The effects of growth factors on in vitro-cultured porcine testicular cells

Testicular niche repair after gonadotoxic treatments: Current knowledge and future directions

The testicular niche, which includes the germ cells, somatic cells, and extracellular matrix, plays a crucial role in maintaining the proper functions of the testis. Gonadotoxic treatments, such as chemotherapy and radiation therapy, have significantly improved the survival rates of cancer patients but have also been shown to have adverse effects on the testicular microenvironment. Therefore, repairing the testicular niche after gonadotoxic treatments is essential to restore its function. In recent years, several approaches, such as stem cell transplantation, gene therapy, growth factor therapy, and pharmacological interventions have been proposed as potential therapeutic strategies to repair the testicular niche. This comprehensive review aims to provide an overview of the current understanding of testis damage and repair mechanisms. We will cover a range of topics, including the mechanism of gonadotoxic action, repair mechanisms, and treatment approaches. Overall, this review highlights the importance of repairing the testicular niche after gonadotoxic treatments and identifies potential avenues for future research to improve the outcomes for cancer survivors.

Strategies for the Generation of Gene Modified Avian Models: Advancement in Avian Germline Transmission, Genome Editing, and Applications

Avian models are valuable for studies of development and reproduction and have important implications for food production. Rapid advances in genome-editing technologies have enabled the establishment of avian species as unique agricultural, industrial, disease-resistant, and pharmaceutical models. The direct introduction of genome-editing tools, such as the clustered regularly interspaced short palindromic repeats (CRISPR) system, into early embryos has been achieved in various animal taxa. However, in birds, the introduction of the CRISPR system into primordial germ cells (PGCs), a germline-competent stem cell, is considered a much more reliable approach for the development of genome-edited models. After genome editing, PGCs are transplanted into the embryo to establish germline chimera, which are crossed to produce genome-edited birds. In addition, various methods, including delivery by liposomal and viral vectors, have been employed for gene editing in vivo. Genome-edited birds have wide applications in bio-pharmaceutical production and as models for disease resistance and biological research. In conclusion, the application of the CRISPR system to avian PGCs is an efficient approach for the production of genome-edited birds and transgenic avian models.

Primary Cultures of Spermatogonia and Testis Cells

Spermatogonial stem cells (SSCs) maintain adult spermatogenesis in mammals by undergoing self-renewal and differentiation into spermatozoa. In order to study the biology of SSCs as related to spermatogenesis, an in vitro, long-term expansion system of SSCs constitutes an ideal tool. In this chapter, we describe a robust culture system for mouse and rat SSCs in vitro. In the presence of GDNF, GFRα1, and bFGF, SSCs maintained on STO feeder layers with serum-free medium continuously proliferate for over 6 months. Complete spermatogenesis in infertile recipient mice can be attained following transplantation of the cultured mouse and rat SSCs. Using the in vitro SSC culture systems, elucidation of stem cell biology can be advanced that significantly advances our understanding of spermatogenesis and male fertility.

Long-Term In Vitro Maintenance of Piglet Testicular Tissue: Effects of Tissue Fragment Size, Preparation Method, and Serum Source

Long-term culture of testicular tissue has important applications, including the preservation of fertility potential of prepubertal boys undergoing gonadotoxic cancer treatment. This study was designed to define optimal conditions for the long-term culture of neonatal porcine testicular tissue as an animal model for preadolescent individuals. Testes from 1 wk old donor piglets were used to examine the effects of tissue fragment size (~2, 4, 6, or 8 mg), preparation method (intact, semi-digested, or physically dispersed fragments), and serum source in the media (fetal bovine serum—FBS—or knockout serum replacement—KSR). Testicular fragments were examined weekly for 4 weeks for tissue integrity, seminiferous cord density and morphology, and gonocyte counts. Testicular tissue integrity was dependent on fragment size and preparation method, where the smallest size (2 mg, p < 0.05) and intact preparation method were advantageous (p < 0.05). Seminiferous cord density decreased over the culture period (p < 0.05). Although the relative number of gonocytes decreased over time for all sizes and methods (p < 0.01), smaller intact fragments (2 and 4 mg) had greater numbers of gonocytes (p < 0.05). Our findings suggest that intact or physically dispersed testicular fragments of the smallest size (2 mg) cultured in KSR-supplemented media could be effectively maintained in vitro for the duration of 4 weeks.

Gdnf Acts as a Germ Cell-Derived Growth Factor and Regulates the Zebrafish Germ Stem Cell Niche in Autocrine- and Paracrine-Dependent Manners

Glial cell line-derived neurotrophic factor (GDNF) and its receptor (GDNF Family Receptor α1-GFRα1) are well known to mediate spermatogonial stem cell (SSC) proliferation and survival in mammalian testes. In nonmammalian species, Gdnf and Gfrα1 orthologs have been found but their functions remain poorly investigated in the testes. Considering this background, this study aimed to understand the roles of the Gdnf-Gfrα1 signaling pathway in zebrafish testes by combining in vivo, in silico and ex vivo approaches. Our analysis showed that zebrafish exhibit two paralogs for Gndf (gdnfa and gdnfb) and its receptor, Gfrα1 (gfrα1a and gfrα1b), in accordance with a teleost-specific third round of whole genome duplication. Expression analysis further revealed that both ligands and receptors were expressed in zebrafish adult testes. Subsequently, we demonstrated that gdnfa is expressed in the germ cells, while Gfrα1a/Gfrα1b was detected in early spermatogonia (mainly in types A_und and A_diff) and Sertoli cells. Functional ex vivo analysis showed that Gdnf promoted the creation of new available niches by stimulating the proliferation of both type A_und spermatogonia and their surrounding Sertoli cells but without changing pou5f3 mRNA levels. Strikingly, Gdnf also inhibited late spermatogonial differentiation, as shown by the decrease in type B spermatogonia and down-regulation of dazl in a co-treatment with Fsh. Altogether, our data revealed that a germ cell-derived factor is involved in maintaining germ cell stemness through the creation of new available niches, supporting the development of spermatogonial cysts and inhibiting late spermatogonial differentiation in autocrine- and paracrine-dependent manners.

