Low dose of zearalenone inhibited the proliferation of porcine prospermatogonia and transformed the physiology through cytokine-cytokine receptor interaction

Zearalenone (ZEA) is a prevalent mycotoxin functions as an endocrine disrupter to the reproductive systems of farm animals, especially in pigs. To evaluate the effect and the underlying molecular changes that occurred when the porcine germline stem cells were exposed to ZEA, prospermatogonia (ProSGs) were enriched and treated with a gradient concentration (0-10 μM) of ZEA for 2-8 days. Our results showed that the ZEA treatment inhibited the proliferation of ProSGs in a dose-dependent manner with a critical concentration at 1 μM. Transcriptome analysis revealed that the differentially expressed genes mainly concentrated on the molecular function of positive regulation of response to stimulus, and the most enriching pathway is cytokine-cytokine receptor interaction. ZEA exposure decreased a buck of cytokine/chemokine expression involved in the inflammatory response and stem cells maintenance/self-renewal, moreover, some energy expenditure and anti-apoptosis genes were also down-regulated, while the up-regulated genes were mainly connected with the innate immunity. These data demonstrate that ZEA induces multiply cellular damage and may eventually do harm to the health and fertility of animals.

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.

Expression of paired box protein PAX7 in prepubertal boar testicular gonocytes

Spermatogenesis involves mitosis, meiosis, growth, and differentiation of spermatogonial stem cells (SSCs), which are capable of self-renewal and differentiation into spermatozoa. Markers of spermatogonia and other spermatogenic cells have been extensively studied in rodents, whereas physiological characteristics and stage-specific markers of germ cells remain largely unknown in large domestic animals. In rodents, paired box protein 7 (PAX7) is known to be a specific marker of a rare spermatogonial subpopulation in adult testes, while being expressed by a large proportion of neonatal testicular germ cells. However, the expression of PAX7 has not yet been investigated in domestic animals. The objective of this study was to characterize PAX7 expression during boar testis development and in in vitro cultured porcine SSCs (pSSCs). Notably, the expression of PAX7 was positively correlated with that of a known boar testis spermatogonial and gonocyte marker, protein gene product 9.5 (PGP9.5), in prepubertal (5-day-old) boar testes but was not observed during or following puberty. Furthermore, the early-stage spermatogonial markers GDNF family receptor alpha-1 (GFRα1) and Sal-like protein 4 (SALL4) were coexpressed in PAX7⁺ testicular cells from 5-day-old boars. PAX7 expression was also maintained in in vitro cultured undifferentiated porcine spermatogonia, with both PAX7 and PGP9.5 strongly expressed in pSSC colonies but not in feeder cells (testicular somatic cells). These data demonstrated that PAX7 expression only occurred in boar testes during prepuberty and was mainly restricted to very early-stage spermatogonial germ cells, such as gonocytes, which implies that PAX7 can be used as a boar gonocyte marker.

Previously claimed male germline stem cells from porcine testis are actually progenitor Leydig cells

Background

Male germline stem cells (mGSCs) offer great promise in regenerative medicine and animal breeding due to their capacity to maintain self-renewal and to transmit genetic information to the next generation following spermatogenesis. Human testis-derived embryonic stem cell-like cells have been shown to possess potential of mesenchymal progenitors, but there remains confusion about the characteristics and origin of porcine testis-derived stem cells.

Methods

Porcine testis-derived stem cells were obtained from primary testicular cultures of 5-day old piglets, and selectively expanded using culture conditions for long-term culture and induction differentiation. The stem cell properties of porcine testis-derived stem cells were subsequently assessed by determining the expression of pluripotency-associated markers, alkaline phosphatase (AP) activity, and capacity for sperm and multilineage differentiation in vitro. The gene expression profile was compared via microarray analysis.

