Containerless vitrification of mammalian oocytes and embryos

Zygote cryobanking applied to CRISPR/Cas9 microinjection in mice

Microinjection of CRISPR/Cas9 requires the availability of zygotes that implies animal breeding, superovulation schemes, and embryo collection. Vitrification of zygotes may allow having ready-to-use embryos and to temporally dissociate the workload of embryo production from microinjection. In this study, fresh (F group) or vitrified (V group) zygotes were microinjected with CRISPR/Cas9 system to test the hypothesis that vitrified zygotes could be a suitable source of embryos for microinjection. In Experiment 1 (in vitro evaluation), B6D2F1/J zygotes were microinjected and cultured until blastocyst stage. Embryo survival and cleavage rates after microinjection were similar between groups (~50% and ~80% respectively; P = NS). Development rate was significantly higher for F than V group (55.0% vs. 32.6%, respectively; P<0.05). Mutation rate did not show statistical differences among groups (P = NS). In Experiment 2 (in vivo evaluation), C57BL/6J zygotes were microinjected and transferred to recipient females. Embryo survival was significantly lower in fresh than in vitrified zygotes (49.2% vs. 62.7%, respectively; P<0.05). Cleavage rate did not show statistical differences (~70%; P = NS). Pregnancy rate (70.0% vs. 58.3%) and birth rate (11.9% vs. 11.2%) were not different between groups (F vs. V group; P = NS). Offspring mutation rate was higher for F than V group, in both heterodimer analysis (73.7% vs. 33.3%, respectively; P = 0.015) and Sanger sequencing (89.5% vs. 41.7%, respectively; P = 0.006). In conclusion, vitrified-warmed zygotes present a viable alternative source for CRISPR/Cas9 microinjection when the production of fresh embryos is impeded by limited technical support. The possibility of zygote cryobanking to perform microinjection sessions on demand seems to be a suitable alternative to avoid the breeding and maintenance of animals all over the year, enhancing the implementation of CRISPR technology.

Refined Techniques for Enabling Long-Term Cryo-Repository Using Vitrification and Laser Warming

Vitrification and ultrarapid laser warming are crucial for the cryopreservation of animal embryos, oocytes, and other cells of medicinal, genetic, and agricultural value. In the present study, we focused on alignment and bonding techniques for a special cryojig that combines a jig tool and jig holder into one piece. This novel cryojig was used to obtain a high laser accuracy of 95% and a successful rewarming rate of 62%. The experimental results indicated that our refined device improved laser accuracy in the warming process after long-term cryo-storage through vitrification. We anticipate that our findings will lead to cryobanking applications that use vitrification and laser nanowarming to preserve cells and tissues from a wide range of species.

Tracking Immature Testicular Tissue after Vitrification In Vitro and In Vivo for Pre-Pubertal Fertility Preservation: A Translational Transgenic Mouse Model

Pediatric cancer survivors experiencing gonadotoxic chemoradiation therapy may encounter subfertility or permanent infertility. However, previous studies of cryopreservation of immature testicular tissue (ITT) have mainly been limited to in vitro studies. In this study, we aim to evaluate in vitro and in vivo bioluminescence imaging (BLI) for solid surface-vitrified (SSV) ITT grafts until adulthood. The donors and recipients were transgenic and wild-type mice, respectively, with fresh ITT grafts used as the control group. In our study, the frozen ITT grafts remained intact as shown in the BLI, scanning electron microscopy (SEM) and immunohistochemistry (IHC) analyses. Graft survival was analyzed by BLI on days 1, 2, 5, 7, and 31 after transplantation. The signals decreased by quantum yield between days 2 and 5 in both groups, but gradually increased afterwards until day 31, which were significantly stronger than day 1 after transplantation (p = 0.008). The differences between the two groups were constantly insignificant, suggesting that both fresh and SSV ITT can survive, accompanied by spermatogenesis, until adulthood. The ITT in both groups presented similar BLI intensity and intact cells and ultrastructures for spermatogenesis. This translational model demonstrates the great potential of SSV for ITT in pre-pubertal male fertility preservation.

Oocyte Cryopreservation in Domestic Animals and Humans: Principles, Techniques and Updated Outcomes

Oocyte cryopreservation plays important roles in basic research and the application of models for genetic preservation and in clinical situations. This technology provides long-term storage of gametes for genetic banking and subsequent use with other assisted reproductive technologies. Until recently, oocytes have remained the most difficult cell type to freeze, as the oocytes per se are large with limited surface area to cytoplasm ratio. They are also highly sensitive to damage during cryopreservation, and therefore the success rate of oocyte cryopreservation is generally poor when compared to noncryopreserved oocytes. Although advancement in oocyte cryopreservation has progressed rapidly for decades, the improvement of cryosurvival and clinical outcomes is still required. This review focuses on the principles, techniques, outcomes and prospects of oocyte cryopreservation in domestic animals and humans.

History and prospects of intracytoplasmic sperm injection (ICSI) and the development of golden hamster ICSI embryos

BACKGROUND

Golden (Syrian) hamsters have many advantages for the study of reproductive biology and developmental biology, including a consistent estrous cycle, a stable superovulation response, and a short gestation period. However, there are serious difficulties in doing in vitro manipulations of hamster embryos, because they are very sensitive to various environmental factors. Thus, biotechnological researches of hamster embryos should be performed with high-level skills of embryo manipulations.

METHODS

The authors summarized the history of hamster intracytoplasmic sperm injection (ICSI) and introduced key points for hamster ICSI, which were found in our previous studies on the production of embryos by ICSI and offspring by embryo transfer.

MAIN FINDINGS

The key points for hamster ICSI were in vitro manipulations under the light-controlled environment, injection of acrosome-less sperm heads into oocytes as soon as possible before spontaneous oocyte activation occurs, and determination of the optimal culture conditions.

CONCLUSION

To our knowledge, there are no available reports on production of offspring from ICSI embryos in hamsters except our reports. Moreover, success rates of hamster ICSI remain very low. For the purpose of spreading hamster ICSI, it is necessary to make further researches to improve manipulation techniques and to resolve experimental problems.

