Vitrification of in vitro-derived bovine embryos: targeting enhancement of quality by refining technology and standardising procedures

Recent advancements to increase success in assisted reproductive technologies in cattle

Assisted reproductive technologies (ART) are fundamental for cattle breeding and sustainable food production. Together with genomic selection, these technologies contribute to reducing the generation interval and accelerating genetic progress. In this paper, we discuss advancements in technologies used in the fertility evaluation of breeding animals, and the collection, processing, and preservation of the gametes. It is of utmost importance for the breeding industry to select dams and sires of the next generation as young as possible, as is the efficient and timely collection of gametes. There is a need for reliable and easily applicable methods to evaluate sexual maturity and fertility. Although gametes processing and preservation have been improved in recent decades, challenges are still encountered. The targeted use of sexed semen and beef semen has obliterated the production of surplus replacement heifers and bull calves from dairy breeds, markedly improving animal welfare and ethical considerations in production practices. Parallel with new technologies, many well-established technologies remain relevant, although with evolving applications. In vitro production (IVP) has become the predominant method of embryo production. Although fundamental improvements in IVP procedures have been established, the quality of IVP embryos remains inferior to their in vivo counterparts. Improvements to facilitate oocyte maturation and development of new culture systems, e.g. microfluidics, are presented in this paper. New non-invasive and objective tools are needed to select embryos for transfer. Cryopreservation of semen and embryos plays a pivotal role in the distribution of genetics, and we discuss the challenges and opportunities in this field. Finally, machine learning (ML) is gaining ground in agriculture and ART. This paper delves into the utilization of emerging technologies in ART, along with the current status, key challenges, and future prospects of ML in both research and practical applications within ART.

Use of Antifreeze Protein from Tenebrio molitor (TmAFP) in Vitrification of In Vitro-Produced Bovine Embryos: An Ultrastructural Study

The objective of this study was to evaluate the effects of different concentrations of antifreeze protein (AFP) extracted from the larva of the beetle, Tenebrio molitor (TmAFP), on vitrification of in vitro-produced bovine embryos. In vitro-produced blastocysts were divided into three experimental groups and vitrified using a cryotop. TmAFP was added to the equilibrium solution (ES) and vitrification solution (VS) at a concentration of 0 ng/mL (control), 500 ng/mL (500TmAFP), or 1000 ng/mL (1000TmAFP). Vitrification was carried out by first placing the blastocysts in ES for 2 minutes (7.5% ethylene glycol [EG] and 7.5% dimethyl sulfoxide [DMSO]). The blastocysts were then transferred to VS (15% EG and 15% DMSO) and promptly deposited on a cryotop stem and submerged in liquid nitrogen. Warming was carried out in three steps with decreasing sucrose concentrations. After warming, the blast cells were cultured for 24 hours for subsequent survival analysis and ultrastructural evaluation. There was a significant difference in the survival rate and expansion in the 500TmAFP group compared with the other groups. The ultrastructural analysis revealed intracellular lesions in all vitrified embryos; however, the embryos of the 500TmAFP and 1000TmAFP groups showed fewer cytoplasmic lesions compared with the control group. Taken together, addition of TmAFP can mitigate cellular changes that involve organelles and cellular components essential for proper functioning and improve the viability of warmed and vitrified in vitro-produced bovine embryos.

Effects of antifreeze protein from Lolium perenne L. (LpAFP) in the vitrification of in vitro-produced bovine embryos

In the present study, the cryoprotective effects of Lolium perenne antifreeze protein (LpAFP) on the vitrification of bovine embryos were evaluated. In vitro-produced blastocysts were divided into two groups: the control group (CG) without the addition of LpAFP and the treatment group (TG) with the addition of 500 ng/ml of LpAFP in the equilibrium and vitrification solution. Vitrification was carried out by transferring the blastocysts to the equilibrium solution [7.5% ethylene glycol (EG) and 7.5% dimethyl sulfoxide (DMSO)] for 2 min and then to the vitrification solution (15% EG, 15% DMSO and 0.5M sucrose). The blastocysts were deposited on a cryotop device and submerged in liquid nitrogen. Warming was carried out in three steps in solutions with different sucrose concentrations (1.0, 0.5, and 0.0 M, respectively). Embryos were evaluated for re-expansion/hatching, the total cell count, and ultrastructural analysis. There was no significant difference in the re-expansion rate 24 h after warming; however, there was variation (P < 0.05) in the hatching rate in the TG and the total number of cells 24 h after warming was higher in the TG (114.87 ± 7.24) when compared with the CG (91.81 ± 4.94). The ultrastructural analysis showed changes in organelles related to the vitrification process but, in the TG, there was less damage to mitochondria and rough endoplasmic reticulum compared with the CG. In conclusion, the addition of 500 ng/ml of LpAFP during the vitrification of in vitro-produced bovine embryos improved the hatching rate and total cell number of blastocysts after warming and mitigated intracellular damage.

