Oocyte electroporation prior to in vitro fertilization is an efficient method to generate single, double, and multiple knockout porcine embryos of interest in biomedicine and animal production.

Genetically modified pigs play a critical role in mimicking human diseases, xenotransplantation, and the development of pigs resistant to viral diseases. The use of programmable endonucleases, including the CRISPR/Cas9 system, has revolutionized the generation of genetically modified pigs. This study evaluates the efficiency of electroporation of oocytes prior to fertilization in generating edited gene embryos for different models. For single gene editing, phospholipase C zeta (PLC ζ) and fused in sarcoma (FUS) genes were used, and the concentration of sgRNA and Cas9 complexes was optimized. The results showed that increasing the concentration resulted in higher mutation rates without affecting the blastocyst rate. Electroporation produced double knockouts for the TPC1/TPC2 genes with high efficiency (79 %). In addition, resistance to viral diseases such as PRRS and swine influenza was achieved by electroporation, allowing the generation of double knockout embryo pigs (63 %). The study also demonstrated the potential for multiple gene editing in a single step using electroporation, which is relevant for xenotransplantation. The technique resulted in the simultaneous mutation of 5 genes (GGTA1, B4GALNT2, pseudo B4GALNT2, CMAH and GHR). Overall, electroporation proved to be an efficient and versatile method to generate genetically modified embryonic pigs, offering significant advances in biomedical and agricultural research, xenotransplantation, and disease resistance. Electroporation led to the processing of numerous oocytes in a single session using less expensive equipment. We confirmed the generation of gene-edited porcine embryos for single, double, or quintuple genes simultaneously without altering embryo development to the blastocyst stage. The results provide valuable insights into the optimization of gene editing protocols for different models, opening new avenues for research and applications in this field.

Optimizing oocyte electroporation for genetic modification of porcine embryos: Evaluation of the parthenogenetic activation.

In reproductive biology, understanding the effects of novel techniques on early embryo development is of paramount importance. To date, the effects of electrical activation on oocytes prior to in vitro fertilization (IVF) are not well understood. The aim of this study was to investigate the effects of oocyte electroporation prior to IVF on embryo development and to differentiate between true embryos and parthenotes by using a TPCN2 knock-out (KO) male to evaluate the presence of the KO allele in the resulting blastocysts. The study consisted of three experiments. The first one examined oocyte electroporation with and without subsequent IVF and found that electroporated oocytes had higher activation rates, increased occurrence of a single pronucleus, and no effect on sperm penetration. Cleavage rates improved in electroporated oocytes, but blastocyst rates remained constant. Genotype analysis revealed a significant increase in the proportion of parthenotes in the electroporated groups compared to the IVF control (30.2 % vs. 6.8 %). The second experiment compared two electroporation media, Opti-MEM and Nuclease-Free Duplex Buffer (DB). DB induced higher oocyte degeneration rates, and lower cleavage and blastocyst rates than Opti-MEM, while parthenogenetic formation remained consistent (60.0 and 48.5 %). In the third experiment, the timing of electroporation relative to IVF was evaluated (1 h before IVF, immediately before IVF and 7 h after IVF). Electroporation immediately before IVF resulted in higher activation rates and different pronuclear proportions compared to the other timing groups. The penetration rate was higher in the immediate electroporation group, and cleavage rate improved in all electroporated groups compared to the control. Blastocyst rates remained constant. Genotyping revealed no significant differences in parthenote proportions among the timing groups, but these were higher than the control (56.25 %, 63.89 %, 51.61 %, 2.44 %, respectively), and showed higher mutation rates when electroporation was performed 7 h after IVF. Overall, this comprehensive study sheds light on the potential of electroporation for creating genetically modified embryos and the importance of media selection and timing in the process, the best media being the Opti-MEM and the more efficient timing regarding mutation rate, 7 h post-IVF, even when the parthenote formation did not differ among electroporated groups. Further studies are needed to reduce the parthenogenetic activation while maintaining high mutation rates to optimize the use of this procedure for the generation of gene-edited pig embryos by oocyte/zygote electroporation.

Electroporation-based Easi-CRISPR yields biallelic insertions of EGFP-HiBiT cassette in immortalized chicken oviduct epithelial cells.

