Hanisch Anja, Silljé Herman H W, Nigg Erich A
Department of Cell Biology, Max-Planck-Institute for Biochemistry, Martinsried, Germany.
EMBO J. 2006 Nov 29;25(23):5504-15. doi: 10.1038/sj.emboj.7601426. Epub 2006 Nov 9.
Chromosome segregation during mitosis requires chromosomes to undergo bipolar attachment on spindle microtubules (MTs) and subsequent silencing of the spindle checkpoint. Here, we describe the identification and characterisation of a novel spindle and kinetochore (KT)-associated complex that is required for timely anaphase onset. The complex comprises at least two proteins, termed Ska1 (Spindle and KT Associated 1) and Ska2. Ska1 associates with KTs following MT attachment during prometaphase. Ska1 and Ska2 interact with each other and Ska1 is required for Ska2 stability in vivo. Depletion of either Ska1 or Ska2 by small interfering RNA results in the loss of both proteins from the KT. The absence of Ska proteins does not disrupt overall KT structure, but KT fibres show an increased cold-sensitivity. Most strikingly, Ska-depleted cells undergo a prolonged checkpoint-dependent delay in a metaphase-like state. This delay is characterised by the recruitment of Mad2 protein to a few KTs and the occasional loss of individual chromosomes from the metaphase plate. These data suggest that the Ska1/2 complex plays a critical role in the maintenance of the metaphase plate and/or spindle checkpoint silencing.
有丝分裂过程中的染色体分离需要染色体在纺锤体微管（MTs）上进行双极附着，并随后使纺锤体检查点沉默。在此，我们描述了一种新型纺锤体和动粒（KT）相关复合物的鉴定与表征，该复合物是及时进入后期所必需的。该复合物至少包含两种蛋白质，称为Ska1（纺锤体和KT相关蛋白1）和Ska2。在前期微管附着后，Ska1与动粒结合。Ska1和Ska2相互作用，并且Ska1是体内Ska2稳定性所必需的。通过小干扰RNA耗尽Ska1或Ska2会导致这两种蛋白质从动粒上消失。Ska蛋白的缺失不会破坏整体动粒结构，但动粒纤维对冷敏感性增加。最引人注目的是，缺乏Ska的细胞在类似中期的状态下会经历长时间的检查点依赖性延迟。这种延迟的特征是Mad2蛋白募集到少数动粒上，以及偶尔有个别染色体从中期板上丢失。这些数据表明，Ska1/2复合物在维持中期板和/或纺锤体检查点沉默中起关键作用。
