Electroporation of sheep zygotes as an alternative to microinjection for the generation of CRISPR/Cas genome edited models

Zygote microinjection is considered the most suitable technique to introduce CRISPR/Cas9 reagents for efficient genome editing in livestock. In this study, zygote electroporation was evaluated as an alternative to microinjection for CRISPR/Cas9-mediated genome editing in sheep. Four experiments were conducted on 3548 cumulus-oocyte complexes. Acid Tyrode's solution (AT) was used to partially degrade the zona pellucida (ZP) to improve reagent entry, resulting in ZP thinning with longer AT exposure (P < 0.05). Although early embryo development was impaired by AT exposure (P < 0.05), blastocyst rates were similar across all groups by day 8. Electroporation conditions were optimized by testing pulse length (1 or 3 ms), with the best results from 6 pulses of 20 V for 3 ms with AT during 60 s. Electroporation with 500 ng/μL Cas9 and 300 ng/μL sgRNA with AT during 60 s achieved a 38.5 % mutation rate. When compared with conventional microinjection, electroporation had higher developmental rates but a lower mutation rate (21.4 % vs. 60.0 %; P < 0.05). These findings suggest that electroporation is a viable, cost-effective technique for genome editing in sheep. Nevertheless, further research will be required to fine-tune electroporation conditions and enhance efficiency in terms of mutation rate.