In vitro comparisons of two cryopreservation techniques for equine embryos: Slow-cooling and open pulled straw (OPS) vitrification

Vitrifying expanded equine embryos collapsed by blastocoel aspiration is less damaging than slow-freezing

The cryotolerance of equine blastocysts larger than 300 μm can be improved by aspirating blastocoele fluid prior to vitrification; however, it is not known whether blastocoele aspiration also enables successful slow-freezing. The aim of this study was therefore to determine whether slow-freezing of expanded equine embryos following blastocoele collapse was more or less damaging than vitrification. Grade 1 blastocysts recovered on day 7 or 8 after ovulation were measured (>300-550 μm, n = 14 and > 550 μm, n = 19) and blastocoele fluid was aspirated prior to slow-freezing in 10% glycerol (n = 14), or vitrification (n = 13) in 16.5% ethylene glycol/16.5% DMSO/0.5 M sucrose. Immediately after thawing or warming, embryos were cultured for 24 h at 38 °C and then graded and measured to assess re-expansion. Control embryos (n = 6) were cultured for 24 h following aspiration of blastocoel fluid, without cryopreservation or exposure to cryoprotectants. Subsequently, embryos were stained to assess live/dead cell proportion (DAPI/TOPRO-3), cytoskeleton quality (Phalloidin) and capsule integrity (WGA). For 300-550 μm embryos, quality grade and re-expansion were impaired after slow-freezing but not affected by vitrification. Slow-freezing embryos >550 μm induced additional cell damage as indicated by a significant increase in dead cell proportion and disruption of the cytoskeleton; neither of these changes were observed in vitrified embryos. Capsule loss was not a significant consequence of either freezing method. In conclusion, slow-freezing of expanded equine blastocysts collapsed by blastocoel aspiration compromises post-thaw embryo quality more than vitrification.

Effect of vitrification on global gene expression dynamics of bovine elongating embryos

Embryo vitrification involves exposure to high concentrations of cryoprotectants and osmotic stress during cooling and warming in the cryopreservation process. Many of these factors can potentially affect gene expression. In this study, invitro-produced bovine embryos at the blastocyst stage were subjected to vitrification. Four recipients each were used for transferring non-vitrified (n=80) and vitrified (n=80) embryos. A total of 12 non-vitrified and 9 vitrified viable day-14 (D14) embryos were recovered by uterine flushing. RNA-seq analysis of the whole embryo or isolated trophectoderm (TE) from vitrified and fresh recovered D14 embryos revealed a total of 927 and 4376 genes with changed expression in embryos and TE isolates, respectively, as a result of vitrification. In addition, we found 671 and 61 genes commonly up- or downregulated in both vitrified whole embryos and TE. Commonly upregulated pathways by vitrification included epithelial adherens junctions, sirtuin signalling, germ cell-sertoli cell junction, ATM signalling, NER and protein ubiquitination pathways. The commonly downregulated pathways included EIF2 signalling, oxidative phosphorylation, mitochondrial dysfunction, regulation of eIF4 and p70S6K signalling and mTOR signalling pathways. Our analysis identified specific pathways and implicated specific gene expression patterns affecting embryo developmental competence that are important to cryopreservation.

Cryopreservation of donkey embryos: Comparison of embryo survival rate after in vitro culture between conventional freezing and vitrification

Embryo cryopreservation ensures that genetic biodiversity is preserved over time. This study evaluates the survival of donkey embryos subjected to slow freezing and vitrification after thawing and in vitro culture. Seven-day-old in vivo produced donkey embryos were subjected to slow freezing (SF, N = 14) or vitrification (VIT, N = 22). After one year of cryopreservation, embryos were warmed, washed and placed in incubation for in vitro culture (IVC). In order to assess the embryo viability, the quality grade and developmental stage were recorded after thawing and after 24 and 48 h of IVC. Eleven embryos (SF = 4 and VIT = 7) were incubated under a time-lapse camera, for up to 68 h, in order to determine the area and growth. The survival rate was not influenced by the procedure but by the developmental stage: after 48 h of IVC blastocyst survival rate (1/8, 12.5%) was significantly lower compared to both morulas (8/12, 66.7%) and early blastocysts (11/16, 68.7%) (P < 0.05). Embryo diameter class at recovery did not significantly influence the survival rate. In terms of the embryos that were judged to be alive after 48 h of IVC, quality grade 1 was observed in 7/8 (88%) and 4/12 (33%) of the SF and VIT embryos, respectively (P < 0.05). After time-lapse analysis, the IVC embryo area as well as growth percentage were statistically higher in the SF than the VIT embryos (P < 0.05). In conclusion, no difference in survival rates was found between the two cryopreservation procedures, although embryo quality was more negatively affected by vitrification.

