Chromosome Instability and Dynamics Laboratory, Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal.
Chromosome Res. 2012 Jul;20(5):563-77. doi: 10.1007/s10577-012-9298-8.
Chromosome positioning at the equator of the mitotic spindle emerges out of a relatively entropic background. At this moment, termed metaphase, all kinetochores have typically captured microtubules leading to satisfaction of the spindle-assembly checkpoint, but the cell does not enter anaphase immediately. The waiting time in metaphase is related to the kinetics of securin and cyclin B1 degradation, which trigger sister-chromatid separation and promote anaphase processivity, respectively. Yet, as judged by metaphase duration, such kinetics vary widely between cell types and organisms, with no evident correlation to ploidy or cell size. During metaphase, many animal and plant spindles are also characterized by a conspicuous "flux" activity characterized by continuous poleward translocation of spindle microtubules, which maintain steady-state length and position. Whether spindle microtubule flux plays a specific role during metaphase remains arguable. Based on known experimental parameters, we have performed a comparative analysis amongst different cell types from different organisms and show that spindle length, metaphase duration and flux velocity combine within each system to obey a quasi-universal rule. As so, knowledge of two of these parameters is enough to estimate the third. This trend indicates that metaphase duration is tuned to allow approximately one kinetochore-to-pole round of microtubule flux. We propose that the time cells spend in metaphase evolved as a quality enhancement step that allows for the uniform stabilization/correction of kinetochore-microtubule attachments, thereby promoting mitotic fidelity.
染色体在有丝分裂纺锤体赤道处的定位是从相对混乱的背景中出现的。在这个时刻，称为中期，所有的动粒都已经捕获了微管，这导致了纺锤体组装检查点的满足，但细胞不会立即进入后期。中期的等待时间与 securin 和 cyclin B1 降解的动力学有关，它们分别触发姐妹染色单体分离和促进后期进程的连续性。然而，从中期持续时间来看，这种动力学在不同的细胞类型和生物之间差异很大，与ploidy 或细胞大小没有明显的相关性。在中期，许多动物和植物纺锤体也以明显的“流动”活性为特征，其特征是纺锤体微管连续向两极迁移，从而维持微管的稳态长度和位置。纺锤体微管流动在中期是否发挥特定作用仍然存在争议。基于已知的实验参数，我们对来自不同生物的不同细胞类型进行了比较分析，结果表明，纺锤体长度、中期持续时间和流动速度在每个系统中结合在一起，遵循一种准普遍规律。因此，了解其中两个参数就足以估计第三个参数。这种趋势表明，中期持续时间的调整是为了允许大约一个动粒到极的微管流动周期。我们提出，细胞在中期花费的时间是作为一个质量增强步骤进化而来的，它允许动粒-微管附着的均匀稳定/校正，从而促进有丝分裂保真度。
