Altered expression of neuronal cell adhesion molecules induced by nerve injury and repair

Expression of adhesion molecules and the establishment of boundaries during embryonic and neural development

Evidence is accumulating that molecules involved in cell-cell and cell-substratum interactions are important in the establishment and maintenance of borders between cell groups during development. In this report, we review evidence supporting this conclusion, particularly in regard to the role of adhesion molecules in the formation of cell collectives and in the modulation of cell and neurite movements.

Ultrastructure of an identified molluscan neuron in organ culture and cell culture following axotomy

We examined the ultrastructure of neuron 5 from the buccal ganglion of the mollusc Helisoma trivolvis after axotomy and organ culture, and after isolation of the same neuron in culture. Buccal ganglia containing axotomized neurons 5 were cultured either in host snails or in Leibovitz medium conditioned with ganglia. In addition, some neurons 5 were isolated from buccal ganglia by micro-dissection and plated into culture. Neuron 5 and its processes were identified in both whole mounts and plastic sections of buccal ganglia after intracellular injection with Lucifer Yellow or horseradish peroxidase. Five days after axotomy of neuron 5, thick sections of buccal ganglia stained with toluidine blue revealed that densely staining basophilic bodies (Nissl bodies) within the cytoplasm had dispersed, i.e., they had undergone chromatolysis. Coincident with chromatolysis was an overall increase in diffuse basophilic staining within the cytoplasm of neuron 5 when maintained in organ culture. The dispersion of Nissl bodies viewed by light microscopy correlated with a more freely arranged rough endoplasmic reticulum and associated polysomes within neuron 5 as seen by electron microscopy. Isolated neurons 5 did not possess densely staining Nissl bodies when examined after 2 days in vitro, thus indicating that chromatolysis occurred earlier in isolated neurons. Furthermore, no increase in diffuse cytoplasmic basophilia was observed within isolated neurons 5 cultured in vitro. However, isolated neurons 5 exhibited a marked increase in the number of lipid-like bodies (0.5-1.5 micron in diameter) that were particularly evident in scanning electron micrographs. Scanning and transmission electron micrographs revealed that the isolated neurons were free of associated glia, but non-neuronal cells (hemocytes) would attach themselves to the somata and neurites. Glia surrounding neuron 5 within buccal ganglia exhibited a marked hypertrophy following axotomy and organ culture. Hypertrophy of glia was absent, however, if ganglia were axotomized and left within the animal or axotomized ganglia were implanted into host animals and examined 5 days later by electron microscopy. These observations indicate that, following axotomy, a molluscan neuron may exhibit different morphological features depending on its microenvironment. In addition, the hypertrophy of glia surrounding neurons in Helisoma was not associated with axotomy per se, but with organ culture.

Nerve growth cone migration onto Schwann cells involves the calcium-dependent adhesion molecule, N-cadherin

The role of calcium-dependent adhesion molecules in the migration of nerve growth cones onto the top of Schwann cells was probed by examination of sensory growth cone-Schwann cell interactions in medium containing either 1.0 mM Ca2+ or 0.1 mM Ca2+. In the presence of 1.0 mM Ca2+ growth cones rapidly migrated onto Schwann cells, spread, and remained for extended periods. However, in 0.1 mM Ca2+ growth cones still made frequent contacts with Schwann cells, but migration onto the upper cell surface was much reduced. This contrast in growth cone-Schwann cell interactions could be switched rapidly by changing the Ca2+ concentration of the culture medium. Growth cones of retinal neurons showed similar calcium-dependence in their migration onto Schwann cells. Antibodies to the calcium-dependent adhesion molecule, N-cadherin, also blocked growth cone migration onto Schwann cells, but antibodies to another neuronal adhesion molecule, L1, had no effect on growth cone-Schwann cell interactions. Immunocytochemical staining for N-cadherin and L1 indicated that growth cones and Schwann cells have N-cadherin on their surfaces, while L1 is present only on axons and growth cones. These results provide two kinds of evidence that N-cadherin is important in the initial interactions of growth cones and Schwann cells.

Purified N-cadherin is a potent substrate for the rapid induction of neurite outgrowth

N-cadherin is the predominant mediator of calcium-dependent adhesion in the nervous system (Takeichi, M. 1988. Development (Camb.). 102: 639-655). Investigations using antibodies to block N-cadherin function (Bixby, J.L., R.L. Pratt, J. Lilien, and L.F. Reichardt. 1987. Proc. Natl. Acad. Sci. USA. 84:2555-2569; Bixby, J.L., J. Lilien, and L.F. Reichardt. 1988. J. Cell Biol. 107:353-362; Tomaselli, K.J., K.N. Neugebauer, J.L. Bixby, J. Lilien, and L.F. Reichardt. 1988. Neuron. 1:33-43) or transfection of the N-cadherin gene into heterologous cell lines (Matsunaga, M., K. Hatta, A. Nagafuchi, and M. Takeichi. 1988. Nature (Lond.). 334:62-64) have provided evidence that N-cadherin, alone or in combination with other molecules, can participate in the induction of neurite extension. We have developed an affinity purification procedure for the isolation of whole N-cadherin from chick brain and have used the isolated protein as a substrate for neurite outgrowth. N-cadherin promotes the rapid extension of neurites from chick ciliary ganglion neurons, which extend few or no neurites on adhesive but noninducing substrates such as polylysine, tissue culture plastic, and collagens. N-cadherin is extremely potent, more so than the L1 adhesion molecule, and comparable to the extracellular matrix protein laminin. Compared to laminin, however. N-cadherin promotes outgrowth from ciliary ganglion neurons extremely rapidly and with a distinct morphology. These results provide a direct demonstration that N-cadherin is sufficient to induce neurite outgrowth when substrate bound and suggest that the mechanism(s) involved may differ from that induced by laminin.

