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At least 19 recordsLinked to original sources
PubMed1998

Spatio-temporal diversity in the microenvironments for neural cell adhesion molecule, neural cell adhesion molecule-polysialic acid, and L1-cell adhesion molecule expression by sensory neurons and their targets during cochleo-vestibular innervation.

Sixteen phases in the microenvironments were defined for the structural development and innervation of the cochleo-vestibular ganglion and its targets. In each phase the cell adhesion molecules, neural cell adhesion molecule, neural cell adhesion molecule-polysialic acid, and L1-cell adhesion molecule, were expressed differentially by cochleo-vestibular ganglion cells, their precursors, and the target cells on which they synapse. Detected by immunocytochemistry in staged chicken embryos, in the otocyst, neural cell adhesion molecule, but not L1-cell adhesion molecule, was localized to the ganglion and hair cell precursors. Ganglionic precursors, migrating from the otocyst, only weakly expressed neural cell adhesion molecule. Epithelial hair cell precursors, remaining in the otocyst, expressed neural cell adhesion molecule, but not L1-cell adhesion molecule. Post-migratory ganglion cell processes expressed both molecules in all stages. The cell adhesion molecules were most heavily expressed by axons penetrating the otic epithelium and accumulated in large amounts in the basal lamina. In the basilar papilla (cochlea), cell adhesion molecule expression followed the innervation gradient. Neural cell adhesion molecule and L1 were heavily concentrated on axonal endings peripherally and centrally. In the rhombencephalon, primitive epithelial cells expressed neural cell adhesion molecule, but not L1-cell adhesion molecule, except in the floorplate. The neuroblasts and their axons expressed L1-cell adhesion molecule, but not neural cell adhesion molecule, when they began to migrate and form the dorsal commissure. There was a stage-dependent, differential distribution of the cell adhesion molecules in the floorplate. Commissural axons expressed both cell adhesion molecules, but their polysialic acid disappeared within the floorplate at later stages. In conclusion, the cell adhesion molecules are expressed by the same cells at different times and places during their development. They are positioned to play different roles in migration, target penetration, and synapse formation by sensory neurons. A multiphasic model provides a morphological basis for experimental analyses of the molecules critical for the changing roles of the microenvironment in neuronal specification.

Animals↗
PubMed1998

Multiple roles of neural cell adhesion molecule, neural cell adhesion molecule-polysialic acid, and L1 adhesion molecules during sensory innervation of the otic epithelium in vitro.

To explore the role of cell adhesion molecules in the innervation of the inner ear, antibody perturbation was used on histotypic co-cultures of the ganglionic and epithelial anlagen derived from the otocyst. When unperturbed, these tissues survived and differentiated in this culture system with outgrowth of fasciculated neuronal fibers which expressed neural cell adhesion molecule and L1. The fibers exhibited target choice and penetration, then branching and spreading within the otic epithelium as individual axons. Treatment of the co-cultures, or of the ganglionic anlagen alone, with anti-neural cell adhesion molecule or anti-L1 Fab fragments produced a defasciculation of fibers but did not affect neurite outgrowth. In the co-cultures this defasciculation was accompanied by a small increase in the number of fibers found in inappropriate tissues. However, the antibodies did not prevent fiber entry to the otic epithelium. In contrast, removal of polysialic acid from neural cell adhesion molecule with endoneuraminadase-N, while producing a similar fiber defasciculation, also increased the incidence of fibers entering the epithelium. Nevertheless, once within the target tissue, the individual fibers responded to either Fab or to desialylation by spreading out more rapidly, branching, and growing farther into the epithelium. The findings suggest that fasciculation is not essential for specific sensory fibers to seek out and penetrate the appropriate target, although it may improve their tracking efficiency. Polysialic acid on neural cell adhesion molecule appears to limit initial penetration of the target epithelium. Polysialic acid as well as neural cell adhesion molecule and L1 function are involved in fiber-target interactions that influence the arborization of sensory axons within the otic epithelium.

