[Austrian Nursing Society in conversation with Mag. Marianne Kriegl. Interview by Harald Verworner].
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The cytoplasmic domain of the large myelin-associated glycoprotein isoform is needed for proper CNS but not peripheral nervous system myelination.
The myelin-associated glycoprotein (MAG) is a member of the immunoglobulin gene superfamily and is thought to play a critical role in the interaction of myelinating glial cells with the axon. Myelin from mutant mice incapable of expressing MAG displays various subtle abnormalities in the CNS and degenerates with age in the peripheral nervous system (PNS). Two distinct isoforms, large MAG (L-MAG) and small MAG (S-MAG), are produced through the alternative splicing of the primary MAG transcript. The cytoplasmic domain of L-MAG contains a unique phosphorylation site and has been shown to associate with the fyn tyrosine kinase. Moreover, L-MAG is expressed abundantly early in the myelination process, possibly indicating an important role in the initial stages of myelination. We have adapted the gene-targeting approach in embryonic stem cells to generate mutant mice that express a truncated form of the L-MAG isoform, eliminating the unique portion of its cytoplasmic domain, but that continue to express S-MAG. Similar to the total MAG knockouts, these animals do not express an overt clinical phenotype. CNS myelin of the L-MAG mutant mice displays most of the pathological abnormalities reported for the total MAG knockouts. In contrast to the null MAG mutants, however, PNS axons and myelin of older L-MAG mutant animals do not degenerate, indicating that S-MAG is sufficient to maintain PNS integrity. These observations demonstrate a differential role of the L-MAG isoform in CNS and PNS myelin.
Alleles↗
Expression of recombinant myelin-associated glycoprotein in primary Schwann cells promotes the initial investment of axons by myelinating Schwann cells.
Myelin-associated glycoprotein (MAG) is an integral membrane protein expressed by myelinating glial cells that occurs in two developmentally regulated forms with different carboxyterminal cytoplasmic domains (L-MAG and S-MAG). To investigate the role of MAG in myelination a recombinant retrovirus was used to introduce a MAG cDNA (L-MAG form) into primary Schwann cells in vitro. Stably infected populations of cells were obtained that constitutively expressed MAG at the cell surface without the normal requirement for neuronal contact to induce expression. Constitutive expression of L-MAG did not affect myelination. In long term co-culture with purified sensory neurons, the higher level of MAG expression on infected Schwann cells was reduced to control levels on cells that formed myelin. On the other hand, unlike normal Schwann cells, infected Schwann cells associated with nonmyelinated axons or undergoing Wallerian degeneration expressed high levels of MAG. This suggests that a posttranscriptional mechanism modulates MAG expression during myelination. Immunostaining myelinating cultures with an antibody specific to L-MAG showed that L-MAG was normally transiently expressed at the earliest stages of myelination. In short term co-culture with sensory neurons, infected Schwann cells expressing only L-MAG segregated and ensheathed larger axons after 4 d in culture provided that an exogenous basal lamina was supplied. Similar activity was rarely displayed by control Schwann cells correlating with the low level of MAG induction after 4 d. These data strongly suggest that L-MAG promotes the initial investment by Schwann cells of axons destined to be myelinated.
Animals↗
Transthoracic Doppler echocardiography of mammary artery grafts to assess graft function.
BACKGROUND: Transthoracic Doppler echocardiography of internal mammary artery grafts (MAGs) has been tested by the supraclavicular approach, but little information is available about the parasternal approach. OBJECTIVE: To evaluate the usefulness of parasternal transthoracic Doppler echocardiography to assess the patency of left and right MAGs. PATIENTS AND METHODS: Forty-eight patients with previous MAGs were divided into two groups on the basis of coronary angiography: 42 patients had patent MAGs and six patients had severe MAG stenosis. Doppler echocardiography of MAGs was performed on all patients, both at baseline and after low-dose dipyridamole infusion. Systolic and diastolic time-velocity integrals and their ratios were obtained, and MAG flow reserve was calculated. RESULTS: Patients with patent MAGs had a predominant diastolic flow, while a prominent systolic pattern was found in the presence of MAG stenosis. In patients with stenosis, baseline Doppler analysis showed a lower diastolic peak velocity (DPV) (P<0.01), diastolic time-velocity integral (P<0.05), and diastolic and systolic time-velocity integral ratios (both P<0.005), and a reduced MAG flow reserve (P<0.001). In the overall population, when adjusting for clinical variables, a multilinear regression analyis underscored MAG flow reserve (beta=0.38, P<0.01) and baseline DPV (beta=0.29, P<0.05) as independent determinants of MAG stenosis (cumulative R2=0.25, P<0.005). CONCLUSIONS: Doppler echocardiographic evaluation of MAGs is a reliable, noninvasive tool to assess MAG patency and functional status of the vessel. MAG blood flow reserve and baseline DPV are independent determinants of MAG stenosis.
