Gamete imprinting: setting epigenetic patterns for the next generation

Mitochondrial Calcium Disorder Affects Early Embryonic Development in Mice through Regulating the ERK/MAPK Pathway

The homeostasis of mitochondrial calcium ([Ca2+]mt) in oocytes plays a critical role in maintaining normal reproductive cellular progress such as meiosis. However, little is known about the association between [Ca2+]mt homeostasis and early embryonic development. Two in vitro mouse MII oocyte models were established by using a specific agonist or inhibitor targeting mitochondrial calcium uniporters (MCU) to upregulate or downregulate [Ca2+]mt concentrations. The imbalance of [Ca2+]mt in MII oocytes causes mitochondrial dysfunction and morphological abnormity, leading to an abnormal spindle/chromosome structure. Oocytes in drug-treated groups are less likely to develop into blastocyst during in vitro culture. Abnormal [Ca2+]mt concentrations in oocytes hindered epigenetic modification and regulated mitogen-activated protein kinase (MAPK) signaling that is associated with gene expression. We also found that MAPK/ERK signaling is regulating DNA methylation in MII oocytes to modulate epigenetic modification. These data provide a new insight into the protective role of [Ca2+]mt homeostasis in early embryonic development and also demonstrate a new mechanism of MAPK signaling regulated by [Ca2+]mt that influences epigenetic modification.

Epigenetic Changes Induced by Maternal Factors during Fetal Life: Implication for Type 1 Diabetes

Organ-specific autoimmune diseases, such as type 1 diabetes, are believed to result from T-cell-mediated damage of the target tissue. The immune-mediated tissue injury, in turn, is known to depend on complex interactions between genetic and environmental factors. Nevertheless, the mechanisms whereby environmental factors contribute to the pathogenesis of autoimmune diseases remain elusive and represent a major untapped target to develop novel strategies for disease prevention. Given the impact of the early environment on the developing immune system, epigenetic changes induced by maternal factors during fetal life have been linked to a likelihood of developing an autoimmune disease later in life. In humans, DNA methylation is the epigenetic mechanism most extensively investigated. This review provides an overview of the critical role of DNA methylation changes induced by prenatal maternal conditions contributing to the increased risk of immune-mediated diseases on the offspring, with a particular focus on T1D. A deeper understanding of epigenetic alterations induced by environmental stressors during fetal life may be pivotal for developing targeted prevention strategies of type 1 diabetes by modifying the maternal environment.

Dynamics in the expression of epigenetic modifiers and histone modifications in perinatal rat germ cells during de novo DNA methylation†

Epigenetic reprogramming during perinatal germ cell development is essential for genomic imprinting and cell differentiation; however, the actors of this key event and their dynamics are poorly understood in rats. Our study aimed to characterize the expression patterns of epigenetic modifiers and the changes in histone modifications in rat gonocytes at the time of de novo DNA methylation. Using transgenic rats expressing Green Fluorescent Protein (GFP) specifically in germ cells, we purified male gonocytes by fluorescent activated cell sorting at various stages of perinatal development and established the transcriptomic profile of 165 epigenetic regulators. Using immunofluorescence on gonad sections, we tracked six histone modifications in rat male and female perinatal germ cells over time, including methylation of histone H3 on lysines 27, 9, and 4; ubiquitination of histone H2A on lysine119; and acetylation of histone H2B on lysine 20. The results revealed the dynamics in the expression of ten-eleven translocation enzymes and DNA methyltransferases in male gonocytes at the time of de novo DNA methylation. Moreover, our transcriptomic data indicate a decrease in histone ubiquitination and methylation coinciding with the beginning of de novo DNA methylation. Decreases in H2AK119Ub and H3K27me3 were further confirmed by immunofluorescence in the male germ cells but were not consistent for all H3 methylation sites examined. Together, our data highlighted transient chromatin remodeling involving histone modifications during de novo DNA methylation. Further studies addressing how these dynamic changes in histone posttranslational modifications could guide de novo DNA methylation will help explain the complex establishment of the male germ cell epigenome.

