Incorrect DNA methylation of the DAZL promoter CpG island associates with defective human sperm

Decoding the Epigenetics of Infertility: Mechanisms, Environmental Influences, and Therapeutic Strategies

Infertility is a complex condition caused by a combination of genetic, environmental, and lifestyle factors. Recent advances in epigenetics have highlighted the importance of epigenetic changes in fertility regulation. This review aims to provide a comprehensive overview of the epigenetic mechanisms involved in infertility, with a focus on DNA methylation, histone modification, and non-coding RNAs. We investigate the specific epigenetic events that occur during gametogenesis, with a focus on spermatogenesis and oogenesis as distinct processes. Furthermore, we investigate how environmental factors such as diet, stress, and toxin exposure can influence these epigenetic changes, potentially leading to infertility. The second part of the review explores epigenetic changes as therapeutic targets for infertility. Emerging therapies that modulate epigenetic marks present promising opportunities for fertility restoration, particularly in spermatogenesis. By summarizing current research findings, this review emphasizes the importance of understanding epigenetic contributions to infertility. Our discussion aims to lay the groundwork for future research directions and clinical applications in reproductive health.

DNA methylation patterns in patients with asthenospermia and oligoasthenospermia

BACKGROUND

Spermatogenesis is a highly regulated and complex process in which DNA methylation plays a crucial role. This study aimed to explore the differential methylation profiles in sperm DNA between patients with asthenospermia (AS) and healthy controls (HCs), those with oligoasthenospermia (OAS) and HCs, and patients with AS and those with OAS.

RESULTS

Semen samples and clinical data were collected from five patients with AS, five patients with OAS, and six age-matched HCs. Reduced representation bisulfite sequencing (RRBS) was performed to identify differentially methylated regions (DMRs) in sperm cells among the different types of patients and HCs. A total of 6520, 28,019, and 16,432 DMRs were detected between AS and HC, OAS and HC, and AS and OAS groups, respectively. These DMRs were predominantly located within gene bodies and mapped to 2868, 9296, and 9090 genes in the respective groups. Of note, 12, 9, and 8 DMRs in each group were closely associated with spermatogenesis and male infertility. Furthermore, BDNF, SMARCB1, PIK3CA, and DDX27; RBMX and SPATA17; ASZ1, CDH1, and CHDH were identified as strong differentially methylated candidate genes in each group, respectively. Meanwhile, the GO analysis of DMR-associated genes in the AS vs. HC groups revealed that protein binding, cytoplasm, and transcription (DNA-templated) were the most enriched terms in the biological process (BP), cellular component (CC), and molecular function (MF), respectively. Likewise, in both the OAS vs. HC and AS vs. OAS groups, GO analysis revealed protein binding, nucleus, and transcription (DNA-templated) as the most enriched terms in BP, CC, and MF, respectively. Finally, the KEGG analysis of DMR-annotated genes and these genes at promoters suggested that metabolic pathways were the most significantly associated across all three groups.

CONCLUSIONS

The current study results revealed distinctive sperm DNA methylation patterns in the AS vs. HC and OAS vs. HC groups, particularly between patients with AS and those with OAS. The identification of key genes associated with spermatogenesis and male infertility in addition to the differentially enriched metabolic pathways may contribute to uncovering the potential pathogenesis in different types of abnormal sperm parameters.

Sperm epigenetics and male infertility: unraveling the molecular puzzle

BACKGROUND

The prevalence of infertility among couples is estimated to range from 8 to 12%. A paradigm shift has occurred in understanding of infertility, challenging the notion that it predominantly affects women. It is now acknowledged that a significant proportion, if not the majority, of infertility cases can be attributed to male-related factors. Various elements contribute to male reproductive impairments, including aberrant sperm production caused by pituitary malfunction, testicular malignancies, aplastic germ cells, varicocele, and environmental factors.

MAIN BODY

The epigenetic profile of mammalian sperm is distinctive and specialized. Various epigenetic factors regulate genes across different levels in sperm, thereby affecting its function. Changes in sperm epigenetics, potentially influenced by factors such as environmental exposures, could contribute to the development of male infertility.

CONCLUSION

In conclusion, this review investigates the latest studies pertaining to the mechanisms of epigenetic changes that occur in sperm cells and their association with male reproductive issues.

Transcriptome Analysis Reveals Spermatogenesis-Related CircRNAs and LncRNAs in Goat Spermatozoa

Mammalian spermatozoa comprises both coding and non-coding RNAs, which are traditionally believed to be a residual of spermatogenesis. The differential expression level of spermatozoal RNAs is also observed between fertile and infertile human, thereby anticipated as potential molecular marker of male fertility. This study investigated the transcriptome profile of goat (Capra hircus) spermatozoa. The sperm transcriptome was analyzed by three different methods viz. RLM-RACE, long-read RNA sequencing (RNAseq) in Nanopore™ platform, and short-read RNAseq in Illumina™ platform. The Illumina™ sequencing discovered 16,604 transcripts with 357 mRNAs having FPKM (fragments per kilobase per million mapped reads) of more than five. The spermatozoal RNA suite included mRNA (94%), rRNA (3%), miscRNA (1%), circRNA (1%), miRNA (1%), etc. This study also predicted circRNAs (127), lncRNAs (655), and imprinted genes (160) that have potential role in male reproduction. The gene ontology analysis revealed the involvement of spermatozoal RNA in regulating male meiosis (TET3, STAT5B), capacitation (ACRBP, CATSPER4), sperm motility (GAS8, TEKT2), spermatogenesis (ADAMTS2, CREB3L4), etc. The spermatozoal RNA were also associated with different biological pathways viz. Wnt signaling pathway, cAMP signaling pathway, AMPK signaling pathway, and MAPK signaling pathways having potential role in spermatogenesis. Overall, this study enlightened the suite of spRNA transcripts in goat and their relevance in male fertility for diagnostic approach.

Unraveling the Impact of Sperm DNA Fragmentation on Reproductive Outcomes

In recent years, there has been a growing interest in identifying subcellular causes of male infertility, and sperm DNA fragmentation (SDF) research has been at the forefront of this focus. DNA damage can occur during spermatogenesis due to faulty chromatin compaction or excessive abortive apoptosis. It can also happen as sperm transit through the genital tract, often induced by oxidative stress. There are several methods for SDF testing, with the sperm chromatin structure assay, terminal deoxynucleotidyl transferase d-UTI nick end labeling (TUNEL) assay, comet assay, and sperm chromatin dispersion test being the most commonly used. Numerous studies strongly support the negative impact of SDF on male fertility potential. DNA damage has been linked to various morphological and functional sperm abnormalities, ultimately affecting natural conception and assisted reproductive technology outcomes. This evidence-based review aims to explore how SDF influences male reproduction and provide insights into available therapeutic options to minimize its detrimental impact.