Implantation of cultured sensory neurons and Schwann cells into lesioned neonatal rat spinal cord. I. Methods for preparing implants from dissociated cells

Our goal was to devise methods of implanting defined populations of the cellular constituents of peripheral nerve into regions of spinal cord injury. This objective derived from the knowledge that the cellular environment of peripheral nerve is known to be supportive of axon regeneration from both central and peripheral neurons. Two of the constituents of the peripheral nerve environment known to influence axonal growth are the Schwann cell and extracellular matrix (particularly basal lamina), both of which can be obtained in culture. We describe here large-scale methods of establishing purified populations of rat sensory neurons to which purified populations of Schwann cells were added. These essentially monolayer preparations were then scrolled and cut into lengths of proper shape and size to provide implants for sites of spinal cord injury in newborn rats. We also describe methods enabling the addition of leptomeningeal components to the implants; this addition contributes a proliferating population of vascular endothelial cells (identified by immunostaining) to the otherwise vasculature-free neuron/Schwann cell implant. Light and electron microscopic observations were made to characterize the implants. When the implant was ready for use, it contained Schwann cells that were differentiated, i.e., had begun to ensheathe axons and form basal lamina. The use of a medium containing human plasma to foster endothelial cell growth led to increased neurite fasciculation and Schwann cell migratory activity in the outgrowth, particularly when the neurons and Schwann cells were cultured on leptomeninges. The second paper in this series reports the deportment of these implants and their influence on corticospinal tract growth after placement into regions of dorsal column injury in neonatal rats (Kuhlengel et al., J. Comp. Neurol 293:74-91, 1990).

NCAM gene expression during the development of cerebellum and dentate gyrus in the mouse

The neural cell adhesion molecule (NCAM) is thought to be involved in several important events during CNS vertebrate development. This study provides additional information concerning the biochemical determination and anatomical localization of NCAM transcripts. Using S1 nuclease protection assays (S1-NPAs), NCAM transcripts in brain appear highest at birth, with NCAM messenger levels reduced some 20-fold by adulthood. By use of in situ hybridization, NCAM mRNA is demonstrated to be developmentally regulated in the cerebellum and hippocampus. The in situ hybridization findings, in addition to providing results to compare with past studies of NCAM immunolocalization, reveal that NCAM expression in dentate gyrus granule cells and cerebellar Purkinje cells is correlated with the final stages of axonal growth, e.g., synaptic stabilization. In situ hybridization demonstrates a developmental outside-to-inside gradient of NCAM transcripts in the dentate gyrus. Neurological mutant mice, reeler and stagger, provide evidence that NCAM expression is normal in the brain regions investigated, and does not correlate with the developmental perturbations present in these strains.

A role for the neural cell adhesion molecule, NCAM, in myoblast interaction during myogenesis

The Ca2(+)-independent neural cell adhesion molecule, NCAM, is expressed by both nerve and muscle cells and has been shown to mediate both nerve-nerve and nerve-muscle cell interaction. A role for NCAM in muscle-muscle cell interaction has been proposed but not demonstrated. Here we report evidence that NCAM is expressed by embryonic chick muscle cells during in vitro development and functions together with Ca2(+)-dependent adhesion molecules in mediating myoblast interaction during the formation of multinucleate cells.

A threshold effect of the major isoforms of NCAM on neurite outgrowth

Interactions between recognition molecules on the surface of neuronal growth cones and guidance cues present in the local cellular environment are thought to account for the growth of neurites in the highly stereospecific manner that contributes to correct target cell innervation. In vitro assays have been used to identify candidate molecular components of this system, either directly by demonstrating their ability to promote neurite outgrowth, or indirectly by the ability of specific antibodies to inhibit neurite outgrowth. The role of the neural cell adhesion molecule (NCAM) in pathway finding is not fully understood. Some immunological studies support a positive role; others do not, and it has been reported that purified NCAM does not support neurite outgrowth. We have previously shown that an arbitrary biochemical index of neurite outgrowth, the relative level of immunoreactive neurofilament protein, is increased when human and rat dorsal root ganglion neurons are cultured on monolayers of cells expressing transfected human NCAM. But, the complexity of growth precluded a simple morphological analysis and we did not determine the 'dose-response' relationship between NCAM expression and neuronal response. Here, we report on the morphology of rat cerebellar neurons cultured on monolayers of 3T3 cells transfected with complementary DNAs encoding all of the main NCAM isoforms found in cells such as astrocytes, Schwann cells and skeletal muscle. The data indicate that both transmembrane and glycosyl-phosphatidylinositol linked NCAM isoforms are potent substrates for neurite extension. A critical threshold value of NCAM expression is required for increased neurite outgrowth. Above this threshold, small increases in NCAM induce substantial increases in neurite outgrowth.

Glial influences on axonal growth in the primary olfactory system

Neurogenesis in the olfactory epithelium continues throughout the entire life of mammals, and it is the axons of these newly formed olfactory receptor neurons that grow into the target tissue after the first cranial nerve is injured, not the regenerating axons of mature cells. These axons are able to enter and grow within the CNS of adult animals, unlike regenerating axons in injured dorsal roots, the majority of which are prevented from penetrating very far into the spinal cord. One reason why the olfactory axons are so successful in entering the CNS may be due, at least partially, to the fact that they are ensheathed by a type of glial cell (the ensheathing cell) that expresses phenotypic features of both astrocyte and Schwann cells. The presence of both L1/Ng-CAM and N-CAM in the plasma membranes of both ensheathing cells and immature olfactory receptor neurons would enable the olfactory axons to use the glial cell surfaces as a substratum on which to grow. It is probably also true that ensheathing cells synthesize and secrete laminin, thus providing an additional adhesive substrate for the olfactory axons, as well as glia-derived nexin and nerve growth factor, both of which are neurite-promoting agents.

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.

