The adhesion molecule on glia (AMOG/beta 2) and alpha 1 subunits assemble to functional sodium pumps in Xenopus oocytes.

The adhesion molecule on glia, AMOG, an integral cell surface glycoprotein highly expressed by cerebellar astrocytes and involved in neuron to astrocyte adhesion and granule neuron migration (Antonicek, H., Persohn, E., and Schachner, M. (1987) J. Cell Biol. 104, 1587-1595) has been identified as a beta 2 subunit isoform of the mouse sodium pump (Gloor, S., Antonicek, H., Sweadner, K.J., Pagliusi, S., Frank, R., Moos, M., and Schachner, M. (1990) J. Cell Biol. 110, 165-174). Here we demonstrate that AMOG/beta 2 expressed by cRNA injection in Xenopus oocytes is capable of combining with endogenous Xenopus alpha 1 subunits or coexpressed Torpedo alpha 1 subunits to yield a functional alpha 1/AMOG sodium pump isozyme. Determinations of the number of ouabain binding sites and ouabain-sensitive 86Rb+ uptake suggest that the alpha 1/AMOG isozyme has slightly lower maximum transport rate and apparent affinity for external K+ than the alpha 1/beta 1 isozyme. Immunoprecipitation of alpha 1/AMOG complexes from digitonin extracts of [35S]methionine-labeled oocytes with a monoclonal anti-AMOG antibody provides direct evidence for a stable association between AMOG and the alpha 1 subunits of Xenopus and Torpedo.     

The novel carbohydrate epitope L3 is shared by some neural cell adhesion molecules

The monoclonal L3 antibody reacts with an N-glycosidically linked carbohydrate structure on at least nine glycoproteins of adult mouse brain. Three out of the L3 epitope-carrying glycoproteins could be identified as the neural cell adhesion molecules L1 and myelin-associated glycoprotein, and the novel adhesion molecule on glia. Expression of the L3 carbohydrate epitope is regulated independently of the protein backbone of these three glycoproteins. Based on the observation that out of three functionally characterized L3 epitope-carrying glycoproteins three fulfill the operational definition of an adhesion molecule, we would like to suggest that they form a new family of adhesion molecules that is distinct from the L2/HNK-1 carbohydrate epitope family of neural cell adhesion molecules. Interestingly, some members in each family appear to be unique to one family while other members belong to the two families.     

The L2/HNK-1 carbohydrate of neural cell adhesion molecules is involved in cell interactions

We investigated whether the L2/HNK-1 carbohydrate epitope, expressed by two unusual glycolipids and several neural adhesion molecules, including L1, neural cell adhesion molecule, J1, and the myelin-associated glycoprotein, is involved in adhesion. Monoclonal L2 antibodies, the L2/HNK-1-reactive, sulfate-3-glucuronyl residue carrying glycolipids (L2 glycolipid) and a tetrasaccharide derived from the L2 glycolipid (L2 tetrasaccharide) were added to microexplant cultures of early postnatal mouse cerebellum, and cell migration and process extension were monitored. On the substrate poly-D-lysine, Fab fragments of L2 antibodies, L2 glycolipid, and L2 tetrasaccharide inhibited outgrowth of astrocytic processes and migration of cell bodies, but only L2 glycolipid and L2 tetrasaccharide reduced neurite outgrowth. On laminin, L2 antibodies, L2 glycolipid, and L2 tetrasaccharide inhibited outgrowth of astrocytic processes. Additionally, L2 glycolipid and L2 tetrasaccharide inhibited cell migration and neurite outgrowth. Several negatively charged glycolipids, lipids, and saccharides were tested for control and found to have no effect on outgrowth patterns, except for sulfatide and heparin, which modified outgrowth patterns in a similar fashion as L2 glycolipid and L2 tetrasaccharide. On astrocytes none of the tested compounds interfered with explant outgrowth. In short-term adhesion assays L2 glycolipid, sulfatide, and heparin inhibited adhesion of neural cells to laminin. L2 glycolipid and sulfatide interfered with neuron to astrocyte and astrocyte to astrocyte adhesion, but not with neuron-neuron adhesion. The most straightforward interpretation of these observations is that the L2/HNK-1 carbohydrate and the sulfated carbohydrates, sulfatide and heparin, act as ligands in cell adhesion.     

