谷原 史倫

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.

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 alpha-galactosyltransferase 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.

BACKGROUND AND AIM: Mosaicism, which is characterized by the presence of wild-type and more than one mutant allele, poses a serious problem in zygotic gene modification through the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 system. Therefore, we used pig embryos to compare the gene editing efficiencies achieved by combining electroporation and lipofection using different aminopeptidase N (APN)-targeting guide RNA (gRNA) sequences. MATERIALS AND METHODS: Six gRNAs (gRNA1-6) with different target sequences were designed to target APN. Zona pellucida (ZP)-intact zygotes collected 10 h after the start of in vitro fertilization (IVF) were electroporated with each gRNA to compare their gene editing efficiency. The gRNA sequences that achieved the lowest and highest mutation rates (gRNA4 and gRNA6, respectively) were selected for additional lipofection to assess gene editing efficiency following combined treatment. As ZP removal is essential for lipofection, ZP-free zygotes were electroporated with gRNA4 or gRNA6 10 h after IVF initiation, followed by lipofection with the same gRNAs 24 or 29 h after IVF initiation. The electroporated ZP-intact and ZP-free zygotes were used as controls. RESULTS: gRNA4 and gRNA6 exhibited the lowest and highest mutation rates, respectively. gRNA4-targeted ZP-free embryos subjected to additional lipofection 29 h after IVF initiation exhibited significantly higher total and biallelic mutation rates than ZP-intact embryos that received only electroporation. Additional lipofection of gRNA6-targeted embryos had no obvious effect on mutation rates. CONCLUSION: Electroporation combined with lipofection using gRNAs with low mutation rates may improve gene editing efficiency in pig embryos. However, the effects may vary based on the timing of gene editing.

The generation of genetically engineered pig models that develop pancreas-specific tumors has the potential to advance studies and our understanding of pancreatic cancer in humans. TP53 mutation causes organ-nonspecific cancers, and PDX1-knockout results in the loss of pancreas development. The aim of the present study was to generate a PDX1-knockout pig chimera carrying pancreas complemented by TP53 mutant cells via phytohemagglutinin (PHA)-mediated blastomere aggregation using PDX1 and TP53 mutant blastomeres, as a pig model for developing tumors in the pancreas with high frequency. First, the concentration and exposure time to PHA to achieve efficient blastomere aggregation were optimized. The results showed that using 300 µg/mL PHA for 10 min yielded the highest rates of chimeric blastocyst formation. Genotyping analysis of chimeric blastocysts derived from aggregated embryos using PDX1- and TP53-edited blastomere indicated that approximately 28.6% carried mutations in both target regions, while 14.3-21.4% carried mutations in one target. After the transfer of the chimeric blastocysts into one recipient, the recipient became pregnant with three fetuses. Deep sequencing analysis of the PDX1 and TP53 regions using ear and pancreas samples showed that one fetus carried mutations in both target genes, suggesting that the fetus was a chimera derived from embryo-aggregated PDX1 and TP53 mutant blastomeres. Two out of three fetuses carried only the PDX1 mutation, indicating that the fetuses developed from embryos not carrying TP53-edited blastomeres. The results of the present study could facilitate the further improvement and design of high-frequency developing pancreatic tumor models in pigs.