美国哥伦比亚大学Dieter Egli小组的最新研究发现，在人类胚胎中利用Cas9切割可去除等位基因特异的染色体。这一研究成果在线发表在2020年10月29日的《细胞》杂志上。

研究人员探究了在父系染色体EYS位点上引入Cas9诱导双链断裂（DSB）的修复结果，该染色体携带的移码突变可导致失明。研究显示最常见的修复结果是微同源介导的末端连接，这发生在胚胎的第一个细胞周期中，其诱导胚胎阅读框的非镶嵌式恢复。

值得注意的是，大约一半的双链断裂并未得到修复，这导致无法检测到父系等位基因，并且诱导有丝分裂后一个或两个染色体臂的丢失。相应地，由于Cas9切割两个等位基因，因此Cas9脱靶切割会引起染色体丢失和半合插入缺失。

这些结果说明了可以对染色体构成进行人为干预，但同时证明了对人胚胎突变校正具有一定挑战性。

据介绍，纠正人胚胎中的致病突变可减轻遗传疾病的危害并改善对具有致病突变夫妇选择替代胚胎的潜力。

附：英文原文

Title: Allele-Specific Chromosome Removal after Cas9 Cleavage in Human Embryos

Author: Michael V. Zuccaro, Jia Xu, Carl Mitchell, Diego Marin, Raymond Zimmerman, Bhavini Rana, Everett Weinstein, Rebeca T. King, Katherine L. Palmerola, Morgan E. Smith, Stephen H. Tsang, Robin Goland, Maria Jasin, Rogerio Lobo, Nathan Treff, Dieter Egli

Issue&Volume: 2020-10-29

Abstract: Correction of disease-causing mutations in human embryos holds the potential to reducethe burden of inherited genetic disorders and improve fertility treatments for coupleswith disease-causing mutations in lieu of embryo selection. Here, we evaluate repairoutcomes of a Cas9-induced double-strand break (DSB) introduced on the paternal chromosomeat the EYS locus, which carries a frameshift mutation causing blindness. We show that the mostcommon repair outcome is microhomology-mediated end joining, which occurs during thefirst cell cycle in the zygote, leading to embryos with non-mosaic restoration ofthe reading frame. Notably, about half of the breaks remain unrepaired, resultingin an undetectable paternal allele and, after mitosis, loss of one or both chromosomalarms. Correspondingly, Cas9 off-target cleavage results in chromosomal losses andhemizygous indels because of cleavage of both alleles. These results demonstrate theability to manipulate chromosome content and reveal significant challenges for mutationcorrection in human embryos.

DOI: 10.1016/j.cell.2020.10.025

Source: https://www.cell.com/cell/fulltext/S0092-8674(20)31389-1