Adhesion of neural cells to extracellular matrix constituents. Involvement of glycosaminoglycans and cell adhesion molecules

Enhanced survival in perineural invasion of pancreatic cancer: an in vitro approach

Pancreatic cancer (PanCa) is characterized by perineural invasion (PNI), early lymph node and liver metastasis, and poor prognosis. PNI is one of the important causes of local recurrence. Little is known about the mechanism of PNI in PanCa. We presented a novel model system that may shed light on the mystery of PNI in PanCa. In this study, mouse dorsal root ganglia (DRGs) and human PanCa cell line (MIA PaCa-2) were cocultured in Matrigel matrix (BD Biosciences, San Jose, CA) to build this PNI model. MIA PaCa-2 cell line alone (control 1) or DRG alone (control 2) was cultured with Matrigel matrix as controls. Neurite outgrowth, cell colony growth, neurite-colony contact, and retrograde extension were observed under inverted microscopy and then were photographed and quantitated with the Optimas imaging system (Optimas Corp., Bothell, MA). At day 14, both the experimental and control 2 samples were harvested and subjected to total RNA isolation and fixed in paraffin-embedded blocks. Slides cut from paraffin blocks were studied with Ki-67 immunostaining and TUNEL assay. Gene profiling was performed using complementary DNA microarray. Overexpressed target genes were verified by quantitative reverse transcriptase polymerase chain reaction. The results showed that reciprocity was observed between neurites and MIA PaCa colonies with 24 hours of coculture. Neurite outgrowth was stimulated in the presence of pancreatic carcinoma cells, which showed 2-fold more area than did control 2. After 72 hours, MIA PaCa colonies cocultured with DRG exhibited 58% more colony area than did control 1. The Ki-67 index of the DRG/MIA PaCa cells (mean, 5.02%) was significantly higher than that in control 1 (mean, 1.18%) (P < .05); in contrast, the apoptotic index in the DRG/MIA PaCa cells was significantly lower (mean, 0.45%) than that in the control 1 (mean, 1.85%) (P < .001). Prosurvival genes MALT1 and TRAF were increased 2-fold in DRG/MIA PaCa compared with controls. We demonstrated that neural-epithelial interaction is a mutually beneficial process for the growth of nerves and PanCa cells. It is possible that oncogenes and growth factors might act synergistically in promoting proliferation and/or inhibiting apoptosis, a survival strategy crucial to the development of PNI in PanCa.

Neuroregulation of the neuroendocrine compartment of the liver

Liver progenitor cells as well as hepatic stellate cells have neuroendocrine features. Progenitor cells express chromogranin-A and neural cell adhesion molecule, parathyroid hormone-related peptide, S-100 protein, neurotrophins, and neurotrophin receptors, while hepatic stellate cells express synaptophysin, glial fibrillary acidic protein, neural cell adhesion molecule, nestin, neurotrophins, and their receptors. This phenotype suggests that these cell types form a neuroendocrine compartment of the liver, which could be under the control of the central nervous system. We recently showed that the parasympathetic nervous system promotes progenitor cell expansion after liver injury, since selective vagotomy reduces the number of progenitor cells after chemical injury in the rat. Similarly, after transplantation, which surgically denervates the liver, human livers that develop hepatitis have fewer progenitor cells than native, fully innervated livers with similar degrees of liver injury. There is also accumulating experimental evidence linking the autonomic system, in particular the sympathetic nervous system (SNS), with the pathogenesis of cirrhosis and its complications. Recently, it has been shown that hepatic stellate cells themselves respond to neurotransmitters. Moreover, inhibition of the SNS reduced fibrosis in carbon tetrachloride-induced liver injury. In view of the denervated state of transplanted livers, it is very important to unravel the neural control mechanisms of regeneration and fibrogenesis. Moreover, since there is a shortage of donor organs, a better understanding of the mechanisms of regeneration could have therapeutic possibilities, which could even obviate the need for orthotopic liver transplantation.

Accumulation of N-CAM 180 at Contact Sites Between Neuroblastoma Cells and Latex Beads Coated with Extracellular Matrix Molecules

Neuronal cells expressing neural cell adhesion molecule (N-CAM) accumulate the largest N-CAM component (N-CAM 180) at cell - cell contact sites. To test whether this accumulation is induced by interactions at the surface membrane, latex beads coated with several purified adhesion molecules or extracellular matrix (ECM) components were co-cultured with neuroblastoma cells. Beads coated with L1, N-CAM, the L2/HNK-1 carbohydrate epitope-carrying molecules from adult mouse brain or laminin from Engelbreth-Holm-Swarm (EHS) sarcoma did not induce an accumulation of N-CAM 180 or L1 at sites of contact suggesting that these molecules are not directly involved in N-CAM 180 accumulation or that their mobility is required for this process. Beads coated with ECM components of the PF-HR9 cell line induced accumulation of N-CAM 180 at sites of contact with neuroblastoma cells. Accumulation was seen at cell bodies of undifferentiated and differentiated neuroblastoma cells, as well as on neurites and growth cones of differentiated neuroblastoma cells. Accumulation of the neural adhesion molecule L1 was also seen, but less prominently and reproducibly. These observations suggest that molecules of the ECM can directly or indirectly, e.g. via molecules linked to N-CAM 180 on the cell surface, induce accumulation of N-CAM 180.

Cell Type-specific Effects of the Neural Adhesion Molecules L1 and N-CAM on Diverse Second Messenger Systems

We have previously shown that the neural adhesion molecules L1 and N-CAM influence second messenger systems when triggered with specific antibodies at the surface of the phaeochromocytoma PC12 cell line (Schuch et al., Neuron, 3, 13 - 20, 1989). To determine whether the two molecules are linked to the same intracellular signalling cascades, independent of the cell type expressing them, or whether different neural cell types respond with different signal transduction mechanisms, we have investigated the effects of antibodies to L1 and N-CAM, and the isolated molecules themselves, on second messenger systems in different neural cell types. We have investigated cultures of cerebellar and dorsal root ganglion neurons and transformed Schwann cells and related these results to those obtained with the PC12 cell line. Here we show that addition of L1 and N-CAM antibodies and the isolated molecules themselves elicit cell type-specific responses that can be modulated by the substrate on which the cells are maintained. Depending on the cell type, cells respond to the triggering of L1 and N-CAM with antibodies, or addition of the purified molecules, by either up-regulation or down-regulation of inositol phosphate turnover, by a rise in intracellular Ca2+ levels dependent on or independent of the opening of voltage-gated Ca2+ channels, or by an increase or decrease in intracellular pH. Moreover, cerebellar neurons expressing N-CAM respond to addition N-CAM, but not to N-CAM antibodies, in contrast to the other neural cell types studied, which respond to both triggers. Furthermore, cerebellar neurons were the only cells to show a rise in cAMP levels in response to any of the ligands tested. This stimulation of cAMP production by L1 antibodies depended on the cross-linking of L1 molecules at the cell surface, whereas the other responses did not depend on clustering of L1. Simultaneous addition of L1 and N-CAM antibodies either elicited an additive or more than additive effect on the intracellular responses which, for cerebellar neurons, depends on the substrate on which the cells are maintained. These observations indicate that L1 and N-CAM or their antibodies activate cell type-specific intracellular signalling systems and that the two molecules can act interdependently or independently of each other.

