Dynamic expression of DNMT3a and DNMT3b isoforms during male germ cell development in the mouse

Different expression patterns of DNA methyltransferases during horse testis development

DNA methyltransferases (DNMTs) are important epigenetic modification during spermatogenesis. To further evaluate the pattern of DNMTs in horse testes during development, we investigated the expression and localization of DNMT1, DNMT3a and DNMT3b at different time points. The qRT-PCR results showed that DNMT1 expression was maintained in testes tissue from 6-month-old (0.5y) to 2-year-old (2y) of age and decreased after 3-year-old (3y) (P < 0.01). The expression levels of DNMT3a and DNMT3b peaked in testes tissue at 3y (P < 0.01). At 4-year-old (4y), the expression of DNMT3a and DNMT3b was decreased and became similar to that at 0.5y. Immunofluorescence of DNMT1, DNMT3a and DNMT3b on testis samples confirmed the differential expression and localization of these three DNA methylation transferases during horse development. Further molecular biological studies are needed to understand the implications of the expression patterns of these DNMTs in horse testes.

Adverse effects of bisphenol A and its analogues on male fertility: An epigenetic perspective

In recent years, there has been growing concern about the adverse effects of endocrine disrupting chemicals (EDCs) on male fertility. Epigenetic modification is critical for male germline development, and has been suggested as a potential mechanism for impaired fertility induced by EDCs. Bisphenol A (BPA) has been recognized as a typical EDC. BPA and its analogues, which are still widely used in various consumer products, have garnered increasing attention due to their reproductive toxicity and the potential to induce epigenetic alteration. This literature review provides an overview of studies investigating the adverse effects of bisphenol exposures on epigenetic modifications and male fertility. Existing studies provide evidence that exposure to bisphenols can lead to adverse effects on male fertility, including declined semen quality, altered reproductive hormone levels, and adverse reproductive outcomes. Epigenetic patterns, including DNA methylation, histone modification, and non-coding RNA expression, can be altered by bisphenol exposures. Transgenerational effects, which influence the fertility and epigenetic patterns of unexposed generations, have also been identified. However, the magnitude and direction of certain outcomes varied across different studies. Investigations into the dynamics of histopathological and epigenetic alterations associated with bisphenol exposures during developmental stages can enhance the understanding of the epigenetic effects of bisphenols, the implication of epigenetic alteration on male fertility, and the health of successive generation.

Preconception paternal mental disorders and child health: Mechanisms and interventions

Mental illness is a significant global health issue with a steady prevalence. High heritability is suspected, but genome-wide association studies only identified a small number of risk genes associated with mental disorders. This 'missing inheritance' can be partially explained by epigenetic heredity. Evidence from numerous animal models and human studies supports the possibility that preconception paternal mental health influences their offspring's mental health via nongenetic means. Here, we review two potential pathways, including sperm epigenetics and seminal plasma components. The current review highlights the role of sperm epigenetics and explores epigenetic message origination and susceptibility to chronic stress. Meanwhile, possible spatiotemporal windows and events that induce sexually dimorphic modes and effects of paternal stress transmission are inferred in this review. Additionally, we discuss emerging interventions that could potentially block the intergenerational transmission of paternal psychiatric disorders and reduce the incidence of mental illness. Understanding the underlying mechanisms by which preconception paternal stress impacts offspring health is critical for identifying strategies supporting healthy development and successfully controlling the prevalence of mental illness.

Genetic control of meiosis surveillance mechanisms in mammals

Meiosis is a specialized cell division that generates haploid gametes and is critical for successful sexual reproduction. During the extended meiotic prophase I, homologous chromosomes progressively pair, synapse and desynapse. These chromosomal dynamics are tightly integrated with meiotic recombination (MR), during which programmed DNA double-strand breaks (DSBs) are formed and subsequently repaired. Consequently, parental chromosome arms reciprocally exchange, ultimately ensuring accurate homolog segregation and genetic diversity in the offspring. Surveillance mechanisms carefully monitor the MR and homologous chromosome synapsis during meiotic prophase I to avoid producing aberrant chromosomes and defective gametes. Errors in these critical processes would lead to aneuploidy and/or genetic instability. Studies of mutation in mouse models, coupled with advances in genomic technologies, lead us to more clearly understand how meiosis is controlled and how meiotic errors are linked to mammalian infertility. Here, we review the genetic regulations of these major meiotic events in mice and highlight our current understanding of their surveillance mechanisms. Furthermore, we summarize meiotic prophase genes, the mutations that activate the surveillance system leading to meiotic prophase arrest in mouse models, and their corresponding genetic variants identified in human infertile patients. Finally, we discuss their value for the diagnosis of causes of meiosis-based infertility in humans.

Mechanisms of chromatin-based epigenetic inheritance

Multi-cellular organisms such as humans contain hundreds of cell types that share the same genetic information (DNA sequences), and yet have different cellular traits and functions. While how genetic information is passed through generations has been extensively characterized, it remains largely obscure how epigenetic information encoded by chromatin regulates the passage of certain traits, gene expression states and cell identity during mitotic cell divisions, and even through meiosis. In this review, we will summarize the recent advances on molecular mechanisms of epigenetic inheritance, discuss the potential impacts of epigenetic inheritance during normal development and in some disease conditions, and outline future research directions for this challenging, but exciting field.

DNA methylome of primary spermatocyte reveals epigenetic dysregulation associated with male sterility of cattleyak

DNA cytosine methylation modification in the germline is of particular importance since it is a highly heritable epigenetic mark. Although cytosine methylation has been analyzed at the genome-scale for several mammalian species, our knowledge of DNA methylation patterns and the mechanisms underlying male hybrid sterility is still limited in domestic animals such as cattleyak. Here we for the first time show the genome-wide and single-base resolution landscape of methylcytosines (mC) in the primary spermatocyte (PSC) genome of yak with normal spermatogenesis and the inter-specific hybrid cattleyak with male infertility. A comparative investigation revealed that widespread differences are observed in the composition and patterning of DNA cytosine methylation between the two methylomes. Global CG or non-CG DNA methylation levels, as well as the number of mC sites, are increased in cattleyak compared to yak. Notably, the DNA methylome in cattleyak PSC exhibits promoter hypermethylation of meiosis-specific genes and piRNA pathway genes with respect to yak. Furthermore, major retrotransposonson classes are predominantly hypermethylated in cattleyak while those are fully hypomethylated in yak. KEGG pathway enrichment indicates Rap1 signaling and MAPK pathways may play potential roles in the spermatogenic arrest of cattleyak. Our present study not only provides valuable insights into distinct features of the cattleyak PSC methylome but also paves the way toward elucidating the complex, yet highly coordinated epigenetic modification during male germline development for inter-specific hybrid animals.

ZFP541 maintains the repression of pre-pachytene transcriptional programs and promotes male meiosis progression

The DSB machinery, which induces the programmed DNA double-strand breaks (DSBs) in the leptotene and zygotene stages during meiosis, is suppressed before the onset of the pachytene stage. However, the biological significance and underlying mechanisms remain largely unclear. Here, we report that ZFP541 is indispensable for the suppression of DSB formation after mid-pachytene. The deletion of Zfp541 in mice causes the aberrant recruitment of DSB machinery to chromosome axes and generation of massive DSBs in late pachytene and diplotene spermatocytes, leading to meiotic arrest at the diplotene stage. Integrated analysis of single-cell RNA sequencing (scRNA-seq) and chromatin immunoprecipitation (ChIP) sequencing data indicate that ZFP541 predominantly binds to promoters of pre-pachytene genes, including meiotic DSB formation-related genes (e.g., Prdm9 and Mei1) and their upstream activators (e.g., Meiosin and Rxra), and maintains their repression in pachytene spermatocytes. Our results reveal that ZFP541 functions as a transcriptional regulator in pachytene spermatocytes, orchestrating the transcriptome to ensure meiosis progression.

