Preservation and transplantation of porcine testis tissue

Determining the optimal time interval between sample acquisition and cryopreservation when processing immature testicular tissue to preserve fertility

The cryopreservation of immature testicular tissue (ITT) prior to gonadotoxic therapy is crucial for fertility preservation in prepubertal boys with cancer. However, the optimal holding time between tissue collection and cryopreservation has yet to be elucidated. Using the bovine model, we investigated four holding times (1, 6, 24, and 48 h) for ITTs before cryopreservation. Biopsies from two-week-old calves were stored in transport medium and cryopreserved following a standard slow-freezing clinical protocol. Thawed samples were then assessed for viability, morphology, and gene expression by haematoxylin and eosin (H&E) staining, immunohistochemistry and real-time quantitative reverse transcription-polymerase chain reaction (RT-qPCR). Analysis failed to identify any significant changes in cell viability when compared between the different groups. Sertoli (Vimentin+) and proliferating cells (Ki67+) were well-preserved. The expression of genes related to germ cells, spermatogenesis (STRA8, PLZF, GFRα-1, C-KIT, THY1, UCHL-1, NANOG, OCT-4, CREM), and apoptosis (HSP70-2) remained stable over 48 h. However, seminiferous cord detachment increased significantly in the 48-h group (p < 0.05), with associated cord and SSC shrinkage. Collectively, our analyses indicate that bovine ITTs can be stored for up to 48 h prior to cryopreservation with no impact on cell viability and the expression levels of key genes. However, to preserve the morphology of frozen-thawed tissue, the ideal processing time would be within 24 h. Testicular tissues obtained from patients for fertility preservation often need to be transported over long distances to be cryopreserved in specialist centres. Our findings highlight the importance of determining optimal tissue transport times to ensure tissue quality in cryopreservation.

The Role of Promyelocytic Leukemia Zinc Finger (PLZF) and Glial-Derived Neurotrophic Factor Family Receptor Alpha 1 (GFRα1) in the Cryopreservation of Spermatogonia Stem Cells

The cryopreservation of spermatogonia stem cells (SSCs) has been widely used as an alternative treatment for infertility. However, cryopreservation itself induces cryoinjury due to oxidative and osmotic stress, leading to reduction in the survival rate and functionality of SSCs. Glial-derived neurotrophic factor family receptor alpha 1 (GFRα1) and promyelocytic leukemia zinc finger (PLZF) are expressed during the self-renewal and differentiation of SSCs, making them key tools for identifying the functionality of SSCs. To the best of our knowledge, the involvement of GFRα1 and PLZF in determining the functionality of SSCs after cryopreservation with therapeutic intervention is limited. Therefore, the purpose of this review is to determine the role of GFRα1 and PLZF as biomarkers for evaluating the functionality of SSCs in cryopreservation with therapeutic intervention. Therapeutic intervention, such as the use of antioxidants, and enhancement in cryopreservation protocols, such as cell encapsulation, cryoprotectant agents (CPA), and equilibrium of time and temperature increase the expression of GFRα1 and PLZF, resulting in maintaining the functionality of SSCs. In conclusion, GFRα1 and PLZF have the potential as biomarkers in cryopreservation with therapeutic intervention of SSCs to ensure the functionality of the stem cells.

Current scenario and challenges ahead in application of spermatogonial stem cell technology in livestock

PURPOSE

Spermatogonial stem cells (SSCs) are the source for the mature male gamete. SSC technology in humans is mainly focusing on preserving fertility in cancer patients. Whereas in livestock, it is used for mining the factors associated with male fertility. The review discusses the present status of SSC biology, methodologies developed for in vitro culture, and challenges ahead in establishing SSC technology for the propagation of superior germplasm with special reference to livestock.

METHOD

Published literatures from PubMed and Google Scholar on topics of SSCs isolation, purification, characterization, short and long-term culture of SSCs, stemness maintenance, epigenetic modifications of SSCs, growth factors, and SSC cryopreservation and transplantation were used for the study.

RESULT

The fine-tuning of SSC isolation and culture conditions with special reference to feeder cells, growth factors, and additives need to be refined for livestock. An insight into the molecular mechanisms involved in maintaining stemness and proliferation of SSCs could facilitate the dissemination of superior germplasm through transplantation and transgenesis. The epigenetic influence on the composition and expression of the biomolecules during in vitro differentiation of cultured cells is essential for sustaining fertility. The development of surrogate males through gene-editing will be historic achievement for the foothold of the SSCs technology.

CONCLUSION

Detailed studies on the species-specific factors regulating the stemness and differentiation of the SSCs are required for the development of a long-term culture system and in vitro spermatogenesis in livestock. Epigenetic changes in the SSCs during in vitro culture have to be elucidated for the successful application of SSCs for improving the productivity of the animals.

Strategies for cryopreservation of testicular cells and tissues in cancer and genetic diseases

Cryopreservation of testicular cells and tissues is useful for the preservation and restoration of fertility in pre-pubertal males expecting gonadotoxic treatment for cancer and genetic diseases causing impaired spermatogenesis. A number of freezing and vitrification protocols have thus been tried and variable results have been reported in terms of cell viability spermatogenesis progression and the production of fertile spermatozoa. A few studies have also reported the production of live offspring from cryopreserved testicular stem cells and tissues in rodents but their replication in large animals and human have been lacking. Advancement in in vitro spermatogenesis system has improved the possibility of producing fertile spermatozoa from the cryopreserved testis and has reduced the dependency on transplantation. This review provides an update on various cryopreservation strategies for fertility preservation in males expecting gonadotoxic treatment. It also discusses various methods of assessing and ameliorating cryoinjuries. Newer developments on in vitro spermatogenesis and testicular tissue engineering for in vitro sperm production from cryopreserved SSCs and testicular tissue are also discussed.

