Mammalian fertility preservation through cryobiology: value of classical comparative studies and the need for new preservation options

Morphological evaluation of adult domestic cat testicular biopsy after vitrification

Testicular biopsies (9 mm3) from domestic cats (n = 10) submitted to orchiectomy were submitted to equilibrium vitrification in the presence of ethylene glycol (EG) alone or combined with dimethylsulfoxide (DMSO) as intracellular cryoprotectants, and sucrose or trehalose as extracellular cryoprotectants. The samples were vitrified with 40% EG or 20% EG + 20% DMSO, plus 0.1 M or 0.5 M of sucrose or trehalose. The study was divided into Step 1 and Step 2. In Step 1, intratubular cells (spermatogonia, spermatids, spermatocytes, and Sertoli cells) were quantified and classified as intact or degenerated (pyknotic and/or vacuolated cells). Cryodamage of seminiferous cords was determined by spermatogonia and Sertoli cell scoring of nuclei alterations, tubular basement membrane detachment, epithelium shrinkage, and tubular measures (total area, epithelium area, larger and smaller diameter, and height of the epithelium). In Step 2, Hoechst 33342 stain and propidium iodide (PI) fluorescent stain were used to assess the cell viability of the four best experimental groups in Step 1. The effect of treatments on all analyses was accessed using analysis of variance (ANOVA), and Fisher's post hoc test at P < 0.05 significance was considered. In Step 1, the mean percentage of spermatogonia and Sertoli cells morphological integrity did not show a difference when using both sugars at different concentrations, but their morphology was more affected when DMSO was used. EG use associated with 0.1 M of sucrose or trehalose positively affected spermatocyte and spermatid morphology, respectively. The larger diameter and epithelium height of seminiferous tubules were increased using DMSO plus 0.5 M sucrose and DMSO plus 0.1 M trehalose. The changes in spermatogonial/Sertoli nucleoli visualization were best scored in the EG groups, while the nuclei condensation was lower with sucrose. The basement membrane was satisfactorily preserved with 0.1 M sucrose. In Step 2, the percentage of cell viability was higher when EG plus 0.1 M sucrose was used. Therefore, DMSO's negative effect on the vitrification of testicular biopsies of adult domestic cats was evident. The EG plus 0.1 M of sucrose or trehalose associations are the most suitable CPAs to preserve the testicular histology structure of adult domestic cats in vitrification.

Carboxylated Poly-L-lysine Potentially Reduces Human Sperm DNA Fragmentation after Freeze-Thawing, and Its Function Is Enhanced by Low-Dose Resveratrol

Sperm DNA fragmentation (SDF) that occurs during the freezing-thawing of sperm may negatively impact the treatment outcomes of assisted reproductive technologies (ART). In a previous study, we developed a human sperm cryopreservation reagent containing carboxylated poly-L-lysine (CPLL) that reduced SDF after freeze-thawing compared with clinically popular cryopreservation reagents containing human serum albumin. However, it is unclear whether CPLL reduces SDF, as it differed from the constituents of the commercial cryopreservation reagents used for comparison. Therefore, here, we examined whether CPLL reduces the SDF of human sperm and evaluated reactive oxygen species (ROS) levels and lipid peroxidation (LPO), which are the causes of SDF; mitochondrial injury, ROS production; and impaired sperm motility. Furthermore, optimal antioxidants and their concentrations that could further enhance the reduction in SDF were determined for future clinical application in ART and underwent the same functional evaluations. CPLL can reduce SDF via inhibition of intracytoplasmic ROS and LPO. Furthermore, the addition of 0.1 mM resveratrol avoided the enhancement of SDF, which potentially affects mitochondrial and cytoplasmic ROS and LPO. This novel human sperm cryopreservation reagent containing CPLL and resveratrol has the potential to improve treatment outcomes in ART using frozen sperm.

