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PubMed1988

Treatment of patients with neuropathy and anti-MAG IgM M-proteins.

Five patients with neuropathy and IgM M-proteins that reacted with myelin-associated glycoprotein (MAG) were treated for 10 to 20 months with cytostatic agents. In 2 patients, a decrease in serum M-protein and in anti-MAG IgM levels coincided with a progressive improvement of neuropathy. No clinical improvement and no decrease of anti-MAG IgM were observed in the other patients. The close relationship between the decrease of anti-MAG M-proteins and clinical improvement in these patients supports the pathogenetic role of the M-protein in the neuropathy.

Aged↗
PubMed2003

Rituximab in the treatment of polyneuropathy associated with anti-MAG antibodies.

No causative or curative therapy exists for the polyneuropathy associated with antibodies to myelin-associated glycoprotein (anti-MAG). Rituximab is a mouse-human chimeric antibody that specifically eliminates B-cells and B-cell precursors. Preliminary results suggest a beneficial effect on antibody-dependent autoimmune diseases. Nine patients with an anti-MAG-associated IgM polyneuropathy received rituximab once weekly for 4 weeks. In all patients, the number of B-cells in the peripheral blood declined below levels of detection, and the IgM levels decreased between 35% and 82% (median, 58%). In eight patients, lowering of the anti-MAG antibody titers of more than 52% was observed. Clinical status improved in six patients, remained stable in two, and worsened in one. The motor nerve conduction velocity improved by at least 10% in one ulnar nerve in seven patients and worsened in two. Rituximab was well tolerated and is a promising new drug in the treatment of patients with anti-MAG-associated polyneuropathy.

Aged↗
PubMed1994

Measurement of intracellular magnesium concentration in 3T3 fibroblasts with the fluorescent indicator Mag-indo-1.

Mag-indo-1, a fluorescent probe for measuring intracellular magnesium concentration, was used in 3T3 fibroblasts with microspectrofluorometry. The complex emission fluorescence spectrum emitted by a single living cell was analyzed with a computerized method, making it possible to evaluate the contribution of each species of Mag-indo-1 to the total fluorescence. The dye self-association observed in solutions at high dye concentration was not encountered in cells. The model of equilibria of Mag-indo-1 (monomer form) with protons, magnesium, and protein was then applied to calculate the intracellular magnesium concentration. The spectral analysis evaluated the contribution of each fluorescent species of Mag-indo-1 (a deprotonated, a magnesium-bound, and a protein-bound form) and of the cell autofluorescence to the total cell fluorescence. This method permitted accurate and reproducible measurements of intracellular magnesium concentration. Finally, this method was applied to the measurement of intracellular magnesium concentration in a 3T3 fibroblast population in exponential growth phase.

3T3 Cells↗
PubMed1994

Are intracellular ionic concentrations accessible using fluorescent probes? The example of Mag-indo-1.

The study of the physicochemical properties of Mag-indo-1, a fluorescent probe used for intracellular magnesium measurements, has shown that in a biological environment the deprotonated form of this probe is in simultaneous equilibrium with a protonated form, a protein and a magnesium-bound form. The complex emission fluorescence spectrum emitted by a single living cell was analyzed using a computerized method, allowing the evaluation of the contribution of each species of the Mag-indo-1 to the cellular fluorescence. This approach used to evaluate intracellular Mg2+ concentration has also shown the variability of the important participation of protein-bound Mag-indo-1 to the cellular fluorescence. Thus the widely used ratioing method, unable to take into account this variability, cannot afford a reliable evaluation of [Mg2+]. Whatever the technique used for investigation (microfluorimetry, flow cytometry, etc.) the evaluation of [Mg2+]i using the fluorescent probe Mag-indo-1 requires a method able to quantify, in complex fluorescence, the fluorescence intensity of the forms involved in the equilibrium with Mg2+.

3T3 Cells↗
PubMed2002

A direct method for regiospecific analysis of TAG using alpha-MAG.

An analytical procedure was developed for regiodistribution analysis of TAG using alpha-MAG prepared by an ethyl magnesium bromide deacylation. In the present communication, the deacylation procedure is shown to lead to representative alpha-MAG, allowing the composition of the native TAG in the alpha-position to be determined directly. The composition in the beta-position can then be estimated from the composition of the alpha-MAG and TAG according to the formula 3 x TAG - 2 x alpha-MAG. The estimates are superior to those obtained using the alpha,beta-DAG and Brockerhoff calculations as they come closer to the theoretical value and have smaller SD. The present procedure, first demonstrated on a synthetic TAG, was then successfully applied to the analysis of borage oil, milkfat, and tuna oil.