Loss of polysialic residues accelerates CNS neural precursor differentiation in pathological conditions

Using the model of lysolecithin-induced demyelination of the corpus callosum in wild-type, NCAM-deficient, and endoneuraminidase-injected mice, we have analyzed the consequences of the loss of expression of NCAM or PSA residues on the migration and proliferation capacities of neural precursors of the subventricular zone (SVZ). We showed that the absence of PSA or NCAM delayed migration of neural precursors to the olfactory bulb and consequently enhanced their recruitment at the lesion site. Moreover, after demyelination, the lack of NCAM but not PSA promoted proliferation in the SVZ and the lesion while the lack of PSA favored the differentiation of the traced cells into the oligodendroglial fate both in the SVZ and in the lesion. As previously demonstrated in vitro (L. Decker et al., 2000, Mol. Cell. Neurosci. 16, 422-439), these data illustrate the involvement of PSA and NCAM in neural precursor motility and differentiation in the normal and injured central nervous system, suggesting distinct roles for these two molecules under pathophysiological conditions.

Oligodendrocyte precursor migration and differentiation: combined effects of PSA residues, growth factors, and substrates

Using the oligosphere strategy (V. Avellana-Adalid et al., 1996, J. Neurosci. Res. 45, 558-570), we compared the migratory behavior of oligodendrocyte preprogenitors (OPP) that expressed the polysialylated form of the neural cell adhesion molecule (PSA-NCAM) and of GD3-positive oligodendrocyte progenitors (OP). To study the role of PSA in OPP migration, we used endoneuraminidase-N, which specifically cleaves PSA from NCAM. Kinetic data showed that (i) migration velocity decreased with time and was favored on polyornithine compared to Matrigel; (ii) cells emerging from spheres enriched in PSA-NCAM+ OPP migrated farther than those from spheres enriched in GD3+ OP, their migration being enhanced by the addition of growth factors; (iii) removal of PSA from NCAM moderately reduced OPP migration and induced their differentiation in GD3+ OP and GFAP+ astrocytes; (iv) blocking integrins reduced their migration, suggesting an alternative mechanism of migration. Altogether these data illustrate that motility and differentiation of OPP involve the combinatorial action of PSA-NCAM, molecules of the ECM and their receptors, and growth factors.

Characterization and isolation of ductular cells coexpressing neural cell adhesion molecule and Bcl-2 from primary cholangiopathies and ductal plate malformations

It has recently been shown that reactive bile ductules display neuroendocrine features, including immunoreactivity for the neural cell adhesion molecule (NCAM). In this study we have compared the immunohistochemical expression of NCAM with that of HEA-125 (biliary specific) and LKM-1 (hepatocyte specific) and other markers relevant to morphogenesis (Bcl-2, EMA) and cell proliferation (Ki-67) in cryostat sections from different chronic liver diseases and from fetal livers at different gestational ages. In parallel, viable NCAM-positive ductular cells were purified from collagenase digests of cirrhotic livers by immunomagnetic separation and characterized by immunocytochemistry and transmission electron microscopy. We demonstrated that reactive ductules with atypical morphology coexpressed NCAM and Bcl-2 and were found mainly in congenital diseases associated with ductal plate malformation and in primary cholangiopathies. On the contrary, reactive ductules with typical morphology were negative for NCAM/Bcl-2 and positive for EMA. Reactive ductules coexpressing NCAM/Bcl-2 were negative for the proliferation marker Ki-67 and appeared to be directly connected with periportal hepatocytes. In fetal livers NCAM/Bcl-2 was transiently expressed during the early developmental stages of ductal plate (10-16 weeks) and started to disappear as the ductal plate began duplicating. NCAM-positive ductal plate cells were Ki-67 negative, becoming positive in duplicated segments. Thus the histogenesis of ductular reactive cells seems to recapitulate the early stages of biliary ontogenesis. In primary cholangiopathies and ductal plate malformations, these cells do not appear to maturate further, and thus abundant ductular structures coexist with vanishing mature ducts. These NCAM-positive ductular cells were immunopurified from patients with chronic cholestatic liver diseases and showed ultrastructural features consistent with a less differentiated phenotype than mature cholangiocytes. These isolated cells represent a useful model for in vitro studies.

Heparan sulfate in the inner limiting membrane of embryonic chicken retina binds basic fibroblast growth factor to promote axonal outgrowth

During neural development retinal ganglion cell axons migrate over the retinal basal lamina (inner limiting membrane, ILM) in directed growth toward the optic nerve. We found that both growth rate and distribution density of the ganglion cell axons on isolated cell-free ILM was greatly inhibited by pretreatment with heparitinase but not with chondroitinase ABC. The persistence of radioactively labeled proteoglycans added to the culture medium eliminated residual heparitinase as an explanation for the inhibition. A cell binding assay showed that heparitinase acted on the ILM to influence axonal behavior without apparent inhibition of cell adhesion. These results indicated that the neurite outgrowth promoting activity of the ILM depended on the heparan sulfate (HS) side chains of its proteoglycans. Basic fibroblast growth factor (bFGF) stimulated additional neuronal sprouting and neurite elongation on the ILM. This neurotropic activity of bFGF was inhibited by heparitinase pretreatment of the ILM, suggesting that bFGF bound to HS on the ILM. The activity of bFGF was enhanced by exogenous heparin added to the culture medium; although heparin alone failed to stimulate either neurite extension or neuronal cell sprouting. These results demonstrate that HS in the ILM possesses neurotropic activity for axons of the ganglion cells by binding bFGF for presentation to cell-surface receptors and may, therefore, play a significant role in stimulating axonal outgrowth during development.

Nerve cell adhesion molecule expression in squamous cell carcinoma of the head and neck: a predictor of propensity toward perineural spread

OBJECTIVE

To evaluate head and neck squamous cell carcinomas (SCCAs) for the expression of nerve cell adhesion molecule (N-CAM). We propose that expression of N-CAM by tumor cells may be associated with perineural invasion in SCCA of the head and neck.

METHODS

Seventy-six archived specimens of histologically proven SCCA were analyzed by immunohistochemistry for the expression of N-CAM. Positive and negative controls were used to assess staining. Two sections of each specimen were reviewed for the presence of perineural invasion. A retrospective chart review was performed for each patient that corresponded to the above specimens.

