The effect of equilibration time on survival and development rates of mouse pronuclear-stage embryos vitrified in solid surface (SSV) and convential straws: In vitro and In vivo evaluations

A Shorter Equilibration Period Improves Post-Warming Outcomes after Vitrification and in Straw Dilution of In Vitro-Produced Bovine Embryos

This study was designed to the optimize vitrification and in-straw warming protocol of in vitro-produced bovine embryos by comparing two different equilibration periods, short equilibrium (SE: 3 min) and long equilibrium (LE: 12 min). Outcomes recorded in vitrified day seven (D7) and day eight (D8) expanded blastocysts were survival and hatching rates, cell counts, apoptosis rate, and gene expression. While survival rates at 3 and 24 h post-warming were reduced (p < 0.05) after vitrification, the hatching rates of D7 embryos vitrified after SE were similar to the rates recorded in fresh non-vitrified blastocysts. The hatching rates of vitrified D8 blastocysts were lower (p < 0.05) than of fresh controls regardless of treatment. Total cell count, and inner cell mass and trophectoderm cell counts were similar in hatched D7 blastocysts vitrified after SE and fresh blastocysts, while vitrified D8 blastocysts yielded lower values regardless of treatment. The apoptosis rate was significantly higher in both treatment groups compared to fresh controls, although rates were lower for SE than LE. No differences emerged in BAX, AQP3, CX43, and IFNτ gene expression between the treatments, whereas a significantly greater abundance of BCL2L1 and SOD1 transcripts was observed in blastocysts vitrified after SE. A shorter equilibration vitrification protocol was found to improve post-warming outcomes and time efficiency after in-straw warming/dilution.

Rapid freezing versus Cryotop vitrification of mouse two-cell embryos

Objective

To compare our in-house method of embryo freezing with Cryotop vitrification in terms of immediate survival, subsequent cleavage and blastocyst formation, and cell numbers in blastocysts.

Methods

Two-cell mouse embryos were randomly allocated into three groups: a non-frozen control group (group 1, n=300), a group that underwent Cryotop vitrification (group 2, n=300), and a group that underwent our in-house freezing method (group 3, n=300).

Results

There were no significant differences between groups 2 and 3 in the immediate survival rate (96.3% vs. 98.6%, respectively; p=0.085), the further cleavage rate (91.7% vs. 95.0%, respectively; p=0.099), or the blastocyst formation rate (80.7% vs. 78.6%, respectively; p=0.437). The cell numbers in the blastocysts from groups 1, 2, and 3 were comparable (88.99±10.44, 88.29±14.79, and 86.42±15.23, respectively; p=0.228). However, the percentage of good-quality blastocysts in the Cryotop vitrification group was significantly higher than in the group in which our in-house method was performed, but was lower than in the control group (58.0%, 37.0%, and 82.7%, respectively; p<0.001).

Conclusion

At present, our method is inferior to the commercial Cryotop vitrification system. However, with further improvements, it has the potential to be useful in routine practice, as it is easier to perform than the current vitrification system.

Effects of laser-assisted hatching and exposure time to vitrification solution on mouse embryo development

Objective

This study was conducted to investigate the efficacy of laser-assisted hatching (LAH) and various vitrification times for embryonic development and blastocyst cell numbers.

Methods

First, 2-cell and 8-cell embryos were collected by flushing out the oviducts. In the control groups, they were vitrified for 8 or 10 minutes without LAH. The LAH groups underwent quarter laser zona thinning-assisted hatching before vitrification (4, 6, and 8 minutes or 4, 7, and 10 minutes, respectively). After incubation, double-immunofluorescence staining was performed.

Results

The hatched blastocyst rate 72 hours after the 2-cell embryos were thawed was significantly higher in the 2LAH-ES8 group (33.3%) than in the other groups (p<0.05). In the control-8 group (22.1±4.6), the cell number of the inner cell mass was higher than in the LAH groups (p<0.05). The number of trophectoderm cells was higher in the 2LAH-ES6 group (92.8±8.9) than in the others (p<0.05). The hatched blastocyst rate 48 hours after the 8-cell embryos were thawed was higher in the 8LAH-ES4 group (45.5%) than in the other groups, but not significantly. The inner cell mass cell number was highest in the 8LAH-ES7 group (19.5±5.1, p<0.05). The number of trophectoderm cells was higher in the 8LAH-ES10 group (73.2±12.1) than in the other groups, but without statistical significance.

Conclusion

When LAH was performed, 2-cell embryos with large blastomeres had a lower hatched blastocyst rate when the exposure to vitrification solution was shorter. Conversely, 8-cell embryos with small blastomere had a higher hatched blastocyst rate when the exposure to vitrification solution was shorter.