Plasma membrane lipid composition and metabolomics analysis of Yorkshire boar sperms with high and low resistance to cryopreservation

The resistance of sperm to freezing varies widely among boars. The semen ejaculate of different boars can be grouped into poor freezability ejaculate (PFE) and good freezability ejaculate (GFE). In this study, five Yorkshire boars each of the GFE and PFE were selected by comparing the changes in sperm motility before and after cryopreservation. Firstly, we found that the sperm plasma membrane of the PFE group showed weak integrity after PI and 6-CFDA staining. Then the electron microscopy results verified that the plasma membrane condition of all segments of GFE was better than that of PFE segments. Furthermore, the lipid composition of sperm plasma membranes in GPE and PFE sperm was analyzed by using mass spectrometry, and 15 lipids showed differences between the two groups. Among those lipids, only phosphatidylcholine (PC) (14:0/20:4) and phosphatidylethanolamine (PE) (14:0/20:4) were higher in PFE. The remaining lipid contents, including those of dihydroceramide (18:0/18:0), four hexosylceramides (18:1/20:1, 18:0/22:1, 18:1/16:0, 18:1/18:0), lactosylceramide (18:1/16:0), two hemolyzed phosphatidylethanolamines (18:2, 20:2), five phosphatidylcholines (16:1/18:2, 18:2/16:1, 14:0/20:4, 16:0/18:3, 18:1/20:2), and two phosphatidylethanolamines (14:0/20:4, 18:1/18:3), were all positively correlated with resistance to cryopreservation (p < 0.05, r > 0.6). Moreover, we analyzed the metabolic profile of sperm using untarget metabolomic. KEGG annotation analysis revealed that the altered metabolites were mainly involved in fatty acid biosynthesis. Finally, we determined that the contents of oleic acid, oleamideetc, N8-acetylspermidine etc., were different between GFE and PFE sperm. In summary, the different lipid metabolism levels and long-chain polyunsaturated fatty acids (PUFAs) in plasma membrane may be key factors contributing to differences in sperm resistance to cryopreservation among boars.

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.

Long-term preservation of germ cells and gonadal tissues at ambient temperatures

Objective

To present an overview of different approaches and recent advances for long-term preservation of germ cells and gonadal tissues at ambient temperatures.

Methods

Review of the existing literature.

Results

Preserving viable spermatozoa, eggs, embryos, and gonadal tissues for the long term is critical in human fertility treatment and for the management of animal populations (livestock, biomedical models, and wild species). The need and number of banked germplasms are growing very fast in all disciplines, but current storage options at freezing temperatures are often constraining and not always sustainable. Recent research indicates that structures and functions of gametes or gonadal tissues can be preserved for the long term using different strategies based on dehydration and storage at supra-zero temperatures. However, more studies are needed in rehydration and reanimation of germplasms (including proper molecular and cellular evaluations).

Conclusions

While a lot of research is still warranted to optimize drying and rehydration conditions for each sample type and each species, alternative preservation methods will change the paradigm in fertility preservation and biobanking. It will transform the way we maintain and manage precious biomaterials for the long term.

Lay summary

Living sperm cells, eggs, embryos, and reproductive tissues can be preserved at freezing temperatures for human fertility treatments and used to manage breeding in livestock, laboratory animals, and wild species through assisted reproduction. These cells can be stored in cell banks and demand for them is growing fast. However, current long-term storage options at freezing temperatures are expensive. Instead of using low temperatures, recent research indicates that these cells can be dried and stored above freezing temperatures for an extended amount of time. While a lot of research is still needed to optimize how different samples are dried and rehydrated, alternative methods of preserving cells will make fertility preservation and cell banking easier. It will also transform the way we keep and manage samples for the long term.

Long-term storage of gametes and gonadal tissues at room temperatures: the end of the ice age?

Long-term preservation of viable spermatozoa, eggs, embryos, and gonadal tissues of good quality is essential in human reproductive medicine and for the population management of livestock, laboratory, and wild species. Instead of using freezing temperatures, encouraging findings indicate that structures and functions of gametes or gonadal tissues can be suspended in trehalose glass after dehydration and then preserved at supra-zero temperatures. As a new era in fertility preservation and biobanking is about to start, the advantages, needs, and implications of germplasm storage at room temperatures must be carefully examined. Although very promising, the development of alternate biobanking strategies does not necessarily mean that the end of the "ice age" (cryopreservation) is near.

