The ability of donkey sperm to induce oocyte activation and mule embryo development after ICSI

Members of the Equus genus exhibit a fascinating capacity for hybridization, giving rise to healthy offspring. Mules, resulting from the mating of a mare with a jack, represent the most prevalent equid hybrid, serving diverse roles in our society. While in vitro embryo production, particularly through Intracytoplasmic Sperm Injection (ICSI), has rapidly gained significance in domestic horses, the in vitro production in other equids remains largely unexplored. Utilizing donkey sperm for fertilizing horse oocytes not only addresses this gap but also provides an opportunity to investigate donkey sperm's fertilization capability in vitro to further improve donkey ICSI. In this work, we initially studied the localization of donkey sperm Phospholipase C zeta (PLCζ) and assessed the sperm's capacity to induce pronuclear formation and maternal SMARCA4 recruitment upon injection into pig oocytes through ICSI. Subsequently, we investigated the injection of donkey sperm into horse oocytes, evaluating in vitro production up to the blastocyst stage using sperm from different jacks, including frozen and refrigerated samples. Distinct patterns of PLCζ localization were observed for donkey sperm cells compared to their horse counterparts. Additionally, donkey sperm exhibits a reduced ability to induce porcine oocyte activation. However, when injected into horse oocytes, donkey sperm demonstrated sufficient capability to induce oocyte activation as no discernible differences in cleavage or blastocyst rates are observed between in vitro produced mules and horse ICSI embryos. Our study not only delineates PLCζ localization in donkey sperm but also suggests potential differences in the ability to induce oocyte activation in pigs compared to horses while observing no distinctions in pronuclear recruitment of SMARCA4. Interestingly, donkey sperm remains sufficiently capable of inducing horse oocyte activation for in vitro mule blastocyst production.

Comparison of ICSI, IVF, and in vivo derived embryos to produce CRISPR-Cas9 gene-edited pigs for xenotransplantation

Genome editing in pigs for xenotransplantation has seen significant advances in recent years. This study compared three methodologies to generate gene-edited embryos, including co-injection of sperm together with the CRISPR-Cas9 system into oocytes, named ICSI-MGE (mediated gene editing); microinjection of CRISPR-Cas9 components into oocytes followed by in vitro fertilization (IVF), and microinjection of in vivo fertilized zygotes with the CRISPR-Cas9 system. Our goal was to knock-out (KO) porcine genes involved in the biosynthesis of xenoantigens responsible for the hyperacute rejection of interspecific xenografts, namely GGTA1, CMAH, and β4GalNT2. Additionally, we attempted to KO the growth hormone receptor (GHR) gene with the aim of limiting the growth of porcine organs to a size that is physiologically suitable for human transplantation. Embryo development, pregnancy, and gene editing rates were evaluated. We found an efficient mutation of the GGTA1 gene following ICSI-MGE, comparable to the results obtained through the microinjection of oocytes followed by IVF. ICSI-MGE also showed higher rates of biallelic mutations compared to the other techniques. Five healthy piglets were born from in vivo-derived embryos, all of them exhibiting biallelic mutations in the GGTA1 gene, with three displaying mutations in the GHR gene. No mutations were observed in the CMAH and β4GalNT2 genes. In conclusion, in vitro methodologies showed high rates of gene-edited embryos. Specifically, ICSI-MGE proved to be an efficient technique for obtaining homozygous biallelic mutated embryos. Lastly, only live births were obtained from in vivo-derived embryos showing efficient multiple gene editing for GGTA1 and GHR.

Preimplantation Developmental Competence of Bovine and Porcine Oocytes Activated by Zinc Chelation

After sperm-oocyte fusion, intracytoplasmic rises of calcium (Ca) induce the release of zinc (Zn) out of the oocyte (Zn sparks). Both phenomena are known to play an essential role in the oocyte activation process. Our work aimed to explore different protocols for activating bovine and porcine oocytes using the novel zinc chelator 1,10-phenanthroline (PHEN) and to compare developmental rates and quality to bovine IVF and parthenogenetic ionomycin-induced embryos in both species. Different incubation conditions for the zinc chelator were tested, including its combination with ionomycin. Embryo quality was assessed by immunofluorescence of SOX2, SOX17, OCT4, and CDX2 and total cell number at the blastocyst stage. Even though blastocyst development was achieved using a zinc chelator in bovine, bypassing calcium oscillations, developmental rates, and blastocyst quality were compromised compared to embryos generated with sperm-induced or ionomycin calcium rise. On the contrary, zinc chelation is sufficient to trigger oocyte activation in porcine. Additionally, we determined the optimal exposure to PHEN for this species. Zinc chelation and artificial induction of calcium rise combined did not improve developmental competence. Our results contribute to understanding the role of zinc during oocyte activation and preimplantation embryo development across different mammalian species.