Aged↗
Myelin-associated glycoprotein inhibits neurite/axon growth and causes growth cone collapse.
We have previously shown that myelin-associated glycoprotein (MAG) inhibits neurite growth from a neuronal cell line. In this study we show that 60% of axonal growth cones of postnatal day 1 hippocampal neurons collapsed when they encountered polystyrene beads coated with recombinant MAG (rMAG). Such collapse was not observed with denatured rMAG. Neurite growth from rat embryonic hippocampal and neonatal cerebellar neurons was also inhibited about 80% on tissue culture substrates coated with rMAG. To investigate further the inhibitory activity of MAG in myelin, we purified myelin from MAG-deficient mice and separated octylglucoside extracts of myelin by diethylaminoethyl (DEAE) ion-exchange chromatography. Although there was no significant difference in neurite growth on myelin purified from MAG-/- and MAG+/+ mice, differences were observed in the fractionated material. The major inhibitory peak that is associated with MAG in normal mice was significantly reduced in MAG-deficient mice. These results suggest that although MAG contributes significantly to axon growth inhibition associated with myelin, its lack in MAG-deficient mice is masked by other non-MAG inhibitors. Axon regeneration in these mice was also examined after thoracic lesions of the corticospinal tracts. A very small number of anterogradely labeled axons extended up to 13.2 mm past the lesion in MAG-/- mice. Although there is some enhancement of axon generation, the poor growth after spinal cord injury in MAG-/- mice may be due to the presence of other non-MAG inhibitors. The in vitro studies, however, provide the first evidence that MAG modulates growth cone behavior and inhibits neurite growth by causing growth cone collapse.
Animals↗
Antitumor activity of magainin analogues against human lung cancer cell lines.
Magainin 1 and magainin 2, originally isolated from African clawed frog Xenopus laevis skin, inhibit the growth of bacteria and fungi. Synthetic magainin A (MAG A) and magainin G (MAG G) are more potent against bacteria and protozoa. In order to determine the antitumor activity of these analogues, we have tested these two analogues against six small cell lung cancer (SCLC) cell lines NCI-H82, NCI-H526, NCI-H678, NCI-H735, NCI-H841, and NCI-H889, which were known to differ by more than 10-fold in their sensitivity to different chemotherapeutic agents, and four normal human fibroblast cell lines. Semiautomated 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays of the six SCLC cell lines revealed average concentrations producing 50% inhibition (IC50) values of 2.6 microM (range, 0.49-9.30 microM) for cisplatin, 2.5 microM (range, 0.39-6.00 microM) for etoposide, and 138.8 nM (range, 55.0-450.0 nM) for doxorubicin. The average IC50 of MAG A was 8.64 microM (range, 6.23-11.7 microM) and that of MAG G was 8.82 microM (range, 4.44-12.5 microM) against the SCLC cell lines. Despite a 10-fold difference in sensitivity to standard chemotherapeutic agents, the IC50 of MAG A and MAG G differs by less than 3-fold. The average IC50 against four normal human fibroblast cell lines was 21.1 microM (range, 12.7-25.6 microM) for MAG A and 29.2 microM (range, 21.3-34.8 microM) for MAG G. Combined exposure to the IC50 concentration of MAG A or MAG G plus IC50 of etoposide or cisplatin decreased the percentage of surviving SCLC cells to 29.0% (range, 26.1-31.7%). MAG A or MAG G had an additive effect when used with standard chemotherapeutic agents. These data suggest that MAG A and MAG G have in vitro antitumor activity against SCLC cell lines.
Antimicrobial Cationic Peptides↗
Microbiome Datahub: an open-access platform integrating environmental metadata, taxonomy, and functional annotation for comprehensive metagenome-assembled genome datasets.
