Article |
Address correspondence to Nicole Schaeren-Wiemers, Neurobiology, Dept. of Research, University Hospital Basel, Pharmacenter, Klingelbergstr. 50, 4056 Basel, Switzerland. Tel.: (41) 61-267-15-41. Fax: (41) 61-267-16-28. email: Nicole.Schaeren-Wiemers{at}unibas.ch
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key Words: axonglia interaction; myelin proteolipids; glycolipid-enriched microdomains; node of Ranvier
A. Bonnet's present address is Kanzlei DF-MP, Munich, Germany.
Abbreviations used in this paper: Caspr, contactin-associated protein/paranodin; CGT, ceramide galactosyl transferase; CNS, central nervous system; DIG, detergent-insoluble glycolipid-enriched complex; GalC, galactosylceramide; KO, knockout; L-MAG, large myelin-associated glycoprotein isoform; MAG, myelin-associated glycoprotein; MAL, myelin and lymphocyte protein; MBP, myelin basic protein; MOG, myelin oligodendrocyte glycoprotein; NaCh, sodium channel; NF, neurofascin; PLP, proteolipid protein; PNS, peripheral nervous system; WT, wild type.
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The myelin and lymphocyte protein (MAL; VIP17/MVP17) shows unique features that make it a tantalizing candidate for regulating the sorting and/or trafficking of particular membrane components in myelinating cells (Frank, 2000). MAL is a nonglycosylated integral membrane protein highly enriched in CNS and PNS myelin (Schaeren-Wiemers et al., 1995a,b). The proteolipid MAL is also a component of lipid rafts in myelinating cells and is associated with glycosphingolipids. These MALglycosphingolipid interactions are believed to result in the formation of proteinlipid microdomains in myelin (Frank et al., 1998). Furthermore, MAL is enriched in rafts and apical membranes of epithelial cells (Zacchetti et al., 1995; Frank et al., 1998). Functional in vitro analyses suggest that MAL is required for apical protein sorting in epithelia (Cheong et al., 1999; Puertollano et al., 1999; Martin-Belmonte et al., 2000). Transgenic mice with increased MAL gene dosage revealed alterations of both axonglia interaction and apical membrane formation in kidney and stomach (Frank et al., 2000). Together, the available data suggest that MAL is involved in the assembly and targeting of apical transport vesicles and in the stabilization and maintenance of glycosphingolipid-rich membrane domains.
We have tested the function of MAL in vivo by generating mice lacking this protein and found that such animals are viable and have a normal life span. The mice appeared grossly normal, but closer inspection revealed defects in the maintenance of multiple domains of myelinated CNS axons, indicating aberrant protein trafficking and/or sorting in mal-deficient oligodendrocytes.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
MAL deficiency results in paranodal abnormalities
Detailed analysis of longitudinal sections of optic nerves from KO mice revealed a large number of abnormal paranodes, with everted paranodal loops projecting away instead of contacting the axon (Fig. 4). Examination of 94 paranodes from two KO animals (3-mo-old) revealed detached and inversely oriented paranodal loops in the majority of the cases (83 of 94; Fig. 4, B, D, and E), whereas in WT animals (Fig. 4, A and C) everted loops were only observed in 2 of 132 analyzed paranodes (unpublished data). Transverse bands, the hallmark of the paranodal axoglia junction of WT nerves (Fig. 4 C, arrowheads), were less regularly organized in KO mice and consisted of diffuse electron-dense material instead of septa (Fig. 4, D and E; arrowheads). Moreover, septa-like structures were frequently absent under some paranodal loops in KO mice (Fig. 4 D, arrow). In very few KO paranodes, transverse bands were still present and had a normal morphology (unpublished data). These analyses demonstrate that although transverse bands were not completely absent in KO animals, they were disrupted and not discretely organized. In contrast to adult KO, which exhibited paranodal abnormalities in 88% of the sites examined, analysis of optic nerves from 20-d-old KO showed everted paranodal loops in only 50% of the cases (Fig. 4 G), suggesting that the paranodal junctions were formed normally during development and then disassembled.