Immunoelectron microscopic localization of the neural cell adhesion molecules L1 and N-CAM during postnatal development of the mouse cerebellum

The cellular and subcellular localization of the neural cell adhesion molecules L1 and N-CAM was studied by pre- and postembedding immunoelectron microscopic labeling procedures in the developing mouse cerebellar cortex. The salient features of the study are: L1 displays a previously unrecognized restricted expression by particular neuronal cell types (i.e., it is expressed by granule cells but not by stellate and basket cells) and by particular subcellular compartments (i.e., it is expressed on axons but not on dendrites or cell bodies of Purkinje cells). L1 is always expressed on fasciculating axons and on postmitotic, premigratory, and migrating granule cells at sites of neuron-neuron contact, but never at contact sites between neuron and glia, thus strengthening the view that L1 is not involved in granule cell migration as a neuron-glia adhesion molecule. While N-CAM antibodies reacting with the three major components of N-CAM (180, 140, and 120 kD) show a rather uniform labeling of all cell types, antibodies to the 180-kD component (N-CAM180) stain only the postmigratory granule cell bodies supporting the notion that N-CAM180, the N-CAM component with the longest cytoplasmic domain, is not expressed before stable cell contacts are formed. Furthermore, N-CAM180 is only transiently expressed on Purkinje cell dendrites. N-CAM is present in synapses on both pre- and post-synaptic membranes. L1 is expressed only preterminally and not in the subsynaptic membranes. These observations indicate an exquisite degree of fine tuning in adhesion molecule expression during neural development and suggest a rich combinatorial repertoire in the specification of cell surface contacts.     

Galectin-3, a β-Galactoside-Binding Animal Lectin, Binds to Neural Recognition Molecules

Abstract: In this study, we have investigated the ability of galectin-3, a β-galactoside-binding animal lectin, to interact in vitro with different neural tissue-derived glycoproteins involved in cell-cell and cell-substrate adhesion. Galectin-3 interacted to varying degrees with the cell recognition molecules L1, the myelin-associated glycoprotein, and the neural cell adhesion molecule and the extracellular matrix molecules tenascin-C and tenascin-R but not with collagen type I. Binding of galectin-3 to the different glycoproteins tested was carbohydrate dependent and could be specifically inhibited by the addition of lactose and, to a lesser extent, galactose.     

Olfactory neurons express a unique glycosylated form of the neural cell adhesion molecule (N-CAM)

mAb-based approaches were used to identify cell surface components involved in the development and function of the frog olfactory system. We describe here a 205-kD cell surface glycoprotein on olfactory receptor neurons that was detected with three mAbs: 9-OE, 5-OE, and 13-OE. mAb 9-OE immunoreactivity, unlike mAbs 5-OE and 13-OE, was restricted to only the axons and terminations of the primary sensory olfactory neurons in the frog nervous system. The 9-OE polypeptide(s) were immunoprecipitated and tested for cross-reactivity with known neural cell surface components including HNK-1, the cell adhesion molecule L1, and the neural cell adhesion molecule (N-CAM). These experiments revealed that 9-OE-reactive molecules were not L1 related but were a subset of the 200-kD isoforms of N-CAM. mAb 9-OE recognized epitopes associated with N-linked carbohydrate residues that were distinct from the polysialic acid chains present on the embryonic form of N-CAM. Moreover, 9-OE N-CAM was a heterogeneous population consisting of subsets both with and without the HNK-1 epitope. Thus, combined immunohistochemical and immunoprecipitation experiments have revealed a new glycosylated form of N-CAM unique to the olfactory system. The restricted spatial expression pattern of this N-CAM glycoform suggests a possible role in the unusual regenerative properties of this sensory system.     

Molecular specialization of astrocyte processes at nodes of Ranvier in rat optic nerve

The HNK-1 and L2 monoclonal antibodies are thought to recognize identical or closely associated carbohydrate epitopes on a family of neural plasma membrane glycoproteins, including myelin-associated glycoprotein, the neural cell adhesion molecule, and the L1 and J1 glycoproteins, all of which have been postulated to play a part in mediating cell-cell interactions in the nervous system. We have used these two antibodies in immunofluorescence and immunogold-electron microscopic studies of semithin and ultrathin frozen sections of adult rat optic nerve, respectively, and we show that they bind mainly to astrocyte processes around nodes of Ranvier. Most other elements of the nerve, including astrocyte cell bodies and large astrocytic processes, are not labeled by the antibodies. To our knowledge, this is the first demonstration that perinodal astrocyte processes are biochemically specialized. We provide evidence that one of the HNK-1+/L2+ molecules concentrated around perinodal astrocyte processes is the J1 glycoprotein; our findings, taken together with previously reported observations, suggest that the other known HNK-1+/L2+ molecules are not concentrated on these processes. Since anti-J1 antibodies previously have been shown to inhibit neuron to astrocyte adhesion in vitro, we hypothesize that J1 may play an important part in the axon-glial interactions that presumably are involved in the assembly and/or maintenance of nodes of Ranvier.     