Formation of organotypic testicular organoids in microwell culture†

Three-dimensional (3D) organoids can serve as an in vitro platform to study cell-cell interactions, tissue development, and toxicology. Development of organoids with tissue architecture similar to testis in vivo has remained a challenge. Here, we present a microwell aggregation approach to establish multicellular 3D testicular organoids from pig, mouse, macaque, and human. The organoids consist of germ cells, Sertoli cells, Leydig cells, and peritubular myoid cells forming a distinct seminiferous epithelium and interstitial compartment separated by a basement membrane. Sertoli cells in the organoids express tight junction proteins claudin 11 and occludin. Germ cells in organoids showed an attenuated response to retinoic acid compared to germ cells in 2D culture indicating that the tissue architecture of the organoid modulates response to retinoic acid similar to in vivo. Germ cells maintaining physiological cell-cell interactions in organoids also had lower levels of autophagy indicating lower levels of cellular stress. When organoids were treated with mono(2-ethylhexyl) phthalate (MEHP), levels of germ cell autophagy increased in a dose-dependent manner, indicating the utility of the organoids for toxicity screening. Ablation of primary cilia on testicular somatic cells inhibited the formation of organoids demonstrating an application to screen for factors affecting testicular morphogenesis. Organoids can be generated from cryopreserved testis cells and preserved by vitrification. Taken together, the testicular organoid system recapitulates the 3D organization of the mammalian testis and provides an in vitro platform for studying germ cell function, testicular development, and drug toxicity in a cellular context representative of the testis in vivo.

Production of germline chimeric quails by transplantation of cryopreserved testicular cells into developing embryos

The germplasm is a resource and tool for the conservation of genetic diversity in animals, including birds. Securing germplasm is limited in most bird species due to difficulties in semen collection and germ cell isolation, lack of germ cell-specific markers, and in vitro culture systems. Here, we report the production of germline chimeric quails by transplant of cryopreserved testicular cells (TCs) into the developing embryo. The testicular germ cell properties were maintained after freeze-thaw, with no significant reduction in cell viability irrespective of storage length. Cryopreserved TCs were transferred into Hamburger Hamilton (HH) stage 14-17 quail embryos, and were demonstrated to migrate into the embryonic gonads with similar efficiency to freshly isolated TCs. Twenty of 81 recipient embryos yielded hatchlings from cryopreserved TCs and the germline transmission efficiency was similar to that of freshly isolated cells. In conclusion, cryopreserved adult quail TCs are capable of (de)differentiation into functional gametes in recipient quail gonads and can generate donor TCs-derived progenies. This system is feasible for the isolation of sufficient germplasm resources from various bird species for conservation purposes.

The study and manipulation of spermatogonial stem cells using animal models

Spermatogonial stem cells (SSCs) are a rare group of cells in the testis that undergo self-renewal and complex sequences of differentiation to initiate and sustain spermatogenesis, to ensure the continuity of sperm production throughout adulthood. The difficulty of unequivocal identification of SSCs and complexity of replicating their differentiation properties in vitro have prompted the introduction of novel in vivo models such as germ cell transplantation (GCT), testis tissue xenografting (TTX), and testis cell aggregate implantation (TCAI). Owing to these unique animal models, our ability to study and manipulate SSCs has dramatically increased, which complements the availability of other advanced assisted reproductive technologies and various genome editing tools. These animal models can advance our knowledge of SSCs, testis tissue morphogenesis and development, germ-somatic cell interactions, and mechanisms that control spermatogenesis. Equally important, these animal models can have a wide range of experimental and potential clinical applications in fertility preservation of prepubertal cancer patients, and genetic conservation of endangered species. Moreover, these models allow experimentations that are otherwise difficult or impossible to be performed directly in the target species. Examples include proof-of-principle manipulation of germ cells for correction of genetic disorders or investigation of potential toxicants or new drugs on human testis formation or function. The primary focus of this review is to highlight the importance, methodology, current and potential future applications, as well as limitations of using these novel animal models in the study and manipulation of male germline stem cells.

Testicular organoids to study cell-cell interactions in the mammalian testis

BACKGROUND

Over the last ten years, three-dimensional organoid culture has garnered renewed interest, as organoids generated from primary cells or stem cells with cell associations and functions similar to organs in vivo can be a powerful tool to study tissue-specific cell-cell interactions in vitro. Very recently, a few interesting approaches have been put forth for generating testicular organoids for studying the germ cell niche microenvironment.

AIM

To review different model systems that have been employed to study germ cell biology and testicular cell-cell interactions and discuss how the organoid approach can address some of the shortcomings of those systems.

RESULTS AND CONCLUSION

Testicular organoids that bear architectural and functional similarities to their in vivo counterparts are a powerful model system to study cell-cell interactions in the germ cell niche. Organoids enable studying samples in humans and other large animals where in vivo experiments are not possible, allow modeling of testicular disease and malignancies and may provide a platform to design more precise therapeutic interventions.