Up-regulation of embryonic NCAM in an EC cell line by retinoic acid

The impact of retinoic acid (RA) on the expression of the neural cell adhesion molecules (NCAMs) and their developmentally regulated polysialic acid (PSA) moiety was studied in embryonal carcinoma (EC) cell lines. These cell lines are known to be capable of RA-induced differentiation into neurons (murine P19 cells) or parietal endoderm (murine F9 cells), respectively. Monoclonal antibodies were employed to monitor expression of NCAM and PSA. F9 and P19 cells were both found to express NCAM but only P19 cells carried the highly polysialylated "embryonic form" of NCAM (E-NCAM). The amount of NCAM in aggregated P19 cells but not in F9 cells was dramatically increased upon treatment with RA. Since NCAMs play an important role in cell interactions during embryogenesis it is tempting to speculate that the regulative impact of RA on NCAMs is related to its morphogenic property.

Transient modulation of Schwann cell antigens after peripheral nerve transection and subsequent regeneration

Schwann cells within the distal portion of a transected nerve undergo a series of poorly understood events in response to injury and loss of axonal contact. These events may influence the regeneration of PNS neurons. In this study we examined the alteration of antigens located in the basal lamina, plasma membrane and cytoplasm of Schwann cells within the distal nerve stump: (a) after a complete transection of the sciatic nerve, and (b) subsequent to reestablished contact between regenerating axons and dedifferentated Schwann cells separated from contact with neurons. Visualization of laminin and heparan sulphate proteoglycan molecules at various intervals after nerve transection always revealed intact basal lamina channels. In response to loss of axonal contact, vimentin expression by Schwann cells within the distal nerve stump increased, becoming a predominant intermediate filament protein of the cytoskeleton while glial fibrillary acid protein (GFAP) expression decreased. This reversal in the prominence of intermediate filament protein was maintained until the onset of axonal reinnervation, at which point expression of GFAP increased and vimentin decreased. Expression of the Schwann cell plasma membrane associated protein, C4, closely mimicked GFAP expression during axon degeneration and subsequent reinnervation. In the normal uninjured nerve, tissue plasminogen activator (tPA) and S-100 were localized in the region near the Schwann cell-axon interface and the outer Schwann cell plasma membrane. In response to loss of axonal contact, the S-100 and tPA immunoreactivity associated with the Schwann cell-axon interface was lost while that localized around the outer Schwann cell plasma membrane remained unchanged. The results of this study demonstrate that Schwann cells modulate a portion of their antigenic repertoire in response to a loss of axonal contact and after contact with regenerating axons.

Immunohistological localization of the adhesion molecules L1, N-CAM, and MAG in the developing and adult optic nerve of mice

The localization of the cell adhesion molecules L1, neural cell adhesion molecule (N-CAM), and myelin-associated glycoprotein (MAG) was studied immunohistologically at the light and electron microscopic levels and immunochemically in the developing and adult mouse optic nerve and retina. The neural adhesion molecule L1 is strongly expressed on the shafts of fasciculating unmyelinated axons at all ages studied from embryonic day 15 through adulthood. Growth cones of retinal ganglion cell axons were weakly L1-positive or L1-negative when contacting glial cells. Unmyelinated axons were not only L1-positive when contacting each other but also when contacting glia, whereas contacts between glial cells were L1-negative at all developmental unmyelinated retinal nerve fiber layer or in the unmyelinated optic nerve head became L1-negative when enwrapped by myelin in the optic nerve proper. At all stages of development N-CAM showed profuse labeling on fasciculating axons, growth cones, and their contact sites with glial cells as well as contacts between glial cells. In contrast to L1, axons remained N-CAM-positive when becoming myelinated. Sometimes, N-CAM was found in compact myelin. However, N-CAM was absent from glial surfaces contacting basement membranes at the interface to meninges, blood vessels, and the vitreous body of the eye. MAG was first detectable intracellularly in oligodendrocytes associated with the endoplasmic reticulum and Golgi apparatus before it became apparent at the cell surface. There it was present on oligodendrocytes prior and during the first stages of ensheathment of axons, both on cell body and processes. After formation of compact myelin MAG remained strongly expressed periaxonally and was only weakly detectable in noncompacted myelin including inner mesaxon and paranodal loops. None of the adhesion molecules was detectable on extracellular matrix, in the meninges, or on endothelial cells. Immunochemical analysis of antigen expression at different developmental stages was in agreement with the immunohistological data. We infer from these observations that L1 is involved in stabilization not only of axon-axon, but also axon-glia contacts, while the more dynamic structure of the growth cone generally expresses less L1. A differential expression of L1 along the course of an axon--being present on its unmyelinated, but absent on its myelinated part--further supports the notion that L1 may be involved in the stabilization of axonal fascicles but not of axon-myelin contacts.(ABSTRACT TRUNCATED AT 400 WORDS)

Neural cell adhesion molecule expression is regulated by Schwann cell-neuron interactions in culture

To investigate the cellular and molecular signals underlying regulation of cell adhesion molecule expression, the influence of interactions between dorsal root ganglion neurons and Schwann cells on their expression of L1 and N-CAM was quantitated by immunogold electronmicroscopy. The numbers of antibody binding sites on cell surfaces of neurons and glia were compared between pure populations and co-cultures. After 3 d of co-culture, expression of L1 was reduced by 91% on Schwann cells and 36% on neurons, with expression in pure cultures being taken as 100%. N-CAM expression was unchanged on neurons and reduced by 43% on Schwann cells. Within 3 d after removal of neurons from Schwann cell-neuron co-cultures by immunocytolysis, expression of L1 and N-CAM on Schwann cell surfaces increased by 69 and 84%, respectively. Cell surface antigens recognized by an antibody to mouse liver membranes were unchanged in co-cultures. Furthermore, in co-cultures of neurons and sciatic nerve fibroblasts neither of the three antibodies detected any changes in expression of antigens when pure and co-cultures were compared. These observations suggest that adhesion molecules are not only involved in neuron-Schwann cell recognition and neurite outgrowth on Schwann cells (Seilheimer, B., and M. Schachner. 1988. J. Cell Biol. 107: 341-351), but that cell interactions, in turn, modulate the extent of adhesion molecule expression.

