Effects of Electroporation Timing and Cumulus Cell Attachment on In Vitro Development and Genome Editing of Porcine Embryos

Pig genome editing using the oviductal nucleic acid delivery (GONAD) method with electroporation would allow the efficient obtention of genetically modified pigs. However, oocytes and zygotes at various stages after ovulation must be targeted, and cumulus cell attachment and mosaic mutations are major obstacles. Therefore, we investigated whether two parameters (electroporation timing and the cumulus cell attachment) influence the effectiveness of multiplex genome editing by electroporation in porcine oocytes or zygotes. Three gRNAs targeting either GGTA1, CMAH or B4GALNT2 were introduced individually into oocytes and zygotes with and without cumulus cells at three different time points, 0 h before in vitro fertilisation (IVF) and 5 h and 10 h after IVF initiation. The introduction of gRNAs into oocytes and zygotes did not significantly affect the rates of blastocyst formation and total mutation of the resulting blastocysts irrespective of cumulus cell attachment and electroporation timing. In conclusion, the electroporation timing and the cumulus cell attachment did not interfere with the efficient delivery of the CRISPR/Cas9 system to the oocytes/zygotes, indicating that porcine genome editing in the oviduct using GONAD method may be possible.