Piglets produced from cloned blastocysts cultured in vitro with GM-CSF

The effects of glucuronic acid and N-acetyl-D-glucosamine on in vitro fertilisation of porcine oocytes

High incidences of polyspermic penetration continue to challenge researchers during porcine in vitro fertilisation (IVF). The aim of this study was to reduce the incidence of polyspermy by increasing the perivitelline space thickness with glucuronic acid and N-acetyl-D-glucosamine (GlcNAc) supplementation during oocyte maturation. After maturation, zona pellucida and perivitelline space thicknesses, intracellular glutathione concentrations and fertilisation kinetics were measured, in addition to embryonic cleavage and blastocyst formation at 48h and 144h after IVF, respectively. There were no significant differences between the treatments for zona pellucida thickness, penetration rates, male pronuclear formation or cortical granule exocytosis. Glucuronic acid supplementation significantly increased (PPPP<0.05) of cleavage and blastocyst formation by 48 and 144h after IVF compared with all other groups. These results indicate that supplementing with 0.005mM glucuronic acid and 0.005mM GlcNAc during oocyte maturation decreases the incidence of polyspermic penetration by increasing perivitelline space thickness and improving embryo development in pigs.

In vitro manipulation techniques of porcine embryos: a meta-analysis related to transfers, pregnancies and piglets

During the last 17 years, considerable advancements have been achieved in the production of pigs, transgenic and non-transgenic, by methods of somatic cell nuclear transfer, in vitro fertilisation, intracytoplasmic sperm injection, microinjection and sperm-mediated gene transfer by artificial insemination. Therefore, a review of the overall efficiency for the developmental competence of embryos produced by these in vitro methods would be useful in order to obtain a more thorough overview of this growing area with respect to its development and present status. In this review a meta-analysis was used to analyse data collected from all published articles with a focus on zygotes and embryos for transfer, pregnancy, full-term development and piglets born. It was generally concluded that an increasing level of in vitro manipulation of porcine embryos decreased the overall efficiency for production of piglets. The techniques of nuclear transfer have been developed markedly through the increasing number of studies performed, and the results have become more stable. Prolonged in vitro culture period did not lead to any negative effect on nuclear transfer embryos after their transfer and it resulted in a similar or even higher litter size. More complete information is needed in future scientific articles about these in vitro manipulation techniques to establish a more solid basis for the evaluation of their status and to reveal and further investigate any eventual problems.

Procedure used for denuding pig oocytes influences oocyte damage, and development of in vitro and nuclear transfer embryos

The effects of different denuding procedures used during the in vitro culture of porcine embryos on oocyte damage and aspects of porcine embryo development were investigated in a series of studies. Oocytes were denuded by vortexing or pipetting after 44h in vitro maturation (IVM) or pre-denuded after 22h IVM. The total oocyte death rate was significantly (P<0.05) higher for pre-denuded (27.3±1.4%) than for vortexed (20.3±1.2%) or pipetted (16.2±2.2%) oocytes. There was no significant difference between the treatments in the percentage of oocytes that extruded the first polar body. The type I cortical granule distribution (reflecting complete maturity) and normal spindle formation rates were significantly lower in the pre-denuding than in the vortexing and pipetting treatments. Blastocyst formation rates were significantly lower for the pre-denuding treatment in PA (25.7±4.5%) and IVF (6.1±1.5%) culture than in the vortexing (PA 42.0±4.5%; IVF 11.2±0.5%) and pipetting (PA 43.4±3.1%; IVF 9.4±1.6%) treatments. The proportion of oocytes developing to blastocysts in SCNT culture was not significantly different between treatments ranging from 9.9±1.8% for pre-denuding to 12.3±2.7% for vortexing. No significant differences in apoptosis or embryonic fragmentation were observed. This study shows that the denuding procedure used for porcine oocytes during the in vitro production of embryos can significantly affect oocyte damage, spindle patterns, oocyte maturation, embryo development but not embryonic apoptosis or the frequency of fragmentation.