Peripheral nerve injury causes transient expression of MHC class I antigens in rat motor neurons and skeletal muscles

After a peripheral nerve lesion (rat facial and sciatic) an induction of major histocompatibility complex (MHC) antigens class I was detected immunohistochemically in skeletal muscle fibers and motor neurons. This MHC expression was transient after a nerve crush, when regeneration occurred, but persisted after a nerve cut, when regeneration was prevented. Since the time course of MHC class I expression correlates to that of regeneration a role for this cell surface molecule in regeneration may be considered.

Expression of cytotactin in the normal and regenerating neuromuscular system

Cytotactin is an extracellular glycoprotein found in a highly specialized distribution during embryonic development. In the brain, it is synthesized by glia, not neurons. It is involved in neuron-glia adhesion in vitro and affects neuronal migration in the developing cerebellum. In an attempt to extend these observations to the peripheral nervous system, we have examined the distribution and localization of cytotactin in different parts of the normal and regenerating neuromuscular system. In the normal neuromuscular system, cytotactin accumulated at critical sites of cell-cell interactions, specifically at the neuromuscular junction and the myotendinous junction, as well at the node of Ranvier (Rieger, F., J. K. Daniloff, M. Pinçon-Raymond, K. L. Crossin, M. Grumet, and G. M. Edelman. 1986. J. Cell Biol. 103:379-391). At the neuromuscular junction, cytotactin was located in terminal nonmyelinating Schwann cells. Cytotactin was also detected near the insertion points of the muscle fibers to tendinous structures in both the proximal and distal endomysial regions of the myotendinous junctions. This was in striking contrast to staining for the neural cell adhesion molecule, N-CAM, which was accumulated near the extreme ends of the muscle fiber. Peripheral nerve damage resulted in modulation of expression of cytotactin in both nerve and muscle, particularly among the interacting tissues during regeneration and reinnervation. In denervated muscle, cytotactin accumulated in interstitial spaces and near the previous synaptic sites. Cytotactin levels were elevated and remained high along the endoneurial tubes and in the perineurium as long as muscle remained denervated. Reinnervation led to a return to normal levels of cytotactin both in inner surfaces of the nerve fascicles and in the perineurium. In dorsal root ganglia, the processes surrounding ganglionic neurons became intensely stained by anticytotactin antibodies after the nerve was cut, and returned to normal by 30 d after injury. These data suggest that local signals between neurons, glia, and supporting cells may regulate cytotactin expression in the neuromuscular system in a fashion coordinate with other cell adhesion molecules. Moreover, innervation may regulate the relative amount and distribution of cytotactin both in muscle and in Schwann cells.

Growth of embryonic retinal neurites elicited by contact with Schwann cell surfaces is blocked by antibodies to L1

Explants from embryonic rat retina plated on Schwann cell monolayers were used to examine the mechanisms by which these central neurons interact with Schwann cell surfaces. Embryonic retinal explants extend neurites reliably on Schwann cell surfaces (Kleitman et al., 1988, J. Neurosci. 8: 653). Antibodies to molecules thought to be present on Schwann cell surfaces (laminin and the 217C antigen), on retinal neurite surfaces (Thy-1.1), or on both surfaces (L1) were tested for their ability to influence this neurite growth. Of these, only antibodies to L1 were effective in blocking retinal neurite extension on Schwann cells. Inhibition of neurite growth by anti-L1 was shown to be specific to growth on Schwann cell surfaces because neurite growth on air-dried collagen (a substratum known to support retinal neurite outgrowth) was not affected. This blockage was dose-dependent. At a low titer of anti-L1 Fab fragments defasciculation of neurites was prominent; at high titers 95% of neurite outgrowth was inhibited. This virtual elimination of the ability of Schwann cell surfaces to support embryonic retinal neurite growth in the presence of antibodies to L1 indicates that binding of the L1 molecule is a critical component of the mechanism by which Schwann cells foster the growth of these neurites. The present experiments concur with the growing body of evidence that L1 plays an important role in supporting neurite growth on cell surfaces and raise the possibility that L1 may also mediate the striking ability of adult retinal axons to regenerate in a peripheral nerve environment.

Peptidergic and adrenergic regulation of the intracellular 3',5'-cyclic adenosine monophosphate content in cultured rat Schwann cells

We investigated the role of neuropeptides and adrenergic agonists in the regulation of intracellular 3',5'-cyclic adenosine monophosphate (cyclic AMP) contents in cultured Schwann cells from sciatic nerve of neonatal Sprague-Dawley rats. Of the neuropeptides examined, vasoactive intestinal polypeptide (VIP) and secretin markedly stimulated the accumulation of intracellular cyclic AMP in a time- and dose-dependent manner with half maximum at 3 and 12 min, and 2.8 X 10(-5) and 5.0 X 10(-5) M, respectively. While somatostatin, substance P, adrenocorticotropin (ACTH), beta-endorphin, and nerve growth factor (NGF) did not show any effect on cyclic AMP metabolism, isoproterenol (IP), norepinephrine (NE) and epinephrine (E) also markedly elevated the Schwann cell cyclic AMP concentration. The rank-order of potency of these adrenergic catecholamines on cyclic AMP accumulation was isoproterenol greater than norepinephrine greater than epinephrine. Simultaneous addition of VIP or secretin to the Schwann cell culture synergistically enhanced the norepinephrine-induced elevation of intracellular cyclic AMP. The effect of norepinephrine was antagonized by a selective beta 1-adrenergic antagonist but not by beta 2- nor alpha-adrenergic antagonists. These results suggest that VIP, secretin, and beta 1-adrenergic agonists alone or synergistically may play a part in the regulation of metabolism of Schwann cells mediated through a cyclic AMP-dependent mechanism.

Expression of neural cell adhesion molecules in normal and pathologic tissues

Because cell-cell and cell-matrix interactions directly affect the growth, differentiation, and morphogenesis of neural tissue, abnormal changes in these processes could have severe pathologic consequences. Over the last few years, it has become possible to investigate these interactions at the molecular level due to advances in the identification and characterization of matrix components and receptors and cell adhesion molecules (CAMs). Emerging evidence suggests that two broad classes of CAMs are represented by the neural CAM, N-CAM, and the epithelial CAM, L-CAM. N-CAM and several other neural adhesion molecules contain immunoglobulin-like domains and do not require calcium for binding. In contrast, L-CAM, N-cadherin, and P-cadherin depend on calcium for activity and share structural features that differ from those of the N-CAM family. All of these CAMs are expressed in early embryos and in a variety of tissues throughout development, although each has a characteristic pattern. Initial studies suggest that injury, oncogenic transformation, and some genetic neurologic disorders are accompanied by changes in CAM expression that alter the adhesive or migratory behavior of cells.