Results

We identified two different types of testis-derived stem cells (termed as C1 and C2 here) during porcine testicular cell culture. The gene expression microarray analysis showed that the transcriptome profile of C1 and C2 differed significantly from each other. The C1 appeared to be morphologically similar to the previously described mouse mGSCs, expressed pluripotency- and germ cell-associated markers, maintained the paternal imprinted pattern of H19, displayed alkaline phosphatase activity, and could differentiate into sperm. Together, these data suggest that C1 represent the porcine mGSC population. Conversely, the C2 appeared similar to the previously described porcine mGSCs with three-dimensional morphology, abundantly expressed Leydig cell lineage and mesenchymal cell-specific markers, and could differentiate into testosterone-producing Leydig cells, suggesting that they are progenitor Leydig cells (PLCs).

Conclusion

Collectively, we have established the expected characteristics and markers of authentic porcine mGSCs (C1). We found for the first time that, the C2, equivalent to previously claimed porcine mGSCs, are actually progenitor Leydig cells (PLCs). These findings provide new insights into the discrepancies among previous reports and future identification and analyses of testis-derived stem cells.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0931-0) contains supplementary material, which is available to authorized users.

Deliverable transgenics & gene therapy possibilities for the testes

Male infertility and hypogonadism are clinically prevalent conditions with a high socioeconomic burden and are both linked to an increased risk in cardiovascular-metabolic diseases and earlier mortality. Therefore, there is an urgent need to better understand the causes and develop new treatments for these conditions that affect millions of men. The accelerating advancement in gene editing and delivery technologies promises improvements in both diagnosis as well as affording the opportunity to develop bespoke treatment options which would both prove beneficial for the millions of individuals afflicted with these reproductive disorders. In this review, we summarise the systems developed and utilised for the delivery of gene therapy and discuss how each of these systems could be applied for the development of a gene therapy system in the testis and how they could be of use for the future diagnosis and repair of common male reproductive disorders.

Conserved and non-conserved characteristics of porcine glial cell line-derived neurotrophic factor expressed in the testis

Glial cell line-derived neurotrophic factor (GDNF) is essential for the self-renewal and proliferation of spermatogonial stem cells (SSCs) in mice, rats, and rabbits. Although the key extrinsic factors essential for spermatogonial proliferation in other mammals have not been determined, GDNF is one of the potential candidates. In this study, we isolated porcine GDNF (pGDNF) cDNAs from neonatal testis and generated recombinant pGDNF to investigate its biological activity on gonocytes/undifferentiated spermatogonia, including SSCs. In porcine testis, long and short forms of GDNF transcripts, the counterparts of pre-(α)pro and pre-(β)pro GDNF identified in humans and rodents, were expressed. The two transcripts encode identical mature proteins. Recombinant pGDNF supported proliferation of murine SSCs in culture, and their stem cell activity was confirmed by a transplantation assay. Subsequently, porcine gonocytes/undifferentiated spermatogonia were cultured with pGDNF; however, pGDNF did not affect their proliferation. Furthermore, GDNF expression was localised to the vascular smooth muscle cells, and its cognate receptor GFRA1 expression was negligible during spermatogonial proliferation in the testes. These results indicate that although pGDNF retains structural similarity with those of other mammals and conserves the biological activity on the self-renewal of murine SSCs, porcine SSCs likely require extrinsic factors other than GDNF for their proliferation.

Optimization of culture conditions for short-term maintenance, proliferation, and colony formation of porcine gonocytes

Background

Gonocytes give rise to spermatogonial stem cells, and thereby play an essential role in establishing spermatogenesis. Optimized culture conditions for gonocytes provide an opportunity for their study and in vitro manipulation for potential application in reproductive technologies. Using six experiments in a step-wise design, we examined the effects of several culture conditions on the maintenance, proliferation, and colony formation of porcine gonocytes. Testis cells from neonatal piglets were cultured for 7 d in DMEM supplemented with 10% fetal bovine serum. The examined culture conditions included using different cell seeding densities, gonocyte proportions, incubation temperatures, sampling strategies, and medium changing regimens.

Results

Confluency of cells was optimal (>90% by ~6 d) when 3.0 × 10⁴ testis cells/cm² containing ~40% gonocytes were used. Incubating the cells at 35 °C or 37 °C resulted in similar cell number and viability at confluency, but incubation at 35 °C resulted in a delayed confluency. In the first 2 d of culture, gonocytes remained mostly floating in the medium and gradually settled over the next 5 d. Consequently, not changing the medium for 7 d (as opposed to changing it every 2 d) led to a significant increase in the number of gonocyte colonies by reducing the loss of “floating gonocytes”.