Genome-Wide DNA Methylation and RNA Analysis Reveal Potential Mechanism of Resistance to Streptococcus agalactiae in GIFT Strain of Nile Tilapia (Oreochromis niloticus )

Streptococcus agalactiae is an important pathogenic bacterium causing great economic loss in Nile tilapia (Oreochromis niloticus) culture. Resistant and susceptible groups sharing the same genome showed significantly different resistance to S. agalactiae in the genetically improved farmed tilapia strain of Nile tilapia. The resistance mechanism is unclear. We determined genome-wide DNA methylation profiles in spleen of resistant and susceptible O. niloticus at 5 h postinfection with S. agalactiae using whole-genome bisulfite sequencing. The methylation status was higher in the spleen samples from resistant fish than in the susceptible group. A total of 10,177 differentially methylated regions were identified in the two groups, including 3725 differentially methylated genes (DMGs) (3129 hyper-DMGs and 596 hypo-DMGs). The RNA sequencing showed 2374 differentially expressed genes (DEGs), including 1483 upregulated and 891 downregulated. Integrated analysis showed 337 overlapping DEGs and DMGs and 82 overlapping DEGs and differentially methylated region promoters. By integrating promoter DNA methylation with gene expression, we revealed four immune-related genes (Arnt2, Nhr38, Pcdh10, and Ccdc158) as key factors in epigenetic mechanisms contributing to pathogen resistance. Our study provided systematic methylome maps to explore the epigenetic mechanism and reveal the methylation loci of pathogen resistance and identified methylation-regulated genes that are potentially involved in defense against pathogens.

Toxic effects of 1-(N-methyl-N-nitrosamino)-1-(3-pyridinyl)-4-butanal on the maturation and subsequent development of murine oocyte

Cigarette smoke can cause follicle destruction and oocyte dysfunction and increase the risks of spontaneous abortion, stillbirth, and tubal ectopic pregnancy, affecting female reproductive health. Third-hand smoke (THS) is residual tobacco smoke existing in the environment long after cigarettes are extinguished, which can react with other compounds in the environment to produce secondary pollutants. However, the effects of THS on the female reproductive system, particularly the maturation of the oocyte, remain unclear. 1-(N-methyl-N-nitrosamino)-1-(3-pyridinyl)-4-butanal (NNA), a component of THS, is a logical biomarker of THS exposure. Thus, this study aims to investigate the toxic effects of NNA on the maturation of murine oocytes and subsequent developmental competence. Herein, murine oocytes were exposed to 0 (control group), 0.1, 1.0, 10, and 50 μM NNA for 24 h. Our results showed that NNA exposure reduced the polar body extrusion rate by causing 8-oxo-deoxyguanosine (8-OHdG) to increase and disrupting the meiotic spindle morphology by inhibiting ERK1/2 activation during in vitro maturation. Additionally, NNA exposure resulted in cleavage and blastocyst rate reduction by altering DNA and histone methylations by reducing 5 mC and H3K4me2 levels and by inducing apoptosis caused by mitochondrial dysfunction and reactive oxygen species accumulation, as shown by the increased superoxide dismutase mRNA level and by the decreased Bcl-x mRNA level. Collectively, our results demonstrate that NNA exposure reduces the maturation and developmental capability of murine oocytes by increasing the risk of DNA damage and abnormal spindle morphology, altering epigenetic modifications, and inducing apoptosis, suggesting the toxic effect of NNA on mammalian productive health.

Epigenetic regulation of progesterone receptors and the onset of labour

Progesterone plays a crucial role in maintaining pregnancy by promoting myometrial quiescence. The withdrawal of progesterone action signals the end of pregnancy and, in most mammalian species, this is achieved by a rapid fall in progesterone concentrations. However, in humans circulating progesterone concentrations remain high up to and during labour. Efforts to understand this phenomenon led to the ‘functional progesterone withdrawal’ hypothesis, whereby the pro-gestation actions of progesterone are withdrawn, despite circulating concentrations remaining elevated. The exact mechanism of functional progesterone withdrawal is still unclear and in recent years has been the focus of intense research. Emerging evidence now indicates that epigenetic regulation of progesterone receptor isoform expression may be the crucial mechanism by which functional progesterone withdrawal is achieved, effectively precipitating human labour despite high concentrations of circulating progesterone. This review examines current evidence that epigenetic mechanisms play a role in determining whether the pro-gestation or pro-contractile isoform of the progesterone receptor is expressed in the pregnant human uterus. We explore the mechanism by which these epigenetic modifications are achieved and, importantly, how these underlying epigenetic mechanisms are influenced by known regulators of uterine physiology, such as prostaglandins and oestrogens, in order to phenotypically transform the pregnant uterus and initiate labour.