Localization of neural cell adhesion molecule in denervated muscle to both the plasma membrane and extracellular compartments by immuno-electron microscopy

The location of neural cell adhesion molecule in mouse skeletal muscle has been investigated using two immuno-electron microscopical techniques. In the first method, 6-micron frozen sections of a normal and a hemi-denervated gluteus muscle were stained by an indirect immunoperoxidase method using a rabbit-derived polyclonal antiserum to neural adhesion molecule as the primary antibody. The stain was visualized with the electron-dense chromogen, diaminobenzidine and the sections fixed, osmicated and processed for electron microscopy whilst still on the slide. Ultrathin sections were cut and viewed in the electron microscope, where the reaction product appeared to be localized in the plasma membrane and on the basal lamina of the muscle fibres. The second method, using a 5-nm immunogold-labelled secondary antibody, confirmed and extended these initial observations. In these experiments, the primary antibody to neural cell adhesion molecule was applied in vivo to hemi-denervated mouse gluteus muscles. The muscles were dissected out 24 h later, divided into denervated and innervated halves and then into junctional and extrajunctional regions. Together with the junctional and extrajunctional regions of normal, control pieces of muscle which had not been incubated with anti-neural cell adhesion molecule, they were lightly fixed, and incubated with the secondary gold-labelled antibody, before further fixation and processing for electron microscopy. Semi-thin, 0.5-micron sections of each were cut and viewed at 20,000 x magnification. Randomly sampled fibres from the extrajunctional regions of the denervated and innervated halves of the hemi-denervated gluteus and the normal, control gluteus were photographed for quantitative analysis. Five micrographs were randomly selected from each group and in these, the numbers, density and position of gold particles were measured using a digitizing tablet. By far the highest number of gold particles was found in the denervated half of the gluteus muscle, there being much less in the innervated half and practically none in the control. The density of gold particles in the denervated muscles was maximal in the plasma membrane-basal lamina complex, but most were located in the extracellular spaces outside this region, where they usually occurred in clusters apparently in association with collagen fibres. We conclude that neural cell adhesion molecule in denervated skeletal muscle is present not only in the plasma membrane but also in the basal lamina and extracellular space.

Peripheral motoneuron interactions with laminin and Schwann cell-derived neurite-promoting molecules: developmental regulation of laminin receptor function

Schwann cells synthesize several neurite outgrowth-promoting molecules and localize them in either the extracellular matrix (ECM; e.g., laminin) or on the plasma membrane (e.g., L1/NgCAM and N-cadherin). Neurite outgrowth by embryonic chick ciliary ganglion (CG) neurons in response to these Schwann cell molecules largely depends on several specific neuronal cell surface receptors: integrin beta 1-class ECM receptors, L1/NgCAM, and N-cadherin (Bixby et al.: Journal of Cell Biology 107:353-361 1988). To address whether neuronal ECM receptors are regulated independently of cell surface adhesion molecules, we studied the ability of dissociated CG neurons from different developmental ages to extend neurites rapidly on 1) substrates coated with the ECM glycoprotein laminin (either from Schwann cell-conditioned medium or purified from the Engelbreth-Holm-Swarm sarcoma) or 2) the surfaces of Schwann cells or Schwannoma (RN22) cells. CG neurons gradually lost the ability between embryonic day 8 (E8) and E14 to attach to and extend neurites in an integrin-dependent fashion on purified laminin or Schwann cell-derived laminin. The inability of E14 CG neurons to respond to laminin was partially reversed after explantation for 2.5 days in vitro, which increased the percentage of responsive neurons approximately ten-fold. E14 neurons remained capable of extending neurites rapidly on the surfaces of Schwann and Schwannoma cells. Thus, the inability of E14 neurons to respond to laminin reflects a specific loss of laminin receptor function, while other receptors, most likely N-cadherin and L1/NgCAM, remain capable of promoting neurite outgrowth on Schwann cell surfaces. Since integrin beta 1-class heterodimers have been shown to function directly as receptors mediating neuronal attachment and process outgrowth on laminin, our results imply that the expression or function of laminin-binding integrin heterodimers is regulated during the development of CG neurons. The apparent loss of integrin receptor function occurs during the period when the axons of CG neurons innervate their targets. Substantial integrin receptor function is recovered when target contact is disrupted by explantation. Thus, the functions of integrin-class receptors in CG neurons may be regulated by target contact.

Regulation of Schwann cell nerve growth factor receptor by cyclic adenosine 3',5'-monophosphate

Previous studies indicated that Schwann cells in immature nerves express nerve growth factor (NGF) receptors, and that this expression is down regulated during development but re-induced by Wallerian degeneration. It was also shown that immature Schwann cells are induced to express galactocerebroside and other molecules characteristic of mature Schwann cells by either contact with an axon or treatment with the cyclic adenosine 3',5'-monophosphate (cAMP) analogues dibutyryl cAMP (dbcAMP) and 8-bromo cAMP or the adenylate cyclase activator forskolin. In the present study, NGF receptors on the surface of cultured Schwann cells were demonstrated by binding of an anti-rat NGF receptor monoclonal antibody or of radioiodinated NGF. Treatment of cultured Schwann cells with cAMP analogues or forskolin resulted in a progressive decrease in both immunoreactive NGF receptors and radioiodinated NGF binding. The cultured Schwann cells contained a polyadenylated RNA species homologous with human melanoma NGF receptor mRNA in sequence and size. The amount of this NGF mRNA was lower in cAMP analogue-treated than in untreated Schwann cells.

