Diverting the food-freezing technology improves the cryopreservation efficiency of induced pluripotent stem cells and derived neurospheres

Introduction

Recent advances in induced pluripotent stem (iPS) technology and regenerative medicine require effective cryopreservation of iPSC-derived differentiated cells and three-dimensional cell aggregates (eg. Spheroids and organoids). Moreover, innovative freezing technologies for keeping food fresh over the long-term rapidly developed in the food industry. Therefore, we examined whether one of such freezing technologies, called "Dynamic Effect Powerful Antioxidation Keeping (DEPAK)," could be effective for the cryopreservation of biological materials.

Methods

We evaluated the efficiency of cryopreservation using DEPAK and Proton freezers, both of which are used in the food industry, compared with conventional slow-freezing methods using a programmable freezer and a cell-freezing vessel. As they are highly susceptible cells to freeze-thaw damage, we selected two suspension cell lines (KHYG-1 derived from human natural killer cell leukemia and THP-1 derived from human acute monocyte leukemia) and two adherent cell lines (OVMANA derived from human ovarian tumors and HuH-7 derived from human hepatocarcinoma). We used two human iPS cell lines, 201B7-Ff and 1231A3, which were either undifferentiated or differentiated into neurospheres. After freezing using the above methods, the frozen cells and neurospheres were immediately transferred to liquid nitrogen. After thawing, we assessed the cryopreservation efficiency of cell viability, proliferation, neurosphere formation, and neurite outgrowth after thawing.

Results

Among the four cryopreservation methods, DEPAK freezing resulted in the highest cell proliferation in suspension and adherent cell lines. Similar results were obtained for the cryopreservation of undifferentiated human iPS cells. In addition, we demonstrated that the DEPAK freezing method sustained the neurosphere formation capacity of differentiated iPS cells to the same extent as unfrozen controls. In addition, we observed that DEPAK-frozen neurospheres exhibited higher viability after thawing and underwent neural differentiation more efficiently than slow-freezing methods.

Conclusions

Our results suggest that diversifying food-freezing technologies can overcome the difficulties associated with the cryopreservation of various biological materials, including three-dimensional cell aggregates.

Boric Acid Improved Cryopreserved Mouse Embryo Development

Boric acid (BA) is an essential trace element that is required to support the metabolic pathways in plants, humans, and animals. The present study investigates the in vitro development and quality of single-cell mouse embryos in a BA-added culture medium after cryopreservation using the solid-surface vitrification method. For this purpose, the pronuclear-stage embryos derived from superovulated C57Bl/6j mouse strains and the one-cell embryos were then cryopreserved using the solid-surface vitrification (SSV) method. After thawing, the embryos were cultured in a BA-added medium at 37 °C in a 5% CO2 environment until the blastocyst stage. The resulting in vitro development rates of the embryos in the control group, SSV group, and SSV + 1.62 × 10-4 μM BA group were 68.11% (36/59), 40.16% (16/48), and 64.92% (28/48) respectively, indicating that the BA supported the in vitro development of the embryos cryopreserved using the SSV method. Our results suggest that the addition of boric acid to the culture media increased the development rate of the embryos that were vitrified using the SSV method.

A simple method for repeated in vivo sperm collection from laboratory mice

PURPOSE

Mouse spermatozoa for archiving laboratory mice or for in vitro fertilization (IVF) are routinely obtained from the cauda epididymis of adult males sacrificed for this purpose. To avoid the death of the donor, we tested whether a precisely timed interruption of the mating act could be used for repeated sperm collection from laboratory mice.

METHODS

Sperm donors (B6D2F1) were mated with a receptive female, and mating behavior was observed. The stud was separated from the female 1-2 s after the onset of the ejaculatory shudder. The ejected copulatory plug with the yellowish viscous ejaculate was carefully removed from the penile cup.

RESULTS

A total of 80 ejaculates were successfully obtained from 100 ejaculations. The latency to first mount was 1.1 ± 1.1 min (mean ± SD) and to ejaculation 8.1 ± 4.7 min. The average number of mounts to ejaculation was 10.5 ± 5.8, and the mean number of spermatozoa per collected ejaculate was 1.86 ± 1.05 × 106. An average fertilization rate of 76% was observed after IVF.

CONCLUSIONS

Separating the stud from the female just before ejaculation is feasible, easy to learn, and requires no special equipment. The sperm count of collected ejaculates is lower than natural ejaculations, but higher than previous in vivo sperm collection methods achieved. We recommend this simple sperm collection method in mice, especially when the donor cannot be sacrificed and/or repeated sperm collection from the same animal is required for experimental purposes.

Preimplantation genetic testing in the current era, a review

BACKGROUND

Preimplantation genetic testing (PGT), also referred to as preimplantation genetic diagnosis (PGD), is an advanced reproductive technology used during in vitro fertilization (IVF) cycles to identify genetic abnormalities in embryos prior to their implantation. PGT is used to screen embryos for chromosomal abnormalities, monogenic disorders, and structural rearrangements.

DEVELOPMENT OF PGT

Over the past few decades, PGT has undergone tremendous development, resulting in three primary forms: PGT-A, PGT-M, and PGT-SR. PGT-A is utilized for screening embryos for aneuploidies, PGT-M is used to detect disorders caused by a single gene, and PGT-SR is used to detect chromosomal abnormalities caused by structural rearrangements in the genome.

PURPOSE OF REVIEW

In this review, we thoroughly summarized and reviewed PGT and discussed its pros and cons down to the minutest aspects. Additionally, recent studies that highlight the advancements of PGT in the current era, including their future perspectives, were reviewed.

CONCLUSIONS

This comprehensive review aims to provide new insights into the understanding of techniques used in PGT, thereby contributing to the field of reproductive genetics.

Vitrification of Mammalian Oocytes: Recent Studies on Mitochondrial Dysfunction

Vitrification of reproductive cells is definitely essential and integral in animal breeding, as well as in assisted reproduction. However, issues accompanied with this technology such as decreased oocyte competency and relatively low embryo survival rates appear to be a tough conundrum that has long perplexed us. As significant organelles in cell metabolism, mitochondria play pivotal roles in numerous pathways. Nonetheless, extensive evidence has demonstrated that vitrification can seriously impair mitochondrial function in mammalian oocytes. Thus, in this article, we summarize the current progress in oocyte vitrification and particularly outline the common mitochondrial abnormalities alongside subsequent injury cascades seen in mammalian oocytes following vitrification. Based on existing literature, we tentatively come up with the potential mechanisms related to mitochondrial dysfunction and generalize efficacious ways which have been recommended to restore mitochondrial function.

