Phenotypic and functional characteristics of spermatogonial stem cells in rats

Reestablishment of spermatogenesis after more than 20 years of cryopreservation of rat spermatogonial stem cells reveals an important impact in differentiation capacity

Treatment of cancer in children is increasingly successful but leaves many prepubertal boys suffering from infertility or subfertility later in life. A current strategy to preserve fertility in these boys is to cryopreserve a testicular biopsy prior to treatment with the expectation of future technologies allowing for the reintroduction of stem cells and restoration of spermatogenesis. Spermatogonial stem cells (SSCs) form the basis of male reproduction, differentiating into all germ cell types, including mature spermatozoa and can regenerate spermatogenesis following transplantation into an infertile testis. Here, we demonstrate that rat SSCs frozen for more than 20 years can be transplanted into recipient mice and produce all differentiating germ cell types. However, compared with freshly isolated cells or those frozen for a short period of time, long-frozen cells do not colonize efficiently and showed reduced production of spermatids. Single-cell RNA sequencing revealed similar profiles of gene expression changes between short- and long-frozen cells as compared with fresh immediately after thawing. Conversely, following transplantation, long-frozen samples showed enhanced stem cell signaling in the undifferentiated spermatogonia compartment, consistent with self-renewal and a lack of differentiation. In addition, long-frozen samples showed fewer round spermatids with detectable protamine expression, suggesting a partial block of spermatogenesis after meiosis resulting in a lack of elongating spermatids. These findings strongly suggest that prolonged cryopreservation can impact the success of transplantation to produce spermatogenesis, which may not be revealed by analysis of the cells immediately after thawing. Our analysis uncovered persistent effects of long-term freezing not found in other cryopreservation studies that lacked functional regeneration of the tissue and this phenomenon must be accounted for any future therapeutic application.

This study shows that spermatogonial stem cells frozen for more than 20 years can repopulate the niche when transplanted into an infertile host, but with lower efficiency and displaying abnormal spermatogenesis compared to fresh or short-term frozen cells. Single-cell RNA sequencing reveals details of the dysregulated signaling.

Unique metabolic phenotype and its transition during maturation of juvenile male germ cells

Human male reproductive development has a prolonged prepubertal period characterized by juvenile quiescence of germ cells with immature spermatogonial stem cell (SSC) precursors (gonocytes) present in the testis for an extended period of time. The metabolism of gonocytes is not defined. We demonstrate with mitochondrial ultrastructure studies via TEM and IHC and metabolic flux studies with UHPLC-MS that a distinct metabolic transition occurs during the maturation to SSCs. The mitochondrial ultrastructure of prepubertal human spermatogonia is shared with prepubertal pig spermatogonia. The metabolism of early prepubertal porcine spermatogonia (gonocytes) is characterized by the reliance on OXPHOS fuelled by oxidative decarboxylation of pyruvate. Interestingly, at the same time, a high amount of the consumed pyruvate is also reduced and excreted as lactate. With maturation, prepubertal spermatogonia show a metabolic shift with decreased OXHPOS and upregulation of the anaerobic metabolism-associated uncoupling protein 2 (UCP2). This shift is accompanied with stem cell specific promyelocytic leukemia zinc finger protein (PLZF) protein expression and glial cell-derived neurotropic factor (GDNF) pathway activation. Our results demonstrate that gonocytes differently from mature spermatogonia exhibit unique metabolic demands that must be attained to enable their maintenance and growth in vitro.

The Progresses of Spermatogonial Stem Cells Sorting Using Fluorescence-Activated Cell Sorting

In recent years, the research on stem cells has been more and more in-depth, and many achievements have been made in application. However, due to the small number of spermatogonial stem cells (SSCs) and deficiency of efficient markers, it is difficult to obtain very pure SSCs, which results in the research on them being hindered. In fact, many methods have been developed to isolate and purify SSCs, but these methods have their shortcomings. Fluorescence-activated cell sorting (FACS), as a method to enrich SSCs with the help of specific surface markers, has the characteristics of high efficiency and accuracy in enrichment of SSCs, thus it is widely accepted as an effective method for purification of SSCs. This review summarizes the recent studies on the application of FACS in SSCs, and introduces some commonly used markers of effective SSCs sorting, aiming to further optimize the FACS sorting method for SSCs, so as to promote the research of germline stem cells and provide new ideas for the research of reproductive biology.

Platelet-derived growth factor-BB and epidermal growth factor promote dairy goat spermatogonial stem cells proliferation via Ras/ERK1/2 signaling pathway

Spermatogonial stem cells (SSCs) have been used for the production of transgenic animals and for the recovery of male fertility. However, the proliferation of SSCs in vitro is still immature, and the mechanisms and pathways involved in the proliferation of SSCs are not clear. Here, the effects of platelet-derived growth factor-BB (PDGF-BB) and epidermal growth factor (EGF) on the proliferation of dairy goat SSCs in vitro were detected. The results showed that 20 ng/ml PDGF-BB or 25 ng/ml EGF was the optimum concentration, and that the BCL2 in the experimental groups was significantly higher than that in the control (P < 0.05), while BAX and BAD were dramatically downregulated (P < 0.05). The pERK1/2 in the experimental groups was about 3-5 times higher than that in the control. After the specific MEK1/2 inhibitor was added, BCL2 was reduced significantly (P < 0.001), while BAX and BAD were upregulated (P < 0.001). The expression of pERK1/2 decreased by 10%-30%. We speculated that these two growth factors may be mediated through the Ras/ERK1/2 signaling pathway to regulate the expression of pERK1/2 protein, and thus enhance the resistance of SSCs to apoptosis. However, further studies are needed to verify this hypothesis.

Investigation of cholestasis-related changes in characteristics of spermatogonial stem cells in testis tissue of male Wistar rats

Paternal metabolic status is an important factor in the health status of offspring. Cholestasis, as a metabolic disorder, significantly disrupts spermatogenesis. Spermatogonial stem cells (SSCs) are considered the dividing germ cells, which maintain spermatogenesis throughout the lifespan. Here, we investigated the in vivo and in vitro effect(s) of cholestasis on SSCs. Cholestasis was induced in rats by bile duct ligation. Four weeks after the cholestasis induction, testicular tissues were analysed using histopathological examinations. The expression of SSC markers, including Plzf and Thy-1, was determined using the immunofluorescent technique. Also, SSCs were isolated from animals, and their proliferation was examined in vitro. The histological examinations revealed that cholestasis caused irregularities in the structure of seminal tubes. Immunostaining showed that the total number of Thy-1- and Plzf-expressing cells was declined in the cholestasis group compared with the control group. In vitro culture of SSCs indicated that the number of SSC colonies and those expressing Plzf were significantly reduced in the culture medium of the cholestasis group. Our results indicated that cholestasis affects the functionality of SSCs and reduces the number and proliferation of them. This finding may be of interest to the effect of metabolic diseases such as cholestasis on spermatogenesis.