Past, present and future of ICSI in livestock species

During the past 2 decades, intracytoplasmic sperm injection (ICSI) has become a routine technique for clinical applications in humans. The widespread use among domestic species, however, has been limited to horses. In horses, ICSI is used to reproduce elite individuals and, as well as in humans, to mitigate or even circumvent reproductive barriers. Failures in superovulation and conventional in vitro fertilization (IVF) have been the main reason for the use of this technology in horses. In pigs, ICSI has been successfully used to produce transgenic animals. A series of factors have resulted in implementation of ICSI in pigs: need to use zygotes for numerous technologies, complexity of collecting zygotes surgically, and problems of polyspermy when there is utilization of IVF procedures. Nevertheless, there have been very few additional reports confirming positive results with the use of ICSI in pigs. The ICSI procedure could be important for use in cattle of high genetic value by maximizing semen utilization, as well as for utilization of spermatozoa from prepubertal bulls, by providing the opportunity to shorten the generation interval. When attempting to utilize ICSI in ruminants, there are some biological limitations that need to be overcome if this procedure is going to be efficacious for making genetic improvements in livestock in the future. In this review article, there is an overview and projection of the methodologies and applications that are envisioned for ICSI utilization in these species in the future.

State of the art of nuclear transfer technologies for assisting mammalian reproduction

The transfer of nuclear genomic DNA from a cell to a previously enucleated oocyte or zygote constitutes one of the main tools for studying epigenetic reprogramming, nucleus-cytoplasm compatibility, pluripotency state, and for genetic preservation or edition in animals. More than 50 years ago, the first experiences in nuclear transfer began to reveal that factors stored in the cytoplasm of oocytes could reprogram the nucleus of another cell and support the development of an embryo with new genetic information. Furthermore, when the nuclear donor cell is an oocyte, egg, or a zygote, the implementation of these technologies acquires clinical relevance for patients with repeated failures in ART associated with poor oocyte quality or mitochondrial dysfunctions. This review describes the current state, scope, and future perspectives of nuclear transfer techniques currently available for assisting mammal reproduction.

Aggregation of Leopardus geoffroyi hybrid embryos with domestic cat tetraploid blastomeres

Heterospecific embryo transfer of an endangered species has been carried out using recipients from related domestic females. Aggregation of an embryo from an endangered species with a tetraploid embryo from the species to be transferred could improve the development of pregnancy to term. The main objective of the present study was to analyze embryo aggregation in domestic cat model using hybrid embryos. For this purpose, we compared in vitro development of synchronic (Sync) or asynchronic (Async) and asynchronic with a tetraploid (Async4n) aggregation of domestic cat IVF embryos. Furthermore, aggregated blastocyst quality was analyzed by evaluation of the total cell number, cell allocation by mitotrackers staining of embryonic cells, expression of Oct4, Nanog, Sox2, Cdx2 genes, number of OCT4+ nuclei, and presence of DNA fragmentation. Additionally, the developmental rates of Async4n aggregation of domestic cat with Leopardus geoffroyi hybrid (hLg) embryos were evaluated. Async aggregation increased blastocyst cell number and the number of OCT4+ nuclei as compared to non-aggregated diploid (2n) and tetraploid (4n) embryos. Moreover, blastocysts produced by Async4n aggregation showed reduced rates of fragmented DNA. No differences were found in the expression of the pluripotent genes, with exception of the Cdx2 expression, which was higher in 4n and aggregated embryos as compared to the control group. Interestingly, hybrids embryos derived by Async4n aggregation with domestic cat embryos had similar rates of blastocysts development as the control. Altogether, the findings support the use of two-cell-fused embryos to generate tetraploid blastomeres and demonstrate that Async4n aggregation generates good quality embryos.

Practical Approaches for Knock-Out Gene Editing in Pigs

Pigs are an important resource for meat production and serve as a model for human diseases. Due to their physiological and anatomical similarities to humans, these animals can recapitulate symptoms of human diseases, becoming an effective model for biomedical research. Although, in the past pig have not been widely used partially because of the difficulty in genetic modification; nowadays, with the new revolutionary technology of programmable nucleases, and fundamentally of the CRISPR-Cas9 systems, it is possible for the first time to precisely modify the porcine genome as never before. To this purpose, it is necessary to introduce the system into early stage zygotes or to edit cells followed by somatic cell nuclear transfer. In this review, several strategies for pig knock-out gene editing, using the CRISPR-Cas9 system, will be summarized, as well as genotyping methods and different delivery techniques to introduce these tools into the embryos. Finally, the best approaches to produce homogeneous, biallelic edited animals will be discussed.

