Axonal regulation of myelin protein mRNA levels in actively myelinating Schwann cells.

Upon transection of a peripheral nerve, axons distal to the transection degenerate. As a consequence of this axonal degeneration, myelin-forming Schwann cells cease biosynthesis of new myelin membrane, contribute to phagocytosis of previously formed myelin, and markedly down-regulate expression of myelin-specific markers. Among the most prominent of these down-regulated markers are the major structural proteins of peripheral myelin, Po and myelin basic protein (MBP). We have used slot blot and in situ hybridization techniques to demonstrate that for actively myelinating Schwann cells, down-regulation of the Po and MBP genes occurs primarily at the level of mRNA expression. Together with other recent data, these findings strongly argue for axonal modulation of Po and MBP gene transcription during active myelination.