|
|
|
Normal formation but impaired maintenance of paranodes in mal KO mice
To examine further whether the paranodal abnormalities observed in mal-deficient mice result from the inability of these fibers to establish normal axoglial contacts during development or are the result of later disassembly of the paranodal junction, we compared the distribution of paranodal components between WT and KO mice at different postnatal ages. Immunohistochemical analysis of mice at P16 revealed that in the cerebellum, myelinated fibers expressed proteolipid protein (PLP) as well as MAL (Fig. 7, B and F). In contrast, in the corpus callosum, myelinated fibers expressed PLP (Fig. 7 A, arrows), but do not yet MAL (Fig. 7 E). Immunofluorescence analysis of Caspr showed paranodal clustering in the corpus callosum of P16 WT as well as in KO animals (Fig. 7, I and K; top), suggesting that during development Caspr clustering occurred normally in the KO. In contrast, at this age, myelination and node formation in the cerebellum was more advanced, as indicated by the higher number of NaCh and Caspr clusters (Fig. 7 N). However, in the cerebellum of P16 KO mice, Caspr was already dispersed and the immunofluorescence signal was weaker (Fig. 7 K, bottom) than in age-matched WT mice (Fig. 7 I). Quantification of Caspr clusters showed a reduction in the cerebellum of P16 KO mice, whereas in the corpus callosum no difference between WT and KO could be detected (Fig. 7 N). At P23, beside PLP, MAL was also expressed in the corpus callosum (Fig. 7, C and G, respectively) and cerebellum (Fig. 7, D and H), and a reduced number of Caspr as well as NF155 clusters was observed in both brain regions (Fig. 7 O). At this age, a dispersed Caspr immunofluorescence was also apparent in paranodes of the corpus callosum of KO mice (Fig. 7 M).
|
|
Western blot analysis of DIGs isolated from myelin membranes revealed that NF155 was exclusively recruited into the insoluble fractions and its incorporation was reduced in KO animals (Fig. 8, B and D). Interestingly, contactin/F3, a DIG component of myelin membranes (Kramer et al., 1997), as well as Caspr, showed reduced levels in these insoluble fractions. Because Caspr is only expressed in axons, we tested our myelin membrane preparations for "axonal" plasma membrane contamination. Western blot analysis of myelin membranes compared with plasma membrane fractions showed that pure axonal membrane proteins such as NF186 (localized at the node of Ranvier) were only detected in the plasma membrane preparation (Fig. 8 E). In contrast, NF155 was found almost exclusively in the myelin membrane fractions, comparable to MAG (Fig. 8 E). Interestingly, Caspr was detected in both membrane preparations, suggesting that the DIG-associated part of Caspr may be included in the myelin membrane fraction. Comparable results were obtained for contactin/F3 (unpublished data; Menon et al., 2003). Further characterization of the different neurofascin isoforms showed that NF186 was only present in the soluble fractions in DIG preparations of plasma membrane preparations, whereas NF155 was exclusively found in the insoluble fractions of myelin membranes (Fig. 8 F). Thus, we conclude that NF155, a protein implicated in the formation of the paranodal septate junction (for review see Poliak and Peles, 2003; Salzer, 2003), is associated with lipid rafts, and that its incorporation into myelin membrane may be dependent on MAL. Our data are consistent with and support the idea that NF155 is important for axonglia interactions and stabilization (Schafer et al., 2004).
NF155 is recruited to rafts during myelin maintenance
From our work, we conclude that paranodes are formed normally during development in mal-deficient mice, but become destabilized during myelin maintenance. Our results also demonstrate that NF155 is strongly reduced at the paranodes and to a lesser extent in myelin membranes of KO animals. Thus, MAL may be important for sorting of NF155 to the paranodes in the adult. This is supported by the fact that in the adult, NF155 is solely found in rafts from myelin membranes. Because NF155 is expressed during myelination and paranode formation, we examined whether NF155 is found in rafts during these early stages of axonglia interactions. We examined DIG preparations from P9 myelin membranes isolated from whole WT mouse brains (Fig. 8 G). In agreement with previous reports, MAL was only present in the insoluble fractions, whereas contactin/F3 was mainly found in the insoluble fractions (Kramer et al., 1999). NF155 as well as L-MAG were only detected in the soluble fractions, indicating that during the early phases of myelin formation NF155 and L-MAG are not recruited to rafts. Our results are consistent with the idea that raft-mediated sorting by MAL plays an important role in the trafficking of particular myelin proteins, such as NF155 and MAG, to the paranodes, and for the stabilization of paranodes in the adult.
