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*

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

While hallmarks of rodent spermatogonia stem cell biomarkers' heterogeneity have recently been identified, their stage and subset distributions remain unclear. Furthermore, it is currently difficult to accurately identify subset-specific SSC marker distributions due to the poor nuclear morphological characteristics associated with fixation in 4% paraformaldehyde. In the present study, testicular cross-sections and whole-mount samples were Bouin fixed to optimize nuclear resolution and visualized by immunohistochemistry (IHC) and immunofluorescence (IF). The results identified an expression pattern of PLZF^highc-KIT^pos in A₁ spermatogonia, while A₂-A₄-differentiating spermatogonia were PLZF^lowc-KIT^pos. Additionally, this procedure was used to examine asymmetrically expressing GFRA1 and PLZF clones, asymmetric A_pr and false clones were distinguished based on the presence or absence of TEX14, a molecular maker of intercellular bridges, despite having identical nuclear morphology and intercellular distances that were <25 μm. In conclusion, this optimized Bouin fixation procedure facilitates the accurate identification of spermatogonium subsets based on their molecular profiles and is capable of distinguishing asymmetric and false clones. Therefore, the findings presented herein will facilitate further morphological and functional analysis studies and provide further insight into spermatogonium subtypes.
Animals ; Cell Differentiation ; Fluorescent Antibody Technique ; Gene Expression Regulation/genetics* ; Glial Cell Line-Derived Neurotrophic Factor Receptors/genetics* ; Immunohistochemistry ; Male ; Mice ; Mice, Inbred C57BL ; Promyelocytic Leukemia Zinc Finger Protein/genetics* ; Proto-Oncogene Proteins c-kit/genetics* ; Seminiferous Tubules/cytology* ; Spermatogenesis ; Spermatogonia/metabolism* ; Testis/cytology* ; Tissue Fixation ; Transcription Factors/genetics*

Nanos2, a member of the Nanos2 gene family, is a specific gene in male germ cells and encodes an evolutionarily conserved RNA binding protein expressed in male primordial germ cells (PGCs) during the embryonic period as well as in the spermatogonial stem cells (SSCs) of the testis. In the embryonic period, Nanos2 promotes the development of male PGCs and inhibits them from meiosis. In the process of spermatogenesis, Nanos2 suppresses the differentiation of SSCs in the testis and maintains the stability of the SSC pool. The knockout of Nanos2 may cause the disappearance of germ cells and sterility in male mice while its overexpression in the testis may lead to accumulation of SSCs in seminiferous tubules. Besides, Nanos2 is involved in the degradation of specific RNAs and possibly associated with some diseases of the male reproductive system. This review focuses on the recent progress in the studies of Nanos2 in the male reproductive system.
Animals ; Cell Differentiation ; Gene Knockout Techniques ; Male ; Meiosis ; Mice ; RNA ; metabolism ; RNA-Binding Proteins ; genetics ; metabolism ; Spermatogenesis ; physiology ; Spermatogonia ; Spermatozoa ; Testis ; cytology

Fertility preservation is a hotspot of research in reproductive medicine, and that of male adolescent cancer patients is drawing even more attention from reproductive and oncologic clinicians. Both cancer and its treatment can decrease semen quality and even induce irreversible damage to fertility. Sperm cryopreservation is an effective method for fertility preservation. In the past few years, marked advances have been made in the cryopreservation, transplantation, and in vitro culture of testis tissue and stem spermatogonial cells. Although still experimental, these approaches may offer some options to those with no mature sperm in the testis. Unfortunately, very few people know and participate in the studies of fertility preservation and the utilization rate of cryopreserved sperm remains low. Therefor reproductive physicians and oncologists are required to make more efforts to search for effective fertility preservation methods for male adolescent cancer patients.
Adolescent ; Cryopreservation ; Fertility Preservation ; methods ; Humans ; Male ; Neoplasms ; therapy ; Semen Analysis ; Semen Preservation ; methods ; Spermatogonia ; Testis ; cytology

OBJECTIVETo isolate, identify and culture human spermatogonial stem cells (SSC) and then obtain purified and enriched human SSCs for research and application.

METHODSWe detected the expression of CD90 in the human testis using the immunofluorescence technique and isolated human testicular spermatogenic cells by two-step enzymatic digestion, followed by differential plating and magnetic-activated cell sorting (MACS) with CD90 as an SSC marker. Then we identified the isolated CD90-positive spermatogenic cells by RT-PCR and immunocytochemistry, and meanwhile cocultured them with Sertoli cells in SG medium in vitro.

RESULTSThe isolated CD90-positive cells showed a relatively homogeneous characteristic in size and morphology and expressed the genes specific for human SSCs, with high expressions (90.5%) of GFRA1, GPR125, and UCHL1. After coculture with Sertoli cells in the SG medium for 2 weeks, the isolated CD90-positive cells maintained a good activity.

CONCLUSIONCD90 can be regarded as a speci- fic marker for human SSCs and used to obtain highly enriched human SSCs by differential plating and MACS. Furthermore, the isolated human SSCs can be cultured in SG medium in vitro.

Adult Stem Cells ; cytology ; Biomarkers ; metabolism ; Cell Separation ; methods ; Cell Shape ; Cell Size ; Coculture Techniques ; Glial Cell Line-Derived Neurotrophic Factor Receptors ; metabolism ; Humans ; Immunohistochemistry ; Male ; Receptors, G-Protein-Coupled ; metabolism ; Sertoli Cells ; Spermatogonia ; cytology ; Testis ; metabolism ; Thy-1 Antigens ; isolation & purification ; metabolism ; Ubiquitin Thiolesterase ; metabolism

OBJECTIVETo study the dynamic changes in the protein marker expression in the spermatogonial stem cells (SSCs) of mice at different ages by iTRAQ protein mass spectrometry and to screen new markers using the bioinformatic proteome database.