Akt-dependent cell size regulation by the adhesion molecule on glia occurs independently of phosphatidylinositol 3-kinase and Rheb signaling

The role of cell adhesion molecules in mediating interactions with neighboring cells and the extracellular matrix has long been appreciated. More recently, these molecules have been shown to modulate intracellular signal transduction cascades critical for cell growth and proliferation. Expression of adhesion molecule on glia (AMOG) is downregulated in human and mouse gliomas, suggesting that AMOG may be important for growth regulation in the brain. In this report, we examined the role of AMOG expression on cell growth and intracellular signal transduction. We show that AMOG does not negatively regulate cell growth in vitro or in vivo. Instead, expression of AMOG in AMOG-deficient cells results in a dramatic increase in cell size associated with protein kinase B/Akt hyperactivation, which occurs independent of phosphatidylinositol 3-kinase activation. AMOG-mediated Akt phosphorylation specifically activates the mTOR/p70S6 kinase pathway previously implicated in cell size regulation, but it does not depend on tuberous sclerosis complex/Ras homolog enriched in brain (Rheb) signaling. These data support a novel role for a glial adhesion molecule in cell size regulation through selective activation of the Akt/mTOR/S6K signal transduction pathway.     

Membrane glycoproteins involved in neurite fasciculation

Lectin affinity chromatography combined with mAb production was used to identify chick neural cell surface molecules related to L1 antigen, a mouse neural glycoprotein implicated in cell-cell adhesion (Rathjen, F. G., and M. Schachner, 1984, EMBO (Eur. Mol. Biol. Organ.) J., 3:1-10). A glycoprotein, G4 antigen, isolated by mAb G4 from adult chick brain is described which comprises a major 135-kD component, a minor doublet at 190 kD, and diffusely migrating bands at 80 and 65 kD in SDS PAGE. This molecule is structurally related to mouse L1 antigen according to NH2-terminal amino acid sequence (50% identity) as well as the behavior of its components in two-dimensional IEF/SDS PAGE gels. A second chicken glycoprotein, F11 antigen, was isolated from adult chick brain using mAb F11. This protein has also a major 135-kD component and minor components at 170 kD and 120 kD. Both immunotransfer analysis with polyclonal antibodies to mAb G4 and to mAb F11 isolate and the behavior on IEF/SDS PAGE gels indicates that the major 135-kD component of F11 antigen is distinct from G4 antigen components. However, the 135-kD component of F11 antigen shares with G4 antigen and the neural cell adhesion molecule (NCAM) the HNK-1/L2 carbohydrate epitope. In immunofluorescence studies, G4 and F11 antigenic sites were found to be associated mainly with the surface of process-bearing cells, particularly in fiber-rich regions of embryonic brain. Although Fab fragments of polyclonal antibodies to mAbs G4 or F11 immunoaffinity isolate only weakly inhibit the Ca2+-independent aggregation of neural cells, they strongly inhibit fasciculation of retinal axons. Together these studies extend the evidence that bundling of axons reflects the combined effects of a group of distinct cell surface glycoproteins.     

Myelin-Associated Glycoprotein Shares an Antigenic Determinant with a Glycoprotein of Human Melanoma Cells