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
A particularly striking observation in our work was the effect of MAL deficiency on the paranodal and juxtaparanodal localization of Caspr and Kv1.2, respectively. Because MAL is expressed in the brain exclusively by oligodendrocytes, we hypothesize that lack of MAL is causing altered axonglia interactions that in turn lead to the drastic changes of Caspr clustering in the paranodal and of Kv1.2 in juxtaparanodal axonal membranes. NF155 is an excellent candidate to cause these impaired axonglia interactions. This cell adhesion molecule is located at the glial side of the paranodal junction (Tait et al., 2000), is associated with the Casprcontactin complex (Charles et al., 2002; Gollan et al., 2003), and is markedly reduced in the absence of paranodal septa (Bhat et al., 2001; Boyle et al., 2001; Poliak et al., 2001). Our proposal is based on the finding that NF155 is almost absent in paranodal loops and is recruited to rafts, identifying it as a potential candidate for MAL-mediated sorting. However, we cannot rule out the possibility that the reduction of NF155 in paranodal loops is a consequence of altered MAL-mediated trafficking of a yet unknown component. Nevertheless, our hypothesis that rafts containing NF155 may play an important role in stabilization and maintenance of the paranodal integrity is in line with the recently proposed model for lipid raftdependent paranode formation (Schafer et al., 2004).
Many of the molecular alterations at the node of Ranvier of mal KO mice are reminiscent of those observed in cgt, cst, mag/cgt, and cd9 KO mice (Coetzee et al., 1996; Bartsch et al., 1997; Dupree et al., 1998; Honke et al., 2002; Marcus et al., 2002; Ishibashi et al., 2004). However, a major difference is that the outward-facing paranodal loops do not lead to translocation of Kv1.2 from the juxtaparanodes to the paranodes. Also in contrast to those mutant mice, which completely lack paranodal septa, there are some structures reminiscent of septa in mal-deficient mice. The latter difference is consistent with the fact that most paranodal loops in mal-deficient mice remained closely attached to the axon, whereas the other mutant mouse lines displayed larger gaps between oligodendrocytes and axons. Another important difference is that we observed alterations only in the CNS, whereas the adult PNS did not seem to be affected by the lack of MAL. This could be due to compensatory mechanisms of another as yet unknown raft-associated proteolipid protein, which might replace the functional role of MAL, or known basic structural differences between myelinated PNS and CNS nerve fibers (Salzer, 2003).
Because MAL is associated with sulfatides (Frank et al., 1998), and lack of sulfatides leads to similar paranodal malformation as seen in our mutants (Honke et al., 2002), we investigated the lipid composition of myelin and plasma membranes in mal-deficient mice. No major alterations in the amounts of sulfatides, galactosylceramide (GalC), or cholesterol were found (unpublished data). Still, it is intriguing that mal-deficient mice display some pathological alterations that are also seen in mice lacking ceramide galactosyl transferase (CGT), CST, MAG, CGT and MAG, or CD9 (Poliak and Peles, 2003). Thus, these molecules may play overlapping roles in mediating axonglia interactions, either by having a function in the sorting and trafficking of the receptor molecules involved or by having receptor properties themselves. Another important common feature shared by these mutants is that the paranodes form normally and independently of MAL (this paper), MAG (Marcus et al., 2002), or galactolipids (Dupree et al., 1998; Ishibashi et al., 2002), but destabilize over time in their absence. Therefore, MAL, MAG, and the galactolipids are not necessary for the initial interactions between the oligodendrocyte and the axon, but rather contribute to the stabilization of CNS paranodes. Consistent with this idea, we show that during the early phases of myelination, clustering of Caspr and NF155 in the paranodes occurred normally in mal-deficient mice. However, at the time when MAL would have been expressed in myelin membranes, the number of Caspr and NF155 clusters was strongly reduced, and on the ultrastructural level, we observed an increasing number of everted paranodal loops. Thus, distinct molecular mechanisms appear to be responsible for the formation and the maintenance of axonglia interactions at the paranode. Beside NF155, MAG may also play a major role in this maintenance process, possibly by stabilizing myelin membrane interactions directly in the paranodal