Monoclonal antibody 18B8, which detects synapse-associated antigens, binds to ganglioside GT3 (II3 (NeuAc)3LacCer)

Ganglioside Profiling of the Human Retina: Comparison with Other Ocular Structures, Brain and Plasma Reveals Tissue Specificities

Gangliosides make a wide family of glycosphingolipids, highly heterogeneous in both the ceramide moiety and the oligosaccharide chain. While ubiquitously expressed in mammalian tissues, they are particularly abundant in the brain and the peripheral nervous system. Gangliosides are known to play a crucial role in the development, maintenance and functional integrity of the nervous system. However, the expression and roles of gangliosides in the retina, although often considered as a window on the brain, has been far less studied. We performed an in-depth analysis of gangliosides of the human retina, especially using powerful LC/MS methods. We compared the pattern of ganglioside classes and ceramide molecular species of this tissue with other ocular structures and with brain and plasma in elderly human individuals. About a hundred of ganglioside molecular species among 15 distinct classes were detected illustrating the huge structural diversity of these compounds. The retina exhibited a very diverse ganglioside profile and shared several common features with the brain (prominence of tetraosylgangliosides, abundance of d20:1 long chain base and 18:0 fatty acid…). However, the retina stood out with the specific expression of GD3, GT3 and AcGT3, which further presented a peculiar molecular species distribution. The unique ganglioside pattern we observed in the human retina suggests that these ganglioside species play a specific role in the structure and function of this tissue. This lipidomic study, by highlighting retina specific ganglioside species, opens up novel research directions for a better understanding of the biological role of gangliosides in the retina.

Cellular targets and mechanistic strategies of remyelination-promoting IgMs as part of the naturally occurring autoantibody repertoire

Immunoglobulins with germline sequences occur in invertebrates and vertebrates and are named naturally occurring autoantibodies (NAbs). NAbs may target foreign antigens, self- or altered self-components and are part of the normal immunoglobulin repertoire. Accumulating evidence indicates that naturally occurring antibodies can act as systemic surveillance molecules, which tag, damaged or stressed cells, invading pathogens and toxic cellular debris for elimination by the immune system. In addition to acting as detecting molecules, certain types of NAbs actively signal in different cell types with a broad range of responses from induction of apoptosis in cancer cells to stimulation of remyelination in glial cells. This review emphasizes functions and characteristics of NAbs with focus on remyelination-promoting mouse and human antibodies. Human remyelination-promoting NAbs are potential therapeutics to combat a wide spectrum of disease processes including demyelinating diseases like multiple sclerosis. We will highlight the identified glycosphingolipid (SL) antigens of polyreactive remyelination-promoting antibodies and their proposed mechanism(s) of action. The nature of the identified antigens suggests a lipid raft-based mechanism for remyelination-promoting antibodies with SLs as most essential raft components. However, accumulating evidence also suggests involvement of other antigens in stimulation of remyelination, which will be discussed in the text.

Immunology in the clinic review series; focus on cancer: glycolipids as targets for tumour immunotherapy

Research into aberrant glycosylation and over-expression of glycolipids on the surface of the majority of cancers, coupled with a knowledge of glycolipids as functional molecules involved in a number of cellular physiological pathways, has provided a novel area of targets for cancer immunotherapy. This has resulted in the development of a number of vaccines and monoclonal antibodies that are showing promising results in recent clinical trials.

Lipid analysis by thin-layer chromatography--a review of the current state

High-performance thin-layer chromatography (HPTLC) is a widely used, fast and relatively inexpensive method of separating complex mixtures. It is particularly useful for smaller, apolar compounds and offers some advantages over HPLC. This review gives an overview about the special features as well as the problems that have to be considered upon the HPTLC analysis of lipids. The term "lipids" is used here in a broad sense and comprises fatty acids and their derivatives as well as substances related biosynthetically or functionally to these compounds. After a short introduction regarding the stationary phases and the methods how lipids can be visualized on an HPTLC plate, the individual lipid classes will be discussed and the most suitable solvent systems for their separation indicated. The focus will be on lipids that are most abundant in biological systems, i.e. cholesterol and its derivates, glycerides, sphingo- and glycolipids as well as phospholipids. Finally, a nowadays very important topic, the combination between HPTLC and mass spectrometric (MS) detection methods will be discussed. It will be shown that this is a very powerful method to investigate the identities of the HPTLC spots in more detail than by the use of common staining methods. Future aspects of HPTLC in the lipid field will be also discussed.

