Regulation of mouse spermatogonial stem cell differentiation by STAT3 signaling

Adrenocorticotropic hormone and its receptor as a novel testicular system involves in the development of spermatogenesis

AIMS

To identify functional membrane-associate-specific SSC markers and examine the development of these cells under in vitro conditions.

MATERIALS AND METHODS

Cells were enzymatically isolated from seminiferous tubules (STs) of immature mice. Spermatogonial cells (Thy1, alpha-6-integrin, and C-KIT) were sorted by FACS. RNA was extracted from these cells for RNAseq analysis. The effect of adrenocorticotropic hormone (ACTH) - the ligand of MC2R- on the development of mouse spermatogonial cells was performed in vitro using a methylcellulose culture system (MCS). Immunofluorescence staining was used to localize MC2R-positive cells in the testes of immature and adult humans and mice and testes of busulfan-treated immature mice.

KEY FINDINGS

Our RNAseq analysis revealed a high expression of melanocortin receptor 2 (MC2R) in Thy1-positive sorted cells. MC2R-positive cells were localized in the periphery of the STs of humans (prepubertal and adults) and mice at immature and adult ages (normal and busulfan-treated mice). MC2R was doubled stained with PLZF and CDH1 (SSC markers). ACTH was localized in mouse testicular germ cells (pre-meiotic, meiotic, and post-meiotic cells) and somatic cells (Sertoli, Leydig, and peritubular cells). The addition of ACTH to isolated cells from mouse STs in MCS significantly increased the development of pre-meiotic and meiotic/post-meiotic cells in vitro.

SIGNIFICANCE

We were able to identify, for the first time, a novel membrane-associated and functional SSC marker (MC2R) with relation to ACTH. This marker can be used in future male fertility preservation strategies. Furthermore, we explored a novel testicular system (ACTH system) that regulates the development of spermatogenesis.

Annona squamosa Fruit Extract Ameliorates Lead Acetate-Induced Testicular Injury by Modulating JAK-1/STAT-3/SOCS-1 Signaling in Male Rats

Lead (Pb) is a common pollutant that is not biodegradable and gravely endangers the environment and human health. Annona squamosa fruit has a wide range of medicinal uses owing to its phytochemical constituents. This study evaluated the effect of treatment with A. squamosa fruit extract (ASFE) on testicular toxicity induced in male rats by lead acetate. The metal-chelating capacity and phytochemical composition of ASFE were determined. The LD50 of ASFE was evaluated by probit analysis. Molecular docking simulations were performed using Auto Dock Vina. Forty male Sprague Dawley rats were equally divided into the following groups: Gp1, a negative control group; Gp2, given ASFE (350 mg/kg body weight (b. wt.)) (1/10 of LD50); Gp3, given lead acetate (PbAc) solution (100 mg/kg b. wt.); and Gp4, given PbAc as in Gp3 and ASFE as in Gp2. All treatments were given by oro-gastric intubation daily for 30 days. Body weight changes, spermatological parameters, reproductive hormone levels, oxidative stress parameters, and inflammatory biomarkers were evaluated, and molecular and histopathological investigations were performed. The results showed that ASFE had promising metal-chelating activity and phytochemical composition. The LD50 of ASFE was 3500 mg/kg b. wt. The docking analysis showed that quercetin demonstrated a high binding affinity for JAK-1 and STAT-3 proteins, and this could make it a more promising candidate for targeting the JAK-1/STAT-3 pathway than others. The rats given lead acetate had defective testicular tissues, with altered molecular, biochemical, and histological features, as well as impaired spermatological characteristics. Treatment with ASFE led to a significant mitigation of these dysfunctions and modulated the JAK-1/STAT-3/SOCS-1 axis in the rats.

Seasonal change of circulating leptin associated with testicular activities of the wild ground squirrels (Citellus dauricus)

The purpose of this study was to explore the variations in the circulating leptin concentrations of the wild ground squirrels in relation to seasonal changes in testicular activities. Hematoxylin-eosin staining showed all types of elongated spermatids and spermatogenic cells existed in the testis in April, while the primary spermatocytes and spermatogonia were most advanced stages of germ cells in June. In addition, the primary spermatocytes, secondary spermatocytes, and spermatogonia were most advanced stages of germ cells in September. The highest circulating leptin concentration was consistent with the maximum body weight results from accumulation of adipose tissue in September. The mRNA expression level of leptin receptor (Ob-R) and STAT3 was lowest in June, raised in September, and remained increased in April. Ob-R and STAT3 were stronger staining in the Leydig cells in July. Moreover, the concentrations of testosterone (T) showed the maximum values in April, the minimum values in June, and significant increases in September. Furthermore, it is worth noting that the levels of T increased with the mRNA levels of Ob-R, STAT3, StAR, and testicular steroidogenic enzymes (3β-HSD, P450c17, and P450scc). Moreover, RNA-seq analyses of testis during the different periods showed that a total of 4209 genes were differentially expressed genes (DEGs); further analysis revealed that DEGs related with the Jak/STAT pathways and reproduction were altered. Taken together, the results suggested that the leptin regulated testicular function through the Jak/STAT pathways and testicular steroidogenic factor expressions.

Germline selection of PTPN11 (HGNC:9644) variants make a major contribution to both Noonan syndrome's high birth rate and the transmission of sporadic cancer variants resulting in fetal abnormality

Some spontaneous germline gain-of-function mutations promote spermatogonial stem cell clonal expansion and disproportionate variant sperm production leading to unexpectedly high transmission rates for some human genetic conditions. To measure the frequency and spatial distribution of de novo mutations we divided three testes into 192 pieces each and used error-corrected deep-sequencing on each piece. We focused on PTPN11 (HGNC:9644) Exon 3 that contains 30 different PTPN11 Noonan syndrome (NS) mutation sites. We found 14 of these variants formed clusters among the testes; one testis had 11 different variant clusters. The mutation frequencies of these different clusters were not correlated with their case-recurrence rates nor were case recurrence rates of PTPN11 variants correlated with their tyrosine phosphatase levels thereby confusing PTPN11's role in germline clonal expansion. Six of the PTPN11 exon 3 de novo variants associated with somatic mutation-induced sporadic cancers (but not NS) also formed testis clusters. Further, three of these six variants were observed among fetuses that underwent prenatal ultrasound screening for NS-like features. Mathematical modeling showed that germline selection can explain both the mutation clusters and the high incidence of NS (1/1000-1/2500).

Interactions Among Brain-Derived Neurotrophic Factor and Neuroimmune Pathways Are Key Components of the Major Psychiatric Disorders

The purpose of this review is to summarize the current knowledge regarding the reciprocal associations between brain-derived neurotrophic factor (BDNF) and immune-inflammatory pathways and how these links may explain the involvement of this neurotrophin in the immune pathophysiology of mood disorders and schizophrenia. Toward this end, we delineated the protein-protein interaction (PPI) network centered around BDNF and searched PubMed, Scopus, Google Scholar, and Science Direct for papers dealing with the involvement of BDNF in the major psychosis, neurodevelopment, neuronal functions, and immune-inflammatory and related pathways. The PPI network was built based on the significant interactions of BDNF with neurotrophic (NTRK2, NTF4, and NGFR), immune (cytokines, STAT3, TRAF6), and cell-cell junction (CTNNB, CDH1) DEPs (differentially expressed proteins). Enrichment analysis shows that the most significant terms associated with this PPI network are the tyrosine kinase receptor (TRKR) and Src homology region two domain-containing phosphatase-2 (SHP2) pathways, tyrosine kinase receptor signaling pathways, positive regulation of kinase and transferase activity, cytokine signaling, and negative regulation of the immune response. The participation of BDNF in the immune response and its interactions with neuroprotective and cell-cell adhesion DEPs is probably a conserved regulatory process which protects against the many detrimental effects of immune activation and hyperinflammation including neurotoxicity. Lowered BDNF levels in mood disorders and schizophrenia (a) are associated with disruptions in neurotrophic signaling and activated immune-inflammatory pathways leading to neurotoxicity and (b) may interact with the reduced expression of other DEPs (CTNNB1, CDH1, or DISC1) leading to multiple aberrations in synapse and axonal functions.