Laying hens are an excellent experimental oviduct model for studying reproduction biology. Because chicken oviduct epithelial cells (cOECs) have a crucial role in synthesizing and secreting ovalbumin, laying hens have been regarded an ideal bioreactor for producing pharmaceuticals in egg white through transgene or gene editing of the ovalbumin (OVA) gene. However, related studies in cOECs are largely limited because of the lack of immortalized model cells. In addition, the editing efficiency of conventional CRISPR-HDR knock-in in chicken cells is suboptimal (ranging from 1 to 10%) and remains elevated. Here, primary cOECs were isolated from young laying hens, then infected with a retrovirus vector of human telomerase reverse transcriptase (hTERT), and immortalized cOECs were established. Subsequently, an electroporation-based Easi-CRISPR (Efficient additions with ssDNA inserts-CRISPR) method was adopted to integrate an EGFP-HiBiT cassette into the chicken OVA locus (immediately upstream of the stop codon). The immortalized cOECs reflected the self-renewal capability and phenotype of oviduct epithelial cells. This is because these cells not only maintained stable proliferation and normal karyotype and had no potential for malignant transformation, but also expressed oviduct markers and an epithelial marker and had a morphology similar to that of primary cOECs. EGFP expression was detected in the edited cells through microscopy, flow cytometry, and HiBiT/Western blotting. The EGFP-HiBiT knock-in efficiency reached 27.9% after a single round of electroporation, which was determined through genotyping and DNA sequencing. Two single cell clones contained biallelic insertions of EGFP-HiBiT donor cassettes. In conclusion, our established immortalized cOECs could act as an in vitro cell model for gene editing in chicken, and this electroporation-based Easi-CRISPR strategy will contribute to the generation of avian bioreactors and other gene-edited (GE) birds.

Efficiency of genetic modification in gene-knockout sperm-derived zygotes followed by electroporation of guide RNA targeting the same gene.

Genetic mosaicism is considered one of the main limitations of the electroporation method used to transfer CRISPR-Cas9/guide RNA (gRNA) into porcine zygotes. We hypothesized that fertilization of oocytes with sperm from gene-deficient boars, in combination with electroporation (EP) to target the same region of the gene in subsequent zygotes, would increase the gene modification efficiency. As myostatin (MSTN) and α1,3-galactosyltransferase (GGTA1) have beneficial effects on agricultural production and xenotransplantation, respectively, we used these two genes to test our hypothesis. Spermatozoa from gene-knockout boars were used for oocyte fertilization in combination with EP to transfer gRNAs targeting the same gene region to zygotes. No significant differences in the rates of cleavage and blastocyst formation as well as in the mutation rates of blastocysts were observed between the wild-type and gene-deficient spermatozoa groups, irrespective of the targeted gene. In conclusion, the combination of fertilization with gene-deficient spermatozoa and gene editing of the same targeted gene region using EP had no beneficial effects on embryo genetic modification, indicating that EP alone is a sufficient tool for genome modification.

Irreversible Electroporation Balloon Therapy for Palliative Treatment of Obstructive Urethral Transitional Cell Carcinoma in Dogs.

Progression of transitional cell carcinoma (TCC) in dogs often leads to urinary obstruction. This observational pilot study aimed to evaluate the safety and efficacy of irreversible electroporation (IRE) balloon therapy for the palliative treatment of TCC with partial urethral obstruction. Three client-owned dogs diagnosed with TCC causing partial urethral obstruction were enrolled. After ultrasonographic and cystoscopic examination, IRE pulse protocols were delivered through a balloon catheter device inflated within the urethral lumen. After the procedure, the patients were kept overnight for monitoring and a recheck was planned 28 days later. No complication was observed during the procedure and postprocedural monitoring. After 28 days, one dog had a complete normalization of the urine stream, one dog had stable stranguria, and one dog was presented with a urethral obstruction secondary to progression of the TCC. On recheck ultrasound, one dog had a 38% diminution of the urethral mass diameter whereas the other two dogs had a mass stable in size. IRE balloon therapy seems to be a feasible and apparently safe minimally invasive novel therapy for the palliative treatment of TCC causing urethral obstruction. Further studies are needed to better characterize the safety, efficacy, and outcome of this therapy.