The repertoire of glycan determinants in the human glycome

The number of glycan determinants that comprise the human glycome is not known. This uncertainty arises from limited knowledge of the total number of distinct glycans and glycan structures in the human glycome, as well as limited information about the glycan determinants recognized by glycan-binding proteins (GBPs), which include lectins, receptors, toxins, microbial adhesins, antibodies, and enzymes. Available evidence indicates that GBP binding sites may accommodate glycan determinants made up of 2 to 6 linear monosaccharides, together with their potential side chains containing other sugars and modifications, such as sulfation, phosphorylation, and acetylation. Glycosaminoglycans, including heparin and heparan sulfate, comprise repeating disaccharide motifs, where a linear sequence of 5 to 6 monosaccharides may be required for recognition. Based on our current knowledge of the composition of the glycome and the size of GBP binding sites, glycoproteins and glycolipids may contain approximately 3000 glycan determinants with an additional approximately 4000 theoretical pentasaccharide sequences in glycosaminoglycans. These numbers provide an achievable target for new chemical and/or enzymatic syntheses, and raise new challenges for defining the total glycome and the determinants recognized by GBPs.

A novel heptasialosyl c-series ganglioside in embryonic chicken brain: its structure and stage-specific expression

A ganglioside of unknown structure (ganglioside X) was purified from chicken brain at embryonic day 12 (E12) and characterized for its structure. Ganglioside X was reactive with a monoclonal antibody A2B5 and migrated below GH1c on thin-layer chromatography (TLC). Extensive treatment of ganglioside X with Clostridium perfringens sialidase produced a single ganglioside product. This ganglioside was identified as GM1 based upon its chromatographic mobility and reactivity to cholera toxin B subunit and anti-GM1 antibody. Partial hydrolysis of ganglioside X by sialidase generated several degradation products including GH1c, GP1c, and GQ1c. Electrospray ionization (ESI)-mass spectrometry (MS) of the permethylated derivative of ganglioside X produced a triple-charged parent ion peak at m/z 1355, which corresponded with the gangliotetraose oligosaccharide structure having seven sialic acids and ceramide with the molecular mass of 566 (as non-methylated form). Collision-induced dissociation (CID)-MS(2) showed fragment ions including those at m/z 1066 and 1931; these two ions matched the structures of (NeuAc)(3)-Gal-Glc-Cer and (NeuAc)(4)-Gal-GalNAc, respectively. These structures were confirmed by CID-MS(3) of the corresponding peaks. Based upon these findings, the structure of ganglioside X was identified as NeuAc-NeuAc-NeuAc-NeuAc-Galbeta1-3GalNAcbeta1-4(NeuAc-NeuAc-NeuAcalpha2-3)Galbeta1-4Glcbeta1-1'Cer. This ganglioside was designated as GS1c. A developmental study demonstrated that GS1c was expressed in chicken brain during a period from E6 to E13 and thereafter decreased rapidly in its concentration. The present study suggests that GS1c may play a specific role in early development of chicken brain.

Occurrence and tissue distribution of c-series gangliosides in the common squid Todarodes pacificus

We have recently demonstrated that the common squid Todarodes pacificus express acidic lipids that were reactive with a monoclonal antibody A2B5. In the present study, two A2B5-reactive acidic lipids were isolated from squid hepatopancreatic tissue and characterized for their structures by methods including glycolipid overlay analysis, product analysis after sialidase treatment, and electrospray ionization-mass spectrometry (ESI-MS). Accordingly, the two acidic lipid were identified as GT3 and GQ1c, respectively. Another A2B5-reactive acidic lipid in the tissue was tentatively assigned to GT2 based upon its reactivity to A2B5 and chromatographic mobility on thin-layer chromatography. The composition and concentration of c-series gangliosides significantly differed among squid tissues (i.e. hepatopancreas, cerebral ganglion, eye lens, and mantle tissue). Interestingly, the percentages of c-series gangliosides within total gangliosides of hepatopancreas and cerebral ganglion were even higher than that of cod fish brain, which is known to be highly enriched with this ganglioside species. These findings strongly support the hypothesis that c-series gangliosides in squid tissues are not derived from ganglioside-containing food intake, but biosynthesized in a tissue-specific manner.

