Immune lysis of reconstituted myelin basic protein--lipid vesicles and myelin vesicles.

To further our understanding of the functions of the major myelin proteins, myelin basic protein (MBP) and proteolipid protein (PLP), and other myelin proteins, such as 2'3'-cyclic nucleotide 3'-phosphodiesterase (CNP) and myelin-associated glycoprotein (MAG), bovine brain myelin was extracted with Triton X-100, and protein complexes in the detergent-soluble fraction were isolated by coimmunoprecipitation and sucrose density gradient sedimentation. MBP, PLP, and the small isoform of MAG (S-MAG) were coimmunoprecipitated from the detergent-soluble fraction by anti-PLP, anti-MBP or anti-MAG monoclonal antibodies. Additionally, a 30 kDa phosphoserine-containing protein and two phosphotyrosine-containing proteins (M(r) 30 and 42 kDa) were found in the coimmunoprecipitates. The 42 kDa protein is probably p42MAPK, in that MAPK was shown also to be present in the immunoprecipitated complex. CNP, the small PLP isoform DM20, the large MAG isoform L-MAG, MOG, CD44, MEK, p44MAPK, and actin were not present in the immunoprecipitates, although they were present in the detergent-soluble fraction. Lipid analysis revealed that the PLP-MBP-S-MAG coimmunoprecipitated with some phospholipids and sulfatide but not cholesterol or galactosylceramide. However, the complex had a high density, indicating that the lipid/protein ratio is low, and it was retained on a Sepharose CL6B column, indicating that it is not a large membrane fragment. Given that MAG is localized mainly in the periaxonal region of myelin, where it interacts with axonal ligands, the PLP-MBP-S-MAG complex may come from these regions, where it could participate in dynamic functions in the myelin sheath and myelin-axonal interactions.

Myelin proteolipid protein, basic protein, the small isoform of myelin‐associated glycoprotein, and p42MAPK are associated in the Triton X‐100 extract of central nervous system myelin

Arvanitis

Yang

Boggs

2002

Effect of liposomes containing cerebroside and cerebroside sulfate on cytoskeleton of cultured oligodendrocytes

Boggs

Wang

2001

Oligodendrocytes (OLs) and the myelin produced by them are enriched in two glycosphingolipids, galactosylceramide (GalC) and its sulfated form, cerebroside sulfate (CBS). We showed earlier that these two glycolipids in opposed liposomal membranes or in methanol solution can adhere to each other. Here we have examined the potential effect of an interaction between GalC/CBS in apposed membranes of oligodendrocytes (OLs) by incubating cultured OLs with GalC/CBS-containing liposomes and observing the effect on the membrane sheets produced by OLs and on the distribution of OL constituents using fluorescent antibodies and confocal microscopy. The GalC/CBS-containing liposomes caused redistribution or a decrease in the density of anti-GalC and anti-MBP staining but had no effect on the density or distribution of staining by anti-PI(4,5)P(2) that remained uniformly distributed in the membrane sheets. There was no apparent change in the area of the membrane sheets nor in the amount of MBP in OL membranes, as determined by slot blots. In addition, the GalC/CBS-containing liposomes caused depolymerization of microtubules and actin filaments suggesting that the interaction of GSL-containing liposomes with the extracellular surface of the OL caused transmission of a signal across the membrane. Because these two glycolipids can adhere to each other across apposed membranes, the liposomal glycolipids may be interacting with a GalC/CBS-enriched signaling domain in the OL plasma membrane.

Membrane‐associated estrogen receptor and caveolin‐1 are present in central nervous system myelin and oligodendrocyte plasma membranes

Arvanitis

Wang

Bagshaw

et al. 2004

The estrogen receptor (ER) is a member of a superfamily of ligand-regulated transcription factors that were thought to localize primarily to the nucleus; however, a membrane-associated ER that can initiate rapid non-genomic cell-signaling events has been identified recently in various cells. The presence of the ER in myelin has not been reported although the nuclear form has been detected in oligodendrocytes. We have shown that an ER with similarities to ERbeta is present in isolated central nervous system (CNS) myelin, the myelin sheath in spinal cord and brain sections, and the oligodendrocyte plasma membrane using two-dimensional (2D) PAGE, mass spectrometry, peptide mass fingerprinting, Western blotting of 1D and 2D gels, and confocal microscopy. Caveolin-1 was also shown to be present in isolated CNS myelin and oligodendrocyte plasma membranes, where it was partially colocalized with ER. After Triton X-100 extraction of myelin, the ER was present in an insoluble low-density glycosphingolipid-enriched fraction and even more in a higher density fraction also containing caveolin and cytoskeletal elements, suggesting that the membrane form of ER may be associated with caveolin or the radial component of myelin. The discovery of the ER in the oligodendrocyte plasma membrane and within the myelin sheath indicates a potential role for estrogen in myelin maintenance or functions.