Although kinetochores normally play a key role in sister chromatid separation and segregation, chromosome fragments lacking kinetochores (acentrics) can in some cases separate and segregate successfully. In Drosophila neuroblasts, acentric chromosomes undergo delayed, but otherwise, normal sister separation, revealing the existence of kinetochore independent mechanisms driving sister chromosome separation. Bulk cohesin removal from the acentric is not delayed, suggesting factors other than cohesin are responsible for the delay in acentric sister separation. In contrast to intact kinetochore-bearing chromosomes, we discovered that acentrics align parallel as well as perpendicular to the mitotic spindle. In addition, sister acentrics undergo unconventional patterns of separation. For example, rather than the simultaneous separation of sisters, acentrics oriented parallel to the spindle often slide past one another toward opposing poles. To identify the mechanisms driving acentric separation, we screened 117 RNAi gene knockdowns for synthetic lethality with acentric chromosome fragments. In addition to well-established DNA repair and checkpoint mutants, this candidate screen identified synthetic lethality with X-chromosome-derived acentric fragments in knockdowns of Greatwall (cell cycle kinase), EB1 (microtubule plus-end tracking protein), and Map205 (microtubule-stabilizing protein). Additional image-based screening revealed that reductions in Topoisomerase II levels disrupted sister acentric separation. Intriguingly, live imaging revealed that knockdowns of EB1, Map205, and Greatwall preferentially disrupted the sliding mode of sister acentric separation. Based on our analysis of EB1 localization and knockdown phenotypes, we propose that in the absence of a kinetochore, microtubule plus-end dynamics provide the force to resolve DNA catenations required for sister separation.

中文翻译：

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姊妹染色体分离的动轴独立机制

尽管动植物通常在姐妹染色单体的分离和分离中起关键作用，但是缺少动植物的染色体片段（无心轴蛋白）在某些情况下仍可以成功分离和分离。在果蝇神经母细胞中，中心染色体发生延迟，但正常情况下姐妹分离，这揭示了驱动姐妹染色体分离的线粒体独立机制的存在。没有将胶凝蛋白从无心菌中去除的过程没有延迟，这表明除粘着蛋白以外的其他因素也导致了无心菌姐妹分离的延迟。与完整的带有线粒体的染色体相反，我们发现无心轴与有丝分裂纺锤体平行且垂直排列。此外，姐妹无心者经历了非常规的分离模式。例如，与其同时分离姐妹，平行于主轴定向的偏心轮经常彼此相对的极滑过。为了确定驱动无心分离的机制，我们筛选了117个RNAi基因敲低的无心染色体片段的合成杀伤力。除了成熟的DNA修复和检查点突变体之外，该候选物筛选还通过在长城（细胞周期激酶），EB1（微管加末端追踪蛋白）和Map205（微管）的敲低物中鉴定了X染色体衍生的无性片段的合成杀伤力。 -稳定蛋白）。额外的基于图像的筛选显示，拓扑异构酶II水平的降低破坏了姐妹无心分离。有趣的是，实时成像显示EB1，Map205和长城的击倒优先破坏了姐妹无心分离的滑动模式。