Molecular heterogeneity and structural evolution during cerebellar ontogeny detected by monoclonal antibody of the mouse cell surface antigen BSP-2

Intrabodies against the Polysialyltransferases ST8SiaII and ST8SiaIV inhibit Polysialylation of NCAM in rhabdomyosarcoma tumor cells

Background

Polysialic acid (polySia) is a carbohydrate modification of the neural cell adhesion molecule (NCAM), which is implicated in neural differentiation and plays an important role in tumor development and metastasis. Polysialylation of NCAM is mediated by two Golgi-resident polysialyltransferases (polyST) ST8SiaII and ST8SiaIV. Intracellular antibodies (intrabodies; IB) expressed inside the ER and retaining proteins passing the ER such as cell surface receptors or secretory proteins provide an efficient means of protein knockdown. To inhibit the function of ST8SiaII and ST8SiaIV specific ER IBs were generated starting from two corresponding hybridoma clones. Both IBs αST8SiaII-IB and αST8SiaIV-IB were constructed in the scFv format and their functions characterized in vitro and in vivo.

Results

IBs directed against the polySTs prevented the translocation of the enzymes from the ER to the Golgi-apparatus. Co-immunoprecipitation of ST8SiaII and ST8SiaIV with the corresponding IBs confirmed the intracellular interaction with their cognate antigens. In CHO cells overexpressing ST8SiaII and ST8SiaIV, respectively, the transfection with αST8SiaII-IB or αST8SiaIV-IB inhibited significantly the cell surface expression of polysialylated NCAM. Furthermore stable expression of ST8SiaII-IB, ST8SiaIV-IB and luciferase in the rhabdomyosarcoma cell line TE671 reduced cell surface expression of polySia and delayed tumor growth if cells were xenografted into C57BL/6 J RAG-2 mice.

Conclusion

Data obtained strongly indicate that αST8SiaII-IB and αST8SiaIV-IB are promising experimental tools to analyze the individual role of the two enzymes during brain development and during migration and proliferation of tumor cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-017-0360-7) contains supplementary material, which is available to authorized users.

The Proteome Profiles of the Cerebellum of Juvenile, Adult and Aged Rats--An Ontogenetic Study

In this study, we searched for proteins that change their expression in the cerebellum (Ce) of rats during ontogenesis. This study focuses on the question of whether specific proteins exist which are differentially expressed with regard to postnatal stages of development. A better characterization of the microenvironment and its development may result from these study findings. A differential two-dimensional polyacrylamide gel electrophoresis (2DE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis of the samples revealed that the number of proteins of the functional classes differed depending on the developmental stages. Especially members of the functional classes of biosynthesis, regulatory proteins, chaperones and structural proteins show the highest differential expression within the analyzed stages of development. Therefore, members of these functional protein groups seem to be involved in the development and differentiation of the Ce within the analyzed development stages. In this study, changes in the expression of proteins in the Ce at different postnatal developmental stages (postnatal days (P) 7, 90, and 637) could be observed. At the same time, an identification of proteins which are involved in cell migration and differentiation was possible. Especially proteins involved in processes of the biosynthesis and regulation, the dynamic organization of the cytoskeleton as well as chaperones showed a high amount of differentially expressed proteins between the analyzed dates.

A crucial role for polysialic acid in developmental interneuron migration and the establishment of interneuron densities in the mouse prefrontal cortex

Polysialic acid (polySia) is a unique glycan modification of the neural cell adhesion molecule NCAM and a major determinant of brain development. Polysialylation of NCAM is implemented by the two polysialyltransferases (polySTs) ST8SIA2 and ST8SIA4. Dysregulation of the polySia-NCAM system and variation in ST8SIA2 has been linked to schizophrenia and other psychiatric disorders. Here, we show reduced interneuron densities in the medial prefrontal cortex (mPFC) of mice with either partial or complete loss of polySia synthesizing capacity by ablation of St8sia2, St8sia4, or both. Cells positive for parvalbumin and perineuronal nets as well as somatostatin-positive cells were reduced in the mPFC of all polyST-deficient lines, whereas calretinin-positive cells and the parvalbumin-negative fraction of calbindin-positive cells were unaffected. Reduced interneuron numbers were corroborated by analyzing polyST-deficient GAD67-GFP knock-in mice. The accumulation of precursors in the ganglionic eminences and reduced numbers of tangentially migrating interneurons in the pallium were observed in polyST-deficient embryos. Removal of polySia by endosialidase treatment of organotypic slice cultures led to decreased entry of GAD67-GFP-positive interneurons from the ganglionic eminences into the pallium. Moreover, the acute loss of polySia caused significant reductions in interneuron velocity and leading process length. Thus, attenuation of polySia interferes with the developmental migration of cortical interneurons and causes pathological changes in specific interneuron subtypes. This provides a possible link between genetic variation in polyST genes, neurodevelopmental alterations and interneuron dysfunction in neuropsychiatric disease.

Band-like arrangement of taste-like sensory cells at the gastric groove: evidence for paracrine communication

The discovery of taste-related elements within the gastrointestinal tract has led to a growing interest in the mechanisms and physiological significance of chemosensory monitoring of chymus composition. Previous work suggests that brush cells located in the “gastric groove,” which parallels the “limiting ridge,” a structure in rodents that divides the fundus from the corpus, are candidate sensory cells. A novel sectioning technique revealed that these cells are arranged in a palisade-like manner forming a band which borders the whole length of the corpus epithelium. Using transgenic PLCβ2 promoter-GFP mice and specific antibodies, we have demonstrated that most of these cells express gustducin, PLCβ2, and TRPM5; typical signaling proteins of gustatory sensory “type II” cells. These molecular features strongly suggest that the cells may be capable of sensing nutrient or non-nutrient constituents of the ingested food. Since there is no evidence that brush cells are endocrine cells, attempts were made to explore how such putative chemosensory cells might transmit the information to “effector” cells. It was found that most of the cells express the neuronal nitric oxide synthase (NOS) suggesting some paracrine interaction with adjacent cells. Moreover, they also express choline acetyltransferase (ChAT) as well as the vesicular protein SNAP25, indicating the potential for cholinergic transmission, possibly with subjacent enteric nerve fibers.

