Intracytoplasmic sperm injection in sturgeon species: A promising reproductive technology of selected genitors

Sturgeons are the most endangered species group and their wild populations continue to decrease. In this study, we apply intracytoplasmic sperm injection (ICSI), an assisted reproductive technology, for the first time in endangered and critically endangered sturgeons. Using various egg-sperm species combinations we performed different ICSI experiments with immobilized pre- or non-activated spermatozoa, single or many, fresh or cryopreserved. Then we evaluated the fertilization success as well as the paternity of the resultant embryos and larvae. Surprisingly, all experimental groups exhibited embryonic development. Normal-shaped feeding larvae produced in all egg-sperm species-combination groups after ICSI using single fresh-stripped non-activated spermatozoa, in one group after ICSI using single fresh-stripped pre-activated spermatozoa, and in one group after ICSI using multiple fresh-stripped spermatozoa. ICSI with single cryopreserved non-activated spermatozoa produced neurula stage embryos. Molecular analysis showed genome integration of both egg- and sperm-donor species in most of the ICSI transplants. Overall, ICSI technology could be used as an assisted reproduction technique for producing sturgeons to rescue valuable paternal genomes.

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.

Ultra-Rapid Freezing Preserves Morphofunctional Integrity and Fertilizing Ability of Epididymal Cat Spermatozoa

Vitrification and ultra-rapid freezing, which are more commonly used for oocytes and embryos, have recently been applied to spermatozoa in an attempt to make semen cryopreservation in field conditions easier compared to conventional freezing. It is well-known that in case of unexpected death of rare and wild animals, preserving epididymal spermatozoa from isolated testicles represents a great chance of salvaging male germplasm for future use in assisted reproductive technologies. The aim of this study was to evaluate the morphofunctional integrity of cat epididymal spermatozoa ultra-rapid frozen in pellets or straws with two different extenders [E1 (Tris buffer with 20% egg yolk and 0.25 M sucrose) or E2 (Ham's F10 with 1% bovine serum albumin and 0.4 M sucrose)] and to test whether spermatozoa preserved by the best combination were able to fertilize oocytes and produce embryos in vitro by intracytoplasmic sperm injection (ICSI) of in vitro matured cat oocytes. The results showed that E1 and E2 in straw or pellet were comparable (at warming, about 30% normal morphology, 45% intact membranes, and 20% intact acrosomes), except for post-warming motility that was better maintained along time by E1 pellet (21.7 ± 7.4% at warming and 3.6 ± 2.9% after 6 h). Such spermatozoa could fertilize conspecific oocytes and support embryonic development (cleavage 35.5%) as well as frozen control spermatozoa (cleavage 54.29%, p = 0.22). In conclusion, cat epididymal spermatozoa better maintained their morphofunctional features after ultra-rapid freezing with E1 and could successfully produce embryos in vitro after ICSI. This underscores their usefulness as cryobanked material for fertility and biodiversity preservation purposes.

Current State of In Vitro Embryo Production in African Lion (Panthera leo)

In the last 30–40 years, in vitro maturation (IVM) and fertilization (IVF) of domestic cat oocytes have been established as part of the panel of assisted reproduction technologies. As a representative of wild felids, the African lion is not yet considered endangered. Nevertheless, the zoo population management of the African lion itself as well as other closely related felids would benefit from the establishment of an IVF system. Here, we aimed to investigate the transferability of domestic cat IVF technology to the African lion. From the ovaries of 42 lionesses aged between 0.75 and 15 years, a total of 933 IVF-suitable oocytes were retrieved and subjected to IVM and IVF. The overall maturation rate was 40.6% and 18.9% of these oocytes cleaved after fertilization, respectively. Embryos were generated by intracytoplasmic sperm cell injection as well as co-culture with epididymal sperm. Improvements in the model system also led to an improved outcome with in vitro produced embryos in the lion. Compared to domestic cats, the transportation of gonads to a specialized laboratory was time-consuming and influenced oocyte quality negatively. In conclusion, the domestic cat IVF system is adoptable for the African lion, although success rates are still lower.

Desiccated cat spermatozoa retain DNA integrity and developmental potential after prolonged storage and shipping at non-cryogenic temperatures

PURPOSE

To evaluate the DNA integrity and developmental potential of microwave-dehydrated cat spermatozoa after storage at - 20 °C for different time periods and/or overnight shipping on dry ice.

