The Effect of Energy Substrate Concentration and Amino Acids on the In Vitro Development of Preimplantation Porcine Embryos

Effects of pyruvate on early embryonic development and zygotic genome activation in pigs

Pyruvate is an important energy substance during early embryonic development of mammals. However, the underlying mechanisms of pyruvate during early embryonic development in pigs and its role in zygotic genome activation (ZGA) are not fully understood. Here, based on a previous RNA-seq dataset of porcine early embryos, we found that pyruvate metabolism-related genes started to be expressed at the 4-cell stage and that pyruvate metabolism-related genes were correlated with porcine ZGA marker genes. To determine the function of pyruvate in porcine embryos, in vitro fertilization (IVF) embryos were cultured in PZM-3 medium (control group); modified PZM-3 medium that only contains pyruvate and lactate plus salts (+P group); or modified PZM-3 medium lacking pyruvate (-P group). The 4-cell arrest rate at 72 h was significantly increased in the -P group compared to the +P group (P < 0.05). In addition, we observed that the reactive oxygen species (ROS) level was significantly increased and that the adenosine triphosphate (ATP) level was significantly (P < 0.05) decreased in the -P group compared to the +P group. Moreover, the expression of ZGA marker genes and SIRT1 protein in embryos was significantly decreased in the -P group compared to the +P group (P < 0.05). Furthermore, the acetylation level of H3K9 was significantly decreased (P < 0.05) and the methylation level of H3K9 was significantly increased (P < 0.05) in the -P group compared to the +P group. In summary, our findings demonstrate that pyruvate affects early embryonic development in pigs by promoting ZGA and reducing oxidative stress levels.

Supplementation of culture medium with L-carnitine improves the development and cryotolerance of in vitro-produced porcine embryos

Porcine oocytes and embryos contain substantial amounts of lipid, with little known regarding its metabolic role during development. This study investigated the role of lipid metabolism and the interaction between carbohydrate and lipid substrates in porcine embryos. Following in vitro fertilisation, presumptive zygotes were transferred to culture medium supplemented with L-carnitine, a co-factor required for the metabolism of fatty acids. In porcine zygote medium-3 (PZM-3), which contains pyruvate and lactate, 3mM L-carnitine was the only dose that improved cleavage rates compared with the control. In the absence of carbohydrates, all doses of L-carnitine from 1.5 to 12mM increased cleavage rates compared with the control. Culture in a PZM-3-based sequential media system (Days 0-3: pyruvate and lactate; Days 4-7: glucose) significantly increased blastocyst cell numbers compared with culture in standard PZM-3. Supplementing PZM-3 with 3mM L-carnitine produced blastocysts with cell numbers equivalent to those obtained in the sequential media system. After vitrification, the post-warming survival rates of blastocysts obtained in media supplemented with 3mM L-carnitine were significantly greater than those of blastocysts obtained in standard PZM-3. In conclusion, L-carnitine supplementation improved embryo development when the medium contained pyruvate and lactate or was lacking carbohydrates completely, indicating a role for fatty-acid metabolism when the embryo's requirements for carbohydrates are not adequately met.

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.

Cryotolerance of in vitro-produced porcine blastocysts is improved when using glucose instead of pyruvate and lactate during the first 2 days of embryo culture

The objective of the present study was to determine the effects of replacing glucose with pyruvate and lactate during the first 48 h of in vitro culture (IVC) in NCSU-23 medium on embryo development, embryo quality and survival of porcine blastocysts after vitrification. To this end, in vitro-produced (IVP) porcine oocytes were cultured with either glucose for 6 days (IVC-Glu) or pyruvate–lactate from Day 0 to Day 2 and then with glucose until Day 6 (IVC-PyrLac). Blastocysts were vitrified on Day 6 using the Cryotop device and, after warming, survival rate and the apoptosis index were evaluated after 24 h incubation in NCSU-23 medium. No significant differences were observed between IVC-Glu and IVC-PyrLac in terms of cleavage rate, blastocyst yield, total number of cells per blastocyst or the apoptosis index (1.82 ± 0.75% vs 3.18 ± 0.88%, respectively) of non-vitrified embryos. However, a significant increase was seen in hatching/hatched blastocysts in the IVC-PyrLac compared with IVC-Glu treatment group (12.71 ± 1.20% vs 3.54 ± 0.47%, respectively). Regardless of treatment, vitrification impaired the survival rate and the apoptosis index. When comparing both treatments after warming, the percentage of apoptotic cells was significantly higher for blastocysts in the IVC-PyrLac compared with IVC-Glu group (18.55 ± 3.49% vs 9.12 ± 2.17%, respectively). In conclusion, under the conditions of the present study, replacement of glucose with pyruvate–lactate during the first 48 h of culture resulted in a lower cryotolerance of IVP porcine embryos.