Isolation and Characterization of Germline Stem Cells in Protogynous Hermaphroditic Monopterus albus

Germline stem cells (GSCs) are a group of unique adult stem cells in gonads that act as important transmitters for genetic information. Donor GSCs have been used to produce offspring by transplantation in fisheries. In this study, we successfully isolated and enriched GSCs from the ovary, ovotestis, and testis of Monopterus albus, one of the most important breeding freshwater fishes in China. Transcriptome comparison assay suggests that a distinct molecular signature exists in each type of GSC, and that different signaling activities are required for the maintenance of distinct GSCs. Functional analysis shows that fGSCs can successfully colonize and contribute to the germline cell lineage of a host zebrafish gonad after transplantation. Finally, we describe a simple feeder-free method for the isolation and enrichment of GSCs that can contribute to the germline cell lineage of zebrafish embryos and generate the germline chimeras after transplantation.

Progress in germline stem cell transplantation in mammals and the potential usage

Germline stem cells (GSCs) are germ cells with the capacities of self-renewal and differentiation into functional gametes, and are able to migrate to their niche and reconstitute the fertility of recipients after transplantation. Therefore, GSCs transplantation is a promising technique for fertility recovery in the clinic, protection of rare animals and livestock breeding. Though this novel technique faces tremendous challenges, numerous achievements have been made after several decades' endeavor. This review summarizes the current knowledge of GSCs transplantation and its utilization in mammals, and discusses the application prospect in reproductive medicine and animal science.

Transcriptional profiling of β-2M-SPα-6+THY1+ spermatogonial stem cells in human spermatogenesis

Male infertility is responsible for approximately half of all cases of reproductive issues. Spermatogenesis originates in a small pool of spermatogonial stem cells (SSCs), which are of interest for therapy of infertility but remain not well defined in humans. Using multiparametric analysis of the side population (SP) phenotype and the α-6 integrin, THY1, and β-2 microglobulin cell markers, we identified a population of human primitive undifferentiated spermatogonia with the phenotype β-2 microglobulin (β-2M)⁻SPα-6⁺THY1⁺, which is highly enriched in stem cells. By analyzing the expression signatures of this SSC-enriched population along with other germinal progenitors, we established an exhaustive transcriptome of human spermatogenesis. Transcriptome profiling of the human β-2M⁻SPα-6⁺THY1⁺ population and comparison with the profile of mouse undifferentiated spermatogonia provide insights into the molecular networks and key transcriptional regulators regulating human SSCs, including the basic-helix-loop-helix (bHLH) transcriptional repressor HES1, which we show to be implicated in maintenance of SSCs in vitro.

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Human β-2M⁻SPα-6⁺THY1⁺ undifferentiated spermatogonia are enriched in stem cells

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Comparative transcriptomics analysis of human and murine spermatogonia

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HES1 is involved in the physiology of SSCs in vitro

DYRK1A Overexpression in Mice Downregulates the Gonadotropic Axis and Disturbs Early Stages of Spermatogenesis

Down syndrome (DS) is the most common chromosomal disorder. It is responsible for intellectual disability (ID) and several medical conditions. Although men with DS are thought to be infertile, some spontaneous paternities have been reported. The few studies of the mechanism of infertility in men with DS are now dated. Recent research in zebrafish has indicated that overexpression of DYRK1A (the protein primarily responsible for ID in DS) impairs gonadogenesis at the embryonic stage. To better ascertain DYRK1A's role in infertility in DS, we investigated the effect of DYRK1A overexpression in a transgenic mouse model. We found that overexpression of DYRK1A impairs fertility in transgenic male mice. Interestingly, the mechanism in mice differs slightly from that observed in zebrafish but, with disruption of the early stages of spermatogenesis, is similar to that seen in humans. Unexpectedly, we observed hypogonadotropic hypogonadism in the transgenic mice.

Co-treatment of testosterone and estrogen mitigates heat-induced testicular dysfunctions in a rat model

The two gonadal steroid hormones, testosterone and estrogen, regulate spermatogenesis by proliferation, differentiation, and apoptosis of testicular cells. It has been reported that heat stress or increased scrotal temperature impairs spermatogenesis in many mammals. Moreover, testicular heat stress has also been shown to suppress testosterone and estrogen biosynthesis. Furthermore, it is well known that testosterone and estrogen are important for testicular activity. Therefore, we hypothesised that exogenous testosterone and estrogen, alone or in combination, might alleviate the testicular activity in a heat-stressed rat model. To the best of our knowledge, this will be the first report of the exogenous treatment of both testosterone and estrogen in the heat-stressed rat. Our results showed that a combined testosterone and estrogen treatment significantly increased sperm concentration. The histopathological analysis also exhibited a normal histoarchitecture in the combined treatment group along with decreased oxidative stress. The improved spermatogenesis in the combined treatment group was also supported by the increase in PCNA, GCNA, tubule diameter, germinal epithelium height, and Johnsen score in the combined treatment group. Furthermore, the combined treatment also increased the expression of Bcl2, pStat3, and active caspase-3 and decreased expression of Bax. Thus, increased proliferation, apoptotic and anti-apoptotic markers, along with improved histology in the combined treatment group suggest that estrogen and testosterone synergistically act to stimulate spermatogenesis by increasing proliferation and differentiation of germ cells and may also remove the heat-induced damaged germ cells by apoptosis. Overall, the final mechanism of testosterone- and estrogen-mediated improvement of testicular activity could be attributed to amelioration of oxidative stress.

Use of alginate hydrogel to improve long-term 3D culture of spermatogonial stem cells: stemness gene expression and structural features

The quality and quantity of a spermatogonial stem-cell (SSC) culture can be measured in less time using a 3D culture in a scaffold. The present study investigated stemness gene expression and the morphological and structural characterization of SSCs encapsulated in alginate. SSCs were harvested from BALB/c neonatal mice testes through two-step mechanical and enzymatic digestion. The spermatogonial populations were separated using magnetic-activated cell sorting (MACS) using an anti-Thy1 antibody and c-Kit. The SSCs then were encapsulated in alginate hydrogel. After 2 months of SSC culturing, the alginate microbeads were extracted and stained to evaluate their histological properties. Real-time polymerase chain reaction (PCR) was performed to determine the stemness gene expression. Scanning electron microscopy (SEM) was performed to evaluate the SSC morphology, density and scaffold structure. The results showed that encapsulated SSCs had decreased expression of Oct4, Sox2 and Nanos2 genes, but the expression of Nanog, Bcl6b and Plzf genes was not significantly altered. Histological examination showed that SSCs with pale nuclei and numerous nucleolus formed colonies. SEM evaluation revealed that the alginate scaffold structure preserved the SSC morphology and density for more than 60 days. Cultivation of SSCs on alginate hydrogel can affect Oct4, Sox2 and Nanos2 expression.

