Identification and characterisation of two surface glycoproteins on cultured cerebellar cells

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.

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.

MB1, a quail leukocyte-endothelium antigen: partial characterization of the cell surface and secreted forms in cultured endothelial cells

We describe here conditions allowing the selective growth in culture of embryonic capillary endothelial cells from quail yolk sac. Such cultures were set up to characterize an antigen present on the endothelial cell surface and to study whether it was secreted in the culture medium. This antigen, MB1, was previously evidenced by a monoclonal antibody raised to quail IgM heavy chain. It is present at the surface of all endothelial and hemopoietic cells (except mature erythrocytes) starting from the hemangioblast, the early mesodermal precursor of blood and vascular endothelial cells. The MB1 epitope is also found on quail plasma molecules of 80 and 125-200 kDa. By immunoprecipitation of either surface or metabolically labeled endothelial cellular material, we have chemically characterized MB1-bearing components as glycoproteins of apparent molecular mass ranging from 80 to 200 kDa and provided evidence for their release into the culture medium. This is consistent with the hypothesis that, in the quail, vascular endothelium participates in the secretion of the alpha-MB1-positive plasmatic components.

Cell surface proteins of cerebellar interneurones and astrocytes cultured in chemically defined and serum-supplemented media

Lactoperoxidase catalysed 125I-iodination of cerebellar interneurone enriched cultures grown in serum-supplemented or in serum-free, chemically defined medium was studied. It was observed that the differences in the adhesion properties of nerve cells under these conditions are accompanied by differences both in the degree of 125I-iodination of the proteins on the plasma membrane of nerve cells and in the profile of the labelled polypeptides resolved by SDS-polyacrylamide gel electrophoresis. The relative labelling of the major 125I-iodinated polypeptides changed with time in both types of cultures, suggesting that alterations in the overall organisation of the neuronal plasma membrane occur during the development of the cells under both culture conditions. The developmental changes affecting the D2 protein (which is nerve cell specific in these cultures) were significantly retarded in the neuronal cultures grown in the serum-free medium compared with those grown in the serum-containing medium: the increase in D2 content was reduced by 7 DIV and the maturational change in the molecular form of D2 was retarded significantly during the whole cultivation period. The degree of surface 125I-iodination of cerebellar astrocytes in culture was only a fraction (7-20% depending on cultivation time and conditions) of that of the neuronal cultures and the labelled polypeptide profiles obtained from the two types of cultures were markedly different. In comparison with cultures in the serum-supplemented medium, astrocytes under the serum-free conditions showed only minor and transient differences in the profile of surface 125I-iodinated proteins, although the morphology of the cells was markedly different.

Changes in the expression of a neuronal surface protein during development of cerebellar neurones in vivo and in culture

The expression of the neurone-specific D2 protein changes both quantitatively and qualitatively during development in vivo and in cultures of cerebellar nerve cells. The total D2 content per unit protein shows a two-fold increase in vivo from birth to postnatal day 6, after which it declines progressively to about 50% of the maximal value. This increase can be accounted for by an immature form of the protein anodic D2 being preferentially expressed at the early stages of cerebellar development. After postnatal day 9 this form gradually switches to a mature form cathodic D2. This switch can be mimicked by neuraminidase treatment, suggesting a developmental loss of sialic acid from the D2 protein. In freshly isolated cells the total D2 content per unit protein is only 30% of that in the corresponding intact tissue from 8-day-old cerebella, but it increases rapidly during the first 8 days of culture to levels similar to those of the equivalent age in vivo. The switch from anodic D2 to cathodic D2 also occurs at a faster rate in culture, probably reflecting the culture conditions that favour differentiation. The changes in the expression of D2 during development of cerebellar nerve cells in culture suggest that anodic D2 is preferentially expressed on nerve cells that are proliferating, migrating, or in the initial stages of differentiation, whereas cathodic D2 is associated with differentiated neurones. The transition between the two forms appears to occur during the formation of interneuronal contacts.

