Successful vitrification of pronuclear-stage rabbit zygotes by minimum volume cooling procedure

Development and Genome Mutation of Bovine Zygotes Vitrified Before and After Genome Editing via Electroporation

BACKGROUND: Cryopreservation of bovine zygotes allows for a flexible schedule of genome editing via electroporation. However, vitrification-induced cell membrane damage may not only affect embryonic development but also genome mutation. OBJECTIVE: To investigate the effects of vitrification of zygotes before and after electroporation treatments on the development and genome mutation of bovine presumptive zygotes. MATERIALS AND METHODS: In vitro-derived bovine zygotes were electroporated with the CRISPR/Cas9 system immediately (Vitrified-EP) or 2 h after incubation (Vitrified-2h-EP) following vitrification and warming, or electroporated before vitrification (EP-vitrified). RESULTS: The development rates of vitrified-warmed zygotes were significantly lower (p < 0.05) than those of control zygotes that were not vitrified. Moreover, no differences were observed in the mutation rates and mutation efficiency of the blastocysts resulting from electroporated zygotes, irrespective of the timing of electroporation treatment. CONCLUSION: Our results suggest that vitrification before and after electroporation treatments does not affect the genome editing of zygotes.

Effect of vitrification at different meiotic stages on epigenetic characteristics of bovine oocytes and subsequently developing embryos

Vitrification by the Cryotop method is frequently used for bovine oocyte cryopreservation. Nevertheless, vitrified oocytes still have reduced developmental competency compared with fresh counterparts. The objective of this study was to compare the effect of vitrification either at the germinal vesicle (GV) stage or at the metaphase II (MII) stage on epigenetic characteristics of bovine oocytes and subsequently developing embryos. Our results demonstrated that vitrification of oocytes at each meiotic stage significantly reduced blastocyst development after in vitro fertilization (IVF). However, vitrification at the GV stage resulted in higher blastocyst development than did vitrification at the MII stage. Irrespective of the meiotic stage, oocyte vitrification did not affect 5-methylcytosine (5mC) immunostaining intensity in oocyte DNA. However, at both stages, it caused a similar reduction of 5mC levels in DNA of subsequently developing blastocysts. Oocyte vitrification had no effect on the intensity of H3K9me3 and acH3K9 immunostaining in oocytes and subsequent blastocysts. The results suggest that irrespective of meiotic stage, oocyte vitrification alters global methylation in resultant embryos although such alteration in the oocytes was not detected. Oocyte vitrification might not influence histone acetylation and methylation in oocytes and resultant embryos. Vitrification at the immature stage was more advantageous for blastocyst development than at the mature stage.

Acoustic Droplet Vitrification Method for High-Efficiency Preservation of Rare Cells

Cryopreservation is a key step for current translational medicine including reproductive medicine, regenerative medicine, and cell therapy. However, it is challenging to preserve rare cells for practical applications due to the difficulty in handling low numbers of cells as well as the lack of highly efficient and biocompatible preservation protocols. Here, we developed an acoustic droplet vitrification method for high-efficiency handling and preservation of rare cells. By employing an acoustic droplet ejection device, we can encapsulate rare cells into water-in-air droplets with a volume from ∼pL to ∼nL and deposit these cell-containing droplets into a droplet array onto a substrate. By incorporating a cooling system into the droplet array substrate, we can vitrify hundreds to thousands of rare cells at an ultrafast speed (about ∼2 s) based on the high surface to volume ratio of the droplets. By optimizing this method with three different cell lines (a human lung cancer cell line, A549 cells, a human liver cell line, L02 cells, and a mouse embryonic fibroblast cell line, 3T3-L1 cells), we developed an effective protocol with excellent cell viability (e.g., >85% for days, >70% for months), proliferation, and adhesion. As a proof-of-concept application, we demonstrated that our method can rapidly handle and efficiently preserve rare cells, highlighting its broad applications in species diversity, basic research, and clinical medicine.

Highly successful production of viable mice derived from vitrified germinal vesicle oocytes

The vitrification of immature germinal vesicle (GV) oocytes is an important way to preserve genetic resources and female fertility. However, it is well known that cryopreserved GV oocytes have very poor developmental ability and that further improvement in this technique is needed. We previously reported the successful vitrification of matured mouse oocytes with enclosed cumulus cells using the calcium-free vitrification solution supplemented with ethylene glycol (EG) by the minimal volume cooling (MVC) method. In this study, we investigated whether our method is applicable to the vitrification of mouse oocytes at the GV stage (GV oocytes). Following maturation and fertilization in vitro, vitrified GV oocytes showed high survival (94.3 ± 2.0%) and maturation (94.3 ± 2.1%) rates. Although the fertilization and blastocyst rates of vitrified oocytes (fertilization: 46.6 ± 4.9% and blastocyst: 46.6 ± 3.0%) were significantly lower than those of fresh oocytes (fertilization: 73.0 ± 7.1% and blastocyst: 71.6 ± 8.0%) (P < 0.01), there were no differences in the ability to develop to term between fresh oocytes (50.0 ± 8.4%) and vitrified oocytes (37.5 ± 4.6%) (P > 0.05). In conclusion, we here show, for the first time, the efficient production of live mice derived from vitrified GV oocytes.