Conclusion

We found that gonocytes require the presence of a critical minimum number of somatic cells for settlement, and can proliferate and form growing colonies even in a basic medium. Large numbers of viable gonocytes remain floating in the medium for several days. The optimized culture conditions in the present study included seeding with 3.0 × 10⁴ testis cells/cm² containing ~40% gonocytes, incubating at 37 °C, and without changing the medium in the first week, which can result in improved colony formation of porcine gonocytes.

Enrichment and In Vitro Culture of Spermatogonial Stem Cells from Pre-Pubertal Monkey Testes

Spermatogonial stem cells (SSCs) are essential for spermatogenesis throughout the lifespan of the male. However, the rarity of SSCs has raised the need for an efficient selection method, but little is known about culture conditions that stimulate monkey SSC proliferation in vitro. In this study, we report the development of effective enrichment techniques and in vitro culturing of germ cells from pre-pubertal monkey testes. Testis cells were analyzed by fluorescence-activated cell sorting techniques and were transplanted into the testes of nude mice to characterize SSCs. Thy-1-positive cells showed a higher number of colonies than the unselected control after xenotransplantation. Extensive colonization of monkey cells in the mouse testes indicated the presence of highly enriched populations of SSCs in the Thy-1-positive sorted cells. Furthermore, monkey testis cells were enriched by differential plating using extracellular matrix, laminin, and gelatin, and then cultured under various conditions. Isolation of monkey testicular germ cells by differential plating increased germ cell purity by 2.7-fold, following the combinational isolation method using gelatin and laminin. These enriched germ cells actively proliferated under culture conditions involving StemPro medium supplemented with bFGF, GDNF, LIF, and EGF at 37 °C. These results suggest that the enrichment and in vitro culture method proposed in the present study for harvesting a large number of functionally active monkey SSCs can be applied as the basis for efficient in vitro expansion of human SSCs.

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.

Simplified isolation and enrichment of spermatogonial stem-like cells from pubertal domestic cats (Felis catus)

The efficiency of spermatogonial stem cell (SSC) isolation and culture from pubertal donors is currently poor primarily, because of contamination with other testicular cells. This study aimed to purify SSC-like cells using different extracellular matrixes and a discontinuous gradient density. In experiment 1, testes (n=6) were analyzed for histology and SSC-related protein expressions (laminin, SSEA-4, DDX-4 and GFRα-1). After enzymatic digestion, the cell suspension was plated onto either a laminin- or gelatin-coated dish. The number of SSC-like cells was determined at 15, 30 and 60 min of culture (experiment 2). Experiment 3 was performed to test whether or not the additional step of Percoll gradient density centrifugation could really improve purification of SSC-like cells. Testicular histology revealed complete spermatogenesis with laminin expression essentially at the basal lamina of the seminiferous tubules. SSEA-4 and GFRα-1 co-localized with DDX-4 in the spermatogonia. The relative percentage of SSC-like cells, as determined by cells expressing SSEA-4 (59.42 ± 2.18%) and GFRα-1 (42.70 ± 1.28%), revealed that the highest SSC-like cell purity was obtained with the 15-min laminin-coated dish compared with other incubation times and gelatin treatment (P<0.05). Percoll treatment prior to laminin selection (15 min) significantly improved SSC-like cell recovery (91.33 ± 0.14%, P<0.001) and purity (83.82 ± 2.05% for SSEA-4 and 64.39 ± 1.51% for GFRα-1, P<0.05). These attached cells demonstrated a typical SSC-like cell morphology and also expressed POU5F1, RET and ZBTB16 mRNA. In conclusion, double enrichment with Percoll gradient density centrifugation and laminin plating highly enriched the SSC-like cells population.

