Plzf regulates germline progenitor self-renewal by opposing mTORC1

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

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

The Current and Future of Biomarkers of Immune Related Adverse Events

With their groundbreaking clinical responses, immune checkpoint inhibitors (ICIs) have ushered in a new chapter in cancer therapeutics. However, they are often associated with life-threatening or organ-threatening autoimmune/autoinflammatory phenomena, collectively termed immune-related adverse events (irAEs). In this review, we will first describe the mechanisms of action of ICIs as well as irAEs. Next, we will review biomarkers for predicting the development of irAEs or stratifying risks.

Protein profile analysis of Jilin white goose testicles at different stages of the laying cycle by DIA strategy

BACKGROUND

Jilin white goose is an excellent local breed in China, with a high annual egg production and laying eggs mainly from February to July each year. The testis, as the only organ that can produce sperm, can affect the sexual maturity and fecundity of male animals. Its growth and development are affected and regulated by a variety of factors. Proteomics is generally applied to identify and quantify proteins in cells and tissues in order to understand the physiological or pathological changes that occur in tissues or cells under specific conditions. Currently, the female poultry reproductive system has been extensively studied, while few related studies focusing on the regulatory mechanism of the reproductive system of male poultry have been conducted.

RESULTS

A total of 1753 differentially expressed proteins (DEPs) were generated in which there were 594, 391 and 768 different proteins showing differential expression in three stages, Initial of Laying Cycle (ILC), Peak of Laying Cycle (PLC) and End of Laying Cycle (ELC). Furthermore, bioinformatics was used to analyze the DEPs. Gene ontology (GO) enrichment, Clusters of Orthologous Groups (COG), Kyoto Encyclopedia of Genes and Genomes (KEGG) and protein-protein interaction (PPI) network analysis were adopted. All DEPs were found to be implicated in multiple biological processes and pathways associated with testicular development, such as renin secretion, Lysosomes, SNARE interactions in vesicle trafficking, the p53 signaling pathway and pathways related to metabolism. Additionally, the reliability of transcriptome results was verified by real-time quantitative PCR by selecting the transcript abundance of 6 selected DEPs at the three stages of the laying cycle.

CONCLUSIONS

The funding in this study will provide critical insight into the complex molecular mechanisms and breeding practices underlying the developmental characteristics of testicles in Jilin white goose.

PRC1 directs PRC2-H3K27me3 deposition to shield adult spermatogonial stem cells from differentiation

Spermatogonial stem cells functionality reside in the slow-cycling and heterogeneous undifferentiated spermatogonia cell population. This pool of cells supports lifelong fertility in adult males by balancing self-renewal and differentiation to produce haploid gametes. However, the molecular mechanisms underpinning long-term stemness of undifferentiated spermatogonia during adulthood remain unclear. Here, we discover that an epigenetic regulator, Polycomb repressive complex 1 (PRC1), shields adult undifferentiated spermatogonia from differentiation, maintains slow cycling, and directs commitment to differentiation during steady-state spermatogenesis in adults. We show that PRC2-mediated H3K27me3 is an epigenetic hallmark of adult undifferentiated spermatogonia. Indeed, spermatogonial differentiation is accompanied by a global loss of H3K27me3. Disruption of PRC1 impairs global H3K27me3 deposition, leading to precocious spermatogonial differentiation. Therefore, PRC1 directs PRC2-H3K27me3 deposition to maintain the self-renewing state of undifferentiated spermatogonia. Importantly, in contrast to its role in other tissue stem cells, PRC1 negatively regulates the cell cycle to maintain slow cycling of undifferentiated spermatogonia. Our findings have implications for how epigenetic regulators can be tuned to regulate the stem cell potential, cell cycle and differentiation to ensure lifelong fertility in adult males.

Zinc Finger and BTB Domain-Containing 20: A Newly Emerging Player in Pathogenesis and Development of Human Cancers

Zinc finger and BTB domain-containing 20 (ZBTB20), which was initially identified in human dendritic cells, belongs to a family of transcription factors (TFs) with an N-terminal BTB domain and one or more C-terminal DNA-binding zinc finger domains. Under physiological conditions, ZBTB20 acts as a transcriptional repressor in cellular development and differentiation, metabolism, and innate immunity. Interestingly, multiple lines of evidence from mice and human systems have revealed the importance of ZBTB20 in the pathogenesis and development of cancers. ZBTB20 is not only a hotspot of genetic variation or fusion in many types of human cancers, but also a key TF or intermediator involving in the dysregulation of cancer cells. Given the diverse functions of ZBTB20 in both health and disease, we herein summarize the structure and physiological roles of ZBTB20, with an emphasis on the latest findings on tumorigenesis and cancer progression.

Postnatal development of mouse spermatogonial stem cells as determined by immunophenotype, regenerative capacity, and long-term culture-initiating ability: a model for practical applications

Spermatogonial stem cells (SSCs) are the foundation of life-long spermatogenesis. While SSC research has advanced greatly over the past two decades, characterization of SSCs during postnatal development has not been well documented. Using the mouse as a model, in this study, we defined the immunophenotypic profiles of testis cells during the course of postnatal development using multi-parameter flow cytometry with up to five cell-surface antigens. We found that the profiles progress over time in a manner specific to developmental stages. We then isolated multiple cell fractions at different developmental stages using fluorescent-activated cell sorting (FACS) and identified specific cell populations with prominent capacities to regenerate spermatogenesis upon transplantation and to initiate long-term SSC culture. The data indicated that the cell fraction with the highest level of regeneration capacity exhibited the most prominent potential to initiate SSC culture, regardless of age. Interestingly, refinement of cell fractionation using GFRA1 and KIT did not lead to further enrichment of regenerative and culture-initiating stem cells, suggesting that when a high degree of SSC enrichment is achieved, standard markers of SSC self-renewal or commitment may lose their effectiveness to distinguish cells at the stem cell state from committed progenitors. This study provides a significant information resource for future studies and practical applications of mammalian SSCs.

Transcriptome Analysis of Key Genes Involved in the Initiation of Spermatogonial Stem Cell Differentiation

PURPOSE

The purpose of this study was to screen the genes and pathways that are involved in spermatogonia stem cell (SSC) differentiation regulation during the transition from Aundiff to A1. Methods: RNA sequencing was performed to screen differentially expressed genes at 1 d and 2 d after SSC differentiation culture. KEGG pathway enrichment and GO function analysis were performed to reveal the genes and pathways related to the initiation of early SSC differentiation.

RESULTS

The GO analysis showed that Rpl21, which regulates cell differentiation initiation, significantly increased after 1 day of SSC differentiation. The expressions of Fn1, Cd9, Fgf2, Itgb1, Epha2, Ctgf, Cttn, Timp2 and Fgfr1, which are related to promoting differentiation, were up-regulated after 2 days of SSC differentiation. The analysis of the KEGG pathway revealed that RNA transport is the most enriched pathway 1 day after SSC differentiation. Hspa2, which promotes the differentiation of male reproductive cells, and Cdkn2a, which participates in the cell cycle, were significantly up-regulated. The p53 pathway and MAPK pathway were the most enriched pathways 2 days after SSC differentiation. Cdkn1a, Hmga2, Thbs1 and Cdkn2a, microRNAs that promote cell differentiation, were also significantly up-regulated.

CONCLUSIONS

RNA transport, the MAPK pathway and the p53 pathway may play vital roles in early SSC differentiation, and Rpl21, Fn1, Cd9, Fgf2, Itgb1, Epha2, Ctgf, Cttn, Timp2, Fgfr1, Hspa2, Cdkn2a, Cdkn1a, Hmga2 and Thbs1 are involved in the initiation of SSC differentiation. The findings of this study provide a reference for further revelations of the regulatory mechanism of SSC differentiation.

Cnot3 is required for male germ cell development and spermatogonial stem cell maintenance

The foundation of spermatogenesis and lifelong fertility is provided by spermatogonial stem cells (SSCs). SSCs divide asymmetrically to either replenish their numbers (self-renewal) or produce undifferentiated progenitors that proliferate before committing to differentiation. However, regulatory mechanisms governing SSC maintenance are poorly understood. Here, we show that the CCR4-NOT mRNA deadenylase complex subunit CNOT3 plays a critical role in maintaining spermatogonial populations in mice. Cnot3 is highly expressed in undifferentiated spermatogonia, and its deletion in spermatogonia resulted in germ cell loss and infertility. Single cell analyses revealed that Cnot3 deletion led to the de-repression of transcripts encoding factors involved in spermatogonial differentiation, including those in the glutathione redox pathway that are critical for SSC maintenance. Together, our study reveals that CNOT3 - likely via the CCR4-NOT complex - actively degrades transcripts encoding differentiation factors to sustain the spermatogonial pool and ensure the progression of spermatogenesis, highlighting the importance of CCR4-NOT-mediated post-transcriptional gene regulation during male germ cell development.