METHODS

Epididymal spermatozoa from domestic cats were microwave-dehydrated on coverslips after trehalose exposure. Dried samples were either assessed immediately, stored for various duration at - 20 °C, or shipped internationally on dry ice before continued storage. Dry-stored spermatozoa were rehydrated before assessing DNA integrity (TUNEL assays) or developmental potential (injection into in vitro matured oocytes followed by in vitro embryo culture for up to 7 days).

RESULTS

Percentages of dried-rehydrated spermatozoa with intact DNA was not significantly affected (P > 0.05) by desiccation and short-term storage (range, 78.9 to 80.0%) but decreased (P < 0.05) with storage over 5 months (range, 71.0 to 75.2%) compared to fresh controls (92.6 ± 2.2%). After oocyte injection with fresh or dried-rehydrated spermatozoa (regardless of storage time), percentages of activation, pronuclear formation, and embryo development were similar (P > 0.05). Importantly, spermatozoa shipped internationally also retained the ability to support embryo development up to the morula stage.

CONCLUSION

Results demonstrated the possibility to sustain DNA integrity and developmental potential of spermatozoa by dry-preservation, even after long-term storage and long-distance shipment at non-cryogenic temperatures. While further studies are warranted, present results demonstrate that dry preservation can be a reliable approach for simple and cost-effective sperm biobanking or shipment.

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.

Epididymal tail solid-surface vitrification as an effective method for domestic cat sperm cryobanking

This study aimed to describe the viability of domestic feline spermatozoa after epididymal tail vitrification. For this, 10 pairs of testis-epididymis complexes were used. The epididymal tails were vitrified using the solid-surface vitrification (SSV) method, in which two vitrification media containing ethylene glycol (EG) 40% or glycerol (GLY) 40% were tested. Vitrification with the presence of EG resulted in better results for all sperm motility parameters (motility, vigour and CASA) compared with GLY (P < 0.05). There were no statistical differences for sperm viability and acrosome integrity, plasma membrane integrity, or overall health of morphologically normal sperm before or after vitrification among experimental groups. In conclusion, epididymal tail vitrification appears to be a suitable method for long-term storage of cat sperm, especially if the procedure is performed with EG as the cryoprotectant.

Maturation and fertilization of African lion (Panthera leo) oocytes after vitrification

The African lion is an excellent model species for the highly endangered Asiatic lion. African lions reproduce well in zoos, leading to the fact that occasionally ovaries and testis are available for in-vitro experiments. We previously performed in-vitro maturation (IVM) and fertilization of lion oocytes and were able to produce advanced embryos after intracytoplasmic sperm injection (ICSI) with cryopreserved sperm. Here we examined whether our in-vitro method is also applicable after vitrification of immature oocytes. Oocytes of four lionesses (5-7 years old) were obtained after euthanasia and immediately processed on site. Half of the oocytes (n = 60) were subjected to IVM for a total of 32-34 h at 39 °C, 5% CO₂ and humidified air atmosphere. The second group (59 oocytes) was vitrified instantly using the Cryotop method. Following 6 days of storage in liquid nitrogen, oocytes were warmed and subjected to IVM as well. Mature oocytes of both groups were fertilized with frozen-thawed African lion sperm using ICSI. Maturation rate was 55% and 49.2% for the control and vitrified group, respectively. In the control group, three oocytes cleaved and another three were arrested at the pronuclei stage. Due to the low fertilization result, a sperm sample of another male was used for the vitrified group. Of the vitrified oocytes 7 cleaved and 9 more oocytes stopped at pronuclei stage. All embryos of the vitrified group did not develop beyond 4 cell stage. This is the first time that African lion in-vitro-derived embryos have been produced following oocyte vitrification.

Meiotic Status Does Not Affect the Vitrification Effectiveness of Domestic Cat Oocytes

Simple Summary

Assisted reproduction techniques (ART) are crucial for preserving endangered animal species. Cryopreservation by vitrification can maintain gamete viability for a long time. Efforts to preserve endangered species within the Felidae family are focused on developing appropriate ART procedures. The domestic cat is a good biomedical model. Unfortunately, the current state of knowledge on vitrification of cat oocytes is inconclusive and the efficiency of ART procedures is low. A key example concerns how the meiotic status of the oocyte influences suitability for vitrification. This is the main question of this study. First, we conducted a toxicity test to make sure that the vitrification solution (VS) we proposed does not have a toxic effect on cat oocytes. Next, we performed vitrification on cat oocytes before (nonmature) and after in vitro maturation (IVM) and checked their developmental potential. There was no negative impact of the applied VS on oocyte maturation and fertilization, demonstrating a possibility to obtain embryos in vitro regardless of the meiotic status. There is a need for more research on vitrification of the domestic cat oocytes as a model species for wild cats.