Three-dimensional testicular organoids as novel in vitro models of testicular biology and toxicology

Organoids are three dimensional structures consisting of multiple cell types that recapitulate the cellular architecture and functionality of native organs. Over the last decade, the advent of organoid research has opened up many avenues for basic and translational studies. Following suit of other disciplines, research groups working in the field of male reproductive biology have started establishing and characterizing testicular organoids. The three-dimensional architectural and functional similarities of organoids to their tissue of origin facilitate study of complex cell interactions, tissue development and establishment of representative, scalable models for drug and toxicity screening. In this review, we discuss the current state of testicular organoid research, their advantages over conventional monolayer culture and their potential applications in the field of reproductive biology and toxicology.

In vitro transplantation of spermatogonial stem cells isolated from human frozen-thawed testis tissue can induce spermatogenesis under 3-dimensional tissue culture conditions

Background

Sperm production is one of the most complex biological processes in the body. In vitro production of sperm is one of the most important goals of researches in the field of male infertility treatment, which is very important in male cancer patients treated with gonadotoxic methods and drugs. In this study, we examine the progression of spermatogenesis after transplantation of spermatogonial stem cells under conditions of testicular tissue culture.

Results

Testicular tissue samples from azoospermic patients were obtained and then these were freeze–thawed. Spermatogonial stem cells were isolated by two enzymatic digestion steps and the identification of these cells was confirmed by detecting the PLZF protein. These cells, after being labeled with DiI, were transplanted in azoospermia adult mice model. The host testes were placed on agarose gel as tissue culture system. After 8 weeks, histomorphometric, immunohistochemical and molecular studies were performed. The results of histomorphometric studies showed that the mean number of spermatogonial cells, spermatocytes and spermatids in the experimental group was significantly more than the control group (without transplantation) (P < 0.05) and most of the cells responded positively to the detection of DiI. Immunohistochemical studies in host testes fragments in the experimental group express the PLZF, SCP3 and ACRBP proteins in spermatogonial cells, spermatocyte and spermatozoa, respectively, which confirmed the human nature of these cells. Also, in molecular studies of PLZF, Tekt1 and TP1, the results indicated that the genes were positive in the test group, while not in the control group.

Conclusion

These results suggest that the slow freezing of SSCs can support the induction of spermatogenesis to produce haploid cells under the 3-dimensional testicular tissue culture.

Comparative efficacies of six different media for cryopreservation of immature buffalo (Bubalus bubalis) calf testis

Buffalo calves have a high mortality rate (~80%) in commercial dairies and testis cryopreservation can provide a feasible option for the preservation of germplasm from immature males that die before attaining sexual maturity. The aim of the present study was to evaluate combinations of 10 or 20% dimethylsulfoxide (DMSO) with 0, 20 or 80% fetal bovine serum (FBS) for cryopreservation of immature buffalo testicular tissues, subjected to uncontrolled slow freezing. Tissues cryopreserved in 20% DMSO with 20% FBS (D20S20) showed total, tubular and interstitial cell viability, number of early apoptotic and DNA-damaged cells, surviving germ and proliferating cells and expression of testicular cell-specific proteins (POU class 5 homeobox (POU5F1), vimentin (VIM) and actin α2 (ACTA2)) similar to that of fresh cultured control (FCC; P>0.05). Expression of cytochrome P450, family 11, subfamily A (CYP11A1) protein and testosterone assay showed that only tissues cryopreserved in D20S20 had Leydig cells and secretory functions identical to that of FCC (P>0.05). High expression of superoxide dismutase2 (SOD2), cold-inducible RNA-binding protein (CIRBP) and RNA-binding motif protein3 (RBM3) proteins in cryopreserved tissues indicated involvement of cell signalling pathways regulating cellular protective mechanisms. Similarity in expression of pro-apoptosis proteins transcription factor tumour protein P53 (TP53) and BCL2-associated X protein (BAX) in D20S20 cryopreserved tissues to that of FCC (P>0.05) suggested lower apoptosis and DNA damage as key reasons for superior cryopreservation.

Establishment of a strain of haemophilia-A pigs by xenografting of foetal testicular tissue from neonatally moribund cloned pigs

Grafting of testicular tissue into immunodeficient mice makes it possible to obtain functional sperm from immature donor animals that cannot be used for reproduction. We have developed a porcine model of human haemophilia A (haemophilia-A pigs) by nuclear transfer cloning from foetal fibroblasts after disruption of the X-linked coagulation factor VIII (F8) gene. Despite having a recessive condition, female F8^+/- cloned pigs died of severe bleeding at an early age, as was the case for male F8^-/Y cloned pigs, thus making it impossible to obtain progeny. In this study, therefore, we produced sperm from F8^-/Y cloned pigs by grafting their foetal testicular tissue into nude mice. Two F8^+/- female pigs were generated from oocytes injected with xenogeneic sperm. Unlike the F8^+/- cloned pigs, they remained asymptomatic, and delivered five F8^-/Y and four F8^+/- pigs after being crossed with wild-type boars. The descendant F8^-/Y pigs conserved the haemophilia phenotype. Thus, the present F8^+/- pigs show resolution of the phenotypic abnormality, and will facilitate production of F8^-/Y pigs as founders of a strain of haemophilia-A pigs for the development of new therapeutics for haemophilia A. This strategy will be applicable to other genetically modified pigs.