Culture supplementation of bFGF, GDNF, and LIF alters in vitro proliferation, colony formation, and pluripotency of neonatal porcine germ cells

Gonocytes in the neonatal testis have male germline stem cell properties and as such have important potential applications in fertility preservation and regenerative medicine. Such applications require further studies aimed at increasing gonocyte numbers and evaluating their pluripotency in vitro. The objective of the present study was to test the effects of basic fibroblast growth factor (bFGF), glial cell line-derived neurotrophic factor (GDNF), and leukemia inhibitory factor (LIF) on in vitro propagation, colony formation, and expression of pluripotency markers of neonatal porcine gonocytes. Testis cells from 1-week-old piglets were cultured in basic media (DMEM + 15% FBS), supplemented with various concentrations of bFGF, GDNF, and LIF, either individually or in combinations, in a stepwise experimental design. Gonocytes and/or their colonies were evaluated every 7 days and the gonocyte- (DBA) and pluripotency-specific markers (POU5F1, SSEA-1, E-cadherin, and NANOG) assessed on day 28. Greatest gonocyte numbers and largest colonies were found in media supplemented with 10 ng/mL bFGF and 10 ng/mL bFGF + 100 ng/mL GDNF + 1500 U/mL LIF, respectively. The resultant gonocytes and colonies expressed both germ cell- and pluripotency-specific markers. These results shed light on the growth hormone requirements of porcine gonocytes for in vitro proliferation and colony formation.

Isolation and in vitro expansion of porcine spermatogonial stem cells

Spermatogonial stem cells (SSCs) are the only adult stem cells capable of passing genetic information to offspring through their ability to both self-renew and differentiate into mature spermatozoa. SSCs can be transplanted to establish donor-derived spermatogenesis in recipient animals, thus offering a novel reproductive tool for multiplication of elite individual animals to benefit livestock production. An optimal SSC culture in vitro can benefit various SSC-based studies and applications, such as mechanistic study of SSC biology, SSC transplantation process and SSC-based transgenesis technique. However, except for some model rodent animals, SSC culture remains an inefficient and unstable process. We here studied a workflow to isolate, purify and in vitro culture porcine SSCs from neonatal pig testes. Pig testicular cells were dissociated by two-step enzymatic digestion with collagenase type IV and trypsin. We enriched the spermatogonia from the testicular cell mix by differential plating for at least 3 times to remove firmly attached non-SSCs. We then tested the optimal culture medium formula by supplementation of different growth factors to the basic medium (DMEM/F12 + 1% FBS) and found that a combination of 20 ng/ml GDNF, 10 ng/ml LIF, 20 ng/ml FGF2 and 20 ng/ml IGF1 had the best effect on SSC growth in our defined experimental system. In the presence of 4 growth factors without specific feeders, the purified SSCs can be cultured in poly-L-lysine- and laminin-coated dishes for 28 days and remain preserving a continuous proliferation without losing the undifferentiated spermatogonial phenotype.

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.

Live-cell imaging and ultrastructural analysis reveal remarkable features of cultured porcine gonocytes

Gonocytes in the neonatal testis have male germline stem cell potential. The objective of the present study was to examine the behavior and ultrastructure of gonocytes in culture. Neonatal porcine testis cells were cultured for 4 weeks and underwent live-cell imaging to explore real-time interactions among cultured cells. This included imaging every 1 h from day 0 to day 3, every 2 h from day 4 to day 7, and every 1 h for 24 h at days 14, 21, and 28. Samples also underwent scanning electron microscopy, transmission electron microscopy, morphometric evaluations, immunofluorescence, and RT-PCR. Live-cell imaging revealed an active amoeboid-like movement of gonocytes, assisted by the formation of extensive cytoplasmic projections, which, using scanning electron microscopy, were categorized into spike-like filopodia, leaf-like lamellipodia, membrane ruffles, and cytoplasmic blebs. In the first week of culture, gonocytes formed loose attachments on top of a somatic cell monolayer and, in week 2, formed grape-like clusters, which, over time, grew in cell number. Starting at week 3 of culture, some of the gonocyte clusters transformed into large multinucleated embryoid body-like colonies (EBLCs) that expressed both gonocyte- and pluripotent-specific markers. The number and diameter of individual gonocytes, the number and density of organelles within gonocytes, as well as the number and diameter of the EBLCs increased over time (P < 0.05). In conclusion, cultured porcine gonocytes displayed extensive migratory behavior facilitated by their various cytoplasmic projections, propagated, and transformed into EBLCs that increased in size and complexity over time.

Investigation of VASA Gene and Protein Expression in Neonate and Adult Testicular Germ Cells in Mice In Vivo and In Vitro

Objective

We aimed to examine the expression levels of the VASA gene and protein in testis sections of neonate and adult mice as well as testicular cell cultures.

Materials and Methods

In this experimental study, in order to investigate the expression of this germ cell marker gene in more detail, we analyzed the expression of VASA by immunocytochemistry, immunohistochemistry and fluidigm reverse transcription-polymerase chain reaction (RT-PCR).

Results

The immunohistochemical assays showed that the VASA protein was exclusively expressed in germ cells in the seminiferous tubules of the neonate and adult testis and not in somatic cells. VASA was not detectable in PLZF positive spermatogonial stem cells (SSCs), was weakly expressed in proliferating spermatogonia, and became abundant in spermatocytes and round spermatozoa. Counting VASA-positive cells in the seminiferous tubules of the neonate and adult testis depicted significant higher expression (P<0.05) of VASA in the adult testis in comparison to its neonate counterpart. SSC colonies were established in vitro after digestion of the testis and characterized by immunocytochemistry for CD90 and stage-specific embryonic antigens 3 (SSEA3). Immunocytochemistry confirmed that in contrast to the not detectable signal in vivo, VASA protein was strongly localized in the cytoplasm of both neonate and adult mouse SSCs under in vitro conditions. The results of Fluidigm RT-PCR revealed a significant higher expression of the germ cell gene VASA in adult SSCs in comparison to neonate SSCs in cell culture (P<0.05).

Conclusion

The VASA protein is, therefore, an extremely specific marker of testicular germ cell differentiation in vivo and mostly expressed in the adult testis in spermatocytes and round spermatids. The immunohistochemical signal in spermatogonia is very low. So, PLZF positive SSCs are negative for VASA in vivo, while in contrast, once isolated from the testicular niche VASA is also strongly expressed in SSCs under in vitro conditions.