Adult human brain expresses four different molecular forms of neural cell adhesion molecules

Using antibodies to rat neural cell adhesion molecules (NCAM), we analyzed the NCAM of adult human brain. Various regions of the brain were analyzed quantitatively by Western blot. Grey matter showed four bands of NCAM with apparent molecular weights of 180,000, 170,000, 140,000 and 120,000. White matter showed one major band with an apparent M(r) of 120,000 and a minor band of 180,000. Cerebellar grey matter contained mainly 170,000, 140,000 and 120,000, white cerebellar white matter had only 180,000 and 120,000 M(1) NCAMS. Spinal cord showed mainly 120,000 M(r) NCAM. Deglycosylation using N-glycanase resulted in 170,000, 160,000, 130,000 and 110,000 M(r) proteins, suggesting that the four forms of human NCAM are derived from individual polypeptides. The presence of 170,000 M(1) NCAM is unique to human brain.

Expression and localization of neural cell adhesion molecule and polysialic acid during chick corneal development

PURPOSE

To assay for expression and localization of neural cell adhesion molecule (NCAM) and polysialic acid (polySia) in the chick cornea during embryonic and postnatal development.

METHODS

Real time quantitative PCR and Western blot analyses were used to determine NCAM expression and polysiaylation in embryonic, hatchling, and adult chick corneas. Immunofluorescence staining for NCAM and polySia was conducted on cryosections of embryonic and adult corneas, whole embryonic corneas, and trigeminal neurons.

RESULTS

NCAM and ST8SiaII mRNA transcripts peaked by embryonic day (E)9, remained steady between E10 and E14 and slowly decreased thereafter during embryonic development. Both gene transcripts showed > 190-fold decline in the adult chick cornea compared with E9. In contrast, ST8SiaIV expression gradually decreased 26.5-fold from E6 to E19, increased thereafter, and rose to the early embryonic level in the adult cornea. Western blot analysis revealed NCAM was polysialylated and its expression developmentally changed. Other polysiaylated proteins aside from NCAM were also detected by Western blot analysis. Five NCAM isoforms including NCAM-120, NCAM-180 and three soluble NCAM isoforms with low molecular weights (87-96 kDa) were present in chick corneas, with NCAM-120 being the predominate isoform. NCAM was localized to the epithelium, stroma, and stromal extracellular matrix (ECM) of the embryonic cornea. In stroma, NCAM expression shifted from anterior to posterior stroma during embryonic development and eventually became undetectable in 20-week-old adult cornea. Additionally, both NCAM and polySia were detected on embryonic corneal and pericorneal nerves.

CONCLUSIONS

NCAM and polySia are expressed and developmentally regulated in chick corneas. Both membrane-associated and soluble NCAM isoforms are expressed in chick corneas. The distributions of NCAM and polySia in cornea and on corneal nerves suggest their potential functions in corneal innervation.

Level and localization of polysialic acid is critical for early peripheral nerve regeneration

PolySia, the most striking post-translational modification of the neural cell adhesion molecule, is down-regulated during postnatal development. After peripheral nerve lesion, polySia is located on neuronal and glial cells normally not synthesizing polySia. However, structural consequences of reduced polySia content for peripheral nerve regeneration have not yet been clear. Furthermore, the contribution of sialyltransferases ST8SiaII and ST8SiaIV for the up-regulation of polySia has not been studied so far. In order to investigate the impact of polySia on regeneration processes of myelinated axons, we examined mouse mutants retaining only one functional sialyltransferase allele. In the absence of ST8SiaII, quantification of myelinated axons revealed a significant decrease in number and size of regenerated fibers without impairment of remyelination. In contrast, St8SiaIV deficiency resulted in increased fiber outgrowth and axonal maturation. Western blot analysis demonstrated that both ST8SiaII and St8SiaIV direct up-regulation of polySia. Cell-specific induction of polySia in myelinating Schwann cells and on regenerated axons in the presence of ST8SiaIV, but not ST8SiaII, indicates that not only the amount of polySia but also its cellular localization has a high impact on the regeneration progress of peripheral nerves.

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

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

Structural analysis of the murine cell adhesion molecule L1 by electron microscopy and computer-assisted modelling

In the present study we have analysed the morphology of two fragments with apparent molecular weights of 180 and 140 kDA (L1-180 and L1-140) derived from the extracellular region of the murine neural cell adhesion molecule L1. The fragment L1-180 consists of almost the entire extracellular part of the molecule, and is built up of six immunoglobulin-like and five fibronectin type III-like domains. Fragment L1-140 lacks one-half of the third, the fourth and the fifth fibronectin type III-like domains. By electron microscopic analysis of rotary-shadowed molecules, L1-140 and L1-180 revealed fibrillar structures 31-43 nm long and 7-12 nm wide with one pronounced globular terminal domain. As determined by complex formation with an L1 antibody, this terminal part of the molecule is formed by the fibronectin type III-like domains. The individual structures showed variation and complexity, and four distinct aspects were identified. These different forms probably represent two-dimensional projections of the same three-dimensional helical structure. Computer-assisted modelling of the L1 molecule, i.e. the protein backbone, showed no strong intramolecular interaction between the different fibronectin type III- or Ig-like domains, suggesting that the formation of the globular part of the molecule is probably achieved by protein-carbohydrate and/or carbohydrate-carbohydrates rather than protein-protein interactions. In addition, our model proposes that interactions occur within the interfaces between the different domains. The highly conserved amino acid residues in these regions point to the necessity of maintaining the orientation between the different domains.

