Tiam1-Rac Signaling Counteracts Eg5 during Bipolar Spindle Assembly to Facilitate Chromosome Congression
Tiam1-Rac Signaling Counteracts Eg5 during Bipolar Spindle Assembly to Facilitate Chromosome Congression
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DOI：
10.1016/j.cub.2010.02.033
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发表时间：
2010-04-13
期刊：
影响因子：
9.2
通讯作者：
Malliri, Angeliki
中科院分区：
文献类型：
--
作者：
Woodcock, Simon A.;Rushton, Helen J.;Malliri, Angeliki
中心体分离是有丝分裂期间双极纺锤体形成和随后染色体分离的关键，通过不同的前期和前中期途径发生[1-3]。驱动蛋白-5（Eg 5）是一种微管（MT）马达，在双极纺锤体组装期间推动中心体分开[4];其抑制导致单极纺锤体和有丝分裂停滞[5，6]。在前期拮抗Eg 5的力量是未知的。在这里，我们确定了一个新的力量产生机制介导的鸟嘌呤核苷酸交换因子（GEF）Tiam 1，依赖于它的能力，激活GTdR的Rac。我们发现，Tiam 1和Rac定位于中心体在前期和前中期，和Tiam 1，通过Rac，通常延缓中心体分离。重要的是，Tiam 1耗尽的细胞在培养和Rac 1缺陷的上皮细胞在体内逃避有丝分裂阻滞诱导Eg 5抑制。此外，Tiam 1缺失的细胞通过前中期的转运更慢，并显示增加的染色体装配错误。值得注意的是，在Tiam 1缺失的细胞中，Eg 5抑制不仅纠正了它们增加的中心体分离，而且纠正了它们的染色体聚集错误和有丝分裂延迟。这些研究结果确定Tiam 1-Rac信号作为第一个拮抗剂的中心体分离在前期，证明其需要在平衡Eg 5诱导的力在体外和体内双极纺锤体组装，并表明，适当的中心体分离在前期促进随后的染色体congression。
Centrosome separation, critical for bipolar spindle formation and subsequent chromosome segregation during mitosis, occurs via distinct prophase and prometaphase pathways [1-3]. Kinesin-5 (Eg5), a microtubule (MT) motor, pushes centrosomes apart during bipolar spindle assembly [4]; its suppression results in monopolar spindles and mitotic arrest [5, 6]. Forces that antagonize Eg5 in prophase are unknown. Here we identify a new force generating mechanism mediated by the guanine nucleotide exchange factor (GEF) Tiam1, dependent on its ability to activate the GTPase Rac. We reveal that Tiam1 and Rac localize to centrosomes during prophase and prometaphase, and Tiam1, acting through Rac, ordinarily retards centrosome separation. Importantly, both Tiam1-depleted cells in culture and Rac1-deficient epithelial cells in vivo escape the mitotic arrest induced by Eg5 suppression. Moreover, Tiam1-depleted cells transit more slowly through prometaphase and display increased chromosome congression errors. Significantly, Eg5 suppression in Tiam1-depleted cells rectifies not only their increased centrosome separation but also their chromosome congression errors and mitotic delay. These findings identify Tiam1-Rac signaling as the first antagonist of centrosome separation during prophase, demonstrate its requirement in balancing Eg5-induced forces during bipolar spindle assembly in vitro and in vivo, and show that proper centrosome separation in prophase facilitates subsequent chromosome congression.