The effects of growth factors on proliferation of spermatogonial stem cells from Guangxi Bama mini-pig

The objective of this study was to investigate the effects of different growth factors on the proliferation of Bama mini-pig spermatogonial stem cells (SSCs) in vitro. The growth factors glial cell line-derived neurotrophic factor (GDNF), leukaemia inhibitory factor (LIF), GDNF family receptor alpha-1 (GFRα1) and basic fibroblast growth factor (bFGF) were investigated. The SSCs were seeded on SIM mouse embryo-derived thioguanine- and ouabain-resistant (STO) feeder layers. Cultivation of the cells were subjected to a factorial design of the growth factors GDNF + bFGF, GDNF + bFGF + GFRα1, LIF + bFGF and LIF + bFGF + GFRα1. The SSCs could propagate for 25 passages in the medium adding GDNF + bFGF + GFRα1, 22 passages in the medium adding GDNF + bFGF, 6 passages in the medium adding LIF + bFGF, or LIF + bFGF + GFRα1. qRT-PCR analysis showed that the highest mRNA expression levels of NANOG, POU5F, DDX4, GFRα1 and UCHL1 were detected in the group adding GDNF + bFGF + GFRα1. The SSCs from the group adding GDNF + bFGF + GFRα1 also showed UCHL1-, DBA- and CDH1-positive staining. Moreover, Stra8 and Scp3 expression, and haploid peak were detected after induction of the SSCs from the group adding GDNF + bFGF + GFRα1. In conclusion, pig SSCs could be maintained for long term in the presence of GDNF, bFGF, and GFRα1.

Progress in in vitro culture and gene editing of porcine spermatogonial stem cells

Research on in vitro culture and gene editing of domestic spermatogonial stem cells (SSCs) is of considerable interest but remains a challenging issue in animal science. In recent years, some progress on the isolation, purification, and genetic manipulation of porcine SSCs has been reported. Here, we summarize the characteristics of porcine SSCs as well current advances in their in vitro culture, potential usage, and genetic manipulation. Furthermore, we discuss the current application of gene editing in pig cloning technology. Collectively, this commentary aims to summarize the progress made and obstacles encountered in porcine SSC research to better serve animal husbandry, improve livestock fecundity, and enhance potential clinical use.

Postnatal testis development in the collared peccary (Tayassu tajacu), with emphasis on spermatogonial stem cells markers and niche

Collared peccaries (Tayassu tajacu) present a unique testis cytoarchitecture, where Leydig cells (LC) are mainly located in cords around the seminiferous tubules (ST) lobes. This peculiar arrangement is very useful to better investigate and understand the role of LC in spermatogonial stem cells (SSCs) biology and niche. Recent studies from our laboratory using adult peccaries have shown that the undifferentiated type A spermatogonia (A_und or SSCs) are preferentially located in ST regions adjacent to the intertubular compartment without LC. Following these studies, our aims were to investigate the collared peccary postnatal testis development, from birth to adulthood, with emphasis on the establishment of LC cytoarchitecture and the SSCs niche. Our findings demonstrated that the unique LC cytoarchitecture is already present in the neonate peccary's testis, indicating that this arrangement is established during fetal development. Based on the most advanced germ cell type present at each time period evaluated, puberty (the first sperm release in the ST lumen) in this species was reached at around one year of age, being preceded by high levels of estradiol and testosterone and the end of Sertoli cell proliferation. Almost all gonocytes and SSCs expressed Nanos1, Nanos2 and GFRA1. The analysis of SSCs preferential location indicated that the establishment of SSCs niche is coincident with the occurrence of puberty. Taken together, our findings reinforced and extended the importance of the collared peccary as an animal model to investigate testis function in mammals, particularly the aspects related to testis organogenesis and the SSCs biology and niche.

Spermatogonial Stem Cell Transplantation: Insights and Outlook for Domestic Animals

The demand for food will increase to an unprecedented level over the next 30 years owing to human population expansion, thus necessitating an evolution that improves the efficiency of livestock production. Genetic gain to improve production traits of domestic animal populations is most effectively achieved via selective use of gametes from animals deemed to be elite, and this principle has been the basis of selective breeding strategies employed by humans for thousands of years. In modern-day animal agriculture, artificial insemination (AI) has been the staple of selective breeding programs, but it has inherent limitations for applications in beef cattle and pig production systems. In this review, we discuss the potential and current state of development for a concept termed Surrogate Sires as a next-generation breeding tool in livestock production. The scheme capitalizes on the capacity of spermatogonial stem cells to regenerate sperm production after isolation from donor testicular tissue and transfer into the testes of a recipient male that lacks endogenous germline, thereby allowing the surrogate male to produce offspring with the donor haplotype via natural mating. This concept provides an effective selective breeding tool to achieve genetic gain that is conducive for livestock production systems in which AI is difficult to implement.

In vitro differentiation of spermatogonial stem cells using testicular cells from Guangxi Bama mini-pig

In this study, we attempted to establish a culture system for in vitro spermatogenesis from spermatogonial stem cells (SSCs) of Bama mini-pig. Dissociated testicular cells from 1-month-old pigs were co-cultured to mimic in vivo spermatogenesis. The testicular cells were seeded in minimum essential medium alpha (α-MEM) supplemented with Knockout serum replacement (KSR). Three-dimensional colonies formed after 10 days of culture. The colonies showed positive staining for SSC-associated markers such as UCHL1, PLZF, THY1, OCT4, Dolichos biflorus agglutinin, and alkaline phosphatase. Induction of SSCs was performed in α-MEM + KSR supplemented with retinoic acid, bone morphogenetic protein 4, activin A, follicle-stimulating hormone, or testosterone. The results showed that STRA8, DMC1, PRM1, and TNP1 were upregulated significantly in the colonies after induction compared to that in testis from 1-month-old pigs, while expression levels of those genes were significantly low compared to those in 2-month-old testis. However, upregulation of ACROSIN was not significant. Replacement of α-MEM and KSR with Iscove's modified Dulbecco's medium and fetal bovine serum did not upregulate expression of these genes significantly. These results indicate that SSCs of Bama mini-pig could undergo differentiation and develop to a post-meiotic stage in α-MEM supplemented with KSR and induction factors.