Germline transmission of MSTN knockout cattle via CRISPR-Cas9.

Although the production of several founder animals (F0) for gene editing in livestock has been reported in cattle, very few studies have assessed germline transmission to the next generation due to the long sexual maturation and gestation periods. The present study aimed to assess the germline transmission of MSTN mutations (-12bps deletion) in MSTN mutant F0 male and female cattle. For this purpose, oocytes and semen were collected after the sexual maturation of MSTN cattle, and embryos produced by in vitro fertilization were analyzed. In addition, the embryos were subjected to additional gene (PRNP) editing using electroporation. Embryos produced by in vitro fertilization with MSTN male and female cattle were transferred to a surrogate, and one calf was successfully born. MSTN heterozygous mutation was shown by sequencing of the F1 calf, which had no health issues. As a further experiment, using electroporation, additional gene-edited embryos fertilized with the MSTN male sperm showed a high mutation rate of PRNP (86.2 ± 3.4%). These data demonstrate that the cattle produced through gene editing matured without health issues and had transmitted MSTN mutation from the germ cells. Also, additional mutation of embryos fertilized with the MSTN male sperm could enable further mutagenesis using electroporation.

Gene editing in porcine embryos using a combination of electroporation and transfection methods.

CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats-CRISPR-associated protein 9) technology is growing rapidly and has been greatly influencing the efficiency and effectiveness of genetic modifications in different applications. One aspect of research gaining importance in the development of the CRISPR/Cas9 system is the introduction of CRISPR materials into target organisms. Although we previously demonstrated the efficacy of electroporation- and lipofection-mediated CRISPR/Cas9 gene disruption in porcine zygotes, we still believe that the efficiency of this system could be improved by combining these two methods. The present study was thus conducted to clarify the effects of a combination of electroporation and lipofection for delivering CRISPR/Cas9 components into zona pellucida (ZP)-intact and -free zygotes. The results revealed that electroporation alone significantly increased the biallelic mutation rates in the resulting blastocysts compared to lipofection alone, irrespective of the presence of ZP. None of ZP-intact zygotes treated by lipofectamine alone had any mutations, suggesting that removal of the ZP is necessary for enabling CRISPR/Cas9-based genome editing via lipofection treatment in the zygotes. Additional lipofectamine treatment after electroporation did not improve the rates of total and biallelic mutations in the resulting blastocysts derived from either ZP-intact or -free zygotes.

Generation of Calpain-3 knock-out porcine embryos by CRISPR-Cas9 electroporation and intracytoplasmic microinjection of oocytes before insemination.

Limb girdle muscular dystrophy type R1 (LGMDR1) is an autosomal recessive myopathy described in humans resulting from a deficiency of calpain-3 protein (CAPN3). This disease lacks effective treatment and an appropriate model, so the generation of KO pigs by CRISPR-Cas9 offers a way to better understand disease ethology and to develop novel therapies. Microinjection is the main method described for gene editing by CRISPR-Cas9 in porcine embryo, but electroporation, which allows handling more embryos faster and easier, has also recently been reported. The objective of the current study was to optimize porcine oocyte electroporation to maximize embryo quality and mutation rate in order to efficiently generate LGMDR1 porcine models. We found that the efficiency of generating CAPN3 KO embryos was highest with 4 electroporation pulses and double sgRNA concentration than microinjection. Direct comparison between microinjection and electroporation demonstrated similar rates of embryo development and mutation parameters. The results of our study demonstrate that oocyte electroporation, an easier and faster method than microinjection, is comparable to standard approaches, paving the way for democratization of transgenesis in pigs.

Visualization of Sox10-positive chromatoblasts by GFP fluorescence in flounder larvae and juveniles using electroporation.

