Koki Takebayashi

Background and Aim: Electroporation-mediated delivery of Clustered-Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein 9 components is an effective approach for genome editing in porcine embryos; however, mosaicism remains a major limitation. Selecting normally fertilized zygotes with two pronuclei (2PN) before electroporation may improve editing uniformity and reduce mosaicism. Therefore, this study investigated the effects of 2PN selection, optimized timing of pronuclear observation, and Hoechst 33342 staining conditions on embryo development and genome editing efficiency in porcine embryos. Materials and Methods: In the first experiment, pronuclear dynamics after in vitro fertilization (IVF) were evaluated by collecting zygotes at 8–24 h post-fertilization, followed by centrifugation, fixation, and Hoechst 33342 staining. In the second experiment, the effects of Hoechst 33342 concentration (5 and 10 μg/mL) and exposure duration (10 and 30 min) on embryo development were assessed using live zygotes collected 20 h after fertilization. In the third experiment, zygotes with visible 2PN selected after centrifugation and Hoechst staining were electroporated with guide RNA targeting the TP53 gene. Developmental competence, mutation efficiency, and mosaicism were compared with non-selected control zygotes. Results: The proportion of zygotes with 2PN gradually increased after fertilization and reached the highest level (47.4%) at 20 h post-IVF before significantly declining at 24 h (p < 0.05). Among the staining conditions tested, treatment with 5 μg/mL Hoechst 33342 for 30 min resulted in the highest blastocyst formation rate (14.3%, p < 0.05). Following electroporation, blastocyst development rates did not differ significantly between the 2PN-selected group (6.5%) and the control group (10.8%). Similarly, the biallelic mutation rate and total mutation efficiency were comparable between selected zygotes (78.6% and 85.5%, respectively) and controls (81.8% and 92.5%, respectively). Conclusion: Selection of porcine zygotes with 2PN before electroporation did not improve genome editing efficiency or reduce mosaicism despite optimization of pronuclear observation timing and Hoechst staining conditions. The persistence of mosaicism may be associated with asynchronous DNA replication between maternal and paternal pronuclei. Although 2PN selection was safe for embryo development, additional strategies targeting pronuclear synchronization and replication timing are required to achieve more uniform genome editing in porcine embryos. Keywords: blastocyst development, CRISPR/Cas9, electroporation, genome editing, Hoechst 33342, mosaicism, porcine embryos, two pronuclei.

Background and Aim: The antioxidant effects of ergothioneine (EGT) on in vitro culture of porcine zygote are not well established. The study investigated the impact of EGT supplementation on meiotic competence and development of porcine oocytes. Materials and Methods: The impact of EGT concentrations (0, 5, 10, 25, 50, and 100 μM) during in vitro maturation (IVM) on the progression of meiotic maturation, fertilization, and blastocyst formation in porcine oocytes was assessed. The DNA fragmentation level was evaluated to determine oocyte and blastocyst quality. Results: The proportion of metaphase II oocytes was significantly greater (p < 0.05) in EGT-cultured oocytes than in control oocytes, regardless of the EGT concentration, and those oocytes with 10 μM or more EGT had fewer DNA-fragmented nuclei (p < 0.05). Blastocysts derived from oocytes cultured with 10 μM EGT had the highest proportion (p < 0.05), while those from control oocytes or oocytes cultured with 50 μM or less EGT had significantly higher proportions. Despite EGT supplementation, there were no noticeable differences in total cell numbers and DNA fragmentation indices in the derived blastocysts. Conclusion: Supplementing with EGT during IVM leads to better oocyte maturation, quality, and embryonic development due to decreased DNA fragmentation. The present study failed to elucidate the mechanism of DNA fragmentation reduction by EGT. More research needs to be conducted to explore the antioxidant mechanism of EGT. Keywords: antioxidant, DNA fragmentation, ergothioneine, maturation, porcine oocytes.

