Pulses of Ca2+ coordinate actin assembly and exocytosis for stepwise cell extension
Pulses of Ca2+ coordinate actin assembly and exocytosis for stepwise cell extension
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DOI：
10.1073/pnas.1700204114
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发表时间：
2017-05
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通讯作者：
Norio Takeshita;Minoas Evangelinos;Lu Zhou;T. Serizawa;Rosa A. Somera-Fajardo;Ling Lu;N. Takaya;G. Ulrich Nienhaus;R. Fischer
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作者：
Norio Takeshita;Minoas Evangelinos;Lu Zhou;T. Serizawa;Rosa A. Somera-Fajardo;Ling Lu;N. Takaya;G. Ulrich Nienhaus;R. Fischer
生物体的昼夜节律控制着许多过程，这些过程以昼夜节律的方式振荡。此外，有许多过程看起来是连续的，但其内在机制却以不同的周期振荡。例如，真核细胞通过脉冲式地延伸其细胞周边而不是通过连续延伸来生长。在这里，我们调查这种振荡增长的分子基础，通过使用独特的尖端生长系统的丝状真菌，肌动蛋白组装，胞吐作用，并同时观察到的增长率。我们提供的证据表明，时间控制肌动蛋白组装和胞吐是协调脉冲Ca 2+流入，导致逐步细胞扩展。这种机制使细胞能够更快地对内部和环境线索做出反应，包括化学和机械刺激。许多真核细胞通过脉冲式地延伸其细胞外围来生长。这一过程的分子机制尚未完全了解。在这里，我们提出了一个全面的逐步细胞延伸模型，利用独特的尖端生长系统的丝状真菌。活细胞成像分析，包括超分辨率显微镜，揭示了真菌构巢曲霉延伸菌丝尖端的振荡方式。F-肌动蛋白和分泌囊泡（SV）积累在菌丝顶端的量振荡与时间的正相关性，而囊泡的数量呈负相关的增长速度。胞内Ca ~（2+）水平与菌丝顶端的F-肌动蛋白和SV含量呈时间正相关。两个Ca 2+通道，MidA和CchA，需要适当的尖端生长和振荡的肌动蛋白聚合，胞吐，和生长速率。这些数据表明一个模型，其中瞬时Ca 2+脉冲引起解聚的F-肌动蛋白在皮层和促进SV融合与质膜，从而延长细胞尖端。随着时间的推移，Ca 2+扩散，F-肌动蛋白和SV再次积累在菌丝顶端。我们的数据提供的证据表明，时间控制肌动蛋白聚合和胞吐是协调脉冲Ca 2+流入，导致逐步细胞扩展。
Significance The day–night rhythm in living organisms controls many processes, which then oscillate in a circadian manner. In addition, there are many processes that appear continuous but the underlying mechanisms oscillate with distinct periods. For example, eukaryotic cells grow by extending their cell periphery in pulses rather than by continuous extension. Here we investigate the molecular basis for such oscillatory growth by using the unique tip growth system of filamentous fungi, where actin assembly, exocytosis, and growth rate were observed simultaneously. We provide evidence that temporally controlled actin assembly and exocytosis are coordinated by pulsed Ca2+ influxes, resulting in stepwise cell extension. This mechanism allows the cells to respond more quickly to both internal and environmental cues, including chemical and mechanical stimuli. Many eukaryotic cells grow by extending their cell periphery in pulses. The molecular mechanisms underlying this process are not yet fully understood. Here we present a comprehensive model of stepwise cell extension by using the unique tip growth system of filamentous fungi. Live-cell imaging analysis, including superresolution microscopy, revealed that the fungus Aspergillus nidulans extends the hyphal tip in an oscillatory manner. The amount of F-actin and secretory vesicles (SV) accumulating at the hyphal tip oscillated with a positive temporal correlation, whereas vesicle amounts were negatively correlated to the growth rate. The intracellular Ca2+ level also pulsed with a positive temporal correlation to the amount of F-actin and SV at the hyphal tip. Two Ca2+ channels, MidA and CchA, were needed for proper tip growth and the oscillations of actin polymerization, exocytosis, and the growth rate. The data indicate a model in which transient Ca2+ pluses cause depolymerization of F-actin at the cortex and promote SV fusion with the plasma membrane, thereby extending the cell tip. Over time, Ca2+ diffuses away and F-actin and SV accumulate again at the hyphal tip. Our data provide evidence that temporally controlled actin polymerization and exocytosis are coordinated by pulsed Ca2+ influx, resulting in stepwise cell extension.