A sulfated 100K-dalton glycoprotein has been shown to be released into the culture medium of melanoma cells. Monoclonal antibodies 10C5 and 11B5, which were raised to human melanoma cells, as well as HNK-1 bind to this glycoprotein. It is shown here that mouse anti-myelin-associated glycoprotein (MAG) carbohydrate antibodies raised to human MAG and a human IgM paraprotein associated with neuropathy also bind to the same 100K molecule. However, anti-MAG antibodies recognizing peptide epitopes do not appear to react with this glycoprotein of melanoma cells, a result suggesting that its similarity to MAG is restricted to shared carbohydrate moieties. The anti-melanoma antibodies (10C5 and 11B5) resemble HNK-1 in binding to MAG and to some 19-28K-dalton glycoproteins and sulfated, glucuronic acid-containing sphingoglycolipids of the peripheral nervous system (PNS). In addition, the anti-melanoma antibodies cross-react with neural cell adhesion molecule (N-CAM), an observation emphasizing the shared antigenicity between MAG and other adhesion molecules. The results demonstrate that the anti-melanoma antibodies fall into a class of monoclonal antibodies (including HNK-1, human IgM paraproteins associated with neuropathy, anti-human MAG antibodies, and L2 antibodies) that are characterized by reactivity against related carbohydrate determinants shared by human MAG, N-CAM, and several protein and lipid glycoconjugates of the PNS.     

Detection of Multisulphated N-Linked Glycans in the L2/HNK-1 Carbohydrate Epitope Expressing Neural Adhesion Molecule P0

P0, the most abundant glycoprotein of PNS myelin, is a homophilic and heterophilic adhesion molecule. P0 is known to contain a glycoform population that expresses the L2/HNK-1 carbohydrate epitope found on other neural adhesion molecules, and to be functionally implicated centrally in neural cell adhesion and neurite outgrowth. This carbohydrate epitope has been characterized previously from glycolipid structures and contains a sulphated glucuronic acid residue. However, the L2/HNK-1 carbohydrate epitope has not been characterized in glycoproteins. Because P0 possesses only one glycosylation sequon, the number of P0 glycoforms is equal to the heterogeneity of the glycan species. Here we report that the carbohydrate analysis of L2/HNK-1-reactive P0 showed the presence of anionic structures containing sialic acid and sulphate in various combinations. At least one sulphate residue was present in 80% of the monosaccharide sequences, and 20% contained three sulphates. High-resolution P4 gel chromatography of the desialylated and desulphated oligosaccharides showed substantial heterogeneity of monosaccharide sequences. Sequential exoglycosidase digestions indicated that the majority of the structures were of the hybrid class, although the sulphated structures were found to be endoglycosidase H-resistant.     

Myelin-associated glycoprotein, a member of the L2/HNK-1 family of neural cell adhesion molecules, is involved in neuron-oligodendrocyte and oligodendrocyte-oligodendrocyte interaction

A monoclonal antibody to the myelin-associated glycoprotein (MAG) was prepared and characterized to probe for the involvement of MAG in cell surface interactions among neural cells in vitro. The antibody reacts specifically with oligodendrocyte cell surface and myelin-rich brain regions as expected from previous investigations. Not all O4 antigen- positive oligodendrocytes express MAG in vitro. Fab fragments of the antibody interfere with neuron to oligodendrocyte and oligodendrocyte to oligodendrocyte adhesion, but not with oligodendrocyte to astrocyte adhesion. MAG-containing liposomes bind to the cell surfaces of the appropriate target cells by a mechanism that is specifically inhibitable by Fab fragments of monoclonal MAG antibodies, demonstrating that MAG is a neural cell adhesion molecule.     

AlphaII-spectrin participates in the surface expression of cell adhesion molecule L1 and neurite outgrowth

AlphaII-spectrin, a basic component of the spectrin-based scaffold which organizes and stabilizes membrane microdomains in most animal cells, has been recently implicated in cell adherence and actin dynamics. Here we investigated the contribution of αΙΙ-spectrin to neuritogenesis, a highly complex cellular process which requires continuous actin cytoskeleton remodeling and cross-talk between extracellular cues and their cell surface receptors, including cell adhesion molecules. Using RNA interference-mediated gene silencing to down-regulate αΙΙ-spectrin expression in human neuroblastoma SH-SY5Y cells, we observed major changes in neurite morphology and cell shape: (1) reduced mean length and a higher number of neurites per cell; occasional long neurites were thinner and displayed abnormal adhesiveness during cell migration resulting in frequent breaks; similar persisting adhesiveness and breaks were also observed in trailing edges of cell bodies; (2) irregular polygonal cell shape in parallel with loss of cortical F-actin from neuronal cell bodies; (3) reduction in protein levels of αΙ- and βΙ-spectrins, but not βΙΙ-spectrin (4) decreased global expression of adhesion molecule L1 and spectrin-binding adapter ankyrin-B, which links L1 to the plasma membrane. Remarkably, αΙΙ-spectrin depletion affected L1 – but not NCAM – cell surface expression, and L1 clustering at growth cones. This study demonstrates that αΙΙ-spectrin is implicated in normal morphology and adhesive properties of neuron cell bodies and neurites, and in cell surface expression and organization of adhesion molecule L1.     