Pre-implantation alcohol exposure and developmental programming of FASD: an epigenetic perspective

Exposure to alcohol during in-utero development can permanently change the developmental programming of physiological responses, thereby increasing the risk of neurological illnesses during childhood and later adverse health outcomes associated with fetal alcohol spectrum disorder (FASD). There is an increasing body of evidence indicating that exposure to alcohol during gestation triggers lasting epigenetic alterations in offspring, long after the initial insult; together, these studies support the role of epigenetics in FASD etiology. However, we still have little information about how ethanol interferes with the fundamental epigenetic reprogramming wave (e.g., erasure and re-establishment of DNA methylation marks) that characterizes pre-implantation embryo development. This review examines key epigenetic processes that occur during pre-implantation development and especially focus on the current knowledge regarding how prenatal exposure to alcohol during this period could affect the developmental programming of the early stage pre-implantation embryo. We will also outline the current limitations of studies examining the in-vivo and in-vitro effects of alcohol exposure on embryos and underline the next critical steps to be taken if we want to better understand the implicated mechanisms to strengthen the translational potential for epigenetic markers for non-invasive early detection, and the treatment of newborns that have higher risk of developing FASD.

HT-2 toxin affects development of porcine parthenotes by altering DNA and histone methylation in oocytes matured in vitro

T-2 toxin is a type A mycotoxin produced by various Fusarium species, while HT-2 toxin is a major metabolite of T-2 toxin. Both T-2 toxin and HT-2 toxin are known to have deleterious effects on animals. Our previous work showed that HT-2 treatment caused the failure of porcine oocyte maturation. In this study, we reported that HT-2 also affected porcine embryo development. In HT-2 toxin treated group, all the percentages of embryos in 2-cell, 4-cell and blastocyst stage were significantly lower compared with those in control groups. We then explored the causes from the epigenetic modification aspect of the oocytes. The analysis of fluorescence intensity showed that 5-methyl cytosine (5 mC) level was increased after exposure to HT-2 toxin in porcine oocytes, indicating that the general DNA methylation level increased in the treated porcine oocytes. In addition, histone modifications were also affected, since our results showed that H3K4me2 and H3K9me2 levels were increased in the oocytes from HT-2-treated group. Therefore, our results indicated that HT-2 toxin decreased porcine embryo developmental competence through altering the epigenetic modifications of oocytes.

Low-Dose Ionizing Radiation Exposure, Oxidative Stress and Epigenetic Programing of Health and Disease

Ionizing radiation exposure from medical diagnostic imaging has greatly increased over the last few decades. Approximately 80% of patients who undergo medical imaging are exposed to low-dose ionizing radiation (LDIR). Although there is widespread consensus regarding the harmful effects of high doses of radiation, the biological effects of low-linear energy transfer (LET) LDIR is not well understood. LDIR is known to promote oxidative stress, however, these levels may not be large enough to result in genomic mutations. There is emerging evidence that oxidative stress causes heritable modifications via epigenetic mechanisms (DNA methylation, histone modification, noncoding RNA regulation). These epigenetic modifications result in permanent cellular transformations without altering the underlying DNA nucleotide sequence. This review summarizes the major concepts in the field of epigenetics with a focus on the effects of low-LET LDIR (<100 mGy) and oxidative stress on epigenetic gene modification. In this review, we show evidence that suggests that LDIR-induced oxidative stress provides a mechanistic link between LDIR and epigenetic gene regulation. We also discuss the potential implication of LDIR exposure during pregnancy where intrauterine fetal development is highly susceptible to oxidative stress-induced epigenetic programing.

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.

Identification and Epigenetic Analysis of a Maternally Imprinted Gene Qpct

Most imprinted genes are concerned with embryonic development, especially placental development. Here, we identified a placenta-specific imprinted gene Qpct. Our results show that Qpct is widely expressed during early embryonic development and can be detected in the telecephalon, midbrain, and rhombencephalon at E9.5b-E11.5. Moreover, Qpct is strikingly expressed in the brain, lung and liver in E15.5. Expression signals for Qpct achieved a peak at E15.5 during placental development and were only detected in the labyrinth layer in E15.5 placenta. ChIP assay results suggest that the modification of histone H3K4me3 can result in maternal activating of Qpct.

