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. 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. 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. We conclude that properties of individual axon subtypes instruct oligodendrocyte behaviors during initial stages of myelination by differentially controlling nascent sheath growth and stabilization.

中文翻译：

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个体神经元亚型控制初始髓鞘生长和稳定

在发育中的中枢神经系统中，前髓鞘化少突胶质细胞通过延伸和收缩过程延伸来采样候选神经轴突。一些接触稳定，导致开始轴突包裹、新生髓鞘形成、同心包裹和鞘伸长，以及鞘稳定或由少突胶质细胞修剪。虽然轴突信号影响髓鞘形成的整个过程，但需要轴突信号的精确少突胶质细胞行为尚未完全了解。在这项研究中，我们调查了髓鞘形成早期事件中的少突胶质细胞行为是由少突胶质细胞内在髓鞘形成程序介导还是被轴突因子覆盖。为了解决这个问题，在轴突包裹和髓鞘形成的最初几小时和几天期间，我们在胚胎和幼虫斑马鱼脊髓中使用了体内延时成像。转基因报告系标记了个体轴突亚型或少突胶质细胞膜。在幼虫斑马鱼脊髓中，单个轴突亚型支持不同的新生鞘生长速率和稳定频率。在初始轴突包裹后的两天期间，少突胶质细胞以不同的速率包裹单个轴突亚型。当下降的网状脊髓轴突被消融时，尽管少突胶质细胞与目标轴突的比例增加，但局部脊髓轴突仍支持恒定的包裹率。