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

Novel adult cortical neuron processing and screening method illustrates sex- and age-dependent effects of pharmaceutical compounds

Neurodegenerative diseases and neurotraumatic injuries are typically age-associated disorders that can reduce neuron survival, neurite outgrowth, and synaptic plasticity leading to loss of cognitive capacity, executive function, and motor control. In pursuit of reducing the loss of said neurological functions, novel compounds are sought that promote neuron viability, neuritogenesis, and/or synaptic plasticity. Current high content in vitro screenings typically use cells that are iPSC-derived, embryonic, or originate from post-natal tissues; however, most patients suffering from neurodegenerative diseases and neurotrauma are of middle-age and older. The chasm in maturity between the neurons used in drug screens and those in a target population is a barrier for translational success of in vitro results. It has been historically challenging to culture adult neurons let alone conduct screenings; therefore, age-appropriate drug screenings have previously not been plausible. We have modified Miltenyi’s protocol to increase neuronal yield, neuron purity, and neural viability at a reduced cost to expand our capacity to screen compounds directly in primary adult neurons. To our knowledge, we developed the first morphology-based screening system using adult cortical neurons and the first to incorporate age and sex as biological variables in a screen using adult cortical neurons. By using primary adult cortical neurons from mice that were 4 to 48 weeks old for screening pharmaceutical agents, we have demonstrated age- and sex-dependent effects on neuritogenesis and neuron survival in vitro. Utilizing age- and sex-appropriate in vitro models to find novel compounds increasing neuron survival and neurite outgrowth, made possible by our modified adult neuron processing method, will greatly increase the relevance of in vitro screening for finding neuroprotective compounds.

Schwann cell interactions during the development of the peripheral nervous system

Schwann cells play a critical role in the development of the peripheral nervous system (PNS), establishing important relationships both with the extracellular milieu and other cell types, particularly neurons. In this review, we discuss various Schwann cell interactions integral to the proper establishment, spatial arrangement, and function of the PNS. We include signals that cascade onto Schwann cells from axons and from the extracellular matrix, bidirectional signals that help to establish the axo-glial relationship and how Schwann cells in turn support the axon. Further, we speculate on how Schwann cell interactions with other components of the developing PNS ultimately promote the complete construction of the peripheral nerve.

Antibody Binding Specificity for Kappa (Vκ) Light Chain-containing Human (IgM) Antibodies: Polysialic Acid (PSA) Attached to NCAM as a Case Study

Antibodies of the IgM isotype are often neglected as potential therapeutics in human trials, animal models of human diseases as well as detecting agents in standard laboratory techniques. In contrast, several human IgMs demonstrated proof of efficacy in cancer models and models of CNS disorders including multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). Reasons for their lack of consideration include difficulties to express, purify and stabilize IgM antibodies, challenge to identify (non-protein) antigens, low affinity binding and fundamental knowledge gaps in carbohydrate and lipid research.

This manuscript uses HIgM12 as an example to provide a detailed protocol to detect antigens by Western blotting, immunoprecipitations and immunocytochemistry. HIgM12 targets polysialic acid (PSA) attached to the neural cell adhesion molecule (NCAM). Early postnatal mouse brain tissue from wild type (WT) and NCAM knockout (KO) mice lacking the three major central nervous system (CNS) splice variants NCAM180, 140 and 120 was used to evaluate the importance of NCAM for binding to HIgM12. Further enzymatic digestion of CNS tissue and cultured CNS cells using endoneuraminidases led us to identify PSA as the specific binding epitope for HIgM12.

Cell adhesion molecule L1 contributes to neuronal excitability regulating the function of voltage-gated Na+ channels

L1 (also known as L1CAM) is a trans-membrane glycoprotein mediating neuron-neuron adhesion through homophilic and heterophilic interactions. Although experimental evidence has implicated L1 in axonal outgrowth, fasciculation and pathfinding, its contribution to voltage-gated Na(+) channel function and membrane excitability has remained unknown. Here, we show that firing rate, single cell spiking frequency and Na(+) current density are all reduced in hippocampal excitatory neurons from L1-deficient mice both in culture and in slices owing to an overall reduced membrane expression of Na(+) channels. Remarkably, normal firing activity was restored when L1 was reintroduced into L1-deficient excitatory neurons, indicating that abnormal firing patterns are not related to developmental abnormalities, but are a direct consequence of L1 deletion. Moreover, L1 deficiency leads to impairment of action potential initiation, most likely due to the loss of the interaction of L1 with ankyrin G that produces the delocalization of Na(+) channels at the axonal initial segment. We conclude that L1 contributes to functional expression and localization of Na(+) channels to the neuronal plasma membrane, ensuring correct initiation of action potential and normal firing activity.

A new mechanism of nervous system plasticity: activity-dependent myelination

The synapse is the focus of experimental research and theory on the cellular mechanisms of nervous system plasticity and learning, but recent research is expanding the consideration of plasticity into new mechanisms beyond the synapse, notably including the possibility that conduction velocity could be modifiable through changes in myelin to optimize the timing of information transmission through neural circuits. This concept emerges from a confluence of brain imaging that reveals changes in white matter in the human brain during learning, together with cellular studies showing that the process of myelination can be influenced by action potential firing in axons. This Opinion article summarizes the new research on activity-dependent myelination, explores the possible implications of these studies and outlines the potential for new research.

Polysialic acid as an antigen for monoclonal antibody HIgM12 to treat multiple sclerosis and other neurodegenerative disorders

CNS regeneration is a desirable goal for diseases of brain and spinal cord. Current therapeutic strategies for the treatment of multiple sclerosis (MS) aim to eliminate detrimental effects of the immune system, so far without reversing disability or affecting long-term prognosis in patients. Approachable molecular targets that stimulate CNS repair are not part of the clinical praxis or have not been identified yet. The purpose of this study was to identify the molecular target of the human monoclonal antibody HIgM12. HIgM12 reverses motor deficits in chronically demyelinated mice, a model of MS. Here, we identified polysialic acid (PSA) attached to the neural cell adhesion molecule (NCAM) as the antigen for HIgM12 by using different NCAM knockout strains and through PSA removal from the NCAM protein core. Antibody binding to CNS tissue and primary cells, antibody-mediated cell adhesion, and neurite outgrowth on HIgM12-coated nitrocellulose was detected only in the presence of PSA as assessed by western blotting, immunoprecipitation, immunocytochemistry, and histochemistry. We conclude that HIgM12 mediates its in vivo and in vitro effects through binding to PSA and has the potential to be an effective therapy for MS and neurodegenerative diseases. The human antibody HIgM12 stimulates neurite outgrowth in vitro and promotes function in chronically demyelinated mice, a model of multiple sclerosis. The cellular antigen for HIgM12 was undetermined. Here, we identified polysialic acid attached to NCAM (neural cell adhesion molecule) as the cellular target for HIgM12. This includes glial fibrillary acidic protein (GFAP)-positive mouse astrocytes (GFAP, red; HIgM12, green; DAPI, blue) among other cell types of the central nervous system. These findings indicate a new strategy for the treatment of neuro-motor disorders including multiple sclerosis.