SPRY4-dependent ERK negative feedback demarcates functional adult stem cells in the male mouse germline†

Niche-derived growth factors support self-renewal of mouse spermatogonial stem and progenitor cells through ERK MAPK signaling and other pathways. At the same time, dysregulated growth factor-dependent signaling has been associated with loss of stem cell activity and aberrant differentiation. We hypothesized that growth factor signaling through the ERK MAPK pathway in spermatogonial stem cells is tightly regulated within a narrow range through distinct intracellular negative feedback regulators. Evaluation of candidate extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK)-responsive genes known to dampen downstream signaling revealed robust induction of specific negative feedback regulators, including Spry4, in cultured mouse spermatogonial stem cells in response to glial cell line-derived neurotrophic factor or fibroblast growth factor 2. Undifferentiated spermatogonia in vivo exhibited high levels of Spry4 mRNA. Quantitative single-cell analysis of ERK MAPK signaling in spermatogonial stem cell cultures revealed both dynamic signaling patterns in response to growth factors and disruption of such effects when Spry4 was ablated, due to dysregulation of ERK MAPK downstream of RAS. Whereas negative feedback regulator expression decreased during differentiation, loss of Spry4 shifted cell fate toward early differentiation with concomitant loss of stem cell activity. Finally, a mouse Spry4 reporter line revealed that the adult spermatogonial stem cell population in vivo is demarcated by strong Spry4 promoter activity. Collectively, our data suggest that negative feedback-dependent regulation of ERK MAPK is critical for preservation of spermatogonial stem cell fate within the mammalian testis.

Comprehensive Analysis of the Transcriptome-Wide m6A Methylome in Shaziling Pig Testicular Development

RNA N6-methyladenosine (m6A) modification is one of the principal post-transcriptional modifications and plays a dynamic role in testicular development and spermatogenesis. However, the role of m6A in porcine testis is understudied. Here, we performed a comprehensive analysis of the m6A transcriptome-wide profile in Shaziling pig testes at birth, puberty, and maturity. We analyzed the total transcriptome m6A profile and found that the m6A patterns were highly distinct in terms of the modification of the transcriptomes during porcine testis development. We found that key m6A methylated genes (AURKC, OVOL, SOX8, ACVR2A, and SPATA46) were highly enriched during spermatogenesis and identified in spermatogenesis-related KEGG pathways, including Wnt, cAMP, mTOR, AMPK, PI3K-Akt, and spliceosome. Our findings indicated that m6A methylations are involved in the complex yet well-organized post-transcriptional regulation of porcine testicular development and spermatogenesis. We found that the m6A eraser ALKBH5 negatively regulated the proliferation of immature porcine Sertoli cells. Furthermore, we proposed a novel mechanism of m6A modification during testicular development: ALKBH5 regulated the RNA methylation level and gene expression of SOX9 mRNA. In addition to serving as a potential target for improving boar reproduction, our findings contributed to the further understanding of the regulation of m6A modifications in male reproduction.

Spermatogonial fate in mice with increased activin A bioactivity and testicular somatic cell tumours

Adult male fertility depends on spermatogonial stem cells (SSCs) which undergo either self-renewal or differentiation in response to microenvironmental signals. Activin A acts on Sertoli and Leydig cells to regulate key aspects of testis development and function throughout life, including steroid production. Recognising that activin A levels are elevated in many pathophysiological conditions, this study investigates effects of this growth factor on the niche that determines spermatogonial fate. Although activin A can promote differentiation of isolated spermatogonia in vitro, its impacts on SSC and spermatogonial function in vivo are unknown. To assess this, we examined testes of Inha KO mice, which feature elevated activin A levels and bioactivity, and develop gonadal stromal cell tumours as adults. The GFRA1+ SSC-enriched population was more abundant and proliferative in Inha KO compared to wildtype controls, suggesting that chronic elevation of activin A promotes a niche which supports SSC self-renewal. Intriguingly, clusters of GFRA1+/EOMES+/LIN28A- cells, resembling a primitive SSC subset, were frequently observed in tubules adjacent to tumour regions. Transcriptional analyses of Inha KO tumours, tubules adjacent to tumours, and tubules distant from tumour regions revealed disrupted gene expression in each KO group increased in parallel with tumour proximity. Modest transcriptional changes were documented in Inha KO tubules with complete spermatogenesis. Importantly, tumours displaying upregulation of activin responsive genes were also enriched for factors that promote SSC self-renewal, including Gdnf, Igf1, and Fgf2, indicating the tumours generate a supportive microenvironment for SSCs. Tumour cells featured some characteristics of adult Sertoli cells but lacked consistent SOX9 expression and exhibited an enhanced steroidogenic phenotype, which could arise from maintenance or acquisition of a fetal cell identity or acquisition of another somatic phenotype. Tumour regions were also heavily infiltrated with endothelial, peritubular myoid and immune cells, which may contribute to adjacent SSC support. Our data show for the first time that chronically elevated activin A affects SSC fate in vivo. The discovery that testis stromal tumours in the Inha KO mouse create a microenvironment that supports SSC self-renewal but not differentiation offers a strategy for identifying pathways that improve spermatogonial propagation in vitro.

Developmental regulators moonlighting as transposons defense factors

BACKGROUND

The germline perpetuates genetic information across generations. To maintain the integrity of the germline, transposable elements in the genome must be silenced, as these mobile elements would otherwise engender widespread mutations passed on to subsequent generations. There are several well-established mechanisms that are dedicated to providing defense against transposable elements, including DNA methylation, RNA interference, and the PIWI-interacting RNA pathway.

OBJECTIVES

Recently, several studies have provided evidence that transposon defense is not only provided by factors dedicated to this purpose but also factors with other roles, including in germline development. Many of these are transcription factors. Our objective is to summarize what is known about these "bi-functional" transcriptional regulators.

MATERIALS AND METHODS

Literature search.

RESULTS AND CONCLUSION

We summarize the evidence that six transcriptional regulators-GLIS3, MYBL1, RB1, RHOX10, SETDB1, and ZBTB16-are both developmental regulators and transposable element-defense factors. These factors act at different stages of germ cell development, including in pro-spermatogonia, spermatogonial stem cells, and spermatocytes. Collectively, the data suggest a model in which specific key transcriptional regulators have acquired multiple functions over evolutionary time to influence developmental decisions and safeguard transgenerational genetic information. It remains to be determined whether their developmental roles were primordial and their transposon defense roles were co-opted, or vice versa.

MAGEB2-Mediated Degradation of EGR1 Regulates the Proliferation and Apoptosis of Human Spermatogonial Stem Cell Lines

Spermatogonial stem cells are committed to initiating and maintaining male spermatogenesis, which is the foundation of male fertility. Understanding the mechanisms underlying SSC fate decisions is critical for controlling spermatogenesis and male fertility. However, the key molecules and mechanisms responsible for regulating human SSC development are not clearly understood. Here, we analyzed normal human testis single-cell sequencing data from the GEO dataset (GSE149512 and GSE112013). Melanoma antigen gene B2 (MAGEB2) was found to be predominantly expressed in human SSCs and further validated by immunohistology. Overexpression of MAGEB2 in SSC lines severely weakened cell proliferation and promoted apoptosis. Further, using protein interaction prediction, molecular docking, and immunoprecipitation, we found that MAGEB2 interacted with early growth response protein 1 (EGR1) in SSC lines. Reexpression of EGR1 in MAGEB2 overexpression cells partially rescued decreased cell proliferation. Furthermore, MAGEB2 was shown to be downregulated in specific NOA patients, implying that abnormal expression of MAGEB2 may impair spermatogenesis and male fertility. Our results offer new insights into the functional and regulatory mechanisms in MAGEB2-mediated human SSC line proliferation and apoptosis.

Differentiation of human spermatogonial stem cells using a human decellularized testicular scaffold supplemented by platelet-rich plasma

BACKGROUND

Effective culture systems for attachment, migration, proliferation, and differentiation of spermatogonial stem cells (SSCs) can be a promising therapeutic modality for preserving male fertility. Decellularized extracellular matrix (ECM) from native testis tissue creates a local microenvironment for testicular cell culture. Furthermore, platelet-rich plasma (PRP) contains various growth factors for the proliferation and differentiation of SSCs.

METHODS

In this study, human testicular cells were isolated and cultured for 4 weeks, and SSCs were characterized using immunocytochemistry (ICC) and flow cytometry. Human testicular tissue was decellularized (0.3% SDS, 1% Triton), and the efficiency of the decellularization process was confirmed by histological staining and DNA content analysis. SSCs were cultured on the human decellularized testicular matrix (DTM) for 4 weeks. The viability and the expression of differentiation genes were evaluated by MTT and real-time polymerase chain reaction (PCR), respectively.