Antifreeze proteins for low-temperature preservation in reproductive medicine: A systematic review over the last three decades

Antifreeze proteins (AFPs) are synthesized by diverse non-mammalian species, allowing them to survive in severely cold environments. Since the 1990s, the scientific literature reports their use for low-temperature preservation of germplasm. The aim of this systematic review was to compile available scientific evidence regarding the use of AFP for low-temperature preservation of several reproductive specimens. Internet databases were consulted using the terms: "antifreeze protein" OR "AFP" OR "antifreeze glycoprotein" OR "AFGP" OR "ice-binding protein" OR "IBP" OR "thermal hysteresis protein" AND "cryopreservation". From 56 articles, 87 experiments testing AFPs in low-temperature preservation of gametes, embryos or reproductive tissues/cells were fully analyzed and outcomes were annotated. A positive outcome was considered as a statistically significant improvement on any parameter evaluated after low-temperature preservation with AFP, whereas a negative outcome included worsening of any evaluated parameter, in comparison to untreated groups or groups treated with a lower concentration of AFP. The findings indicated that research on the use of AFP as a cryoprotectant for reproductive specimens has increased markedly over the past decade. Some experiments reported both positive and negative results, which depended, on AFP concentration in the preservation media. Variation in the outcomes associated with species was also observed. Among the 66 experiments conducted in mammals, 77.3% resulted in positive, and 28.8% in negative outcomes after the use of AFP. In fishes, positive and negative outcomes were observed in 71.4% and 33.3% of 21 experiments, respectively. Most positive outcomes included preserving cell post-warming survival. The beneficial effect of AFP supports its use in cryobiological approaches used in human and veterinary medicines and animal protein industry. Moreover, combination of different AFP types, or AFP with antioxidants, or even the use of AFP-biosimilar, comprise some promising approaches to be further explored in cryopreservation.

Cryopreservation: An Overview of Principles and Cell-Specific Considerations

The origins of low-temperature tissue storage research date back to the late 1800s. Over half a century later, osmotic stress was revealed to be a main contributor to cell death during cryopreservation. Consequently, the addition of cryoprotective agents (CPAs) such as dimethyl sulfoxide (DMSO), glycerol (GLY), ethylene glycol (EG), or propylene glycol (PG), although toxic to cells at high concentrations, was identified as a necessary step to protect against rampant cell death during cryopreservation. In addition to osmotic stress, cooling and thawing rates were also shown to have significant influence on cell survival during low temperature storage. In general, successful low-temperature cell preservation consists of the addition of a CPA (commonly 10% DMSO), alone or in combination with additional permeating or non-permeating agents, cooling rates of approximately 1ºC/min, and storage in either liquid or vapor phase nitrogen. In addition to general considerations, cell-specific recommendations for hepatocytes, pancreatic islets, sperm, oocytes, and stem cells should be observed to maximize yields. For example, rapid cooling is associated with better cryopreservation outcomes for oocytes, pancreatic islets, and embryonic stem cells while slow cooling is recommended for cryopreservation of hepatocytes, hematopoietic stem cells, and mesenchymal stem cells. Yields can be further maximized by implementing additional pre-cryo steps such as: pre-incubation with glucose and anti-oxidants, alginate encapsulation, and selecting cells within an optimal age range and functional ability. Finally, viability and functional assays are critical steps in determining the quality of the cells post-thaw and improving the efficiency of the current cryopreservation methods.

Heterotopic autotransplantation of ovarian tissue in a large animal model: Effects of cooling and VEGF

Heterotopic and orthotopic ovarian tissue autotransplantation techniques, currently used in humans, will become promising alternative methods for fertility preservation in domestic and wild animals. Thus, this study describes for the first time the efficiency of a heterotopic ovarian tissue autotransplantation technique in a large livestock species (i.e., horses) after ovarian fragments were exposed or not to a cooling process (4°C/24 h) and/or VEGF before grafting. Ovarian fragments were collected in vivo via an ultrasound-guided biopsy pick-up method and surgically autografted in a subcutaneous site in both sides of the neck in each mare. The blood flow perfusion at the transplantation site was monitored at days 2, 4, 6, and 7 post-grafting using color-Doppler ultrasonography. Ovarian grafts were recovered 7 days post-transplantation and subjected to histological analyses. The exposure of the ovarian fragments to VEGF before grafting was not beneficial to the quality of the tissue; however, the cooling process of the fragments reduced the acute hyperemia post-grafting. Cooled grafts compared with non-cooled grafts contained similar values for normal and developing preantral follicles, vessel density, and stromal cell apoptosis; lower collagen type III fibers and follicular density; and higher stromal cell density, AgNOR, and collagen type I fibers. In conclusion, VEGF exposure before autotransplantation did not improve the quality of grafted tissues. However, cooling ovarian tissue for at least 24 h before grafting can be beneficial because satisfactory rates of follicle survival and development, stromal cell survival and proliferation, as well as vessel density, were obtained.