Identification of the major proteins that promote neuronal process outgrowth on Schwann cells in vitro

Schwann cells have a unique role in regulating the growth of axons during regeneration and presumably during development. Here we show that Schwann cells are the best substrate yet identified for promoting process growth in vitro by peripheral motor neurons. To determine the molecular interactions responsible for Schwann cell regulation of axon growth, we have examined the effects of specific antibodies on process growth in vitro, and have identified three glycoproteins that play major roles. These are the Ca2+-independent cell adhesion molecule (CAM), L1/Ng-CAM; the Ca2+-dependent CAM, N-cadherin; and members of the integrin extracellular matrix receptor superfamily. Two other CAMs present on neurons and/or Schwann cells-N-CAM and myelin-associated glycoprotein-do not appear to be important in regulating process growth. Our results imply that neuronal growth cones use integrin-class extracellular matrix receptors and at least two CAMs--N-cadherin and L1/Ng-CAM-for growth on Schwann cells in vitro and establish each of these glycoproteins as a strong candidate for regulating axon growth and guidance in vivo.

Studies of adhesion molecules mediating interactions between cells of peripheral nervous system indicate a major role for L1 in mediating sensory neuron growth on Schwann cells in culture

The involvement of the adhesion molecules L1, N-CAM, and J1 in adhesion and neurite outgrowth in the peripheral nervous system was investigated. We prepared Schwann cells and fibroblasts (from sciatic nerves) and neurons (from dorsal root ganglia) from 1-d mice. These cells were allowed to interact with each other in a short-term adhesion assay. We also measured outgrowth of dorsal root ganglion neurons on Schwann cell and fibroblast monolayers. Schwann cells (which express L1, N-CAM, and J1) adhered most strongly to dorsal root ganglion neurons by an L1-dependent mechanism and less by N-CAM and J1. Schwann cell-Schwann cell adhesion was mediated by L1 and N-CAM, but not J1. Adhesion of fibroblasts (which express N-CAM, but not L1 or J1) to neurons or Schwann cells was mediated by L1 and N-CAM and not J1. However, inhibition by L1 and N-CAM antibodies was found to be less pronounced with fibroblasts than with Schwann cells. N-CAM was also strongly involved in fibroblast-fibroblast adhesion. Neurite outgrowth was most extensive on Schwann cells and less on fibroblasts. A difference in extent of neurite elongation was seen between small- (10-20 microns) and large- (20-35 microns) diameter neurons, with the larger neurons tending to exhibit longer neurites. Fab fragments of polyclonal L1, N-CAM, and J1 antibodies exerted slightly different inhibitory effects on neurite outgrowth, depending on whether the neurites were derived from small or large neurons. L1 antibodies interfered most strikingly with neurite outgrowth on Schwann cells (inhibition of 88% for small and 76% for large neurons), while no inhibition was detectable on fibroblasts. Similarly, although to a smaller extent than L1, N-CAM appeared to be involved in neurite outgrowth on Schwann cells and not on fibroblasts. Antibodies to J1 only showed a very small effect on neurite outgrowth of large neurons on Schwann cells. These observations show for the first time that identified adhesion molecules are potent mediators of glia-dependent neurite formation and attribute to L1 a predominant role in neurite outgrowth on Schwann cells which may be instrumental in regeneration.

Cerebellar allografts in brain of quaking mice

Fragments of normal embryonic cerebellum were transplanted into adult Quaking mice to examine using peroxidase-antiperoxidase immunocytochemistry the development of genetically normal tissue in an abnormal host environment. The Quaking mouse animals used as hosts are characterized by defective myelin associated glycoprotein. Normal characteristic expression and distribution of neurofilaments was observed in the cerebellar grafts. Nonphosphorylated epitopes of neurofilaments were seen in Purkinje cell bodies and dendrites. The phosphorylated epitopes of neurofilaments were observed in basket cell axons. Phosphorylated epitopes were also present in numerous myelinated axons, which were probably fibers from deep cerebellar nuclei. These data support the notion that neurogenesis with alternative connections can occur in transplants. Staining patterns with myelin associated glycoprotein and myelin basic protein also suggest that normal myelination occurs in grafts transplanted to the brains of Quaking mice.

Immunoelectron microscopic localization of neural cell adhesion molecules (L1, N-CAM, and myelin-associated glycoprotein) in regenerating adult mouse sciatic nerve

The localization of the neural cell adhesion molecules L1, N-CAM, and the myelin-associated glycoprotein was studied by pre- and postembedding staining procedures at the light and electron microscopic levels in transected and crushed adult mouse sciatic nerve. During the first 2-6 d after transection, myelinated and nonmyelinated axons degenerated in the distal part of the proximal stump close to the transection site and over the entire length of the distal part of the transected nerve. During this time, regrowing axons were seen only in the proximal, but not in the distal nerve stump. In most cases L1 and N-CAM remained detectable at cell contacts between nonmyelinating Schwann cells and degenerating axons as long as these were still morphologically intact. Similarly, myelin-associated glycoprotein remained detectable in the periaxonal area of the degenerating myelinated axons. During and after degeneration of axons, nonmyelinating Schwann cells formed slender processes which were L1 and N-CAM positive. They resembled small-diameter axons but could be unequivocally identified as Schwann cells by chronical denervation. Unlike the nonmyelinating Schwann cells, only few myelinating ones expressed L1 and N-CAM. At the cut ends of the nerve stumps a cap developed (more at the proximal than at the distal stump) that contained S-100-negative and fibronectin-positive fibroblast-like cells. Most of these cells were N-CAM positive but always L1 negative. Growth cones and regrowing axons expressed N-CAM and L1 at contact sites with these cells. Regrowing axons of small diameter were L1 and N-CAM positive where they made contact with each other or with Schwann cells, while large-diameter axons were only poorly antigen positive or completely negative. 14 d after transection, when regrowing axons were seen in the distal part of the transected nerve, regrowing axons made L1- and N-CAM-positive contacts with Schwann cells. When contacting basement membrane, axons were rarely found to express L1 and N-CAM. Most, if not all, Schwann cells associated with degenerating myelin expressed L1 and N-CAM. In crushed nerves, the immunostaining pattern was essentially the same as in the cut nerve. During formation of myelin, the sequence of adhesion molecule expression was the same as during development: L1 disappeared and N-CAM was reduced on myelinating Schwann cells and axons after the Schwann cell process had turned approximately 1.5 loops around the axon. Myelin-associated glycoprotein then appeared both periaxonally and on the turning loops of Schwann cells in the uncompacted myelin.(ABSTRACT TRUNCATED AT 400 WORDS)