Electrochemical Biosensors for Whole Blood Analysis: Recent Progress, Challenges, and Future Perspectives

Whole blood, as one of the most significant biological fluids, provides critical information for health management and disease monitoring. Over the past 10 years, advances in nanotechnology, microfluidics, and biomarker research have spurred the development of powerful miniaturized diagnostic systems for whole blood testing toward the goal of disease monitoring and treatment. Among the techniques employed for whole-blood diagnostics, electrochemical biosensors, as known to be rapid, sensitive, capable of miniaturization, reagentless and washing free, become a class of emerging technology to achieve the target detection specifically and directly in complex media, e.g., whole blood or even in the living body. Here we are aiming to provide a comprehensive review to summarize advances over the past decade in the development of electrochemical sensors for whole blood analysis. Further, we address the remaining challenges and opportunities to integrate electrochemical sensing platforms.

Sperm epigenetics landscape: correlation with embryo quality, reproductive outcomes and offspring's health

Epigenetics refers to how gene expression and function are modulated without modifying the DNA sequence but through subtle molecular changes or interactions with it. As spermatogenesis progresses, male germ cells suffer plenty of epigenetic modifications, resulting in the definitive epigenome of spermatozoa conditioning its functionality, and this process can be altered by several internal and external factors. The paternal epigenome is crucial for sperm function, fertilization, embryo development, and offspring's health, and altered epigenetic states are associated with male infertility with or without altered semen parameters, embryo quality impairment, and worse ART outcomes together with the future offspring's health risks mainly through intergenerational transmission of epigenetic marks. Identifying epigenetic biomarkers may improve male factor diagnosis and the development of targeted therapies, not only to improve fertility but also to allow an early detection of risk and disease prevention in the progeny. While still there is much research to be done, hopefully in the near future, improvements in high-throughput technologies applied to epigenomes will permit our understanding of the underlying epigenetic mechanisms and the development of diagnostics and therapies leading to improved reproductive outcomes. In this review, we discuss the mechanisms of epigenetics in sperm and how epigenetics behave during spermatogenesis. Additionally, we elaborate on the relationship of sperm epigenetics with sperm parameters and male infertility, and highlight the impact of sperm epigenetic alterations on sperm parameters, embryo quality, ART outcomes, miscarriage rates and offspring's health. Furthermore, we provide insights into the future research of epigenetic alterations in male infertility.

Genome-wide methylation analyses of human sperm unravel novel differentially methylated regions in asthenozoospermia

Aims & objectives: To investigate DNA methylation patterns in asthenozoospermic and normozoospermic sperm and to explore the potential roles of differential methylations in the etiology of the disease. Materials & methods: The authors performed whole-genome bisulfite sequencing analysis between normozoospermic controls and asthenozoospermic individuals. Results: The authors identified 238 significant differentially methylated regions. These differentially methylated regions were annotated to 114 protein-coding genes, with many genes showing associations with spermatogenesis, sperm motility etc. Conclusion: There are plenty of genomic regions exhibiting altered DNA methylation in asthenozoospermia, a number of which are located within or adjacent to sperm-related genes, suggesting novel methylation markers of asthenozoospermia and potential epigenetic regulation mechanisms through DNA methylation in the disease.

Altered methyltransferase gene expression, mitochondrial copy number and 4977-bp common deletion in subfertile men with variable sperm parameters

Semen parameters have been found to predict reproductive success poorly and are the most prevalent diagnostic tool for male infertility. There are few conflicting reports regarding the correlation of DNMT genes expression, mitochondrial DNA copy number (mtDNAcn) and deletion (mtDNAdel) with different sperm parameters. To investigate DNMT mRNA level, mtDNAcn and deletion in infertile men, with different sperm parameters, compared with fertile men, semen samples from 30 men with unknown male infertility and normal sperm parameters (experimental group I), 30 infertile patients with at least two abnormal sperm parameters (experimental group II) and 30 fertile normozoospermic men (control group) were collected. After semen analysis, total RNA and DNA were extracted. The isolated DNA was used for assessing the respective mtDNAcn and the presence of common 4977 bp deletion in mtDNA by applying real-time quantitative PCR and multiplex PCR, respectively. Synthesized cDNA from total RNAs was used to quantify DNMT1, DNMT3A and DNMT3B transcripts in study groups by using real-time quantitative reverse-transcription PCR. Significantly higher proportions of mtDNAcn were found in experimental group II. DNMT1 was significantly downregulated in both experimental groups and 4977 bp deletion was not detected. Progressive motility and normal morphology were significantly and negatively correlated with mtDNAcn. A significant positive correlation was detected between sperm parameters and DNMT1 mRNA levels. In conclusion, infertile men with different sperm parameter qualities showed elevated mtDNA content. Abnormal sperm parameters associated with DNMT1 gene expression indicate the possibility of changes in some epigenetic aspects of spermatogenesis in subfertile men with different sperm parameters.

Multiomics analysis of male infertility

Infertility affects 8-12% of couples globally, and the male factor is a primary cause in approximately 50% of couples. Male infertility is a multifactorial reproductive disorder, which can be caused by paracrine and autocrine factors, hormones, genes, and epigenetic changes. Recent studies in rodents and most notably in humans using multiomics approach have yielded important insights into understanding the biology of spermatogenesis. Nonetheless, the etiology and pathogenesis of male infertility are still largely unknown. In this review, we summarized and critically evaluated findings based on the use of advanced technologies to compare normal and obstructive azoospermia (OA) versus non-obstructive azoospermia (NOA) men, including whole-genome bisulfite sequencing (WGBS), single cell RNA-seq (scRNA-seq), whole exome sequencing (WES), and ATAC-seq. It is obvious that the multiomics approach is the method of choice for basic research and clinical studies including clinical diagnosis of male infertility.

Advanced molecular approaches in male infertility diagnosis

In the recent years a special attention has been given to a major health concern namely to male infertility, defined as the inability to conceive after 12 months of regular unprotected sexual intercourse, taken into account the statistics that highlight that sperm counts have dropped by 50-60% in recent decades. According to the WHO, infertility affects approximately 9% of couples globally, and the male factor is believed to be present in roughly 50% of cases, with exclusive responsibility in 30%. The aim of this manuscript is to present an evidence-based approach for diagnosing male infertility that includes finding new solutions for diagnosis and critical outcomes, retrieving up-to-date studies and existing guidelines. The diverse factors that induce male infertility generated in a vast amount of data that needed to be analysed by a clinician before a decision could be made for each individual. Modern medicine faces numerous obstacles as a result of the massive amount of data generated by the molecular biology discipline. To address complex clinical problems, vast data must be collected, analysed, and used, which can be very challenging. The use of artificial intelligence (AI) methods to create a decision support system can help predict the diagnosis and guide treatment for infertile men, based on analysis of different data as environmental and lifestyle, clinical (sperm count, morphology, hormone testing, karyotype, etc.) and "omics" bigdata. Ultimately, the development of AI algorithms will assist clinicians in formulating diagnosis, making treatment decisions, and predicting outcomes for assisted reproduction techniques.

Association of methyltetrahydrofolate reductase gene mutation, homocysteine level with semen quality of Iraqi infertile males

Background

Infertility is very common condition and almost 50% of cases are due to male factors. Several genetic and environmental factors are responsible for the poor quality and reduced number of sperms in several cases of infertility. The present study was designed to investigate the association between semen parameters, homocysteine, and the risk of C677T polymorphism of MTHFR gene in infertile males of Iraqi population.