METHODSBased on the postnatal weeks, we divided 80 healthy male C57BL/6 mice into eight age groups of equal number, harvested their testicular tissues, extracted proteins following purification of the SSCs by compound enzyme digestion and magnetic-activated cell sorting. Then we analyzed and identified proteins using two-dimensional electrophoresis, protein mass spectrometry, and protein database information.

RESULTSTotally, 248,510 mass spectra were obtained from the MS experiment and 1132 proteins were identified. By the criteria of >1.2-fold for protein abundance difference and P value <0.05, we identified 298 differentially expressed proteins and 9 currently known makers of SSCs (PCNA, GFRalpha1, CDH1, Annexin A7, UCHL1, VASA, CD49f, CD29, and PLZf). Compara- tive analysis showed different expressions of the proteins in the SSCs of the mice of different ages, and the differences in the expressions of GFRalpha1, CD49f, and CD29 were consistent with the findings in other published literature. Ten proteins (P63, CD71, CD98, K19, ACE, K18, K15, K17, SH2, and SH3) were selected as SSC markers to be further studied.

CONCLUSIONThe proteins in SSCs are differentially expressed in mice of different ages. The technology of iTRAQ protein mass spectrometry can be used to analyze and compare the proteome information of mouse SSCs, obtain differentially expressed proteins in mice of different ages, and thus offers a new ap- proach to further analysis and study of the function and roles of these differential proteins.

Adult Stem Cells ; cytology ; metabolism ; Age Factors ; Animals ; Biomarkers ; analysis ; metabolism ; Cell Separation ; methods ; Electrophoresis, Gel, Two-Dimensional ; Male ; Mass Spectrometry ; Mice ; Mice, Inbred C57BL ; Proteins ; analysis ; metabolism ; Spermatogonia ; cytology

OBJECTIVETo establish an in vitro model of cultured mouse testis using rotary aerobic culture.

METHODSRotary aerobic incubation with optimized culture conditions was used for in vitro culture of mouse testis, and the morphology of the cultured testicular tissues was compared with that cultured in Transwell chambers. The changes in the testicular tissue structure were examined using HE staining, and the cell proliferation was assessed with BrdU staining. Testosterone concentrations in the culture medium were tested with radioimmunoassay and the expression of the functionally related proteins in the testis was detected using immunohistochemistry.

RESULTSThe testicular tissue cultured by optimized rotary aerobic culture presented with more intact histological structure with the size of the testis ranged from 0.3 to 0.8 mm(3). In the two culture systems, the prolifeation index of the spermatogonia increased and that of Sertoli cells decreased with time, and such changes in spermatogonia and Sertoli cell proliferation indices became statistically significant at 3 days (P<0.05) and 5 days (P<0.05) of culture, respectively, as compared with those at 1 day. The concentration of testoerone in the culture media decreased significantly with incubation time (P<0.05). At 3 days of culture, the protein expression of 3β-hydroxysteroid dehydrogenase, cytochrome P450 17α-hydroxylase and cholesterol side-chain cleavage enzyme was detected in Leydig cell cytoplasm and vimentin expression in Sertoli cell cytoplasm.

CONCLUSIONAn in vitro model of cultured mouse testis has been successfully established using rotary aerobic incubation.

17-Hydroxysteroid Dehydrogenases ; metabolism ; Animals ; Cholesterol Side-Chain Cleavage Enzyme ; metabolism ; Culture Media ; chemistry ; Leydig Cells ; cytology ; Male ; Mice ; Organ Culture Techniques ; Radioimmunoassay ; Sertoli Cells ; cytology ; Spermatogonia ; cytology ; Testis ; Testosterone ; chemistry ; Vimentin ; metabolism

The effects of over-expression of testis-specific expressed gene 1 (TSEG-1) on the viability and apoptosis of cultured spermatogonial GC-1spg cells were investigated, and the immortal spermatogonial cell line GC-1spg (CRL-2053™) was obtained as the cell model in order to explore the function of TSEG-1. We transfected the eukaryotic vector of TSEG-1, named as pEGFP-TSEG-1 into cultured spermatogonial GC-1spg cells. Over-expression of TSEG-1 inhibited the proliferation of GC-1spg cells, and arrested cell cycle slightly at G0/G1 phase. Transfection of TSEG-1 attenuated the transcript levels of Ki-67, PCNA and cyclin D1. In addition, over-expression of TSEG-1 induced early and late apoptosis, and reduced the mitochondrial membrane potential of GC-1spg cells. Moreover, transfection of TSEG-1 significantly enhanced the ratio of Bax/Bcl-2 and transcript levels of caspase 9, and decreased the expression of Fas and caspase 8 in GC-1spg cells. These results indicated over-expression of TSEG-1 suppresses the proliferation and induces the apoptosis of GC-1spg cells, which establishes a basis for further study on the function of TSEG-1.
Animals ; Caspase 8 ; biosynthesis ; genetics ; Cell Line ; Cyclin D1 ; biosynthesis ; genetics ; G1 Phase ; physiology ; Histones ; genetics ; metabolism ; Ki-67 Antigen ; biosynthesis ; genetics ; Male ; Mice ; Proliferating Cell Nuclear Antigen ; biosynthesis ; genetics ; Resting Phase, Cell Cycle ; physiology ; Spermatogonia ; cytology ; metabolism ; bcl-2-Associated X Protein ; biosynthesis ; genetics