Vitrification-induced activation of lysosomal cathepsin B perturbs spindle assembly checkpoint function in mouse oocytes

As the age of child-bearing increases and correlates with infertility, cryopreservation of female gametes is becoming common-place in ART. However, the developmental competence of vitrified oocytes has remained low. The underlying mechanisms responsible for reduced oocyte quality post-vitrification are largely unknown. Mouse cumulus-oocyte complexes were vitrified using a cryoloop technique and a mixture of dimethylsulphoxide, ethylene glycol and trehalose as cryoprotectants. Fresh and vitrified/thawed oocytes were compared for chromosome alignment, spindle morphology, kinetochore-microtubule attachments, spindle assembly checkpoint (SAC) and aneuploidy. Although the majority of vitrified oocytes extruded the first polar body (PB), they had a significant increase of chromosome misalignment, abnormal spindle formation and aneuploidy at metaphase II. In contrast to controls, vitrified oocytes extruded the first PB in the presence of nocodazole and etoposide, which should induce metaphase I arrest in a SAC-dependent manner. The fluorescence intensity of mitotic arrest deficient 2 (MAD2), an essential SAC protein, at kinetochores was reduced in vitrified oocytes, indicating that the SAC is weakened after vitrification/thawing. Furthermore, we found that vitrification-associated stress disrupted lysosomal function and stimulated cathepsin B activity, with a subsequent activation of caspase 3. MAD2 localization and SAC function in vitrified oocytes were restored upon treatment with a cathepsin B or a caspase 3 inhibitor. This study was conducted using mouse oocytes, therefore confirming these results in human oocytes is a prerequisite before applying these findings in IVF clinics. Here, we uncovered underlying molecular pathways that contribute to an understanding of how vitrification compromises oocyte quality. Regulating these pathways will be a step toward improving oocyte quality post vitrification and potentially increasing the efficiency of the vitrification program.

In Situ Vitrification of Lung Cancer Organoids on a Microwell Array

Three-dimensional cultured patient-derived cancer organoids (PDOs) represent a powerful tool for anti-cancer drug development due to their similarity to the in vivo tumor tissues. However, the culture and manipulation of PDOs is more difficult than 2D cultured cell lines due to the presence of the culture matrix and the 3D feature of the organoids. In our other study, we established a method for lung cancer organoid (LCO)-based drug sensitivity tests on the superhydrophobic microwell array chip (SMAR-chip). Here, we describe a novel in situ cryopreservation technology on the SMAR-chip to preserve the viability of the organoids for future drug sensitivity tests. We compared two cryopreservation approaches (slow freezing and vitrification) and demonstrated that vitrification performed better at preserving the viability of LCOs. Next, we developed a simple procedure for in situ cryopreservation and thawing of the LCOs on the SMAR-chip. We proved that the on-chip cryopreserved organoids can be recovered successfully and, more importantly, showing similar responses to anti-cancer drugs as the unfrozen controls. This in situ vitrification technology eliminated the harvesting and centrifugation steps in conventional cryopreservation, making the whole freeze–thaw process easier to perform and the preserved LCOs ready to be used for the subsequent drug sensitivity test.

Mitochondrial function, blastocyst development and live foals born after ICSI of immature vitrified/warmed equine oocytes matured with or without melatonin

Oocyte vitrification is considered experimental in the horse with only three live foals reported. The oxidative conditions induced by vitrification could in part explain the poor results and melatonin, a powerful antioxidant, could stimulate ROS metabolization and restore mitochondrial function in these oocytes. Our objective was to determine the oxidative status of vitrified equine oocytes and to analyze the effect of melatonin on mitochondrial-specific ROS (mROS), oocyte maturation, ICSI embryo development and viability. Immature, abattoir-derived oocytes were held for 15 h and vitrified in a final concentration of 20% EG, 20% DMSO and 0.65 M trehalose. In Experiment 1, overall ROS was determined by DCHF-DA; vitrification increased ROS production compared to non-vitrified controls (1.29 ± 0.22 vs 0.74 ± 0.25 a. u.; P = 0.0156). In Experiment 2, mROS was analyzed by MitoSOX™ in vitrified/warmed oocytes matured with (+) or without (-) supplementation of 10^-9 M melatonin; mROS decreased in vitrified and non-vitrified oocytes matured in presence of melatonin (P < 0.05). In Experiment 3, we assessed the effect of melatonin supplementation on oocyte maturation, embryo development after ICSI, and viability by pregnancy establishment. Melatonin did not improve oocyte maturation, cleavage or blastocyst rate of non-vitrified oocytes. However, vitrified melatonin (+) oocytes reached similar cleavage (61, 75 and 77%, respectively) and blastocyst rate (15, 29 and 26%, respectively) than non-vitrified, melatonin (+) and (-) oocytes. Vitrified, melatonin (-) oocytes had lower cleavage (46%) and blastocyst rate (9%) compared to non-vitrified groups (P < 0.05), but no significant differences were observed when compared to vitrified melatonin (+). Although the lack of available recipients precluded the transfer of every blastocyst produced in our study, transferred embryos from non-vitrified oocytes resulted in 50 and 83% pregnancy rates while embryos from vitrified oocytes resulted in 17 and 33% pregnancy rates, from melatonin (+) and (-) treatments respectively. Two healthy foals, one colt from melatonin (+) and one filly from melatonin (-) treatment, were born from vitrified/warmed oocytes. Gestation lengths (considering day 0 = day of ICSI) were 338 days for the colt and 329 days for the filly, respectively. Our work showed for the first time that in the horse, as in other species, intracellular reactive oxygen species are increased by the process of vitrification. Melatonin was useful in reducing mitochondrial-related ROS and improving ICSI embryo development, although the lower pregnancy rate in presence of melatonin should be further analyzed in future studies. To our knowledge this is the first report of melatonin supplementation to an in vitro embryo culture system and its use to improve embryo developmental competence of vitrified oocytes following ICSI.

Does the number of embryos loaded on a single cryo-carrier affect post-vitrification survival rate?

BACKGROUND

We aimed to assess whether the survival rate of embryos is influenced by the number of embryos/oocytes loaded on a single cryo-carrier during vitrification.

