The mammalian doublesex homolog DMRT1 is a transcriptional gatekeeper that controls the mitosis versus meiosis decision in male germ cells. Dev Cell. 2010;19:612-624. [PMID: 20951351 DOI: 10.1016/j.devcel.2010.09.010]

Sex differences in spiders: from phenotype to genomics

Sexual reproduction is pervasive in animals and has led to the evolution of sexual dimorphism. In most animals, males and females show marked differences in primary and secondary sexual traits. The formation of sex-specific organs and eventually sex-specific behaviors is defined during the development of an organism. Sex determination processes have been extensively studied in a few well-established model organisms. While some key molecular regulators are conserved across animals, the initiation of sex determination is highly diverse. To reveal the mechanisms underlying the development of sexual dimorphism and to identify the evolutionary forces driving the evolution of different sexes, sex determination mechanisms must thus be studied in detail in many different animal species beyond the typical model systems. In this perspective article, we argue that spiders represent an excellent group of animals in which to study sex determination mechanisms. We show that spiders are sexually dimorphic in various morphological, behavioral, and life history traits. The availability of an increasing number of genomic and transcriptomic resources and functional tools provides a great starting point to scrutinize the extensive sexual dimorphism present in spiders on a mechanistic level. We provide an overview of the current knowledge of sex determination in spiders and propose approaches to reveal the molecular and genetic underpinnings of sexual dimorphism in these exciting animals.

An ex vivo Approach to Study Hormonal Control of Spermatogenesis in the Teleost Oreochromis niloticus

As the male reproductive organ, the main task of the testis is the production of fertile, haploid spermatozoa. This process, named spermatogenesis, starts with spermatogonial stem cells, which undergo a species-specific number of mitotic divisions until starting meiosis and further morphological maturation. The pituitary gonadotropins, luteinizing hormone, and follicle stimulating hormone, are indispensable for vertebrate spermatogenesis, but we are still far from fully understanding the complex regulatory networks involved in this process. Therefore, we developed an ex vivo testis cultivation system which allows evaluating the occurring changes in histology and gene expression. The experimental circulatory flow-through setup described in this work provides the possibility to study the function of the male tilapia gonads on a cellular and transcriptional level for at least 7 days. After 1 week of culture, tilapia testis slices kept their structure and all stages of spermatogenesis could be detected histologically. Without pituitary extract (tilPE) however, fibrotic structures appeared, whereas addition of tilPE preserved spermatogenic cysts and somatic interstitium completely. We could show that tilPE has a stimulatory effect on spermatogonia proliferation in our culture system. In the presence of tilPE or hCG, the gene expression of steroidogenesis related genes (cyp11b2 and stAR2) were notably increased. Other testicular genes like piwil1, amh, or dmrt1 were not expressed differentially in the presence or absence of gonadotropins or gonadotropin containing tilPE. We established a suitable system for studying tilapia spermatogenesis ex vivo with promise for future applications.

Parallel Evolution of Two dmrt1-Derived Genes, dmy and dm-W, for Vertebrate Sex Determination

Animal sex-determining genes, which bifurcate for female and male development, are diversified even among closely related species. Most of these genes emerged independently from various sex-related genes during species diversity as neofunctionalization-type genes. However, the common mechanisms of this divergent evolution remain poorly understood. Here, we compared the molecular evolution of two sex-determining genes, the medaka dmy and the clawed frog dm-W, which independently evolved from the duplication of the transcription factor-encoding masculinization gene dmrt1. Interestingly, we detected parallel amino acid substitutions, from serine (S) to threonine (T), on the DNA-binding domains of both ancestral DMY and DM-W, resulting from positive selection. Two types of DNA-protein binding experiments and a luciferase reporter assay demonstrated that these S-T substitutions could strengthen the DNA-binding abilities and enhance the transcriptional regulation function. These findings suggest that the parallel S-T substitutions may have contributed to the establishment of dmy and dm-W as sex-determining genes.

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We detected parallel amino acid substitutions in two sex-determining genes, dmy and dm-W

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Both the substitutions from dmrt1 duplication are under positive selection

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These substitutions enhanced their DNA-binding activity as transcription factors

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These substitutions might have contributed to the establishment of dmy and dm-W

Genome-Wide identification of doublesex and Mab-3-Related transcription factor (DMRT) genes in nile tilapia (oreochromis niloticus)

Doublesex and Mab-3-related transcription factor (DMRT) gene family is extensively known for its contribution in sex determination and differentiation across phyla. Here we report the identification of five DM (doublesex and mab-3) domain genes in the Nile tilapia which includes DMRT1, DMRTa2, DMRT2a, DMRT2b and DMRT3a. The full-length sequence of DMRT genes ranges from 3526 (DMRTA2) to 1471bp (DMRT1) which encode putative proteins series from 469 to 372 amino acids. All the DMRT proteins contained at least one conserved DNA-binding DM domain. Sub-cellular localization and gene ontology revealed DMRT1 protein is maximum localized in nuclear region and gene ontology analysis showed the molecular function of 48.2%, biological process 43.6% and cellular component 25%. Chromosomal location and synteny analysis displayed that DMRT genes mostly cluster linkage group 12. Altogether, our findings provide vital genomic information for future studies of biochemical, physiological, and phylogenetic studies on DMRT genes in teleost.

Transcription of the Sox30 Gene Is Positively Regulated by Dmrt1 in Nile Tilapia

The Sox family member Sox30 is highly expressed in the testis of several vertebrate species and has been shown to play key roles in spermiogenesis. However, its transcription regulation remains unclear. Here, we analyzed the Sox30 promoter from the teleost fish Nile tilapia (Oreochromis niloticus) and predicted a putative cis-regulatory element (CRE) for doublesex and mab-3 related transcription factor 1 (Dmrt1), a male-specific transcription factor involved in male sex differentiation. Transcriptional profiling revealed that Sox30 and Dmrt1 similarly exhibited a high expression in tilapia testes from 90 days after hatching (dah) to 300 dah, and the transcription of the Sox30 gene was reduced about one-fold in the testes of male tilapia with Dmrt1 knockdown. Further dual-luciferase reporter assay confirmed that Dmrt1 overexpression significantly promoted transcriptional activity of the Sox30 promoter and this promotion was decreased following the mutation of putative CRE for Dmrt1 within the Sox30 promoter. Chromatin immunoprecipitation-based PCR (ChIP-PCR) and electrophoretic mobility shift assay (EMSA) demonstrated that Dmrt1 directly binds to putative CRE within the Sox30 promoter. These results together indicate that Dmrt1 positively regulates the transcription of the tilapia Sox30 gene by directly binding to specific CRE within the Sox30 promoter.