Evaluation of co-cultured spermatogonial stem cells encapsulated in alginate hydrogel with Sertoli cells and their transplantation into azoospermic mice

An in vitro spermatogonial stem cell (SSC) culture can serve as an effective technique to study spermatogenesis and treatment for male infertility. In this research, we compared the effect of a three-dimensional alginate hydrogel with Sertoli cells in a 3D culture and co-cultured Sertoli cells. After harvest of SSCs from neonatal mice testes, the SSCs were divided into two groups: SSCs on a 3D alginate hydrogel with Sertoli cells and a co-culture of SSCs with Sertoli cells for 1 month. The samples were evaluated by quantitative reverse transcription polymerase chain reaction (qRT-PCR) assays and bromodeoxyuridine (BrdU) tracing, haematoxylin and eosin (H&E) and periodic acid-Schiff (PAS) staining after transplantation into an azoospermic testis mouse. The 3D group showed rapid cell proliferation and numerous colonies compared with the co-culture group. Molecular assessment showed significantly increased integrin alpha-6, integrin beta-1, Nanog, Plzf, Thy-1, Oct4 and Bcl2 expression levels in the 3D group and decreased expression levels of P53, Fas, and Bax. BrdU tracing, and H&E and PAS staining results indicated that the hydrogel alginate improved spermatogenesis after transplantation in vivo. This finding suggested that cultivation of SSCs on alginate hydrogel with Sertoli cells in a 3D culture can lead to efficient proliferation and maintenance of SSC stemness and enhance the efficiency of SSC transplantation.

The evolutionarily conserved gene, Fam114a2, is dispensable for fertility in mouse

Family with sequence similarity 114 member A2 (Fam114a2) is sperm binding protein that is highly conserved in mammals with homologs both in fungi and plants. Previous studies have demonstrated that miR-762 and P63 are two crucial players of spermatogenesis, and CricFM114A2 regulates their expression. Thus, the current study was focused on describing the role of Fam114a2 in spermatogenesis by generating Fam114a2 knockout (Fam114a2^-/-) mice using CRISPR/Cas9 genome editing techniques. We identified that Fam114a2^-/- mouse has normal fertility and normal morphology of sperm. Furthermore, histological investigation of testicular and epididymis tissues showed no subtle difference, and seminiferous tubules comprised of all stages of germ cells, including mature spermatozoa in Fam114a2^-/- mice. Moreover, cytological investigation of spermatocytes in the progression of prophase I also did not display any notable difference in Fam114a2^-/- mice. Additionally, normal expression of p63 and miR-762 was observed in Fam114a2^+/+ and Fam114a2^-/- testis indicating that Fam114a2 is not involved in the direct regulation of in mice spermatogenesis. Moreover, the removal of Fam114a2 in mouse did not affect the expression of its paralogue Fam114a1 in multiple tissues. Taken together our data determined that Fam114a2 is not essential for male fertility and spermatogenesis in mice.

Interleukin-6 deficiency modulates testicular function by increasing the expression of suppressor of cytokine signaling 3 (SOCS3) in mice

Several cytokines have been reported to participate in spermatogenesis, including interleukin-6 (IL6). However, not many studies have been conducted on the loss of Il6 on the male reproductive tract. Nonetheless, there is considerable knowledge regarding the pathological and physiological role of IL6 on spermatogenesis. In this way, this study evaluated the impact of Il6 deficiency on mice testicles in the absence of infection or inflammation. We showed that Il6 deficiency increases daily sperm production, the number of spermatids, and the testicular testosterone and dihydrotestosterone levels. Besides that, mice with a deleted Il6 (IL6KO) showed increased testicular SOCS3 levels, with no changes in pJAK/JAK and pSTAT3/STAT3 ratios. It is worth noting that the aforementioned pathway is not the only pathway to up-regulate SOCS3, nor is it the only SOCS3 target, thus proposing that the increase of SOCS3 in the testis occurs independently of the JAK-STAT signaling in IL6KO mice. Therefore, we suggest that the lack of Il6 drives androgenic production by increasing SOCS3 in the testis, thus leading to an increase in spermatogenesis.

The Emerging Roles of JNK Signaling in Drosophila Stem Cell Homeostasis

The Jun N-terminal kinase (JNK) pathway is an evolutionary conserved kinase cascade best known for its roles during stress-induced apoptosis and tumor progression. Recent findings, however, have identified new roles for this pleiotropic pathway in stem cells during regenerative responses and in cellular plasticity. Here, we provide an overview of recent findings about the new roles of JNK signaling in stem cell biology using two well-established Drosophila models: the testis and the intestine. We highlight the pathway’s roles in processes such as proliferation, death, self-renewal and reprogramming, and discuss the known parallels between flies and mammals.

FGF9 promotes mouse spermatogonial stem cell proliferation mediated by p38 MAPK signalling

Objectives

Fibroblast growth factor 9 (FGF9) is expressed by somatic cells in the seminiferous tubules, yet little information exists about its role in regulating spermatogonial stem cells (SSCs).

Materials and Methods

Fgf9 overexpression lentivirus was injected into mouse testes, and PLZF immunostaining was performed to investigate the effect of FGF9 on spermatogonia in vivo. Effect of FGF9 on SSCs was detected by transplanting cultured germ cells into tubules of testes. RNA‐seq of bulk RNA and single cell was performed to explore FGF9 working mechanisms. SB203580 was used to disrupt p38 MAPK pathway. p38 MAPK protein expression was detected by Western blot and qPCR was performed to determine different gene expression. Small interfering RNA (siRNA) was used to knock down Etv5 gene expression in germ cells.

Results

Overexpression of Fgf9 in vivo resulted in arrested spermatogenesis and accumulation of undifferentiated spermatogonia. Exposure of germ cell cultures to FGF9 resulted in larger numbers of SSCs over time. Inhibition of p38 MAPK phosphorylation negated the SSC growth advantage provided by FGF9. Etv5 and Bcl6b gene expressions were enhanced by FGF9 treatment. Gene knockdown of Etv5 disrupted the growth effect of FGF9 in cultured SSCs along with downstream expression of Bcl6b.

Conclusions

Taken together, these data indicate that FGF9 is an important regulator of SSC proliferation, operating through p38 MAPK phosphorylation and upregulating Etv5 and Bcl6b in turn.

Super-enhancer switching drives a burst in gene expression at the mitosis-to-meiosis transition

Due to bursts in the expression of thousands of germline-specific genes, the testis has the most diverse and complex transcriptome of all organs. By analyzing the male germline of mice, we demonstrate that the genome-wide reorganization of super-enhancers (SEs) drives bursts in germline gene expression after the mitosis-to-meiosis transition. SE reorganization is regulated by two molecular events: the establishment of meiosis-specific SEs via A-MYB (MYBL1), a key transcription factor for germline genes, and the resolution of SEs in mitotically proliferating cells via SCML2, a germline-specific Polycomb protein required for spermatogenesis-specific gene expression. Prior to entry into meiosis, meiotic SEs are preprogrammed in mitotic spermatogonia to ensure the unidirectional differentiation of spermatogenesis. We identify key regulatory factors for both mitotic and meiotic enhancers, revealing a molecular logic for the concurrent activation of mitotic enhancers and suppression of meiotic enhancers in the somatic and/or mitotic proliferation phases.