In vitro oligodendrogliotrophic properties of cell adhesion molecules in the immunoglobulin superfamily: myelin-associated glycoprotein and N-CAM

To determine if cell recognition molecules interact trophically with oligodendrocytes (OCs), their effect as growth substrates for differentiating oligodendroblasts was studied in primary culture. Oligodendroblasts purified from postnatal rat cerebrum by immunopanning were plated on substratum-bound cell adhesion molecules or extracellular matrix glycoproteins in chemically defined medium in which OCs terminally differentiate but survive poorly. Growth on myelin-associated glycoprotein (MAG) and neural cell adhesion molecule (N-CAM) selectively increased the number of viable cells per culture 2 weeks after plating as much as tenfold and sixfold, respectively, over background survival on an albumin substrate, whereas L1, tenascin-R, tenascin-C, fibronectin, and laminin were ineffective. Neither MAG nor N-CAM stimulated bromodeoxyuridine incorporation into cultures, indicating that enhanced proliferation did not contribute to better survival. Compared to growth on polyornithine alone, oligodendroblast differentiation in the added presence of MAG or N-CAM was qualitatively unchanged; > 90% of surviving cells developed into OCs that matured further by immunocytochemical and morphological criteria. A striking difference, however, was the quantitative effect of MAG and N-CAM substrates on oligodendrite outgrowth, increasing myelin-like membrane formation two- to threefold (> 8 x 10(3) microns2/cell). These findings support the concept that autotypic or heterotypic cell contact-mediated signaling by recognition molecules at the OC surface contributes trophic support of myelinogenesis.

Subventricular zone-olfactory bulb migratory pathway in the adult mouse: cellular composition and specificity as determined by heterochronic and heterotopic transplantation

To gain insight into cellular and molecular mechanisms subserving neuronal cell migration in the adult mouse forebrain, we have first investigated the cellular composition of the subventricular zone-olfactory bulb pathway (SVZ-OB). The pathway was essentially composed of cells with neuronal and astrocytic identities, neuronal cells being four times more numerous than astrocytes. Neuronal cells (precursors and some young postmitotic neurons) formed continuous cellular strands of migratory cells from the anterior horn of the lateral ventricle to the olfactory bulb. These chains of migrating cells moved within channels formed by the processes of a special subpopulation of astrocytes. The neuronal cells expressed the embryonic form of polysialic acid neural cell adhesion molecule, and the astrocytes were tenascin-C positive, thus preserving an embryonic cellular environment. Through transplantation experiments, the second part of this study attempted to analyze the functional properties of the adult SVZ-OB pathway. Early postnatal (P2-13) cerebellar progenitor cells, taken from a transgenic mouse line in which cerebellar granule cells and molecular layer interneurons (basket/stellate cells) expressed the reporter gene lacZ, were implanted in the SVZ-OB pathway of adult wild-type mice. Unlike grafted SVZ cells that migrate all along the pathway, none of the cerebellar precursors reached the olfactory bulb, although some of them were able to migrate along the caudal one-third of the pathway. The majority (over 67%) of the migrating cells were progenitors that acquired the phenotype of basket/stellate cells. Granule cell progenitors and most granule cells did not survive transplantation. These results show that the adult SVZ-OB pathway is not a "passive generic guidance" for all classes of premigratory neurons. From the two types of grafted cerebellar progenitors, only those with migratory capability and that do not follow radial glial axes are able to translocate along the SVZ-OB pathway. Furthermore, the basket/stellate cell progenitors are specified at the time of grafting: Neither their identity nor the pace of expression of their major distinctive features are influenced by local signals emanating from the adult forebrain.

Neural cell adhesion molecule (NCAM) as a quantitative marker in synaptic remodeling

The neural cell adhesion molecule (NCAM) participates in adhesion and neuritic outgrowth during nervous system development. In the adult brain, NCAM is considered to be involved in neuronal sprouting and synaptic remodeling. The NCAM concentration of brain tissue has proved to be a useful marker of these processes, especially when viewed in comparison with the concentration of a marker of mature synapses, e.g. D3-protein (SNAP-25) or synaptophysin. The present review focusses on studies of adult brain in which NCAM concentration estimates and NCAM/D3 ratios have been used to evaluate the rate of synaptic remodeling in brain damage and degenerative diseases.

The mouse homeodomain protein Phox2 regulates Ncam promoter activity in concert with Cux/CDP and is a putative determinant of neurotransmitter phenotype

Transcriptional regulation of the gene encoding the cell adhesion receptor NCAM (neural cell adhesion molecule), a putative effector molecule of a variety of morphogenetic events, is likely to involve important regulators of morphogenesis. Here we identify two mouse homeodomain proteins that bind to an upstream regulatory element in the Ncam promoter: Cux, related to Drosophila cut and human CDP, and Phox2, a novel protein with a homeodomain related to that of the Drosophila paired gene. In transient transfection experiments, Cux was found to be a strong inhibitor of Ncam promoter activity, and this inhibition could be relieved by simultaneously overexpressing Phox2. These results suggest that the Ncam gene might be a direct target of homeodomain proteins and provide a striking example of regulatory cross-talk between homeodomain proteins of different classes. Whereas the expression pattern of Cux/CDP includes many NCAM-negative sites, Phox2 expression was restricted to cells also expressing Ncam or their progenitors. The localisation data thus strongly reinforce the notion that Phox2 plays a role in transcriptional activation of Ncam in Phox2-positive cell types. In the peripheral nervous system, Phox2 was strongly expressed in all ganglia of the autonomic nervous system and more weakly in some cranial sensory ganglia, but not in the sensory ganglia of the trunk. Phox2 transcripts were detected in the primordia of sympathetic ganglia as soon as they form. Phox2 expression in the brain was confined to spatially restricted domains in the hindbrain, which correspond to the noradrenergic and adrenergic nuclei once they are identifiable. All Phox2-expressing components of the peripheral nervous system are at least transiently adrenergic or noradrenergic. In the developing brain, Phox2 was expressed at all known locations of (nor)adrenergic neurones and of their precursors. These results suggest that Phox2, in addition to regulating the NCAM gene, may be part of the regulatory cascade that controls the differentiation of neurons towards this neurotransmitter phenotype.