Tumor suppressor CEBPA interacts with and inhibits DNMT3A activity

DNA methyltransferases (DNMTs) catalyze DNA methylation, and their functions in mammalian embryonic development and diseases including cancer have been extensively studied. However, regulation of DNMTs remains under study. Here, we show that CCAAT/enhancer binding protein α (CEBPA) interacts with the long splice isoform DNMT3A, but not the short isoform DNMT3A2. CEBPA, by interacting with DNMT3A N-terminus, blocks DNMT3A from accessing DNA substrate and thereby inhibits its activity. Recurrent tumor-associated CEBPA mutations, such as preleukemic CEBPA^N321D mutation, which is particularly potent in causing AML with high mortality, disrupt DNMT3A association and cause aberrant DNA methylation, notably hypermethylation of PRC2 target genes. Consequently, leukemia cells with the CEBPA^N321D mutation are hypersensitive to hypomethylation agents. Our results provide insights into the functional difference between DNMT3A isoforms and the regulation of de novo DNA methylation at specific loci in the genome. Our study also suggests a therapeutic strategy for the treatment of CEBPA-mutated leukemia with DNA-hypomethylating agents.

Short-Term Hypothermic Holding of Mouse Immature Testicular Tissue Does Not Alter the Expression of DNA Methyltransferases and Global DNA Methylation Level, Post-Organotypic Culture

INTRODUCTION

Cryopreservation of immature-testicular-tissue (ITT) prior to gonadotoxic treatment, while experimental, is the only recommended option for fertility preservation in prepubertal boys. The handling and manipulation of ITT prior to banking could influence the functionality, genetic and epigenetic integrity of cells.

OBJECTIVES

To investigate the impact of length of hypothermic holding of mouse ITT on the relative mRNA expression of the DNA methyltransferases (DNMTs) and global DNA methylation, post 14-days of organotypic culture.

METHODS

ITT from 6-day old mice were handled at hypothermic temperature (4 °C) for 6 and 24 h prior to 14-days organotypic culture. Relative mRNA expression of Dnmt1, Dnmt3a, and Dnmt3b along with global DNA methylation was measured from the cultured ITT.

RESULTS

No significant variation in the expression of Dnmt1, Dnmt3a, and Dnmt3b was observed in relation to varying holding time periods used. Further, global DNA methylation was comparable between 0, 6 and 24 h holding groups.

CONCLUSIONS

Short-term holding of ITT at 4 °C does not affect the DNA methylation process post organotypic culture. While fully acknowledging the limitations of this approach in the mouse model, the results we presented in this report will be of significant interest to the field.

Dnmt3aa but Not Dnmt3ab Is Required for Maintenance of Gametogenesis in Nile Tilapia (Oreochromis niloticus)

Dnmt3a, a de novo methyltransferase, is essential for mammalian germ line DNA methylation. Only one Dnmt3a is identified in mammals, and homozygous mutants of Dnmt3a are lethal, while two Dnmt3a paralogs, dnmt3aa and dnmt3ab, are identified in teleosts due to the third round of genome duplication, and homozygous mutants of dnmt3aa and dnmt3ab are viable in zebrafish. The expression patterns and roles of dnmt3aa and dnmt3ab in gonadal development remain poorly understood in teleosts. In this study, we elucidated the precise expression patterns of dnmt3aa and dnmt3ab in tilapia gonads. Dnmt3aa was highly expressed in oogonia, phase I and II oocytes and granulosa cells in ovaries and spermatogonia and spermatocytes in testes, while dnmt3ab was mainly expressed in ovarian granulosa cells and testicular spermatocytes. The mutation of dnmt3aa and dnmt3ab was achieved by CRISPR/Cas9 in tilapia. Lower gonadosomatic index (GSI), increased apoptosis of oocytes and spermatocytes and significantly reduced sperm quality were observed in dnmt3aa^−/− mutants, while normal gonadal development was observed in dnmt3ab^−/− mutants. Consistently, the expression of apoptotic genes was significantly increased in dnmt3aa^−/− mutants. In addition, the 5-methylcytosine (5-mC) level in dnmt3aa^−/− gonads was decreased significantly, compared with that of dnmt3ab^−/− and wild type (WT) gonads. Taken together, our results suggest that dnmt3aa, not dnmt3ab, plays important roles in maintaining gametogenesis in teleosts.

Curcumin as an indirect methylation inhibitor modulates the effects of Toxoplasma gondii on genes involved in male fertility

Toxoplasma gondii is a common protozoan parasite, which infects warm-blooded mammals, including mice and humans, throughout the world. The negative effects of T. gondii infection on the human reproductive system have been documented, especially in females. However, only few studies have examined the effects of T. gondii infection on the male reproductive system. Previous research shows that T. gondii can induce DNA methylation in some gene promoters, which are key regulators of spermatogenesis. Therefore, this study aimed to evaluate the effects of curcumin on the activity of DNA methyltransferases (DNMTs), as well as selected genes, involved in spermatogenesis in spermatogenic cells. In the spermatogenic cells exposed to T. gondii, there was a significant increase in DNMT1 and DNMT3A gene expression and a significant reduction in HSPA1A, MTHR, and DAZL gene expression, compared to the controls. The present results showed that curcumin could regulate changes in T. gondii-mediated gene expression. The effect of T. gondii on DNMT activity was also investigated in this study. A 40 % increase in DNMT activity was observed due to T. gondii infection. However, DNMT activity was restored by treatment with 20 μM curcumin for eight hours. The results revealed that T. gondii increases the NF-κB activity, compared to the control group. The increase in NF-κB activity, induced by T. gondii, was inhibited by curcumin. In conclusion, T. gondii, by increasing DNMT expression and activity, leads to an increase in NF-κB activity in cells. On the other hand, curcumin reduced DNA methylation, induced by T. gondii, owing to its NF-κB-inhibiting properties. Therefore, curcumin, as a hypomethylating agent, can be potentially used to alleviate the negative effects of T. gondii on the male reproductive system.

Differential expression of DNA methyltransferases and demethylases among the various testicular germ cell tumor subtypes

Aim: Characterize DNA methyltransferases/demethylases expression in testicular germ cell tumors (TGCTs). Methods:In silico analysis of TCGA database, assessment of transcript levels of most relevant enzymes in four TGCT cell lines and validation in patient cohort (real-time quantitative polymerase chain reaction; immunohistochemistry). Results:DNMT3A, DNMT3B and TET2 were the most differentially expressed between seminomas (SEs) and nonseminomas (NSs). DNMT3B was significantly overexpressed in NS-related cell lines, and the opposite was found for TET2. Significantly higher DNMT3A/B mRNA expression was observed in NS, indicating a role for de novo methylation in reprogramming. Significantly higher TET2 protein expression was observed in SEs, suggesting active demethylation contributes for SE hypomethylated state. More differentiated histologies disclosed distinct expression patterns. Conclusion: DNA-modifying enzymes are differentially expressed between TGCT subtypes, influencing reprogramming and differentiation.