Development of cerebellar cells in neuron-enriched cultures: cell surface proteins

Lactoperoxidase catalyzed 125I-iodination of 8-day-old rat cerebellar cultures enriched in interneurons, mainly granule cells, was studied during a period 1-8 days in vitro, when the mature appearance of the cultures develop. Autoradiography of the surface iodinated constituents after separation by SDS-polyacrylamide gel electrophoresis showed a limited number of heavily labeled bands, including polypeptides of apparent molecular weight (X 10(3] of 140, 88, 68, 58 and 53 daltons. Their relative proportion in terms of 125I-content changed during the development of the cultures. Initially, the labeled 140 kdaltons band (P140) was dominant. Using crossed immunoelectrophoresis with an antiserum raised against immature rat cerebellar plasma membrane preparations (anti-BPM serum) that primarily recognizes one neuronal surface antigen (D2)33, it was established that the P140 comprises the D2 protein. In contrast to the amount of D2, which increases during the 8-day culture period, the labeling of P140 decreased sharply after 2 DIV. This decline coincided with a developmental change in the molecular forms of D2 involving desialylation. Treatment of 2 DIV cultures with neuraminidase, which reproduces the D2 developmental change, prior to 125I-iodination resulted in a marked reduction in the labeling of P140, whereas the other major labeled group of polypeptides in the 50 kdalton range were little affected. Further experiments showed that the D2 protein is phosphorylated in the plasma membrane. It was found that some of the surface labeled proteins, including P140, are released into the culture medium, but apparently in a non-phosphorylated form. Thus it would appear that a significant part of the polypeptide chain of D2, which is an integral membrane constituent, is exposed on the cell surface, and that either D2 has an anchorage within the membrane that is phosphorylated but is not released or D2 is rapidly dephosphorylated when it is shed from the membrane.

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

The monoclonal antibody anti-BSP-2 defines a set of glycoproteins present on the neuronal cell surface in dissociated mouse cerebellar cultures and on neurons and astrocytes in sections of the mouse cerebellum. This antibody was used in the present study to characterize the antigens recognized in cerebellar cultures and in the developing and adult mouse cerebellum in vivo. In extracts from cerebellar cultures and from late postnatal or adult cerebellum, the anti-BSP-2 antibody reacted with a triplet of glycosylated polypeptide chains of 180,000, 140,000 and 120,000 mol. wt. Early postnatal cerebellum contained a different form of BSP-2 antigen which migrated as one broad or several closely spaced diffuse bands in the 190,000-250,000 mol. wt. region of SDS polyacrylamide gels. During cerebellar ontogeny, the adult pattern emerged gradually between postnatal days 5 and 13. The cellular expression of the BSP-2 antigen was studied by immunohistochemistry on sections of the developing cerebellum. At postnatal day 3, the antigen was found mainly on cell bodies and fibers of the Bergmann glia and on astrocytes of the granular layer. Immature granule cells of the outer zone of the external granular layer lacked the antigen, but they appeared to acquire the antigen during their migration to the internal granular layer. At postnatal day 13, the immunofluorescence pattern was not different from the one seen in the adult. These results suggest that the neonatal 190,000-250,000 mol. wt. form of BSP-2 may at least in part be expressed by astroglial cells and they show a close correlation between the emergence of the adult forms of the antigen and the appearance of labeled granule cells in the internal granular layer. In vitro degradation implying cleavage of sialic acid residues, but probably also proteolysis and/or cleavage of different glycans converted the neonatal form of BSP-2 into the triplet pattern and ultimately into a p120 component. Neuraminidase digestion of the adult antigens produced small molecular weight shifts without converting one band into the other, but endogenous enzyme activities were capable of degrading the p180 and p140 bands by converting them into the p120 protein. Our findings support the idea that distinct, but structurally similar surface glycoproteins created by post-translational modifications from a common precursor molecule may be expressed by different cell types or during different developmental stages. As shown by sequential immunoprecipitation experiments, BSP-2 and the rat neuronal membrane protein D2 may belong to the same family of surface glycoproteins.