Long-term Preservation of Testicular Tissue Integrity and Viability Using Vitrification in the Endangered Black-Footed Ferret (Mustela Nigripes)

Simple Summary

In addition to semen preservation, systematic cryo-banking of testicular tissues is critical to preserve the genetic value of recently deceased or neutered black-footed ferrets. Mature sperm cells produced from vitrified-warmed tissues could be used for in vitro fertilization over multiple generations, which would enhance the genetic management of this rare and endangered species. The objective of the study was to evaluate structural and functional properties of vitrified testicular tissues directly after warming or after warming plus a short period of in vitro culture. Fresh, vitrified/warmed, and warmed/cultured tissues from five adults were analyzed through histology, DNA fragmentation, cell survival, and germ cell composition. Percentages of intact seminiferous tubules decreased right after vitrification/warming and improved after culture (reaching same percentages as the fresh controls). While proportions of cells with intact DNA and viable cells were affected by vitrification/warming, they were then similar or better after additional culture than in the fresh tissue. Proportions of cells labeled with differentiation markers also increased during in vitro culture. We demonstrated for the first time that black-footed ferret testicular tissues can be vitrified and revived, which will potentially contribute to new strategies to enhance assisted reproduction as well as conservation efforts in that rare and endangered species.

Abstract

Systematic cryo-banking of semen and testicular tissues is critical to preserve the genetic value of recently deceased or neutered black-footed ferrets (BFFs). Specifically, recovering or producing mature sperm cells from vitrified-warmed issues offers additional options in assisted reproduction. This could, in turn, enhance the genetic management of this rare and endangered species over multiple generations. The objective of the study was to evaluate structural properties, DNA fragmentation, cell viability, and germ cell composition in vitrified testicular tissues from BFFs directly after warming or after warming plus a short in vitro culture period. Tissue biopsies from five adult BFFs were either kept fresh or vitrified with a standard protocol (using dimethylsulphoxide (DMSO) and glycerol) and warmed at 50 °C for 5 s. Some of the warmed samples were then cultured in vitro for 24 h. Fresh, warmed, and warmed/cultured tissues were analyzed using different indicators: histology of seminiferous tubules, intact Sertoli cells (vimentin labeling), DNA integrity, cell viability, germ cell composition (Oct4 and Boule labeling). Percentages of intact seminiferous tubules decreased after vitrification/warming and returned to the level of fresh samples after culture. While percentages of cells labeled with vimentin, with intact DNA integrity, or proportions of viable cells were affected by vitrification/warming, they all reached similar or better levels than the fresh tissue after culture. Proportions of cells labeled with Boule antibodies also improved during in vitro culture post-warming. We demonstrated for the first time that BFF testes subjected to vitrification, rapid warming, and short in vitro culture were viable and maintained the ability to resume germ cell progression. Cryopreserved testicular tissues could potentially contribute to new strategies to enhance BFF assisted reproduction as well as conservation efforts.

