Stage-specific regulation of undifferentiated spermatogonia by AKT1S1-mediated AKT-mTORC1 signaling during mouse spermatogenesis

Undifferentiated spermatogonia are composed of a heterogeneous cell population including spermatogonial stem cells (SSCs). Molecular mechanisms underlying the regulation of various spermatogonial cohorts during their self-renewal and differentiation are largely unclear. Here we show that AKT1S1, an AKT substrate and inhibitor of mTORC1, regulates the homeostasis of undifferentiated spermatogonia. Although deletion of Akt1s1 in mouse appears not grossly affecting steady-state spermatogenesis and male mice are fertile, the subset of differentiation-primed OCT4+ spermatogonia decreased significantly, whereas self-renewing GFRα1+ and proliferating PLZF+ spermatogonia were sustained. Both neonatal prospermatogonia and the first wave spermatogenesis were greatly reduced in Akt1s1-/- mice. Further analyses suggest that OCT4+ spermatogonia in Akt1s1-/- mice possess altered PI3K/AKT-mTORC1 signaling, gene expression and carbohydrate metabolism, leading to their functionally compromised developmental potential. Collectively, these results revealed an important role of AKT1S1 in mediating the stage-specific signals that regulate the self-renewal and differentiation of spermatogonia during mouse spermatogenesis.

Puberty Blocker and Aging Impact on Testicular Cell States and Function

Spermatogonial stem cell (SSC) acquisition of meiotogenetic state during puberty to produce genetically diverse gametes is blocked by drugs collectively referred as 'puberty blocker' (PB). Investigating the impact of PB on juvenile SSC state and function is challenging due to limited tissue access and clinical data. Herein, we report largest clinically annotated juvenile testicular biorepository with all children with gender dysphoria on chronic PB treatment highlighting shift in pediatric patient demography in US. At the tissue level, we report mild-to-severe sex gland atrophy in PB treated children. We developed most extensive integrated single-cell RNA dataset to date (>100K single cells; 25 patients), merging both public and novel (52 month PB-treated) datasets, alongside innovative computational approach tailed for germ cells and evaluated the impact of PB and aging on SSC. We report novel constitutional ranges for each testicular cell type across the entire age spectrum, distinct effects of treatments on prepubertal vs adult SSC, presence of spermatogenic epithelial cells exhibiting post-meiotic-state, irrespective of age, puberty status, or PB treatment. Further, we defined distinct effects of PB and aging on testicular cell lineage composition, and SSC meiotogenetic state and function. Using single cell data from prepubertal and young adult, we were able to accurately predict sexual maturity based both on overall cell type proportions, as well as on gene expression patterns within each major cell type. Applying these models to a PB-treated patient that they appeared pre-pubertal across the entire tissue. This combined with the noted gland atrophy and abnormalities from the histology data raise a potential concern regarding the complete 'reversibility' and reproductive fitness of SSC. The biorepository, data, and research approach presented in this study provide unique opportunity to explore the impact of PB on testicular reproductive health.

Lipofection-Based Delivery of CRISPR/Cas9 Ribonucleoprotein for Gene Editing in Male Germline Stem Cells

Gene editing in the murine germline is a valuable approach to investigate germ cell maturation and generate mouse models. Several studies demonstrated that CRISPR/Cas9 alters the genome of cultured male mouse germline stem cells delivered by electroporation of plasmids. Recently, we showed proof-of-principle that gene knockout can be effectively targeted in mouse germline stem cells by lipofecting Cas9:gRNA ribonucleoproteins. In this protocol, we describe a simple, fast, and cheap workflow for gene editing via the lipofection of non-integrative ribonucleoproteins in murine male germline stem cells.

Transcription factor E4F1 dictates spermatogonial stem cell fate decisions by regulating mitochondrial functions and cell cycle progression

BACKGROUND

Spermatogonial stem cells (SSCs) provide a foundation for robust and continual spermatogenesis in mammals. SSCs self-renew to maintain a functional stem cell pool and differentiate to supply committed progenitors. Metabolism acts as a crucial determinant of stem cell fates; however, factors linking metabolic programs to SSC development and maintenance are poorly understood.

RESULTS

We analyzed the chromatin accessibility of undifferentiated spermatogonia at the single-cell level and identified 37 positive TF regulators that may have potential roles in dictating SSC fates. The transcription factor E4F1 is expressed in spermatogonia, and its conditional deletion in mouse germ cells results in progressive loss of the entire undifferentiated spermatogonial pool. Single-cell RNA-seq analysis of control and E4f1-deficient spermatogonia revealed that E4F1 acts as a key regulator of mitochondrial function. E4F1 binds to promotors of genes that encode components of the mitochondrial respiratory chain, including Ndufs5, Cox7a2, Cox6c, and Dnajc19. Loss of E4f1 function caused abnormal mitochondrial morphology and defects in fatty acid metabolism; as a result, undifferentiated spermatogonia were gradually lost due to cell cycle arrest and elevated apoptosis. Deletion of p53 in E4f1-deficient germ cells only temporarily prevented spermatogonial loss but did not rescue the defects in SSC maintenance.

CONCLUSIONS

Emerging evidence indicates that metabolic signals dictate stem cell fate decisions. In this study, we identified a list of transcription regulators that have potential roles in the fate transitions of undifferentiated spermatogonia in mice. Functional experiments demonstrated that the E4F1-mediated transcription program is a crucial regulator of metabolism and SSC fate decisions in mammals.

Transcriptome-wide Dynamics of m6A mRNA Methylation During Porcine Spermatogenesis

Spermatogenesis is a continual process that occurs in the testes, in which diploid spermatogonial stem cells (SSCs) differentiate and generate haploid spermatozoa. This highly efficient and intricate process is orchestrated at multiple levels. N6-methyladenosine (m6A), an epigenetic modification prevalent in mRNAs, is implicated in the transcriptional regulation during spermatogenesis. However, the dynamics of m6A modification in non-rodent mammalian species remains unclear. Here, we systematically investigated the profile and role of m6A during spermatogenesis in pigs. By analyzing the transcriptomic distribution of m6A in spermatogonia, spermatocytes, and round spermatids, we identified a globally conserved m6A pattern between porcine and murine genes with spermatogenic function. We found that m6A was enriched in a group of genes that specifically encode the metabolic enzymes and regulators. In addition, transcriptomes in porcine male germ cells could be subjected to the m6A modification. Our data show that m6A plays the regulatory roles during spermatogenesis in pigs, which is similar to that in mice. Illustrations of this point are three genes (SETDB1, FOXO1, and FOXO3) that are crucial to the determination of the fate of SSCs. To the best of our knowledge, this study for the first time uncovers the expression profile and role of m6A during spermatogenesis in large animals and provides insights into the intricate transcriptional regulation underlying the lifelong male fertility in non-rodent mammalian species.

Lineage Tracing of Spermatogonial Stem Cells Within the Male Germline

Spermatogonial stem cells (SSCs) are the fundamental units from which continuous spermatogenesis arises. Although our knowledge regarding the basic properties of SSCs has grown, driven primarily through the advancement of techniques and technologies to study SSCs, the mechanisms controlling their fate remain largely unknown. Among the modern strategies to evaluate SSCs, lineage tracing is among the few established approaches that allow for functional assessment of stem cell capacity. As a result, lineage tracing continues to forge new discoveries underlying the basic attributes of SSCs as well as the molecular factors that govern SSC function. Traditional approaches to lineage tracing with dyes or radioactive labels suffer from progressive loss after successive cell divisions or unintentional label transfer to neighboring cells. To address these limitations, genetic approaches primarily leveraging transgenic technologies have prevailed as the preferred avenue for modern lineage tracing. This chapter will discuss current protocols for effective genetic lineage tracing and address applications of this technology, considerations when designing lineage tracing experiments, and the methods involved in utilizing lineage tracing to study SSCs and other cell populations.