Cell-surface DEAD-box polypeptide 4-immunoreactive cells and gonocytes are two distinct populations in postnatal porcine testes

DEAD-box polypeptide 4 (DDX4) is an evolutionally conserved ATP-dependent RNA helicase that is exclusively expressed in germ cell lineage. Although DDX4 is believed to reside and function in the cytoplasm, recent studies in mice and humans suggest that its epitope is expressed on the cell surface of a small subpopulation in the ovary, putative oogonial stem cells. No study has examined whether such cell-surface DDX4(+) cells exist in the testes of any species. In this study, we explored cell-surface DDX4(+) cells in postnatal porcine testes before the onset of spermatogenesis, where gonocytes, which are the precursors of spermatogonial stem cells, are the only germ cell population. Transfection experiments demonstrated that recombinant porcine DDX4 can be expressed on the cell surface, and cell-surface DDX4-immunoreactive cells were identified in the testis by flow cytometry. Although the DDX4-expressing cells identified in the testis were indeed gonocytes, the cell-surface DDX4-immunoreactive cells expressed negligible DDX4 mRNA and protein levels. Furthermore, they did not express other germ cell markers, such as ZBTB16, NANOS2, and DAZL, but prominently expressed early primordial germ cell markers, such as PRDM1, IFITM3, and EPCAM. Nonetheless, the cell-surface DDX4-immunoreactive cells generated neither germ cell colonies nor teratomas following transplantation into immunocompromised mouse testes. Taken together, these results demonstrate that testicular cell-surface DDX4-immunoreactive cells are not germ cells and constitute a distinct subpopulation that is different from gonocytes. Moreover, the subpopulation in porcine testes might be species specific because no DDX4-immunoreactive cells were found in postnatal mouse testes.

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.

Lentiviral modification of enriched populations of bovine male gonocytes

Undifferentiated germ cells have the capacity to develop into sperm capable of fertilizing oocytes and contributing genetic material to subsequent generations. The most primitive prepubertal undifferentiated germ cells include gonocytes and undifferentiated spermatogonia, including spermatogonial stem cells (SSC). Gonocytes, present in the testis at birth, differentiate into SSC, which maintain spermatogenesis for the remainder of the male's life. Because of their capacity to contribute to lifelong spermatogenesis, undifferentiated germ cells are attractive targets for genetic modification to produce transgenic animals, including cattle. To maximize the efficiency of genetic modification of bovine gonocytes and SSC, effective enrichment techniques need to be developed. Selection of bovine gonocytes using differential plating was improved 8-fold (P < 0.001) when using a combination of extracellular matrix proteins, including laminin, fibronectin, collagen type IV, and gelatin, compared to using laminin and gelatin alone. Selected cells labeled with PKH26 formed colonies of donor-derived germ cells after transplantation into recipient mouse testes, indicating putative stem cell function. Significantly more colonies (P < 0.001) per 1 × 10(5) viable transplanted cells were formed from isolated nonadherent cells (203 ± 23.2) compared to adherent (20 ± 2.7) or Percoll (45.5 ± 4.5) selected cells. After selection, some gonocytes were transduced using a lentiviral vector containing the transgene for the enhanced green fluorescent protein. Transduction efficiency was 17%. Collectively, these data demonstrate effective methods for the selection and genetic modification of bovine undifferentiated germ cells.

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.

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.

Viral transduction of male germline stem cells results in transgene transmission after germ cell transplantation in pigs

Genetic modification of germline stem cells (GSCs) is an alternative approach to generate large transgenic animals where transgenic GSCs are transplanted into a recipient testis to generate donor-derived transgenic sperm. The objective of the present study was to explore the application of viral vectors in delivering an enhanced green fluorescent protein (EGFP) transgene into GSCs for production of transgenic gametes through germ cell transplantation. Both adeno-associated virus (AAV)- and lentivirus (LV)-based vectors were effective in transducing pig GSCs, resulting in the production of transgenic sperm in recipient boars. Twenty-one boars treated with busulfan to deplete endogenous GSCs and nine nontreated boars received germ cell transplantation at 12 wk of age. Semen was collected from recipient boars from 5 to 7 mo posttransplantation when boars became sexually mature, and semen collection continued for as long as 5 yr for some boars. The percentage of ejaculates that were positive for the EGFP transgene ranged from 0% to 54.8% for recipients of AAV vector-transduced germ cells (n = 17) and from 0% to 25% for recipients of LV vector-transduced germ cells (n = 5). When semen from two AAV recipients was used for in vitro fertilization (IVF), 9.09% and 64.3% of embryos were transgenic. Semen collected from two LV-vector recipients produced 7.7% and 26.3% transgenic IVF embryos. Here, we not only demonstrated AAV-mediated GSC transduction in another large animal model (pigs) but also showed, to our knowledge for the first time, that LV-mediated GSC transduction resulted in transgene transmission in pigs.