Characteristics of testicular cell development of 5-day-old mice in culture in vitro

The crude testicular cells (CTCs) contain many cell types, such as Sertoli cells, leydig cells, spermatogonial stem cells (SSCs), spermatocytes, and other somatic testicular cells, that secrete various growth factors needed in spermatogenesis. The objective of this study was to characterize development of 5-day-old mice testicular cells cultured. Crude testicular cells prepared from the testes of 5-day-old male mice were cultured in Dulbecco's Modified Eagle Medium and incubated at 37°C in a 5% CO₂ atmosphere for 6 days. The results demonstrated that the testicular cells developed rapidly with a population doubling time (PDT) of 0.63 days and more than 90% of cells were viable after being cultured for 3 days. The number of Sertoli-like cells increased significantly over days 1, 3, and 6 to 22.1%, 34.6%, and 50.1%, respectively. A significant increase was also observed in fibroblast-like cells (15.5% on day 1 to 28.8% on day 3 and to 26.6% on day 6). In contrast, the number of spermatogonia-like cells decreased significantly (54.3%, 30.4%, and 18.7%, on days 1, 3, and 6, respectively). These data indicated that the developmental pattern of the testicular cell in this study might be affected by the niche provided by the cultured testicular cells.

Leptin promotes proliferation of neonatal mouse stem/progenitor spermatogonia

PURPOSE

To keep and increase spermatogonial stem cell number (SSC) is the only available option for pediatric cancer survivors to maintain fertility. Leptin is secreted by the epididymal white adipose tissue and has receptors on stem/progenitor spermatogonia. The purpose of this study is to demonstrate dose- and time-dependent proliferative effect of leptin on stem/progenitor spermatogonia cultures from prepubertal mice testes.

METHODS

CD90.2 (+) stem/progenitor spermatogonia were isolated from the C57BL/6 mouse testis on postnatal day 6 and placed in culture. The proliferative effect of leptin supplementation was assessed by colony formation (diameter and number), WST proliferation assays, and xCELLigence real-time cell analysis (RTCA) on days 3, 5, and 7 of culture. Expressions of p-ERK1/2, p-STAT3, total STAT3, and p-SHP2 levels were determined by western blot analysis.

RESULTS

Leptin supplementation of 100 ng/ml increased the diameter (p = 0.001) and number (p = 0.01) of colonies in stem/progenitor spermatogonial cultures and caused higher proliferation by WST-1 (p = 0.009) compared with the control on day 7. The EC50 was calculated as 114 ng/ml for leptin by RTCA. Proliferative dose of leptin induced increased expression of p-ERK1/2 (p = 0.009) and p-STAT3 (p = 0.023) on stem/progenitor spermatogonia when compared with the untreated group.

CONCLUSION

The results indicated that leptin supplementation exhibited a dose- and time-dependent proliferative effect on stem/progenitor spermatogonia that was associated with increased expression of ERK1/2 and STAT3 pathways while maintaining their undifferentiated state. This output presents a new agent that may help to expand the stem/progenitor spermatogonia pool from the neonatal testis in order to autotransplant after cancer treatment.

Role of pyroglutamylated RFamide peptide43 in germ cell dynamics in mice testes in relation to energy metabolism

QRFP is a neuropeptide that regulates glucose homeostasis and increases insulin sensitivity in tissues. We have previously shown that QRFP and its receptor (GPR103) are predominantly expressed in germ cells and Sertoli cells, respectively, in mice testes. In the present study, we report that QRFP caused an increase in PCNA and a decrease in p27Kip1 expressions in the testis under both in vivo and ex vivo conditions. Besides, via an in vivo study, cell cycle analysis by FACS showed an increase in 2C cells and a decrease in 1C cells. QRFP also induced expression of GDNF and phosphorylation of Akt and ERK-1/2. Together these results suggest that QRFP has a proliferative effect on germ cells in mice testes, since it caused a proportional increase in the mitotic activity and the number of spermatogonial cells. Further, observations of increased expressions of STAT-3 and Neurog3 in treated mice suggest that QRFP treatment regulates priming of undifferentiated spermatogonia to undergo differentiation, while a decrease in c-Kit expression indicate that spermatogonia at this time point are in an undifferentiated state. In addition, QRFP administration also caused an increase in intratesticular levels of glucose and lactate, and in LDH activity accompanied by increased expressions of GLUT-3 and LDH-C in the testis. Also, the phosphorylation of IR-β and expressions of p-Akt and p-mTOR were increased under ex vivo conditions in testicular tissue. In conclusion, our findings suggest that QRFP treatment caused proliferation of germ cells independently from the hypothalamic-pituitary axis via regulation of testicular energy metabolism.

A Model of Differential Mammary Growth Initiation by Stat3 and Asymmetric Integrin-α6 Inheritance

Multiple cancer-related genes both promote and paradoxically suppress growth initiation, depending on the cell context. We discover an explanation for how this occurs for one such protein, Stat3, based on asymmetric cell division. Here, we show that Stat3, by Stathmin/PLK-1, regulates mitotic spindle orientation, and we use it to create and test a model for differential growth initiation. We demonstrate that Integrin-α6 is polarized and required for mammary growth initiation. Spindles orient relative to polar Integrin-α6, dividing perpendicularly in normal cells and parallel in tumor-derived cells, resulting in asymmetric or symmetric Integrin-α6 inheritance, respectively. Stat3 inhibition randomizes spindle orientation, which promotes normal growth initiation while reducing tumor-derived growth initiation. Lipid raft disruption depolarizes Integrin-α6, inducing spindle-orientation-independent Integrin-α6 inheritance. Stat3 inhibition no longer affects the growth of these cells, suggesting Stat3 acts through the regulation of spindle orientation to control growth initiation.

High temperature suppressed SSC self-renewal through S phase cell cycle arrest but not apoptosis

BACKGROUND

High temperature has a very adverse effect on mammalian spermatogenesis and eventually leads to sub- or infertility through either apoptosis or DNA damage. However, the direct effects of heat stress on the development of spermatogonial stem cells (SSCs) are still unknown because SSCs are rare in the testes.

METHODS

In the present study, we first used in vitro-cultured SSCs to study the effect of heat shock treatment on SSC development. Then, we used RNA-Seq analysis to identify new genes or signalling pathways implicated in the heat stress response.

RESULTS

We found that 45 min of 43 °C heat shock treatment significantly inhibited the proliferation of SSCs 2 h after treatment but did not lead to apoptosis. In total, 17,822 genes were identified by RNA-Seq after SSC heat shock treatment. Among these genes, we found that 200 of them had significantly changed expression, with 173 upregulated and 27 downregulated genes. The number of differentially expressed genes in environmental information processing pathways was 37, which was the largest number. We screened the candidate JAK-STAT signalling pathway on the basis of inhibition of cell cycle progression and found that the JAK-STAT pathway was inhibited after heat shock treatment. The flow cytometry results further confirmed that heat stress caused S phase cycle arrest of SSCs.

CONCLUSION

Our results showed that heat shock treatment at 43 °C for 45 min significantly inhibited SSC self-renewal through S phase cell cycle arrest but not apoptosis.