METHODS

This was a retrospective study that included 974 patients who underwent thawing of 1896 embryo-warming cycles between September 2016 and January 2020. A distinct analysis was made for cleavage stage embryos (2-10-cell stage) and blastocysts. For vitrification, embryos were placed in a Cryotop™ open device using a SAGE vitrification kit following the manufacturer's instructions. Warming was carried using a SAGE warming vitrification kit according the manufacturer's instructions.

RESULTS

Total post-vitrification survival rates of embryos at the cleavage stage or blastocyst stage was 94.8%. At the cleavage stage, cryo-preserving three embryos per single cryo-carrier gave the highest full intact embryo survival rate (91.5%) compared with one or two embryo(s) per single cryo-carrier (85.7%, P < 0.0002 and 87.3%, P < 0.004). Conversely, post warmed full intact blastocyst survival rate for two blastocysts was significantly lower compared with one blastocyst (76.7% vs. 87.9%, P < 0.0193) per single cryo-carrier.

CONCLUSION

Post-thawing survival rate following vitrification is affected by the number of embryos per single cryo-carrier undergoing the vitrification equilibration phase, with the optimum number of three cleaved embryos or one blastocyst per single cryo-carrier. Further studies are required to determine the optimum number of cleaved embryos or blastocysts that should be loaded onto a single cryo-carrier vitrification device.

Cryopreservation of infectious Cryptosporidium parvum oocysts achieved through vitrification using high aspect ratio specimen containers

Infection with protozoa of the genus Cryptosporidium is a leading cause of child morbidity and mortality associated with diarrhea in the developing world. Research on this parasite has been impeded by many technical limitations, including the lack of cryopreservation methods. While cryopreservation of Cryptosporidium oocysts by vitrification was recently achieved, the method is restricted to small sample volumes, thereby limiting widespread implementation of this procedure. Here, a second-generation method is described for cryopreservation of C. parvum oocysts by vitrification using custom high aspect ratio specimen containers, which enable a 100-fold increase in sample volume compared to previous methods. Oocysts cryopreserved using the described protocol exhibit high viability, maintain in vitro infectivity, and are infectious to interferon-gamma (IFN-γ) knockout mice. Importantly, the course of the infection is comparable to that observed in mice infected with unfrozen oocysts. Vitrification of C. parvum oocysts in larger volumes will expedite progress of research by enabling the sharing of isolates among different laboratories and the standardization of clinical trials.

Development of assisted reproductive technologies in small animal species for their efficient preservation and production

Assisted reproductive technologies (ARTs) are widely used in the animal industry, human clinics, and for basic research. In small laboratory animal species such as mice, ARTs are essential for the production of animals for experiments, the preservation of genetic resources, and for the generation of new strains of genetically modified animals. The RIKEN BioResource Research Center (BRC) is one of the largest repositories of such animal bioresources, and maintains approximately 9,500 strains of mice with a variety of genetic backgrounds. We have sought to devise ARTs specific to the reproductive and physiological characteristics of each strain. Such ARTs include superovulation, in vitro fertilization (IVF), the cryopreservation of embryos and spermatozoa, transportation of cryopreserved materials and embryo transfer (ET). Of these, superovulation likely has the most influence on animal production because it determines the quantity of starting material for other ARTs. Superovulation using anti-inhibin serum combined with estrous synchronization has resulted in approximately a three-fold increase in production efficiency with IVF-ET in the C57BL/6J strain. Wild-derived strains are important as genetically diverse resources for murine rodents (Genus Mus), and many are unique to the BRC. We have also successfully developed ARTs for more than 50 wild-derived strains, which have been cryopreserved for future use. Our work to improve and develop ARTs for mice and other small laboratory species will contribute to the cost-effectiveness of routine operations at repository centers, and to the provision of high quality animals for research use.

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.

Characterization of Laser Gold Nanowarming: A Platform for Millimeter-Scale Cryopreservation

Preventing ice formation during cryopreservation by vitrification has led to the successful storage and banking of numerous cellular- and tissue-based biomaterials. In their breakthrough work, Peter Mazur's group achieved over 90% survival by using a laser warming technique for 100 μm mice oocytes that were cooled in 0.1 μL droplets with 2.3 M CPA and extracellularly loaded India ink (laser absorber). Laser warming can provide rapid and uniform warming rates to "outrun" damaging ice crystal growth. Here we generalize Mazur's technique for microliter-sized droplets using laser nanowarming to rewarm millimeter-scale biomaterials when loaded extracellularly and/or intracellularly with biocompatible 1064 nm resonant gold nanoparticles. First, we show that droplets containing low-concentration cryoprotectants (such as 2 M propylene glycol ± 1 M trehalose) can be rapidly cooled at rates up to 90 000 °C/min by plunging into liquid nitrogen to achieve either a visually transparent state (i.e., vitrified) or a cloudy with ice (i.e., nonvitrified) state. Both modeling and experiments were then used to characterize the laser nanowarming process for different laser energy (2-6 J), pulse length (1-20 ms), droplet volume (0.2-1.8 μL), cryoprotectant (2-3 M), and gold concentration (0.77 × 10¹⁷-4.8 × 10¹⁷ nps/m³) values to assess physical and biological success. Physical success was achieved by finding conditions that minimize cloudiness and white spots within the droplets during cooling and warming as signs of damaging ice formation and ice crystallization, respectively. Biological success was achieved using human dermal fibroblasts to find conditions that achieve ≥90% cell viability normalized to controls postwarming. Thus, physical and biological success can be achieved using this platform cryopreservation approach of rapid cooling and laser gold nanowarming in millimeter-scale systems.

The golden (Syrian) hamster as a model for the study of reproductive biology: Past, present, and future

BACKGROUND

The golden (Syrian) hamster (Mesocricetus auratus) is a small rodent that belongs to the Cricetidae family. It has several unique features that are advantageous for the study of reproductive and developmental biology, including a consistent estrous cycle (4 days), high responsiveness to conventional superovulation regimens, and the short gestation period (16 days).

METHODS

Based on the published reports, the development in assisted reproductive technology (ART) in the golden hamsters was summarized.

