Physiological Laboratory, University of Liverpool, Liverpool, UK.
EMBO J. 2011 Mar 2;30(5):906-19. doi: 10.1038/emboj.2011.15. Epub 2011 Feb 4.
Kinetochore fibres (K-fibres) of the spindle apparatus move chromosomes during mitosis. These fibres are discrete bundles of parallel microtubules (MTs) that are crosslinked by inter-MT 'bridges' that are thought to improve fibre stability during chromosomal movement. The identity of these bridges is unknown. Clathrin is a multimeric protein that has been shown to stabilise K-fibres during early mitosis by a mechanism independent of its role in membrane trafficking. In this study, we show that clathrin at the mitotic spindle is in a transforming acidic colied-coil protein 3 (TACC3)/colonic, hepatic tumour overexpressed gene (ch-TOG)/clathrin complex. The complex is anchored to the spindle by TACC3 and ch-TOG. Ultrastructural analysis of clathrin-depleted K-fibres revealed a selective loss of a population of short inter-MT bridges and a general loss of MTs. A similar loss of short inter-MT bridges was observed in TACC3-depleted K-fibres. Finally, immunogold labelling confirmed that inter-MT bridges in K-fibres contain clathrin. Our results suggest that the TACC3/ch-TOG/clathrin complex is an inter-MT bridge that stabilises K-fibres by physical crosslinking and by reducing rates of MT catastrophe.
纺锤体装置的动粒纤维（K 纤维）在有丝分裂过程中移动染色体。这些纤维是平行微管（MTs）的离散束，由 MT 之间的“桥”交联，这些桥被认为可以提高染色体运动过程中纤维的稳定性。这些桥的身份尚不清楚。网格蛋白是一种多聚蛋白，已被证明通过一种独立于其在膜运输中的作用的机制，在有丝分裂早期稳定 K 纤维。在这项研究中，我们表明，有丝分裂纺锤体中的网格蛋白存在于转化酸性卷曲螺旋蛋白 3（TACC3）/结肠、肝脏肿瘤过表达基因（ch-TOG）/网格蛋白复合物中。该复合物通过 TACC3 和 ch-TOG 锚定在纺锤体上。网格蛋白耗尽的 K 纤维的超微结构分析显示，短 MT 桥的选择性缺失和 MT 的普遍缺失。在 TACC3 耗尽的 K 纤维中也观察到短 MT 桥的类似缺失。最后，免疫金标记证实 K 纤维中的 MT 桥含有网格蛋白。我们的结果表明，TACC3/ch-TOG/网格蛋白复合物是一种 MT 桥，通过物理交联和降低 MT 崩溃的速度来稳定 K 纤维。