region, as MAG is expressed at low levels in CNS paranodal loops (Bartsch et al., 1989). Alternatively, MAG may mediate internodal axonglia interactions because it is expressed in the periaxonal myelin membrane (Schachner and Bartsch, 2000). MAL is predominantly located in compact myelin (Schaeren-Wiemers et al., 1995b; Frank et al., 1998), but it was also found in noncompacted compartments such as Schmidt-Lanterman incisures in the PNS where it colocalizes with MAG (Erne et al., 2002). Whether MAL and MAG are colocalized in paranodal membranes in the CNS could not be elucidated yet due to the lack of suitable reagents. Analysis of MAG in myelin membranes as well as CHAPS-insoluble DIGs isolated from KO and WT brain myelin showed a comparable reduction of 40% in the mutant, indicating that within the myelin membrane of the mutant brain, MAG appears to be still surrounded by (or interacting with) a comparable subset of myelin lipids. Thus, MAL may play a functional role in sorting and trafficking of MAG that is not dependent on its raft association in myelin membranes. However, the sorting and trafficking mechanisms for myelin membrane proteins are not yet fully understood. The reduction of the total amounts of MAG could either be due to a less efficient transport to the myelin membranes or to reduced protein synthesis. Analysis of whole-brain homogenates revealed a comparable reduction of MAG as in myelin membranes (unpublished data) excluding accumulation of MAG in the oligodendrocyte endosomal/lysosomal system. Furthermore, quantitative RT-PCR analysis of four 3-mo-old WT and four age-matched KO animals did not show a reduction in S- or L-MAG mRNA expression levels in the brain of mal-deficient mice (unpublished data). Therefore, the remaining protein may undergo rapid or enhanced degradation in the absence of MAL.
GalC and sulfatide account for one third of the myelin lipids and are enriched in lipid rafts. Hence, lack of MAL may impair efficient trafficking of glycolipids such as GalC and sulfatides particularly to the paranodal compartment at the time when the axonglia contacts should be stabilized. According to the model of Schafer et al. (2004), galactolipids may have an important role in stabilization of axonglial contacts by promoting the formation of NF155-containing lipid rafts during myelin maintenance. This conclusion is based on the observation that the absence of GalC or sulfatides results in paranodal disruption and concurrent reduction of NF155-containing lipid rafts (Schafer et al., 2004). From our work, we cannot elucidate whether the GalC and sulfatide levels in the paranode mal KO mice differ from that of WT animals. Less GalC and/or sulfatides might be incorporated into the "paranodal lipid rafts," and therefore impair stabilization. Interestingly, a recent report suggests that GalC levels may directly regulate MAL expression. In the arylsulfatase KO animals, beside an accumulation of sulfatide, there are reduced levels of GalC in myelin membranes accompanied by reduced expression levels of MAL protein and mRNA (Saravanan et al., 2004). In contrast, overexpression of CGT led to an increase in MAL expression and to an enrichment of MAL in myelin membranes (unpublished data). The expression of other myelin proteins such as PLP, MBP, and MAG was not affected, indicating that a tight balance between galactolipids (particularly GalC) and MAL levels exists that may be important for the formation of particular lipid rafts or plasma membrane microdomains.
In conclusion, we demonstrate that the raft-associated myelin protein MAL plays an important role in the maintenance of the myelin sheath and in normal axonglia and gliaglia membrane interactions, suggesting that lipid rafts within particular oligodendrocyte compartments may be critical for the maintenance of the axonmyelin sheath integrity.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Tissue and myelin preparations
Mice were decapitated and tissues were rapidly dissected and either used directly or snap-frozen at 80°C for myelin preparation, or embedded in O.C.T. compound (Miles Laboratory) and frozen on dry ice for immunohistochemistry. For paraffin embedding, tissues were fixed in 4% PFA, dehydrated, and embedded in Paraplast Plus (Sherwood Medical). Tissues for EM were either perfusion fixed (Bartsch et al., 1995) or immersed in a modified Karnovsky solution (Annefeld et al., 1990). For postfixation with osmium tetroxide, dehydration, and Epon embedding, see Bartsch et al. (1995).
Myelin membrane isolation and preparation of CHAPS detergent extracts were performed as described previously (Erne et al., 2002).