Acylation↗
PubMed1985

Immunocytochemical localization of MAG, MBP and P0 protein in acute and relapsing demyelinating lesions of Theiler's virus infection.

Acute demyelinating and relapsing demyelinating lesions from spinal cords of mice infected with the WW strain of Theiler's encephalomyelitis virus (TMEV) were studied immunocytochemically with antisera to various myelin constituents. Acute lesions were studied for differences in the distribution of myelin basic protein (MBP) and myelin associated glycoprotein (MAG). Relapsing lesions, characterized by demyelination of areas previously remyelinated by Schwann cells, were studied for differences in the distribution of P0 and MAG. In both instances the earliest lesions were characterized by preferential disappearance of MBP and P0 respectively when compared to MAG. In well-developed lesions, MAG, MBP and P0 were absent in essentially equal proportion. These observations are in agreement with previous findings suggesting a primary loss of myelin rather than a direct attack on oligodendrocytes as the main pathogenetic mechanism of demyelination in this viral model.

Acute Disease↗
PubMed1992

Anti-MAG IgM paraproteins from some patients with polyneuropathy associated with IgM paraproteinemia also react with sulfatide.

Sera from five of 11 patients with neuropathy associated with IgM paraproteinemia (NAIgMPP) and reactivity against myelin-associated glycoprotein (MAG) also had elevated levels of IgM against sulfatide. Although three patients had anti-sulfatide IgM titers of less than or equal to 1:1000, two patients had titers of greater than or equal to 1:50,000. Absorption of patient serum with sulfatide revealed that anti-MAG IgM paraproteins in two patients with high titer anti-sulfatide IgM crossreacted with sulfatide. Our study is the first to show that some anti-MAG IgM paraproteins crossreact with sulfatide, a major acidic glycolipid of myelin. Moreover, some patients with NAIgMPP have polyclonal anti-sulfatide IgM in addition to anti-MAG IgM paraproteins. Therefore, sulfatide may be a target antigen in some patients with NAIgMPP.

Antibodies↗
PubMed2004

Ce-Y14 and MAG-1, components of the exon-exon junction complex, are required for embryogenesis and germline sexual switching in Caenorhabditis elegans.

Y14 is a component of the splicing-dependent exon-exon junction complex (EJC) and is involved in the mRNA quality control system called nonsense-mediated mRNA decay. It has recently been shown that together with another EJC component, Mago, the Drosophila homologue DmY14/Tsunagi is required for proper localization of oskar mRNA during oogenesis, a process critical for posterior formation in Drosophila development. Here we show that the nematode Caenorhabditis elegans Ce-Y14 and MAG-1 (Mago homologue) are required for late embryogenesis and proper germline sexual differentiation. Like in other organisms, Ce-Y14 preferentially binds to spliced mRNA and specifically interacts with MAG-1. Consistent with the evolutionarily conserved interaction between Y14 and Mago homologues, suppression of Ce-Y14 by RNAi resulted in the same phenotypes as those caused by RNAi of mag-1 lethality during late embryogenesis and masculinization of the adult hermaphrodite germline. Our results demonstrate that the evolutionarily conserved interaction between two EJC components, Ce-Y14 and MAG-1, has critical developmental roles in C. elegans.

Animals↗
PubMed2005

Shear stress alters the expression of myelin-associated glycoprotein (MAG) and myelin basic protein (MBP) in Schwann cells.

Schwann cells within a peripheral nerve respond robustly after an axonal injury. Recent results have revealed that Schwann cells undergo concurrent proliferation and apoptosis after a chronic nerve injury that is independent of axonal pathology. Although the exact nature of the stimulus that produces this Schwann cell response remains unknown, we postulated that this response may be triggered directly by mechanical stimuli. Thus, we sought to determine how pure Schwann cells responded to a sustained shear stress in the form of laminar fluid flow by evaluating for proliferation, expression of S-100, myelin-associated glycoprotein (MAG), and myelin basic protein (MBP). Immunohistochemistry demonstrated that the Schwann cells were positive for S-100, MAG, and MBP in greater than 99% of the experimental cells. Stimulated cells also revealed an increased rate of proliferation by as much as 100% (p<.001). The mRNA expression of MAG and MBP was down-regulated by 21% (p<.035) and 18% (p<.015), respectively, in experimental cells from RT-PCR assays. Furthermore, Western blot showed a down-regulation in MAG and MBP protein expression by 29% (p<.035) and 35% (p<.02), respectively. This study provides novel information regarding Schwann cell direct response to this physical stimulus that is not secondary to an axonal injury.