RESULTS

Perineural invasion was present in 28 (37%) of the 76 patients evaluated for the expression of N-CAM. N-CAM expression was demonstrated in 38 (50%) of the 76 specimens. The incidence of N-CAM expression was significantly associated with perineural invasion (P = .002). There was no significant association between the presence of staining or the presence of perineural invasion and the incidence of locoregional recurrence, distant metastasis, or survival status; however, the mean follow-up was only 13.6 months (range, 1-49 mo).

CONCLUSION

There is a positive correlation between the presence of N-CAM expression and perineural invasion in SCCA of the head and neck. The expression of this adhesion molecule by tumor cells may facilitate both homophilic cell-to-cell and heterophilic cell-to-substrate adhesion, thereby enabling the tumor cells to use the perineural tissues or neural cells, or both as a conduit for perineural spread.

The role of glycoproteins in neural development function, and disease

Glycoproteins play key roles in the development, structuring, and subsequent functioning of the nervous system. However, the complex glycosylation process is a critical component in the biosynthesis of CNS glycoproteins that may be susceptible to the actions of toxicological agents or may be altered by genetic defects. This review will provide an outline of the complexity of this glycosylation process and of some of the key neural glycoproteins that play particular roles in neural development and in synaptic plasticity in the mature CNS. Finally, the potential of glycoproteins as targets for CNS disorders will be discussed.

VASE-encoded peptide modifies NCAM- and L1-mediated neurite outgrowth

Interactions between the neural cell adhesion molecule (NCAM) with NCAM-expressing neurons (trans-interaction) stimulate outgrowth of neurites. The extent of NCAM-triggered neurite outgrowth depends on the presence of 10 amino acids derived from the variable alternatively spliced exon (VASE or pi-exon) in the fourth immunoglobulin-like domain of NCAM (Ig4): NCAM with VASE reduces and without VASE enhances neurite outgrowth in cis- or trans-interaction. We have investigated the role of VASE in neurite outgrowth by characterizing the receptors at the cell surface of cultured cerebellar neurons. Results from experiments with L1 and NCAM antibodies and with cerebellar neurons derived from wild-type or NCAM-deficient mice show that substrate-coated Ig4 with VASE (Ig4+) or without VASE (Ig4-) stimulates neurite outgrowth by a trans-interaction with L1 and that Ig4- promotes neurite outgrowth more strongly than Ig4+ by a transinteraction with NCAM.

Expression of the neural adhesion molecule L1 in the deafferented dentate gyrus

Expression of the neural adhesion molecule L1 and its potential involvement in axonal sprouting were examined in the deafferented rat dentate gyrus. We focused on the dentate gyrus because of its well-defined cytoarchitecture and well-characterized neuronal degeneration and sprouting response following entorhinal cortex lesions. In the molecular layer of the dentate gyrus, a trilaminar staining pattern was observed, with the middle molecular layer exhibiting slightly denser immunolabeling compared to both inner and outer molecular layers. Two to 12 days after a unilateral entorhinal cortex lesion, a progressive loss of L1 immunolabeling was noted in the ipsilateral middle and outer molecular layers, followed by a substantial reappearance of immunostaining 65 days after lesion incidence. The width of the immunostained ipsilateral inner molecular layer revealed a progressive widening and by postlesion day 65 occupied about 50% of the total width of the molecular layer. Immunoelectron microscopy localized L1 to the surface of unmyelinated axons in both normal and deafferented dentate gyrus. In situ hybridization revealed L1 messenger RNA confined to neurons throughout the hippocampal formation, but did not indicate changes in L1 messenger RNA levels in the hippocampus, dentate gyrus, entorhinal cortex or basal forebrain in response to unilateral entorhinal cortex lesions. Changes in L1 immunolabeling in the deafferented dentate gyrus corresponded in a spatial and temporal manner to changes of the synaptic marker synaptophysin and axonal marker phosphorylated tau. Results of the present study are most consistent with the view that L1 is expressed on reinnervating fibers after they make synaptic contacts with other structures. Thus, L1 appears to be involved in the maturation and stabilization of reinnervating fibers and consequently may play an important role in the repair process of the lesioned adult CNS.

CD9 of mouse brain is implicated in neurite outgrowth and cell migration in vitro and is associated with the alpha 6/beta 1 integrin and the neural adhesion molecule L1

We describe here a novel monoclonal antibody (mab H6) which recognizes CD9, an integral cell surface constituent previously described in cells of the hematopoietic lineage and involved in the aggregation of platelets. Mab H6 was raised against membranes of immature mouse astrocytes and reacted with a protein of 25-27 kD in detergent extracts of adult mouse brain membranes. Sequence analysis of the N-terminal amino acids revealed an identity of 96% with CD9 from mouse kidney. CD9 was localized in the central and peripheral mouse nervous systems: in the spinal cord of 11-day-old mouse embryos, CD9 was strongly expressed in the floor and roof plates. In the adult mouse sciatic nerve, myelin sheaths were highly CD9-immunoreactive. Mab H6 reacted with the cell surfaces of both glial cells and neurons in culture and inhibited migration of neuronal cell bodies, neurite fasciculation and outgrowth of astrocytic processes from cerebellar microexplants. Neurite outgrowth from isolated small cerebellar neurons was increased in the presence of mab H6 on substrate-coated laminin, but not on substrate-coated poly-L-lysine. Addition of mab H6 elicited an increase in intracellular Ca2+ concentration in these cells on substrate-coated laminin. Immunoprecipitates of CD9 from cultured mouse neuroblastoma N2A cells contained the alpha 6/beta 1 integrin. Moreover, preparations of CD9 immunoaffinity-purified from adult mouse brain using a mab H6 column contained the neural adhesion molecule L1, but not other neural adhesion molecules. CD9 bound to L1, but not to NCAM or MAG. Both the alpha 6/beta 1 integrin and L1 could be induced to coredistribute with CD9 on the surface of cultured neuroblastoma N2A cells. The combined observations suggest that CD9 can associate with L1 and alpha 6/beta 1 integrin to influence neural cell interactions in vitro.

Identification of the border between fibronectin type III homologous repeats 2 and 3 of the neural cell adhesion molecule L1 as a neurite outgrowth promoting and signal transducing domain

To determine the domains of the neural cell adhesion molecule L1 involved in neurite outgrowth, we have generated monoclonal antibodies against L1 and investigated their effects on neurite outgrowth of small cerebellar neurons in culture. When the 10 antibodies were coated as substrate, only antibody 557.B6, which recognizes an epitope represented by a synthetic peptide comprising amino acids 818 to 832 at the border between the fibronectin type III homologous repeats 2 and 3, was as efficacious as L1 in promoting neurite outgrowth, increasing intracellular levels of Ca2+, and stimulating the turnover of inositol phosphates. These findings suggest that neurite outgrowth and changes in these second messengers are correlated. Such a correlation was confirmed by the ability of Ca2+ channel antagonists and pertussis toxin to inhibit neurite outgrowth on L1 and antibody 557.B6. These observations indicate for the first time a distinct site on cell surface-bound L1 as a prominent signal-transducing domain through which the recognition events appear to be funneled to trigger neurite outgrowth, increase turnover of inositol phosphates, and elevate intracellular levels of Ca2+.