Fertility restoration with spermatogonial stem cells

PURPOSE OF REVIEW

This review evaluates the state of the art in terms of challenges and strategies used to restore fertility with spermatogonial stem cells retrieved from prepubertal boys affected by cancer. Although these boys do not yet produce spermatozoa, the only option to preserve their fertility is cryopreservation of spermatogonial stem cells in the form of testicular cell suspensions or whole tissue pieces. Different techniques have been described to achieve completion of spermatogenesis from human, spermatogonial stem cells but none is yet ready for clinical application. A crucial point to address is gaining a full understanding of spermatogonial stem cell niche pathophysiology, where germ cells undergo proliferation and differentiation. Various fertility restoration approaches will be presented depending on the presence of an intact niche, dissociated niche, or reconstituted niche.

RECENT FINDINGS

Testicular organoids open the way to providing further insights into the niche. They can recreate the three-dimensional architecture of the testicular microenvironment in vitro, allowing a large number of applications, from physiology to drug toxicity investigations.

SUMMARY

In addition to the full elucidation of the niche microenvironment, achieving fertility restoration from cryopreserved human spermatogonial stem cells implies overcoming other important challenges. Testicular organoids might prove to be essential tools to progress in this field.

Effects of various cryoprotectants on the quality of frozen-thawed immature bovine (Qinchuan cattle) calf testicular tissue

To investigate the effects of different concentrations of various cryoprotectants (CPs) on the cell viability as well as expression of spermatogenesis-related genes, such as CREM, Stra8 and HSP70-2 in frozen-thawed bovine calf testicular tissue, immature bovine (Qinchuan cattle) calf testicular tissue was collected and cryopreserved in the cryomedia containing different concentrations (5%, 10%, 15% and 20%) of the following three CPs: glycerol, ethylene glycol (EG) and dimethyl sulphoxide (DMSO) respectively. After 1 month cryopreservation in liquid nitrogen, cell viability was evaluated using Trypan blue exclusion under a bright-field microscope. The mRNA expression of the three genes was also evaluated using qRT-PCR. The results indicated that different concentrations of glycerol, EG and DMSO in cryomedia during cryopreservation could protect bovine calf testicular tissue in various ways to avoid freezing or cryopreservation-induced expression changes in spermatogenesis-related genes. The highest cell viability and the three spermatogenesis-related genes (CREM, Stra8 and HSP70-2) expression level came from the cryomedia containing glycerol, EG and DMSO at 10% concentration respectively (p < .05). Meanwhile, compared with the other CPs, the frozen-thawed bovine calf testicular tissue treated with 10% DMSO exhibited the highest cell viability and mRNA expression level of the spermatogenesis-related genes (CREM, Stra8 and HSP70-2).

Fertility preservation through gonadal cryopreservation

Fertility preservation is an area of immense interest in today's society. The most effective and established means of fertility preservation is cryopreservation of gametes (sperm and oocytes) and embryos. Gonadal cryopreservation is yet another means for fertility preservation, especially if the gonadal function is threatened by premature menopause, gonadotoxic cancer treatment, surgical castration, or diseases. It can also aid in the preservation of germplasm of animals that die before attaining sexual maturity. This is especially of significance for valuable, rare, and endangered animals whose population is affected by high neonatal/juvenile mortality because of diseases, poor management practices, or inbreeding depression. Establishing genome resource banks to conserve the genetic status of wild animals will provide a critical interface between ex-situ and in-situ conservation strategies. Cryopreservation of gonads effectively lengthens the genetic lifespan of individuals in a breeding program even after their death and contributes towards germplasm conservation of prized animals. Although the studies on domestic animals are quite promising, there are limitations for developing cryopreservation strategies in wild animals. In this review, we discuss different options for gonadal tissue cryopreservation with respect to humans and to laboratory, domestic, and wild animals. This review also covers recent developments in gonadal tissue cryopreservation and transplantation, providing a systematic view and the advances in the field with the possibility for its application in fertility preservation and for the conservation of germplasm in domestic and wild species.

Replacement of serum with ocular fluid for cryopreservation of immature testes

Cryopreservation of immature testis is a feasible approach for germplasm preservation of male animals. Combinations of dimethyl sulfoxide (DMSO) and foetal bovine serum (FBS) are used for testis cryopreservation. However, an alternative to FBS is needed, because FBS is expensive. Buffalo ocular fluid (BuOF), a slaughter house by-product, could be an economical option. The objective of the present study was to assess whether BuOF can replace FBS for cryopreservation of immature mouse (Mus musculus), rat (Rattus norvegicus), and buffalo (Bubalus bubalis) testes. Results showed that rodent and buffalo testes frozen in DMSO (10% for rodents and 20% for buffalo) with 20% FBS or BuOF had similar numbers of viable and DNA-damaged cells (P > 0.05). The expression of cell proliferation- (PCNA) and apoptosis-specific proteins (Annexin V and BAX/BCL2 ratio) were also comparable in mouse and buffalo testes frozen in DMSO with FBS or BuOF (P > 0.05). Interestingly, rat testis frozen in DMSO with BuOF had lower expression of Annexin V protein than testis frozen in DMSO with FBS (P < 0.05). The percentage of meiotic germ cells (pachytene-stage spermatocytes) in xenografts from testis frozen either in DMSO with BuOF or FBS did not significantly differ in rats or buffalo (P > 0.05). These findings provide evidence that BuOF has potential to replace FBS for cryopreservation of immature rodent and buffalo testis. Further investigation is needed to explore whether BuOF can replace FBS for testis cryopreservation of other species.