Mechanisms regulating mammalian spermatogenesis and fertility recovery following germ cell depletion

Mammalian spermatogenesis is a highly complex multi-step process sustained by a population of mitotic germ cells with self-renewal potential known as spermatogonial stem cells (SSCs). The maintenance and regulation of SSC function are strictly dependent on a supportive niche that is composed of multiple cell types. A detailed appreciation of the molecular mechanisms underpinning SSC activity and fate is of fundamental importance for spermatogenesis and male fertility. However, different models of SSC identity and spermatogonial hierarchy have been proposed and recent studies indicate that cell populations supporting steady-state germline maintenance and regeneration following damage are distinct. Importantly, dynamic changes in niche properties may underlie the fate plasticity of spermatogonia evident during testis regeneration. While formation of spermatogenic colonies in germ-cell-depleted testis upon transplantation is a standard assay for SSCs, differentiation-primed spermatogonial fractions have transplantation potential and this assay provides readout of regenerative rather than steady-state stem cell capacity. The characterisation of spermatogonial populations with regenerative capacity is essential for the development of clinical applications aimed at restoring fertility in individuals following germline depletion by genotoxic treatments. This review will discuss regulatory mechanisms of SSCs in homeostatic and regenerative testis and the conservation of these mechanisms between rodent models and man.

PLZF suppresses differentiation of mouse spermatogonial progenitor cells via binding of differentiation associated genes

Promyelocytic leukaemia zinc finger (PLZF) is a key factor in inhibiting differentiation of spermatogonial progenitor cells (SPCs), but the underlying mechanisms are still largely unknown. In this study, the regulation of PLZF on Kit, Stra8, Sohlh2, and Dmrt1 (SPCs differentiation related genes) was investigated. We found some PLZF potential binding sites existed in the promoters of Kit, Stra8, Sohlh2, and Dmrt1. Additionally, the expressions of KIT, STRA8, SOHLH2, and DMRT1 were upregulated when PLZF was knockdown in SPCs. Furthermore, chromatin immunoprecipitation quantitative polymerase chain reaction revealed PLZF directly bound to the promoters of Kit, Stra8, Sohlh2, and Dmrt1. Besides, dual luciferase assay verified PLZF repressed those gene expressions. Collectively, our finding indicate that PLZF binds to the promoter regions of Kit, Stra8, Sohlh2, and Dmrt1 to regulate SPCs differentiation, which facilitate us to further understand the regulatory mechanism of PLZF in SPCs fates.

Human germ cell tumours from a developmental perspective

Human germ cell tumours (GCTs) are derived from stem cells of the early embryo and the germ line. They occur in the gonads (ovaries and testes) and also in extragonadal sites, where migrating primordial germ cells are located during embryogenesis. This group of heterogeneous neoplasms is unique in that their developmental potential is in effect determined by the latent potency state of their cells of origin, which are reprogrammed to omnipotent, totipotent or pluripotent stem cells. Seven GCT types, defined according to their developmental potential, have been identified, each with distinct epidemiological and (epi)genomic features. Heritable predisposition factors affecting the cells of origin and their niches likely explain bilateral, multiple and familial occurrences of the different types of GCTs. Unlike most other tumour types, GCTs are rarely caused by somatic driver mutations, but arise through failure to control the latent developmental potential of their cells of origin, resulting in their reprogramming. Consistent with their non-mutational origin, even the malignant tumours of the group are characterized by wild-type TP53 and high sensitivity for DNA damage. However, tumour progression and the rare occurrence of treatment resistance are driven by embryonic epigenetic state, specific (sub)chromosomal imbalances and somatic mutations. Thus, recent progress in understanding GCT biology supports a comprehensive developmental pathogenetic model for the origin of all GCTs, and provides new biomarkers, as well as potential targets for treatment of resistant disease.

Independent evolution for sex determination and differentiation in the DMRT family in animals

Some DMRT family genes including arthropod dsx, nematode mab-3, and vertebrate dmrt1 are involved in sex determination and/or differentiation in bilaterian animals. Although there have been some reports about evolutionary analyses of the family by using its phylogenetic trees, it is still undecided as to whether these three sex determination-related genes share orthologous relationships or not. To clarify this question, we analyzed evolutional relationships among the family members in various bilaterians by using not only phylogenetic tree analysis, but also synteny analysis. We found that only four genes, dmrt2a/2b, dmrt3, dmrt4/5 and dmrt93B were commonly present in invertebrate bilateria. The syntenies of dmrt2a/2b-dmrt3 and dmrt4/5-dmrt93B are conserved before and after two rounds of whole genome duplication in the ancestral vertebrate. Importantly, this indicates that dmrt1 must have appeared in the common vertebrate ancestor. In addition, dmrt1, dsx, or mab-3 formed each different cluster at a distance in our phylogenetic tree. From these findings, we concluded that the three sex determination-related genes, dmrt1, dsx, and mab-3 have no orthologous relationships, and suggested independent evolution for sex determination and differentiation in the DMRT gene family. Our results may supply clues about why sex-determining systems have diverged during animal evolution.

Summary: Three DMRT family genes, vertebrate dmrt1, arthropod dsx and nematode mab-3, involved in sex determination and primary sex differentiation have no orthologous relationships, indicating independent evolution in bilaterian animals.

Retinoic acid signaling in regulation of meiosis during embryonic development in mice

In the embryonic gonads of mice, the genetic and epigenetic regulatory programs for germ cell sex specification and meiosis induction or suppression are intertwined. The quest for garnering comprehensive understanding of these programs has led to the emergence of retinoic acid (RA) as an important extrinsic factor, which regulates initiation of meiosis in female fetal germ cells that have attained a permissive epigenetic ground state. In contrast, germ cells in fetal testis are protected from the exposure to RA due to the activity of CYP26B1, an RA metabolizing enzyme, which is highly expressed in fetal testis. In this review, we provide an overview of the molecular mechanisms operating in fetal gonads of mice, which enable regulation of meiosis via RA signaling.

Phylogenetic analysis and embryonic expression of panarthropod Dmrt genes

Background

One set of the developmentally important Doublesex and Male-abnormal-3 Related Transcription factors (Dmrt) is subject of intense research, because of their role in sex-determination and sexual differentiation. This likely non-monophyletic group of Dmrt genes is represented by the Drosophila melanogaster gene Doublesex (Dsx), the Caenorhabditis elegans Male-abnormal-3 (Mab-3) gene, and vertebrate Dmrt1 genes. However, other members of the Dmrt family are much less well studied, and in arthropods, including the model organism Drosophila melanogaster, data on these genes are virtually absent with respect to their embryonic expression and function.