RESULTS

Histological evaluation and DNA content analysis showed that the components of ECM were preserved during decellularization. Our results showed that after 4 weeks of culture, the expression levels of BAX, BCL-2, PLZF, and SCP3 were unchanged, while the expression of PRM2 significantly increased in the cells cultured on DTM supplemented with PRP (ECM-PRP). In addition, the expression of GFRA1 was significantly decreased in the ECM group compared to the control and PRP groups. Furthermore, the MTT test indicated that viability was significantly enhanced in cells plated on DTM supplemented with PRP.

CONCLUSION

Our study demonstrated that DTM supplemented with PRP can provide an effective culture system for the differentiation and viability of SSCs.

Ubiquitin protein E3 ligase ASB9 suppresses proliferation and promotes apoptosis in human spermatogonial stem cell line by inducing HIF1AN degradation

BACKGROUND

Spermatogonial stem cells (SSCs) are critical for sustaining spermatogenesis. Even though several regulators of SSC have been identified in rodents, the regulatory mechanism of SSC in humans has yet to be discovered.

METHODS

To explore the regulatory mechanisms of human SSCs, we analyzed publicly available human testicular single-cell sequencing data and found that Ankyrin repeat and SOCS box protein 9 (ASB9) is highly expressed in SSCs. We examined the expression localization of ASB9 using immunohistochemistry and overexpressed ASB9 in human SSC lines to explore its role in SSC proliferation and apoptosis. Meanwhile, we used immunoprecipitation to find the target protein of ASB9 and verified its functions. In addition, we examined the changes in the distribution of ASB9 in non-obstructive azoospermia (NOA) patients using Western blot and immunofluorescence.

RESULTS

The results of uniform manifold approximation and projection (UMAP) clustering and pseudotime analysis showed that ASB9 was highly expressed in SSCs, and its expression gradually increased during development. The immunohistochemical and dual-color immunofluorescence results displayed that ASB9 was mainly expressed in nonproliferating SSCs. Overexpression of ASB9 in the SSC line revealed significant inhibition of cell proliferation and increased apoptosis. We predicted the target proteins of ASB9 and verified that hypoxia-inducible factor 1-alpha inhibitor (HIF1AN), but not creatine kinase B-type (CKB), has a direct interaction with ASB9 in human SSC line using protein immunoprecipitation experiments. Subsequently, we re-expressed HIF1AN in ASB9 overexpressing cells and found that HIF1AN reversed the proliferative and apoptotic changes induced by ASB9 overexpression. In addition, we found that ABS9 was significantly downregulated in some NOA patients, implying a correlation between ASB9 dysregulation and impaired spermatogenesis.

CONCLUSION

ASB9 is predominantly expressed in human SSCs, it affects the proliferation and apoptotic process of the SSC line through HIF1AN, and its abnormal expression may be associated with NOA.

Nuclear receptor modulators inhibit osteosarcoma cell proliferation and tumour growth by regulating the mTOR signaling pathway

Osteosarcoma is the most common primary malignant bone tumour in children and adolescents. Chemoresistance leads to poor responses to conventional therapy in patients with osteosarcoma. The discovery of novel effective therapeutic targets and drugs is still the main focus of osteosarcoma research. Nuclear receptors (NRs) have shown substantial promise as novel therapeutic targets for various cancers. In the present study, we performed a drug screen using 29 chemicals that specifically target 17 NRs in several different human osteosarcoma and osteoblast cell lines. The retinoic acid receptor beta (RARb) antagonist LE135, peroxisome proliferator activated receptor gamma (PPARg) antagonist T0070907, liver X receptor (LXR) agonist T0901317 and Rev-Erba agonist SR9011 significantly inhibited the proliferation of malignant osteosarcoma cells (U2OS, HOS-MNNG and Saos-2 cells) but did not inhibit the growth of normal osteoblasts. The effects of these NR modulators on osteosarcoma cells occurred in a dose-dependent manner and were not observed in NR-knockout osteosarcoma cells. These NR modulators also significantly inhibited osteosarcoma growth in vivo and enhanced the antitumour effect of doxorubicin (DOX). Transcriptomic and immunoblotting results showed that these NR modulators may inhibit the growth of osteosarcoma cells by regulating the PI3K/AKT/mTOR and ERK/mTOR pathways. DDIT4, which blocks mTOR activation, was identified as one of the common downstream target genes of these NRs. DDIT4 knockout significantly attenuated the inhibitory effects of these NR modulators on osteosarcoma cell growth. Together, our results revealed that modulators of RARb, PPARg, LXRs and Rev-Erba inhibit osteosarcoma growth both in vitro and in vivo through the mTOR signaling pathway, suggesting that treatment with these NR modulators is a novel potential therapeutic strategy.

The Role of Promyelocytic Leukemia Zinc Finger (PLZF) and Glial-Derived Neurotrophic Factor Family Receptor Alpha 1 (GFRα1) in the Cryopreservation of Spermatogonia Stem Cells

The cryopreservation of spermatogonia stem cells (SSCs) has been widely used as an alternative treatment for infertility. However, cryopreservation itself induces cryoinjury due to oxidative and osmotic stress, leading to reduction in the survival rate and functionality of SSCs. Glial-derived neurotrophic factor family receptor alpha 1 (GFRα1) and promyelocytic leukemia zinc finger (PLZF) are expressed during the self-renewal and differentiation of SSCs, making them key tools for identifying the functionality of SSCs. To the best of our knowledge, the involvement of GFRα1 and PLZF in determining the functionality of SSCs after cryopreservation with therapeutic intervention is limited. Therefore, the purpose of this review is to determine the role of GFRα1 and PLZF as biomarkers for evaluating the functionality of SSCs in cryopreservation with therapeutic intervention. Therapeutic intervention, such as the use of antioxidants, and enhancement in cryopreservation protocols, such as cell encapsulation, cryoprotectant agents (CPA), and equilibrium of time and temperature increase the expression of GFRα1 and PLZF, resulting in maintaining the functionality of SSCs. In conclusion, GFRα1 and PLZF have the potential as biomarkers in cryopreservation with therapeutic intervention of SSCs to ensure the functionality of the stem cells.

MAST4 controls cell cycle in spermatogonial stem cells

Spermatogonial stem cell (SSC) self-renewal is regulated by reciprocal interactions between Sertoli cells and SSCs in the testis. In a previous study, microtubule-associated serine/threonine kinase 4 (MAST4) has been studied in Sertoli cells as a regulator of SSC self-renewal. The present study focused on the mechanism by which MAST4 in Sertoli cells transmits the signal and regulates SSCs, especially cell cycle regulation. The expression of PLZF, CDK2 and PLZF target genes was examined in WT and Mast4 KO testes by Immunohistochemistry, RT-qPCR and western blot. In addition, IdU and BrdU were injected into WT and Mast4 KO mice and cell cycle of SSCs was analysed. Finally, the testis tissues were cultured in vitro to examine the regulation of cell cycle by MAST4 pathway. Mast4 KO mice showed infertility with Sertoli cell-only syndrome and reduced sperm count. Furthermore, Mast4 deletion led to decreased PLZF expression and cell cycle progression in the testes. MAST4 also induced cyclin-dependent kinase 2 (CDK2) to phosphorylate PLZF and activated PLZF suppressed the transcriptional levels of genes related to cell cycle arrest, leading SSCs to remain stem cell state. MAST4 is essential for maintaining cell cycle in SSCs via the CDK2-PLZF interaction. These results demonstrate the pivotal role of MAST4 regulating cell cycle of SSCs and the significance of spermatogenesis.

E-cadherin maintains the undifferentiated state of mouse spermatogonial progenitor cells via β-catenin

Background

Cadherins play a pivotal role in facilitating intercellular interactions between spermatogonial progenitor cells (SPCs) and their surrounding microenvironment. Specifically, E-cadherin serves as a cellular marker of SPCs in many species. Depletion of E-cadherin in mouse SPCs showed no obvious effect on SPCs homing and spermatogenesis.

Results

Here, we investigated the regulatory role of E-cadherin in regulating SPCs fate. Specific deletion of E-cadherin in germ cells was shown to promote SPCs differentiation, evidencing by reduced PLZF⁺ population and increased c-Kit⁺ population in mouse testes. E-cadherin loss down-regulated the expression level of β-catenin, leading to the reduced β-catenin in nuclear localization for transcriptional activity. Remarkably, increasing expression level of Cadherin-22 (CDH22) appeared specifically after E-cadherin deletion, indicating CDH22 played a synergistic effect with E-cadherin in SPCs. By searching for the binding partners of β-catenin, Lymphoid enhancer-binding factor 1 (LEF1), T-cell factor (TCF3), histone deacetylase 4 (HDAC4) and signal transducer and activator 3 (STAT3) were identified as suppressors of SPCs differentiation by regulating acetylation of differentiation genes with PLZF.