The SPOM-adapted IVM system improves in vitro production of bovine embryos

This study aimed to test the effects of an IVM SPOM adaptation (SPOM-adapted IVM) on the production, total number of cells (TNC), apoptosis, and cryotolerance (post-warming survival and cytoskeleton actin integrity) of bovine IVP embryos. Two experiments were conducted with two experimental groups based on IVM treatment: A control group (TCM 199 without FCS) and an SPOM-adapted group (TCM 199 with forskolin and IBMX in pre-IVM and IVM with cilostamide). The first experiment evaluated embryo in vitro production, TNC, and apoptosis rate on D9 of development. In the second experiment, embryos were vitrified/warmed at D7 (control fresh and vitrified; SPOM-adapted fresh and vitrified) and assessed regarding post-warming survival rates and cytoskeleton actin integrity. Statistical analysis was performed using GraphPad INSTAT software at a significance level of 5%. An increase (p < 0.05) in blastocyst production was observed in the SPOM-adapted group comparing to the control group. There was no difference (p > 0.05) in the TNC or apoptosis rate between the groups. Regarding cryopreservation, no differences were found (p > 0.05) in actin integrity or post-warming survival rates between the vitrified groups. In both vitrified groups, we observed a significantly lower uninjured pattern of actin integrity compared to the fresh groups (p < 0.05). We conclude that the SPOM-adapted IVM system is beneficial for blastocyst production and does not affect the quality and cryotolerance of the produced embryos.

Rescue of caprine fetal ovaries, vitrification and follicular development after xenotransplantation in two immunodeficient mice models

Domestic and wild goats are very susceptible animals to predation, specially when pregnancy occurs. This study aimed to evaluate the use of goat fetal ovarian tissue for vitrification followed by xenotransplantation and fresh xenotransplantation in two immunosuppressed mice models (C57BL/6 SCID and Balb-C NUDE). Goat fetus ovaries were collected in slaughterhouses, divided into small cortical pieces and were destined for fresh xenotransplantation (FX) and cryopreservation followed by xenotransplantation (CX). Five recipients from each lineage were used for FX and 10 animals from each lineage for CX. The mice were euthanized after 65 postoperative days, and the transplants were collected for microscopic assessment. The blood plasma was collected for estradiol measurement. Independently of mice strain, all recipients presented complete estrus cycle in FX and 80% after CX groups. Follicles were observed at all development stages without morphological changes. The volume density and total vessel surface observed in the transplants were different (p <0.01) between groups. The estradiol levels in the recipients did not differ (p <0.05) among the treatments. Thus, it is possible to activate the preantral follicles in the ovaries of fetuses by optimizing germplasm utilization and conservation of domestic and endangered wild goats that are in predatory situations, undesirable drowning or accidental death, since provided conditions for xenotransplantation are performed.

Integrating fertility preservation and cryo-banking into the conservation of rare and endangered deer species

More than 50 deer species live in diverse ecosystems around the world. Unfortunately, most of them are threatened or endangered because of over-hunting, poaching or habitat destruction. Protection of wild populations (in situ) and management of animal collections in zoos and breeding centres (ex situ) are complementary conservation efforts relying on multidisciplinary approaches. Reproductive biology of deer species is one of the critical areas that still needs to be thoroughly studied to ensure the success of in situ or ex situ programs. Interestingly, there is a vast diversity in reproductive traits within the deer family (from anatomy to breeding-season patterns). On the basis of this fundamental knowledge, adapted reproductive biotechnologies have been developed to enhance reproduction and preserve fertility of individuals. Early works on artificial insemination (AI), in vitro fertilisation (IVF), and germplasm freezing in the more common red deer, sika deer and white-tailed deer have been highly inspiring to projects aiming at saving endangered deer species. A few fawn births following AI or IVF using frozen semen have been reported in wild species (e.g. Eld’s deer, Rucervus eldii thamin); however, assisted reproductive techniques and cryo-banking are currently not integrated into the management of rare and endangered populations. Knowing that many deer populations are rapidly declining in situ and ex situ, there is now an urgent need for better strategies and more fertility preservation options. The objectives of the present article are to review (1) existing reproductive biotechnologies to preserve fertility of different deer species and (2) how to integrate these approaches into the management of rare and endangered populations to address conservation issues.