Carboxylated ε-poly-L-lysine, a cryoprotective agent, is an effective partner of ethylene glycol for the vitrification of embryos at various preimplantation stages

It has been known that different protocols are used for embryo preservation at different stages due to different sensitivity to the physical and physiological stress caused by vitrification. In this study, we developed a common vitrification protocol using carboxlated ε-poly-l-lysine (COOH-PLL), a new cryoprotective agent for the vitrification of mouse embryos at different stages. The IVF-derived Crl:CD1(ICR) x B6D2F1/Crl pronuclear, 2-cell, 4-cell, and 8-cell, morula and blastocyst stage embryos were vitrified with 15% (v/v) ethylene glycol (EG) and 10% (w/v) COOH-PLL (E15P15) or 15% (v/v) EG and 15% (v/v) dimethyl sulfoxide (E15D15) using the minimal volume cooling method. The survival of vitrified embryos from pronuclear to blastocyst stages was equivalent between E15P15 and E15D15 groups. However, the rate of development to blastocysts was significantly lower in E15P15 than E15D15. The rates of survival and development to blastocysts were dramatically improved by a slight modification of EG and COOH-PLL concentrations (E20P10). After transferring 17 (E20P10) and 15 (E15D15) vitrified/warmed blastocysts, 8 and 7 pups were obtained (47.1% and 46.7%, respectively). Taken together, these results indicate that our vitrification protocol is appropriate for the vitrification of mouse embryos at different stages.

Self-Pressurized Rapid Freezing as Cryo-Fixation Method for Electron Microscopy and Cryopreservation of Living Cells

Reduction or complete prevention of ice crystal formation during freezing of biological specimens is mandatory for two important biological applications: (1) cryopreservation of living cells or tissues for long-term storage, and (2) cryo-fixation for ultrastructural investigations by electron microscopy. Here, a protocol that is fast, easy-to-use, and suitable for both cryo-fixation and cryopreservation is described. Samples are rapidly cooled in tightly sealed metal tubes of high thermal diffusivity and then plunged into a liquid cryogen. Due to the fast cooling speed and high-pressure buildup internally in the confined volume of the metal tubes, ice crystal formation is reduced or completely prevented, resulting in vitrification of the sample. For cryopreservation, however, a similar principle applies to prevent ice crystal formation during re-warming. A detailed description of procedures for cooling (and re-warming) of biological samples using this technique is provided. © 2018 by John Wiley & Sons, Inc.

Survival and developmental competence of bovine embryos at different developmental stages and separated blastomeres after vitrification in different solutions

Generating techniques to enhance the success of blastomere separation is important for bovine economy, because it increases the number of transferable embryos. This study aimed to identify the optimum cryoprotectants for the vitrification of bovine embryos and the separation of blastomeres at different stages. In experiment 1, expanded blastocysts were vitrified in two different vitrification solutions, either (1) ethylene glycol (EG) + propylene glycol (PG) or (2) EG. The survival rate of blastocysts in the EG + PG was higher than that of the EG. In experiment 2, intact two-cell and eight-cell stage embryos were vitrified in the same solutions used in experiment 1. The EG + PG produced more dead embryos than the EG (P < 0.05). In the EG, the rate of blastocyst formation was similar for the vitrified two- and eight-cell embryos and the non-vitrified ywo-cell embryos. In experiment 3, separated blastomeres of two- and eight-cell embryos were vitrified in EG. There was no difference in the rate of blastocyst formation and total number of cells between the two vitrified groups. In summary, at the blastocyst stage, EG + PG was superior, based on both survival rates and cell numbers; however, at the 2-8 cell stage, the use of EG alone was better than the other groups.

Safety and efficiency of oocyte vitrification

As the oocyte is the starting point for a new life, artificial reproductive technology (ART) techniques should not affect the (ultra) structural and functional integrity, or the developmental competence. Oocyte vitrification -one of the most significant achievements in human ART during the past decade- should therefore be a safe and efficient technique. This review discusses the principles and developments of the existing and future techniques, applications possibilities and safety concerns. The broad range of vitrification media and devices that are currently available, show differences in their effects on the oocyte ultrastructure and preimplantation development. It is not yet fully decided whether this has an influence on the obstetric and neonatal outcome, since only limited information is available with different media and devices. For autologous oocytes, the obstetric and neonatal outcomes appear promising and comparable to pregnancies obtained with fresh oocytes. This however, is not the case for heterologous fresh or vitrified oocytes, where the immunological foreign foetus induces adverse obstetric and neonatal outcomes. Besides the oocyte vitrification process itself, the effect of multiple stimulations (for oocyte banking or for oocyte donors), seems to influence the possibility to develop gynaecological cancers further in life. Automated vitrification/warming should offer a consistent, cross-contamination free process that offers the highest safety level for the users. They should also produce more consistent results in survival, development and clinical pregnancies between different IVF clinics.