131 In vitro nuclear maturation and blastocyst developmental rates after intracytoplasmic sperm injection of equine oocytes held for 24 h at room temperature in Tyrode’s albumin lactate pyruvate-Hepes (TALP-h) or in a commercial embryo holding medium

The interest in equine intracytoplasmic sperm injection (ICSI) for commercial and research applications has rapidly increased. Shipping immature oocytes at room temperature has been proven successful, and to identify the optimal conditions for holding oocytes, several mediums are being tested. The aim of this study was to compare the effect of holding equine oocytes in Tyrode’s albumin lactate pyruvate-Hepes (TALP-h, Bavister and Yanagimachi 1977 Biol. Reprod. 16, 228-237) medium or in commercial embryo holding medium (EHM, Syngro® Holding) on invitro nuclear maturation rates and pre-implantation embryo development after ICSI. Cumulus–oocyte complexes (COCs) were recovered from ovaries of slaughtered mares and assigned randomly in 2-mL cryovials with TALP-h or EHM, with a maximum of 30 oocytes per cryovial. COCs were shipped to the ICSI laboratory at 20 to 25°C for 24 to 28h followed by IVM for 24h in a humidified atmosphere of 5% CO2 in air at 38.5°C. Maturation medium was TCM-199 with 10% fetal bovine serum, 1μL mL−1 insulin-transferrin-selenium, 1mM sodium pyruvate, 100mM cysteamine, and 0.1mg mL−1 FSH. After mechanical cumulus cell removal, nuclear maturation rate was assessed using a stereomicroscope. Oocytes with an intact oolemma and extrusion of the first polar body (PB) were classified as mature, oocytes without a visible PB were considered immature, and oocytes without an intact oolemma were considered degenerate. Matured oocytes were subjected to ICSI without piezo-drill system (one proved stallion) in 20-μL droplets of TALP-h with a 7-μm glass sharp micropipette in an inverted microscope (Nikon Eclipse TE-300 microscope) using hydraulic micromanipulators (Narishige, Medical Systems). Presumptive ICSI zygotes were cultured in DMEM F12/Global Total® with 6% fetal bovine serum for 9 days at 38.5°C in a humidified atmosphere of 5% O2 and 5% CO2 in air. On Day 5 of culture, cleavage was recorded and medium was refreshed. Blastocysts rates were recorded on Day 7 and 9 of culture. Invitro nuclear maturation rates are shown in Table 1. We observed a significantly higher proportion of immature oocytes in the EHM group compared with the TALP-h group. After ICSI of some matured oocytes of each group, no significant differences were observed in cleavage or blastocyst rate (Table 1). Our results suggest that either TALP-h or commercial embryo holding medium are suitable for oocyte shipping and to support blastocyst development after ICSI. Table 1. Invitro nuclear maturation rates and pre-implantation embryo development after intracytoplasmic sperm injection (ICSI) Maturation rates Medium Oocytes Mature [n (%)] Immature [n (%)] Degenerate [n (%)] TALP-h 315 173 (54.9) 26 (8.3)a 116 (36.8) EHM 273 132 (48.4) 55 (20.1)b 86 (31.5) Total 588 305 (51.9) 81 (13.8) 202 (34.4) Embryo development ICSI (n) Cleaved [n (%)] Day 7 Blastocyst [n (%)] Day 9 Blastocyst [n (%)] TALP-h 35 23 (65.7) 7 (20) 9 (25.7) EHM 26 19 (73.1) 3 (11.5) 5 (19.2) Total 61 42 (68.9) 10 (16.4) 14 (23) a,bDifferent superscript letters indicate statistical significance (Fisher’s exact test, P<0.05).

81 Pronuclear formation and SMARCA4 incorporation after intracytoplasmic sperm injection (ICSI) or assisted ICSI in pig zygotes