Abstract

Cryopreservation is important for animal fertility and biodiversity. Unfortunately, cryopreservation of feline oocytes is still an experimental technique. The aims of this study were to analyze the potential toxicity of the cryoprotectants in the vitrification solution (VS) on cat oocytes and to investigate whether the meiotic status of oocytes influences their developmental potential after vitrification. Two experiments were conducted with the VS composed of 20% ethylene glycol, 20% dimethyl sulfoxide, 20% fetal calf serum, 1.5 M trehalose, and 10% Ficoll PM-70: (1) toxicity assessment of the VS on immature cumulus oocyte complexes (COCs), and subsequently in vitro maturation (IVM) and in vitro fertilization; (2) assessment of the influence of the meiotic status on vitrification effectiveness, where immature and in vitro matured COCs were vitrified on the Cryotop. After rewarming, vitrified oocytes were subjected to IVM (immature) and intracytoplasmic sperm injection (ICSI) with fresh epididymal sperm. The toxicity test revealed no negative effect of oocyte exposure to the applied VS on their developmental potential (p > 0.05). Although the vitrification procedure itself significantly reduced the meiotic competence of oocytes, their meiotic status before vitrification (immature vs. in vitro matured) did not influence fertilization and morula rates. The only parameter affected by vitrification was the rate of oocytes suitable for ICSI, which was significantly lower for immature oocytes. Regardless of the meiotic status of vitrified oocytes, morphologically normal morulae were obtained. Moreover, the two meiotic stages examined are suitable for vitrification, with mature oocytes being a better choice when a well-equipped laboratory is available.

Development of feline embryos produced using freeze-dried sperm

Freeze drying has been developed as a new sperm preservation method that eliminates the necessity of using liquid nitrogen. An advantage of freeze-dried sperm is that it can be stored at 4 °C and transported at room temperature. To develop assisted reproductive techniques (ARTs) for domestic cats, we evaluated the effect of the freeze-dry procedure on cat sperm DNA by analyzing DNA integrity (experiment 1) and by generating cat embryos using freeze-dried sperm that had been preserved for several months (experiment 2). In experiment 1, the rate of DNA damage to freeze-dried sperm was not significantly different than that of sperm cryopreserved with liquid nitrogen (P > 0.05). In experiment 2, the proportions of cleaved embryos, morulae, and blastocysts and the cell number of blastocysts did not differ between experimental groups in which fresh sperm and freeze-dried sperm were used (P > 0.05). In addition, we generated feline blastocysts using freeze-dried sperm stored for 1-5 months. These results support an expansion of the repertoire of ARTs that are potentially applicable to both domestic and endangered species of cats.

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.

ARTs in Wild Felid Conservation Programmes in Poland and in the World

With the exception of the domestic cat, all felid species (Felidae) are currently threatened with extinction in their natural habitat. To develop effective and optimal wild cat conservation programmes with assisted reproductive technology (ART) it is necessary to combine advances from different disciplines of science, starting from the biology of the species, through research into the population and habitat, assisted reproductive technologies, establishment of gene banks, developing bioinformatic systems, and ending with biodiversity and endangered species management. In the last few years knowledge of felid reproduction has expanded considerably thanks to comparative studies utilising the domestic cat as a research model for endangered wild cats. Basic reproductive techniques utilised in both domestic cat breeding and rescuing wild felid populations that are threatened with extinction include semen collection and cryopreservation, artificial insemination, oocyte collection, in vitro maturation, in vitro fertilisation, somatic cloning, and embryo transfer. The main directions in which assisted reproductive technologies are being developed in wild cat conservation implementations and the contribution of Polish research centres in advancing these methods are presented.

Effect of storage time on the quality of cauda epididymal spermatozoa of West African dwarf (WAD) rams

