STUDIES ON THE EFFECTS OF ALTERED PMP22 EXPRESSION DURING MYELINATIONIN-VITRO

Severe inherited dysmyelinating diseases of the peripheral nervous sys tem, the Charcot-Marie-Tooth type1A disease (CMT1A) and the hereditary neuropathy with liability to pressure palsies (HNPP) are associated w ith a large DNA duplication or deletion of a chromosomal region contai ning the peripheral myelin protein 22 (PMP22) gene. It has been sugges ted that a gene dosage effect involving PMP22 is responsible for the p athological phenotype, We investigated if altered PMP22 expression aff ects the onset of myelin formation and the ultrastructure of myelin. R at Schwann cell cultures were stably infected with recombinant retrovi rus vectors harboring the rat PMP22 cDNA in sense or antisense orienta tion. Schwann cells over- or underexpressing PMP22 were cocultured wit h purified DRG neurons under conditions that promote myelination. We e xamined PMP22 expression and localization in the myelin forming cultur es by RT-PCR, immunohistochemistry and confocal microscopy, and we ana lyzed myelin ultrastructure by electron microscopy. Our results demons trate that abnormal levels of PMP22 expression do not impair the early stages of myelination and membrane compaction and do not interfere wi th the expression of other myelin genes. Our observations further indi cate that PMP22 is involved more in controlling myelin thickness and s tability than in the events determining the initial steps of myelin fo rmation. (C) 1997 Wiley-Liss, Inc.