Direct comparison of Cryotop® vitrification and Bicell® freezing on recovery of functional rat pancreatic islets

Two protocols, Bicell^® freeze-thawing and Cryotop^® vitrification-warming, were compared for suitability in cryopreserving rat pancreatic islets (101-150 μm in mean diameter). Immediate survival rates of post-thaw and post-warm islets (50 and 57%, respectively), assessed by FDA/PI double staining, were lower than that of fresh control islets (90%). Most of the PI-positive dead cells were detected in peripheral area of post-warm islets, and were removed after subsequent 24 h culture (survival rate; 85% vs 59% in post-thaw islets). Quantitative PCR analysis showed that Bicell^® freeze-thawing compromised expression of genes relating to β-cell function (Pdx1 and Glut2), but not to one of apoptotic pathways (Bax/Bcl2 ratio). Expression of these genes was maintained in islets before and after the Cryotop^® vitrification-warming. Values of stimulus index (SI) for 20 mM/3 mM glucose-stimulated insulin secretion were 6.7, 1.9 and 3.9 in fresh control, post-thaw and post-warm islets, respectively. The SI values after 24 h culture were 4.1, 1.9 and 3.1, respectively. Larger islets (>150 μm in diameter) had comparable survival rates, but lower SI values after Cryotop^® vitrification-warming when compared to smaller counterparts. These results suggest that rat pancreatic islets can be cryopreserved by Cryotop^® vitrification-warming rather than Bicell^® freeze-thawing, without considerable loss of in vitro β-cell function.

Development of Cheaper Embryo Vitrification Device Using the Minimum Volume Method

This study was designed to compare the efficiency of the Cryotop and Calibrated plastic inoculation loop (CPIL) devices for vitrification of rabbit embryos on in vitro development and implantation rate, offspring rate at birth and embryonic and fetal losses. CPIL is a simple tool used mainly by microbiologists to retrieve an inoculum from a culture of microorganisms. In experiment 1, embryos were vitrified using a Cryotop device and a CPIL device. There were no significant differences in hatched/hatching blastocyst stage rates after 48 h of culture among the vitrified groups (62±4.7% and 62±4.9%, respectively); however, the rates were significantly lower (P<0.05) than those of the fresh group (95±3.4%). In experiment 2, vitrified embryos were transferred using laparoscopic technique. The number of implanted embryos was estimated by laparoscopy as number of implantation sites at day 14 of gestation. At birth, total offspring were recorded. Embryonic and fetal losses were calculated as the difference between implanted embryos and embryos transferred and total born at birth and implanted embryos, respectively. The rate of implantation and development to term was similar between both vitrification devices (56±7.2% and 50±6.8% for implantation rate and 40±7.1% and 35±6.5% for offspring rate at birth); but significantly lower than in the fresh group (78±6.6% for implantation rate and 70±7.2% for offspring rate at birth, P<0.05). Likewise, embryonic losses were similar between both vitrification devices (44±7.2% and 50±6.8%), but significantly higher than in the fresh group (23±6.6%, P < 0.05). However, fetal losses were similar between groups (10±4.4%, 15±4.8% and 8±4.2%, for vitrified, Cryotop or CPIL and fresh, respectively). These results indicate that the CPIL device is as effective as the Cryotop device for vitrification of rabbit embryos, but at a cost of €0.05 per device.

State of actin cytoskeleton and development of slow-frozen and vitrified rabbit pronuclear zygotes

This study was focused on the effect of cryopreservation on the state of actin cytoskeleton and development of rabbit pronuclear zygotes. Zygotes were collected from superovulated females and immediately used for 1) slow-freezing in a solution containing 1.5 M 1,2-propanediol and 0.2 M sucrose, or 2) vitrification in a solution containing 42.0% (v/v) of ethylene glycol, 18.0% (w/v) of dextran and 0.3 M sucrose as cryoprotectants. After thawing or warming, respectively, zygotes were evaluated for 1) actin distribution, 2) in vitro or 3) in vivo development to blastocyst. Comparing actin filaments distribution, a significantly higher number of vitrified zygotes with actin distributed in cell border was observed (55 ± 7.7 vs. 74 ± 6.1% for slow-frozen vs. vitrified, respectively). After 24 and 72 h of in vitro development, significant differences in the cleavage and morula rate among the groups were observed (9 ± 2.4 and 3 ± 1.3 vs. 44 ± 3.0 and 28 ± 2.7% for slow-frozen vs. vitrified, respectively). None of the slow-frozen zygotes reached the blastocyst stage, in contrast to the vitrified counterparts (11 ± 1.9%). Under in vivo culture conditions, a significant difference in blastocyst rate was observed between vitrified and fresh embryos (6 ± 1.5 vs. 35 ± 4.4% respectively). Our results showed that alterations in actin cytoskeleton and deteriorated development are more evident in slow-frozen than vitrified pronuclear zygotes. Vitrification method seems to be a more effective option for rabbit zygotes cryopreservation, although pronuclear zygotes manipulation per se resulted in a notable decrease in embryo development.