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

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

Functional topography of the myelin-associated glycoprotein. I. Mapping of domains by electron microscopy

The functional topography of the myelin-associated glycoprotein (MAG) was investigated by electron microscopic analysis of rotary-shadowed molecules of a MAG fragment (MAG 90) comprising the five immunoglobulin-like domains of the extracellular part of the molecule. MAG 90 molecules appeared as rod-like structures (18.5 +/- 1.2 nm long and 4.0 +/- 0.8 nm wide) with a globular domain at one end. Antibodies directed against the amino- and carboxy-terminus of MAG 90 interacted with the non-globular terminal region, indicating that the molecule is bent in the globular region with the amino- and carboxy-terminal arms in close apposition to each other. An antibody which interferes with the binding of MAG to neurons interacted predominantly with the globular domain of MAG 90. The fibril-forming collagen types I, III and V bound mainly to the non-globular terminal region of MAG 90, whereas the majority of heparin molecules interacted with the globular region of the molecule. The L2/HNK-1 carbohydrate structure was localized at the non-globular region in the protein fragment comprising the fourth and fifth immunoglobulin-like domains.

Identification of a novel neuron-specific surface antigen in the developing nervous system, by monoclonal antibody 4C5

Monoclonal antibody 4C5 was obtained after immunization of Balb/c mice with a crude membrane preparation derived from the brains of 15-day-old rat embryos. As revealed by immunocytochemistry on primary cell cultures from embryonic rat brain, it was shown that the antigen recognized by monoclonal antibody 4C5 (4C5 antigen) is localized on the cell surface of the neurons. Preliminary biochemical characterization showed that it is a peripheral protein with a molecular weight of 94,000. The 4C5 antigen does not appear to be linked with other polypeptides by S--S bonds and contains few or no disulphide intramolecular bridges. N-Glycanase digestion indicated that the protein is probably not glycosylated. Monoclonal antibody 4C5 crossreacts with membrane fractions from rat, rabbit, pig and human developing brain. It was shown by immunohistochemistry that the 4C5 antigen is widely distributed in the embryonic and adult rat brain. In the peripheral nervous system 4C5 immunoreactivity was present in dorsal root ganglion neurons. Immunoblotting and immunohistochemistry on dissociated cells from rat brain and on tissue sections of brain and dorsal root ganglia revealed an age-dependent decline in the expression of the epitope recognized by monoclonal antibody 4C5, in the central and peripheral nervous system. In particular, intense 4C5 immunoreactivity was observed during the embryonic and early postnatal ages. By the second postnatal week, expression of the protein was greatly reduced, becoming very weak at later stages of development and in the adult animal. In PC12 cell cultures, expression of the 4C5 antigen was intense in proliferating cells while being greatly reduced after nerve growth factor induced differentiation of these cells. The increased expression of the 4C5 antigen in proliferating PC12 cells and the prominent presence of this molecule during a time of neuronal migration suggest that it is involved in these developmental events.

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.

Interactions of the neural cell adhesion molecule and the myelin-associated glycoprotein with collagen type I: involvement in fibrillogenesis

To gain insights into the functional role of the molecular association between neural adhesion molecules and extracellular matrix constituents, soluble forms of the myelin-associated glycoprotein (MAG) and the neural cell adhesion molecule (N-CAM), representing most of the extracellular domains of the molecules, were investigated in their ability to modify fibrillogenesis of collagen type I. MAG and N-CAM retarded the rate of fibril formation, as measured by changes in turbidity, and increased the diameter of the fibrils formed, but did not change the banding pattern when compared to collagen type I in the absence of adhesion molecules. Scatchard plot analysis of the binding of MAG and N-CAM to the fibril-forming collagen types I, II, III, and V suggest one binding site for N-CAM and two binding sites for MAG. Binding of MAG, but not of N-CAM, to collagen type I was decreased during fibril formation, probably due to a reduced accessibility of one binding site for MAG during fibrillogenesis. These results indicate that the neural adhesion molecules can influence the configuration of extracellular matrix constituents, thus, implicating them in the modulation of cell-substrate interactions.

Proteolytic modification of neural cell adhesion molecule (NCAM) by the intracellular proteinase calpain

The neural cell adhesion molecule, NCAM, is concentrated in synaptic regions and thus may contribute to the formation and maintenance of connections between brain cells. We present evidence that the cytoplasmic domain of NCAM can be experimentally modified by the intracellular calcium-dependent proteinase, calpain. This degradation could provide a mechanism for rapidly uncoupling and reorganizing synaptic contacts.

PAC 1: an epitope associated with two novel glycoprotein components of isolated postsynaptic densities and a novel cytoskeleton-associated polypeptide

