Laboratory of Molecular Neuroscience, German Center for Neurodegenerative Diseases (DZNE), 10117, Berlin, Germany.
Institute of Chemistry and Biochemistry, Freie Universität Berlin, 14195, Berlin, Germany.
Nat Commun. 2023 Oct 23;14(1):6730. doi: 10.1038/s41467-023-42372-6.
Neuronal transmission relies on the regulated secretion of neurotransmitters, which are packed in synaptic vesicles (SVs). Hundreds of SVs accumulate at synaptic boutons. Despite being held together, SVs are highly mobile, so that they can be recruited to the plasma membrane for their rapid release during neuronal activity. However, how such confinement of SVs corroborates with their motility remains unclear. To bridge this gap, we employ ultrafast single-molecule tracking (SMT) in the reconstituted system of native SVs and in living neurons. SVs and synapsin 1, the most highly abundant synaptic protein, form condensates with liquid-like properties. In these condensates, synapsin 1 movement is slowed in both at short (i.e., 60-nm) and long (i.e., several hundred-nm) ranges, suggesting that the SV-synapsin 1 interaction raises the overall packing of the condensate. Furthermore, two-color SMT and super-resolution imaging in living axons demonstrate that synapsin 1 drives the accumulation of SVs in boutons. Even the short intrinsically-disordered fragment of synapsin 1 was sufficient to restore the native SV motility pattern in synapsin triple knock-out animals. Thus, synapsin 1 condensation is sufficient to guarantee reliable confinement and motility of SVs, allowing for the formation of mesoscale domains of SVs at synapses in vivo.
神经元传递依赖于神经递质的调节分泌，这些递质被包装在突触小泡（SVs）中。数百个 SVs 聚集在突触末梢。尽管它们被束缚在一起，但 SVs 具有高度的流动性，因此它们可以在神经元活动期间被招募到质膜进行快速释放。然而，SVs 的这种约束如何与其流动性相一致仍然不清楚。为了弥合这一差距，我们在天然 SVs 的重组系统和活神经元中采用超快单分子跟踪（SMT）。SVs 和突触结合蛋白 1（synapsin 1），这是最丰富的突触蛋白，形成具有液态特性的凝聚物。在这些凝聚物中，synapsin 1 的运动在短（即 60nm）和长（即数百 nm）范围内都减慢，这表明 SV-synapsin 1 相互作用提高了凝聚物的整体包装密度。此外，活轴突中的双色 SMT 和超分辨率成像表明，synapsin 1 驱动 SVs 在末梢中的积累。即使是 synapsin 1 的短的固有无序片段也足以恢复 synapsin 三重敲除动物中 SV 的天然运动模式。因此，synapsin 1 的凝聚足以保证 SVs 的可靠约束和流动性，允许在体内突触形成 SVs 的介观域。