Conclusions

Two surface markers of SPCs, E-cadherin and Cadherin-22, synergically maintain the undifferentiation of SPCs via the pivotal intermediate molecule β-catenin. LEF1, TCF3, STAT3 and HDAC4 were identified as co-regulatory factors of β-catenin in regulation of SPC fate. These observations revealed a novel regulatory pattern of cadherins on SPCs fate.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00880-w.

Metabolic transitions define spermatogonial stem cell maturation

STUDY QUESTION

Do spermatogonia, including spermatogonial stem cells (SSCs), undergo metabolic changes during prepubertal development?

SUMMARY ANSWER

Here, we show that the metabolic phenotype of prepubertal human spermatogonia is distinct from that of adult spermatogonia and that SSC development is characterized by distinct metabolic transitions from oxidative phosphorylation (OXPHOS) to anaerobic metabolism.

WHAT IS KNOWN ALREADY

Maintenance of both mouse and human adult SSCs relies on glycolysis, while embryonic SSC precursors, primordial germ cells (PGCs), exhibit an elevated dependence on OXPHOS. Neonatal porcine SSC precursors reportedly initiate a transition to an adult SSC metabolic phenotype at 2 months of development. However, when and if such a metabolic transition occurs in humans is ambiguous.

STUDY DESIGN, SIZE, DURATION

To address our research questions: (i) we performed a meta-analysis of publicly available and newly generated (current study) single-cell RNA sequencing (scRNA-Seq) datasets in order to establish a roadmap of SSC metabolic development from embryonic stages (embryonic week 6) to adulthood in humans (25 years of age) with a total of ten groups; (ii) in parallel, we analyzed single-cell RNA sequencing datasets of isolated pup (n = 3) and adult (n = 2) murine spermatogonia to determine whether a similar metabolic switch occurs; and (iii) we characterized the mechanisms that regulate these metabolic transitions during SSC maturation by conducting quantitative proteomic analysis using two different ages of prepubertal pig spermatogonia as a model, each with four independently collected cell populations.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Single testicular cells collected from 1-year, 2-year and 7-year-old human males and sorted spermatogonia isolated from 6- to 8-day (n = 3) and 4-month (n = 2) old mice were subjected to scRNA-Seq. The human sequences were individually processed and then merged with the publicly available datasets for a meta-analysis using Seurat V4 package. We then performed a pairwise differential gene expression analysis between groups of age, followed by pathways enrichment analysis using gene set enrichment analysis (cutoff of false discovery rate < 0.05). The sequences from mice were subjected to a similar workflow as described for humans. Early (1-week-old) and late (8-week-old) prepubertal pig spermatogonia were analyzed to reveal underlying cellular mechanisms of the metabolic shift using immunohistochemistry, western blot, qRT-PCR, quantitative proteomics, and culture experiments.

MAIN RESULTS AND THE ROLE OF CHANCE

Human PGCs and prepubertal human spermatogonia show an enrichment of OXPHOS-associated genes, which is downregulated at the onset of puberty (P < 0.0001). Furthermore, we demonstrate that similar metabolic changes between pup and adult spermatogonia are detectable in the mouse (P < 0.0001). In humans, the metabolic transition at puberty is also preceded by a drastic change in SSC shape at 11 years of age (P < 0.0001). Using a pig model, we reveal that this metabolic shift could be regulated by an insulin growth factor-1 dependent signaling pathway via mammalian target of rapamycin and proteasome inhibition.

LARGE SCALE DATA

New single-cell RNA sequencing datasets obtained from this study are freely available through NCBI GEO with accession number GSE196819.

LIMITATIONS, REASONS FOR CAUTION

Human prepubertal tissue samples are scarce, which led to the investigation of a low number of samples per age. Gene enrichment analysis gives only an indication about the functional state of the cells. Due to limited numbers of prepubertal human spermatogonia, porcine spermatogonia were used for further proteomic and in vitro analyses.

WIDER IMPLICATIONS OF THE FINDINGS

We show that prepubertal human spermatogonia exhibit high OXHPOS and switch to an adult-like metabolism only after 11 years of age. Prepubescent cancer survivors often suffer from infertility in adulthood. SSC transplantation could provide a powerful tool for the treatment of infertility; however, it requires high cell numbers. This work provides key insight into the dynamic metabolic requirements of human SSCs across development that would be critical in establishing ex vivo systems to support expansion and sustained function of SSCs toward clinical use.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by the NIH/NICHD R01 HD091068 and NIH/ORIP R01 OD016575 to I.D. K.E.O. was supported by R01 HD100197. S.K.M. was supported by T32 HD087194 and F31 HD101323. The authors declare no conflict of interest.

mTORC1 and mTORC2 Complexes Regulate the Untargeted Metabolomics and Amino Acid Metabolites Profile through Mitochondrial Bioenergetic Functions in Pancreatic Beta Cells

Background: Pancreatic beta cells regulate bioenergetics efficiency and secret insulin in response to glucose and nutrient availability. The mechanistic Target of Rapamycin (mTOR) network orchestrates pancreatic progenitor cell growth and metabolism by nucleating two complexes, mTORC1 and mTORC2. Objective: To determine the impact of mTORC1/mTORC2 inhibition on amino acid metabolism in mouse pancreatic beta cells (Beta-TC-6 cells, ATCC-CRL-11506) using high-resolution metabolomics (HRM) and live-mitochondrial functions. Methods: Pancreatic beta TC-6 cells were incubated for 24 h with either: RapaLink-1 (RL); Torin-2 (T); rapamycin (R); metformin (M); a combination of RapaLink-1 and metformin (RLM); Torin-2 and metformin (TM); compared to the control. We applied high-resolution mass spectrometry (HRMS) LC-MS/MS untargeted metabolomics to compare the twenty natural amino acid profiles to the control. In addition, we quantified the bioenergetics dynamics and cellular metabolism by live-cell imaging and the MitoStress Test XF24 (Agilent, Seahorse). The real-time, live-cell approach simultaneously measures the oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) to determine cellular respiration and metabolism. Statistical significance was assessed using ANOVA on Ranks and post-hoc Welch t-Tests. Results: RapaLink-1, Torin-2, and rapamycin decreased L-aspartate levels compared to the control (p = 0.006). Metformin alone did not affect L-aspartate levels. However, L-asparagine levels decreased with all treatment groups compared to the control (p = 0.03). On the contrary, L-glutamate and glycine levels were reduced only by mTORC1/mTORC2 inhibitors RapaLink-1 and Torin-2, but not by rapamycin or metformin. The metabolic activity network model predicted that L-aspartate and AMP interact within the same activity network. Live-cell bioenergetics revealed that ATP production was significantly reduced in RapaLink-1 (122.23 ± 33.19), Torin-2 (72.37 ± 17.33) treated cells, compared to rapamycin (250.45 ± 9.41) and the vehicle control (274.23 ± 38.17), p < 0.01. However, non-mitochondrial oxygen consumption was not statistically different between RapaLink-1 (67.17 ± 3.52), Torin-2 (55.93 ± 8.76), or rapamycin (80.01 ± 4.36, p = 0.006). Conclusions: Dual mTORC1/mTORC2 inhibition by RapaLink-1 and Torin-2 differentially altered the amino acid profile and decreased mitochondrial respiration compared to rapamycin treatment which only blocks the FRB domain on mTOR. Third-generation mTOR inhibitors may alter the mitochondrial dynamics and reveal a bioenergetics profile that could be targeted to reduce mitochondrial stress.

Histone methyltransferase DOT1L is essential for self-renewal of germline stem cells

Self-renewal of spermatogonial stem cells is vital to lifelong production of male gametes and thus fertility. However, the underlying mechanisms remain enigmatic. Here, we show that DOT1L, the sole H3K79 methyltransferase, is required for spermatogonial stem cell self-renewal. Mice lacking DOT1L fail to maintain spermatogonial stem cells, characterized by a sequential loss of germ cells from spermatogonia to spermatids and ultimately a Sertoli cell only syndrome. Inhibition of DOT1L reduces the stem cell activity after transplantation. DOT1L promotes expression of the fate-determining HoxC transcription factors in spermatogonial stem cells. Furthermore, H3K79me2 accumulates at HoxC9 and HoxC10 genes. Our findings identify an essential function for DOT1L in adult stem cells and provide an epigenetic paradigm for regulation of spermatogonial stem cells.