Antibodies
Anti-MAL rabbit antiserum was raised against a recombinant GST-coupled polypeptide comprising the 53 NH2-terminal amino acids of MAL (GST-TM1) and was affinity purified. Additional rabbit pAbs were used as follows: anti-L-MAG (Erb et al., 2003), anti-PLP (from Dr. K.-A. Nave, Max-Planck-Institute of Experimental Medicine, Göttingen, Germany), anti-Caspr (from Dr. E. Peles, Weizmann Institute of Science, Rehovot, Israel), anti-NF155 and anti-NF155/186 (from Dr. P. Brophy, University of Edinburgh, Edinburgh, UK), and anti-contactin/F3 (from Dr. J. Trotter, Johannes Gutenberg University, Mainz, Germany). Monoclonal mouse antibodies were as follows: Anti-MBP (130137; Boehringer), anti-MAG (C513; Boehringer), anti-MOG (from Dr. R. Reynolds, Imperial College London, London, UK), anti-NaCh (Sigma-Aldrich), anti-Caspr (from Dr. E. Peles), and anti-Kv1.2 (Upstate Biotechnology). Secondary antibodies for immunohistochemical and Western blot analysis were as follows: Goat antimouse IgG-peroxidase, goat antirabbit IgG-peroxidase (Sigma-Aldrich), ABC Elite antimouse and antirabbit kit (Vector Laboratories), goat antimouse IgG-Cy3, goat-anti-rabbit IgG-Cy2, goat antimouse IgG-Cy5 (Jackson Laboratories), and goat antirabbit IgG-Alexa 488 (Molecular Probes, Inc.).
Immunohistochemistry, fluorescence confocal microscopy, and EM
Cryostat sections of fresh frozen tissues (710 µm) were mounted on gelatin/chromalaun-coated slides, dried at RT, and fixed for 1 h in 10% buffered formalin solution. Permeabilization with 70% ethanol was done overnight at RT (Caspr and Kv1.2 immunohistochemistry). For anti-NaCh stainings, tissue sections were fixed in methanol for 20 min at 20°C. Paraffin sections (5 µm) were dried overnight and processed (Erne et al., 2002). LacZ staining was performed as described previously (Leone et al., 2003).
Double staining for confocal fluorescence microscopy was performed by incubating tissues with primary antibodies overnight at 4°C or for 1 h at RT. Sections analysis: inverted scanning confocal microscope (LSM 510; Carl Zeiss MicroImaging, Inc.). 1-µm optical sections were transferred to a silicon graphics workstation (Silicon Graphics Inc.) for processing with Imaris software (Bitplane AG). Cluster counting for Caspr, NF155/186, Kv1.2, and NaCh was performed by acquiring confocal image stacks with a constant volume of 73 x 73 x 7.5 µm and constant detection sensitivities. Particles were extracted and reconstructed using constant threshold values and voxel resolution in the Imaris surpass program. Particles with sizes lower than 0.7 µm3 were excluded. The number of clusters within a stack were averaged over 610 stacks per animal, section, and area (two animals). Transmission microscopy was performed on a microscope (DMRE, Leica). Ultrastructural analysis of tissues was performed with a transmission electron microscope (Morgani 268D; Philips). Fiber diameter, myelin sheath thickness, and g-ratio of optic nerve fibers were measured in 100 fibers from each genotype with the AnalySIS image analysis system (Soft Imaging System GmbH).
SDS-PAGE and Western blot analysis
Protein samples were separated on 15% polyacrylamide gels (8% for MAG, contactin/F3, caspr, and NF155/186; Erne et al., 2002).
Quantification of Western blot results
To achieve a linear relation between the amount of analyzed myelin protein and the resulting signal intensity, the optimal range of analyzed myelin protein was determined for each antibody used. Within this range, five different amounts (5, 4, 3, 2, and 1 µg) from a WT and a KO myelin protein pool (n = 3) were analyzed in parallel on the same blot. Signal intensities were analyzed with the MultiImage cabinet and camera (Alpha Innotech Corporation), and were quantified with the "Spot Denso" module of the Chemilmager v5.5 software. Signal intensities were plotted against the amount of analyzed myelin protein (or DIGs), and trend lines through the values obtained for WT and KO samples were added. The ratio of the slopes of KO and WT trend lines reflects the amount of the analyzed myelin protein in the KO relative to the WT pool (Fig. 8 D). For statistical analysis, single WT and KO signal intensities from the dilution series were extrapolated to 100% of analyzed myelin or DIGs for each experiment. The mean value of all experiments with SDs and P values (t test) were determined for each experiment.