Long-Term Propagation of Porcine Undifferentiated Spermatogonia

Spermatogonial stem cells (SSCs) provide the foundation for spermatogenesis and fertility throughout the adult life of a male. Genetic manipulations of SSCs combined with germ cell transplantation present a novel approach for gene therapy and production of genetically modified animals. However, the rarity of SSCs within mammalian testes remains an impediment to related applications, making in vitro expansion of SSCs a prerequisite. Nevertheless, long-term culture systems of SSCs from large animals have not been established yet. In this study, we developed an optimized in vitro culture condition for porcine undifferentiated spermatogonia. The germ cells were isolated and enriched from 7-day-old porcine testes by an optimized differential planting. We tested different feeder layers and found that neonatal autologous Sertoli cells acted better than the SIM mouse embryo-derived thioguanine- and ouabain-resistant (STO) cell line and adult Sertoli cells. The effects of several growth factors were also investigated. Using neonatal Sertoli cells as feeder and Dulbecco's modified eagle medium: nutrient mixture F-12 (DMEM/F12) culture medium supplemented with 10% KSR and four cytokines, the undifferentiated spermatogonia can proliferate in vitro for at least 2 months without loss of stemness. The expression of SSC markers indicated that the cultured cells maintained SSC expression profiles. Moreover, xenotransplantation and in vitro induction showed that the long-term cultured cells preserved the capacity to colonize in vivo and differentiate in vitro, respectively, demonstrating the presence of SSCs in the cultured cells. In conclusion, the conditions described in this study can support the normal proliferation of porcine undifferentiated spermatogonia with stemness and normal karyotype for at least 2 months. This culture system will serve as a basic refinement in the future studies and facilitate studies on SSC biology and genetic manipulation of male germ cells.

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.

Vitrified canine testicular cells allow the formation of spermatogonial stem cells and seminiferous tubules following their xenotransplantation into nude mice

Belgian Malinois (BM), one of the excellent military dog breeds in South Korea, is usually castrated before sexual maturation. Therefore, the transfer of their genetic features to the next generation is difficult. To overcome this, testicular cells from 4-month-old BMs were frozen. Testicular cells were thawed after 3 months and cultured in StemPro-34 medium. Spermatogonial stem cell (SSC) characteristics were determined by the transplantation of the cultured germ cell-derived colonies (GDCs) into empty testes, containing only several endogenous SSCs and Sertoli cells, of immunodeficient mice, 4 weeks after busulfan treatment. Following the implantation, the transplanted cells localized in the basement membrane of the seminiferous tubules, and ultimately colonized the recipient testes. Xenotransplantation of GDCs together with testicular somatic cells conjugated with extracellular matrix (ECM), led to the formation of de novo seminiferous tubules. These seminiferous tubules were mostly composed of Sertoli cells. Some germ cells were localized in the basement membrane of seminiferous tubules. This study revealed that BM-derived SSCs, obtained from the castrated testes, might be a valuable tool for the transfer of BM genetic features to the next generation.

Subculture of Germ Cell-Derived Colonies with GATA4-Positive Feeder Cells from Neonatal Pig Testes

Enrichment of spermatogonial stem cells is important for studying their self-renewal and differentiation. Although germ cell-derived colonies (GDCs) have been successfully cultured from neonatal pig testicular cells under 31°C conditions, the short period of in vitro maintenance (<2 months) limited their application to further investigations. To develop a culture method that allows for in vitro maintenance of GDCs for long periods, we subcultured the GDCs with freshly prepared somatic cells from neonatal pig testes as feeder cells. The subcultured GDCs were maintained up to passage 13 with the fresh feeder cells (FFCs) and then frozen. Eight months later, the frozen GDCs could again form the colonies on FFCs as shown in passages 1 to 13. Immunocytochemistry data revealed that the FFCs expressed GATA-binding protein 4 (GATA4), which is also detected in the cells of neonatal testes and total testicular cells, and that the expression of GATA4 was decreased in used old feeder cells. The subcultured GDCs in each passage had germ and stem cell characteristics, and flow cytometric analyses revealed that ~60% of these cells were GFRα-1 positive. In conclusion, neonatal pig testes-derived GDCs can be maintained for long periods with GATA4-expressing testicular somatic cells.

bFGF signaling-mediated reprogramming of porcine primordial germ cells

Primordial germ cells (PGCs) have the ability to be reprogrammed into embryonic germ cells (EGCs) in vitro and are an alternative source of embryonic stem cells. Other than for the mouse, the systematic characterization of mammalian PGCs is still lacking, especially the process by which PGCs convert to pluripotency. This hampers the understanding of germ cell development and the derivation of authenticated EGCs from other species. We observed the morphological development of the genital ridge from Bama miniature pigs and found primary sexual differentiation in the E28 porcine embryo, coinciding with Blimp1 nuclear exclusion in PGCs. To explore molecular events involved in porcine PGC reprogramming, transcriptome data of porcine EGCs and fetal fibroblasts (FFs) were assembled and 1169 differentially expressed genes were used for Gene Ontology analysis. These genes were significantly enriched in cell-surface receptor-linked signal transduction, in agreement with the activation of LIF/Stat3 signaling and FGF signaling during the derivation of porcine EG-like cells. Using a growth-factor-defined culture system, we explored the effects of bFGF on the process and found that bFGF not only functioned at the very beginning of PGC dedifferentiation by impeding Blimp1 nuclear expression via a PI3K/AKT-dependent pathway but also maintained the viability of cultured PGCs thereafter. These results provide further insights into the development of germ cells from livestock and the mechanism of porcine PGC reprogramming.

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.