Results

Here we investigate the complete set of Dmrt genes in members of all main groups of Arthropoda and a member of Onychophora, extending our data to Panarthropoda as a whole. We confirm the presence of at least four families of Dmrt genes (including Dsx-like genes) in Panarthropoda and study their expression profiles during embryogenesis. Our work shows that the expression patterns of Dmrt11E, Dmrt93B, and Dmrt99B orthologs are highly conserved among panarthropods. Embryonic expression of Dsx-like genes, however, is more derived, likely as a result of neo-functionalization after duplication.

Conclusions

Our data suggest deep homology of most of the panarthropod Dmrt genes with respect to their function that likely dates back to their last common ancestor. The function of Dsx and Dsx-like genes which are critical for sexual differentiation in animals, however, appears to be much less conserved.

Electronic supplementary material

The online version of this article (10.1186/s12983-019-0322-0) contains supplementary material, which is available to authorized users.

Medroxyprogesterone acetate affects sex differentiation and spermatogenesis in zebrafish

Medroxyprogesterone acetate (MPA) is a widely used synthetic progestin and it has been frequently detected in aquatic environments. However, its effects on aquatic organisms remain largely unknown. Here we investigated the chronic effects of MPA on sex differentiation and gonad development in zebrafish. Zebrafish larvae at 20 days post fertilization (dpf) were exposed to 4.32, 42.0, and 424 ng L^-1 of MPA until they reached 140 dpf. The results showed that chronic exposure to 42.0 ng L^-1 of MPA caused 60% proportion of males as well as significant up-regulation of dmrt1 (˜1.79 fold) and hsd17b3 (˜1.92 fold). Histological analysis showed MPA significantly increased the frequency of immature spermatocytes accompanied with the increased transcription of dmrt1 (˜2.06 fold) and ar (˜1.73 fold) in the testes. Meanwhile, MPA exposure significantly increased the transcription of lhb at all exposure concentrations in the males. In contrast, it significantly suppressed the transcription of lhb (˜-8.06-fold) and fshb (˜-6.35-fold) at 42.0 ng L^-1 in the females. Collectively our results demonstrated that MPA had androgenic activity, and could affect sex differentiation and spermatogenesis in zebrafish at environmentally relevant concentrations. The findings from this study suggest that MPA in the aquatic environment may pose potential androgenic risks to fish populations.

Regulation of long non-coding RNAs and circular RNAs in spermatogonial stem cells

Spermatogonial stem cells (SSCs) are one of the most significant stem cells with the potentials of self-renewal, differentiation, transdifferentiation and dedifferentiation, and thus, they have important applications in reproductive and regenerative medicine. They can transmit the genetic and epigenetic information across generations, which highlights the importance of the correct establishment and maintenance of epigenetic marks. Accurate transcriptional and post-transcriptional regulation is required to support the highly coordinated expression of specific genes for each step of spermatogenesis. Increasing evidence indicates that non-coding RNAs (ncRNAs), including long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), play essential roles in controlling gene expression and fate determination of male germ cells. These ncRNA molecules have distinct characteristics and biological functions, and they independently or cooperatively modulate the proliferation, apoptosis and differentiation of SSCs. In this review, we summarized the features, biological function and fate of mouse and human SSCs, and we compared the characteristics of lncRNAs and circRNAs. We also addressed the roles and mechanisms of lncRNAs and circRNAs in regulating mouse and human SSCs, which would add novel insights into the epigenetic mechanisms underlying mammalian spermatogenesis and provide new approaches to treat male infertility.

Recent Research Advances in Mitosis during Mammalian Gametogenesis

Mitosis is a highly sophisticated and well-regulated process during the development and differentiation of mammalian gametogenesis. The regulation of mitosis plays an essential role in keeping the formulation in oogenesis and gametogenesis. In the past few years, substantial research progress has been made by showing that cyclins/cyclin-dependent kinase (CDK) have roles in the regulation of meiosis. In addition, more functional signaling molecules have been discovered in mitosis. Growing evidence has also indicated that miRNAs influence cell cycling. In this review, we focus on specific genes, cyclins/Cdk, signaling pathways/molecules, and miRNAs to discuss the latest achievements in understanding their roles in mitosis during gametogenesis. Further elucidation of mitosis during gametogenesis may facilitate delineating all processes of mammalian reproduction and the development of disease treatments.

DMRT1 repression using a novel approach to genetic manipulation induces testicular dysgenesis in human fetal gonads

STUDY QUESTION

Does loss of DMRT1 in human fetal testis alter testicular development and result in testicular dysgenesis?

SUMMARY ANSWER

DMRT1 repression in human fetal testis alters the expression of key testicular and ovarian determining genes, and leads to focal testicular dysgenesis.

WHAT IS KNOWN ALREADY

Testicular dysgenesis syndrome (TDS) is associated with common testicular disorders in young men, but its etiology is unknown. DMRT1 has been shown to play a role in the regulation of sex differentiation in the vertebrate gonad. Downregulation of DMRT1 in male mice results in trans-differentiation of Sertoli cells into granulosa (FOXL2⁺) cells resulting in an ovarian gonadal phenotype.

STUDY DESIGN, SIZE, DURATION

To determine the effect of DMRT1 repression on human fetal testes, we developed a novel system for genetic manipulation, which utilizes a Lentivral delivered miRNA during short-term in vitro culture (2 weeks). A long-term (4–6 weeks) ex vivo xenograft model was used to determine the subsequent effects of DMRT1 repression on testicular development and maintenance. We included first and second-trimester testis tissue (8–20 weeks gestation; n = 12) in the study.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Human fetal testes were cultured in vitro and exposed to either of two DMRT1 miRNAs (miR536, miR641), or to scrambled control miRNA, for 24 h. This was followed by a further 14 days of culture (n = 3–4), or xenografting (n = 5) into immunocompromised mice for 4–6 weeks. Tissues were analyzed by histology, immunohistochemistry, immunofluorescence and quantitative RT-PCR. Endpoints included histological evaluation of seminiferous cord integrity, mRNA expression of testicular, ovarian and germ cell genes, and assessment of cell number and protein expression for proliferation, apoptosis and pluripotency factors. Statistical analysis was performed using a linear mixed effect model.