A monoclonal antibody has been raised which recognizes an epitope, PAC 1 (postsynaptic density and cytoskeleton enriched), which is specifically associated with two novel glycoprotein components of forebrain postsynaptic density preparations and a novel neuronal cytoskeletal-associated polypeptide. The monoclonal antibody has been used to study the cellular and subcellular localization of these molecules and for the partial characterization of all three PAC 1 antigens in the rat. The PAC 1 epitope is present on two concanavalin A binding glycoproteins of apparent molecular weights 130,000 (pgp130) and 117,000 (pgp117). Both species are enriched in preparations of rat forebrain postsynaptic densities and to a lesser extent in synaptic membranes. The epitope is also expressed by a polypeptide of 155,000 mol. wt, cp155. This molecule is highly enriched in cytoskeleton rather than membrane preparations. Enzymic removal of N-linked carbohydrate lowers the molecular weights of the PAC 1 glycoproteins pgp130 and pgp117 by 11,000 and 14,000 respectively, and suggests that cp155 is not glycosylated. Detergent, alkaline and salt extractions of postsynaptic densities and synaptic membranes indicate that pgp130 and pgp117 are integral membrane glycoproteins and are tightly bound components of postsynaptic density preparations. Immunocytochemical studies of adult rat forebrain show prominent staining of pyramidal cell dendrites and perikarya. There is no evidence of glial staining. Electron microscope studies show staining of microtubules together with punctate deposits of plasma membrane-associated reaction product. Several criteria have been used to show that pgp130 and pgp117 do not correspond to other known neuronal glycoproteins of similar molecular weight. We conclude that the PAC 1 epitope is expressed by two novel synaptic glycoproteins which are very probably integral components of the postsynaptic density and by a novel neuronal cytoskeleton-associated protein.

Establishment of permanent astroglial cell lines, able to differentiate in vitro, from transgenic mice carrying the polyoma virus large T gene: an alternative approach to brain cell immortalization

Permanent untransformed cell lines have been established from the cerebral cortex of transgenic mice that carry the polyoma virus large T gene. The immortalized cells described here synthesize laminin and neural cell adhesion molecules and induce primary neurons to develop neuritic processes. As shown by immunofluorescence and immunoblotting assays, they begin to synthesize the glial fibrillary acidic protein (GFAP) after confluence. Double labelling experiments indicated that GFAP expression is reversibly correlated with the arrest of cell division. The present cells also display adrenergic, serotoninergic, and high levels of muscarinic receptors coupled to the phosphatidylinositol signalling pathway. Taken together, our data show that these cell lines constitute homogeneous cell material that has retained the main differentiative, functional, and growth properties of normal astrocytes. Therefore, such clonal untransformed cell lines should be useful for further molecular studies, addressing terminal differentiation of glial cells, glioneuronal interactions, and astroglial expression of receptors for neurotransmitters. Furthermore, we suggest that this approach of cell immortalization by the use of transgenic mice carrying a non-transforming oncogene might be extended to a variety of cell types.

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

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

Binding properties of the neural cell adhesion molecule to different components of the extracellular matrix

A soluble form of the neural cell adhesion molecule (N-CAM) was obtained from 100,000-g supernatants of crude brain membrane fractions by incubation for 2 h at 37 degrees C. The isolated N-CAM, consisting of one polypeptide chain with a molecular mass of 110 kilodaltons (N-CAM 110), was studied for its binding specificity to different components of the extracellular matrix (ECM). N-CAM 110 bound to different types of collagen (collagen types I-VI and IX). The binding efficiency was dependent on salt concentration and could be called specific according to the following criteria: (a) Binding showed substrate specificity (binding to collagens, but not to other ECM components, such as laminin or fibronectin). (b) Binding of N-CAM 110 to heat-denatured collagens was absent or substantially reduced. (c) Binding was saturable (Scatchard plot analyses were linear with KD values in the range of 9.3-2.0 X 10(-9) M, depending on the collagen type and buffer conditions). Binding of N-CAM 110 to collagens could be prevented in a concentration-dependent manner by the glycosaminoglycans heparin and chondroitin sulfate. N-CAM 110 also interacted with immobilized heparin, and this interaction could be prevented by heparin and chondroitin sulfate. Thus, in addition to its role in cell-cell adhesion, N-CAM is a binding partner for different ECM components, an observation suggesting that it also serves as a substrate adhesion molecule in vivo.

Developmentally regulated expression of the neural cell adhesion molecule (NCAM) by mouse thymocytes

The expression of the neural cell adhesion molecule (NCAM) has been investigated during thymus ontogeny. NCAM mRNA was readily detectable at day 19 of gestation, the youngest age studied. Its level declined after birth to become undetectable at 3 weeks of age. Cell surface expression of NCAM protein was detected on 14% of day 15 fetal thymocytes and peaked during the perinatal period, when around 40% of the thymocytes expressed low to medium levels of NCAM. At postnatal day 2, the vast majority of the NCAM+ cells were also CD4+ and CD8+. At embryonic day 15, NCAM appeared also to be expressed by CD4- thymocytes since 14% of the cells were already NCAM+ whereas CD4 was virtually undetectable. In frozen section of the newborn thymus, surface staining for NCAM was present on a subpopulation of cells in the cortex, rare in the medulla and absent from the sub-capsular area. In conjunction with other cell adhesion molecules, NCAM could play a role in cell interactions during thymic development.

Characterization of a heparan sulfate proteoglycan that copurifies with the neural cell adhesion molecule

We have demonstrated previously that the neural cell adhesion molecule (NCAM) interacts with a neuronal heparan sulfate proteoglycan. The binding of this proteoglycan(s) by NCAM appears to be required for NCAM-mediated cell adhesion, although the mechanism is unclear. In the present study we show that a heparan sulfate proteoglycan copurifies with NCAM, and provide an initial biochemical characterization of the proteoglycan. The copurification of a heparan sulfate proteoglycan with NCAM was demonstrated following immunopurification of NCAM from a detergent extract of cell membranes derived from Na2(35)SO4-labeled neural retinal cells. A large-molecular-weight, 35SO4-labeled molecule copurified with NCAM isolated from these neural cell cultures, and was resistant to chondroitinase ABC treatment, but degraded completely by nitrous acid treatment. These results indicate that the molecule is a heparan sulfate proteoglycan. Although this proteoglycan copurifies with NCAM, it is not detected when the neuron-glia cell adhesion molecule (NgCAM) is immunopurified using the 8D9 monoclonal antibody. The heparan sulfate proteoglycan may also be a membrane-associated proteoglycan since it interacts with phenyl-Sepharose. Molecular weight characterization of the proteoglycan by gel filtration chromatography indicates a molecular weight of 400-520 kDa. The heparan sulfate glycosaminoglycan chains were shown to have an average molecular weight of approximately 40 kDa, and the polypeptide backbone was estimated to be 120 kDa by polyacrylamide gel electrophoresis. These data therefore demonstrate that a neuronal heparan sulfate proteoglycan copurifies with NCAM.