Pigs are considered an important experimental model for their biological similarities to humans, including their potential as organ donors in xenotransplantation. Unfortunately, in this species conventional invitro fertilization results in high polyspermic rates. ICSI avoids polyspermy and ICSI-mediated gene edition could be a powerful technique to produce genetically modified pigs. However, ICSI is not yet efficient in pigs. Moreover, the ATP-dependent chromatin remodeller, SMARCA4, translocates to the pronuclei soon after fertilization and its mislocalization or reduction leads to poor embryo development. The aim of this study was to assess whether assisted activation or the use of the piezo drill (PD) during ICSI improves pronuclear (PN) formation rates and to analyse SMARCA4 intensity levels in pronuclei. First, cumulus–oocyte complexes were collected from slaughterhouse ovaries and matured invitro for 44h. Matured and denuded oocytes were subjected to (1) ICSI (n=47), (2) ICSI assisted by PD (ICSIp, n=21), (3) ICSI assisted by electrical activation (ICSIe, n=39), and (4) electrical activation as an haploid parthenogenetic control (HAP, n=21). Presumptive zygotes were fixed for 20min in 4% formaldehyde solution 18h after injection or activation and incubated with SMARCA4 antibody (1:100) and Alexa Fluor (1:1000) as a secondary antibody. Then, the zygotes were classified according to the presence of PN in 2 PN (2-PN), 1 PN with the presence of a semi-condensed or condensed sperm (1-PN), and semi-condensed or condensed sperm with no evidence of PN (no activation). Zygotes that exhibited a different pattern were included in the “other” category. A region of interest was drawn around each PN and the average pixel intensity of SMARCA4 was determined with ImageJ image processing software. Data were analysed by Fisher’s exact test and Kruskal–Wallis test using GraphPad software (GraphPad Inc.). Differences were considered significant at P<0.05. We found no significant differences in 2-PN formation rates among groups after ICSI (ICSI n=16, 34.04%; ICSIe n=10, 25.64%; ICSIp n=6, 28.57%). As expected, the majority of the HAP zygotes exhibited 1 PN (n=14, 66.67%). In contrast, in most of the zygotes of all experimental groups, SMARCA4 was found to be localised in both PN, being absent in polar bodies, metaphase plate, or condensed sperm. Interestingly, out of the total 2-PN porcine ICSI zygotes of all experimental groups (n=25), 7 zygotes (28%) showed clear asymmetric intensity levels between PN. The rest of the ICSI zygotes (n=18, 72%) showed a similar SMARCA4 intensity level between PN. In conclusion, our results suggest that neither the use of piezo drill or electrical activation improves PN formation or SMARCA4 pattern. It remains to be determined whether the asymmetric levels of SMARCA4 between PN observed in some zygotes could be associated with a lower embryo developmental competence.

Time of first polar body extrusion affects the developmental competence of equine oocytes after intracytoplasmic sperm injection

Assisted reproduction techniques (ARTs) have become widespread in the equine breeding industry. In particular, the combination of oocyte recovery from live mares followed by IVM and intracytoplasmic sperm injection (ICSI) has increased markedly among the ARTs used with valuable or low-fertility animals. There is currently no consensus among research groups regarding the optimal oocyte maturation period to produce high-quality embryos. In this study, we report the maturation dynamics of equine oocytes at different time points, from 20 to 40h (Experiment 1). In addition, in Experiment 2, equine ICSI blastocysts were produced from oocytes that exhibited early (up to 24h) or late (28-30h) extrusion of the first polar body (PB). Blastocyst rates and diameter were recorded and embryo quality was assessed by analysing the number of apoptotic cells and Yes-associated protein 1 (YAP1) expression. By 20h of IVM, 42% of oocytes were mature, and the remaining oocytes matured within the next 17h of IVM. Although no differences were found in cell apoptosis or the number of YAP1-positive cells between groups exhibiting early and late PB extrusion, embryos from the early group (Group I) exhibited an improved total cell number and blastocyst rate compared to embryos from the late group (Group II) (18.60% vs 10.17% respectively).

Horse ooplasm supports in vitro preimplantation development of zebra ICSI and SCNT embryos without compromising YAP1 and SOX2 expression pattern

Several equids have gone extinct and many extant equids are currently considered vulnerable to critically endangered. This work aimed to evaluate whether domestic horse oocytes support preimplantation development of zebra embryos obtained by intracytoplasmic sperm injection (ICSI, zebroid) and cloning, and to study the Hippo signaling pathway during the lineage specification of trophectoderm cells and inner cell mass cells. We first showed that zebra and horse sperm cells induce porcine oocyte activation and recruit maternal SMARCA4 during pronuclear formation. SMARCA4 recruitment showed to be independent of the genetic background of the injected sperm. No differences were found in blastocyst rate of ICSI hybrid (zebra spermatozoon into horse egg) embryos relative to the homospecific horse control group. Interestingly, zebra cloned blastocyst rate was significantly higher at day 8. Moreover, most ICSI and cloned horse and zebra blastocysts showed a similar expression pattern of SOX2 and nuclear YAP1 with the majority of the nuclei positive for YAP1, and most SOX2+ nuclei negative for YAP1. Here we demonstrated that horse oocytes support zebra preimplantation development of both, ICSI and cloned embryos, without compromising development to blastocyst, blastocyst cell number neither the expression of SOX2 and YAP1. Our results support the use of domestic horse oocytes as a model to study in vitro zebra embryos on behalf of preservation of valuable genetic.

