Cancer Institute of the Japanese Foundation for Cancer Research, Division of Experimental Pathology, 3-8-31 Ariake, Koto-ku, Tokyo 135-8550, Japan.
Tokyo Institute of Technology, Department of Biological Sciences, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8501, Japan.
Nat Cell Biol. 2016 Jun;18(6):692-9. doi: 10.1038/ncb3353. Epub 2016 May 2.
The formation of mitotic chromosomes requires both compaction of chromatin and the resolution of replicated sister chromatids. Compaction occurs during mitotic prophase and prometaphase, and in prophase relies on the activity of condensin II complexes. Exactly when and how sister chromatid resolution occurs has been largely unknown, as has its molecular requirements. Here, we established a method to visualize sister resolution by sequential replication labelling with two distinct nucleotide derivatives. Quantitative three-dimensional imaging then allowed us to measure the resolution of sister chromatids throughout mitosis by calculating their non-overlapping volume within the whole chromosome. Unexpectedly, we found that sister chromatid resolution starts already at the beginning of prophase, proceeds concomitantly with chromatin compaction and is largely completed by the end of prophase. Sister chromatid resolution was abolished by inhibition of topoisomerase IIα and by depleting or preventing mitotic activation of condensin II, whereas blocking cohesin dissociation from chromosomes had little effect. Mitotic sister chromatid resolution is thus an intrinsic part of mitotic chromosome formation in prophase that relies largely on DNA decatenation and shares the molecular requirement for condensin II with prophase compaction.
有丝分裂染色体的形成既需要染色质的紧缩，也需要复制的姐妹染色单体的分辨率。紧缩发生在有丝分裂前期和前中期，在前期依赖于凝聚素 II 复合物的活性。姐妹染色单体分辨率发生的确切时间和方式在很大程度上是未知的，其分子要求也是如此。在这里，我们建立了一种通过用两种不同的核苷酸衍生物进行连续复制标记来可视化姐妹分辨率的方法。然后，通过定量的三维成像，我们可以通过计算整个染色体中姐妹染色单体的非重叠体积来测量有丝分裂过程中姐妹染色单体的分辨率。出乎意料的是，我们发现姐妹染色单体的分辨率早在前期开始就已经开始了，与染色质紧缩同时进行，并在前期结束时基本完成。拓扑异构酶 IIα 的抑制作用以及凝聚素 II 的有丝分裂激活的耗尽或阻止，会使姐妹染色单体的分辨率丧失，而阻止着丝粒从染色体上解离的作用则很小。因此，有丝分裂姐妹染色单体的分辨率是前期有丝分裂染色体形成的固有部分，主要依赖于 DNA 解缠结，并与前期紧缩共享凝聚素 II 的分子要求。
