Identification of tubulin associated with rat brain myelin

Abstract

During development, axons in both the central and peripheral nervous systems become ensheathed with myelin [ 11. Biochemical manifestations of myelination include rapid accumulation of the myelin membrane proteins [2,3]. These can be divided into three classes; the proteolipid proteins, the basic proteins and the Wolfgram proteins [3-61. The Wolfgram proteins are characterized as the high molecular weight proteins of the myelin fraction [4]. The Wolfgram proteins can be resolved electrophoretically into several polypeptides [2,3,7-91, two of which, WI and W2, have been characterized immunochemically [IO]. The_ myelin membrane is principally derived from oligodendroglia plasma membrane [5,6]. A major protein component which is synthesized by glial and neuronal cells is tubulin [ 1 l131, the subunit protein of microtubules [ 14,151. Tubulin can be associated with membranes [ 16181, and was shown to accumulate in the particulate fraction of brain with maturation [ 131, concomitantly with myelin formation [ 19 1. Together, these observations suggest the possibility that tubulin may be a component of the myelin membrane. By the criteria of SDS-polyacrylamide gel electrophoresis for molecular weight determination, peptide mapping and colchicine binding, we have now demonstrated that tubulin is a constituent of the high molecular weight portion of the myelin fraction.