Models and Methods for Evaluating Regeneration of Spermatogenesis After Cytotoxic Treatments

Cytotoxic exposure, predominantly during radiation and/or chemotherapy treatment for cancer, interferes with fertility in men. While moderate doses cause temporary azoospermia allowing eventual recovery of spermatogenesis, higher doses of sterilizing agents can cause permanent sterility by killing the spermatogonial stem cells (SSCs). In this chapter, the methods involved in the following aspects of cytotoxic regeneration are described: (i) designing rodent and non-human primate models for regeneration of spermatogenesis after cytotoxic treatment by radiation and chemotherapy; (ii) analysis of SSCs with respect to the impact of the cytotoxic treatment, including analysis of spermatogonial clones, scoring the testicular section to analyze the extent of spermatogenic recovery, preparation of testicular and epididymal sperm, and collection of semen in non-human primates for sperm analysis; and (iii) preparation and delivery of a GnRH antagonist and steroids for enhancement or induction of spermatogonial differentiation, leading to the regeneration of spermatogenesis, largely applicable in the rat model.

Primary Cultures of Spermatogonia and Testis Cells

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

Identification of Germline Stem Cells in Zebrafish

Both male and female zebrafish have a population of germline stem cells that produce gametes throughout the life of the fish. These cells localize to specific regions in the gonads and can be identified because they uniquely express the nanos2 gene, which encodes a conserved regulator of translation. A method is presented here for identifying germline stem cells in the ovary and testis using a combined protocol for whole-mount fluorescent RNA in situ hybridization to detect nanos2 mRNA and immunofluorescence to detect the pan-germ cell marker Vasa.

Rattus norvegicus Spermatogenesis Colony-Forming Assays

Knowledge gaps persist on signaling pathways and metabolic states in germ cells sufficient to support spermatogenesis independent of a somatic environment. Consequently, methods to culture mammalian stem cells through spermatogenesis in defined systems have not been established. Lack of success at culturing mammalian stem cells through spermatogenesis in defined systems reflects an inability to experimentally recapitulate biochemical events that develop in germ cells within the testis-specific seminiferous epithelium. Complex germ and somatic cell associations that develop each seminiferous epithelial cycle support such a hypothesis, conceivably explaining why highly pure mammalian spermatogonia do not effectively develop into and through meiosis without somatic cells. Here, we outline an in vitro spermatogenesis colony-forming assay to study how differentiating spermatogonial syncytia develop from rat spermatogonial stem cell lines. Robust spermatogonial differentiation under defined culture conditions, once established, is anticipated to facilitate molecular biology studies on pre-meiotic steps in gametogenesis by providing soma-free bioassays to systematically identify spermatogenic factors that promote meiotic progression in vitro.

A novel high throughput screen to identify candidate molecular networks that regulate spermatogenic stem cell functions

Spermatogenic regeneration is key for male fertility and relies on activities of an undifferentiated spermatogonial population. Here, a high throughput approach with primary cultures of mouse spermatogonia was devised to rapidly predict alterations in functional capacity. Combining the platform with a large scale RNAi screen of transcription factors, we generated a repository of new information from which pathway analysis was able to predict candidate molecular networks regulating regenerative functions. Extending from this database, the SRCAP-CREBBP/EP300 complex was found to mediate differential levels of histone acetylation between stem cell and progenitor spermatogonia to influence expression of key self-renewal genes including the previously undescribed testis specific transcription factor ZSCAN2. Single cell RNA sequencing analysis revealed that ZSCAN2 deficiency alters key cellular processes in undifferentiated spermatogonia such as translation, chromatin modification, and ubiquitination. In Zscan2 knockout mice, while spermatogenesis was moderately impacted during steady-state, regeneration after cytotoxic insult was significantly impaired. Together, these findings have validated the utility of our high throughput screening approach and have generated a transcription factor database that can be utilized for uncovering novel mechanisms governing spermatogonial functions.

In vitro impact of genistein and mono(2-ethylhexyl) phthalate (MEHP) on the eicosanoid pathway in spermatogonial stem cells

Perinatal exposures to endocrine disrupting chemicals (EDCs) alter the male reproductive system. Infants are exposed to genistein (GEN) through soy-based formula, and to Mono(2-ethylhexyl) Phthalate (MEHP), metabolite of the plasticizer DEHP. Spermatogonial stem cells (SSCs) are formed in infancy and their integrity is essential for spermatogenesis. Thus, understanding the impact of EDCs on SSCs is critical. Prostaglandins (PGs) are inflammatory mediators synthesized via the eicosanoid pathway starting with cyclooxygenases (Coxs), that regulate physiological and pathological processes. Our goal was to study the eicosanoid pathway in SSCs and examine whether it was disrupted by GEN and MEHP, potentially contributing to their adverse effects. The mouse C18-4 cell line used as SSC model expressed high levels of Cox1 and Cox2 genes and proteins, and eicosanoid pathway genes similarly to levels measured in primary rat spermatogonia. Treatments with GEN and MEHP at 10 and 100 μM decreased Cox1 gene and protein expression, whereas Cox2, phospholipase A2, prostaglandin synthases transcripts, PGE2, PGF2a and PGD2 were upregulated. Simultaneously, the transcript levels of spermatogonia progenitor markers Foxo1 and Mcam and differentiated spermatogonial markers cKit and Stra8 were increased. Foxo1 was also increased by EDCs in primary rat spermatogonia. This study shows that the eicosanoid pathway is altered during SSC differentiation and that exposure to GEN and MEHP disrupts this process, mainly driven by GEN effects on Cox2 pathway, while MEHP acts through an alternative mechanism. Thus, understanding the role of Cox enzymes in SSCs and how GEN and MEHP exposures alter their differentiation warrants further studies.

Boosting effect of testosterone on GDNF expression in Sertoli cell line (TM4); comparison between TM3 cells-produced and exogenous testosterone

The Glial cell-derived neurotrophic factor (Gdnf) and testosterone induce the spermatogonial stem cells (SSCs) self-renewal and spermatogenesis, respectively. In present study the stimulating role of testosterone on Sertoli cells to produce Gdnf, and the possible effect of Gdnf on Gfrα1 and c-RET expressions were investigated. The TM4 cells (line Sertoli cells) were co-cultured with [0.1, 0.2 and 0.4 (ng/ml)] of exogenous and TM3 (line Leydig cells)-produced testosterones, and consequently the TM4-produced Gdnf concentration was evaluated. Next, the SSCs were co-cultured with the TM-4 derived media (endogenous Gdnf) and exogenous Gdnf [0.1, 0.2, and 0.4 ng/ml)]. The 0.1 and 0.2 ng/ml endogenous and 3 concentrations of exogenous testosterone up-regulated the Gdnf expression versus non-treated Sertoli cells. The TM4-produced and exogenous Gdnfs, in all concentrations, up-regulated the receptors expression. In conclusion, the testosterone, solely, stimulates the Gdnf synthesis and the Gdnf, individually, amplifies its receptor's expression at mRNA and protein levels.

MKK7-mediated phosphorylation of JNKs regulates the proliferation and apoptosis of human spermatogonial stem cells

BACKGROUND

Human spermatogonial stem cells (SSCs) are the basis of spermatogenesis. However, little is known about the developmental regulatory mechanisms of SSC due to sample origin and species differences.