Methods

This Case–control study has been conducted from February 2019 to July 2021 at a molecular laboratory in the Anatomy and Histology Department/college of Medicine/University of Kufa/Najaf/Iraq. It was composed of 353 infertile male patients. They were divided into five groups: 90 azoospermic, 84 oligospermia, 64 asthenospermic, 50 oligoasthenospermic, and 65 teratospermic with an age range 20–46 years compared with 100 fertile males as control with age range 21–49 years. In order to detect homocysteine levels, we used Hcy ELISA Kit. C677T mutation of MTHFR gene was employed by PCR–RFLP technique.

Results

Our data revealed three genotypes of MTHFR C677T, 167 (47.3%) subjects had CC genotype, 116 (32.9%) subjects had CT genotype and 70 (21.1%) subjects had TT genotype. Furthermore, T allele was associated with higher risk of infertility in all patients groups for any genetic model. In total infertile subjects (codominant model: CT vs. CC, OR = 2.0, 95% C.I = 1.2–3.3, P = 0.011; TT vs. CC, OR = 4.8, 95% C.I = 3.3–8.2, P = 0.0003; dominant model: CT + TT vs. CC, OR = 2.8, 95% C.I = 1.7–4.5, P = 0.0001). Oligoasthenospermic patients associated with higher risk in CT heterozygous genotype (OR = 2.8, 95% C.I = 1.0–4.9, P = 0.03) and TT homozygous of mutant allele (OR = 6.3, 95% C.I = 1.9–9.2, P = 0.002). Homocystein level was elevated in all infertile groups when compared with control group (P < 0.01), but the elevation was marked in oligoasthenospermia group. As well as, the level of Serum Hcy exhibited the highest value in TT mutant genotype (39.7 µmol/ml) followed by CT genotype (28.5 µmol/ml) while the lowest level of Hcy recorded in CC genotype (14.6 µmol/ml) for oligoasthenospermia group.

Conclusions

By relating the MTHFR C677T gene mutation with a higher homocystein level, the results showed that Iraqi males with this mutation are more likely to suffer from infertility.

Somatic cell-derived BMPs induce premature meiosis in male germ cells during the embryonic stage by upregulating Dazl expression

Although germ cell fate is believed to be determined by signaling factors from differentiated somatic cells, the molecular mechanism behind this process remains obscure. In this study, premature meiosis in male germ cells was observed during the embryonic stage by conditional activation of β-catenin in Sertoli cells. Somatic and germ cell transcriptome results indicated that the BMP signaling pathway was enriched after β-catenin activation. In addition, we observed a decreased DNA methylation within a reduction of DNMT3A in germ cells of β-catenin activated testes and reversed increase after inhibiting BMP signaling pathway with LDN-193189. We also found that Dazl expression was increased in β-catenin activated testes and decreased after LDN treatment. Taken together, this study demonstrates that male germ cells entered meiosis prematurely during the embryonic stage after β-catenin activated in Sertoli cells. BMP signaling pathway involved in germ cell meiosis initiation by mediating DNA methylation to induce meiotic genes expression.

Sperm DNA integrity status is associated with DNA methylation signatures of imprinted genes and non-imprinted genes

PURPOSE

To evaluate the association between the DNA methylation of specific genes and sperm DNA integrity status in human sperm samples.

METHODS

A total of 166 semen samples were evaluated (86 controls and 80 cases with impaired sperm DNA integrity). We detected the methylation status of 257 CpG sites among two imprinted genes (H19 and SNRPN) and four non-imprinted genes related to male infertility (MTHFR, GSTM1, DAZL, and CREM) by using a targeted next-generation sequencing method.

RESULTS

Differential methylation was found in 43 CpG sites of the promoters of the six candidate genes. H19, SNRPN, MTHFR, DAZL, GSTM1, and CREM contained 22, 12, 1, 4, 0, and 4 differentially methylated CpG sites (P<0.05), respectively. The imprinting genes were associated with relatively higher rates of differentially methylated CpG sites (28.21% in H19 and 41.38% in SNRPN) than the non-imprinting genes. One CpG site in H19 remained significant after performing strict Bonferroni correction.

CONCLUSION

In this study, we found that different site-specific DNA methylation signatures were correlated with sperm DNA integrity status. Further studies are needed to investigate the specific mechanisms leading to the epigenetic modifications.

Epigenetics of Male Infertility: The Role of DNA Methylation

In recent years, a number of studies focused on the role of epigenetics, including DNA methylation, in spermatogenesis and male infertility. We aimed to provide an overview of the knowledge concerning the gene and genome methylation and its regulation during spermatogenesis, specifically in the context of male infertility etiopathogenesis. Overall, the findings support the hypothesis that sperm DNA methylation is associated with sperm alterations and infertility. Several genes have been found to be differentially methylated in relation to impaired spermatogenesis and/or reproductive dysfunction. Particularly, DNA methylation defects of MEST and H19 within imprinted genes and MTHFR within non-imprinted genes have been repeatedly linked with male infertility. A deep knowledge of sperm DNA methylation status in association with reduced reproductive potential could improve the development of novel diagnostic tools for this disease. Further studies are needed to better elucidate the mechanisms affecting methylation in sperm and their impact on male infertility.

Deoxyribonucleic acid methylation signatures in sperm deoxyribonucleic acid fragmentation

OBJECTIVE

To evaluate Deoxyribonucleic acid (DNA) methylation patterns in sperm from men with differential levels of sperm DNA fragmentation index (DFI).

DESIGN

Prospective study.

SETTING

University-affiliated reproductive medicine center.

PATIENT(S)

A total of 278 male patients consulting for couple infertility were recruited from the First Affiliated Hospital of Wenzhou Medical University.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Genome-wide DNA methylation analysis was performed using Infinium MethylationEPIC BeadChip on spermatozoal DNA from 20 male patients. Differentially methylated regions (DMRs) were identified and validated using targeted bisulfite amplicon sequencing in spermatozoal DNA from 266 males.

RESULT(S)

Unsupervised hierarchical clustering analysis revealed three main clusters corresponding to sperm DFI levels (low, medium, or high). Between-cluster comparisons identified 959 (medium-low), 738 (high-medium), and 937 (high-low) DMRs. Sixty-six DMRs were validated in the 266-sample cohort, of which nine CpG fragments corresponding to nine genes (BLCAP, DIRAS3, FAM50B, GNAS, MEST, TSPAN32, PSMA8, SYCP1, and TEX12) exhibited significantly altered methylation in those with high DFI (≥25%) compared with those with low DFI (<25%).

CONCLUSION(S)

We identified and validated a distinct DNA methylation signature associated with sperm DNA damage in a large, unselected cohort. These results indicate that sperm DNA damage may affect DNA methylation patterns in human sperm.

