate with the timing and pattern of thalamocortical innervation. These layer-specific differences can be eliminated from embryonic day 16 slices by enzymatic removal of chondroitin sulfate (CS). The cortical plate (a zone avoided by thalamic axons in vivo) possesses inhibitory activity (anti-adhesive, neurite repelling) and the intermediate zone and subplate (in which thalamic axons normally grow) possess stimulatory activity (adhesive, neurite promoting), both of which are chondroitinase sensitive. These opposing activities appear not to reflect the presence of different CS proteoglycans (CSPGs) in different zones, but rather the presence of differentially localized CS-binding molecules, which can be competed away by soluble CS. This model reconciles conflicting reports on the actions of CSPGs in neural development, and suggests a role for CSPGs in the organization of matrix-bound cues in the brain.

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].

Compartmental distribution of sulfated glycosaminoglycans in lateral and medial midbrain astroglial cultures

Sulfated glycosaminoglycans (S-GAGs) were isolated from the pericellular (P), intracellular (I), and extracellular (E) compartments of astrocytes cultures from lateral (L) and medial (M) sectors of embryonic mouse midbrain; these sectors differ in their ability to support neurite growth (L, permissive, M, non-permissive for growth) and laminin deposition patterns (L, fibrillar; M, punctate pattern). The total amount of S-GAGs in M cultures was twice that in L cultures and was particularly high in the P compartment of M glia. Both glial cultures showed heparan sulfate (HS) in the three cellular compartments but chondroitin sulfate (CS) GAGs were vestigial in I and P compartments of L glia. Our results suggest that M and L astrocytes are heterogeneous concerning the ability to synthesize GAGs and distribute them among the different cellular compartments. Together with other data (Garcia-Abreu et al: J Neurosci Res 40:471, 1995; Garcia-Abreu et al: Neuroreport 6:761, 1995), the present results suggest that this heterogeneous features might be at least partially responsible for the differential effects of L and M glial cultures on the growth of midbrain neurons and may also be involved in complex ways in the guidance of axons at the brain midline.

Glial cell interactions with tenascin-C: adhesion and repulsion to different tenascin-C domains is cell type related

The multimodular glycoprotein tenascin-C is transiently expressed, predominantly by glial cells, during the development of the central and peripheral nervous systems. This extracellular matrix glycoprotein is involved in the control of cell adhesion, neuron migration and neurite outgrowth. Distinct functional properties for neuronal cell types have been attributed to separate tenascin-C domains using antibody perturbation studies and in vitro experiments on tenascin-C fragments. In order to study potential roles of tenascin-C for glial cell biology, a library of recombinant tenascin-C domains was used in a bioassay in vitro. Embryonic day 14 astrocytes, various astroglial-derived cell lines (C6, A7 and Neu7) and oligodendroglial-derived cell types (Oli-neu and G26-20) were examined in an adhesion assay and compared to the neuroblastoma cell line N2A. A binding site for most cell types, except for A7 and N2A, could be assigned to the first three fibronectin type III domains. Repulsive properties could be mapped to three different sites the epidermal growth factor-like repeats, fibronectin type III repeats 4 and 5 and to the alternatively spliced region of the molecule. The responses to these repulsive sites varied according to the cell type. These data are consistent with the interpretation that different cell types express distinct sets of tenascin-C receptors which might regulate cellular responses via distinct second messenger pathways.

Cell attachment to frozen sections of injured adult mouse brain: effects of tenascin antibody and lectin perturbation of wound-related extracellular matrix molecules

Previous studies describing the use of cryoculture methods have focused on the efficacy of the method for studying neuron attachment and neurite outgrowth on intact sections of nerve, and rodent and even human brain. The cryoculture method has shown promise for determining the presence of cell attachment- and neurite-growth-inhibiting molecules in such specimens, and some studies have also attempted to neutralize such molecules with antibodies to myelin inhibitory proteins, nerve growth factor, or factors present in conditioned media that may counteract the repulsiveness of some of these molecules preserved in sections of, for example, myelinated nerves or adult brain white matter. The present study describes the novel use of lesioned central nervous system cryocultures as substrates for investigating the attachment of embryonic neurons and PC12 cells. In addition to demonstrating the use of this novel scar substrate to extend previous 'scar-in-a-dish' models (David et al. (1990) Neuron, 5:463-469; Rudge and Silver (1990) J. Neurosci., 10: 3594-3603; Rudge et al. (1989) Exp. Neurol., 103: 1-16), the present study also describes antibody and lectin perturbations of putative inhibitory molecules that result in an enhanced attachment of cells to cryosection cultures of brain and spinal cord wounds.

