AUTHOR=Zhou Shiwei , Cai Bei , He Chong , Wang Ying , Ding Qiang , Liu Jiao , Liu Yao , Ding Yige , Zhao Xiaoe , Li Guanwei , Li Chao , Yu Honghao , Kou Qifang , Niu Wenzhi , Petersen Bjoern , Sonstegard Tad , Ma Baohua , Chen Yulin , Wang Xiaolong TITLE=Programmable Base Editing of the Sheep Genome Revealed No Genome-Wide Off-Target Mutations JOURNAL=Frontiers in Genetics VOLUME=10 YEAR=2019 URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2019.00215 DOI=10.3389/fgene.2019.00215 ISSN=1664-8021 ABSTRACT=

Since its emergence, CRISPR/Cas9-mediated base editors (BEs) with cytosine deaminase activity have been used to precisely and efficiently introduce single-base mutations in genomes, including those of human cells, mice, and crop species. Most production traits in livestock are induced by point mutations, and genome editing using BEs without homology-directed repair of double-strand breaks can directly alter single nucleotides. The p.96R > C variant of Suppressor cytokine signaling 2 (SOCS2) has profound effects on body weight, body size, and milk production in sheep. In the present study, we successfully obtained lambs with defined point mutations resulting in a p.96R > C substitution in SOCS2 by the co-injection of BE3 mRNA and a single guide RNA (sgRNA) into sheep zygotes. The observed efficiency of the single nucleotide exchange in newborn animals was as high as 25%. Observations of body size and body weight in the edited group showed that gene modification contributes to enhanced growth traits in sheep. Moreover, targeted deep sequencing and unbiased family trio-based whole genome sequencing revealed undetectable off-target mutations in the edited animals. This study demonstrates the potential for the application of BE-mediated point mutations in large animals for the improvement of production traits in livestock species.