Prenatal Exposure to Bisphenol A, E, and S Induces Transgenerational Effects on Male Reproductive Functions in Mice

This study was performed to examine the transgenerational effects of bisphenol (BP) A analogs, BPE, and BPS on male reproductive functions using mice as a model. CD-1 mice (F0) were orally exposed to control treatment (corn oil), BPA, BPE, or BPS (0.5 or 50 µg/kg/day) from gestational day 7 (the presence of vaginal plug = 1) to birth. Mice from F1 and F2 offspring were used to generate F3 males. Prenatal exposure to BPA, BPE, and BPS decreased sperm counts and/or motility and disrupted the progression of germ cell development as morphometric analyses exhibited an abnormal distribution of the stages of spermatogenesis in F3 males. Dysregulated serum levels of estradiol-17β and testosterone, as well as expression of steroidogenic enzymes in F3 adult testis were also observed. In the neonatal testis, although apoptosis and DNA damage were not affected, mRNA levels of DNA methyltransferases, histone methyltransferases, and their associated factors were increased by BP exposure. Furthermore, BP exposure induced immunoreactive expression of DNMT3A in Sertoli cells, strengthened DNMT3B, and weakened H3K9me2 and H3K9me3 in germ cells of the neonatal testis, whereas DNMT1, H3K4me3, and H3K27ac were not affected. In adult testis, stage-specific DNMT3B was altered by BP exposure, although DNMT3A, H3K9me2, and H3K9me3 expression remained stable. These results suggest that prenatal exposure to BPA, BPE, and BPS induces transgenerational effects on male reproductive functions probably due to altered epigenetic modification following disruption of DNMTs and histone marks in the neonatal and/or adult testis.

Global changes in epigenomes during mouse spermatogenesis: possible relation to germ cell apoptosis

Mammalian spermatogenesis is characterized by disproportionate germ cell apoptosis. The high frequency of apoptosis is considered a safety mechanism that serves to avoid unfavorable transmission of paternal aberrant genetic information to the offspring as well as elimination mechanism for removal of overproduced immature or damaged spermatogenic cells. The molecular mechanisms involved in the induction of germ cell apoptosis include both intrinsic mitochondrial Bcl-2/Bax and extrinsic Fas/FasL pathways. However, little is known about the nuclear trigger of those systems. Recent studies indicate that epigenomes are essential in the regulation of gene expression through remodeling of the chromatin structure, and are genome-like transmission materials that reflect the effects of various environmental factors. In spermatogenesis, epigenetic errors can act as the trigger for elimination of germ cells with abnormal chromatin structure, abnormal gene expression and/or morphological defects (disordered differentiation). In this review, we focus on the relationship between global changes in epigenetic parameters and germ cell apoptosis in mice and other mammals.

The preconception environment and sperm epigenetics

BACKGROUND

Infertility is a common reproductive disorder, with male factor infertility accounting for approximately half of all cases. Taking a paternal perceptive, recent research has shown that sperm epigenetics, such as changes in DNA methylation, histone modification, chromatin structure, and noncoding RNA expression, can impact reproductive and offspring health. Importantly, environmental conditions during the preconception period has been demonstrated to shape sperm epigenetics.

OBJECTIVES

To provide an overview on epigenetic modifications that regulate normal gene expression and epigenetic remodeling that occurs during spermatogenesis, and to discuss the epigenetic alterations that may occur to the paternal germline as a consequence of preconception environmental conditions and exposures.

MATERIALS AND METHODS

We examined published literature available on databases (PubMed, Google Scholar, ScienceDirect) focusing on adult male preconception environmental exposures and sperm epigenetics in epidemiologic studies and animal models.

RESULTS

The preconception period is a sensitive developmental window in which a variety of exposures such as toxicants, nutrition, drugs, stress, and exercise, affects sperm epigenetics.

DISCUSSION AND CONCLUSION

Understanding the environmental legacy of the sperm epigenome during spermatogenesis will enhance our understanding of reproductive health and improve reproductive success and offspring well-being.

DNA methylation and the core pluripotency network

From the onset of fertilization, the genome undergoes cell division and differentiation. All of these developmental transitions and differentiation processes include cell-specific signatures and gradual changes of the epigenome. Understanding what keeps stem cells in the pluripotent state and what leads to differentiation are fascinating and biomedically highly important issues. Numerous studies have identified genes, proteins, microRNAs and small molecules that exert essential effects. Notably, there exists a core pluripotency network that consists of several transcription factors and accessory proteins. Three eminent transcription factors, OCT4, SOX2 and NANOG, serve as hubs in this core pluripotency network. They bind to the enhancer regions of their target genes and modulate, among others, the expression levels of genes that are associated with Gene Ontology terms related to differentiation and self-renewal. Also, much has been learned about the epigenetic rewiring processes during these changes of cell fate. For example, DNA methylation dynamics is pivotal during embryonic development. The main goal of this review is to highlight an intricate interplay of (a) DNA methyltransferases controlling the expression levels of core pluripotency factors by modulation of the DNA methylation levels in their enhancer regions, and of (b) the core pluripotency factors controlling the transcriptional regulation of DNA methyltransferases. We discuss these processes both at the global level and in atomistic detail based on information from structural studies and from computer simulations.

Goat DNMT3B: An indel mutation detection, association analysis with litter size and mRNA expression in gonads

DNA methyltransferase 3β (DNMT3B) is a gene encoding a de novo methylation enzyme that is required for DNA methylation during mammalian embryo development. Previous genome-wide association analysis suggested DNMT3B is a candidate gene for goat fertility, but there is no study on the effect of DNMT3B on litter size in goat. The aim of this study was to identify possible insertion/deletion (indel) mutations associated with litter size. Seven putative indels were designed to study their association with litter size, but just one 11-bp insertion variant of intron 22 (the last intron) was found in healthy female Shaanbei white cashmere goats (SBWC goats) (n = 1534). Statistical analysis showed that the 11-bp insertion was related to the first-born litter size (P < 0.01) and the goats with the deletion/deletion genotype had a higher average first-born litter size (P < 0.01). In addition, the expression profile of the DNMT3B mRNA in goat was detected, which revealed significant differences in DNMT3B mRNA expression in the gonads. Additionally, the results of western blotting revealed that the ovaries of mothers of multi-lamb (MML) had a higher level of DNMT3B protein than the ovaries of mothers of single-lamb (MSL). Furthermore, the mRNA of DNMT3B was widely expressed in male goats. Differences in mRNA expression levels were observed in the ovaries of MSL and MML. These findings indicated that the 11-bp indel in DNMT3B was significantly associated with first-born litter size, which can be used for marker-assisted selection (MAS) of goats for breeding.

Disorders of Sexual Development: Current Status and Progress in the Diagnostic Approach

Disorders of sexual development (DSD) are conditions with an atypical chromosomal, gonadal or phenotypic sex, which leads to differences in the development of the urogenital tract and different clinical phenotypes. Some genes have been implicated in the sex development during gonadal and functional differentiation where the maintenance of the somatic sex of the gonad as either male or female is achieved by suppression of the alternate route. The diagnosis of DSD requires a structured approach, involving a multidisciplinary team and different molecular techniques. We discuss the dimorphic genes and the specific pathways involved in gonadal differentiation, as well as new techniques for genetic analysis and their diagnostic value including epigenetic mechanisms, expanding the evidence in the diagnostic approach of individuals with DSD to increase knowledge of the etiology.

Does co-transplantation of mesenchymal and spermatogonial stem cells improve reproductive efficiency and safety in mice?