Animals↗
PubMed1984

Myelin associated glycoprotein (MAG) in Wallerian degeneration of the optic nerve.

The content of myelin associated glycoprotein (MAG) was studied in the rabbit optic nerves undergoing Wallerian degeneration after ophthalmectomy . MAG was estimated according to the method described by Matthieu and Quarles (1973). The results of the studies demonstrated only negligible changes in the content of MAG in the course of central Wallerian degeneration. These experiments do not support the assumption that the periaxionally localized MAG of the central myelin is as a rule seriously involved in subcellular mechanisms functioning in early stages of central demyelinating processes.

Animals↗
PubMed2002

A phase I and pharmacokinetic study of MAG-CPT, a water-soluble polymer conjugate of camptothecin.

Polymeric drug conjugates are a new and experimental class of drug delivery systems with pharmacokinetic promises. The antineoplastic drug camptothecin was linked to a water-soluble polymeric backbone (MAG-CPT) and administrated as a 30 min infusion over 3 consecutive days every 4 weeks to patients with malignant solid tumours. The objectives of our study were to determine the maximal tolerated dose, the dose-limiting toxicities, and the plasma and urine pharmacokinetics of MAG-CPT, and to document anti-tumour activity. The starting dose was 17 mg m(-2) day(-1). Sixteen patients received 39 courses at seven dose levels. Maximal tolerated dose was at 68 mg m(-2) day(-1) and dose-limiting toxicities consisted of cumulative bladder toxicity. MAG-CPT and free camptothecin were accumulated during days 1-3 and considerable amounts of MAG-CPT could still be retrieved in plasma and urine after 4-5 weeks. The half-lives of bound and free camptothecin were equal indicating that the kinetics of free camptothecin were release rate dependent. In summary, the pharmacokinetics of camptothecin were dramatically changed, showing controlled prolonged exposure of camptothecin. Haematological toxicity was relatively mild, but serious bladder toxicity was encountered which is typical for camptothecin and was found dose limiting.

Acrylamides↗
PubMed2001

Jule from the fish Xiphophorus is the first complete vertebrate Ty3/Gypsy retrotransposon from the Mag family.

Jule is the second complete long-terminal-repeat (LTR) Ty3/Gypsy retrotransposon identified to date in vertebrates. Jule, first isolated from the poeciliid fish Xiphophorus maculatus, is 4.8 kb in length, is flanked by two 202-bp LTRs, and encodes Gag (structural core protein) and Pol (protease, reverse transcriptase, RNase H, and integrase, in that order) but no envelope. There are three to four copies of Jule per haploid genome in X. maculatus. Two of them are located in a subtelomeric region of the sex chromosomes, where they are associated with the Xmrk receptor tyrosine kinase genes, of which oncogenic versions are responsible for the formation of hereditary melanoma in Xiphophorus. One almost intact copy of Jule was found in the first intron of the X-chromosomal allele of the Xmrk proto-oncogene, and a second, more corrupted copy is present only 56 nt downstream of the polyadenylation signal of the Xmrk oncogene. Jule-related elements were detected by Southern blot hybridization with less than 10 copies per haploid genome in numerous other poeciliids, as well as in more divergent fishes, including the medakafish Oryzias latipes and the tilapia Oreochromis niloticus. Database searches also identified Jule-related sequences in the zebrafish Danio rerio and in both genome project pufferfishes, Fugu rubripes and Tetraodon nigroviridis. Phylogenetic analysis revealed that Jule is the first member of the Mag family of Ty3/Gypsy retrotransposons described to date in vertebrates. This family includes the silkworm Mag and sea urchin SURL retrotransposons, as well as sequences from the nematode Caenorhabditis elegans. Additional related elements were identified in the genomes of the malaria mosquito Anopheles gambiae and the nematode Ascaris lumbricoides. Phylogeny of Mag-related elements suggested that the Mag family of retrotransposons is polyphyletic and is constituted of several ancient lineages that diverged before their host genomes more than 600 MYA.

Amino Acid Motifs↗
PubMed2005

Contradictory supranormal function in hydronephrotic kidneys: fact or artifact on pediatric MAG-3 renal scans?