The objectives of the study were to develop a protocol for preserving Western African Dwarf (WAD) ram cauda epididymal semen that could be applied in preserving and storing the semen of endangered species/genetically valuable animals in case of death and to study the morphometric characteristic of epididymides after refrigerated storage. Thirty testes-epididymides were collected immediately after slaughter from mature WAD rams and transported in ice chest at (4.5-6 °C) to the laboratory. The samples were either processed immediately or stored in a refrigerator at 5 °C for 6, 12, 24, 48 h. The results indicate that the semen motility decreased (P <  0.05) when compared to the control [87.5 ± 2.1% (0 h), to 85.0 ± 1.8% (6 h), 73.3 ± 3.6% (12 h), 53.3 ± 2.5% (24 h) and 50.0 ± 2.9% (48 h)]. The sperm concentration also decreased (P <  0.05) as duration of storage increased (0 h) 157.5 ± 8.2, (6 h) 152.3 ± 5.8, (12 h) 125.3 ± 4.4, (24 h) 106.2 ± 2.9, (48 h) 98.5 ± 3.5. Semen viability decreased as duration of storage increased from the 0 h to 48 h [(P <  0.05; 84.0 ± 1.4%, 82.8 ± 2.2%, 77.3 ± 1.7%, 69.8 ± 1.5%, and 66.5 ± 1.2%, respectively]. Furthermore, there was a decrease (P <  0.05) in percentage of intact acrosome as duration of storage increased [(0 h) 90.7 ± 1.0%; (6 h) 89.3 ± 2.0%; (12 h) 85.5 ± 1.6%; (24 h) 70.0 ± 2.4%; and (48 h) 73.3 ± 2.1%]. The results from this study indicate that epididymal semen of WAD rams recovered and preserved at 5 °C for 48 h may be used for artificial insemination.

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.

Dry Preservation of Spermatozoa: Considerations for Different Species

The current gold standard for sperm preservation is storage at cryogenic temperatures. Dry preservation is an attractive alternative, eliminating the need for ultralow temperatures, reducing storage maintenance costs, and providing logistical flexibility for shipping. Many seeds and anhydrobiotic organisms are able to survive extended periods in a dry state through the accumulation of intracellular sugars and other osmolytes and are capable of returning to normal physiology postrehydration. Using techniques inspired by nature's adaptations, attempts have been made to dehydrate and dry preserve spermatozoa from a variety of species. Most of the anhydrous preservation research performed to date has focused on mouse spermatozoa, with only a small number of studies in nonrodent mammalian species. There is a significant difference between sperm function in rodent and nonrodent mammalian species with respect to centrosomal inheritance. Studies focused on reproductive technologies have demonstrated that in nonrodent species, the centrosome must be preserved to maintain sperm function as the spermatozoon centrosome contributes the dominant nucleating seed, consisting of the proximal centriole surrounded by pericentriolar components, onto which the oocyte's centrosomal material is assembled. Preservation techniques used for mouse sperm may therefore not necessarily be applicable to nonrodent spermatozoa. The range of technologies used to dehydrate sperm and the effect of processing and storage conditions on fertilization and embryogenesis using dried sperm are reviewed in the context of reproductive physiology and cellular morphology in different species.

Normozoospermic versus teratozoospermic domestic cats: differential testicular volume, sperm morphometry, and subpopulation structure during epididymal maturation

Teratozoospermia (<40% morphologically normal spermatozoa/ejaculate) is a frequent phenomenon in feline species. This research was carried out to study the possible differences in testicular volume, differential sperm morphometric traits, and potential differences regarding the sperm subpopulational structure during epididymal sperm maturation in teratozoospermic feline donors. Epididymal sperm samples were collected from the caput (R1), corpus (R2), and cauda (R3) epididymidis in two donor groups (N: normozoospermic; T: teratozoospermic). Aliquots were assessed for concentration, viability, motility, and acrosomal integrity. Sperm morphometric descriptors from CASA-Morph analysis were analyzed by the Principal Component Analysis (PCA) and clustering analyses. Irrespective of the group analyzed, PCA revealed two Principal Components (PCs) for each epididymal region explaining more than the 93% of the variance. Surprisingly, the number of subpopulations remained constant in regions R1-R2-R3 irrespective of the donor group analyzed. However, the distribution of these subpopulations was found to be structurally different and strongly influenced by the epididymal region and the donor group. In conclusion, testicular morphometry and the sperm subpopulation structure were different in N and T donors. The alterations in subpopulations during epididymal maturation could be used as a potential clinical indicator of teratozoospermic individuals since an important influence of teratozoospermia on sperm subpopulation structure has been demonstrated.