MAIN FINDINGS

The technical ease of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) in this species has contributed to our understanding of the basic mechanisms of mammalian fertilization in the last century. However, a strong developmental block in vitro of hamster embryos and unavailability of gene-modified strains has hampered its broader use in biomedical fields. A recently developed in vivo transfection method has enabled us to generate gene knockout hamsters without any major obstacles. It would be interesting to revisit the genes whose functions could not be identified using mouse models.

CONCLUSION

The authors expect that gene knockout hamsters might be able to substitute for mice-at least in part-for better understanding of gene functions in mammals including humans.

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.

Cryopreservation of infectious Cryptosporidium parvum oocysts

Cryptosporidiosis in an enteric infection caused by Cryptosporidium parasites and is a major cause of acute infant diarrhea in the developing world. A major bottleneck to research progress is the lack of methods to cryopreserve Cryptosporidium oocysts, thus requiring routine propagation in laboratory animals. Here, we report a method to cryopreserve C. parvum oocysts by ultra-fast cooling. Cryopreserved oocysts exhibit high viability and robust in vitro excystation, and are infectious to interferon-γ knockout mice. The course of the infection is comparable to what we observe with unfrozen oocysts. Oocyst viability and infectivity is not visibly changed after several weeks of cryogenic storage. Cryopreservation will facilitate the sharing of oocysts from well-characterized isolates and transgenic strains among different laboratories.

Minimum volume Spatula MVD vitrification method improves embryo survival compared to traditional slow freezing, both for in vivo and in vitro produced mice embryos

This study was conducted to compare the effect of minimum volume Spatula MVD vitrification (VIT) versus traditional slow freezing (SLF) of mouse embryos. A total of 2,617 8-cell in vivo derived and 2-cell in vitro produced B6D2 mouse embryos were subjected to freezing/thawing or vitrification/warming, while fresh embryos were used as control group. Embryo recovery, survival and development rate, pregnancy rate and offspring production were analyzed. In Experiment 1, 8-cell in vivo derived embryos were subjected to in vitro culture, resulting in greater survival and development rates at 3.5 days post coitum stage in VIT than in SLF group (P < 0.05). Although both methods reached an acceptable hatching rate (41.0% and 49.7% for VIT and SLF, respectively; P=NS), it was significantly lower respect to the control group (67.8%, P < 0.01). In Experiment 2, 2-cell in vitro produced mouse embryos showed a similar recovery rate from the device after freezing/thawing or vitrification/warming (∼84%), however survival rate was significantly higher for vitrified/warmed (94.7%) than frozen/thawed embryos (85.1%; P < 0.01). Vitrified/warmed and control fresh embryos were transferred to surrogate mothers, revealing no differences both in pregnancy and offspring production rates. Our data demonstrate that minimum volume Spatula MVD method is a simple home-made useful technique for vitrification of 2-cell and 8-cell mouse embryos produced either in vitro or in vivo.

Production of blastocysts following in vitro maturation and fertilization of dromedary camel oocytes vitrified at the germinal vesicle stage

Cryopreservation of oocytes would serve as an alternative to overcome the limited availability of dromedary camel oocytes and facilitate improvements in IVP techniques in this species. Our goal was to develop a protocol for the vitrification of camel oocytes at the germinal vesicle (GV) stage using different cryoprotectant combinations: 20% EG and 20% DMSO (VS1), 25% EG plus 25% DMSO (VS2) or 25% EG and 25% glycerol (VS3) and various cryo-carriers; straws or open pulled-straw (OPS) or solid surface vitrification (SSV); and Cryotop. Viable oocytes were cultured in vitro for 30 h. Matured oocytes were fertilized with epididymal spermatozoa and then cultured in vitro in modified KSOMaa medium for 7 days. Survival and nuclear maturation rates were significantly lower (P ≤ 0.05) in oocytes exposed to VS3 (44.8% and 34.0%, respectively) than those exposed to VS1 (68.2% and 48.0%, respectively) and VS2 (79.3% and 56.9%, respectively). Although recovery rates were significantly lower (P ≤ 0.05) in SSV and Cryotop vitrified oocytes (66.9% to 71.1%) than those vitrified by straws with VS1 or VS2 solutions (86.3% to 91.0%), survival rates were higher in the SSV and Cryotop groups (90.7% to 94.8%) than in the straw and OPS groups (68.2% to 86.5%). Among vitrified groups, maturation and fertilization rates were the highest in the Cryotop-VS2 group (51.8% and 39.2%, respectively). These values were comparable to those seen in the controls (59.2% and 44.6%, respectively). Cleavage (22.5% to 27.9%), morula (13.2% to 14.5%), and blastocyst (6.4% to 8.5%) rates were significantly higher (P ≤ 0.05) in SSV and Cryotop groups than in straws. No significant differences were observed in these parameters between the Cryotop and control groups. We report for the first time that dromedary oocytes vitrified at the GV-stage have the ability to be matured, fertilized and subsequently develop in vitro to produce blastocysts at frequencies comparable to those obtained using fresh oocytes.

Comparison of The Effects of Vitrification on Gene Expression of Mature Mouse Oocytes Using Cryotop and Open Pulled Straw

Background

Oocyte cryopreservation is an essential part of the assisted reproductive technology (ART), which was recently introduced into clinical practice. This study aimed to evaluate the effects of two vitrification systems-Cryotop and Open Pulled Straw (OPS)-on mature oocytes gene expressions.

MATERIALS AND METHODS

In this experimental study, the survival rate of metaphase II (MII) mouse oocytes were assessed after cryopreservation by vitrification via i. OPS or ii. Cryotop. Then we compared the fertilization rate of oocytes produced via these two methods. In the second experiment, we determined the effects of the two vitrification methods on the expression of Hspa1a, mn-Sod, and ß-actin genes in vitrified-warmed oocytes. Denuded MII oocytes were vitrified in two concentrations of vitrification solution (VS1 and VS2) by Cryotop and straw. We then compared the results using the two vitrification methods with fresh control oocytes.