Production of quail (Coturnix japonica) germline chimeras by transfer of Ficoll-enriched spermatogonial stem cells

Due to the absence of long-term in vitro germline competent stem cell maintenance systems and efficient methods for germline transmission, efforts to develop an effective transgenic system in quail has remained limited. To overcome this limitation, here we produced germline chimeric quails through transplantation of spermatogonial stem cells (SSCs) enriched by density gradient methods utilizing Ficoll-Paque PLUS (Ficoll), Percoll and sucrose solution as a practical strategy for germline transmission in quail. For all gradient methods, testicular cells were separated as two fractions, and the expression levels of SSC-specific genes (GFRA1, ITGA6, ITGB1) and pluripotency genes (NANOG, POUV) were examined. As a result, quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and RNA probe hybridization analysis revealed that the upper fraction that was separated by Ficoll showed the highest expression of SSC-specific and pluripotency genes among all fractions. Cells in the upper Ficoll gradient fraction also displayed reduced heterochromatin distribution, as observed in differentiated spermatogonia using transmission electron microscopy (TEM). These results indicate that SSCs were enriched in the upper fraction by Ficoll density gradient centrifugation. Subsequent transplantation experiments revealed that the efficiency of germline transmission to donor-derived gametes in the germline chimeras with transplanted SSCs and whole testicular cells was 0-13.2% and 0-4.4%, respectively. Collectively, these results demonstrate that quail SSCs were easily enriched with a density gradient method and that this method is a feasible and practical way to preserve the germplasm of quail. Furthermore, we can expect to apply this method in research examining the production of transgenic quail and preservation of avian species.

Direct modification of spermatogonial stem cells using lentivirus vectors in vivo leads to efficient generation of transgenic rats

Spermatogonial stem cells (SSCs) transmit genetic information to the next progeny in males. Thus, SSCs are a potential target for germline modifications to generate transgenic animals. In this study, we report a technique for the generation of transgenic rats by in vivo manipulation of SSCs with a high success rate. SSCs in juvenile rats were transduced in vivo with high titers of lentivirus harboring enhanced green fluorescent protein and mated with wild-type females to create founder rats. These founder rats expressed the transgene and passed on the transgene with an overall success rate of 50.0%. Subsequent generations of progeny from the founder rats both expressed and passed on the transgene. Thus, direct modification of SSCs in juvenile rats is an effective means of generating transgenic rats through the male germline. This technology could be adapted to larger animals, in which existing methods for gene modification are inadequate or inapplicable, resulting in the generation of transgenic animals in a variety of species.

Does co-transplantation of mesenchymal and spermatogonial stem cells improve reproductive efficiency and safety in mice?

Background

Spermatogonial stem cell transplantation (SSCT) is a promising therapy in restoring the fertility of childhood cancer survivors. However, the low efficiency of SSCT is a significant concern. SSCT could be improved by co-transplanting transforming growth factor beta 1 (TGFβ1)-induced mesenchymal stem cells (MSCs). In this study, we investigated the reproductive efficiency and safety of co-transplanting spermatogonial stem cells (SSCs) and TGFβ1-induced MSCs.

Methods

A mouse model for long-term infertility was used to transplant SSCs (SSCT, n = 10) and a combination of SSCs and TGFβ1-treated MSCs (MSi-SSCT, n = 10). Both transplanted groups and a fertile control group (n = 7) were allowed to mate naturally to check the reproductive efficiency after transplantation. Furthermore, the testes from transplanted males and donor-derived male offspring were analyzed for the epigenetic markers DNA methyltransferase 3A (DNMT3A) and histone 4 lysine 5 acetylation (H4K5ac).

Results

The overall tubular fertility index (TFI) after SSCT (76 ± 12) was similar to that after MSi-SSCT (73 ± 14). However, the donor-derived TFI after MSi-SSCT (26 ± 14) was higher compared to the one after SSCT (9 ± 5; P = 0.002), even after injecting half of the number of SSCs in MSi-SSCT. The litter sizes after SSCT (3.7 ± 3.7) and MSi-SSCT (3.7 ± 3.6) were similar but differed significantly with the control group (7.6 ± 1.0; P < 0.001). The number of GFP⁺ offspring per litter obtained after SSCT (1.6 ± 0.5) and MSi-SSCT (2.0 ± 1.0) was also similar. The expression of DNMT3A and H4K5ac in germ cells of transplanted males was found to be significantly reduced compared to the control group. However, in donor-derived offspring, DNMT3A and H4K5ac followed the normal pattern.

Conclusion

Co-transplanting SSCs and TGFβ1-treated MSCs results in reproductive efficiency as good as SSCT, even after transplanting half the number of SSCs. Although transplanted males showed lower expression of DNMT3A and H4K5ac in donor-derived germ cells, the expression was restored to normal levels in germ cells of donor-derived offspring. This procedure could become an efficient method to restore fertility in a clinical setup, but more studies are needed to ensure safety in the long term.

Testicular endothelial cells promote self-renewal of spermatogonial stem cells in rats†

Spermatogonial stem cells (SSCs) are the basis of spermatogenesis in male due to their capability to multiply in numbers by self-renewal and subsequent meiotic processes. However, as SSCs are present in a very small proportion in the testis, in vitro proliferation of undifferentiated SSCs will facilitate the study of germ cell biology. In this study, we investigated the effectiveness of various cell lines as a feeder layer for rat SSCs. Germ cells enriched for SSCs were cultured on feeder layers including SIM mouse embryo-derived thioguanine and ouabain-resistant cells, C166 cells, and mouse and rat testicular endothelial cells (TECs) and their stem cell potential for generating donor-derived colonies and offspring was assessed by transplantation into recipient testes. Rat germ cells cultured on TECs showed increased mRNA and protein levels of undifferentiated spermatogonial markers. Rat SSCs derived from these germ cells underwent spermatogenesis and generated offspring when transplanted into recipients. Collectively, TECs can serve as an effective feeder layer that enhances the proliferative and self-renewal capacity of cultured rat SSCs while preserving their stemness properties.