Recent advances of oocyte/embryo vitrification in mammals from rodents and large animals

Vitrification is a valuable technology that enables semipermanent preservation and long-distance or international transportation of genetically modified and native animals. In laboratory mice, vitrification maintains and transports embryos, and many institutions and companies sell vitrified embryos. In contrast, despite numerous papers reporting on vitrification in livestock over the past decade, practical implementation has yet to be achieved. However, with advances in genome editing technology, it is anticipated that the number of genetically modified domestic animals will increase, leading to a rise in demand for vitrification of oocytes and embryos. Here, we provide an objective overview of recent advancements in vitrification technology for livestock, drawing a comparison with the current developments in laboratory animals. Additionally, we explore the future prospects for vitrification in livestock, focusing on its potential benefits and drawbacks.

Cryopreservation of rat embryos at all developmental stages by small-volume vitrification procedure and rapid warming in cryotubes

Intracellular ice formation during cryopreservation is lethal to the cell, including during warming. Here, we examined the effect of sample volume and warming rate on the cryopreservation success of 1-cell rat embryos based on successful development into blastocysts in vitro and to term in vivo following embryo transfer. Embryos were equilibrated in 5% propylene glycol solution for 10 min, held for 40 s at 0 °C in cryopreservation solution (5%PG + PEPeS), and cooled by immersion in liquid nitrogen. When 1-cell embryos were cryopreserved in a volume of 30-100 μL at a cooling rate of 5830-7160 °C/min and warmed at 35,480-49,400 °C/min by adding 1 mL of 0.3 M sucrose solution at 50 °C, 17.3-28.8% developed into blastocysts, compared with 57.0% of untreated embryos. However, when 1-cell embryos were cryopreserved in a smaller volume of 15 μl at 7950 °C/min and warmed at 68,850 °C/min, 58.8 ± 10.6% developed into blastocysts and 50.0 ± 7.4% developed to term, comparable to that of non-treated embryos (57.0 ± 5.4% and 51.4 ± 3.1%, respectively). Cryopreserved embryos at other developmental stages also showed high in vitro culture potential similar to that of the control. Using a conventional cryotube and a small-volume vitrification procedure with rapid warming, we achieved high levels of subsequent rat embryonic development at all developmental stages.

Effect of blastocyst shrinkage on assisted reproductive outcomes: a retrospective cohort study describing a new morphological evaluation of blastocyst pre-vitrification and post-warming

BACKGROUND

The failure of frozen-thawed blastocysts to re-expand adequately within a few hours after warming has been reported to have a negative impact on assisted reproductive technology (ART) outcomes. However, the extent to which this failure truly affects ART outcomes has not yet been presented in a manner that is easily understandable to medical practitioners and patients. This study aimed to assess the effects of blastocyst shrinkage on ART outcomes and determine a more effective morphological evaluation approach for use in clinical settings.

METHODS

This retrospective observational cohort study of frozen-thawed blastocyst transfer cycles was conducted from April 2017 to March 2022. Overall, 1,331 cycles were eligible for inclusion, of which 999 were good-quality blastocysts (GQB) and 332 were non-good-quality blastocysts (non-GQB). All frozen-thawed blastocyst transfer cycles performed during the specified study period were included in the study. Exclusion criteria were established to mitigate potential sources of bias as these cycles could impact implantations. We calculated rates and age-adjusted odds ratios of implantation, clinical pregnancy, ongoing pregnancy, and live birth of the re-expansion group, which showed sufficient expansion, and shrinkage group, which showed insufficient expansion. We also calculated the implantation, clinical pregnancy, ongoing pregnancy, and live birth rates of the re-expansion and shrinkage groups for each morphological scoring system parameter.

RESULTS

A reduced ART outcome was observed with use of blastocysts with shrinkage after vitrification/warming. The age-adjusted odds ratios for implantation, clinical pregnancy, ongoing pregnancy, and live birth were lower in the shrinkage group than in the re-expansion group.

CONCLUSIONS

This study examined the adverse effect of blastocyst shrinkage after warming and recovery culturing on reproductive outcomes in a clinically useful manner by retrospectively examining a substantial number of frozen-thawed embryo transfer cycles. The study findings can possibly reduce concerns regarding over- or under-estimation of blastocyst implantation by allowing providers and patients to refer to the data.

Oocyte and embryo cryopreservation in assisted reproductive technology: past achievements and current challenges

Cryopreservation has revolutionized the treatment of infertility and fertility preservation. This review summarizes the milestones that paved the way to the current routinary clinical implementation of this game-changing practice in assisted reproductive technology. Still, evidence to support "the best practice" in cryopreservation is controversial and several protocol adaptations exist that were described and compared here, such as cumulus-intact vs. cumulus-free oocyte cryopreservation, artificial collapse, assisted hatching, closed vs. open carriers, and others. A last matter of concern is whether cryostorage duration may impact oocyte/embryo competence, but the current body of evidence in this regard is reassuring. From social and clinical perspectives, oocyte and embryo cryopreservation has evolved from an afterthought when assisted reproduction was intended for immediate pregnancy with supernumerary embryos of secondary interest to its current purpose, which primarily is to preserve fertility long-term and more comprehensively allow for family planning. However, the initial consenting process, which still is geared to short-term fertility care, may no longer be relevant when the individuals that initially preserved the tissues have completed their reproductive journey. A more encompassing counseling model is required to address changing patient values over time.

The Cold Futures of Mouse Genetics: Modes of Strain Cryopreservation Since the 1970s

Cryopreservation, or the freezing of embryos or sperm, has become a routine part of many research projects involving laboratory mice. In this article, we combine historical and sociological methods to produce a cryopolitical analysis of this less explored aspect of animal research. We provide a longitudinal account of mouse embryo and semen storage and uses in the UK and show that cryopreservation enabled researchers to overcome particular challenges-fears of strain loss, societal disapproval, and genetic drift-in ways which enabled the continued existence of strains and contributed to the scaling up of mouse research since World War II. We use the theoretical lens of cryopolitics to explore three different, yet overlapping, cryopolitical strategies that we identify. All share the ability to ensure the continued maintenance of genetically defined strains without the need for continually breeding colonies of mice. We argue that, in contrast to more common imaginaries of species conservation, the cryopolitical rationale can best be understood as purposefully not letting the strain die without requiring animals to live. The ability to freeze mice, then, had the potential to unsettle who the objects of care are in mouse research, from individual animals to the concept of the strain itself.