RESULTS

mn-Sod expression increased in the vitrified-warmed group both in OPS and Cryotop compared with the controls. We only detected Hspa1a in VS1 and control groups using Cryotop. The survival rate of the oocytes was 91.2% (VS1) and 89.2% (VS2) in the Cryotop groups (P=0.902) and 85.5% (VS1) and 83.6% (VS2) in the OPS groups (P=0.905). There were no significant differences between the Cryotop and the OPS groups (P=0.927). The survival rate in the Cryotop or the OPS groups was, nevertheless, significantly lower than the control group (P<0.001). The fertilization rates of the oocytes were 39% (VS1) and 34% (VS2) in the Cryotop groups (P=0.902) and 29 %( VS1) and 19.7% (VS2) in the OPS groups (P=0.413). The fertilization rates were achieved without significant differences among the Cryotop and OPS groups (P=0.755).

CONCLUSION

Our results indicated that Cryotop vitrification increases both cooling and warming rates, but both Cryotop and OPS techniques have the same effect on the mouse oocytes after vitrification.

The Impact of Vitrification in Artificial Reproductive Technology Programmes

Cryopreservation is an integral part of the current methods of assisted reproductive technology (ART). In the past two decades, slow freezing has been replaced worldwide by vitrification due to its association with improved survival rates and clinical outcomes comparable to fresh embryo transfers. Successful embryo vitrification programmes have led to a significant reduction in the incidences of two major complications of ART: ovarian hyperstimulation syndrome and multiple gestations. Multiple embryo transfer cycles from the single ovum aspiration cycle have had a cumulative effect on the numbers of live births. Oocyte vitrification has also helped women to delay their pregnancies for medical or social reasons. This has made oocyte banking a viable option for better synchronisation of oocyte donation programmes. The emerging field of ovarian tissue vitrification has made fertility preservation possible for women undergoing gonadotoxic therapy. In this review, we have discussed the basic principles and methodology of slow freezing and vitrification along with its need and impact on ART.

Glycine increases preimplantation development of mouse oocytes following vitrification at the germinal vesicle stage

Ice-free cryopreservation, referred to as vitrification, is receiving increased attention in the human and animal assisted reproduction. However, it introduces the detrimental osmotic stress by adding and removing high contents of cryoprotectants. In this study, we evaluated the effects of normalizing cell volume regulation by adding glycine, an organic osmolyte, during vitrification of mouse germinal vesicle stage oocyte and/or subsequent maturation on its development. The data showed that glycine supplementation in either vitrification/thawing or maturation medium significantly improved the cytoplasmic maturation of MII oocytes manifested by spindle assembly, chromosomal alignment, mitochondrial distribution, euploidy rate, and blastocyst development following fertilization in vitro, compared to the control without glycine treatment. Furthermore, glycine addition during both vitrification/thawing and maturation further enhanced the oocyte quality demonstrated by various markers, including ATP contents and embryo development. Lastly, the effect of anti-apoptosis was also observed when glycine was added during vitrification. Our result suggests that reducing osmotic stress induced by vitrification could improve the development of vitrified mouse oocyte.

Production of Live Offspring from Vitrified-Warmed Oocytes Collected at Metaphase I Stage

Vitrification of matured oocytes is widely adopted in human clinics and animal research laboratories. Cryopreservation of immature oocytes, particularly those at metaphase I (MI), remains a challenge. In the present work, mouse MI oocytes denuded of cumulus cells were vitrified and warmed (V/W) either prior to (V/W-BEFORE-IVM, n = 562) or after (V/W-AFTER-IVM, n = 664) in vitro maturation (IVM). Derivative metaphase II (MII) oocytes were then used for intracytoplasmic sperm injection (ICSI). In the control groups, in vivo matured MII oocytes were used freshly (FRESH-MII, n = 517) or after V/W (MII-V/W, n = 617). In vitro and in vivo developmental competencies were compared among groups. Satisfactory blastocyst rates were achieved in V/W-BEFORE-IVM (27.5%) and V/W-AFTER-IVM (32.4%) groups, albeit as expected still lower than those from fresh-MII (56.1%) or MII-V/W (45.6%) oocytes. Similarly, the term development rates from V/W-BEFORE-IVM and V/W-AFTER-IVM were 12.4% and 16.7% respectively, acceptable but lower than those of the fresh-MII (41.2%) and MII-V/W (23.3%) groups. These data demonstrate that oocytes collected at MI stage are amenable to V/W, which can be performed before or after IVM with acceptable development rates including production of healthy pups. These findings provide useful knowledge to researchers and clinical practitioners for preservation and use of the otherwise discarded MI oocytes.

High-Throughput Non-Contact Vitrification of Cell-Laden Droplets Based on Cell Printing

Cryopreservation is the most promising way for long-term storage of biological samples e.g., single cells and cellular structures. Among various cryopreservation methods, vitrification is advantageous by employing high cooling rate to avoid the formation of harmful ice crystals in cells. Most existing vitrification methods adopt direct contact of cells with liquid nitrogen to obtain high cooling rates, which however causes the potential contamination and difficult cell collection. To address these limitations, we developed a non-contact vitrification device based on an ultra-thin freezing film to achieve high cooling/warming rate and avoid direct contact between cells and liquid nitrogen. A high-throughput cell printer was employed to rapidly generate uniform cell-laden microdroplets into the device, where the microdroplets were hung on one side of the film and then vitrified by pouring the liquid nitrogen onto the other side via boiling heat transfer. Through theoretical and experimental studies on vitrification processes, we demonstrated that our device offers a high cooling/warming rate for vitrification of the NIH 3T3 cells and human adipose-derived stem cells (hASCs) with maintained cell viability and differentiation potential. This non-contact vitrification device provides a novel and effective way to cryopreserve cells at high throughput and avoid the contamination and collection problems.

