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Expression and localization of myelin basic protein in oligodendrocytes and transfected fibroblasts
E Barbarese1, C Barry, C H Chou
1Department of Neurology, University of Connecticut Health Center, Farmington 06032.
Abstract:
Myelin basic protein (MBP) is a major structural component of myelin. It is expressed exclusively in myelinating glia (oligodendrocytes in the CNS and Schwann cells in the PNS) and is localized to the cytoplasmic surface of the plasma membrane and myelin membrane produced by these cells. The work described here concerns the mechanism of plasma membrane localization of MBP in myelinating glial cells and whether it involves differentiated functions specific to these cells or general functions of plasma membrane assembly common to all cells. To this end, the subcellular localization of endogenous MBP in mouse oligodendrocytes was compared with that of transiently expressed MBP in monkey fibroblasts (Cos-1 cells) transfected with an MBP expression vector containing cDNA for rat 14K MBP. The steady-state levels of MBP-specific RNA and of MBP polypeptide expressed in the transfected fibroblasts were comparable to the levels expressed in oligodendrocytes in primary culture. MBP localization was analyzed in whole cells by immunofluorescence and in specific intracellular compartments by subcellular fractionation. The results show that MBP expressed in wild-type oligodendrocytes is localized to the plasma membrane. In contrast, MBP expressed in transfected fibroblasts appears dispersed in the cytoplasm and is distributed uniformly among the various subcellular fractions.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Myelin basic protein (MBP) localization to the plasma membrane is specific to myelinating glia. This suggests a specialized mechanism, not a general cell function, is required for proper MBP targeting in the central and peripheral nervous systems.
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Myelin basic protein (MBP) is crucial for myelin structure.
- MBP is exclusively found in myelinating glia (oligodendrocytes and Schwann cells).
- MBP localizes to the cytoplasmic side of plasma and myelin membranes.
Purpose of the Study:
- To investigate the mechanism of MBP plasma membrane localization in myelinating glia.
- To determine if MBP localization relies on cell-specific functions or general membrane assembly processes.
Main Methods:
- Compared endogenous MBP localization in mouse oligodendrocytes with transiently expressed MBP in monkey fibroblasts (Cos-1 cells).
- Analyzed MBP expression levels (RNA and polypeptide) in both cell types.
- Utilized immunofluorescence and subcellular fractionation to assess MBP localization.
Main Results:
- Endogenous MBP in oligodendrocytes was correctly localized to the plasma membrane.
- Transiently expressed MBP in fibroblasts was dispersed throughout the cytoplasm.
- MBP distribution in fibroblasts was uniform across subcellular fractions, unlike in oligodendrocytes.
Conclusions:
- MBP plasma membrane localization in myelinating glia is dependent on cell-specific mechanisms.
- General cellular functions are insufficient for correct MBP targeting.
- This highlights specialized pathways in glial cells for myelin component localization.