Relevance of sperm imprinted gene methylation on assisted reproductive technique outcomes and pregnancy loss: a systematic review

Recent evidence suggests that gamete-imprinted genes play a role in embryo and placenta development and growth. This systematic review aimed to evaluate whether altered methylation of sperm-imprinted genes associates with sperm DNA fragmentation (SDF), pregnancy loss rate and assisted reproductive technique (ART) outcome. To accomplish this, Pubmed, MEDLINE, Cochrane, Academic One Files, Google Scholar, and Scopus databases were used for search strategy from each database inception until December 2020. Specific keywords were used. Studies satisfying the PECOS (Population, Exposure, Comparison/Comparator, Outcomes, Study design) model were retrieved. Ten studies could be included in the qualitative analysis. A significant association was reported between increased SDF rate and aberrant methylation of H19/IGF2 and KCNQ1 genes by two studies. A significantly lower H19 methylation was found in patients with idiopathic recurrent pregnancy loss (RPL) and in infertile patients compared to fertile men. Methylation of GLT2, PEG1/MEST, and ZAC/PLACL1 were similar in patients with RPL and controls. The ART outcome was similar in patients with aberrant and normal methylation of H19, SNRPN, KCNQ1OT1, PEG1/MEST, LIT1, PEG3, NESPAS, and GLT2. By contrast, a study showed an association between altered GLT2 methylation and more inferior ART results. If further confirmed by well-sized studies, these data might be helpful to identify possible epigenetic predictors of ART outcome. Particularly, aberrant methylation of H19/IGF2 and KCNQ1 genes might represent interesting targets that deserve further investigation.

DNA methylation in human sperm: a systematic review

BACKGROUND

Studies in non-human mammals suggest that environmental factors can influence spermatozoal DNA methylation, and some research suggests that spermatozoal DNA methylation is also implicated in conditions such as subfertility and imprinting disorders in the offspring. Together with an increased availability of cost-effective methods of interrogating DNA methylation, this premise has led to an increasing number of studies investigating the DNA methylation landscape of human spermatozoa. However, how the human spermatozoal DNA methylome is influenced by environmental factors is still unclear, as is the role of human spermatozoal DNA methylation in subfertility and in influencing offspring health.

OBJECTIVE AND RATIONALE

The aim of this systematic review was to critically appraise the quality of the current body of literature on DNA methylation in human spermatozoa, summarize current knowledge and generate recommendations for future research.

SEARCH METHODS

A comprehensive literature search of the PubMed, Web of Science and Cochrane Library databases was conducted using the search terms 'semen' OR 'sperm' AND 'DNA methylation'. Publications from 1 January 2003 to 2 March 2020 that studied human sperm and were written in English were included. Studies that used sperm DNA methylation to develop methodologies or forensically identify semen were excluded, as were reviews, commentaries, meta-analyses or editorial texts. The Grading of Recommendations, Assessment, Development and Evaluations (GRADE) criteria were used to objectively evaluate quality of evidence in each included publication.

OUTCOMES

The search identified 446 records, of which 135 were included in the systematic review. These 135 studies were divided into three groups according to area of research; 56 studies investigated the influence of spermatozoal DNA methylation on male fertility and abnormal semen parameters, 20 studies investigated spermatozoal DNA methylation in pregnancy outcomes including offspring health and 59 studies assessed the influence of environmental factors on spermatozoal DNA methylation. Findings from studies that scored as 'high' and 'moderate' quality of evidence according to GRADE criteria were summarized. We found that male subfertility and abnormal semen parameters, in particular oligozoospermia, appear to be associated with abnormal spermatozoal DNA methylation of imprinted regions. However, no specific DNA methylation signature of either subfertility or abnormal semen parameters has been convincingly replicated in genome-scale, unbiased analyses. Furthermore, although findings require independent replication, current evidence suggests that the spermatozoal DNA methylome is influenced by cigarette smoking, advanced age and environmental pollutants. Importantly however, from a clinical point of view, there is no convincing evidence that changes in spermatozoal DNA methylation influence pregnancy outcomes or offspring health.

WIDER IMPLICATIONS

Although it appears that the human sperm DNA methylome can be influenced by certain environmental and physiological traits, no findings have been robustly replicated between studies. We have generated a set of recommendations that would enhance the reliability and robustness of findings of future analyses of the human sperm methylome. Such studies will likely require multicentre collaborations to reach appropriate sample sizes, and should incorporate phenotype data in more complex statistical models.

The marker of alkyl DNA base damage, N7-methylguanine, is associated with semen quality in men

Sperm DNA contains a range of DNA base damage that can arise, in part, from exposure to methylating agents. However, the effects are not fully characterized and so the aim of this study was to investigate associations between semen quality and the levels of N7-methyldeoxyguanosine (N7-MedG), a marker of exposure to methylating agents, and other markers of DNA damage and DNA methylation. Sperm samples were collected from 105 men attending an assisted reproduction clinic as part of a couple undergoing treatment for infertility and semen quality assessed manually according to WHO guidelines. Semen levels of N7-MedG, quantified by immunoslotblot, were significantly higher in men with sperm concentration < 15 × 10⁶/ml (p ≤ 0.01), semen volume < 1.5 ml (p ≤ 0.05) and also in men with any aspect of semen quality below WHO reference levels (p ≤ 0.001). Measures of neutral Comet DNA damage were correlated with semen quality in a univariate analysis but not after adjustment for N7-MedG levels. Sperm concentration was negatively associated with % methylation at the gene for DAZL but no other marker of global or gene-specific DNA methylation. Results support the hypothesis that the known toxic and DNA damaging properties of alkylating agent exposure may have direct deleterious consequences on semen quality.

Hypomethylation of the DAZ3 promoter in idiopathic asthenospermia: a screening tool for liquid biopsy

Given the role of the deleted in azoospermia gene in male infertility, whether the somatic deleted in azoospermia methylation status is associated with idiopathic asthenospermia should be determined. To investigate the methylation levels of the deleted in azoospermia promoter in peripheral white blood cells from idiopathic asthenospermia patients relative to those in normozoospermia controls, 61 ethylene diamine tetraacetic acid anticoagulant blood samples were drawn from all participants for DNA isolation. The deleted in azoospermia promoter methylation ratio was detected by MassARRAY-based methylation quantification and confirmed by quantitative methylation-specific polymerase chain reaction. A MassARRAY-based methylation analysis showed that the deleted in azoospermia 3 promoter (0 to − 2 kbp) was significantly hypomethylated in peripheral white blood cells from idiopathic asthenospermia males, specifically one CpG site (− 246 to − 247). Quantitative methylation-specific polymerase chain reaction data further confirmed that the methylation level of the deleted in azoospermia 3 promoter region in idiopathic asthenospermia patients was significantly lower than that in normozoospermia males. The area under the receiver operating characteristic curve determined by quantitative methylation-specific polymerase chain reaction was 0.737 (95% confidence interval: 0.552 to 0.924), with a sensitivity of 53.9% and a specificity of 88.2% at a cut-off level of 74.7%. Therefore, our results suggested that methylation ratio detection of the deleted in azoospermia 3 promoter region by real-time polymerase chain reaction assay is a promising and feasible tool for liquid biopsy in the clinical laboratories. The methylation status of other reported infertility-related genes should also be investigated in peripheral white blood cells.

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.

Unraveling epigenomic abnormality in azoospermic human males by WGBS, RNA-Seq, and transcriptome profiling analyses

PURPOSE

To determine associations between genomic DNA methylation in testicular cells and azoospermia in human males.