96 Evaluation of CRISPR/Cas9 alternative delivery in parthenogenetic porcine embryos

Porcine genetic editing is considered promising in biomedical research, particularly for xenotransplantation. However, invitro porcine embryo production is less efficient than in other animal models. Thus, we aimed to perform a rapid optimization essay by producing parthenogenetic porcine embryos to evaluate transgenesis delivery and CRISPR/Cas9 editing efficiency. First, PCX-enhanced green fluorescent protein (EGFP) plasmid was microinjected (30ng μL−1) into a diploid parthenogenic zygote with (lipo+) or without lipofectamine (lipo−), since it has been shown that this transfection reagent improves transgene delivery and increases its expression in bovine embryos (Vichera et al. 2011 Reprod. Domest. Anim. 46, 214-220; https://doi.org/10.1111/j.1439-0531.2010.01642.x). Briefly, invitro-matured oocytes were electrically activated, followed by incubation in synthetic oviductal fluid medium containing 6-dimethylaminopyridine. Embryos were invitro cultured until Day 7, and EGFP-positive (EGFP+) embryos were corroborated at Day 5. Data were analysed using Fisher's exact test. Cleavage rates were no different among groups (EGFP/lipo−: 40%, n=28; EGFP/lipo+: 45%, n=41; control: 41, 3%, n=45; P>0.05). Also, no significant difference in the percentage of EGFP+ embryos was observed between EGFP/lipo+ (31%, n=13) and EGFP/Lipo− (18%, n=5) groups. Although blastocyst rate showed no statistical difference among groups, a lower blastocyst percentage tendency was observed in the EGFP/Lipo+ group compared with the control group (EGFP/Lipo+: 5%, n=2; control: 20%, n=9; P=0.051), suggesting that the presence of lipofectamine and EGFP plasmid may affect embryo development. Next, two guides (single guide (sg) RNA) were designed for the internal regions of GGTA1, CMAH, and VWF target genes, involved in hyperacute rejection and coagulation in xenotransplantation. A liposome-DNA mixture was used: DNA for sgRNA and Cas9, with and without lipofectamine (10× dilution; CRISPR/lipo+, CRISPR/lipo−), diluted to half concentration with 10% polyvinylpyrrolidone, resulting in a final concentration of 20ng ul−1 for all sgRNA and 40ng ul−1 for Cas9. A total of 2 pL of the mixtures was microinjected into the diploid parthenogenetic zygotes which were invitro cultured until Day 7. Genetic editing was corroborated by analysing the presence of a double cut directed by the two sgRNA designed for the target genes, resulting in an amplicon with lower molecular weight compared to the wild-type PCR fragment. No differences in cleavage or blastocyst rates were observed among groups (blastocyst rates: CRISPR/Lipo−: 12%, n=13; CRISPR/Lipo+: 10%, n=7; control: 15%, n=18; P>0.05). Finally, one embryo showed a single deletion for GGTA1 and another showed a double deletion in GGTA1 and VWF genes, out of seven embryos from the CRISPR/Lipo+ group. No gene deletion was confirmed in any of the embryos from the CRISPR/Lipo− group. These results are preliminary data (more experiments are currently being done) suggesting that microinjection of CRISPR/Cas9 with lipofectamine could be used as an alternative delivery system, since it seems to have no impact on porcine embryo development.

24 Asynchronic tetraploid complementation and embryo quality in domestic cat and Leopardus geoffroyi hybrid embryos

Fusion of 2-cell embryos generates tetraploid (4n) blastomeres with an increased commitment to trophectoderm. Complementation of embryos from endangered species with 4n blastomeres derived from a phylogenetically related domestic species could improve healthy pregnancy establishment after embryo transfer in domestic females. However, generation, development, and quality of tetraploid complemented embryos in felids remain unstudied. Therefore, our objectives were (1) to evaluate tetraploidy of 2-cell fused embryos; (2) to analyse the blastocyst cell number, distribution after synchronic (S) or asynchronic (AS) complementation, OCT4+ cells, DNA-fragmentation levels and CDX2 gene expression of IVF complemented embryos; and (3) to evaluate the developmental rates of tetraploid complemented Felis catus-Leopardus geoffroyi hybrid embryos. After ovariectomy, Felis catus oocytes were IVM and subjected to IVF. For Experiment 1 (n=66), 2-cell embryos (2n) were exposed to two 30-ms DC pulses at 8 kV cm−1 electric field in fusion media. Fused (4n) and nonfused embryos were cultured invitro in 50-μL drops of modified Tyrode's medium. Karyotype analysis was performed at Day 4. For Experiment 2 (n=24), zona-free IVF embryos were aggregated S (4-cell-2n/4-cell-2n) or AS (4-cell-2n/2-cell-2n and 4-cell-2n/1-cell-4n). For Experiment 3 (n=36), blastocysts generated by AS complementation (4-cell-2n/2-cell-2n and 4-cell-2n/1-cell-4n) were either fixed with 4% paraformaldehyde for immunofluorescence and terminal deoxynucleotidyl transferase dUTP nick end labeling assay or saved in RNA-Later for RT-qPCR analysis. For this experiment, nonaggregated 2n and 4n blastocysts were used as a control. For Experiment 4 (n=60), IVM oocytes were co-incubated with Leopardus geoffroyi and Felis catus (control) spermatozoa and then 4-cell-2n heterologous embryos were complemented with 1-cell-4n homologous IVF embryos. Data were analysed by Fisher's exact test. Our results showed that 67% of the 2-cell fused embryos were 4n. Moreover, 82% of nonfused embryos were aneuploids compared with 78% of 2n embryos in the control group. The AS complemented blastocysts (4-cell-2n/1-cell-4n and 4-cell-2n/2-cell-2n) had significantly higher cell number compared with S complemented (4-cell-2n/4-cell-2n) or noncomplemented embryos. The AS complementation also increased the number of OCT4+ cells independently of the ploidy of the embryos. Interestingly, AS tetraploid complemented embryos had significantly lower number of cells with fragmented DNA. No differences were found in CDX2 expression among complemented embryos; however, noncomplemented 2n blastocysts showed a significantly lower expression compared with the others group. Finally, we observed that AS complementation of 2n hybrid embryos with 4n homologous embryos reached similar blastocyst rates, 70 and 88%, respectively. Our findings support the use of 2-cell fused embryos to generate 4n blastomeres and demonstrated that tetraploid complementation generates good quality embryos, providing evidences that encourage the use of this technology to improve the developmental competence of interspecific embryos after transfer.