Direct Measurement of Water States in Cryopreserved Cells Reveals Tolerance toward Ice Crystallization

Complex living systems such as mammalian cells can be arrested in a solid phase by ultrarapid cooling. This allows for precise observation of cellular structures as well as cryopreservation of cells. The state of water, the main constituent of biological samples, is crucial for the success of cryogenic applications. Water exhibits many different solid states. If it is cooled extremely rapidly, liquid water turns into amorphous ice, also called vitreous water, a glassy and amorphous solid. For cryo-preservation, the vitrification of cells is believed to be mandatory for cell survival after freezing. Intracellular ice crystallization is assumed to be lethal, but experimental data on the state of water during cryopreservation are lacking. To better understand the water conditions in cells subjected to freezing protocols, we chose to directly analyze their subcellular water states by cryo-electron microscopy and tomography, cryoelectron diffraction, and x-ray diffraction both in the cryofixed state and after warming to different temperatures. By correlating the survival rates of cells with their respective water states during cryopreservation, we found that survival is less dependent on ice-crystal formation than expected. Using high-resolution cryo-imaging, we were able to directly show that cells tolerate crystallization of extra- and intracellular water. However, if warming is too slow, many small ice crystals will recrystallize into fewer but bigger crystals, which is lethal. The applied cryoprotective agents determine which crystal size is tolerable. This suggests that cryoprotectants can act by inhibiting crystallization or recrystallization, but they also increase the tolerance toward ice-crystal growth.

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.

Comparison of Cryotop and micro volume air cooling methods for cryopreservation of bovine matured oocytes and blastocysts

This study was designed to compare the efficiency of the Cryotop method and that of two methods that employ a micro volume air cooling (MVAC) device by analyzing the survival and development of bovine oocytes and blastocysts vitrified using each method. In experiment I, in vitro-matured (IVM) oocytes were vitrified using an MVAC device without direct contact with liquid nitrogen (LN₂; MVAC group) or directly plunged into LN₂ (MVAC in LN₂ group). A third group of IVM oocytes was vitrified using a Cryotop device (Cryotop group). After warming, vitrified oocytes were fertilized in vitro. There were no significant differences in cleavage and blastocyst formation rates among the three vitrified groups, with the rates ranging from 53.1% to 56.6% and 20.0% to 25.5%, respectively; however, the rates were significantly lower (P < 0.05) than those of the fresh control group (89.3% and 43.3%, respectively) and the solution control group (87.3% and 42.0%, respectively). In experiment II, in vitro-produced (IVP) expanded blastocysts were vitrified using the MVAC, MVAC in LN₂ and Cryotop methods, warmed and cultured for survival analysis and then compared with the solution control group. The rate of development of vitrified-warmed expanded blastocysts to the hatched blastocyst stage after 24 h of culture was lower in the MVAC in LN₂ group than in the solution control group; however, after 48–72 h of culture, the rates did not significantly differ between the groups. These results indicate that the MVAC method without direct LN₂ contact is as effective as the standard Cryotop method for vitrification of bovine IVM oocytes and IVP expanded blastocysts.

Preserving human cells for regenerative, reproductive, and transfusion medicine

Cell cryopreservation maintains cellular life at sub-zero temperatures by slowing down biochemical processes. Various cell types are routinely cryopreserved in modern reproductive, regenerative, and transfusion medicine. Current cell cryopreservation methods involve freezing (slow/rapid) or vitrifying cells in the presence of a cryoprotective agent (CPA). Although these methods are clinically utilized, cryo-injury due to ice crystals, osmotic shock, and CPA toxicity cause loss of cell viability and function. Recent approaches using minimum volume vitrification provide alternatives to the conventional cryopreservation methods. Minimum volume vitrification provides ultra-high cooling and rewarming rates that enable preserving cells without ice crystal formation. Herein, we review recent advances in cell cryopreservation technology and provide examples of techniques that are utilized in oocyte, stem cell, and red blood cell cryopreservation.

Cryopreservation in ART and concerns with contamination during cryobanking

The cryopreservation of gametes and embryos is vital to numerous fields of reproductive biology, including assisted human reproduction. With improved culture conditions, there are an increasing number of embryos to cryopreserve for potential use in subsequent cycles. Many of the gametes and embryos in human IVF are cryopreserved in open systems. Because liquid nitrogen is not sterile, concerns have been raised with regard to contamination from the liquid nitrogen and also cross-contamination between patients' germplasm. Human gamete and embryo cryopreservation are discussed, with recommendations on how to minimize and eliminate contamination, emphasizing the benefits of closed vitrification devices.