AIM

To investigates the mechanisms involved in the proliferation of human SSC.

METHODS

The expression of mitogen-activated protein kinase kinase 7 (MKK7) in human testis was identified using immunohistochemistry and western blotting (WB). MKK7 was knocked down using small interfering RNA, and cell proliferation and apoptosis were detected by WB, EdU, cell counting kit-8 and fluorescence-activated cell sorting. After bioinformatic analysis, the interaction of MKK7 with c-Jun N-terminal kinases ( JNKs ) was verified by protein co-immunoprecipitation and WB. The phosphorylation of JNKs was inhibited by SP600125, and the phenotypic changes were detected by WB, cell counting kit-8 and fluorescence-activated cell sorting.

RESULTS

MKK7 is mainly expressed in human SSCs, and MKK7 knockdown inhibits SSC proliferation and promotes their apoptosis. MKK7 mediated the phosphorylation of JNKs, and after inhibiting the phosphorylation of JNKs, the phenotypic changes of the cells were similar to those after MKK7 downregulation. The expression of MKK7 was significantly downregulated in patients with abnormal spermatogenesis, suggesting that abnormal MKK7 may be associated with spermatogenesis impairment.

CONCLUSION

MKK7 regulates the proliferation and apoptosis of human SSC by mediating the phosphorylation of JNKs.

Valproic acid promotes the in vitro differentiation of human pluripotent stem cells into spermatogonial stem cell-like cells

Background

Studying human germ cell development and male infertility is heavily relied on mouse models. In vitro differentiation of human pluripotent stem cells into spermatogonial stem cell-like cells (SSCLCs) can be used as a model to study human germ cells and infertility. The current study aimed to develop the SSCLC induction protocol and assess the effects of the developed protocol on SSCLC induction.

Methods

We examined the effects of valproic acid (VPA), vitamin C (VC) and the combination of VPA and VC on the SSCLC induction efficiency and determined the expression of spermatogonial genes of differentiated cells. Haploid cells and cells expressed meiotic genes were also detected. RNA-seq analysis was performed to compare the transcriptome between cells at 0 and 12 days of differentiation and differently expressed genes were confirmed by RT-qPCR. We further evaluated the alteration in histone marks (H3K9ac and H3K27me3) at 12 days of differentiation. Moreover, the SSCLC induction efficiency of two hiPSC lines of non-obstructive azoospermia (NOA) patients was assessed using different induction protocols.

Results

The combination of low concentrations of VPA and VC in the induction medium was most effective to induce SSCLCs expressing several spermatogonial genes from human pluripotent stem cells at 12 days of differentiation. The high concentration of VPA was more effective to induce cells expressing meiotic genes and haploid cells. RNA-seq analysis revealed that the induction of SSCLC involved the upregulated genes in Wnt signaling pathway, and cells at 12 days of differentiation showed increased H3K9ac and decreased H3K27me3. Additionally, two hiPSC lines of NOA patients showed low SSCLC induction efficiency and decreased expression of genes in Wnt signaling pathway.

Conclusions

VPA robustly promoted the differentiation of human pluripotent stem cells into SSCLCs, which involved the upregulated genes in Wnt signaling pathway and epigenetic changes. hiPSCs from NOA patients showed decreased SSCLC induction efficiency and Wnt signaling pathway gene expression, suggesting that SSC depletion in azoospermia testes might be associated with inactivation of Wnt signaling pathway. Our developed SSCLC induction protocol provides a reliable tool and model to study human germ cell development and male infertility.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02621-1.

Germ Cell Transplantation in Stallion Testes

The production of donor-derived sperm using spermatogonial stem cell transplantation has been studied in various animals including mice, rats, goats, boar, dogs, sheep, and monkeys. However, germ cell transplantation has not been applied in stallions. The objective of this study was to produce donor germ cell-derived sperm using germ cell transplantation in stallions. Donor germ cells were transplanted into the parenchyma of 3 recipient stallions that had been treated with busulfan IV injections of 15 mg/kg body weight. For the preparation of donor single germ cells, tissue (20 g) from each testis was subjected to a 2-enzyme digestion procedure. Donor testicular germ cells in minimum essential medium α supplemented with 10% fetal bovine serum were transplanted in the testis of recipient stallions at a rate of 2 ml/min. The semen of each recipient stallion was collected using an artificial vagina at 8 weeks after germ cell transplantation. General sperm evaluation and libido tests were performed. Microsatellite fingerprinting with 17 markers was performed to identify the presence of donor-derived sperm in the semen of the recipient stallions. Sperm were observed to have total and progressive motility exceeding 50% throughout the experimental period. The libido of the recipient stallions was unchanged. No donor-derived sperm could be detected in the semen of the recipient stallions by genotyping. In conclusion, the transplantation of donor germ cells into the testicular parenchyma of stallions was not an optimal transplantation technique for producing donor-derived sperm.

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

PURPOSE

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

METHOD

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

RESULT

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

CONCLUSION

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

Proper timing of a quiescence period in precursor prospermatogonia is required for stem cell pool establishment in the male germline

The stem cell-containing undifferentiated spermatogonial population in mammals, which ensures continual sperm production, arises during development from prospermatogonial precursors. Although a period of quiescence is known to occur in prospermatogonia prior to postnatal spermatogonial transition, the importance of this has not been defined. Here, using mouse models with conditional knockout of the master cell cycle regulator Rb1 to disrupt normal timing of the quiescence period, we found that failure to initiate mitotic arrest during fetal development leads to prospermatogonial apoptosis and germline ablation. Outcomes of single-cell RNA-sequencing analysis indicate that oxidative phosphorylation activity and inhibition of meiotic initiation are disrupted in prospermatogonia that fail to enter quiescence on a normal timeline. Taken together, these findings suggest that key layers of programming are laid down during the quiescent period in prospermatogonia to ensure proper fate specification and fitness in postnatal life.

Stem cell-based therapies for fertility preservation in males: Current status and future prospects

With the decline in male fertility in recent years, strategies for male fertility preservation have received increasing attention. In this study, by reviewing current treatments and recent publications, we describe research progress in and the future directions of stem cell-based therapies for male fertility preservation, focusing on the use of spermatogonial stem cells (SSCs), SSC niches, SSC-based testicular organoids, other stem cell types such as mesenchymal stem cells, and stem cell-derived extracellular vesicles. In conclusion, a more comprehensive understanding of the germ cell microenvironment, stem cell-derived extracellular vesicles, and testicular organoids will play an important role in achieving male fertility preservation.

Single-cell RNAseq analysis of testicular germ and somatic cell development during the perinatal period

Pro-spermatogonia (SG) serve as the gateway to spermatogenesis. Using single-cell RNA sequencing (RNAseq), we studied the development of ProSG, their SG descendants and testicular somatic cells during the perinatal period in mice. We identified both gene and protein markers for three temporally distinct ProSG cell subsets, including a migratory cell population with a transcriptome distinct from the previously defined T1- and T2-ProSG stages. This intermediate (I)-ProSG subset translocates from the center of seminiferous tubules to the spermatogonial stem cell (SSC) 'niche' in its periphery soon after birth. We identified three undifferentiated SG subsets at postnatal day 7, each of which expresses distinct genes, including transcription factor and signaling genes. Two of these subsets have the characteristics of newly emergent SSCs. We also molecularly defined the development of Sertoli, Leydig and peritubular myoid cells during the perinatal period, allowing us to identify candidate signaling pathways acting between somatic and germ cells in a stage-specific manner during the perinatal period. Our study provides a rich resource for those investigating testicular germ and somatic cell developmental during the perinatal period.