Zebrafish neurons express two L1-related molecules during early axonogenesis

Partial clones coding for two L1-related genes, zebrafish L1.1 and L1.2, were isolated from a zebrafish embryonic cDNA library. The homology analysis, based on the deduced amino acid sequences of L1.1 and L1.2, revealed that the two molecules are most closely related to each other and to mouse L1. Analysis by in situ hybridization revealed that during embryonic development of the nervous system the L1.1 and L1.2 messages are restricted to postmitotic neurons and that the onset of expression correlates with the initiation of axonogenesis. L1.1 is expressed by all known classes of neurons, consistent with an important general function during axonal outgrowth. Most of the neurons also express L1.2. However, L1.2 either is undetectable or is expressed at very low levels in the neurons of the olfactory placodes, anterior lateral line/acoustic ganglia complex, posterior lateral line ganglion, and in late developing hindbrain neurons. In the spinal cord, L1.2 message is detected only in a subpopulation of Rohon-Beard cells. This suggests the possibility that different levels of L1.2 expression may serve to distinguish different populations of neurons and their axons.

Molecular basis of interactions between regenerating adult rat thalamic axons and Schwann cells in peripheral nerve grafts I. Neural cell adhesion molecules

To gain insight into the possible molecular mechanisms underlying axonal regeneration of neurons of the adult central nervous system (CNS), we have investigated, by in situ hybridization and by immunocytochemistry, the localization and sites of synthesis of the neurite outgrowth-promoting cell surface molecules L1, N-CAM and its highly sialylated form, N-CAM-PSA, in and around peripheral nerve grafts implanted into the thalamus of adult rats. Normal unoperated adult rat thalamus contains N-CAM and L1 but no N-CAM-PSA immunoreactive axons. Between 7 days and 13 weeks after graft implantation, L1, N-CAM and N-CAM-PSA were all present at the surface of axonal sprouts in the brain parenchyma close to grafts and in the central parts of Schwann cell columns within grafts. Schwann cell membranes were L1 and N-CAM positive at all postgraft survival times, more strongly at 2-4 weeks than other times, but were associated with N-CAM-PSA reaction product only where they abutted N-CAM-PSA positive axons. Schwann cell membranes apposed to basal laminae (which were avoided by regenerating CNS axons) were L1, N-CAM and N-CAM-PSA negative. Between 3 days and 8 weeks after grafting, N-CAM and L1 mRNA were generally weakly upregulated in neurons of the ipsilateral thalamus, but, most conspicuously, L1 mRNA was strongly upregulated in the neurons of the thalamic reticular nucleus; these neurons are known to regenerate axons very effectively into peripheral nerve grafts and are the probable source of most of the axons which enter thalamic grafts. N-CAM and L1 mRNA were also strongly upregulated in presumptive Schwann cells in the graft. These results show that regenerating CNS axons (re)express N-CAM-PSA and upregulate L1 and N-CAM, suggesting that all of these molecules may play a role in cellular interactions during the regeneration of CNS axons. Furthermore L1 synthesis appears to be particularly well correlated with the ability of CNS neurons to regenerate axons into peripheral nerve grafts.

Several extracellular domains of the neural cell adhesion molecule L1 are involved in homophilic interactions

The neural cell adhesion molecule L1 is a multidomain protein that plays important roles in cell adhesion, migration, and neurite outgrowth. It can interact with itself by a self-binding, i.e., homophilic adhesion mechanism (Kadmon et al.: J Cell Biol 110: 193-208, 1990a). To determine the domains of L1 involved in homophilic binding, we have generated protein fragments of L1 in a prokaryotic and a eukaryotic expression system and used these covalently coupled to fluorescent microspheres to quantify aggregation between them by cytofluorometric analysis. Protein fragments containing the first and second Ig-like domains and the third fibronectin type III homologous repeat showed avid self-binding. Ig-like domains III and IV also showed some self-binding, whereas Ig-like domains V and VI and fibronectin type III homologous repeats 1 and 2 as well as 4 and 5 were less or not active. Binding between different domains was also observed: fibronectin type III homologous repeats 4 and 5 interacted with Ig-like domains I and II, and fibronectin type III homologous repeats 3-5 interacted with all Ig-like domains. These results were confirmed by experiments testing the binding of fragment-conjugated microspheres to substrate-coated L1 or to cell surface-expressed L1 on cultured neurons. Binding of L1 to itself was interfered with by all protein fragments tested, suggesting that also less avidly binding domains of L1 contribute to homophilic binding. These observations indicate prominent functional roles of both Ig-like domains and fibronectin type III homologous repeats in homophilic binding of L1.

PECAM-1: its expression and function as a cell adhesion molecule on hemopoietic and endothelial cells

PECAM-1, the platelet-endothelial cell adhesion molecule, is expressed on a variety of mature hemopoietic cell types (including neutrophils, monocytes and T cell subsets) and is also present on endothelia. In such cases, this glycoprotein functions as either a homotypic or heterotypic adhesion molecule contributing to cell migration, inflammatory processes and wound healing. We have recently shown that PECAM-1 is expressed on a variety of hemopoietic progenitor cell types and on stromal macrophages from human bone marrow. In this review, we discuss the possible functional significance of this molecule for both hemopoietic cell differentiation and for mature cells.

The interaction of vascular endothelial cells and dorsal root ganglion neurites is mediated by vitronectin and heparan sulfate proteoglycans

The interaction of peripheral nerve and blood vessels during development was studied by using DRG explant culture plated on confluent monolayer of vascular endothelial cells (VEC). The comparison of neurite length on various substrates showed a preference of DRG neurites in the following order; thrombospondin > laminin, vitronectin > fibronectin, VEC monolayer > collagen I, rat astrocyte monolayer. On layers of fibroblasts (3T3) or gliomas (C6), neurite extension was not observed. To identify the neurite outgrowth promoting adhesion molecules on VEC surface, several antibodies and synthetic peptides were added to the culture medium of DRG. With vitronectin antibody or with peptides containing the Arg-Gly-Asp (RGD) sequence, 30-40% of neurite outgrowth was inhibited and these two effects were not additive. Therefore, a part of neurite outgrowth in this system is mediated by vitronectin in RGD dependent manner. Another molecule which promotes neurite outgrowth on VEC was identified by a new monoclonal antibody (MAb) EC1. In the Western blot analysis, the immunoreactive band which was over 400 kDa was intensified by guanidine HCl extraction. EC1 immunoreactive band disappeared after the treatment of heparitinase but not with other glycolyases, indicating that EC1 antigen is heparan sulfate proteoglycan(s). The DRG neurite outgrowth was inhibited by MAb EC1 by about 30-40%. By the combination of MAb EC1 and RGD peptide, the neurite outgrowth in explant culture was inhibited by about 50%, and in DRG dissociated culture nearly 100% inhibition was observed. Thus, for the DRG neurite elongation on VEC, vitronectin and heparan sulfate proteoglycan(s) are playing crucial roles.