Cryopreservation of testicular tissue or testicular cell suspensions: a pivotal step in fertility preservation

BACKGROUND

Germ cell depletion caused by chemical or physical toxicity, disease or genetic predisposition can occur at any age. Although semen cryopreservation is the first reflex for preserving male fertility, this cannot help out prepubertal boys. Yet, these boys do have spermatogonial stem cells (SSCs) that able to produce sperm at the start of puberty, which allows them to safeguard their fertility through testicular tissue (TT) cryopreservation. SSC transplantation (SSCT), TT grafting and recent advances in in vitro spermatogenesis have opened new possibilities to restore fertility in humans. However, these techniques are still at a research stage and their efficiency depends on the amount of SSCs available for fertility restoration. Therefore, maintaining the number of SSCs is a critical step in human fertility preservation. Standardizing a successful cryopreservation method for TT and testicular cell suspensions (TCSs) is most important before any clinical application of fertility restoration could be successful.

OBJECTIVE AND RATIONALE

This review gives an overview of existing cryopreservation protocols used in different animal models and humans. Cell recovery, cell viability, tissue integrity and functional assays are taken into account. Additionally, biosafety and current perspectives in male fertility preservation are discussed.

SEARCH METHODS

An extensive PubMED and MEDline database search was conducted. Relevant studies linked to the topic were identified by the search terms: cryopreservation, male fertility preservation, (immature)testicular tissue, testicular cell suspension, spermatogonial stem cell, gonadotoxicity, radiotherapy and chemotherapy.

OUTCOMES

The feasibility of fertility restoration techniques using frozen-thawed TT and TCS has been proven in animal models. Efficient protocols for cryopreserving human TT exist and are currently applied in the clinic. For TCSs, the highest post-thaw viability reported after vitrification is 55.6 ± 23.8%. Yet, functional proof of fertility restoration in the human is lacking. In addition, few to no data are available on the safety aspects inherent to offspring generation with gametes derived from frozen-thawed TT or TCSs. Moreover, clarification is needed on whether it is better to cryopreserve TT or TCS.

WIDER IMPLICATIONS

Fertility restoration techniques are very promising and expected to be implemented in the clinic in the near future. However, inter-center variability needs to be overcome and the gametes produced for reproduction purposes need to be subjected to safety studies. With the perspective of a future clinical application, there is a dire need to optimize and standardize cryopreservation and safety testing before using frozen-thawed TT of TCSs for fertility restoration.

Effect of Antioxidants and Apoptosis Inhibitors on Cryopreservation of Murine Germ Cells Enriched for Spermatogonial Stem Cells

Spermatogonial stem cells (SSCs) are germline stem cells that serve as the foundation of spermatogenesis to maintain fertility throughout a male’s lifetime. To treat male infertility using stem cell banking systems and transplantation, it is important to be able to preserve SSCs for long periods of time. Therefore, this study was conducted to develop an optimal cryopreservation protocol for SSCs using antioxidants and apoptosis inhibitors in freezing medium. No differences were observed compared to controls when SSCs were cryopreserved in the presence of apoptosis inhibitors by themselves. However, mouse germ cells cryopreserved in basal medium containing the antioxidant hypotaurine (14 mM) resulted in significantly greater proliferation potential and mitochondrial activity. Furthermore, treatment groups with combinations containing 200 mM trehalose and 14 mM hypotaurine showed higher proliferation rates compared to controls. In addition, several serum free conditions were evaluated for SSC cryopreservation. Treatment media containing 10% or 20% knockout serum replacement resulted in similar cryopreservation results compared to media containing FBS. SSC transplantation was also performed to confirm the functionality of SSCs frozen in 14 mM hypotaurine. Donor SSCs formed normal spermatogenic colonies and sperm in the recipient testis. These data indicate that inclusion of 14 mM hypotaurine in cryopreservation media is an effective way to efficiently cryopreserve germ cells enriched for SSCs and that knockout serum replacement can replace FBS in germ cell cryopreservation media.

Beyond the mouse monopoly: studying the male germ line in domestic animal models

Spermatogonial stem cells (SSCs) are the foundation of spermatogenesis and essential to maintain the continuous production of spermatozoa after the onset of puberty in the male. The study of the male germ line is important for understanding the process of spermatogenesis, unravelling mechanisms of stemness maintenance, cell differentiation, and cell-to-cell interactions. The transplantation of SSCs can contribute to the preservation of the genome of valuable individuals in assisted reproduction programs. In addition to the importance of SSCs for male fertility, their study has recently stimulated interest in the generation of genetically modified animals because manipulations of the male germ line at the SSC stage will be maintained in the long term and transmitted to the offspring. Studies performed mainly in the mouse model have laid the groundwork for facilitating advancements in the field of male germ line biology, but more progress is needed in nonrodent species in order to translate the technology to the agricultural and biomedical fields. The lack of reliable markers for isolating germ cells from testicular somatic cells and the lack of knowledge of the requirements for germ cell maintenance have precluded their long-term maintenance in domestic animals. Nevertheless, some progress has been made. In this review, we will focus on the state of the art in the isolation, characterization, culture, and manipulation of SSCs and the use of germ cell transplantation in domestic animals.

Short-term hypothermic preservation of human testicular tissue: the effect of storage medium and storage period

OBJECTIVE

To optimize the storage medium and period during short-term preservation of human testicular tissue.

DESIGN

First, human testicular tissue fragments from five patients were kept at 4°C for 3 days in different media (Dulbecco's modified Eagle's medium [DMEM]/F12, DMEM/F12 + 20% human serum albumin [HSA], DMEM/F12 + 50% HSA, and HSA). Secondly, fragments from four patients were kept in DMEM/F12 for 3, 5, or 8 days at 4°C.

SETTING

Laboratory research environment.