METHODS

This was a case-control study investigating the differences and conservations in DNA methylation, genome-wide DNA methylation, and bulk RNA-Seq for transcriptome profiling using testicular biopsy tissues from NOA and OA patients. Differential methylation and different conserved methylation regions associated with azoospermia were identified by comparing genomic DNA methylation of testicular seminiferous cells derived from NOA and OA patients.

RESULTS

The genome methylation modification of testicular cells from NOA patients was disordered, and the reproductive-related gene expression was significantly different.

CONCLUSION

Our findings not only provide valuable knowledge of human spermatogenesis but also paved the way for the identification of genes/proteins involved in male germ cell development. The approach presented in this report provides a powerful tool to identify responsible biomolecules, and/or cellular changes (e.g., epigenetic abnormality) that induce male reproductive dysfunction such as OA and NOA.

Increased DNA methylation in the spermatogenesis-associated (SPATA) genes correlates with infertility

BACKGROUND

Spermatogenesis-associated (SPATA) family of genes plays important roles in spermatogenesis, sperm maturation or fertilization. The knockout studies in mice have demonstrated that SPATA genes are crucial for fertility. Gene expression and genetic polymorphism studies have further suggested their correlation with infertility; however, methylation analysis of SPATA genes in human male infertility has not yet been undertaken.

OBJECTIVES

To analyze the methylation status of SPATA4, SPATA5 and SPATA6 genes in oligozoospermic male infertility.

MATERIALS AND METHODS

In the present study, we have analyzed DNA methylation pattern in the promoter regions of SPATA4, SPATA5 and SPATA6 genes in oligozoospermic patients and compared it with normozoospermic fertile controls. Semen samples were obtained from 30 oligozoospermic infertile and 19 normozoospermic fertile controls, and DNA methylation levels of the target gene promoters were analyzed by amplicon based deep sequencing methylation analysis using MiSeq.

RESULTS

SPATA4 (P < 0.0008), SPATA5 (P = 0.009) and SPATA6 (Promoter, P < 0.0005; Exon 1, P = 0.0128) genes were significantly hypermethylated in oligozoospermic patients in comparison to controls. This is the first study reporting a higher methylation in the promoters of SPATA4, SPATA5 and SPATA6 in oligozoospermic infertile individuals in comparison to the normozoospermic fertile controls.

DISCUSSION

Altered methylation of SPATA genes would affect pathways involved in sperm production or affect various processes linked to sperm fertility.

CONCLUSION

In conclusion, hypermethylation in the SPATA4, SPATA5 and SPATA6 genes correlates with oligozoospermic infertility.

Epigenetics and human reproduction: the primary prevention of the noncommunicable diseases

Epigenetic regulation of gene expression plays a key role in affecting human health and diseases with particular regard to human reproduction. The major concern in this field is represented by the epigenetic modifications in the embryo and the increased risk of long-life disorders induced by the use of assisted reproduction techniques, able to affect the epigenetic assessment in the first steps of embryo development. In this review, we analyze the correlation between epigenetic modifications and human reproduction, suggesting that the reversibility of the epigenetic processes could represent a novel resource for the treatment of the couple's infertility and that parental lifestyle in periconceptional period could be considered as an important issue of primary prevention.

High-resolution analysis of germ cells from men with sex chromosomal aneuploidies reveals normal transcriptome but impaired imprinting

Background

The most common sex chromosomal aneuploidy in males is Klinefelter syndrome, which is characterized by at least one supernumerary X chromosome. While these men have long been considered infertile, focal spermatogenesis can be observed in some patients, and sperm can be surgically retrieved and used for artificial reproductive techniques. Although these gametes can be used for fertility treatments, little is known about the molecular biology of the germline in Klinefelter men. Specifically, it is unclear if germ cells in Klinefelter syndrome correctly establish the androgenetic DNA methylation profile and transcriptome. This is due to the low number of germ cells in the Klinefelter testes available for analysis.

Results

Here, we overcame these difficulties and successfully investigated the epigenetic and transcriptional profiles of germ cells in Klinefelter patients employing deep bisulfite sequencing and single-cell RNA sequencing. On the transcriptional level, the germ cells from Klinefelter men clustered together with the differentiation stages of normal spermatogenesis. Klinefelter germ cells showed a normal DNA methylation profile of selected germ cell-specific markers compared with spermatogonia and sperm from men with normal spermatogenesis. However, germ cells from Klinefelter patients showed variations in the DNA methylation of imprinted regions.

Conclusions

These data indicate that Klinefelter germ cells have a normal transcriptome but might present aberrant imprinting, showing impairment in germ cell development that goes beyond mere germ cell loss.

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0720-3) contains supplementary material, which is available to authorized users.

DAZL is a master translational regulator of murine spermatogenesis

Expression of DAZ-like (DAZL) is a hallmark of vertebrate germ cells, and is essential for embryonic germ cell development and differentiation, yet the gametogenic function of DAZL has not been fully characterized and most of its in vivo direct targets remain unknown. We showed that postnatal stage-specific deletion of Dazl in mouse germ cells did not affect female fertility, but caused complete male sterility with gradual loss of spermatogonial stem cells, meiotic arrest and spermatid arrest. Using the genome-wide high-throughput sequencing of RNAs isolated by cross-linking immunoprecipitation and mass spectrometry approach, we found that DAZL bound to a large number of testicular mRNA transcripts (at least 3008) at the 3'-untranslated region and interacted with translation proteins including poly(A) binding protein. In the absence of DAZL, polysome-associated target transcripts, but not their total transcripts, were significantly decreased, resulting in a drastic reduction of an array of spermatogenic proteins and thus developmental arrest. Thus, DAZL is a master translational regulator essential for spermatogenesis.

Effects of ten–eleven translocation 1 (Tet1) on DNA methylation and gene expression in chicken primordial germ cells

Ten–eleven translocation 1 (Tet1) is involved in DNA demethylation in primordial germ cells (PGCs); however, the precise regulatory mechanism remains unclear. In the present study the dynamics of 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) in developing PGCs and the role of Tet1 in PGC demethylation were analysed. Results show that 5mC levels dropped significantly after embryonic Day 4 (E4) and 5hmC levels increased reaching a peak at E5–E5.5. Interestingly, TET1 protein was highly expressed during E5 to E5.5, which showed a consistent trend with 5hmC. The expression of pluripotency-associated genes (Nanog, PouV and SRY-box 2 (Sox2)) and germ cell-specific genes (caveolin 1 (Cav1), piwi-like RNA-mediated gene silencing 1 (Piwi1) and deleted in azoospermia-like (Dazl)) was upregulated after E5, whereas the expression of genes from the DNA methyltransferase family was decreased. Moreover, the Dazl gene was highly methylated in early PGCs and then gradually hypomethylated. Knockdown of Tet1 showed impaired survival and proliferation of PGCs, as well as increased 5mC levels and reduced 5hmC levels. Further analysis showed that knockdown of Tet1 led to elevated DNA methylation levels of Dazl and downregulated gene expression including Dazl. Thus, this study reveals the dynamic epigenetic reprogramming of chicken PGCs invivo and the molecular mechanism of Tet1 in regulating genomic DNA demethylation and hypomethylation of Dazl during PGC development.