Background

Spermatogonial stem cell transplantation (SSCT) is a promising therapy in restoring the fertility of childhood cancer survivors. However, the low efficiency of SSCT is a significant concern. SSCT could be improved by co-transplanting transforming growth factor beta 1 (TGFβ1)-induced mesenchymal stem cells (MSCs). In this study, we investigated the reproductive efficiency and safety of co-transplanting spermatogonial stem cells (SSCs) and TGFβ1-induced MSCs.

Methods

A mouse model for long-term infertility was used to transplant SSCs (SSCT, n = 10) and a combination of SSCs and TGFβ1-treated MSCs (MSi-SSCT, n = 10). Both transplanted groups and a fertile control group (n = 7) were allowed to mate naturally to check the reproductive efficiency after transplantation. Furthermore, the testes from transplanted males and donor-derived male offspring were analyzed for the epigenetic markers DNA methyltransferase 3A (DNMT3A) and histone 4 lysine 5 acetylation (H4K5ac).

Results

The overall tubular fertility index (TFI) after SSCT (76 ± 12) was similar to that after MSi-SSCT (73 ± 14). However, the donor-derived TFI after MSi-SSCT (26 ± 14) was higher compared to the one after SSCT (9 ± 5; P = 0.002), even after injecting half of the number of SSCs in MSi-SSCT. The litter sizes after SSCT (3.7 ± 3.7) and MSi-SSCT (3.7 ± 3.6) were similar but differed significantly with the control group (7.6 ± 1.0; P < 0.001). The number of GFP⁺ offspring per litter obtained after SSCT (1.6 ± 0.5) and MSi-SSCT (2.0 ± 1.0) was also similar. The expression of DNMT3A and H4K5ac in germ cells of transplanted males was found to be significantly reduced compared to the control group. However, in donor-derived offspring, DNMT3A and H4K5ac followed the normal pattern.

Conclusion

Co-transplanting SSCs and TGFβ1-treated MSCs results in reproductive efficiency as good as SSCT, even after transplanting half the number of SSCs. Although transplanted males showed lower expression of DNMT3A and H4K5ac in donor-derived germ cells, the expression was restored to normal levels in germ cells of donor-derived offspring. This procedure could become an efficient method to restore fertility in a clinical setup, but more studies are needed to ensure safety in the long term.

Developmental kinetics and transcriptome dynamics of stem cell specification in the spermatogenic lineage

Continuity, robustness, and regeneration of cell lineages relies on stem cell pools that are established during development. For the mammalian spermatogenic lineage, a foundational spermatogonial stem cell (SSC) pool arises from prospermatogonial precursors during neonatal life via mechanisms that remain undefined. Here, we mapped the kinetics of this process in vivo using a multi-transgenic reporter mouse model, in silico with single-cell RNA sequencing, and functionally with transplantation analyses to define the SSC trajectory from prospermatogonia. Outcomes revealed that a heterogeneous prospermatogonial population undergoes dynamic changes during late fetal and neonatal development. Differential transcriptome profiles predicted divergent developmental trajectories from fetal prospermatogonia to descendant postnatal spermatogonia. Furthermore, transplantation analyses demonstrated that a defined subset of fetal prospermatogonia is fated to function as SSCs. Collectively, these findings suggest that SSC fate is preprogrammed within a subset of fetal prospermatogonia prior to building of the foundational pool during early neonatal development.

In neonatal testes, prospermatogonia generate both spermatogonia for the first wave of spermatogenesis and spermatogonial stem cells (SSCs) for maintenance of spermatogenesis in males. Here the authors characterize the development of mouse SSCs from prospermatogonia using single-cell RNA-seq and transplantation assays.

DNA methylation and histone post-translational modifications in the mouse germline following in-vitro maturation of fresh or cryopreserved prepubertal testicular tissue

RESEARCH QUESTION

Do cryopreservation and in-vitro culture procedures affect the expression of DNA methyltransferases (DNMT) and histone-modifying enzymes, as well as the establishment of DNA methylation and histone post-translational modifications (PTM) in germ cells in prepubertal mouse testicular tissue?

DESIGN

This study investigated the expression of epigenetic modification enzymes, DNA methylation and histone PTM, and the spermatogenic progression after in-vitro maturation of fresh or cryopreserved mouse prepubertal testicular tissue. Fresh or cryopreserved testicular fragments from 6-7 days post-partum mice were cultured for 30 days in the presence of retinol with or without FSH.

RESULTS

The in-vitro maturation of fresh or cryopreserved tissue allowed the differentiation of spermatogonia into spermatozoa. Differences in the levels of transcripts encoding epigenetic modification enzymes (Dnmt1, Dnmt3a, Jarid1b, Src1, Sirt1, Hdac1) were found between 30-day tissue cultures and age-matched in-vivo controls. DNMT1/DNMT3a expression and the presence of 5-methylcytosine (5mC) were detected in spermatogonia and leptotene/zygotene spermatocytes in cultures. The relative 5mC fluorescence intensity was similar in spermatozoa produced in cultures of cryopreserved tissues or in vivo. H3K4me3, H3K9ac and H4K8ac were present in all germ cell types but differences in the proportion of germ cells containing these epigenetic marks were found after cultures.

CONCLUSIONS

Despite differences with the in-vivo situation, DNA methylation and histone methylation and acetylation occur in the mouse germline in in-vitro matured fresh or cryopreserved mouse prepubertal testicular tissue, and the expression of the enzymes catalysing these epigenetic modifications are maintained in vitro.

The efficacy of chronic zinc oxide nanoparticles using on testicular damage in the streptozotocin-induced diabetic rat model

Testicular impairment is a common complication of Diabetes mellitus (DM). Zinc Oxide Nanoparticles (ZnO NPs) are a novel agent for Zn delivery with antidiabetic and antioxidant activities. However, few reports were recorded on it. The current study aimed to investigate the possible ameliorating effect of ZnO NPs treatment on testicular tissues alterations in streptozotocin (STZ)-induced diabetic rats. Therefore, thirty mature male Wistar rats were divided into three main groups: Control group (n = 18) was subdivided equally into three subgroups (negative control, vehicle and ZnO NPs), Diabetic group (n = 6) and ZnO NPs-treated diabetic group (n = 6). Induction of diabetes was done by a single intraperitoneal injection of STZ (60 mg/kg bw). The rats were orally treated by ZnO NPs (10 mg/kg bw) for 30 constitutive days. At the end of the experiment, blood glucose and serum testosterone levels were measured. Also, testicular tissues were obtained for histopathological investigations and immunohistochemical staining with anti-PCNA (proliferating cell marker), anti-ssDNA (apoptotic cell marker), anti-SOX9 (Sertoli cell marker), anti-Stella (spermatogonia marker), anti-STRA8 (preleptotene and early-leptotene spermatocytes marker), anti-DMC1 (leptotene and zygotene spermatocytes marker), anti-Dnmt3a (a marker for cells under DNA methylation) and anti-α-SMA (peritubular myoid cell marker). The biochemical analysis revealed that diabetes resulted in a significant elevation in blood glucose level and a reduction in serum testosterone level. Moreover, histopathological investigations revealed disorganized seminiferous epithelium and sever hyalinization with vacuolization of the testicular interstitium containing Leydig cells. The immunohistochemical findings support spermatogenesis impairment in the diabetic group. However, ZnO NPs treatment restores architecture of seminiferous epithelium and Leydig cells. Furthermore, more PCNA, SOX9, Stella, STRA8, DMC1 and Dnmt3a immunopositive cells with an improvement of peritubular α-SMA immunopositive expression, as well as few ssDNA-immunopositive cells were detected in the seminiferous epithelium. This study suggested the possible protective role of orally administered ZnO NPs on testicular alterations in the STZ-induced diabetic group via steroidogenesis and spermatogenesis enhancement. In addition, further researches are acquired for evaluation mechanism of ZnO NPs treatment via oral or parenteral routes in a dose-dependent manner to identify the more effective route and dose in the treatment of testicular diabetic complications.