Laminin is produced by early rat astrocytes in primary culture

The production of laminin by early rat astrocytes in primary culture was investigated by double immunofluorescence staining for laminin and the glial fibrillary acidic protein (GFAP), a defined astrocyte marker. In early cultures (3 d in vitro; 3 DIV) cytoplasmic laminin was detected in all the GFAP-positive cells which formed the major population (80%) of the nonneuronal cells present in cultures from 20-21-d embryonic, newborn, or 5-d-old rat brains. Monensin treatment (10 microM, 4 h) resulted in accumulation of laminin in the Golgi region, located using labeled wheat germ agglutinin. Laminin started gradually to disappear from the cells with the time in culture, was absent in star-shaped, apparently mature astrocytes, but remained as pericellular matrix deposits. The disappearance of cellular laminin was dependent on the age of the animal and the time in culture so that it started earlier in cultures from 5-d-old rat brains (5 DIV) and approximately following the in vivo age difference in cultures from newborn (12 DIV) and embryonic (14 DIV) rat brains. Our results indicate that laminin is a protein of early astrocytes and also deposited by them in primary culture, thus suggesting a role for this glycoprotein in the development of the central nervous system.

Monoclonal antibodies as neural cell surface markers

A comparison is made of the immunohistochemistry at the ultrastructural level of three monoclonal antibodies directed against surface components of DNS cells. Hybridomas secreting these antibodies were obtained from two cell fusions of a rat myeloma cell line and immune splenocytes derived from rats immunized either with primary mouse brain cultured cells or membrane components. In cultures one antibody, anti-BSP2 (Brain Surface Protein-2), was preferentially directed against neurons while another, anti-BSP-3 (Brain Surface Protein-3), preferentially labeled astrocytes. In mouse cerebellar sections, both labeled the surface of Purkinje cells, granule cells and astrocytes. In addition a cytoplasm localization was apparent in granule cells and astrocytes. Another antibody anti-MESA-1 (Mouse Endothelial Surface Antigen-1) reacted exclusively with the surface of endothelial cells lining blood vessels. These data are discussed with reference to the biochemical nature of the corresponding antigens and to known glycoproteins of neural cell membranes.

Tissue- and developmental stage-specific forms of a neural cell surface antigen linked to differences in glycosylation of a common polypeptide

We have previously identified a cell surface glycoprotein of the mouse nervous system named brain cell surface protein-2 (BSP-2). Here we report that this antigen is not a single, discrete entity, but a family of antigenically and structurally related molecules. Three components of 180, 140, and 120 K were characteristic for more mature nervous tissues. Adult cerebral cortex contained the 140-K and 120-K antigens, adult spinal cord only the 120-K, and dorsal root ganglia from young mice mainly the 180-K component. Very different forms of the antigen that migrated as a diffuse zone from 180-250-K in SDS-polyacrylamide gels were found in immature nervous tissues. A molecule different from the previous ones was found in a neuroblastoma line. Evidence is presented that the structural diversity of BSP-2 is due to differences in glycosylation. This result indicates that cell type- and developmental stage-specific glycoprotein patterns previously found in the nervous system may in part be due to different glycosylation of identical polypeptides. The finding that a neural cell surface protein may be glycosylated in different ways has important implications for the generation of cell surface specificity.

A new brain cell surface glycoprotein identified by monoclonal antibody

Of 207 monoclonal antibodies produced against cultured mouse cerebellar cells, 16 reacted with cerebellar cell surfaces and 4 reacted with glycoproteins. One of them, called an anti-BSP-3 (Brain cell Surface Protein-3) defines a 48,000 molecular weight protein which can be iodinated at the surface of cultured cerebellar cells. Lectin-binding and sugar incorporation studies established the glycoprotein nature of the antigen. Astroglia (glial fibrillary acidic protein-positive cells) in primary cerebellar cultures were labelled intensely for this antigen by the indirect immunofluorescence method while neuronal cells and their processes were more weakly labelled. Fibronectin-positive cells were negative for BSP-3. In cerebellar sections using the immunoperoxidase method at both the optical and electron microscope levels, the difference in staining intensity between astrocytes and neuronal cells was not significant: in Purkinje cells and in the large neurones present in the deep cerebellar nuclei the immunoperoxidase percipitate was confined to the plasma, membrane while in both astrocytes and granule cells cytoplasmic labelling was also observed. Oligodendrocytes do not appear to react with the anti-BSP-3 monoclonal antibody; neither do endothelial or leptomeningeal cells. The availability of a monoclonal antibody produced by a stable hybridoma line will be a powerful tool in attempts to purify the BSP-3 antigen and to elucidate its function.

