Infertility has become one of the most serious diseases worldwide, and 50% of this disease can be attributed to male-related factors. Spermatogenesis, by definition, is a complex process by which spermatogonial stem cells (SSCs) self-renew to maintain stem cell population within the testes and differentiate into mature spermatids. It is of great significance to uncover gene regulation and signaling pathways that are involved in the fate determinations of SSCs with aims to better understand molecular mechanisms underlying human spermatogenesis and identify novel targets for gene therapy of male infertility. Significant achievement has recently been made in demonstrating the signaling molecules and pathways mediating the fate decisions of mammalian SSCs. In this review, we address key gene regulation and crucial signaling transduction pathways in controlling the self-renewal, differentiation, and apoptosis of SSCs, and we illustrate the networks of genes and signaling pathways in SSC fate determinations. We also highlight perspectives and future directions in SSC regulation by genes and their signaling pathways. This review could provide novel insights into the genetic regulation of normal and abnormal spermatogenesis and offer molecular targets to develop new approaches for gene therapy of male infertility.
Humans ; Male ; Signal Transduction/physiology* ; Apoptosis/physiology* ; Spermatogenesis/physiology* ; Cell Differentiation ; Adult Germline Stem Cells/physiology* ; Spermatogonia/cytology* ; Gene Expression Regulation ; Animals ; Infertility, Male/genetics* ; Cell Self Renewal/genetics*

Mouse spermatogenesis entails the maintenance and self-renewal of spermatogonial stem cells (SSCs), which require a complex web-like signaling network transduced by various cytokines. Although brain-derived neurotrophic factor (BDNF) is expressed in Sertoli cells in the testis, and its receptor tropomyosin receptor kinase B (TrkB) is expressed in the spermatogonial population containing SSCs, potential functions of BDNF for spermatogenesis have not been uncovered. Here, we generate BDNF conditional knockout mice and find that BDNF is dispensable for in vivo spermatogenesis and fertility. However, in vitro , we reveal that BDNF -deficient germline stem cells (GSCs) exhibit growth potential not only in the absence of glial cell line-derived neurotrophic factor (GDNF), a master regulator for GSC proliferation, but also in the absence of other factors, including epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), and insulin. GSCs grown without these factors are prone to differentiation, yet they maintain expression of promyelocytic leukemia zinc finger ( Plzf ), an undifferentiated spermatogonial marker. Inhibition of phosphoinositide 3-kinase (PI3K), mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK), and Src pathways all interfere with the growth of BDNF-deficient GSCs. Thus, our findings suggest a role for BDNF in maintaining the undifferentiated state of spermatogonia, particularly in situations where there is a shortage of growth factors.
Animals ; Male ; Brain-Derived Neurotrophic Factor/genetics* ; Spermatogonia/cytology* ; Mice ; Spermatogenesis/genetics* ; Mice, Knockout ; Cell Differentiation ; Glial Cell Line-Derived Neurotrophic Factor/genetics* ; Promyelocytic Leukemia Zinc Finger Protein/genetics* ; Cell Survival/physiology* ; Signal Transduction/physiology* ; Cell Proliferation/physiology*

Icariin is a pure compound derived from Epimedium brevicornu Maxim, and it helps the regulation of male reproduction. Nevertheless, the role and underlying mechanisms of Icariin in mediating male germ cell development remain to be clarified. Here, we have demonstrated that Icariin promoted proliferation and DNA synthesis of mouse spermatogonial stem cells (SSCs). Furthermore, surface plasmon resonance iron (SPRi) and molecular docking (MOE) assays revealed that phosphodiesterase 5A (PDE5A) was an important target of Icariin in mouse SSCs. Mechanically, Icariin decreased the expression level of PDE5A. Interestingly, hydrogen peroxides (H 2 O 2 ) enhanced the expression level of phosphorylation H2A.X (p-H2A.X), whereas Icariin diminished the expression level of p-H2A.X and DNA damage caused by H 2 O 2 in mouse SSCs. Finally, our in vivo animal study indicated that Icariin protected male reproduction. Collectively, these results implicate that Icariin targets PDE5A to regulate mouse SSC viability and DNA damage and improves male reproductive capacity. This study thus sheds new insights into molecular mechanisms underlying the fate decisions of mammalian SSCs and offers a scientific basis for the clinical application of Icariin in male reproduction.
Male ; Animals ; Flavonoids/pharmacology* ; Mice ; Cyclic Nucleotide Phosphodiesterases, Type 5/drug effects* ; DNA Damage/drug effects* ; Cell Survival/drug effects* ; Cell Proliferation/drug effects* ; Spermatogonia/drug effects* ; Reproduction/drug effects* ; Adult Germline Stem Cells/metabolism* ; DNA Replication/drug effects*