BACKGROUND: Metagenome-assembled genomes (MAGs) provide crucial insights into the genomic diversity of uncultured microbes. However, MAG datasets deposited in public repositories such as INSDC are often difficult to reuse due to heterogeneous quality, inconsistent taxonomic and functional annotations, and insufficiently curated environmental metadata. While secondary MAG databases such as MGnify, IMG/M, and SPIRE provide standardized resources, they reconstruct MAGs de novo from public metagenomic reads and therefore do not represent the original MAGs reported in publications. RESULTS: To address this gap, we developed Microbiome Datahub, an open-access platform that systematically aggregates and re-annotates original MAGs from INSDC. We collected 214,427 MAGs, predicted genes by DFAST, performed quality assessment with CheckM, standardized taxonomic assignments with GTDB-Tk, inferred 27 phenotypic traits using Bac2Feature, assigned proteins to MBGD ortholog clusters and KEGG Orthology IDs using PZLAST, and annotated environmental metadata with the Metagenome and Microbes Environmental Ontology. Across these MAGs, the average completeness was 80.5% and contamination 1.8%; notably, the most frequent values were >95% completeness and <1% contamination, indicating that the majority of MAGs are of high quality. Comparative analyses showed that Microbiome Datahub provides phylogenetically and environmentally diverse MAGs: while the majority originated from vertebrate gut environments, a substantial number were also recovered from other habitats such as groundwater, including nearly 10,000 MAGs from the Patescibacteria. Inference of 27 phenotypic traits, including optimum growth temperature, further revealed ecological differentiation across phyla. Protein clustering revealed 56 million identity 40% clusters, with the majority unique compared with MGnify and GlobDB, and ~19% of proteins unassigned to MBGD ortholog clusters, underscoring their novelty. CONCLUSIONS: Microbiome Datahub integrates MAG genome sequences, gene and protein predictions, quality metrics, environmental and taxonomic annotations, ortholog cluster assignments, and phenotype predictions, all accessible via a web interface, API, and bulk downloads. By combining original MAGs with curated metadata and functional annotations, Microbiome Datahub constitutes a comprehensive and reusable resource that will accelerate microbiome and microbial genomics research. Video Abstract.
Metagenome↗
Differential intracellular sorting of the myelin-associated glycoprotein isoforms.
Myelin-associated glycoprotein (MAG), a myelin-specific protein, is expressed as two isoforms, designated as L-MAG and S-MAG. Both share identical extracellular and transmembrane domains but differ in their cytoplasmic domains. L-MAG is expressed earlier during myelination than S-MAG. These features, as well as others, suggest that the isoforms have different functions. To confirm this hypothesis, both isoforms were expressed transiently and stably in Madin-Darby canine kidney (MDCK) epithelial cells, and the localization of the isoforms was studied. In both transiently and stably transfected cells, L-MAG sorted primarily to the basolateral membrane. In single transfected cells, S-MAG sorted primarily to the apical membrane. When groups of adjacent cells became transiently transfected, S-MAG accumulated at areas of cell-cell contact within the basolateral membrane. In stably transfected cells S-MAG sorted to the basolateral membrane. The data suggest that L-MAG contains an invariable basolateral sorting signal, but that the sorting of S-MAG is dependent upon extrinsic factors, such as coexpression by adjacent (contacting) cells. As MDCK cells sort the MAG isoforms differently, these data support the hypothesis that the MAG isoforms do perform different functions.
Animals↗
The expression of recombinant large myelin-associated glycoprotein cytoplasmic domain and the purification of native myelin-associated glycoprotein from rat brain and peripheral nerve.
The myelin-associated glycoprotein (MAG) is a transmembrane protein of the immunoglobulin superfamily existing as two isoforms (L-MAG and S-MAG) that are differentially expressed by myelinating glial cells of the central and peripheral nervous systems, where MAG represents 1 and 0.1% of the total myelin proteins, respectively. The polypeptide chains of the two isoforms differ only by the carboxy terminus of their respective cytoplasmic domains, which most probably determine the isoform-specific functions. Here, we describe the expression of the L-MAG cytoplasmic domain as a GST fusion protein. The recombinant protein was used to raise polyclonal antibodies against the L-MAG-specific carboxy terminus and against the region of the MAG cytoplasmic domain common to both S-MAG and L-MAG. These antibodies, which function in dot blotting, Western blotting, and immunoprecipitation, were used to immunopurify native MAG from both rat brain and peripheral nerves in quantities and purity sufficient for the realization of most biochemical and functional studies. The antibodies and the recombinant and native MAG proteins provide much needed tools for the study of the common and isoform-specific properties and functions of L-MAG and S-MAG.