Animals↗
PubMed1989

Identity of Leu-19 (CD56) leukocyte differentiation antigen and neural cell adhesion molecule.

Neural cell adhesion molecule (N-CAM) is a membrane glycoprotein expressed on neural and muscle tissues that is involved in homotypic adhesive interactions. We have demonstrated that N-CAM also is expressed on hematopoietic cells, and is recognized by the anti-Leu-19 mAb. Leu-19 is preferentially expressed on NK cells and T lymphocytes that mediate MHC-unrestricted cytotoxicity, but is also present on some myeloid leukemia cell lines. On NK cells, T cells, the KG1a.5 hematopoietic cell line, and a neuroblastoma cell line, Leu-19 is a approximately 140-kD polypeptide with N-linked carbohydrates and abundant sialic acid residues. Sequential immunoprecipitation and peptide mapping demonstrated that the Leu-19 and N-CAM molecules expressed on leukocyte and neuroblastoma cell lines are similar structures. These findings suggest that the Leu-19 antigen on leukocytes may be involved in cell adhesion, analogous to the function on N-CAM on neural cells.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1998

Neurite fasciculation mediated by complexes of axonin-1 and Ng cell adhesion molecule.

Neural cell adhesion molecules composed of immunoglobulin and fibronectin type III-like domains have been implicated in cell adhesion, neurite outgrowth, and fasciculation. Axonin-1 and Ng cell adhesion molecule (NgCAM), two molecules with predominantly axonal expression exhibit homophilic interactions across the extracellular space (axonin- 1/axonin-1 and NgCAM/NgCAM) and a heterophilic interaction (axonin-1-NgCAM) that occurs exclusively in the plane of the same membrane (cis-interaction). Using domain deletion mutants we localized the NgCAM homophilic binding in the Ig domains 1-4 whereas heterophilic binding to axonin-1 was localized in the Ig domains 2-4 and the third FnIII domain. The NgCAM-NgCAM interaction could be established simultaneously with the axonin-1-NgCAM interaction. In contrast, the axonin-1-NgCAM interaction excluded axonin-1/axonin-1 binding. These results and the examination of the coclustering of axonin-1 and NgCAM at cell contacts, suggest that intercellular contact is mediated by a symmetric axonin-12/NgCAM2 tetramer, in which homophilic NgCAM binding across the extracellular space occurs simultaneously with a cis-heterophilic interaction of axonin-1 and NgCAM. The enhanced neurite fasciculation after overexpression of NgCAM by adenoviral vectors indicates that NgCAM is the limiting component for the formation of the axonin-12/NgCAM2 complexes and, thus, neurite fasciculation in DRG neurons.

Animals↗
PubMed1993

Neuronal 'differentiation' of murine neuroblastoma cells induced by neocarzinostatin: neural cell adhesion molecules.

Neural crest tumor cells which have been pharmacologically induced in culture to undergo neuronal 'differentiation' have been proposed as a model for normal neural crest cell differentiation. We have previously reported that murine neuroblastoma cells treated with the antineoplastic agent neocarzinostatin (NCS) adopt the light microscopic appearance of differentiated neurons. After undergoing morphologic change, the cells no longer divide. As part of an effort to compare the process of differentiation in these cells with what is known about normal neural crest cells, we have examined the cellular distribution and isoform complement of neural cell adhesion molecules (NCAMs) in native and NCS-treated neuroblastoma cells. Our studies show that NCS induces profound changes in NCAM distribution. Immunohistochemical staining indicates that, in contrast to native neuroblastoma cells, more than 80% of treated cells display surface NCAM by 4 days following treatment. Unlike the case for normal neurons, NCAM is uniformly distributed over the treated cell surface. Neuroblastoma cells treated with NCS are more avidly adherent to culture plates coated with NCAM than are control neuroblastoma cells, reflecting the homophilic binding characteristics of NCAM. Interestingly, Western blot analysis for NCAM demonstrates similar total cellular content of a single NCAM species in both control and treated neuroblastoma cells. Furthermore, this 120 kDa mol. wt. NCAM is an isoform of NCAM not found on normally differentiated cerebellar neurons. While the presence of NCAM on these treated murine neuroblastoma cells is evidence for 'differentiation' along neuronal lines, the isoform complement and cell surface distribution of NCAM in treated cells are not normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

[The expression of neural cell adhesion molecule (NCAM), neural invasion and recurrence patterns in rectal cancer--a study using anti-NACM (neural cell adhesion molecule) antibody].