![]() |
Acknowledgments |
---|
This work was supported by the Swiss National Science Foundation (to N. Schaeren-Wiemers and U. Suter), the Roche Research Foundation (to N. Schaeren-Wiemers), the Swiss Muscle Disease Foundation, the National Center of Competence in Research "Neural Plasticity and Repair", and the Swiss Bundesamt for Science related to the Commission of the European Communities, specific RTD program "Quality of Life and Management of Living Resources," QLK6-CT-2000-00179 (to U. Suter).
Submitted: 15 June 2004
Accepted: 14 July 2004
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Annefeld, M., B. Erne, and Y. Rasser. 1990. Ultrastructural analysis of rat articular cartilage following treatment with dexamethasone and glycosaminoglycan-peptide complex. Clin. Exp. Rheumatol. 8:151157.[Medline]
Arroyo, E.J., and S.S. Scherer. 2000. On the molecular architecture of myelinated fibers. Histochem. Cell Biol. 113:118.[CrossRef][Medline]
Bartsch, S., D. Montag, M. Schachner, and U. Bartsch. 1997. Increased number of unmyelinated axons in optic nerves of adult mice deficient in the myelin-associated glycoprotein (MAG). Brain Res. 762:231234.[CrossRef][Medline]
Bartsch, U., F. Kirchhoff, and M. Schachner. 1989. Immunohistological localization of the adhesion molecules L1, N-CAM, and MAG in the developing and adult optic nerve of mice. J. Comp. Neurol. 284:451462.[Medline]
Bartsch, U., D. Montag, S. Bartsch, and M. Schachner. 1995. Multiply myelinated axons in the optic nerve of mice deficient for the myelin-associated glycoprotein. Glia. 14:115122.[Medline]
Bhat, M.A., J.C. Rios, Y. Lu, G.P. Garcia-Fresco, W. Ching, M. St Martin, J. Li, S. Einheber, M. Chesler, J. Rosenbluth, et al. 2001. Axon-glia interactions and the domain organization of myelinated axons requires neurexin IV/Caspr/Paranodin. Neuron. 30:369383.[CrossRef][Medline]
Boyle, M.E., E.O. Berglund, K.K. Murai, L. Weber, E. Peles, and B. Ranscht. 2001. Contactin orchestrates assembly of the septate-like junctions at the paranode in myelinated peripheral nerve. Neuron. 30:385397.[CrossRef][Medline]
Charles, P., S. Tait, C. Faivre-Sarrailh, G. Barbin, F. Gunn-Moore, N. Denisenko-Nehrbass, A.M. Guennoc, J.A. Girault, P.J. Brophy, and C. Lubetzki. 2002. Neurofascin is a glial receptor for the paranodin/Caspr-contactin axonal complex at the axoglial junction. Curr. Biol. 12:217220.[CrossRef][Medline]
Cheong, K.H., D. Zacchetti, E.E. Schneeberger, and K. Simons. 1999. VIP17/MAL, a lipid raft-associated protein, is involved in apical transport in MDCK cells. Proc. Natl. Acad. Sci. USA. 96:62416248.
Coetzee, T., N. Fujita, J. Dupree, R. Shi, A. Blight, K. Suzuki, and B. Popko. 1996. Myelination in the absence of galactocerebroside and sulfatide: normal structure with abnormal function and regional instability. Cell. 86:209219.[Medline]
Dupree, J.L., T. Coetzee, A. Blight, K. Suzuki, and B. Popko. 1998. Myelin galactolipids are essential for proper node of Ranvier formation in the CNS. J. Neurosci. 18:16421649.