High throughput cryopreservation of cells by rapid freezing of sub-μl drops using inkjet printing--cryoprinting

We have successfully used inkjet printing to cryopreserve 3T3 mouse fibroblast cells and human neuroprogenitor cells (NPCs) derived from human embryonic stem cells (hESCs). Sessile drops of volume 114 nl were formed by printing cell suspensions containing dimethyl sulphoxide (DMSO) as a cryoprotection agent (CPA) at rates in the region 100 Hz-20 kHz, from individual droplets of 380 pl. After printing and a freeze/thaw cycle (with a minimum 24 hours hold period at liquid N2 temperature), 3T3 cells showed an average viability of >90% with CPA concentration <0.8 M at all drop deposition rates. This is a significantly lower CPA concentration than normally used with conventional cryopreservation methods. Cell viability shows a small variation with the polymer substrates used, with the best results obtained using a polyimide substrate. The viability of 3T3 cells after 2 months storage at liquid nitrogen temperature was slightly reduced compared to the cells held for 24 hours but there was no significant further deterioration after 4 or 6 months storage. The viability of NPCs after an identical freeze/thaw cycle were only 55% but this is comparable with conventional cryopreservation methods that use much higher CPA concentrations. A parallel series of experiments printing cells onto substrates held at 195 K or directly into liquid N2 showed considerable variation in cell survival rate with drop deposition rate. Cell suspensions required higher levels of CPA than when printing followed by freezing. At low deposition rates a combination of DMSO and polyethylene glycol (PEG) was needed to allow cell viability after freezing. These results show that inkjet printing provides a practical high throughput method for the cryopreservation of cells with lower CPA concentrations than are required for current low volume cryopreservation methods.

Efficient cryopreservation of mouse embryos by modified droplet vitrification (MDV)

The aim of this study was to assess modified droplet vitrification (MDV) for the cryopreservation of early developmental mouse embryos. Mouse embryos were equilibrated in holding solution for 3 min followed by immersion in vitrification solution for 30-45 s, and then three embryos per 3-μL vitrification droplet were directly dropped into liquid nitrogen. Vitrified embryos were warmed to examine their developmental potential both in vitro and in vivo. The results demonstrated that MDV vitrified and warmed embryos had a survival rate of 98.1-99.6% (P>0.05); however, blastocyst development post warming and culture in vitro demonstrated that vitrified 4-celled, 8-celled, 16-celled, morulae, and blastocyst embryos had significant higher developmental potentials (94.7-99.5%) than those from zygotes (9.2%) and 2-celled embryos (85.7%) (P<0.05). Compared to CryoLoop and CryoTech vitrification, MDV showed similar results with regards to rates of survival, blastocyst development, but with the higher hatching rate (76.1% vs. 64.0-67.3%) (P<0.05). Cryopreservation by MDV resulted in a similar blastocyst developmental potential in 4-celled and 16 celled embryos from ICR (94.7-99.5%), C57BL/6J (94.7-96.4%), and their crossbred F1 strain (97.9-98.9%) (P>0.05). After embryo transfer of vitrified ICR embryos from 4-celled, 16-celled, morulae and blastocyst stage, 40.7-43.7% of the embryos developed into live offspring (P>0.05), but MDV vitrification resulted in the highest birth rate (43.8%) compared to CryoLoop (38.3%) and CryoTech (35.4%) (P<0.05), when 4-celled mouse embryos were used for vitrification. Our study clearly demonstrated that MDV is the most efficient vitrification to cryopreserve embryos at least 4-celled and advanced stages, which can be used to preserve important mouse genomes from different strains and different developmental stages.

"Universal" vitrification of cells by ultra-fast cooling

Long-term preservation of live cells is critical for a broad range of clinical and research applications. With the increasing diversity of cells that need to be preserved (e.g. oocytes, stem and other primary cells, genetically modified cells), careful optimization of preservation protocols becomes tedious and poses significant limitations for all but the most expert users. To address the challenge of long-term storage of critical, heterogeneous cell types, we propose a universal protocol for cell vitrification that is independent of cell phenotype and uses only low concentrations of cryoprotectant (1.5 M PROH and 0.5 M trehalose). We employed industrial grade microcapillaries made of highly conductive fused silica, which are commonly used for analytical chemistry applications. The minimal mass and thermal inertia of the microcapillaries enabled us to achieve ultrafast cooling rates up to 4,000 K/s. Using the same low, non-toxic concentration of cryoprotectant, we demonstrate high recovery and viability rates after vitrification for human mammary epithelial cells, rat hepatocytes, tumor cells from pleural effusions, and multiple cancer cell lines.

Effective cryopreservation of golden Syrian hamster embryos by open pulled straw vitrification

Golden Syrian hamster embryos are difficult to cryopreserve due to their high sensitivity to cryoprotectants and in vitro handling. The objective of this study is to develop a robust open pulled straw (OPS) vitrification technique for cryopreserving hamster embryos at various developmental stages. We first systematically tested the concentrations of cryoprotectants and the exposure times of two-cell embryos to various vitrification solutions. We identified pretreatment of two-cell embryos with 10% (v/v) ethylene glycol (EG) + 10% (v/v) dimethylsulfoxide (DMSO) for 30 s followed by exposure in the vitrification solution, EDFS30 (containing 15% EG + 15% DMSO), for 30 s before plunging into liquid nitrogen (two-step exposure method) as the optimal OPS vitrification protocol. We then investigated the resourcefulness of this protocol for vitrifying hamster embryos at different developmental stages. The results showed that high blastocyst rates from embryos vitrified at two-cell, four-cell, eight-cell, or morula stage (62%, 78%, 80%, or 72%, respectively), but not those verified at pronuclear (0%) or blastocyst stage (24%; P < 0.05), were achieved by this protocol. When embryos vitrified at the two-cell stage were recovered and then directly transferred to recipient females, 29% of them developed to term, a development rate not significantly different (P > 0.05) from the 40% birth rate of the unvitrified controls. In conclusion, we have developed an effective two-step OPS vitrification protocol for hamster embryos.

Perinatal outcomes for transfer of blastocysts vitrified and warmed in defined solutions with recombinant human albumin: 374 babies born after 898 embryo transfers

PURPOSE

To assess the efficacy of a novel, defined vitrification procedure using recombinant human albumin (rHA) for cryopreservation of human blastocysts.

DESIGN

Retrospective study.

SETTING

Private IVF clinic.

PATIENTS

1,496 patients received vitrified/warmed embryo transfer (ET).

METHODS

Surplus blastocysts, and blastocysts from patients undergoing elective embryo cryopreservation, were vitrified/warmed using Cryotop carriers in homemade solutions containing either human serum albumin (HSA) or rHA.

