Pronuclear formation of freeze-dried canine spermatozoa microinjected into mouse oocytes

Damages and stress responses in sperm cells and other germplasms during dehydration and storage at nonfreezing temperatures for fertility preservation

Long-term preservation of sperm, oocytes, and gonadal tissues at ambient temperatures has the potential to lower the costs and simplify biobanking in human reproductive medicine, as well as for the management of animal populations. Over the past decades, different dehydration protocols and long-term storage solutions at nonfreezing temperatures have been explored, mainly for mammalian sperm cells. Oocytes and gonadal tissues are more challenging to dehydrate so little to no progress have been made. Currently, the detrimental effects of the drying process itself are better characterized than the impact of long-term storage at nonfreezing temperatures. While structural and functional properties of germ cells can be preserved after dehydration, a long list of damages and stresses in nuclei, organelles, and cytoplasmic membranes have been reported and sometimes mitigated. Characterizing those damages and better understanding the response of germ cells and tissues to the stress of dehydration is fundamental. It will contribute to the development of optimal protocols while proving the safety of alternative storage options for fertility preservation. The objective of this review is to (1) document the types of damages and stress responses, as well as their mitigation in cells dried with different techniques, and (2) propose new research directions.

Assisted reproductive techniques for canines: preservation of genetic material in domestic dogs

Assisted reproductive techniques (ARTs), such as artificial insemination, in vitro fertilization, and cryopreservation of gametes/zygotes, have been developed to improve breeding and reproduction of livestock and for the treatment of human infertility. Their widespread use has contributed to improvements in human health and welfare. However, in dogs, only artificial insemination using frozen semen is readily available as an ART to improve breeding and control genetic diversity. A recent priority in sperm cryopreservation is the development of alternatives to egg yolk, which is widely used as a component of the sperm extender. Egg yolk can vary in composition among batches and is prone to contamination by animal pathogens. The latter can be a problem for international exchange of cryopreserved semen. Low-density lipoprotein and skim milk are promising candidates for use as extenders, to ensure fertility after artificial insemination. Although not tested for its effects on fertility following artificial insemination, polyvinyl alcohol may also be a useful alternative to egg yolk as an extender. The development of cryopreservation techniques for canine embryos lags behind that for other mammals, including humans. However, given the success of non-surgical embryo transfer in 2011, studies have sought to refine this approach for practical use. Research on sperm cryopreservation has yielded satisfactory results. However, investigation of other approaches, such as cryopreservation of oocytes and gonadal tissues, remains insufficient. Techniques for the efficient induction of estrus may aid in the development of successful canine ARTs.

Molecular and Histological Evaluation of Sheep Ovarian Tissue Subjected to Lyophilization

Simple Summary

Freeze-drying (or lyophilization) is a method to preserve cells and tissues in which frozen material is dried by sublimation of ice. One of the main advantages is that nitrogen and dry ice are no longer required for the storage and shipment of biological material, which can be kept at room temperature or 4 °C, resulting in enormous reductions in costs. Although widely used to preserve biomolecules and macromolecular assemblies, freeze-drying of cells and tissues is currently experimental. Here, we lyophilized sheep ovarian tissue with a novel device named Darya and assessed effects on tissue integrity and gene expression. We show that ovarian tissue survives lyophilization procedures, maintaining its general structure and reacting to the different experimental steps by regulation of specific genes. Our results contribute to the optimization of protocols to freeze-dry ovarian tissues and may find application in programs of animal and human reproductive tissue preservation.