Analysis of gene expression in granulosa cells post-maturation to evaluate oocyte culture systems in the domestic cat

Maturation of oocytes is a prerequisite for successful embryo development. The fertilization competence of in vivo derived oocytes is significantly higher than that of oocytes matured in vitro. Commonly evaluated morphological criteria for oocyte maturation do not reflect the complexity and quality of maturation processes. Oocytes and granulosa cells are communicating closely in a bidirectional way during follicular growth and maturation. Assessing the mRNA expression of specific genes in granulosa cells could be a non-invasive way to evaluate the conditions of in vitro oocyte maturation. The objective of this study was to elucidate the influence of two different FSH additives on the in vitro maturation rate and gene expression of cumulus-oocytes complexes in domestic cat. Feline oocytes were matured in a medium, supplemented with LH and 0.02 IU/ml porcine FSH versus 0.02 IU or 1.06 IU/ml human FSH. Granulosa cells were separated from oocytes directly after 24 hr of maturation or after additional 12 hr of in vitro fertilization. Gene expression levels were analysed by quantitative PCR for aromatase, antimullerian hormone, follicle stimulating hormone receptor (FSHR), luteinizing hormone/choriogonadotropin receptor (LHCGR) and prostaglandin E synthase. Neither oocyte maturation rate nor gene expression levels differed after 24 or 36 hr in all three groups. However, variations were discovered in correlations of expression levels, for instance for FSHR and LHCG, indicating differences in the fine-tuning of in vitro maturation processes under varying FSH supplementations. We suppose that correlation between gene expressions of selected genes suggests a superior maturation quality of feline oocytes.

Evaluation of sperm recovered after slaughter from cauda epididymides of red Sokoto bucks

AIM

Viable spermatozoa could be recovered from the cauda epididymides for the purpose of preservation of genetic material of male animals with desirable traits and for use in reproductive biotechnology. The aim of this study was to determine the effect of storage time on testicular and epididymal biometry, sperm reserves and epididymal sperm characteristics of red Sokoto bucks post mortem.

MATERIALS AND METHODS

Testes-epididymides were collected immediately after slaughter of mature red Sokoto bucks and transported in ice chest to the laboratory. The samples were either processed immediately or stored at 5°C in refrigerator for 24, 48 h and then processed. The testes and epididymides were measured and weighed. Sperm motility, concentration, livability, morphology, intact acrosome, and sperm reserves from different treatment groups including control were evaluated and means (±standard error of mean) were recorded.

RESULTS

There was no significant difference (p>0.05) in the testicular and epididymal dimensions determined between the means of the groups. Percent sperm motility and viability decreased significantly (p<0.05) after 24 h from 69.00±0.46 and 71.27±0.50% to 50.60±0.48 and 60.47±0.70% at 48 h, respectively. Significant decreases (p<0.05) in epididymal sperm concentration and intact acrosome from 2.86±0.08 and 92.87±0.39 at 0 to 24 h of storage, respectively, were observed.

CONCLUSION

The results of this study suggest that spermatozoa recovered from the epididymides of red Sokoto bucks were viable after storage for up to 48 h. Furthermore, this finding offers some hope that epididymal sperm recovered post-mortem can be used in assisted reproductive technologies.

Cryopreservation of feline oocytes by vitrification using commercial kits and slush nitrogen technique

Assisted reproductive techniques are a valuable tool for conservation breeding of endangered species. Cryopreservation methods are the basis of gamete banks, supporting genetic diversity preservation. Unfortunately, cryopreservation of feline oocytes is still considered an experimental technique. The aim of this study was to compare two commercial kits, with our protocol for vitrification of cat oocytes (IZW), which comprises a three-step method with ethylene glycol, DMSO, fetal calf serum, trehalose and Ficoll PM-70. Furthermore, we applied slush nitrogen (SN₂ ) for ultra-rapid freezing to improve survival rates. Cumulus-oocyte complexes were collected from domestic cat ovaries by slicing and vitrified at immature stage using Cryotop as storage device. Vit Kit^® Freeze/Thaw (n = 89) showed the lowest maturation percentage obtained after warming (10.1%). A significant difference in maturation percentage of oocytes was found between Kitazato^® kit (38.7%, n = 137) and IZW protocol (24.5%, n = 143). The cleavage after ICSI of warmed and matured oocytes (20.7% and 28.6%, respectively) and the morula percentage (18. 2% and 22.5%, respectively), however, did not reveal any significant difference between the two methods. Application of SN₂ did not result in any improvement of oocytes' cryopreservation. Maturation percentage of the oocytes vitrified by IZW method with SN₂ (n = 144) decreased until 6.1%, without any cleavage after fertilization. For Kitazato^® (n = 62), only 17.7% were able to undergo maturation and cleavage percentage dropped to 18.2%, not reaching morula stage. These data demonstrate that feline oocytes can be vitrified either by our IZW method or by commercial Kitazato^® kit, but the use of SN₂ is improving neither maturation nor cleavage percentages when combined with these procedures.