The specificity of monoclonal antibody A2B5 to c-series gangliosides

To examine the specificity of monoclonal antibody A2B5, four A2B5-reactive gangliosides (designated as G-1, G-2, G-3 and G-4) were purified from bonito fish brain. Ganglioside-1, -2, and -3 migrated above GD1b, below GQ1b, and far below GQ1b on thin-layer chromatography. Ganglioside-4 had the slowest chromatographic mobility and migrated below G-3. The structures of these gangliosides were characterized by overlay analysis with glycolipid-specific ligands, product analysis after sialidase or mild acid treatment, and electrospray ionization-mass spectrometry (ESI-MS). Accordingly, G-1, G-2 and G-3 were identified to be GT3, GQ1c and GP1c, respectively. The ganglioside G-4 was shown to have the following structure: NeuAc-NeuAc-NeuAc-Galbeta1-3Gal NAcbeta1-4(NeuAc-NeuAc-NeuAcalpha2-3)Galbeta1-4Glcbeta1-1'Cer. The antibody A2B5 reacted with these c-series gangliosides, but not with GD3 and other gangliosides and neutral glycosphingolipids. The antigenic epitope for A2B5 was assumed to include the trisialosyl residue connected to the inner galactose of the hemato- or ganglio-type oligosaccharide structure of gangliosides. Phylogenetic analysis of brain gangliosides using the A2B5 preparation demonstrated that c-series gangliosides are enriched in lower animals, especially bony fish of different species. The monoclonal antibody A2B5 would be a useful tool for examining the distribution and function of c-series gangliosides.

Expression of c-series gangliosides in rat hepatocytes and liver tissues

C-series gangliosides in rat hepatocytes and liver tissues were analyzed by thin-layer chromatographic (TLC) immunostaining with the specific monoclonal antibody A2B5. Primary cultures of hepatocytes isolated from adult rats were immunostained positively by A2B5. TLC immunostaining with A2B5 of gangliosides from the cells suggested that rat hepatocytes express c-series gangliosides including GT3, GT1c, GQ1c, and GP1c. Expression of c-series gangliosides in cultured hepatocytes was modulated by growth conditions of cells. The amount of GT3 was increased significantly by epidermal growth factor, while the contents of polysialo species such as GT1c, GQ1c, and GP1c were enhanced by higher cell density in culture. Examination of c-series gangliosides in rat liver tissues showed a unique developmental profile with a shift from GT3-dominant to polysialo species-dominant composition in late embryonic stages. These results suggest that the expression of c-series gangliosides in rat hepatocytes is regulated in a growth- and development-dependent manner.

Cholera toxin binds to differentiating neurons in the developing murine basal ganglia

Cell-surface expression of gangliosides in the developing mammalian central nervous system is temporally-regulated in a cell-type and regionally specific fashion. Gangliosides may be involved in cell-cell and cell-matrix interactions, and can act synergystically with several growth factors or growth factor receptors. Thus, a role for gangliosides in the regulation of neuronal stem cell proliferation and differentiation has been suggested. We have previously shown that cholera toxin B subunit (CTB), which binds to the ganglioside GM1, binds heterogeneously to dissociated neuroepithelial cells from the developing mouse telencephalon. We stained fixed sections of the ganglionic eminences (GE) of fetal mouse brains and found that CTB labels regions which contain differentiating neurons, but does not stain the rapidly dividing neuroepithelial cells in the ventricular zone. We dissociated cells from the GE on day 14 of gestation (E14), labeled the cells with CTB-FITC, and separated them by flow cytometry. We found the highest level of CTB binding in postmitotic cells which had begun to express markers of neuronal differentiation. When CTB-sorted cells were placed into short-term (48 h) cell culture, high CTB binding continued to correlate with fewer numbers of proliferating cells and larger numbers of differentiating neurons. CTB binding and fluorescence activated cell sorting appear to be useful for separating populations of differentiating neurons from immature, proliferating cells. These studies further lead us to suggest that GM1 plays a role in the differentiation of neurons in the basal ganglia.

Thin-layer chromatographic procedures for lipid separation

This review focuses on the thin-layer chromatographic (TLC) separation aspects of lipid analysis. Since the space limitations do not permit, the quantitative aspects of the analyses are not discussed at length although some indications of appropriate methodology and detection reagents will be indicated. Many separations carried out by TLC have the prerequisite of proper sample preparation. Using proper sample clean-up prior to TLC enables one to carry out precise separation as well as sensitive quantitation. Thus, the discussions are divided into the two main topics--sample preparation and TLC. Examples of applications are limited to those which illustrate the capabilities of the technique as well as practicability. Since there are a number of reviews in the literature, the discussions herein are focused mainly on reports after 1985.

