Isolation, genetic manipulation, and transplantation of canine spermatogonial stem cells: progress toward transgenesis through the male germ-line

Comparison of two methods of sperm- and testis-mediated gene transfer in production of transgenic animals: A systematic review

Transgenic (Tg) animal technology is one of the growing areas in biology. Various Tg technologies, each with its own advantages and disadvantages, are available for generating Tg animals. These include zygote microinjection, electroporation, viral infection, embryonic stem cell or spermatogonial stem cell-mediated production of Tg animals, sperm-mediated gene transfer (SMGT), and testis-mediated gene transfer (TMGT). However, there are currently no comprehensive studies comparing SMGT and TMGT methods, selecting appropriate gene delivery carriers (such as nanoparticles and liposomes), and determining the optimal route for gene delivery (SMGT and TMGT) for producing Tg animal. Here we aim to provide a comprehensive assessment comparing SMGT and TMGT methods, and to introduce the best carriers and gene transfer methods to sperm and testis to generate Tg animals in different species. From 2010 to 2022, 47 studies on SMGT and 25 studies on TMGT have been conducted. Mice and rats were the most commonly used species in SMGT and TMGT. Regarding the SMGT approach, nanoparticles, streptolysin-O, and virus packaging were found to be the best gene transfer methods for generating Tg mice. In the TMGT method, the best gene transfer methods for generating Tg mice and rats were virus packaging, dimethyl sulfoxide, electroporation, and liposome. Our study has shown that the efficiency of producing Tg animals varies depending on the species, gene carrier, and method of gene transfer.

Three-dimensional morphometry of the testis in dog using design-unbiased stereology

Testis is considered the main organ of the male reproductive system. Dogs are used as a suitable experimental model of testicular diseases in humans. From the veterinary aspect, several disorders have been reported to affect the testis in dogs. Thus, the objective of the present study was to investigate the morphometrical features of the dog testis using design-based stereology. The testes of six male dogs were used. Isotropic, uniform random sections were obtained and processed for light microscopy. Testicular total volume and the fractional volume of the seminiferous tubules, interstitial tissue and germinal epithelium were measured using the Cavalieri's estimator and the point counting system. Germinal epithelial surface area was estimated using test lines, and total length of seminiferous tubules was analysed using the counting frames. The total volume of testis was calculated 13.64 ± 1.94 cm3 . The relative volume fractions of the seminiferous tubules, interstitial tissue and germinal layer expressed as a percentage of total testicular volume were found to be 75.87 ± 6.11%, 23.68 ± 5.15% and 64.15 ± 4.82%, respectively. The surface area of the germinal layer was 915.25 ± 150.48 cm2 . The thickness of germinal layer was estimated to be 96.18 ± 10.72 μm. The total length of seminiferous tubules measured 290.8 ± 35.86 m. No statistical difference in investigated parameters was found between the left and right testes (p > 0.05). Our data might contribute to the male reproductive knowledge, help develop experimental studies in this field and possibly lead to advancement in the diagnosis and treatment of testicular diseases in the dog.

Optimizing Immature Testicular Tissue and Cell Transplantation Results: Comparing Transplantation Sites and Scaffolds

For patients who had testicular tissue cryopreserved before receiving gonadotoxic therapies, transplantation of testicular tissues and cells has been recommended as a potential therapeutic option. There are no studies that indicate the generation of sperm after human immature testicular tissue (ITT) or spermatogonial stem cells (SSCs) transplantation. The use of releasing scaffolds and localized drug delivery systems as well as the optimizing transplantation site can play an effective role in increasing the efficiency and improving the quality of testicular tissue and cell transplantation in animal models. Current research is focused on optimizing ITT and cell transplantation, the use of releasing scaffolds, and the selection of the right transplantation site that might restore sperm production or male infertility treatment. By searching the PubMed and Google Scholar databases, original and review papers were collected. Search terms were relevant for SSCs and tissue transplantation. In this review, we'll focus on the potential advantages of using scaffolds and choosing the right transplantation site to improve transplantation outcomes.