Impact of cryopreservation on viability, gene expression and function of enteric nervous system derived neurospheres

Introduction: Impairment of both the central and peripheral nervous system is a major cause of mortality and disability. It varies from an affection of the brain to various types of enteric dysganglionosis. Congenital enteric dysganglionosis is characterized by the local absence of intrinsic innervation due to deficits in either migration, proliferation or differentiation of neural stem cells. Despite surgery, children's quality of life is reduced. Neural stem cell transplantation seems a promising therapeutic approach, requiring huge amounts of cells and multiple approaches to fully colonize the diseased areas completely. A combination of successful expansion and storage of neural stem cells is needed until a sufficient amount of cells is generated. This must be combined with suitable cell transplantation strategies, that cover all the area affected. Cryopreservation provides the possibility to store cells for long time, unfortunately with side effects, i.e., upon vitality. Methods: In this study we investigate the impact of different freezing and thawing protocols (M1-M4) upon enteric neural stem cell survival, protein and gene expression, and cell function. Results: Freezing enteric nervous system derived neurospheres (ENSdN) following slow-freezing protocols (M1-3) resulted in higher survival rates than flash-freezing (M4). RNA expression profiles were least affected by freezing protocols M1/2, whereas the protein expression of ENSdN remained unchanged after treatment with protocol M1 only. Cells treated with the most promising freezing protocol (M1, slow freezing in fetal calf serum plus 10% DMSO) were subsequently investigated using single-cell calcium imaging. Freezing of ENSdN did not alter the increase in intracellular calcium in response to a specific set of stimuli. Single cells could be assigned to functional subgroups according to response patterns and a significant shift towards cells responding to nicotine was observed after freezing. Discussion: The results demonstrate that cryopreservation of ENSdN is possible with reduced viability, only slight changes in protein/gene expression patterns and without an impact on the neuronal function of different enteric nervous system cell subtypes, with the exception of a subtle upregulation of cells expressing nicotinergic acetylcholine receptors. In summary, cryopreservation presents a good method to store sufficient amounts of enteric neural stem cells without neuronal impairment, in order to enable subsequent transplantation of cells into compromised tissues.

Vitrification and nanowarming enable long-term organ cryopreservation and life-sustaining kidney transplantation in a rat model

Banking cryopreserved organs could transform transplantation into a planned procedure that more equitably reaches patients regardless of geographical and time constraints. Previous organ cryopreservation attempts have failed primarily due to ice formation, but a promising alternative is vitrification, or the rapid cooling of organs to a stable, ice-free, glass-like state. However, rewarming of vitrified organs can similarly fail due to ice crystallization if rewarming is too slow or cracking from thermal stress if rewarming is not uniform. Here we use "nanowarming," which employs alternating magnetic fields to heat nanoparticles within the organ vasculature, to achieve both rapid and uniform warming, after which the nanoparticles are removed by perfusion. We show that vitrified kidneys can be cryogenically stored (up to 100 days) and successfully recovered by nanowarming to allow transplantation and restore life-sustaining full renal function in nephrectomized recipients in a male rat model. Scaling this technology may one day enable organ banking for improved transplantation.

An all-37 °C thawing method improves the clinical outcomes of vitrified frozen-thawed embryo transfer: a retrospective study using a case-control matching analysis

PURPOSE

The purpose of this study is to assess the impact of different temperatures and incubation times on the clinical outcomes of FET cycles during the thawing procedure and to select a better thawing method to improve clinical outcomes.

METHODS

This retrospective study included 1734 FET cycles from January 1, 2020, to January 30, 2022. Embryos vitrified using a KITAZATO Vitrification Kit were thawed at 37 °C in all steps (the case group, denoted the "all-37 °C" group) or at 37 °C and then at room temperature (RT; the control group, denoted the "37 °C-RT" group), according to the kit instructions. The groups were matched 1:1 to avoid confounding.

RESULTS

After case-control matching, 366 all-37 °C cycles and 366 37 °C-RT cycles were included. The baseline characteristics were similar (all P > 0.05) between the two groups after matching. FET of the all-37 °C group yielded a higher clinical pregnancy rate (CPR; P = 0.009) and implantation rate (IR; P = 0.019) than FET of the 37 °C-RT group. For blastocyst transfers, the CPR (P = 0.019) and IR (P = 0.025) were significantly higher in the all-37 °C group than in the 37 °C-RT group. For D3-embryo transfers, the CPR and IR were non-significantly higher in the all-37 °C group than in the 37 °C-RT group (P > 0.05).

CONCLUSIONS

Thawing vitrified embryos at 37 °C in all steps with shortening wash time can enhance CPR and IR in FET cycles. Well-designed prospective studies are warranted to further evaluate the efficacy and safety of the all-37 °C thawing method.

Post-thaw viability of mouse preantral follicles after cryopreservation with cryotube freezing and OPS vitrification procedures

In the field of reproductive science, there is an increased interest in the application of ovarian preantral follicles. Since the ovary contains a great amount of preantral follicles (PAF), the cryopreservation and in vitro culture of such follicles support the fertility preservation of domestic animals with high genetic value, endangered or zoo animals, and women before anticancer therapy. To date, no standard freezing or vitrification protocol is available in human or animals. The aim of the present study was to examine the viability of preantral follicles cryopreserved using freezing or vitrification protocols: cryotube freezing or OPS vitrification.

A 3D-Printed Large Holding Capacity Device for Minimum Volume Cooling Vitrification of Embryos in Prolific Livestock Species

Although many devices have been developed to reduce sample volume, with an explosion of methods appearing in the literature over the last decade, commercially available devices with simultaneous vitrification of a larger number of embryos are scarce, with the apparent gap for their use in prolific livestock species. In this study, we investigated the effectiveness of a new three-dimensional (3D)-printed device that combines minimum volume cooling vitrification with simultaneous vitrification of a larger number of rabbit embryos. Late morulae/early blastocysts were vitrified with the open Cryoeyelet^® device (n = 175; 25 embryos per device), the open Cryotop^® device (n = 175; 10 embryos per device), and the traditional closed French mini-straw device (n = 125; 25 embryos per straw) and compared in terms of in vitro development and reproductive performance after transfer to adoptive mothers. Fresh embryos constituted the control group (n = 125). In experiment 1, there was no difference in the development rate to the blastocyst hatching stage between the CryoEyelet^® and the other devices. In experiment 2, the CryoEyelet^® device showed a higher implantation rate compared with the Cryotop^® (6.3% unit of SD, p = 0.87) and French mini-straw^® (16.8% unit of SD, p = 1.00) devices. In terms of offspring rate, the CryoEyelet^® device was similar to the Cryotop^® device but superior to the French straw device. Regarding embryonic and fetal losses, the CryoEyelet^® showed lower embryonic losses compared to other vitrification devices. The analysis of bodyweight showed that all devices showed a similar outcomes-a higher birthweight but a lower body weight at puberty than those in the fresh transfer embryos group. In summary, the CryoEyelet^® device can be used for the vitrification of many late morulae or early blastocyst stage rabbit embryos per device. Further studies should be performed to evaluate the CryoEyelet^® device in other polytocous species for the simultaneous vitrification of a large number of embryos.