Effect of sphingosine-1-phosphate on cryopreserved sheep testicular explants cultured in vitro

Complete spermatogenesis has been achieved in vitro in mouse testicular explants with resulting sperm used to produce pups after Intra Cytoplasm Sperm Injection and Embryo Transfer. In the present study, we evaluated the influence of sphingosine-1-phosphate (S1P) on spermatogenesis of frozen-thawed lamb testis explants in vitro. Thawed testicular pieces were cultured for 12 d on agarose blocks in serum-free growth medium containing 0, 2, 5 or 10 μM S1P. At the end of D6 and D12, some pieces were fixed and processed for histology. Other pieces were processed for RNA isolation and quantitation of proliferation (PCNA, Ki67) and differentiation (PLZF) markers and genes involved in S1P signaling (S1PR1, SGPL1, SGPP1, AKT1 and NFKBIA) by qPCR. Histology revealed an increase (P < 0.05) in seminiferous cord (SC) diameter under all culture conditions, except 5 and 10 μM S1P by D6. In the presence of 5 μM S1P, percentage of gonocytes decreased (P < 0.05) by D6 (control, 24.9% vs. S1P, 10.3%) with a concomitant increase (P < 0.05) in spermatogonia formation (control, 74.4% vs. S1P, 88.1%). S1P induced PCNA or Ki67 expression by D6, whereas PLZF was up-regulated (P < 0.05) by D6 in 2 μM S1P and D12 in 5 & 10 μM S1P. Expression of SGPL1 and SGPP1 increased 4-12-fold in tissues cultured in 10 μM S1P by D12 compared to D12 control. AKT1 and NFKBIA mRNA expression was low (P < 0.05) in 5 and or 10 μM S1P treatments on D6. These results demonstrate that S1P promotes germ cell proliferation during first week of culture and may exert an anti-apoptotic influence on the seminiferous cord in sheep testicular explants in vitro.

Expression of mitofusin 2 in human sperm and its relationship to sperm motility and cryoprotective potentials

Mitofusin 2 is a kind of mitochondria membrane protein that has been implicated in maintenance of mitochondrial morphology and function. However, the expression and function of mitofusin 2 in human sperm are not well described at present. The aim of this study was to explore the location of mitofusin 2 in human sperm and to discover its relationship to human sperm functions like motility and cryoprotective potentials. Our result showed that mitofusin 2 is specifically localized in the 5-7 μm midpiece between the neck and main part of human sperm tail. The expression level of mitofusin 2 in human sperm was significantly different between the normozoospermia and asthenozoospermia groups ( P < 0.05); meanwhile, the sperm of the asthenozoospermia group had a lower mitochondrial membrane potential ( P < 0.05), but the results of TUNEL assay did not show significant difference between the two groups. Furthermore, we found that the expression level of mitofusin 2 in the freeze-resistant group (cryo-survival rate >40%) was significantly higher than that of the freeze-intolerant group (cryo-survival rate ≤40%) ( P < 0.05). These results demonstrate that the expression level of mitofusin 2 is related to motility and cryoprotective potentials of human sperm. Mitofusin 2 may play a crucial role in the function of human sperm, which needs further research to discover the mechanism. Impact statement The exact function of mitochondria in human sperm before and during fertilization process remains controversial. MFN2 is a kind of mitochondria membrane protein and participates in the regulation of mitochondrial morphology and function. In this study, we discover the relationship of MFN2 expression to human sperm motility and cryoprotective potentials. Our results suggest that MFN2 could be a new target for the mechanism research of asthenozoospermia. MFN2 may also serve as a protein marker predicting the ability of human sperm to sustain cryopreservation.

The mutual benefits of research in wild animal species and human-assisted reproduction

Studying the reproductive biology of wild animal species produces knowledge beneficial to their management and conservation. However, wild species also share intriguing similarities in reproductive biology with humans, thereby offering alternative models for better understanding the etiology of infertility and developing innovative treatments. The purpose of this review is to raise awareness in different scientific communities about intriguing connections between wild animals and humans regarding infertility syndromes or improvement of fertility preservation. The objectives are to (1) highlight commonalities between wild species and human fertility, (2) demonstrate that research in wild species-assisted reproductive technologies can greatly enhance success in human reproductive medicine, and (3) recognize that human fertility preservation is highly inspiring and relevant to wild species conservation. In addition to having similar biological traits in some wild species and humans, the fact of sharing the same natural environment and the common needs for more options in fertility preservation are strong incentives to build more bridges that will eventually benefit both animal conservation and human reproductive medicine.

