后期促进复合物/环体(APC/C)激活剂Cdc20的消耗使中期细胞停滞,有丝分裂细胞周期蛋白(细胞周期蛋白B)和Separase抑制剂Securin的高水平。在哺乳动物细胞中,这种阻滞已被用于使用参与纺锤体组装检查点的药物治疗癌症,最近,与APC/C的化学抑制剂虽然大多数细胞长时间停留在有丝分裂中经历凋亡,其他人跳过胞质分裂,进入G1与未分离的染色体。这个过程,称为有丝分裂滑移,在癌细胞中产生非整倍性并增加基因组不稳定性。这里,我们通过Cdc20同源物slp1的转录沉默来分析有丝分裂中停滞的裂变酵母细胞的行为。虽然slp1的消耗很容易在中期停止细胞,这种停滞只是短暂的,大多数细胞最终经历胞质分裂并显示稳定的有丝分裂去磷酸化。值得注意的是,这发生在不存在细胞周期蛋白B(Cdc13)降解的情况下。我们调查了磷酸酶活性在这些事件中的参与,并证明PP2A-B55Pab1是预防中隔所必需的,在逮捕期间,其CDK介导的抑制促进胞质分裂的诱导。相比之下,PP2A-B56Par1的缺失完全消除了间隔。我们表明,这种作用部分是由于该突变体进入有丝分裂,CDK活性降低。有趣的是,PP2A-B55Pab1和PP2A-B56Par1以及Clp1(出芽的酵母有丝分裂磷酸酶Cdc14的同系物)都是在逃逸过程中对有丝分裂底物进行去磷酸化所必需的。最后,我们表明,由RFX转录因子Sak1控制的有丝分裂转录波促进了胞质分裂的诱导,并且还需要PP2A-B56Par1在独立于CDK的机制中的活性。
Depletion of the Anaphase-Promoting Complex/Cyclosome (APC/C) activator Cdc20 arrests cells in metaphase with high levels of the mitotic cyclin (Cyclin B) and the Separase inhibitor Securin. In mammalian cells this arrest has been exploited for the treatment of cancer with drugs that engage the spindle assembly checkpoint and, recently, with chemical inhibitors of the APC/C. While most cells arrested in mitosis for prolonged periods undergo apoptosis, others skip cytokinesis and enter G1 with unsegregated chromosomes. This process, known as mitotic slippage, generates aneuploidy and increases genomic instability in the cancer cell. Here, we analyze the behavior of fission yeast cells arrested in mitosis through the transcriptional silencing of the Cdc20 homolog slp1. While depletion of slp1 readily halts cells in metaphase, this arrest is only transient and a majority of cells eventually undergo cytokinesis and show steady mitotic dephosphorylation. Notably, this occurs in the absence of Cyclin B (Cdc13) degradation. We investigate the involvement of phosphatase activity in these events and demonstrate that PP2A-B55Pab1 is required to prevent septation and, during the arrest, its CDK-mediated inhibition facilitates the induction of cytokinesis. In contrast, deletion of PP2A-B56Par1 completely abrogates septation. We show that this effect is partly due to this mutant entering mitosis with reduced CDK activity. Interestingly, both PP2A-B55Pab1 and PP2A-B56Par1, as well as Clp1 (the homolog of the budding yeast mitotic phosphatase Cdc14) are required for the dephosphorylation of mitotic substrates during the escape. Finally, we show that the mitotic transcriptional wave controlled by the RFX transcription factor Sak1 facilitates the induction of cytokinesis and also requires the activity of PP2A-B56Par1 in a mechanism independent of CDK.