Electrical stimuli in the central nervous system microenvironment

Electrical stimulation to manipulate the central nervous system (CNS) has been applied as early as the 1750s to produce visual sensations of light. Deep brain stimulation (DBS), cochlear implants, visual prosthetics, and functional electrical stimulation (FES) are being applied in the clinic to treat a wide array of neurological diseases, disorders, and injuries. This review describes the history of electrical stimulation of the CNS microenvironment; recent advances in electrical stimulation of the CNS, including DBS to treat essential tremor, Parkinson's disease, and depression; FES for the treatment of spinal cord injuries; and alternative electrical devices to restore vision and hearing via neuroprosthetics (retinal and cochlear implants). It also discusses the role of electrical cues during development and following injury and, importantly, manipulation of these endogenous cues to support regeneration of neural tissue.

Single chain fragment variable antibodies developed by using as target the 3rd fibronectin type III homologous repeat fragment of human neural cell adhesion molecule L1 promote cell migration and neuritogenesis

L1CAM plays important roles during ontogeny, including promotion of neuronal cell migration and neuritogenesis, and stimulation of axonal outgrowth, fasciculation and myelination. These functions are at least partially exerted through a 16-mer amino acid sequence in the third fibronectin type III-like repeat of L1, which associates with several interaction partners, including integrins, other adhesion molecules and growth factor receptors. Here, using the Tomlinson I library for phage display, we obtained two single-chain variable fragment antibodies (scFvs) against this peptide sequence of human L1, hereafter called H3 peptide. Both scFvs recognize the H3 peptide and the extracellular domain of L1, as tested by enzyme-linked immunosorbent assay (ELISA), Western blot analysis and immunofluorescence staining of L1 expresssing cells. Furthermore, both scFvs reduce U-87 MG cell adhesion to fibronectin, while stimulating cell migration. Application of scFvs to human neuroblastoma SK-N-SH cells promote process outgrowth. Similar to triggering of endogenous L1 functions at the cell surface, both scFvs activate the signal transducers Erk and Src in these cells. Our results indicate that scFvs against a functionally pivotal domain in L1 trigger its regeneration-beneficial functions in vitro, encouraging thoughts on therapy of neurodegenerative diseases in the hope to ameliorate human nervous system diseases.

Promotion of spinal cord regeneration by neural stem cell-secreted trimerized cell adhesion molecule L1

The L1 cell adhesion molecule promotes neurite outgrowth and neuronal survival in homophilic and heterophilic interactions and enhances neurite outgrowth and neuronal survival homophilically, i.e. by self binding. We investigated whether exploitation of homophilic and possibly also heterophilic mechanisms of neural stem cells overexpressing the full-length transmembrane L1 and a secreted trimer engineered to express its extracellular domain would be more beneficial for functional recovery of the compression injured spinal cord of adult mice than stem cells overexpressing only full-length L1 or the parental, non-engineered cells. Here we report that stem cells expressing trimeric and full-length L1 are indeed more efficient in promoting locomotor recovery when compared to stem cells overexpressing only full-length L1 or the parental stem cells. The trimer expressing stem cells were also more efficient in reducing glial scar volume and expression of chondroitin sulfates and the chondroitin sulfate proteoglycan NG2. They were also more efficient in enhancing regrowth/sprouting and/or preservation of serotonergic axons, and remyelination and/or myelin sparing. Moreover, degeneration/dying back of corticospinal cord axons was prevented more by the trimer expressing stem cells. These results encourage the view that stem cells engineered to drive the beneficial functions of L1 via homophilic and heterophilic interactions are functionally optimized and may thus be of therapeutic value.

Disruption of laminin in the peripheral nervous system impedes nonmyelinating Schwann cell development and impairs nociceptive sensory function

The mechanisms controlling the differentiation of immature Schwann cells (SCs) into nonmyelinating SCs is not known. Laminins are extracellular matrix proteins critical for myelinating SC differentiation, but their roles in nonmyelinating SC development have not been established. Here, we show that the peripheral nerves of mutant mice with laminin-deficient SCs do not form Remak bundles, which consist of a single nonmyelinating SC interacting with multiple unmyelinated axons. These mutant nerves show aberrant L1 and neural cell adhesion molecule (N-CAM) expression pattern during development. The homophilic and heterophilic interactions of N-CAM are also impaired in the mutant nerves. Other molecular markers for nonmyelinating SCs, including Egr-1, glial fibrillary acidic protein, and AN2/NG2, are all absent in adult mutant nerves. Analysis of expression of SC lineage markers demonstrates that nonmyelinating SCs do not develop in mutant nerves. Additionally, mutant mice are insensitive to heat stimuli and show a decreased number of C-fiber sensory neurons, indicating reduced nociceptive sensory function. These results show that laminin participates in nonmyelinating SC development and Remak bundle formation and suggest a possible role for laminin deficiency in peripheral sensory neuropathies.

Rho kinase inhibitors Y27632 and H1152 augment neurite extension in the presence of cultured Schwann cells

Background

RhoA and Rho kinase inhibitors overcome the inhibition of axonal regeneration posed by central nervous system (CNS) substrates.

Methods

To investigate if inhibition of the Rho pathway augments the neurite extension that naturally occurs in the peripheral nervous system (PNS) following nerve damage, dorsal root ganglion neurons and Schwann cell co-cultures were incubated with culture medium, C3 fusion toxin, and the Rho kinase (ROCK) inhibitors Y27632 and H1152. The longest neurite per neuron were measured and compared. Incubation with Y27632 and H1152 resulted in significantly longer neurites than controls when the neurons were in contact with Schwann cells. When separated by a porous P.E.T. membrane, only the group incubated with H1152 developed significantly longer neurites. This work demonstrates that Rho kinase inhibition augments neurite elongation in the presence of contact with a PNS-like substrate.

