Tetrad Graduate Program, University of California, San Francisco, San Francisco, CA 94143, USA; Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, CA 94143, USA.
Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, CA 94143, USA; MCB Graduate Program, University of Washington, Seattle, WA 98195, USA.
Curr Biol. 2017 Jun 5;27(11):1692-1699.e3. doi: 10.1016/j.cub.2017.04.058. Epub 2017 May 25.
The kinetochore links chromosomes to dynamic spindle microtubules and drives both chromosome congression and segregation. To do so, the kinetochore must hold on to depolymerizing and polymerizing microtubules. At metaphase, one sister kinetochore couples to depolymerizing microtubules, pulling its sister along polymerizing microtubules [1, 2]. Distinct kinetochore-microtubule interfaces mediate these behaviors: active interfaces transduce microtubule depolymerization into mechanical work, and passive interfaces generate friction as the kinetochore moves along microtubules [3, 4]. Despite a growing understanding of the molecular components that mediate kinetochore binding [5-7], we do not know how kinetochores physically interact with polymerizing versus depolymerizing microtubule bundles, and whether they use the same mechanisms and regulation to do so. To address this question, we focus on the mechanical role of the essential load-bearing protein Hec1 [8-11] in mammalian cells. Hec1's affinity for microtubules is regulated by Aurora B phosphorylation on its N-terminal tail [12-15], but its role at the interface with polymerizing versus depolymerizing microtubules remains unclear. Here we use laser ablation to trigger cellular pulling on mutant kinetochores and decouple sisters in vivo, and thereby separately probe Hec1's role on polymerizing versus depolymerizing microtubules. We show that Hec1 tail phosphorylation tunes friction along polymerizing microtubules and yet does not compromise the kinetochore's ability to grip depolymerizing microtubules. Together, the data suggest that kinetochore regulation has differential effects on engagement with growing and shrinking microtubules. Through this mechanism, the kinetochore can modulate its grip on microtubules over mitosis and yet retain its ability to couple to microtubules powering chromosome movement.
着丝粒将染色体与动态的纺锤体微管连接，并驱动染色体的向心聚集和分离。为此，着丝粒必须抓住正在解聚和聚合的微管。在中期，一个姐妹着丝粒与正在解聚的微管相连，拉动其姐妹沿着正在聚合的微管移动[1,2]。不同的着丝粒-微管界面介导这些行为：活性界面将微管解聚转化为机械功，而被动界面在着丝粒沿着微管移动时产生摩擦力[3,4]。尽管人们对介导着丝粒结合的分子成分有了越来越多的了解[5-7]，但我们不知道着丝粒如何与聚合和去聚合的微管束物理相互作用，以及它们是否使用相同的机制和调节来实现这一点。为了解决这个问题，我们专注于在哺乳动物细胞中必需的承重蛋白 Hec1 的机械作用[8-11]。Hec1 对微管的亲和力受其 N 端尾部的 Aurora B 磷酸化调节[12-15]，但其在与聚合和去聚合微管的界面上的作用仍不清楚。在这里，我们使用激光消融在活细胞中触发对突变着丝粒的细胞牵拉，并在体内分离姐妹染色体，从而分别探测 Hec1 在聚合和去聚合微管上的作用。我们表明，Hec1 尾部磷酸化调节了沿着聚合微管的摩擦力，但不影响着丝粒抓住去聚合微管的能力。总之，这些数据表明，着丝粒的调节对与生长和收缩微管的结合有不同的影响。通过这种机制，着丝粒可以在整个有丝分裂过程中调节其对微管的抓握，同时保持其与驱动染色体运动的微管耦联的能力。