Differentiation-regulated loss of the polysialylated embryonic form and expression of the different polypeptides of the neural cell adhesion molecule by cultured oligodendrocytes and myelin

The expression of the neural cell adhesion molecule (N-CAM) on cultured murine oligodendrocytes, their precursors, and myelin was examined by indirect immunofluorescence, biosynthetic radiolabeling followed by immunoprecipitation and Western blot analysis, using antibodies specific for various forms of the molecule. In all culture systems studied, whether the oligodendrocytes were cultured as an enriched fraction containing precursor cells or in the presence of astrocytes and neurons, a similar differentiation-stage-related expression of N-CAM was seen. At early developmental stages many tetanus toxin receptor- and A2B5 antigen-positive putative oligodendrocyte precursors with bipolar morphology were seen and found to express N-CAM in its embryonic form. Of the 04 antigen-positive immature oligodendrocytes with few slender processes most expressed N-CAM, but few the embryonic form of N-CAM. The more mature 01 or 010 antigen-positive oligodendrocytes were found to express exclusively the adult form of N-CAM. Oligodendrocytes synthesized the 120 and 140 kD forms of N-CAM (N-CAM 120 and N-CAM 140), but not N-CAM 180, although with differentiation, N-CAM 120 predominated in oligodendrocytes and also in pure myelin. N-CAM 120 could be released from oligodendrocytes and myelin by phosphatidylinositol-specific phospholipase C, suggesting that in both oligodendrocytes and myelin N-CAM 120 is inserted into the membrane by covalent linkage to phosphatidylinositol.

Identification and cDNA cloning of a new member of the L2/HNK-1 family of neural surface glycoproteins

Rabbit antibodies raised against a 135- to 140-kD glycoprotein isolated from the culture medium of mouse forebrain explants were used for the identification and cloning of a complex of mouse neural cell surface glycoproteins. The antibodies recognized a 135-kD surface protein which shared the L2/HNK-1 epitope with several neural cell adhesion molecules. Three homologous complementary deoxyribonucleic acid (cDNA) clones were isolated from a mouse brain cDNA library prepared in the expression vector lambda gt11, one of which was sequenced and found to lack sequence homologies with known proteins. In Northern blots, this clone hybridized with a single 6.3 kb messenger ribonucleic acid (mRNA). In immunoblots of mouse brain extracts, antibodies raised in rabbits against the fusion protein encoded by it stained two glycoproteins of 135 and 90 kD, which we designated F3.135 and F3.90. In the developing mouse cerebellum, F3 antigenic sites were found predominantly on parallel fibers and on postmitotic neurons. In fetal brain cell cultures, F3 antigen was detected at the surface of cells with neuronal morphology, but the antibodies also stained some non-neuronal cells in a pattern characteristic of matrix components. Because all proteins carrying the L2/HNK-1 epitope identified so far have a role in cell adhesion, it can be anticipated that the F3 surface proteins also are involved in cell-interaction phenomena.

Expression of a developmental stage-specific antigen by neuronal precursor cells of human fetal cerebellum

A monoclonal antibody that was prepared against human neuroblastoma cells was shown to react strongly with fetal brain and moderately with adult brain by quantitative absorption testing. Immunoperoxidase staining demonstrated expression of the antigen by neuronal precursor cells in the cerebellar external granular layer of a 24- to 26-week fetus but not by their mature derivatives in the granular and molecular layers of adult cerebellum. The antigen was also present on subventricular cells of fetal cerebral cortex, as well as adult and fetal astrocytes. The expression of this antigen by neuronal precursor cells in the external granular layer but not their mature derivatives suggests that it is a stage-specific marker for cerebellar neuronal development.

Neuronal and glial markers of the central nervous system

This brief review evaluates the expression of cell-specific markers on differentiated neural cells and, where necessary, on their developing precursors. Within these limitations only the commonly used markers are discussed and those deemed unequivocal are only briefly appraised.

Developmental expression of neural cell adhesion molecules of oligodendrocytes in vivo and in culture

Previously, we have shown that oligodendrocyte adhesion molecules are related to the 120,000-Mr neural cell adhesion molecule (NCAM-120). In this report, we present further evidence that the oligodendrocyte adhesion molecule is NCAM-120. Studies on the expression of NCAM-120 and other molecular forms of NCAM in vivo in rat brain, in vitro in primary mixed cultures, and in cultures enriched for oligodendrocytes are described. Western blot analysis of rat brain using anti-NCAM showed that NCAM-120 first appears at postnatal day 7 and increases in quantity thereafter, coincident with the development of oligodendrocytes in vivo and comparable to the expression of myelin basic protein. Purified oligodendrocytes from 4-week-old rat brains expressed only NCAM-120. Quantitation of various forms of NCAMs in rat brain showed marked age-related differences in the expression of three molecular forms of NCAM. Immunofluorescence analysis showed that oligodendrocytes, at all ages tested, expressed NCAM, but in older oligodendrocytes, the intensity of staining was less. Western blot analysis of oligodendrocyte-enriched cultures showed that from day 1 after isolation (12 days of age) through day 7 after isolation (18 days of age) only NCAM-120 is seen. A possible role for NCAM in myelination and remyelination is discussed.