Evaluation of spermatozoal function-useful tools or just science

Conventional microscopic semen analysis does not provide precise information on the fertilizing potential of a male. The traditional basis for semen evaluation is that male fertility is dependent on production of a "proper" concentration/number of motile, morphologically normal spermatozoa in excess to achieve conception. Many independent studies, especially in human medicine, have demonstrated that the absolute number of spermatozoa does not accurately determine fertility, but their functional competence. Many functional tests of spermatozoa are developed over the last decades. Computer-assisted sperm analysis (CASA) and flow cytometry have become the gold standard for semen assessment in specialized andrology laboratories. Other functional assays, such as gamete interaction tests, provide additional information regarding the real fertilizing potential of sperm cells. From this point of view, such tests are valuable diagnostic tools in fertility disorders and may be helpful to make a decision which method of treatment to use: pharmacological therapy, intrauterine insemination, introduction of classic IVF, ICSI or exclusion from a breeding programme. The most useful gamete interaction tests include induced acrosome reaction, zona pellucida binding assay, oocyte penetration assay and hyaluronan binding assay. In recent years, andrology has entered into a new era of sophisticated OMICS methods. Genomics, epigenomics, transcriptomics and proteomics brought high hopes for rapid progress in clinical diagnostics.

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.

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.

Evaluation of cheetah and leopard spermatozoa developmental capability after interspecific ICSI with domestic cat oocytes

The ICSI procedure is potentially of great value for felids, and it has not been extensively studied in these species. The objectives of this work were to determine the best conditions for ICSI in the domestic cat (DC) to generate interspecific embryos by injecting cheetah (Ch) and leopard (Leo) spermatozoa. Firstly, DC oocytes were matured with insulin-transferrin-selenium (ITS) or without it (MM) and cultured using atmospheric (21%) or low (5%) oxygen tension after ICSI. The group ITS-5%O2 showed the highest blastocyst rate (p < 0.05), 20.9% vs 8.7%, 7% and 6.5%, for MM-21%O2 , MM-5%O2 and ITS-21%O2 , respectively. The best conditions were used to generate the interspecific embryos, together with ionomycin activation (Io) after ICSI. Interspecific embryos resulted in high rates of blastocysts that were not positively affected by Io activation: 32.6% vs 21% for Ch and Ch-Io, 9.8% vs 21% for Leo and Leo-Io, and 20% vs 17.4% for DC and DC-Io. We also evaluated DNA-fragmented nuclei of experiment 1 and 2 blastocysts, using TUNEL assay. The fragmented nucleus proportion was higher in the ITS-5%O2 group, 67.6%. Surprisingly, interspecific blastocysts showed the lowest fragmented nucleus proportion: 27% and 29.9% for Ch and Leo, respectively. We concluded that ITS and 5%O2 improve blastocyst formation in DC, although with a concomitant increase in DNA fragmentation. Most importantly, cheetah and leopard spermatozoa were able to generate blastocysts without artificial activation, which suggests that developmental capacity of wild felid spermatozoa can be evaluated by interspecific ICSI. This technique should be used to assist wild felid reproduction.

The influence of recombinant feline oviductin on different aspects of domestic cat (Felis catus) IVF and embryo quality

Oviductin is known to be a key player providing a convenient environment for the process of fertilization affecting this by direct interaction with oocytes and sperm. As in vitro embryo production in the context of assisted reproduction for endangered felids is still in the process of optimization, oviductin might be used to improve IVF results. Recombinant His-tagged feline oviductin was expressed by transformed Escherichia coli BL21DE3 cells. The protein was purified by immobilized metal ion affinity chromatography. The effect of the recombinant protein was characterized in three experiments: a hemizona assay for sperm binding analysis, the IVF outcome, and the relative mRNA expression levels in blastocysts after IVF. A significant higher number of bound sperm cells were found after incubation in oviductin. No significant effect on cleavage, morula, and blastocyst rates with or without oviductin incubation during IVF could be observed. However, the relative mRNA abundance of GJA1, a gene, whose expression level is known to be a marker of embryo quality, was significantly increased (P value less than 0.05) in blastocysts after oviductin treatment. In contrast to this, expression of OCT4, HSP70, DNMT1, DNMT3A, BAX, IGF1R, and GAPDH was not significantly affected. We assume that our recombinant oviductin in its current nonglycosylated form is able to enhance sperm binding. Despite of a missing significant effect on IVF outcome, embryo quality in terms of relative GJA1 expression is influenced positively. These promising results demonstrate the value of recombinant oviductin for the IVF in cats.