Mutations in the nervous system--specific HSN2 exon of WNK1 cause hereditary sensory neuropathy type II

Hereditary sensory and autonomic neuropathy type II (HSANII) is an early-onset autosomal recessive disorder characterized by loss of perception to pain, touch, and heat due to a loss of peripheral sensory nerves. Mutations in hereditary sensory neuropathy type II (HSN2), a single-exon ORF originally identified in affected families in Quebec and Newfoundland, Canada, were found to cause HSANII. We report here that HSN2 is a nervous system-specific exon of the with-no-lysine(K)-1 (WNK1) gene. WNK1 mutations have previously been reported to cause pseudohypoaldosteronism type II but have not been studied in the nervous system. Given the high degree of conservation of WNK1 between mice and humans, we characterized the structure and expression patterns of this isoform in mice. Immunodetections indicated that this Wnk1/Hsn2 isoform was expressed in sensory components of the peripheral nervous system and CNS associated with relaying sensory and nociceptive signals, including satellite cells, Schwann cells, and sensory neurons. We also demonstrate that the novel protein product of Wnk1/Hsn2 was more abundant in sensory neurons than motor neurons. The characteristics of WNK1/HSN2 point to a possible role for this gene in the peripheral sensory perception deficits characterizing HSANII.

Adeno-associated virus-mediated L1 expression promotes functional recovery after spinal cord injury

Paucity of permissive molecules and abundance of inhibitory molecules in the injured spinal cord of adult mammals prevent axons from successful regeneration and, thus, contribute to the failure of functional recovery. Using an adeno-associated viral (AAV) vector, we expressed the regeneration-promoting cell adhesion molecule L1 in both neurons and glia in the lesioned spinal cord of adult mice. Exogenous L1, detectable already 1 week after thoracic spinal cord compression and immediate vector injection, was expressed at high levels up to 5 weeks, the longest time-period studied. Dissemination of L1-transduced cells throughout the spinal cord was wide, spanning over more than 10 mm rostral and 10 mm caudal to the lesion scar. L1 was not detectable in the fibronectin-positive lesion core. L1 overexpression led to improved stepping abilities and muscle coordination during ground locomotion over a 5-week observation period. Superior functional improvement was associated with enhanced reinnervation of the lumbar spinal cord by 5-HT axons. Corticospinal tract axons did not regrow beyond the lesion scar but extended distally into closer proximity to the injury site in AAV-L1-treated compared with control mice. The expression of the neurite outgrowth-inhibitory chondroitin sulphate proteoglycan NG2 was decreased in AAV-L1-treated spinal cords, along with reduction of the reactive astroglial marker GFAP. In vitro experiments confirmed that L1 inhibits astrocyte proliferation, migration, process extension and GFAP expression. Analyses of intracellular signalling indicated that exogenous L1 activates diverse cascades in neurons and glia. Thus, AAV-mediated L1 overexpression appears to be a potent means to favourably modify the local environment in the injured spinal cord and promote regeneration. Our study demonstrates a clinically feasible approach of promising potential.

Neural cell adhesion molecule L1-transfected embryonic stem cells promote functional recovery after excitotoxic lesion of the mouse striatum

We have generated a murine embryonic stem cell line constitutively expressing L1 at all stages of neural differentiation to investigate the effects of L1 overexpression on stem cell proliferation, migration, differentiation, cell death, and ability to influence drug-induced rotation behavior in an animal model of Huntington's disease. L1-transfected cells showed decreased cell proliferation in vitro, enhanced neuronal differentiation in vitro and in vivo, and decreased astrocytic differentiation in vivo without influencing cell death compared with nontransfected cells. L1 overexpression also resulted in an increased yield of GABAergic neurons and enhanced migration of embryonic stem cell-derived neural precursor cells into the lesioned striatum. Mice grafted with L1-transfected cells showed recovery in rotation behavior 1 and 4 weeks, but not 8 weeks, after transplantation compared with mice that had received nontransfected cells, thus demonstrating for the first time that a recognition molecule is capable of improving functional recovery during the initial phase in a syngeneic transplantation paradigm.

Combination of engineered neural cell adhesion molecules and GDF-5 for improved neurite extension in nerve guide concepts

Current therapeutical approaches for the treatment of severe lesions in the peripheral nervous system rely on the use of autologous tissue or the body's own Schwann cells. However, these approaches are limited and alternative strategies for peripheral nerve regeneration are required. Here we evaluate combinations of a variety of neuronal regeneration factors including engineered cell adhesion molecules and growth factors in embryonic model neurons to test the possible improvement of artificial nerve guides by cooperative mechanisms. Cell adhesion molecules L1 and neurofascin synergistically promote neurite elongation. The outgrowth promoting properties of both proteins can be combined and further increased within one chimeric protein. Addition of growth and differentiation factor 5 (GDF-5) further enhances neurite outgrowth in a substrate-independent manner. This effect is not due to a protective mode of action of GDF-5 against pro-apoptotic stimuli. Consequently, the study supports the idea that different modes of action of pro-regenerative factors may contribute synergistically to neurite outgrowth and emphasizes the applicability of combinations of proteins specifically involved in development of the nervous system for therapeutical approaches.

Quantification of N-CAM and N-cadherin expression in axotomized and crushed rat sciatic nerve

Adhesion molecules are important in supporting axonal regeneration. Qualitative studies have described increased expression of neural cell adhesion molecule (NCAM) and N-cadherin in models of nerve injury allowing active regeneration. In this study we have used quantitative immunohistochemistry to compare expression of NCAM and N-cadherin after nerve injury either with active regeneration (crush) into the distal stump or without (axotomy and capping). Quantification was performed 15 days after axotomy in proximal and distal stumps. Quantification after crush either proximal, distal or within the crushed area was performed at 2, 7, 15 and 30 days after injury. Axotomy induced increases in expression in proximal stumps between two and three times those in uninjured nerves for both molecules. In distal stumps, N-cadherin levels increased seven-fold, yet NCAM levels did not exceed control values. After crush, NCAM immunoreactivity increased in the crushed area and distal stump in contrast to axotomy and NCAM-positive axons co-localized with PGP9.5. N-cadherin levels in the distal stump increased above control levels, but the magnitude of the increase seen after crush was different to those seen after axotomy. In conclusion, increased expression of adhesion molecules, particularly NCAM, in the distal stump of injured nerves is dependent upon the presence of regenerating axons.

