The myelin sheaths produced by oligodendrocytes in the central nervous system (CNS) are crucial for the function of neural circuits and neural health. The distribution of these insulating sheaths varies significantly between brain regions 1, neuronal subtypes 2, and individual axons, but the mechanism controlling this pattern remains unclear. Although previous studies have shown that each oligodendrocyte process produces a single myelin sheath, this axonal sheath-like structure is highly branched on the axons of complex circuits and significantly limits myelin formation 6. Here, we found that the axonal insertion rates of the single myelination process differ in zebrafish and mice. This enables a single oligodendrocyte process to pass through the Lanvier axon branching points and nodes before embedding, forming myelin chains connected by thin cytoplasmic processes. In the cerebral cortex, these "auxiliary bridge" structures expand the myelin regions produced by a single oligodendrocyte cell along the highly branched axons of intermediate neurons. Although flexible wrapping reduces the need for oligodendrocytes, the terminal sheaths in the myelin chains are more prone to degeneration in the aged brain, indicating that they are more susceptible to cellular and environmental stress and contribute more to myelin loss. This research was published in Nature under the title "Flexible ensheathment of axons enables myelination of complex CNS networks".
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DOI: 10.1038/s41586-026-10312-1