Monoclonal IgM reactive with several gangliosides in a chronic relapsing polyneuropathy

A possibly pathogenic serum monoclonal IgM lambda from a patient with chronic relapsing polyneuropathy was shown to react with the disialosyl-lactosyl residue (NeuAc alpha 2-8NeuAc alpha 2-3) -Gal beta 1-4Glc expressed by GD1b, GT1b, GQ1b, GD2 and GD3. A part of this epitope in terminal position in GM3, GD1a and LM1 was also recognized by the IgM lambda.

Isolation and characterization of a soluble lactose-binding lectin from postnatal chicken retina

We investigated the presence of endogenous lectins in postnatal chicken retinal tissue assaying the hemagglutinating activity of crude soluble extracts of the tissue that was homogenized in a buffer supplemented with different sugars. Lactose was the most effective sugar to extract an hemagglutinating activity. Using similar extraction conditions, other sugars, such as glucose, N-acetylglucosamine, mannose, fucose, glucuronic and sialic acid, were ineffective to extract any significant hemagglutinating activity. The lectin was purified by affinity chromatography on lactosyl-Sepharose. SDS-PAGE and isoelectric focusing analyses showed that it has a subunit molecular weight of 16 kDa and a pI about 4.5. The retinal lectin cross-reacted immunologically with a rabbit antiserum raised against a lectin purified from adult chicken liver, which is a CLL-I (Beyer et al.: J Biol Chem 255:4236-4239, 1980) or C-16 (Sakakura et al.: J Biol Chem 265:21573-21579, 1990) form of chicken endogenous soluble lactose-binding lectins. Gel filtration studies showed that the oligomeric structure of the retinal lectin is dependent on the ionic strength of the elution buffer. The lectin hemagglutinating activity and the amount of lectin protein reached their highest levels at late developmental stages of the retinal tissue, suggesting that retinal lectin might have a functional role during terminal differentiation of retinal cells.

GD3/proteosome vaccines induce consistent IgM antibodies against the ganglioside GD3

The gangliosides of melanoma and other tumours of neuroectodermal origin are suitable targets for immune intervention with tumour vaccines. The optimal vaccines in current use contain ganglioside plus bacillus Calmette-Guérin and induce considerable morbidity. We have screened a variety of new adjuvants in the mouse, and describe one antigen-delivery system, proteosomes, which is especially effective. Highly hydrophobic Neisserial outer membrane proteins (OMP) form multimolecular liposome-like vesicular structures termed proteosomes which can readily incorporate amphiphilic molecules such as GD3 ganglioside. The optimal GD3/proteosome vaccine formulation for induction of GD3 antibodies in the mouse is determined. Interestingly, the use of potent immunological adjuvants in addition to proteosomes augments the IgM and IgG antibody titres against OMP in these vaccines but GD3 antibody titres are unaffected. The application of proteosomes to enhance the immune response to GD3 extends the concept of the proteosome immunopotentiating system from lipopeptides to amphipathic carbohydrate epitopes such as cell-surface gangliosides. The demonstrated safety of meningococcal OMP in humans and the data in mice presented here suggest that proteosome vaccines have potential for augmenting the immunogenicity of amphipathic tumour antigens in humans.

Ganglioside expression on human malignant melanoma assessed by quantitative immune thin-layer chromatography