Ultrarapid vitrification of mouse oocytes and embryos

Cryopreservation facilitates long-term storage of gametes and embryos for numerous purposes. For example, cryobanking of unique mouse strains, particularly transgenic mice, offers important protection of valuable genetics. It also provides a practical solution for facilities trying to house large numbers of research animals or those looking to relocate without the risk of introducing an animal-derived pathogen. Furthermore, cryopreservation is currently being used for fertility preservation both in humans and as a safeguard for endangered animals. Ultrarapid vitrification offers an elegant, quick, and very reliable method for cryopreservation of mouse oocytes and embryos. Furthermore, research into the effects on mouse oocyte and embryo physiology has indicated that ultrarapid vitrification is superior to conventional slow freezing. High survival rates, embryo development, and viability are routinely achieved with the ultrarapid vitrification method described in this chapter.

Vitrification procedure decreases inositol 1,4,5-trisphophate receptor expression, resulting in low fertility of pig oocytes

Although cryopreservation of mammalian oocytes is an important technology, it is well known that unfertilized oocytes, especially in pigs, are highly sensitive to low temperature and that cryopreserved oocytes show low fertility and developmental ability. The aim of the present study was to clarify why porcine in vitro matured (IVM) oocytes at the metaphase II (MII) stage showed low fertility and developmental ability after vitrification. In vitro matured cumulus oocyte complexes (COCs) were vitrified with Cryotop and then evaluated for fertility through in vitro fertilization (IVF). Although sperm-penetrated oocytes were observed to some extent (30-40%), the rate of pronuclear formation was low (9%) and none of them progressed to the two-cell stage. The results suggest that activation ability of cryopreserved oocytes was decreased by vitrification. We examined the localization and expression level of the type 1 inositol 1,4,5 trisphosphate receptor (IP3 R1), the channel responsible for Ca(2+) release during IVF in porcine oocytes. Localization of IP3 R1 close to the plasma membrane and total expression level of IP3 R1 protein were both decreased by vitrification. In conclusion, our present study indicates that vitrified-warmed porcine COCs showed a high survival rate but low fertility after IVF. This low fertility seems to be due to the decrease in IP3 R1 by the vitrification procedure.

Generation of live offspring from vitrified mouse oocytes of C57BL/6J strain

In mammals, unfertilized oocytes are one of the most available stages for cryopreservation because the cryopreserved oocytes can be used for assisted reproductive technologies, including in vitro fertilization (IVF) and intracytoplasmic sperm injection. However, it has generally been reported that the fertility and developmental ability of the oocytes are reduced by cryopreservation. C57BL/6J mice, an inbred strain, are used extensively for the production of transgenic and knockout mice. If the oocytes from C57BL/6J mice can be successfully cryopreserved, the cryopreservation protocol used will contribute to the high-speed production of not only gene-modified mice but also hybrid mice. Very recently, we succeeded in the vitrification of mouse oocytes derived from ICR (outbred) mice. However, our protocol can be applied to the vitrification of oocytes from an inbred strain. The aim of the present study was to establish the vitrification of oocytes from C57BL/6J mice. First, the effect of cumulus cells on the ability of C57BL/6J mouse oocytes to fertilize and develop in vitro was examined. The fertility and developmental ability of oocyte-removed cumulus cells (i.e., denuded oocytes, or DOs) after IVF were reduced compared to cumulus oocyte complexes (COCs) in both fresh and cryopreserved groups. Vitrified COCs showed significantly (P<0.05) higher fertility and ability to develop into the 2-cell and blastocyst stages compared to the vitrified DOs with cumulus cells and vitrified DOs alone. The vitrified COCs developed to term at a high success rate, equivalent to the rate obtained with IVF using fresh COCs. Taken together, our results demonstrate that we succeeded for the first time in the vitrification of mouse oocytes from C57BL/6J mice. Our findings will also contribute to the improvement of oocyte vitrification not only in animals but also in clinical applications for human infertility.

Delaying embryo development by storing at 4°C for synchronization to recipients in microinjection technique in rabbits

Short-term storage of embryos at low temperature induces developmental arrest of the embryo and would appear to be a valuable aid in embryo-transfer techniques to avoid wasting embryos. Embryo storage at 4°C was examined to allow synchronization with embryo-transfer recipients using the microinjection technique. Superovulation was induced in female Japanese White donor rabbits four days before mating with males. At the same time, control recipients were injected with human chorionic gonadotropin (hCG) to allow synchronization (R1); the hCG injections were delayed by 24 h in the experimental group (R2). DNA constructs for expressing human C-reactive protein or apolipoprotein AII were microinjected into the male pronuclei of the ova. The microinjected embryos were immediately transferred to recipients (R1) or stored at 4°C in phosphate-buffered saline containing 10% fetal bovine serum. After 17-20 h, the stored embryos were incubated at 37°C for one hour, and the morphologically normal embryos were transferred to recipients (R2). In the R1 rabbits, 855 embryos were transferred to 29 recipients, and 72.4% of the recipients became pregnant. Seven of the 84 offspring were transgenic. In the R2 rabbits, 478 embryos were transferred to 16 recipients, and 62.5% of the recipients became pregnant. Two of the 39 offspring were transgenic. There were no differences in pregnancy rate, litter size and transgenic integration rate between R1 and R2. These results suggest that the short-term 4°C storage of microinjected embryos can be a valuable method for synchronization with recipients, and reducing wastage of embryos and the sacrifice of rabbits.