Multigenerational impacts of bile exposure are mediated by TGR5 signaling pathways

Besides their well-known roles in digestion and fat solubilization, bile acids (BAs) have been described as signaling molecules activating the nuclear receptor Farnesoid-X-receptor (FXRα) or the G-protein-coupled bile acid receptor-1 (GPBAR-1 or TGR5). In previous reports, we showed that BAs decrease male fertility due to abnormalities of the germ cell lineage dependent on Tgr5 signaling pathways. In the presentstudy, we tested whether BA exposure could impact germ cell DNA integrity leading to potential implications for progeny. For that purpose, adult F0 male mice were fed a diet supplemented with cholic acid (CA) or the corresponding control diet during 3.5 months prior mating. F1 progeny from CA exposed founders showed higher perinatal lethality, impaired BA homeostasis and reduced postnatal growth, as well as altered glucose metabolism in later life. The majority of these phenotypic traits were maintained up to the F2 generation. In F0 sperm cells, differential DNA methylation associated with CA exposure may contribute to the initial programming of developmental and metabolic defects observed in F1 and F2 offspring. Tgr5 knock-out mice combined with in vitro strategies defined the critical role of paternal Tgr5 dependent pathways in the multigenerational impacts of ancestral CA exposure.

Characterization of Genetic and Epigenetic Variation in Sperm and Red Blood Cells from Adult Hatchery and Natural-Origin Steelhead, Oncorhynchus mykiss

While the goal of most conservation hatchery programs is to produce fish that are genetically and phenotypically indistinguishable from the wild stocks they aim to restore, there is considerable evidence that salmon and steelhead reared in hatcheries differ from wild fish in phenotypic traits related to fitness. Some evidence suggests that these phenotypic differences have a genetic basis (e.g., domestication selection) but another likely mechanism that remains largely unexplored is that differences between hatchery and wild populations arise as a result of environmentally-induced heritable epigenetic change. As a first step toward understanding the potential contribution of these two possible mechanisms, we describe genetic and epigenetic variation in hatchery and natural-origin adult steelhead, Oncorhynchus mykiss, from the Methow River, WA. Our main objectives were to determine if hatchery and natural-origin fish could be distinguished genetically and whether differences in epigenetic programming (DNA methylation) in somatic and germ cells could be detected between the two groups. Genetic analysis of 72 fish using 936 SNPs generated by Restriction Site Associated DNA Sequencing (RAD-Seq) did not reveal differentiation between hatchery and natural-origin fish at a population level. We performed Reduced Representation Bisulfite Sequencing (RRBS) on a subset of 10 hatchery and 10 natural-origin fish and report the first genome-wide characterization of somatic (red blood cells (RBCs)) and germ line (sperm) derived DNA methylomes in a salmonid, from which we identified considerable tissue-specific methylation. We identified 85 differentially methylated regions (DMRs) in RBCs and 108 DMRs in sperm of steelhead reared for their first year in a hatchery environment compared to those reared in the wild. This work provides support that epigenetic mechanisms may serve as a link between hatchery rearing and adult phenotype in steelhead; furthermore, DMRs identified in germ cells (sperm) highlight the potential for these changes to be passed on to future generations.

m6A mRNA modification regulates mammalian spermatogenesis

Mammalian spermatogenesis is a highly specialized differentiation process involving precise regulatory mechanisms at the transcriptional, posttranscriptional, and translational levels. Emerging evidence has shown that N⁶-methyladenosine (m⁶A), an epitranscriptomic regulator of gene expression, can influence pre-mRNA splicing, mRNA export, turnover, and translation, which are controlled in the male germline to ensure coordinated gene expression. In this review, we summarize the typical features of m⁶A RNA modification on mRNA during male germline development, and highlight the function of writers, erasers, and readers of m⁶A during mouse spermatogenesis.

Genome-wide identification, evolution of DNA methyltransferases and their expression during gonadal development in Nile tilapia

DNA methyltransferases (dnmts) are responsible for DNA methylation and play important roles in organism development. In this study, seven dnmts genes (dnmt1, dnmt2, dnmt3aa, dnmt3ab, dnmt3ba, dnmt3bb.1, dnmt3bb.2) were identified in Nile tilapia. Comprehensive analyses of dnmts were performed using available genome databases from representative animal species. Phylogenetic analysis revealed that the dnmts family were highly conserved in teleosts. Based on transcriptome data from eight adult tilapia tissues, the dnmts were found to be dominantly expressed in the head kidney, testis and ovary. Analyses of the gonadal transcriptome data in different developmental stages revealed that all dnmts were expressed in both ovary and testis, and four de novo dnmts (dnmt3aa, dnmt3ab, dnmt3bb.1, dnmt3bb.2) showed higher expression in the testis than in the ovary. Furthermore, during sex reversal induced by Fadrozole, the expression of these four de novo dnmts increased significantly in treated group compared to female control group. By in situ hybridization, the seven dnmts were found to be expressed mainly in phase I and II oocytes of the ovary and spermatocytes of the testis. When gonads were incubated with a methyltransferase inhibitor (5-AzaCdR) in vitro, the expression of dnmts genes were down-regulated significantly, while the expression of cyp19a1a (a key gene in female pathway) and dmrt1 (a key gene in male pathway) increased significantly. Our results revealed the conservation of dnmts during evolution and indicated a potential role of dnmts in epigenetic regulation of gonadal development.

Cocaine alters the mouse testicular epigenome with direct impact on histone acetylation and DNA methylation marks

RESEARCH QUESTION

Recent evidence suggests that cocaine administration in animal models can trigger non-genetic inheritance of addiction traits from father to offspring, affecting development and behaviour. Is chronic cocaine intake involved in alterations of epigenetic homeostasis in the testis?

DESIGN

Epigenetic marks and mediators in testis and isolated germ cells of adult mice treated with cocaine (10 mg/kg) or vehicle (sterile saline solution) were evaluated in an intermittent binge protocol: three intraperitoneal injections, 1 h apart, one day on/off for 13 days, collecting tissue 24 h after the last binge administration (day 14).

RESULTS

It was shown that chronic cocaine intake in mice disrupts testicular epigenetic homeostasis, increasing global methylated cytosine levels in DNA from germ cells and sperm. Cocaine also increased testicular and germ cell acetylated histone 3 and 4 and decreased expression of histone deacetylases HDAC1/2. Immunolocalization studies showed that HDAC1/2 and acetylated histone 3 and 4 proteins localize to meiotic germ cells. Analysis of mRNA expression in isolated germ cells shows decreased levels of Hdac1/2/8, Dnmt3b and Tet1 and increased levels of Dnmt3a gene expression after cocaine treatment.

CONCLUSIONS

Cocaine intake is associated with testicular toxicity and significant reproductive function impairment. The results presented here broaden the basic knowledge of the impact of addictive stimulants on testicular pathophysiology, fertility and male reproductive health and imply that altered epigenetic homeostasis by cocaine may have potential consequences on future generations.