Erb, M., A.J. Steck, K.A. Nave, and N. Schaeren-Wiemers. 2003. Differential expression of L- and S-MAG upon cAMP stimulated differentiation in oligodendroglial cells. J. Neurosci. Res. 71:326337.[CrossRef][Medline]
Erne, B., S. Sansano, M. Frank, and N. Schaeren-Wiemers. 2002. Rafts in adult peripheral nerve myelin contain major structural myelin proteins and myelin and lymphocyte protein (MAL) and CD59 as specific markers. J. Neurochem. 82:550562.[CrossRef][Medline]
Frank, M. 2000. MAL, a proteolipid in glycosphingolipid enriched domains: functional implications in myelin and beyond. Prog. Neurobiol. 60:531544.[CrossRef][Medline]
Frank, M., M.E. van der Haar, N. Schaeren-Wiemers, and M.E. Schwab. 1998. rMAL is a glycosphingolipid-associated protein of myelin and apical membranes of epithelial cells in kidney and stomach. J. Neurosci. 18:49014913.
Frank, M., S. Atanasoski, S. Sancho, J.P. Magyar, T. Ruelicke, M.E. Schwab, and U. Suter. 2000. Progressive segregation of unmyelinated axons in peripheral nerves, myelin alterations in the CNS, and cyst formation in the kidneys of myelin and lymphocyte protein-overexpressing mice. J. Neurochem. 75:19271939.[CrossRef][Medline]
Gollan, L., D. Salomon, J.L. Salzer, and E. Peles. 2003. Caspr regulates the processing of contactin and inhibits its binding to neurofascin. J. Cell Biol. 163:12131218.
Honke, K., Y. Hirahara, J. Dupree, K. Suzuki, B. Popko, K. Fukushima, J. Fukushima, T. Nagasawa, N. Yoshida, Y. Wada, and N. Taniguchi. 2002. Paranodal junction formation and spermatogenesis require sulfoglycolipids. Proc. Natl. Acad. Sci. USA. 99:42274232.
Ishibashi, T., J.L. Dupree, K. Ikenaka, Y. Hirahara, K. Honke, E. Peles, B. Popko, K. Suzuki, H. Nishino, and H. Baba. 2002. A myelin galactolipid, sulfatide, is essential for maintenance of ion channels on myelinated axon but not essential for initial cluster formation. J. Neurosci. 22:65076514.
Ishibashi, T., L. Ding, K. Ikenaka, Y. Inoue, K. Miyado, E. Mekada, and H. Baba. 2004. Tetraspanin protein CD9 is a novel paranodal component regulating paranodal junctional formation. J. Neurosci. 24:96102.
Kim, T., and S.E. Pfeiffer. 1999. Myelin glycosphingolipid/cholesterol-enriched microdomains selectively sequester the non-compact myelin proteins CNP and MOG. J. Neurocytol. 28:281293.[CrossRef][Medline]
Kim, T., K. Fiedler, D.L. Madison, W.H. Krueger, and S.E. Pfeiffer. 1995. Cloning and characterization of MVP17: a developmentally regulated myelin protein in oligodendrocytes. J. Neurosci. Res. 42:413422.[Medline]
Koch, T., T. Brugger, A. Bach, G. Gennarini, and J. Trotter. 1997. Expression of the immunoglobulin superfamily cell adhesion molecule F3 by oligodendrocyte-lineage cells. Glia. 19:199212.[CrossRef][Medline]
Kramer, E.M., T. Koch, A. Niehaus, and J. Trotter. 1997. Oligodendrocytes direct glycosyl phosphatidylinositol-anchored proteins to the myelin sheath in glycosphingolipid-rich complexes. J. Biol. Chem. 272:89378945.
Kramer, E.M., C. Klein, T. Koch, M. Boytinck, and J. Trotter. 1999. Compartmentation of Fyn kinase with glycosylphosphatidylinositol-anchored molecules in oligodendrocytes facilitates kinase activation during myelination. J. Biol. Chem. 274:2904229049.
Leone, D.P., S. Genoud, S. Atanasoski, R. Grausenburger, P. Berger, D. Metzger, W.B. Macklin, P. Chambon, and U. Suter. 2003. Tamoxifen-inducible glia-specific Cre mice for somatic mutagenesis in oligodendrocytes and Schwann cells. Mol. Cell. Neurosci. 22:430440.[CrossRef][Medline]
Magin, T.M., J. McWhir, and D.W. Melton. 1992. A new mouse embryonic stem cell line with good germ line contribution and gene targeting frequency. Nucleic Acids Res. 20:37953796.[Medline]
Magyar, J.P., C. Ebensperger, N. Schaeren-Wiemers, and U. Suter. 1997. Myelin and lymphocyte protein (MAL/MVP17/VIP17) and plasmolipin are members of an extended gene family. Gene. 189:269275.[CrossRef][Medline]
Marcus, J., J.L. Dupree, and B. Popko. 2002. Myelin-associated glycoprotein and myelin galactolipids stabilize developing axoglial interactions. J. Cell Biol. 156:567577.