Shortened equilibration time can compromise clinical outcomes in human embryo vitrification

Vitrification is an important way to cryopreserve human embryos and the recommended time of embryo exposure to the vitrification solution is 1 min. However, practically speaking, the duration of embryos exposure to equilibration solution can vary from 5 to 15 min. The purpose of this study was to investigate the effect of different equilibration times on the outcomes of frozen-thawed embryo transfer cycles. The data were collected from our medical records from January 2012 to June 2013 and a total of 517 cycles were included. These cycles were divided into four groups according to the equilibration time: (i) 5-6 min; (ii) 7-8 min; (iii) 9-10 min and (iv) 11-12 min. The results show that there were no differences in terms of survival rate and fully intact embryo rate among the four groups. However, lower clinical pregnancy, embryo implantation and live birth rates were observed in the 5-6 min exposure group (54.6%, 31.9% and 48.2%, respectively) compared with the three other groups. The corresponding rates in the 9-10 min group (73.5%, 47.6% and 64.7%) were the highest. This study indicated that different equilibration times influenced the clinical outcomes of human embryo vitrification and vitrification with shortened equilibration time compromised the clinical outcomes. Appropriate prolongation of the equilibrium time would probably improve the clinical outcomes.

Cryopreservation of mammalian embryos: Advancement of putting life on hold

Rodent transgenesis and human-assisted reproductive programs involve multistep handling of preimplantation embryos. The efficacy of production and quality of results from conventionally scheduled programs are limited by temporal constraints other than the quality and quantities of embryos per se. The emergence of vitrification, a water ice-free cryopreservation technique, as a reliable way to arrest further growth of preimplantation embryos, provides an option to eliminate the time constraint. In this article, current and potential applications of cryopreservation to facilitate laboratory animal experiments, colony management, and human-assisted reproductive programs are reviewed. Carrier devices developed for vitrification in the last two decades are compared with an emphasis on their physical properties that infer cooling rate of samples and sterility assurance. Biological impacts of improved cryopreservation on preimplantation embryos are also discussed.

Effect of the polyvinylpyrrolidone concentration of cryoprotectant on mouse embryo development and production of pups: 7.5% of PVP is beneficial for in vitro and in vivo development of frozen-thawed mouse embryos

In this study, we investigated the effect of polyvinylpyrrolidone (PVP) concentration on in vitro and in vivo development of 2 cell stage, vitrified ICR mouse embryos using a cryoprotectant consisting of ethylene glycol (EG) and sucrose. M2 was selected as the basic medium for vitrification and thawing. After equilibration with 4% (v/v) EG at 37 C for 15 min, the embryos were vitrified with 35% EG, 5, 6 or 7.5% (w/v) PVP and 0.4 M sucrose at 37 C for 30 sec. One week later, the cryotubes of cryopreserved embryos in liquid nitrogen were directly immersed into a 37 C water bath for 1 min and transferred serially into 300 microl of 0.5 or 0.3 M sucrose at room temperature for 5 min and M2 medium at 37 C for 10 min. The surviving embryos were cultured in KSOM (potassium simplex optimized medium) for 96-120 h in an atmosphere of 5% CO(2) in humidified air. Survival was evaluated by morphological appearance, including membrane integrity and presence of apoptotic blastomeres after thawing. For in vivo evaluation, blastocysts were transferred to the uteri of pseudopregnant mice. The survival rates of the 5 and 7.5% PVP concentration groups showed a significantly higher difference compared with that of the 6% PVP group (85.5 and 86.5 vs. 71.2%), respectively. Each pup in the of 5 and 6% groups was cannibalized immediately after parturition. A litter of live pups was obtained from only the 7.5% PVP groups. Our study indicated that supplementation of EG and sucrose cryoprotectant solution with 7.5% PVP is optimal for successful vitrification of 2-cell stage ICR mouse embryos.

Cryogenic effect of antifreeze protein on transgenic mouse ovaries and the production of live offspring by orthotopic transplantation of cryopreserved mouse ovaries

The purpose of the present study was to evaluate the cryogenic effect of antifreeze protein (AFP) on transgenic mouse ovaries which is expressed AFP type III from Ocean pout and the production of live offspring by orthotopic transplantation of cryopreserved mouse ovaries. In this study, whole transgenic and nontransgenic mouse ovaries were vitrified with 20% DMSO and 20% EG in M2 medium supplemented with 0.5 M sucrose. All vitrified and toxicity control and fresh ovaries were transplanted orthotopically into ovariectomized recipients bilaterally. For fresh ovaries transplantation, 5 mice delivered litters of 18 and 19 live pups in first and second matings, respectively. For toxicity control of chemicals, 6 mice delivered litters of 22 and 23 live pups. For nontransgenic mouse ovaries (vitrified) transplantation, 7 mice delivered litters of 22 and 23 live pups. For transgenic mouse ovaries (vitrified) transplantation, 10 mice delivered litters of 35 and 37 live pups. Litter sizes from pups of freshly transplanted ovaries were not significantly different from AFP-transplanted transgenic ovaries but those from nontransgenic-transplanted ovaries were significantly different from the AFP-transplanted transgenic ovaries group (P < 0.05). In this study, for the first time, it was shown that the ovarian tissue of AFP transgenic mice was protected from cryopreservation by vitrification. These results demonstrate that a normal reproductive lifespan can be restored by orthotopic transplantation of AFP transgenic-vitrified ovary.