Quantitative analysis of rat brain neurons developing in primary cultures. II. Changes in the distribution of N-CAM associated to neuronal cell surfaces

Cultured rat fetal brain cells underwent morphological differentiation, as quantitatively described in the companion paper. In the same system, biochemical and immunolabeling studies were performed to analyze the developmental changes in neural cell adhesion molecule (N-CAM) distribution and quantity at the cell surface of neurons. The cell surface-associated N-CAM, related to the culture protein content, remained stable during the two-week period under study, as demonstrated by 125I-protein A binding assays. Immunogold labeling experiments, both in transmission and scanning electron microscopy, indicated a dramatic decrease in N-CAM site density in each membrane compartment, perikarya and neurites. This temporal variation of N-CAM distribution was not accompanied by differences in N-CAM site density between these two membrane compartments. On the other hand, individual perikarya, observed in scanning electron microscopy, showed various levels of labeling. In addition, immunoblot experiments demonstrated the absence of chemical modulation of N-CAM during the period under study, since the high molecular weight (embryonic) form remained dominant. Moreover, an increase in the total N-CAM amount was detected, contrasting with the stable quantity of cell surface-associated N-CAM. This suggested the existence of an N-CAM intracellular pool in cultured neurons. Finally, since the neurite membrane surface area increased 9-fold (companion paper) and since only a 5-fold decrease in N-CAM site density was observed in this compartment, N-CAM supply to neurite membranes was postulated.

The cellular neurobiology of neuronal development: the cerebellar granule cell

Cerebellar granule cells in vivo and in vitro have been widely used in the study of the cellular neurobiology of neuronal development. We have described the basic neuroanatomical data on the granule cell in the developing and mature cerebellum. The importance of the cytoskeleton in determining the morphology of the granule cell and in process outgrowth and cell migration has been described. Extensive information is now available on the composition of the granule cell cytoskeleton. Cell surface glycoproteins are thought to be involved in the control of cell adhesion and cellular interactions during development. A number of surface molecules belonging to either the N-CAM or the Ng-CAM groups of glycoproteins have been studied in detail in the cerebellum. The role of these proteins in cell adhesion and in granule cell-astroglial interactions during granule cell migration has been reviewed. The survival and differentiation of neurones is controlled by soluble trophic factors. Several factors have been described which act as trophic factors for granule cells in vitro and may do the same in vivo. The numerous studies that have been carried out on the cerebellar granule cell have allowed us to describe certain aspects of the cellular neurobiology of this class of neurones as an example with general significance for the understanding of neuronal differentiation and function.

Brain astrocytes express region-specific surface glycoproteins in culture

Astrocytes derived from the mouse brain mesencephalon and striatum regulate neuronal morphogenesis in a region-specific manner in vitro. To begin defining molecular mechanisms that may underlie this functional heterogeneity, lectin probes were used to compare surface glycoproteins expressed by astrocytes from different brain regions. These experiments demonstrated marked differences in surface glycoproteins depending on the anatomic origin of the astrocytes. In particular, mesencephalic and cerebellar astrocytes express a fucosylated glycoprotein with an apparent molecular weight of 190 kD that is absent or rarely expressed by striatal or cortical astrocytes. These findings raise the possibility that carbohydrate diversity of astrocyte surface molecules may play a role in the heterogeneity of region-specific neuron-glial interactions.

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.

Identification of a cDNA clone that contains the complete coding sequence for a 140-kD rat NCAM polypeptide

Neural cell adhesion molecules (NCAMs) are cell surface glycoproteins that appear to mediate cell-cell adhesion. In vertebrates NCAMs exist in at least three different polypeptide forms of apparent molecular masses 180, 140, and 120 kD. The 180- and 140-kD forms span the plasma membrane whereas the 120-kD form lacks a transmembrane region. In this study, we report the isolation of NCAM clones from an adult rat brain cDNA library. Sequence analysis indicated that the longest isolate, pR18, contains a 2,574 nucleotide open reading frame flanked by 208 bases of 5' and 409 bases of 3' untranslated sequence. The predicted polypeptide encoded by clone pR18 contains a single membrane-spanning region and a small cytoplasmic domain (120 amino acids), suggesting that it codes for a full-length 140-kD NCAM form. In Northern analysis, probes derived from 5' sequences of pR18, which presumably code for extracellular portions of the molecule hybridized to five discrete mRNA size classes (7.4, 6.7, 5.2, 4.3, and 2.9 kb) in adult rat brain but not to liver or muscle RNA. However, the 5.2- and 2.9-kb mRNA size classes did not hybridize to either a large restriction fragment or three oligonucleotides derived from the putative transmembrane coding region and regions that lie 3' to it. The 3' probes did hybridize to the 7.4-, 6.7-, and 4.3-kb message size classes. These combined results indicate that clone pR18 is derived from either the 7.4-, 6.7-, or 4.3-kb adult rat brain RNA size class. Comparison with chicken and mouse NCAM cDNA sequences suggests that pR18 represents the amino acid coding region of the 6.7- or 4.3-kb mRNA. The isolation of pR18, the first cDNA that contains the complete coding sequence of an NCAM polypeptide, unambiguously demonstrates the predicted linear amino acid sequence of this probable rat 140-kD polypeptide. This cDNA also contains a 30-base pair segment not found in NCAM cDNAs isolated from other species. The significance of this segment and other structural features of the 140-kD form of NCAM can now be studied.

Differential adhesivity of neuroepithelial cells and pioneering circumferential axons

To determine the initial growth pattern of pioneering axons and investigate the factors that may influence their guidance, the lateral margin of a stage 16+ chick brachial spinal cord was examined in serial thin sections. The specimen was prepared with hypertonic fixative which partially shrank the tissue and increased extracellular space. The retention of surface contact after shrinkage was used as an index of the relative adhesiveness between cells in situ. Six axons and growth cones were found within the reconstructed tissue; five were oriented dorsoventrally and one apparent motor neuron growth cone was oriented radially. The five circumferential axons originated from presumptive interneurons distributed in a dispersed pattern along the neural tube lateral wall. Four terminated with growth cones, and each extended a short distance (less than 30 microns) ventrally along the outer margin. No contact was found between these nonfasciculating axons or growth cones. Thus, the earliest intracentral axons appear to grow dorsoventrally from the outset with no appreciable wandering. Morphological features that may indicate their mechanism of guidance, including preformed cellular guides, extracellular channels, contact with basal lamina, and intercellular junctions were not found. The preferential retention of surface contact between adjacent endfeet, as well as between pioneering circumferential axons and neuroepithelial cells, suggests that these particular surfaces are mutually adherent. These findings are consistent with a proposed dorsal-to-ventral adhesive gradient mechanism of circumferential axonal guidance.