Neural invasion may be one of the main causes of local recurrence, but its mechanism has not been sufficiently clarified. We previously reported that the expression of NCAM on cancer cells was correlated with neural invasion in pancreatic cancer. In this study, we examined the neural affinity of rectal cancer cells and the relationship between neural invasion and recurrence patterns of rectal cancers. A total of 64 rectal adenocarcinoma were examined. Specimens from 17 patients (27%) revealed perineural invasion. The incidence of neural invasion increased with the frequency of venous invasion and the degree of lymph node metastasis, but not significantly. The incidence of the expression of NCAM in rectal cancer cell was 45.3 percent. Neural invasion of rectal carcinoma was significantly related to the expression of NCAM (p < 0.05). NCAM immunocytolocalization was classified into the focal type, and the diffuse type. Concerning the recurrence type, 8 of 9 cases that developed local recurrence showed either presence of neural invasion or expression of NCAM. Liver metastasis was associated with absence of neural invasion or NCAM expression. The expression of NCAM may contribute to local recurrence, whereas the absence of NCAM may predict liver metastasis.

Adenocarcinoma↗
PubMed1984

Alteration of the retinotectal map in Xenopus by antibodies to neural cell adhesion molecules.

The neural cell adhesion molecule (N-CAM) mediates neuron-neuron adhesion, is ubiquitous in the nervous system of developing and mature vertebrates, and undergoes major alterations in both amount and distribution during development. Perturbation of homophilic (N-CAM to N-CAM) binding by univalent fragments of specific anti-N-CAM antibodies has previously been found to alter neural tissue patterns in vitro. To show that significant alterations can also occur in vivo, antibodies to Xenopus N-CAM were embedded in agarose microcylinders and implanted in the tecta of juvenile Xenopus laevis frogs that were undergoing regeneration of their retinotectal projections; 1 week later, the effects of implantation on the projection pattern from the optic nerve were determined. Both polyclonal and monoclonal antibodies to N-CAM distorted the retinotectal projection pattern and greatly decreased the precision of the projection; these alterations recovered to near normal after an additional 3 weeks. Similar but smaller effects were obtained when normally developing froglets received tectal implants. In control animals, implants of immunoglobulins from preimmune serum and monoclonal antibodies not directed against N-CAM had little or no effect on the pattern. The results suggest that neuronal adhesion mediated by N-CAM is important in establishing and maintaining the precision and topography of neural patterns.

Aging↗
PubMed1986

Structural and immunological characterization of the amino-terminal domain of mammalian neural cell adhesion molecules.

The neural cell adhesion molecules (N-CAMs) are a group of structurally and immunologically related glycoproteins found in vertebrate neural tissues. Adult brain N-CAMs have apparent molecular weights of 180,000 and 140,000 with an additional form at 120,000 in murine brain. In embryonic brain, N-CAMs are represented by a highly sialylated form with an apparent molecular weight greater than 180,000. We have used monoclonal antibodies that cross-react with N-CAMs of various mammalian species to purify N-CAMs from adult murine and bovine brains and from embryonic murine brains. We determined the amino acid sequences of the amino-terminal domains of these molecules: Leu-Gln-Val-Asp-Ile-Val-Pro-Ser-Gln-Gly-Glu-Ile-Ser-Val-Gly-Glu-Ser. This sequence is highly conserved among all three forms of adult murine brain N-CAM as well as embryonic murine brain N-CAM and adult bovine brain N-CAM. Based on this sequence, we synthesized an undecapeptide and used it to raise a site-directed polyclonal antiserum. This antiserum reacted with the intact N-CAM in liquid phase radioimmunoassays, immunoblotting experiments, and immunofluorescent labeling of cells. The antiserum also reacted with N-CAMs in extracts of brain tissues from different species, confirming the highly conserved nature of the amino-terminal domain of mammalian N-CAMs. Immunofluorescence experiments indicated that this domain resides on the outer surfaces of cells that express N-CAMs, in both primary neuronal cell culture and in cell lines.