Oxidative Stress and Oocyte Cryopreservation: Recent Advances in Mitigation Strategies Involving Antioxidants

Oocyte cryopreservation is widely used in assisted-reproductive technology and animal production. However, cryopreservation not only induces a massive accumulation of reactive oxygen species (ROS) in oocytes, but also leads to oxidative-stress-inflicted damage to mitochondria and the endoplasmic reticulum. These stresses lead to damage to the spindle, DNA, proteins, and lipids, ultimately reducing the developmental potential of oocytes both in vitro and in vivo. Although oocytes can mitigate oxidative stress via intrinsic antioxidant systems, the formation of ribonucleoprotein granules, mitophagy, and the cryopreservation-inflicted oxidative damage cannot be completely eliminated. Therefore, exogenous antioxidants such as melatonin and resveratrol are widely used in oocyte cryopreservation to reduce oxidative damage through direct or indirect scavenging of ROS. In this review, we discuss analysis of various oxidative stresses induced by oocyte cryopreservation, the impact of antioxidants against oxidative damage, and their underlying mechanisms. We hope that this literature review can provide a reference for improving the efficiency of oocyte cryopreservation.

Application of Nanoparticles and Melatonin for Cryopreservation of Gametes and Embryos

Cryopreservation of gametes and embryos, a technique widely applied in human infertility clinics and to preserve desirable genetic traits of livestock, has been developed over 30 years as a component of the artificial insemination process. A number of researchers have conducted studies to reduce cell toxicity during cryopreservation using adjuvants leading to higher gamete and embryo survival rates. Melatonin and Nanoparticles are novel cryoprotectants and recent studies have investigated their properties such as regulating oxidative stresses, lipid peroxidation, and DNA fragmentation in order to protect gametes and embryos during vitrification. This review presented the current status of cryoprotectants and highlights the novel biomaterials such as melatonin and nanoparticles that may improve the survivability of gametes and embryos during this process.

Temperature-pressure correlations of cryoprotective additives for the design of constant volume cryopreservation protocols

In the recent years, the use of constant volume (isochoric) cryopreservation, in medicine and biotechnology has captured more attention from the research community and now there is an increasing interest in the use of this new technology. It has been established that the thermodynamics of isochoric freezing is different from that of isobaric (constant pressure) freezing. This study provides researchers in the field experimental results for various compositions of cryoprotectants commonly used in isobaric cryopreservation, in terms of temperature-pressure-molar concentration correlation. It also reveals experimental isochoric thermodynamic data for the following cryoprotectants, commonly used in isobaric cryopreservation: dimethyl sulfoxide, trehalose, ethylene glycol and diethylene glycol. Currently, the data on the pressure-temperature correlation in an isochoric system of cryoprotectants used in isobaric cryopreservation is not available. Our new experimental results indicate that the studied concentrations for each of the CPAs, lower and expands the range of temperatures in which cryopreservation by isochoric freezing can be safely practiced. We consider that these experiments will aid researchers developing new isochoric cryopreservation protocols.

History of fertility preservation

Background: Fertility preservation refers to a procedure performed to maintain the ability to become pregnant before receiving treatment with a risk of fertility loss, such as chemo- or radiation therapy. Examples of fertility-preserving procedures include freezing, sperm freezing, embryo freezing through in vitro fertilization, and ovarian tissue freezing.Current Concepts: Until the late 1990s, awareness of fertility preservation among clinicians and patients was relatively low, and the only way to preserve and restore fertility in women with cancer was the cryopreservation of embryos. However, as the survival rate of cancer patients increased and the treatment results of various diseases improved, interest in quality of life such as pregnancy and childbirth after treatment gradually increased, and became a driving force for the development of fertility preservation. In the 2000s, several centers began cryopreserving ovarian tissue, including primordial follicles from young patients before chemotherapy. Currently, ovarian tissue cryopreservation can be used in combination with in vitro maturation and egg vitrification techniques. Novel methods to improve follicle survival after transplantation are currently being investigated. Methods to improve follicle survival after transplantation and new ovarian protective agents to protect the ovaries from cytotoxic agents are currently being studied.Discussion and Conclusion: Advances in fertility-preserving technologies in the future will contribute to the delivery of healthy children by providing tailored treatments and more individualized fertility-preserving strategies to patients whose fertility is at risk.

Cryopreservation Methods and Frontiers in the Art of Freezing Life in Animal Models

The development in cryobiology in animal breeding had revolutionized the field of reproductive medicine. The main objective to preserve animal germplasm stems from variety of reasons such as conservation of endangered animal species, animal diversity, and an increased demand of animal models and/or genetically modified animals for research involving animal and human diseases. Cryopreservation has emerged as promising technique for fertility preservation and assisted reproduction techniques (ART) for production of animal breeds and genetically engineered animal species for research. Slow rate freezing and rapid freezing/vitrification are the two main methods of cryopreservation. Slow freezing is characterized by the phase transition (liquid turning into solid) when reducing the temperature below freezing point. Vitrification, on the other hand, is a phenomenon in which liquid solidifies without the formation of ice crystals, thus the process is referred to as a glass transition or ice-free cryopreservation. The vitrification protocol applies high concentrations of cryoprotective agents (CPA) used to avoid cryoinjury. This chapter provides a brief overview of fundamentals of cryopreservation and established methods adopted in cryopreservation. Strategies involved in cryopreserving germ cells (sperm and egg freezing) are included in this chapter. Last section describes the frontiers and advancement of cryopreservation in some of the important animal models like rodents (mouse and rats) and in few large animals (sheep, cow etc).

Cryopreservation of Anopheles stephensi embryos

The ability to cryopreserve mosquitoes would revolutionize work on these vectors of major human infectious diseases by conserving stocks, new isolates, lab-bred strains, and transgenic lines that currently require continuous life cycle maintenance. Efforts over several decades to develop a method for cryopreservation have, until now, been fruitless: we describe here a method for the cryopreservation of Anopheles stephensi embryos yielding hatch rates of ~ 25%, stable for > 5 years. Hatched larvae developed into fertile, fecund adults and blood-fed females, produced fully viable second generation eggs, that could be infected with Plasmodium falciparum at high intensities. The key components of the cryopreservation method are: embryos at 15-30 min post oviposition, two incubation steps in 100% deuterated methanol at - 7 °C and - 14.5 °C, and rapid cooling. Eggs are recovered by rapid warming with concomitant dilution of cryoprotectant. Eggs of genetically modified A. stephensi and of A. gambiae were also successfully cryopreserved. This enabling methodology will allow long-term conservation of mosquitoes as well as acceleration of genetic studies and facilitation of mass storage of anopheline mosquitoes for release programs.