The ganglioside composition of 20 human malignant melanomas and 5 normal tissues (muscle, spleen, kidney, liver and brain) was analyzed by high-performance thin-layer chromatography (HPTLC) and immune HPTLC using a panel of antiganglioside monoclonal antibodies, and quantified by photodensitometry. The most prominent gangliosides were GM3 and GD3, present in all 20 melanomas; however these were expressed in the 5 normal tissues as well. GD2, GM2, GT3 and 9-O-Ac-GD3 were each expressed in at least 17 of 20 melanomas, but distribution on the normal tissues examined was largely restricted to brain. The detection of several additional glycolipids was studied. GMI was highly expressed in normal brain tissue, but was not detected in any melanoma biopsies, and SGPG was detected in neither. Fuc-GMI was identified in 3 melanoma specimens and a base-sensitive ganglioside, not previously identified in melanoma, was detected in 4 of 20 melanomas with the anti-GD2 MAb 3F8. This compound is most likely O-acetylated GD2. GD3 lactones were identified in 16 of 20 melanoma biopsies, however the proportion that are naturally occurring rather than artifacts of extraction is unclear. The total expression of the more restricted gangliosides (GM2, GD2, GT3 and 9-O-Ac-GD3) in these 20 melanomas ranged between 2.4 and 102.5 micrograms/g, representing 8 x 10(6) to 3 x 10(8) ganglioside molecules per cell. This number of tumor-surface antigens provides the rationale for a polyvalent anti-melanoma vaccine containing GM2, GD2, GT3 and 9-O-Ac-GD3.

Dietary carcinogens and the risk for glioma and meningioma in Germany

A population-based case-control study was performed in South-West Germany in 1987/88 with 115 histological confirmed glioma and 81 meningioma cases and 418 randomly selected controls. On the basis of information from a food-frequency questionnaire and questions on food preparation and food supply, the role of dietary carcinogens, in particular N-nitroso compounds or their precursors, on risk for glioma and meningioma were analyzed by multiple logistic regression. Eleven food groups were investigated. The intake of processed meat was significantly associated with an increased risk of glioma. The intake of any food group was not significantly related to meningioma risk. Among single meat products, a significantly higher risk of glioma was found for cooked ham, processed pork meat and fried bacon. For the consumption of 3 N-nitrosamines, assessed from the intake of processed meat and cheese, significant positive relations to glioma risk were found. These N-nitrosamines were also related to meningioma risk, although to a less pronounced extent. The risk for occurrence of glioma was significantly increased for those using vegetable fat frequently for deep frying, as compared with non-users. For the dietary intake of nitrate, nitrite, vitamin C, specific alcoholic beverages, total alcohol, and water from a non-central supply, no elevated risk was found in this study.

A ceramide analogue (PDMP) inhibits glycolipid synthesis in fish embryos

Glycolipids were depleted from medaka embryos using 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), an inhibitor of glucosylceramide synthetase. Embryos cultured in the presence of 20 microM PDMP exhibited a dramatic decline in glycolipid synthesis and cell surface expression. Metabolic labeling of glucosylceramide declined by 87% on Days 3-6 of development and 72% on Days 7-10 (hatching occurred on Day 10). In parallel, PDMP-treated embryos exhibited a striking loss of several tissue-specific glycolipid antigens, including 9-O-acetyl GD3 from brain and retina, GT3/GQ1C from brain, neural tube, and retina, and sulfated glycolipid from skin and gut. Despite these changes in glycolipid expression, PDMP-treated embryos were fully viable with no evidence of developmental abnormality. PDMP appears to provide a useful tool for identifying glycolipid antigens in embryos and investigating their role in development.

Analytical detection of 9(4)-O-acetylated sialoglycoproteins and gangliosides using influenza C virus

The unique glycoprotein of influenza C virus, designated hemagglutinin (HEF), exhibits three functions: hemagglutination, esterase activity, and fusion factor. As the virus uses 9-O-acetylated sialic acid as a high-affinity receptor determinant for attachment to cells, its binding activity was used to reveal O-acetylated sialic acid residues after polyacrylamide gel electrophoresis and transfer onto nitrocellulose sheets of proteins and thin-layer chromatography of lipids. The specificity of the binding for O-acetylated sialoglycoconjugates was investigated. Our results showed that influenza C virus could detect the different forms of the two murine glycophorins which are known to be O-acetylated sialoglycoconjugates. The virus also bound to O-acetylated gangliosides isolated from embryonic chicken brain such as purified O-acetylated NeuAc alpha (2-8)NeuAc alpha (2-8)NeuAc alpha (2-3)Gal beta (1-4)Glc beta (1-1)ceramide (GT3). The esterase activity of the HEF protein of influenza C virus was used to unmask the sialic acid. After its deacetylation by the virus enzyme, the O-acetylated GT3 was recognized by a monoclonal antibody which binds only to the nonacetylated derivative. The results presented here show that influenza C virus is a discriminating analytical probe for identifying O-acetylated sialoglycoconjugates directly after Western blotting of proteins and thin-layer chromatography of lipids, thus providing a new analytical tool.