Amino Acid Sequence↗
PubMedDate not supplied

Differentiation state-dependent surface mobilities of two forms of the neural cell adhesion molecule.

The neural cell adhesion molecule (N-CAM) has been implicated in morphogenetic events during formation of the nervous system. Three forms of N-CAM exist, all glycoprotein chains, of relative molecular masses 180,000 (180K), 140K and 120K (N-CAM180, N-CAM140 and N-CAM120) which are differentially expressed on neural cell types and during development. The three chains are thought to carry similar if not identical amino-acid sequences on their extracellular amino-terminal domains, but differ in the length of their carboxy-terminal cytoplasmic region. They occur in highly sialylated embryonic and less sialylated adult forms. N-CAM180 is selectively expressed in more differentiated neural cells and may play a role in the stabilization of cell contacts. To investigate this, we have studied in the surface membrane of a mouse neuroblastoma cell line N2A the lateral mobility of the two predominant forms of N-CAM, N-CAM180 and N-CAM140, as a function of differentiation. Here we report that as judged by fringe pattern photobleaching, the surface mobility of N-CAM140 is higher than that of N-CAM180, suggesting an association of N-CAM180 with the cytoskeleton or other stabilizing factors. We also show that brain spectrin, a membrane-cytoskeleton linker protein, binds only to N-CAM180. The immobilization of N-CAM in differentiated N2A cells is achieved by a shift in expression from N-CAM140 to N-CAM180.

Animals↗
PubMed1984

Evolutionary conservation of key structures and binding functions of neural cell adhesion molecules.

The neural cell adhesion molecule N-CAM is a sialic acid-rich, cell surface glycoprotein that mediates cell adhesion by a homophilic mechanism. Its binding function has been implicated in both morphogenesis and histogenesis; during development it changes in amount at the cell surface and perinatally it undergoes a decrease in sialic acid content (embryonic--adult conversion) with an increase in binding efficacy. In the present study, salient aspects of the structure and the mutual binding specificities of N-CAMs from a variety of vertebrate species were examined to determine whether (N-CAM)-mediated adhesion mechanisms have been conserved during evolution. N-CAM immunoreactivity was detected in a series of polypeptides of characteristic molecular weight extracted from brain tissues of all vertebrate species tested, including mammals, birds, reptiles, amphibia, and bony and cartilaginous fish. Adhesion mediated by N-CAM occurred across species lines as indicated by the co-aggregation of chicken and mouse neural cells. By using a quantitative membrane vesicle aggregation assay, the efficacy of cross-species brain membrane vesicle adhesion in various pairings (chicken-mouse, chicken-frog, mouse-frog) was found to be similar to the efficacy of intra-species adhesion. Effective cross-species aggregation of brain membrane vesicles also occurred in embryonic-embryonic, adult-adult, and embryonic-adult pairings. In a control experiment, embryonic chicken liver membrane vesicles (which do not contain N-CAM) did not co-aggregate with embryonic chicken brain membrane vesicles. Cross-species co-aggregation could be inhibited by Fab' fragments of antibodies of N-CAM and was most effectively inhibited in the presence of mixtures made from the Fab' fragments of specific antibodies prepared against the N-CAMs from each of the animal species constituting a co-aggregating pair. These results suggest that, in accord with the proposed role of N-CAM as a regulator of morphogenesis, both the specificity of the binding region of the molecule and its basic chemical structure have been highly conserved during evolution.

Animals↗
PubMed1983

Kinetics of homophilic binding by embryonic and adult forms of the neural cell adhesion molecule.