Cryodevices developed for minimum volume cooling vitrification of bovine oocytes

Unfertilized bovine oocytes can be efficiently cryopreserved only when an extremely rapid cooling rate (>20,000°C/min) is applied to oocytes with a very limited amount of surrounding vitrification solution. This protocol is defined as minimum volume cooling (MVC) vitrification. Various types of cryodevices, such as open pulled straw, Cryoloop, and Cryotop, have been developed to accelerate the cooling efficacy. Furthermore, hollow fibers with nano-scale pores, triangle nylon mesh sheets, and multilayer silk fibroin sheets have been optimized for the loading of large quantities of oocytes and/or the subsequent removal of excess vitrification solution, without requiring skillful operation to transfer individual oocytes using fine capillaries. This article provides an up-to-date review of cryodevices suitable for the MVC vitrification of bovine oocytes at the immature (germinal vesicle-) and mature (metaphase II-) stages.

Translating Basic Research to Animal Agriculture

Procedures to maintain viability of mammalian gametes and embryos in vitro, including cryopreservation, have been exceedingly valuable for my research over the past 55 years. Keeping sperm viable in vitro enables artificial insemination, which, when combined with selective breeding, often is the most effective approach to making rapid genetic change in a population. Superovulation and embryo transfer constitute a parallel approach for amplifying reproduction of female mammals. More recent developments include sexing of semen, in vitro fertilization, cloning by nuclear transfer, and genetic modification of germline cells, tools that are enabled by artificial insemination and/or embryo transfer for implementation. I have been fortunate in being able to contribute to the development of many of the above techniques, and to use them for research and applications for improving animal agriculture. Others have built on this work to circumvent human infertility, assist reproduction of companion animals, and rescue endangered species. It also has been a privilege to teach, mentor, and be mentored in this area. Resulting worldwide friendships have enriched me personally and professionally. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Improved developmental potential of mouse vitrified-warmed oocytes achieved by culturing in recovery medium with glutathione ethyl ester (GSH-OEt)

PURPOSE

The aim of the present study was to investigate the effect of glutathione ethyl ester (GSH-OEt) in the recovery medium on the developmental competence of mouse vitrified-warmed MII oocytes.

METHODS

Vitrified-warmed oocytes were incubated for 1 h in recovery medium in the presence or absence of 0.5 mM GSH-OEt. The authors examined the effects of GSH-OEt, first on the levels of glutathione (GSH) and reactive oxygen species (ROS) in vitrified-warmed oocytes, and second, on in vitro blastocyst development, division speed to blastocysts, and total cell numbers of blastocysts from vitrified-warmed oocytes fertilized by Intracytoplasmic sperm injection (ICSI).

RESULTS

Adding GSH-OEt to the recovery medium significantly (p < 0.05) increased GSH content and decreased ROS levels in vitrified-warmed oocytes. The blastocyst rate did not differ significantly between the two groups, but the speed of development to blastocysts in the GSH-OEt (+) group was significantly more rapid. In addition, the total blastocyst cell number was significantly higher in the GSH-OEt (+) group than in the GSH-OEt (-) group (92.8 ± 5.1 vs. 71.4 ± 3.5, p < 0.01).

CONCLUSION

Adding GSH-OEt to the recovery medium of vitrified-warmed mouse oocytes enhances the development potential of oocytes and improves the quality of blastocysts.

Mitophagy is involved in the mitochondrial dysfunction of vitrified porcine oocytes

Mitochondrial dysfunction is considered a crucial factor aggravating oocyte viability after vitrification-warming. To clarify the role of mitophagy in mitochondrial extinction of vitrified porcine oocytes, mitochondrial function, ultrastructural characteristics, mitochondria-lysosomes colocalization, and mitophagic proteins were detected with or without chloroquine (CQ) treatment. The results showed that vitrification caused mitochondrial dysfunction, including increasing reactive oxygen species production, decreasing mitochondrial membrane potential, and mitochondrial DNA copy number. Damaged mitochondrial cristae and mitophagosomes were observed in vitrified oocytes. A highly fused fluorescence distribution of mitochondria and lysosomes was also observed. In the detection of mitophagic flux, mitophagy was demonstrated as increasing fluorescence aggregation of microtubule-associated protein light chain 3B (LC3B), enhanced colocalization between LC3B, and voltage-dependent anion channels 1 (VDAC1), and upregulated LC3B-II/I protein expression ratio. CQ inhibited the degradation of mitophagosomes in vitrified oocytes, manifested as decreased mitochondria-lysosomes colocalization, increased fluorescence fraction of VDAC1 overlapping LC3B, increased LC3B-II/I protein expression ratio, and p62 accumulation. The inhibition of mitophagosomes degradation by CQ aggravated mitochondrial dysfunction, including increased oxidative damage, reduced mitochondrial function, and further led to loss of oocyte viability and developmental potentiality. In conclusion, mitophagy is involved in the regulation of mitochondrial function during porcine oocyte vitrification.

Cryopreservation Protocols for Genetically Engineered Mice

Protocols for cryopreservation of mouse embryos and sperm are important for preserving genetically engineered mice (GEMs) used in research to study human development and diseases. Embryo cryopreservation is mainly carried out using either of two protocols: controlled gradual cooling or vitrification. Sperm cryopreservation protocols include two methodologies that are commonly referred to as JAX and CARD. Quality-control measures are necessary to ensure that GEMs are properly cryopreserved so that they can be retrieved for future use. An archiving system is also important in keeping proper records of frozen sperm and embryos. Frozen embryos and sperm are now preferred over live mice for shipping to distant locations. This article describes detailed protocols used in cryopreservation of mouse embryos and sperm, as well as their retrieval to live mice. © 2021 U.S. Government. Sperm cryopreservation Basic Protocol 1: JAX protocol for sperm cryopreservation Support Protocol 1: JAX protocol for making sperm cryopreservation medium Basic Protocol 2: JAX protocol for IVF of mouse sperm Alternate Protocol 1: Modified CARD protocol for sperm cryopreservation Support Protocol 2: CARD protocol for making sperm cryopreservation medium Alternate Protocol 2: CARD protocol for IVF of mouse sperm Embryo cryopreservation Basic Protocol 3: Cryopreserving and thawing 2-cell embryos Alternate Protocol 3: Cryopreserving and thawing 8-cell to morula-stage embryos Surgical transfer of embryos Basic Protocol 4: Infundibulum transfer of 2-cell to morula-stage embryos.

Archiving genetically altered animals: a review of cryopreservation and recovery methods for genome edited animals

With the ever-expanding numbers of genetically altered (GA) animals created in this new age of CRISPR/Cas, tools for helping the management of this vast and valuable resource are essential. Cryopreservation of embryos and germplasm of GA animals has been a widely used tool for many years now, allowing for the archiving, distribution and colony management of stock. However, each year brings an array of advances, improving survival rates of embryos, success rates of in-vitro fertilisation and the ability to better share lines and refine the methods to preserve them. This article will focus on the mouse field, referencing the latest developments and assessing their efficacy and ease of implementation, with a brief note on other common genetically altered species (rat, zebrafish, Xenopus, avian species and non-human Primates).