MAIN RESULTS AND THE ROLE OF CHANCE

DMRT1 repression (miR536/miR641) resulted in a loss of DMRT1 protein expression in a sub-population of Sertoli cells of first trimester (8–11 weeks gestation) human fetal testis; however, this did not affect the completion of seminiferous cord formation or morphological appearance. In second-trimester testis (12–20 weeks gestation), DMRT1 repression (miR536/miR641) resulted in disruption of seminiferous cords with absence of DMRT1 protein expression in Sertoli (SOX9⁺) cells. No differences in proliferation (Ki67⁺) were observed and apoptotic cells (CC3⁺) were rare. Expression of the Sertoli cell associated gene, SOX8, was significantly reduced (miR536, 34% reduction, P = 0.031; miR641 36% reduction, P = 0.026), whilst SOX9 expression was unaffected. Changes in expression of AMH (miR536, 100% increase, P = 0.033), CYP26B1 (miR641, 38% reduction, P = 0.05) and PTGDS (miR642, 30% reduction, P = 0.0076) were also observed. Amongst granulosa cell associated genes, there was a significant downregulation in R-spondin 1 expression (miR536, 76% reduction, P < 0.0001; miR641, 49% reduction, P = 0.046); however, there were no changes in expression of the granulosa cell marker, FOXL2. Analysis of germ cell associated genes demonstrated a significant increase in the expression of the pluripotency gene OCT4 (miR536, 233%, P < 0.001). We used the xenograft system to investigate the longer-term effects of seminiferous cord disruption via DMRT1 repression. As was evident in vitro for second-trimester samples, DMRT1 repression resulted in focal testicular dysgenesis similar to that described in adults with TDS. These dysgenetic areas were devoid of germ cells, whilst expression of FOXL2 within the dysgenetic areas, indicated trans-differentiation from a male (Sertoli cell) to female (granulosa cell) phenotype.

LIMITATIONS, REASONS FOR CAUTION

Human fetal testis tissue is a limited resource; however, we were able to demonstrate significant effects of DMRT1 repression on the expression of germ and somatic cell genes, in addition to the induction of focal testicular dysgenesis, using these limited samples. In vitro culture may not reflect all aspects of human fetal testis development and function; however, the concurrent use of the xenograft model which represents a more physiological system supports the validity of the in vitro findings.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings have important implications for understanding the role of DMRT1 in human testis development and in the origin of testicular dysgenesis. In addition, we provide validation of a novel system that can be used to determine the effects of repression of genes that have been implicated in gonadal development and associated human reproductive disorders.

STUDY FUNDING/COMPETING INTEREST(S)

This project was funded by a Wellcome Trust Intermediate Clinical Fellowship (Grant No. 098522) awarded to RTM. LBS was supported by MRC Programme Grant MR/N002970/1. RAA was supported by MRC Programme Grant G1100357/1. RMS was supported by MRC Programme Grant G33253. This work was undertaken in the MRC Centre for Reproductive Health which is funded by the MRC Centre grant MR/N022556/1. The funding bodies had no input into the conduct of the research or the production of this manuscript. The authors have declared no conflicts of interest.

SOHLHs Might Be Gametogenesis-Specific bHLH Transcriptional Regulation Factors in Crassostrea gigas

The self-renewal and differentiation of germ cells are essential for gametogenesis and reproduction. In mammals, the transcription factors SOHLH1 and SOHLH2, two members of the bHLH family, are specifically expressed in the gonads, and play an important role in spermatocyte and oocyte differentiation. In our previous study, we performed a phylogenetic analysis of the Lophotrochozoa bHLH genes, and two Sohlh were identified in the Pacific oyster Crassostrea gigas. Based on the genomes of other species that have complete genomic information, we further analyzed the phylogenetics of the Sohlh in this study. The results indicate that the Sohlh are ancient genes that were lost in many species during evolution, including in some invertebrates, and lower vertebrates. The phylogenetic tree shows that Sohlh1 and Sohlh2 are located in different scaffolds and that they have low similarity, suggesting early separation in invertebrates. We used RNA-seq and RT-PCR to examine the mRNA expression of the Sohlh in C. gigas (termed Cg-Sohlh), we found that Cg-Sohlh1, and Cg-Sohlh2 are specifically expressed in the gonads. During gonadal development, the mRNA expression levels of both genes increased from the proliferative stage and reached the highest level at the growth stage (P < 0.05). Then, the expression level decreased until the resting stage. In addition, immunohistochemistry was used to determine that the Cg-SOHLH1 protein was specifically expressed in the spermatogonia and spermatocytes. Cg-Sohlh2 mRNA was expressed in both the male and female gonads, while Cg-Sohlh1 mRNA was highly expressed in the female gonads at all developmental stages except for the resting stage. These data indicate that Cg-SOHLH might be gonad-specific regulatory factors, similar to mammalian SOHLH, and that Cg-SOHLH1 might be involved in spermatogonial differentiation. This study lays the foundation to further determine the functional role of SOHLH in mollusk gametogenesis and provides a foundation to better understand the regulatory mechanism of gametogenesis in invertebrates.

Heterogeneity of primordial germ cells

Primordial germ cells (PGCs) must complete a complex and dynamic developmental program during embryogenesis to establish the germline. This process is highly conserved and involves a diverse array of tasks required of PGCs, including migration, survival, sex differentiation, and extensive epigenetic reprogramming. A common theme across many organisms is that PGC success is heterogeneous: only a portion of all PGCs complete all these steps while many other PGCs are eliminated from further germline contribution. The differences that distinguish successful PGCs as a population are not well understood. Here, we examine variation that exists in PGCs as they navigate the many stages of this developmental journey. We explore potential sources of PGC heterogeneity and their potential implications in affecting germ cell behaviors. Lastly, we discuss the potential for PGC development to function as a multistage selection process that assesses heterogeneity in PGCs to refine germline quality.

Testicular germ cell tumor: a comprehensive review

Testicular tumors are the most common tumors in adolescent and young men and germ cell tumors (TGCTs) account for most of all testicular cancers. Increasing incidence of TGCTs among males provides strong motivation to understand its biological and genetic basis. Gains of chromosome arm 12p and aneuploidy are nearly universal in TGCTs, but TGCTs have low point mutation rate. It is thought that TGCTs develop from premalignant intratubular germ cell neoplasia that is believed to arise from the failure of normal maturation of gonocytes during fetal or postnatal development. Progression toward invasive TGCTs (seminoma and nonseminoma) then occurs after puberty. Both inherited genetic factors and environmental risk factors emerge as important contributors to TGCT susceptibility. Genome-wide association studies have so far identified more than 30 risk loci for TGCTs, suggesting that a polygenic model fits better with the genetic landscape of the disease. Despite high cure rates because of its particular sensitivity to platinum-based chemotherapy, exploration of mechanisms underlying the occurrence, progression, metastasis, recurrence, chemotherapeutic resistance, early diagnosis and optional clinical therapeutics without long-term side effects are urgently needed to reduce the cancer burden in this underserved age group. Herein, we present an up-to-date review on clinical challenges, origin and progression, risk factors, TGCT mouse models, serum diagnostic markers, resistance mechanisms, miRNA regulation, and database resources of TGCTs. We appeal that more attention should be paid to the basic research and clinical diagnosis and treatment of TGCTs.