Expression of the Neural Recognition Molecule L1 by Cultured Neural Cells is influenced by K+ and the Glutamate Receptor Agonist NMDA

To investigate the influence of neuronal activity on the expression of neural recognition molecules, cultures of neural cell lines and dissociated cells of early postnatal mouse cerebellum were maintained in the presence of elevated concentrations of K+ and the glutamate agonist N-methyl-d-aspartate (NMDA). Levels of expression of the neural adhesion molecules L1 and N-CAM at the cell surface were measured by an enzyme-linked immunosorbent assay. Expression of L1 was up-regulated in neuroblastoma N2A cells after 1 day of maintenance in 40 and 60 mM K+, but not in phaeochromocytoma PC12 cells. Expression levels of N-CAM and antigens recognized by the monoclonal antibody A2B5 or by polyclonal antibodies to crude membrane fractions of liver were not significantly altered by elevated K+ concentrations in these two cell lines. In monolayer cultures of early postnatal mouse cerebellum, an increase of 60% in expression of L1, but not N-CAM or A2B5, was seen at 20 and 40 mM K+. This increase in L1 expression was specifically inhibitable by the Ca2+ channel blocker nicardipine. NMDA at a concentration of 100 microM increased levels of L1, but not of N-CAM. This increase was inhibitable by the NMDA antagonists 2-amino-5-phosphonovalerate and MK-801, but not significantly by the kainate/quisqualate antagonist 6-cyano-7-nitroquinoxaline-2,3-dione. The increase in L1 expression at higher K+ concentrations was not inhibitable by the NMDA antagonists, indicating that the K+-mediated increase in L1 expression is not due to release of glutamate by cerebellar neurons. These observations indicate that compounds influencing neuronal membrane properties, and thus neuronal excitability, are capable of regulating the expression of L1. In a more general context, these findings suggest that previously observed changes in synaptic connectivity in situ, resulting from activity-dependent fine tuning of neuronal morphology, may be mediated by alterations in the expression of recognition molecules.

The difference in E-cadherin expression between nonvascularized and vascularized nerve grafts: study in the rat sciatic nerve model

BACKGROUND

We investigated the expression of E-cadherin during nerve regeneration after nonvascularized and vascularized nerve grafts.

MATERIALS AND METHODS

We used the rat sciatic nerve model. E-cadherin expression was detected by Western blot analysis and immunofluorescent staining with anti E-cadherin monoclonal antibody. The level of E-cadherin expression was calculated as the amount relative to that of E-cadherin expression of normal control nerve. Furthermore, repair of the neural tissue structure was examined by toluidine blue staining.

RESULTS

In both cases, the level of E-cadherin expression decreased at first, and then gradually increased. The maximum level was 1.61 +/- 0.066-fold in the nonvascularized nerve graft and 2.254 +/- 0.071-fold in the vascularized nerve graft. From the 1st to the 16th postoperative weeks, the level of E-cadherin expression in the vascularized nerve graft was significantly higher than that in the nonvascularized nerve graft. In the immunofluorescent staining, E-cadherin expression was almost negative or decreased immediately after the operation, but the degree of expression was gradually increased in Schwann cells. The degree of E-cadherin expression in the vascularized nerve graft was greater than that in the nonvascularized nerve graft. In toluidine blue staining, the velocity of tissue repair was more rapid in the vascularized nerve graft than in the nonvascularized graft.

CONCLUSION

These results demonstrate that the E-cadherin expression of grafted nerve was increased during the nerve regeneration, and the expression was mainly observed in Schwann cells. Because the level of E-cadherin expression was significantly higher in the vascularized nerve graft than in the nonvascularized nerve graft, the level of E-cadherin expression may affect the rapidity of nerve regeneration.

Detection of E-cadherin expression after nerve repair in a rat sciatic nerve model

The authors investigated E-cadherin expression during nerve regeneration after nerve suture using the rat sciatic nerve model. Five rats were used during each postoperative period. E-cadherin expression was detected by Western blot analysis and immunofluorescent staining with an anti-E-cadherin monoclonal antibody. The level of E-cadherin expression was calculated as the amount relative to that found in normal control nerve. The level of E-cadherin expression was decreased at first, and then gradually increased. The maximum level of E-cadherin was 1.92 +/- 0.07 fold in the sutured nerve. The level of E-cadherin expression in the sutured nerve was significantly greater (p < 0.0001) than that of the normal control nerve from postoperative day 3 to 21, and that of sutured nerve returned to the control level by postoperative day 28. The immunofluorescent staining results indicated that E-cadherin expression was almost negative or decreased immediately after the operation, but the degree of expression increased gradually in Schwann's cells. The degree of E-cadherin expression was significantly greater than that of normal control nerves from postoperative day 7 to 14, and returned to the control level by postoperative day 21. These results demonstrate that E-cadherin expression increases during nerve regeneration, and the expression was observed mainly in Schwann's cells. The degree of E-cadherin expression may affect the rate of nerve regeneration.

Immunohistochemical localization of the neural cell adhesion molecule in the rat sciatic nerve

The neural cell adhesion molecule (NCAM) has been widely studied in the early embryonal development of the nervous system. The data about NCAM distribution in the peripheral nerves during postnatal life are scant and some controversial. In the present study, the NCAM localization in the sciatic nerves of 15-day-old Wistar rats has been studied. Semi-thin sections of the nerves were immunotested with a polyclonal antibody (Santa Cruz Biotechnology) that recognizes rat NCAM. The antibody was visualized with donkey anti-goat IgG, conjugated to 12 nm colloidal gold, and silver amplification. In the myelinated nerve fibres, the immunoreactivity was associated with the axons, mainly with their plasma membrane, which was unstained in the nodes of Ranvier. The myelin sheaths and the myelinating Schwann cells were negative. The extracellular matrix and the bundles of non-myelinated nerve fibres were immunopositive.

Differential expression of trkB.T1 and trkB.T2, truncated trkC, and p75(NGFR) in the cochlea prior to hearing function

Prior to the onset of hearing, synchronous cellular, neuronal, and morphogenetic processes participate in the development of a functional cochlea. We have studied the expression of different splice forms of trkB and trkC as well as p75(NGFR) in rat and mouse cochlea within this critical developmental period, using in situ hybridization, PCR, Northern blotting, and immunohistochemical analyses. An antibody to full-length trkB receptors proved to detect full-length trkB receptors as well as truncated trkB.T2 but not trkB. T1 isoforms. Full-length trkB and trkC isoforms as well as trkB.T2 but not trkB.T1 receptors were noted in cochlear neurons. A transient expression of trkB.T1 and trkB.T2 was observed at the epithelial-mesenchymal border of the spiral ligament during this time. A sequential appearance of trkB.T1, the low-affinity neurotrophin receptor p75(NGFR), and trkB.T2 in epithelial cochlear cells correlated with the formation of the inner sulcus of the organ. A differential expression of presumptive trkB.T2 in hair and supporting cells was observed concomitant with the maturation of the distinct innervation pattern of these cells. A gradual shift from p75(NGFR) to truncated trkC receptors in Pillar cells occurred during the formation of the tunnel of Corti. A distinct expression of full-length trkC correlated with the time of differentiation of the stria vascularis. Finally, an expression of trkB.T1 and trkB.T2 in oligodendrocytes, full-length trkB and trkC in nerve fibers, and p75(NGFR) in Schwann cells was noted at the glial interface of the VIIIth nerve during the establishment of the glial transition zone. These various transitory neurotrophin receptor expression patterns, which were related to final maturation processes of the cochlea, may provide new insights into the as yet obscure role of neurotrophin receptors in nonneuronal tissue.