Piglets produced from in vivo blastocysts vitrified using the Cryologic Vitrification Method (solid surface vitrification) and a sealed storage container

The objective was to develop a simple successful porcine cryopreservation protocol that prevented contact between embryos and liquid nitrogen, avoiding potential contamination risks. In vivo-derived blastocysts were collected surgically from donor pigs, and two porcine embryo vitrification protocols (one used centrifugation to polarize intracytoplasmic lipids, whereas the other did not) were compared using the Cryologic Vitrification Method (CVM), which used solid surface vitrification. The CVM allowed embryos to be vitrified, without any contact between embryos and liquid nitrogen. Both protocols resulted in similar in vitro survival rates (90% and 94%) and cell number (89 ± 5 and 99 ± 5) after 48 h in vitro culture of vitrified and warmed blastocysts. The protocol that did not use centrifugation was selected for continued use. To protect vitrified embryos from contact with liquid nitrogen and potential contamination during storage, a sealed outer container was developed. Use of this sealed outer container did not affect in vitro survival of cryopreserved blastocysts. In vivo blastocysts (n = 151) were collected, vitrified, and stored using the selected protocol and sealed container. These embryos were subsequently warmed and transferred to six recipients; five became pregnant and farrowed a total of 26 piglets. This embryo vitrification method allowed porcine embryos to be successfully vitrified and stored without any contact with liquid nitrogen.

A prospective randomized sibling-oocyte study of two media systems for culturing cleavage-stage embryos-impact on fertilization rate

PURPOSE

Although several media systems have been developed, data from prospective randomised clinical studies are still lacking. In the present study we compared the effects of 2 different media systems on embryo morphology and development at days 2/3 using sibling oocytes.

METHODS

In this prospective sibling-split trial, 1206 oocytes from 110 women were divided via alternate allocation to fertilization and culture in media system A (G-IVF (TM) v5 PLUS/ G-1(TM) v5 PLUS) or for fertilization and culture in media system B (Universal IVF medium/EmbryoAssist (TM)).

RESULTS

The use of media system A significantly increased the normal fertilization rate (73.5% versus 67.2%; p = 0.030) and embryo utilization rate (55.5% versus 42.9%; p = 0.001), whereas polyploidy and embryo quality were similar in the two groups.

CONCLUSION

The different impacts on fertilization and early embryo development between the two commercially available and commonly used media systems show the importance of evaluation of the efficacy of existing sequential culture media and the need to further improve media for in vitro development of human embryos.

In vitro and in vivo characterization of putative porcine embryonic stem cells

We have developed a new method for the isolation of porcine embryonic stem cells (ESCs) from in vivo-derived and in vitro-produced embryos. Here we describe the isolation and characterization of several ESC lines established using this method. Cells from these lines were passaged up to 14 times, during which they were repeatedly cryopreserved. During this time, ESCs maintained their morphology and continued to express Oct 4, Nanog, and SSEA1. These cells formed embryoid bodies in suspension culture, and could be directed to differentiate into various lineages representative of all three germ layers in vitro. When injected into blastocysts these cells localized in the inner cell mass of blastocysts. To examine their pluripotency further, cells were injected into host blastocysts and transferred to recipient animals. Of the six transfers undertaken, one recipient became pregnant and gave birth to a litter of one male and three female piglets. Microsatellite analysis of DNA extracted from the tail tissue of these piglets indicated that two female piglets were chimaeric.

Production of cloned sei whale (Balaenoptera borealis) embryos by interspecies somatic cell nuclear transfer using enucleated pig oocytes

In this study, we examined the feasibility of using subzonal cell injection with electrofusion for interspecies somatic cell nuclear transfer (iSCNT) to produce sei whale embryos and to improve their developmental capacity by investigating the effect of osmolarity and macromolecules in the culture medium on the in vitro developmental capacity. Hybrid embryos produced by the electrofusion of fetal whale fibroblasts with enucleated porcine oocytes were cultured in modified porcine zygote medium-3 to examine the effects of osmolarity and fetal serum on their in vitro developmental capacity. More than 66% of the whale somatic cells successfully fused with the porcine oocytes following electrofusion. A portion (60~81%) of the iSCNT whale embryos developed to the two- to four-cell stages, but no embryos were able to reach the blastocyst stage. This developmental arrest was not overcome by increasing the osmolarity of the medium to 360 mOsm or by the addition of fetal bovine or fetal whale serum. Our results demonstrate that sei whale-porcine hybrid embryos may be produced by SCNT using subzonal injection and electrofusion. The pig oocytes partly supported the remodeling and reprogramming of the sei whale somatic cell nuclei, but they were unable to support the development of iSCNT whale embryos to the blastocyst stage.

Adding essential amino acids at a low concentration improves the development of in vitro fertilized porcine embryos

The aims of this study were to investigate improvements to the pig preimplantation embryo culture system using in vitro produced embryos. For experiment 1, the optimum time to change the medium from NCSU23 containing 0.6 mM glucose, 0.2 mM pyruvate, 5.7 mM lactate and nonessential amino acids to NCSU23 containing 5.6 mM glucose and both essential and nonessential amino acids was examined. There were no statistically significant differences in blastocyst rates or cell number when the medium was changed at 48, 72 or 96 h, although there was a consistent trend for the 96 h treatment to produce fewer blastocysts with fewer cells. For experiment 2, the addition of essential amino acids at either a 1:50 or a 1:100 dilution of the purchased stock solution for day 1 to 6 or for days 3 to 6 only was investigated. Adding essential amino acids at a 1:50 dilution for day 3 to 6 significantly reduced the blastocyst rate and adding them at a 1:50 dilution from day 1 to 6 significantly reduced both the blastocyst rate and blastocyst cell number compared to when it was added at a 1:100 dilution. Embryos were produced by IVF, cultured for 6 days and good quality blastocysts were transferred into 6 synchronized pseudopregnant recipients (24 to 35 blastocysts per recipient) resulting in 4 pregnancies and 21 live birth piglets. These results show that adding essential amino acids at a 1:100 dilution provided the best culture conditions and the blastocysts produced were able to attain full term development after transfer.