Directional neurite outgrowth and axonal differentiation of embryonic hippocampal neurons are promoted by a neurite outgrowth domain of the B2-chain of laminin

Molecular cues involved in directional neurite outgrowth and axonal differentiation of embryonic hippocampal neurons were studied on substrates coated in a striped 5 microns pattern with synthetic peptides from a neurite outgrowth (RDIAEIIKDI, P1543) and cell attachment (CDPGYIGSR, P364) domain of the B2- and B1-chains of laminin, respectively. Both peptides supported neuronal attachment, but only the B2-chain-derived P1543 promoted expression of a mature neuronal phenotype. Directional neurite outgrowth and axonal differentiation of embryonic hippocampal neurons were selectively induced by striped substrates of the B2-chain-derived P1543. Axonal differentiation was determined by expression of a phosphorylated epitope of the 200 kDa neurofilament protein in the longer "axonal" neurite of the bipolar embryonic hippocampal neurons. Ethanol (100 mM), a neuroactive compound known to delay neuronal development, impaired both directional neurite outgrowth and expression of a phosphorylated epitope of the 200 kDa neurofilament protein on a patterned P1543 substratum. The present results provide direct evidence that a 10 amino acid peptide (P1543), derived from a neurite outgrowth domain of the B2-chain of laminin, may be an axonal guidance and differentiation factor for embryonic hippocampal neurons in vitro.

Kainic acid activates transient expression of tenascin-C in the adult rat hippocampus

Kainic acid-induced limbic seizures enhance expression of tenascin-C (TN) in the hippocampus of adult rats. TN mRNA was detectable by in situ hybridization in many granule cells in the dentate gyrus 4.5 hr after kainic acid injection but not in saline-injected animals (controls) or in animals killed 2 or 24 hr after injection. Thirty days after kainic acid injection, TN mRNA was detectable only in pyramidal cells of CA3 and CA1. At the protein level, TN was detectable by immunocytochemistry in control animals in the strata oriens and lacunosum moleculare of CA1, in the molecular layer, and within a narrow area at the inner surface of the granule cell layer in the dentate gyrus. Twenty-four hours after kainic acid injection, TN immunoreactivity was enhanced in these areas and throughout the granule cell layer. Thirty days after kainic acid injection, TN immunoreactivity was downregulated in these areas, while it was prominent in the stratum oriens and in clusters of immunoreactivity in the stratum lucidum of CA3. Western blot analysis of the hippocampus showed a peak of TN expression 24 hr after kainic acid injection. These observations show that TN expression is upregulated in predominantly neuronal cells already by 4.5 hr after kainic acid injection, coincident with activation of granule cells and sprouting of axon terminals, whereas the remaining TN expression 30 days after injection relates to pyramidal cells in CA1 and CA3, coincident with an astroglial response, as marked by a strong expression of glial fibrillary acidic protein.

Young neurons from the adult subependymal zone proliferate and migrate along an astrocyte, extracellular matrix-rich pathway

The subependymal zone (SEZ) of the lateral ventricle of adult rodents has long been known to be mitotically active. There has been increased interest in the SEZ, since it has been demonstrated that neuroepithelial stem cells residing there generate neurons in addition to glia in vitro. In the present study, we have examined parasagittal sections of the adult mouse brain using immunocytochemistry for extracellular matrix (ECM) molecules (tenascin and chondroitin sulfate-containing proteoglycans), glial fibrillary acidic protein (GFAP, a cytoskeletal protein prominently expressed by immature and reactive astrocytes), RC-2 (a radial glial and immature astrocyte cytoskeletal marker), TuJ1 (a class III beta-tubulin isoform expressed solely by postmitotic and adult neurons), nestin (a cytoskeletal protein associated with stem cells), neuron-specific enolase, and bromodeoxyuridine (BrdU, which is taken up by dividing cells). Our results demonstrate that a population of young neurons reside within an ECM-rich, GFAP-positive astrocyte pathway from the rostral SEZ all the way into the olfactory bulb. Furthermore, BrdU labeling studies indicate that there is a high level of cell division along the entire length of this path, and double-labeling studies indicate that neurons committed to a neuronal lineage (i.e., TuJ1+) take up BrdU (suggesting they are in the DNA synthesis phase of the cell cycle), again along the entire length of the SEZ "migratory pathway." Thus, the SEZ appears to retain the ability to produce neurons and glia throughout the life of the animal, functioning as a type of "brain marrow." The implications of these findings are discussed in relation to the role that such a glial/ ECM-rich boundary (as seen in the embryonic cortical subplate and other developing areas) may play in: confining the migratory populations and maintaining them in a persistent state of immaturity; facilitating their migration to the olfactory bulb, where they are incorporated into established adult circuitries; and potentially altering SEZ cell cycle dynamics that eventually lead to cell death.