Epigenetics of Male Fertility: Effects on Assisted Reproductive Techniques

During the last decades the study of male infertility and the introduction of the assisted reproductive techniques (ARTs) has allowed to understand that normal sperm parameters do not always predict fertilization. Sperm genetic components could play an important role in the early stages of embryonic development. Based on these acquisitions, several epigenetic investigations have been developed on spermatozoa, with the aim of understanding the multifactorial etiology of male infertility and of showing whether embryonic development may be influenced by sperm epigenetic abnormalities. This article reviews the possible epigenetic modifications of spermatozoa and their effects on male fertility, embryonic development and ART outcome. It focuses mainly on sperm DNA methylation, chromatin remodeling, histone modifications and RNAs.

Comparative whole genome DNA methylation profiling of cattle sperm and somatic tissues reveals striking hypomethylated patterns in sperm

Background

Although sperm DNA methylation has been studied in humans and other species, its status in cattle is largely unknown.

Results

Using whole-genome bisulfite sequencing (WGBS), we profiled the DNA methylome of cattle sperm through comparison with three somatic tissues (mammary gland, brain, and blood). Large differences between cattle sperm and somatic cells were observed in the methylation patterns of global CpGs, pericentromeric satellites, partially methylated domains (PMDs), hypomethylated regions (HMRs), and common repeats. As expected, we observed low methylation in the promoter regions and high methylation in the bodies of active genes. We detected selective hypomethylation of megabase domains of centromeric satellite clusters, which may be related to chromosome segregation during meiosis and their rapid transcriptional activation upon fertilization. We found more PMDs in sperm cells than in somatic cells and identified meiosis-related genes such asKIF2B and REPIN1, which are hypomethylated in sperm but hypermethylated in somatic cells. In addition to the common HMRs around gene promoters, which showed substantial differences between sperm and somatic cells, the sperm-specific HMRs also targeted to distinct spermatogenesis-related genes, including BOLL, MAEL, ASZ1, SYCP3, CTCFL, MND1, SPATA22, PLD6, DDX4, RBBP8, FKBP6, and SYCE1. Although common repeats were heavily methylated in both sperm and somatic cells, some young Bov-A2 repeats, which belong to the SINE family, were hypomethylated in sperm and could affect the promoter structures by introducing new regulatory elements.

Conclusions

Our study provides a comprehensive resource for bovine sperm epigenomic research and enables new discoveries about DNA methylation and its role in male fertility.

Differential promoter methylation of DAZL gene in bulls with varying seminal parameters

In India, cross-breeding of indigenous cattle with exotic cattle such as Holstein Friesian and Jersey has been going on since last four decades to improve milk production. Although it has led to increased milk yield, the subfertility in male cross-bred progeny has remained a significant problem. Epigenetic modifications (DNA methylation, histone modifications and chromatin remodelling) are regarded as key players influencing gene expression. DAZL gene plays an important role in germline development and gametogenesis. The methylation and mRNA expression level of this gene have been significantly negatively correlated in the testes of cattle-yak hybrids and their parents. This study analysed the methylation profile of DAZL gene promoter in bull spermatozoa in an attempt to speculate its role in cross-bred cattle subfertility. Semen samples from Sahiwal, Holstein Friesian and Frieswal bulls (Sahiwal X Holstein Friesian) with varying semen motility parameters were collected, and DNA was isolated. Methylation-specific primers were used to amplify part of promoter and exon 1 of DAZL gene using bisulphite-converted DNA. The amplified products were sequenced after cloning in pTZ57R/T vector. Sequence analysis revealed significantly higher DNA methylation of DAZL gene in Frieswal bulls with poor motility (28.26%) as compared to medium (15.21%) and high motility phenotype (6.52%). In pure-bred counterparts, Sahiwal and Holstein Friesian, epigenetic marks were more in the former (15.21%) than the latter (4.34%), but in both cases, the values were lower as compared to the poor motility Frieswal bulls. This suggests that differential hypermethylation of the CpG islands could possibly influence reproductive parameters in bovines.

Impairment of sperm DNA methylation in male infertility: a meta-analytic study

Considering the widespread use of assisted reproductive techniques (ART), DNA methylation of specific genes involved in spermatogenesis achieves increasingly clinical relevance, representing a possible explanation of increased incidence of syndromes related to genomic imprinting in medically assisted pregnancies. Several trials suggested a relationship between male sub-fertility and sperm DNA methylation, although its weight on seminal parameters alteration is still a matter of debate. To evaluate whether aberrant sperm DNA methylation of imprinted genes is associated with impaired sperm parameters. Meta-analysis of controlled clinical trials evaluating imprinted genes sperm DNA methylation comparing men with idiopathic infertility to fertile controls. Twenty-four studies were included, allowing a meta-analytic evaluation for H19, MEST, SNRPN, and LINE-1. When a high heterogeneity of the results was demonstrated, the random effect model was used. H19 methylation levels resulted significantly lower in 879 infertile compared with 562 fertile men (7.53%, 95% CI: 5.14-9.93%, p < 0.001), suggesting a 9.91-fold higher risk ratio to show aberrant sperm DNA methylation (95% CI: 5.55-17.70, p < 0.001, I²  = 19%) in infertile men. The mean MEST methylation level was significantly higher in 846 infertile compared with 353 fertile men (3.35%, 95% CI: 1.41-5.29%, p < 0.001), as well as for SNRPN comparing 301 infertile men with 124 controls (3.23%, 95% CI: 0.75-5.72%, p < 0.001). LINE-1 methylation levels did not differ between 291 infertile men and 198 controls (0.44%, 95% CI: -2.04-1.16%, p = 0.63). The meta-analytic approach demonstrated that male infertility is associated with altered sperm methylation at H19, MEST, and SNRPN. Although its role in infertility remains unclear, sperm DNA methylation could be associated with the epigenetic risk in ART. In this setting, before proposing this analysis in clinical practice, an accurate identification of the most representative genes and a cost-effectiveness evaluation should be assessed in ad hoc prospective studies.

RNA immunoprecipitation identifies novel targets of DAZL in human foetal ovary

Study question

Can novel meiotic RNA targets of DAZL (deleted in azoospermia-like) be identified in the human foetal ovary?

Summary answer

SYCP1 (synaptonemal complex protein-1), TEX11 (testis expressed 11) and SMC1B (structural maintenance of chromosomes 1B) are novel DAZL targets in the human foetal ovary, thus DAZL may have previously unrecognised roles in the translational regulation of RNAs involved in chromosome cohesion and DNA recombination in the oocyte from the time of initiation of meiosis.

What is known already

The phenotype of Dazl deficiency in mouse is infertility in both sexes and DAZL has also been linked to infertility in humans. Few studies have explored targets of this RNA-binding protein. The majority of these investigations have been carried out in mouse, and have focussed on the male thus the basis for its central function in regulating female fertility is largely unknown.

Study design size, duration

We carried out RNA sequencing after immunoprecipitation of endogenous DAZL from human foetal ovarian tissue (17 weeks of gestation, obtained after elective termination of pregnancy) to identify novel DAZL targets involved in meiosis (n = 3 biological replicates).