81 Generation of presumptive domestic cat tetraploid embryos and its application for asynchronic complementation with diploid blastomeres

Tetraploid complementation has been extensively used to verify the pluripotency of stem cells and also for improving placenta formation when tetraploid embryos are aggregated synchronously or asynchronously with diploid (2n) embryos. Generation of tetraploid embryos can be achieved by the electric fusion of a 2-cell embryo. However, the optimal electric intensity pulse to generate tetraploid embryos has not been studied in the feline. The aims of this study were to (1) evaluate the optimal fusion conditions to achieve the highest fusion rate without affecting embryo developmental competence, (2) compare the in vitro development of synchronic and asynchronic aggregated domestic cat IVF embryos, and (3) assess pre-implantation development of embryos generated by asynchronic complementation of presumptive 1-cell tetraploid embryos with diploid blastomeres. Domestic cat cumulus-oocyte complexes were matured in vitro on 21% O2 in air at 38.5°C for 22h. The IVF embryos were generated by co-incubation of in vitro-matured oocytes with 2×106 motile spermatozoa mL−1 on 21% O2 in air at 38.5°C for 18 to 20h. After 24h of IVF, 2-cell embryos were selected. For Experiment 1, membrane fusion of 2-cell IVF embryos (n=164) was performed with two 30-ms DC pulses at different electric field (0.8, 2, 4, and 8 kV/cm) in fusion media (Mannitol, MgSO4, CaCl2, and polyvinyl alcohol). Presumptive fused embryos and nonfused were cultured in vitro in 50-µL drops of modified Tyrode’s medium on 6.5% CO2 in air at 38.5°C (Pope et al. 2006 Methods in Molecular Biology 254, 227-244). Cleavage was determined 24h after pulse. For Experiment 2, zona pellucida-free IVF embryos (n=110) were synchronically (two 4-cell embryos) or asynchronically (one 4-cell embryo and one 2-cell embryo) aggregated in 1 microwell. For Experiment 3, 1-cell presumptive tetraploid embryo (2-cell fused embryo) was asynchronically complemented with a 4-cell embryo (n=38). For all experiments, blastocyst stage was evaluated at Day 8, and embryos presenting more than one structure per microwell were considered non-aggregated. Data were analysed by Fisher’s exact test using GraphPad Prism 6.0 (GraphPad Inc., San Diego, CA, USA), and differences were considered significant at P<0.05. The highest fusion rates (30 and 46%) with the best developmental competence (31 and 46%) were observed with 4 and 8 Kv/cm electric pulses, respectively. Electric fusion did not affect the embryo developmental competence. We observed that synchronic and asynchronic complementation reached similar blastocysts rates (54 and 65%, respectively), indicating that both techniques are suitable for tetraploid embryo complementation. Finally, when presumptive tetraploid embryos were asynchronically complemented with diploid blastomeres, the high blastocyst rate (90%) was obtained from embryos that form only one structure (aggregated embryos). Further experiments will be performed to track the distribution of cells using mitotrackers after complementation using tetraploid IVF and diploid somatic cell nuclear transfer embryos.