High-dose folic acid supplementation alters the human sperm methylome and is influenced by the MTHFR C677T polymorphism

Dietary folate is a major source of methyl groups required for DNA methylation, an epigenetic modification that is actively maintained and remodeled during spermatogenesis. While high-dose folic acid supplementation (up to 10 times the daily recommended dose) has been shown to improve sperm parameters in infertile men, the effects of supplementation on the sperm epigenome are unknown. To assess the impact of 6 months of high-dose folic acid supplementation on the sperm epigenome, we studied 30 men with idiopathic infertility. Blood folate concentrations increased significantly after supplementation with no significant improvements in sperm parameters. Methylation levels of the differentially methylated regions of several imprinted loci (H19, DLK1/GTL2, MEST, SNRPN, PLAGL1, KCNQ1OT1) were normal both before and after supplementation. Reduced representation bisulfite sequencing (RRBS) revealed a significant global loss of methylation across different regions of the sperm genome. The most marked loss of DNA methylation was found in sperm from patients homozygous for the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism, a common polymorphism in a key enzyme required for folate metabolism. RRBS analysis also showed that most of the differentially methylated tiles were located in DNA repeats, low CpG-density and intergenic regions. Ingenuity Pathway Analysis revealed that methylation of promoter regions was altered in several genes involved in cancer and neurobehavioral disorders including CBFA2T3, PTPN6, COL18A1, ALDH2, UBE4B, ERBB2, GABRB3, CNTNAP4 and NIPA1. Our data reveal alterations of the human sperm epigenome associated with high-dose folic acid supplementation, effects that were exacerbated by a common polymorphism in MTHFR.

Elusive inheritance: Transgenerational effects and epigenetic inheritance in human environmental disease

Epigenetic mechanisms involving DNA methylation, histone modification, histone variants and nucleosome positioning, and noncoding RNAs regulate cell-, tissue-, and developmental stage-specific gene expression by influencing chromatin structure and modulating interactions between proteins and DNA. Epigenetic marks are mitotically inherited in somatic cells and may be altered in response to internal and external stimuli. The idea that environment-induced epigenetic changes in mammals could be inherited through the germline, independent of genetic mechanisms, has stimulated much debate. Many experimental models have been designed to interrogate the possibility of transgenerational epigenetic inheritance and provide insight into how environmental exposures influence phenotypes over multiple generations in the absence of any apparent genetic mutation. Unexpected molecular evidence has forced us to reevaluate not only our understanding of the plasticity and heritability of epigenetic factors, but of the stability of the genome as well. Recent reviews have described the difference between transgenerational and intergenerational effects; the two major epigenetic reprogramming events in the mammalian lifecycle; these two events making transgenerational epigenetic inheritance of environment-induced perturbations rare, if at all possible, in mammals; and mechanisms of transgenerational epigenetic inheritance in non-mammalian eukaryotic organisms. This paper briefly introduces these topics and mainly focuses on (1) transgenerational phenotypes and epigenetic effects in mammals, (2) environment-induced intergenerational epigenetic effects, and (3) the inherent difficulties in establishing a role for epigenetic inheritance in human environmental disease.

Testicular oocytes in MRL/MpJ mice possess similar morphological, genetic, and functional characteristics to ovarian oocytes

In general, mammalian males produce only spermatozoa in their testes and females produce only oocytes in their ovaries. However, newborn MRL/MpJ male mice produce oocytes within their testes. In this study, we examined the initiation and progression of oogenesis in fetal and neonatal MRL/MpJ mouse testes and evaluated the characteristics of testicular oocytes. Germ cells with positive reactions to oogenesis markers such as NOBOX oogenesis homeobox and synaptonemal complex protein 3 were observed in the MRL/MpJ fetal testes on embryonic day 18.5. These fetal testicular oocytes possessed maternal-specific methylation patterns of histone and DNA. The level of DNA methylation was still low in postnatal testicular oocytes at day 14 after birth. Additionally, the postnatal testicular oocytes contained both X and Y chromosomes and had the ability to fuse with sperm. These results suggest that some XY germ cells in fetal testes of MRL/MpJ mice enter meiosis prematurely, undergo oogenesis, and differentiate into oocytes. In addition, MRL/MpJ testicular oocytes have the ability to carry on oogenesis before and shortly after birth until they obtain some of the morphological, epigenetic, and functional characteristics of oocytes.

