Serum factors and hydrocortisone influence the synthesis of myelin basic proteins in mouse brain primary cultures.

Mouse brain primary cultures were used to study the influence of serum factors and hydrocortisone on myelin basic protein (MBP) gene expression. Serum factors increased the synthesis of the MBP isoforms in 18-day and older cultures. Synthesis of the 17 and 18.5 kDa MBPs steadily increased from 14 to 26 DIV (days in vitro). Synthesis of the 14 kDa MBP reached a peak at 22 days, after which it fell off rapidly. Addition of serum to the medium also stimulated MBP mRNA expression. However, in the presence of serum, maximal stimulation of MBP mRNA expression occurred at 16-20 days, significantly earlier than maximal stimulation of 17 and 18.5 kDa MBP synthesis by serum. These observations suggest that serum influences both transcriptional and post-transcriptional steps in the expression of the MBP genes in primary cultures. Hydrocortisone increased the synthesis of the 14, 18.5 and 17 kDa MBP isoforms by two- to three-fold. This effect was seen in cultures older than 15 DIV. This effect of hydrocortisone on the synthesis of the MBPs may be responsible for the increase in the steady state levels of MBP in the presence of hydrocortisone. These studies suggest a role for serum factors and hydrocortisone in the transcriptional and post-transcriptional steps of MBP gene expression. They also suggest that this role may be developmentally regulated.