Stimulatory effect of opioid peptides and naloxone on rat spinal cord cells in primary dissociated culture

Opioid peptides leu-enkephalin, a synthetic analog of enkephalin dalargin and an opiate receptor blocker naloxone were studied for their morphological effect on the cells of dissociated cultures of rat spinal cord. Low density seeding of cells (3.10(5);6.10(5) cells/ml) on collagen substrate was performed to document that opioid peptides increase the number of cultured cells and neurite outgrowth and lead to the activation of the initiated processes of aggregate formation. Upon higher density of plating (5.10(6) cells/ml) with poly-L-lysine as a substrate, activation of the aggregate formation process was demonstrated, both opioid peptides and naloxone leading to an increase in the size of aggregates. Statistical treatment of the results obtained in this set of experiments documented that leu-enkephalin, dalargin and naloxone increased 2.2-, 2.2-2.6-, 2.4-fold, respectively, the size of aggregates compared to the control, i.e. the reaction of spinal cord cells to opioid peptides and opiate receptor blocker naloxon was unidirected. The total effect of opioid peptides and naloxon resulted in a 3.6-fold increase in the size of the aggregates compared to the control. The data obtained in this study allow the assumption that opioid peptides and naloxone, while activating spinal cord cells via receptors of a different type, manifest the properties of factors thus increasing survival and adhesion of spinal cord cells in culture.

Increase in extracellular NCAM and amyloid precursor protein following induction of long-term potentiation in the dentate gyrus of anaesthetized rats

The extracellular concentrations of the amyloid precursor protein (APP) and neural-cell adhesion molecule (NCAM) in the dentate gyrus of the anaesthetized rat were assayed before and after the induction of long-term potentiation (LTP) in vivo. Levels of high molecular weight neurofilament protein and activity of the lysosomal enzyme arylsulphatase were measured as internal controls and indicators of neuronal damage. Ninety minutes after the induction of LTP, the concentrations of NCAM and APP increased, in an NMDA-dependent manner, in the absence of changes in neurofilament and arylsulphatase levels. The delayed changes in the extracellular concentration of these molecules may reflect events leading to morphological modifications following LTP.

Expression of thrombospondin in the adult nervous system

Thrombospondin (TSP) is an extracellular matrix molecule that has been previously associated with neural development and neurite outgrowth in vitro. Little is known, however, about the expression of TSP in the adult nervous system. In this study, TSP localization was examined in nervous tissue from adult mouse, goldfish, newt, and adult and juvenile Xenopus. TSP was associated with neurons in the brains of all species examined. TSP was present in central nerve tracts capable of regeneration, such as the goldfish, Xenopus, and newt optic nerves, but was absent from tracts not capable of regeneration, such as the mouse optic nerve. TSP was also present in the neuropil of goldfish and newt spinal cord, but was restricted to motor neurons in mice and adult Xenopus. In addition, TSP was observed in sciatic nerves of mice, Xenopus, and newt. These results indicate a correlation between the presence of TSP and the potential for successful nerve regeneration across a wide range of animal classes.

Lectin-binding patterns in the development of the cerebellum

We studied the binding distribution of several lectins, Con A, DBA, UEA and WGA, in the embryonic development of the chick cerebellum between stages 18 to 45 of Hamburger and Hamilton. We observed a differential labeling (in intensity and distribution) in the migratory and cortical layers of the cerebellum anlage with these different lectins. The different distributions and modifications in the labeling pattern suggest intense variations of the glycoproteins and glycosaminoglycans in the extracellular matrix during development. These variations coincide with cellular and organizational phenomena in the migratory and cortical layers, and suggest compartmentalization of the Purkinje cell labeling.

Perineuronal nets--a specialized form of extracellular matrix in the adult nervous system

One century ago, Camillo Golgi described 'perineuronal nets' enwrapping the cell bodies and proximal dendrites of certain neurons in the adult mammalian central nervous system and suggested that they represent a supportive and protective scaffolding. Although other neuroanatomists validated the existence of these nets on selected neurons in the adult brain, there was a lack of agreement on their origins, composition and function. The application of modern molecular and ultrastructural methods has brought new insights and a renewed interest in these classic observations. Recent data suggest that perineuronal nets result from the visualization of extracellular matrix molecules that are confined to the space interposed between glial processes and the nerve cells that they outline. The material confined to these spaces can be visualized selectively by antibodies directed to glycoproteins (e.g., tenascin and restrictin/janusin), proteoglycans (e.g., chondroitin sulfates), markers for hyaluronan as well as by lectins recognizing N-acetylgalactosamine and by monoclonal antibodies directed to epitopes on unknown molecules (e.g., HNK-1, VC1.1 and Cat 301). This review examines the emerging clarification of classical observations of perineuronal nets and the functional implications suggested by their molecular composition. Also discussed are studies that further extend observations on the time of development and of the specificity in the occurrence of perineuronal nets. In the adult brain the molecules constituting the 'perineuronal nets of matrix' could serve as recognition molecules between certain neurons and their surrounding cells and participate in the selection and consolidation of their relationship.

Expression of L1 cell adhesion molecule is associated with lymphoma growth and metastasis

The cell adhesion molecule (CAM) L1 is involved in homotypic and heterotypic adhesion between neural cells. It has recently also been identified on leucocytes. We have investigated the expression of L1 on hematopoietic tumor cell lines and found that several tumors including the ESb-MP lymphoma are positive for L1. A potential role for L1 in spontaneous metastasis formation was examined using these cells. From wild-type (wt) L1high lymphoma cells we selected by a fluorescence-activated cell sorter (FACS) stable L1low expression variants. Syngeneic DBA/2 mice injected subcutaneously with L1low clones showed faster primary tumor growth, developed visceral metastases significantly faster and died earlier than animals carrying L1high wt cells. L1 high revertants from the L1low variants showed again a reduced metastatic capacity and a malignancy similar to the wt cells. Expression of L1 on the tumor variants and revertants correlated directly with their homotypic aggregation behaviour in vitro. L1 expression correlated negatively with metastatic capacity. These results suggest that L1 molecules may contribute to the overall malignant potential of the lymphoma cells, presumably by interfering with cell-cell interactions critical for tumor growth and dissemination.