173 Assessment of the first polar body quality and viability in bovine

In female gametes, after the first asymmetric meiotic division, a mature oocyte in metaphase II and a first polar body (PB1) are generated. The PB1 contains one of each pair of homologous chromosomes present in the mature oocyte and its DNA can be used for preconception genetic diagnosis. The PB1 degenerates shortly after extrusion, possibly due to an apoptotic process; however, it has not yet been elucidated in bovine. Therefore, the objective of this study was to evaluate PB1 morphology changes, plasma membrane integrity, and the presence of DNA fragmentation during in vitro maturation (IVM). To this aim, cumulus-oocyte complexes collected from slaughterhouse ovaries were cultured in maturation medium in different groups according to IVM time: 16, 18, 20, 22, 24, and 26h. The PB1 were classified into 5 categories according to their morphology: grade (G)1, round PB1 with intact smooth membrane; G2, round or ovoid PB1 with intact membrane; G3, broken PB1 with a small PB1 fragment; G4, broken PB1 with a big PB1 fragment; and G5, completely damaged PB1. Grades 1 and 2 were considered good quality. Plasma membrane integrity was assessed by propidium iodide (PI) DNA staining; PI is a fluorescent intercalating agent that cannot cross the membrane of live cells. The presence of DNA fragmentation was detected at 16, 22, and 26h by TUNEL assay. Data were analysed by two-way ANOVA and Bonferroni post hoc test using GraphPad Prism 5.0 (GraphPad Inc., San Diego, CA, USA) and differences were considered significant at P < 0.05. Our results (mean%±s.e.m.) showed that significantly more oocytes assessed at 18, 20, 22, and 24h after onset of IVM presented high-quality (G1) PB1 (18 h: 61.5±13.4%, 20 h: 73.5±9.6%, 22 h: 61.0±9.5%, 24 h: 60±5.1%), compared with those assessed at 16 and 26h (43.0±4.7%, 22.3±3.4%, respectively). The percentage of G2 PB1 did not change throughout the period studied (16 h: 34.0±13.5%, 18 h: 29.9±14.1%, 20 h: 22.0±7.1%, 22 h: 26.5±4.2%, 24 h: 23.3±4.9%, 26 h: 21.33±9.9%), but was significantly lower than that of G1 PB1 at 20, 22, and 24h. The proportion of damaged (G5) PB1 started to increase at 24h (14.3±8.6%), being highest at 26h (30.0±10.5%), in parallel with positive PI staining (P<0.05). Moreover, there was a significant increase of PB1 with DNA fragmentation at 26h (82.0±18.0%) compared with 16h (13.9±9.0%) and 22h (2.5±2.5%). Altogether, these findings demonstrate that PB1 remains stable and of good quality between 18 and 24 h; however, after this time, plasma membrane integrity is compromised and the DNA is fragmented, suggesting the occurrence of an apoptotic process. Our results could be helpful to determine the optimal time for using PB1 as a potential donor of genetic material.

165 Effect of Dimethyl Sulfoxide Supplementation During In Vitro Maturation on the Genetic Expression Pattern of Bovine Blastocyst

Supplementation of bovine oocytes with 0.5% (v/v) dimethylsulfoxide (DMSO) during in vitro maturation (IVM) results in increased blastocysts rates (Ynsaurralde et al. 2016 Reprod. Fertil. Dev. 29, 201-202). Recently, an important role of DMSO in stem cell differentiation has been observed, attributed to modulation of gene expression. However, the effect of DMSO suplementation during in vitro maturation on gene expression profiles and embryo quality have not been evaluated so far. Thus, we examinated the effect of DMSO during IVM on the expression of some key genes (Sox2, Oct4, and Cdx2) and on the degree of DNA fragmentation at the blastocyst stage. To this aim, cumulus–oocyte complexes collected from slaughterhouse ovaries were matured in TCM-199 containing 10% fetal bovine serum, 10 µg mL−1 FSH, 0.3 mM sodium pyruvate, 100 mM cysteamine, and 2% antibiotic-antimycotic for 24 h, at 6.5% CO2 in humidified air and 38.5°C. Maturation media was supplemented with 0, 0.5, or 0.75% (v/v) DMSO. In vitro fertilization (IVF) was performed with 16 × 106 spermatozoa per mL for 5 h. Afterwards, presumptive zygotes were cultured in SOF for 7 days at 38.5°C and 5% O2. Three pools of 5 blastocysts were analysed for each treatment. Gene expression analysis was performed by real-time qPCR and DNA fragmentation of blastocysts was measured by TUNEL assay (n = 8, 7, and 14 blastocysts analysed for 0, 0.5, and 0.75% v/v DMSO, respectively). The results were statistically analysed using ANOVA with a completely randomised model by InfoStat software Version 1.1 (https://www.infostat.com.ar/). The pluripotency marker genes Sox2 and Oct4 were up-regulated in blastocysts only when the oocytes were matured in 0.75% DMSO, whereas the trophoblastic marker Cdx2 showed no differences among treatments. No differences were detected in the number of TUNEL-positive cells among treatments: 10/65 (15%) in 0%, 19/110 (18%) in 0.5%, and 18/98 (20%) in 0.75% (v/v) DMSO. In conclusion, supplementation with 0.5% (v/v) DMSO, as previously published, increases the production of blastocysts without disrupting the expression pattern of the evaluated genes.