Spermatogonial stem cells

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

Development of An Artificial Male Germ Cell Niche Using Electrospun Poly Vinyl Alcohol/Human Serum Albumin/Gelatin Fibers

Objective

Recent achievements in stem cell biotechnology, nanotechnology and tissue engineering have led to development of novel approaches in regenerative medicine. Azoospermia is one of the challenging disorders of the reproductive system. Several efforts were made for isolation and culture of testis-derived stem cells to treat male infertility. However, tissue engineering is the best approach to mimic the three dimensional microenvironment of the testis in vitro. We investigated whether human testis-derived cells (hTCs) obtained by testicular sperm extraction (TESE) can be cultured on a homemade scaffold composed of electrospun nanofibers of homogeneous poly (vinyl alcohol)/human serum albumin/gelatin (PVA/HSA/gelatin).

Materials and Methods

In this experimental lab study, human TCs underwent two steps of enzymatic cell isolation and five culture passages. Nanofibrous scaffolds were characterized by scanning electron microscopy (SEM) and Fourier- transform infrared spectroscopy (FTIR). Attachment of cells onto the scaffold was shown by hematoxylin and eosin (H&E) staining and SEM. Cell viability study using MTT [3-(4, 5-dimethyl-2-thiazolyl) -2, 5-diphenyl -2H- tetrazolium bromide] assay was performed on days 7 and 14.

Results

Visualization by H&E staining and SEM indicated that hTCs were seeded on the scaffold. MTT test showed that the PVA/HSA/gelatin scaffold is not toxic for hTCs.

Conclusion

It seems that this PVA/HSA/gelatin scaffold is supportive for growth of hTCs.

Purging of malignant cell contamination prior to spermatogonia stem cell autotransplantation to preserve fertility: progress & prospects

PURPOSE OF REVIEW

This systematic review evaluates the state of the art in terms of strategies used to detect and remove contaminated malignant cells from testicular biopsy prior to spermatogonia stem cells (SSCs) autotransplantation to restore fertility.

RECENT FINDINGS

Several trials have been done in past two decades to determine the reliable methods of detecting and purging cancer cells prior to SSCs autotransplantation.

SUMMARY

The success in treating childhood cancer has dramatically increased over the past few decades. This leads to increasing demand for a method of fertility preservation for patients with pediatric cancer, as many cancer therapies can be gonadotoxic. Storing the SSCs prior to chemo- or radiation therapies and transplanting them back has been tested as a method of restoring fertility in rodents and nonhuman primate models. This has promise for restoring fertility in childhood cancer survivors. One of the major concerns is the possibility of malignant cell presence in testicular tissue biopsies that could re-introduce cancer to the patient after SSCs autotransplantation. Non-solid cancers - especially hematologic malignancies - have the risk of being transplanted back into patients after SSCs cryopreservation even if they were only present in small number in the stored testicular tissue biopsy.

Cped1 promotes chicken SSCs formation with the aid of histone acetylation and transcription factor Sox2

Spermatogonial stem cells (SSCs) may apply to gene therapy, regenerative medicine in place of embryonic stem cells (ESCs). However, the application of SSCs was severely limited by the low induction efficiency and the lack of thorough analysis of the regulatory mechanisms of SSCs formation. Current evidences have demonstrated multiple marker genes of germ cells, while genes that specifically regulate the formation of SSCs have not been explored. In our study, cadherin-like and PC-esterase domain containing 1 (Cped1) expressed specifically in SSCs based on RNA-seq data analysis. To study the function of Cped1 in the formation of SSCs, we successfully established a CRISPR/Cas9 knockout system. The gene disruption frequency is 37% in DF1 and 25% in ESCs without off-target effects. Knockout of Cped1 could significantly inhibit the formation of SSCs in vivo and in vitro The fragment of -1050 to -1 bp had the activity as Cped1 gene promoter. Histone acetylation could regulate the expression of Cped1. We added 5-azaeytidi (DNA methylation inhibitors) and TSA (histone deacetylase inhibitors) respectively during the cultivation of SSCs. TSA was validated to promote the transcription of Cped1. Dual-luciferase reporter assay revealed that active control area of the chicken Cped1 gene is -296 to -1 bp. There are Cebpb, Sp1, and Sox2 transcription factor binding sites in this region. Point-mutation experiment results showed that Sox2 negatively regulates the transcription of Cped1. Above results demonstrated that Cped1 is a key gene that regulates the formation of SSCs. Histone acetylation and transcription factor Sox2 participate in the regulation of Cped1.

Biology and manipulation technologies of male germline stem cells in mammals

BACKGROUND

Spermatogonial stem cells (SSCs) are the origin of sperm and defined by their functions of "colonization in the testis" and "spermatogenesis". In vitro manipulation techniques of SSCs contribute to a wide variety of fields including reproductive medicine and molecular breeding. This review presents the recent progress of the biology and manipulation technologies of SSCs.

METHODS

Research articles regarding SSC biology and technologies were collected and summarized.

MAIN FINDINGS

Dr. Ralph Brinster developed the spermatogonial transplantation technique that enables SSC detection by functional markers. Using this technique, cultured SSCs, termed germline stem (GS) cells, were established from the mouse. GS cells provide the opportunity to produce genome-edited animals without using zygotes. In vitro spermatogenesis allows production of haploid germ cells from GS cells without spermatogonial transplantation. The recent advancement of pluripotent stem cell culture techniques has also achieved production of functional GS-like cells in addition to male/female germ cells.

CONCLUSION

Although in vitro manipulation techniques of GS cells have been developed for the mouse, it appears to be difficult to apply these techniques to other species. Understanding and control of interspecies barriers are required to extend this technology to nonrodent mammals.

Gasoline exhaust damages spermatogenesis through downregulating α6-integrin and β1-integrin in the rat model

The health influence of air pollution has been an international public health concern. Increasing evidence has suggested that air pollution has been associated with decreased sperm quality. However, the underlying molecular mechanisms are still not fully elucidated. We aimed to verify whether gasoline exhaust leads to reproductive impairment by injuring spermatogonial stem cells and explore its underlying molecular mechanism. Twenty male Sprague-Dawley rats were randomly divided into two groups: the exposure group (n = 10) and the control group (n = 10). After 6-month exposure, the sperm count and morphology were determined. The histological changes in the seminiferous tubules were examined by HE staining. The expression of α6-integrin and β1-integrin was assessed with Quantitative RT-PCR, Western blot and Immunohistochemical staining. Compared with control group, male rats exposed to gasoline exhaust showed significantly reduced sperm count, increased sperm abnormality rate and the total number of spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids were decreased. (all p < .01). The expression levels of α6-integrin and β1-integrin in the exposure group were significantly lower than those in the control group (all p < .01). Our study showed that exposure to gasoline exhaust caused impairment to spermatogonial stem cells through downregulating α6-integrin and β1-integrin.