PATIENT(S)

Adult human testicular tissue.

INTERVENTION(S)

Biopsy and short-term storage of human testicular tissue at different conditions.

MAIN OUTCOME MEASURE(S)

Viability, general tissue morphology, Sertoli cell morphology, number of spermatogonia, and apoptosis. The experimental conditions were compared with fresh control samples.

RESULT(S)

Storing human testicular tissue in DMEM/F12 did not alter any of the investigated parameters. In most conditions containing HSA, tissue morphology was altered, and in all of them the Sertoli cell morphology was affected. The number of spermatogonia was only affected when tissue was stored in 100% HSA. In the second part of the study, tissue morphology deteriorated significantly as of 5 days of hypothermic storage, and Sertoli cell morphology after 8 days.

CONCLUSION(S)

Human testicular tissue can be preserved for 3 days at 4°C in DMEM/F12 without altering tissue morphology, Sertoli cell morphology, number of spermatogonia, or number of apoptotic cells.

Enrichment and culture of spermatogonia from cryopreserved adult bovine testis tissue

Propagation of bovine spermatogonial stem cells (SSCs) from the cryopreserved testicular tissue is essential for the application of SSCs-related techniques. To explore the appropriate conditions for in vitro culture of bovine spermatogonia (containing putative SSCs), Sertoli cell monolayer and serum concentration were set as two main control factors. Morphological examination showed that the intactness and structure of adult bovine testicular tissue were well maintained after cryopreservation. The enriched bovine spermatogonia were large round CD9 and promyelocytic leukemia zinc finger protein (PLZF) positive cells, with high nucleocytoplasmic ratios and multiple types including single, paired-, aligned-cells or grape cluster-like colonies in vitro. In Sertoli cell co-culture system, bovine spermatogonia attached quickly and proliferated obviously faster than those in the system without Sertoli cells. Serum-free media was no good for the attachment and proliferation of bovine spermatogonia. When 2.5%, 5% and 10% fetal bovine serum (FBS) was employed in the media, spermatogonia attached easily and divided quickly to form paired-, chained-cells or grape cluster-like colonies with comparable percentages in all groups. However, the contaminated somatic cells proliferated robustly in groups containing 5% and 10% FBS. Together, bovine spermatognia isolated from cryopreserved adult testis tissue express CD9 and PLZF, can survive and proliferate conspicuously in Sertoli cell co-culture system, and low serum provides an optimal condition for the survival and proliferation of bovine spermatogonia because of avoiding the rapid growth of testis somatic cells.

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.

Germ cell differentiation in cryopreserved, immature, Indian spotted mouse deer (Moschiola indica) testes xenografted onto mice

Death of immature animals is one of the reasons for the loss of genetic diversity of rare and endangered species. Because sperm cannot be collected from immature males, cryobanking of testicular tissue combined with testis xenografting is a potential option for conservation. The objective of this study was to evaluate the establishment of spermatogenesis in cryopreserved immature testicular tissues from Indian spotted mouse deer (Moschiola indica) after ectopic xenografting onto immunodeficient nude mice. Results showed that testis tissues that were frozen in cryomedia containing either 10% DMSO with 80% fetal bovine serum (D10S80) or 20% DMSO with 20% fetal bovine serum (D20S20) had significantly more (P < 0.01) terminal deoxynucleotidyl transferase-mediated dUTP nick end labeled positive interstitial cells when compared with fresh testis tissues (46.3 ± 3.4 and 51.9 ± 4.0 vs. 22.8 ± 2.0). Xenografted testicular tissues showed degenerated seminiferous tubules 24 weeks after grafting in testes that had been cryopreserved in D20S20; alternatively, pachytene spermatocytes were the most advanced germ cells in testes that were cryopreserved in D10S80. Proliferating cell nuclear antigen staining confirmed the proliferative status of spermatocytes, and the increases in tubular and lumen diameters indicated testicular maturation in xenografts. However, persistent anti-Müllerian hormone staining in Sertoli cells of xenografts revealed incomplete testicular maturation. This study reports that cryopreserved testis tissue that had been xenografted from endangered animals onto mice resulted in the establishment of spermatogenesis with initiation of meiosis. These findings are encouraging for cryobanking of testicular tissues from immature endangered animals to conserve their germplasm.

Morphologic and proliferative characteristics of goat type A spermatogonia in the presence of different sets of growth factors

PURPOSE

The present study by using different growth factors was aimed to develop the best practical culture condition for purification of goat undifferentiated SSCs and their colonization under in vitro and in vivo conditions.

METHODS

The enzymatically isolated SSCs obtained from one month old goat testes were cultured in DMEM plus FCS supplemented with different sets of growth factors (GDNF, LIF, bFGF, and EGF) for 2 weeks. At the end of each week, the morphological characteristics of cells and colonies alongside with purification rate of undifferentiated type A spermatogonia were evaluated by immunocytochemical staining and flow cytometry.

RESULTS

The number and size of colonies in treatment groups were significantly (P < 0.01) higher than corresponding values in control group. In immunocytochemical evaluation, the proportion of KIT and PGP9.5 positive cells were significantly (P < 0.001) higher in control and treatment groups, respectively.

CONCLUSIONS

The culture medium comprising all four growth factors, especially the one supplemented with the higher concentration of GDNF, was superior to the other groups with respect to the population of undifferentiated type A spermatogonia and its propagation in culture system. Additionally, goat SSCs could colonize within the mouse testis following xenotransplantation.