Abstract

Cryopreservation is routinely used to preserve cells and tissues; however, long time storage brings many inconveniences including the use of liquid nitrogen. Freeze-drying could enable higher shelf-life stability at ambient temperatures and facilitate transport and storage. Currently, the possibility to freeze-dry reproductive tissues maintaining vitality and functions is still under optimization. Here, we lyophilized sheep ovarian tissue with a novel device named Darya and a new vitrification and drying protocol and assessed effects on tissue integrity and gene expression. The evaluation was performed immediately after lyophilization (Lio), after rehydration (LR0h) or after two hours of in vitro culture (IVC; LR2h). The tissue survived lyophilization procedures and maintained its general structure, including intact follicles at different stages of development, however morphological and cytoplasmic modifications were noticed. Lyophilization, rehydration and further IVC increasingly affected RNA integrity and caused progressive morphological alterations. Nevertheless, analysis of a panel of eight genes showed tissue survival and reaction to the different procedures by regulation of specific gene expression. Results show that sheep ovarian tissue can tolerate the applied vitrification and drying protocol and constitute a valid basis for further improvements of the procedures, with the ultimate goal of optimizing tissue viability after rehydration.

An Update on Semen Physiology, Technologies, and Selection Techniques for the Advancement of In Vitro Equine Embryo Production: Section II

Simple Summary

In order to improve fertilization and pregnancy rates within artificial insemination or in vitro fertilization techniques in horses, producers may choose to select the best sperm within an ejaculate. In this paper, we review conventional and novel methods of sperm selection.

Abstract

As the use of assisted reproductive technologies (ART) and in vitro embryo production (IVP) expand in the equine industry, it has become necessary to further our understanding of available semen selection techniques. This segment of our two-section review will focus on the selection of spermatozoa based on quality and sex for equine intracytoplasmic sperm injection (ICSI), as well as current and future developments in sperm sorting technologies. Ultimately, novel methods of semen selection will be assessed based on their efficacy in other species and their relevance and future application towards ARTs in the horse.

Freeze Drying as a Method of Long-Term Conservation of Mammalian Semen – A Review

With the development of biotechnological methods that allow the manipulation and free exchange of genetic material, the methods for collecting and storing such material need to be improved. To date, freezing in liquid nitrogen has allowed the storage of cells and entire plant and animal tissues for practically unlimited times. However, alternatives are still being sought to eliminate the constant need to maintain samples at a low temperature. Lyophilization or freeze drying is an alternative to standard freezing procedures. The storage of samples (lyophilisates) does not require specialised equipment but only refines the preservation method itself. In the case of cells capable of movement e.g., sperm, they lose the ability to reach the oocyte in vivo and for in vitro fertilization (IVF) because of the lyophilization process. However, freeze-dried sperm may be used for in vitro fertilization by intracytoplasmic sperm injection (ICSI), based on the results obtained in cleavage, embryo development and the production of live born offspring after embryo transfer. Studies on the lyophilization of sperm have been performed on many animal species, both in the laboratory and in livestock. This conservation method is considered to create biobanks for genetically valuable and endangered species with the simultaneous application of ICSI. This review article aimed to present the issues of the freeze-drying process of mammalian semen and help find solutions that will improve this technique of the long-term preservation of biological material.

Preservation of Mammalian Sperm by Freeze-Drying

Long-term preservation of mammalian sperm at suprazero temperatures is desired to save storage and space costs, as well as to facilitate transport of preserved samples. This can be accomplished by the freeze-drying of sperm samples. Although freeze-drying results in immotile and membrane-compromised sperm, intracytoplasmic sperm injection (ICSI) can be used to introduce such an immotile sperm into an oocyte and thus start the fertilization process. So far, it has been shown that improved freeze-drying protocols preserve chromosomal integrity and oocyte-activating factor(s) in rodent and mammalian species at 4 °C for several years and at ambient temperature for up to 1 year depending on species, which permits shipping freeze-dried samples at ambient temperature. This chapter concisely reviews freeze-drying of mammalian sperm first and then presents a simple freeze-drying protocol.