Spermatogonial stem cells and spermatogenesis in mice, monkeys and men

Continuous spermatogenesis in post-pubertal mammals is dependent on spermatogonial stem cells (SSCs), which balance self-renewing divisions that maintain stem cell pool with differentiating divisions that sustain continuous sperm production. Rodent stem and progenitor spermatogonia are described by their clonal arrangement in the seminiferous epithelium (e.g., A_single, A_paired or A_aligned spermatogonia), molecular markers (e.g., ID4, GFRA1, PLZF, SALL4 and others) and most importantly by their biological potential to produce and maintain spermatogenesis when transplanted into recipient testes. In contrast, stem cells in the testes of higher primates (nonhuman and human) are defined by description of their nuclear morphology and staining with hematoxylin as A_dark and A_pale spermatogonia. There is limited information about how dark and pale descriptions of nuclear morphology in higher primates correspond with clone size, molecular markers or transplant potential. Do the apparent differences in stem cells and spermatogenic lineage development between rodents and primates represent true biological differences or simply differences in the volume of research and the vocabulary that has developed over the past half century? This review will provide an overview of stem, progenitor and differentiating spermatogonia that support spermatogenesis; identifying parallels between rodents and primates where they exist as well as features unique to higher primates.

Human spermatogonial markers

In this review, we provide an up-to-date compilation of published human spermatogonial markers, with focus on the three nuclear subtypes A_dark, A_pale and B. In addition, we have extended our recently published list of putative spermatogonial markers with protein expression and RNA-sequencing data from the Human Protein Atlas and supported these by literature evidence. Most importantly, we have put substantial effort in acquiring a comprehensive list of new and potentially interesting markers by refiltering the raw data of 15 published germ cell expression datasets (four human, eleven rodent) and subsequent building of intersections to acquire a robust, cross-species set of spermatogonia-enriched or -specific transcripts.

Profiling of miRNAs in porcine germ cells during spermatogenesis

Spermatogenesis includes mitosis of spermatogonia, meiosis of pachytene spermatocytes and spermiogenesis of round spermatids. MiRNAs as a ~22 nt small noncoding RNA are involved in regulating spermatogenesis at post-transcriptional level. However, the dynamic miRNAs expression in the developmental porcine male germ cells remains largely undefined. In this study, we purified porcine spermatogonia, pachytene spermatocytes and round spermatids using a STA-PUT apparatus. A small RNA deep sequencing and analysis were conducted to establish a miRNAs profiling in these male germ cells. We found that 19 miRNAs were differentially expressed between spermatogonia and pachytene spermatocytes, and 74 miRNAs differentially expressed between pachytene spermatocytes and round spermatids. Furthermore, 91 miRNAs were upregulated, while 108 miRNAs were downregulated in spermatozoa. We demonstrated that ssc-miR-10a-5p, ssc-miR-125b, ssc-let-7f and ssc-miR-186 were highly expressed in spermatogonia, pachytene spermatocytes, round spermatids and spermatozoa respectively. The findings could provide novel insights into roles of miRNAs in regulation of porcine spermatogenesis.

Embryonic stem cell derived germ cells induce spermatogenesis after transplantation into the testes of an adult mouse azoospermia model

The present study aimed to: (i) identify the exogenous factors that allow in vitro differentiation of mouse spermatogonial stem cells (SSCs) from embryonic stem cells (ESCs); (ii) evaluate the effects of Sertoli cells in SSC enrichment; and (iii) assess the success of transplantation using in vitro differentiated SSCs in a mouse busulfan-treated azoospermia model. A 1-day-old embryoid body (EB) received 5 ng/ml of bone morphogenetic protein 4 (BMP4) for 4 days, 3 µM retinoic acid (RA) in a SIM mouse embryo-derived thioguanine and ouabain resistant (STO) co-culture system for 7 days, and was subsequently co-cultured for 2 days with Sertoli cells in the presence or absence of a leukaemia inhibitory factor (LIF), basic fibroblast growth factor (bFGF) and RA composition, and in the presence of these factors in simple culture medium. Higher viability, proliferation and germ cell gene expression were seen in the presence of the LIF, bFGF and RA composition, on top of Sertoli cells. Immunocytochemistry results showed higher CDH1 expression in this group. Sertoli co-culture had no effects on SSC proliferation. Eight weeks after transplantation, injected cells were observed at the base of the seminiferous tubules and in the recipient testes. The number of spermatogonia and the mass of the testes were higher in transplanted testes relative to the control group. It seems that transplantation of these cells can be useful in infertility treatment.

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.

CD61 promotes the differentiation of canine ADMSCs into PGC-like cells through modulation of TGF-β signaling

Previous studies have shown that CD61 (integrin-β3) promotes the differentiation of human umbilical cord mesenchymal stem cells (hUC-MSCs) into germ-like cells. However, the mechanism remains unclear. In this study, we showed that overexpression of CD61 in canine adipose-derived mesenchymal stem cells (cADMSCs) promotes their differentiation into primordial germ cell (PGC)-like cells. Quantitative real-time PCR, immunocytochemistry and western blot detected higher levels of PGC-specific markers in CD61-overexpressed cADMSCs compared with those in control cells. Moreover, phosphorylation of Smad2, a downstream mediator of transforming growth factor beta (TGF-β), was increased in CD61-overexpressed cADMSCs than that in control cells. However, the expression of PGC-specific markers was downregulated in cADMSCs treated with a TGF-β inhibitor. These results suggested that CD61 could induce cADMSCs to differentiate into PGC-like cells by relying on the activation of TGF-β pathway. ADMSCs possess a considerable potential in treating the infertility of rare animal species.