Distinctive molecular features of regenerative stem cells in the damaged male germline

Maintenance of male fertility requires spermatogonial stem cells (SSCs) that self-renew and generate differentiating germ cells for production of spermatozoa. Germline cells are sensitive to genotoxic drugs and patients receiving chemotherapy can become infertile. SSCs surviving treatment mediate germline recovery but pathways driving SSC regenerative responses remain poorly understood. Using models of chemotherapy-induced germline damage and recovery, here we identify unique molecular features of regenerative SSCs and characterise changes in composition of the undifferentiated spermatogonial pool during germline recovery by single-cell analysis. Increased mitotic activity of SSCs mediating regeneration is accompanied by alterations in growth factor signalling including PI3K/AKT and mTORC1 pathways. While sustained mTORC1 signalling is detrimental for SSC maintenance, transient mTORC1 activation is critical for the regenerative response. Concerted inhibition of growth factor signalling disrupts core features of the regenerative state and limits germline recovery. We also demonstrate that the FOXM1 transcription factor is a target of growth factor signalling in undifferentiated spermatogonia and provide evidence for a role in regeneration. Our data confirm dynamic changes in SSC functional properties following damage and support an essential role for microenvironmental growth factors in promoting a regenerative state.

Male germline regeneration after damage is dependent on spermatogonial stem cells (SSCs) but pathways mediating the regenerative response are unclear. Here the authors define roles for growth factor signalling and mTORC1 in SSC-driven regeneration.

Rapamycin Ameliorates Radiation-Induced Testis Damage in Mice

Male infertility is an important problem in human and animal reproduction. The testis is the core of male reproduction, which is very sensitive to radiation. The decline of male reproductive ability is a common trend in the world. Radiation is a physical factor leading to abnormal male reproductive function. To investigate the potential mechanisms of testicular damage induced by radiation and explore effective strategies to alleviate radiation-induced testis injury, C57BL/6 mice were irradiated with 8.0 Gy of X-ray irradiation. Testis and epididymis were collected at days 1, 3, and 7 after radiation exposure to analyze spermatogonia and sperm function. The results showed that radiation significantly destroyed testicular structure and reduced the numbers of spermatogonia. These were associated with mTORC1 signaling activation, decreased cellular proliferation and increased apoptotic cells in the irradiated testis. Rapamycin significantly blocked mTORC1 signaling pathway in the irradiated testis. Inhibition of mTORC1 signaling pathway by rapamycin treatment after radiation could significantly improve cell proliferation in testis and alleviate radiation-induced testicular injury after radiation exposure. Rapamycin treatment benefited cell survival in testis to maintain spermatogenesis cycle at 35 days after irradiation. These findings imply that rapamycin treatment can accelerate testis recovery under radiation condition through inhibiting mTORC1 signaling pathway.

ROCK ‘n TOR: An Outlook on Keratinocyte Stem Cell Expansion in Regenerative Medicine via Protein Kinase Inhibition

Keratinocyte stem cells play a fundamental role in homeostasis and repair of stratified epithelial tissues. Transplantation of cultured keratinocytes autografts provides a landmark example of successful cellular therapies by restoring durable integrity in stratified epithelia lost to devastating tissue conditions. Despite the overall success of such procedures, failures still occur in case of paucity of cultured stem cells in therapeutic grafts. Strategies aiming at a further amplification of stem cells during keratinocyte ex vivo expansion may thus extend the applicability of these treatments to subjects in which endogenous stem cells pools are depauperated by aging, trauma, or disease. Pharmacological targeting of stem cell signaling pathways is recently emerging as a powerful strategy for improving stem cell maintenance and/or amplification. Recent experimental data indicate that pharmacological inhibition of two prominent keratinocyte signaling pathways governed by apical mTOR and ROCK protein kinases favor stem cell maintenance and/or amplification ex vivo and may improve the effectiveness of stem cell-based therapeutic procedures. In this review, we highlight the pathophysiological roles of mTOR and ROCK in keratinocyte biology and evaluate existing pre-clinical data on the effects of their inhibition in epithelial stem cell expansion for transplantation purposes.

mTOR activity is essential for retinal pigment epithelium regeneration in zebrafish

The retinal pigment epithelium (RPE) plays numerous critical roles in maintaining vision and this is underscored by the prevalence of degenerative blinding diseases like age-related macular degeneration (AMD), in which visual impairment is caused by progressive loss of RPE cells. In contrast to mammals, zebrafish possess the ability to intrinsically regenerate a functional RPE layer after severe injury. The molecular underpinnings of this regenerative process remain largely unknown yet hold tremendous potential for developing treatment strategies to stimulate endogenous regeneration in the human eye. In this study, we demonstrate that the mTOR pathway is activated in RPE cells post-genetic ablation. Pharmacological and genetic inhibition of mTOR activity impaired RPE regeneration, while mTOR activation enhanced RPE recovery post-injury, demonstrating that mTOR activity is essential for RPE regeneration in zebrafish. RNA-seq of RPE isolated from mTOR-inhibited larvae identified a number of genes and pathways dependent on mTOR activity at early and late stages of regeneration; amongst these were components of the immune system, which is emerging as a key regulator of regenerative responses across various tissue and model systems. Our results identify crosstalk between macrophages/microglia and the RPE, wherein mTOR activity is required for recruitment of macrophages/microglia to the RPE injury site. Macrophages/microglia then reinforce mTOR activity in regenerating RPE cells. Interestingly, the function of macrophages/microglia in maintaining mTOR activity in the RPE appeared to be inflammation-independent. Taken together, these data identify mTOR activity as a key regulator of RPE regeneration and link the mTOR pathway to immune responses in facilitating RPE regeneration.

The netrin-1 receptor UNC5C contributes to the homeostasis of undifferentiated spermatogonia in adult mice

In adult testis, the cell mobility is essential for spermatogonia differentiation and is suspected to regulate spermatogonial stem cell fate. Netrin-1 controls cell migration and/or survival according to the cellular context. Its involvement in some self-renewing lineages raises the possibility that Netrin-1 could have a role in spermatogenesis. We show that in addition to Sertoli cells, a fraction of murine undifferentiated spermatogonia express the Netrin-1 receptor UNC5c and that UNC5c contributes to spermatogonia differentiation. Receptor loss in Unc5c^rcm males leads to the concomitant accumulation of transit-amplifying progenitors and short syncytia of spermatogonia. Without altering cell death rates, the consequences of Unc5c loss worsen with age: the increase in quiescent undifferentiated progenitors associated with a higher spermatogonial stem cell enriched subset leads to the spermatocyte I decline. We demonstrate in vitro that Netrin-1 promotes a guidance effect as it repulses both undifferentiated and differentiating spermatogonia. Finally, we propose that UNC5c triggers undifferentiated spermatogonia adhesion/ migration and that the repulsive activity of Netrin-1 receptors could regulate spermatogonia differentiation, and maintain germ cell homeostasis.

Retinoblastoma-E2F Transcription Factor Interplay Is Essential for Testicular Development and Male Fertility

The retinoblastoma (RB) protein family members (pRB, p107 and p130) are key regulators of cell cycle progression, but also play crucial roles in apoptosis, and stem cell self-renewal and differentiation. RB proteins exert their effects through binding to E2F transcription factors, which are essential developmental and physiological regulators of tissue and organ homeostasis. According to the canonical view, phosphorylation of RB results in release of E2Fs and induction of genes needed for progress of the cell cycle. However, there are eight members in the E2F transcription factor family with both activator (E2F1-3a) and repressor (E2F3b-E2F8) roles, highlighting the functional diversity of RB-E2F pathway. In this review article we summarize the data showing that RB-E2F interaction is a key cell-autonomous mechanism responsible for establishment and maintenance of lifelong male fertility. We also review the expression pattern of RB proteins and E2F transcription factors in the testis and male germ cells. The available evidence supports that RB and E2F family members are widely and dynamically expressed in the testis, and they are known to have versatile roles during spermatogenesis. Knowledge of the function and significance of RB-E2F interplay for testicular development and spermatogenesis comes primarily from gene knock-out (KO) studies. Several studies conducted in Sertoli cell-specific pRB-KO mice have demonstrated that pRB-mediated inhibition of E2F3 is essential for Sertoli cell functional maturation and cell cycle exit, highlighting that RB-E2F interaction in Sertoli cells is paramount to male fertility. Similarly, ablation of either pRB or E2F1 in the germline results in progressive testicular atrophy due to germline stem cell (GSC) depletion, emphasizing the importance of proper RB-E2F interplay for germline maintenance and lifelong sperm production. In summary, while balanced RB-E2F interplay is essential for cell-autonomous maintenance of GSCs and, the pRB-E2F3 system in Sertoli cells is critical for providing GSC niche thus laying the basis for spermatogenesis.