Animals↗
Comparison of the phosphorylation of myelin-associated glycoprotein in cultured oligodendrocytes and Schwann cells.
Phosphorylation of the large and small isoforms of myelin-associated glycoprotein (L- and S-MAG) was investigated in primary oligodendrocyte cultures and in immortalized Schwann cells by incubating the cells with inorganic [32P]phosphate and immunoprecipitating MAG. In oligodendrocytes, both L- and S-MAG were phosphorylated, but L-MAG was much more heavily labeled. In Schwann cells, most of the phosphorylation was in S-MAG, which is the predominant isoform expressed by these cells. In both types of cells, the principal phosphorylated amino acid in MAG was serine. Radioactive phosphothreonine and phosphotyrosine were also detected in the MAG from oligodendrocytes. In Schwann cells, there was less phosphorylation of threonine and labeled phosphotyrosine was not detected. In both oligodendrocytes and Schwann cells, the phosphorylation of MAG was stimulated by phorbol ester and a calcium ionophore, but not by forskolin. The results indicate that the phosphorylation of MAG is catalyzed by protein kinase C and possibly other calcium-activated kinases in both types of myelinating cells, but not by cAMP-activated kinase. An inhibitor of tyrosine phosphatase, ammonium vanadate, increased the amount of radioactive phosphate in MAG several fold in both oligodendrocytes and Schwann cells. However, even in the presence of vanadate, the great majority of radioactivity in MAG was in phosphoserine and only a small amount was in phosphotyrosine, suggesting that tyrosine phosphorylation of other proteins may indirectly increase the phosphorylation of MAG. The current status of our understanding of MAG phosphorylation is reviewed in the context of similarities and differences between our results and other reports in the literature.
Animals↗
Sialic acid specificity of myelin-associated glycoprotein binding.
Myelin-associated glycoprotein (MAG), a nervous system cell adhesion molecule, is an I-type lectin that binds to sialylated glycoconjugates, including gangliosides bearing characteristic structural determinants (Yang, L. J.-S., Zeller, C. B., Shaper, N. L., Kiso, M., Hasegawa, A., Shapiro, R. E., and Schnaar, R. L. (1996) Proc. Natl. Acad. Sci. U.S.A. 93, 814-818). Two cell adhesion systems, COS-1 monkey kidney fibroblasts transiently transfected to express MAG and Chinese hamster ovary (CHO) cells stably transfected to express MAG, were used to probe the structural specificity of MAG-ganglioside binding. Both cell types bound to the same gangliosides: GQ1b alpha (IV3NeuAc,III6NeuAc,II3(NeuAc)2Gg4Cer) > GT1b = GD1a > GM3 > GM1, GD1b, and GQ1b (the latter do not support adhesion). Binding was enhanced by pretreatment of MAG-expressing cells with neuraminidase. MAG-expressing Chinese hamster ovary cells bound directly to gangliosides resolved on thin layer chromatograms, allowing detection of MAG binding species in a mixture. The simplest ganglioside ligand for MAG was GM3 bearing N-acetylneuraminic acid, whereas GM3 bearing N-glycolylneuraminic acid did not support adhesion. Chemical modifications of N-acetylneuraminic acid residues (on GD1a) abrogated MAG binding. Mild periodate oxidation of sialic acids to their corresponding seven-carbon (or eight-carbon) sialic acid aldehydes abolished MAG binding, as did further conversion to the corresponding primary alcohols. Eliminating the anionic charge by ethyl esterification, amidation, or reduction also abolished MAG-mediated cell adhesion. These data demonstrate that MAG-ganglioside binding is highly specific and defines key carbohydrate structural determinants for MAG-mediated cell adhesion to gangliosides.
Animals↗
Chromosomal location of the mouse gene that encodes the myelin-associated glycoproteins.
The two myelin-associated glycoprotein (MAG) species, designated large MAG (L-MAG) and small MAG (S-MAG), are believed to be generated by differential splicing from a single RNA transcript. We have now defined the genetic locus encoding the two MAG proteins in the mouse. Analysis of a panel of interspecies somatic cell hybrids indicated that all MAG coding sequences reside on chromosome 7. Following the inheritance of a restriction fragment length polymorphism associated with MAG coding sequences allowed the locus to be positioned 0.5 centimorgans from the locus Abpa (androgen binding protein alpha) on proximal chromosome 7. These data strongly support the hypothesis that a single gene encodes the two MAG proteins, and we propose the name Mag for this locus. This localization places Mag in close proximity to the neurological mutant locus qv (quivering) and raises the possibility of a functional relationship or identity between Mag and qv. However, an analysis of the MAG gene, its RNA transcripts, and its protein products revealed no abnormalities in homozygous qv mutant mice, suggesting that this chromosomal linkage is not etiologically significant.