JAK/STAT signaling in stem cells and regeneration: from Drosophila to vertebrates

The JAK/STAT pathway is a conserved metazoan signaling system that transduces cues from extracellular cytokines into transcriptional changes in the nucleus. JAK/STAT signaling is best known for its roles in immunity. However, recent work has demonstrated that it also regulates critical homeostatic processes in germline and somatic stem cells, as well as regenerative processes in several tissues, including the gonad, intestine and appendages. Here, we provide an overview of JAK/STAT signaling in stem cells and regeneration, focusing on Drosophila and highlighting JAK/STAT pathway functions in proliferation, survival and cell competition that are conserved between Drosophila and vertebrates.

JNK/STAT signalling pathway is involved in fluoride-induced follicular developmental dysplasia in female mice

Excessive fluoride (F) intake decreases the development of potential oocytes by inducing oxidative stress and apoptosis in female mice in our previous study. This study aims to investigate the underlying mechanisms of F-induced follicular developmental dysplasia. Pathomorphological changes in the ovary tissues were observed under light and transmission electron microscopes. DNA damage and proliferation in granulosa cells were analysed by TUNEL staining and BrdU measurement. The protein expression of cell proliferation related regulatory factors including JNK, STAT3, STAT5, CDK2, CDK4, PCNA and Ki67 in the ovary tissues was measured by immunohistochemistry and Western blot analyses. Results indicated that the structure of granulosa cells in the ovary was seriously damaged by excessive F, evident by the swollen endoplasmic reticulum, mitochondria with vacuoles and nucleus shrinkage. F treatment also considerably enhanced the apoptosis and inhibited the proliferation of granulosa cells. The number of granulosa cells around the oocyte decreased after F treatment. The expression levels of STAT3, CDK2, CDK4 and Ki67 in the ovary tissues were up-regulated, and STAT5 and PCNA did not change significantly after F treatment, whereas JNK expression was down-regulated with increasing F dose. In summary, changes in the expression levels of JNK, STAT3, STAT5, CDK2, CDK4, PCNA and Ki67 in the JNK/STAT signalling pathway are involved in F-induced follicular dysplasia in the ovary.

PAK1 Promotes the Proliferation and Inhibits Apoptosis of Human Spermatogonial Stem Cells via PDK1/KDR/ZNF367 and ERK1/2 and AKT Pathways

Spermatogonial stem cells (SSCs) have significant applications in reproductive and regenerative medicine. However, nothing is known about genes in mediating human SSCs. Here we have explored for the first time the function and mechanism of P21-activated kinase 1 (PAK1) in regulating the proliferation and apoptosis of the human SSC line. PAK1 level was upregulated by epidermal growth factor (EGF), but not glial cell line-derived neurotrophic factor (GDNF) or fibroblast growth factor 2 (FGF2). PAK1 promoted proliferation and DNA synthesis of the human SSC line, whereas PAK1 suppressed its apoptosis in vitro and in vivo. RNA sequencing identified that PDK1, ZNF367, and KDR levels were downregulated by PAK1 knockdown. Immunoprecipitation and Western blots demonstrated that PAK1 interacted with PDK1. PDK1 and KDR levels were decreased by ZNF367-small interfering RNAs (siRNAs). The proliferation of the human SSC line was reduced by PDK1-, KDR-, and ZNF367-siRNAs, whereas its apoptosis was enhanced by these siRNAs. The levels of phos-ERK1/2, phos-AKT, and cyclin A were decreased by PAK1-siRNAs. Tissue arrays showed that PAK1 level was low in non-obstructive azoospermia patients. Collectively, PAK1 was identified as the first molecule that controls proliferation and apoptosis of the human SSC line through PDK1/KDR/ZNF367 and the ERK1/2 and AKT pathways. This study provides data on novel gene regulation and networks underlying the fate of human SSCs, and it offers new molecular targets for human SSCs in translational medicine.

MiR-663a Stimulates Proliferation and Suppresses Early Apoptosis of Human Spermatogonial Stem Cells by Targeting NFIX and Regulating Cell Cycle

Human spermatogonial stem cells (SSCs) could have significant applications in reproductive medicine and regenerative medicine because of their great plasticity. The fate determinations of human SSCs are mediated by epigenetic factors. However, nothing is known about the regulation of non-coding RNA on human SSCs. Here we have explored for the first time the expression, function, and target of miR-663a in human SSCs. MiR-663a was upregulated in human spermatogonia compared with pachytene spermatocytes, as indicated by microRNA microarray and real-time PCR. CCK-8 and 5-Ethynyl-2′-deoxyuridine (EDU) assays revealed that miR-663a stimulated cell proliferation and DNA synthesis of human SSCs. Annexin V and propidium iodide (PI) staining and flow cytometry demonstrated that miR-663a inhibited early and late apoptosis of human SSCs. Furthermore, NFIX was predicted and verified as a direct target of miR-663a. NFIX silencing led to an enhancement of cell proliferation and DNA synthesis and a reduction of the early apoptosis of human SSCs. NFIX silencing neutralized the influence of miR-663a inhibitor on the proliferation and apoptosis of human SSCs. Finally, both miR-663a mimics and NFIX silencing upregulated the levels of cell cycle regulators, including Cyclin A2, Cyclin B1, and Cyclin E1, whereas miR-663a inhibitor had an adverse effect. Knockdown of Cyclin A2, Cyclin B1, and Cyclin E1 led to the decrease in the proliferation of human SSCs. Collectively, miR-663a has been identified as the first microRNA that promotes the proliferation and DNA synthesis and suppresses the early apoptosis of human SSCs by targeting NFIX via cell cycle regulators Cyclin A2, Cyclin B1, and Cyclin E1. This study thus provides novel insights into the molecular mechanisms underlying human spermatogenesis, and it could offer novel targets for treating male infertility and other human diseases.

Regionally distinct patterns of STAT3 phosphorylation in the seminiferous epithelia of mouse testes

In mouse testes, Sertoli cells support the continuous process of spermatogenesis, which is dependent on seminiferous epithelial cycles along the longitudinal axis of the seminiferous tubule. Sertoli cell function is modulated partly by local cytokines and/or growth factors derived from adjacent tissues such as blood vessels, macrophages, rete testis, etc. However, the spatial activation patterns by local signals in vivo remain unclear. In this study, we focused on Signal Transducers and Activators of Transcription (STAT) signaling in Sertoli cells, because STAT is a major crucial cytokine transducer for somatic cyst cell regulation in Drosophila testis niches. In mouse testes, STAT3 was ubiquitously expressed in Sertoli cells throughout the seminiferous tubules. Phosphorylated STAT3 (p-STAT3) was predominantly observed in the Sertoli cells within the valve-like structure adjacent to the rete testis (i.e., the Sertoli valve [SV]) in the terminal segment of the proximal seminiferous tubules. In the distal seminiferous tubules with active spermatogenesis, most Sertoli cells were negative for anti-p-STAT3 staining. Albeit rarely, a small patch of several p-STAT3-positive Sertoli cells was detected frequently in seminiferous epithelial cycle stages I-VI. Such p-STAT3-positive ratios in the convoluted seminiferous epithelia were significantly increased in germ cell-less testes than in the wild-type testes, but with considerably lower ratios than in the SV region. These findings imply that regionally distinct patterns of STAT3 phosphorylation in the Sertoli cells depend on either location or spermatogenic activity in normal healthy testes in vivo, highlighting a novel entry point to understanding STAT signaling in mammalian spermatogenesis.