Increasing efficiency in production of cloned piglets

The low efficiency in obtaining piglets after production of cloned embryos was challenged in two steps-first by performing in vitro culture for 5-6 days after cloning to obtain later-stage embryos for more precise selection for transfer, and second by reducing the number of embryos transferred per recipient sow. The data set consisted of combined results from a 4-year period where cloning was performed to produce piglets that were transgenic for important human diseases. For this, different transgenes and cell types were used, and the cloning work was performed by several persons using oocytes from different pig breeds, but following a standardized and optimized protocol. Results showed that in vitro culture is possible with a relatively stable rate of transferable embryos around 41% and a pregnancy rate around 90%. Furthermore, a reduction from around 80 embryos to 40 embryos transferred per recipient was possible without changing the efficiency of around 14% (piglets born out of embryos transferred). It was concluded that this approach can increase the efficiency in obtaining piglets by means of in vitro culture and selection of high-quality embryos with subsequent transfer into more recipients. Such changes can also reduce the need for personnel, time, and material when working with this technology.

The evolution of porcine embryo in vitro production

The in vitro production of porcine embryos has presented numerous challenges to researchers over the past four decades. Some of the problems encountered were specific to porcine gametes and embryos and needed the concerted efforts of many to overcome. Gradually, porcine embryo in vitro production systems became more reliable and acceptable rates of blastocyst formation were achieved. Despite the significant improvements, the problem of polyspermic fertilization has still not been adequately resolved and the embryo in vitro culture conditions are still considered to be suboptimal. Whereas early studies focused on increasing our understanding of the reproductive processes involved, the technology evolved to the point where in vitro-matured oocytes and in vitro-produced embryos could be used as research material for developing associated reproductive technologies, such as SCNT and embryo cryopreservation. Today, the in vitro procedures used to mature oocytes and culture embryos are integral to the production of transgenic pigs by SCNT. This review discusses the major achievements, advances, and knowledge gained from porcine embryo in vitro production studies and highlights the future research perspectives of this important technology.

Use of the CRISPR/Cas9 system to produce genetically engineered pigs from in vitro-derived oocytes and embryos

Targeted modification of the pig genome can be challenging. Recent applications of the CRISPR/Cas9 system hold promise for improving the efficacy of genome editing. When a designed CRISPR/Cas9 system targeting CD163 or CD1D was introduced into somatic cells, it was highly efficient in inducing mutations. When these mutated cells were used with somatic cell nuclear transfer, offspring with these modifications were created. When the CRISPR/Cas9 system was delivered into in vitro produced presumptive porcine zygotes, the system was effective in creating mutations in eGFP, CD163, and CD1D (100% targeting efficiency in blastocyst stage embryos); however, it also presented some embryo toxicity. We could also induce deletions in CD163 or CD1D by introducing two types of CRISPRs with Cas9. The system could also disrupt two genes, CD163 and eGFP, simultaneously when two CRISPRs targeting two genes with Cas9 were delivered into zygotes. Direct injection of CRISPR/Cas9 targeting CD163 or CD1D into zygotes resulted in piglets that have mutations on both alleles with only one CD1D pig having a mosaic genotype. We show here that the CRISPR/Cas9 system can be used by two methods. The system can be used to modify somatic cells followed by somatic cell nuclear transfer. System components can also be used in in vitro produced zygotes to generate pigs with specific genetic modifications.

Cell cycle synchronization of leukemia inhibitory factor (LIF)-dependent porcine-induced pluripotent stem cells and the generation of cloned embryos

Nuclear transfer (NT) from porcine iPSC to create cloned piglets is unusually inefficient. Here we examined whether such failure might be related to the cell cycle stage of donor nuclei. Porcine iPSC, derived here from the inner cell mass of blastocysts, have a prolonged S phase and are highly sensitive to drugs normally used for synchronization. However, a double-blocking procedure with 0.3 μM aphidicolin for 10 h followed by 20 ng/ml nocodazole for 4 h arrested 94.3% of the cells at G2/M and, after release from the block, provided 70.1% cells in the subsequent G1 phase without causing any significant loss of cell viability or pluripotent phenotype. Nuclei from different cell cycle stages were used as donors for NT to in vitro-matured metaphase II oocytes. G2/M nuclei were more efficient than either G1 and S stage nuclei in undergoing first cleavage and in producing blastocysts, but all groups had a high incidence of chromosomal/nuclear abnormalities at 2 h and 6 h compared with non-synchronized NT controls from fetal fibroblasts. Many G2 embryos extruded a pseudo-second polar body soon after NT and, at blastocyst, tended to be either polyploid or diploid. By contrast, the few G1 blastocysts that developed were usually mosaic or aneuploid. The poor developmental potential of G1 nuclei may relate to lack of a G1/S check point, as the cells become active in DNA synthesis shortly after exit from mitosis. Together, these data provide at least a partial explanation for the almost complete failure to produce cloned piglets from piPSC.