Molecular markers of putative spermatogonial stem cells in the domestic cat

Spermatogonial stem cells (SSCs) are an important tool for fertility preservation and species conservation. The ability to expand SSCs by in vitro culture is a crucial premise for their use in assisted reproduction. Because SSCs represent a small proportion of the germ cells in the adult testis, culture success is aided by pre-enrichment through sorting techniques based on cell surface-specific markers. Given the importance of the domestic cat as a model for conservation of endangered wild felids, herein we sought to examine culture conditions as well as molecular markers for cat SSCs. Using a cell culture medium for mouse SSCs supplemented with glial cell-derived neurotrophic factor (GDNF), germ cells from prepuberal cat testes remained viable in culture for up to 43 days. Immunohistochemistry for promyelocytic leukaemia zinc finger (PLZF) protein on foetal, prepuberal and adult testis sections revealed a pattern of expression consistent with the labelling of undifferentiated spermatogonia. Fluorescence-activated cell sorting (FACS) with an antibody against epithelial cell adhesion molecule (EPCAM) was used to sort live cells. Then, the gene expression profile of EPCAM-sorted cells was investigated through RT-qPCR. Notably, EPCAM (+) cells expressed relatively high levels of CKIT (CD117), a surface protein typically expressed in differentiating germ cells but not SSCs. Conversely, EPCAM (-) cells expressed relatively high levels of POU domain class 5 transcription factor 1 (POU1F5 or OCT4), clearly a germ line stem cell marker. These results suggest that cat SSCs would probably be found within the population of EPCAM (-) cells. Future studies should identify additional surface markers that alone or in combination can be used to further enrich SSCs from cat germ cells.

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

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

Human spermatogonial stem cells display limited proliferation in vitro under mouse spermatogonial stem cell culture conditions

OBJECTIVE

To study the ability of human spermatogonial stem cells (hSSCs) to proliferate in vitro under mouse spermatogonial stem cell (mSSC) culture conditions.

DESIGN

Experimental basic science study.

SETTING

Reproductive biology laboratory.

PATIENT(S)

Cryopreserved testicular tissue with normal spermatogenesis obtained from three donors subjected to orchiectomy due to a prostate cancer treatment.

INTERVENTION(S)

Testicular cells used to create in vitro cell cultures corresponding to the following groups: [1] unsorted human testicular cells, [2] differentially plated human testicular cells, and [3] cells enriched with major histocompatibility complex class 1 (HLA^-)/epithelial cell surface antigen (EPCAM⁺) in coculture with inactivated testicular feeders from the same patient.

MAIN OUTCOME MEASURE(S)

Analyses and characterization including immunocytochemistry and quantitative reverse-transcription polymerase chain reaction for somatic and germ cell markers, testosterone and inhibin B quantification, and TUNEL assay.

RESULT(S)

Putative hSSCs appeared in singlets, doublets, or small groups of up to four cells in vitro only when testicular cells were cultured in StemPro-34 medium supplemented with glial cell line-derived neurotrophic factor (GDNF), leukemia inhibitory factor (LIF), basic fibroblast growth factor (bFGF), and epidermal growth factor (EGF). Fluorescence-activated cell sorting with HLA^-/EPCAM⁺ resulted in an enrichment of 27% VASA⁺/UTF1⁺ hSSCs, compared to 13% in unsorted controls. Coculture of sorted cells with inactivated testicular feeders gave rise to an average density of 112 hSSCs/cm² after 2 weeks in vitro compared with unsorted cells (61 hSSCs/cm²) and differentially plated cells (49 hSSCS/cm²). However, putative hSSCs rarely stained positive for the proliferation marker Ki67, and their presence was reduced to the point of almost disappearing after 4 weeks in vitro.

CONCLUSION(S)

We found that hSSCs show limited proliferation in vitro under mSSC culture conditions. Coculture of HLA^-/EPCAM⁺ sorted cells with testicular feeders improved the germ cell/somatic cell ratio.

Production of fertile sperm from in vitro propagating enriched spermatogonial stem cells of farmed catfish, Clarias batrachus

Spermatogenesis is a highly co-ordinated and complex process. In vitro propagation of spermatogonial stem cells (SSCs) could provide an avenue in which to undertake in vivo studies of spermatogenesis. Very little information is known about the SSC biology of teleosts. In this study, collagenase-treated testicular cells of farmed catfish (Clarias batrachus, popularly known as magur) were purified by Ficoll gradient centrifugation followed by magnetic activated cell sorting using Thy1.2 (CD90.2) antibody to enrich for the spermatogonial cell population. The sorted spermatogonial cells were counted and gave ~3 × 106 cells from 6 × 106 pre-sorted cells. The purified cells were cultured in vitro for >2 months in L-15 medium containing fetal bovine serum (10%), carp serum (1%) and other supplements. Microscopic observations depicted typical morphological SSC features, bearing a larger nuclear compartment (with visible perinuclear bodies) within a thin rim of cytoplasm. Cells proliferated in vitro forming clumps/colonies. mRNA expression profiling by qPCR documented that proliferating cells were Plzf + and Pou2+, indicative of stem cells. From 60 days onwards of cultivation, the self-renewing population differentiated to produce spermatids (~6 × 107 on day 75). In vitro-produced sperm (2260 sperm/SSC) were free swimming in medium and hence motile (non-progressive) in nature. Of those, 2% were capable of fertilizing and generated healthy diploid fingerlings. Our documented evidence provides the basis for producing fertile magur sperm in vitro from cultured magur SSCs. Our established techniques of SSC propagation and in vitro sperm production together should trigger future in vivo experiments towards basic and applied biology research.

Pluripotency and differentiation of cells from human testicular sperm extraction: An investigation of cell stemness

Human male germ-line stem cells (hmGSCs) and human testis-derived embryonic stem cell-like (htESC-like) cells are claimed to be in vitro pluripotent counterparts of spermatogonial stem cells (SSCs), but the origin and pluripotency of human testis-derived cell cultures are still under debate. The aim of this study was to generate putative pluripotent stem cells in vitro from human testicular sperm-extracted (TESE) samples of infertile men, and to assess their pluripotency and capacity to differentiate. TESE samples were minced, enzymatically disaggregated and dispersed into single-cell or cluster suspensions, and then cultured. Initially, cell clusters resembled those described for hmGSCs and htESC-like cells, and were positive for markers such as OCT4/POU5F1, NANOG, and TRA-2-54. Prolonged propagation of cell clusters expressing pluripotency markers did not thrive; instead, the cells that emerged possessed characteristics of mesenchymal stromal cells (MSCs) such as STRO-1, CD105/EGLN1, CD13/ANPEP, SOX9, vimentin, and fibronectin. KIT, SOX2, and CD44 were not expressed by these MSCs. The multipotential differentiation capacity of these cells was confirmed using Oil Red-O and Alizarin Red staining after induction with specific culture conditions. It is therefore concluded that pluripotent stem cells could not be derived using the conditions previously reported to be successful for TESE samples.

