Genome editing of porcine zygotes via lipofection of two guide RNAs using a CRISPR/Cas9 system

CRISPR/Cas9-based multiplex genome editing via electroporation is relatively efficient; however, lipofection is versatile because of its ease of use and low cost. Here, we aimed to determine the efficiency of lipofection in CRISPR/Cas9-based multiplex genome editing using growth hormone receptor (GHR) and glycoprotein alphagalactosyltransferase 1 (GGTA1)-targeting guide RNAs (gRNAs) in pig zygotes. Zona pellucida-free zygotes were collected 10 h after in vitro fertilization and incubated with Cas9, gRNAs, and Lipofectamine 2000 (LP2000) for 5 h. In Experiment 1, we evaluated the mutation efficiency of gRNAs targeting either GHR or GGTA1 in zygotes transfected using LP2000 and cultured in 4-well plates. In Experiment 2, we examined the effects of the culture method on the development, mutation rate, and mutation efficiency of zygotes with simultaneously double-edited GHR and GGTA1, cultured using 4-well (group culture) and 25-well plates (individual culture). In Experiment 3, we assessed the effect of additional GHR-targeted lipofection before and after simultaneous double gRNA-targeted lipofection on the mutation efficiency of edited embryos cultured in 25-well plates. No significant differences in mutation rates were observed between the zygotes edited with either gRNA. Moreover, the formation rate of blastocysts derived from GHR and GGTA1 double-edited zygotes was significantly increased in the 25-well plate culture compared to that in the 4-well plate culture. However, mutations were only observed in GGTA1 when zygotes were transfected with both gRNAs, irrespective of the culture method used. GHR mutations were detected only in blastocysts derived from zygotes subjected to GHR-targeted lipofection before simultaneous double gRNA-targeted lipofection. Overall, our results suggest that additional lipofection before simultaneous double gRNA-targeted lipofection induces additional mutations in the zygotes.