Small-volume vitrification and rapid warming yield high survivals of one-cell rat embryos in cryotubes†

To cryopreserve cells, it is essential to avoid intracellular ice formation during cooling and warming. One way to achieve this is to convert the water inside the cells into a non-crystalline glass. It is currently believed that to accomplish this vitrification, the cells must be suspended in a very high concentration (20-40%) of a glass-inducing solute, and subsequently cooled very rapidly. Herein, we report that this belief is erroneous with respect to the vitrification of one-cell rat embryos. In the present study, one-cell rat embryos were vitrified with 5 μL of EFS10 (a mixture of 10% ethylene glycol (EG), 27% Ficoll, and 0.45 M sucrose) in cryotubes at a moderate cooling rate, and warmed at various rates. Survival was assessed according to the ability of the cells to develop into blastocysts and to develop to term. When embryos were vitrified at a 2613 °C/min cooling rate and thawed by adding 1 mL of sucrose solution (0.3 M, 50 °C) at a warming rate of 18 467 °C/min, 58.1 ± 3.5% of the EFS10-vitrified embryos developed into blastocysts, and 50.0 ± 4.7% developed to term. These rates were similar to those of non-treated intact embryos. Using a conventional cryotube, we achieved developmental capabilities in one-cell rat embryos by rapid warming that were comparable to those of intact embryos, even using low concentrations (10%) of cell-permeating cryoprotectant and at low cooling rates.

Initiation of cell volume regulation and unique cell volume regulatory mechanisms in mammalian oocytes and embryos

The period beginning with the signal for ovulation, when a fully-grown oocyte progresses through meiosis to become a mature egg that is fertilized and develops as a preimplantation embryo, is crucial for healthy development. The early preimplantation embryo is unusually sensitive to cell volume perturbations, with even moderate decreases in volume or dysregulation of volume-regulatory mechanisms resulting in developmental arrest. To prevent this, early embryos possess mechanisms of cell volume control that are apparently unique to them. These rely on the accumulation of glycine and betaine (N, N, N-trimethylglycine) as organic osmolytes-compounds that can provide intracellular osmotic support without the deleterious effects of inorganic ions. Preimplantation embryos also have the same mechanisms as somatic cells that mediate rapid responses to deviations in cell volume, which rely on inorganic ion transport. Both the unique, embryo-specific mechanisms that use glycine and betaine and the inorganic ion-dependent mechanisms undergo major changes during meiotic maturation and preimplantation development. The most profound changes occur immediately after ovulation is triggered. Before this, oocytes cannot regulate their volume, since they are strongly attached to their rigid extracellular matrix shell, the zona pellucida. After ovulation is triggered, the oocyte detaches from the zona pellucida and first becomes capable of independent volume regulation. A complex set of developmental changes in each cell volume-regulatory mechanism continues through egg maturation and preimplantation development. The unique cell volume-regulatory mechanisms in eggs and preimplantation embryos and the developmental changes they undergo appear critical for normal healthy embryo development.

Cryopreservation of Porcine Embryos: Recent Updates and Progress

Cryopreservation of embryos is important for long-distance embryo transfer and conservation of genetic resources. Porcine research is important for animal husbandry and biomedical research. However, porcine embryos are difficult to cryopreserve because of their high cytoplasmic lipid content and sensitivity to chilling stress. Vitrification is more efficient than slow freezing, and vitrification is mostly used in embryo cryopreservation. So far, the vitrification process of porcine embryos has been continuously improved, resulting in improved survival rates of warmed embryos and farrowing rates after the transplant procedure. It is worth noting that automatic vitrification has made great progress, which is expected to promote the standardization and application of vitrification. In this article, the vitrification process of porcine embryos at the blastula stage and early development stages is reviewed in detail. In addition, the efficiency of different vitrification systems was compared. In addition, we summarize technology that can improve the survival rate of cryopreserved porcine embryos, such as delipidation methods (including physical delipidation and chemical delipidation) and medium improvements (including chemically defined media and adding antioxidants). Meanwhile, gene expression changes during cryopreservation are also elaborated.

Electrosterically stabilized cellulose nanocrystals demonstrate ice recrystallization inhibition and cryoprotection activities

Ice recrystallization inhibitors have emerged as novel cryoprotectants to improve cell viability for cryopreservation. Nanocelluloses were identified as new materials for ice recrystallization inhibition (IRI); however, conventional nanocelluloses aggregate and lose IRI activity at high ionic strengths, which limit their application as cryoprotectants. In this study, we synthesized a novel group of nanocelluloses - electrosterically stabilized cellulose nanocrystals (ECNCs), which remained dispersed and IRI-active at high ionic strengths. ECNCs improved the post-thaw viability of HCT-116 colorectal cancer cells in slow/fast freezing-slow thawing protocols in the presence of 1-20% v/v dimethyl sulfoxide (DMSO), as well as in slow/fast freezing-fast thawing protocols at reduced DMSO concentrations. The effectiveness in cryoprotection did not match the IRI activity in ECNCs, polyethylene glycol (PEG), and polyvinyl alcohol (PVA); and in ECNCs with different surface charge densities. Overall, ECNCs demonstrated IRI and cryoprotection activities, but the mechanism of cryoprotection remains unknown.

Equilibrium vitrification of mouse embryos using low concentrations of cryoprotectants

Previously, we developed a method for vitrification of mouse embryos in a near-equilibrium state using EFS35c, PB1 medium containing 35% (v/v) ethylene glycol, and 0.98 M sucrose. This method has advantages in both slow freezing and vitrification. However, since the vitrification solution in this method contains high concentrations of cryoprotectants and thus has high osmolality, the solution would injure oocytes and embryos with high sensitivity to chemical toxicity and high osmolality. In this study, we examined whether embryos could be vitrified in a near-equilibrium state using a solution containing low concentrations of cryoprotectants and thus with low osmolality. To investigate whether embryos were vitrified in a near-equilibrium state, 2-cell mouse embryos were vitrified with EDFS10/10a, PB1 medium containing 10% (v/v) ethylene glycol, 10% (v/v) DMSO, and 0.4 M sucrose, in liquid nitrogen, stored at -80 °C for 4-28 days, and warmed in water at 25 °C. The viability of the embryos was evaluated by the appearance of embryos after warming and developmental ability. When embryos were vitrified in liquid nitrogen using EDFS10/10a, the survival and developmental ability into blastocysts after storage at -80 °C for 7 days were high, indicating that embryos were vitrified in a near-equilibrium state. A high proportion of embryos vitrified with EDFS10/10a developed to term after transportation with dry ice, re-cooling in liquid nitrogen, and transfer to recipients. Therefore, new equilibrium vitrification developed in this study may be useful for oocytes and embryos that are highly sensitive to the toxicity of cryoprotectants and high osmolality.