Identification of candidate genes in regulation of spermatogenesis in sheep testis following dietary vitamin E supplementation

Dietary vitamin E supplementation is beneficial to semen quality in different sheep and goat breeds. The aim of this research was to further investigate the effect of vitamin E in sheep on spermatogenesis and its regulatory mechanisms using RNA-seq. Thirty male Hu lambs were randomly divided into three groups. The animals received 0, 200 or 2000 IU/day vitamin E dietary supplementation for 105 days, and its effects were subsequently evaluated. The results indicate vitamin E supplementation increased the number of germ cells in the testes and epididymides. The positive effects were reduced, however, in animals that received 2000 IU/d vitamin E. Using the RNA-seq procedure, there was detection of a number of differentially expressed genes such as NDRG1, FSCN3 and CYP26B1 with these genes being mainly related to the regulation of spermatogenesis. Supplementation with 2000 IU/d vitamin E supplementation resulted in a lesser abundance of skeleton-related transcripts such as TUBB, VIM and different subtypes of collagen, and there was also an effect on the ECM-receptor interaction pathway. These changes appear to be responsible for the lesser beneficial effect of the greater vitamin E concentrations. The results provide a novel insight into the regulation of spermatogenesis by vitamin E at the molecular level, however, for a precise understanding of functions of the affected genes there needs to be further study.

A novel evolutionary conserved mechanism of RNA stability regulates synexpression of primordial germ cell-specific genes prior to the sex-determination stage in medaka

Dmrt1 is a highly conserved transcription factor, which is critically involved in regulation of gonad development of vertebrates. In medaka, a duplicate of dmrt1-acting as master sex-determining gene-has a tightly timely and spatially controlled gonadal expression pattern. In addition to transcriptional regulation, a sequence motif in the 3' UTR (D3U-box) mediates transcript stability of dmrt1 mRNAs from medaka and other vertebrates. We show here that in medaka, two RNA-binding proteins with antagonizing properties target this D3U-box, promoting either RNA stabilization in germ cells or degradation in the soma. The D3U-box is also conserved in other germ-cell transcripts, making them responsive to the same RNA binding proteins. The evolutionary conservation of the D3U-box motif within dmrt1 genes of metazoans-together with preserved expression patterns of the targeting RNA binding proteins in subsets of germ cells-suggest that this new mechanism for controlling RNA stability is not restricted to fishes but might also apply to other vertebrates.

Immunolocalization of DMRTB1 in human testis with normal and impaired spermatogenesis

BACKGROUND

The transcription factor DMRTB1 plays a pivotal role in coordinating the transition between mitosis and meiosis in murine germ cells. No reliable data are available for human testis.

OBJECTIVES

The present study aims to examine the testicular expression pattern of DMRTB1 in men showing normal and impaired spermatogenesis.

MATERIALS AND METHODS

Immunohistochemistry was performed using 54 human testicular biopsy specimens and a commercial rabbit polyclonal anti-DMRTB1 primary antibody. RT-PCR complemented immunohistochemistry. To further characterize immunopositive cells and possible co-localization, the proliferation marker Ki-67, the tumor marker PLAP, and an anti-DMRT1 antibody were used.

RESULTS

In men with normal spermatogenesis, a strong immunoreactivity was detectable in a subset of spermatogonia (38.34 ± 2.14%). Some spermatocytes showed a weak immunostaining. Adjacent Sertoli cells were immunonegative. Compared with a hematoxylin and eosin overview staining, these immunopositive cells were almost exclusively identified as A_pale and B spermatogonia and primary spermatocytes in (pre-)leptotene, zygotene, and pachytene stages. In patients with spermatogenic arrest at spermatogonial level, an altered staining pattern was found. No immunoreactivity was detected in Sertoli cells in Sertoli cell-only syndrome. In germ cell neoplasia in situ (GCNIS) tubules, except for a few (0.4 ± 0.03%), pre-invasive tumor cells were immunonegative. Seminoma cells showed no immunostaining.

DISCUSSION

According to previous findings in mice, it seems reasonable that DMRTB1 is expressed in these normal germ cell populations. Moreover, altered staining pattern in spermatogenic arrest at spermatogonial stage suggests a correlation with mitosis and transformation into B spermatogonia. The absence of DMRTB1 in GCNIS cells and tumor cells might be associated with uncontrolled neoplastic cell proliferation and progression into invasive germ cell tumors. Further research is required to elucidate, for example, the role of DMRTB1 in the malignant transformation of human germ cells.

CONCLUSION

Our data indicate a relevant role for DMRTB1 regarding the entry of spermatogonia into meiosis in men.

Genetic regulation of sex determination and maintenance in zebrafish (Danio rerio)

Over the last several decades zebrafish (Danio rerio) has become a major model organism for the study of vertebrate development and physiology. Given this, it may be surprising how little is known about the mechanism that zebrafish use to determine sex. While zebrafish are a gonochoristic species (having two sexes) that do not switch sex as adults, it was appreciated early on that sex ratios obtained from breeding lab domesticated lines were not typically a 1:1 ratio of male and female, suggesting that sex was not determined by a strict chromosomal mechanism. Here we will review the recent progress toward defining the genetic mechanism for sex determination in both wild and domesticated zebrafish.

New insights into the genetics of spermatogenic failure: a review of the literature

Genetic anomalies are known to affect about 15% of infertile patients with azoospermia or severe oligozoospermia. Despite a throughout diagnostic work-up, in up to the 72% of the male partners of infertile couples, no etiological factor can be found; hence, the cause of infertility remains unclear. Recently, several novel genetic causes of spermatogenic failure (SPGF) have been described. The aim of this review was to collect all the available evidence of SPGF genetics, matching data from in-vitro and animal models with those in human beings to provide a comprehensive and updated overview of the genes capable of affecting spermatogenesis. By reviewing the literature, we provided a list of 60 candidate genes for SPGF. Their investigation by Next Generation Sequencing in large cohorts of patients with apparently idiopathic infertility would provide new interesting data about their racial- and ethnic-related prevalence in infertile patients, likely raising the diagnostic yields. We propose a phenotype-based approach to identify the genes to look for.

Genetic regulation of sex determination and maintenance in zebrafish (Danio rerio)

Over the last several decades zebrafish (Danio rerio) has become a major model organism for the study of vertebrate development and physiology. Given this, it may be surprising how little is known about the mechanism that zebrafish use to determine sex. While zebrafish are a gonochoristic species (having two sexes) that do not switch sex as adults, it was appreciated early on that sex ratios obtained from breeding lab domesticated lines were not typically a 1:1 ratio of male and female, suggesting that sex was not determined by a strict chromosomal mechanism. Here we will review the recent progress toward defining the genetic mechanism for sex determination in both wild and domesticated zebrafish.

