Programmable nucleases like the popular CRISPR/Cas9 system allow for precision genome engineering by inducing a site-specific DNA double strand break (DSB) within a genome. The DSB is repaired by endogenous DNA repair pathways, either nonhomologous end joining (NHEJ) or homology directed repair (HDR). The predominant and error-prone NHEJ pathway often results in small nucleotide insertions or deletions that can be used to construct knockout alleles. Alternatively, HDR activity can result in precise modification incorporating exogenous DNA fragments into the cut site. However, genetic recombination in mammalian systems through the HDR pathway is an inefficient process and requires cumbersome laboratory methods to identify the desired accurate insertion events. This is further compromised by the activity of the competing DNA repair pathway, NHEJ, which repairs the majority of nuclease induced DNA DSBs and also is responsible for mutagenic insertion and deletion events at off-target locations throughout the genome. Various methodologies have been developed to increase the efficiency of designer nuclease-based HDR mediated gene editing. Here, we review these advances toward modulating the activities of the two critical DNA repair pathways, HDR and NHEJ, to enhance precision genome engineering.

中文翻译：

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调节DNA修复途径以改善精密基因组工程

诸如流行的CRISPR / Cas9系统之类的可编程核酸酶可通过在基因组内诱导位点特异性DNA双链断裂（DSB）来进行精确的基因组工程设计。通过非同源末端连接（NHEJ）或同源定向修复（HDR）的内源性DNA修复途径修复DSB。占主导地位且容易出错的NHEJ途径通常会导致小的核苷酸插入或缺失，可用于构建敲除等位基因。或者，HDR活性可导致精确的修饰，将外源DNA片段掺入切割位点。但是，通过HDR途径在哺乳动物系统中进行基因重组是一个低效的过程，需要繁琐的实验室方法才能鉴定出所需的准确插入事件。竞争性DNA修复途径NHEJ的活性进一步损害了这一点，它修复了大多数核酸酶诱导的DNA DSB，并且还负责整个基因组中脱靶位置的诱变插入和缺失事件。已经开发出各种方法来提高基于设计者核酸酶的HDR介导的基因编辑的效率。在这里，我们审查这些进展，以调节两个关键的DNA修复途径，HDR和NHEJ的活动，以提高精确的基因组工程。