Functional cooperation between the neural adhesion molecules L1 and N- CAM is carbohydrate dependent

The neural cell adhesion molecules L1 and N-CAM have been suggested to interact functionally by formation of a complex between the two molecules (Kadmon, G., A. Kowitz, P. Altevogt, and M. Schachner. 1990. J. Cell Biol. 110:193-208). To determine the molecular mechanisms underlying this functional cooperation, we have studied the contribution of carbohydrates to the association of the two molecules at the cell surface. Aggregation or adhesion between L1- and N-CAM-positive neuroblastoma N2A cells was reduced when the synthesis of complex and/or hybrid glycans was modified by castanospermine. Fab fragments of polyclonal antibodies to L1 inhibited aggregation and adhesion of castanospermine-treated cells almost completely, whereas untreated cells were inhibited by approximately 50%. Fab fragments of polyclonal antibodies to N-CAM did not interfere with the interaction between castanospermine-treated cells, whereas they inhibited aggregation or adhesion of untreated cells by approximately 50%. These findings indicate that cell interactions depending both on L1 and N-CAM ("assisted homophilic" binding) can be reduced to an L1-dominated interaction ("homophilic binding"). Treatment of cells with the carbohydrate synthesis inhibitor swainsonine did not modify cell aggregation in the absence or presence of antibodies compared with untreated cells, indicating that castanospermine-sensitive, but swainsonine-insensitive glycans are involved. To investigate whether the appropriate carbohydrate composition is required for an association of L1 and N-CAM in the surface membrane (cis-interaction) or between L1 on one side and L1 and N-CAM on the other side of interacting partner cells (trans-interaction), an L1-positive lymphoid tumor cell line was coaggregated with and adhered to neuroblastoma cells in the various combinations of castanospermine-treated and untreated cells. The results show that it is the cis-interaction between L1 and N-CAM that depends on the appropriate carbohydrate structures.     

The adhesion molecule on glia (AMOG) is a homologue of the beta subunit of the Na,K-ATPase

AMOG (adhesion molecule on glia) is a Ca2(+)-independent adhesion molecule which mediates selective neuron-astrocyte interaction in vitro (Antonicek, H., E. Persohn, and M. Schachner. 1987. J. Cell Biol. 104:1587-1595). Here we report the structure of AMOG and its association with the Na,K-ATPase. The complete cDNA sequence of mouse AMOG revealed 40% amino acid identity with the previously cloned beta subunit of rat brain Na,K-ATPase. Immunoaffinity-purified AMOG and the beta subunit of detergent-purified brain Na,K-ATPase had identical apparent molecular weights, and were immunologically cross-reactive. Immunoaffinity-purified AMOG was associated with a protein of 100,000 Mr. Monoclonal antibodies revealed that this associated protein comprised the alpha 2 (and possibly alpha 3) isoforms of the Na,K-ATPase catalytic subunit, but not alpha 1. The monoclonal AMOG antibody that blocks adhesion was shown to interact with Na,K-ATPase in intact cultured astrocytes by its ability to increase ouabain-inhibitable 86Rb+ uptake. AMOG-mediated adhesion occurred, however, both at 4 degrees C and in the presence of ouabain, an inhibitor of the Na,K-ATPase. Both AMOG and the beta subunit are predicted to be extracellularly exposed glycoproteins with single transmembrane segments, quite different in structure from the Na,K-ATPase alpha subunit or any other ion pump. We hypothesize that AMOG or variants of the beta subunit of the Na,K-ATPase, tightly associated with an alpha subunit, are recognition elements for adhesion that subsequently link cell adhesion with ion transport.     

Developmentally regulated cell-cell adhesion in Dictyostelium purpureum is mediated by a glycoprotein synthesized in nonadhesive cells

Upon starvation the cellular slime mold, Dictyostelium purpureum, develops a form of cell-cell adhesion aiding in the formation of large multicellular aggregates, which are capable of further differentiation. The molecule that mediates this adhesion is a glycoprotein of Mr approximately 40,000. The protein shares a common carbohydrate epitope with another well-characterized cell adhesion molecule from Dictyostelium discoideum, contact sites A, but the polypeptides to which it is attached differ for each species. Although mediating a developmental form of adhesiveness, the protein is synthesized in vegetative cells at a time when they do not adhere. Most of the vegetative protein is associated with cell membranes and appears to be on the surface of these cells. The protein is compared to other cell adhesion molecules from other species of cellular slime molds, and possible explanations for its inability to function in vegetative cells are discussed.     