Glial cell line-derived neurotrophic factor in combination with insulin-like growth factor 1 and basic fibroblast growth factor promote in vitro culture of goat spermatogonial stem cells

Growth factors are increasingly considered as important regulators of spermatogonial stem cells (SSCs). This study investigated the effects of various growth factors (GDNF, IGF1, bFGF, EGF and GFRalpha-1) on purification and colonization of undifferentiated goat SSCs under in vitro and in vivo conditions. Irrespective of the culture condition used, the first signs of developing colonies were observed from day 4 of culture onwards. The number of colonies developed in GDNF + IGF1 + bFGF culture condition was significantly higher than the other groups (p < 0.05). In contrast, the size of colonies developed in GDNF + EGF + LIF culture condition was significantly higher than the other groups (p < 0.05). Immunocytochemical stationing for specific biomarkers of somatic cells (vimentin, alpha-inhibin and α-SMA) and spermatogonial cells (PLZF, THY 1, VASA, alpha-1 integrin, bet-1 integrin and DBA) revealed that both cell types existed in developing colonies, irrespective of the culture condition used. Even though, the relative abundance of VASA, FGFR3, OCT4, PLZF, BCL6B and THY1 transcription factors in GDNF + IGF1 + bFGF treatment group was significantly higher than the other groups (p < 0.05). Additionally, goat SSCs developed in the latter culture condition could colonize within the seminiferous tubules of the germ-cell depleted recipient mice following xenotransplantation. Obtained results demonstrated that combination of GDNF with IGF1 and bFGF promote in vitro culture of goat SSCs while precludes uncontrolled proliferation of somatic cells.

THY1 is a surface marker of porcine gonocytes

Gonocytes are important for the study of spermatogenesis. Identification and isolation of gonocytes has been reported in rodents but not in pigs due to a lack of molecular markers for gonocytes. The objective of this study was to identify THY1 expression in porcine testicular tissue and subsequently utilise THY1 as a marker to isolate and enrich porcine gonocytes from testes of newborn piglets. Immunohistochemical analysis showed that THY1 was expressed in gonocytes. Double-immunofluorescent analysis of THY1 and ZBTB16 indicated that THY1 and ZBTB16 were partially co-localised in gonocytes. Double-immunofluorescent analysis of both THY1 and GATA4 suggested that THY1(+) cells were not Sertoli cells. Magnetic-activated cell sorting of THY1(+) cells yielded a cell population with an enrichment of UCHL1(+) gonocytes 3.4-fold of that of the unsorted testicular cell population. Western blot and quantitative reverse transcription-polymerase chain reaction analyses confirmed that the selected THY1(+) fraction had a higher expression of UCHL1 than the unsorted cells. In conclusion, the study demonstrated that THY1 is a surface marker of gonocytes in testes of pre-pubertal boars and could be utilised to identify and isolate porcine gonocytes. The findings will also facilitate culture and manipulation of male germline stem cells.

Identification and in vitro derivation of spermatogonia in beagle testis

BACKGROUND

In vitro culture of spermatogonial stem cells (SSCs) is important for exploration of SSCs self-renewal, differentiation, and manipulation. There are several reports on rodent SSC cultures; however, data on SSC cultures in domestic animals are limited. To provide basic scientific information on canine SSC cultures, we report canine testes development, and the development of spermatogonia-derived colonies (SDCs) for in vitro cultures.

METHODOLOGY/PRINCIPAL FINDINGS

Testes from 2-, 3-, and 12-month-old beagles were used for histology, immunohistochemistry, in vitro culture, immunocytochemistry, and PCR. Protein gene product 9.5 (PGP9.5)-positive spermatogonia, both single and paired, were found to be abundant in the testes of 2-month-old beagles. stempro-34 and Dulbecco's modified Eagle medium with 5% fetal bovine serum provided as useful substrates for culture of SDCs, and fibroblast growth factor (FGF) played a key role in colony formation. Colonies were positive for alkaline phosphatase and anti-PGP9.5 staining. The early spermatogonia and stem cell markers such as octamer binding protein 4 (Oct4), Nanog homeobox (Nanog), promyelocytic leukemia zinc finger (PLZF), PGP9.5, and GDNF family receptor alpha-1 (GFRα-1) were expressed in the colonies at higher levels than in the testis tissue.

CONCLUSIONS

Testes of the 2-month-old beagles had abundant single and paired spermatogonia, which can be used for derivation of SDCs, and FGF was important for colony formation.

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.

Maintenance of potential spermatogonial stem cells in vitro by GDNF treatment in a chondrichthyan model (Scyliorhinus canicula L.)

Previous work in dogfish, Scyliorhinus canicula, has identified the testicular germinative area as the spermatogonial stem cell niche. In the present study, an in vitro co-culture system of spermatogonia and somatic cells from the germinative area was developed. Long-term maintenance of spermatogonia has been successful, and addition of GDNF has promoted the development of clones of spermatogonia expressing stem cell characteristics such as alkaline phosphatase activity and has allowed maintenance of self-renewal in spermatogonia for at least 5 mo under culture conditions, notably by decreasing cell apoptosis. Furthermore, clones of spermatogonia expressed the receptor of GDNF, GFRalpha1, which is consistent with the effect of GDNF on cells despite the lack of identification of a GDNF sequence in the dogfish's transcriptome. However, a sequence homologous to artemin has been identified, and in silico analysis supports the hypothesis that artemin could replace GDNF in the germinative area in dogfish. This study, as the first report on long-term in vitro maintenance of spermatogonia in a chondrichthyan species, suggests that the GFRalpha1 signaling function in self-renewal of spermatogonial stem cells is probably conserved in gnathostomes.

Cloning and expression characteristics of the pig Stra8 gene

Stra8 (Stimulated by Retinoic Acid 8) is considered a meiotic gatekeeper gene. Using reverse transcriptase PCR and rapid amplification of cDNA ends (RACE), the complete sequence of the pig Stra8 gene was cloned. Bioinformatics analyses of this sequence were performed. Using semi-quantitative methods, the expression characteristics of Stra8 in Testis, cauda epididymis, body epididymis, caput epididymis, seminal vesicles, prostate gland, Cowper's gland, heart, liver, spleen, lung, kidney, stomach, hypothalamus, pituitary gland, cerebrum, cerebellum, and hippocampus of adult Meishan boar and sow tissues were examined. The expression pattern in the testis of 2-, 30-, 60-, 90-, and 150-day old Meishan boars were analyzed using real-time PCR. We constructed a eukaryotic expression vector for the Stra8 gene and used it to transfect NIH-3T3 cells and third generation pig spermatogonial stem cells (SSCs) cultured in vitro. Testes weight and sperm count in the cauda epididymis were evaluated at various time points. The results showed that the length of the pig Stra8 gene cDNA was 1444 bp encoding 366 amino acids with one typical helix-loop-helix (HLH) domain. It is testes-specific expression. Expression was first detected in boar testis starting at day 2, and its expression significantly (p<0.05) increased with age and body weight. When NIH-3T3 cells and pig SSCs were transfected with the eukaryotic expression vector EGFP (enhanced green fluorescent protein)-N1-pStra8, it was expressed in the cytoplasm of NIH-3T3 cells. However, in SSCs, Stra8 was expressed predominantly in cytoplasm and few in nucleus. Our data suggest that perhaps Stra8 acts as a transcription factor to initiate meiosis in young boar.