Changes in neural cell adhesion molecule (NCAM) structure during vertebrate neural development

Changes in carbohydrate and polypeptide form of the neural cell adhesion molecule (NCAM) have been documented during the development of central nervous system tissue in both chicken and frog. The carbohydrate variations reflect a high and low content of polysialic acid, and for the two vertebrates examined the expression of these forms is similar. At very early stages of neural development NCAM with a low content of polysialic acid is present, during histogenesis of the central nervous system NCAM with a high content of polysialic acid dominates, and there is a gradual return to NCAM with a low content of polysialic acid as the animals approach maturity. In contrast, the order of expression of the major NCAM polypeptide forms is different in the chicken and frog. These findings suggest that changes in sialic acid are a fundamental aspect of the function of NCAM in development, whereas NCAM polypeptide differences may affect events associated with a particular vertebrate. Studies have demonstrated that a decreased sialic acid content enhances the adhesion properties of NCAM. On this basis, we propose that NCAM with a low content of polysialic acid functions both to maintain integrity of neuroepithelium during morphogenesis of the early embryo and to stabilize differentiated structures in the adult, while the decreased adhesive function of NCAM with a high content of polysialic acid provides more plasticity in cell interactions during cell migration, axon outgrowth, and formation of neural circuits.

Acquisition of a brief behavioral experience in the presence of neuron-specific and D2-CAM/N-CAM-specific antisera

The effect of intraventricular infusion of D2-CAM/N-CAM directed antibodies prior to the acquisition of a passive-avoidance paradigm is described. The antisera used in this study were the neuron specific anti-BPM and a D2-CAM/N-CAM specific serum, anti-D2. Anti-BPM reliably inhibited paradigm acquisition when recall was ascertained at 24 and 48 hours and no effect was noted with absorbed anti-BPM or in sham-operated animals. This effect was time-dependent and no inhibition of memory formation was noted when the antiserum was administered at 6 and 10 hours after training. In contrast, infusion of anti-D2 had no effect on paradigm acquisition. These findings are discussed in relation to the potential synaptogenic events associated with memory formation.

Postnatal D2-CAM/N-CAM sialylation state is controlled by a developmentally regulated Golgi sialyltransferase

Golgi-enriched fractions have been isolated from rat brain of increasing postnatal age and defined by electron microscopy and distribution of marker enzymes. The expression of sialyltransferase activity associated with these fractions has been demonstrated to developmentally decrease and this appeared to be, in part, dependent on endogenous competitive inhibition. The developmental regulation of this activity paralleled the sialylation state of the neural cell adhesion molecule (D2-CAM/N-CAM) and could be demonstrated to be capable of endogenously sialylating this protein in the isolated Golgi fractions. In 12-day-old animals the majority of the transferred [14C]sialic acid was found to be associated with the high-molecular-weight [greater than 200 kilodaltons (kd)] form of D2-CAM/N-CAM, indicative of the protein having been heavily sialylated. Sialylation of the individual D2-CAM/N-CAM polypeptides was also demonstrated in both 12-day and adult animals and transfer was evident only in the 180-kd and 115-kd components and not in the 140-kd component. In contrast, Golgi-enriched fractions prepared from adult animals showed little capability of heavily sialylating D2-CAM/N-CAM to any significant extent.

Production of monoclonal antibodies selective for aggregation-competent chick neural retina cells. An immunosuppressive approach

We present here a rapid means of preparing mouse monoclonal antibodies which bind selectively to aggregation-competent, embryonic chick neural retina cells. The approach couples two existing technologies: well-defined procedures for manipulating the adhesive properties of embryonic retinal cells through control of the dissociation conditions, and an immunosuppressive technique designed to reduce the immune response against unwanted 'background' antigens. This approach greatly increases the likelihood of generating monoclonal antibodies directed against cell surface molecules mediating intracellular adhesion in this tissue. Fab prepared from the combined supernates of all IgG-producing clones obtained in this manner inhibited retinal Ca2+-dependent adhesion, suggesting that at least one clone in the group was reactive with elements of the Ca2+-dependent adhesion mechanism.

The N-CAM D2-protein as marker for synaptic remodelling in the red nucleus

We have followed the time-course of changes in the concentration of 3 neuronal and one glial antigen in the red nucleus in rats after unilateral lesion of the cerebellorubral connections. The neuronal markers were the neuronal cell adhesion molecule (N-CAM) D2-protein which is prevalent in newly formed neuronal membranes, and the D1- and D3-proteins, which are found mainly in mature neuronal membranes. The glial marker was S-100, a cytoplasmic protein. Six days after the lesion no changes in the concentration of the markers were found in the partially deafferentiated red nucleus. However, 10 days after the lesion the D2-protein concentration was significantly increased, in contrast to the D1-protein concentration which was decreased. After a further 3 days the D2-protein concentration began to decrease, approaching the still significantly decreased D1-protein concentration. Twenty-one days after the lesion the marker protein concentrations were not significantly changed from normal. However, whereas the concentrations of neuronal membrane markers were lower, the glial S-100 concentration showed a tendency to increase. Furthermore, although the changes in D3-protein concentration were unable to reach statistical significance alone they always followed the direction of D1-protein and were significantly in variance with the changes in D2-protein and S-100 concentrations. Our results support the notion of the N-CAM D2-protein as a useful marker for synaptic turnover in adult brain.