Mettl3-/Mettl14-mediated mRNA N6-methyladenosine modulates murine spermatogenesis

Spermatogenesis is a differentiation process during which diploid spermatogonial stem cells (SSCs) produce haploid spermatozoa. This highly specialized process is precisely controlled at the transcriptional, posttranscriptional, and translational levels. Here we report that N⁶-methyladenosine (m⁶A), an epitranscriptomic mark regulating gene expression, plays essential roles during spermatogenesis. We present comprehensive m⁶A mRNA methylomes of mouse spermatogenic cells from five developmental stages: undifferentiated spermatogonia, type A₁ spermatogonia, preleptotene spermatocytes, pachytene/diplotene spermatocytes, and round spermatids. Germ cell-specific inactivation of the m⁶A RNA methyltransferase Mettl3 or Mettl14 with Vasa-Cre causes loss of m⁶A and depletion of SSCs. m⁶A depletion dysregulates translation of transcripts that are required for SSC proliferation/differentiation. Combined deletion of Mettl3 and Mettl14 in advanced germ cells with Stra8-GFPCre disrupts spermiogenesis, whereas mice with single deletion of either Mettl3 or Mettl14 in advanced germ cells show normal spermatogenesis. The spermatids from double-mutant mice exhibit impaired translation of haploid-specific genes that are essential for spermiogenesis. This study highlights crucial roles of mRNA m⁶A modification in germline development, potentially ensuring coordinated translation at different stages of spermatogenesis.

STAT3 signal that mediates the neural plasticity is involved in willed-movement training in focal ischemic rats

Willed-movement training has been demonstrated to be a promising approach to increase motor performance and neural plasticity in ischemic rats. However, little is known regarding the molecular signals that are involved in neural plasticity following willed-movement training. To investigate the potential signals related to neural plasticity following willed-movement training, littermate rats were randomly assigned into three groups: middle cerebral artery occlusion, environmental modification, and willed-movement training. The infarct volume was measured 18 d after occlusion of the right middle cerebral artery. Reverse transcription-polymerase chain reaction (PCR) and immunofluorescence staining were used to detect the changes in the signal transducer and activator of transcription 3 (STAT3) mRNA and protein, respectively. A chromatin immunoprecipitation was used to investigate whether STAT3 bound to plasticity-related genes, such as brain-derived neurotrophic factor (BDNF), synaptophysin, and protein interacting with C kinase 1 (PICK1). In this study, we demonstrated that STAT3 mRNA and protein were markedly increased following 15-d willed-movement training in the ischemic hemispheres of the treated rats. STAT3 bound to BDNF, PICK1, and synaptophysin promoters in the neocortical cells of rats. These data suggest that the increased STAT3 levels after willed-movement training might play critical roles in the neural plasticity by directly regulating plasticity-related genes.

JAK-STAT signaling regulation of chicken embryonic stem cell differentiation into male germ cells

The Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling is crucial in chicken germ stem cell differentiation, but its role in the regulation of germ cell differentiation is unknown. To address this, cucurbitacin I or interleukin 6 was used to inhibit or activate JAK-STAT signaling during embryonic stem cells (ESCs) differentiation. The expression of downstream JAK-STAT signaling molecules was assessed by Western blotting and quantitative real-time polymerase chain reaction (qRT-PCR). PAS, and immunohistochemical staining of frozen sections was used to determine the appearance of primordial germ cells (PGCs) and, later, spermatogonial stem cells (SSCs) during gonadal development. Inhibition of the JAK-STAT signaling resulted in decreased expression of JAK2 and STAT3 as well as of PGCs markers; moreover, the proportion of CVH and C-KIT positive cells as well as the yield of PGCs were remarkably decreased, and the gonad was smaller than that of control samples. Conversely, activation of JAK-STAT resulted in increased expression of JAK2 and STAT3 as well as that of PGC marker CVH. In addition, the proportion of CVH and C-KIT-positive cells as well as the PGC yield was increased, and the gonad was significantly larger than that from control samples. Collectively, our results suggested that JAK-STAT effectively promoted the formation of PGCs in the genital ridge during early embryogenesis in vivo and played a positive role in the regulation of ESC to SSC differentiation in vitro, with JAK2 and STAT3 functioning as pivotal factors for intracellular signal transduction.

The Glial Cell-Derived Neurotrophic Factor (GDNF)-responsive Phosphoprotein Landscape Identifies Raptor Phosphorylation Required for Spermatogonial Progenitor Cell Proliferation

Cytokine-dependent renewal of stem cells is a fundamental requisite for tissue homeostasis and regeneration. Spermatogonial progenitor cells (SPCs) including stem cells support life-long spermatogenesis and male fertility, but pivotal phosphorylation events that regulate fate decisions in SPCs remain unresolved. Here, we described a quantitative mass-spectrometry-based proteomic and phosphoproteomic analyses of SPCs following sustained stimulation with glial cell-derived neurotrophic factor (GDNF), an extrinsic factor supporting SPC proliferation. Stimulated SPCs contained 3382 identified phosphorylated proteins and 12141 phosphorylation sites. Of them, 325 differentially phosphorylated proteins and 570 phosphorylation sites triggered by GDNF were highly enriched for ERK1/2, GSK3, CDK1, and CDK5 phosphorylating motifs. We validated that inhibition of GDNF/ERK1/2-signaling impaired SPC proliferation and increased G2/M cell cycle arrest. Significantly, we found that proliferation of SPCs requires phosphorylation of the mTORC1 component Raptor at Ser⁸⁶³ Tissue-specific deletion of Raptor in mouse germline cells results in impaired spermatogenesis and progressive loss of spermatogonia, but in vitro increased phosphorylation of Raptor by raptor over-expression in SPCs induced a more rapidly growth of SPCs in culture. These findings implicate previously undescribed signaling networks in governing fate decision of SPCs, which is essential for the understanding of spermatogenesis and of potential consequences of pathogenic insult for male infertility.

Glycolysis-Optimized Conditions Enhance Maintenance of Regenerative Integrity in Mouse Spermatogonial Stem Cells during Long-Term Culture

The application of spermatogonial stem cell (SSC) transplantation for regenerating male fertility requires amplification of SSC number in vitro during which the integrity to re-establish spermatogenesis must be preserved. Conventional conditions supporting proliferation of SSCs from mouse pups have been the basis for developing methodology with adult human cells but are unrefined. We found that the integrity to regenerate spermatogenesis after transplantation declines with advancing time in primary cultures of pup SSCs and that the efficacy of deriving cultures from adult SSCs is limited with conventional conditions. To address these deficiencies, we optimized the culture environment to favor glycolysis as the primary bioenergetics process. In these conditions, regenerative integrity of pup and adult SSCs was significantly improved and the efficiency of establishing primary cultures was 100%. Collectively, these findings suggest that SSCs are primed for conditions favoring glycolytic activity, and matching culture environments to their bioenergetics is critical for maintaining functional integrity.