Spermatogonial stem cells from domestic animals: progress and prospects

Spermatogenesis, an elaborate and male-specific process in adult testes by which a number of spermatozoa are produced constantly for male fertility, relies on spermatogonial stem cells (SSCs). As a sub-population of undifferentiated spermatogonia, SSCs are capable of both self-renewal (to maintain sufficient quantities) and differentiation into mature spermatozoa. SSCs are able to convert to pluripotent stem cells during in vitro culture, thus they could function as substitutes for human embryonic stem cells without ethical issues. In addition, this process does not require exogenous transcription factors necessary to produce induced-pluripotent stem cells from somatic cells. Moreover, combining genetic engineering with germ cell transplantation would greatly facilitate the generation of transgenic animals. Since germ cell transplantation into infertile recipient testes was first established in 1994, in vivo and in vitro study and manipulation of SSCs in rodent testes have been progressing at a staggering rate. By contrast, their counterparts in domestic animals, despite the failure to reach a comparable level, still burgeoned and showed striking advances. This review outlines the recent progressions of characterization, isolation, in vitro propagation, and transplantation of spermatogonia/SSCs from domestic animals, thereby shedding light on future exploration of these cells with high value, as well as contributing to the development of reproductive technology for large animals.

Germline stem cells: toward the regeneration of spermatogenesis

Improved therapies for cancer and other conditions have resulted in a growing population of long-term survivors. Infertility is an unfortunate side effect of some cancer therapies that impacts the quality of life of survivors who are in their reproductive or prereproductive years. Some of these patients have the opportunity to preserve their fertility using standard technologies that include sperm, egg, or embryo banking, followed by IVF and/or ET. However, these options are not available to all patients, especially the prepubertal patients who are not yet producing mature gametes. For these patients, there are several stem cell technologies in the research pipeline that may give rise to new fertility options and allow infertile patients to have their own biological children. We will review the role of stem cells in normal spermatogenesis as well as experimental stem cell-based techniques that may have potential to generate or regenerate spermatogenesis and sperm. We will present these technologies in the context of the fertility preservation paradigm, but we anticipate that they will have broad implications for the assisted reproduction field.

Phenotypic characterization and in vitro propagation and transplantation of the Nile tilapia (Oreochromis niloticus) spermatogonial stem cells

In association with in vitro culture and transplantation, isolation of spermatogonial stem cells (SSCs) is an excellent approach for investigating spermatogonial physiology in vertebrates. However, in fish, the lack of SSC molecular markers represents a great limitation to identify/purify these cells, rendering it difficult to apply several valuable biotechnologies in fish-farming. Herein, we describe potential molecular markers, which served to phenotypically characterize, cultivate and transplant Nile tilapia SSCs. Immunolocalization revealed that Gfra1 is expressed exclusively in single type A undifferentiated spermatogonia (Aund, presumptive SSCs). Likewise, the expression of Nanos2 protein was observed in Aund cells. However, Nanos2-positive spermatogonia have also been identified in cysts with two to eight germ cells that encompass type A differentiated spermatogonia (Adiff). Moreover, we also established effective primary culture conditions that allowed the Nile tilapia spermatogonia to expand their population for at least one month while conserving their original undifferentiated (stemness) characteristics. The maintenance of Aund spermatogonial phenotype was demonstrated by the expression of early germ cell specific markers and, more convincingly, by their ability to colonize and develop in the busulfan-treated adult Nile tilapia recipient testes after germ cell transplantation. In addition to advancing our knowledge on the identity and physiology of fish SSCs, these findings provide the first step in establishing a system that will allow fish SSCs expansion in vitro, representing an important progress towards the development of new biotechnologies in aquaculture, including the possibility of producing transgenic fish.

Establishment and in vitro culture of porcine spermatogonial germ cells in low temperature culture conditions

The objective of this study was to establish a porcine spermatogonial germ cell (pSGC) line and develop an in vitro culture system. Isolated total testicular cells (TTCs) from 5-day-old porcine testes were primary cultured at 31, 34, and 37°C. Although the time of colony appearance was delayed at 31°C, strong alkaline phosphatase staining, expressions of pluripotency marker genes such as OCT4, NANOG, and THY1, and the gene expressions of the undifferentiated germ cell markers PLZF and protein gene product 9.5 (PGP9.5) were identified compared to 34 and 37°C. Cell cycle analysis for both pSGC and feeder cells at the three temperatures revealed that more pSGCs were in the G2/M phase at 31°C than 37°C at the subculture stage. In vitro, pSGCs could stably maintain undifferentiated germ cell and stem cell characteristics for over 60days during culture at 31°C. Xenotransplantation of pSGCs to immune deficient mice demonstrated a successful colonization and localization on the seminiferous tubule basement membrane in the recipient testes. In conclusion, pSGCs from neonatal porcine were successfully established and cultured for long periods under a low temperature culture environment in vitro.

In vitro propagation of male germline stem cells from piglets

PURPOSE

To study the effects of serum and growth factors on propagation of porcine male germline stem cells (MGSCs) in vitro and develop a culture system for these stem cells.

METHODS

Fresh testicular cells from neonatal piglets were obtained by mechanical dissociation and collagenase-trypsin digestion. After differential plating, non-adhering cells were cultured in media supplemented with different concentrations of serum (0, 1 %, 2 %, 5 %, 10 %). After 10 days of primary culture, the cells were maintained in media supplemented with different concentrations of growth factors (basic fibroblast growth factor and epidermal growth factor at 1, 5, 10 ng/ml). The number of MGSC-derived colonies with different sizes was determined in each treatment to assess the effects of serum concentrations and growth factors.

