Evidence for regulation of myelin protein synthesis by contact between adjacent Schwann cell plasma membranes

The spontaneously immortalized S16 Schwann cell line expresses higher level s of myelin-associated glycoprotein (MAG) and PO glycoprotein and their mes senger RNAs when grown at high density than at low density [Sasagasako et a l: J Neurochem 1996;66:1432-1439]. This up-regulation of myelin protein exp ression at high density is not associated with decreased cellular prolifera tion and may be caused by direct cell-to-cell contact. To investigate the h ypothesis that increased mRNA levels for myelin proteins are caused by cont act between Schwann cells, sparse S16 cell cultures were treated for 48 h w ith plasma-membrane-enriched fractions isolated from dense S16 cells. The t reatment had no effect on the proliferation of the cells, but MAG and PO mR NAs were elevated 2- and 1.3-fold, respectively, in comparison to untreated cells. These effects on levels of myelin protein mRNAs were eliminated by pretreatment of the membrane fraction with heat or trypsin and were not cau sed by plasma membrane fractions from NIH 3T3 cells. These data support the hypothesis that homotypic contact between Schwann cells up-regulates expre ssion of myelin proteins and suggest the possibility of autotypic contact-m ediated regulation of myelinogenesis by adjacent spiraled membranes of indi vidual Schwann cells. Copyright (C) 2000 S. Karger AG, Basel .