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Cloning and characterization of MVP17: a developmentally regulated myelin protein in oligodendrocytes
T Kim1, K Fiedler, D L Madison
1Department of Microbiology, School of Medicine, University of Connecticut, Farmington 06030-3205, USA.
Abstract:
The remarkable quantities of myelin membrane produced by oligodendrocytes has led us to examine the mechanisms involved in the sorting and transport of proteins and lipids during myelinogenesis. Noting that it has been proposed that proteins destined for the apical surface of polarized epithelial cells co-cluster with glycolipid-rich microdomains during sorting and transport from the trans-Golgi network (Simons and van Meer: Biochemistry 27:6197-6202, 1988; Simons and Wandinger-Ness: Cell 62:207-210, 1990), we hypothesized that the glycolipid-rich oligodendrocytes may adopt this mechanism for myelinogenesis. Protein-lipid complexes from oligodendrocytes and myelin were isolated utilizing detergent insolubility and two-dimensional gel electrophoresis. A developmentally regulated protein, MVP17 (myelin vesicular protein of 17 kDa), was identified. Microsequencing of the N-terminal peptide revealed a high homology to human T-cell MAL protein (Alonso and Weissman: Proc Natl Acad Sci USA 84:1997-2001, 1987). The corresponding MVP17 cDNA was isolated from an oligodendrocyte cDNA library. The predicted protein sequence showed 88.9% identity with MAL, and the hydrophobicity profile suggested four transmembrane domains. In vitro translation demonstrated a signal at the deduced Mr of approximately 17 kDa. Northern analyses indicated that MVP17 mRNA expression is restricted to brain and kidney and that this expression is up-regulated in oligodendrocytes and brain during the period of active myelination. These data suggest that MVP17 is involved in myelin biogenesis and/or myelin function.
Insights
Oligodendrocytes, the cells that produce myelin, may use glycolipid-rich microdomains to sort and transport myelin proteins, like MVP17, during myelinogenesis. This process is crucial for myelin biogenesis and function.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Oligodendrocytes produce large amounts of myelin membrane.
- Polarized epithelial cells utilize glycolipid-rich microdomains for protein sorting and transport.
- The mechanisms of myelin protein and lipid sorting during myelinogenesis are not fully understood.
Purpose of the Study:
- To investigate the mechanisms of protein and lipid sorting during myelinogenesis in oligodendrocytes.
- To test the hypothesis that oligodendrocytes use glycolipid-rich microdomains for myelin protein transport, similar to polarized epithelial cells.
Main Methods:
- Isolation of protein-lipid complexes from oligodendrocytes and myelin using detergent insolubility.
- Two-dimensional gel electrophoresis for protein analysis.
- Microsequencing, cDNA isolation, in vitro translation, and Northern blot analysis for protein characterization and expression studies.
Main Results:
- A developmentally regulated protein, myelin vesicular protein of 17 kDa (MVP17), was identified.
- MVP17 shows high homology to the human T-cell MAL protein and predicted to have four transmembrane domains.
- MVP17 mRNA expression is upregulated in brain and oligodendrocytes during active myelination and is also found in the kidney.
Conclusions:
- MVP17 is likely involved in the biogenesis and/or function of myelin.
- The data support the hypothesis that oligodendrocytes may employ glycolipid-rich microdomains for myelinogenesis, involving proteins like MVP17.