RESULTS

The number of MGSC-derived colonies was significantly higher in the presence of 1 % rather than 10 % fetal bovine serum (FBS). Basic fibroblast growth factor (bFGF) at 1, 5 ng/ml and epidermal growth factor (EGF) at 5, 10 ng/ml significantly promoted colony formation. Immunocytochemistry, reverse transcriptase-polymerase chain reaction (RT-PCR) and xenotransplantation assays demonstrated the presence of functional stem cells in cultured cell population.

CONCLUSIONS

In vitro propagation of porcine MGSCs could be maintained in the presence of 1 % FBS and supplementation of growth factors for 1 month.

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

The dog is recognized as a highly predictive model for preclinical research. Its size, life span, physiology, and genetics more closely match human parameters than do those of the mouse model. Investigations of the genetic basis of disease and of new regenerative treatments have frequently taken advantage of canine models. However, full utility of this model has not been realized because of the lack of easy transgenesis. Blastocyst-mediated transgenic technology developed in mice has been very slow to translate to larger animals, and somatic cell nuclear transfer remains technically challenging, expensive, and low yield. Spermatogonial stem cell (SSC) transplantation, which does not involve manipulation of ova or blastocysts, has proven to be an effective alternative approach for generating transgenic offspring in rodents and in some large animals. Our recent demonstration that canine testis cells can engraft in a host testis, and generate donor-derived sperm, suggests that SSC transplantation may offer a similar avenue to transgenesis in the canine model. Here, we explore the potential of SSC transplantation in dogs as a means of generating canine transgenic models for preclinical models of genetic diseases. Specifically, we i) established markers for identification and tracking canine spermatogonial cells; ii) established methods for enrichment and genetic manipulation of these cells; iii) described their behavior in culture; and iv) demonstrated engraftment of genetically manipulated SSC and production of transgenic sperm. These findings help to set the stage for generation of transgenic canine models via SSC transplantation.

Pluripotent cells in farm animals: state of the art and future perspectives

Pluripotent cells, such as embryonic stem (ES) cells, embryonic germ cells and embryonic carcinoma cells are a unique type of cell because they remain undifferentiated indefinitely in in vitro culture, show self-renewal and possess the ability to differentiate into derivatives of the three germ layers. These capabilities make them a unique in vitro model for studying development, differentiation and for targeted modification of the genome. True pluripotent ESCs have only been described in the laboratory mouse and rat. However, rodent physiology and anatomy differ substantially from that of humans, detracting from the value of the rodent model for studies of human diseases and the development of cellular therapies in regenerative medicine. Recently, progress in the isolation of pluripotent cells in farm animals has been made and new technologies for reprogramming of somatic cells into a pluripotent state have been developed. Prior to clinical application of therapeutic cells differentiated from pluripotent stem cells in human patients, their survival and the absence of tumourigenic potential must be assessed in suitable preclinical large animal models. The establishment of pluripotent cell lines in farm animals may provide new opportunities for the production of transgenic animals, would facilitate development and validation of large animal models for evaluating ESC-based therapies and would thus contribute to the improvement of human and animal health. This review summarises the recent progress in the derivation of pluripotent and reprogrammed cells from farm animals. We refer to our recent review on this area, to which this article is complementary.

Endogenous EGF maintains Sertoli germ cell anchoring junction integrity and is required for early recovery from acute testicular ischemia/reperfusion injury

Administration of exogenous epidermal growth factor (EGF) improves testicular injury after acute ischemia–reperfusion (IR) stress, but the molecular basis is poorly understood. The role of endogenous EGF in testicular recovery and the underlying intracellular signaling pathways involved were herein investigated. In mice, testicular IR injury significantly enhanced the expression level of endogenousEgfat the very beginning of reperfusion. Expression of EGF receptor (Egfr(ErbB1)) was accordingly upregulated 3 h after reperfusion. Deprivation of majority of circulated EGF by sialoadenectomy aggravated testicular detriment (especially in pachytene spermatocytes), enhanced germ cell apoptosis, and thereafter resulted in impaired meiotic differentiation after IR insult. Mechanistically, endogenous EGF signaling appeared to be indispensable for the proper maintenance of Sertoli germ cells anchoring junction dynamics during the early testicular recovery. We also provided thein vitroevidences in a well-established rat Sertoli germ cell co-cultures model that the pro-survival effect of endogenous EGF on germ cells in response to testicular IR insult is mediated, at least in part, via the phosphatidylinositol 3-kinase/pAkt pathway. Collectively, our results suggest that the augment of endogenous EGF during the early testicular recovery may act on top of an endocrinous cascade orchestrating the intimate interactions between Sertoli cells and germ cells and may operate as indispensable defensive mechanism in response to testicular IR stress. Future studies in this field would shed light on this complicated pathogenesis.

Effects of glial cell line-derived neurotrophic factor, fibroblast growth factor 2 and epidermal growth factor on proliferation and the expression of some genes in buffalo (Bubalus bubalis) spermatogonial cells

The present study evaluated the effects of glial cell line-derived neurotrophic factor (GDNF), fibroblast growth factor (FGF) 2 and epidermal growth factor (EGF) on proliferation and the expression of some genes in spermatogonial cells. Spermatogonial cells were isolated from prepubertal buffalo testes and enriched by double enzyme treatment, filtration through 80- and 60-μm nylon mesh filters, differential plating on lectin-coated dishes and Percoll density gradient centrifugation. Cells were then cultured on a buffalo Sertoli cell feeder layer and formed colonies within 15–18 days. The colonies were found to predominantly contain undifferentiated Type A spermatogonia because they bound Dolichos biflorus agglutinin and did not express c-kit. The colonies expressed alkaline phosphatase, NANOG, octamer-binding transcription factor (OCT)-4 and tumour rejection antigen (TRA)-1–60. Cells were subcultured for 15 days, with or without growth factor supplementation. After 15 days, colony area and the relative mRNA abundance of PLZF were higher (P < 0.05) following supplementation with 40 ng mL–1 GDNF + 10 ng mL–1 EGF + 10 ng mL–1 FGF2 than with the same concentrations of GDNF alone or GDNF plus either EGF or FGF2. Expression of TAF4B was higher (P < 0.05) in the presence of FGF2, whereas the expression of THY1 was not affected by growth factor supplementation. In the Sertoli cell feeder layer, EGF and FGF2 decreased (P < 0.05), whereas GDNF increased (P < 0.05), the relative mRNA abundance of ETV5 compared with control. In conclusion, an in vitro culture system that incorporates various growth factors was developed for the short-term culture of buffalo spermatogonia.

