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Developmental changes of tau protein and mRNA in cultured rat brain oligodendrocytes
M Gorath1, T Stahnke, T Mronga
1Department of Biology, Molecular Neurobiology, University of Oldenburg, Oldenburg, Germany.
Abstract:
Oligodendrocytes elaborate an extensive network of multibranched processes and flat membranous sheets. Microtubules (MT) participate in the elaboration and stabilization of myelin-forming processes and are essential for cellular sorting processes. Microtubule-associated proteins (MAPs) are involved in the regulation and stabilization of the dynamic MT network. It has been shown previously that oligodendrocytes express the MAP tau, a phosphoprotein most abundant in neurons of the CNS. In this article, we demonstrate for the first time that oligodendrocytes contain all six tau isoforms, and that tau mRNA and protein expression is developmentally regulated. Immunoblot analysis reveals that tau protein is more abundant, and mature isoforms are more prominent at later stages of development. During the first week of culture maturation, a marked decrease in phosphorylation is observable. Using an RT-PCR approach, we can show that oligodendrocytes express small amounts of exon 3 containing isoforms and that during culture maturation, tau mRNA splice products with 3 MT-binding domains (3R) decrease and mRNA with 4 MT-binding domains (4R) increase. In situ hybridization study demonstrates that tau mRNA is present in precursor cells and in mature oligodendrocytes. Tau mRNA is actively transported into the cellular processes, is specifically present in the primary and some of the secondary processes, enriched at the turning and branching points and the growing tips, and often appears as small patches. Hence, localized tau translation at specific sites in the cellular extensions might contribute to the regulation of MT stability during process formation, early axonal contact establishment, and myelination.
Insights
Oligodendrocytes express all six tau isoforms, with expression and splicing changing during development. Localized tau translation may stabilize microtubules for myelin formation.
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Oligodendrocytes form myelin sheaths, requiring stable microtubule networks.
- Microtubule-associated proteins (MAPs), like tau, regulate microtubule dynamics.
- Previous studies indicated tau expression in oligodendrocytes, but isoform diversity and regulation were unclear.
Purpose of the Study:
- To investigate the presence and developmental regulation of all tau isoforms in oligodendrocytes.
- To determine the localization and potential function of tau mRNA and protein in oligodendrocyte processes.
Main Methods:
- Immunoblot analysis to detect tau protein abundance and isoforms.
- RT-PCR to analyze tau mRNA splicing variants (3R and 4R).
- In situ hybridization to localize tau mRNA within cells and processes.
Main Results:
- Oligodendrocytes express all six tau isoforms, with developmental regulation of protein abundance and isoform prominence.
- Tau mRNA splicing shifts from 3-repeat (3R) to 4-repeat (4R) isoforms during culture maturation.
- Tau mRNA is actively transported into cellular processes, enriched at specific sites, suggesting localized translation.
Conclusions:
- Oligodendrocytes express a complete repertoire of tau isoforms, regulated developmentally.
- Tau mRNA localization and potential localized translation in cellular extensions may play a role in microtubule stabilization during oligodendrocyte process formation and myelination.