Live-cell imaging reveals a stable cohesin-chromatin interaction after but not before DNA replication
Live-cell imaging reveals a stable cohesin-chromatin interaction after but not before DNA replication
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DOI：
10.1016/j.cub.2006.06.068
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发表时间：
2006-08-08
期刊：
影响因子：
9.2
通讯作者：
Ellenberg, Jan
中科院分区：
文献类型：
--
作者：
Gerlich, Daniel;Koch, Birgit;Ellenberg, Jan
粘附素是一种多亚单位蛋白质复合体，连接姐妹染色单体从复制到分离[1，2]。DNA[3-5]上缺乏明显的粘附素靶向特异性序列，以及粘附素分子排列成一个大环[6-8]，这导致了粘附素作为直接拓扑连接物的工作假设[9，10]。为了保持姐妹染色单体的一致性，这种连锁需要稳定地存在于细胞周期的整个S和G2期。出乎意料的是，粘附素在末期就已经与染色质结合，在前期以一种依赖于磷酸化的方式从染色体上解离出一大部分[11-17]，而后期的启动只需要对一小部分粘附素进行蛋白水解性切割[18，19]。这些观察提出了一个问题，即在细胞周期中，粘附素如何以及何时与染色质相互作用。在这里，我们报告了细胞周期依赖于与染色质结合的粘附素的稳定性。利用光漂白和定量活细胞成像，我们鉴定了几个具有不同染色质结合稳定性的粘附素池。虽然所有染色质结合的粘附素在复制前平均停留时间不到25min后解离，但大约三分之一的粘附素在S相后结合得更稳定，并持续到中期，与介导姐妹染色单体之间凝聚的长寿命链接一致。
Cohesin is a multisubunit protein complex that links sister chromatids from replication until segregation [1, 2]. The lack of obvious cohesin-targeting-specific sequences on DNA [3-5], as well as cohesin's molecular arrangement as a large ring [6-8], has led to the working hypothesis that cohesin acts as a direct topological linker [9, 10]. To preserve the identity of sister chromatids, such a linkage would need to stably persist throughout the entire S and G2 phases of the cell cycle. Unexpectedly, cohesin binds chromatin already in telophase, and a large fraction dissociates from chromosomes during prophase in a phosphorylation-dependent manner [11-17], whereas initiation of anaphase requires proteolytic cleavage of only a small fraction of cohesin [18,19]. These observations raised the question of how and when cohesin interacts with chromatin during the cell cycle. Here, we report a cell-cycle dependence in the stability of cohesin binding to chromatin. Using photobleaching and quantitative live-cell imaging, we identified several cohesin pools with different chromatin binding stabilities. Although all chromatin bound cohesin dissociated after a mean residence time of less than 25 min before replication, about one-third of cohesin was bound much more stably after S phase and persisted until metaphase, consistent with long-lived links mediating cohesion between sister chromatids.