Spermatogonial stem cell markers and niche in equids

Spermatogonial stem cells (SSCs) are the foundation of spermatogenesis and are located in a highly dynamic microenvironment called "niche" that influences all aspects of stem cell function, including homing, self-renewal and differentiation. Several studies have recently identified specific proteins that regulate the fate of SSCs. These studies also aimed at identifying surface markers that would facilitate the isolation of these cells in different vertebrate species. The present study is the first to investigate SSC physiology and niche in stallions and to offer a comparative evaluation of undifferentiated type A spermatogonia (Aund) markers (GFRA1, PLZF and CSF1R) in three different domestic equid species (stallions, donkeys, and mules). Aund were first characterized according to their morphology and expression of the GFRA1 receptor. Our findings strongly suggest that in stallions these cells were preferentially located in the areas facing the interstitium, particularly those nearby blood vessels. This distribution is similar to what has been observed in other vertebrate species. In addition, all three Aund markers were expressed in the equid species evaluated in this study. These markers have been well characterized in other mammalian species, which suggests that the molecular mechanisms that maintain the niche and Aund/SSCs physiology are conserved among mammals. We hope that our findings will help future studies needing isolation and cryopreservation of equids SSCs. In addition, our data will be very useful for studies that aim at preserving the germplasm of valuable animals, and involve germ cell transplantation or xenografts of equids testis fragments/germ cells suspensions.

Proliferation of small number of human spermatogonial stem cells obtained from azoospermic patients

PURPOSE

This study aims to proliferate spermatogonial stem cells (SSCs) and compare the in-vitro effects of laminin and growth factors on the proliferation of adult human SSC.

METHODS

Isolated testicular cells were cultured in DMEM supplemented with 5 % fetal calf serum (FCS). During the culture, enriched spermatogonial cells were treated with a combination of glial cell line-derived neurotrophic factor (GDNF), basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and mouse leukemia inhibitory factor (LIF) in the presence or absence of human placental laminin-coated dishes. Cluster assay was performed during culture. Presence of spermatogonia was determined by an ultrastructural study of the cell clusters, reverse transcription polymerase chain reaction (RT-PCR) for spermatogonial markers and xenotransplantation to the testes of busulfan-treated recipient mice. Statistical significance between mean values was determined using statistical ANOVA tests.

RESULTS

The findings indicated that the addition of GDNF, bFGF, EGF and LIF on laminin-coated dishes significantly increased in-vitro spermatogonial cell cluster formation in comparison with the control group (p ≤ 0.001). The expression of spermatogonial markers was maintained throughout the culture period. Furthermore, a transplantation experiment showed the presence of SSC among the cultured cells. In addition, a transmission electron microscopy (TEM) study suggested the presence of spermatogonial cells of typical morphology among the cluster cells.

CONCLUSIONS

It can be concluded that human SSCs obtained from non-obstructive azoospermic (NOA) patients had the ability to self-renew in the culture system. This system can be used for the propagation of a small number of these cells from small biopsies.

Pluripotency of male germline stem cells

The ethical issues and public concerns regarding the use of embryonic stem (ES) cells in human therapy have motivated considerable research into the generation of pluripotent stem cell lines from non-embryonic sources. Numerous reports have shown that pluripotent cells can be generated and derived from germline stem cells (GSCs) in mouse and human testes during in vitro cultivation. The gene expression patterns of these cells are similar to those of ES cells and show the typical self-renewal and differentiation patterns of pluripotent cells in vivo and in vitro. However, the mechanisms underlying the spontaneous dedifferentiation of GSCs remain to be elucidated. Studies to identify master regulators in this reprogramming process are of critical importance for understanding the gene regulatory networks that sustain the cellular status of these cells. The results of such studies would provide a theoretical background for the practical use of these cells in regenerative medicine. Such studies would also help elucidate the molecular mechanisms underlying certain diseases, such as testicular germ cell tumors.

Of stem cells and germ cells

Stem cells have an intrinsic capacity to self-renew and can differentiate to at least one specialized cell type. Different types of stem cells exist that can be cultured in vitro. The identity of the stem cells is marked by their origin and differentiation potential. Germ cells have similarities with pluripotent stem cells but are of a special order: They do not self-renew and are already differentiated, but they have the capacity to form a complete new organism after fertilization. This review focuses on pluripotent stem cells and discusses possibilities of generating pluripotent stem cells from germ cell precursors and possibilities of generating germ cells from stem cells. As it accompanies a plenary lecture at the 15th annual ESDAR Conference 2011, the overview is focused on stem cells from farm animal species and on results from my own research group.

Isolation of enriched carp spermatogonial stem cells from Labeo rohita testis for in vitro propagation

The in vitro culture system for spermatogonial stem cells (SSCs) is a powerful tool for exploring molecular mechanisms of male gametogenesis and gene manipulation. Very little information is available for fish SSC biology. Our aim was to isolate highly pure SSCs from the testis of commercially important farmed carp, Labeo rohita. The minced testis of L. rohita was dissociated with collagenase. Dissociated cells purified by two-step Ficoll gradient centrifugation followed by magnetic activated cell sorting (MACS) using Thy1.2 (CD90.2) antibody dramatically heightened recovery rate for spermatogonial cells. The purified cells were cultured in vitro conditions for more than two months in L-15 media containing 10% fetal bovine serum (FBS), 1% carp serum, and other nutrients. The proliferative cells were dividing as validated by 5-bromo-2'-deoxyuridine (BrdU) incorporation assay and formed colonies/clumps with the typical characteristics of SSCs A majority of enriched cell population represented a Vasa(+), Pou5f1/pou5f1(+), Ssea-1(+), Tra-1-81(+), plzf(+), Gfrα1/gfrα1(-), and c-Kit/c-kit(-) as detected by immunocytochemical and/or quantitative real-time polymerase chain reaction (RT-PCR) analyses. Thus, Thy1(+) SSCs were enriched with greater efficiency from the mixed population of testicular cells of L. rohita. A population of enriched spermatogonial cells could be cultured in an undifferentiated state. The isolated SSCs could provide avenue for undertaking research on basic and applied reproductive biology.