A new selection criterion to assess good quality ovine blastocysts after vitrification and to predict their transfer into recipients

The feasibility to accurately select viable embryos would be valuable for improving pregnancy rates and avoiding futile transfer attempts. The aim of our study was to assess if in vitro-produced embryo quality could be determined by the timing of blastocoelic cavity re-expansion after vitrification, warming, and in vitro culture using sheep as a model. Blastocysts were produced in vitro, vitrified/warmed, and cultured in TCM-199 plus 10% FCS for 72 hr. Embryos were divided into two groups: re-expanded within 8 hr (A) and from 8 to 16 hr (B) of IVC after warming. Fast re-expanded blastocysts showed higher in vitro hatching rates and total cell number calculated on the hatched blastocysts compared with slow re-expanded ones (P < 0.01). Peroxide status evaluation (P < 0.01) and TUNEL test (P < 0.05) revealed a higher number of positive cells in group B compared with group A. The quantitative analysis of protein synthesis revealed a higher synthesis in fast compared with slow re-expanded embryos (P < 0.05). Quantitative RT-PCR showed that 90-kDa Heat Shock Protein beta was more expressed in group A than in group B (P < 0.05), while the quantity of P34(cdc2), Cyclin b, Aquaporin 3, Na/K ATPase, and Actin did not differ between the two groups. Pregnancy rates after transfer to synchronized recipients were higher in fast compared to slow re-expanded blastocysts (P < 0.05). Our results evidenced that timing of blastocoelic cavity re-expansion after vitrification/warming and in vitro culture can be considered as a reliable index of in vitro produced embryo quality and developmental potential.

Oocyte cryopreservation: oocyte assessment and strategies for improving survival

Despite significant progress in cryopreservation of mammalian oocytes and embryos, many of the molecular and biochemical events that underlie this technology are poorly understood. In recent years, researchers have focused on obtaining viable oocytes that are developmentally competent. Even under the most favourable conditions, experimental approaches have achieved only limited success compared with fresh oocytes used in routine in vitro embryo production. Chilling injuries and toxic effects of the cryoprotectants are the major adverse consequences following cryoprocedures. To overcome these problems, different strategies have been developed for improving cryopreservation results. These strategies include reducing container volumes, increasing the thermal gradient, changing the cell surface/volume ratio, enhancing cryotolerance by supplementation with various additives or modifying the lipid composition of the oocyte membrane. In order to develop new strategies for reducing the various forms of stress associated with oocyte cryopreservation, it is fundamental to gain a better understanding of the major changes responsible for poor post-thaw survival. With this knowledge, we hope that oocyte cryostorage will become a fully reliable reproductive technique in the near future.

Gene expression profiles of vitrified in vivo derived 8-cell stage mouse embryos detected by high density oligonucleotide microarrays

Very little is known about the effect of vitrification on gene functions after warming. The goals of our study were to compare the gene expression patterns, and identify those most affected. For this, 8-cell stage embryos were collected from ICR mice and vitrified with solid surface vitrification technique, while maintaining equal numbers of embryos as control. Total RNAs were extracted and two rounds of amplification were employed. Finally three micrograms of contrasting RNA samples were hybridized on the Agilent Mouse 22 K oligonucleotide slides and the results were analyzed with subsequent verification by independent real-time PCR analyses. The two rounds of amplification with 5 ng tRNA input have yielded 15-16 microg of cRNA. The analyses of repeated hybridizations showed 20,183 genes/ESTs as common signatures, and unsupervised analysis identified 628 differentially expressed (P < 0.01) genes. However, with at least 1.5-fold change considerations, 183 genes were differentially expressed (P < 0.01) out of which 107 were upregulated. The independent analysis with real-time PCR and unamplified samples fully confirmed the results of microarray, indicating the linearity of amplification. Furthermore, this novel gene expression study for vitrified embryos identified many new candidate genes with overrepresentation in some important biological processes. Thus, it is possible to conclude that the expression pattern reflected a broad spectrum of consequences of vitrification on embryos, with most effects on metabolism, regulatory role and stress response genes and allowed the identification of new candidate marker genes for cryosurvival.