Improving Cryopreservation Efficiency and Pregnancy Rate through Superovulation with Follicle-Stimulating Hormone in Korean Hanwoo Cows via Ovum Pick Up

The aim of this study was to devise an efficient technique for generating embryos from high-quality bovine females. Oocytes were collected from 20 control and 15 Hanwoo (Bos taurus coreanae) females treated with the FSH. A combination of decreasing FSH doses (36, 36, 24, and 24 mg, 12 h apart), progesterone, estrogen, and prostaglandins were administered to synchronize and mildly stimulate the animals. The FSH-treated group (1125 oocytes) and control group (1022 oocytes) exhibited a higher proportion of grade A and B oocytes (88.2%) than the other grades (p < 0.05), with most at the germinal vesicle 2 stage (64.0%). Moreover, the FSH-treated group achieved a notably higher blastocyst rate (44.7%) compared to the control group (31.1%) (p < 0.05). After undergoing vitrification and in vitro culture (IVC) warming, embryos in the FSH group exhibited higher re-expansion rates (grade 1: 86.9%; grades 2 and 3: 57.9%) compared to those in the control (p < 0.05). This highlights the positive impact of FSH treatment on in vitro embryo production (IVEP) and the OPU rate.

Embryo morphokinetics derived from fresh and vitrified bovine oocytes predict blastocyst development and nuclear abnormalities

Embryo development is a dynamic process and critical stages may go unnoticed with the use of traditional morphologic assessments, especially the timing of embryonic divisions and aberrant zygotic cleavage patterns. Bovine embryo development is impaired after oocyte vitrification, but little is known about the underlying morphokinetic behavior. Here, bovine zygotes from fresh (n = 708) and vitrified oocytes (n = 182) were monitored by time-lapse imaging and the timing and nature of early blastomere divisions were modeled to find associations with blastocyst development at day 8. The predictive potential of morphokinetic parameters was analyzed by logistic regression and receiver operating characteristic curve analysis to determine optimal cut-off values. Lag-phase was highly correlated with embryo development. Remarkably, 100% of zygotes that reached the blastocyst stage showed a lag-phase. Fast first cleavage increased the chance of blastocyst development to 30% with a cut-off of 32 h and 22 min. Aberrant zygotic cleavage events, including multipolar division, unequal blastomere sizes, and membrane ruffling resulted in decreased blastocyst development. Multipolar division leads to uneven blastomeres, which was associated with anuclear and multinuclear blastomeres, indicating genome segregation errors. Moreover, we described for the first time morphokinetics of embryos derived from vitrified bovine oocytes. Vitrification severely affected blastocyst development, although lower cryoprotectant concentration in equilibration solutions seems to be less detrimental for embryo yield. Impaired development was linked to slow cleavages, lower lag-phase incidence, and increased early embryonic arrest. Typically, less than 15% of the embryos produced from vitrified oocytes reached more than eight cells. Interestingly, the rate of abnormal first cleavage events was not affected by oocyte vitrification. In conclusion, time to first cleavage, the presence of a lag-phase, and the absence of aberrant zygotic cleavage were the best predictors of bovine blastocyst development for both fresh and vitrified oocytes.

Alpha-lipoic acid improves bovine preimplantation blastocyst quality and cryotolerance

In vitro embryo production has grown in recent decades due to its great potential for cattle production. However, the quality of in vitro-produced embryos is lower compared with those produced in vivo. The postfertilization culture environment has a major influence on bovine embryo quality. We hypothesize that the inclusion of the inclusion of alpha-lipoic acid (ALA) in the in vitro culture (IVC) medium during the first 24 h would have positive effects on embryo development in vitro and cryotolerance. The aims of this study were to evaluate the antioxidant effect of ALA in IVC medium for 24 h on bovine zygotes (21 h post in vitro fertilization, IVF), day 2 cleaved embryos (46 h post-IVF), and to assess embryo quality, developmental competence, and cryotolerance after vitrification. In all experiments, IVC medium was the Control, and 2.5 μM ALA was the treatment implemented. Viability and reactive oxygen species (ROS) levels in zygotes and day 2 embryos did not differ from the Control (P > 0.05). Supplementation with ALA increased total blastocyst and hatching rates (P < 0.05). It also improved embryo quality, evidenced by the increased blastocyst total cell number and the percentage of excellent-quality embryos observed (P < 0.05). In embryos cultured with ALA and then vitrified, ALA reduced intracellular ROS levels in warmed blastocysts (P < 0.05). In conclusion, ALA supplementation to IVC medium during 24 h is a new advantage in improving embryo quality for assisted bovine reproduction.

