基因编辑之“新宠”—单碱基基因组编辑系统

The “new favorite” of gene editing technology—single base editors

近年发展起来的人工核酸酶可通过引起特定位点的DNA双链断裂实现对目的片段的有效编辑。为进一步提高碱基修改的效率和精确度,2016年研究者们利用CRISPR/Cas9识别特定DNA序列的功能,结合胞嘧啶脱氨酶的生化活性发明了将胞嘧啶高效转换为胸腺嘧啶(C>T)的嘧啶单碱基编辑系统(base editor)。这一系统虽然能精准实现嘧啶直接转换,大大提高精确基因编辑效率,但美中不足的是无法对嘌呤进行修改。近期,Nature报道了将细菌中的t RNA腺嘌呤脱氨酶定向进化形成具有催化DNA腺嘌呤底物的脱氨酶,将其与Cas9系统融合发明了具有高效催化腺嘌呤转换为鸟嘌呤的新工具—腺嘌呤单碱基编辑系统(ABEs,adenine base editors)。本文总结了单碱基编辑工具的发展历程和最新研究进展,着重介绍ABEs的研发过程,并对单碱基编辑工具今后的应用方向和研发方向进行展望。

Programmable nucleases are cutting edge genetic technology which edits targeted DNA sequences through generation of site-specific double-strand DNA breaks(DSBs). To improve the efficiency and precision of genetic modification, scientists have developed a single-base editing system(base editor) through combining of CRISPR/Cas9 system with cytosine deaminase. Compared with Cas9 system, this base editor can convert cytosine to thymine(C > T) at specific site more efficiently without inducing DSBs to avoid generation of indels. However, the base editor can only generate transition of pyrimidine but could not modify purines. Recently, Nature published a novel base editing system to convert adenine to guanine(ABEs, adenine base editors) through fusion of Cas9 nickase to a modified deaminase which is evolved through screening of random library based on t RNA adenine deaminase from E. coli. Here, we summarize the development of single-base editing tools and the latest research progress, especially the optimization process of ABEs, as well as the potential directions of the base editors.