David Sandeep, Pinter Katherine, Nguyen Keziah-Khue, Lee David S, Lei Zhengchang, Sokolova Yuliya, Sheets Lavinia, Kindt Katie S
Section on Sensory Cell Development and Function, National Institute on Deafness and other Communication Disorders, Bethesda, Maryland, USA.
National Institutes of Health-Brown University Graduate Partnership Program, Bethesda, Maryland, USA.
J Physiol. 2024 Oct 7. doi: 10.1113/JP286263.
Sensory hair cells of the inner ear utilize specialized ribbon synapses to transmit sensory stimuli to the central nervous system. This transmission necessitates rapid and sustained neurotransmitter release, which depends on a large pool of synaptic vesicles at the hair-cell presynapse. While previous work in neurons has shown that kinesin motor proteins traffic synaptic material along microtubules to the presynapse, the mechanisms of this process in hair cells remain unclear. Our study demonstrates that the kinesin motor protein Kif1a, along with an intact microtubule network, is essential for enriching synaptic vesicles at the presynapse in hair cells. Through genetic and pharmacological approaches, we disrupt Kif1a function and impair microtubule networks in hair cells of the zebrafish lateral-line system. These manipulations led to a significant reduction in synaptic-vesicle populations at the presynapse in hair cells. Using electron microscopy, in vivo calcium imaging, and electrophysiology, we show that a diminished supply of synaptic vesicles adversely affects ribbon-synapse function. Kif1aa mutants exhibit dramatic reductions in spontaneous vesicle release and evoked postsynaptic calcium responses. Furthermore, kif1aa mutants exhibit impaired rheotaxis, a behaviour reliant on the ability of hair cells in the lateral line to respond to sustained flow stimuli. Overall, our results demonstrate that Kif1a-mediated microtubule transport is critical to enrich synaptic vesicles at the active zone, a process that is vital for proper ribbon-synapse function in hair cells. KEY POINTS: Kif1a mRNAs are present in zebrafish hair cells. Loss of Kif1a disrupts the enrichment of synaptic vesicles at ribbon synapses. Disruption of microtubules depletes synaptic vesicles at ribbon synapses. Kif1aa mutants have impaired ribbon-synapse and sensory-system function.
内耳的感觉毛细胞利用特殊的带状突触将感觉刺激传递到中枢神经系统。这种传递需要快速且持续的神经递质释放，这依赖于毛细胞突触前的大量突触小泡。虽然之前在神经元中的研究表明驱动蛋白运动蛋白沿着微管将突触物质运输到突触前，但这个过程在毛细胞中的机制仍不清楚。我们的研究表明，驱动蛋白运动蛋白Kif1a与完整的微管网络一起，对于在毛细胞的突触前富集突触小泡至关重要。通过遗传和药理学方法，我们破坏了斑马鱼侧线系统毛细胞中Kif1a的功能并损害了微管网络。这些操作导致毛细胞突触前的突触小泡数量显著减少。利用电子显微镜、体内钙成像和电生理学，我们表明突触小泡供应减少会对带状突触功能产生不利影响。Kif1aa突变体表现出自发小泡释放和诱发的突触后钙反应的显著降低。此外，kif1aa突变体表现出趋流性受损，这种行为依赖于侧线中毛细胞对持续流动刺激做出反应的能力。总体而言，我们的结果表明，Kif1a介导的微管运输对于在活跃区富集突触小泡至关重要，这一过程对于毛细胞中正常的带状突触功能至关重要。要点：Kif1a mRNA存在于斑马鱼毛细胞中。Kif1a的缺失会破坏带状突触处突触小泡的富集。微管的破坏会耗尽带状突触处的突触小泡。Kif1aa突变体的带状突触和感觉系统功能受损。