Participants/materials, setting, methods

Using quantitative RT-PCR, we examined the expression of selected RNAs identified by our immunoprecipitation across gestation, and visualised the expression of potential target SMC1B in relation to DAZL, with a combination of in situ hybridisation and immunohistochemistry. 3′ untranslated region (3′UTR)-luciferase reporter assays and polysome profile analysis were used to investigate the regulation of three RNA targets by DAZL, representing key functionalities: SYCP1, TEX11 and SMC1B.

Main results and the role of chance

We identified 764 potential RNA targets of DAZL in the human foetal ovary (false discovery rate 0.05 and log-fold change ≥ 2), with functions in synaptonemal complex formation (SYCP1, SYCP3), cohesin formation (SMC1B, RAD21), spindle assembly checkpoint (MAD2L1, TRIP13) and recombination and DNA repair (HORMAD1, TRIP13, TEX11, RAD18, RAD51). We demonstrated that the translation of novel targets SYCP1 (P = 0.004), TEX11 (P = 0.004) and SMC1B (P = 0.002) is stimulated by the presence of DAZL but not by a mutant DAZL with impaired RNA-binding activity.

Large scale data

The raw data are available at GEO using the study ID: GSE81524.

Limitations, reasons for caution

This analysis is based on identification of DAZL targets at the time when meiosis starts in the ovary: it may have other targets at other stages of oocyte development, and in the testis. Representative targets were validated, but detailed analysis was not performed on the majority of putative targets.

Wider implications of the findings

These data indicate roles for DAZL in the regulation of several key functions in human oocytes. Through the translational regulation of novel RNA targets SMC1B and TEX11, DAZL may have a key role in regulating chromosome cohesion and DNA recombination; two processes fundamental in determining oocyte quality and whose establishment in foetal life may support lifelong fertility.

Study funding and competing interest(s)

This study was supported by the UK Medical Research Council (grant no G1100357 to R.A.A. and an intramural MRC programme grant to I.R.A.). The authors declare no competing interests.

Global methylation status of sperm DNA in carriers of chromosome structural aberrations

Male infertility might be clearly associated with aberrant DNA methylation patterns in human spermatozoa. An association between oxidative stress and the global methylation status of the sperm genome has also been suggested. The aim of the present study was to determine whether the global sperm DNA methylation status was affected in the spermatozoa of carriers of chromosome structural aberrations. The relationships between the 5-methylcytosine (m⁵C) levels in spermatozoa and chromatin integrity status were evaluated. The study patients comprised male carriers of chromosome structural aberrations with reproductive failure (n = 24), and the controls comprised normozoospermic sperm volunteers (n = 23). The global m⁵C level was measured using thin-layer chromatography (TLC) and immunofluorescence (IF) techniques. The sperm chromatin integrity was assessed using aniline blue (AB) staining and TUNEL assay. The mean m⁵C levels were similar between the investigated chromosome structural aberrations carriers (P) and controls (K). However, sperm chromatin integrity tests revealed significantly higher values in chromosomal rearrangement carriers than in controls (P < 0.05). Although the potential relationship between sperm chromatin integrity status and sperm DNA fragmentation and the m⁵C level juxtaposed in both analyzed groups (P vs K) was represented in a clearly opposite manner, the low chromatin integrity might be associated with the high hypomethylation status of the sperm DNA observed in carriers of chromosome structural aberrations.

Sex of co-twin affects the in vitro developmental competence of oocytes derived from 6- to 8-week-old lambs

Several intrinsic factors (age, genotype, liveweight) influence the reliability of juvenile in vitro fertilisation embryo transfer (JIVET) programs. Limited evidence indicates that variability between lambs is reduced in twin-born lambs. We examined the impact of birth type (single, twin, triplet) and sex of the co-twin (with age, birthweight and liveweight as covariates) on JIVET outcomes. Birth type did not influence any parameter studied. However, blastocysts produced, as a percentage of embryos cleaved or total cumulus–oocyte complexes collected, was higher (P < 0.05) for females born with a female co-twin (67.0 ± 6.1, 57.5 ± 6.0 respectively) compared with those born with a male co-twin (26.9 ± 6.5, 22.3 ± 6.2 respectively; least-square mean ± s.e.m.). Blastocyst rates for lambs born with a male co-twin did not differ significantly from lambs born either as singles (39.5 ± 6.7%, 34.6 ± 6.5% respectively) or triplets (43.1 ± 10.6%, 36.5 ± 10.3% respectively). Other parameters were not influenced by sex of the co-twin. These results are indicative of an enhancement effect of the female co-twin on oocyte development. From a practical perspective, selecting lambs for a JIVET program based on litter size and sex of the co-twin is warranted.

Environmental pollutants: genetic damage and epigenetic changes in male germ cells

About a quarter of the human diseases occurs for exposure to air pollution. The male reproductive system, and especially spermatogenesis, seems to be particularly sensitive. As result, male infertility is increasing in industrial countries becoming a top priority for public health. In addition to psychological distress and economic constraints, poorer semen quality may have trans-generational effects including congenital malformations in the offspring and predispose to later onset adult diseases. Genetic and epigenetic alterations are involved in the failure of spermatogenesis. In this paper, we reviewed the major evidences of the effects of air pollutants on male infertility as well as the role of sperm DNA damage and epigenetic changes in affecting spermatogenesis. A better knowledge on the effects of air contaminants on the molecular mechanisms leading to infertility is of huge importance to help clinicians in identifying the cause of infertility but above all, in defining preventive and therapeutic protocols.

Genome-Scale Assessment of Age-Related DNA Methylation Changes in Mouse Spermatozoa

DNA methylation plays important roles in the production and functioning of spermatozoa. Recent studies have suggested that DNA methylation patterns in spermatozoa can change with age, but the regions susceptible to age-related methylation changes remain to be fully elucidated. In this study, we conducted genome-scale DNA methylation profiling of spermatozoa obtained from C57BL/6N mice at 8 weeks (8w), 18 weeks (18w) and 17 months of age (17m). There was no substantial difference in the global DNA methylation patterns between 18w and 17m samples except for a slight increase of methylation levels in long interspersed nuclear elements in the 17m samples. We found that maternally methylated imprinting control regions (mICRs) and spermatogenesis-related gene promoters had 5–10% higher methylation levels in 8w samples than in 18w or 17m samples. Analysis of individual sequence reads suggested that these regions were fully methylated (80–100%) in a subset of 8w spermatozoa. These regions are also known to be highly methylated in a subset of postnatal spermatogonia, which might be the source of the increased DNA methylation in 8w spermatozoa. Another possible source was contamination by somatic cells. Although we carefully purified the spermatozoa, it was difficult to completely exclude the possibility of somatic cell contamination. Further studies are needed to clarify the source of the small increase in DNA methylation in the 8w samples. Overall, our findings suggest that DNA methylation patterns in mouse spermatozoa are relatively stable throughout reproductive life.