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.

Capabilities and challenges of examination of gene expression for quality assessment of domestic cat embryos

Early embryos are characterized by an accurately controlled gene expression pattern that might be deregulated during in vitro culture (IVC). The expression pattern of the developmental genes may serve as markers for embryo quality. Here, we examined the temporal pattern of relative mRNA abundance of genes important for early embryonic development in embryos produced by different fertilization methods [in vitro fertilization (IVF) vs intracytoplasmic sperm cell injection (ICSI)] and sperm sources (fresh vs frozen-thawed) applying reverse transcriptase (RT) PCR. The temporal pattern of gene expression was found to be gene specific and similar in all four examined groups in a semi-quantitative assay. In morulae, higher relative mRNA levels were found in embryos generated with fresh sperm, whereas in blastocysts, mRNA abundance tended to be higher in embryos produced with cryopreserved sperm cells. This indicates an influence of sperm cryopreservation on the temporal gene expression pattern in early cat embryos. We also examined relative mRNA abundances by real-time quantitative RT-PCR in blastocysts. In this context, blastocysts produced with fresh semen tended to have lower DNA methyltransferase 3A (DNMT3A) but higher gap junction protein alpha 1 (GJA1) and octamer-binding transcription factor 4 (OCT4) mRNA levels compared with those derived with frozen-thawed semen. We conclude that assessing embryo quality by measuring gene expression pattern in early embryos is challenging because of a high variability between individual embryos.

Cryoprotective effect of different glycerol concentrations on domestic cat spermatozoa

Cryopreservation of spermatozoa is a pivotal tool in assisted reproduction, and studies aiming to establish optimal freezing/thawing protocols are essential to enhance sperm survival. The objectives of the present study were to (1) compare the cryoprotective efficiency of three different glycerol concentrations (3%, 5%, and 7%) on the basis of post-thaw sperm quality and (2) investigate whether the incidence of morphologically abnormal sperm in fresh samples is related to cryodamage sensitivity. Semen was collected from six tomcats using an artificial vagina (total 18 ejaculates). Each ejaculate was diluted using Tris-egg yolk-based extender (TEY), evaluated, equally divided into three aliquots, and rediluted using TEY with and without glycerol to achieve final concentrations of 3%, 5%, and 7%. Samples were loaded into 0.25 mL straws, equilibrated for 60 minutes at 5 °C, frozen, and then thawed at 46 °C for 12 seconds. Fresh and frozen-thawed samples were evaluated for sperm motion parameters (computer-assisted sperm analysis), plasma membrane integrity (PMI; propidium iodide and carboxyfluorescein diacetate), and DNA integrity (acridine orange). Plasma and acrosomal membrane integrity were assessed by flow cytometry (propidium iodide and fluorescein isothiocyanate-conjugated pea (Pisum sativum) agglutinin) immediately after thawing. Sperm motion parameters were also evaluated at 30 and 60 minutes of postincubation. For all treatment groups, cryopreservation significantly impaired the PMI and sperm motion parameters, except for straightness and amplitude of lateral head displacement. DNA integrity showed a slight reduction (P < 0.05) when 3% glycerol was used. The percentage of total motility, progressive motility, and rapid spermatozoa were significantly lower immediately after thawing and up to 60 minutes of incubation for the 3% glycerol group when compared with 5% and 7%. No difference (P > 0.05) was found for PMI, acrosome integrity, and DNA integrity among post-thaw groups. However, higher (P < 0.05) incidence of viable cells with reacted acrosome and dead cells with intact acrosome were observed with 7% and 3% glycerol, respectively. Percentage of morphologically abnormal spermatozoa in fresh sample was positively correlated with PMI only in the 3% glycerol group and negatively correlated with sperm motility in the 5% and 7% groups. In conclusion, the final concentration of 5% glycerol offered better cryoprotective effect for ejaculated cat sperm, and the relationship found between prefreezing sperm morphology and post-thaw sperm quality showed to be dependent on final glycerol concentration.