Japanese flounder are left-right asymmetrical, with features, such as dark, ocular-side specific pigmentation. This pigmentation arises during metamorphic stages, along with the asymmetric differentiation of adult-type chromatophores. Additionally, among juveniles, tank-reared specimens commonly show ectopic pigmentation on their blind sides. In both cases, neural crest-derived Sox10-positive progenitor cells at the dorsal fin base are hypothesized to contribute to chromatophore development. Here, we developed a method to visualize Sox10-positive cells via green fluorescent protein (GFP) fluorescence to directly monitor their migration and differentiation into chromatophores in vivo. Electroporation was applied to introduce GFP reporter vectors into the dorsal fin base of larvae and juveniles. Cre-loxP system vectors were also tested to enable cell labeling even after a decrease in sox10 expression levels. In larvae, undifferentiated Sox10-positive progenitor cells were labeled in the dorsal fin base, whereas newly differentiated adult-type chromatophores were seen dispersed on the ocular side. In juveniles, Sox10-positive cells were identified in the connective tissue of the dorsal fin base and observed prominently in areas of ectopic pigmentation, including several labeled melanophores. Thus, it was suggested that during metamorphic stages, Sox10-positive cells at the dorsal fin base contribute to adult-type chromatophore development, whereas in juveniles, they persist as precursors in the connective tissue, which in response to stimuli migrate to generate ectopic pigmentation. These findings contribute to elucidating pigmentation mechanisms, as well as abnormalities seen in hatchery-reared flounders. The electroporation method may be adapted to diverse animals as an accessible gene transfer method in various research fields, including developmental and biomedical studies.

Generation of CD163-edited pig via electroporation of the CRISPR/Cas9 system into porcine in vitro-fertilized zygotes.

CD163 is a putative fusion receptor for virus of porcine reproductive and respiratory syndrome (PRRS). In this study, we introduced a CRISPR/Cas9 system [guide RNAs (gRNAs) with Cas9 protein] targeting the CD163 gene into in vitro-fertilized porcine zygotes by electroporation to generate CD163-modified pigs. First, we designed four types of gRNAs that targeted distinct sites in exon 7 of the CD163 gene. Cas9 protein with different gRNAs was introduced into in vitro-fertilized zygotes by electroporation. When the electroporated zygotes were allowed to develop to blastocysts in vitro and the genome editing efficiency was evaluated using these blastocysts, three (gRNA1, 2, and 4) of the four gRNAs tested successfully edited the CD163 gene. To generate CD163-knockout pigs, a total of 200 electroporated zygotes using these three gRNAs were transferred into the oviducts of oestrous-synchronized surrogate and the surrogate gave birth to eight piglets. Subsequent sequence analysis revealed that one of the piglets carried no wild-type sequence in CD163 gene. The other seven piglets carried only wild-type sequence. Thus, we successfully generated a CD163-edited pig by electroporation of the CRISPR/Cas9 system into in vitro-fertilized zygotes, although further improvement is required to generate genetically modified pigs with high efficiency.

Effects of electroporation treatment using different concentrations of Cas9 protein with gRNA targeting Myostatin (MSTN) genes on the development and gene editing of porcine zygotes.

This study was conducted to investigate the effect of seven concentrations of Cas9 protein (0, 25, 50, 100, 200, 500, and 1,000 ng/µl) on the development and gene editing of porcine embryos. This included the target editing and off-target effect of embryos developed from zygotes that were edited via electroporation of the Cas9 protein with guide RNA targeting Myostatin genes. We found that the development to blastocysts of electroporated zygotes was not affected by the concentration of Cas9 protein. Although the editing rate, which was defined as the ratio of edited blastocysts to total examined blastocysts, did not differ with Cas9 protein concentration, the editing efficiency, which was defined as the frequency of indel mutations in each edited blastocyst, was significantly decreased in the edited blastocysts from zygotes electroporated with 25 ng/µl of Cas9 protein compared with that of blastocysts from zygotes electroporated with higher Cas9 protein concentrations. Moreover the frequency of indel events at the two possible off-target sites was not significantly different with different concentrations of Cas9 protein. These results indicate that the concentration of Cas9 protein affects gene editing efficiency in embryos but not the embryonic development, gene editing rate, and non-specific cleavage of off-target sites.

Evaluation of multiple gene targeting in porcine embryos by the CRISPR/Cas9 system using electroporation.