Cold case: Small animal gametes cryobanking

Germplasm preservation of animals, whether they are valuable domestic breeds or rare species, is the main goal of gamete cryobanking. Dogs and cats act as models for this purpose thanks to the wide availability of biological material which can be employed to experiment protocols that can then be applied to wild animals. This review is focused on spermatozoa, oocytes and gonadal tissues cryobanking in small domestic animals, which is still an unsolved case. Like in a courtroom, evidences of cryoinjuries affecting cellular structures will be presented, penalties as loss of functionality due to cellular alterations will be described, and appeal as strategies to protect gametes from damages or rescue their functionality will be discussed. Differences and similarities between single cell or tissue cryopreservation will be highlighted, together with the rationale for the choice of one type of preservation or another and the fundamental principles which they are based on. The deep analysis of different aspects that still hamper the success of cryopreservation in small animals can help clarify where research is most needed. Therefore, as in a cold case, investigation should remain open in order to hopefully find the solution and make these procedures more and more efficient in the future.

High post-thaw survival of ram sperm after partial freeze-drying

BACKGROUND

Recrystallization damages occur when a frozen sample is held at high subzero temperatures and when the warming process is too slow.

METHODS

In this work, ram semen diluted in two different concentrations of sugar solutions (Lyo A consisted of 0.4 M sorbitol and 0.25 M trehalose, and the second, Lyo B composed of 0.26 M sorbitol and 0.165 M trehalose) in egg yolk and Tris medium were compared after freezing 10 μL samples to: (1) - 10, - 25, and - 35 °C and thawing. (2) Freezing to - 10 and - 25 °C, holding for 1 h and then thawing, and (3) freezing to - 10 and - 25 °C and drying for 1 h at these temperatures at a vacuum of 80 mTorr, prior thawing. For drying, we used a new freeze-drying apparatus (Darya, FertileSafe, Israel) having a condensation temperature below - 110 °C and a vacuum pressure of 10-100 mTorr that is reached in less than 10s.

RESULTS

Results showed that samples in Lyo B solution frozen at - 25 °C had significantly higher sperm motility in partially freeze-dried samples than frozen samples (46.6 ± 2.8% vs 1.2 ± 2.5%, P < 0.001). Moreover, partially dried samples in Lyo B showed higher motility than Lyo A at - 25 °C (46.6 ± 2.8% vs 35 ± 4%). Cryomicroscopy and low-temperature/low-pressure environmental scanning electronic microscope demonstrated that the amount of the ice crystals present in partially dried samples was lower than in the frozen samples.

CONCLUSION

Holding the sperm at high subzero temperatures is necessary for the primary drying of cells during the freeze-drying process. Rapid freeze-drying can be achieved using this new device, which enables to reduce recrystallization damages.

In vitro developmental ability of ovine oocytes following intracytoplasmic injection with freeze-dried spermatozoa

Freeze-drying (FD) is a new and alternative method to preserve spermatozoa in refrigeration or at room temperature. Suitable protection is required to maintain the sperm DNA integrity during the whole process and storage. The aim of this study was to examine the effect of rosmarinic acid and storage temperature on the DNA integrity of freeze-dried ram sperm. In addition, we evaluated the in vitro developmental ability to the blastocyst stage of oocytes injected with freeze-dried sperm. Ram sperm was freeze-dried in basic medium and in this medium supplemented with 105 µM rosmarinic acid. The vials were stored for 1 year at 4 °C and at room temperature. Frozen sperm was used as control. After rehydration, sperm DNA damage was evaluated, observing that the percentage of spermatozoa with DNA damage decreased significantly in the presence of rosmarinic acid, without differences between the two storage temperatures. Moreover, no differences were observed between the freeze-dried group and the frozen-thawed group in terms of blastocyst formation rate. We proved for the first time that ovine spermatozoa can be lyophilized effectively, stored at room temperature for long term, reconstituted and further injected into oocytes with initial embryo development.