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Regenerative integrity of SSCs declines over time in conventional culture

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Glycolysis-optimized (GO) culture improves regenerative integrity of SSCs

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GO conditions enhance the long-term culture of SSCs from adult mice

CYP1A1 based on metabolism of xenobiotics by cytochrome P450 regulates chicken male germ cell differentiation

This study aimed to explore the regulatory mechanism of metabolism of xenobiotics by cytochrome P450 during the differentiation process of chicken embryonic stem cells (ESCs) into spermatogonial stem cells (SSCs) and consummate the induction differentiation system of chicken embryonic stem cells (cESCs) into SSCs in vitro. We performed RNA-Seq in highly purified male ESCs, male primordial germ cells (PGCs), and SSCs that are associated with the male germ cell differentiation. Thereinto, the metabolism of xenobiotics by cytochrome P450 was selected and analyzed with Venny among male ESC vs male PGC, male PGC vs SSC, and male ESC vs SSC groups and several candidates differentially expressed genes (DEGs) were excavated. Finally, quantitative real-time PCR (qRT-PCR) detected related DEGs under the condition of retinoic acid (RA) induction in vitro, and the expressions were compared with RNA-Seq. By knocking down CYP1A1, we detected the effect of CYP1A1-mediated metabolism of xenobiotics by cytochrome P450 on male germ cell differentiation by qRT-PCR and immunocytochemistry. Results showed that 17,742 DEGs were found during differentiation of ESCs into SSCs and enriched in 72 differently significant pathways. Thereinto, the metabolism of xenobiotics by cytochrome P450 was involved in the whole differentiation process of ESCs into SSCs and several candidate DEGs: CYP1A1, CYP3A4, CYP2D6, ALDH3B1, and ALDH1A3 were expressed with the same trend with RNA-Seq. Knockdown of CYP1A1 caused male germ cell differentiation under restrictions. Our findings showed that the metabolism of xenobiotics by cytochrome P450 was significantly different during the process of male germ cell differentiation and was persistently activated when we induced cESCs to differentiate into SSCs with RA in vitro, which illustrated that the metabolism of xenobiotics by cytochrome P450 played a crucial role in the differentiation process of ESCs into SSCs.

Role of the testis interstitial compartment in spermatogonial stem cell function

Intricate cellular and molecular interactions ensure that spermatogonial stem cells (SSCs) proceed in a step-wise differentiation process through spermatogenesis and spermiogenesis to produce sperm. SSCs lie within the seminiferous tubule compartment, which provides a nurturing environment for the development of sperm. Cells outside of the tubules, such as interstitial and peritubular cells, also help direct SSC activity. This review focuses on interstitial (interstitial macrophages, Leydig cells and vasculature) and peritubular (peritubular macrophages and peritubular myoid cells) cells and their role in regulating the SSC self-renewal and differentiation in mammals. Leydig cells, the major steroidogenic cells in the testis, influence SSCs through secreted factors, such as insulin growth factor 1 (IGF1) and colony-stimulating factor 1 (CSF1). Macrophages interact with SSCs through various potential mechanisms, such as CSF1 and retinoic acid (RA), to induce the proliferation or differentiation of SSCs respectively. Vasculature influences SSC dynamics through CSF1 and vascular endothelial growth factor (VEGF) and by regulating oxygen levels. Lastly, peritubular myoid cells produce one of the most well-known factors that is required for SSC self-renewal, glial cell line-derived neurotrophic factor (GDNF), as well as CSF1. Overall, SSC interactions with interstitial and peritubular cells are critical for SSC function and are an important underlying factor promoting male fertility.

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.

Germline Stem Cell Competition, Mutation Hot Spots, Genetic Disorders, and Older Fathers

Some de novo human mutations arise at frequencies far exceeding the genome average mutation rate. Examples include the common mutations at one or a few sites in the genes that cause achondroplasia, Apert syndrome, multiple endocrine neoplasia type 2B, and Noonan syndrome. These mutations are recurrent, provide a gain of function, are paternally derived, and are more likely to be transmitted as the father ages. Recent experiments have tested whether the high mutation frequencies are due to an elevated mutation rate per cell division, as expected, or to an advantage of the mutant spermatogonial stem cells over wild-type stem cells. The evidence, which includes the surprising discovery of testis mutation clusters, rules out the former model but not the latter. We propose how the mutations might alter spermatogonial stem cell function and discuss how germline selection contributes to the paternal age effect, the human mutational load, and adaptive evolution.

Plasticity of male germline stem cells and their applications in reproductive and regenerative medicine

Spermatogonial stem cells (SSCs), also known as male germline stem cells, are a small subpopulation of type A spermatogonia with the potential of self-renewal to maintain stem cell pool and differentiation into spermatids in mammalian testis. SSCs are previously regarded as the unipotent stem cells since they can only give rise to sperm within the seminiferous tubules. However, this concept has recently been challenged because numerous studies have demonstrated that SSCs cultured with growth factors can acquire pluripotency to become embryonic stem-like cells. The in vivo and in vitro studies from peers and us have clearly revealed that SSCs can directly transdifferentiate into morphologic, phenotypic, and functional cells of other lineages. Direct conversion to the cells of other tissues has important significance for regenerative medicine. SSCs from azoospermia patients could be induced to differentiate into spermatids with fertilization and developmental potentials. As such, SSCs could have significant applications in both reproductive and regenerative medicine due to their unique and great potentials. In this review, we address the important plasticity of SSCs, with focuses on their self-renewal, differentiation, dedifferentiation, transdifferentiation, and translational medicine studies.

Extrinsic and intrinsic factors controlling spermatogonial stem cell self-renewal and differentiation

Spermatogonial stem cells (SSCs), the stem cells responsible for male fertility, are one of a small number of cells with the abilities of both self-renewal and generation of large numbers of haploid cells. Technology improvements, most importantly, transplantation assays and in vitro culture systems have greatly expanded our understanding of SSC self-renewal and differentiation. Many important molecules crucial for the balance between self-renewal and differentiation have been recently identified although the exact mechanism(s) remain largely undefined. In this review, we give a brief introduction to SSCs, and then focus on extrinsic and intrinsic factors controlling SSCs self-renewal and differentiation.

Targeted Disruption of miR-17-92 Impairs Mouse Spermatogenesis by Activating mTOR Signaling Pathway

The miR-17-92 cluster and its 6 different mature microRNAs, including miR-17, miR-18a, miR-19a, miR-20a, miR-19b-1, and miR-92a, play important roles in embryo development, immune system, kidney and heart development, adipose differentiation, aging, and tumorigenicity. Currently, increasing evidence indicates that some members of miR-17-92 cluster may be critical players in spermatogenesis, including miR-17, miR-18a, and miR-20a. However, the roles and underlying mechanisms of miR-17-92 in spermatogenesis remain largely unknown. Our results showed that the targeted disruption of miR-17-92 in the testes of adult mice resulted in severe testicular atrophy, empty seminiferous tubules, and depressed sperm production. This phenotype is partly because of the reduced number of spermatogonia and spermatogonial stem cells, and the significantly increased germ cell apoptosis in the testes of miR-17-92-deficient mice. In addition, overactivation of the mammalian target of rapamycin signaling pathway and upregulation of the pro-apoptotic protein Bim, Stat3, c-Kit, and Socs3 were also observed in miR-17-92-deficient mouse testes, which might be, at least partially if not all, responsible for the aforementioned phenotypic changes in mutant testes. Taken together, these findings suggest that miR-17-92 is essential for normal spermatogenesis in mice.