This study assessed the feasibility of testis tissue cryopreservation (TTC) for fertility preservation in prepubescent boys with cryptorchidism. From January 2014 to December 2022, the University Hospital of Copenhagen (Rigshospitalet, Copenhagen, Denmark) implemented TTC for 56 boys with cryptorchidism to preserve their reproductive potential. Testis tissue samples were collected during orchiopexy (32 cases) or at subsequent follow-up procedures (24 cases), necessitated by an increased risk of infertility as indicated by hormonal assessments and/or findings from initial surgical biopsies. Testis samples were procured for TTC and pathological analysis. The cohort had an average age of 1.3 (range: 0.3-3.8) years at the time of orchiopexy, with 91.1% presenting bilateral cryptorchidism. The study revealed a median germ cell count of 0.39 (range: 0-2.88) per seminiferous tubule, with germ cells detected in 98.0% of the bilateral biopsies and 100% of the unilateral, indicating a substantial potential for fertility in these immature tissues. A dark spermatogonia (Ad) was detected in 37 out of 56 patients evaluated, with a median Ad spermatogonia count of 0.027 (range: 0.002-0.158) per seminiferous tubule. A total of 30.2% of the samples lacked Ad spermatogonia, indicative of potential gonadotrophin insufficiency. The median hormone levels measured were as follows: follicle-stimulating hormone (FSH) at 0.69 (range: 0.16-2.5) U l -1 , luteinizing hormone (LH) at 0.21 (range: 0.05-3.86) U l -1 , and inhibin B at 126 (range: 17-300) pg ml -1 . Despite early orchiopexy, 20%-25% of boys with cryptorchidism remain at risk for future infertility, substantiating the necessity of TTC as a precaution. The study highlights the need for refined predictive techniques to identify boys at higher risk of future infertility.
Humans ; Male ; Cryptorchidism/pathology* ; Cryopreservation ; Testis/pathology* ; Fertility Preservation/methods* ; Child, Preschool ; Infant ; Orchiopexy ; Spermatogonia/pathology* ; Infertility, Male/etiology*

Meiotic initiation is a critical step in gametogenesis. Recently, some genes required for meiotic initiation have been identified. However, meiosis-initiating factors and the underlying mechanisms are far from being fully understood. We have established a long-term culture system of spermatogonial stem cells (SSCs) and an in vitro model of meiotic initiation using mouse SSCs. Our previous study revealed that the RNA-binding protein RBFOX2 may regulate meiotic initiation, but the role and the mechanism need to be further elucidated. In this study, we constructed RBFOX2 knockdown SSC lines by using lentivirus-mediated gene delivery method, and found that the knockdown SSCs underwent normal self-renewal, mitosis and differentiation. However, they were unable to initiate meiosis when treated with retinoic acid, and they underwent apoptosis. These results indicate that RBFOX2 plays an essential role in meiotic initiation of spermatogonia. This work provides new clues for understanding the functions of RNA-binding proteins in meiotic initiation.
Mice ; Male ; Animals ; Spermatogonia/metabolism* ; Meiosis/genetics* ; Cell Differentiation ; Tretinoin/pharmacology* ; Mitosis ; Testis/metabolism*