Primary structure of ICAM-1 demonstrates interaction between members of the immunoglobulin and integrin supergene families

Intercellular adhesion molecule 1 (ICAM-1) is a 90 kd inducible surface glycoprotein that promotes adhesion in immunological and inflammatory reactions. ICAM-1 is a ligand of lymphocyte function-associated antigen-1 (LFA-1), an alpha beta complex that is a member of the integrin family of cell-cell and cell-matrix receptors. ICAM-1 is encoded by an inducible 3.3 kb mRNA. The amino acid sequence specifies an integral membrane protein with an extracellular domain of 453 residues containing five immunoglobulin-like domains. Highest homology is found with neural cell adhesion molecule (NCAM) and myelin-associated glycoprotein (MAG), which also contain five Ig-like domains. NCAM and MAG are nervous system adhesion molecules, but unlike ICAM-1, NCAM is homophilic. The ICAM-1 and LFA-1 interaction is heterophilic and unusual in that it is between members of the immunoglobulin and intergrin families. Unlike other integrin ligands, ICAM-1 does not contain an RGD sequence.     

Roles, regulation, and mechanism of polysialic acid function during neural development

The polysialylated form of the neural cell adhesion molecule (PSA-NCAM) appeared during the evolution of vertebrates as a new mechanism for regulation of cell interactions. This large and abundant glycoprotein can exert steric effects at the cell surface that lead to the attenuation of cell-cell bonds mediated not only by NCAM but also a variety of other adhesion receptors. PSA-NCAM expression changes both as a result of developmental programs and physiological inputs. This global modulation of cell-cell attachment has been shown to facilitate cell migration, axon pathfinding and targeting, and plastic changes in the embryonic and adult nervous system.     

Human Neuroectoderm-Derived Cell Line Secretes Fibronectin that Shares the HNK-1/10C5 Carbohydrate Epitope with Neural Cell Adhesion Molecules

A human malignant melanoma cell line, Melur, secretes several glycoproteins that contain a unique carbohydrate epitope shared by neural cell adhesion molecules and recognized by the monoclonal antibodies HNK-1, L2, and 10C5. In this report, we present evidence that one of the major melanoma glycoproteins containing the HNK-1/10C5 epitope is the cell adhesion molecule, fibronectin, or a fibronectin-like molecule. Melanoma-derived fibronectin was isolated from serum-free conditioned medium by gelatin-Sepharose affinity adsorption and shown to react with monoclonal antibodies HNK-1 and 10C5 in Western blot analysis. HNK-1-containing fibronectin was purified on a gelatin-Sepharose column followed by an affinity column using a monoclonal antibody against the HNK-1 carbohydrate. The purified HNK-1-fibronectin then could be incorporated into the extracellular matrix of hamster fibroblasts in vitro, and such a matrix was detectable using the HNK-1 monoclonal antibody in an immunofluorescence assay. Of the seven neuroectoderm-derived tumor cell lines tested, only the Melur melanoma cell secreted fibronectin containing the HNK-1 carbohydrate. Identification of human neuroectoderm-derived fibronectin as a potential carrier of the HNK-1 carbohydrate suggests a new role for fibronectin in neural development and regeneration, and represents a new model for studying the function of this carbohydrate domain in neural cell adhesion.     

Functional expression of a full-length cDNA coding for rat neural cell adhesion molecule L1 mediates homophilic intercellular adhesion and migration of cerebellar neurons.

Neural cell adhesion molecule L1 is postulated to be involved in cell-cell interaction, neurite elongation, fasciculation of axons, cell migration, and myelination. To determine the function of L1 directly, we have transfected rat L1 cDNA into mouse fibroblast L cells. Stable transformants expressing L1 showed uniform surface expression of the molecule without phenotypic changes. Dispersed L1-expressing transfectants aggregated with faster kinetics than control cells in a homophilic manner. Divalent cations were not required for this cell aggregation. L1-transfected cells markedly enhanced neuronal cell adhesion and migration in co-culture with rat cerebellar neurons. These results indicate that L1 is involved in a determinant step of neural development through molecular interactions.