Retention of structure and function of the cat germinal vesicle after air-drying and storage at suprazero temperature

The study explored a novel approach for preserving the maternal genome without the entire oocyte by air-drying the cat germinal vesicle (GV) in the presence of the disaccharide trehalose. Specifically, we examined GV structure and function after desiccation, storage at 4 °C (up to 32 wk), and rehydration including the ability to resume meiosis after injection into a fresh, conspecific cytoplast. In experiment 1, DNA integrity was similar to fresh controls after 1 and 4 wk storage in the presence of trehalose, but was more fragmented at later time points (especially after 32 wk). Nuclear envelope integrity was sustained in >90% of oocytes stored for 0, 4, or 16 wk regardless of protective treatment. In experiment 2, compacted, air-dried GVs were stored for 2 or 4 wk, rehydrated, and injected into fresh cytoplasts. After culture for 24 h in vitro, up to 73% of oocytes reconstructed with desiccated GVs preserved in trehalose resumed meiosis compared to 30% of those dried in the absence of the disaccharide. At each storage time point, trehalose presence during air-drying was advantageous for resumption of meiosis, with >20% of oocytes completing nuclear maturation to metaphase II. This demonstrates a potential for preserving the female genome using the GV alone and for multiple weeks after desiccation. Trehalose enhanced the process by retaining the ability of a dried and rehydrated GV to resume communication with the surrounding cytoplasm of the recipient oocyte to permit reaching metaphase II and likely sustain subsequent embryo development.

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.

Influence of culture medium composition on relative mRNA abundances in domestic cat embryos

Different culture conditions have been used to produce domestic cat embryos. As part of the in vitro procedures, the medium composition significantly affects the quality of the embryo development also. Quality assessments based on cleavage kinetics and blastomere symmetry are useful, but embryos also can differ in their relative gene expression patterns despite similar morphological characteristics. The aim of this study was to compare cat embryos produced with two different in vitro culture systems routinely used in two different laboratories [Smithsonian Conservation Biology Institute, Washington D.C., USA (SCBI) and Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany (IZW)]. Specifically, relative mRNA expression patterns of critical genes for pre-implantation embryo development were assessed in both conditions. Embryos were produced in parallel in both culture systems by IVF using frozen-thawed ejaculated semen in the United States and fresh epididymal sperm in Germany. Success of embryo development in vitro was recorded as well as relative mRNA abundances [DNA methyltransferases 1 and 3A (DNMT1, DNMT3A), gap junction protein alpha 1 (GJA1), octamer-binding transcription factor 4 [OCT4], insulin-like growth factors 1 and 2 receptors (IGF1R, IGF2R), beta-actin (ACTB)] in pools of days 4-5 morulae by semi-quantitative RT-PCR assay. Percentages of cleaved embryos were similar (p > 0.05) between both culture systems, regardless of the location. OCT4 mRNA abundance was higher (p < 0.05) in embryos derived in the SCBI culture system compared with those from the IZW system when epididymal sperm was used for IVF. No clear correlation between the expression pattern and the culture system could be found for all other genes. It is suggested that OCT4 expression might be affected by the media composition in some conditions and can be the indicator of a better embryo quality.

Comparative cryobiological traits and requirements for gametes and gonadal tissues collected from wildlife species

A major challenge to retaining viability of frozen gametes and reproductive tissues is to understand and overcome species-specificities, especially because there is substantial diversity in cryobiological properties and requirements among cell types and tissues. Systematic studies can lead to successful post-thaw recovery, especially after determining: 1) membrane permeability to water and cryoprotectant, 2) cryoprotectant toxicity, 3) tolerance to osmotic changes, and 4) resistance to cooling and freezing temperatures. Although species-dependency ultimately dictates the ability of specific cells and tissues to survive freeze-thawing, there are commonalities between taxa that allow a protocol developed for one species to be useful information for another. This is the reason for performing comparative cryopreservation studies among diverse species. Our laboratory has compared cellular cryotolerance, especially in spermatozoa, in a diverse group of animals-from corals to elephants-for more than 30 yrs. Characterizing the biophysical traits of gametes and tissues is the most efficient way to develop successful storage and recovery protocols, but, such data are only available for a few laboratory, livestock, and fish species, with virtually all others (wild mammals, birds, reptiles, and amphibians) having gone unstudied. Nonetheless, when a rare animal unexpectedly dies, there is no time to understand the fundamentals of biophysics. In these emergencies, it is necessary to rely on experience and the best data from taxonomically-related species. Fortunately, there are some general similarities among most species, which, for example, allow adequate post-thaw viability. Regardless, there is a priority for more information on biophysical traits and freezing tolerance of distinctive biomaterials, especially for oocytes and gonadal tissues, and even for common, domesticated animals. Our colleague, Dr John Critser was a pioneer in cryobiology, earning that moniker because of his advocacy and devotion to understanding the differences (and similarities) among species to better store living genetic material.