“Kiss-shrink-run” unifies mechanisms for synaptic vesicle exocytosis and hyperfast recycling
Chang-Lu Tao, Chong-Li Tian, Yun-Tao Liu, Zhen-Hang Lu, Lei Qi, Xiaowei Li, Chao Li, Xuefeng Shen, Minling Gu, Wen-Lan Huang, Shuo Liu, Lei-Qing Yang, Zhenghan Liao, Xiaomin Ma, Jing Wu, Jianyuan Sun, Peiyi Wang, Pak-Ming Lau, Z. Hong Zhou, Guo‐Qiang Bi
Abstract
Synaptic vesicle (SV) exocytosis underpins neuronal communication, yet its nanoscale dynamics remain poorly understood owing to limitations in visualizing rapid events in situ. Here, we used optogenetics-coupled, time-resolved cryo-electron tomography to capture SV exocytosis in rat hippocampal synapses. Within 4 milliseconds of synaptic activation, SVs transiently "kiss" the plasma membrane, forming a ~4-nanometer lipidic fusion pore flanked by putative soluble NSF-attachment protein receptor (SNARE) complexes and then rapidly "shrink" to approximately half of their original surface area. By 70 milliseconds, most shrunken SVs recycle via a "run-away" pathway, whereas others collapse into the presynaptic membrane. Ultrafast endocytosis retrieves the expanded presynaptic membrane after 100 milliseconds. These findings reveal a "kiss-shrink-run" mechanism of SV exocytosis and hyperfast recycling, reconciling conflicting models and elucidating the efficiency and fidelity of synaptic transmission.