Relative safety of various spermatogenic stem cell purification methods for application in spermatogenic stem cell transplantation

Background

Spermatogonial stem cell (SSC) transplantation technology as a promising option for male fertility preservation has received increasing attention, along with efficient SSC purification technology as a necessary technical support; however, the safety of such application in patients with tumors remains controversial.

Methods

In this study, we used a green fluorescent protein mouse xenograft model of B cell acute lymphocytic leukemia. We isolated and purified SSCs from the testicular tissue of model mice using density gradient centrifugation, immune cell magnetic bead separation, and flow cytometry. The purified SSCs were transplanted into convoluted seminiferous tubules of the nude mice and C57BL/6 male mice subjected to busulfan. The development and proliferation of SSCs in the recipient testis were periodically tested, along with whether B cell acute lymphocytic leukemia was induced following SSC implantation. The genetic characteristics of the offspring obtained from natural mating were also observed.

Results

In testicular leukemia model mice, a large number of BALL cells infiltrated into the seminiferous tubule, spermatogenic cells, and sperm cells in the testis tissue decreased. After spermatogonial stem cell transplantation, the transplanted SSCs purified by immunomagnetic beads and flow cytometry methods colonized and proliferated extensively in the basement of the seminiferous tubules of mice; a large number of spermatogenic cells and sperm were found in recipient testicular tissue after 12 weeks of SSC transplantation. In leukemia detection in nude mice after transplantation in the three SSC purification groups, a large number of BALL cells could be detected in the blood of recipient mice 2–3 weeks after transplantation in the density gradient centrifugation group, but not in the blood of the flow cytometry sorting group and the immunomagnetic bead group after 16 weeks of observation.

Conclusions

In this study, we confirmed that immunomagnetic beads and flow cytometry methods of purifying SSCs from the testicular tissue of the testicular leukemia mouse model could be safely applied to the SSC transplantation technology without concomitant tumor implantation. The results thus provide a theoretical basis for the application of tumor SSC cryopreservation for fertility preservation in patients with tumors.

Testicular tissue cryopreservation is the preferred method to preserve spermatogonial stem cells prior to transplantation

RESEARCH QUESTION

Which cryopreservation method better protects reproductive potential: the cryopreservation of a testicular cell suspension (TCS) or the cryopreservation of testicular tissue (TET)?

DESIGN

Two cryopreservation strategies for spermatogonial stem cells (SSCs) were compared in a mouse model: cryopreservation as TET or as TCS. Evaluated outcomes were number of viable cells after thawing, number and length of donor-derived colonies after spermatogonial stem cell transplantation (SSCT), number of litters, litter size and number of donor-derived pups after mating.

RESULTS

Compared with cryopreserving TCS, cryopreservation of TET resulted in significantly higher numbers of viable cells after thawing (TET: 13.4  ×  10⁴ ± 7.2  ×  10⁴ versus TCS: 8.2  ×  10⁴ ± 2.7  ×  10⁴; P = 0.0002), more (TET: 47.6 ± 19.2 versus TCS: 18.5 ± 13.0; P = 0.0039) and longer (TET: 5.2 ± 1.0 mm versus TCS: 2.7 ± 1.5 mm; P = 0.0016) donor-derived colonies, and more donor-derived pups per litter (TET: 2.2 ± 0.2 versus TCS: 0.5 ± 0.1; P = 0.0008).

CONCLUSIONS

Cryopreservation of TET is the preferred method to cryopreserve SSCs prior to SSCT in a mouse model.

Generating Genetically Engineered Mice Using a Spermatogonial Stem Cell-Mediated Method

Mouse spermatogonial stem cells (SSCs) can be grown in culture for long periods. Cultured SSCs, also called germline stem (GS) cells, maintain themselves by self-renewing proliferation while retaining the ability to differentiate into sperm. Thus, when transplanted into the seminiferous tubules of a host mouse testis, they settle in the basal compartment of the tubules and establish spermatogenenic colonies. The sperm produced in the host are competent to produce offspring. This can be exploited for the generation of genetically modified mice, through the transplantation of genetically modified GS cells. In this section, we describe a method of genome editing-mediated GS cell modification and transplantation.

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.

miR-34c disrupts spermatogonial stem cell homeostasis in cryptorchid testes by targeting Nanos2

BACKGROUND

Cryptorchidism as a common genitourinary malformation with the serious complication of male infertility draws widespread attention. With several reported miRNAs playing critical roles in spermatogonial stem cells (SSCs), we aimed to explore the fundamental function of the highly conserved miR-34c in cryptorchidism.

METHODS

To explore whether miR-34c participates in spermatogenesis by regulating Nanos2, we examined the effect of overexpression and inhibition for miR-34c on Nanos2 expression in GC-1 cells. Moreover, the expression levels of miR-34c and Nanos2 with cryptorchidism in humans and mice were examined. Furthermore, the homeostasis of SSCs was evaluated through counting the number of promyelocytic leukemia zinc finger (PLZF) positive spermatogonia in murine cryptorchid testes.

RESULTS

In the present study, we show that miR-34c could inhibit the expression of Nanos2 in GC-1 cells. Meanwhile, miR-34c significantly decreased in both the testicular tissues of patients with cryptorchidism and surgery-induced murine model of cryptorchidism. Western blot revealed that the protein level of Nanos2 was up-regulated and showed to be negatively correlated to the expression of miR-34c in our model. The abnormal expression of miR-34c/Nanos2 disrupted the balance between SSC self-renewal and differentiation, eventually damaging the spermatogenesis of cryptorchid testes.

CONCLUSIONS

The miR-34c/Nanos2 pathway provides new insight into the mechanism of male infertility caused by cryptorchidism. Our results indicate that miR-34c may serve as a biological marker for treatment of infertility caused by cryptorchidism.

What is the best protocol to cryopreserve immature mouse testicular cell suspensions?

RESEARCH QUESTION

From a clinical perspective, which parameters grant optimal cryopreservation of mouse testicular cell suspensions?

DESIGN

We studied the effect of different cryopreservation rates, the addition of sugars, different vessels and the addition of an apoptotic inhibitor on the efficiency of testicular cell suspension cryopreservation. After thawing and warming, testicular cell suspensions were transplanted to recipient mice for further functional assay. After selecting the optimal cryopreservation procedure, a second experiment compared the transplantation efficiency between the selected freezing protocol and fresh testicular cell suspensions.

RESULTS

Multiple- and single-step freezing did not differ significantly in terms of recovered viable cells (RVC) (33 ± 28% and 38 ± 25%). The addition of sucrose did not result in a higher RVC (33 ± 20%). Cells frozen in vials recovered better than those frozen in straws (52 ± 20% versus 33 ± 20%; P = 0.0049). The inclusion of an apoptosis inhibitor (z-VAD[Oe]-FMK) significantly increased the RVC after thawing (61 ± 18% versus 50 ± 17%; P = 0.0480). When comparing the optimal cryopreservation procedure with fresh testicular cell suspensions, a lower RVC (63 ± 11% versus 92 ± 4%; P < 0.0001) and number of donor-derived spermatogonial stem cell colonies per testis (34.04 ± 2.34 versus 16.78 ± 7.76; P = 0.0051) were observed.

CONCLUSION

Upon freeze-thawing or vitrification-warming, and assessment of donor-derived spermatogenesis after transplantation, Dulbecco's modified Eagle's medium supplemented with 1.5M dimethyl-sulphoxide, 10% fetal calf serum and 60 µM of Z-VAD-(OMe)-FMK in vials at a freezing rate of -1°C/min was optimal.