Porcine Germ Cells Phenotype during Embryonic and Adult Development

Primordial germ cells (PGCs) are the precursors of gametes. Due to their importance for the formation and reproduction of an organism, understanding the mechanisms and pathways of PGCs and the differences between males and females is essential. However, there is little research in domestic animals, e.g., swine, regarding the epigenetic and pluripotency profiles of PGCs during development. This study analyzed the expression of epigenetic and various pluripotent and germline markers associated with the development and differentiation of PGCs in porcine (pPGCs), aiming to understand the different gene expression profiles between the genders. The analysis of gonads at different gestational periods (from 24 to 35 days post fertilization (dpf) and in adults) was evaluated by immunofluorescence and RT-qPCR and showed phenotypic differences between the gonads of male and female embryos. In addition, the pPGCs were positive for OCT4 and VASA; some cells were H3k27me3 positive in male embryos and adult testes. In adults, the cells of the testes were positive for germline markers, as confirmed by gene expression analysis. The results may contribute to understanding the pPGC pathways during reproductive development, while also contributing to the knowledge needed to generate mature gametes in vitro.

Detection of spermatogonial stem cells in testicular tissue of dogs with chronic asymptomatic orchitis

Chronic asymptomatic idiopathic orchitis (CAO) is an important but neglected cause of acquired infertility due to non-obstructive azoospermia (NOA) in male dogs. The similarity of the pathophysiology in infertile dogs and men supports the dog's suitability as a possible animal model for studying human diseases causing disruption of spermatogenesis and evaluating the role of spermatogonial stem cells (SSCs) as a new therapeutic approach to restore or recover fertility in cases of CAO. To investigate the survival of resilient stem cells, the expression of the protein gene product (PGP9.5), deleted in azoospermia like (DAZL), foxo transcription factor 1 (FOXO1) and tyrosine-kinase receptor (C-Kit) were evaluated in healthy and CAO-affected canine testes. Our data confirmed the presence of all investigated germ cell markers at mRNA and protein levels. In addition, we postulate a specific expression pattern of FOXO1 and C-Kit in undifferentiated and differentiating spermatogonia, respectively, whereas DAZL and PGP9.5 expressions were confirmed in the entire spermatogonial population. Furthermore, this is the first study revealing a significant reduction of PGP9.5, DAZL, and FOXO1 in CAO at protein and/or gene expression level indicating a severe disruption of spermatogenesis. This means that chronic asymptomatic inflammatory changes in CAO testis are accompanied by a significant loss of SSCs. Notwithstanding, our data confirm the survival of putative stem cells with the potential of self-renewal and differentiation and lay the groundwork for further research into stem cell-based therapeutic options to reinitialize spermatogenesis in canine CAO-affected patients.

Effects of therapeutic ultrasound and moderate heat on stallion testes

Transplantation of stem cells into dysfunctional testes is currently being investigated as a therapeutic option for men and stallions with advanced testicular degeneration. This series of "proof of concept" studies aimed to identify a safe and efficient method of inducing severe testicular degeneration to create an optimal equine recipient model for intratesticular stem cell transplantation (SCT). Two ex vivo and two in vivo experiments were conducted. At first, forty testes obtained from castrations were used to identify an effective therapeutic ultrasound (TUS) device and the protocol for increasing intratesticular temperature in stallions. Six min of treatment using the Vetrison Clinic Portable TUS machine raised the intratesticular temperature by 8°C-12.5 °C. This protocol was applied to treat three scrotal testes in three Miniature horse stallions, three times, every other day. Contralateral testes served as controls. There were signs of slight tubular degeneration in treated testes two and three weeks after TUS treatment. The number of seminiferous tubules (STs) with exfoliated germ cells (GCs) was increased in one testis only, three weeks after treatment. The degree of apoptosis of GCs was higher in each treated testis in comparison to the contralateral control testis. Next, the ability of various heating devices to increase intratesticular temperatures to at least 43 °C in stallion testes was tested, using twenty testes obtained from castrations. ThermaCare® Lower Back & Hip Pain Therapy Heatwrap (TC heat wrap) reliably increased intratesticular temperatures and kept them continuously between 43 °C and 48 °C for seven to 8 h. In the follow-up in vivo study, the left testes of three Miniature horse stallions were treated with TUS, after which both testes of each stallion were treated with moderate heat provided by the TC heat wrap (three times, every other day, for 5 h each time). There were signs of moderate tubular degeneration in the samples from all treated testes obtained three weeks after treatments (Heat only or Heat/TUS): areas with hypospermatogenesis, spermatogenic arrest, vacuolized Sertoli cells, numerous STs with exfoliated GCs, increased degree of GCs apoptosis, and changes in three histomorphometric numeric attributes of STs. We concluded that TUS or TC wraps increase intratesticular temperature of the isolated stallion testes. Further, treatment with TUS or moderate heat may induce mild to moderate degenerative changes in stallion testes. However, to achieve more robust result - severe testicular degeneration, our treatment protocol has to be modified.