Evaluation of spermatozoal function-useful tools or just science

Conventional microscopic semen analysis does not provide precise information on the fertilizing potential of a male. The traditional basis for semen evaluation is that male fertility is dependent on production of a "proper" concentration/number of motile, morphologically normal spermatozoa in excess to achieve conception. Many independent studies, especially in human medicine, have demonstrated that the absolute number of spermatozoa does not accurately determine fertility, but their functional competence. Many functional tests of spermatozoa are developed over the last decades. Computer-assisted sperm analysis (CASA) and flow cytometry have become the gold standard for semen assessment in specialized andrology laboratories. Other functional assays, such as gamete interaction tests, provide additional information regarding the real fertilizing potential of sperm cells. From this point of view, such tests are valuable diagnostic tools in fertility disorders and may be helpful to make a decision which method of treatment to use: pharmacological therapy, intrauterine insemination, introduction of classic IVF, ICSI or exclusion from a breeding programme. The most useful gamete interaction tests include induced acrosome reaction, zona pellucida binding assay, oocyte penetration assay and hyaluronan binding assay. In recent years, andrology has entered into a new era of sophisticated OMICS methods. Genomics, epigenomics, transcriptomics and proteomics brought high hopes for rapid progress in clinical diagnostics.

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.

From the Cover: Sperm Molecular Biomarkers Are Sensitive Indicators of Testicular Injury following Subchronic Model Toxicant Exposure

Traditional testis histopathology endpoints remain the gold standard for evaluating testicular insult and injury in a non-clinical setting, but are invasive and unfeasible for monitoring these effects clinically in humans. Assessing testicular injury in humans relies on semen and serum hormone analyses, both of which are insensitive and poor indicators of effect. Therefore, we hypothesized that sperm messenger RNA (mRNA) transcripts and DNA methylation marks can be used as translatable and sensitive indicators or testicular injury. Dose-response studies using adult male Fischer 344 rats subchronically exposed to model Sertoli cell toxicants (0.14, 0.21, and 0.33% 2,5-hexanedione, and 30, 50, and 70 mg/kg/day carbendazim), and a model germ cell toxicant (1.4, 3.4, and 5.1 mg/kg/day cyclophosphamide) for 3 months were evaluated for testicular injury by traditional histopathological endpoints, changes in sperm mRNA transcript levels using custom PCR arrays, and alterations in sperm DNA methylation via reduced representation bisulfite sequencing. Testis histopathological evaluation and PCR array analysis of the sperm transcriptome identified dose-dependent changes elicited by toxicant exposure (P < 0.05). Global sperm DNA methylation analysis of subchronic 0.33% 2,5-hexandione and 5.1 mg/kg/day cyclophosphamide exposure using a Monte Carlo approach did not identify differentially methylated regions (methylation difference > 10% and q < 0.05) with robust signatures. Overall, these results suggest that sperm mRNA transcripts are sensitive indicators of low dose toxicant-induced testicular injury in the rat, while sperm DNA methylation changes are not. Additionally, the Monte Carlo analysis is a powerful approach that can be used to assess the robustness of signals resulting from -omic studies.

The effect of parental 5,10-methylenetetrahydrofolate reductase 677C/T and 1298A/C gene polymorphisms on response to single-dose methotrexate in tubal ectopic pregnancy

OBJECT

The aim of this study was to assess the effect of parental 5,10-methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms (677C/T and 1298A/C) on response to single-dose methotrexate (MTX) treatment in tubal ectopic pregnancy (TEP).

MATERIALS AND METHODS

In this prospective cohort study, cases with unruptured TEPs were grouped into two according to their response to single-dose MTX treatment (Group 1: responsive, n:88; Group 2: unresponsive, n:21). The groups were compared with regard to baseline demographic and clinical parameters. As a main outcome measure, the independent effects of parental MTHFR gene polymorphisms on response to single dose MTX treatment were evaluated.

RESULTS

One hundred and nine unruptured TEP were included in the final analysis. The mean maternal age was 29.30 ± 5.21 years, gravity 2 (min-max: 1-5), parity 1 (min-max: 0-4). The median serum beta-human chorionic gonadotropin (β-hCG) was 1403.35 MI/I (Q₁-Q₃: 517-2564). The overall response rate was 81% (88/109). The groups were similar with respect to basic baseline demographic data and serum β-hCG level. Binary logistic regression analysis showed that the presence of parental MTHFR677C/T and 1298A/C polymorphism were not independent factor predicting treatment success (p > 0.05). The only independent factor for resistance to single dose MTX was the previous TEP (OR: 4.47 (1.18-16.9)).

CONCLUSION

Parental MTHFR 677C/T and 1298A/C mutations do not predict the outcome of single dose intramuscular MTX treatment in unruptured TEP.

Highly conserved epigenetic regulation of BOULE and DAZL is associated with human fertility

Separation of germ cells from somatic cells is a widespread feature of animal sexual reproduction, with a core set of germ cell factors conserved among diverse animals. It is not known what controls their conserved gonad-specific expression. Core components of epigenetic machinery are ancient, but its role in conserved tissue expression regulation remains unexplored. We found that promoters of the reproductive genes BOULE and DAZL exhibit differential DNA methylation, consistent with their gonad-specific expression in humans and mice. Low or little promoter methylation from the testicular tissue is attributed to spermatogenic cells of various stages in the testis. Such differential DNA methylation is present in the orthologous promoters not only of other mammalian species, but also of chickens and fish, supporting a highly conserved epigenetic mechanism. Furthermore, hypermethylation of DAZL and BOULE promoters in human sperm is associated with human infertility. Our data strongly suggest that epigenetic regulation may underlie conserved germ-cell-specific expression, and such a mechanism may play an important role in human fertility.-Zhang, C., Xue, P., Gao, L., Chen, X., Lin, K., Yang, X., Dai, Y., Xu, E. Y. Highly conserved epigenetic regulation of BOULE and DAZL is associated with human fertility.

Epigenetics: A key paradigm in reproductive health

It is well established that there is a heritable element of susceptibility to chronic human ailments, yet there is compelling evidence that some components of such heritability are transmitted through non-genetic factors. Due to the complexity of reproductive processes, identifying the inheritance patterns of these factors is not easy. But little doubt exists that besides the genomic backbone, a range of epigenetic cues affect our genetic programme. The inter-generational transmission of epigenetic marks is believed to operate via four principal means that dramatically differ in their information content: DNA methylation, histone modifications, microRNAs and nucleosome positioning. These epigenetic signatures influence the cellular machinery through positive and negative feedback mechanisms either alone or interactively. Understanding how these mechanisms work to activate or deactivate parts of our genetic programme not only on a day-to-day basis but also over generations is an important area of reproductive health research.

Intra- and inter-individual differences in human sperm DNA methylation

There is growing evidence that sperm DNA methylation is important in maintaining proper sperm health and function. Previous studies have associated sperm DNA methylation levels with sperm quality and function, however, little is known regarding the intra- and inter-individual variability in sperm methylation levels. This study characterizes this variation. Sperm epigenetic differences between successive semen samples from 12 patients were examined to identify the intra- and inter-individual differences globally across the genome, and in specifically defined genomic regions using the Illumina Infinium HumanMethylation450 BeadChips. Methylation analysis identified a bimodal distribution in the methylation levels that were non-uniformly distributed across the different genomic regions. The methylation levels were highly correlated in both the intra- and inter-individual comparisons. The intra-individual methylation levels were more highly correlated than the inter-individual comparison both globally and across the defined genomic regions, demonstrating that sperm DNA methylation levels are relatively stable between semen sample collections.