Martin-Belmonte, F., R. Puertollano, J. Millan, and M.A. Alonso. 2000. The MAL proteolipid is necessary for the overall apical delivery of membrane proteins in the polarized epithelial Madin-Darby canine kidney and fischer rat thyroid cell lines. Mol. Biol. Cell. 11:20332045.
Menon, K., M.N. Rasband, C.M. Taylor, P. Brophy, R. Bansal, and S.E. Pfeiffer. 2003. The myelin-axolemmal complex: biochemical dissection and the role of galactosphingolipids. J. Neurochem. 87:9951009.[CrossRef][Medline]
Poliak, S., and E. Peles. 2003. The local differentiation of myelinated axons at the nodes of Ranvier. Nat. Rev. Neurosci. 4:968980.[Medline]
Poliak, S., L. Gollan, D. Salomon, E.O. Berglund, R. Ohara, B. Ranscht, and E. Peles. 2001. Localization of Caspr2 in myelinated nerves depends on axon-glia interactions and the generation of barriers along the axon. J. Neurosci. 21:75687575.
Puertollano, R., F. Martin-Belmonte, J. Millan, M.C. de Marco, J.P. Albar, L. Kremer, and M.A. Alonso. 1999. The MAL proteolipid is necessary for normal apical transport and accurate sorting of the influenza virus hemagglutinin in Madin-Darby canine kidney cells. J. Cell Biol. 145:141151.
Salzer, J.L. 2003. Polarized domains of myelinated axons. Neuron. 40:297318.[Medline]
Saravanan, V.P.M., N. Schaeren-Wiemers, D. Klein, R. Sandhoff, A. Schwarz, A. Yaghootfam, V. Gieselmann, and S. Franken. 2004. Specific downregulation and mistargetting of the proteolipid protein MAL in a glycolipid storage disorder. Neurobiol. Dis. 16:396406.[CrossRef][Medline]
Schachner, M., and U. Bartsch. 2000. Multiple functions of the myelin-associated glycoprotein MAG (siglec-4a) in formation and maintenance of myelin. Glia. 29:154165.[CrossRef][Medline]
Schaeren-Wiemers, N., C. Schaefer, D.M. Valenzuela, G.D. Yancopoulos, and M.E. Schwab. 1995a. Identification of new oligodendrocyte- and myelin-specific genes by a differential screening approach. J. Neurochem. 65:1022.[Medline]
Schaeren-Wiemers, N., D.M. Valenzuela, M. Frank, and M.E. Schwab. 1995b. Characterization of a rat gene, rMAL, encoding a protein with four hydrophobic domains in central and peripheral myelin. J. Neurosci. 15:57535764.[Abstract]
Schafer, D.P., R. Bansal, K.L. Hedstrom, S.E. Pfeiffer, and M.N. Rasband. 2004. Does paranode formation and maintenance require partitioning of neurofascin 155 into lipid rafts? J. Neurosci. 24:31763185.
Simons, M., E.M. Kramer, C. Thiele, W. Stoffel, and J. Trotter. 2000. Assembly of myelin by association of proteolipid protein with cholesterol- and galactosylceramide-rich membrane domains. J. Cell Biol. 151:143154.
Tait, S., F. Gunn-Moore, J.M. Collinson, J. Huang, C. Lubetzki, L. Pedraza, D.L. Sherman, D.R. Colman, and P.J. Brophy. 2000. An oligodendrocyte cell adhesion molecule at the site of assembly of the paranodal axoglial junction. J. Cell Biol. 150:657666.
Zacchetti, D., J. Peranen, M. Murata, K. Fiedler, and K. Simons. 1995. VIP17/MAL, a proteolipid in apical transport vesicles. FEBS Lett. 377:465469.[CrossRef][Medline]