The Evolution of the Cryopreservation Techniques in Reproductive Medicine—Exploring the Character of the Vitrified State Intra- and Extracellularly to Better Understand Cell Survival after Cryopreservation

Nowadays, cryopreservation of gametes and embryos is a fundamental, integral, and indispensable part of infertility treatment or fertility preservation. Cryopreservation is not only needed for the policy of single embryo transfer and cryopreservation of surplus embryos, but for deferring embryo transfer in the case of ovarian hyperstimulation syndrome, uterine pathologies, and suboptimal endometrium built-up or when preimplantation genetic testing is needed. Several current strategies in assisted reproduction technology (ART) would be inconceivable without highly efficient cryopreservation protocols. Nevertheless, cryopreservation hampered for a long time, especially in terms of low survival rates after freezing and thawing. Only the technical progress during the last decades, namely, in regard to the implementation and advancement of vitrification, leveraged its application, and thus, even allows the cryopreservation of human oocytes—a process that is far from being easy. This review aims to provide a deeper insight into the physical processes of cryopreservation and to explore the character of the vitrified state in the extra and intracellular milieu in order to demonstrate that the common denominator to all cryopreservation procedures is the establishment of an intracellular amorphous condition that hinders the likelihood of crystallization.

Cryopreservation of mouse resources

The cryopreservation of sperm and embryos is useful to efficiently archive valuable resources of genetically engineered mice. Till date, more than 60,000 strains of genetically engineered mice have been archived in mouse banks worldwide. Researchers can request for the archived mouse strains for their research projects. The research infrastructure of mouse banks improves the availability of mouse resources, the productivity of research projects, and the reproducibility of animal experiments. Our research team manages the mouse bank at the Center for Animal Resources and Development in Kumamoto University and continuously develops new techniques in mouse reproductive technology to efficiently improve the system of mouse banking. In this review, we introduce the activities of mouse banks and the latest techniques used in mouse reproductive technology.

Mouse embryo assay for human in vitro fertilization quality control: a fresh look

The mouse embryo assay (MEA) has been used in the field of human in vitro fertilization (IVF) for multiple purposes such as developing embryo culture media, quality control within the laboratory, and procedural training and proficiency testing for embryology staff. In addition, manufacturing companies use the MEA as a means of quality control for the development of embryo culture media and medical devices and to meet the standards of testing for FDA approval of new products. It has long been considered by embryologists and laboratory scientists whether the MEA is an accurate or sensitive test in the quality assessment of culture media and medical devices or if use of this testing is more an obligation. There is no uniformly accepted gold standard method for IVF lab quality control or FDA approval. This review aims to revisit the role of the use of mouse embryos in the formulation of IVF media for clinical use and the different methods of employing the mouse embryo assay for quality control. In addition, we will review the use of the MEA as an important adjunct in the training for embryology staff and fellows in training in reproductive endocrinology and infertility (REI), as well as alternatives to the use of the MEA for these purposes.

Effects of Cryopreservation on Cell Metabolic Activity and Function of Biofabricated Structures Laden with Osteoblasts

Biofabrication and maturation of bone constructs is a long-term task that requires a high degree of specialization. This specialization falls onto the hierarchy complexity of the bone tissue that limits the transfer of this technology to the clinic. This work studied the effects of the short-term cryopreservation on biofabricated osteoblast-containing structures, with the final aim to make them steadily available in biobanks. The biological responses studied include the osteoblast post-thawing metabolic activity and the recovery of the osteoblastic function of 3D-bioprinted osteoblastic structures and beta tricalcium phosphate (β-TCP) scaffolds infiltrated with osteoblasts encapsulated in a hydrogel. The obtained structures were cryopreserved at −80 °C for 7 days using dimethyl sulfoxide (DMSO) as cryoprotectant additive. After thawing the structures were cultured up to 14 days. The results revealed fundamental biological aspects for the successful cryopreservation of osteoblast constructs. In summary, immature osteoblasts take longer to recover than mature osteoblasts. The pre-cryopreservation culture period had an important effect on the metabolic activity and function maintain, faster recovering normal values when cryopreserved after longer-term culture (7 days). The use of β-TCP scaffolds further improved the osteoblast survival after cryopreservation, resulting in similar levels of alkaline phosphatase activity in comparison with the non-preserved structures. These results contribute to the understanding of the biology of cryopreserved osteoblast constructs, approaching biofabrication to the clinical practice.

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.

Equivalent clinical outcome after vitrified-thawed blastocyst transfer using semi-automated embryo vitrification system compared with manual vitrification method

PURPOSE

This study compared Gavi®, an automated system for the equilibration and dehydration steps of vitrification, and a manual vitrification procedure in terms of effects on clinical outcomes.

METHODS

The authors retrospectively compared survival rate, and clinical and perinatal outcomes after vitrified-thawed single blastocyst transfer between Gavi® (G method) in 398 cases and Cryotop® (C method) in 208 cases.

RESULTS

With C and G methods, survival rates were 98.6% (208/211) and 99.3% (398/401), total pregnancy rates were 34.3% (72/208) and 33.4% (133/398), and total miscarriage rates were 22.2% (16/72) and 24.8% (33/133), respectively. Among women <35 years old, pregnancy rates were 41.1% (30/73) and 40.5% (62/153) and miscarriage rates were 13.3% (4/30) and 16.1% (10/62) with C and G methods, respectively. Among women ≥35 years old, pregnancy rates were 31.1% (42/135) and 29.0% (71/245) and miscarriage rates were 28.6% (12/42) and 32.4% (23/71) with C and G methods, respectively. C and G methods showed no significant differences in any trials, including gestational age, cesarean section rate, or birthweight (P > .05 each).

CONCLUSIONS

Gavi® showed comparable clinical outcomes to the manual vitrification method and can be considered an alternative vitrification procedure in assisted reproductive technology.

A History of Mouse Genetics: From Fancy Mice to Mutations in Every Gene

The laboratory mouse has become the model organism of choice in numerous areas of biological and biomedical research, including the study of congenital birth defects. The appeal of mice for these experimental studies stems from the similarities between the physiology, anatomy, and reproduction of these small mammals with our own, but it is also based on a number of practical reasons: mice are easy to maintain in a laboratory environment, are incredibly prolific, and have a relatively short reproductive cycle. Another compelling reason for choosing mice as research subjects is the number of tools and resources that have been developed after more than a century of working with these small rodents in laboratory environments. As will become obvious from the reading of the different chapters in this book, research in mice has already helped uncover many of the genes and processes responsible for congenital birth malformations and human diseases. In this chapter, we will provide an overview of the methods, scientific advances, and serendipitous circumstances that have made these discoveries possible, with a special emphasis on how the use of genetics has propelled scientific progress in mouse research and paved the way for future discoveries.