The CRISPR/Cas9 system now allows for unprecedented possibilities of genome editing. However, there are some limitations, including achieving efficient one-step multiple genome targeting to save costs, time, and ensure high quality. In the present study, we investigated the efficiency of one-step multiple gene modification by electroporation in porcine zygotes using pooled guide RNAs (gRNAs) targeting CMAH, GHR, GGTA1, and PDX1. We first selected the best-performing gRNA from three different designs for each gene based on the effect on embryo development and mutation efficiency. The three gRNAs showed equivalent effects on the rates of blastocyst formation in each targeted gene; however, gRNAs CMAH #2, GHR #3, GGTA1 #3, and PDX1 #3 showed the highest biallelic mutation rate, although the total mutation rate of PDX1 #3 was significantly lower than that of PDX1 #1. Therefore, CMAH #2, GHR #3, GGTA1 #3, and PDX1 #1 were used as a mixture in electroporation to further clarify whether multiple genes can be targeted simultaneously. Individual sequencing of 43 blastocysts at the target sites of each gene showed mutations in one and two target genes in twenty-four (55.8%) and nine (20.9%) blastocysts, respectively. No mutation was detected in any target gene in ten (23.3%) blastocysts and no blastocysts had a mutation in three or more target genes. These results indicate that electroporation could effectively deliver multiple gRNAs and Cas9 protein into porcine zygotes to target multiple genes in a one-step process. However, the technique requires further development to increase the success rate of multiple gene modification.

High-Frequency Irreversible Electroporation for Treatment of Primary Liver Cancer: A Proof-of-Principle Study in Canine Hepatocellular Carcinoma.

PURPOSE: To determine the safety and feasibility of percutaneous high-frequency irreversible electroporation (HFIRE) for primary liver cancer and evaluate the HFIRE-induced local immune response. MATERIALS AND METHODS: HFIRE therapy was delivered percutaneously in 3 canine patients with resectable hepatocellular carcinoma (HCC) in the absence of intraoperative paralytic agents or cardiac synchronization. Pre- and post-HFIRE biopsy samples were processed with histopathology and immunohistochemistry for CD3, CD4, CD8, and CD79a. Blood was collected on days 0, 2, and 4 for complete blood count and chemistry. Numeric models were developed to determine the treatment-specific lethal thresholds for malignant canine liver tissue and healthy porcine liver tissue. RESULTS: HFIRE resulted in predictable ablation volumes as assessed by posttreatment CT. No detectable cardiac interference and minimal muscle contraction occurred during HFIRE. No clinically significant adverse events occurred secondary to HFIRE. Microscopically, a well-defined ablation zone surrounded by a reactive zone was evident in the majority of samples. This zone was composed primarily of maturing collagen interspersed with CD3+/CD4-/CD8- lymphocytes in a proinflammatory microenvironment. The average ablation volumes for the canine HCC patients and the healthy porcine tissue were 3.89 cm3 ± 0.74 and 1.56 cm3 ± 0.16, respectively (P = .03), and the respective average lethal thresholds were 710 V/cm ± 28.2 and 957 V/cm ± 24.4 V/cm (P = .0004). CONCLUSIONS: HFIRE can safely and effectively be delivered percutaneously, results in a predictable ablation volume, and is associated with lymphocytic tumor infiltration. This is the first step toward the use of HFIRE for treatment of unresectable liver tumors.

Health-related quality of life in dogs treated with electrochemotherapy and/or interleukin-12 gene electrotransfer.

The aim of this study was to evaluate the owners' perception of health-related quality of life (HRQoL) of dogs after treatment with electrochemotherapy (ECT) alone or combined with interleukin-12 gene electrotransfer (IL-12 GET) and/or surgery. The owners of 44 dogs with histologically different tumours were offered the ¼Cancer Treatment Form« at least one month after treatment. The owners assessed their dogs' quality of life (QoL) after treatment as good (mean 7.4) (from 1-very poor to 10-excellent) and the general health compared with the initial diagnosis of cancer as improving (mean 3.9) (from 1-worse to 5-better). The assessment of the current QoL was better within the group of dogs treated with non-invasive treatment (ECT and/or IL-12 GET only), compared with those that received invasive treatment, where, in addition to ECT and/or IL-12 GET, surgery was performed (p < .05). The owners of dogs that achieved an objective response (OR) to the treatment assessed the QoL as significantly better compared with those whose dogs did not respond to the treatment (p < .05). The majority of the owners (86.4%) would opt for the therapy again, regardless of the financial costs. In conclusion, the results of this study demonstrate that the majority of the owners of dogs assessed their dogs' QoL as good and felt that it improved after the treatment, especially in dogs, treated with non-invasive treatment and in those that responded to the treatment. This supports further use of ECT and IL-12 GET as suitable methods for the treatment of selected tumours in veterinary medicine.

