The nanoscale organization of the F-actin cytoskeleton in neurons comprises membrane-associated periodical rings, bundles, and longitudinal fibers. The F-actin rings have been observed predominantly in axons but only sporadically in dendrites, where fluorescence nanoscopy reveals various patterns of F-actin arranged in mixed patches. These complex dendritic F-actin patterns pose a challenge for investigating quantitatively their regulatory mechanisms. We developed here a weakly supervised deep learning segmentation approach of fluorescence nanoscopy images of F-actin in cultured hippocampal neurons. This approach enabled the quantitative assessment of F-actin remodeling, revealing the disappearance of the rings during neuronal activity in dendrites, but not in axons. The dendritic F-actin cytoskeleton of activated neurons remodeled into longitudinal fibers. We show that this activity-dependent remodeling involves Ca2+ and NMDA-dependent mechanisms. This highly dynamic restructuring of dendritic F-actin based submembrane lattice into longitudinal fibers may serve to support activity-dependent membrane remodeling, protein trafficking and neuronal plasticity.

中文翻译：

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神经元活动重塑树突而不是海马神经元轴突中基于F-肌动蛋白的亚膜晶格

神经元中F-肌动蛋白细胞骨架的纳米级组织包括膜相关的周期性环，束和纵向纤维。F-肌动蛋白环主要在轴突中观察到，仅在树突中偶发地观察到，其中荧光纳米显微镜检查显示混合排列中的F-肌动蛋白有多种模式。这些复杂的树突状F-肌动蛋白模式对定量研究其调控机制提出了挑战。我们在这里开发了一种在培养的海马神经元中F-肌动蛋白的荧光纳米图像的弱监督深度学习分割方法。这种方法使F-肌动蛋白重塑的定量评估，揭示了树突中神经元活动过程中环的消失，而在轴突中则没有。活化神经元的树突状F-肌动蛋白细胞骨架重塑成纵向纤维。我们表明这种活动依赖的重塑涉及Ca 2 +和NMDA依赖的机制。这种基于树突状F-肌动蛋白的亚膜晶格高度动态地重组为纵向纤维可能有助于支持依赖于活性的膜重塑，蛋白质运输和神经元可塑性。