Developmentally expressed O-acetyl ganglioside GT3 in fetal rat cerebral cortex

Monoclonal antibody M6704, established against the chick neural tube, was shown to recognize a trisialosyl residue, NeuAc alpha 2-8NeuAc alpha 2-8NeuAc alpha 2-3-R of C-series gangliosides. Using this antibody, the developmental changes of C-series gangliosides in fetal rat cerebral cortex have been examined. Two dimensional thin layer chromatography (TLC) enzyme-immunostaining analysis revealed that alkali treatment resulted in a great increase in GT3 that amounted to more than 85% of the total GT3 detected. The alkalilabile form was easily degraded to form GT3 by the action of the receptor-destroying enzyme of influenza C virus, sialate O-acetylesterase, indicating that the antigen was most probably 9-O-acetyl-NeuAc containing GT3. The ganglioside was highly enriched at the 14th gestation day, gradually decreased, and was not detected in adult rat cerebral cortex.

The glycosphingolipid composition of the human hepatoma cell line,Hep-G2

The origin of plasma glycosphingolipids in normal individuals and the mechanisms by which tumor-associated glycosphingolipid antigens enter the plasma in patients with cancer are largely unknown. The Hep-G2 human hepatoma cell line retains many of the characteristics of differentiated hepatocytes including the ability to synthesize and secrete lipoproteins. Preliminary results indicated that newly synthesized Hep-G2 cell glycosphingolipids are coupled to the secreted lipoproteins. This suggests that this cell line may offer an interesting model for studying glycosphingolipid secretion, transfer, and shedding. We now report on the chemical and immunological characterization of Hep-G2 cell glycosphingolipids. Five major glycosphingolipids were purified and biochemically characterized: glycosylceramide, lactosyl ceramide, ceramide trihexoside, ganglioside GM3, and lactosyl sulfatide. Four additional minor components (3-fucosyl-lactosamine containing glycolipids, asialo GM2, galactosylgloboside, and ganglioside GM1) were identified using a combination of exoglycosidase digestion and immunostaining of thin-layer chromatography plates with specific carbohydrate binding proteins. This demonstrates that although this cell line synthesizes a limited number of major glycosphingolipids, it retains the ability to produce at least small amounts of structures in the lactoneo, globo, and ganglio series of glycosphingolipids. These studies show that it will be possible to investigate the mechanisms of secretion by Hep-G2 cells of different classes of these molecules such as neutral glycosphingolipids, gangliosides, and sulfatides.

Ganglioside composition in human meningiomas

The ganglioside composition in meningioma specimens from 20 patients was analyzed to find potential meningioma-associated structures. The characterization was performed by immunological staining with specific monoclonal antibodies to ganglioside antigens and fast atom bombardment-mass spectrometry. The major gangliosides were GM3 and GD3, and most of the meningioma specimens could be divided into a "GM3-rich" or a "GD3-rich" group. Gangliosides of the gangliotetraose series were represented by GM1, GD1a, GD1b, and GT1b, which were found in minor amounts in all the specimens. The ratios of GM1/GD1a and GD1a/GD1b differed from that in normal brain, and therefore existence of this series could not be explained by contamination with brain material. Ganglioside 3'-isoLM1, found in human malignant glioma, could not be detected in any meningioma specimen.

Synaptophysin expression during synaptogenesis in the rat cerebellar cortex

In order to study the mechanisms of synaptogenesis in the rat cerebellar cortex, a library of monoclonal antibodies has been generated against proteins of the isolated synapse. One recognizes a glycosylated 38 kDa protein that is concentrated in the synaptic vesicle fraction and resembles synaptophysin biochemically in its molecular weight, charge, and pattern of glycosylation. In the adult cerebellar cortex, the antisynaptophysin(mabQ155) immunoreactivity is codistributed with synapses. Immunoreactivity is strongest in the molecular layer where punctate deposits of reaction product outline the Purkinje cell dendrites. Discrete small profiles, consistent with the distribution of basket cell axon terminals, surround the Purkinje cells, and in the granular layer the synaptic glomeruli are intensely stained. There is no immunoreactivity in the white matter axon tracts. Electron microscope immunocytochemistry confirms the synaptic location of the antigen and suggests that the reaction product is associated with synaptic vesicles. Both round and flat vesicle populations are immunoreactive. Antisynaptophysin(mabQ155) has been used to follow synaptogenesis in the developing rat cerebellum. In the newborn rat (P0), despite the paucity of synapses, there is some specific immunoreactivity, especially in the subcortical white matter. Electron microscopy shows that the antigenicity is associated with vesicles within growth cones, filopodia, and immature axon profiles. During development, antisynaptophysin immunoreactivity increases progressively, along with the maturing cell populations, for both the granule cell-Purkinje cell and the mossy fiber-granule cell synapses. Quantitative biochemical analysis confirms the cytochemical results. These data suggest that neuronal growth cones express a synapse-specific antigen before complete morphological synapses are present.