Perineuronal nets provide a polyanionic, glia-associated form of microenvironment around certain neurons in many parts of the rat brain

The nature and function of previously described perineuronal nets are still obscure. In the present study their polyanionic components were demonstrated in the rat brain using colloidal iron hydroxide (CIH) staining. In subcortical regions, such as the red nucleus, cerebellar, and vestibular nuclei, most neurons were ensheathed by CIH-binding material. In the cerebral cortex perineuronal nets were seen around numerous nonpyramidal neurons. Biotinylated hyaluronectin revealed that hyaluronan occurs in perineuronal nets. Two plant lectins [Wisteria floribunda agglutinin (WFA) and Vicia villosa agglutinin (VVA)] with affinity for N-acetylgalactosamine visualized perineuronal nets similar to those rich in anionic components. Glutamic acid decarboxylase (GAD)-immunoreactive synaptic boutons were shown to occupy numerous meshes of perineuronal VVA-positive nets. Electron microscopically, VVA binding sites were scattered throughout perisynaptic profiles, but accumulated at membranes and in the extracellular space except not in synaptic clefts. To investigate the spatial relationship between glial cell processes and perineuronal nets, two astrocytic markers (S100-protein and glutamine synthetase) were visualized at the light and electron microscopic level. Two methods to detect microglia by the use of Griffonia simplicifolia agglutinin (GSA I-B4) and the monoclonal antibody, OX-42, were also applied. Labelled structures forming perineuronal nets were observed with both astrocytic, but not with microglial, markers. It is concluded that perineuronal nets are composed of a specialized type of glia-associated extracellular matrix rich in polyanionic groups and N-acetylgalactosamine. The net-like appearance is due to perisynaptic arrangement of the astrocytic processes and these extracellular components. Similar to the ensheathment of nodes of Ranvier, perineuronal nets may provide a special ion buffering capacity required around various, perhaps highly active, types of neurons.

Regulation of NCAM by growth factors in serum-free myotube cultures

Regulation of the neural cell adhesion molecule (NCAM) was examined in primary cultures of chick skeletal muscle grown in serum-free defined medium. Relative levels of NCAM (per microgram protein) increased 20-30% in myotubes grown on Matrigel, a reconstituted basement membrane preparation, compared to those grown on collagen; total NCAM levels on Matrigel were increased 40-55% due to the additional increase in total protein. A dose dependent increase in relative NCAM levels in myotubes grown on Matrigel in defined medium was observed with the addition of adsorbed horse serum, while relative NCAM levels in myotubes grown on collagen were unaffected by altering the serum concentration. Thus, extracellular matrix molecules and soluble factors exert trophic effects on myotube NCAM expression. Similar developmental changes in the expression of the different molecular size forms of NCAM occurred in myotubes grown on collagen and Matrigel: levels of 150K and 135K Mr forms decreased during development, while 125K remained prominent in older myotubes. Relative NCAM levels were specifically enhanced 11-26% by several factors: nerve growth factor, thyroxine, insulin-like growth factor II, dibutyryl cyclic AMP, veratridine (a sodium ion channel agonist), and nisoldipine (a calcium ion channel agonist). Total protein and overall myotube development in serum-free cultures were enhanced by fetuin, insulin-like growth factor II, acidic fibroblast growth factor, calcitonin gene-related peptide, dibutyryl cyclic AMP, and veratridine. Thus, changes in extracellular matrix, intracellular calcium, and sodium ions, as well as extracellular trophic factors, such as nerve growth factor, thyroxine, and insulin-like growth factor II, may regulate muscle NCAM expression during embryonic development.

The neural cell adhesion molecule (NCAM) heparin binding domain binds to cell surface heparan sulfate proteoglycans

The neural cell adhesion molecule (NCAM) has been strongly implicated in several aspects of neural development. NCAM mediated adhesion has been proposed to involve a homophilic interaction between NCAMs on adjacent cells. The heparin binding domain (HBD) is an amino acid sequence within NCAM and has been shown to be involved in NCAM mediated adhesion but the relationship of this domain to NCAM segments mediating homophilic adhesion has not been defined. In the present study, a synthetic peptide corresponding to the HBD has been used as a substrate to determine its role in NCAM mediated adhesion. A neural cell line expressing NCAM (B35) and its derived clone which does not express NCAM (B35 clone 3) adhered similarly to plates coated with HBD peptide. A polyclonal antiserum to NCAM inhibited B35 cell-HBD peptide adhesion by only 10%, a value not statistically different from inhibition caused by preimmune serum. Both these experiments suggested no direct NCAM-HBD interactions. To test whether the HBD peptide bound to cell surface heparan sulfate proteoglycans (HSPG), HSPG synthesis was inhibited using beta-D-xyloside. After treatment, B35 cell adhesion to the HBD peptide, but not to control substrates, was significantly decreased. B35 cell adhesion to the HBD peptide could be inhibited by 10(-7) M heparin but not chondroitin sulfate. Preincubation of the substrate (HBD peptide) with heparin caused dramatic reduction of B35 cell-HBD peptide adhesion whereas preincubation of B35 cells with heparin caused only modest reductions in cell-HBD adhesion. Furthermore, inhibition of HSPG sulfation with sodium chlorate also decreased the adhesion of B35 cells to the HBD peptide. These results strongly suggest that, within the assay system, the NCAM HBD does not participate in homophilic interactions but binds to cell surface heparan sulfate proteoglycan. This interaction potentially represents an important mechanism of NCAM adhesion and further supports the view that NCAM has multiple structurally independent binding sites.

Different extracellular domains of the neural cell adhesion molecule (N-CAM) are involved in different functions

The neural cell adhesion molecule (N-CAM) engages in diverse functional roles in neural cell interactions. Its extracellular part consists of five Ig-like domains and two fibronectin type III homologous (type III) repeats. To investigate the functional properties of the different structural domains of the molecule in cell interactions and signal transduction to the cell interior, we have synthesized, in a bacterial expression system, the individual domains and tandem sets of individual domains as protein fragments. These protein fragments were tested for their capacity to influence adhesion and spreading of neuronal cell bodies, promote neurite outgrowth, and influence cellular migration patterns from cerebellar microexplants in vitro. Ig-like domains I and II and the combined type III repeats I-II were most efficient for adhesion of neuronal cell bodies, when coated as substrates. Neurite outgrowth was best on the substrate-coated combined type III repeats I-II, followed by the combined Ig-like domains I-V and Ig-like domain I. Spreading of neuronal cell bodies was best on substrate-coated combined type III repeats I-II, followed by Ig-like domain I and the combined Ig-like domains I-V. The cellular migration pattern from cerebellar microexplant cultures plated on a mixture of laminin and poly-L-lysine was modified by Ig-like domains I, III, and IV, while Ig-like domains II and V and the combined type III repeats I-II did not show significant modifications, when added as soluble fragments. Outgrowth of astrocytic processes from the explant core was influenced only by Ig-like domain I. Metabolism of inositol phosphates was strongly increased by Ig-like domain I and less by the Ig-like domains II, III, IV, and V, and not influenced by the combined type III repeats I-II. Intracellular concentrations of Ca2+ and pH values were increased only by the Ig-like domains I and II. Intracellular levels of cAMP and GMP were not influenced by any protein fragment. These experiments indicate that different domains of N-CAM subserve different functional roles in cell recognition and signal transduction, and are functionally competent without nervous system-derived carbohydrate structures.

