Role of axonal components during myelination

Abstract

Myelination is a multistep ordered process whereby Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS), produce and extend membranous processes that envelop axons. Mechanisms that regulate this complex process are not well understood. Advances in deciphering the regulatory components of myelination have been carried out primarily in the PNS and although the mechanisms for triggering and directing myelination are not known, it is well established that myelination does not occur in the absence of axons or axon/neuron-derived factors. This appears to be true both in PNS and CNS. Progress in understanding CNS myelinogenesis has been relatively slow because of the unavailability of a suitable culture system, which, in turn, is partly due to complexity in the cellular organization of the CNS. Though the myelin composition differs between PNS and CNS, the regulation of myelination seems to parallel rather than differ between these two systems. This article reviews the regulatory role of axonal components during myelination. The first half consists of an overview of in vitro and in vivo studies carried out in the nervous system. The second half discusses the use of a cerebellar slice culture system and generation of anti-axolemma monoclonal antibodies to investigate the role of axonal membrane components that participate in myelination. It also describes the characterization of an axonal protein involved in myelination.