Animals↗
Myelin associated glycoproteins confer heterophilic adhesion properties to an immortalized optic nerve derived cell line.
We have transfected an immortalized optic nerve-derived cell line with the cDNA's encoding the two isoforms of MAG. Our aim was to assess whether expression of L-MAG (72 KDa) and S-MAG (67 KDa) in these cells confer adhesion properties when a suspension of single cells is allowed to aggregate. The selected cell lines expressed MAG mRNAs and proteins of the appropriate molecular size, and the proteins were targeted correctly to the plasma membrane. Both L-MAG and S-MAG-expressing transfectants exhibited enhanced self-adhesive properties, aggregating with faster kinetics and forming larger aggregates than MAG-negative control cells. The interaction appears to be mostly heterophilic since MAG+ and MAG- cells which were labeled with a fluorescent probe bound equally well to pre-aggregated MAG+ transfectants and their interaction was blocked by monoclonal anti-MAG antibodies. A further finding which supports the role of MAG in adhesion was the observation that MAG was preferentially localized at the junctions between cells, in confluent cultures.
Animals↗
Specificity of human IgM M-proteins that bind to myelin-associated glycoprotein: peptide mapping, deglycosylation, and competitive binding studies.
Ten patients with neuropathy and IgM M-proteins that bind to the myelin-associated glycoprotein (MAG) were studied to determine whether the M-proteins bind to common regions of MAG and whether the reactive determinants contain carbohydrate residues. The M-protein of one patient was biotinylated, and binding to human MAG was quantitated by enzyme-linked immunosorbent assay (ELISA) by using avidin-biotin-peroxidase complexes. Serum from the same patient and nine others, but not from controls, competed with the biotinylated M-protein for binding to human MAG. Bovine MAG was digested with staph protease or cleaved with cyanogen bromide, and the resultant fragments were separated by electrophoresis and were transferred onto nitrocellulose sheets. Serum from all patients immunostained the peptide fragments identically. Bovine MAG was deglycosylated by trifluoromethanesulfonic acid, and binding of the M-proteins to MAG and to deglycosylated MAG was tested by immunoblotting. None of the patient's M-proteins bound to deglycosylated MAG. Deglycosylated MAG was visualized by using a mouse monoclonal antibody, GEN-S3, directed at the polypeptide core of MAG. The effectiveness of deglycosylation was ascertained by electrophoresis and by binding of biotinylated concanavalin A. These data and the observed identical species specificity of the M-proteins suggest that the respective anti-MAG M-proteins all bind to the same region in MAG and that the reactive determinants may contain carbohydrate moieties.
Animals↗
Biosynthesis and expression of the myelin-associated glycoprotein in cultured oligodendrocytes from adult bovine brain.
The biosynthesis and expression of myelin-associated glycoprotein (MAG) were investigated in cultured oligodendrocytes isolated from adult bovine brain. Western blotting revealed two prominent MAG bands that were present in comparable amounts; the larger component electrophoresed above the 97 kD standard but was slightly smaller than the MAG band in purified bovine myelin, and the smaller component electrophoresed below the 97 kD standard. In comparison to other precursors of oligosaccharides, inorganic [35S]sulfate was a relatively specific isotope for labeling MAG relative to other glycoproteins in the cells. Sulfate labeled only the larger of the two MAG components, which contains complex N-linked oligosaccharides, but which appears to be glycosylated to a lesser extent than MAG in vivo. The smaller MAG band in the cells is a form with high-mannose oligosaccharides and was not detected in purified bovine myelin. Both the large and small MAG components were expressed on the oligodendrocyte surface as indicated by their sensitivity to neuraminidase and/or trypsin treatment of live cells. MAG was also released by the oligodendrocytes into the culture medium. The MAG in the medium was slightly smaller than that in the cells, suggesting that it may be released from the cell surface by limited proteolysis. The release of MAG by myelin-forming cells could be relevant to physiological roles that have been postulated for soluble forms of MAG and other adhesion proteins.
Animals↗
Myelin-associated glycoprotein in myelin and expressed by Schwann cells inhibits axonal regeneration and branching.
