Department of Physiology & Biophysics, University of Washington, Seattle, United States.
Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, United States.
Elife. 2023 Dec 27;12:RP89467. doi: 10.7554/eLife.89467.
During mitosis, kinetochore-attached microtubules form bundles (k-fibers) in which many filaments grow and shorten in near-perfect unison to align and segregate each chromosome. However, individual microtubules grow at intrinsically variable rates, which must be tightly regulated for a k-fiber to behave as a single unit. This exquisite coordination might be achieved biochemically, via selective binding of polymerases and depolymerases, or mechanically, because k-fiber microtubules are coupled through a shared load that influences their growth. Here, we use a novel dual laser trap assay to show that microtubule pairs growing are coordinated by mechanical coupling. Kinetic analyses show that microtubule growth is interrupted by stochastic, force-dependent pauses and indicate persistent heterogeneity in growth speed during non-pauses. A simple model incorporating both force-dependent pausing and persistent growth speed heterogeneity explains the measured coordination of microtubule pairs without any free fit parameters. Our findings illustrate how microtubule growth may be synchronized during mitosis and provide a basis for modeling k-fiber bundles with three or more microtubules, as found in many eukaryotes.
在有丝分裂过程中，动粒附着的微管形成束（k 纤维），其中许多纤维近乎完美地同步生长和缩短，以对齐和分离每个染色体。然而，单个微管的生长速度存在内在的差异，为了使 k 纤维作为一个整体发挥作用，这些差异必须得到严格的调控。这种精细的协调可能是通过生物化学途径实现的，选择性地结合聚合酶和解聚酶，或者是通过机械途径实现的，因为 k 纤维微管通过共享的负载耦合在一起，从而影响它们的生长。在这里，我们使用一种新的双激光捕获测定法表明，生长中的微管对通过机械耦合进行协调。动力学分析表明，微管生长被随机的、依赖力的停顿打断，并表明在非停顿期间生长速度持续存在异质性。一个简单的模型，同时包含依赖力的停顿和持续的生长速度异质性，解释了微管对的测量协调，而不需要任何自由拟合参数。我们的发现说明了微管生长如何在有丝分裂过程中同步进行，并为使用三对或更多微管的 k 纤维束建模提供了基础，这种结构在许多真核生物中都存在。