With the rapid development of gene editing technology, the study of spermatogonial stem cells (SSCs) holds great significance in understanding spermatogenesis and its regulatory mechanism, developing transgenic animals, gene therapy, infertility treatment and protecting rare species. Biogenesis of lysosome-related organelles complex 1 subunit 1 (BLOC1S1) is believed to have anti-brucella potential. Exploring the impack of BLOC1S1 on goat SSCs not only helps investigate the ability of BLOC1S1 to promote SSCs proliferation, but also provides a cytological basis for disease-resistant breeding research. In this study, a BLOC1S1 overexpression vector was constructed by homologous recombination. The BLOC1S1 overexpression cell line of goat spermatogonial stem cells was successfully constructed by lentivirus packaging, transfection and puromycin screening. The overexpression efficiency of BLOC1S1 was found to be 18 times higher using real time quantitative PCR (RT-qPCR). Furthermore, the results from cell growth curve analysis, flow cytometry for cell cycle detection, and 5-ethynyl-2'-deoxyuridine (EdU) staining showed that BLOC1S1 significantly increased the proliferation activity of goat SSCs. The results of RT-qPCR, immunofluorescence staining and Western blotting analyses revealed up-regulation of proliferation-related genes (PCNA, CDK2, CCND1), and EIF2S3Y, a key gene regulating the proliferation of spermatogonial stem cells. These findings strongly suggest that the proliferative ability of goat SSCs can be enhanced through the EIF2S3Y/ERK pathway. In summary, this study successfully created a goat spermatogonial stem cell BLOC1S1 overexpression cell line, which exhibited improved proliferation ability. This research laid the groundwork for exploring the regulatory role of BLOC1S1 in goat spermatogonia and provided a cell platform for further study into the biological function of BLOC1S1. These findings also establish a foundation for breeding BLOC1S1 overexpressing goats.
Animals ; Male ; Goats ; Stem Cells ; Spermatogonia/metabolism* ; Cell Proliferation ; Flow Cytometry ; Testis/metabolism*

Previous studies have shown that long-term spermatogonial stem cells (SSCs) have the potential to spontaneously transform into pluripotent stem cells, which is speculated to be related to the tumorigenesis of testicular germ cells, especially when p53 is deficient in SSCs which shows a significant increase in the spontaneous transformation efficiency. Energy metabolism has been proved to be strongly associated with the maintenance and acquisition of pluripotency. Recently, we compared the difference in chromatin accessibility and gene expression profiles between wild-type (p53^+/+) and p53 deficient (p53^-/-) mouse SSCs using the Assay for Targeting Accessible-Chromatin with high-throughput sequencing (ATAC-seq) and transcriptome sequencing (RNA-seq) techniques, and revealed that SMAD3 is a key transcription factor in the transformation of SSCs into pluripotent cells. In addition, we also observed significant changes in the expression levels of many genes related to energy metabolism after p53 deletion. To further reveal the role of p53 in the regulation of pluripotency and energy metabolism, this paper explored the effects and mechanism of p53 deletion on energy metabolism during the pluripotent transformation of SSCs. The results of ATAC-seq and RNA-seq from p53^+/+ and p53^-/- SSCs revealed that gene chromatin accessibility related to positive regulation of glycolysis and electron transfer and ATP synthesis was increased, and the transcription levels of genes encoding key glycolytic enzymes and regulating electron transport-related enzymes were markedly increased. Furthermore, transcription factors SMAD3 and SMAD4 promoted glycolysis and energy homeostasis by binding to the chromatin of the Prkag2 gene which encodes the AMPK subunit. These results suggest that p53 deficiency activates the key enzyme genes of glycolysis in SSCs and enhances the chromatin accessibility of genes associated with glycolysis activation to improve glycolysis activity and promote transformation to pluripotency. Moreover, SMAD3/SMAD4-mediated transcription of the Prkag2 gene ensures the energy demand of cells in the process of pluripotency transformation and maintains cell energy homeostasis by promoting AMPK activity. These results shed light on the importance of the crosstalk between energy metabolism and stem cell pluripotency transformation, which might be helpful for clinical research of gonadal tumors.
Animals ; Mice ; AMP-Activated Protein Kinases ; Chromatin ; Energy Metabolism ; Gene Deletion ; Stem Cells ; Tumor Suppressor Protein p53/genetics* ; Spermatogonia/cytology* ; Male

