Comparison of chemically mediated CRISPR/Cas9 gene editing systems using different nonviral vectors in porcine embryos.

The transfection efficiency of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas ribonucleoprotein complexes was compared using three nonviral vector transfection reagents: nonliposomal polymeric (TransIT-X2), lipid nanoparticle delivery (CRISPRMAX), and peptide (ProteoCarry) systems. Porcine zona pellucida-free zygotes and embryos were incubated for 5 h with CRISPR-associated protein 9 (Cas9), guide RNA (gRNA) targeting GGTA1, and one of the reagents. In Experiment 1, optimization of Cas9 protein to gRNA molar ratios of 1:2, 2:2, and 4:2, along with single or double doses of reagents, was performed on zygotes at 10 h post-in vitro fertilization. In Experiment 2, optimization of timing was performed at 10 or 29 h post-in vitro fertilization, using optimal molar ratios and reagent doses. Blastocyst formation, mutation rates, and mutation efficiency were measured in each experiment. For each reagent, a 4:2 Cas9:gRNA molar ratio and addition of a double reagent dose exhibited a higher mutation rate; however, blastocyst rate tended to decrease compared with that of control. Moreover, the optimal transfection time varied depending on the reagent, and the proportions of blastocysts carrying mutations were <34%. In conclusion, the above three transfectants allowed gene editing of porcine zygotes and embryos; however, this newly established chemistry-based technology needs further improvement, especially regarding editing efficiency and embryo development.