Xenografting of testicular tissue pieces: 12 years of an in vivo spermatogenesis system

Spermatogenesis is a dynamic and complex process that involves endocrine and testicular factors. During xenotransplantation of testicular tissue fragments into immunodecifient mice, a functional communication between host brain and donor testis is established. This interaction allows for the progression of spermatogenesis and recovery of fertilisation-competent spermatozoa from a broad range of mammalian species. In the last few years, significant progress has been achieved in testis tissue xenografting that improves our knowledge about the factors determining the success of grafting. The goal of this review is to provide up to date information about the role of factors such as donor age, donor species, testis tissue preservation or type of recipient mouse on the efficiency of this technique. Applications are described and compared with other techniques with similar purposes. Recent work has demonstrated that testicular tissue xenografting is used as a model to study gonadotoxicity of drugs and to obtain sperm from valuable young males.

Spermatozoa isolated from cat testes retain their structural integrity as well as a developmental potential after refrigeration for up to 7 days

The objective of this study was to compare the efficiency of preservation media for isolated feline testicular spermatozoa as well as the concentrations of bovine serum albumin (BSA) on: (1) the membrane (sperm membrane integrity (SMI)) and DNA integrity of spermatozoa; and (2) the developmental potential of spermatozoa after intracytoplasmic sperm injection (ICSI). Isolated cat spermatozoa were stored in HEPES-M199 medium (HM) or Dulbecco's phosphate-buffered saline (DPBS) at 4°C for up to 7 days. Results indicated that HM maintained a better SMI than DPBS throughout the storage periods (P > 0.05). When spermatozoa were stored in HM supplemented with BSA at different concentrations (4, 8 or 16 mg/ml), SMI obtained from HM containing 8 and 16 mg/ml BSA was higher than with 4 mg/ml BSA (P < 0.05). DNA integrity of spermatozoa stored in HM with 16 mg/ml BSA for 7 days was poorer than that of the fresh control, but the subsequent percentages of cleavage, morula, blastocyst produced by ICSI, as well as their average blastomere numbers of blastocysts, were similar (P > 0.05). In summary, cat spermatozoa immediately isolated from testicular tissue can be stored as a suspension in basic buffered medium at 4°C for up to 7 days. BSA supplementation into the medium improves membrane integrity of the spermatozoa during cold storage. Testicular spermatozoa stored in HM containing 16 mg/ml BSA retained full in vitro developmental potential after ICSI, similar to that of fresh controls even though DNA integrity had slightly declined.

Genetic and Epigenetic Changes After Spermatogonial Stem Cell Culture and Transplantation

Men with testicular failure, either primary or secondary, have been shown to be interested in fertility preservation. Spermatogonial stem cell (SSC) transplantation is currently being investigated as a treatment for this. Currently this experimental technique consists of cryopreservation of a testicular biopsy prior to cancer treatment, followed by optional in vitro expansion of SSCs and auto transplantation after cancer treatment. This technique may restore the pool of SSCs resulting in restoration of spermatogenesis. While this technique has not been applied to humans due to its highly experimental nature and concerns of malignant contamination, animal studies have been successful. While the offspring obtained from SSCs appear to be healthy in rodent models, there is relatively little data on any genetic and epigenetic changes that occur in either the transplanted SSCs or offspring. In humans, male germ cells undergo unique and extensive chromatin and epigenetic remodeling soon after their destiny as a spermatocyte has been secured. Errors in this remodeling may cause altered genetic information to be transmitted to offspring, resulting in abnormalities. This is particularly pertinent for cancer patients as SSCs obtained from these men may have a predisposition for genetic instability even prior to starting gonadotoxic therapies. In this article, landmarks in the evolution of SSC transplantation are reviewed, along with presently known genetic, epigenetic, and imprinting abnormalities that may occur after in vitro propagation and transplantation.

Generation of live piglets for the first time using sperm retrieved from immature testicular tissue cryopreserved and grafted into nude mice

Cryopreservation of immature testicular tissues is essential for increasing the possibilities of offspring generation by testicular xenografting for agricultural or medical purposes. However, successful production of offspring from the sperm involved has never been reported previously. In the present study, therefore, using intracytoplasmic sperm injection (ICSI), we examined whether xenogeneic sperm obtained from immature pig testicular tissue after cryopreservation would have the capacity to produce live piglets. Testicular fragments from 9- to 11-day-old piglets were vitrified after 10- or 20-min immersion in vitrification solution containing ethylene glycol (EG), polyvinyl pyrrolidone (PVP) and trehalose as cryoprotectants, and then stored in liquid nitrogen for more than 140 days. Thirty nude mice were assigned to each immersion-time group. Testicular fragments were transplanted under the back skin of castrated mice immediately after warming and removal of the cryoprotectants. Blood and testicular grafts were then recovered from the recipient mice on days 60, 120, 180 and 230−350 (day 0 =  grafting). Histological assessment of the testicular grafts and analyses of inhibin and testosterone production revealed no significant differences between the two immersion-time groups, indicating equal growth activity of the cryopreserved tissues. A single sperm obtained from a mouse in each group on day 230−350 was injected into an in vitro-matured porcine oocyte, and then the ICSI oocytes were transferred to the oviducts of estrus-synchronized recipient gilts. One out of 4 gilts that had received oocytes fertilized using sperm from the 10-min immersion group delivered 2 live piglets, and one of another 4 gilts from the 20-min group delivered 4 live piglets. Thus, we have successfully generated porcine offspring utilizing sperm from immature testicular tissues after cryopreservation and transplantation into nude mice. The present model using pigs will be applicable to many large animals, since pigs are phylogenetically distant from the murine recipients.