Cryopreservation in trehalose preserves functional capacity of murine spermatogonial stem cells

Development of techniques to isolate, culture, and transplant human spermatogonial stem cells (SSCs) has the future potential to treat male infertility. To maximize the efficiency of these techniques, methods for SSC cryopreservation need to be developed to bank SSCs for extended periods of time. Although, it has been demonstrated that SSCs can reinitiate spermatogenesis after freezing, optimal cryopreservation protocols that maximize SSC proliferative capacity post-thaw have not been identified. The objective of this study was to develop an efficient cryopreservation technique for preservation of SSCs. To identify efficient cryopreservation methods for long-term preservation of SSCs, isolated testis cells enriched for SSCs were placed in medium containing dimethyl sulfoxide (DMSO) or DMSO and trehalose (50 mM, 100 mM, or 200 mM), and frozen in liquid nitrogen for 1 week, 1 month, or 3 months. Freezing in 50 mM trehalose resulted in significantly higher cell viability compared to DMSO at all thawing times and a higher proliferation rate compared to DMSO for the 1 week freezing period. Freezing in 200 mM trehalose did not result in increased cell viability; however, proliferation activity was significantly higher and percentage of apoptotic cells was significantly lower compared to DMSO after freezing for 1 and 3 months. To confirm the functionality of SSCs frozen in 200 mM trehalose, SSC transplantation was performed. Donor SSCs formed spermatogenic colonies and sperm capable of generating normal progeny. Collectively, these results indicate that freezing in DMSO with 200 mM trehalose serves as an efficient method for the cryopreservation of SSCs.

Optimization of the conditions of isolation and culture of dairy goat male germline stem cells (mGSC)

Male germline stem cells (mGSC) reside in the basement of seminiferous tubules of the testis and have the capacity of self-renewal and differentiation into sperm throughout the life of animals. Reports on mice and human mGSC have demonstrated that mGSC are an unlimited resource of pluripotent stem cells for sperm production. The conditions of isolation and culture of mouse and human mGSC are well developed; however, the systematic culture conditions of dairy goat mGSC are still deficient although there have been several reports of successful cultures. With the present research, several key elements of isolation and culture of dairy goat mGSC have been determined. Details for the conditions of isolation of dairy testicular spermatogonium cells were optimized, and effects of several extracellular matrix types, ages of dairy goat, and cytokines on enrichment and culture of mGSC were compared. Biological characteristics of the cells were also evaluated by RT-PCR and immunofluorescent staining. The results indicated there is one kind of enzyme cocktail (CTHD (1mg/ml collagenase, 10μg/ml DNase, 1mg/ml hyaluronidase and 1mg/ml trypsin) combined TD (0.25% trypsin and 10mg/ml DNaseI)) that can be used to successfully isolate dairy goat testicular spermatogonium cells efficiently; and fibronectin as well as laminin were efficient extracellular matrix to enrich mGSC among the extracellular matrix types evaluated. Age of dairy goat clearly influenced the cultures of dairy goat mGSC with the efficiency of establishment of an mGSC line being greater if the age of the dairy goat is younger. Some cytokines e.g. BIO (A GSK3 inhibitor, 6-bromoindirubin-3'-oxime) and basic fibroblast growth factor (bFGF) acted positively on the maintenance of proliferation and pluripotency of mGSC. Leukemia inhibitory factor (LIF) might, however, inhibit the proliferation of dairy goat mGSC. These cultured mGSC maintained similar characteristics as mouse and human mGSC. These results provide an efficient system to isolate and culture of dairy goat mGSC.