DNA methyltransferase 3A isoform b contributes to repressing E-cadherin through cooperation of DNA methylation and H3K27/H3K9 methylation in EMT-related metastasis of gastric cancer

DNA methyltransferase 3A (DNMT3A) has been recognised as a key element of epigenetic regulation in normal development, and the aberrant regulation of DNMT3A is implicated in multiple types of cancers, especially haematological malignancies. However, its clinical significance and detailed functional role in solid tumours remain unknown, although abnormal expression has gained widespread attention in these cancers. Here, we show that DNMT3A isoform b (DNMT3Ab), a member of the DNMT3A isoform family, is critical for directing epithelial-mesenchymal transition (EMT)-associated metastasis in gastric cancer (GC). DNMT3Ab is positively linked to tumour-node-metastasis (TNM) stage, lymph node metastasis and poor prognosis in GC patients. Overexpression of DNMT3Ab promotes GC cell migration and invasion as well as EMT through repression of E-cadherin. Meanwhile, DNMT3Ab promotes lung metastasis of GC in vivo. Mechanistic studies indicate that DNMT3Ab mediates the epigenetic inaction of the E-cadherin gene via DNA hypermethylation and histone modifications of H3K9me2 and H3K27me3. Depletion of DNMT3Ab effectively restores the expression of E-cadherin and reverses TGF-β-induced EMT by reducing DNA methylation, H3K9me2 and H3K27me3 levels at the E-cadherin promoter. Importantly, DNMT3Ab cooperated with H3K9me2 and H3K27me3 contributes to the transcriptional regulation of E-cadherin in a Snail-dependent manner. Further, gene expression profiling analysis indicates that multiple metastasis-associated genes and oncogenic signalling pathways are regulated in response to DNMT3Ab overexpression. These results identify DNMT3Ab as a crucial regulator of metastasis-related genes in GC. Targeting the DNMT3Ab/Snail/E-cadherin axis may provide a promising therapeutic strategy in the treatment of metastatic GC with high DNMT3Ab expression.

Sperm chromatin and DNA integrity, methyltransferase mRNA levels, and global DNA methylation in oligoasthenoteratozoospermia

Objective

To investigate sperm chromatin/DNA integrity, global DNA methylation, and DNMT mRNA transcription in men with oligoasthenoteratozoospermia (OAT) compared with normozoospermic men.

Methods

Semen samples from 32 OAT patients who comprised the case group and 32 normozoospermic men who comprised the control group were isolated and purified using a standard gradient isolation procedure according to World Health Organization criteria. DNMT1, DNMT3A, and DNMT3B transcripts were then compared between groups using real-time quantitative reverse-transcription polymerase chain reaction. Global DNA methylation in sperm was determined by an enzyme-linked immunosorbent assay. Protamine deficiency and the proportion of apoptotic spermatozoa were evaluated using chromomycin A3 (CMA3), aniline blue (AB), and toluidine blue (TB) staining, as well as the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The p-values <0.05 were considered to indicate statistical significance.

Results

Significantly higher proportions of AB+, TB+, CMA3+, and TUNEL+ spermatozoa, as well as DNMT3A and DNMT3B transcription, were found in the OAT group. Positive correlations were detected between sperm parameters, DNA/chromatin damage, and DNMT3A and DNMT3B transcripts. Global DNA methylation was significantly higher in the OAT patients and had a significant correlation with abnormal results of all sperm chromatin integrity tests, but was not associated with DNMT1, DNMT3A, or DNMT3B expression.

Conclusion

Oligoasthenoteratozoospermic men showed abnormal sperm parameters, abnormal chromatin/DNA integrity, and a higher global DNA methylation rate, as well as overexpression of DNMT mRNA.

Isoform-specific localization of DNMT3A regulates DNA methylation fidelity at bivalent CpG islands

DNA methylation is a prevalent epigenetic modification involved in transcriptional regulation and essential for mammalian development. While the genome-wide distribution of this mark has been studied to great detail, the mechanisms responsible for its correct deposition, as well as the cause for its aberrant localization in cancers, have not been fully elucidated. Here, we have compared the activity of individual DNMT3A isoforms in mouse embryonic stem and neuronal progenitor cells and report that these isoforms differ in their genomic binding and DNA methylation activity at regulatory sites. We identify that the longer isoform DNMT3A1 preferentially localizes to the methylated shores of bivalent CpG island promoters in a tissue-specific manner. The isoform-specific targeting of DNMT3A1 coincides with elevated hydroxymethylcytosine (5-hmC) deposition, suggesting an involvement of this isoform in mediating turnover of DNA methylation at these sites. Through genetic deletion and rescue experiments, we demonstrate that this isoform-specific recruitment plays a role in de novo DNA methylation at CpG island shores, with potential implications on H3K27me3-mediated regulation of developmental genes.

An Initial Investigation of an Alternative Model to Study rat Primordial Germ Cell Epigenetic Reprogramming

BACKGROUND

Primordial germ cells (PGC) are the precursors of the gametes. During pre-natal development, PGC undergo an epigenetic reprogramming when bulk DNA demethylation occurs and is followed by sex-specific de novo methylation. The de novo methylation and the maintenance of the methylation patterns depend on DNA methyltransferases (DNMTs). PGC reprogramming has been widely studied in mice but not in rats. We have previously shown that the rat might be an interesting model to study germ cell development. In face of the difficulties of getting enough PGC for molecular studies, the aim of this study was to propose an alternative method to study rat PGC DNA methylation. Rat embryos were collected at 14, 15 and 19 days post-coitus (dpc) for the analysis of 5mC, 5hmC, DNMT1, DNMT3a and DNMT3b expression or at 16dpc for treatment 5-Aza-CdR, a DNMT inhibitor, in vitro.

METHODS

Once collected, the gonads were placed in 24-well plates previously containing 45μm pore membrane and medium with or without 5-Aza-CdR. The culture was kept for five days and medium was changed daily. The gonads were either fixed or submitted to RNA extraction.

RESULTS

5mC and DNMTs labelling suggests that PGC are undergoing epigenetic reprogramming around 14/15dpc. The in vitro treatment of rat embryonic gonads with 1 μM of 5-Aza-CdR lead to a loss of 5mC labelling and to the activation of Pax6 expression in PGC, but not in somatic cells, suggesting that 5-Aza-CdR promoted a PGC-specific global DNA hypomethylation.

CONCLUSIONS

This study suggests that the protocol used here can be a potential method to study the wide DNA demethylation that takes place during PGC reprogramming.

Testicular Dnmt3 expression and global DNA methylation are down-regulated by gonadotropin releasing hormones in the ricefield eel Monopterus albus

In vertebrates, DNA methyltransferase 3 (Dnmt3) homologues are responsible for de novo DNA methylation and play important roles in germ cell development. In the present study, four dnmt3 genes, dnmt3aa, dnmt3ab, dnmt3ba and dnmt3bb.1, were identified in ricefield eels. Real-time quantitative PCR analysis showed that all four dnmt3 mRNAs were detected broadly in tissues examined, with testicular expression at relatively high levels. In the testis, immunostaining for all four Dnmt3 forms was mainly localized to spermatocytes, which also contained highly methylated DNA. All three forms of Gonadotropin-releasing hormone (Gnrh) in the ricefield eel were shown to decrease the expression of dnmt3 genes in the in vitro incubated testicular fragments through cAMP and IP₃/Ca²⁺ pathways. Moreover, in vivo treatment of male fish with three forms of Gnrh decreased significantly the testicular Dnmt3 expression at both mRNA and protein levels, and the global DNA methylation levels. These results suggest that the expression of Dnmt3 and global DNA methylation in the testis of ricefield eels are potentially down-regulated by Gnrh, and reveal a novel regulatory mechanism of testicular Dnmt3 expression in vertebrates.