Proteostasis regulated by testis-specific ribosomal protein RPL39L maintains mouse spermatogenesis

Maintaining proteostasis is important for animal development. How proteostasis influences spermatogenesis that generates male gametes, spermatozoa, is not clear. We show that testis-specific paralog of ribosomal large subunit protein RPL39, RPL39L, is required for mouse spermatogenesis. Deletion of Rpl39l in mouse caused reduced proliferation of spermatogonial stem cells, malformed sperm mitochondria and flagella, leading to sub-fertility in males. Biochemical analyses revealed that lack of RPL39L deteriorated protein synthesis and protein quality control in spermatogenic cells, partly due to reduced biogenesis of ribosomal subunits and ribosome homeostasis. RPL39/RPL39L is likely assembled into ribosomes via H/ACA domain containing NOP10 complex early in ribosome biogenesis pathway. Furthermore, Rpl39l null mice exhibited compromised regenerative spermatogenesis after chemical insult and early degenerative spermatogenesis in aging mice. These data demonstrate that maintaining proteostasis is important for spermatogenesis, of which ribosome homeostasis maintained by ribosomal proteins coordinates translation machinery to the regulation of cellular growth.

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Rpl39l deletion causes reduced spermatogenesis and subfertility in male mice

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SSC proliferation, mitochondria and sperm flagella compromised in Rpl39l^–/– mice

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Rpl39l deletion affects ribosomal LSU formation and protein quality control

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Aberrant proteostasis affects spermatogenesis and regeneration

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

BACKGROUND

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSION

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

Loss of Ubiquitin Carboxy-Terminal Hydrolase L1 Impairs Long-Term Differentiation Competence and Metabolic Regulation in Murine Spermatogonial Stem Cells

Spermatogonia are stem and progenitor cells responsible for maintaining mammalian spermatogenesis. Preserving the balance between self-renewal of spermatogonial stem cells (SSCs) and differentiation is critical for spermatogenesis and fertility. Ubiquitin carboxy-terminal hydrolase-L1 (UCH-L1) is highly expressed in spermatogonia of many species; however, its functional role has not been identified. Here, we aimed to understand the role of UCH-L1 in murine spermatogonia using a Uch-l1^−/− mouse model. We confirmed that UCH-L1 is expressed in undifferentiated and early-differentiating spermatogonia in the post-natal mammalian testis. The Uch-l1^−/− mice showed reduced testis weight and progressive degeneration of seminiferous tubules. Single-cell transcriptome analysis detected a dysregulated metabolic profile in spermatogonia of Uch-l1^−/− compared to wild-type mice. Furthermore, cultured Uch-l1^−/− SSCs had decreased capacity in regenerating full spermatogenesis after transplantation in vivo and accelerated oxidative phosphorylation (OXPHOS) during maintenance in vitro. Together, these results indicate that the absence of UCH-L1 impacts the maintenance of SSC homeostasis and metabolism and impacts the differentiation competence. Metabolic perturbations associated with loss of UCH-L1 appear to underlie a reduced capacity for supporting spermatogenesis and fertility with age. This work is one step further in understanding the complex regulatory circuits underlying SSC function.

Loss of tyrosine kinase receptor Ephb2 impairs proliferation and stem cell activity of spermatogonia in culture†

Germline stem and progenitor cells can be extracted from the adult mouse testis and maintained long-term in vitro. Yet, the optimal culture conditions for preserving stem cell activity are unknown. Recently, multiple members of the Eph receptor family were detected in murine spermatogonia, but their roles remain obscure. One such gene, Ephb2, is crucial for maintenance of somatic stem cells and was previously found enriched at the level of mRNA in murine spermatogonia. We detected Ephb2 mRNA and protein in primary adult spermatogonial cultures and hypothesized that Ephb2 plays a role in maintenance of stem cells in vitro. We employed CRISPR-Cas9 targeting and generated stable mutant SSC lines with complete loss of Ephb2. The characteristics of Ephb2-KO cells were interrogated using phenotypic and functional assays. Ephb2-KO SSCs exhibited reduced proliferation compared to wild-type cells, while apoptosis was unaffected. Therefore, we examined whether Ephb2 loss correlates with activity of canonical pathways involved in stem cell self-renewal and proliferation. Ephb2-KO cells had reduced ERK MAPK signaling. Using a lentiviral transgene, Ephb2 expression was rescued in Ephb2-KO cells, which partially restored signaling and proliferation. Transplantation analysis revealed that Ephb2-KO SSCs cultures formed significantly fewer colonies than WT, indicating a role for Ephb2 in preserving stem cell activity of cultured cells. Transcriptome analysis of wild-type and Ephb2-KO SSCs identified Dppa4 and Bnc1 as differentially expressed, Ephb2-dependent genes that are potentially involved in stem cell function. These data uncover for the first time a crucial role for Ephb2 signaling in cultured SSCs.

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

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

RNA-binding protein ELAVL2 plays post-transcriptional roles in the regulation of spermatogonia proliferation and apoptosis

Objectives

RNA‐binding proteins (RBPs) play essential post‐transcriptional roles in regulating spermatogonial stem cells (SSCs) maintenance and differentiation. We identified a conserved and SSCs‐enriched RBP ELAVL2 from our single‐cell sequencing data, but its function and mechanism in SSCs were unclear.

Materials and methods

Expressions of ELAVL2 during human and mouse testis development were validated. Stable C18‐4 and TCam‐2 cell lines with overexpression and knockdown of ELAVL2 were established, which were applied to proliferation and apoptosis analysis. RNA immunoprecipitation and sequencing were used to identify ELAVL2 targets, and regulatory functions of ELAVL2 on target mRNAs were studied. Proteins interacting with ELAVL2 in human and mouse testes were identified using immunoprecipitation and mass spectrometric, which were validated by in vivo and in vitro experiments.

Results

ELAVL2 was testis‐enriched and preferentially expressed in human and mouse SSCs. ELAVL2 was down‐regulated in NOA patients. ELAVL2 promoted proliferation and inhibited apoptosis of C18‐4 and TCam‐2 cell lines via activating ERK and AKT pathways. ELAVL2 associated with mRNAs encoding essential regulators of SSCs proliferation and survival, and promoted their protein expression at post‐transcriptional level. ELAVL2 interacted with DAZL in vivo and in vitro in both human and mouse testes.

Conclusions

Taken together, these results indicate that ELAVL2 is a conserved SSCs‐enriched RBP that down‐regulated in NOA, which regulates spermatogonia proliferation and apoptosis by promoting protein expression of targets.

NANOS2 is a sequence-specific mRNA-binding protein that promotes transcript degradation in spermatogonial stem cells

Spermatogonial stem cells (SSCs) sustain spermatogenesis and fertility throughout adult male life. The conserved RNA-binding protein NANOS2 is essential for the maintenance of SSCs, but its targets and mechanisms of function are not fully understood. Here, we generated a fully functional epitope-tagged Nanos2 mouse allele and applied the highly stringent cross-linking and analysis of cDNAs to define NANOS2 RNA occupancy in SSC lines. NANOS2 recognizes the AUKAAWU consensus motif, mostly found in the 3' untranslated region of defined messenger RNAs (mRNAs). We find that NANOS2 is a regulator of key signaling and metabolic pathways whose dosage or activity are known to be critical for SSC maintenance. NANOS2 interacts with components of CCR4-NOT deadenylase complex in SSC lines, and consequently, NANOS2 binding reduces the half-lives of target transcripts. In summary, NANOS2 contributes to SSC maintenance through the regulation of target mRNA stability and key self-renewal pathways.

Transcriptomic and epigenomic profiling of young and aged spermatogonial stem cells reveals molecular targets regulating differentiation

Spermatogonial stem cells (SSC), the foundation of spermatogenesis and male fertility, possess lifelong self-renewal activity. Aging leads to the decline in stem cell function and increased risk of paternal age-related genetic diseases. In the present study, we performed a comparative genomic analysis of mouse SSC-enriched undifferentiated spermatogonia (Oct4-GFP+/KIT-) and differentiating progenitors (Oct4-GFP+/KIT+) isolated from young and aged testes. Our transcriptome data revealed enormous complexity of expressed coding and non-coding RNAs and alternative splicing regulation during SSC differentiation. Further comparison between young and aged undifferentiated spermatogonia suggested these differentiation programs were affected by aging. We identified aberrant expression of genes associated with meiosis and TGF-β signaling, alteration in alternative splicing regulation and differential expression of specific lncRNAs such as Fendrr. Epigenetic profiling revealed reduced H3K27me3 deposition at numerous pro-differentiation genes during SSC differentiation as well as aberrant H3K27me3 distribution at genes in Wnt and TGF-β signaling upon aging. Finally, aged undifferentiated spermatogonia exhibited gene body hypomethylation, which is accompanied by an elevated 5hmC level. We believe this in-depth molecular analysis will serve as a reference for future analysis of SSC aging.