Introduction of a plasmid and a protein into bovine and swine cells by water-in-oil droplet electroporation.

Instrument cost is a major problem for the transduction of DNA fragments and proteins into cells. Water-in-oil droplet electroporation (droplet-EP) was recently invented as a low-cost and effective method for the transfection of plasmids into cultured human cells. We here applied droplet-EP to livestock animal cells. Although it is difficult to transfect plasmids into bovine fibroblasts using conventional lipofection methods, droplet-EP enabled us to introduce an enhanced green fluorescent protein (EGFP)-expressing plasmid into bovine earlobe fibroblasts. The optimal transfection condition was 3.0 kV, which allowed 19.1% of the cells to be transfected. For swine earlobe fibroblasts, the maximum transfection efficacy was 14.0% at 4.0 kV. After transfection with droplet-EP, 69.1% of bovine and 76.5% of swine cells were viable. Furthermore, droplet-EP successfully transduced Escherichia coli recombinant EGFP into frozen-thawed bovine sperm at 1.5 kV. Flow cytometry analysis revealed that 71.5% of spermatozoa exhibited green fluorescence after transfection. Overall, droplet-EP is suitable for the transfection of plasmids and proteins into cultured livestock animal cells.

Efficient derivation of knock-out and knock-in rats using embryos obtained by in vitro fertilization.

Rats are effective model animals and have contributed to the development of human medicine and basic research. However, the application of reproductive engineering techniques to rats is not as advanced compared with mice, and genome editing in rats has not been achieved using embryos obtained by in vitro fertilization (IVF). In this study, we conducted superovulation, IVF, and knock out and knock in using IVF rat embryos. We found that superovulation effectively occurred in the synchronized oestrus cycle and with anti-inhibin antiserum treatment in immature rats, including the Brown Norway rat, which is a very difficult rat strain to superovulate. Next, we collected superovulated oocytes under anaesthesia, and offspring derived from IVF embryos were obtained from all of the rat strains that we examined. When the tyrosinase gene was targeted by electroporation in these embryos, both alleles were disrupted with 100% efficiency. Furthermore, we conducted long DNA fragment knock in using adeno-associated virus and found that the knock-in litter was obtained with high efficiency (33.3-47.4%). Thus, in this study, we developed methods to allow the simple and efficient production of model rats.

Simplified pipelines for genetic engineering of mammalian embryos by CRISPR-Cas9 electroporation†.

Gene editing technologies, such as CRISPR-Cas9, have important applications in mammalian embryos for generating novel animal models in biomedical research and lines of livestock with enhanced production traits. However, the lack of methods for efficient introduction of gene editing reagents into zygotes of various species and the need for surgical embryo transfer in mice have been technical barriers of widespread use. Here, we described methodologies that overcome these limitations for embryos of mice, cattle, and pigs. Using mutation of the Nanos2 gene as a readout, we refined electroporation parameters with preassembled sgRNA-Cas9 RNPs for zygotes of all three species without the need for zona pellucida dissolution that led to high-efficiency INDEL edits. In addition, we optimized culture conditions to support maturation from zygote to the multicellular stage for all three species that generates embryos ready for transfer to produce gene-edited animals. Moreover, for mice, we devised a nonsurgical embryo transfer method that yields offspring at an efficiency comparable to conventional surgical approaches. Collectively, outcomes of these studies provide simplified pipelines for CRISPR-Cas9-based gene editing that are applicable in a variety of mammalian species.

Comparison between electroporation and polyfection in pig sperm: efficiency and cell viability implications.

