Sorbonne Université, INSERM, Institute of Myology, Centre of Research in Myology, UMRS 974, Paris, France.
Aix Marseille Université, CNRS, INP UMR7051, NeuroCyto, Marseille, France.
Nat Commun. 2019 Dec 20;10(1):5803. doi: 10.1038/s41467-019-13835-6.
Recent super-resolution microscopy studies have unveiled a periodic scaffold of actin rings regularly spaced by spectrins under the plasma membrane of axons. However, ultrastructural details are unknown, limiting a molecular and mechanistic understanding of these enigmatic structures. Here, we combine platinum-replica electron and optical super-resolution microscopy to investigate the cortical cytoskeleton of axons at the ultrastructural level. Immunogold labeling and correlative super-resolution/electron microscopy allow us to unambiguously resolve actin rings as braids made of two long, intertwined actin filaments connected by a dense mesh of aligned spectrins. This molecular arrangement contrasts with the currently assumed model of actin rings made of short, capped actin filaments. Along the proximal axon, we resolved the presence of phospho-myosin light chain and the scaffold connection with microtubules via ankyrin G. We propose that braided rings explain the observed stability of the actin-spectrin scaffold and ultimately participate in preserving the axon integrity.
最近的超分辨率显微镜研究揭示了轴突质膜下肌动蛋白环周期性支架的存在，这些肌动蛋白环由 spectrins 规则间隔排列。然而，其超微结构细节尚不清楚，限制了对这些神秘结构的分子和机制理解。在这里，我们结合铂复制电子和光学超分辨率显微镜来研究轴突皮质细胞骨架的超微结构水平。免疫金标记和相关的超分辨率/电子显微镜使我们能够明确地将肌动蛋白环解析为由两条长的、相互交织的肌动蛋白丝连接而成的辫子，由排列整齐的 spectrins 组成密集的网格。这种分子排列与目前假设的由短的、加帽的肌动蛋白丝组成的肌动蛋白环模型形成对比。在近端轴突中，我们通过 ankyrin G 解析了磷酸化肌球蛋白轻链的存在和支架与微管的连接。我们提出，编织环解释了观察到的肌动蛋白 spectrin 支架的稳定性，并最终参与了轴突完整性的维持。