Enrichment of Mouse Spermatogonial Stem Cells by the Stem Cell Dye CDy1

Spermatogonial stem cells (SSCs) comprise a small population of germ cells with self-renewal potential. Previous studies have shown that SSCs share several common features with stem cells in other self-renewing tissues, including surface markers and proliferative machinery. However, studies of SSCs are severely handicapped by the small number of SSCs and the lack of SSC-specific markers. In the present study, we examined the utility of CDy1 and Rh123, both of which are used for the collection of stem cells in several self-renewing tissues. CDy1 stained germline stem (GS) cells, cultured spermatogonia enriched for SSC activity, after in vitro incubation without exerting toxic effects. Unlike previously reported stem cell-specific dyes, CDy1 was also useful for enrichment of SSCs in both GS cell culture and mature adult testes. Spermatogonial transplantation showed that ∼1 in 66.7 cells exhibited SSC activity after CDH1-based magnetic cell selection and CDy1 staining. In contrast, although Rh123 was previously used successfully to collect SSCs from cryptorchid testes, it was not possible to recover SSCs from both GS cell cultures and wild-type testes. Thus, CDy1 staining will provide a useful strategy for the enrichment of SSCs and may be used in conjunction with other reagents for the enrichment of SSCs.

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

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

Analysis of POU5F1, c-Kit, PLAP, AP2γ and SALL4 in gonocytes of patients with cryptorchidism

Cryptorchidism is a risk factor for the development of testicular germ cell tumors (TGCTs). The most common type of TGCT in cryptorchidism is seminoma. The intratubular germ cell neoplasia unclassified (ITGCNU) is a histological pattern preceding the development of seminomas and non-seminomas. It was suggested that in patients with cryptorchidism, the gonocytes remained undifferentiated with pluripotent abilities expressing proteins like POU domain class 5 transcription factor 1 (POU5F1), tyrosine kinase receptor c-Kit, placental-like alkaline phosphatase (PLAP), the transcription factor AP2γ and sal-like protein 4 (SALL4) that confer to the gonocytes this ability and therefore make them susceptible to develop ITGCNU. The aim of the present study was to determine if the gonocytes of patients with cryptorchidism express POU5F1, c-Kit, PLAP, AP2γ and SALL4 proteins after their differentiation period. Based on this, we evaluated samples of testicular tissue from newborns to 16-year old subjects with or without cryptorchidism in search of POU5F1, c-Kit, PLAP, AP2γ and SALL4 using immunocytochemical method, the results of which were validated by RT-PCR. The results showed that control subjects witnessed a down-regulation in the expression of these five proteins in the first year of life, which eventually disappeared. On the other hand, it was determined that 21.6% (8/37) of the patients with cryptorchidism continued to express, at least, one of the proteins analyzed in this study after the second year of life. And only 5.4% (2/37) of the patients were positive to the five markers. These data sustain the proposed hypothesis that in cryptorchid patients, ITGCNU arises from gonocytes that fail in their differentiation process to spermatogonia with conservation of the proteins (POU5F1, c-Kit, PLAP, AP2γ and SALL4) that maintain pluripotency and undifferentiated characteristics and which are responsible for making the gonocytes susceptible to malignancy. However, we cannot guarantee that these patients present neoplastic transformation.

Determination phase at transition of gonocytes to spermatogonial stem cells improves establishment efficiency of spermatogonial stem cells in domestic cats

The development of germ cells has not been entirely documented in the cat especially the transition phase of the gonocyte to the spermatogonial stem cell (G/SSC). The aims of study were to examine testicular development and to identify the G/SSC transition in order to isolate and culture SSCs in vitro. Testes were divided into 3 groups according to donor age (I, < 4 months; II, 4–6 months; and III, > 6 months). In Exp. 1, we studied testicular development by histology, transmission electron microscopy and immunohistochemistry. In Exp. 2, we determined the expression of GFRα-1, DDX-4 and c-kit and performed flow cytometry. The SSCs isolated from groups II and III were characterized by RT-PCR and TEM (Exp. 3). Chronological changes in the G/SSC transition were demonstrated. The size, morphology and ultrastructure of SSCs were distinguishable from those of gonocytes. The results demonstrated that group II contained the highest numbers of SSCs per seminiferous cord/tubule (17.66 ± 2.20%) and GFRα-1⁺ cells (14.89 ± 5.66%) compared with the other groups. The findings coincided with an increased efficiency of SSC derivation in group II compared with group III (74.33 ± 2.64% vs. 23.33 ± 2.23%). The colonies expressed mRNA for GFRA1, ZBTB16, RET and POU5F1. Our study found that the G/SSC transition occurs at 4–6 months of age. This period is useful for isolation and improves the establishment efficiency of cat SSCs in vitro.

Petasites japonicus Stimulates the Proliferation of Mouse Spermatogonial Stem Cells

Oriental natural plants have been used as medical herbs for the treatment of various diseases for over 2,000 years. In this study, we evaluated the effect of several natural plants on the preservation of male fertility by assessing the ability of plant extracts to stimulate spermatogonial stem cell (SSC) proliferation by using a serum-free culture method. In vitro assays showed that Petasites japonicus extracts, especially the butanol fraction, have a significant effect on germ cells proliferation including SSCs. The activity of SSCs cultured in the presence of the Petasites japonicus butanol fraction was confirmed by normal colony formation and spermatogenesis following germ cell transplantation of the treated SSCs. Our findings could lead to the discovery of novel factors that activate SSCs and could be useful for the development of technologies for the prevention of male infertility.

Artificial gametes from stem cells

The generation of artificial gametes is a real challenge for the scientific community today. In vitro development of human eggs and sperm will pave the way for the understanding of the complex process of human gametogenesis and will provide with human gametes for the study of infertility and the onset of some inherited disorders. However, the great promise of artificial gametes resides in their future application on reproductive treatments for all these people wishing to have genetically related children and for which gamete donation is now their unique option of parenthood. This is the case of infertile patients devoid of suitable gametes, same sex couples, singles and those fertile couples in a high risk of transmitting serious diseases to their progeny. In the search of the best method to obtain artificial gametes, many researchers have successfully obtained human germ cell-like cells from stem cells at different stages of differentiation. In the near future, this field will evolve to new methods providing not only viable but also functional and safe artificial germ cells. These artificial sperm and eggs should be able to recapitulate all the genetic and epigenetic processes needed for the correct gametogenesis, fertilization and embryogenesis leading to the birth of a healthy and fertile newborn.