Expression of Thy-1, H-2, and NS-4 cell surface antigens and tetanus toxin receptors in early postnatal and adult mouse cerebellum

The expression of several cell surface components (Thy-1, H-2 and NS-4 antigens and tetanus toxin receptors) was studied by indirect immunofluorescence in situ using histological sections and in vitro using freshly dissociated and cultured cells from mouse cerebellum. Thy-1 alloantigen is expressed in adult cerebellum predominantly in neuron-rich regions, i.e. molecular, Purkinje cell, and granular layers, however, it is not detectable at postnatal day 8. In cerebellar cultures of 6-day-old mice Thy-1 is absent from more than 99% of all cells when these are maintained as monolayers in vitro for up to 3 days. After 4 days in vitro some GFA protein-positive astrocytes and some fibronectin-positive fibroblast-like cells start to express Thy-1 antigen. After 14 days in vitro not all fibroblast-like cells and astrocytes are Thy-1 antigen-positive. Neurons with small cell bodies and oligodendrocytes never express Thy-1 at any stage examined. H-2 is not expressed sufficiently to be detectable in histological sections in early postnatal or adult cerebellum. In cerebellar cultures of 6-day-old mice H-2 becomes detectable on some fibroblast-like cells and some astrocytes after 7 days in culture. In histological sections of adult and early postnatal cerebellum NS-4 antigen and tetanus toxin receptors are expressed at higher levels on more mature granule cells. In cerebellar cultures NS-4 antigen and tetanus toxin receptors are expressed on neurons. Occasionally some astroglia can also show detectable levels of expression. NS-4 antigen is also present on some 04 antigen-positive oligodendrocytes, while tetanus toxin receptors are never detectable on these cells.

Clones of human cytotoxic T lymphocytes derived from an allosensitized individual: HLA specificity and cell surface markers

By planned immunization of a volunteer, two stable (greater than or equal to 6 months), specific, alloreactive cytolytic T-cell clones have been established from his peripheral blood lymphocytes. One clone reacts with all serologically defined HLA-Cw3 cells from our panel, whereas the other defines a split within the serological HLA-B40 specificity. The two cytotoxic clones are SmIg-negative, E-rosette positive, EA and EAC rosette-negative, HLA-A, -B and -C- positive, and also HLA-DR- or 'Ia like'-positive. In addition, they present very similar patterns of iodinated cell surface molecules as analysed by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE), contrasting with that of an EBV cell line derived from the same donor.

Monoclonal antibody against cell surface glycoprotein of neurons

A monoclonal antibody, named BSP-2, has been produced against glycoproteins extracted from neonatal mouse brain. Its reactivity with live cells established the surface location of the antigen. In primary cultures of dissociated cerebellar cells, the antibody bound to neuronal cell types, but not to astrocytes nor to fibroblasts. Immunoprecipitates prepared with the BSP-2 antibody contained a triplet of high-molecular weight glycoproteins with apparent molecular weights of 180,000, 140,000 and 120,000.

Biosynthetic incorporation of [75Se]selenomethionine: a new method for labelling lymphocyte membrane antigens

A novel approach for radiolabelling lymphocyte membrane antigens is described. This technique is based on the use of the gamma-emitting amino acid analogue [75Se]selenomethionine. Human HLA-A, B, C and DR heavy and light chains and mouse Ia antigens were efficiently labelled by this technique and were precipitated with monoclonal antibodies. Approximately the same radioactivity was incorporated into the HLA-A, B, C chains whether [75Se]selenomethionine, [35S]methionine or [3H]leucine were used as precursors. Easily detectable as a gamma-emitter, [75Se]selenomethionine thus constitutes a useful biosynthetic label of lymphocyte surface antigens. The same method was used to label immunoglobulins produced by hybridomas and to determine the nature of the secreted light chains.