Nanoscale level gelatin-based scaffolds enhance colony formation of porcine testicular germ cells

The extracellular matrix is important in cell growth, proliferation, and differentiation. Gelatin, a support for adhering cells, is used for coating culture plate surfaces of several primary and stem cells. However, gelatin characteristics on culture plates and its cell interactions are not understood. Here, we aimed to identify the effect of gelatin topography on culture plates on the proliferation and colony formation of porcine spermatogonial germ cells (pSGC). To generate different surface topographies, gelatin powder was dissolved in H₂O at varying melting temperatures (40, 60, 80, and 120 °C) and coated on the surface of the culture plates. At 40 °C, the pores of the gelatin scaffold were regular ellipses 5-6 μm in diameter and 10-30 nm in thickness. However, at 120 °C, irregular pores 20-30 μm in diameter and 10-20 nm in thickness were obtained. Additionally, the number of attached cells and pSGC colonies were significantly more at 40 °C than at 120 °C after a week of culture. Interestingly, the feeder cells did not settle properly at 120 °C but detached easily from the culture dishes. PSGC colonies were 100 μm in diameter at 40 °C, with small and detached colonies observed at 120 °C. Thus, optimal topography of gelatin was obtained at 40 °C, which was sufficient for the proliferation of feeder cells and the formation of pSGC colonies. Thus, gelatin scaffold conditions at 40 °C and 60 °C were optimal for the derivation and culture of pSGC, and gelatin surface morphology is important for the maintenance of supportive feeder cells for pSGC proliferation and colony formation.

Sertoli, Leydig, and Spermatogonial Cells’ Specific Gene and Protein Expressions as Dog Testes Evolve from Immature into Mature States

Sertoli, Leydig, and spermatogonial cells proliferate and differentiate from birth to puberty and then stay stable in adulthood. We hypothesized that expressions of spermatogenesis-associated genes are not enhanced with a mere increase of these cells’ numbers. To accept this postulation, we investigated the abundances of Sertoli cell-specific FSHR and AMH, Leydig cell-specific LHR and INSL3, and spermatogonia-specific THY1 and CDH1 markers in immature and mature canine testis. Four biological replicates of immature and mature testes were processed, and RT-PCR was performed to elucidate the cells’ specific markers. The data were analyzed by ANOVA, using the 2−∆∆Ct method to ascertain differences in mRNA expressions. In addition, Western blot and IHC were performed. Gene expressions of all the studied cells’ specific markers were down-regulated (p < 0.05) in adult testis compared with immature testis. Western blot and immunohistochemistry showed the presence of these proteins in the testis. Protein expressions were greater in immature testis compared with mature testis (p < 0.05). Despite the obvious expansion of these cells’ numbers from immature to adult testis, the cells’ specific markers were not enriched in mature testis compared with immature dog testis. The results support the postulation that the gene expressions do not directly correlate with the increase of the cell numbers during post-natal development but changes in gene expressions show functional significance.

In vitro propagation of XXY human Klinefelter spermatogonial stem cells: A step towards new fertility opportunities