CpG methylation participates in regulation of hepatitis B virus gene expression in host sperm and sperm-derived embryos

AIM

This study was undertaken to investigate relationship between hepatitis B virus (HBV) CpG methylation and HBV gene transcription in sperm and sperm-derived embryos.

METHODS

HBV-infected patient sperm and HBV plasmid-transfected donor sperm were subjected to interspecific in vitro fertilization, methylation-specific PCR, bisulfite sequencing PCR, reverse transcription PCR and real-time quantitative PCR.

RESULTS

Positive methylation bands for CpG islands II and III in the HBV genome were observed in patient sperm but not in controls, and methylation percentages of CpG sites varied among different patient sperm samples. After fertilization, CpG sites were highly demethylated in embryos. Transcriptional levels of HBV X and S genes increased with decrease in CpG site methylation percentages.

CONCLUSION

HBV CpG sites can be methylated in patient sperm before maturation. Methylation of CpG islands II and III participates in transcriptional regulation of HBV X and S genes, respectively, in sperm and sperm-derived embryos.

Epigenetic: A new approach to etiology of infertility

Infertility is a complex disease which could be caused by male and female factors. The etiology from both factors needs further study. There are some approaches to understanding the etiology of infertility, one of them is epigenetic. Epigenetic modifications consist of DNA methylation, histone modifications, and chromatin remodelling. Male and female germinal cells undergo epigenetic modifications dynamically during differentiation into matured sperm and oocyte cells. In a male, the alteration of DNA methylation in spermatogenesis will cause oligo/asthenozoospermia. In addition, the histone methylation, acetylation, or other histone modification may lead sperm lose its ability to fertilize oocyte. Similarly, in a female, the alteration of DNA methylation and histone modification affects oogenesis, created aneuploidy in fertilized oocytes and resulted in embryonic death in the uterus. Alteration of these epigenetic modification patterns will cause infertility, both in male and female.

DNA methyltransferases exhibit dynamic expression during spermatogenesis

DNA methylation is one of the epigenetic marks and plays critically important functions during spermatogenesis in mammals. DNA methylation is catalysed by DNA methyltransferase (DNMT) enzymes, which are responsible for the addition of a methyl group to the fifth carbon atom of the cytosine residues within cytosine-phosphate-guanine (CpG) and non-CpG dinucleotide sites. Structurally and functionally five different DNMT enzymes have been identified in mammals, including DNMT1, DNMT2, DNMT3A, DNMT3B and DNMT3L. These enzymes mainly play roles in two DNA methylation processes: maintenance and de novo. While DNMT1 is primarily responsible for maintenance methylation via transferring methyl groups to the hemi-methylated DNA strands following DNA replication, both DNMT3A and DNMT3B are capable of methylating unmodified cytosine residues, known as de novo methylation. However, DNMT3L indirectly participates in de novo methylation, and DNMT2 carries out methylation of the cytosine 38 in the anticodon loop of aspartic acid transfer RNA. To date, many studies have been performed to determine spatial and temporal expression levels and functional features of the DNMT in the male germ cells. This review article comprehensively discusses dynamic expression of the DNMT during spermatogenesis and their relationship with male infertility development in the light of existing investigations.

DNA methylation in spermatogenesis and male infertility

Infertility is a significant problem for human reproduction, with males and females equally affected. However, the molecular mechanisms underlying male infertility remain unclear. Spermatogenesis is a highly complex process involving mitotic cell division, meiosis cell division and spermiogenesis; during this period, unique and extensive chromatin and epigenetic modifications occur to bring about specific epigenetic profiles in spermatozoa. It has recently been suggested that the dysregulation of epigenetic modifications, in particular the methylation of sperm genomic DNA, may serve an important role in the development of numerous diseases. The present study is a comprehensive review on the topic of male infertility, aiming to elucidate the association between sperm genomic DNA methylation and poor semen quality in male infertility. In addition, the current status of the genetic and epigenetic determinants of spermatogenesis in humans is discussed.

5-aza-2'-deoxycytidine impairs mouse spermatogenesis at multiple stages through different usage of DNA methyltransferases

Mammalian spermatogenesis is a progressive process comprising spermatogonial proliferation, spermatocytic meiosis, and later spermiogenesis, which is considered to be under the regulation of epigenetic parameters. To gain insights into the significance of DNA methylation in early spermatogenesis, 5-azadC was used as a molecular biological tool to mimic the level of DNA methylation in vivo. Since the drug is incorporated into DNA during the S-phase, spermatogonia and spermatocytes would be affected primarily in mouse spermatogenesis. Adult male ICR mice were intraperitoneally injected with 5-azadC at a dose of 0.25mg/kg/day for 10 consecutive days, allowing us to examine its maximum effect on the kinetics of spermatogonia and spermatocytes. In this short-term protocol, 5-azadC induced significant histological abnormalities, such as a marked increase in apoptosis of spermatogonia and spermatocytes, followed by severe loss of spermatids, while after termination of 5-azadC treatment, normal histology was restored in the testis within 35days. Quantification of the methylation level of CCGG sites as well as whole DNA showed spermatogonial hypomethylation, which correlated with increased apoptosis of spermatogonia. Interestingly, the hypomethylated cells were simultaneously positive for tri-methylated histone H3 at K4. On the other hand, no changes in methylation level were found in spermatocytes, but PCNA staining clearly showed disordered accumulation of S-phase spermatocytes, which increased their apoptosis in stage XII. In addition, different immunohistochemical staining pattern was found for DNA methyltransferases (DNMTs); DNMT1was expressed in the majority of all germ cells, but DNMT3a and b were only expressed in spermatogonia. Our results indicate that 5-azadC caused DNA hypomethylation in spermatogonia, but induced prolongation of S-phase in spermatocytes, resulting in the induction of apoptosis in both cases. Thus, 5-azadC affects spermatogenesis at more than one differentiation stage with different mechanisms, probably due to the specific usage of DNMTs.

DNA methylation dynamics in plants and mammals: overview of regulation and dysregulation

DNA methylation is a major epigenetic marking mechanism regulating various biological functions in mammals and plant. The crucial role of DNA methylation has been observed in cellular differentiation, embryogenesis, genomic imprinting and X-chromosome inactivation. Furthermore, DNA methylation takes part in disease susceptibility, responses to environmental stimuli and the biodiversity of natural populations. In plant, different types of environmental stress have demonstrated the ability to alter the archetype of DNA methylation through the genome, change gene expression and confer a mechanism of adaptation. DNA methylation dynamics are regulated by three processes de novo DNA methylation, methylation maintenance and DNA demethylation. These processes have their similarities and differences between mammals and plants. Furthermore, the dysregulation of DNA methylation dynamics represents one of the primary molecular mechanisms of developing diseases in mammals. This review discusses the regulation and dysregulation of DNA methylation in plants and mammals. Copyright © 2016 John Wiley & Sons, Ltd.