Efficient enhancement of lentiviral transduction efficiency in murine spermatogonial stem cells

Spermatogonial stem cells (SSCs) are the foundation of spermatogenesis throughout postnatal life in male and have the ability to transmit genetic information to the subsequent generation. In this study, we have optimized the transduction efficiency of SSCs using a lentiviral vector by considering different multiplicity of infection (MOI), duration of infection, presence or absence of feeder layer and polycationic agents. We tested MOI of 5, 10 or 20 and infection duration of 6, 9 or 12 h respectively. After infection, cells were cultured for 1 week and as a result, the number of transduced SSCs increased significantly for MOI of 5 and 10 with 6 h of infection. When the same condition (MOI of 5 with 6 hours) was applied in presence or absence of STO feeder layer and infected SSCs were cultured for 3 weeks on the STO feeder layer, a significant increase in the number of transduced cells was observed for without the feeder layer during infection. We subsequently studied the effects of polycationic agents, polybrene and dioctadecylamidoglycyl spermine (DOGS), on the transduction efficiency. Compared with the polybrene treatment, the recovery rate of the transduced SSCs was significantly higher for the DOGS treatment. Therefore, our optimization study could contribute to the enhancement of germ-line modification of SSCs using lentiviral vectors and in generation of transgenic animals.

The Sda/GM2-glycan is a carbohydrate marker of porcine primordial germ cells and of a subpopulation of spermatogonia in cattle, pigs, horses and llama

Spermatogonia are a potential source of adult pluripotent stem cells and can be used for testis germ cell transplantation. Markers for the isolation of these cells are of great importance for biomedical applications. Primordial germ cells and prepubertal spermatogonia in many species can be identified by their binding of Dolichos biflorus agglutinin (DBA). This lectin binds to two different types of glycans, which are α-linked N-acetylgalactosamine (GalNac) and β-linked GalNac, if this is part of the Sda or GM2 glycotopes. We used the MAB CT1, which is specific for the trisaccharides motif NeuAcα2-3(GalNAcβ1-4)Galβ1-, which is common to both Sda and GM2 glycotopes, to further define the glycosylation of DBA binding germ cells. In porcine embryos, CT1 bound to migratory germ cells and gonocytes. CT1/DBA double staining showed that the mesonephros was CT1 negative but contained DBA-positive cells. Gonocytes in the female gonad became CT1 negative, while male gonocytes remained CT1 positive. In immunohistological double staining of cattle, pig, horse and llama testis, DBA and CT1 staining was generally colocalised in a subpopulation of spermatogonia. These spermatogonia were mainly single, sometimes paired or formed chains of up to four cells. Our data show that the Sda/GM2 glycotope is present in developing germ cells and spermatogonia in several species. Owing to the narrower specificity of the CT1 antibody, compared with DBA, the former is likely to be a useful tool for labelling and isolation of these cells.

Efficient purification of neonatal porcine gonocytes with Nycodenz and differential plating

Gonocytes are the only type of germ cells present in the postnatal testis and give rise to spermatogonial stem cells. Purification of gonocytes has important implications for the study and manipulation of these cells and may provide insights for the ongoing investigation of the male germline stem cells. To obtain a pure population of gonocytes from piglet testis cells, a wide range of Nycodenz concentrations were investigated for density gradient centrifugation. We also examined differential plating of testis cells for various culture durations with different extracellular matrix (ECM) components (fibronectin, poly-d-lysine, poly-l-lysine, laminin and collagen Types I and IV). Gonocytes were highly enriched in pellets of testis cells after using 17% Nycodenz centrifugation to a purity of 81 ± 9%. After culturing testis cells on plates precoated with different ECM components for 120 min, the proportion of gonocytes increased among non-adherent cells (suspended in the medium), with fibronectin or poly-d-lysine resulting in the greatest (up to 85%) and laminin in the lowest (54%) gonocyte proportion. Combining the most promising ECM coatings (fibronectin and poly-d-lysine) and further extension of their culture duration to 240 min did not improve final gonocyte purity. However, centrifugation with 17% Nycodenz followed by differential plating with fibronectin and poly-d-lysine coating further purified gonocytes among the collected cells to >90%. These results provide a simple, quick and efficient approach for obtaining highly enriched populations of piglet gonocytes for use in the study and manipulation of these germline stem cells.