Mammalian gonocyte and spermatogonia differentiation: recent advances and remaining challenges

The production of spermatozoa relies on a pool of spermatogonial stem cells (SSCs), formed in infancy from the differentiation of their precursor cells, the gonocytes. Throughout adult life, SSCs will either self-renew or differentiate, in order to maintain a stem cell reserve while providing cells to the spermatogenic cycle. By contrast, gonocytes represent a transient and finite phase of development leading to the formation of SSCs or spermatogonia of the first spermatogenic wave. Gonocyte development involves phases of quiescence, cell proliferation, migration, and differentiation. Spermatogonia, on the other hand, remain located at the basement membrane of the seminiferous tubules throughout their successive phases of proliferation and differentiation. Apoptosis is an integral part of both developmental phases, allowing for the removal of defective cells and the maintenance of proper germ–Sertoli cell ratios. While gonocytes and spermatogonia mitosis are regulated by distinct factors, they both undergo differentiation in response to retinoic acid. In contrast to postpubertal spermatogenesis, the early steps of germ cell development have only recently attracted attention, unveiling genes and pathways regulating SSC self-renewal and proliferation. Yet, less is known on the mechanisms regulating differentiation. The processes leading from gonocytes to spermatogonia have been seldom investigated. While the formation of abnormal gonocytes or SSCs could lead to infertility, defective gonocyte differentiation might be at the origin of testicular germ cell tumors. Thus, it is important to better understand the molecular mechanisms regulating these processes. This review summarizes and compares the present knowledge on the mechanisms regulating mammalian gonocyte and spermatogonial differentiation.

Differential nanoreprotoxicity of silver nanoparticles in male somatic cells and spermatogonial stem cells

Background

Silver nanoparticles (AgNPs) possess unique physical, chemical, and biological properties. AgNPs have been increasingly used as anticancer, antiangiogenic, and antibacterial agents for the treatment of bacterial infections in open wounds as well as in ointments, bandages, and wound dressings. The present study aimed to investigate the effects of two different sizes of AgNPs (10 nm and 20 nm) in male somatic Leydig (TM3) and Sertoli (TM4) cells and spermatogonial stem cells (SSCs).

Methods

Here, we demonstrate a green and simple method for the synthesis of AgNPs using Bacillus cereus culture supernatants. The synthesized AgNPs were characterized using ultraviolet and visible absorption spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy (TEM). The toxicity of the synthesized AgNPs was evaluated by the effects on cell viability, metabolic activity, oxidative stress, apoptosis, and expression of genes encoding steroidogenic and tight junction proteins.

Results

AgNPs inhibited the viability and proliferation of TM3 and TM4 cells in a dose- and size-dependent manner by damaging cell membranes and inducing the generation of reactive oxygen species, which in turn affected SSC growth on TM3 and TM4 as feeder cells. Small AgNPs (10 nm) were more cytotoxic than medium-sized nanoparticles (20 nm). TEM revealed the presence of AgNPs in the cell cytoplasm and nucleus, and detected mitochondrial damage and enhanced formation of autosomes and autolysosomes in the AgNP-treated cells. Flow cytometry analysis using Annexin V/propidium iodide staining showed massive cell death by apoptosis or necrosis. Real-time polymerase chain reaction and western blot analyses indicated that in TM3 and TM4 cells, AgNPs activated the p53, p38, and pErk1/2 signaling pathways and significantly downregulated the expression of genes related to testosterone synthesis (TM3) and tight junctions (TM4). Furthermore, the exposure of TM3 and TM4 cells to AgNPs inhibited proliferation and self-renewal of SSCs.

Conclusion

Our results suggest that AgNPs exhibit size-dependent nanoreprotoxicity in male somatic cells and SSCs, strongly suggesting that applications of AgNPs in commercial products must be carefully evaluated. Further studies of AgNPs-induced nanoreprotoxicity in animal models are required.

Construction and analysis of a protein-protein interaction network related to self-renewal of mouse spermatogonial stem cells

Spermatogonial stem cells (SSCs) are responsible for sustained spermatogenesis throughout the reproductive life of the male. Extensive studies of SSCs have identified dozens of genes that play important roles in sustaining or controlling the pool of SSCs in the mammalian testis. However, there is still limited knowledge of whether or how these key genes interact with each other during SSC self-renewal. Here, we constructed a protein-protein interaction (PPI) network for SSC self-renewal based on interactions between 23 genes essential for SSC self-renewal, which were obtained from a text mining system, and the interacting partners of the 23 key genes, which were differentially expressed in SSCs. The SSC self-renewal PPI network consisted of 246 nodes connected by 844 edges. Topological analyses of the PPI network were conducted to identify genes essential for maintenance of SSC self-renewal. The subnetwork of the SSC self-renewal network suggested that the 23 key genes involved in SSC self-renewal were connected together through other 94 genes. Clustering of the whole network and subnetwork of SSC self-renewal revealed several densely connected regions, implying significant molecular interaction modules essential for SSC self-renewal. Notably, we found the 23 genes to be responsible for SSC self-renewal by forming a continuous PPI network centered on Pou5f1. Our study indicates that it is feasible to explore important proteins and regulatory pathways in biological activities by combining a PPI database with the high-throughput data of gene expression profiles.

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.

Establishment of a proteome profile and identification of molecular markers for mouse spermatogonial stem cells

Spermatogonial stem cells (SSCs) are undifferentiated cells that are required to maintain spermatogenesis throughout the reproductive life of mammals. Although SSC transplantation and culture provide a powerful tool to identify the mechanisms regulating SSC function, the precise signalling mechanisms governing SSC self-renewal and specific surface markers for purifying SSCs remain to be clearly determined. In the present study, we established a steady SSC culture according to the method described by Shinohara's lab. Fertile progeny was produced after transplantation of cultured SSCs into infertile mouse testis, and the red fluorescence exhibited by the culture cell membranes was stably and continuously transmitted to the offspring. Next, via advanced mass spectrometry and an optimized proteomics platform, we constructed the proteome profile, with 682 proteins expressed in SSCs. Furthermore bioinformatics analysis showed that the list contained several known molecules that are regulated in SSCs. Several nucleoproteins and membrane proteins were chosen for further exploration using immunofluorescence and RT-PCR. The results showed that SALL1, EZH2, and RCOR2 are possibly involved in the self-renewal mechanism of SSCs. Furthermore, the results of tissue-specific expression analysis showed that Gpat2 and Pld6 were uniquely and highly expressed in mouse testes and cultured SSCs. The cellular localization of PLD6 was further explored and the results showed it was primarily expressed in the spermatogonial membrane of mouse testes and cultured SSCs. The proteins identified in this study form the basis for further exploring the molecular mechanism of self-renewal in SSCs and for identifying specific surface markers of SSCs.

