SIGNALS THAT INITIATE MYELINATION IN THE DEVELOPING MAMMALIAN NERVOUS-SYSTEM

The myelination of axons by oligodendrocytes in the central nervous sy stem and Schwann cells in the peripheral nervous system is essential f or the establishment of saltatory conduction. Ln the absence or destru ction of the myelin sheath, as seen in demyelinating diseases, impulse conduction is impeded resulting in severe sensory and motor deficits. Axon myelination is the culmination of a sequence of events that begi ns with the differentiation of glial cells and proceeds to the transcr iption and translation of myelin genes, the elaboration of a myelin sh eath, and the recognition and ensheathment of axons. This review exami nes the regulatory mechanisms for each of these steps and compares and contrasts the role of the axon in initiating myelination in the centr al and peripheral nervous system.