Clathrin-mediated endocytosis has characteristic features in neuronal dendrites and presynapses, but how membrane proteins are internalized along the axon shaft remains unclear. We focused on clathrin-coated structures and endocytosis along the axon initial segment (AIS) and their relationship to the periodic actin-spectrin scaffold that lines the axonal plasma membrane. A combination of super-resolution microscopy and platinum-replica electron microscopy on cultured neurons revealed that AIS clathrin-coated pits form within “clearings”, circular areas devoid of actin-spectrin mesh. Actin-spectrin scaffold disorganization increased clathrin-coated pit formation. Cargo uptake and live-cell imaging showed that AIS clathrin-coated pits are particularly stable. Neuronal plasticity-inducing stimulation triggered internalization of the clathrin-coated pits through polymerization of branched actin around them. Thus, spectrin and actin regulate clathrin-coated pit formation and scission to control endocytosis at the AIS.

中文翻译：

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肌动蛋白-血影蛋白亚膜支架限制沿近端轴突的内吞作用


网格蛋白介导的内吞作用在神经元树突和突触前具有特征，但膜蛋白如何沿着轴突轴内化仍不清楚。我们重点研究了沿着轴突起始段（AIS）的网格蛋白包被结构和内吞作用，以及它们与排列在轴突质膜上的周期性肌动蛋白-血影蛋白支架的关系。对培养的神经元进行超分辨率显微镜和铂复制品电子显微镜的结合显示，AIS 网格蛋白包被的凹坑形成在“空地”内，即没有肌动蛋白-血影蛋白网的圆形区域。肌动蛋白-血影蛋白支架的解体增加了网格蛋白包被的小凹的形成。货物摄取和活细胞成像表明 AIS 网格蛋白包被的凹坑特别稳定。神经元可塑性诱导刺激通过网格蛋白包被的小凹周围的分支肌动蛋白的聚合来触发内化。因此，血影蛋白和肌动蛋白调节网格蛋白包被的小凹的形成和分裂，以控制 AIS 的内吞作用。