Saligenin cyclic-o-tolyl phosphate (SCOTP) induces autophagy of rat spermatogonial stem cells

Tri-ortho-cresyl phosphate (TOCP) has been widely used as plasticizers, plastic softeners, and flame-retardants in industry, which can be metabolized to High-toxic saligenin cyclic-o-tolyl phosphate (SCOTP). Our previous results found that TOCP could disrupt the seminiferous epithelium in the testis and induce autophagy of rat spermatogonial stem cells. Little is known about the toxic effect of SCOTP on rat spermatogonial stem cells. The present study showed that SCOTP decreased viability of rat spermatogonial stem cells in a dose-dependent manner. Both LC3-II and the ratio of LC3-II/LC3-I were significantly increased; autophagy proteins atg5 and Beclin 1 were also markedly increased after treatment with SCOTP, indicating SCOTP could induce autophagy of the cells. Ultrastructural observation under the transmission electron microscopy (TEM) indicated that there were autophagic vacuoles in the cytoplasm in the SCOTP-treated cells. However, cell cycle arrest was not observed by flow cytometry; and the mRNA levels of p21, p27, p53 and cyclin D1 in the cells were also not affected by SCOTP. Meanwhile, SCOTP didn't induce apoptosis of the cells. In summary, we showed that SCOTP could induce autophagy of rat spermatogonial stem cells, without affecting cell cycle and apoptosis.

AZFc deletions do not affect the function of human spermatogonia in vitro

Azoospermic factor c (AZFc) deletions are the underlying cause in 10% of azoo- or severe oligozoospermia. Through extensive molecular analysis the precise genetic content of the AZFc region and the origin of its deletion have been determined. However, little is known about the effect of AZFc deletions on the functionality of germ cells at various developmental steps. The presence of normal, fertilization-competent sperm in the ejaculate and/or testis of the majority of men with AZFc deletions suggests that the process of differentiation from spermatogonial stem cells (SSCs) to mature spermatozoa can take place in the absence of the AZFc region. To determine the functionality of AZFc-deleted spermatogonia, we compared in vitro propagated spermatogonia from six men with complete AZFc deletions with spermatogonia from three normozoospermic controls. We found that spermatogonia of AZFc-deleted men behave similar to controls during culture. Short-term (18 days) and long-term (48 days) culture of AZFc-deleted spermatogonia showed the same characteristics as non-deleted spermatogonia. This similarity was revealed by the same number of passages, the same germ cell clusters formation and similar level of genes expression of spermatogonial markers including ubiquitin carboxyl-terminal esterase L1 (UCHL1), zinc finger and BTB domain containing 16 (ZBTB16) and glial cell line-derived neurotrophic factor family receptor alpha 1 (GFRA1), as well as germ cell differentiation markers including signal transducer and activator of transcription 3 (STAT3), spermatogenesis and oogenesis specific basic helix-loophelix 2 (SOHLH2), v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (KIT) and synaptonemal complex protein 3 (SYCP3). The only exception was melanoma antigen family A4 (MAGEA4) which showed significantly lower expression in AZFc-deleted samples than controls in short-term culture while in long-term culture it was hardly detected in both AZFc-deleted and control spermatogonia. These data suggest that, at least in vitro, spermatogonia of AZFc-deleted men are functionally similar to spermatogonia from non-deleted men. Potentially, this enables treatment of men with AZFc deletions by propagating their SSCs in vitro and autotransplanting these SSCs back to the testes to increase sperm counts and restore fertility.

Asymmetrical allocation of JAK1 mRNA during spermatogonial stem cell division in Xenopus laevis

During Xenopus spermatogenesis, each primary spermatogonium (PG), the largest single cell in the testis, undergoes mitotic divisions with a concomitant decrease in size to produce smaller differentiating spermatogonia. The spermatogonial stem cells (SSCs) occur in this PG population. Taking advantage of identifiable and isolatable properties of Xenopus SSCs, we examined JAK1 gene expression during the spermatogenesis because there have been reports on the important role of JAK/STAT pathway in regulating the status of SSCs in Drosophila and mouse. Surprisingly, in situ hybridization revealed the presence of JAK1 mRNA in the differentiating spermatogonia and primary spermatocytes as well as some PGs. Inhibition of JAK1 activity in the testis caused a decrease in percentage of BrdU-incorporating spermatogonia, suggesting that JAK1 was at least involved in regulation of spermatogonial proliferation. Interestingly, single cell reverse transcription-polymerase chain reaction (RT-PCR) clearly showed two different types of SSCs: SSCs with JAK1 mRNA (JAK1⁺ ) or without JAK1 mRNA (JAK1^- ). Since JAK1^- SSC level was increased by induction of testis regeneration, self-renewing SSCs were thought to be JAK1^- . In addition, we found barrel-shaped PGs, in which JAK1 mRNA was localized asymmetrically to one half of the cell. The stainability with propidium iodide and morphology of two nuclei in the barrel-shaped PG were similar to those of PG nucleus. Based on the above observations, we propose the hypothesis that JAK1⁺ SSC is preparing for production of PGs destined to differentiate (destined PGs) and the accumulated JAK1 mRNA in the SSC is distributed exclusively into the destined PGs through mitotic division.

Mammalian gonocyte and spermatogonia differentiation: recent advances and remaining challenges

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

Xenotransplantation exposes the etiology of azoospermia factor (AZF) induced male sterility

Ramathal et al. have employed an elegant xenotransplantation technique to study the fate of human induced pluripotent stem cells (hiPSCs) from fertile males and from males carrying Y chromosome deletions of the azoospermia factor (AZF) region. When placed in a mouse testis niche, hiPSCs from fertile males differentiate into germ cell-like cells (GCLCs). Highlighting the crucial role of cell autonomous factors in male sterility, hiPSCs derived from azoospermic males prove to be less successful under similar circumstances. Their studies argue that the agametic "Sertoli cell only" phenotype of two of the AZF deletions likely arises from a defect in the maintenance of germline stem cells (GSCs) rather than from a defect in their specification. These observations underscore the importance of the dialogue between the somatic niche and its inhabitant stem cells, and open up interesting questions concerning the functioning of the somatic niche and how it communicates to the GSCs.

Tri-ortho-cresyl phosphate induces autophagy of rat spermatogonial stem cells

Tri-ortho-cresyl phosphate (TOCP) has been widely used as plasticizers, plastic softeners, and flame retardants in industry and reported to have a deleterious effect on the male reproductive system in animals besides delayed neurotoxicity. Our preliminary results found that TOCP could disrupt the seminiferous epithelium in the testis and inhibit spermatogenesis, but the precise mechanism is yet to be elucidated. This study shows that TOCP inhibited viability of rat spermatogonial stem cells in a dose-dependent manner. TOCP could not lead to cell cycle arrest in the cells; the mRNA levels of p21, p27, p53, and cyclin D1 in the cells were also not affected by TOCP. Meanwhile, TOCP did not induce apoptosis of rat spermatogonial stem cells. After treatment with TOCP, however, both LC3-II and the ratio of LC3-II/LC3-I were markedly increased; autophagy proteins ATG5 and beclin 1 were also increased after treatment with TOCP, indicating that TOCP could induce autophagy in the cells. Ultrastructural observation under the transmission electron microscopy indicated that autophagic vesicles in the cytoplasm containing extensively degraded organelles such as mitochondria and endoplasmic reticulum increased significantly after the cells were treated with TOCP. In summary, we have shown that TOCP can inhibit viability of rat spermatogonial stem cells and induce autophagy of the cells, without affecting cell cycle and apoptosis.