The mammalian CNS does not regenerate after injury due largely to myelin-specific inhibitors of axonal growth. The PNS, however, does regenerate once myelin is cleared and myelin proteins are down-regulated by Schwann cells. Myelin-associated glycoprotein (MAG), a sialic acid binding protein, is a potent inhibitor of neurite outgrowth when presented to neurons in culture. Here, we present additional evidence that strongly supports the suggestion that MAG contributes to the overall inhibitory properties of myelin. When myelin from MAG-/- mice is used as a substrate, axonal length is 100 and 60% longer for neonatal cerebellar and older DRG neurons, respectively, compared to MAG+/+ myelin. The converse is true for neurites from neonatal DRG neurons, which are twice as long on MAG+/+ relative to MAG-/- myelin, consistent with MAG's dual role of promoting axonal growth from neonatal DRG neurons but inhibiting growth in older DRG and all other postnatal neurons examined. Furthermore, desialylating neurons reverses inhibition by CNS myelin by 45%. Contrary to previous reports, under these conditions PNS myelin is also inhibitory for axonal regeneration. Importantly, results using PNS MAG-/- myelin as a substrate suggest that MAG contributes to this inhibition. Finally, when Schwann cells not expressing MAG and permissive for axonal growth are induced to express MAG by retroviral infection, not only is axonal outgrowth greatly inhibited by these cells but so also is neurite branching. This suggests for the first time that MAG not only affects axonal regeneration but may also play a role in the control of axonal sprouting.
Animals↗
Expression of myelin-associated glycoprotein isoforms after sciatic nerve crush injury in mice.
The large myelin-associated glycoprotein isoform (L-MAG) protein and small myelin-associated glycoprotein isoform (S-MAG) protein were demonstrated after sciatic nerve crush injury in mice by an immunoblotting technique using specific antibodies to the L-MAG protein and the S-MAG protein, respectively. Immunoblots indicated a rapid decrease in expression of both isoform proteins in the crushed sciatic nerves to < 10% of the control side. By 13 d after injury, L-MAG protein expression had quickly recovered to 100% of the control level. Following the increase in L-MAG protein expression, S-MAG protein expression recovered to 100% by 20 d after injury. It has been reported that the developmental maximum expression of L-MAG protein precedes that of S-MAG protein in both central and peripheral nervous system (CNS and PNS). Our previous work demonstrated that L-MAG mRNA was characteristically induced at the time of most active myelination, including remyelination in the CNS. We here have shown the expression of L-MAG protein precedes that of S-MAG protein during active remyelination in the PNS. This suggests that it plays an important role in the early stage of myelin formation.
Animals↗
Gangliosides are neuronal ligands for myelin-associated glycoprotein.
Nerve cells depend on specific interactions with glial cells for proper function. Myelinating glial cells are thought to associate with neuronal axons, in part, via the cell-surface adhesion protein, myelin-associated glycoprotein (MAG). MAG is also thought to be a major inhibitor of neurite outgrowth (axon regeneration) in the adult central nervous system. Primary structure and in vitro function place MAG in an immunoglobulin-related family of sialic acid-binding lactins. We report that a limited set of structurally related gangliosides, known to be expressed on myelinated neurons in vivo, are ligands for MAG. When major brain gangliosides were adsorbed as artificial membranes on plastic microwells, only GT1b and GD1a supported cell adhesion of MAG-transfected COS-1 cells. Furthermore, a quantitatively minor ganglioside expressed on cholinergic neurons, GQ1b alpha (also known as Chol-1 alpha-b), was much more potent than GT1b or GD1a in supporting MAG-mediated cell adhesion. Adhesion to either GT1b or GQ1b alpha was abolished by pretreatment of the adsorbed gangliosides with neuraminidase. On the basis of structure-function studies of 19 test glycosphingolipids, an alpha 2,3-N-acetylneuraminic acid residue on the terminal galactose of a gangliotetraose core is necessary for MAG binding, and additional sialic acid residues linked to the other neutral core saccharides [Gal(II) and GalNAc(III)] contribute significantly to binding affinity. MAG-mediated adhesion to gangliosides was blocked by pretreatment of the MAG-transfected COS-1 cells with anti-MAG monoclonal antibody 513, which is known to inhibit oligodendrocyte-neuron binding. These data are consistent with the conclusion that MAG-mediated cell-cell interactions involve MAG-ganglioside recognition and binding.
Animals↗