Roles of Stra8 and Tcerg1l in retinoic acid induced spermatogonial differentiation in mouse†

Retinoic acid (RA) induces spermatogonial differentiation, but the mechanism by which it operates remains largely unknown. We developed a germ cell culture assay system to study genes involved in spermatogonial differentiation triggered by RA. Stimulated by RA 8 (Stra8), a RA-inducible gene, is indispensable for meiosis initiation, and its deletion results in a complete block of spermatogenesis at the pre-leptotene/zygotene stage. To interrogate the role of Stra8 in RA mediated differentiation of spermatogonia, we derived germ cell cultures from the neonatal testis of both wild type and Stra8 knock-out mice. We provide the first evidence that Stra8 plays a crucial role in modulating the responsiveness of undifferentiated spermatogonia to RA and facilitates transition to a differentiated state. Stra8-mediated differentiation is achieved through the downregulation of a large portfolio of genes and pathways, most notably including genes involved in the spermatogonial stem cell self-renewal process. We also report here for the first time the role of transcription elongation regulator-1 like (Tcerg1l) as a downstream effector of RA-induced spermatogonial differentiation.

RNA helicase DDX5 acts as a critical regulator for survival of neonatal mouse gonocytes

OBJECTIVES

Mammalian spermatogenesis is a biological process of male gamete formation. Gonocytes are the only precursors of spermatogonial stem cells (SSCs) which develop into mature spermatozoa. DDX5 is one of DEAD-box RNA helicases and expresses in male germ cells, suggesting that Ddx5 plays important functions during spermatogenesis. Here, we explore the functions of Ddx5 in regulating the specification of gonocytes.

MATERIALS AND METHODS

Germ cell-specific Ddx5 knockout (Ddx5-/- ) mice were generated. The morphology of testes and epididymides and fertility in both wild-type and Ddx5-/- mice were analysed. Single-cell RNA sequencing (scRNA-seq) was used to profile the transcriptome in testes from wild-type and Ddx5-/- mice at postnatal day (P) 2. Dysregulated genes were validated by single-cell qRT-PCR and immunofluorescent staining.

RESULTS

In male mice, Ddx5 was expressed in germ cells at different stages of development. Germ cell-specific Ddx5 knockout adult male mice were sterile due to completely devoid of germ cells. Male germ cells gradually disappeared in Ddx5-/- mice from E18.5 to P6. Single-cell transcriptome analysis showed that genes involved in cell cycle and glial cell line-derived neurotrophic factor (GDNF) pathway were significantly decreased in Ddx5-deficient gonocytes. Notably, Ddx5 ablation impeded the proliferation of gonocytes.

CONCLUSIONS

Our study reveals the critical roles of Ddx5 in fate determination of gonocytes, offering a novel insight into the pathogenesis of male sterility.

Culture bovine prospermatogonia with 2i medium

Germplasm cryopreservation and expansion of gonocytes/prospermatogonia or spermatogonial stem cells (SSCs) are important; however, it's difficult in cattle. Since inhibitors of Mek1/2 and Gsk3β (2i) can enhance pluripotency maintenance, effects of 2i-based medium on the cultivation of bovine prospermatogonia from the cryopreserved tissues were examined. The testicular tissues of newborn bulls were well cryopreserved. High mRNA levels of prospermatogonium/SSC markers (PLZF, GFRα-1) and pluripotency markers (Oct4/Pouf5, Sox2, Nanog) were detected and the PLZF⁺ /GFRα-1⁺ prospermatogonia were consistently identified immunohistochemically in the seminiferous cords. Using differential plating and Percoll-based centrifugation, 41.59% prospermatogonia were enriched and they proliferated robustly in 2i medium. The 2i medium boosted mRNA abundances of Pouf5, Sox2, Nanog, GFRα-1, PLZF, anti-apoptosis gene Bcl2, LIF receptor gene LIFR and enhanced PLZF protein expression, but suppressed mRNA expressions of spermatogonial differentiation marker c-kit and pro-apoptotic gene Bax, in the cultured prospermatogonia. It also alleviated H₂ O₂ -induced apoptosis of the enriched cells and decreased histone H3 lysine (K9) trimethylation (H3K9me3) and its methylase Suv39h1/2 mRNA level in the cultured seminiferous cords. Overall, 2i medium improves the cultivation of bovine prospermatogonia isolated from the cryopreserved testes, by inhibiting Suv39h1/2-mediated H3K9me3 through Mek1/2 and Gsk3β signalling, evidencing successful cryopreservation and expansion of bovine germplasm.

Metabolic Requirements for Spermatogonial Stem Cell Establishment and Maintenance In Vivo and In Vitro

The spermatogonial stem cell (SSC) is a unique adult stem cell that requires tight physiological regulation during development and adulthood. As the foundation of spermatogenesis, SSCs are a potential tool for the treatment of infertility. Understanding the factors that are necessary for lifelong maintenance of a SSC pool in vivo is essential for successful in vitro expansion and safe downstream clinical usage. This review focused on the current knowledge of prepubertal testicular development and germ cell metabolism in different species, and implications for translational medicine. The significance of metabolism for cell biology, stem cell integrity, and fate decisions is discussed in general and in the context of SSC in vivo maintenance, differentiation, and in vitro expansion.

Mechanistic target of rapamycin kinase (Mtor) is required for spermatogonial proliferation and differentiation in mice

Spermatogonial development is a vital prerequisite for spermatogenesis and male fertility. However, the exact mechanisms underlying the behavior of spermatogonia, including spermatogonial stem cell (SSC) self-renewal and spermatogonial proliferation and differentiation, are not fully understood. Recent studies demonstrated that the mTOR complex 1 (mTORC1) signaling pathway plays a crucial role in spermatogonial development, but whether MTOR itself was also involved in any specific process of spermatogonial development remained undetermined. In this study, we specifically deleted Mtor in male germ cells of mice using Stra8-Cre and assessed its effect on the function of spermatogonia. The Mtor knockout (KO) mice exhibited an age-dependent perturbation of testicular development and progressively lost germ cells and fertility with age. These age-related phenotypes were likely caused by a delayed initiation of Mtor deletion driven by Stra8-Cre. Further examination revealed a reduction of differentiating spermatogonia in Mtor KO mice, suggesting that spermatogonial differentiation was inhibited. Spermatogonial proliferation was also impaired in Mtor KO mice, leading to a diminished spermatogonial pool and total germ cell population. Our results show that MTOR plays a pivotal role in male fertility and is required for spermatogonial proliferation and differentiation.

An mTORC1-dependent switch orchestrates the transition between mouse spermatogonial stem cells and clones of progenitor spermatogonia

Spermatogonial stem cells (SSCs) sustain spermatogenesis by balancing self-renewal and initiation of differentiation to produce progenitor spermatogonia committed to forming sperm. To define the regulatory logic among SSCs and progenitors, we performed single-cell RNA velocity analyses and validated results in vivo. A predominant quiescent SSC population spawns a small subset of cell-cycle-activated SSCs via mitogen-activated protein kinase (MAPK)/AKT signaling. Activated SSCs form early progenitors and mTORC1 inhibition drives activated SSC accumulation consistent with blockade to progenitor formation. Mechanistically, mTORC1 inhibition suppresses transcription among spermatogonia and specifically alters expression of insulin growth factor (IGF) signaling in early progenitors. Tex14^−/− testes lacking intercellular bridges do not accumulate activated SSCs following mTORC1 inhibition, indicating that steady-state mTORC1 signaling drives activated SSCs to produce progenitor clones. These results are consistent with a model of SSC self-renewal dependent on interconversion between activated and quiescent SSCs, and mTORC1-dependent initiation of differentiation from SSCs to progenitor clones.

Suzuki et al. define relationships between subsets of adult mouse SSCs and progenitor spermatogonia using single-cell RNA velocity analyses and in vivo validations. Quiescent SCCs convert to cell-cycle-activated SCCs via MAPK/AKT signaling. Activated SCCs are driven to become early progenitor clones ready to initiate differentiation through mTORC1 signaling.