Klinefelter Syndrome (KS) is characterized by a masculine phenotype, supernumerary sex chromosomes (47, XXY), and impaired fertility due to loss of spermatogonial stem cells (SSCs). Early testicular cryopreservation could be an option for future fertility treatments in these patients, including SSCs transplantation or in vitro spermatogenesis. It is critically essential to adapt current in vitro SSCs propagation systems as a fertility option for KS patients. KS human testicular samples (13,15- and 17-year-old non-mosaic KS boys) were donated by patients enrolled in an experimental testicular tissue banking program. Testicular cells were isolated from cryopreserved tissue and propagated in long-term culture for 110 days. Cell-specific gene expression confirmed the presence of all four main cell types found in testes: Spermatogonia, Sertoli, Leydig, and Peritubular cells. A population of ZBTB16⁺ undifferentiated spermatogonia was identified throughout the culture using digital PCR. Flow cytometric analysis also detected an HLA^-/CD9⁺/CD49f⁺ population, indicating maintenance of a stem cell subpopulation among the spermatogonial cells. FISH staining for chromosomes X and Y showed most cells containing an XXY karyotype with a smaller number containing either XY or XX. Both XY and XX populations were able to be enriched by magnetic sorting for CD9 as a spermatogonia marker. Molecular karyotyping demonstrated genomic stability of the cultured cells, over time. Finally, single-cell RNAseq analysis confirmed transcription of ID4, TCN2, and NANOS 3 within a population of putative SSCs population. This is the first study showing successful isolation and long-term in vitro propagation of human KS testicular cells. These findings could inform the development of therapeutic fertility options for KS patients, either through in vitro spermatogenesis or transplantation of SSC, in vivo.

Spermatogonial Stem Cell Transplantation in Large Animals

Simple Summary

The spermatogonial stem cell (SSC) is the only adult stem cell in males to transmit genetic information to offspring. SSC transplantation (SSCT) is a laboratory technique to regenerate spermatogenesis in recipient males, thus can be used as a novel breeding tool to benefit animal production. Although successful SSCT in rodent models has been established, progress in realizing SSCT in large animals has been limited. Here we discuss what we learned in this area from past experiments and highlight possible directions in developing effective SSCT protocol in large animals.

Abstract

Spermatogonial stem cell transplantation (SSCT) can restore male fertility through transfer of germline between donor and recipient males. From an agricultural perspective, SSCT could be an important next-generation reproductive and breeding tool in livestock production. Current SSCT approaches in large animals remain inefficient and many technical details need further investigation. This paper reviews the current knowledge on SSCT in large animals, addressing (1) donor spermatogonial stem cell (SSC) preparation, (2) recipient male treatment, and (3) SSC injection, homing, and detection. The major studies showing unequivocal evidence of donor SSC-derived spermatogenesis in large animals (mainly in livestock for breeding purpose) are summarized to discuss the current status of the field and future directions.

Step by Step about Germ Cells Development in Canine

Simple Summary

The progression of germ cells is a remarkable event that allows biological discovery in the differ-entiation process during in vivo and in vitro development. This is crucial for understanding one toward making oogenesis and spermatogenesis. Companion animals, such as canine, could offer new animal models for experimental and clinical testing for translation to human models. In this review, we describe the latest and more relevant findings on germ cell development. In addition, we showed the methods available for obtaining germ cells in vitro and the characterization of pri-mordial germ cells and spermatogonial stem cells. However, it is necessary to further conduct basic research in canine to clarify the beginning of germ cell development.

Abstract

Primordial germ cells (PGCs) have been described as precursors of gametes and provide a connection within generations, passing on the genome to the next generation. Failures in the formation of gametes/germ cells can compromise the maintenance and conservation of species. Most of the studies with PGCs have been carried out in mice, but this species is not always the best study model when transposing this knowledge to humans. Domestic animals, such as canines (canine), have become a valuable translational research model for stem cells and therapy. Furthermore, the study of canine germ cells opens new avenues for veterinary reproduction. In this review, the objective is to provide a comprehensive overview of the current knowledge on canine germ cells. The aspects of canine development and germ cells have been discussed since the origin, specifications, and development of spermatogonial canine were first discussed. Additionally, we discussed and explored some in vitro aspects of canine reproduction with germ cells, such as embryonic germ cells and spermatogonial stem cells.