OBJECTIVES: Contradictory supranormal renal function (SRF) in unilateral hydronephrosis is a debatable subject resulting from the methodology of nuclear renography or the characteristics of the patient. In this study, we aimed to investigate the frequency and comparison of SRF with MAG-3 scans by 8 different technical analyses in pediatric hydronephrosis. METHODS: We reviewed Tc-99m MAG-3 scans in 82 children with unilateral hydronephrosis (52 male, 30 female, mean age: 47.7 +/- 64.5 months). Of 82, 34 also had Tc-99m DMSA scans. Data were reprocessed with 4 different regions of background activity (subrenal, perirenal C-type, perirenal ring, and lateral) at 2 different time intervals (1-2 and 2-3 minute), and 8 different estimates of MAG-3 differential renal function (DRF) were obtained in 67 patients. SRF was defined as DRF greater than 55% in the hydronephrotic kidney. RESULTS: The routine processing protocol showed only 3 renal units with SRF, and all were on the right side (3.6%). After reprocessing, a total of 10 dilated kidneys had SRF in 1 or more of DRF estimates (5.2% of all estimations). These cases were significantly younger (8.1 +/- 6.7 vs. 42.5 +/- 52.5, P < 0.05) and had a larger renal area ratio (1.25 +/- .24 vs. 1.07 +/- .21, P < 0.05). There was no SRF with DMSA. In comparison between MAG-3 and DMSA DRF in 20 children who underwent both tests within 3 months, the best correlation was obtained when C-type correction was used for both agents at 2 time intervals (r: .86 and .84 for early and late time intervals, P < 0.00001, respectively). CONCLUSIONS: SRF in unilateral hydronephrosis is, at least, in part, technical in origin in this particular pediatric patient population with tubular immaturity (ie, physiological high background activity) and asymmetric kidney size.

Adolescent↗
PubMedDate not supplied

Immunocytochemical study of P0 glycoprotein, P1 and P2 basic proteins, and myelin-associated glycoprotein (MAG) in lesions of idiopathic polyneuritis.

To investigate the mechanism of myelin breakdown in idiopathic polyneuritis, paraffin and Epon sections of lesions were immunostained with antisera to four proteins in myelin sheaths. Three of these (P0, P2, and BP) are constituents of compact myelin whereas myelin-associated glycoprotein (MAG) is restricted to membranes near Schwann cell cytoplasm in periaxonal and paranodal regions and in Schmidt-Lanterman clefts. In early lesions, there were focal abnormalities in P2, P0, and BP immunostaining of paranodal and internodal myelin. No single protein was affected selectively and lesions occurred in fibres of all sizes, not just in larger fibres selectively stained by P2 antiserum. Early changes in MAG immunostaining occurred only in regions where myelin immunostaining also was abnormal. More severe, late changes in the distribution of P0, P2, and BP and MAG were consistent with the sequence of myelinated fibre alterations seen in segmental demyelination and Wallerian degeneration. In regenerating fibres, MAG antiserum stained periaxonal regions intensely; thin regenerating myelin sheaths were stained by P0, and BP antisera, but not by P2 antiserum. The results show that myelin sheath changes are identified more easily in immunostained sections than in conventional histological preparations. Our data also suggest that in idiopathic neuritis, myelin sheaths are the primary target and that the breakdown of myelin and its proteins is not secondary to Schwann cell damage.

Adult↗
PubMed1996

Chromatin structure and transcriptional activity of MAG gene.

Myelin associated glycoprotein (MAG) is an essential component of the periaxonal architecture of the myelin sheath. Because of its potent neurite growth repressive activity, MAG is also likely to play an important role in axonal guidance during the CNS development, and to be responsible for abortive neuronal regeneration in adult CNS. The MAG gene chromatin from approximately -1.6 to +0.6 kb features MNase hypersensitivity that may delineate the gene control region. The proximal upstream region of the gene is organized into an array of five nucleosomes with hypersensitive linkers. The core promoter is located within the first upstream linker that becomes highly hypersensitive in the course of oligodendrocyte differentiation. The adjacent upstream region contains positive and negative enhancers that are likely to streamline oligodendrocyte specific expression of the gene. The TATA-less core promoter contains novel, as yet uncharacterized initiator elements that direct the assembly of transcriptional complexes. The promoter appears to be controlled by both, the addition of activating trans-factors and removal of inhibitory trans-factors as progenitor cells differentiate into mature oligodendrocyte. The developmental activation of the gene is also concomitant with profound DNA demethylation that may provide auxiliary regulatory mechanisms. Hence, the upregulation of the MAG gene in differentiating oligodendrocytes entails chromatin remodeling as well as changes in the assortment of nuclear trans-factors.

