The cell biology of CNS myelination

• The leading edge of myelin membrane winds around the axon while spreading laterally.
• Actin filament disassembly promotes axon wrapping by myelin membrane.
• Synthesis of MBP triggers actin filament disassembly and axon wrapping.
• Axon factors might modulate myelination, modulating sheath thickness and length.

Myelination of axons in the central nervous system results from the remarkable ability of oligodendrocytes to wrap multiple axons with highly specialized membrane. Because myelin membrane grows as it ensheaths axons, cytoskeletal rearrangements that enable ensheathment must be coordinated with myelin production. Because the myelin sheaths of a single oligodendrocyte can differ in thickness and length, mechanisms that coordinate axon ensheathment with myelin growth likely operate within individual oligodendrocyte processes. Recent studies have revealed new information about how assembly and disassembly of actin filaments helps drive the leading edge of nascent myelin membrane around and along axons. Concurrently, other investigations have begun to uncover evidence of communication between axons and oligodendrocytes that can regulate myelin formation.