199 Efficient Knock-out of Ovine β-Lactoglobulin (BLG) Gene and Knock-in of Recombinant Human Factor IX (rhFIX) Under BLG Native Regulatory Sequences in Somatic Cells and Zygotes Using TALEN Nuclease

Site-specific genetic engineering is a valuable tool for pharmaceutical research and development of biomedical models. Despite engineered nucleases allow targeted gene edition in a rather simple fashion; few reports are available so far on specific gene knock-in (KI) combined with engineered nucleases in domestic species. Here, we evaluated the possibility of inducing specific KI of cDNAs coding for proteins of pharmaceutical interest under the control of milk native promoter sequences, taking advantage of the TALEN system, both in ovine somatic cells and in zygotes. We designed 2 TALENs, targeting exons 1 and 5 of ovine β-lactoglobulin gene (BLG), respectively, and a homologous recombination vector (pHR), carrying recombinant human factor IX (rhFIX) flanked by homology arms contiguous to the TALEN target sites. In an initial set of experiments, 5 × 105 to 1 × 106 ovine fibroblasts were transfected with 1 μg of each TALEN mRNA, with or without 50 ng μL−1 pHR. The feasibility of inducing knock-out (KO) was confirmed by Cel1 assay. The deletion of the genomic region between TALEN target sites and the occurrence of HR in cell lysates were assessed by PCR. Also, 576 individual colonies were picked up and analyzed by PCR. The deletion of the region between TALEN target sites was achieved with 7.8% efficiency (45/576). The incidence of HR in cells was 0.5% (3/576), as detected by PCR. In order to evaluate the system in zygotes, laparoscopic AI was performed on synchronized and superovulated ewes. Zygotes were recovered 16 h after AI and cytoplasmically injected with (1) 5 ng μL−1 TALEN mix (2.5 ng μL−1 oaBLG T1.1 + 2.5 ng μL−1 oaBLG T5.1) (5TM); (2) 5 ng μL−1 TALEN mix + 25 ng μL−1 pHR-hFIX plasmid (5TM+25pRH); or (3) 15 ng μL−1 TALEN mix (7.5 ng μL−1 oaBLG T1.1 + 7.5 ng μL−1 oaBLG T5.1) + 50 ng μL−1 pHR-hFIX (15TM+50pRH). A non-injected control (NIC) was also included. Embryo analysis was conducted on whole-genome amplified DNA from blastocysts, followed by PCR and sequencing. Non-parametric Fisher test was applied to detect significant differences among treatments. Although blastocyst rates for NIC and 5TM did not statistically differ, 5TM+25pRH and 15TM+50pRH groups resulted in lower blastocysts rates than the NIC [P < 0.05; 13/17 (76%), 6/15 (40%), 4/15 (26%) and 2/14 (14%) for NIC, 5TM, 5TM+25pRH and 15TM+50pRH respectively]. It was possible to detect the PCR product compatible with deletion of the entire region among TALEN target sites in 6/6 blastocysts (100%) from the group 5TM, 3/4 blastocysts (75%) from the group 5TM+25pRH and 2/2 (100%) blastocysts from the group 15TM+50pRH. HR was detected in 1/2 (50%) blastocysts injected with 15TM+50pRH and in 1/4 (25%) blastocysts injected with 5TM+25pRH, by PCR and sequencing of the PCR products. Our results indicate that TALEN combined with homologous recombination constitutes a powerful platform for the production of proteins of pharmaceutical interest under native regulatory sequences in the milk of genetically modified animals.

Assessing Tn5 and Sleeping Beauty for transpositional transgenesis by cytoplasmic injection into bovine and ovine zygotes

Transgenic domestic animals represent an alternative to bioreactors for large-scale production of biopharmaceuticals and could also provide more accurate biomedical models than rodents. However, their generation remains inefficient. Recently, DNA transposons allowed improved transgenesis efficiencies in mice and pigs. In this work, Tn5 and Sleeping Beauty (SB) transposon systems were evaluated for transgenesis by simple cytoplasmic injection in livestock zygotes. In the case of Tn5, the transposome complex of transposon nucleic acid and Tn5 protein was injected. In the case of SB, the supercoiled plasmids encoding a transposon and the SB transposase were co-injected. In vitro produced bovine zygotes were used to establish the cytoplasmic injection conditions. The in vitro cultured blastocysts were evaluated for reporter gene expression and genotyped. Subsequently, both transposon systems were injected in seasonally available ovine zygotes, employing transposons carrying the recombinant human factor IX driven by the beta-lactoglobulin promoter. The Tn5 approach did not result in transgenic lambs. In contrast, the Sleeping Beauty injection resulted in 2 lambs (29%) carrying the transgene. Both animals exhibited cellular mosaicism of the transgene. The extraembryonic tissues (placenta or umbilical cord) of three additional animals were also transgenic. These results show that transpositional transgenesis by cytoplasmic injection of SB transposon components can be applied for the production of transgenic lambs of pharmaceutical interest.