Zinc Finger Transcription Factor Zbtb16 Coordinates the Response to Energy Deficit in the Mouse Hypothalamus

The central nervous system controls feeding behavior and energy expenditure in response to various internal and external stimuli to maintain energy balance. Here we report that the newly identified transcription factor zinc finger and BTB domain containing 16 (Zbtb16) is induced by energy deficit in the paraventricular (PVH) and arcuate (ARC) nuclei of the hypothalamus via glucocorticoid (GC) signaling. In the PVH, Zbtb16 is expressed in the anterior half of the PVH and co-expressed with many neuronal markers such as corticotropin-releasing hormone (Crh), thyrotropin-releasing hormone (Trh), oxytocin (Oxt), arginine vasopressin (Avp), and nitric oxide synthase 1 (Nos1). Knockdown (KD) of Zbtb16 in the PVH results in attenuated cold-induced thermogenesis and improved glucose tolerance without affecting food intake. In the meantime, Zbtb16 is predominantly expressed in agouti-related neuropeptide/neuropeptide Y (Agrp/Npy) neurons in the ARC and its KD in the ARC leads to reduced food intake. We further reveal that chemogenetic stimulation of PVH Zbtb16 neurons increases energy expenditure while that of ARC Zbtb16 neurons increases food intake. Taken together, we conclude that Zbtb16 is an important mediator that coordinates responses to energy deficit downstream of GCs by contributing to glycemic control through the PVH and feeding behavior regulation through the ARC, and additionally reveal its function in controlling energy expenditure during cold-evoked thermogenesis via the PVH. As a result, we hypothesize that Zbtb16 may be involved in promoting weight regain after weight loss.

What has single-cell RNA-seq taught us about mammalian spermatogenesis?

Mammalian spermatogenesis is a complex developmental program that transforms mitotic testicular germ cells (spermatogonia) into mature male gametes (sperm) for production of offspring. For decades, it has been known that this several-weeks-long process involves a series of highly ordered and morphologically recognizable cellular changes as spermatogonia proliferate, spermatocytes undertake meiosis, and spermatids develop condensed nuclei, acrosomes, and flagella. Yet, much of the underlying molecular logic driving these processes has remained opaque because conventional characterization strategies often aggregated groups of cells to meet technical requirements or due to limited capability for cell selection. Recently, a cornucopia of single-cell transcriptome studies has begun to lift the veil on the full compendium of gene expression phenotypes and changes underlying spermatogenic development. These datasets have revealed the previously obscured molecular heterogeneity among and between varied spermatogenic cell types and are reinvigorating investigation of testicular biology. This review describes the extent of available single-cell RNA-seq profiles of spermatogenic and testicular somatic cells, how those data were produced and evaluated, their present value for advancing knowledge of spermatogenesis, and their potential future utility at both the benchtop and bedside.

The Synergistic Effect of an ATP-Competitive Inhibitor of mTOR and Metformin on Pancreatic Tumor Growth

BACKGROUND

The mechanistic target of rapamycin complex 1 (mTORC1) is a nutrient-sensing pathway and a key regulator of amino acid and glucose metabolism. Dysregulation of the mTOR pathways is implicated in the pathogenesis of metabolic syndrome, obesity, type 2 diabetes, and pancreatic cancer.

OBJECTIVES

We investigated the impact of inhibition of mTORC1/mTORC2 and synergism with metformin on pancreatic tumor growth and metabolomics.

METHODS

Cell lines derived from pancreatic tumors of the KPC (KrasG12D/+; p53R172H/+; Pdx1-Cre) transgenic mice model were implanted into the pancreas of C57BL/6 albino mice (n = 10/group). Two weeks later, the mice were injected intraperitoneally with daily doses of 1) Torin 2 (mTORC1/mTORC2 inhibitor) at a high concentration (TH), 2) Torin 2 at a low concentration (TL), 3) metformin at a low concentration (ML), 4) a combination of Torin 2 and metformin at low concentrations (TLML), or 5) DMSO vehicle (control) for 12 d. Tissues and blood samples were collected for targeted xenometabolomics analysis, drug concentration, and cell signaling.

RESULTS

Metabolomic analysis of the control and treated plasma samples showed differential metabolite profiles. Phenylalanine was significantly elevated in the TLML group compared with the control (+426%, P = 0.0004), whereas uracil was significantly lower (-38%, P = 0.009). The combination treatment reduced tumor growth in the orthotopic mouse model. TLML significantly decreased pancreatic tumor volume (498 ± 104 mm3; 37%; P < 0.0004) compared with control (1326 ± 134 mm3; 100%), ML (853 ± 67 mm3; 64%), TL (745 ± 167 mm3; 54%), and TH (665 ± 182 mm3; 50%) (ANOVA and post hoc tests). TLML significantly decreased tumor weights (0.66 ± 0.08 g; 52%) compared with the control (1.28 ± 0.19 g; 100%) (P < 0.002).

CONCLUSIONS

The combination of mTOR dual inhibition by Torin 2 and metformin is associated with an altered metabolomic profile and a significant reduction in pancreatic tumor burden compared with single-agent therapy, and it is better tolerated.

Conversion from spermatogonia to spermatocytes: Extracellular cues and downstream transcription network

Spermatocyte (spc) formation from spermatogonia (spg) differentiation is the first step of spermatogenesis which produces prodigious spermatozoa for a lifetime. After decades of studies, several factors involved in the functioning of a mouse were discovered both inside and outside spg. Considering the peculiar expression and working pattern of each factor, this review divides the whole conversion of spg to spc into four consecutive development processes with a focus on extracellular cues and downstream transcription network in each one. Potential coordination among Dmrt1, Sohlh1/2 and BMP families mediates Ngn3 upregulation, which marks progenitor spg, with other changes. After that, retinoic acid (RA), as a master regulator, promotes A1 spg formation with its helpers and Sall4. A1-to-B spg transition is under the control of Kitl and impulsive RA signaling together with early and late transcription factors Stra8 and Dmrt6. Finally, RA and its responsive effectors conduct the entry into meiosis. The systematic transcription network from outside to inside still needs research to supplement or settle the controversials in each process. As a step further ahead, this review provides possible drug targets for infertility therapy by cross-linking humans and mouse model.

Short time exposure to low concentration of zinc oxide nanoparticles up-regulates self-renewal and spermatogenesis-related gene expression

Extensive application of zinc oxide (ZnO) nanoparticles (NPs) in everyday life results in increased exposure to these NPs. Spermatogonial stem cells (SSCs) guarantee sperm production throughout the male reproductive life by providing a balance between self-renewal and differentiation. We used an in vitro platform to investigate the ZnO NPs effects on SSCs. We successfully synthesized ZnO NPs. In order to investigate these NPs, we isolated SSCs from mouse testes and cultured them in vitro. Our results confirmed the uptake of ZnO NPs by the cultured SSCs. We observed a dose- and time-dependent decrease in SSC viability. Both spherical and nanosheet ZnO NPs had the same cytotoxic effects on the SSCs, irrespective of their shapes. Moreover, we have shown that short time (one day) exposure of SSCs to a low concentration of ZnO NPs (10 μg/mL) promoted expressions of specific genes (Plzf, Gfr α1 and Bcl6b) for SSC self-renewal and differentiation genes (Vasa, Dazl, C-kit and Sycp3) expressed by spermatogonia during spermatogenesis. Our study provides the first insight into ZnO NPs function in SSCs and suggests a new function for ZnO NPs in the male reproductive system. We demonstrated that ZnO NPs might promote spermatogenesis via upregulation of gene expression related to SSC self-renewal and differentiation at low concentrations. Additional research should clarify the possible effect of ZnO NPs on the SSC genome and its effects on human SSCs.

The rapamycin analog Everolimus reversibly impairs male germ cell differentiation and fertility in the mouse†

Sirolimus, also known as rapamycin, and its closely related rapamycin analog (rapalog) Everolimus inhibit "mammalian target of rapamycin complex 1" (mTORC1), whose activity is required for spermatogenesis. Everolimus is Food and Drug Administration approved for treating human patients to slow growth of aggressive cancers and preventing organ transplant rejection. Here, we test the hypothesis that rapalog inhibition of mTORC1 activity has a negative, but reversible, impact upon spermatogenesis. Juvenile (P20) or adult (P>60) mice received daily injections of sirolimus or Everolimus for 30 days, and tissues were examined at completion of treatment or following a recovery period. Rapalog treatments reduced body and testis weights, testis weight/body weight ratios, cauda epididymal sperm counts, and seminal vesicle weights in animals of both ages. Following rapalog treatment, numbers of differentiating spermatogonia were reduced, with concomitant increases in the ratio of undifferentiated spermatogonia to total number of remaining germ cells. To determine if even low doses of Everolimus can inhibit spermatogenesis, an additional group of adult mice received a dose of Everolimus ∼6-fold lower than a human clinical dose used to treat cancer. In these animals, only testis weights, testis weight/body weight ratios, and tubule diameters were reduced. Return to control values following a recovery period was variable for each of the measured parameters and was duration and dose dependent. Together, these data indicate rapalogs exerted a dose-dependent restriction on overall growth of juvenile and adult mice and negative impact upon spermatogenesis that were largely reversed; following treatment cessation, males from all treatment groups were able to sire offspring.