Yang S S, Yeh E, Salmon E D, Bloom K
Department of Biology, University of North Carolina, Chapel Hill 27599-3280, USA.
J Cell Biol. 1997 Jan 27;136(2):345-54. doi: 10.1083/jcb.136.2.345.
Activation of a facultative, dicentric chromosome provides a unique opportunity to introduce a double strand DNA break into a chromosome at mitosis. Time lapse video enhanced-differential interference contrast analysis of the cellular response upon dicentric activation reveals that the majority of cells initiates anaphase B, characterized by pole-pole separation, and pauses in mid-anaphase for 30-120 min with spindles spanning the neck of the bud before completing spindle elongation and cytokinesis. The length of the spindle at the delay point (3-4 microm) is not dependent on the physical distance between the two centromeres, indicating that the arrest represents surveillance of a dicentric induced aberration. No mid-anaphase delay is observed in the absence of the RAD9 checkpoint gene, which prevents cell cycle progression in the presence of damaged DNA. These observations reveal RAD9-dependent events well past the G2/M boundary and have considerable implications in understanding how chromosome integrity and the position and state of the mitotic spindle are monitored before cytokinesis.
兼性双着丝粒染色体的激活为在有丝分裂时将双链DNA断裂引入染色体提供了独特的机会。对双着丝粒激活后细胞反应的延时视频增强微分干涉对比分析表明，大多数细胞启动后期B，其特征为两极分离，并在后期中期暂停30 - 120分钟，纺锤体跨越芽颈部，然后完成纺锤体伸长和胞质分裂。延迟点处纺锤体的长度（3 - 4微米）不依赖于两个着丝粒之间的物理距离，这表明停滞代表对双着丝粒诱导畸变的监测。在没有RAD9检查点基因的情况下未观察到后期中期延迟，RAD9检查点基因在存在受损DNA时会阻止细胞周期进展。这些观察结果揭示了远超G2/M边界的依赖RAD9的事件，并且对于理解在胞质分裂之前如何监测染色体完整性以及有丝分裂纺锤体的位置和状态具有重要意义。