The neural cell adhesion molecule, N-CAM, is a cell surface glycoprotein found on embryonic and adult neurons and on a variety of ectodermal and mesodermal tissues in very early embryos. During development, it shows local variations in prevalence at the cell surface as well as conversion from an embryonic form (E form) with high sialic acid content to an adult form (A form) with lesser amounts of this sugar. This E leads to A conversion occurs on different schedules in different brain regions, and it has been hypothesized that both the conversion and the prevalence changes are related to early regulation of pattern formation and connectivity. In order to identify precisely the consequences of these mechanisms of local cell surface modulation of N-CAM, an assay was developed to measure the rate of aggregation either of vesicles reconstituted from lipid and purified N-CAM or of native brain membrane vesicles. In both preparations, aggregation was greater than 95% inhibitable by specific anti-(N-CAM) Fab' fragments. The rates of aggregation of reconstituted N-CAM vesicles and native brain vesicles were found to be inversely related to the sialic acid content of their N-CAM molecules, with full desialylation resulting in about a 4-fold increase in rate over E-form N-CAM. Intermediate rates were obtained both with A-form N-CAM (which contains only one-third of the sialic acid content of E-form N-CAM) and with partially desialylated E-form N-CAM. The rate of coaggregation of reconstituted vesicles containing E-form N-CAM with reconstituted vesicles containing A-form N-CAM was also intermediate, implying that desialylation did not change the nature of (N-CAM)-(N-CAM) binding but only its rate. Even larger alterations in vesicle aggregation rate were seen when the amount of N-CAM per vesicle was altered. A 2-fold increase in the N-CAM-to-lipid ratio of reconstituted vesicles resulted in a greater than 30-fold increase in their rate of aggregation. Moreover, desialylation did not cause a further increase in the rate of aggregation of these already rapidly aggregating vesicles. These results in a model system demonstrate the large range of binding rates that are obtainable by various forms of local surface modulation of N-CAM. They are consistent with the proposal that similar alterations affecting (N-CAM)-mediated cell adhesion in vivo may be major factors in pattern formation during development of the nervous system.

Age Factors↗
PubMed1987

Biosynthesis, membrane association, and release of N-CAM-120, a phosphatidylinositol-linked form of the neural cell adhesion molecule.

The neural cell adhesion molecule (N-CAM) of rodents comprises three distinct proteins of Mr 180,000, 140,000, and 120,000 (designated N-CAM-180, -140, and -120). They are expressed in different proportions by different tissues and cell types. but the individual contribution of each form to cell adhesion is presently unknown. Previous studies have shown that the two N-CAM species of higher relative molecular mass span the membrane whereas N-CAM-120 lacks a transmembrane domain and can be released from the cell surface by phosphatidylinositol-specific phospholipase C. In this report, we provided evidence that N-CAM-120 contained covalently bound phosphatidylinositol and studied N-CAM-120 from its biosynthesis to its membrane insertion and finally to its release from the cell surface. Evidence was presented showing that the lipid tail of N-CAM-120 contained ethanolamine as is the case for other lipid-linked molecules. The phospholipid anchor was attached to the protein during the first minutes after completion of the polypeptide chain. This process took place in the endoplasmic reticulum as judged from endoglycosidase H digestion experiments. Immediately after a 2-min pulse with [35S]methionine, we detected also a short-lived precursor that had not yet acquired the lipid tail. Pulse-chase studies established that N-CAM-120 was transported to the cell surface from which it was slowly released into the extracellular milieu. The molecules recovered in the incubation medium appeared to have lost all of their bound fatty acid but only around half of the ethanolamine. Upon fractionation of brain tissue, approximately 75% of N-CAM-120 was recovered with a membrane fraction and approximately 25% in a membrane-free supernatant. A small proportion (approximately 6%) was found to be resistant to extraction by non-ionic detergent. A major posttranslational modification of N-CAM is polysialylation. Our results showed that also N-CAM-120 was polysialylated in the young postnatal brain and released in this form from cultured cerebellar cells. The presence of N-CAM in a form that can be released from the cell surface and accumulates in the extracellular fluid suggests a novel mechanism by which N-CAM-mediated adhesion may be modulated.

