Individual neuronal subtypes control initial myelin sheath growth and stabilization
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RESEARCH ARTICLE
Open Access
Individual neuronal subtypes control initial myelin sheath growth and stabilization Heather N. Nelson, Anthony J. Treichel, Erin N. Eggum, Madeline R. Martell, Amanda J. Kaiser, Allie G. Trudel, James R. Gronseth, Samantha T. Maas, Silas Bergen and Jacob H. Hines*
Abstract Background: In the developing central nervous system, pre-myelinating oligodendrocytes sample candidate nerve axons by extending and retracting process extensions. Some contacts stabilize, leading to the initiation of axon wrapping, nascent myelin sheath formation, concentric wrapping and sheath elongation, and sheath stabilization or pruning by oligodendrocytes. Although axonal signals influence the overall process of myelination, the precise oligodendrocyte behaviors that require signaling from axons are not completely understood. In this study, we investigated whether oligodendrocyte behaviors during the early events of myelination are mediated by an oligodendrocyte-intrinsic myelination program or are over-ridden by axonal factors. Methods: To address this, we utilized in vivo time-lapse imaging in embryonic and larval zebrafish spinal cord during the initial hours and days of axon wrapping and myelination. Transgenic reporter lines marked individual axon subtypes or oligodendrocyte membranes. Results: In the larval zebrafish spinal cord, individual axon subtypes supported distinct nascent sheath growth rates and stabilization frequencies. Oligodendrocytes ensheathed individual axon subtypes at different rates during a two-day period after initial axon wrapping. When descending reticulospinal axons were ablated, local spinal axons supported a constant ensheathment rate despite the increased ratio of oligodendrocytes to target axons. Conclusion: We conclude that properties of individual axon subtypes instruct oligodendrocyte behaviors during initial stages of myelination by differentially controlling nascent sheath growth and stabilization. Keywords: Glia, Oligodendrocyte, Myelination, Myelin sheath
Background Ensheathment of nerve axons with myelin is an essential process during vertebrate neural development. Oligodendrocytes are specialized central nervous system (CNS) ensheathing cells that extend multiple membrane processes to sample candidate axons, initiate and perform spiral axon wrapping, then extend along axons to form a mature myelin sheath (reviewed by [1, 2]). Alternatively, oligodendrocytes can retract and prune myelin sheaths [3–5], as well as modify the thickness of individual sheaths in response to external stimuli [6]. These * Correspondence: [email protected] Biology Department, Winona State University, Winona, MN, USA
complex steps take place over the course of days or weeks, and ultimately are responsible for mature myelin sheaths being positioned at the right location, time, and parameters [7–9]. Numerous distinct cell behaviors and specialized mechanisms are deployed during these steps, including dynamic process extension and retraction, cell-type recognition, cell adhesion, and protrusi
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