Adult↗
PubMed2003

Neurotrophins elevate cAMP to reach a threshold required to overcome inhibition by MAG through extracellular signal-regulated kinase-dependent inhibition of phosphodiesterase.

Inhibitors of regeneration in myelin, such as myelin-associated glycoprotein (MAG), play an important role in preventing regeneration after CNS injury. Elevation of cAMP, either with dibutyryl-cAMP (db-cAMP) or by priming with a variety of neurotrophins, overcomes inhibition by MAG and myelin. However, activation of cAMP is not generally regarded as a signaling pathway for neurotrophins. Here we show that the NGF-like neurotrophins overcome inhibition by MAG by activating tyrosine kinase receptors. We also show that activation of extracellular signal-regulated kinase (Erk) by BDNF is required to overcome inhibition by MAG, and that activated Erk transiently inhibits phosphodiesterase 4 (PDE4), the enzyme that hydrolyzes cAMP. Inhibition of PDE4 then allows cAMP to increase and so initiates the pathway to overcome inhibition. Furthermore, we also show that basal levels of Erk activation and basal cAMP levels contribute to the effects of db-cAMP by pushing the combined levels of cAMP above a threshold required to overcome inhibition. Together, these results not only show how NGF-like neurotrophins can elevate cAMP and overcome inhibition but also point to a novel mechanism of cross talk in neurons from the Erk to the cAMP signaling pathways.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1989

Immunohistological localization of the adhesion molecules L1, N-CAM, and MAG in the developing and adult optic nerve of mice.

The localization of the cell adhesion molecules L1, neural cell adhesion molecule (N-CAM), and myelin-associated glycoprotein (MAG) was studied immunohistologically at the light and electron microscopic levels and immunochemically in the developing and adult mouse optic nerve and retina. The neural adhesion molecule L1 is strongly expressed on the shafts of fasciculating unmyelinated axons at all ages studied from embryonic day 15 through adulthood. Growth cones of retinal ganglion cell axons were weakly L1-positive or L1-negative when contacting glial cells. Unmyelinated axons were not only L1-positive when contacting each other but also when contacting glia, whereas contacts between glial cells were L1-negative at all developmental unmyelinated retinal nerve fiber layer or in the unmyelinated optic nerve head became L1-negative when enwrapped by myelin in the optic nerve proper. At all stages of development N-CAM showed profuse labeling on fasciculating axons, growth cones, and their contact sites with glial cells as well as contacts between glial cells. In contrast to L1, axons remained N-CAM-positive when becoming myelinated. Sometimes, N-CAM was found in compact myelin. However, N-CAM was absent from glial surfaces contacting basement membranes at the interface to meninges, blood vessels, and the vitreous body of the eye. MAG was first detectable intracellularly in oligodendrocytes associated with the endoplasmic reticulum and Golgi apparatus before it became apparent at the cell surface. There it was present on oligodendrocytes prior and during the first stages of ensheathment of axons, both on cell body and processes. After formation of compact myelin MAG remained strongly expressed periaxonally and was only weakly detectable in noncompacted myelin including inner mesaxon and paranodal loops. None of the adhesion molecules was detectable on extracellular matrix, in the meninges, or on endothelial cells. Immunochemical analysis of antigen expression at different developmental stages was in agreement with the immunohistological data. We infer from these observations that L1 is involved in stabilization not only of axon-axon, but also axon-glia contacts, while the more dynamic structure of the growth cone generally expresses less L1. A differential expression of L1 along the course of an axon--being present on its unmyelinated, but absent on its myelinated part--further supports the notion that L1 may be involved in the stabilization of axonal fascicles but not of axon-myelin contacts.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1984

Conversion of myelin-associated glycoprotein (MAG) to a smaller derivative by calcium activated neutral protease (CANP)-like enzyme in myelin and inhibition by E-64 analogue.

Using the immunoblot technique, we found that an incubation of purified human myelin in 10 mM Tris-HCl buffer at pH 7.5 resulted in the conversion of the myelin-associated glycoprotein (MAG) to a smaller derivative (dMAG). Exogenously added 5 mM CaCl2 accelerated the conversion of MAG. In buffer containing more than 100 microM of EGTA, the conversion was inhibited. In addition, the existence of endogenous calcium in purified myelin was confirmed using atomic absorption spectroscopy. The conversion was also inhibited partially by one of the thiol protease inhibitors, E-64 analogue (E-64-a). These observations suggest that the conversion of MAG is mediated by calcium-activated neutral protease (CANP)-like enzyme.

Calpain↗