Abstract
Author SummaryThe nervous system is often thought as two distinct halves: the central nervous system (CNS), which consists of the brain and spinal cord, and the peripheral nervous system (PNS), which includes the nerves that control movement and sense the environment. The cells within these two halves, however, do not commonly mix. To address how cells are segregated within these two compartments of the nervous system, we used live, transgenic zebrafish embryos to watch nerve development. Our study shows that CNS-residing myelinating glia (nonneuronal cells that wrap around nerves to ensure nerve impulse conduction) are restricted from entering the PNS by a cell we call motor exit point (MEP) glia. MEP glia originate from within the CNS, and then migrate into the PNS, divide, and produce cells that ensheath and myelinate spinal motor root axons. Ablation of MEP glia causes CNS glia to migrate inappropriately into the PNS, disrupting the normal boundary that is present between the CNS and PNS. Overall, the identification and characterization of MEP glia identifies an aspect of peripheral nerve composition that may be pertinent in human health and disease.
Highlights
The central nervous system (CNS) and peripheral nervous system (PNS) have been thought of as two, distinct halves of one organ system that are fused into a functional unit by bundles of motor and sensory axons
The nervous system is often thought as two distinct halves: the central nervous system (CNS), which consists of the brain and spinal cord, and the peripheral nervous system (PNS), which includes the nerves that control movement and sense the environment
Our study shows that CNS-residing myelinating glia are restricted from entering the PNS by a cell we call motor exit point (MEP) glia
Summary
The CNS and PNS have been thought of as two, distinct halves of one organ system that are fused into a functional unit by bundles of motor and sensory axons. Elegant neural crest ablation studies in chick have demonstrated that even in the absence of neural crest and all of its derivatives, including BCCs, a population of glial cells is still found along spinal motor nerve roots, demonstrating that they originate from a nonneural crest progenitor [16,17,18,19] All of these studies led us to hypothesize that there may be a second glial population associated with spinal motor root axons that is distinct from neural crest-derived BCCs/glia and that it is this population that is responsible for segregating myelinating glia at the MEP
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