Hollow fiber vitrification: a novel method for vitrifying multiple embryos in a single device

Current embryo vitrification methods with proven efficacy are based on the minimum volume cooling (MVC) concept by which embryos are vitrified and rewarmed ultrarapidly in a very small amount of cryopreserving solution to ensure the high viability of the embryos. However, these methods are not suitable for simultaneously vitrifying a large number of embryos. Here, we describe a novel vitrification method based on use of a hollow fiber device, which can easily hold as many as 40 mouse or 20 porcine embryos in less than 0.1 μl of solution. Survival rates of up to 100% were obtained for mouse embryos vitrified in the presence of 15% DMSO, 15% ethylene glycol and 0.5 M sucrose using the hollow fiber vitrification (HFV) method, regardless of the developmental stage of the embryos (1-cell, 2-cell, morula or blastocyst; n = 50/group). The HFV method was also proven to be effective for vitrifying porcine in vitro- and in vivo-derived embryos that are known to be highly cryosensitive. For porcine embryos, the blastocyst formation rate of in vitro maturation (IVM)-derived parthenogenetic morulae after vitrification (48/65, 73.8%) did not decrease significantly compared with non-vitrified embryos (59/65, 90.8%). Transfer of 72 in vivo-derived embryos vitrified at the morula/early blastocyst stages to 3 recipients gave rise to 29 (40.3%) piglets. These data demonstrate that the HFV method enables simultaneous vitrification of multiple embryos while still adhering to the MVC concept, and this new method is very effective for cryopreserving embryos of mice and pigs.

Emerging technologies in medical applications of minimum volume vitrification

Cell/tissue biopreservation has broad public health and socio-economic impact affecting millions of lives. Cryopreservation technologies provide an efficient way to preserve cells and tissues targeting the clinic for applications including reproductive medicine and organ transplantation. Among these technologies, vitrification has displayed significant improvement in post-thaw cell viability and function by eliminating harmful effects of ice crystal formation compared to the traditional slow freezing methods. However, high cryoprotectant agent concentrations are required, which induces toxicity and osmotic stress to cells and tissues. It has been shown that vitrification using small sample volumes (i.e., <1 µl) significantly increases cooling rates and hence reduces the required cryoprotectant agent levels. Recently, emerging nano- and micro-scale technologies have shown potential to manipulate picoliter to nanoliter sample sizes. Therefore, the synergistic integration of nanoscale technologies with cryogenics has the potential to improve biopreservation methods.

In-straw cryoprotectant dilution for bovine embryos vitrified using Cryotop

The aim of this study was to develop an in-straw dilution method suitable for 1-step bovine embryo transfer of vitrified embryos using the Cryotop vitrification-straw dilution (CVSD) method. The development of embryos vitrified using the CVSD method was compared with those of embryos cryopreserved using in-straw vitrification-dilution (ISVD) and conventional slow freezing, outside dilution of straw (SFODS) methods. In Experiment 1, in vitro-produced (IVP) embryos cryopreserved using the CVSD method were diluted, warmed and exposed to the dilution solution at various times. When vitrified IVP embryos were exposed to the dilution solution for 30 min after warming, the rates of embryos developing to the hatched blastocyst stage after 72 h of culture (62.0-72.5%) were significantly lower (P<0.05) than those of embryos exposed to the solution for 5 and 10 min (82.4-94.3%), irrespective of supplementation with 0.3 M sucrose in the dilution solution. In Experiment 2, the rate of embryos developing to the hatching blastocyst stage after 48 h of culture in IVP embryos cryopreserved using the SFODS method (75.0%) was significantly (P<0.05) lower than those of embryos cryopreserved using the CVSD and ISVD methods (93.2 and 97.3%, respectively). In Experiment 3, when in vivo-produced embryos that had been cryopreserved using the CVSD, ISVD and SFODS methods and fresh embryos were transferred to recipient animals, no significant differences were observed in the conception and delivery rates among groups. In Experiment 4, when IVP embryos derived from oocytes collected by ovum pick-up that had been cryopreserved using the CVSD and ISVD methods and fresh embryos were transferred to recipient animals, no significant differences were observed in the conception rates among groups. Our results indicate that this simplified regimen of warming and diluting Cryotop-vitrified embryos may enable 1-step bovine embryo transfer without the requirement of a microscope or other laboratory equipment.