Animals↗
PubMed1987

Chronic low-level lead exposure impairs embryonic to adult conversion of the neural cell adhesion molecule.

The neural cell adhesion molecule (N-CAM) is a complex of surface glycoproteins that are developmentally regulated and believed to be intimately involved in the orderly structuring of the CNS. Here the effect of chronic low-level lead exposure on their expression in the postnatally developing cerebellum is described. Rat pups were chronically exposed to lead via their dam's drinking water which contained either 200 or 400 mg PbCl2/L from time of birth. Pup postnatal blood lead levels ranged between 10 and 20 micrograms/dl until day 16 after which they became elevated to 40 micrograms/dl on day 20. During this period the developmental sialylation state of N-CAM, which is believed to regulate cell-cell interaction, fibre outgrowth, and synapse formation, was monitored by rocket immunoelectrophoresis. In control animals the expected desialylation of N-CAM was found to occur at times coincident with postnatal synaptogenesis. In contrast, desialylation in animals chronically exposed to lead was found to be significantly impaired when blood lead levels exceeded 20 micrograms/dl. This could not be attributed to lead-induced undernutrition or alterations in immunoprecipitate formation. These observations could account for the neurobehavioural deficits that are known to be induced at similar blood lead levels, and the potential contribution of impaired N-CAM desialylation to synaptic elaboration is discussed.

Aging↗
PubMed1989

Heterogeneity of soluble neural cell adhesion molecule.

Soluble neural cell adhesion molecule (NCAM) from rat brain neuronal cell culture media consists predominantly of a polypeptide of Mr approximately 115,000. Minor amounts of a polypeptide of Mr approximately 180,000 and two inconsistently appearing components of Mr 160,000 and 145,000 are also observed. The Mr 115,000 component is derived from the neuronal membrane NCAM components NCAM-A of Mr 190,000, NCAM-B of Mr 140,000, or both. Thus, as a part of the catabolism of membrane NCAM-A plus -B, a minor fraction is posttranslationally cleaved and recovered in the media as discernible soluble NCAM polypeptides. The half-life of membrane NCAM-A plus -B is less than 24 h. Astrocyte culture media contains a predominant soluble NCAM component of Mr 120,000 derived from membrane-associated NCAM-C. A close comparison of deglycosylated soluble NCAM from astrocyte and neuronal cultures showed a small but consistent difference in Mr, a result suggesting that different NCAM polypeptides are released from the membrane of neurons and astrocytes. In contrast to the Mr 115,000-120,000 NCAM polypeptides, the Mr 180,000 polypeptide from neuronal culture media does not seem to be derived from membrane-attached NCAM and may therefore represent a secreted NCAM isoform.

Animals↗
PubMed1986

Developmental study of detergent solubility and polypeptide composition of the neural cell adhesion molecule.

The neural cell adhesion molecule (N-CAM), a glycoprotein synthesized by neurons, glial cells and muscle cells, is involved in cell-cell adhesion. In this report we describe developmental changes in the amount of N-CAM polypeptides in rat forebrain and in detergent solubility of N-CAM. The amount of N-CAM changed during development with a peak in early postnatal life. N-CAM was composed of the following polypeptides: HMr (molecular weight between 250,000 and 350,000 daltons), A (200,000 daltons), B (135,000 daltons) and C (115,000 daltons). In embryonic life N-CAM consisted of 10% HMr, 26% A, 53% B and 11% C. During development only the relative amount of polypeptide C increased significantly, from 11% at embryonic day 17 to 22% at postnatal day 4. Postnatally the polypeptide composition of N-CAM did not change. No Triton X-100 insoluble N-CAM was observed in early development, but at postnatal day 40 14% of N-CAM was Triton X-100 insoluble. This fraction was shown to consist of polypeptide C.