Models of in vitro spermatogenesis

Understanding the mechanisms that lead to the differentiation of male germ cells from their spermatogonial stem cells through meiosis to give rise to mature haploid spermatozoa has been a major quest for many decades. Unlike most other cell types this differentiation process is more or less completely dependent upon the cells being located within the strongly structured niche provided by mature Sertoli cells within an intact seminiferous epithelium. While much new information is currently being obtained through the application and description of relevant gene mutations, there is still a considerable need for in vitro models with which to explore the mechanisms involved. Not only are systems of in vitro spermatogenesis important for understanding the basic science, they have marked pragmatic value in offering ex vivo systems for the artificial maturation of immature germ cells from male infertility patients, as well as providing opportunities for the transgenic manipulation of male germ cells. In this review, we have summarized literature relating to simplistic culturing of germ cells, co-cultures of germ cells with other cell types, especially with Sertoli cells, cultures of seminiferous tubule fragments, and briefly mention the opportunities of xenografting larger testicular pieces. The majority of methods are successful in allowing the differentiation of small steps in the progress of spermatogonia to spermatozoa; few tolerate the chromosomal reduction division through meiosis, and even fewer seem able to complete the complex morphogenesis which results in freely swimming spermatozoa. However, recent progress with complex culture environments, such as 3-d matrices, suggest that possibly success is now not too far away.

Effects of different levels of dietary selenium on the proliferation of spermatogonial stem cells and antioxidant status in testis of roosters

The objective of this study was to investigate the different levels of dietary Se (from sodium selenite) on the proliferation of SSCs (spermatogonial stem cells) in testis of roosters. Also, the antioxidant status and Se content in blood plasma and testis were evaluated. A total of eighty 12-week-old Hy-Line Variety white roosters at an averaged body weight of 1.38 ± 0.2 kg were selected and randomly divided into four experimental groups. They were fed with the basal diet (0.044 mgSe/kg DM) supplemented with 0 (control), 0.5, 1.0 or 2.0 mgSe/kg DM (from sodium selenite). After the feeding experiment, blood and testis samples were collected for analysis of the antioxidant status and Se concentration. The testis samples were also used to examine the Thy-1 and β1-integrin mRNA expression by RT-PCR and detect the population of SSCs by immunofluorescence analysis. The results show that Se concentration in blood and testis of the animals was progressively increased with the increasing Se level in diet. The highest GSH-Px (glutathione peroxidase) activity and lowest MDA content in blood and testis was obtained in the treatment of 0.5mg/kg. RT-PCR analysis showed that mRNA expression of SSCs markers were significantly lower in the control and 1.0mg/kg groups when compared with that in the treatment of 0.5mg/kg. A similar trend was observed in the population of SSCs analyzed by immunofluorescence assay. These data suggest that dietary Se can influence the population of SSCs of roosters during spermatogenesis and that oxidative stress can modulate SSCs behavior through regulating some key factors during spermatogenesis.

In vitro culture and characterization of spermatogonial stem cells on Sertoli cell feeder layer in goat (Capra hircus)

PURPOSE

To develop an efficient protocol for isolation, purification and long-term culture of spermatogonial stem cell (SSC) in goat.

METHODS

The isolation of SSC was performed by testicular disaggregation by enzymatic digestion using collagenase IV, trypsin and DNase I. Further SSCs were enriched using Percoll density gradient centrifugation. The purity of SSCs was assessed by immunocytochemistry (ICC) using α6 integrin. The SSCs were co-cultured on Sertoli cell feeder layer. The SSC colonies were characterized by studying the expression of SSC specific markers (viz., α6 integrin and PLZF) using ICC. The abundance of mRNAs encoding the markers of SSC (viz., β1 integrin and Oct-4) and Sertoli cells (viz., vimentin) was also assayed using quantitative real-time PCR (qPCR).

RESULTS

The viability of isolated testicular cells was > 90 % and the Percoll density gradient method resulted in 3.65 folds enrichment with a purity of 82.5 %. Co-culturing of SSCs with Sertoli cell feeder layer allowed the maintenance of stable SSC colonies even after one and half months of culture. The results of ICC analysis showed the expression of α6 integrin and PLZF in almost all the SSC colonies. qPCR analysis revealed a differential expression of mRNAs encoding β1 integrin, Oct-4 and vimentin markers.

CONCLUSION

Results of this study demonstrate a simple enzymatic digestion and Percoll density gradient method for isolation and enrichment of SSCs, and suitability of Sertoli cell feeder layer for long term in vitro culture of SSC in goats. Results also suggest the possible application of non-caprine antibodies against SSC specific markers for the identification and subsequent assessment of SSCs in goats.

Fluorescence- and magnetic-activated cell sorting strategies to isolate and enrich human spermatogonial stem cells

OBJECTIVE

To determine the molecular characteristics of human spermatogonia and optimize methods to enrich spermatogonial stem cells (SSCs).

DESIGN

Laboratory study using human tissues.

SETTING

Research institute.

PATIENT(S)

Healthy adult human testicular tissue.

INTERVENTION(S)

Human testicular tissue was fixed or digested with enzymes to produce a cell suspension. Human testis cells were fractionated by fluorescence-activated cell sorting (FACS) and magnetic-activated cell sorting (MACS).

MAIN OUTCOME MEASURE(S)

Immunostaining for selected markers, human-to-nude mouse xenotransplantation assay.

RESULT(S)

Immunohistochemistry costaining revealed the relative expression patterns of SALL4, UTF1, ZBTB16, UCHL1, and ENO2 in human undifferentiated spermatogonia as well as the extent of overlap with the differentiation marker KIT. Whole mount analyses revealed that human undifferentiated spermatogonia (UCHL1+) were typically arranged in clones of one to four cells whereas differentiated spermatogonia (KIT+) were typically arranged in clones of eight or more cells. The ratio of undifferentiated-to-differentiated spermatogonia is greater in humans than in rodents. The SSC colonizing activity was enriched in the THY1dim and ITGA6+ fractions of human testes sorted by FACS. ITGA6 was effective for sorting human SSCs by MACS; THY1 and EPCAM were not.

CONCLUSION(S)

Human spermatogonial differentiation correlates with increased clone size and onset of KIT expression, similar to rodents. The undifferentiated-to-differentiated developmental dynamics in human spermatogonia is different than rodents. THY1, ITGA6, and EPCAM can be used to enrich human SSC colonizing activity by FACS, but only ITGA6 is amenable to high throughput sorting by MACS.