Neural cell adhesion molecules modulate tyrosine phosphorylation of tubulin in nerve growth cone membranes

Triggering neural cell adhesion molecules of the immunoglobulin superfamily with specific ligands or antibodies inhibited the phosphorylation of tryosyl residues in a subpopulation of alpha- and beta-tubulin associated with membranes from a subcellular fraction of nerve growth cones from fetal rat brain. Preincubation of these membranes with purified extracellular fragments of L1, N-CAM, or myelin-associated glycoprotein, or with antibodies directed against the extracellular domains of L1 or N-CAM, inhibited pp60c-src-dependent phosphorylation of tubulin in an endogenous membrane kinase reaction. Other proteins that affect neurite outgrowth (fibronectin, laminin, antibodies against N-cadherin) had no effect. The results suggest that cell adhesion molecules transduce cell surface events to intracellular signals by modulating the activity of protein tyrosine kinases or phosphatases in axonal membranes to influence cytoskeletal dynamics at the growth cone.

Astrocyte-derived TGF-beta 2 and NGF differentially regulate neural recognition molecule expression by cultured astrocytes

Because of the importance of neural recognition molecules expressed by glial cells to mediate interactions with neurons, growth factors and cytokines known to be functional during morphogenesis and in diseases of the nervous system were studied for their effects on recognition molecule expression by cultured immature and mature astrocytes from several brain regions. In cultures of immature astrocytes, transforming growth factors-beta 1 (TGF-beta 1) and -beta 2 (TGF-beta 2) and nerve growth factor (NGF) increased expression of the neural adhesion molecule L1, leading to a glia-mediated L1-specific increase in neurite outgrowth of dorsal root ganglion neurons on the astrocyte substrate. L1 expression induced by TGF-beta was inhibited by addition of antibodies to NGF, suggesting that TGF-beta influences L1 expression by modulating production of NGF by astrocytes. TGF-beta 1 and -beta 2 decreased expression of N-CAM by immature astrocytes. Since N-CAM expression was not affected by NGF and antibodies to NGF did not abolish the TGF-beta-induced decrease in N-CAM expression, NGF did not appear to be the mediator for regulating expression of N-CAM. Expression of the adhesion molecule on glia (AMOG) was not affected by any factor. NGF and TGF-beta 2 in latent form, but not TGF-beta 1 were found in the culture supernatants. Addition of interferon-gamma (IFN-gamma), interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), platelet-derived growth factor (PDGF), or basic fibroblast growth factor (bFGF) to the cultures did not change recognition molecule expression. REcognition molecule expression by mature astrocytes was not found to be modified by any of the factors tested. In view of the observation that levels of L1 and N-CAM expression correlated with the presence of TGF-beta 2 and NGF in the culture supernatants of immature astrocytes, an autocrine regulatory mechanism for recognition molecule expression by these cells is suggested to play a crucial role in regulation of neuron-glia interactions.

Beta amyloid precursor protein mediates neuronal cell-cell and cell-surface adhesion

The beta-amyloid precursor protein (APP) is a membrane-bound glycoprotein which has been proposed to play a role both as a growth factor and a mediator of cell adhesion. Using the Neuro-2A neuroblastoma cell line, we have investigated the capacity of APP to mediate neural cell adhesion. The cells express the protein at a high level, the immunohistochemical staining pattern at the level of the membrane having a punctate pattern. Fab' fragments of antibodies to the extracellular portion of the molecule were found to inhibit cell binding to a collagen substrate, but not to laminin, fibronectin, or poly-l-lysine. Fab' fragments of antibodies to the nerve cell adhesion molecule N-CAM also inhibited binding of Neuro-2A cells specifically to collagen. This inhibition of cell-surface binding was accompanied by a repression of neurite outgrowth in differentiating cells in the presence of antibodies. APP antibodies also inhibited neuron-neuron and neuron-glial binding, but not glial-glial cell adhesion. These data suggest that the APP, which is expressed primarily on differentiated neuronal cells, may play a role in the mediation of both cell-cell and cell-substrate adhesion.

Retention of J1/tenascin and the polysialylated form of the neural cell adhesion molecule (N-CAM) in the adult olfactory bulb

To gain insight into the cellular and molecular mechanisms underlying neurogenesis in adult mouse olfactory bulb, several adhesion molecules expressed by glial cells and neurons were investigated. In the germinal zone of the olfactory bulb, the subependymal layer of the rostral region of the lateral ventricles, two adhesion molecules are detectable that are characteristic of early morphogenetic events: J1/tenascin and the polysialylated form, the so-called embryonic form, of N-CAM. The polysialylated form of N-CAM is expressed by most cells in the subependymal layer, and by some astrocytes and neurons in the granular layer adjacent to the subependymal layer. This suggests that bipotential precursor cells retain expression of the embryonic form during their migration from the subependymal layer and during the first stages of differentiation into neurons and glia. Expression of the polysialylated form of N-CAM is also retained in monolayer cultures of six-day-old olfactory bulbs, 55 days after seeding in vitro. J1/tenascin was detectable in the subependymal layer using two monoclonal antibodies. The immunostaining pattern was different between the two antibodies and more restricted to the subependymal layer than when staining with polyclonal J1 antibodies was performed, indicating that J1/tenascin exists in distinct isoforms. Finally, our observations suggest that, in the adult olfactory bulb, L1 is not only a neuron-neuron adhesion molecule, but it may also be involved in neuron-glia interactions, since it is found at contact sites between these two cell types. L1, therefore, may be a neuron-glia adhesion molecule in some parts of the CNS, while it is not in others.

Degradation of underlying extracellular matrix by sensory neurons during neurite outgrowth

The ability of differentiating sensory neurons to remodel a fibronectin substratum was examined. During the early stages of neurite outgrowth, fibronectin was cleared from areas beneath the neuronal soma and processes. The removal of fibronectin occurred in the presence and absence of plasminogen and was associated with the release of fibronectin fragments into the culture medium. The degradation of fibronectin was dependent upon neuronal contact with the substratum. Extraction of cells with the nonionic detergent Triton X-114 identified plasminogen activator and plasmin associated with the cell surface. These findings suggest that the plasminogen activator/plasmin system may play an important role in the interaction of differentiating sensory neurons with the extracellular matrix during axonal outgrowth.