The expression of an N-CAM serum fragment is positively correlated with severity of negative features in type II schizophrenia

The expression of a 70-kD serum fragment of the neural cell adhesion molecule (N-CAM) in schizophrenia is described. Schizophrenic patients (n = 40) were found to have statistically significant increases (p less than 0.0001) in serum N-CAM levels when compared to normal individuals (n = 26), and this could not be associated with age or sex. This difference was more marked (p less than 0.0001) between type II schizophrenics (n = 13) and normal individuals (n = 26) than when patients in the overlap group between type I and type II schizophrenia (n = 18) were compared to normal individuals (p less than 0.001). This difference remained significant (p less than 0.01) when overlap patients were compared to those of type II schizophrenia. Furthermore, schizophrenic patients with lower serum N-CAM proved to be better responders to neuroleptic therapy. We suggest that these elevated serum N-CAM levels reflect an increased synaptic turnover rate in this psychotic state.

A comparative study of the effects of chronic axotomy, crush lesion and re-anastomosis of the rat sural nerve on horseradish peroxidase labelling of primary sensory neurons

Chronic axotomy is detrimental to the incorporation of horseradish peroxidase (HRP) by neurons of the central and peripheral nervous system. Using the rat sural nerve as a model, this study aimed to determine the effects of other types of nerve injury on the peroxidase labelling of dorsal root ganglion (DRG) cells. Compared to the decreased labelling occurring shortly after permanent transection of the sural axons at the ankle, crush injury of the nerve had no effect on the number and size distribution of peroxidase-stained cells. Re-anastomosing the sural nerve to its own distal segment or to the tibial nerve delayed the changes in HRP neuronal labelling, which subsequently were less severe in neurons allowed to reinnervate their own nerve. It also sustained the incorporation of HRP by many large DRG neurons, a function which is lost shortly after these cells are chronically axotomized. Nerve re-anastomosis also prevented the retrograde atrophy of myelinated and unmyelinated nerve fibers which is triggered by permanent transection. Based on the preservation of fiber counts in the sural nerves proximal to the site of surgery, with no evidence of degeneration, our observations possibly reflect alterations in the peroxidase metabolism of DRG neurons depending on the type of axonal injury they sustained and the possibility they had upon regeneration to contact endoneurial tubes and ultimately their original end-organs.

Expression of nerve growth factor receptor during human peripheral nerve development

The expression of NGF receptors on human Schwann cells during development and myelination and in culture was analyzed using a murine monoclonal antibody to human NGF receptor. Nonmyelinated femoral nerves from 13- to 14-week fetuses stained strongly for NGF receptor, whereas tissues from later stages of development showed a decrease in the staining intensity. These changes correlated with the initiation of myelination (17-19 weeks), as observed by phase-contrast and electron microscopy, and the reactivity with monoclonal antibody 4C5, a marker of mature Schwann cells. In adult nerves, only the perineurium and few endoneurial cells were stained with anti-NGF receptor antibody. Cultured human fetal Schwann cells were positive for NGF receptor by immunofluorescence irregardless of donor age or length of time in culture. The decreased staining of NGF receptor with nerve maturation may reflect a dependence of antigen expression on Schwann cell differentiation and/or neuron-Schwann cell interaction.

Neuron-glia cell adhesion molecule interacts with neurons and astroglia via different binding mechanisms

The neuron-glia cell adhesion molecule (Ng-CAM) is present in the central nervous system on postmitotic neurons and in the periphery on neurons and Schwann cells. It has been implicated in binding between neurons and between neurons and glia. To understand the molecular mechanisms of Ng-CAM binding, we analyzed the aggregation of chick Ng-CAM either immobilized on 0.5-micron beads (Covaspheres) or reconstituted into liposomes. The results were correlated with the binding of these particles to different types of cells as well as with cell-cell binding itself. Both Ng-CAM-Covaspheres and Ng-CAM liposomes individually self-aggregated, and antibodies against Ng-CAM strongly inhibited their aggregation; the rate of aggregation increased approximately with the square of the concentration of the beads or the liposomes. Much higher rates of aggregation were observed when the ratio of Ng-CAM to lipid in the liposome was increased. Radioiodinated Ng-CAM on Covaspheres and in liposomes bound both to neurons and to glial cells and in each case antibodies against Ng-CAM inhibited 50-90% of the binding. Control preparations of fibroblasts and meningeal cells did not exhibit significant binding. Adhesion between neurons and glia within and across species (chick and mouse) was explored in cellular assays after defining markers for each cell type, and optimal conditions of shear, temperature, and cell density. As previously noted using chick cells (Grumet, M., S. Hoffman, C.-M. Chuong, and G. M. Edelman. 1984 Proc. Natl. Acad. Sci. USA. 81:7989-7993), anti-Ng-CAM antibodies inhibited neuron-neuron and neuron-glia binding. In cross-species adhesion assays, binding of chick neurons to mouse astroglia and binding of mouse neurons to chick astroglia were both inhibited by anti-Ng-CAM antibodies. To identify whether the cellular ligands for Ng-CAM differed for neuron-neuron and neuron-glia binding, cells were preincubated with specific antibodies, the antibodies were removed by washing, and Ng-CAM-Covasphere binding was measured. Preincubation of neurons with anti-Ng-CAM antibodies inhibited Ng-CAM-Covasphere binding but similar preincubation of astroglial cells did not inhibit binding. In contrast, preincubation of astroglia with anti-astroglial cell antibodies inhibited binding to these cells but preincubation of neurons with these antibodies had no effect. Together with the data on Covaspheres and liposome aggregation, these findings suggested that Ng-CAM-Covaspheres bound to Ng-CAM on neurons but bound to different molecules on astroglia.(ABSTRACT TRUNCATED AT 400 WORDS)

