中国科学院分子细胞科学卓越创新中心孟飞龙等研究人员合作发现，C-G编辑产生的双链断裂导致缺失、颠换和易位。2024年1月23日，《自然—细胞生物学》杂志在线发表了这项成果。

研究人员进行了深入的结果分析和基因剖析，揭示了C-to-G碱基编辑器（CGBE）会产生大量中间双链断裂（DSB），而DSB是几种副产物的核心。不完美的DSB末端连接通过末端切除、模板插入或末端填充过程中的异常转换导致小的缺失。在编辑靶点和源自Cas9/脱氨酶的非靶点之间检测到了染色体易位。对DNA修复因子的基因筛选显示，脱碱基位点处理在DSB形成中起着核心作用。用自杀酶HMCES屏蔽脱碱基位点可减少CGBE引发的DSB，从而提供了一种有效的方法，在不影响置换的情况下最大限度地减少DSB触发的事件。

这项工作表明，CGBE可引发有害的中间DSB，因此在治疗应用中需要慎重考虑，而HMCES辅助的CGBE有望成为更安全的工具。

据悉，碱基编辑器（BE）可在不破坏DNA双链的情况下进行碱基替换。除了精确的替换，碱基编辑器还会通过不明确的机制产生低频“随机”副产物。

附：英文原文

Title: C-to-G editing generates double-strand breaks causing deletion, transversion and translocation

Author: Huang, Min Emma, Qin, Yining, Shang, Yafang, Hao, Qian, Zhan, Chuanzong, Lian, Chaoyang, Luo, Simin, Liu, Liu Daisy, Zhang, Senxin, Zhang, Yu, Wo, Yang, Li, Niu, Wu, Shuheng, Gui, Tuantuan, Wang, Binbin, Luo, Yifeng, Cai, Yanni, Liu, Xiaojing, Xu, Ziye, Dai, Pengfei, Li, Simiao, Zhang, Liang, Dong, Junchao, Wang, Jian, Zheng, Xiaoqi, Xu, Yingjie, Sun, Yihua, Wu, Wei, Yeap, Leng-Siew, Meng, Fei-Long

Issue&Volume: 2024-01-23

Abstract: Base editors (BEs) introduce base substitutions without double-strand DNA cleavage. Besides precise substitutions, BEs generate low-frequency ‘stochastic’ byproducts through unclear mechanisms. Here, we performed in-depth outcome profiling and genetic dissection, revealing that C-to-G BEs (CGBEs) generate substantial amounts of intermediate double-strand breaks (DSBs), which are at the centre of several byproducts. Imperfect DSB end-joining leads to small deletions via end-resection, templated insertions or aberrant transversions during end fill-in. Chromosomal translocations were detected between the editing target and off-targets of Cas9/deaminase origin. Genetic screenings of DNA repair factors disclosed a central role of abasic site processing in DSB formation. Shielding of abasic sites by the suicide enzyme HMCES reduced CGBE-initiated DSBs, providing an effective way to minimize DSB-triggered events without affecting substitutions. This work demonstrates that CGBEs can initiate deleterious intermediate DSBs and therefore require careful consideration for therapeutic applications, and that HMCES-aided CGBEs hold promise as safer tools.

DOI: 10.1038/s41556-023-01342-2

Source: https://www.nature.com/articles/s41556-023-01342-2