R.D. Berlin Center for Cell Analysis and Modeling and Department of Cell Biology, UConn Health, Farmington, CT 06030.
A.N. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119992, Russia.
Mol Biol Cell. 2021 Mar 1;32(5):435-445. doi: 10.1091/mbc.E20-08-0546. Epub 2021 Jan 13.
Microtubules (MTs) often form a polarized array with minus ends anchored at the centrosome and plus ends extended toward the cell margins. Plus ends display behavior known as dynamic instability-transitions between rapid shortening and slow growth. It is known that dynamic instability is regulated locally to ensure entry of MTs into nascent areas of the cytoplasm, but details of this regulation remain largely unknown. Here, we test an alternative hypothesis for the local regulation of MT behavior. We used microsurgery to isolate a portion of peripheral cytoplasm from MTs growing from the centrosome, creating cytoplasmic areas locally depleted of MTs. We found that in sparsely populated areas MT plus ends persistently grew or paused but never shortened. In contrast, plus ends that entered regions of cytoplasm densely populated with MTs frequently transitioned to shortening. Persistent growth of MTs in sparsely populated areas could not be explained by a local increase in concentration of free tubulin subunits or elevation of Rac1 activity proposed to enhance MT growth at the cell leading edge during locomotion. These observations suggest the existence of a MT density-dependent mechanism regulating MT dynamics that determines dynamic instability of MTs in densely populated areas of the cytoplasm and persistent growth in sparsely populated areas.
微管（MTs）通常形成一个极化的阵列，负端锚定在中心体，正端向细胞边缘延伸。正端表现出一种称为动态不稳定性的行为——快速缩短和缓慢生长之间的转换。已知动态不稳定性受到局部调节，以确保 MT 进入细胞质的新生区域，但这种调节的细节在很大程度上仍不清楚。在这里，我们测试了一种局部调节 MT 行为的替代假设。我们使用显微手术从中心体生长的 MT 中分离出一部分外周细胞质，从而在局部区域耗尽 MT。我们发现，在稀疏的区域，MT 正端持续生长或暂停，但从不缩短。相比之下，进入 MT 密集的细胞质区域的正端经常发生缩短。在稀疏区域 MT 的持续生长不能用局部增加游离微管亚基的浓度或 Rac1 活性的升高来解释，这被认为在运动过程中增强细胞前缘的 MT 生长。这些观察结果表明，存在一种 MT 密度依赖性机制来调节 MT 动力学，从而决定细胞质密集区域中 MT 的动态不稳定性和稀疏区域中 MT 的持续生长。