Cryopreservation of grey wolf (Canis lupus) testicular tissue

Development of genomic preservation technologies for canids, especially for seasonally breeding species like the grey wolf (Canis lupus), is needed in advance of growing species conservation concerns. Here, we evaluated the efficacy of two cryopreservation protocols - needle immersion vitrification (NIV) and slow freezing (SF) on grey wolf (n = 7) testicular tissue morphology. NIV samples were equilibrated in a 7.5% v/v dimethyl sulfoxide (DMSO or Me2SO) + 7.5% ethylene glycol (EG) solution in minimum essential medium with 20% FBS for 10 min at 4 °C, then exposed to 15% DMSO + 15% EG + 0.5 M sucrose for 10 min at 4 °C before plunging into liquid nitrogen. For slow freezing, we assessed two cryoprotectant (CPA) strategies, DMSO, 15% v/v alone (SF-D) or 7.5% EG + 7.5% DMSO (SF-ED). Following thawing, there were no significant differences in seminiferous tubule area among treatment groups, although all cryopreserved tissues displayed reduced tubule size compared with fresh controls and increased apoptosis, the latter reaching significance for SF-D treated tissues. Slow freezing improved maintenance of testis architecture, with minimal detachment of seminiferous tubule basement membranes post-thaw. Spermatogonia densities were reduced in NIV tissues compared with fresh, with no differences in spermatocyte, spermatid, or Sertoli cell counts, or germ cell marker DDX4⁺ cell densities among groups. In sum, we conclude that slow freezing better maintained morphology of cryopreserved testicular tissues compared with needle vitrification with 15% each DMSO and EG and 0.5 M sucrose, and that DMSO + EG combination SF supports cell viability. This represents a first step in the development of male gonadal tissue preservation strategies for the grey wolf.

Review of injection techniques for spermatogonial stem cell transplantation

BACKGROUND

Although the prognosis of childhood cancer survivors has increased dramatically during recent years, chemotherapy and radiation treatments for cancer and other conditions may lead to permanent infertility in prepubertal boys. Recent developments have shown that spermatogonial stem cell (SSC) transplantation may be a hope for restoring fertility in adult survivors of childhood cancers. For this reason, several centres around the world are collecting and cryopreserving testicular tissue or cells anticipating that, in the near future, some patients will return for SSC transplantation. This review summarizes the current knowledge and utility of SSC transplantation techniques.

OBJECTIVE AND RATIONALE

The aim of this narrative review is to provide an overview of the currently used experimental injection techniques for SSC transplantation in animal and human testes. This is crucial in understanding and determining the role of the different techniques necessary for successful transplantation.

SEARCH METHODS

A comprehensive review of peer-reviewed publications on this topic was performed using the PubMed and Google Scholar databases. The search was limited to English language work and studies between 1994 (from the first study on SSC transplantation) and April 2019. Key search terms included mouse, rat, boar, ram, dog, sheep, goat, cattle, monkey, human, cadaver, testes, SSC transplantation, injection and technique.

OUTCOMES

This review provides an extensive clinical overview of the current research in the field of human SSC transplantation. Rete testis injection with ultrasonography guidance currently seems the most promising injection technique thus far; however, the ability to draw clear conclusions is limited due to long ischemia time of cadaver testis, the relatively decreased volume of the testis, the diminishing size of seminiferous tubules, a lack of intratesticular pressure and leakage into the interstitium during the injection on human cadaver testis. Current evidence does not support improved outcomes from multiple infusions through the rete testes. Overall, further optimization is required to increase the efficiency and safety of the infusion method.

WIDER IMPLICATIONS

Identifying a favourable injection method for SSC transplantation will provide insight into the mechanisms of successful assisted human reproduction. Future research could focus on reducing leakage and establishing the optimal infusion cell concentrations and pressure.

Spermatogonial stem cells

Spermatogonial stem cells (SSCs) are the most primitive spermatogonia in the testis and have an essential role to maintain highly productive spermatogenesis by self-renewal and continuous generation of daughter spermatogonia that differentiate into spermatozoa, transmitting genetic information to the next generation. Since the 1950s, many experimental methods, including histology, immunostaining, whole-mount analyses, and pulse-chase labeling, had been used in attempts to identify SSCs, but without success. In 1994, a spermatogonial transplantation method was reported that established a quantitative functional assay to identify SSCs by evaluating their ability to both self-renew and differentiate to spermatozoa. The system was originally developed using mice and subsequently extended to nonrodents, including domestic animals and humans. Availability of the functional assay for SSCs has made it possible to develop culture systems for their ex vivo expansion, which dramatically advanced germ cell biology and allowed medical and agricultural applications. In coming years, SSCs will be increasingly used to understand their regulation, as well as in germline modification, including gene correction, enhancement of male fertility, and conversion of somatic cells to biologically competent male germline cells.