Functional assessment of spermatogonial stem cell purity in experimental cell populations

Historically, research in spermatogonial biology has been hindered by a lack of validated approaches to identify and isolate pure populations of the various spermatogonial subsets for in-depth analysis. In particular, although a number of markers of the undifferentiated spermatogonial population have now been characterized, standardized methodology for assessing their specificity to the spermatogonial stem cell (SSC) and transit amplifying progenitor pools has been lacking. To date, SSC content within an undefined population of spermatogonia has been inferred using either lineage tracing or spermatogonial transplantation analyses which generate qualitative and quantitative data, respectively. Therefore, these techniques are not directly comparable, and are subject to variable interpretations as to a readout that is representative of a ‘pure’ SSC population. We propose standardization across the field for determining the SSC purity of a population via use of a limiting dilution transplantation assay that would eliminate subjectivity and help to minimize the generation of inconsistent data on ‘SSC’ populations. In the limiting dilution transplantation assay, a population of LacZ-expressing spermatogonia are selected based on a putative SSC marker, and a small, defined number of cells (i.e. 10 cells) are microinjected into the testis of a germ cell-deficient recipient mouse. Using colony counts and an estimated colonization efficiency of 5%; a quantitative value can be calculated that represents SSC purity in the starting population. The utilization of this technique would not only be useful to link functional relevance to novel markers that will be identified in the future, but also for providing validation of purity for marker-selected populations of spermatogonia that are commonly considered to be SSCs by many researchers in the field of spermatogenesis and stem cell biology.

Testicular germ line cell identification, isolation, and transplantation in two North American catfish species

Our aim was to transplant blue catfish germ line stem cells into blastulae of triploid channel catfish embryos to produce interspecific xenogenic catfish. The morphological structure of the gonads of blue catfish (Ictalurus furcatus) in ~ 90- to 100-day-old juveniles, two-year-old juveniles, and mature adults was studied histologically. Both oogonia (12-15 μm, diameter with distinct nucleus 7-8 μm diameter) and spermatogonia (12-15 μm, with distinct nucleus 6-7.5 μm diameter) were found in all ages of fish. The percentage of germ line stem cells was higher in younger blue catfish of both sexes. After the testicular tissue was trypsinized, a discontinuous density gradient centrifugation was performed using 70, 45, and 35% Percoll to enrich the percentage of spermatogonial stem cells (SSCs). Four distinct cell bands were generated after the centrifugation. It was estimated that 50% of the total cells in the top band were type A spermatogonia (diameter 12-15 μm) and type B spermatogonia (diameter 10-11 μm). Germ cells were confirmed with expression of vasa. Blastula-stage embryos of channel catfish (I. punctatus) were injected with freshly dissociated blue catfish testicular germ cells as donor cells for transplantation. Seventeen days after the transplantation, 33.3% of the triploid channel catfish fry were determined to be xenogenic catfish. This transplantation technique was efficient, and these xenogenic channel catfish need to be grown to maturity to verify their reproductive capacity and to verify that for the first time SSCs injected into blastulae were able to migrate to the genital ridge and colonize. These results open the possibility of artificially producing xenogenic channel catfish males that can produce blue catfish sperm and mate with normal channel catfish females naturally. The progeny would be all C × B hybrid catfish, and the efficiency of hybrid catfish production could be improved tremendously in the catfish industry.

Expression patterns and role of SDF-1/CXCR4 axis in boar spermatogonial stem cells

The signaling of chemokine stromal cell-derived factor (SDF)-1 and its receptor C-X-C motif chemokine receptor 4 (CXCR4) is involved in the cellular proliferation, survival, and migration of various cell types. Although SDF-1/CXCR4 has been implicated in the maintenance of the spermatogonial population during mouse testis development, their expression patterns and functions in boar testis remain unclear. In the present study, the expression pattern of SDF-1 and CXCR4 was determined during pre-pubertal and post-pubertal stage boar testes and in vitro cultured porcine spermatogonial stem cells (pSSCs). The role of these proteins in colony formation in cultured pSSCs was also investigated. Interestingly, SDF-1 expression was observed in PGP 9.5-positve spermatogonia in all developing stages of boar testis; however, CXCR4 expression was only detected in spermatogonia from 5-day-old boar testis. In addition, SDF-1 and CXCR4 expression was observed in cultured pSSCs from 5-day-old boar testes, and inhibition of the CXCR4 receptor signaling pathway by AMD3100 significantly decreased the colony formation of pSSCs. These results suggest that SDF-1 and CXCR4 are useful markers for detecting stage-specific spermatogonia in boar testis. Our results reveal the role of the SDF-1/CXCR4 axis in pSSC in vitro culture.

Species-specific expression of phosphoglycerate kinase 2 (PGK2) in the developing porcine testis

Whereas stage-specific markers for spermatogonial cells have been well investigated in mouse, the specific markers of germ cells in the testis of domestic animals have not been well defined. Phosphoglycerate kinase (PGK), an enzyme that converts 1,3-bisphosphoglycerate and adenosine diphosphate to 3-phosphoglycerate and adenosine triphosphate, has two isozymes: PGK1 and PGK2. In mouse, PGK1 exists only during the early stages of spermatogenesis, and PGK2 is then expressed during the pachytene spermatocyte stage. In this study, we investigated the localization of PGK2 in the developing porcine testis, and compared the similarities and differences in its expression with that of the PGK2 in mouse. The PGK2 protein was found to be exclusively expressed in spermatids of the adult mouse testis, whereas PGK2-positive cells were observed in the prepubertal and postpubertal testes of pigs. Based on this result, we examined the expression of PGK2 in in vitro-cultured porcine undifferentiated spermatogonia and found it to be maintained in the cultured cells. To verify this result and identify the spermatogonial stem cell-like potential in recipient testes, PKH26 dye-stained PGK2-positive cells were transplanted into the testes of busulfan-treated immunodeficient mouse that had been depleted of both testicular germ cells and somatic cells. The transplanted cells colonized the recipient testis at 8 weeks post transplantation, and fluorescence microscopy identified the cells in the basement membranes of the seminiferous tubules of the injected mouse. Taken together, our results suggest that PGK2 is expressed differently in the testes of mouse and pigs according to developmental stage. This finding should contribute to the study of spermatogenesis and the production of transgenic domestic animals through in vitro spermatogonial sperm cell culture.

Magnetic-Based Cell Isolation Technique for the Selection of Stem Cells

Magnetic-activated cell sorting (MACS) is the technology that is recently used as a magnetic-based cell isolation/purification technique. This technique enables the isolation and selection of germ, hematopoietic, and somatic stem cells including skin stem cells (SkSCs). Here, we have tried to describe the isolation of stem cells by MACS using CD34 antigen for SkSCs, again CD34 for hematopoietic stem cells (HSCs) and Thy-1 for spermatogonial stem cells (SpSCs). MACS allowed the isolation of CD34+, CD34+, and Thy-1+ human SkSCs, HSCs, and SpSCs with minimum 98% purity.