Alterations of cell-surface carbohydrates during differentiation and development

Expression of many cell-surface carbohydrates is controlled temporally and spatially by developmental programs. This subject is reviewed from 5 viewpoints: structural changes revealed by chemical analysis, cell-surface markers useful for cell identification and separation, core proteins carrying the developmentally regulated carbohydrate chain, glycosyltransferases responsible for the change and the biological meaning of the phenomenon. The differentiation systems covered are mainly early mammalian embryogenesis and the differentiation of blood and nerve cells.

Developmental expression in embryonic rat and chicken brain of a polysialoganglioside-antigen reacting with the monoclonal antibody Q 211

The monoclonal mouse antibody Q 211 binds to an antigen, which is expressed by postmitotic growing neurons of embryonic chicken and rat brain. In chicken, thin layer chromatography (TLC) immunostaining confirms the presence of the Q 211 antigen in at least 3 different polysialoganglioside fractions. One comigrates on TLC plates with GP1c and the others with gangliosides, which have been previously preliminary characterized as GQ1c, and as a hexasialoganglioside. Thus, 3 sialic acid residues linked to the inner galactose of a complete tetraose moiety is suggested as the common epitope of the different Q 211-antigen-active gangliosides. Also in the embryonic rat brain, immunohistochemistry reveals a transient expression of the Q 211 antigen in areas containing growing nerve fibres. Unlike chicken, however, in the rat the staining is restricted to early thalamocortical innervations and to a fibre system (probably long distance projections) connecting the mamillary body with the hippocampus formation. In ganglioside extracts from rat forebrain 2 polysialogangliosides are shown by immuno-TLC to bind Q 211. One of these fractions, occurring transiently and in parallel with histochemical staining, comigrates on TLC plates with chicken GP1c. The other comigrates with the second main Q 211 antigen-containing band of chicken, which was preliminary identified as GQ1c.

A monoclonal antibody, WCC4, recognizes a developmentally regulated ganglioside containing alpha-galactose and alpha-fucose present in the rat nervous system

A monoclonal antibody, WCC4, raised against PC12 cells, recognizes a ganglioside which is present in low concentrations in the postnatal rat nervous system. The antigen is also present in the adrenal and kidney, as determined immunohistochemically, but is not detectable in liver or spleen. A neutral glycosphingolipid is also immunoreactive. In the present report, the chemical characterization of this ganglioside, isolated from PC12 cells, and the anatomical distribution of the antigens recognized by the WCC4 antibody are described. By enzymatic cleavage of terminal saccharide moieties, the ganglioside is identified as alpha-galactosyl, (alpha-fucosyl) GM1. The ganglioside increases in concentration postnatally to day 35 (P35) and is present in a slightly diminished concentration in the adult. Immunohistochemical studies revealed that this glycolipid is also present on neuronal cell soma throughout the cerebrum, cerebellum and spinal cord. It is expressed in highest concentration in the molecular layer of the dentate gyrus and is also present in the olfactory bulb, the molecular layer of the hippocampus, the piriform cortex, the olfactory tubercle and the entorhinal cortex. The dentate molecular layer receives most of its innervation from neurons in the entorhinal cortex, and gangliosides are known to have an effect on plasticity following entorhinal cortical lesions. Therefore, the WCC4 antibody should prove to be a useful tool for the study of the role of endogenous gangliosides in this region of the nervous system.