Aging↗
PubMed1985

A developmental study of the biosynthesis of the neural cell adhesion molecule.

The neural cell adhesion molecule (N-CAM) is a glycoprotein found in neurons, glial cells and muscle cells. In this report we describe developmental changes in biosynthesis of N-CAM polypeptides in rat forebrain explant cultures. N-CAM was synthesized as the following polypeptides: HMr (Mr between 250,000 and 350,000), A (200,000 Mr), B (135,000 Mr) and C (115,000 Mr). The biosynthetic pattern of N-CAM polypeptides changed during development: the biosynthesis of HMr and C increased relative to A and B. N-CAM biosynthesis decreased 100-fold from embryonic day 17 to postnatal day 25; N-CAM turnover decreased 350-fold during the same period. N-CAM polysialylation and sulfatation decreased markedly with age, whereas phosphorylation seemed to be constant during development. Only polypeptides A and B were phosphorylated, whereas A, B and C were sulfated. A was more sulfated and phosphorylated than B. It is concluded that the above described modulations of N-CAM may be of importance in the developmental regulation of cell-cell adhesion.

Age Factors↗
PubMed1986

Rapid axonal transport of the neural cell adhesion molecule.

The neural cell adhesion molecule (NCAM) is a cell-surface glycoprotein that mediates cell-cell interactions in the nervous system during development. In the present study, we demonstrate that NCAM is axonally transported in 3-d-old chick retinal ganglion cells and that it travels within the fast component of axonal transport (FC). Proteins were radiolabeled in retinal ganglion cell bodies after intraocular injection of 35S-methionine. The presence of radiolabeled NCAM in the optic nerves and contralateral tecta was detected by specific immunoadsorption to a monoclonal antibody. Major radioactive polypeptide bands at relative mobilities of approximately 200,000, 150,000, and 120,000 Mr (after SDS-PAGE) were recognized by the anti-NCAM antibody. These bands comigrated in 1-dimensional gels with components of purified NCAM from chick brain. The 2 largest NCAM polypeptides (at 200,000 and 150,000 Mr) were found to be transported in this system, while the 120,000 Mr form was apparently not transported. The ratio and electrophoretic profiles of the 2 transported forms of NCAM remained similar in the retina, optic nerve, chiasm, tract, and tectum, suggesting that there is no interconversion of the 2 major polypeptides. The fraction of NCAM in the 35S-labeled FC proteins appears to be at least an order of magnitude less than in the plasma membrane, suggesting that the turnover rate of NCAM at this age is slower than for other membrane proteins of the CNS.

Animals↗
PubMed1985

Structural and functional studies on N-CAM neural cell adhesion molecules.

The neural cell adhesion molecules N-CAM are to date the best characterized adhesion molecules of the nervous system. They have a high content of sialic acid residues which are present in the form of unusual sialic acid polymers. During development, a 3 fold decrease in the sialic acid content is observed. These changes in the degree of sialylation profoundly affect the binding properties of the molecules. A subpopulation of mouse brain N-CAM bears a carbohydrate determinant shared with other brain cell surface proteins and with the HNK-1 antigen of natural killer cells. Not only the carbohydrate side chains but also the protein moieties of the N-CAMs are heterogeneous. Three polypeptides of 180 K, 140 K and 120 K have been characterized in mouse brain. The 180 K and 140 K chains span the membrane. They differ mainly by the length of their cytoplasmic extensions. These intracellular domains are unusually long and contain phosphorylated serine residues. The 120 K chain exists in two forms, one membrane-bound and one soluble. Earlier studies had shown the presence of N-CAM on neurones and astrocytes of the mouse central nervous system, whereas cultured astrocytes had been reported to be N-CAM-negative. Recent results show that N-CAM is also expressed on astrocytes in culture. To study expression and heterogeneity of N-CAM polypeptides at the mRNA and gene level, cDNA clones for mouse N-CAM have been isolated. They reveal multiple mRNA species in mouse brain. By contrast, the corresponding sequences seem to be present only a few times, perhaps only once, in the mouse genome.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