Induction of LIF-mRNA by TGF-beta 1 in Schwann cells

Schwann cell is a cell type that forms myelin sheath and provides trophic supports for neuronal cells by producing neurotrophic factors such as neurotrophins and neurokines in both normal and traumatic situations. It was recently reported that after lesion of sciatic nerve, mRNA for cholinergic differentiation factor (CDF)/leukemia inhibitory factor (LIF) is induced in nonneuronal cells in the nerve. However, the source of LIF-mRNA and the mechanism of LIF-mRNA regulation have remained largely unknown. In the present study, we searched for factors regulating the LIF-mRNA expression in cultured Schwann cells isolated from newborn rat sciatic nerve. Among various growth factors and cytokines tested, TGF beta-1 exerted the most prominent effect on the induction of LIF-mRNA in the cultured Schwann cells. The effect of TGF-beta 1 on the increase of LIF-mRNA levels was suppressed by either staurosporine or H-7 suggesting the role of PKC or PKC-like protein kinase activity in the induction of LIF-mRNA. The induction of LIF mRNA by TGF-beta 1 was suppressed in the co-culture of the Schwann cells with embryonic rat DRG neurons. The addition of ascorbic acid, which is known to promote myelination in this co-culture system, further suppressed the TGF-beta 1 induction of LIF-mRNA. These results suggest that Schwann cells respond to TGF-beta 1 in a lesion situation to produce LIF, which supports neuronal survival and regeneration. The re-establishment of neuron-Schwann cell interaction would in turn suppress the LIF production to terminate its action during the lesion situation.

Identification and characterization of differentiation-dependent Schwann cell surface antigens by novel monoclonal antibodies: introduction of a marker common to the non-myelin-forming phenotype

In an attempt to identify and characterize novel Schwann cell surface molecules with putative functions during development, maintenance, and regeneration of the peripheral nervous system (PNS), we have produced monoclonal antibodies against viable neonatal rat Schwann cells. Using a sensitive live cell ELISA protocol, three monoclonal antibodies reactive with cultured Schwann cells, designated 27B10, 26F2, and 27C7 were isolated. The 27B10 and 26F2 antibodies specifically labelled forskolin-stimulated secondary Schwann cells in vitro as determined by live cell ELISA implying that the expression of the antigens in situ is regulated by axonal contact. The observation that the antigens seemed to be associated with both Schwann cell phenotypes clearly discriminated them from the well characterized myelin proteins as well as from molecules known to be confined to the non-myelin-forming phenotype. Interestingly, both antigens were found to be concentrated at the nodes of Ranvier. Further studies therefore have to show whether the identified antigens share structural or functional homology with adhesion or channel molecules, which display a similar distribution. Following transection of the adult sciatic nerve, the 26F2 antigen was rapidly down-regulated in the distal nerve stump. The 27C7 antibody reacted with an 80 kDa cell surface molecule common to non-myelin-forming Schwann cells. No differences in expression of the antigen between forskolin-treated and untreated Schwann cells in vitro were found, suggesting that the antigen is expressed independently from axonal contact. Two weeks after nerve transection in the absence of myelinating Schwann cells, the antigen was associated with S-100-positive Schwann cells of the distal nerve stump. The antigen was found to be expressed also by non-neuronal tissues, the level of the protein declined towards the adult stage. Comparison of the 27C7 antigen with previously described marker molecules suggests that we have identified a novel Schwann cell surface antigen of the non-myelin-forming phenotype.

Augmentation of adherens junction formation in mesenchymal cells by co-expression of N-CAM or short-term stimulation of tyrosine-phosphorylation

Adherens-type junctions (AJ) are specialized intercellular contacts, mediated by cadherins and characterized by the association with actin filaments through a vinculin- and catenin-rich submembrane plaque. We describe here two mechanisms which potentiate AJ formation in mesenchymal cells. These include the augmentation of AJ by the co-expression of another adhesion molecule, namely NCAM, and the stimulation of tyrosine phosphorylation. These effects were obtained in NIH-3T3 cells, which, under normal conditions, have poor cadherin- and vinculin-containing intercellular junctions. The transfection of these cells with cDNA encoding the 140kD NCAM resulted in the extensive formation of cadherin- and vinculin-rich AJ, demonstrating a cooperativity between the two junctional systems. AJ could also be induced in 3T3, and in CEF and COS cells, upon a brief exposure to H2O2/vanadate, which elevates cellular levels of phosphotyrosine due to inhibition of tyrosine-specific phosphatases. This induction was, however, transient since prolonged exposure to H2O2/vanadate resulted in an overall destruction of AJ and detachment of cells from each other and from the extracellular matrix. AJ formation appears, therefore, to be modulated by a variety of factors including the level of expression of its intrinsic components, the cooperative effect of other adhesion molecules, and by tyrosine-phosphorylation.

In vitro differentiation of E-N-CAM expressing rat neural precursor cells isolated by FACS during prenatal development

Most fetal rat brain cells expressing the embryonal, highly sialylated form of the cell adhesion molecule N-CAM (E-N-CAM) are precursor cells, as judged from the absence of marker molecules specific for mature neural cell types. However, the detection of E-N-CAM+ cells in frozen sections does not provide information on the lineage-specific differentiation of these cells during development. To investigate their differentiation behaviour in vitro, E-N-CAM+ cells were isolated at different times of brain development by fluorescence-activated cell sorting (FACS), using a monoclonal antibody (Mab RB21-7) which specifically recognizes polysialic acid (PSA) residues on E-N-CAM. Double-immunofluorescence analyses showed that the majority of E-N-CAM+ cells isolated on prenatal days 15 to 18 differentiated into neurons while a small subset of Mab RB21-7 binding cells proved to be astrocytic precursors and/or bipotential. The proportion of E-N-CAM+ astrocytic precursors increased during later development (prenatal day 22) concomitantly with the onset of gliogenesis. While conversion of E-N-CAM to mature forms of N-CAM was never observed in neurons during cultivation, E-N-CAM+ cells of the astrocyte lineage switched to N-CAM soon after the onset of GFAP expression. A lineage-specific transition of E-N-CAM to mature N-CAM expression is, therefore, suggested for these astrocytic progenitor cells during rat brain development.

