Lu Ying, Cross Frederick
The Rockefeller University, New York, NY 10065, USA.
Mol Biol Cell. 2009 Mar;20(5):1576-91. doi: 10.1091/mbc.e08-10-1042. Epub 2009 Jan 14.
In budding yeast, three interdigitated pathways regulate mitotic exit (ME): mitotic cyclin-cyclin-dependent kinase (Cdk) inactivation; the Cdc14 early anaphase release (FEAR) network, including a nonproteolytic function of separase (Esp1); and the mitotic exit network (MEN) driven by interaction between the spindle pole body and the bud cortex. Here, we evaluate the contributions of these pathways to ME kinetics. Reducing Cdk activity is critical for ME, and the MEN contributes strongly to ME efficiency. Esp1 contributes to ME kinetics mainly through cohesin cleavage: the Esp1 requirement can be largely bypassed if cells are provided Esp1-independent means of separating sister chromatids. In the absence of Esp1 activity, we observed only a minor ME delay consistent with a FEAR defect. Esp1 overexpression drives ME in Cdc20-depleted cells arrested in metaphase. We have found that this activity of overexpressed Esp1 depended on spindle integrity and the MEN. We defined the first quantitative measure for Cdc14 release based on colocalization with the Net1 nucleolar anchor. This measure indicates efficient Cdc14 release upon MEN activation; release driven by Esp1 in the absence of microtubules was inefficient and incapable of driving ME. We also found a novel role for the MEN: activating Cdc14 nuclear export, even in the absence of Net1.
在出芽酵母中,有三条相互交错的途径调节有丝分裂退出(ME):有丝分裂周期蛋白 - 细胞周期蛋白依赖性激酶(Cdk)失活;Cdc14早期后期释放(FEAR)网络,包括分离酶(Esp1)的非蛋白水解功能;以及由纺锤极体与芽皮质之间的相互作用驱动的有丝分裂退出网络(MEN)。在此,我们评估这些途径对ME动力学的贡献。降低Cdk活性对ME至关重要,并且MEN对ME效率有很大贡献。Esp1主要通过黏连蛋白切割对ME动力学起作用:如果为细胞提供不依赖Esp1的姐妹染色单体分离方式,Esp1的需求在很大程度上可以被绕过。在没有Esp1活性的情况下,我们仅观察到与FEAR缺陷一致的轻微ME延迟。Esp1过表达可在中期停滞的Cdc20缺失细胞中驱动ME。我们发现过表达的Esp1的这种活性依赖于纺锤体完整性和MEN。我们基于与Net1核仁锚定物的共定位定义了Cdc14释放的首个定量测量方法。该测量方法表明MEN激活后Cdc14有效释放;在没有微管的情况下由Esp1驱动的释放效率低下且无法驱动ME。我们还发现了MEN的一个新作用:即使在没有Net1的情况下也能激活Cdc14的核输出。