Xenotransplantation of canine spermatogonial stem cells (cSSCs) regulated by FSH promotes spermatogenesis in infertile mice

Background

Xenotransplantation of spermatogonial stem cells (SSCs) has become a popular topic in various research fields because manipulating these cells can provide insights into the mechanisms associated with germ cell lines and the entire spermatogenesis process; moreover, these cells can be used in several biotechnology applications. To achieve successful xenotransplantation, the in vitro microenvironment in which SSCs are cultured should be an ideal microenvironment for self-renewal and similar to the in vivo testicular microenvironment. The age of the donor, the correct spermatogenesis cycle, and the quality of the donor tissue are also important. Although cell culture-related factors, such as the in vitro supplementation of hormonal factors, are known to promote successful xenotransplantation in mice, little is known about the influence of these factors on SSCs in vitro or in vivo in other mammalian species, such as dogs (Canis lupus familiaris). In this context, the goals of this study were to test the effect of follicle-stimulating hormone (FSH) on canine spermatogonial stem cell (cSSC) cultures since this hormone is related to the glial cell-derived neurotrophic factor (GDNF) signaling pathway, which is responsible for the self-renewal and maintenance of these cells in vivo, and to investigate the microenvironment of the SSC culture after FSH supplementation. Additionally, in vivo analyses of transplanted FSH-supplemented cSSCs in the testes of infertile mice were performed to assess the capacity of cSSCs to develop, maintain, and restore spermatogenesis.

Methods

SSCs from canine prepubertal testes (aged 3 months) were cultured in vitro in the presence of FSH (10 IU L⁻¹). GFRA1 transcript expression was detected to confirm the spermatogonia population in culture and the effect of FSH on these cells. The protein and transcript levels of late germ cell markers (GFRA1, DAZL, STRA8, PLZF, and CD49f) and a pluripotency marker (OCT4) were detected at 72 and 120 h to confirm the cSSC phenotype. In vivo experiments were performed by transplanting GFP+ cSSCs into infertile mice, and a 10-week follow-up was performed. Histological and immunofluorescence analyses were performed to confirm the repopulation capacity after cSSC xenotransplantation in the testis.

Results

Supplementation with FSH in cell culture increased the number of cSSCs positive for GFRA1. The cSSCs were also positive for the pluripotency and early germline marker OCT4 and the late germline markers PLZF, DAZL, C-kit, and GFRA-1. The in vivo experiments showed that the cSSCs xenotransplanted into infertile mouse testes were able to repopulate germline cells in the seminiferous tubules of mice.

Conclusions

In conclusion, our results showed for the first time that the treatment of cSSC cultures with FSH can promote in vitro self-renewal, increase the population of germline cells, and possibly influence the success of spermatogenesis in infertile mice in vivo.

Stem cells on regenerative and reproductive science in domestic animals

Stem cells are undifferentiated and self-renewable cells that present new possibilities for both regenerative medicine and the understanding of early mammalian development. Adult multipotent stem cells are already widely used worldwide in human and veterinary medicine, and their therapeutic signalling, particularly with respect to immunomodulation, and their trophic properties have been intensively studied. The derivation of embryonic stem cells (ESCs) from domestic species, however, has been challenging, and the poor results do not reflect the successes obtained in mouse and human experiments. More recently, the generation of induced pluripotent stem cells (iPSCs) via the forced expression of specific transcription factors has been demonstrated in domestic species and has introduced new potentials in regenerative medicine and reproductive science based upon the ability of these cells to differentiate into a variety of cells types in vitro. For example, iPSCs have been differentiated into primordial germ-like cells (PGC-like cells, PGCLs) and functional gametes in mice. The possibility of using iPSCs from domestic species for this purpose would contribute significantly to reproductive technologies, offering unprecedented opportunities to restore fertility, to preserve endangered species and to generate transgenic animals for biomedical applications. Therefore, this review aims to provide an updated overview of adult multipotent stem cells and to discuss new possibilities introduced by the generation of iPSCs in domestic animals, highlighting the possibility of generating gametes in vitro via PGCL induction.