Restricted localization of L1 and N-CAM at sites of contact between Schwann cells and neurites in culture

Schwann cell-axon contacts in developing and regenerating peripheral nerve in situ contain high levels of the recognition molecules L1 and N-CAM, while the molecules are not detectable at the ab-axonal cell surface of Schwann cells. To investigate whether Schwann cells, axons, or both contribute to the localization of the molecules at Schwann cell-axon contacts, a heterologous cell culture system consisting of Schwann cells from mice and neurons from chicken was investigated by immunoelectron microscopy using species-specific L1 and N-CAM antibodies. We showed that Schwann cells expressed both molecules only at sites of contact between Schwann cells and neurites and other Schwann cells. Schwann cells not in contact with other cells expressed both molecules on their entire cell surface. In contrast, neurites expressed G4, an L1-related molecule in chicken, on their entire cell surface independently of whether they were in contact with other cells or not. Thus, cultured Schwann cells localize L1 and N-CAM selectively at cell contact sites and may thereby stabilize their attachment to the neighboring cellular partners.

Lateral patterns of the neural cell adhesion molecule on the surface of hippocampal cells developing in vitro

In monolayer cultures of hippocampal neurons from newborn rats, an immunocytochemical quantitative study was carried out to investigate age-dependent arrangement of the neural cell adhesion molecules in different parts of cell membranes. On the fifth and 12th day in vitro, neural cell adhesion molecules were labelled with specific antibodies and protein A conjugated to colloidal gold particles. Samples of randomly selected electron micrographs that displayed labelled membrane fragments of cell bodies, growth cones, and axons were numerically analysed for the five- and 12-day in vitro neurons. Neural cell adhesion molecules surface topography was quantitatively described and compared, using a statistical stereological approach. The mean surface density of labelled neural cell adhesion molecules was found to be approximately 2.5 times higher in growth cone membranes relative to somatic and axonal membranes in five-day in vitro neurons. By the 12th day in vitro, this density decreases in somatic membranes (approximately 18%) and increases in axonal membranes (approximately 60%). Representative spectra of lateral intervals between labels as well as images that show typical topography of label on membrane surfaces were simulated. The results revealed regular patterns of neural cell adhesion molecules on the somatic surface and allowed consideration of neural cell adhesion molecules arrangement in a view of membrane adhesion properties. Participation of cytoskeleton in neural cell adhesion molecules rearrangement is discussed.

Changes in the neural cell adhesion molecule patterns on the rat glial cell surfaces with development and contact formation in vitro

In monolayer cultures of newborn rat hippocampal cells, immunogold-labelling at the electron microscope level was used to study quantitatively the neural cell adhesion molecule (N-CAM) arrangement on the surface of glial soma and processes on 5 and 12 days in vitro (DIV). Four corresponding samples of micrographs were formed. To quantify the labelling, a stochastic geometry approach was used. Spectra of lateral distances between labels as well as simulated images of the surface label arrangement (invisible in micrographs) were derived and compared. The data show that, on both 5 and 12 DIV, N-CAM density on the surface of processes is approximately 2 times higher than that in somata; 12-DIV cells showing a lower (approximately 25%) N-CAM surface density as compared with the 5-DIV cells. This suggests that N-CAM expression in glia surfaces decreases while the cells form contacts, and N-CAM sorting between soma and processes remains stable. The simulated topographies of the lateral N-CAM arrangement might highlight fundamental mechanisms that underlie formation of the neural network.

Laminin A, B1, and B2 chain gene expression in transected and regenerating nerves: regulation by axonal signals

Laminin A, B1, and B2 chain mRNA levels in degenerating and regenerating mouse sciatic nerves were examined using northern blot analysis. In normal intact nerves, B1 and B2 mRNA steady-state levels were high, but when the nerves were crushed, the steady-state levels of B1 and B2 mRNA per milligram wet tissue weight of the distal segments of the nerves increased five- to eightfold over that of control levels as the total RNA and beta-actin mRNA levels increased, suggesting that these increases were the consequence of Schwann cell proliferation after axotomy. When the steady-state levels of B1 and B2 mRNA were normalized as the ratio to total RNA or beta-actin mRNA levels, however, they drastically decreased to about 20% of the normal nerve levels in the nerve segments distal to both the crush and transection sites 1 day after injury. In the crushed nerves, B1 and B2 mRNA levels gradually increased as the regenerating nerves arrived at the distal segments and reestablished normal axon-Schwann cell contact, and then returned to normal levels on the 21st day. In the transected nerves, where Schwann cells continued to be disconnected from axons, both B1 and B2 mRNA levels remained low. Cultured Schwann cells expressed detectable levels of B1 and B2 chain mRNA which significantly increased when the cells were cocultured with sensory neurons. However, mRNA for A chain was not detectable in the normal, axotomized nerves or in cultured Schwann cells. These data indicate that Schwann cells express laminin B1 and B2 chain mRNA that are up-regulated by axonal or neuronal contact, but they do not express A chain mRNA.

Cell-cell contact modulates expression of cell adhesion molecule L1 in PC12 cells

The effect of cell contact on the expression of cell adhesion molecule L1 was investigated. The rat pheochromocytoma cell line PC12 cells were cultured at various densities in the presence or absence of the nerve growth factor. The addition of the nerve growth factor promoted the expression of L1. The expression of L1 was higher when the cells were cultured at high density than when done at low density both in the presence or absence of the nerve growth factor. Immunohistochemical staining of L1 showed that the expression of L1 was higher in the cells contacting each other. These results show that cell interaction affects the expression of cell adhesion molecule L1 in the PC12 cells.

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.

Analysis of promoter activity and 5' genomic structure of the neural cell adhesion molecule L1

To gain insight into the molecular mechanisms underlying the regulation of expression of the neural cell adhesion molecule L1 and into the exon-intron structure of the L1 gene, a genomic clone from the mouse was characterized. The clone was identified by screening an EMBL3 library with an L1-specific cDNA probe and comprises approximately 15 kb, in which the first 2,206 nucleotides of the coding region are included. Of the 5 of 6 immunoglobulin (Ig)-like domains sequenced, all are encoded by 2 exons, with the first exon being smaller than the second. The exon encoding the signal peptide is separated from a mini-exon containing 15 bp by a large intron, approximately 2.6 kb in length, whereas the other introns are smaller, with the coding information for the Ig-like domains 3-5 clustered in a 1,643-bp-long fragment with introns only 110-217 bp in length. The 5' upstream region of the clone comprises 5 kb, with the first 112 bp lying upstream to the coding sequence and containing a start site for transcription. No consensus sequence for a TATA box was found. Consensus DNA sequences for the binding of the gene products of Hox 1.3, engrailed and bicoid, are localized upstream to the transcription start site. A 1,262-bp fragment containing part of the first exon showed promoter activity in neuroblastoma cells, but hardly in L cells and not in CHO cells, indicating that this fragment is sufficient for neural cell directed promoter activity.