Sperm freeze-drying and micro-insemination for biobanking and maintenance of genetic diversity in mammals

Breeding by natural mating is ideal for maintaining animal populations. However, the lack of breeding space resulting from an increased number of strains and the decline in fertility caused by inbreeding inhibits the reproduction of subsequent generations. Reproductive technologies, such as gamete preservation and artificial fertilisation, have been developed to overcome these problems. These approaches efficiently produce offspring of laboratory, domestic and wild animals, and can also be used to treat human infertility. Gamete preservation using sperm contributes to improvements in reproductive systems and enables the use of smaller breeding spaces. Although cryopreservation with liquid nitrogen has been used to preserve spermatozoa, freeze-drying without liquid nitrogen, a novel method, facilitates long-term storage of spermatozoa. This method has recently been applied to maintain animal strains. Micro-insemination techniques, such as intracytoplasmic sperm injection (ICSI), are exceptional for improving assisted reproduction. ICSI can be used to fertilise oocytes, even with immotile and immature spermatozoa that are unsuitable for AI and IVF. Reproductive technologies provide a substantial advantage for biobanking and maintaining the genetic diversity of laboratory, domestic and wild animals. This review covers the latest method of sperm freeze-drying and micro-insemination, and future possibilities for maintaining animal strains and populations.

Sperm cryopreservation update: Cryodamage, markers, and factors affecting the sperm freezability in pigs

Cryopreservation is the most efficient method for long-term preservation of mammalian sperm. However, freeze-thawing procedures may strongly impair the sperm function and survival and thus decrease the reproductive performance. In addition, the sperm resilience to withstand cryopreservation, also known as freezability, presents a high individual variability. The present work summarizes the principles of cryoinjury and the relevance of permeating and nonpermeating cryoprotective agents. Descriptions about sperm cryodamage are mainly focused on boar sperm, but reference to other mammalian species is also made when relevant. Main cryoinjuries not only regard to sperm motility and membrane integrity, but also to the degradation effect exerted by freeze-thawing on other important components for sperm fertilizing ability, such as mRNAs. After delving into the main differences between good and poor freezability boar ejaculates, those protein markers predicting the sperm ability to sustain cryopreservation are also mentioned. Moreover, factors that may influence sperm freezability, such as season, diet, breed, or ejaculate fractions are discussed, together with the effects of different additives, like seminal plasma and antioxidants. After briefly referring to the effects of long-term sperm preservation in frozen state and the reproductive performance of frozen-thawed boar sperm, this work speculates with new research horizons on the preservation of boar sperm, such as vitrification and freeze-drying.

Freeze-dried dog sperm: Dynamics of DNA integrity

Freeze-drying (FD) has been proposed as an alternative method to preserve spermatozoa. During the FD procedure, sperm DNA might become damaged by both freezing and drying stresses caused by the endonucleases, the oxidative stress and the storage conditions. We examined the DNA integrity of dog sperm freeze-dried with two kinds of chelating agents in FD buffers and storage at two different temperatures. Ejaculated sperm from four dogs were suspended in basic medium (10 mM Tris-HCl buffer+50 mM NaCl) supplemented with 50 mM EGTA or with 50 mM EDTA and then freeze-dried. Sperm samples were stored at 4°C as room temperature, and the analysis of DNA damage was performed after a month and 5 months of storage using a Sperm Chromatin Dispersion test. We found four different sperm populations according to the size of the halos around the sperm head: (1) absent halo, (2) <6 μm, (3) 6-10 μm, (4) >10 μm. All of them coexisted in each freeze-dried dog semen samples and differed significantly among different treatments. The highest percentage of spermatozoa with halo >10 μm was obtained when the semen samples were freeze-dried in EDTA medium and stored at room temperature for five months. Results suggested that both, the kind of chelating agent as well as storage temperature and period, influenced DNA integrity of freeze-dried dog sperm.

Freeze-drying of mammalian sperm

Long-term preservation of mammalian sperm at suprazero temperatures is desired to save storage and space costs as well as to facilitate transport of preserved samples. This can be accomplished by the freeze-drying of sperm samples. Although freeze-drying results in immotile and membrane-compromised sperm, intracytoplasmic sperm injection (ICSI) can be used to introduce such an immotile sperm into an oocyte and thus start the fertilization process. So far, it has been shown that improved freeze-drying protocols preserve chromosomal integrity and oocyte-activating factor(s) at 4 °C for several years and at ambient temperature for approximately 1 month, which permits shipping freeze-dried samples at ambient temperature. This chapter concisely reviews freeze-drying of mammalian sperm first and then presents a simple freeze-drying protocol.