Aflatoxin B1 is toxic to porcine oocyte maturation

As a toxic secondary metabolite of Aspergillus species, Aflatoxin B1 (AFB1) is a major food and feed contaminant in tropical and sub-tropical regions with high temperature and humidity. It has been reported to be toxic to the female reproductive system in laboratory and domestic animals. In the present study, the influence of acute exposure to AFB1 (10 and 50 μM, 44h) on porcine oocyte maturation and its possible mechanism were investigated. The maturation rates of oocytes decreased significantly in the presence of 50 μM of AFB1. Cell cycle analysis showed that most oocytes were arrested at germinal vesicle breakdown or meosis I stage. However, actin assembly, spindle structure and chromosome alignment were not disrupted after exposure to 50 μM AFB1. Further study showed that DNA methylation levels increased in treated oocytes (50 μM). Histone methylation levels were also analysed after treatment (50 μM): H3K27me3 and H3K4me2 levels decreased, whereas H3K9me3 level increased, indicating that epigenetic modification was affected. AFB1 treatment (50 μM) also induced oxidative stress and further led to autophagy, as shown by accumulation of reactive oxygen species, up-regulated LC3 protein expression and increased mRNA levels of ATG3, ATG5 and ATG7. Annexin V-FITC staining assay revealed that AFB1 treatment (50 μM) resulted in oocyte early apoptosis, which was confirmed by increased Bak, Bax, Bcl-xl mRNA levels. Collectively, our results suggest that AFB1 disrupts porcine oocyte maturation through changing epigenetic modifications as well as inducing oxidative stress, excessive autophagy and apoptosis.

The effects of in utero bisphenol A exposure on reproductive capacity in several generations of mice

In utero bisphenol A (BPA) exposure affects reproductive function in the first generation (F1) of mice; however, not many studies have examined the reproductive effects of BPA exposure on subsequent generations. In this study, pregnant mice (F0) were orally dosed with vehicle, BPA (0.5, 20, and 50 μg/kg/day) or diethylstilbestrol (DES; 0.05 μg/kg/day) daily from gestation day 11 until birth. F1 females were used to generate the F2 generation, and F2 females were used to generate the F3 generation. Breeding studies at the ages of 3, 6, and 9 months were conducted to evaluate reproductive capacity over time. Further, studies were conducted to evaluate pubertal onset, litter size, and percentage of dead pups; and to calculate pregnancy rate, and mating, fertility, and gestational indices. The results indicate that BPA exposure (0.5 and 50 μg/kg/day) significantly delayed the age at vaginal opening in the F3 generation compared to vehicle control. Both DES (0.05 μg/kg/day) and BPA (50 μg/kg/day) significantly delayed the age at first estrus in the F3 generation compared to vehicle control. BPA exposure reduced gestational index in the F1 and F2 generations compared to control. Further, BPA exposure (0.5 μg/kg/day) compromised the fertility index in the F3 generation compared to control. Finally, in utero BPA exposure reduced the ability of female mice to maintain pregnancies as they aged. Collectively, these data suggest that BPA exposure affects reproductive function in female mice and that some effects may be transgenerational in nature.

Transient DNMT1 suppression reveals hidden heritable marks in the genome

Genome-wide demethylation and remethylation of DNA during early embryogenesis is essential for development. Imprinted germline differentially methylated domains (gDMDs) established by sex-specific methylation in either male or female germ cells, must escape these dynamic changes and sustain precise inheritance of both methylated and unmethylated parental alleles. To identify other, gDMD-like sequences with the same epigenetic inheritance properties, we used a modified embryonic stem (ES) cell line that emulates the early embryonic demethylation and remethylation waves. Transient DNMT1 suppression revealed gDMD-like sequences requiring continuous DNMT1 activity to sustain a highly methylated state. Remethylation of these sequences was also compromised in vivo in a mouse model of transient DNMT1 loss in the preimplantation embryo. These novel regions, possessing heritable epigenetic features similar to imprinted-gDMDs are required for normal physiological and developmental processes and when disrupted are associated with disorders such as cancer and autism spectrum disorders. This study presents new perspectives on DNA methylation heritability during early embryo development that extend beyond conventional imprinted-gDMDs.