Neural cell adhesion molecule in aged mouse muscle

Expression of the neural cell adhesion molecule was compared in endplate and non-endplate regions of skeletal muscles of mature and old CBF-1 mice, in order to determine whether age-related changes in neuromuscular morphology were correlated with age changes in neural cell adhesion molecule expression. Three muscles were examined: two (soleus and sternomastoid) showed age-related regionalization of nerve terminals as one manifestation of increased synaptic remodelling while the third (diaphragm) did not. Relative neural cell adhesion molecule content in these muscles was measured by densitometry of immunoblots after concentration by affinity chromatography. Expression of the major 140,000 mol. wt form of neural cell adhesion molecule, which was most abundant in the endplate region, was increased in sternomastoid and soleus of old compared to adult mouse, but was unchanged with age in diaphragm. A 70,000-80,000 mol. wt presumably proteolytic polypeptide fragment of neural cell adhesion molecule was increased in immunoblots of all old muscles. Immunocytochemical studies of skeletal muscles showed no difference in neural cell adhesion molecule cellular distribution in mature vs old mice, but in motor nerve of sternomastoid, the number of neural cell adhesion molecule-positive nerve fibers was increased in old mice. Several lines of evidence indicated that partial denervation was rare in old CBF-1 mice, and therefore could not account for the findings above. Selective increase of 140,000 mol. wt neural cell adhesion molecule expression in the junctional regions of those muscles of old mice which show neuromuscular remodelling indicates that this adhesion molecule may play a role in the age-related instability of motor nerve terminals.

Molecular cloning of NILE glycoprotein and evidence for its continued expression in mature rat CNS

The NILE glycoprotein is a rat neuronal cell adhesion molecule which has been reported to be very similar in structure, function, and distribution to the mouse L1 glycoprotein. Here we report the complete nucleotide sequence of the NILE message (5,208 nucleotides) and the deduced amino acid sequence of the NILE polypeptide (1,257 amino acids). The predicted NILE protein is 96% identical to L1 at the amino acid level, confirming that the two molecules are homologues. The sequence information shows that NILE is a transmembrane molecule with an extensive ectodomain and a much smaller cytoplasmic domain. The extracellular portion of the molecule contains six immunoglobulin C-2 type domains followed by five fibronectin type III repeats. These two structural motifs are characteristic of several other cell adhesion molecules. The cytoplasmic tails of NILE and L1 are identical to each other and distinct from the cytoplasmic regions of all other cell adhesion molecules except Ng-CAM and neuroglian. Several possible sites for phosphorylation are present in the cytoplasmic tail of NILE. Antisera were produced against two NILE-beta-galactosidase fusion proteins containing distinct segments of the NILE polypeptide: the cytoplasmic domain and the segment containing fibronectin type III repeats. Immunoblots with these antisera and Northern blots with a NILE cDNA probe indicate that NILE continues to be expressed in most areas of the mature rat brain. This contradicts previous immunofluorescence data, which suggested that NILE was substantially down-regulated in maturing nerve fiber tracts. This raises the possibility that NILE could be masked in situ by interactions with other cell surface molecules.

Induction of NILE/L1 glycoprotein during neuronal differentiation of the embryonal carcinoma cell line EC1003

A new clone of the mouse embryonal carcinoma cell line 1003 (EC 1003.16) can be maintained in an undifferentiated state in serum-containing medium. Shifting these cells to serum-free, hormonally defined medium causes them to differentiate morphologically and acquire a number of molecular properties characteristic of neurons. Whereas undifferentiated cells lack the NILE/L1 glycoprotein, expression of this neuronal cell adhesion molecule is induced in the differentiating cells. Message for NILE/L1 becomes detectable after 5 days in serum-free medium, and cell-surface NILE/L1 can first be seen at this same time. Changes in two other cell adhesion molecules occur in parallel with the induction of NILE/L1. Fibronectin receptor is present on undifferentiated cells, but is down-regulated by the differentiating neurons. The neural cell adhesion molecule (N-CAM) undergoes a shift from the very adhesive adult form to the less adhesive, highly sialylated embryonic form. These changes would appear to emphasize the role of NILE/L1 in adhesive interactions involving differentiating neurons. Some changes in ganglioside expression also occur during EC 1003.16 differentiation. Undifferentiated cells express the D 1.1 ganglioside but lack gangliosides that are reactive with the monoclonal antibody A2B5. Differentiating cells lose D 1.1 and become A2B5-positive. Since D 1.1 is characteristic of undifferentiated neuroepithelial cells and A2B5 reactivity is a marker for several types of differentiated neurons, these changes in vitro appear to mimic events that occur in vivo.

Isolation and sequence of partial cDNA clones of human L1: homology of human and rodent L1 in the cytoplasmic region

We have isolated cDNA clones coding for the human homologue of the neuronal cell adhesion molecule L1. The nucleotide sequence of the cDNA clones and the deduced primary amino acid sequence of the carboxy terminal portion of the human L1 are homologous to the corresponding sequences of mouse L1 and rat NILE glycoprotein, with an especially high sequences identity in the cytoplasmic regions of the proteins. There is also protein sequence homology with the cytoplasmic region of the Drosophila cell adhesion molecule, neuroglian. The conservation of the cytoplasmic domain argues for an important functional role for this portion of the molecule.

Recombinant peripheral myelin protein P0 confers both adhesion and neurite outgrowth-promoting properties

To probe into the functional properties of the major peripheral myelin cell surface glycoprotein P0, its ability to confer adhesion and neurite outgrowth-promoting properties was studied in cell culture. To this aim, P0 was expressed as integral membrane glycoprotein at the surface of CV-1 cells with the help of a recombinant vaccinia virus expression system. Furthermore, the immunoglobulin-like extracellular domain of P0 (P0-ED) was expressed as soluble protein in a bacterial expression system and used as substrate coated to plastic dishes or as competitor in cell adhesion and neurite outgrowth-promoting assays. The adhesion of P0-expressing CV-1 cells to P0-ED substrate was specifically inhibitable by polyclonal P0 antibodies (54% +/- 6%). In addition, the specific interaction between P0 molecules could be reduced (49% +/- 8%) by adding soluble P0-ED to the culture medium, demonstrating that the homophilic interaction between recombinant P0 molecules can be mediated, at least on one partner of interacting molecules, by the unglycosylated Ig-like domain. Substrate-coated P0-ED also conferred adhesion and neurite outgrowth ability to dorsal root ganglion neurons with neurites of a mean length of about 150 microns. This neurite outgrowth was specifically inhibitable by soluble P0 (74% +/- 14%) and P0 antibodies (65% +/- 9%). These observations indicate that P0 is capable of displaying two different types of functional roles in the myelination process of peripheral nerves: The heterophilic interaction with neurons may be responsible for the recognition between axon and myelinating Schwann cell at the onset of myelination, whereas the homophilic interaction may indicate its role in the self-recognition of the apposing loops of Schwann cell surface membranes during the myelination process and in the mature compact myelin sheath.