Optimal Stage for Cryotop Vitrification of Porcine Embryos

Different development stages of porcine embryos have different tolerance to low temperature. Therefore, we took the porcine embryos after parthenogenetic activation (PA) as the model, to explore the optimal development stage for vitrification during morula (D4), early blastocyst (D5), and expanded blastocyst (D6) after PA (D0). Embryos were observed with microscope and analyzed by different staining after cryo-recovery for 24 hours. The quality of embryos was damaged after vitrification, including embryonic nuclei, DNA, cytoskeleton, and organelles. The re-expansion rate at 24 hours of D5 embryos was significantly higher than those of D4 and D6 embryos (D5 vs. D4 vs. D6, 27.620 ± 0.041 vs. 7.809 ± 0.027 vs. 13.970 ± 0.032, p < 0.05). Therefore, D5 embryos were selected as research objects to explore the effect of vitrification on lipid in vitrified embryos. The results showed that the expression levels of perilipin PLIN3 messenger RNA (mRNA) and triacylglycerol synthesis-related genes AGPAT1 and DGAT mRNA are significantly reduced (p < 0.05). Vitrification affected lipid synthesis, which might have an irreversible impact on embryonic development. In conclusion, our data demonstrated that the optimal stage of vitrification was D5 for early blastocysts.

High in vitro survival rate of sheep in vitro produced blastocysts vitrified with a new method and device

Background

To advance the use of embryo vitrification in veterinary practice, we developed a system in which embryo vitrification, warming and dilution can be performed within a straw. Ovine in vitro produced embryos (IVEP) were vitrified at either early (EBs: n = 74) or fully expanded blastocyst stage (FEBs: n = 195), using a new device named “E.Vit”, composed by a 0.25-mL straw with a 50-μm pore polycarbonate grid at one end. Embryos at each stage (EBs and FEBs) were vitrified by either Two-step (TS) or Multi-step (MS; 6 different concentrations of vitrification solutions) protocol. Non-vitrified embryos (n = 102) were maintained in in vitro culture as a control. Warming consisted of placing the straws directly into 1.5 mL tubes containing a TCM-199 solution with three decreasing concentrations of sucrose. Blastocyst re-expansion, embryo survival and hatching rate were evaluated at 2, 24 and 48 h post warming. The number of apoptotic cells was determined by TUNEL assay.

Results

Blastocyst re-expansion (2 h) after warming was higher (P < 0.05) in FEBs group, vitrified with the MS and TS methods (77.90% and 71.25%, respectively) compared with the EBs group (MS: 59.38% and TS: 48.50%, respectively). Survival rates of vitrified FEBs after 24 h IVC were higher (P < 0.001) in both methods (MS and TS) than vitrified EBs (MS: 56.25%; TS: 42.42%) and was higher (P < 0.05) in the MS method (94.19%) compared with those in TS (83.75%). After 48 h of culture the hatching rate for FEBs vitrified in MS system (91.86%) was similar to control (91.89%), but higher than FEB TS (77.5%) and EBs vitrified in MS (37.5%) and TS (33.33%). Number of apoptotic cells were higher in EBs, irrespective of the system used, compared to FEBs. The number of apoptotic cells in FEBs vitrified with MS was comparable to the control.

Conclusions

A high survival rate of IVP embryos can be achieved by the new “E.Vit” device with hatching rates in vitro comparable with control fresh embryos. This method has the potential for use in direct embryo transfer in field conditions.

Melatonin Improves In Vitro Development of Vitrified-Warmed Mouse Germinal Vesicle Oocytes Potentially via Modulation of Spindle Assembly Checkpoint-Related Genes

The present study aimed to investigate the effect of melatonin (MT) supplementation on in vitro maturation of vitrified mouse germinal vesicle (GV) oocytes. The fresh oocytes were randomly divided into three groups: untreated (control), or vitrified by open-pulled straw method without (vitrification group) or with MT supplementation (vitrification + MT group). After warming, oocytes were cultured in vitro, then the reactive oxygen species (ROS) and glutathione (GSH) levels, mitochondrial membrane potential, ATP levels, spindle morphology, mRNA expression of spindle assembly checkpoint (SAC)-related genes (Mps1, BubR1, Mad1, Mad2), and their subsequent developmental potential in vitro were evaluated. The results showed that vitrification/warming procedures significantly decreased the percentage of GV oocytes developed to metaphase II (MII) stage, the mitochondrial membrane potential, ATP content, and GSH levels, remarkably increased the ROS levels, and significantly impaired the spindle morphology. The expressions of SAC-related genes were also altered in vitrified oocytes. However, when 10-7 mol/L MT was administered during the whole length of the experiment, the percentage of GV oocytes matured to MII stage was significantly increased, and the other indicators were also significantly improved and almost recovered to the normal levels relative to the control. Thus, we speculate that MT might regulate the mitochondrial membrane potential, ATP content, ROS, GSH, and expression of SAC-related genes, potentially increasing the in vitro maturation of vitrified-warmed mouse GV oocytes.