MAIN OUTCOME MEASURES

Clinical and neonatal outcomes regarding the vitrified/warmed ET procedures.

RESULTS

The HSA and rHA groups had a total of 1,163 and 898 vitrified/warmed cycles, respectively. Embryo survival rates (98.7% vs. 98.9%, respectively) and the number of embryos transferred (1.08 ± 0.01 vs. 1.06 ± 0.01, respectively) were similar in the HSA and rHA groups. Clinical pregnancy rates/ET were higher (P < 0.05) in the rHA group (56.0%) than in the HSA group (51.5%). The HSA and rHA groups had similar live delivery rates/pregnancy (72.2% vs. 72.3%, respectively) and perinatal outcomes, including birth weight (2,988 ± 28 vs. 3,046 ± 26 g, respectively). Birth defects occurred in 0.9% and 1.6% of neonates in the HSA and rHA groups, respectively.

CONCLUSIONS

rHA effectively replaced HSA for human embryo vitrification procedures, and yielded high rates of pregnancy and live births after vitrified/warmed ET. This new approach will support the development of defined ART systems, which will eliminate the variation and risks associated with the use of blood-derived products.

Vitrification solution without sucrose for cryopreservation in mouse blastocysts

Objective

This study was designed to investigate the survival rate of vitrified mouse blastocysts depending on the presence or absence of sucrose in vitrification solution.

Methods

Mouse two-cell embryos were collected and cultured to blastocysts. Two vitrification solutions were prepared. The control solution was composed of 25% glycerol, 25% ethylene glycol, and 0.5 M sucrose (G25E250.5S) containing 2.5 mL glycerol, 2.5 mL ethylene glycol, 2 mL SSS, and 0.855 g sucrose in 5 mL PB1. The experimental solution was composed of 25% glycerol and 25% ethylene glycol (G25E25) and contained 2.5 mL glycerol and 2.5 mL ethylene glycol in 5 mL PB1. Artificial shrinkage was conducted by aspirating the blastocoelic fluid using an ICSI pipette. To examine the effect of sucrose in the vitrification solution on the survival rate of mouse blastocysts, the shrunken-equilibrated blastocysts were rehydrated or vitrified after being exposed to one of the two vitrification solutions. After exposure and the vitrification-thawing process, the re-expansion rate and hatching rate were evaluated after 6 hours of in vitro culture.

Results

The re-expansion rate of mouse blastocysts exposed to vitrification solution with and without sucrose were not different in the experimental solution (without sucrose) (98%) and the control solution (with sucrose) (92%) (p>0.05). The hatching rate was higher in the experimental solution (95%) than in the control solution (88%), but did not differ across two treatments (p>0.05). The re-expansion rate of mouse blastocysts vitrified in the control solution was 92% and 94%, respectively (p>0.05), and the hatching rate was higher in the experimental solution (90%) than in the control solution (74%) (p<0.05).

Conclusion

Sucrose need not be added in vitrification solution for freezing of artificially shrunken mouse blastocysts.

Cryopreservation of oocytes and embryos

Two hundred years have passed since the first description of supercooled water by Gey-Lussac to the recently high survival rates of embryo and oocytes after vitrification. This review discusses important milestones that have made vitrification the method of choice for oocytes and embryos cryopreservation. We will go through the first cells ever to survive low temperature exposure in the beginning of the last century, the finding of glycerol in the late 1940s and the first mouse and bovine embryos freezing in the 1970s. During the 1980s, embryo vitrification began and the time since is a tribute to the development of oocytes vitrification. Standardization and an automatic vitrification procedure are currently under development. The next evolutionary step in oocyte and embryo cryopreservation will be preserving them in the dry state at room temperature, allowing home storage for future use a reality.

Development of a modified straw method for vitrification of in vitro-produced bovine blastocysts and various genes expression in between the methods

This study evaluated a modified plastic straw loading method for vitrification of in vitro-produced bovine blastocysts. A modified straw was used with a depressed area on its inner surface to which embryos attach. In vitro-produced blastocysts were randomly assigned into three groups: (i) blastocysts attached to the inner surface of a plastic straw (aV), (ii) blastocysts attached to the inner surface of a modified plastic straw (maV), and (iii) non-vitrified blastocysts (control). The recovery rates were not significantly different between aV and maV groups (95.8% vs. 94.3%). The post-thaw survival rate did not significantly differ between aV and maV groups (86.4% vs. 88.2%). The total cell numbers of blastocyst was higher in control than in aV and maV groups (142 ± 21.8 vs. 117 ± 29.7 and 120 ± 25.2; P < 0.05), but not significantly differ between aV and maV groups. The mRNA levels of pro-apoptosis related genes Bax and Caspase-3 were higher in aV and maV than in control (P < 0.05). By contrast, the mRNA levels of anti-apoptotic genes Bcl-2 and Mcl-1 and of antioxidant-related genes MnSOD and Prdx5 were lower in aV and maV than in control (P < 0.05). Confocal microscopy analysis of Golgi apparatus and mitochondria showed that the fluorescence intensity of Golgi apparatus and mitochondria was higher in control than in aV and maV groups. In conclusion, both aV and maV methods can be used to successfully vitrify IVP blastocysts, with maV method to be preferable because of its easiness in embryo loading.

The new Rapid-i carrier is an effective system for human embryo vitrification at both the blastocyst and cleavage stage

BACKGROUND

The Rapid-i is a new FDA cleared closed carrier for embryo vitrification. The cooling rate of - 1220°C/min is far lower than that reported with open vitrification systems such as the cryoloop (-15,000°C/min). Little published data is currently available on this device. This study presents our initial clinical data, as well as live birth outcomes, with the Rapid-i. The efficacy of this device for the cryopreservation of cleavage, as well as blastocyst stage human embryos is also analyzed. We further compare outcomes to those achieved with the cryoloop, an "open" vitrification system routinely used in our laboratory.