Organization and Management of Conservation Programs and Research in Domestic Animal Genetic Resources

Creating national committees for domestic animal genetic resources within genetic resource national commissions is recommended to organize in situ and ex situ conservation initiatives. In situ conservation is a high priority because it retains traditional zootechnical contexts and locations to ensure the long-term survival of breeds. In situ actions can be based on subsidies, technical support, structure creation, or trademark definition. Provisional or permanent relocation of breeds may prevent immediate extinction when catastrophes, epizootics, or social conflicts compromise in situ conservation. Ex situ in vivo (animal preservation in rescue or quarantine centers) and in vitro methods (germplasm, tissues/cells, DNA/genes storage) are also potential options. Alert systems must detect emergencies and summon the national committee to implement appropriate procedures. Ex situ coordinated centers must be prepared to permanently or provisionally receive extremely endangered collections. National germplasm banks must maintain sufficient samples of national breeds (duplicated) in their collections to restore extinct populations at levels that guarantee the survival of biodiversity. A conservation management survey, describing national and international governmental and non-governmental structures, was developed. Conservation research initiatives for international domestic animal genetic resources from consortia centralize the efforts of studies on molecular, genomic or geo-evolutionary breed characterization, breed distinction, and functional gene identification. Several consortia also consider ex situ conservation relying on socioeconomic or cultural aspects. The CONBIAND network (Conservation for the Biodiversity of Local Domestic Animals for Sustainable Rural Development) exemplifies conservation efficiency maximization in a low-funding setting, integrating several Latin American consortia with international cooperation where limited human, material, and economic resources are available.

Direct transfer of frozen-thawed bovine embryos and its application in cattle reproduction management

Embryo transfer entails many procedures and techniques, of which embryo freezing is an important component in bovine embryo transfer. Embryo freezing techniques have been developed over the last 40 years, allowing practical availability, and have become essential for cattle reproduction management under field conditions. The direct transfer methods of frozen-thawed, in vivo-derived, and in vitro-produced (IVF) bovine embryos using 1.5 M ethylene glycol (EG) with or without sucrose (SUC) are used widely under on-farm conditions, not only in Japan but also globally. The direct transfer method using 1.5 M glycerol (GLY) and 0.25 M SUC (GLY-SUC) is used mainly in Japan. The pregnancy rate with direct transfer of frozen-thawed bovine embryos in either EG or GLY-SUC has been found to not differ from conventional freezing with GLY and traditional dilution techniques. Pregnancy rates following direct transfer of frozen-thawed bovine embryos were affected by the developmental stage of the embryos and the parity of the recipients. The use of ultrasound-guided on-farm ovum pickup is ushering in a new revolution for the commercial application of IVF embryos. Globally, for the first time more IVF bovine embryos were transferred in 2017 than produced in vivo. More than 60% of IVF embryos were transferred fresh due to a low pregnancy rate of frozen-thawed IVF embryos. Many factors seemed to be involved in improving the survival rate of frozen-thawed IVF embryos. Therefore, further research is needed to improve the freezing tolerance of IVF embryos to develop efficient direct transfer methods analogous to those used for in vivo embryos.

Numerical solution of inward solidification of a dilute ternary solution towards a semi-permeable spherical cell

Modeling a cell's response to encroaching ice has informed the development of cryopreservation protocols for four decades. It has been well documented that knowledge of the cellular state as a function of media and cooling rate faciliate informed cryopreservation protocol design and explain mechanisms of damage. However, previous efforts have neglected the interaction between solutes and the encroaching ice front and their effects on the cell state. To address this, here we examine the cryobiologically relevant setting of a spherically-symmetric model of a biological cell separated by a ternary fluid mixture from an encroaching solid-liquid interface. The cell and liquid regions contain cell membrane impermeable intracellular and extracellular salts, respectively, a cell membrane permeable solute commonly used in cryopreservation protocols known as a cryoprotective agent (CPA), and water as a membrane permeable solvent. As cooling and solidification proceed the extracellular chemical environment evolves and leads to mass transport across the cell membrane. Consequently, both the solidification front and the cell membrane are free boundaries whose dynamics are coupled through transport processes in the solid, liquid and cell regions. We describe a numerical procedure to solve this coupled free-boundary problem based on a domain transformation and method of lines approach. We also investigate how the thermal and chemical states inside the cell are influenced by different cooling protocols at the external boundary. Finally, we observe that the previously unaccounted-for partial solute rejection at the advancing solid-liquid interface increases the CPA and salt concentrations in the extracellular liquid as a function of the interface speed and segregation coefficients, suggesting that previous model predictions of the cell state during cryopreservation were inaccurate.

The Use of Antifreeze Proteins in the Cryopreservation of Gametes and Embryos

The cryopreservation of gametes and embryos is a technique widely used in reproductive biology. This technology helps in the reproductive management of domesticated animals, and it is an important tool for gene banking and for human-assisted reproductive technologies. Antifreeze proteins are naturally present in several organisms exposed to subzero temperatures. The ability for these proteins to inhibit ice recrystallization together with their ability to interact with biological membranes makes them interesting molecules to be used in cryopreservation protocols. This mini-review provides a general overview about the use of antifreeze proteins to improve the short and long term storage of gametes and embryos.

Long-term outcomes of freeze-all strategy: A retrospective analysis from a single ART center in Japan

PURPOSE

To demonstrate the benefits of the freeze-all strategy for in vitro fertilization treatment based on retrospective analyses.

METHODS

Post-thaw embryo survival rates of slow-frozen embryos in 294 cycles and vitrified embryos in 12 195 cycles were assessed. Progesterone (P4) and estradiol (E2) levels per mature oocyte by age category were assessed in 9081 cycles and pregnancy rates with fresh embryo transfer and frozen-thawed embryo transfer by P4 level were assessed in 1535 cycles.

RESULTS

The survival rates of frozen-thawed embryos were 92.5% with slow freezing and 99.1% with vitrification. P4 levels on the day of human chorionic gonadotropin (hCG) injection showed a trend toward an increase with age. The pregnancy rate per mature oocyte with fresh embryo transfer decreased dependently upon P4 level, while that with frozen-thawed embryo transfer was not affected by P4 level. The pregnancy rates with frozen-thawed embryo transfer were higher than those with fresh embryo transfer in patients aged 42 years or younger.

CONCLUSIONS

The freeze-all strategy is a valuable treatment option which allows the separation of an embryo transfer cycle from an oocyte retrieval cycle, especially for patients with high P4 levels at oocyte retrieval and patients of advanced maternal age.