Recent advances and prospects in germplasm preservation of rare and endangered species

Fertility preservation strategies using cryopreservation have enormous potential for helping sustain and protect rare and endangered species, especially to assist managing or 'rescuing' the genomes of genetically valuable individuals. However, wide-scale applications are still limited by significant physiological variations among species and a sheer lack of fundamental knowledge about basic reproductive traits as well as in germplasm cryobiology. Cryo-studies have been conducted in more species (mainly vertebrates) in the recent years but a vast majority still remains un-studied. Semen cryopreservation represents the most extensive effort with live births reported in more and more species after artificial insemination. Oocyte freezing remains challenging and unsuccessful in wild species and will require more research before becoming a standard procedure. As an alternative to fully grown gametes, gonadal tissue preservation has become a promising option in vertebrates. Yet, more fertility preservation options are necessary to save species so a change in strategy might be required. It is worthwhile thinking beyond systematic characterizations and considering the application of cutting edge approaches to universally preserve the fertility of a vast array of species.

On the horizon for fertility preservation in domestic and wild carnivores

Innovations are emerging from the growing field of fertility preservation for humans and laboratory animals that are relevant to protecting and propagating valuable domestic and wild carnivores. These extend beyond the 'classical' approaches associated with sperm, oocyte and embryo freezing to include gonadal tissue preservation combined with in vitro culture or xenografting, all of which have potential for rescuing vast amounts of unused and wasted germplasm. Here, we review approaches under development and predicted to have applied value within the next decade, including the following: (i) direct use of early-stage gametes for in vitro fertilization; (ii) generation of more mature gametes from gonadal tissue or stem cells; (iii) simplification, enhanced safety and efficacy of cryopreservation methods; and (iv) biostabilization of living cells and tissues at ambient temperatures. We believe that all of these fertility preservation strategies will offer knowledge and tools to better manage carnivores that serve as human companions, valuable biomedical models or require assistance to reverse endangerment.

Lyophilization is suitable for storage and shipment of fresh tissue samples without altering RNA and protein levels stored at room temperature

Lyophilization has been widely used for preservation, such as in food industry, pharmacy, biotechnology and tissues engineering, etc. However, there is no report on whether it could affect stability of RNA and protein levels in biological tissue samples. Herein we show that lyophilization can be used for storage of biological tissue samples without loss of bioactivities even stored at room temperature for 7-14 days. To address this issue, C57BL mouse tissues were prepared and dried by lyophilization and a baking method, respectively, followed by examination of morphological structure and total proteins by SDS-PAGE as well as gelatin zymography. Subsequently, the stability of RNAs and proteins, which were lyophilized and stored at room temperature (23°C) for 14 days was further examined by RT-PCR, SDS-PAGE and western blot. Results demonstrated that lyophilization did not alter total protein activities of various tissues, including enzyme activities, immunoreactivities and phosphorylation, and did not affect several RNAs in lyophilized tissues. Taken together, lyophilization may represent a valuable approach for preservation and long-distance shipment of biological samples, particularly for the international exchange of biological samples without altering their bioactivities.

Genome of non-living cells: trash or recycle?

Reproductive technologies have been often used as a tool in research not strictly connected with developmental biology. In this study, we retrace the experimental routes that have led to the adoption of two reproductive technologies, ICSI and somatic cell nuclear transfer (SCNT), as biological assays to probe the 'functionality' of the genome from dead cells. The structural peculiarities of the spermatozoa nucleus, namely its lower water content and its compact chromatin structure, have made it the preferred cell for these experiments. The studies, primarily focused on mice, have demonstrated an unexpected stability of the spermatozoa nuclei, which retained the capacity to form pronuclei once injected into the oocytes even after severe denaturing agents like acid treatment and high-temperature exposure. These findings inspired further research culminating in the production of mice after ICSI of lyophilized spermatozoa. The demonstrated non-equivalence between cell vitality and nuclear vitality in spermatozoa prompted analogous studies on somatic cells. Somatic cells were treated with the same physical stress applied to spermatozoa and were injected into enucleated sheep oocytes. Despite the presumptive fragile nuclear structure, nuclei from non-viable cells (heat treated) directed early and post-implantation embryonic development on nuclear transfer, resulting in normal offspring. Recently, lyophilized somatic cells used for nuclear transfer have developed into normal embryos. In summary, ICSI and SCNT have been useful tools to prove that alternative strategies for storing banks of non-viable cells are realistic. Finally, the potential application of freeze-dried spermatozoa and cells is also discussed.