Effect of cryotop vitrification on preimplantation developmental competence of murine morula and blastocyst stage embryos

Vitrification is an effective method for the cryopreservation of mammalian embryos. Nevertheless, it is unclear which embryonic developmental stage is the most suited for vitrification and would ensure maximal developmental competence upon subsequent warming. This study, therefore, compared the effects of cryotop vitrification on the developmental competence of murine morula and blastocyst stage embryos. Additionally, trophectoderm (TE) and inner cell mass (ICM) cell numbers were compared in two hatched blastocyst groups derived from vitrified morulae and blastocysts, respectively. The post-vitrification survival rates for mouse embryos at the morula and blastocyst stage were 95.4% (186/195) and 96.5% (195/202), respectively. The blastocyst formation rate was significantly lower for vitrified morulae (90.3%) compared with the non-vitrified control group (98.4%) (P < 0.05). The hatching rates were similar between the vitrified morula (79.6%) and the vitrified blastocyst (81.0%) groups. When further development to the fully hatched blastocyst stage was compared, fully hatched blastocysts derived from vitrified morulae had significantly higher cell counts for both the ICM and TE lineage, as compared with hatched blastocysts derived from vitrified blastocysts (P < 0.001). Cryotop vitrification of mouse embryos at the morula stage rather than blastocyst stage would thus ensure a higher degree of post-warming developmental competence.

Vitrification of canine cumulus-oocyte complexes in DAP213 with a cryotop holder

Purpose

The effects of the cryoprotectant and the container (holder) used for the vitrification of canine germinal vesicle stage oocytes were examined to improve the cryopreservation method for canine oocytes and embryos.

Methods

Canine cumulus-oocyte complexes (COCs) were collected from ovaries, and were vitrified with E30S (30% ethylene glycol and 0.5 M sucrose) or DAP213 (2 M dimethyl sulfoxide, 1 M acetamide, and 3 M propylene glycol) solution held by a cryotube or cryotop sheets. After warming, the oocytes were stained with propidium iodide for the assessment of their plasma membrane integrity.

Results

In all the vitrification groups, more than 65% of the vitrified oocytes displayed a normal morphology (E30S-top, 65.6%; DAP-tube, 67.3%; DAP-top, 80.0%). However, when assessed by propidium iodide staining, the viability of oocytes in the DAP-top group (43.6%) was higher than that in the E30S-top group (21.3%, P < 0.05). Furthermore, the viability of the oocytes in the DAP-top group (43.6%) was higher than that in the DAP-tube group (4.1%, P < 0.05).

Conclusions

These results suggest that a combination of DAP213 as the cryoprotectant and a cryotop sheet as the holder improved viability after the vitrification of canine oocytes at the germinal vesicle stage.

Comparison of traditional and modified (VitMaster) methods of rabbit embryo vitrification

In spite of their cryobiological efficacy, minimum-volume vitrification methods suffer from the risk of microbiological contamination and are technically and/or manually demanding. In this study, the effects of a traditional, slightly modified vitrification method and vitrification using supercooled liquid nitrogen (VitMaster) applied for rabbit morula-stage embryos were compared. Embryos were equilibrated in a solution containing 1,2-propanediol (2.72 M) and glycerol (1.36 M) for 7 min and vitrified in 0.25-ml insemination straws after 1-min exposure to a vitrification solution containing additionally 1.0 M sucrose. Cooling was performed in 'normal' or supercooled liquid nitrogen. Regardless of the cooling method applied, high in vitro survival and development rates of vitrified embryos were obtained. All embryos were intact after warming, and 61 out of 65 (93.8%) and 23 out of 24 (95.8%) embryos developed to the blastocyst stage after 48-h in vitro culture of embryos vitrified in 'normal' or supercooled liquid nitrogen, respectively. The results suggest higher developmental ability of embryos vitrified in supercooled liquid nitrogen (91.7% vs . 83.1% of embryos vitrified traditionally developed to more advanced, expanding and/or hatching blastocyst stages). In vivo survival rate, tested for the traditional vitrification system only, revealed that 36.8% of embryos developed to term. The results show promise for establishing a fully successful method for rabbit embryo vitrification.

Vitrification of cleavage stage mouse embryos by the cryoloop procedure

By decreasing the volume of the cryoprotective solution it is possible to increase dramatically the freezing speed and - at the same time - reduce the toxicity and osmotic side effects of cryoprotectants (CPA). The objective of our study was to vitrify Day-3 cleavage stage mouse embryos (n = 229) with the cryoloop technology using a new composition of vitrification media. Embryos were exposed to a 2-step loading of CPA, ethylene glycol (EG) and propylene glycol (PG), before being placed on the surface of a thin filmy layer formed from the vitrification solution in a small nylon loop, then they were rapidly submerged into liquid nitrogen. After warming, the CPA was diluted out from the embryos by a 3-step procedure. Survival of embryos was based on morphological appearance after thawing and continued development to expanded blastocysts upon subsequent 48-hour culture. Embryos of the two control groups were either treated likewise except that they were not vitrified, or cultured in vitro without any treatment. Our data show that a high percentage of embryos survived (92.7%) vitrification in the mixture of EG and PG combined with cryoloop carrier and developed normally (89.1%) in vitro after thawing. To our knowledge this is the first report of the successful vitrification of cleavage stage mouse embryos using VitroLoop vitrification procedure.