CAMs and Igs: cell adhesion and the evolutionary origins of immunity

The lymphoid system and cells of immunity are as morphologically well defined as those of any complex organ but in addition they show dynamic long-range interactions between the fluid tissues (lymphocytes, monocytes, etc.) and the solid, vascular and generative tissues and organs which they comprise. Given the observation that CAMs are present in epithelial components of lymphoid organs, it appears that, in their ontogeny, the organs of immunity will share a common principle of morphoregulation by CAMs with brains, feathers and other parts of the phenotype. As discussed here, this principle is a regulatory one operating across many levels of organization from the genes to tissues and back again (see Fig. 1). At some early point in the evolution of the immune system, a gene corresponding to an N-CAM precursor must have duplicated to provide a basis for the Ig superfamily with its increasing specializations for recognition and for cellular regulation during the immune response. Lymphocyte cellular families also developed later specializations (along with other leukocytes) for adhesive functions accessory to specific recognition. As far as we can see, the molecules for these accessory functions only remotely resemble CAMs, but closely resemble receptors for matrix molecules and SAMs. What CAMs and Ig superfamily members have in common is an evolutionary path and important roles in mediating complex regulatory responses that arise from cell-cell interactions. In the one case, this regulation leads to morphology, and in the other, to immune recognition. The first depends directly upon pattern (the formation of definite tissue structure); the regulation of the second also depends upon pattern to the extent that its function is dependent upon the morphology of lymphoid organs and vasculature. But although specific immune recognition depends locally upon adhesion through special mechanisms, it does not lead to morphology. One must not therefore impute too much in the physiological sense to the resemblance among brain molecules and molecules of the immune system. CAMs themselves are not directly histotypic at the level of individual differentiated cells but rather are used to link early tissue boundaries in induction and function in a wide variety of different tissues. As a consequence, N-CAM is central to the formation and maintenance of neural tissue but has a much wider tissue distribution and a fundamental role in very early embryogenesis as is the case with other primary CAMs. Thus, the immune system did not evolve from the nervous system, but from a cell adhesion system essential to both.(ABSTRACT TRUNCATED AT 400 WORDS)

Myelinated, but not unmyelinated axons, reversibly down-regulate N-CAM in Schwann cells

There is evidence from chicks and mice that N-CAM expression in Schwann cells is subject to significant regulation during development and following injury. In the present work, rat sciatic nerve and immunohistochemical methods have been used to study developmental and injury-related modulation of N-CAM in Schwann cells, using cell type specific markers to identify different Schwann cell populations, and cell counting to quantify their size. The study has sought to determine unambiguously whether immature Schwann cells in developing nerves and denervated Schwann cells in injured adult nerves express surface N-CAM, and has investigated the temporal relationship between the gradual loss of surface N-CAM and the differentiation of myelin-forming Schwann cells, monitored by the sequential appearance of the glycolipid galactocerebroside and the myelin-specific protein P0. Further points examined are whether this down-regulation of N-CAM is rapidly reversible following loss of axonal contact, and whether N-CAM reappearance in Schwann cells depends on protein synthesis. In nerves from 17- to 18-day embryos, 90% of the Schwann cells, identified with Ran-1 antibodies, expressed surface N-CAM. In nerves from newborn rats many cells are in the early stage of myelin synthesis and therefore express galactocerebroside, although they have not yet acquired P0. Suspension staining of dissociated cells from this nerve showed that 92% of the galactocerebroside-positive cells were also N-CAM positive. In suspension staining of nerves from 5-day, 10-day and adult rats, P0-positive cells were essentially N-CAM negative.(ABSTRACT TRUNCATED AT 250 WORDS)

Skeletal muscle neural cell adhesion molecule (N-CAM): changes in protein and mRNA species during myogenesis of muscle cell lines

Qualitative and quantitative changes in neural cell adhesion molecule (N-CAM) protein and mRNA forms were measured during myogenesis in G8-1 and C2 cell lines. Indirect immunofluorescence assay showed that N-CAM was constitutively expressed by myoblasts in culture and that myotubes appeared to be stained more strongly. These changes were quantified using a dot blot assay. N-CAM levels increased almost 4-fold in G8-1 cells and 15-fold in C2 cells during myogenesis. The kinetics of accumulation of N-CAM were not coordinate with other muscle markers such as creatine kinase or acetylcholine receptor levels, since N-CAM accumulated significantly ahead of these markers. Immunoblotting showed that myogenesis was not associated with changes in the extent of sialylation of N-CAM. However, distinct changes in desialo forms were observed after neuraminidase treatment. Myogenesis was accompanied by increases in 125- and 155-kD desialo forms with minor changes in 120- and 145-kD forms. Biosynthetic labeling studies showed that myoblasts specifically expressed a transmembrane isoform of 145 kD that was phosphorylated and was down-regulated in myotubes. Pulse-chase analysis of myotubes showed that the 120-kD isoform and an isoform of 145 kD that co-migrated with, but was distinct from, the 145 kD transmembrane isoform of myoblasts were precursors of the 125- and 155-kD isoforms, respectively, that accumulated in myotubes. The 125- and 155-kD isoforms in myotubes are linked to the cell membrane via phosphatidylinositol linkage and can be released by phospholipase C. Indirect immunofluorescence analysis showed that phosphatidylinositol specific phospholipase C specifically released N-CAM from the myotube membrane generating N-CAM-free myotubes, while myoblasts were unaffected by this treatment. Three N-CAM mRNA species were observed in mouse muscle cell lines. Myoblasts were characterized by their expression of 6.7- and 5.2-kb transcripts while myotubes express 5.2- and 2.9-kb transcripts. Thus, myogenesis is qualitatively associated with a down regulation of the 6.7-kb transcript and an up regulation of the 5.2- and 2.9-kb transcript.