Stabilization of chromatin topology safeguards genome integrity
Stabilization of chromatin topology safeguards genome integrity
复制标题
DOI：
10.1038/s41586-019-1659-4
复制
发表时间：
2019-10-24
期刊：
影响因子：
64.8
通讯作者：
Lukas, Claudia
中科院分区：
文献类型：
--
作者：
Ochs, Fena;Karemore, Gopal;Lukas, Claudia
为了保护基因组的完整性，以应对DNA双链断裂（DSB），哺乳动物细胞动员相邻的染色质来保护DNA末端免受过度切除，这可能会破坏修复保真度并对健康染色体造成损害（1）。这种形式的基因组监视由53 BP 1协调，其在DSB的积累触发RIF 1和shieldin-CST-POLa复合物的顺序募集（2）。这条通路如何反映和影响三维核结构尚不清楚。在这里，我们使用超分辨率显微镜显示，53 BP 1和RIF 1形成一个自主的功能模块，稳定在DNA断裂位点的三维染色质拓扑结构。该过程由53 BP 1在与拓扑相关结构域（TAD）序列共定位的致密染色质区域的积累启动，然后将RIF 1募集到这些结构域之间的边界。53 BP 1和RIF 1的交替分布使单个DBS位点处的几个相邻的TAD大小的结构稳定成有序的圆形排列。53 BP 1或RIF 1（但不是shieldin）的耗尽破坏了这种排列，并导致DSB侧翼染色质的解压缩，染色质间空间的减少，DNA修复蛋白的异常扩散和DNA末端的过度切除。类似的拓扑结构的扭曲是由内聚素的耗尽引发的，这表明DNA断裂后染色质结构的维持涉及形成三维核组织的基本机制。由于DSB-侧翼染色质的拓扑稳定性独立于DNA修复，我们提出，除了提供一个结构支架来保护DNA末端免受异常处理外，53 BP 1和RIF 1还保护了被DNA断裂破坏的基因座的表观遗传完整性。
To safeguard genome integrity in response to DNA double-strand breaks (DSBs), mammalian cells mobilize the neighbouring chromatin to shield DNA ends against excessive resection that could undermine repair fidelity and cause damage to healthy chromosomes(1). This form of genome surveillance is orchestrated by 53BP1, whose accumulation at DSBs triggers sequential recruitment of RIF1 and the shieldin-CST-POLa complex(2). How this pathway reflects and influences the three-dimensional nuclear architecture is not known. Here we use super-resolution microscopy to show that 53BP1 and RIF1 form an autonomous functional module that stabilizes three-dimensional chromatin topology at sites of DNA breakage. This process is initiated by accumulation of 53BP1 at regions of compact chromatin that colocalize with topologically associating domain (TAD) sequences, followed by recruitment of RIF1 to the boundaries between such domains. The alternating distribution of 53BP1 and RIF1 stabilizes several neighbouring TAD-sized structures at a single DBS site into an ordered, circular arrangement. Depletion of 53BP1 or RIF1 (but not shieldin) disrupts this arrangement and leads to decompaction of DSB-flanking chromatin, reduction in interchromatin space, aberrant spreading of DNA repair proteins, and hyper-resection of DNA ends. Similar topological distortions are triggered by depletion of cohesin, which suggests that the maintenance of chromatin structure after DNA breakage involves basic mechanisms that shape three-dimensional nuclear organization. As topological stabilization of DSB-flanking chromatin is independent of DNA repair, we propose that, besides providing a structural scaffold to protect DNA ends against aberrant processing, 53BP1 and RIF1 safeguard epigenetic integrity at loci that are disrupted by DNA breakage.