Background and Aim: Mosaicism – the presence of both wild-type and mutant alleles – is a serious problem for zygotic gene modification through gene editing using the Clustered regularly interspaced short palindromic repeats-Cas9 (CRISPR/ Cas9) system. Different delivery methods, such as microinjection (MI), electroporation (EP), and transfection (TF), can be used to transfer CRISPR/Cas9 components into porcine zygotes. This study aimed to develop a method that combines MI, EP, and TF to improve mutation efficiency mediated through the CRISPR/Cas9 system for a triple-gene knockout in pigs. Materials and Methods: The study consisted of three groups: The MI group with three simultaneously microinjected guide RNAs (gRNAs) targeting α-1,3-galactosyltransferase (GGTA1), cytidine 32 monophosphate-N-acetylneuraminic acid hydroxylase (CMAH), and β-1,4-N-acetyl-galactosaminyltransferase 2 (B4GALNT2); the MI + EP group with two gRNAs targeting GGTA1 and B4GALNT2 genes delivered into zygotes through MI, followed by EP of gRNA targeting the CMAH 1 h later; and the MI + EP + TF group with MI of gRNA targeting GGTA1 gene into zygotes, followed by EP of gRNA targeting CMAH 1 h later, and then TF of gRNA targeting the B4GALNT2 gene into zona-free zygotes after another hour. Results: The rate of blastocysts carrying mutations in one or two gene(s) was significantly higher in the MI + EP + TF group than in the MI group. However, the blastocyst formation rate of zygotes in the MI + EP + TF group was lower than that of the zygotes in the other treatment groups. Conclusion: The combination of CRISPR/Cas9 delivery methods may improve the mutation efficiency of triple-gene edited porcine blastocysts.

Background and Aim: We previously developed the gene-editing by electroporation (EP) of Cas9 protein method, in which the CRISPR/Cas9 system was introduced into porcine in vitro fertilized (IVF) zygotes through EP to disrupt a target gene. This method should be further developed, and a combination of EP and MI methods should be evaluated in pigs. This study aimed to determine that a combination of microinjection (MI) and EP of CRISPR/Cas9 system could increase the rates of biallelic mutation for triple-gene knockout in porcine blastocysts. We targeted the pancreatic and duodenal homeobox1 (PDX1) gene using cytoplasmic MI 1 h before or after EP, which was used to edit alpha-1,3-galactosyltransferase (GGTA1) and cytidine 32 monophosphate-N-acetylneuraminic acid hydroxylase (CMAH) genes in porcine zygotes. Materials and Methods: We introduced guide RNAs targeting PDX1, GGTA1, and CMAH with the Cas9 protein into IVF zygotes (one-cell stage) through EP 10 h after the start of IVF (IVF; EP group) or in combination with MI (1 h before, MI-EP group, or after EP treatment EP-MI group) and evaluated the blastocyst formation rate and efficiency of target mutations in the resulting blastocysts. Results: Our results revealed a significant reduction in the rate of blastocyst formation in the two groups that underwent MI before and after EP (MI-EP and EP-MI group), compared with that in the groups treated with EP alone (EP group) (p=0.0224 and p<0.0001, respectively) and control (p=0.0029 and p<0.0001, respectively). There was no significant difference in the total mutation rates among the treatment groups in the resulting blastocysts. As an only positive effect of additional MI treatment, the rate of blastocysts carrying biallelic mutations in at least one target gene was higher in the MI-EP group than in the EP group. However, there was no difference in the rates of embryos carrying biallelic mutations in more than 2 target genes. Conclusion: These results indicate that although a combination of MI and EP does not improve the mutation efficiency or biallelic mutation for triple-gene knockout, MI treatment before EP is better to reduce mortality in porcine zygotic gene editing through a combination of MI and EP.

Liposome-mediated gene transfer has become an alternative method for establishing a gene targeting framework, and the production of mutant animals may be feasible even in laboratories without specialized equipment. However, how this system functions in mammalian oocytes and embryos remains unclear. The present study was conducted to clarify whether blastocyst genome editing can be performed by treatment with lipofection reagent, guide RNA, and Cas9 for 5 h without using electroporation or microinjection. A mosaic mutation was observed in blastocysts derived from zona pellucida (ZP)-free oocytes following lipofection treatment, regardless of the target genes. When lipofection treatment was performed after in vitro fertilization (IVF), no significant differences in the mutation rates or mutation efficiency were found between blastocysts derived from embryos treated at 24 and 29 h from the start of IVF. Only blastocysts from embryos exposed to lipofection treatment at 29 h after IVF contained biallelic mutant. Furthermore, there were no significant differences in the mutation rates or mutation efficiency between blastocysts derived from embryos at the 2- and 4-cell stages. This suggests that lipofection-mediated gene editing can be performed in ZP-free oocytes and ZP-free embryos; however, other factors affecting the system efficiency should be further investigated.