Regulation of myelination: Schwann cell transition from a myelin-maintaining state to a quiescent state after permanent nerve transection

J. F. Poduslo, Peter J Dyck, C. T. Berg

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Abstract

Permanent nerve transection of the adult rat sciatic nerve forces Schwann cells in the distal nerve segment from a myelin-maintaining to a quiescent state. This transition was followed by serial morphometric evaluation of the percentage fascicular area having myelin (myelin percent of area) in transverse sections of the distal nerve segment and revealed a rapid decline from a normal value of 36.6% to 3.2% by 14 days for the sciatic nerve to <1.0% throughout the remaining time course (up to 105 days). No evidence of axonal reentry into the distal nerve segment or new myelin formation was observed at times under 70 days. In some of the distal nerve segments at 70, 90, and 105 days, new myelinated fibers were observed that usually consisted of only a few myelinated fibers at the periphery and in the worst case amounted to 1.6% (myelin percent of area). Radioactive precursor incorporation of [3H]mannose into endoneural slices at 4 and 7 days after transection revealed two species of the major myelin glycoprotein, P0), with M(r) of 28,500 and 27,700. By 14 days after nerve transection, only the 27,700 M(r) species remained. Incorporation of [3H]mannose into the 27,700 M(r) species increased progressively to 35 days after transection and then began to decline at 70 and 105 days. Alterations in the oligosaccharide structure of this down-regulated myelin glycoprotein accounted for the progressive increase in mannose incorporation. Lectin affinity chromatography of pronase-digested P0 glycopeptides on concanavalin A-Sepharose revealed that the 28,500 M(r) species of P0 had the complex-type oligosaccharide as the prodominant oligosaccharide structure (92%). In contrast, the high mannose-type oligosaccharide was the predominate structure for the 27,700 M(r) form, which increased to 70% of the total radioactivity by 35 days after nerve transection. Since the biosynthesis of the complex-type oligosaccharide chains on glycoproteins involves high mannose-type intermediates, the mechanism of down-regulation in the biosynthesis of this major myelin glycoprotein, therefore, results in a biosynthetic switch from the complex-type oligosaccharide structure as an end product to the predominantly high mannose-type oligosaccharide structure as a biosynthetic intermediate. This biosynthetic switch occurs gradually between 7 and 14 days after nerve transection and likely reflects a decreased rate of processing through the Golgi apparatus. It remains to be determined if the high mannose-type oligosaccharide chain on P0 can undergo additional processing steps in this permanent nerve transection model.

Original languageEnglish (US)
Pages (from-to)388-400
Number of pages13
JournalJournal of Neurochemistry
Volume44
Issue number2
StatePublished - 1985

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Schwann Cells
Myelin Sheath
Oligosaccharides
Mannose
Cells
Glycoproteins
Biosynthesis
Sciatic Nerve
Myelin P0 Protein
Switches
Switch Genes
Affinity chromatography
Pronase
Glycopeptides
Fibers
Reentry
Radioactivity
Golgi Apparatus
Processing
Affinity Chromatography

ASJC Scopus subject areas

  • Biochemistry
  • Cellular and Molecular Neuroscience

Cite this

Regulation of myelination : Schwann cell transition from a myelin-maintaining state to a quiescent state after permanent nerve transection. / Poduslo, J. F.; Dyck, Peter J; Berg, C. T.

In: Journal of Neurochemistry, Vol. 44, No. 2, 1985, p. 388-400.

Research output: Contribution to journalArticle

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abstract = "Permanent nerve transection of the adult rat sciatic nerve forces Schwann cells in the distal nerve segment from a myelin-maintaining to a quiescent state. This transition was followed by serial morphometric evaluation of the percentage fascicular area having myelin (myelin percent of area) in transverse sections of the distal nerve segment and revealed a rapid decline from a normal value of 36.6{\%} to 3.2{\%} by 14 days for the sciatic nerve to <1.0{\%} throughout the remaining time course (up to 105 days). No evidence of axonal reentry into the distal nerve segment or new myelin formation was observed at times under 70 days. In some of the distal nerve segments at 70, 90, and 105 days, new myelinated fibers were observed that usually consisted of only a few myelinated fibers at the periphery and in the worst case amounted to 1.6{\%} (myelin percent of area). Radioactive precursor incorporation of [3H]mannose into endoneural slices at 4 and 7 days after transection revealed two species of the major myelin glycoprotein, P0), with M(r) of 28,500 and 27,700. By 14 days after nerve transection, only the 27,700 M(r) species remained. Incorporation of [3H]mannose into the 27,700 M(r) species increased progressively to 35 days after transection and then began to decline at 70 and 105 days. Alterations in the oligosaccharide structure of this down-regulated myelin glycoprotein accounted for the progressive increase in mannose incorporation. Lectin affinity chromatography of pronase-digested P0 glycopeptides on concanavalin A-Sepharose revealed that the 28,500 M(r) species of P0 had the complex-type oligosaccharide as the prodominant oligosaccharide structure (92{\%}). In contrast, the high mannose-type oligosaccharide was the predominate structure for the 27,700 M(r) form, which increased to 70{\%} of the total radioactivity by 35 days after nerve transection. Since the biosynthesis of the complex-type oligosaccharide chains on glycoproteins involves high mannose-type intermediates, the mechanism of down-regulation in the biosynthesis of this major myelin glycoprotein, therefore, results in a biosynthetic switch from the complex-type oligosaccharide structure as an end product to the predominantly high mannose-type oligosaccharide structure as a biosynthetic intermediate. This biosynthetic switch occurs gradually between 7 and 14 days after nerve transection and likely reflects a decreased rate of processing through the Golgi apparatus. It remains to be determined if the high mannose-type oligosaccharide chain on P0 can undergo additional processing steps in this permanent nerve transection model.",
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