Chromosomal integrity and DNA damage in freeze-dried spermatozoa

Freeze-drying technology may one day be used to preserve mammalian spermatozoa indefinitely without cryopreservation. Freeze-dried mouse spermatozoa stored below 4°C for up to 1 year have maintained the ability to fertilize oocytes and support normal development. The maximum storage period for spermatozoa increases at lower storage temperatures. Freeze-drying, per se, may reduce the integrity of chromosomes in freeze-dried mouse spermatozoa, but induction of chromosomal damage is suppressed if spermatozoa are incubated with divalent cation chelating agents prior to freeze-drying. Nevertheless, chromosomal damage does accumulate in spermatozoa stored at temperatures above 4°C. Currently, no established methods or strategies can prevent or reduce damage accumulation, and damage accumulation during storage is a serious obstacle to advances in freeze-drying technology. Chromosomal integrity of freeze-dried human spermatozoa have roughly background levels of chromosomal damage after storage at 4°C for 1 month, but whether these spermatozoa can produce healthy newborns is unknown. The safety of using freeze-dried human spermatozoa must be evaluated based on the risks of heritable chromosome and DNA damage that accumulates during storage.

Characterization of chromosomal damage accumulated in freeze-dried mouse spermatozoa preserved under ambient and heat stress conditions

Structural chromosome aberrations and DNA damage generated in freeze-dried mouse spermatozoa were investigated. Freeze-dried sperm samples were preserved at 4, 25 and 50°C for short duration (1 day to 2 months) and at 25°C for long duration (2 years). The spermatozoa were injected into mouse oocytes to analyse the chromosomes of the zygotes at the first cleavage metaphase. Chromosome break of the chromosome-type aberrations was the most common type of structural chromosome aberrations observed in all freeze-dried samples. The frequency of chromatid exchanges rapidly increased in freeze-dried spermatozoa preserved at 50°C for 1-5 days. The frequency of chromatid-type aberrations (break and exchange) gradually increased in freeze-dried spermatozoa preserved at 25°C for up to 2 months. Alkaline comet assay revealed significant migration of damaged DNA accumulated in freeze-dried spermatozoa preserved at 50°C for 3 days and 25°C for 2 years. However, no DNA damage was detected using the same sperm samples by neutral comet assay, which can detect mostly DNA double-strand breaks in cellular DNA. These results suggest that DNA single-strand breaks were accumulated in freeze-dried spermatozoa preserved under ambient or heat conditions, and then chromatid-type aberrations, especially the chromatid exchanges, were formed via post-replication repair system in zygotes.

A novel method for detection of chromosomal integrity in cryopreserved livestock spermatozoa using artificially fused mouse oocytes

PURPOSE

The aim of the present study was to investigate the effect of mouse oocyte volume on the efficiency of chromosomal analysis in livestock spermatozoa.

METHODS

Oocytes were injected with bull, ram, boar and dog sperm heads, and then fused with enucleated mouse oocytes.

RESULTS

The increment of oocyte volume increased the rates of morphologically normal oocytes after sperm injection, which induced much higher rates of overall chromosome detection in bull, ram and dog spermatozoa. The recipient oocyte volume did not affect the chromosomal integrity. Furthermore, in bull, the chromosomal integrity detected by fused mouse oocytes was similar to that derived from a homologous system. On the other hand, chromosomal plates of boar spermatozoa could not be detected despite the use of fused oocytes.

CONCLUSION

These data indicate that fused mouse oocytes improved the efficiency of chromosome detection in bull, ram and dog spermatozoa.