Cell adhesion molecules in adrenal medulla grafts: enhancement of chromaffin cell L1/Ng-CAM expression and reorganization of extracellular matrix following transplantation

Intracerebral adrenal medulla grafts have been used in human patients as an experimental treatment for Parkinson's disease, based on studies in animal models of this disorder. However, alterations in chromaffin cell properties after transplantation and the factors controlling graft survival are poorly understood. Since cell adhesion molecules (CAMs) are involved in regeneration and development of neural tissue in vivo and in vitro, the present study was undertaken to determine the expression of CAMs in adrenal medulla isografts. Fragments of rat adrenal medulla were implanted into the right lateral ventricle. The majority of grafts survived quite well, for up to 2 months (the longest studied period). The implanted chromaffin cells did not develop extensive processes. The cells retained tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) immunoreactivity, while phenylethanolamine N-methyltransferase (PNMT) expression was decreased. Surviving transplanted chromaffin cells showed enhancement and spreading of surface L1/Ng-CAM expression as compared to normal chromaffin cells in adrenal medulla. The implanted chromaffin cells demonstrated only partial conversion to neuronal phenotypes. These chromaffin cells did not develop extensive processes, but showed an enhancement of L1/Ng-CAM expression. Surviving chromaffin cells were accompanied by reorganization of their closely associated extracellular matrix (ECM). As compared to normal in situ adrenal medulla, graft ECM demonstrated a substantial increase of L1/Ng-CAM and laminin immunoreactivities and a distinct decrease in J1/tenascin expression. Some adrenal medulla grafts degenerated, particularly when misplaced within the host brain parenchyma. In these cases the grafts showed fragmentation of ECM and gradual disappearance of CAMs. These results suggest that surviving adrenal medulla grafts exhibit increased synthesis of certain CAMs by chromaffin cells, which may be involved in interactions between chromaffin cells and the surrounding ECM. It is speculated that both surviving and degenerating adrenal medulla grafts could provide CAMs and ECM components including laminin to host brain and this way contribute to functional effects of grafts.

Differential splicing generates a nervous system-specific form of Drosophila neuroglian

We recently described the characterization and cloning of Drosophila neuroglian, a member of the immunoglobulin superfamily. Neuroglian contains six immunoglobulin-like domains and five fibronectin type III domains and shows strong sequence homology to the mouse neural cell adhesion molecule L1. Here we show that the neuroglian gene generates at least two different protein products by tissue-specific alternative splicing. The two protein forms differ in their cytoplasmic domains. The long form is restricted to the surface of neurons in the CNS and neurons and some support cells in the PNS; in contrast, the short form is expressed on a wide range of other cells and tissues. Thus, whereas the mouse L1 gene appears to encode only one protein that functions largely as a neural cell adhesion molecule, its Drosophila homolog, the neuroglian gene, encodes at least two protein forms that may play two different roles, one as a neural cell adhesion molecule and the other as a more general cell adhesion molecule involved in other tissues and imaginal disc morphogenesis.

Antibodies to the L1 adhesion molecule inhibit Schwann cell ensheathment of neurons in vitro

To investigate whether neural adhesion molecules are involved in neuron-induced Schwann cell differentiation, cocultures of pure dorsal root ganglion neurons, and Schwann cells were maintained in the presence of antibodies to evaluate possible perturbing effects. Several parameters characteristic of differentiating Schwann cells were studied, such as transition of spindle-shaped to flattened, i.e., more epithelioid morphology, association with neuronal cell bodies, ensheathment of neurites, production of basal lamina and collagen fibrils, and expression of the myelin associated glycoprotein (MAG). A complete ablation of Schwann cell differentiation in all features studied was seen with antibodies to the neural adhesion molecule L1. Antibodies to N-CAM did not reduce the association of Schwann cells with neurites but abolished the interdigitation of Schwann cell processes into neurite bundles, while leaving the other parameters studied unaffected. Fab fragments of antibodies to J1, MAG, and mouse liver membranes did not interfere with the manifestation of any of these parameters. None of the antibodies changed incorporation of [3H]thymidine into Schwann cells.

Immunoelectron-microscopic localization of the 180 kD component of the neural cell adhesion molecule N-CAM in postsynaptic membranes

In order to investigate the expression of cell adhesion molecules in synapses, we have studied the localization of the neural cell adhesion molecule N-CAM in the cerebellum and hippocampus of adult mice by immunocytological and immunochemical methods. Of the three molecular components of N-CAM with relative molecular masses (Mr) of 120, 140, and 180 kD, N-CAM 120 is not detectable in synaptosomal membranes, whereas N-CAM 140 is expressed on both pre- and postsynaptic membranes and N-CAM 180 is restricted to postsynaptic sites, with localization of the N-CAM 180-specific epitope in postsynaptic densities. Specificity of immunoreactivity is indicated by the observation that antibodies to the neural cell adhesion molecule L1 do not label synaptic membranes, whereas antibodies to two major components of postsynaptic densities, actin and erythrocyte spectrin, react with synaptic structures. Interestingly, N-CAM 180 is only detectable in subpopulations of synapses in the intact tissue. Isolated synaptosomes, opened for unimpeded accessibility of antibody by hypoosmotic treatment, also reveal a partial expression of N-CAM 180 in that 67% are labeled by antibodies to N-CAM 180, while antibodies to actin and erythrocyte spectrin react with 95% and 88% of all synaptosomes, respectively. N-CAM 180 does not appear to be differentially expressed in synapses of a particular morphological type, but is detectable in all types of synapses in the cerebellum and hippocampus, except for mossy fiber synapses and synapses between basket and Purkinje cells, which are generally N-CAM 180-negative. Since N-CAM 180 has been shown to be characteristic of stabilized or stabilizing cell contacts, possibly by its association with the cytoskeleton-membrane linker protein spectrin (Pollerberg et al.: J. Cell Biol. 101:1921-1929, '85; Nature 324:462-465, '86; Cell Tissue Res. 250:227-236, '87), we would like to suggest N-CAM 180 plays an important role in determining the stability of contacts between pre- and postsynaptic membranes and state of synaptic activity.