METHODS

Human embryos were vitrified at either the 8-10 cell stage or else the blastocyst stage. The vitrification protocol was: 7.5% DMSO/7.5% ethylene glycol (EG) (2-3 min) followed by incubation in 15% DMSO /15% EG (45 sec) before loading on the vitrification carrier. Cryoprotectant was removed during warming by sequential washes in 0.25 M and 0.125 M sucrose in culture medium. Clinical outcome data for frozen cycles between January 2011 and August 2012 were stratified according to carrier and cell stage. The student t-test and chi square test were used to compare results. P value of < 0.05 was considered significant.

RESULTS

A total of 486 vitrified-warmed embryos were assessed and 92% of them were transferred. The clinical pregnancy rate (CPR) and implantation rate (IR) with Rapid-i vitrified blastocysts were 59% and 49%, versus 47% and 37%, respectively for cleavage stage embryos. This was not statistically different from results with the cryoloop vitrified blastocysts (CPR 46%, IR 38%) nor the cleavage stage vitrified embryos (CPR 49%, IR 35%). To date, there have been 31 deliveries of 34 healthy infants from Rapid-i vitrified embryos, with another 12 pregnancies still on-going.

CONCLUSIONS

The Rapid-i offers an excellent alternative to existing open vitrification devices for embryo cryopreservation at the 8-10 cell stage as well as the blastocyst stage. Use of this type of "closed" sealed system that prevents direct contact between the embryos and liquid nitrogen reduces the potential risk of sample cross-contamination or infection. These preliminary data and live birth outcomes have paved the way toward transitioning to a closed vitrification system in our own IVF program.

A numerical study on distributions during cryoprotectant loading caused by laminar flow in a microchannel

In this work, we conduct a computational study on the loading of cryoprotective agents into cells in preparation for cryopreservation. The advantages of microfluidics in cryopreserving cells include control of fluid flow parameters for reliable cryoprotectant loading and reproducible streamlined processing of samples. A 0.25 m long, three inlet T-junction microchannel serves as an idealized environment for this process. The flow field and concentration distribution are determined from a computational fluid dynamics study and cells are tracked as inert particles in a Lagrangian frame. These particles are not confined to streamlines but can migrate laterally due to the Segre-Sildeberg effect for particles in a shear flow. During this tracking, the local concentration field surrounding the cell is monitored. This data are used as input into the Kedem-Katchalsky equations to numerically study passive solute transport across the cell membrane. As a result of the laminar flow, each cell has a unique pathline in the flow field resulting in different residence times and a unique external concentration field along its path. However, in most previous studies, the effect of a spatially varying concentration field on the transport across the cell membrane is ignored. The dynamics of this process are investigated for a population of cells released from the inlet. Using dimensional analysis, we find a governing parameter α, which is the ratio of the time scale for membrane transport to the average residence time in the channel. For [Formula: see text], cryoprotectant loading is completed to within 5% of the target concentration for all of the cells. However, for [Formula: see text], we find the population of cells does not achieve complete loading and there is a distribution of intracellular cryoprotective agent concentration amongst the population. Further increasing α beyond a value of 2 leads to negligible cryoprotectant loading. These simulations on populations of cells may lead to improved microfluidic cryopreservation protocols where more consistent cryoprotective agent loading and freezing can be achieved, thus increasing cell survival.

Cryopreservation of testicular and epididymal sperm: techniques and clinical outcomes of assisted conception

The introduction of the technique of intracytoplasmic sperm injection to achieve fertilization, especially using surgically retrieved testicular or epididymal sperm from men with obstructive or non-obstructive azoospermia, has revolutionized the field of assisted reproduction. The techniques for the retrieval of spermatozoa vary from relatively simple percutaneous sperm aspiration to open excision (testicular biopsy) and the more invasive Micro-TESE. The probability of retrieving spermatozoa can be as high as 100% in men with obstructive azoospermia (congenital bilateral absence of the vas deferens, status post-vasectomy). However, in nonobstructive azoospermia, successful sperm retrieval has been reported in 10-100% of cases by various investigators. The surgical retrieval and cryopreservation of sperm, especially in men with non-obstructive azoospermia, to some extent ensures the availability of sperm at the time of intracytoplasmic sperm injection. In addition, this strategy can avoid unnecessary ovarian stimulation in those patients intending to undergo in vitro fertilization-intracytoplasmic sperm injection with freshly retrieved testicular sperm when an absolute absence of sperm in the testis is identified. Several different methods for the cryopreservation of testicular and epididymal sperm are available. The choice of the container or carrier may be an important consideration and should take into account the number or concentration of the sperm in the final preparation. When the number of sperm in a testicular biopsy sample is extremely low (e.g., 1-20 total sperm available), the use of an evacuated zona pellucida to store the cryopreserved sperm has been shown to be an effective approach.

Production of good-quality blastocyst embryos following IVF of ovine oocytes vitrified at the germinal vesicle stage using a cryoloop

The cryopreservation of immature oocytes at the germinal vesicle (GV) stage would create an easily accessible, non-seasonal source of female gametes for research and reproduction. The present study investigated the ability of ovine oocytes vitrified at the GV stage using a cryoloop to be subsequently matured, fertilised and cultured in vitro to blastocyst-stage embryos. Selected cumulus–oocyte complexes obtained from mature ewes at the time of death were randomly divided into vitrified, toxicity and control groups. Following vitrification and warming, viable oocytes were matured in vitro for 24 h. Matured oocytes were either evaluated for nuclear maturation, spindle and chromosome configuration or fertilised and cultured in vitro for 7 days. No significant differences were observed in the frequencies of IVM (oocytes at the MII stage), oocytes with normal spindle and chromatin configuration and fertilised oocytes among the three groups. Cleavage at 24 and 48 h post insemination was significantly decreased (P < 0.01) in vitrified oocytes. No significant differences were observed in the proportion of blastocyst development between vitrified and control groups (29.4% v. 45.1%, respectively). No significant differences were observed in total cell numbers, the number of apoptotic nuclei or the proportion of diploid embryos among the three groups. In conclusion, we report for the first time that ovine oocytes vitrified at the GV stage using a cryoloop have the ability to be matured, fertilised and subsequently developed in vitro to produce good-quality blastocyst embryos at frequencies comparable to those obtained using fresh oocytes.