Chromosome Dynamics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan.
Department of Life Science, Graduate School of Arts and Sciences, The University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan.
Science. 2017 Jun 23;356(6344):1284-1287. doi: 10.1126/science.aam9702. Epub 2017 May 18.
The nucleosome is the fundamental structural unit of eukaryotic chromatin. During mitosis, duplicated nucleosome fibers are organized into a pair of rod-shaped structures (chromatids) within a mitotic chromosome. However, it remains unclear whether nucleosome assembly is indeed an essential prerequisite for mitotic chromosome assembly. We combined mouse sperm nuclei and cell-free egg extracts depleted of the histone chaperone Asf1 and found that chromatid-like structures could be assembled even in the near absence of nucleosomes. The resultant "nucleosome-depleted" chromatids contained discrete central axes positive for condensins, although they were more fragile than normal nucleosome-containing chromatids. Combinatorial depletion experiments underscored the central importance of condensins in mitotic chromosome assembly, which sheds light on their functional cross-talk with nucleosomes in this process.
核小体是真核染色质的基本结构单位。在有丝分裂过程中，复制的核小体纤维组织成有丝分裂染色体中的一对杆状结构（染色单体）。然而，核小体的组装是否确实是有丝分裂染色体组装的必要前提尚不清楚。我们将小鼠精子核与缺乏组蛋白伴侣 Asf1 的无细胞卵提取物相结合，发现即使在几乎没有核小体的情况下，也可以组装染色单体样结构。所得到的“核小体缺失”染色单体包含了用于浓缩物的离散中心轴，尽管它们比正常含有核小体的染色单体更脆弱。组合耗竭实验强调了浓缩物在有丝分裂染色体组装中的核心重要性，这揭示了它们在该过程中与核小体的功能相互作用。