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.

Cell-cell interactions during the migration of myelin-forming cells transplanted in the demyelinated spinal cord

In the present paper, Dil-labeled myelin-forming cells were traced after their transplantation at a distance from a lysolecithin induced lesion in the adult wild-type and shiverer mouse spinal cord. Optical and ultrastructural observations indicate that after their transplantation, Dil-labeled Schwann cells and oligodendrocyte progenitors were found at the level of the graft as well as at the level of the lesion thus confirming that myelin-forming cells were able to migrate in the adult lesioned CNS (Gout et al., Neurosci Lett 87:195-199, 1988). Between the graft and the lesion, labeled Schwann cells and oligodendrocyte progenitors were absent in the gray matter, but were found as previously described, in specific locations (Baron-Van Evercooren et al., J Neurosci Res 35:428-438, 1993; Vignais et al., J Dev Neurosci 11:603-612, 1993). Both cell types were found along blood vessel walls and more precisely in the Virchow-Robin perivascular spaces. They were identified in the meninges among meningeal cells, collagen fibers, or occasionally in direct contact with the basement membrane forming the glia limitans. In addition to these findings, three major observations were made. In the ependymal region, myelin-forming cells were localized between or at the basal pole of ependymocytes. While Dil-labeled oligodendrocyte progenitors were noted to migrate along the outer surface of myelin sheats in CNS wild-type and shiverer white matter, Schwann cells were excluded from this structure in the wild-type mouse spinal cord. Moreover, in the shiverer mouse, migrating Schwann cells did not seem to interact directly with myelin sheats nor with mature oligodendrocytes. Finally, both cell types were seen to invade extensively the spinal peripheral roots. Our ultrastructural observations clearly suggest that multiple cell-cell and cell-substrate interactions rule the migration of myelin-forming cells in the adult CNS infering that multiple mechanisms are involved in this process.

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.

Cell and molecular analysis of the developing and adult mouse subventricular zone of the cerebral hemispheres

The subventricular zone (SVZ) of the lateral ventricle remains mitotically active in the adult mammalian central nervous system (CNS). Recent studies have suggested that this region may contain neuronal precursors (neural stem cells) in adult rodents. A variety of neuronal and glial markers as well as three extracellular matrix (ECM) markers were examined with the hope of understanding factors that may affect the growth and migration of neurons from this region throughout development and in the adult. This study has characterized the subventricular zone of late embryonic, postnatal, and adult mice using several neuronal markers [TuJ1, nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d), neuron-specific enolase (NSE)], glial markers [RC-2, vimentin, glial fibrillary acidic protein (GFAP), galactocerebroside (Gal-C)], ECM markers [tenascin-C (TN-C), chondroitin sulfate, a chondroitin sulfate proteoglycan termed dermatan sulfate-dependent proteoglycan-1 (DSD-1-PG)], stem-cell marker (nestin), and proliferation-specific marker [bromodeoxyuridine (BrdU)]. TuJ1+ and nestin+ cells (neurons and stem cells, respectively) persist in the region into adulthood, although the numbers of these cells become more sparse as the animal develops, and they appear to be immature compared to the cells in surrounding forebrain structures (e.g., not expressing NSE and having few, if any, processes). Likewise, NADPH-d+ cells are found in and around the SVZ during early postnatal development but become more sparse in the proliferative zone through maturity, and, by adulthood, only a few labeled cells can be found at the border between the SVZ and surrounding forebrain structures (e.g., the striatum), and even smaller numbers of positive cells can be found within the adult SVZ proper. BrdU labeling also seems to decrease significantly after the first postnatal week, but it still persists in the SVZ of adult animals. The disappearance of RC-2+ (radial) glia during postnatal development and the persistence of glial-derived ECM molecules such as tenascin and chondroitin sulfate proteoglycans (as well as other "boundary" molecules) in the adult SVZ may be associated with a persistence of immaturity, cell death, and a lack of cell emigration from the SVZ in the adult.