Cryotops versus open-pulled straws (OPS) as carriers for the cryopreservation of bovine oocytes: effects on spindle and chromosome configuration and embryo development

Two experiments were designed to assess the effectiveness of cryopreserving bovine MII oocytes using cryotops as the carrier system for vitrification. In the first experiment, we examined the developmental competence of oocytes after: (i) vitrification in open-pulled straws (OPS method); or (ii) vitrification in <0.1mul medium droplet on the surface of a specially constructed fine polypropylene strip attached to a plastic handle (Cryotop method). In the second experiment, warmed oocytes that had been vitrified in OPS or cryotops were fixed to analyze spindle and chromosome configuration. In all experiments both cow and calf oocytes were used. Significantly different fertilization rates were observed between the vitrification groups: 31.5% and 20.2% for the cow and calf oocytes vitrified in OPS, respectively, versus 46.1% and 46.4% for the oocytes vitrified using cryotops. After in vitro fertilization, 3.8% of the calf oocytes and 5.3% of the cow oocytes developed to the blastocyst stage. All blastocysts from vitrified oocytes resulted from the Cryotop method. A significantly lower percentage of the OPS-vitrified calf oocytes showed a normal spindle configuration (37.8%) compared to control fresh oocytes (69.9%), while normal spindle and chromosome configurations were observed in a significantly higher proportion of the cryotop-vitrified calf oocytes (60.2%). For the cow oocytes, 60.6% in the OPS group and 60.3% in the Cryotop group exhibited a normal morphology after warming. These findings suggest the cryotop system is a more efficient carrier for vitrification than OPS for the cryopreservation of bovine oocytes.

Conventional freezing, straw, and open-pulled straw vitrification of mouse two pronuclear (2-PN) stage embryos

Little is known on the cryopreservation of mouse pronuclear (PN) stage embryos. In the present experiment the mouse 2-PN stage embryos were cryopreserved by conventional freezing, straw, or open-pulled straw (OPS) vitrificaiton methods. The conventional freezing solution was 1.5 mol/L ethylene glycol (EG), and vitrification solutions were EFS30 (30% EG, Ficoll, and sucrose), EFS40 (40% EG, Ficoll, and sucrose), EDFS30 (15% EG, 15%dimethyl sulfoxide [DMSO], Ficoll, and sucrose), or EDFS40 (20% EG, 20%DMSO, Ficoll, and sucrose). The blastocyst rate of 2-PN stage embryos cryopreserved by conventional method (30.4%) was lower than those vitrified by straw method with EDFS (56.9% to 69.1%), by OPS method (66.0% to 85.7%), and that of control (80.8%) (P < 0.05). With a given vitrificaiton solution EFS30, EFS40, EDFS30, or EDFS40, the blastocyst rate of embryos vitrified by the OPS method (66.7%, 66.0%, 85.7%, or 76.9%) was higher than that of those vitrified by the straw method (46.8%, 43.8%, 69.1%, or 56.9%) (P < 0.05). When mouse 2-PN-stage embryos were vitrified with EDFS30 by straw or OPS method, the highest blastocyst rate was achieved (69.1% or 85.7%) and was similar to that of the control, respectively. The embryos transfer results revealed that the full-term development of blastocysts derived from 2-PN stage embryos vitrified by OPS method with EDFS30 (19.9%) was similar to that of the control (23.5%), and higher than that of those cryopreserved by conventional freezing (9.3%) (P < 0.05). The present research demonstrates that the OPS method, especially with EDFS30, is more effective in cryopreserving mouse 2-PN embryos.

Cryopreservation and in vitro maturation of germinal vesicle stage oocytes of animals for application in assisted reproductive technology

Cryopreservation, in vitro maturation, fertilization and culture can be applied to various processes across a wide range of species, that is, for the breeding and reproduction of farm animals, preservation of genetic variants in laboratory animals, and the conservation of wild species. In particular, the storage of oocytes by cryopreservation and IVM following cryopreservation, might become effective alternative assisted reproduction treatments for infertile patients. For example, in a clinical context, these techniques might be important for patients who are at risk of losing their ovarian function because of extirpative therapy, chemotherapy or radiation. Thus, it is important for assisted reproductive technology to improve IVM and cryopreservation techniques. In the present review, we introduce our recent studies on vitrification and IVM of germinal vesicle stage oocytes in animals.