Epigenetic processes in the male germline

Sperm undergo some of the most extensive chromatin modifications seen in mammalian biology. During male germline development, paternal DNA methylation marks are erased and established on a global scale through waves of demethylation and de novo methylation. As spermatogenesis progresses, the majority of the histones are removed and replaced by protamines, enabling a tighter packaging of the DNA and transcriptional shutdown. Following fertilisation, the paternal genome is rapidly reactivated, actively demethylated, the protamines are replaced with histones and the embryonic genome is activated. The development of new assays, made possible by high-throughput sequencing technology, has resulted in the revisiting of what was considered settled science regarding the state of DNA packaging in mammalian spermatozoa. Researchers have discovered that not all histones are replaced by protamines and, in certain experiments, various species of RNA have been detected in what was previously considered transcriptionally quiescent spermatozoa. Most controversially, several groups have suggested that environmental modifications of the epigenetic state of spermatozoa may operate as a non-DNA-based form of inheritance, a process known as ‘transgenerational epigenetic inheritance’. Other developments in the field include the increased focus on the involvement of short RNAs, such as microRNAs, long non-coding RNAs and piwi-interacting RNAs. There has also been an accumulation of evidence illustrating associations between defects in sperm DNA packaging and disease and fertility. In this paper we review the literature, recent findings and areas of controversy associated with epigenetic processes in the male germline, focusing on DNA methylation dynamics, non-coding RNAs, the biology of sperm chromatin packaging and transgenerational inheritance.

Gestational hypoxia and epigenetic programming of brain development disorders

Adverse environmental conditions faced by an individual early during its life, such as gestational hypoxia, can have a profound influence on the risk of diseases, such as neurological disorders, in later life. Clinical and preclinical studies suggest that epigenetic programming of gene expression patterns in response to maternal stress have a crucial role in the fetal origins of neurological diseases. Herein, we summarize recent studies regarding the role of epigenetic mechanisms in the developmental programming of neurological diseases in offspring, primarily focusing on DNA methylation/demethylation and miRNAs. Such information could increase our understanding of the fetal origins of adult diseases and help develop effective prevention and intervention against neurological diseases.

Zearalenone exposure affects epigenetic modifications of mouse eggs

Zearalenone (ZEA) is a mycotoxin produced by various Fusarium fungi, which has been shown to cause several cases of mycotoxicosis in farm animals and humans. However, there is no evidence regarding the effect of ZEA on mouse egg developmental competence. In this study, we found that the activation rate of maturated oocytes was affected in mice by ZEA treatment, indicating that ZEA affects egg developmental competence. And we explored possible mechanisms of low mouse maturated oocyte developmental competence after ZEA treatment from an epigenetic modification perspective. The fluorescence intensity analysis showed that 5-methyl cytosine level increased after ZEA treatment, indicating that the general DNA methylation level increased in the treated eggs. Moreover, histone methylations were also altered: H3K4me2 as well as H3K9me3 and H4K20me1, me2, me3 levels decreased in eggs that were cultured in high-dose ZEA medium. Thus, our results indicated that ZEA decreased egg developmental competence by affecting the epigenetic modifications.

Effect of mycotoxin-containing diets on epigenetic modifications of mouse oocytes by fluorescence microscopy analysis

Mycotoxins, such as aflatoxin (AF), fumonisin B1, zearalenone (ZEA), and deoxynivalenol (DON), are commonly found in many food commodities. Mycotoxins have been shown to increase DNA methylation levels in a human intestinal cell line. We previously showed that the developmental competence of oocytes was affected in mice that had been fed a mycotoxin-containing diet. In this study, we explored possible mechanisms of low mouse oocyte developmental competence after mycotoxin treatment in an epigenetic modification perspective. Mycotoxin-contaminated maize (DON at 3,875 μg/kg, ZEA at 1,897 μg/kg, and AF at 806 μg/kg) was included in diets at three different doses (mass percentage: 0, 15, and 30%) and fed to mice for 4 weeks. The fluorescence intensity analysis showed that the general DNA methylation levels increased in oocytes from high dose mycotoxin-fed mice. Mouse oocyte histone methylation was also altered. H3K9me3 and H4K20me3 level increased in oocytes from mycotoxin-fed mice, whereas H3K27me3 and H4K20me2 level decreased in oocytes from mycotoxin-fed mice. Thus, our results indicate that naturally occurring mycotoxins have effects on epigenetic modifications in mouse oocytes, which may be one of the reasons for reduced oocyte developmental competence.

Epigenetic status in the offspring of spontaneous and assisted conception

STUDY QUESTION

Is DNA methylation in buccal cell DNA from children born following IVF (in vitro fertilization) and ICSI (intra-cytoplasmic sperm injection) different from that of spontaneously conceived children?

