Min Hee Jung

Several CRISPR-Cas9 orthologues have been used for genome editing. Here, we present the smallest Cas9 orthologue characterized to date, derived from Campylobacter jejuni (CjCas9), for efficient genome editing in vivo. After determining protospacer-adjacent motif (PAM) sequences and optimizing single-guide RNA (sgRNA) length, we package the CjCas9 gene, its sgRNA sequence, and a marker gene in an all-in-one adeno-associated virus (AAV) vector and produce the resulting virus at a high titer. CjCas9 is highly specific, cleaving only a limited number of sites in the human or mouse genome. CjCas9, delivered via AAV, induces targeted mutations at high frequencies in mouse muscle cells or retinal pigment epithelium (RPE) cells. Furthermore, CjCas9 targeted to the Vegfa or Hif1a gene in RPE cells reduces the size of laser-induced choroidal neovascularization, suggesting that in vivo genome editing with CjCas9 is a new option for the treatment of age-related macular degeneration.

The CRISPR/Cas9 system is widely applied in genome engineering due to its simplicity and versatility. Although this has revolutionized genome-editing technology, knockin animal generation via homology directed repair (HDR) is not as efficient as nonhomologous end-joining DNA-repair-dependent knockout. Although its double-strand break activity may vary, Cas9 derived from Streptococcus pyogenens allows robust design of single-guide RNAs (sgRNAs) within the target sequence; However, prescreening for different sgRNA activities delays the process of transgenic animal generation. To overcome this limitation, multiple sets of different sgRNAs were examined for their knockin efficiency. We discovered profound advantages associated with single-stranded oligo-donor-mediated HDR processes using overlapping sgRNAs (sharing at least five base pairs of the target sites) as compared with using non-overlapping sgRNAs for knock-in mouse generation. Studies utilizing cell lines revealed shorter sequence deletions near target mutations using overlapping sgRNAs as compared with those observed using non-overlapping sgRNAs, which may favor the HDR process. Using this simple method, we successfully generated several transgenic mouse lines harboring loxP insertions or single-nucleotide substitutions with a highly efficiency of 18–38%. Our results demonstrate a simple and efficient method for generating transgenic animals harboring foreign-sequence knockins or short-nucleotide substitutions by the use of overlapping sgRNAs. A method to improve the efficiency of repairing double-stranded DNA breaks facilitates the production of animals with edited genomes. The CRISPR/Cas9 system has been revolutionising biomedical research as it allows the insertion or deletion of any DNA sequence at specific sites by making double-strand DNA breaks. However, the insertion of precise genetic changes is limited by the relatively low efficiency of the repair mechanism, which requires a template DNA molecule to promote error-free repair of the DNA strands. A team of South Korean scientists led by Su Cheong Yeom at Seoul National University and Han Woong Lee at Yonsei University show that delivering multiple overlapping single-guide RNAs (that share at least five base pairs of the target sequence) as a DNA template significantly improves the repair and thus the production of mice with a targeted gene insertion.

// Mi-Young Park 1, * , Min Hee Jung 2, * , Eun Young Eo 1 , Seokjoong Kim 2 , Sang Hoon Lee 1, 3 , Yeon Joo Lee 1, 3 , Jong Sun Park 1, 3 , Young Jae Cho 1, 3 , Jin Haeng Chung 4 , Cheol Hyeon Kim 5 , Ho Il Yoon 1, 3 , Jae Ho Lee 1, 3 , Choon-Taek Lee 1, 3 1 Division of Pulmonology and Critical Care Medicine, Department of Internal Medicine and Respiratory Center, Seoul National University Bundang Hospital, Seongnam, Republic of Korea 2 Toolgen Inc., Seoul, Republic of Korea 3 Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea 4 Department of Pathology, Seoul National University Bundang Hospital, Seongnam, Republic of Korea 5 Department of Internal Medicine, Korea Cancer Center Hospital, Seoul, Republic of Korea * These authors contributed equally to this work Correspondence to: Choon-Taek Lee, email: ctlee@snu.ac.kr Keywords: lung cancer, resistance, EGFR T790M, CRISPR/Cas9 Received: August 15, 2016      Accepted: March 21, 2017      Published: March 31, 2017 ABSTRACT Tyrosine kinase inhibitors (TKIs) such as gefitinib and erlotinib are effective against lung adenocarcinomas harboring epidermal growth factor receptor (EGFR) mutations. However, cancer cells can develop resistance to these agents with prolonged exposure; in over 50% of cases, this is attributable to the EGFR T790M mutation. Moreover, additional resistance mutations can arise with the use of new drugs. Cancer cell lines with specific mutations can enable the study of resistance mechanisms. In this study, we introduced the EGFR T790M mutation into the PC9 human lung cancer cell line—which has a deletion in exon 19 of the EGFR gene—by clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas)9-mediated genome editing. EGFR pyrosequencing and peptide nucleic acid clamping revealed that PC9 cells with EGFR T790M generated by CRISPR/Cas 9 had a higher T790M mutation rate than those with the same mutation generated by long-term exposure to gefitinib (PC9-G); moreover, resistance to gefitinib in these clones was higher than that in PC9-G cells. The clones were also highly sensitive to the 3rd-generation EGFR TKI AZD9291, which is cytotoxic to lung cancer cells with EGFR T790M. The CRISPR/Cas9 programmable nuclease system can be used to generate various cancer cell lines with specific mutations that can facilitate studies on resistance mechanisms and drug efficacy.