KIT as a therapeutic target for non-oncological diseases

KIT is a receptor tyrosine kinase that after binding to its ligand stem cell factor activates signaling cascades linked to biological processes such as proliferation, differentiation, migration and cell survival. Based on studies performed on SCF and/or KIT mutant animals that presented anemia, sterility, and/or pigmentation disorders, KIT signaling was mainly considered to be involved in the regulation of hematopoiesis, gametogenesis, and melanogenesis. More recently, novel animal models and ameliorated cellular and molecular techniques have led to the discovery of a widen repertoire of tissue compartments and functions that are being modulated by KIT. This is the case for the lung, heart, nervous system, gastrointestinal tract, pancreas, kidney, liver, and bone. For this reason, the tyrosine kinase inhibitors that were originally developed for the treatment of hemato-oncological diseases are being currently investigated for the treatment of non-oncological disorders such as asthma, rheumatoid arthritis, and alzheimer's disease, among others. The beneficial effects of some of these tyrosine kinase inhibitors have been proven to depend on KIT inhibition. This review will focus on KIT expression and regulation in healthy and pathologic conditions other than cancer. Moreover, advances in the development of anti-KIT therapies, including tyrosine kinase inhibitors, and their application will be discussed.

Primordial follicle activation is affected by the absence of Sohlh1 in mice

Previous studies have reported that only primordial follicles and empty follicles can be found in 7.5 days postparturition (dpp) Sohlh1^-/- mouse ovaries and females are infertility. There appears to be a defect in follicle development during the primordial-to-primary follicle transition in Sohlh1^-/- mouse ovaries. However, detailed analyses of these phenomena have not been performed. In this study, we used Sohlh1^-/- transgenic mice to explore the role of Sohlh1 in folliculogenesis. The results showed that only primordial follicles and empty follicles can be observed in Sohlh1^-/- ovaries from 0.5 to 23.5 dpp. The expression of Foxo3 and FOXO3 was downregulated; nucleocytoplasmic shuttling of FOXO3 was normal in 7.5-dpp Sohlh1^+/+ but not Sohlh1^-/- ovaries; and primordial follicle activation (PFA) was not observed in 7.5-dpp Sohlh1^-/- mice. The expression levels of KIT, AKT, and P308-AKT were downregulated (p < 0.05), whereas that of P473-AKT was not significantly changed (p > 0.05). The KIT/PI3K/AKT pathway was inhibited. Furthermore, we conducted a dual luciferase assay and chromatin immunoprecipitation. The results showed that SOHLH1 can upregulate the Kit gene by binding to the -3698 bp E-box motif. The absence of Sohlh1 may affect PFA in mouse ovaries via downregulation of Kit and inhibition of the KIT/PI3K/AKT pathway.

Single-Cell RNA Sequencing Analysis Reveals Sequential Cell Fate Transition during Human Spermatogenesis

Spermatogenesis generates mature male gametes and is critical for the proper transmission of genetic information between generations. However, the developmental landscapes of human spermatogenesis remain unknown. Here, we performed single-cell RNA sequencing (scRNA-seq) analysis for 2,854 testicular cells from donors with normal spermatogenesis and 174 testicular cells from one nonobstructive azoospermia (NOA) donor. A hierarchical model was established, which was characterized by the sequential and stepwise development of three spermatogonia subtypes, seven spermatocyte subtypes, and four spermatid subtypes. Further analysis identified several stage-specific marker genes of human germ cells, such as HMGA1, PIWIL4, TEX29, SCML1, and CCDC112. Moreover, we identified altered gene expression patterns in the testicular somatic cells of one NOA patient via scRNA-seq analysis, paving the way for further diagnosis of male infertility. Our work allows for the reconstruction of transcriptional programs inherent to sequential cell fate transition during human spermatogenesis and has implications for deciphering male-related reproductive disorders.

GILZ-dependent modulation of mTORC1 regulates spermatogonial maintenance

Male fertility is dependent on spermatogonial stem cells (SSCs) that self-renew and produce differentiating germ cells. Growth factors produced within the testis are essential for SSC maintenance but intrinsic factors that dictate the SSC response to these stimuli are poorly characterised. Here, we have studied the role of GILZ, a TSC22D family protein and spermatogenesis regulator, in spermatogonial function and signalling. Although broadly expressed in the germline, GILZ was prominent in undifferentiated spermatogonia and Gilz deletion in adults resulted in exhaustion of the GFRα1⁺ SSC-containing population and germline degeneration. GILZ loss was associated with mTORC1 activation, suggesting enhanced growth factor signalling. Expression of deubiquitylase USP9X, an mTORC1 modulator required for spermatogenesis, was disrupted in Gilz mutants. Treatment with an mTOR inhibitor rescued GFRα1⁺ spermatogonial failure, indicating that GILZ-dependent mTORC1 inhibition is crucial for SSC maintenance. Analysis of cultured undifferentiated spermatogonia lacking GILZ confirmed aberrant activation of ERK MAPK upstream mTORC1 plus USP9X downregulation and interaction of GILZ with TSC22D proteins. Our data indicate an essential role for GILZ-TSC22D complexes in ensuring the appropriate response of undifferentiated spermatogonia to growth factors via distinct inputs to mTORC1.

A Comprehensive Roadmap of Murine Spermatogenesis Defined by Single-Cell RNA-Seq

Spermatogenesis requires intricate interactions between the germline and somatic cells. Within a given cross section of a seminiferous tubule, multiple germ and somatic cell types co-occur. This cellular heterogeneity has made it difficult to profile distinct cell types at different stages of development. To address this challenge, we collected single-cell RNA sequencing data from ∼35,000 cells from the adult mouse testis and identified all known germ and somatic cells, as well as two unexpected somatic cell types. Our analysis revealed a continuous developmental trajectory of germ cells from spermatogonia to spermatids and identified candidate transcriptional regulators at several transition points during differentiation. Focused analyses delineated four subtypes of spermatogonia and nine subtypes of Sertoli cells; the latter linked to histologically defined developmental stages over the seminiferous epithelial cycle. Overall, this high-resolution cellular atlas represents a community resource and foundation of knowledge to study germ cell development and in vivo gametogenesis.