Biosynthesis and expression of gangliosides during differentiation of chick embryo retina cells in vitro

Cells from neural retina from 7-day chick embryos were cultured on polylysine-coated dishes up to 7 days. The small, round-shaped cells at seeding differentiated progressively, and after 4 days in vitro the majority had enlarged bodies and abundant processes. The content of protein and DNA was essentially unchanged during the entire period of culture. The incorporation of radioactivity from [3H]glucosamine into gangliosides declined slightly, reaching about 65% of the initial values at the end of the culture period. The proliferating activity measured by the incorporation of [3H]thymidine into DNA decreased to 10% or less of the initial value after 3 days in vitro. Almost at the same chronological times as in ovo, the synthesis of GD3 and of a ganglioside partially identified as GT3 decreased from 70 and 19% of the total incorporation into gangliosides in the first 20 h of culture to about 7 and 5%, respectively, after 3 days in vitro. Conversely, the synthesis of GD1a increased from about 6% at the beginning to about 70% at the end of the culture times. Immunocytochemical analyses of the expression of gangliotetraosyl gangliosides in cultured cells showed that these gangliosides appeared in the bodies and processes of cells having neuronal morphology; very little immunostaining of the scarce flattened cells, probably Müller cells, was found. The results indicate that the changes in ganglioside metabolism, which lead to decreased synthesis of gangliosides lacking the galactosyl-N-acetyl-galactosaminyl disaccharide end and to increased synthesis of gangliotetraosyl gangliosides, occur in cells that in culture differentiate into neurons.

Recent advances in identifying the functions of gangliosides

The recent development of several new approaches has proven extremely useful in identifying functions for gangliosides, the sialic-acid containing glycosphingolipids. The first is the incorporation of exogenous gangliosides into the plasma membrane of ganglioside-deficient cells. Using this approach, specific gangliosides have been identified as the receptors for certain bacterial toxins and viruses and as important factors in the organization of fibronectin into an extracellular matrix. The second approach has been a ligand blotting technique which allows detection of ganglioside-binding proteins such as toxins and antibodies. Gangliosides are separated by thin-layer chromatography and overlain with the protein of interest. Specific binding of the ligand to gangliosides can then be detected by either direct or indirect methods. The third approach is the use of the B or binding subunit of cholera toxin as a specific probe for endogenous plasma membrane ganglioside function. The ability of the B subunit to alter the growth of cells directly demonstrates a role for gangliosides as biotransducers of signals for the regulation of cell growth.

Carbohydrate sequences detected by murine monoclonal antibodies

The carbohydrate sequences of cell surface glycolipids change during differentiation and oncogenic transformation. To detect these structural changes, murine monoclonal antibodies have been produced in many different laboratories. Some of these antibodies are used to distinguish various cell types such as normal and transformed cells, while others are used to analyze developmentally regulated antigens. Recently, the structures of many of these carbohydrate antigens have been determined. The availability of these well-defined monoclonal antibodies will be useful for the study of the regulation and function of glycoconjugates.

A cell surface molecule distributed in a dorsoventral gradient in the perinatal rat retina

Brain topography may have its earliest expression as spatial gradients of molecules controlling the deposition of neurones and neuronal processes. In the vertebrate visual system there is evidence that the stereotyped alignment of central retinal projections relies on an initial spatially organized distribution of molecules in both the retina and its central target nuclei. We used an immunological approach to look for molecules that are so organized and produced a monoclonal antibody (JONES) which shows a pronounced dorsal to ventral gradient of binding in the rat retina throughout the period when retinal ganglion cell axons are forming topographically organized projections within the central nervous system (CNS). Binding is present throughout the radial thickness of the retinal epithelium in regions where postmitotic neurones are generated but is not associated with any consistent histological characteristic of the tissue. The antibody was shown to bind on the cell surface of freshly dissociated retinal cells, and dorsal retinal quadrants were found in vitro to have nearly twice as much antigen as ventral retinal quadrants. Initial biochemical characterization of the target epitope reveals that it is a lipid present in chloroform/methanol extracts from perinatal retina and is sensitive to neuraminidase digestion.

GD2 ganglioside biosynthesis is a distinct biochemical event in human melanoma tumor progression

Gangliosides from cell cultures established from melanocytic lesions, representing different stages of melanoma tumor progression, were analyzed by chemical and immunological means on thin-layer chromatograms. The GD2 ganglioside and N-acetylgalactosaminyl transferase, which catalyzes the biosynthesis of GD2 from its precursor GD3, were detected in cultures established from advanced primary and metastatic melanomas, but not in cultures of normal melanocytes. Immunohistochemical studies on tissue sections from all progression stages confirmed GD2 expression only in these advanced lesions. A distinct biochemical event thus coincides with the onset of faster growth and acquisition of metastatic competence in human melanoma tumor progression.