Regulation of pluripotency of inner cell mass and growth and differentiation of trophectoderm of the bovine embryo by colony stimulating factor 2

Colony-stimulating factor 2 (CSF2) enhances competence of the bovine embryo to establish and maintain pregnancy after the embryo is transferred into a recipient. Mechanisms involved could include regulation of lineage commitment, growth, or differentiation of the inner cell mass (ICM) and trophectoderm (TE). Experiments were conducted to evaluate regulation by CSF2 of pluripotency of the ICM and differentiation and growth of the TE. Embryos were cultured with 10 ng/ml recombinant bovine CSF2 or a vehicle control from Days 5 to 7 or 6 to 8 postinsemination. CSF2 increased the number of putative zygotes that developed to blastocysts when the percent of embryos becoming blastocysts in the control group was low but decreased blastocyst yield when blastocyst development in controls was high. ICM isolated from blastocysts by lysing the trophectoderm using antibody and complement via immunosurgery were more likely to survive passage when cultured on mitomycin C-treated fetal fibroblasts if derived from blastocysts treated with CSF2 than if from control blastocysts. There was little effect of CSF2 on characteristics of TE outgrowths from blastocysts. The exception was a decrease in outgrowth size for embryos treated with CSF2 from Days 5 to 7 and an increase in expression of CDX2 when treatment was from Days 6 to 8. Expression of the receptor subunit gene CSF2RA increased from the zygote stage to the 9-16 cell stage before decreasing to the blastocyst stage. In contrast, CSF2RB was undetectable at all stages. In conclusion, CSF2 improves competence of the ICM to survive in a pluripotent state and alters TE outgrowths. Actions of CSF2 occur through a signaling pathway that is likely to be independent of CSF2RB.

Chromosomes in the porcine first polar body possess competence of second meiotic division within enucleated MII stage oocytes

To determine whether chromosomes in the porcine first polar body (PB1) can complete the second meiotic division and subsequently undergo normal pre-implantation embryonic development, we examined the developmental competence of PB1 chromosomes injected into enucleated MII stage oocytes by nuclear transfer method (chromosome replacement group, CR group). After parthenogenetic activation (PA) or in vitro fertilization (IVF), the cleavage rate of reconstructed oocytes in the IVF group (CR-IVF group, 36.4 ± 3.2%) and PA group (CR-PA group, 50.8 ± 4.2%) were significantly lower than that of control groups in which normal MII oocytes were subjected to IVF (MII-IVF group, 75.8 ± 1.5%) and PA (MII-PA group, 86.9 ± 3.7%). Unfertilized rates was significantly higher in the CR-IVF group (48.6 ± 3.3%) than in the MII-IVF group (13.1 ± 3.4%). The blastocyst formation rate was 8.3 ± 1.9% in the CR-PA group, whereas no blastocyst formation was observed in the CR-IVF group. To produce tetraploid parthenogenetic embryos, intact MII stage oocytes injected with PB1 chromosomes were electrically stimulated, treated with 7.5 μg/mL cytochalasin B for 3 h (MII oocyte + PB1 + CB group), and then cultured without cytochalasin B. The average cleavage rate of reconstructed oocytes was 72.5% (48 of 66), and the blastocyst formation rate was 18.7% (9 of 48). Chromosome analysis showed similar proportions of haploid and diploid cells in the control (normal MII oocytes) and CR groups after PA; overall, 23.6% of blastocysts were tetraploid in the MII oocyte + PB1 + CB group. These results demonstrate that chromosomes in PB1 can participate in normal pre-implantation embryonic development when injected into enucleated MII stage oocytes, and that tetraploid PA blastocysts are produced (although at a low proportion) when PB1 chromosomes are injected into intact MII stage oocytes.