Protein expression of the transcription factors DMRT1, TCLF5, and OCT4 in selected germ cell neoplasms of the testis

In the present study, we investigated protein expression of the transcription factors mammalian doublesex and mab-3 related transcription factor 1 (DMRT1), basic helix-loop-helix transcription factor-like 5 (TCLF5), and octamer-binding transcription factor 4 (OCT4) in normal human spermatogenesis, testicular mixed germ cell-sex cord stromal tumor (MGC-SCST), spermatocytic tumor, and seminoma. In normal human spermatogenesis, DMRT1 is expressed in the nuclei of spermatogonia but not in those of more mature germ cells. By way of contrast, TCLF5 is expressed in the nuclei of some clusters of primary spermatocytes that have entered meiosis 1, in secondary spermatocytes, and in round (early) spermatids in the seminiferous tubules of adults during the reproductive years. OCT4 is expressed in primordial germ cells but not in the seminiferous tubules of the normal adult testis during the reproductive years. DMRT1 is expressed in the germ cells of both testicular MGC-SCST and spermatocytic tumor, whereas TCLF5 is not expressed in either neoplasm. These low-grade neoplasms, however, differ histologically in that all the germ cell nuclei of testicular MGC-SCST resemble spermatogonia, whereas in spermatocytic tumor, the nuclei of the medium-sized and large cells resemble those of primary spermatocytes. Both neoplasms lack expression of OCT4. By way of contrast, in seminoma, a fully malignant testicular germ cell tumor, the germ cell nuclei express OCT4 but do not express either DMRT1 or TCLF5.

Loss of DMRT1 gene in a Mos 45,XY,-9[8]/46,XY,r(9)[29]/47,XY,+idic r(9)× 2[1]/46,XY,idic r(9)[1]/46,XY[1] female presenting with short stature

Background

A 46,XY sex reversal syndrome is characterized by discordant genetic and phenotypic sex, leading to normal external female genitalia, undeveloped gonads and presence of Müllerian structures in an otherwise 46,XY individual. Chromosome 9pter aberrations, such as ring chromosome have been reported to cause 46,XY disorders of sex development (DSD), due to involvement of DMRT1 gene located at the 9p24.3 region.

Case presentation

This study presents a unique case of a 12-year-old female with mos 46,XY, (r)9[31]/45,XY,-9[9] karyotype, presenting with intellectual disability and short stature, mimicking Turner syndrome. Re-karyotyping was performed using standard GTL-banding technique. Further cytogenetic study using standard metaphase fluorescent in situ hybridization (FISH) technique was applied to cultured lymphocytes from peripheral blood, hybridized using green control probe specific to 9q21 loci, and red DMRT1 probe specific to 9p24.3 loci. Cytogenetics and FISH analysis revealed mos 45,XY,-9[8]/46,XY,r(9)[29]/47,XY,+idic r(9)× 2[1]/46,XY,idic r(9)[1]/46,XY[1] and haploinsufficiency of DMRT1 gene in most cells. CGH array revealed a deletion around 1.25 Mb at 9p24.3 loci [arr 9p24.3(204,193-1,457,665)× 1] and three duplications around 13 Mb [9p24.3p22.3(1,477,660-14,506,754)× 3] near the breakage point that formed the ring chromosome 9.

Conclusions

The clinical presentation of the subject that mimics Turner syndrome highlights the importance of cytogenetic analysis to detect the possibility of ring chromosome 9. Sex reversal due to haploinsufficiency of DMRT1 gene in ring chromosome 9 structures is exceedingly rare with only a handful of cases ever reported. This finding further highlights the importance of DMRT1 gene in sex determination and differentiation in males. More research is required to pinpoint the exact mechanism that underlies sex reversal caused by DMRT1 haploinsufficiency.

Expression and cellular localization of double sex and mab-3 related transcription factor 1 in testes of postnatal Small-Tail Han sheep at different developmental stages

Double sex and mab-3 related transcription factor 1 (Dmrt1), an evolutionarily conserved gene, is a sex-related gene expressed in male gonads, that is involved in the regulation of sex differentiation, testicular development and reproductive function maintenance. Until now, functional studies on the Dmrt1 gene in sheep (Ovis aries) have been lacking. In this study, testis, heart, liver, spleen, lung, kidney and longissimus dorsi muscle tissues were collected from Small-Tail Han sheep at 0, 2, 5, 12 and 24months after birth (mab). Dmrt1 expression and cellular localization were detected in various testicular tissues by quantitative real time PCR (qRT-PCR), western blot and immunohistochemistry methods. The morphological structures of testicular tissues at different developmental stages were observed by hematoxylin & eosin (HE) staining. The Dmrt1 mRNA expression levels in 12 and 24 mab sheep were significantly higher than those in 0 and 2 mab sheep (P<0.05), and Dmrt1 protein expression showed a similar trend. The qRT-PCR results in various tissues at 12 mab showed that Dmrt1 mRNA was predominantly expressed in testes. Immunohistochemical staining in testes at different developmental stages showed that Dmrt1 protein immunoreactive responses were mainly localized in Sertoli cells and gonocytes at 0, 2 and 5 mab, while they were localized in spermatocytes, sperm cells and some spermatogonia and Sertoli cells at 12 and 24 mab. We speculate that the Dmrt1 gene plays a vital role in postnatal sheep spermatogenesis, perhaps by regulating the maturation and functional maintenance of Sertoli cells, the proliferation and differentiation of gonocytes in prepubertal sheep testes, and the mitosis and meiosis of germ cells in adult sheep, but the specific mechanisms underlying these phenomena must be further studied and verified.

ABBREVIATIONS

Human spermatogonial markers

In this review, we provide an up-to-date compilation of published human spermatogonial markers, with focus on the three nuclear subtypes A_dark, A_pale and B. In addition, we have extended our recently published list of putative spermatogonial markers with protein expression and RNA-sequencing data from the Human Protein Atlas and supported these by literature evidence. Most importantly, we have put substantial effort in acquiring a comprehensive list of new and potentially interesting markers by refiltering the raw data of 15 published germ cell expression datasets (four human, eleven rodent) and subsequent building of intersections to acquire a robust, cross-species set of spermatogonia-enriched or -specific transcripts.

Mapping the expression of the sex determining factor Doublesex1 in Daphnia magna using a knock-in reporter

Sexually dimorphic traits are common and widespread among animals. The expression of the Doublesex-/Mab-3-domain (DM-domain) gene family has been widely studied in model organisms and has been proven to be essential for the development and maintenance of sex-specific traits. However, little is known about the detailed expression patterns in non-model organisms. In the present study, we demonstrated the spatiotemporal expression of the DM-domain gene, doublesex1 (dsx1), in the crustacean Daphnia magna, which parthenogenetically produces males in response to environmental cues. We developed a dsx1 reporter strain to track dsx1 activity in vivo by inserting the mCherry gene into the dsx1 locus using the TALEN-mediated knock-in approach. After confirming dsx1 expression in male-specific traits in juveniles and adults, we performed time-lapse imaging of embryogenesis. Shortly after gastrulation stage, a presumptive primary organiser, named cumulus, first showed male-specific dsx1 expression. This cell mass moved to the posterior growth zone that distributes dsx1-expressing progenitor cells across the body during axial elongation, before embryos start male-specific dsx1 expression in sexually dimorphic structures. The present study demonstrated the sex-specific dsx1 expression in cell populations involved in basal body formation.