One-step warming does not affect the in vitro viability and cryosurvival of cryotop-vitrified donkey embryos

The objective of this study was to compare the effects of two warming protocols (three-step vs. one-step dilution) on embryo quality, post-warming embryo survival and embryo cell viability of donkey embryos vitrified by the Cryotop method. Twenty, Day 7-8, grade 1-2 donkey embryos were measured, morphologically evaluated and vitrified using the Cryotop technique. Embryos were then randomly warmed using two different warming procedures: (i) W3 (three-step dilution; n = 11): embryos were warmed in 1 M, 0.5 M and 0 M sucrose, and (ii) W1/0.5 (one-step dilution; n = 9): embryos were warmed directly in 0.5 M sucrose. After 3 and 24 h of warming, the embryos were measured and evaluated for their morphology, developmental stage and viability (Propidium Iodide-Hoechst 33,342 dyes). Although both treatments decreased embryo quality after warming (P < 0.05), no significant differences (P > 0.05) were observed between protocols in terms of post-warming embryo quality, diameter and embryo survival. Greater percentages of dead cells (P < 0.001) were observed when embryos were warmed directly in 0.5 M sucrose (one-step dilution) when compared to the three-step protocol. The percentage of ruptured embryos was 27.3% and 0% in W3 and W1/0.5 protocols (P = 0.0893), respectively. In conclusion, warming Cryotop-vitrified donkey embryos directly in 0.5 M sucrose had no negative effects on embryo quality and post-warming embryo survival. Moreover, one-step protocol may help to prevent rupture when donkey embryos warmed directly in 0.5 M sucrose. These results observed in vitro must be verified by embryo transfer.

The cryoprotective effect of Ficoll 70 on the post-warming survival and quality of Cryotop-vitrified donkey embryos

Many domestic donkey breeds are at risk of extinction, there is a critical urgency for genome resource banking. In the present study, we examined whether the use of Ficoll 70 added to the vitrification medium containing ethylene glycol (EG), dimethyl sulfoxide (DMSO) and sucrose improves the cryotolerance of donkey in vivo derived embryos. Day 7-8, grade 1-2 donkey embryos were measured and morphologically evaluated and then vitrified-warmed using the Cryotop technique. Before vitrification, embryos were randomly distributed into two groups: (i) VS1 (n = 14): vitrified using 15% EG + 15% DMSO + 0.5 M sucrose; and (ii) VS2 (n = 10): vitrified in the same medium supplemented also with 18% of Ficoll 70. After 24 h of warming, the embryos were measured and evaluated for their morphology, development and viability (Propidium Iodide-Hoechst 33342 dyes). Post-warming survival was numerically higher but not significantly different (P > 0.05) when embryos were vitrified in VS2 (70%) compared to VS1 (57.1%). Embryo rupture was only observed in the VS1 group (21.4%, 3/14). Higher embryo diameter was observed in all groups after 24 h culture (P < 0.05). No significant differences (P > 0.05) were observed among treatments in terms of percentages of cell death. These results demonstrate that the addition of Ficoll 70 to the vitrification medium is not a pre-requisite for successful vitrification of donkey embryos. However, its addition seems to enhance some of the post-warming embryo quality characteristics. Since no statistically significant evidence was found, further studies should be conducted in order to confirm our findings.

Effect of cryopreservation technique and season on the survival of in vitro produced cattle embryos

Embryo cryopreservation is a major tool for conservation and propagation of genetically superior animals. However, it adversely affects the survival of embryos. The objective of this study was to determine the effects of cryopreservation technique (vitrification compared with slow freezing) and different seasons in which oocytes were obtained on the post-warming survival of in vitro produced (IVP) cattle morulae. In experiment 1, morulae (Day 6 post-IVF), obtained from abattoir-sourced oocytes during spring, summer, fall and winter over a period of 3.5 years, were subjected to either vitrification (n=271 morulae), slow freezing (n=281 morulae) or no freezing (control; n=249 morulae). After warming, the morulae were cultured to the expanded blastocyst stage (Day 8 post-IVF). Data were compared using Glimmix procedure in SAS(®). Blastocyst rate differed (P<0.05) among the treatments: unfrozen control (78±3.6%), vitrification (52±4.6%) and slow freezing (35±4.2%). The re-expansion of vitrified morulae upon warming was not correlated with subsequent blastocyst rate (r=-0.048; P>0.05). The morulae produced during fall season had lesser (P<0.05) cleavage and morula rates (67±1.6%; Day 2 post-IVF and 22±1.4%; Day 6 post-IVF, respectively) than all other seasons (74±1.1 and 30±1.2%, respectively). Blastocyst rate was the least (P<0.05) when oocytes were collected during the summer season in both control and slowly frozen groups. Blastocyst development rate did not change due to season in vitrification group (P>0.05). In conclusion, vitrification is a more desirable technique than slow freezing for cryopreservation of IVP cattle morulae. If the slow freezing method is employed, greater success can be achieved using oocytes collected in the winter and spring with a primary contributing factor being lesser morulae development if oocytes are collected in the fall and also the lesser blastocyst formation of cryopreserved morulae when oocytes are collected in the summer.