Adeno-associated virus-mediated delivery of genes to mouse spermatogonial stem cells

Spermatogenesis is a complicated process that originates from spermatogonial stem cells (SSCs), which have self-renewal activity. Because SSCs are the only stem cells in the body that transmit genetic information to the next generation, they are an attractive target for germline modification. Although several virus vectors have been successfully used to transduce SSCs, cell toxicity or insertional mutagenesis of the transgene has limited their usage. Adeno-associated virus (AAV) is unique among virus vectors because of its target specificity and low toxicity in somatic cells, and clinical trials have shown that it has promise for gene therapy. However, there are conflicting reports on the possibility of germline integration of AAV into the genome of male germ cells, including SSCs. Here, we examined the usefulness of AAV vectors for exploring germline gene modification in SSCs. AAV1 infected cultured SSCs without apparent toxicity. Moreover, SSCs that were infected in fresh testis cells generated normal appearing spermatogenic colonies after spermatogonial transplantation. A microinsemination experiment produced offspring that underwent excision of the floxed target gene by AAV1-mediated Cre expression. Analysis of the offspring DNA showed no evidence of AAV integration, suggesting a low risk of germline integration by AAV infection. Although more extensive experiments are required to assess the risk of germline integration, our results show that AAV1 is useful for genetic manipulation of SSCs, and gene transduction by AAV will provide a useful approach to overcome potential problems associated with previous virus vector-mediated gene transduction.

The effects of melatonin on colonization of neonate spermatogonial mouse stem cells in a three-dimensional soft agar culture system

BACKGROUND

Melatonin is a pleiotropic hormone with powerful antioxidant activity both in vivo and in vitro. The present study aimed to investigate the effects of melatonin on the proliferation efficiency of neonatal mouse spermatogonial stem cells (SSCs) using a three-dimensional soft agar culture system (SACS) which has the capacity to induce development of SSCs similar to in vivo conditions.

METHODS

SSCs were isolated from testes of neonate mice and their purities were assessed by flow cytometry using PLZF antibody. Isolated testicular cells were cultured in the upper layer of the SACS in αMEM medium in the absence or presence of melatonin extract for 4 weeks.

RESULTS

The identity of colonies was confirmed by alkaline phosphatase staining and immunocytochemistry using PLZF and α6 integrin antibodies. The number and diameter of colonies of SSCs in the upper layer were evaluated at days 14 and 28 of culture. The number and diameter of colonies of SSCs were significantly higher in the melatonin group compared with the control group. The levels of expression of ID-4 and Plzf, unlike c-kit, were significantly higher in the melatonin group than in the control group.

CONCLUSIONS

Results of the present study show that supplementation of the culture medium (SACS) with 100 μM melatonin significantly decreased reactive oxygen species (ROS) production in the treated group compared with the control group, and increased SSC proliferation.

Retinoic acid deficiency leads to an increase in spermatogonial stem number in the neonatal mouse testis, but excess retinoic acid results in no change

The onset of spermatogenesis occurs in response to retinoic acid (RA), the active metabolite of vitamin A. However, whether RA plays any role during establishment of the spermatogonial stem cell (SSC) pool is unknown. Because designation of the SSC population and the onset of RA signaling in the testis that induces differentiation have similar timing, this study asked whether RA influenced SSC establishment. Whole mount immunofluorescence and flow cytometric analysis using the Id4-eGfp transgenic reporter mouse line revealed an enrichment for ID4-EGFP+ cells within the testis following inhibition of RA synthesis by WIN 18,446 treatment. Transplantation analyses confirmed a significant increase in the number of SSCs in testes from RA-deficient animals. Conversely, no difference in the ID4-EGFP+ population or change in SSC number were detected following exposure to an excess of RA. Collectively, reduced RA altered the number of SSCs present in the neonatal testis but precocious RA exposure in the neonatal testis did not, suggesting that RA deficiency causes a greater proportion of progenitor undifferentiated spermatogonia to retain their SSC state past the age when the pool is thought to be determined.

Horse spermatogonial stem cell cryopreservation: feasible protocols and potential biotechnological applications

The establishment of proper conditions for spermatogonial stem cells (SSCs) cryopreservation and storage represents an important biotechnological approach for the preservation of the genetic stock of valuable animals. This study demonstrates the effects of different cryopreservation protocols on the survival rates and phenotypic expression of SSCs in horses. The cells were enzymatically isolated from testes of eight adult horses. After enrichment and characterization of germ cells in the suspension, the feasibility of several cryopreservation protocols were evaluated. Three different cryomedia compositions, associated with three different methods of freezing (vitrification, slow-freezing and fast-freezing) were evaluated. Based on the rates of viable SSCs found before and after thawing, as well as the number of recovered cells after cryopreservation, the best results were obtained utilizing the DMSO-based cryomedia associated with the slow-freezing method. In addition, when isolated cells were cultured in vitro, MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay and immunofluorescence analysis indicated that the cryopreserved cells were as metabolically active as the fresh cells and were also expressing typical SSCs proteins (VASA, NANOS2 and GFRA1). Therefore, our results indicate that equine SSCs can be cryopreserved without impairment of structure, function, or colony-forming abilities.

Effects of different Sertoli cell types on the maintenance of adult spermatogonial stem cells in vitro

Spermatongonial stem cells (SSCs) are unique testis cells that are able to proliferate, differentiate, and transmit genetic information to the next generation. However, the effect of different Sertoli cell types on the expression of specific SSC genes is not yet well understood. In this study, we compare the in vitro effect of adult Sertoli cells, embryonic Sertoli cells, and TM4 (a Sertoli cell line) as feeder layers on the expression of SSC genes. SSCs were isolated from the testis of adult male mice and purified by differential plating. Following enrichment, SSCs were cultivated for 1 and 2 wk in the presence of various feeders. The expression of SSC-specific genes (Mvh, ZBTB, and c-kit) was evaluated by real-time polymerase chain reaction. Our results revealed that expression of the specific SSC genes was significantly higher in the embryonic Sertoli cells after 1 and 2 wk compared to the adult Sertoli cells and the TM4 group. Our finding suggest that co-culturing of SSCs with embryonic Sertoli cells is helpful for in vitro cultivation of SSCs and might improve the self-renewal of these stem cells.

Estimation of the distribution of low-intensity ultrasound mechanical index as a parameter affecting the proliferation of spermatogonia stem cells in vitro

Considering the use of physical and mechanical stimulation, such as low-intensity ultrasound for proliferation and differentiation of stem cells, it is essential to understand the physical and acoustical mechanisms of acoustic waves in vitro. Mechanical index is used for quantifying acoustic cavitation and the relationship between acoustic pressure and the frequency. In this study, modeling of the mechanical index was applied to provide treatment protocol and to understand the effective physical processes on reproducibility of stem cells. Due to low intensity of ultrasound, Rayleigh integral model has been used for acoustic pressure computation. The acoustic pressure and mechanical index equations are modeled and solved to estimate optimal mechanical index for 28, 40, 150kHz and 1MHz frequencies. This model are solved in different intensities and distances from transducer in cylindrical coordinates. Based on the results of the mechanical index, regions with threshold mechanical index of 0.7 were identified for extracting of radiation arrangement to cell medium. Acoustic pressure distribution along the axial and radial was extracted. In order to validate the results of the modeling, the acoustic pressure in the water and near field depth was measured by a piston hydrophone. Results of modeling and experiments show that the model is consistent well to experimental results with 0.91 and 0.90 correlation of coefficient (p<0.05) for 1MHz and 40kHz. Low-intensity ultrasound with 0.40 mechanical index is more effective on enhancing the proliferation rate of the spermatogonia stem cells during the seven days of culture. In contrast, higher mechanical index has a harmful effect on the spermatogonial stem cells. Thus, considering cavitation threshold of different materials is necessary to find effective mechanical index ranges on proliferation for the used frequencies. This acoustic propagation model and ultrasound mechanical index assessments can be used with acceptable accuracy, for the extraction special arrangement of acoustic exposure used in biological conditions in vitro. This model provides proper treatment planning in vitro and in vivo by estimating the cavitation phenomenon.