Mono-butyl phthalate-induced mouse testis injury is associated with oxidative stress and down-regulated expression of Sox9 and Dazl

Mono-butyl phthalate (MBP) has reproductive toxicity but the related mechanisms have not been fully elucidated in vivo. We exposed male Balb/c mice to MBP by gavage at doses of 0, 25, 50, 100, 200 mg/kg for 14 days, and then evaluated the testicular alterations at the histological and molecular levels. MBP reduced mouse sperm count along with sperm malformation and seminiferous tubule degeneration in a dose-dependent manner. MBP dosed at 200 mg/kg significantly increased reactive oxygen species and malondialdehyde content in mouse testes. High doses of MBP (200 mg/kg) also significantly reduced mRNA expressions of testis growth and function related genes (Sox9 and Dazl). Our findings suggest that oxidative stress and down-regulated expression of Sox9 and Dazl may play important roles in MBP-induced testis injury.

Regulation of mitosis-meiosis transition by the ubiquitin ligase β-TrCP in male germ cells

The mitosis-meiosis transition is essential for spermatogenesis. Specific and timely downregulation of the transcription factor DMRT1, and consequent induction of Stra8 expression, is required for this process in mammals, but the molecular mechanism has remained unclear. Here, we show that β-TrCP, the substrate recognition component of an E3 ubiquitin ligase complex, targets DMRT1 for degradation and thereby controls the mitosis-meiosis transition in mouse male germ cells. Conditional inactivation of β-TrCP2 in male germ cells of β-TrCP1 knockout mice resulted in sterility due to a lack of mature sperm. The β-TrCP-deficient male germ cells did not enter meiosis, but instead underwent apoptosis. The induction of Stra8 expression was also attenuated in association with the accumulation of DMRT1 at the Stra8 promoter in β-TrCP-deficient testes. DMRT1 contains a consensus β-TrCP degron sequence that was found to bind β-TrCP. Overexpression of β-TrCP induced the ubiquitylation and degradation of DMRT1. Heterozygous deletion of Dmrt1 in β-TrCP-deficient spermatogonia increased meiotic cells with a concomitant reduction of apoptosis. Collectively, our data indicate that β-TrCP regulates the transition from mitosis to meiosis in male germ cells by targeting DMRT1 for degradation.

Polycomb directs timely activation of germline genes in spermatogenesis

Maezawa et al. show that Polycomb-repressive complex 1 (PRC1) directs timely activation of germline genes during spermatogenesis.

During spermatogenesis, a large number of germline genes essential for male fertility are coordinately activated. However, it remains unknown how timely activation of this group of germline genes is accomplished. Here we show that Polycomb-repressive complex 1 (PRC1) directs timely activation of germline genes during spermatogenesis. Inactivation of PRC1 in male germ cells results in the gradual loss of a stem cell population and severe differentiation defects, leading to male infertility. In the stem cell population, RNF2, the dominant catalytic subunit of PRC1, activates transcription of Sall4, which codes for a transcription factor essential for subsequent spermatogenic differentiation. Furthermore, RNF2 and SALL4 together occupy transcription start sites of germline genes in the stem cell population. Once differentiation commences, these germline genes are activated to enable the progression of spermatogenesis. Our study identifies a novel mechanism by which Polycomb directs the developmental process by activating a group of lineage-specific genes.

Germline Stem Cell Activity Is Sustained by SALL4-Dependent Silencing of Distinct Tumor Suppressor Genes

Sustained spermatogenesis in adult males and fertility recovery following germ cell depletion are dependent on undifferentiated spermatogonia. We previously demonstrated a key role for the transcription factor SALL4 in spermatogonial differentiation. However, whether SALL4 has broader roles within spermatogonia remains unclear despite its ability to co-regulate genes with PLZF, a transcription factor required for undifferentiated cell maintenance. Through development of inducible knockout models, we show that short-term integrity of differentiating but not undifferentiated populations requires SALL4. However, SALL4 loss was associated with long-term functional decline of undifferentiated spermatogonia and disrupted stem cell-driven regeneration. Mechanistically, SALL4 associated with the NuRD co-repressor and repressed expression of the tumor suppressor genes Foxl1 and Dusp4. Aberrant Foxl1 activation inhibited undifferentiated cell growth and survival, while DUSP4 suppressed self-renewal pathways. We therefore uncover an essential role for SALL4 in maintenance of undifferentiated spermatogonial activity and identify regulatory pathways critical for germline stem cell function.

DMRT proteins and coordination of mammalian spermatogenesis

DMRT genes encode a deeply conserved family of transcription factors that share a unique DNA binding motif, the DM domain. DMRTs regulate development in a broad variety of metazoans and they appear to have controlled sexual differentiation for hundreds of millions of years. In mice, starting during embryonic development, three Dmrt genes act sequentially to help establish and maintain spermatogenesis. Dmrt1 has notably diverse functions that include repressing pluripotency genes and promoting mitotic arrest in embryonic germ cells, reactivating prospermatogonia perinatally, establishing and maintaining spermatogonial stem cells (SSCs), promoting spermatogonial differentiation, and controlling the mitosis/meiosis switch. Dmrt6 acts in differentiating spermatogonia to coordinate an orderly exit from the mitotic/spermatogonial program and allow proper timing of entry to the meiotic/spermatocyte program. Finally, Dmrt7 takes over during the first meiotic prophase to help choreograph a transition in histone modifications that maintains transcriptional silencing of the sex chromosomes. The combined action of these three Dmrt genes helps ensure robust and sustainable spermatogenesis.

Gene knockout of Zmym3 in mice arrests spermatogenesis at meiotic metaphase with defects in spindle assembly checkpoint

ZMYM3, a member of the MYM-type zinc finger protein family and a component of a LSD1-containing transcription repressor complex, is predominantly expressed in the mouse brain and testis. Here, we show that ZMYM3 in the mouse testis is expressed in somatic cells and germ cells until pachytene spermatocytes. Knockout (KO) of Zmym3 in mice using the CRISPR-Cas9 system resulted in adult male infertility. Spermatogenesis of the KO mice was arrested at the metaphase of the first meiotic division (MI). ZMYM3 co-immunoprecipitated with LSD1 in spermatogonial stem cells, but its KO did not change the levels of LSD1 or H3K4me1/2 or H3K9me2. However, Zmym3 KO resulted in elevated numbers of apoptotic germ cells and of MI spermatocytes that are positive for BUB3, which is a key player in spindle assembly checkpoint. Zmym3 KO also resulted in up-regulated expression of meiotic genes in spermatogonia. These results show that ZMYM3 has an essential role in metaphase to anaphase transition during mouse spermatogenesis by regulating the expression of diverse families of genes.