Myelin Basic Protein mRNA Translocation in Oligodendrocytes Involves Microtubules and is Inhibited by Astrocytes in Vitro

Abstract

Cells are capable of targeting newly synthesized proteins to their appropriate subcellular locations by macromolecular sorting mechanisms. Recent findings indicate that some protein targeting is achieved through differential sorting at the mRNA level (Lawrence and Singer, 1986; see reviews by Hesketh and Pryme, 1991) and that this process can reduce the possibility of incorrect targeting of proteins to the desired subcellular compartments. In the central nervous system (CNS), oligodendrocytes synthesize several proteins that are incorporated into the myelin membrane that ensheathes axons. Myelin basic proteins (MBPs) constitute about 30% of the total myelin proteins. They are highly cationic and interact with virtually any negatively-charged molecule. Thus, targeting the MBP mRNAs to the oligodendrocyte processes prior to translation would help prevent inappropriate interactions of MBP polypeptides with other cellular components. MBP mRNA has been shown to be translocated into the processes of oligodendrocytes both in vivo (Trapp et al., 1987; Verity and Campagnoni, 1988) and in vitro (Amur-Umarjee et al., 1990a). The mechanism by which MBP mRNAs are translocated within the oligodendrocyte and an understanding of factors that regulate the process are yet to be elucidated.