Progress and biotechnological prospects in fish transgenesis

The history of transgenesis is marked by milestones such as the development of cellular transdifferentiation, recombinant DNA, genetic modification of target cells, and finally, the generation of simpler genetically modified organisms (e.g. bacteria and mice). The first transgenic fish was developed in 1984, and since then, continuing technological advancements to improve gene transfer have led to more rapid, accurate, and efficient generation of transgenic animals. Among the established methods are microinjection, electroporation, lipofection, viral vectors, and gene targeting. Here, we review the history of animal transgenesis, with an emphasis on fish, in conjunction with major developments in genetic engineering over the past few decades. Importantly, spermatogonial stem cell modification and transplantation are two common techniques capable of revolutionizing the generation of transgenic fish. Furthermore, we discuss recent progress and future biotechnological prospects of fish transgenesis, which has strong applications for the aquaculture industry. Indeed, some transgenic fish are already available in the current market, validating continued efforts to improve economically important species with biotechnological advancements.

In vitro generation of Sertoli-like and haploid spermatid-like cells from human umbilical cord perivascular cells

BACKGROUND

First trimester (FTM) and term human umbilical cord-derived perivascular cells (HUCPVCs), which are rich sources of mesenchymal stem cells (MSCs), can give rise to Sertoli cell (SC)-like as well as haploid germ cell (GC)-like cells in vitro using culture conditions that recapitulate the testicular niche. Gamete-like cells have been produced ex vivo using pluripotent stem cells as well as MSCs. However, the production of functional gametes from human stem cells has yet to be achieved.

METHODS

Three independent lines of FTM and term HUCPVCs were cultured using a novel 5-week step-wise in vitro differentiation protocol recapitulating key physiological signals involved in testicular development. SC- and GC-associated phenotypical properties were assessed by real-time polymerase chain reaction (RT-PCR), quantitative PCR immunocytochemistry, flow cytometry, and fluorescence in-situ hybridization (FISH). Functional spermatogonial stem cell-like properties were assessed using a xenotranplantation assay.

RESULTS

Within 3 weeks of differentiation, two morphologically distinct cell types emerged including large adherent cells and semi-attached round cells. Both early GC-associated markers (VASA, DAZL, GPR125, GFR1α) and SC-associated markers (FSHR, SOX9, AMH) were upregulated, and 5.7 ± 1.2% of these cells engrafted near the inner basal membrane in a xenograft assay. After 5 weeks in culture, 10-30% of the cells were haploid, had adopted a spermatid-like morphology, and expressed PRM1, Acrosin, and ODF2. Undifferentiated HUCPVCs secreted key factors known to regulate spermatogenesis (LIF, GDNF, BMP4, bFGF) and 10-20% of HUCPVCs co-expressed SSEA4, CD9, CD90, and CD49f. We hypothesize that the paracrine properties and cellular heterogeneity of HUCPVCs may explain their dual capacity to differentiate to both SC- and GC-like cells.

CONCLUSIONS

HUCPVCs recapitulate elements of the testicular niche including their ability to differentiate into cells with Sertoli-like and haploid spermatid-like properties in vitro. Our study supports the importance of generating a niche-like environment under ex vivo conditions aiming at creating mature GC, and highlights the plasticity of HUCPVCs. This could have future applications for the treatment of some cases of male infertility.

Transplantation as a Quantitative Assay to Study Mammalian Male Germline Stem Cells

In mammals, the activities of spermatogonial stem cells (SSCs) provide the foundation for continual spermatogenesis throughout a male's reproductive lifetime. At present, the defining characteristics of SSCs and mechanisms controlling their fate decisions are not well understood. Transplantation is a definitive functional measure of stem cell capacity for male germ cells that can be used as an assay to provide an unequivocal quantification of the SSC content in an experimental cell population. Here, we discuss the procedure for mice and provide protocols for preparing donor germ cell suspensions from testes directly or primary cultures of spermatogonia for transplantation, enriching for SSCs, preparing recipient males, microinjection into recipient testes, and considerations for experimental design.

Rattus norvegicus Spermatogenesis Colony-Forming Assays

Knowledge gaps persist on signaling pathways and metabolic states in germ cells sufficient to support spermatogenesis independent of a somatic environment. Consequently, methods to culture mammalian stem cells through spermatogenesis in defined systems have not been established. Lack of success at culturing mammalian stem cells through spermatogenesis in defined systems reflects an inability to experimentally recapitulate biochemical events that develop in germ cells during a seminiferous epithelial cycle. Complex germ and somatic cell associations that develop each seminiferous epithelial cycle support such a hypothesis, conceivably explaining why highly pure mammalian spermatogonia have not developed into meiosis, much less through meiosis without somatic cells. Here, we outline an in vitro spermatogenesis colony-forming assay to study how differentiating spermatogonial syncytia develop from rat spermatogonial stem cell lines. Robust spermatogonial differentiation under defined culture conditions will facilitate molecular biology studies on pre-meiotic steps in gamete development, and provide a soma-free bioassay to identify spermatogenic factors that promote meiotic progression in vitro.

Identification of Germ-Line Stem Cells in Zebrafish

Both male and female zebrafish have a population of germ-line stem cells that produce gametes throughout the life of the fish. These cells localize to specific regions in the gonads and can be identified because they uniquely express the nanos2 gene, which encodes a conserved regulator of translation. A method is presented here for identifying germ-line stem cells in the ovary and testis using a combined protocol for whole-mount fluorescent RNA in situ hybridization to detect nanos2 mRNA and immunofluorescence to detect the pan-germ cell marker Vasa.

Visualization and Lineage Tracing of Pax7+ Spermatogonial Stem Cells in the Mouse

The precise identity of spermatogonial stem cells-the germline stem cell of the adult testis-remains a controversial topic. Technical limitations have included the lack of specific markers and methods for lineage tracing of A_single spermatogonia and their subsets. Immunolocalization of proteins in tissue sections has been a standard tool for the in situ identification and visualization of rare cellular subsets. However, these studies are limited by the need for faithful and reliable protein markers to define these cell types, as well as the availability of specific antibodies to these markers. Here we describe the use of a monoclonal antibody to Pax7 as a means to detect spermatogonial stem cells (SSCs) both in tissue sections and in intact seminiferous tubules. Furthermore, we describe methods for lineage tracing as an alternative method to visualize Pax7⁺ spermatogonial stem cells and their progeny.

LncRNA AK015322 promotes proliferation of spermatogonial stem cell C18-4 by acting as a decoy for microRNA-19b-3p

Long noncoding RNAs (lncRNAs) have been reported to play important roles in male reproduction. In our previous research, we studied the expression profile of lncRNAs in mouse male germ cells including spermatogonial stem cell, type A spermatogonia, pachytene spermatocyte, and round spermatid by microarray method, which showed that testis-enriched lncRNA AK015322 is highly expressed in spermatogonial stem cell. In this study, we found that AK015322 promotes proliferation of mouse spermatogonial stem cell line C18-4 in vitro. Furthermore, bioinformatic analysis, real-time PCR, and luciferase assay validated that AK015322 serves as a decoy of microRNA-19b-3p (miR-19b-3p), antagonizes its function, and attenuates the repression of its endogenous target transcriptional factor Ets-variant 5 (ETV5) which was a pivotal gene for spermatogonial stem cell self-renewal. Taken together, our results suggest that a variety of lncRNAs may regulate male reproduction through serving as competing-endogenous RNAs to modulate the function of germ cells.