Establishment of a surgically induced cryptorchidism canine recipient model for spermatogonial stem cell transplantation

Transplantation of spermatogonial stem cells (SSCs) in experimental animal models has been used to study germ line stem cell biology and to produce transgenic animals. The species-specific recipient model preparation is important for the characterization of SSCs and the production of offspring. Here, we investigated the effects of surgically induced cryptorchidism in dog as a new recipient model for spermatogonial stem cell transplantation. Artificially unilateral or bilateral cryptorchidism was induced in ten mature male dogs by surgically returning the testis and epididymis to the abdominal cavity. The testes and epididymides were collected every week after the induction of artificial cryptorchidism (surgery) for one month. To determine the effect of surgical cryptorchidism, the seminiferous tubule diameter was measured and immunohistochemistry using PGP9.5 and GATA4 antibodies was analyzed. The diameters of the seminiferous tubules of abdominal testes were significantly reduced compared to those of the scrotal testes. Immunohistochemistry results showed that PGP9.5 positive undifferentiated spermatogonia were significantly reduced after surgical cryptorchidism induction, but there were no significant changes in GATA-4 positive sertoli cells. To evaluate the testis function recovery rate, orchiopexy was performed on two dogs after 30 days of bilateral cryptorchidism. In the orchiopexy group, SCP3 positive spermatocytes were detected, and spermatogenesis was recovered 8 weeks after orchiopexy. In this study, we provided optimum experimental conditions and time for surgical preparation of a recipient canine model for SSC transplantation. Additionally, our data will contribute to recipient preparation by using surgically induced cryptorchidism in non-rodent species.

Immunolocalization of proteins in the spermatogenesis process of canine

Spermatogenesis is a process in which differentiated cells are produced and the adult stem cell population-known as spermatogonial stem cells (SSCs)-is continuously replenished. However, the molecular mechanisms underlying these processes are not fully understood in the canine species. We addressed this in this study by analysing the expression of specific markers in spermatogonia of seminiferous tubules of canine testes. SSCs at different stages of reproductive development (prepubertal and adult) were examined by immunohistochemistry and flow cytometry. Glial cell-derived neurotrophic factor family receptor alpha-1 (GFRA1), deleted in azoospermia-like (DAZL) and promyelocytic leukaemia zinc finger (PLZF) were expressed in SSCs, while stimulated by retinoic acid gene 8 (STRA8) was detected only in undifferentiated spermatogonia in prepubertal testis and differentiated spermatogonia and spermatocytes in adult canine. Octamer-binding transcription factor 4 (OCT4) showed an expression pattern, and the levels did not differ between the groups examined. However, C-kit expression varied as a function of reproductive developmental stage. Our results demonstrate that these proteins play critical roles in the self-renewal and differentiation of SSCs and can serve as markers to identify canine spermatogonia at specific stages of development.

Conservation of spermatogonial stem cell marker expression in undifferentiated felid spermatogonia

Spermatogonial stem cells (SSCs) are distinct in their ability to self-renew, transmit genetic information, and persist throughout the life of an individual. These characteristics make SSCs a useful tool for addressing diverse challenges such as efficient transgenic production in nonrodent, biomedical animal models, or preservation of the male genome for species in which survival of frozen-thawed sperm is low. A requisite first step to access this technology in felids is the establishment of molecular markers. This study was designed to evaluate, in the domestic cat (Felis catus), the expression both in situ and following enrichment in vitro of six genes (GFRA1, GPR125, ZBTB16, POU5F1, THY1, and UCHL1) that had been previously identified as SSC markers in other species. Antibodies for surface markers glial cell line-derived neurotrophic factor family receptor alpha 1, G protein-coupled receptor 125, and thymus cell antigen 1 could not be validated, whereas Western blot analysis of prepubertal, peripubertal, and adult cat testis confirmed protein expression for the intracellular markers ubiquitin carboxy-terminal hydrolase 1, zinc finger and BTB domain-containing protein 16, and POU domain, class 5, transcription factor 1. Colocalization of the markers by immunohistochemistry revealed that several cells within the subpopulation adjacent to the basement membrane of the seminiferous tubules and identified morphologically as spermatogonia, expressed all three intracellular markers. Studies performed on cheetah (Acinonyx jubatus) and Amur leopard (Panthera pardus orientalis) testis exhibited a conserved expression pattern in protein molecular weights, relative abundance, and localization of positive cells within the testis. The expression of the three intracellular SSC marker proteins in domestic and wild cat testes confirms conservation of these markers in felids. Enrichment of marker transcripts after differential plating was also observed. These markers will facilitate further studies in cell enrichment and IVC of felid SSCs enabling both production of transgenic domestic cats and preservation of the male genome from rare and endangered felids.