SummaryThe aim of this study was to optimize protocols for electroporation (EP) and polyfection (PLF) using polyethyleneimine (PEI) for pig sperm transfection and to determine which method was the most efficient. For EP standardization, different voltages, amounts and times of electric pulses were tested using propidium iodide (PI) as reporter. For PLF standardization, different concentrations of fluorescein isothiocyanate (FITC)-labelled PEI (PEI/FITC) were incubated with sperm for different periods of time. Flow cytometry was performed to evaluate the best protocol in terms of cell viability, including cytoplasmic membrane, acrosome, chromatin integrities and mitochondrial potential using the FITC probe, PI, acridine orange (AO) and JC1. Transfections with the plasmid pmhyGENIE-5 were carried out under optimum conditions for each procedure (EP: 500 volts, 500 µs and two pulses; PLF: PEI 0.5 mg/ml and incubation time 10 min). Transfection efficacy was assessed by fluorescence in situ hybridization (FISH). A lower transfection rate was observed for sperm in the control group (17.8%) compared with EP (36.7%), with PLF (76.8%) being the most efficient. These results suggest that the EP and PEI could be an efficient and low cost transfection method for swine sperm. Notably, treated cells showed higher plasmatic the membrane damage (PMD) and/or acrosome damage (AD) indexes, therefore the combination of this procedure with biotechniques that facilitate fecundation (i.e. in vitro fertilization or intracytoplasmic sperm injection) or even inclusion of antioxidant or anti-apoptotic drugs to improve spermatozoa viability would be important.

Reproductive technologies for the generation and maintenance of valuable animal strains.

Many types of mutant and genetically engineered strains have been produced in various animal species. Their numbers have dramatically increased in recent years, with new strains being rapidly produced using genome editing techniques. In the rat, it has been difficult to produce knockout and knock-in strains because the establishment of stem cells has been insufficient. However, a large number of knockout and knock-in strains can currently be produced using genome editing techniques, including zinc-finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN), and the clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 9 (Cas9) system. Microinjection technique has also contributed widely to the production of various kinds of genome edited animal strains. A novel electroporation method, the "Technique for Animal Knockout system by Electroporation (TAKE)" method, is a simple and highly efficient tool that has accelerated the production of new strains. Gamete preservation is extremely useful for maintaining large numbers of these valuable strains as genetic resources in the long term. These reproductive technologies, including microinjection, TAKE method, and gamete preservation, strongly support biomedical research and the bio-resource banking of animal models. In this review, we introduce the latest reproductive technologies used for the production of genetically engineered animals, especially rats, using genome editing techniques and the efficient maintenance of valuable strains as genetic resources. These technologies can also be applied to other laboratory animals, including mice, and domestic and wild animal species.

Effects of voltage strength during electroporation on the development and quality of in vitro-produced porcine embryos.

This study was conducted to determine suitable conditions for an experimental method in which the CRISPR/Cas9 system is introduced into in vitro-produced porcine zygotes by electroporation. In the first experiment, when putative zygotes derived from in vitro fertilization (IVF) were electroporated by either unipolar or bipolar pulses, keeping the voltage, pulse duration and pulse number fixed at 30 V/mm, 1 msec and five repeats, respectively, the rate of blastocyst formation from zygotes electroporated by bipolar pulses decreased compared to zygotes electroporated by unipolar pulses. In the second experiment, the putative zygotes were electroporated by electroporation voltages ranging from 20 V/mm-40 V/mm with five 1-msec unipolar pulses. The rate of cleavage and blastocyst formation of zygotes electroporated at 40 V/mm was significantly lower (p < .05) than that of zygotes electroporated at less than 30 V/mm. Moreover, the apoptotic nuclei indices of blastocysts derived from zygotes electroporated by voltages greater than 30 V/mm significantly increased compared with those from zygotes electroporated by voltages less than 25 V/mm (p < .05). When zygotes were electroporated with Cas9 mRNA and single-guide RNA (sgRNA) targeting site in the FGF10 exon 3, the proportions of blastocysts with targeted genomic sequences were 7.7% (2/26) and 3.6% (1/28) in the embryos derived from zygotes electroporated at 25 V/mm and 30 V/mm, respectively. Our results indicate that electroporation at 25 V/mm may be an acceptable condition for introducing Cas9 mRNA and sgRNA into pig IVF zygotes under which the viability of the embryos is not significantly affected.