Histological and transcriptome analyses of testes from Duroc and Meishan boars

Meishan boars are known for their early sexual maturity. However, they exhibit a significantly smaller testicular size and a reduced proportion of Sertoli cells and daily sperm production compared with Duroc boars. The testes of Duroc and Meishan boars at 20, 75 and 270 days of age were used for histological and transcriptome analyses. Haematoxylin-eosin staining was conducted to observe histological structure of the testes in Duroc and Meishan boars at different ages. Although spermatogenesis occurred prior to 75 days in Meishan boars, the number of spermatogonia and Sertoli cells in Meishan boars were less than in Duroc boars at adulthood. The diameters of the seminiferous tubules of the testes differed significantly during the initiation of development of the seminiferous tubules between the two breeds. We obtained differentially expressed functional genes and analysed seven pathways involved in male sexual maturity and spermatogenesis using RNA-seq. We also detected four main alternative splicing events and many single nucleotide polymorphisms from testes. Eight functionally important genes were validated by qPCR, and Neurotrophin 3 was subjected to quantification and cellular localization analysis. Our study provides the first transcriptome evidence for the differences in sexual function development between Meishan and Duroc boars.

Retracted article: In vitro derivation of mammalian germ cells from stem cells and their potential therapeutic application

Pluripotent stem cells (PSCs) are a unique type of cells because they exhibit the characteristics of self-renewal and pluripotency. PSCs may be induced to differentiate into any cell type, even male and female germ cells, suggesting their potential as novel cell-based therapeutic treatment for infertility problems. Spermatogenesis is an intricate biological process that starts from self-renewal of spermatogonial stem cells (SSCs) and leads to differentiated haploid spermatozoa. Errors at any stage in spermatogenesis may result in male infertility. During the past decade, much progress has been made in the derivation of male germ cells from various types of progenitor stem cells. Currently, there are two main approaches for the derivation of functional germ cells from PSCs, either the induction of in vitro differentiation to produce haploid cell products, or combination of in vitro differentiation and in vivo transplantation. The production of mature and fertile spermatozoa from stem cells might provide an unlimited source of autologous gametes for treatment of male infertility. Here, we discuss the current state of the art regarding the differentiation potential of SSCs, embryonic stem cells, and induced pluripotent stem cells to produce functional male germ cells. We also discuss the possible use of livestock-derived PSCs as a novel option for animal reproduction and infertility treatment.

Evidence in duck for supporting alteration of incubation temperature may have influence on methylation of genomic DNA

Incubation temperature has an immediate and long-term influence on the embryonic development in birds. DNA methylation as an important environment-induced mechanism could serve as a potential link between embryos’ phenotypic variability and temperature variation, which reprogrammed by DNA (cytosine-5)-methyltransferases (DNMTS) and Methyl-CpG binding domain proteins (MBPS) 3&5 (MBD3&5). Five genes in DNMTS and MBPS gene families were selected as target genes, given their important role in epigenetic modification. In this study, we aimed to test whether raising incubation temperature from 37.8°C to 38.8°C between embryonic days (ED) 1–10, ED10–20 and ED20–27 have effect on DNA methylation and whether DNMTS, MBPS play roles in thermal epigenetic regulation of early development in duck. Real-time quantitative PCR analysis showed that increased incubation temperature by 1°C has remarkably dynamic effect on gene expression levels of DNMTS and MBPS. Slight changes in incubation temperature significantly increased mRNA levels of target genes in breast muscle tissue during ED1–10, especially for DNMT1, DNMT3A and MBD5. In addition, higher temperature significantly increased enzyme activities of DNMT1 in leg muscle during ED10–20, liver tissue during ED1–10, ED20–27 and DNMT3A in leg muscle and breast muscle tissue during ED10–20. These results suggest that incubation temperature has an extended effect on gene expression levels and enzyme activities of DNMTS and MBPS, which provides evidence that incubation temperature may influence DNA methylation in duck during early developmental stages. Our data indicated that DNMTS and MBPS may involved in thermal epigenetice regulation of embryos during the early development in duck. The potential links between embryonic temperature and epigenetic modification need further investigation

MicroRNAs and DNA methylation as epigenetic regulators of mitosis, meiosis and spermiogenesis

Spermatogenesis is composed of three distinctive phases, which include self-renewal of spermatogonia via mitosis, spermatocytes undergoing meiosis I/II and post-meiotic development of haploid spermatids via spermiogenesis. Spermatogenesis also involves condensation of chromatin in the spermatid head before transformation of spermatids to spermatozoa. Epigenetic regulation refers to changes of heritably cellular and physiological traits not caused by modifications in the DNA sequences of the chromatin such as mutations. Major advances have been made in the epigenetic regulation of spermatogenesis. In this review, we address the roles and mechanisms of epigenetic regulators, with a focus on the role of microRNAs and DNA methylation during mitosis, meiosis and spermiogenesis. We also highlight issues that deserve attention for further investigation on the epigenetic regulation of spermatogenesis. More importantly, a thorough understanding of the epigenetic regulation in spermatogenesis will provide insightful information into the etiology of some unexplained infertility, offering new approaches for the treatment of male infertility.

TET proteins and the control of cytosine demethylation in cancer

The discovery that ten-eleven translocation (TET) proteins are α-ketoglutarate-dependent dioxygenases involved in the conversion of 5-methylcytosines (5-mC) to 5-hydroxymethylcytosine (5-hmC), 5-formylcytosine and 5-carboxycytosine has revealed new pathways in the cytosine methylation and demethylation process. The description of inactivating mutations in TET2 suggests that cellular transformation is in part caused by the deregulation of this 5-mC conversion. The direct and indirect deregulation of methylation control through mutations in DNA methyltransferase and isocitrate dehydrogenase (IDH) genes, respectively, along with the importance of cytosine methylation in the control of normal and malignant cellular differentiation have provided a conceptual framework for understanding the early steps in cancer development. Here, we review recent advances in our understanding of the cytosine methylation cycle and its implication in cellular transformation, with an emphasis on TET enzymes and 5-hmC. Ongoing clinical trials targeting the activity of mutated IDH enzymes provide a proof of principle that DNA methylation is targetable, and will trigger further therapeutic applications aimed at controlling both early and late stages of cancer development.

The de novo DNA methyltransferase DNMT3A in development and cancer

DNA methylation, one of the best-characterized epigenetic modifications, plays essential roles in development, aging and diseases. The de novo DNA methyltransferase DNMT3A is responsible for the establishment of de novo genomic DNA methylation patterns and, as such, involved in normal development as well as in many diseases including cancer. In recent years, our understanding of this important protein has made significant progress, which was facilitated by stunning development in the analysis of the DNA methylome of multiple organs and cell types. In this review, recent developments in the characterization of DNMT3A were discussed with special emphasis on the roles of DNMT3A in development and cancer.

Dynamics of 5-hydroxymethylcytosine during mouse spermatogenesis

Little is known about how patterns of DNA methylation change during mammalian spermatogenesis. 5 hmC has been recognized as a stable intermediate of DNA demethylation with potential regulatory functions in the mammalian genome. However, its global pattern in germ cells has yet to be addressed. Here, we first conducted absolute quantification of 5 hmC in eight consecutive types of mouse spermatogenic cells using liquid chromatography-tandem mass spectrometry, and then mapped its distributions in various genomic regions using our chemical labeling and enrichment method coupled with deep sequencing. We found that 5 hmC mapped differentially to and changed dynamically in genomic regions related to expression regulation of protein-coding genes, piRNA precursor genes and repetitive elements. Moreover, 5 hmC content correlated with the levels of various transcripts quantified by RNA-seq. These results suggest that the highly ordered alterations of 5 hmC in the mouse genome are potentially crucial for the differentiation of spermatogenic cells.