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.

Isolation and Identification of Prepubertal Buffalo (Bubalus bubalis) Spermatogonial Stem Cells

Isolation and culture of spermatogonial stem cells (SSCs) are attractive for production of genetic modified offspring. In the present study, buffalo spermatogonial stem-like cells were isolated, cultured and expression pattern of different germ cell marker genes were determined. To recover spermatogonia, testes from age 3 to 7 months of buffalo were decapsulated, and seminiferous tubules were enzymatically dissociated. Two types of cells, immature sertoli cell and type A spermatogonia were observed in buffalo testes in this stage. Germ cell marker genes, OCT3/4 (Pou5f1), THY-1, c-kit, PGP9.5 (UCHL-1) and Dolichos biflorus agglutinin, were determined to be expressed both in mRNA and protein level by reverse transcription polymerase chain reaction and immunostaining in buffalo testes and buffalo spermatogonial stem-like cells, respectively. In the following, when the isolated buffalo buffalo spermatogonial stem-like cells were cultured in the medium supplemented 2.5% fetal bovine serum and 40 ng/mL glial cell-derived neurotrophic factor medium, SSCs proliferation efficiency and colony number were significantly improved than those of other groups (p<0.05). These findings may help in isolation and establishing long term in vitro culture system for buffalo spermatogonial stem-like cells, and accelerating the generation of genetic modified buffaloes.

Establishment and characterization of a telomerase-immortalized canine bronchiolar epithelial cell line

Dogs are susceptible to infectious diseases that occur primarily in the respiratory tract. The airway epithelium acts as a first line of defense and is constantly exposed to microorganisms present in the environment. Respiratory epithelial cells have recently gained wide use as a cell model for studying the pathogenesis of human, murine or swine respiratory pathogen infections. However, studies of the pathogenic mechanisms of canine pathogens have been hindered by the lack of reliable respiratory cell lines. Here, we cultured primary canine bronchiolar epithelial cells (CBECs), whose characteristics were confirmed by their expression of the epithelial cell-specific marker cytokeratin 18, and have provided protocols for their isolation and ex vivo expansion. Further, we established immortalized CBECs containing the human telomerase reverse transcriptase (hTERT) gene via transfection of primary CBECs with the recombinant plasmid pEGFP-hTERT. Immortalized bronchiolar epithelial cells (hTERT-CBECs) retain the morphological and functional features of primary CBECs, as indicated by reverse transcriptase polymerase chain reaction, proliferation assays, karyotype analysis, telomerase activity assay, and Western blotting, which demonstrate that hTERT-CBECs have higher telomerase activity, an extended proliferative lifespan, and a diploid complement of chromosomes, even after Passage 50. Moreover, this cell line is not transformed, as evaluated using soft agar assays and tumorigenicity analysis in nude mice, and can therefore be safely used in future studies. The isolation and establishment of stable hTERT-CBECs is of great importance for use as an in vitro model for mechanistic studies of canine pathogenic infections.

Spermatogonial stem cells: Current biotechnological advances in reproduction and regenerative medicine

Spermatogonial stem cells (SSCs) are the germ stem cells of the seminiferous epithelium in the testis. Through the process of spermatogenesis, they produce sperm while concomitantly keeping their cellular pool constant through self-renewal. SSC biology offers important applications for animal reproduction and overcoming human disease through regenerative therapies. To this end, several techniques involving SSCs have been developed and will be covered in this article. SSCs convey genetic information to the next generation, a property that can be exploited for gene targeting. Additionally, SSCs can be induced to become embryonic stem cell-like pluripotent cells in vitro. Updates on SSC transplantation techniques with related applications, such as fertility restoration and preservation of endangered species, are also covered on this article. SSC suspensions can be transplanted to the testis of an animal and this has given the basis for SSC functional assays. This procedure has proven technically demanding in large animals and men. In parallel, testis tissue xenografting, another transplantation technique, was developed and resulted in sperm production in testis explants grafted into ectopical locations in foreign species. Since SSC culture holds a pivotal role in SSC biotechnologies, current advances are overviewed. Finally, spermatogenesis in vitro, already demonstrated in mice, offers great promises to cope with reproductive issues in the farm animal industry and human clinical applications.