Ovarian features in white-tailed deer (Odocoileus virginianus) fawns and does

The knowledge about ovarian reserve is essential to determine the reproductive potential and to improve the methods of fertility control for overpopulated species, such as white-tailed deer (Odocoileus virginianus). The goal of this study was to evaluate the effect of age on the female reproductive tract of white-tailed deer, focusing on ovarian features. Genital tracts from 8 prepubertal and 10 pubertal females were used to characterize the preantral follicle population and density, morphology, distribution of follicular classes; stromal cell density; and apoptosis in the ovary. In addition, uterus and ovary weights and dimensions were recorded; and the number and the size of antral follicles and corpus luteum in the ovary were quantified. Overall, fawns had a greater (P < 0.05) preantral follicle population, percentage of normal follicles, and preantral follicle density than does. The mean stromal cell density in ovaries of fawns and does differed among animals but not between age groups. The apoptotic signaling did not differ (P > 0.05) between the ovaries of fawns and does. However, apoptotic ovarian cells negatively (P < 0.001) affected the preantral follicle morphology and density, and conversely, a positive correlation was observed with stromal cell density. As expected, the uteri and ovaries were larger (P < 0.002) and heavier (P < 0.001) in does than in fawns. In conclusion, this study has shown, for the first time, the preantral follicle population and distribution of classes, rate of morphologically normal follicles, and density of preantral follicles and stromal cells in white- tailed deer. Therefore, the findings herein described lead to a better understanding of the white-tailed deer ovarian biology, facilitating the development of new methods of fertility control.

Ovarian fragment sizes affect viability and morphology of preantral follicles during storage at 4°C

The method of transportation and the conditions imposed on the ovarian tissue are pivotal aspects for the success of ovarian tissue cryopreservation (OTC). The aim of this study was to evaluate the effect of the size of the ovarian tissue (e.g. whole ovary, biopsy size and transplant size) during different times of storage (0, 6, 12 and 24 h) on the structural integrity of equine ovarian tissue transported at 4°C. Eighteen pairs of ovaries from young mares (<10 years old) were harvested in a slaughterhouse and processed to simulate the fragment sizes (biopsy and transplant size groups) or kept intact (whole ovary group) and stored at 4°C for up to 24 h in α-MEM-enriched solution. The effect of the size of the ovarian tissue was observed on the morphology of preantral follicles, stromal cell density, DNA fragmentation and mitochondrial membrane potential. The results showed that (i) biopsy size fragments had more morphologically normal preantral follicles after 24 h of storage at 4°C; (ii) mitochondrial membrane potential was the lowest during each storage time when the whole ovary was used; (iii) DNA fragmentation rate in the ovarian cells of all sizes of fragments increased as storage was prolonged and (iv) transplant size fragments had increased stromal cell density during storage at cool temperature. In conclusion, the biopsy size fragment was the best to preserve follicle morphology for long storage (24 h); however, transportation/storage should be prior determined according to the distance (time of transportation) between patient and reproduction centers/clinics.

Aquaglyceroporins 3 and 7 in bull spermatozoa: identification, localisation and their relationship with sperm cryotolerance

The present study aimed to determine the localisation of aquaglyceroporins 3 (AQP3) and 7 (AQP7) in bull spermatozoa and their relationship with the sperm cell’s resilience to withstand cryopreservation (i.e. cryotolerance). A total of 18 bull ejaculates were cryopreserved and their sperm quality analysed before and after freeze–thawing. The presence and localisation of AQP3 and AQP7 was determined through immunoblotting and immunocytochemistry. AQP3 was found in the mid-piece and AQP7 in the mid-piece and post-acrosomal region of bull spermatozoa. Immunoblotting showed specific signal bands at 30 and 60 kDa for AQP3 and at 25 kDa for AQP7. Neither the relative abundance of AQP3 and AQP7 nor their localisation patterns was altered by cryopreservation but individual differences between bull ejaculates were found in immunoblots. In order to determine whether these individual differences were related to sperm cryotolerance, bull ejaculates were classified as having good (GFE) or poor freezability (PFE) on the basis of their sperm quality after thawing. While the relative abundance of AQP3 before cryopreservation did not differ between ejaculates with GFE and PFE, the abundance of AQP7 was higher in GFE than in PFE ejaculates. This finding was further confirmed through principal component and linear regression analyses. In conclusion, the relative abundance of AQP7 in fresh semen may be used as a marker to predict bull sperm cryotolerance.

