Horio T, Hotani H
Nature. 1986;321(6070):605-7. doi: 10.1038/321605a0.
It has previously been shown that two populations of microtubules coexist in a dynamically unstable manner in vitro: those in one population elongate while those in the other shorten and finally disappear. This conclusion was based on changes in the number and length distribution of microtubules after dilution of the microtubule solution. Here, we demonstrate directly that growing and shortening populations coexist in steady-state conditions, by visualization of the dynamic behaviour of individual microtubules in vitro by dark-field microscopy. Real-time video recording reveals that both ends of a microtubule exist in either the growing or the shortening phase and alternate quite frequently between the two phases in a stochastic manner. Moreover, growing and shortening ends can coexist on a single microtubule, one end continuing to grow simultaneously with shortening at the other end. We find no correlation in the phase conversion either among individual microtubules or between the two ends of a single microtubule. The two ends of any given microtubule have remarkably different characteristics; the active end grows faster, alternates in phase more frequently and fluctuates in length to a greater extent than the inactive end. Microtubule-associated proteins (MAPs) suppress the phase conversion and stabilize microtubules in the growing phase.
先前的研究表明，在体外，两种微管群体以动态不稳定的方式共存：一种群体中的微管伸长，而另一种群体中的微管缩短并最终消失。这一结论是基于微管溶液稀释后微管数量和长度分布的变化得出的。在此，我们通过暗视野显微镜观察体外单个微管的动态行为，直接证明了生长和缩短的群体在稳态条件下共存。实时视频记录显示，微管的两端要么处于生长阶段，要么处于缩短阶段，并以随机方式在两个阶段之间频繁交替。此外，生长端和缩短端可以在单个微管上共存，一端继续生长，而另一端同时缩短。我们发现，在单个微管之间或单个微管的两端之间，相转换没有相关性。任何给定微管的两端具有明显不同的特征；活性端生长更快，相交替更频繁，长度波动比非活性端更大。微管相关蛋白（MAPs）抑制相转换并使处于生长阶段的微管稳定。
