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Axons modulate the expression of proteolipid protein in the CNS
S S Scherer1, H H Vogelbacker, J Kamholz
1Department of Neurology, Hospital of the University of Pennsylvania, Philadelphia 19104-0181.
Insights
Oligodendrocytes need axons to maintain proteolipid protein (PLP) and myelin basic protein (MBP) mRNA levels. Axonal integrity is crucial for the high proportion of distally initiated PLP transcripts seen in early myelination.
Area of Science:
- Neuroscience
- Molecular Biology
- Cell Biology
Background:
- Myelin, a crucial component of the central nervous system (CNS), is formed by oligodendrocytes.
- Proteolipid protein (PLP) and myelin basic protein (MBP) are key structural proteins of CNS myelin.
- The regulation of myelin gene expression during development and in response to axonal injury is not fully understood.
Purpose of the Study:
- To investigate the regulation of PLP mRNA expression in the developing rat cerebrum.
- To examine the impact of axonal degeneration on PLP and MBP mRNA levels in the optic nerve.
- To determine the role of axons in maintaining specific PLP transcript initiation patterns.
Main Methods:
- Quantitative analysis of PLP and MBP mRNA expression using techniques like Northern blotting or RT-PCR.
- Induction of Wallerian degeneration in rat optic nerves via enucleation.
- Comparison of mRNA levels and transcript initiation sites in developing, mature, and degenerating tissues.
Main Results:
- PLP mRNA transcripts are initiated from two distinct start site clusters.
- During peak expression in developing cerebrum, distal PLP transcript initiation is more prevalent.
- Axonal degeneration in optic nerves leads to a significant decrease in PLP and MBP mRNA levels and a shift in PLP transcript initiation patterns.
- The proportion of distally initiated PLP transcripts in degenerating nerves resembles that of normal adult nerves.
Conclusions:
- Oligodendrocytes depend on axonal contact to maintain normal steady-state levels of PLP and MBP mRNA.
- Axonal integrity is essential for sustaining the high proportion of distally initiated PLP transcripts characteristic of early myelination.
- These findings highlight the intricate axonal-oligodendrocyte communication necessary for myelin homeostasis and development.
Abstract:
We examined the expression of mRNA encoding proteolipid protein (PLP), the major myelin protein in the CNS, in developing rat cerebrum, and in normal and degenerating optic nerves. PLP transcripts were initiated at two clusters of start sites that were separated by about 30 base pairs. During the peak of PLP mRNA expression in developing cerebrum, a higher proportion of PLP transcripts were initiated from the distal start site, furthest from the open reading frame, than in mature cerebrum. We enucleated one eye of immature rats to cause Wallerian degeneration in the optic nerve. In these degenerating optic nerves, the steady state levels of PLP mRNA fell markedly, and the proportion of distally initiated PLP transcripts declined to the same proportion found in normal adult nerves. Changes in myelin gene expression were not limited to PLP mRNA, as the steady-state levels of myelin basic protein (MBP) mRNA paralleled those of PLP mRNA in the developing cerebrum and in degenerating optic nerves. Thus, oligodendrocytes require axons to maintain their normal levels of PLP and MBP transcripts and the high proportion of distally initiated PLP transcripts that characterize early myelination.