Reciprocal localization of transcription factors YY1 and CP2c in spermatogonial stem cells and their putative roles during spermatogenesis

Maintaining stemness and permitting differentiation mediated by combinations of transcription factors (TFs) are key aspects of mammalian spermatogenesis. It has been established that yin yang 1 (YY1), a target factor of mammalian polycomb repressive complex 2 (PRC2) and a regulator of stemness, is involved in the stable maintenance of prophase stage spermatocytes. Recently, we have demonstrated that the TF CP2c partners with YY1 in some cells to antagonistically regulate the other protein's function. To date, the functional roles of YY1 and CP2c in spermatogonial stem cells and their derived germ cells remain unclear. Here, we investigated the expression of YY1 and CP2c in mouse gonocytes and germ cells using tissue immunohistochemical and immunofluorescence analyses. At E14.5, both YY1 and CP2c were stained in gonocytes and Sertoli cells in testicular cords, showing different proportion and density of immunoreactivity. However, in adult testes, YY1 was localized in the nuclei of spermatogonial stem cells and spermatocytes, but not in spermatozoa. It was also detected in spermatogonia and spermatids in a stage-specific manner during spermatogenic cycle. CP2c could be detected mostly in the cytoplasm of spermatocytes but not at all in spermatogonial stem cells, indicating mutually exclusive expression of CP2c and YY1. Interestingly, however, CP2c was stained in the cytoplasm and nucleus of spermatogonia at elongation and release stages, and co-localized with YY1 in the nucleus at grouping, maturation, and releasing stages. Neither YY1 nor CP2c was expressed in spermatozoa. Our data indicate that YY1 strongly localizes in the spermatogonial stem cells and co-localizes heterogeneously with CP2c to permit spermatogenesis, and also suggest that YY1 is essential for stemness of spermatogonial stem cells (SCs) whereas CP2c is critical for the commitment of spermatogonia and during the progression of spermatogonia to spermatids. This evaluation expands our understanding of the molecular mechanism of spermatogonia formation as well as spermatogenesis in general.

Data on in vivo phenotypes of GFRα1-positive spermatogonia stimulated by interstitial GDNF signals in mouse testes

This article contains the data related to the research article “in vivo dynamics of GFRα1-positive spermatogonia stimulated by GDNF signals using a bead transplantation assay” (Uchida et al., 2016) [1]. A novel transplantation assay of growth factor-soaked beads into the mammalian testicular interstitium was developed, in order to examine the effects of various soluble factors on in vivo dynamics of the spermatogonia including spermatogonial stem cells (SSC). Here we provide the image data of GFRα1-positive stem/progenitor spermatogonia in mouse seminiferous tubules near the beads soaked in GDNF (glial cell-derived neurotrophic factor), one of the SSC niche factors. The data provide various phenotypes of GFRα1-positive spermatogonia induced by bead-derived GDNF signals, which are useful to understand the active state of GFRα1-positive stem/progenitor spermatogonia in vivo.

Transcription Factor GLIS3: A New and Critical Regulator of Postnatal Stages of Mouse Spermatogenesis

In this study, we identify a novel and essential role for the Krüppel-like zinc finger transcription factor GLI-similar 3 (GLIS3) in the regulation of postnatal spermatogenesis. We show that GLIS3 is expressed in gonocytes, spermatogonial stem cells (SSCs) and spermatogonial progenitors (SPCs), but not in differentiated spermatogonia and later stages of spermatogenesis or in somatic cells. Spermatogenesis is greatly impaired in GLIS3 knockout mice. Loss of GLIS3 function causes a moderate reduction in the number of gonocytes, but greatly affects the generation of SSCs/SPCs, and as a consequence the development of spermatocytes. Gene expression profiling demonstrated that the expression of genes associated with undifferentiated spermatogonia was dramatically decreased in GLIS3-deficient mice and that the cytoplasmic-to-nuclear translocation of FOXO1, which marks the gonocyte-to-SSC transition and is necessary for SSC self-renewal, is inhibited. These observations suggest that GLIS3 promotes the gonocyte-to-SSC transition and is a critical regulator of the dynamics of early postnatal spermatogenesis. Stem Cells 2016;34:2772-2783.

In vitro effects of date palm (Phoenix dactylifera L.) pollen on colonization of neonate mouse spermatogonial stem cells

ETHNOPHARMACOLOGICAL RELEVANCE

Date palm (Phoenix dactylifera L.) pollen (DPP) is widely used as a folk remedy for male infertility treatment, and has well known medicinal effects.

AIM OF THE STUDY

This study aimed to determine the in vitro effects of DPP on the efficiency of neonate mouse spermatogonial stem cells (SSCs) proliferation.

MATERIAL AND METHODS

Sertoli and SSCs were isolated from 6 to 10-days-old mouse testes, and their identity was confirmed using immunocytochemistry against cytokeratin for sertoli cells and PLZF, Oct-4 and CDH-1 for SSCs. Isolated testicular cells were cultured in the absence or presence of 0.06, 0.25 and 0.62mg/ml concentrations of DPP aqueous extract for 2 weeks. The number and diameter of SSC colonies were assessed during third, 7th, 9th and 14th day of culture, and the expression of the Mvh, GFRα-1 and Oct-4 was evaluated using quantitative PCR at the end of the culture period. The significance of the data was analyzed using ANOVA and paired samples t-test and Tukey and Bonferroni test as post hoc tests at the level of p≤0.05.

RESULTS

Pattern assay of colony formation showed that SSCs numbers increased in the present of 0.62mg/ml concentration of DPP extract with higher slop relative to other groups (P <0.05). Colony diameters had no significant difference between groups in 3th, 7th, 9th and 14th days after culture. The Mvh and Oct-4 genes expression had no significant difference between groups, while GFRα1 expression was increased significantly in cells treated with 0.06mg/ml concentration relative to other groups (P<0.05).

CONCLUSION

It seems that co-culture of SSCs with sertoli sells in the presence of low doses of DPP can increase SSCs proliferation and keep their stemness state, while higher concentrations can differentiate the treated cells.

In vivo dynamics of GFRα1-positive spermatogonia stimulated by GDNF signals using a bead transplantation assay

In mouse testes, spermatogonial stem cells (SSCs), a subpopulation of GFRα1 (GDNF family receptor-α1)-positive spermatogonia, are widely distributed along the convoluted seminiferous tubules. The proliferation and differentiation of the SSCs are regulated in part by local expression of GDNF (glial cell-derived neurotorphic factor), one of major niche factors for SSCs. However, the in vivo dynamics of the GDNF-stimulated GFRα1-positive spermatogonia remains unclear. Here, we developed a simple method for transplanting DiI-labeled and GDNF-soaked beads into the mouse testicular interstitium. By using this method, we examined the dynamics of GFRα1-positive spermatogonia in the tubular walls close to the transplanted GDNF-soaked beads. The bead-derived GDNF signals were able to induce the stratified aggregate formation of GFRα1-positive undifferentiated spermatogonia by day 3 post-transplantation. Each aggregate consisted of tightly compacted Asingle and marginal Apaired-Aaligned GFRα1-positive spermatogonia and was surrounded by Aaligned GFRα1-negative spermatogonia at more advanced stages. These data not only provide in vivo evidence for the inductive roles of GDNF in forming a rapid aggregation of GFRα1-positive spermatogonia but also indicate the usefulness of this in vivo assay system of various growth factors for the stem/progenitor spermatogonia in mammalian spermatogenesis.

Conservation of spermatogonial stem cell marker expression in undifferentiated felid spermatogonia

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