Continuous self-renewal and differentiation of spermatogonial stem cells (SSCs) is vital for maintenance of adult spermatogenesis. Although several spermatogonial stem cell regulators have been extensively investigated in rodents, regulatory mechanisms of human SSC self-renewal and differentiation have not been fully established. We analyzed single-cell sequencing data from the human testis and found that forkhead box P4 (FOXP4) expression gradually increased with development of SSCs. Further analysis of its expression patterns in human testicular tissues revealed that FOXP4 specifically marks a subset of spermatogonia with stem cell potential. Conditional inactivation of FOXP4 in human SSC lines suppressed SSC proliferation and significantly activated apoptosis. FOXP4 expressions were markedly suppressed in tissues with dysregulated spermatogenesis. These findings imply that FOXP4 is involved in human SSC proliferation, which will help elucidate on the mechanisms controlling the fate decisions in human SSCs.
Adult ; Humans ; Male ; Cell Differentiation ; Cell Proliferation ; Forkhead Transcription Factors/metabolism* ; Spermatogenesis/genetics* ; Spermatogonia/metabolism* ; Stem Cells/metabolism* ; Testis/metabolism*

Although somatic cells can be reprogrammed to pluripotent stem cells (PSCs) with pure chemicals, authentic pluripotency of chemically induced pluripotent stem cells (CiPSCs) has never been achieved through tetraploid complementation assay. Spontaneous reprogramming of spermatogonial stem cells (SSCs) was another non-transgenic way to obtain PSCs, but this process lacks mechanistic explanation. Here, we reconstructed the trajectory of mouse SSC reprogramming and developed a five-chemical combination, boosting the reprogramming efficiency by nearly 80- to 100-folds. More importantly, chemical induced germline-derived PSCs (5C-gPSCs), but not gPSCs and chemical induced pluripotent stem cells, had authentic pluripotency, as determined by tetraploid complementation. Mechanistically, SSCs traversed through an inverted pathway of in vivo germ cell development, exhibiting the expression signatures and DNA methylation dynamics from spermatogonia to primordial germ cells and further to epiblasts. Besides, SSC-specific imprinting control regions switched from biallelic methylated states to monoallelic methylated states by imprinting demethylation and then re-methylation on one of the two alleles in 5C-gPSCs, which was apparently distinct with the imprinting reprogramming in vivo as DNA methylation simultaneously occurred on both alleles. Our work sheds light on the unique regulatory network underpinning SSC reprogramming, providing insights to understand generic mechanisms for cell-fate decision and epigenetic-related disorders in regenerative medicine.
Male ; Mice ; Animals ; Cellular Reprogramming/genetics* ; Tetraploidy ; Pluripotent Stem Cells/metabolism* ; Induced Pluripotent Stem Cells/metabolism* ; DNA Methylation ; Spermatogonia/metabolism* ; Germ Cells/metabolism*

Continuous spermatogenesis depends on the self-renewal and differentiation of spermatogonial stem cells (SSCs). SSCs, the only male reproductive stem cells that transmit genetic material to subsequent generations, possess an inherent self-renewal ability, which allows the maintenance of a steady stem cell pool. SSCs eventually differentiate to produce sperm. However, in an in vitro culture system, SSCs can be induced to differentiate into various types of germ cells. Rodent SSCs are well defined, and a culture system has been successfully established for them. In contrast, available information on the biomolecular markers and a culture system for livestock SSCs is limited. This review summarizes the existing knowledge and research progress regarding mammalian SSCs to determine the mammalian spermatogenic process, the biology and niche of SSCs, the isolation and culture systems of SSCs, and the biomolecular markers and identification of SSCs. This information can be used for the effective utilization of SSCs in reproductive technologies for large livestock animals, enhancement of human male fertility, reproductive medicine, and protection of endangered species.
Adult Germline Stem Cells ; Animals ; Cell Differentiation ; Male ; Spermatogenesis ; Spermatogonia ; Stem Cells