Biobanking efforts and new advances in male fertility preservation for rare and endangered species

Understanding and sustaining biodiversity is a multi-disciplinary science that benefits highly from the creation of organized and accessible collections of biomaterials (Genome Resource Banks). Large cryo-collections are invaluable tools for understanding, cataloging, and protecting the genetic diversity of the world's unique animals and plants. Specifically, the systematic collection and preservation of semen from rare species has been developed significantly in recent decades with some biobanks now being actively used for endangered species management and propagation (including the introduction of species such as the black-footed ferret and the giant panda). Innovations emerging from the growing field of male fertility preservation for humans, livestock species, and laboratory animals are also becoming relevant to the protection and the propagation of valuable domestic and wild species. These new approaches extend beyond the “classical” methods associated with sperm freezing to include testicular tissue preservation combined with xenografting or in vitro culture, all of which have potential for rescuing vast amounts of unused germplasm. There also are other options under development that are predicted to have a high impact within the next decade (stem cell technologies, bio-stabilization of sperm cells at ambient temperatures, and the use of genomics tools). However, biobanking efforts and new fertility preservation strategies have to expand the way beyond mammalian species, which will offer knowledge and tools to better manage species that serve as valuable biomedical models or require assistance to reverse endangerment.

Cryobiology: principles, species conservation and benefits for coral reefs

Coral reefs are some of the oldest, most diverse and valuable ecosystems on Earth because they can support one-quarter of all marine life in our oceans. Despite their importance, the world’s coral reefs continue to be degraded at unprecedented rates by local and global threats that are warming and creating a more acidic ocean. This paper explores the reproductive challenges of coral for ex situ conservation, using IVF and cryopreservation, and our practical biobanking methods. Coral present challenges for cryopreservation because their reproductive period is often limited to a few nights yearly, they are mostly hermaphrodites with diverse modes of reproduction, including asexual reproduction (i.e. fragmentation and parthenogenesis) and sexual reproduction (i.e. self- and cross-fertilisation) and they express physiological toxins that can inhibit cryopreservation. We have banked spermatozoa from 12 coral species using the same field-hardy methods and have created new coral with thawed spermatozoa. In addition, we describe the cryopreservation of coral symbionts, whose physiology only permits the highest success seasonally. As part of a multidisciplinary conservation strategy, these collections may provide a major hedge against extinction for corals facing the damaging effects of climate change and loss of genetic diversity, and promise to help offset threats to our reefs worldwide.

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.

Slow freezing, but not vitrification supports complete spermatogenesis in cryopreserved, neonatal sheep testicular xenografts

The ability to spur growth of early stage gametic cells recovered from neonates could lead to significant advances in rescuing the genomes of rare genotypes or endangered species that die unexpectedly. The purpose of this study was to determine, for the first time, the ability of two substantially different cryopreservation approaches, slow freezing versus vitrification, to preserve testicular tissue of the neonatal sheep and subsequently allow initiation of spermatogenesis post-xenografting. Testis tissue from four lambs (3-5 wk old) was processed and then untreated or subjected to slow freezing or vitrification. Tissue pieces (fresh, n = 214; slow freezing, then thawing, n = 196; vitrification, then warming, n = 139) were placed subcutaneously under the dorsal skin of SCID mice and then grafts recovered and evaluated 17 wk later. Grafts from fresh and slow frozen tissue contained the most advanced stages of spermatogenesis, including normal tubule architecture with elongating spermatids in ~1% (fresh) and ~10% (slow frozen) of tubules. Fewer than 2% of seminiferous tubules advanced to the primary spermatocyte stage in xenografts derived from vitrified tissue. Results demonstrate that slow freezing of neonatal lamb testes was far superior to vitrification in preserving cellular integrity and function after xenografting, including allowing ~10% of tubules to retain the capacity to resume spermatogenesis and yield mature spermatozoa. Although a first for any ruminant species, findings also illustrate the importance of preemptive studies that examine cryo-sensitivity of testicular tissue before attempting this type of male fertility preservation on a large scale.