Distribution of P0 protein and the myelin-associated glycoprotein in peripheral nerves from Trembler mice

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Abstract
The Trembler mouse has a dysymelination of peripheral nerves that includes hypomyelination, failure of myelin compaction, and demyelination/remyelination. We have localized the myelin proteins P0 and myelin associated glycoprotein in Trembler peripheral nerve and correlated their distributions with the ultrastructure of myelin internodes. Immunocytochemically, myelin-associated glycoprotein was localized in Schwann cell periaxonal membranes, Schmidt-Lanterman incisures, paranodal loops, and internal and external mesaxons. P0 staining was located over compact myelin and regions of Schwann cell cytoplasm rich in Golgi membranes. An unusual abundance of small, P0-stained, Golgi-related vesicles was found in some Schwann cells. P0 protein was also detected in multiple spiral wraps of myelin-associated glycoprotein-positive mesaxon membranes. At some sites the periodicity of the myelin membranes was intermediate to that found in mesaxon membranes and compact myelin. The distance between apposing extracellular leaflets was similar to that found in mesaxon membranes, while the cytoplasmic leaflets were fused but twice as thick as normal major dense lines. These intermediate membranes were stained by P0 and myelin-associated glycoprotein antiserum. These studies suggest that altered transport and/or translocation of P0 and myelin-associated glycoprotein results in defective myelin compaction in Trembler peripheral nerve.