The neural cell adhesion molecule N-CAM enhances L1-dependent cell-cell interactions

On neural cells, the cell adhesion molecule L1 is generally found coexpressed with N-CAM. The two molecules have been suggested, but not directly shown, to affect each other's function. To investigate the possible functional relationship between the two molecules, we have characterized the adhesive interactions between the purified molecules and between cultured cells expressing them. Latex beads were coated with purified L1 and found to aggregate slowly. N-CAM-coated beads did not aggregate, but did so after addition of heparin. Beads coated with both L1 and N-CAM aggregated better than L1-coated beads. Strongest aggregation was achieved when L1-coated beads were incubated together with beads carrying both L1 and N-CAM. In a binding assay, the complex of L1 and N-CAM bound strongly to immobilized L1, but not to the cell adhesion molecules J1 or myelin-associated glycoprotein. N-CAM alone did not bind to these glycoproteins. Cerebellar neurones adhered to and sent out processes on L1 immobilized on nitrocellulose. N-CAM was less effective as substrate. Neurones interacted most efficiently with the immobilized complex of L1 and N-CAM. They adhered to this complex even when its concentration was at least 10 times lower than the lowest concentration of L1 found to promote adhesion. The complex became adhesive for cells only when the two glycoproteins were preincubated together for approximately 30 min before their immobilization on nitrocellulose. The adhesive properties between cells that express L1 only or both L1 and N-CAM were also studied. ESb-MP cells, which are L1-positive, but N-CAM negative, aggregated slowly under low Ca2+. Their aggregation could be completely inhibited by antibodies to L1 and enhanced by addition of soluble N-CAM to the cells before aggregation. N2A cells, which are L1 and N-CAM positive aggregated well under low Ca2+. Their aggregation was partially inhibited by either L1 or N-CAM antibodies and almost completely by the combination of both antibodies. N2A and ESb-MP cells coaggregated rapidly and their interaction was similarly inhibited by L1 and N-CAM antibodies. These results indicate that L1 is involved in two types of binding mechanisms. In one type, L1 serves as its own receptor with slow binding kinetics. In the other, L1 is modulated in the presence of N-CAM on one cell (cis-binding) to form a more potent receptor complex for L1 on another cell (trans-binding).

Immunocytochemical localization of the neural cell adhesion molecules L1, N-CAM, and J1 in Pacinian corpuscles of the mouse during development, in the adult and during regeneration

The immunocytochemical localization of the neural cell adhesion molecules L1, N-CAM and J1/tenascin was investigated by light and electron microscopical techniques in murine Pacinian corpuscles during development, in the adult and in the regenerating state. In adult corpuscles, L1 was present only at contact sites between the sensory axon and inner core lamellae. From birth, the earliest stage tested, until day 7, L1 was additionally expressed on lamellar processes of the inner core cells. N-CAM was expressed in developing and adult corpuscles on lamellae and somata of the inner and outer core cells at their contact sites but was hardly detectable at contact sites between axolemma and inner core lamellae. J1/tenascin was found only in association with the extracellular material of the inner core, especially with the two radial clefts and the boundary space between inner and outer core. In developing corpuscles, J1/tenascin became detectable on extracellular material with the onset of inner core differentiation at approximately day 2. After transection or crush of the sciatic nerve, L1 disappeared from the corpuscles but reappeared with regrowing axons at contact sites between axonal membranes and inner core cells. At any regenerative stage inner core cells remained L1-negative. In denervated and reinnervated corpuscles the expression pattern of N-CAM and J1/tenascin did not differ from the normal adult. These observations suggest that a sensory organ, the Pacinian corpuscle, differs from the sciatic nerve and the neuromuscular junction in that its expression of adhesion molecules remains the same in the denervated state as in the innervated adult. Furthermore, in the denervated Pacinian corpuscle, adhesion molecule expression does not resemble that of any developmental stage tested. Thus, other cures than regulation of adhesion molecule expression patterns might be involved in the successful reinnervation of sensory corpuscles.

J1-160 and J1-180 are oligodendrocyte-secreted nonpermissive substrates for cell adhesion

The glia-derived J1 extracellular matrix glycoproteins have been referred to as J1-160/J1-180 (the developmentally late appearing lower molecular weight group) and J1-200/J1-220 (the developmentally early appearing higher molecular group immunochemically related to tenascin). Members of the two groups show distinct cross-reactivities. To characterize the structural and functional differences between these J1 glycoproteins, two monoclonal antibodies were generated which recognize only the members of the lower molecular weight group. The two antibodies detect immunochemical similarities among the members of the lower molecular weight group, but do not react with J1/tenascin. J1-160 and J1-180 are specifically expressed by differentiated oligodendrocytes in culture and by myelin of the central nervous system and have not been found in the peripheral nervous system nor in any other organ of the adult mice tested. Electron microscopic examination of rotary-shadowed J1-160 and J1-180 reveals, respectively, dimeric and trimeric (tribrachion) kink-armed rodlike structures, which are linked by disulfide bridges. J1-160/J1-180 are nonpermissive substrates for the attachment and spreading of early postnatal small cerebellar neurons, astrocytes, and fibroblasts. In a mixture with laminin, J1-160/J1-180 are nonpermissive substrates for neurons, but not for astrocytes or fibroblasts. The repulsive effect toward neurons can be neutralized by one of the monoclonal antibodies, but not by the other. These observations are discussed in the context of cell interactions during regeneration in the mammalian nervous system.

Expression of L1 and N-CAM cell adhesion molecules during development of the mouse olfactory system

The expression of the neural adhesion molecules L1 and N-CAM has been studied in the embryonic and early postnatal olfactory system of the mouse in order to gain insight into the function of these molecules during development of a neural structure which retains neuronal turnover capacities throughout adulthood. N-CAM was slightly expressed and L1 was not significantly expressed in the olfactory placode on Embryonic Day 9, the earliest stage tested. Rather, N-CAM was strongly expressed in the mesenchyme underlying the olfactory placode. In the developing nasal pit, L1 and N-CAM were detectable in the developing olfactory epithelium, but not in regions developing into the respiratory epithelium. At early developmental stages, expression of the so-called embryonic form of N-CAM (E-N-CAM) coincides with the expression of N-CAM, whereas at later developmental stages and in the adult it is restricted to a smaller number of sensory cell bodies and axons, suggesting that the less adhesive embryonic form is characteristic of morphogenetically dynamic neuronal structures. Moreover, E-N-CAM is highly expressed at contact sites between olfactory axons and their target cells in the glomeruli of the olfactory bulb. L1 and N-CAM 180, the component of N-CAM that accumulates at cell contacts by interaction with the cytoskeleton are detectable as early as the first axons extend toward the primordial olfactory bulb. L1 remains prominent throughout development on axonal processes, both at contacts with other axons and with ensheathing cells. Contrary to N-CAM 180 which remains detectable on differentiating sensory neuronal cell bodies, L1 is only transiently expressed on these and is no longer detectable on primary olfactory neuronal cell bodies in the adult. Furthermore, whereas throughout development L1 has a molecular form similar to that seen in other parts of the developing and adult central nervous systems, N-CAM and, in particular, N-CAM 180 retain their highly sialylated form at least partially throughout all ages studied. These observations suggest that E-N-CAM and N-CAM 180 are characteristic of developmentally active structures and L1 may not only be involved in neurite outgrowth, but also in stabilization of contacts among fasciculating axons and between axons and ensheathing cells, as it has previously been found in the developing peripheral nervous system.