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Differential expression of two mRNA species indicates a dual function of peripheral myelin protein PMP22 in cell
1Department of Neurology, Heinrich-Heine-University of Düsseldorf, Germany.
Abstract:
Two peripheral myelin protein PMP22 transcripts, CD25 and SR13, have been identified by Northern blot and RNA-polymerase chain reaction (PCR) methods in rat. The CD25 and SR13 mRNA species (each approximately 1.8 kb in size) differ significantly in their 5'-untranslated region (5'-UTR) sequences but encode the same protein. While CD25 mRNA is largely confined to the peripheral nervous system, the SR13 transcript is more ubiquitously expressed in rat tissues. Both transcripts are differentially expressed during postnatal sciatic nerve development. While CD25 expression steadily increases from low levels in neonates up to a maximum at postnatal day 14, SR13 mRNA levels are elevated at birth but decrease throughout adulthood. CD25 and SR13 transcripts are expressed at very low constant levels in developing and adult brain. In degenerating and regenerating segments of injured peripheral nerve changes in CD25 mRNA levels clearly resemble the expression pattern of other myelin genes, whereas expression of SR13 is inversely correlated with the time course of Schwann cell proliferation. In cultured rat meningeal fibroblasts SR13 mRNA expression is strictly growth arrest-specific and independent of forskolin. On the other hand, regulation of CD25 mRNA levels in these cells is more complex with respect to interfering effects of serum and forskolin. In cultured Schwann cells neither CD25 nor SR13 expression is growth arrest-specific. However, both transcript levels are consistently enhanced by forskolin under all conditions of cell growth tested. Expression of CD25 (but not SR13) depends on high Schwann cell density. Our results substantiate the hypothesis that PMP22 serves two biological functions, one related to cell growth (SR13) and another to myelination (CD25).
Insights
Peripheral myelin protein PMP22 has two transcripts, CD25 and SR13, with distinct roles. CD25 is linked to myelination in the peripheral nervous system, while SR13 is associated with cell growth.
Area of Science:
- Neuroscience
- Molecular Biology
- Genetics
Background:
- Peripheral myelin protein 22 (PMP22) is crucial for myelin sheath formation.
- Two distinct PMP22 transcripts, CD25 and SR13, have been identified in rats.
- These transcripts share identical coding sequences but differ in their 5'-untranslated regions.
Purpose of the Study:
- To investigate the differential expression and functional roles of CD25 and SR13 PMP22 transcripts.
- To understand the regulation of these transcripts during nerve development, injury, and in different cell types.
Main Methods:
- Northern blot analysis
- Reverse transcription polymerase chain reaction (RT-PCR)
- Cell culture (Schwann cells, meningeal fibroblasts)
Main Results:
- CD25 mRNA is predominantly expressed in the peripheral nervous system and its levels increase during postnatal sciatic nerve development, correlating with myelination.
- SR13 mRNA is ubiquitously expressed, with higher levels at birth that decrease with age, and is associated with cell growth arrest.
- Both transcripts are regulated by forskolin in cultured Schwann cells, and CD25 expression is dependent on Schwann cell density.
Conclusions:
- PMP22 likely serves dual functions: CD25 is primarily involved in myelination, while SR13 is related to cell growth.
- Differential expression and regulation of these transcripts suggest distinct biological roles for PMP22 isoforms.