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MEBA derepresses the proximal myelin basic protein promoter in oligodendrocytes
C Taveggia1, A Pizzagalli, M L Feltri
1DIBIT and Department of Neurology, San Raffaele Scientific Institute, 20132 Milan, Italy.
Abstract:
The central nervous system expression of myelin basic protein (MBP) is restricted to oligodendrocytes and is developmentally regulated; these regulatory features are transcriptionally mediated. We have previously shown that the proximal 149 nucleotides of the MBP promoter were both necessary and sufficient to activate the transcription of MBP in cultured oligodendrocytes, but not in other cell types. Sequences within the distal portion of this promoter, which contains a nuclear factor 1 (NF1) binding site, repressed activation of the MBP promoter in Cos-7 cells, but not in oligodendrocytes. We now describe a sequence upstream of and partially overlapping the NF1 site that activates the MBP promoter in oligodendrocytes, but not in Cos-7 cells. A protein complex binds to this site, designated MEBA (myelinating glia-enriched DNA binding activity), and is enriched in nuclear extracts prepared from the brain, oligodendrocytes, and Schwann cells. The amount of MEBA parallels MBP expression and myelinogenesis in the developing brain and parallels new MBP expression as purified oligodendrocytes differentiate. Mutational analyses of binding and function distinguish MEBA, an activator, from NF1, a repressor of MBP transcription, and suggest that MEBA consists of at least two proteins. Because the binding sites of MEBA and NF1 overlap, we suggest that MEBA may either compete with or modify NF1 binding, thereby activating the MBP promoter in oligodendrocytes.
Insights
Researchers identified a novel DNA-binding activity, myelinating glia-enriched DNA binding activity (MEBA), that activates myelin basic protein (MBP) transcription in oligodendrocytes. MEBA
Area of Science:
- Neuroscience
- Molecular Biology
- Gene Regulation
Background:
- Myelin basic protein (MBP) expression in the central nervous system is developmentally regulated and specific to oligodendrocytes.
- Transcriptional regulation controls MBP expression, with previous studies identifying promoter regions essential for oligodendrocyte-specific activation.
- A distal promoter region containing a nuclear factor 1 (NF1) binding site was found to repress MBP transcription in non-oligodendroglial cells.
Purpose of the Study:
- To identify and characterize novel regulatory elements and DNA-binding proteins involved in oligodendrocyte-specific MBP gene transcription.
- To elucidate the mechanism by which MEBA interacts with NF1 to modulate MBP promoter activity.
Main Methods:
- Analysis of MBP promoter activity in cultured oligodendrocytes and Cos-7 cells.
- Identification and characterization of a novel DNA-binding activity, MEBA, using nuclear extracts from brain and glial cells.
- Mutational analysis of MEBA and NF1 binding sites to determine their functional roles in MBP transcription.
Main Results:
- A novel sequence upstream of the NF1 site activates the MBP promoter specifically in oligodendrocytes.
- A protein complex, MEBA (myelinating glia-enriched DNA binding activity), binds to this activating sequence and is enriched in glial cells.
- MEBA levels correlate with MBP expression and myelinogenesis during brain development and oligodendrocyte differentiation.
- Mutational studies distinguish MEBA as an activator from NF1 as a repressor, suggesting MEBA may compete with or modify NF1 binding.
Conclusions:
- MEBA is a key activator of MBP transcription in oligodendrocytes, playing a crucial role in myelinogenesis.
- The overlapping binding sites of MEBA and NF1 suggest a regulatory mechanism involving competition or modification of binding to control MBP gene expression.
- MEBA likely comprises at least two proteins, indicating a complex regulatory interaction at the MBP promoter.