Feasibility of salvaging genetic potential of post-mortem fawns: production of sperm in testis tissue xenografts from immature donor white-tailed deer (Odocoileus virginianus) in recipient mice

The purpose of this study was to evaluate the long-term outcome of testis tissue xenografting from immature deer. Testis tissue was collected post-mortem from a 2-mo-old white-tailed deer fawn (Odocoileus virginianus) and small fragments of the tissue were grafted under the back skin of immunodeficient recipient mice (n = 7 mice; 8 fragments/mouse). Single xenograft samples were removed from representative recipient mice every 2 mo from grafting for up to 14 mo post-grafting. The retrieved xenografts were evaluated for seminiferous tubular density (per mm(2)) and tubular diameter, as well as for seminiferous tubular morphology and identification of the most advanced germ cell type present in each tubule cross section. Overall, 63% of the grafted testis fragments were recovered as xenografts. Testis tissue xenografts showed a gradual testicular development starting with tubular expansion by 2 mo, presence of spermatocytes by 6 mo post-grafting, round and elongated spermatids by 8 mo, followed by fully-formed sperm by 12 mo post-grafting. The timing of complete spermatogenesis generally corresponded to the reported timing of sexual maturation in white-tailed deer. This study demonstrated, for the first time, that testis tissue xenografting from immature deer donors into recipient mice can successfully result in testicular maturation and development of spermatogenesis in the grafts up to the stage of sperm production. These results may therefore provide a model for salvaging genetic material from immature male white-tailed deer that die before reaching sexual maturity.

Isolation, identification, and culture of goat spermatogonial stem cells using c-kit and PGP9.5 markers

INTRODUCTION

Presently the techniques for making transgenic animals are cumbersome, required costly instruments and trained man-power. The ability of spermatogonial stem cells (SSCs) to integrate foreign genes has provided the opportunity for developing alternate methods for generation of transgenic animals. One of the big challenges in this field is development of the methods to identify and purify donor SSCs by antibody mediated cell sorting.

PURPOSE

The present study was aimed to identify goat subpopulations of SSCs using polyclonal antibodies against PGP9.5 and c-kit molecular markers as well as the growth characteristics of SSCs during short term culture.

METHODS

One month old goats' testicular samples were subjected for immunohistochemical and immunocytochemical evaluations. The enzymatically isolated SSCs were cultured in DMEM plus FCS supplemented with (treatment) or without (control) growth factors (GDNF, LIF, FGF, and EGF) for 2 weeks. At the end of culture the morphological characteristics of SSCs colonies and immunocytochemical staining were evaluated.

RESULTS

The number and size of colonies in treatment groups were significantly (P < 0.01) higher than corresponding values in controls. The presence of PGP 9.5 and c-kit antigens was confirmed in immunocytochemical evaluation. In immunocytochemical evaluation, the proportion of c-kit and PGP9.5 positive cells were significantly (P < 0.001) higher in control and treatment groups, respectively.

CONCLUSIONS

The presence of PGP9.5 and c-kit antigens was confirmed in goat SSCs. Moreover, culture medium supplementation with growth factors could effectively retain the undifferentiation status of SSCs, reflected as a higher population of PGP9.5 positive cells, after short term culture.

Germ cell transplantation and testis tissue xenografting in mice

Germ cell transplantation was developed by Dr. Ralph Brinster and colleagues at the University of Pennsylvania in 1994(1,2). These ground-breaking studies showed that microinjection of germ cells from fertile donor mice into the seminiferous tubules of infertile recipient mice results in donor-derived spermatogenesis and sperm production by the recipient animal(2). The use of donor males carrying the bacterial β-galactosidase gene allowed identification of donor-derived spermatogenesis and transmission of the donor haplotype to the offspring by recipient animals(1). Surprisingly, after transplantation into the lumen of the seminiferous tubules, transplanted germ cells were able to move from the luminal compartment to the basement membrane where spermatogonia are located(3). It is generally accepted that only SSCs are able to colonize the niche and re-establish spermatogenesis in the recipient testis. Therefore, germ cell transplantation provides a functional approach to study the stem cell niche in the testis and to characterize putative spermatogonial stem cells. To date, germ cell transplantation is used to elucidate basic stem cell biology, to produce transgenic animals through genetic manipulation of germ cells prior to transplantation(4,5), to study Sertoli cell-germ cell interaction(6,7), SSC homing and colonization(3,8), as well as SSC self-renewal and differentiation(9,10). Germ cell transplantation is also feasible in large species(11). In these, the main applications are preservation of fertility, dissemination of elite genetics in animal populations, and generation of transgenic animals as the study of spermatogenesis and SSC biology with this technique is logistically more difficult and expensive than in rodents. Transplantation of germ cells from large species into the seminiferous tubules of mice results in colonization of donor cells and spermatogonial expansion, but not in their full differentiation presumably due to incompatibility of the recipient somatic cell compartment with the germ cells from phylogenetically distant species(12). An alternative approach is transplantation of germ cells from large species together with their surrounding somatic compartment. We first reported in 2002, that small fragments of testis tissue from immature males transplanted under the dorsal skin of immunodeficient mice are able to survive and undergo full development with the production of fertilization competent sperm(13). Since then testis tissue xenografting has been shown to be successful in many species and emerged as a valuable alternative to study testis development and spermatogenesis of large animals in mice(14).