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. Microsc. Res. Tech. 41:379–392, 1998. © 1998 Wiley‐Liss, Inc.

NGF Controls Axonal Receptivity to Myelination by Schwann Cells or Oligodendrocytes

“…It is generally thought that characteristics of the axons themselves are critical for defining whether or not they will become myelinated (Colello and Pott, 1997;Raval-Fernandes and Rome, 1998). Two observations have led to the presumption that the axonal signals that control central myelination are likely to be very similar to those that control peripheral myelination.…”

NG2 cells response to axonal alteration in the spinal cord white matter in mice with genetic disruption of neurofilament light subunit expression

“…It is well accepted that the axon calibre controls the onset and rate of myelin formation, i.e., the thickness of the myelin sheath normally increases with axon calibre [ 29 ], although some reports suggested no apparent correlation between myelination and axonal size [ 30 ]. In our results, the G-ratio has decreased significantly at both ages of 2 and 6 months, suggesting a significant decrease in the diameter of axons and/or a significant increase in the thickness of myelin sheath.…”

Mechanisms Underlying the Process of Demyelination in Multiple Sclerosis

“…of different animal species, in particular of mice, rats, and gerbils, are successfully used [54,55]. For in vitro culturing, tissue samples of practically all divisions of the nervous system can be used [56,57]. The tissue for culturing can be obtained both from embryos and at the early stages of postnatal development of animals (on the 1st to 7th postnatal day) [58].…”