Cryobanking of farm animal gametes and embryos as a means of conserving livestock genetics

In the last few decades, farm animal genetic diversity has rapidly declined, mainly due to changing market demands and intensification of agriculture. But, since the removal of single species can affect the functioning of global ecosystems, it is in the interest of international community to conserve the livestock genetics and to maintain biodiversity. Increasing awareness on the reduction of breed diversity has prompted global efforts for conservation of farm animal breeds. The goals of conservation are to keep genetic variation as gene combinations in a reversible form and to keep specific genes of interest. For this purpose two types of strategies are usually proposed: in situ and ex situ conservation. In situ conservation is the breed maintaining within the livestock production system, in its environment through the enhancement of its production characteristics. Ex situ in vivo conservation is the safeguard of live animals in zoos, wildlife parks, experimental farms or other specialized centres. Ex situ in vitro conservation is the preservation of genetic material in haploid form (semen and oocytes), diploid (embryos) or DNA sequences. In the last few years, ex situ in vitro conservation programs of livestock genetic resources have focused interest on cryopreservation of gametes, embryos and somatic cells as well as testis and ovarian tissues, effectively lengthening the genetic lifespan of individuals in a breeding program even after the death. However, although significant progress has been made in semen, oocytes and embryo cryopreservation of several domestic species, a standardized procedure has not been established yet. The aim of the present review is to describe the cryobanking purposes, the collection goals, the type of genetic material to store and the reproductive biotechnologies utilized for the cryopreservation of farm animal gametes and embryos.

Blastocyst rate and live births from vitrification and slow-cooled two-cell mouse embryos

OBJECTIVE

The purpose of this study was to develop a closed vitrification system, compare vitrification to a slow-cooled cryopreservation method, and compare the pup rate between both methods using two-cell mouse embryos.

DESIGN

Randomized, prospective animal study.

SETTING

Hospital-based IVF practice.

ANIMAL(S)

B6C3F1 mouse embryos.

INTERVENTION(S)

Two-cell mouse embryos were cryopreserved using a slow-cooled or vitrification method and then thawed at a later date. The embryos were cultured and transferred to recipient females.

MAIN OUTCOME MEASURE(S)

Embryos were observed for blastocyst rate and pups were observed for phenotypic anomalies and weighed at 30, 60, and 90 days after birth.

RESULT(S)

Neither the blastocyst rate, pup rate, nor pup weights were significantly different when the two cryopreservation methods were compared.

CONCLUSION(S)

Because there were no differences in blastocyst rates, pup rates, or pup weights, we plan to further investigate the potential effects of vitrification on genotypic damage via the Comet Assay.

Open-pulled Straw (OPS) Vitrification of Mouse Hatched Blastocysts

This study was first employed to investigate the developmental potential of mouse hatched blastocyts (HBs) vitrified by a two-step open-pulled straw (OPS) method. HBs were obtained by culture of morulae in vitro. First, the embryos were placed in four cryprotectant solutions - that is, 10% ethylene glycol (EG), 10%E + 10%D (10% EG and 10% dimethyl sulphoxide (DMSO) in mPBS), EFS30 (30% EG, Ficoll, and sucrose) and EDFS30 (15% EG, 15% DMSO, Ficoll, and sucrose)--at 25 degrees C for 0.5 to 10 min, respectively, to determine their optimal survival after rapid dilution in 0.5 M sucrose. Secondly, based on the above best survival, the embryos were plunged into liquid nitrogen after first pretreatment in 10%E for 0.5 min and then 0.5 min equilibration in EFS30 (Group 1), or 10%E + 10%D and EDFS30 for 0.5 min, respectively (Group 2). When warming, three methods were used to dilute the cryoprotectants from the vitrified embryos. The embryos were assessed by the re-expansion of the blastocoel or development to term. The result showed that all the vitrified-warmed HBs got high in vitro survival rates (83.7% to 98.9%). The highest in vitro survival rates (87.8% in Group 1, 98.9% in Group 2) were obtained when the vitrified embryos were diluted first in 0.3 M sucrose for 5 min, then in 0.15 M sucrose for 2 min (method C). When the vitrified embryos diluted with method C were transferred, their survival rate in vivo (35.5% to 42.2% of the total) were similar to (P > 0.05) that of control (45.7%). These results demonstrate OPS method was highly efficient for the cryopreservation of mouse HBs.