Yao Chi-Kuang, Liu Yu-Tzu, Lee I-Chi, Wang You-Tung, Wu Ping-Yen
Institute of Biological Chemistry, Academia Sinica, Nankang, Taipei, Taiwan.
Neuroscience Program in Academia Sinica, Academia Sinica, Nankang, Taipei, Taiwan.
PLoS Biol. 2017 Apr 17;15(4):e2000931. doi: 10.1371/journal.pbio.2000931. eCollection 2017 Apr.
Clathrin-mediated endocytosis (CME) and activity-dependent bulk endocytosis (ADBE) are two predominant forms of synaptic vesicle (SV) endocytosis, elicited by moderate and strong stimuli, respectively. They are tightly coupled with exocytosis for sustained neurotransmission. However, the underlying mechanisms are ill defined. We previously reported that the Flower (Fwe) Ca2+ channel present in SVs is incorporated into the periactive zone upon SV fusion, where it triggers CME, thus coupling exocytosis to CME. Here, we show that Fwe also promotes ADBE. Intriguingly, the effects of Fwe on CME and ADBE depend on the strength of the stimulus. Upon mild stimulation, Fwe controls CME independently of Ca2+ channeling. However, upon strong stimulation, Fwe triggers a Ca2+ influx that initiates ADBE. Moreover, knockout of rodent fwe in cultured rat hippocampal neurons impairs but does not completely abolish CME, similar to the loss of Drosophila fwe at the neuromuscular junction, suggesting that Fwe plays a regulatory role in regulating CME across species. In addition, the function of Fwe in ADBE is conserved at mammalian central synapses. Hence, Fwe exerts different effects in response to different stimulus strengths to control two major modes of endocytosis.
网格蛋白介导的内吞作用（CME）和活性依赖的批量内吞作用（ADBE）是突触小泡（SV）内吞作用的两种主要形式，分别由适度刺激和强烈刺激引发。它们与胞吐作用紧密耦合以维持神经传递。然而，其潜在机制尚不清楚。我们之前报道过，存在于突触小泡中的Flower（Fwe）钙通道在突触小泡融合时会整合到活性区周围，在那里它触发CME，从而将胞吐作用与CME耦合。在这里，我们表明Fwe也促进ADBE。有趣的是，Fwe对CME和ADBE的影响取决于刺激的强度。在轻度刺激下，Fwe独立于钙通道控制CME。然而，在强烈刺激下，Fwe触发钙内流，启动ADBE。此外，在培养的大鼠海马神经元中敲除啮齿动物的fwe会损害但不会完全消除CME，这与果蝇fwe在神经肌肉接头处缺失的情况类似，表明Fwe在跨物种调节CME中起调节作用。此外，Fwe在ADBE中的功能在哺乳动物中枢突触中是保守的。因此，Fwe根据不同的刺激强度发挥不同的作用，以控制两种主要的内吞模式。