SUMMARY ANSWER

DNA methylation in the imprinted gene, small nuclear ribonucleoprotein polypeptide N (SNRPN), was higher in children conceived by ICSI and in those born to women with the longest duration of infertility regardless of the method of conception.

WHAT IS KNOWN ALREADY

Fertility treatment is associated with a small but significant increase in the risk of a range of adverse obstetric outcomes, birth defects and longer term sequelae, but the biological basis for this is unknown. A growing evidence base suggests that epigenetics may play a role in subfertility and the link between fertility and health.

STUDY DESIGN, SIZE, DURATION

In this retrospective cohort study of children born between 2002 and 2008, we measured DNA methylation in paternally expressed gene 3 (PEG3), insulin-like growth factor II (IGF2), SNRPN, long interspersed nuclear element 1 (LINE1) and the insulin gene (INS) in buccal cell DNA from children born following IVF (n = 49) and ICSI (n = 20) and compared them with a matched spontaneous conception group (n = 86).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Participants were identified from the Aberdeen Maternity and Neonatal Databank and IVF and ICSI pregnancies were matched to spontaneous conception pregnancies on year of birth and maternal age at delivery. Only singleton pregnancies following fresh embryo transfer were included. DNA methylation was determined by pyrosequencing. Regression with adjustment for covariates was used to determine the effect of infertility on offspring DNA methylation.

MAIN RESULTS AND THE ROLE OF CHANCE

SNRPN methylation in the offspring was linked to fertility treatment in the parents. This effect was specific to children conceived using ICSI and was apparent in the comparison of ICSI versus spontaneous conception (1.03%; 95% CI 0.10, 1.97; P = 0.031), ICSI versus standard IVF (1.13%; 95% CI 0.04, 2.23; P = 0.043) and ICSI versus standard IVF and spontaneous conception (1.05; 95% CI 0.15, 1.94; P = 0.023). In all comparisons, the use of ICSI was associated with a higher level of SNRPN methylation in the offspring. A higher level of SNRPN methylation in the offspring was also associated with a longer duration of infertility in the parents. This was observed in all cases of infertility (0.18% per year of infertility; 95% CI 0.02, 0.33; P = 0.026) and after excluding ICSI cases (0.21% per year of infertility; 95% CI 0.04, 0.37; P = 0.017). There was a significant increase in the level of LINE1 methylation with age between birth and 7 years (0.77% per year; 95% CI 0.49, 1.05; P < 0.001). Methylation in the INS gene decreased significantly over the same period (-0.46% per year; 95% CI -0.89, -0.03; P = 0.035). There was no evidence from this cross-sectional data that methylation within the imprinted genes changed over the first 7 years of life.

LIMITATIONS, REASONS FOR CAUTION

The ICSI sample size was limited but the groups were carefully selected and well matched and the SNRPN findings were consistent across different outcomes.

WIDER IMPLICATIONS OF THE FINDINGS

The results of this study provide support for a role for epigenetics, and imprinting in particular, in fertility. The specific changes point to possible long-term consequences of fertility treatment for the health and fertility of future generations.

STUDY FUNDING/COMPETING INTEREST(S)

The authors report no conflict of interest in relation to this work. Funding was provided by the University of Aberdeen and the Scottish Government.

TRIAL REGISTRATION NUMBER

Not applicable.

PIWI-interacting RNAs (piRNAs) - a mouse testis perspective

Over the past decade, PIWI-interacting RNAs (piRNAs) have emerged as the most intriguing class of small RNAs. Almost every aspect of piRNA biology defies established rules of the RNA interference world while the scope of piRNA functional potential spans from transcriptional gene silencing to genome defense to transgenerational epigenetic phenomena. This review will focus on the genomic origins, biogenesis, and function of piRNAs in the mouse testis - an exceptionally robust experimental system amenable to genetic, cell-biological, molecular, and biochemical studies. Aided and frequently guided by knowledge obtained in insect, worm, and fish germ cells, mouse spermatogenesis has emerged as the primary model in understanding the role of this conserved pathway in mammals.

Biomarkers of chemotherapy-induced testicular damage

Increasing numbers of men are having or wanting children after chemotherapy treatment. This can be attributed to improvements in cancer therapies that increase survival. However, a side effect of most chemotherapy drugs is disruption of spermatogenesis and a drastic reduction in sperm count and quality. Although many men eventually recover reproductive function, as indicated by normal semen analyses, there is no clinical test that can assess sperm quality at a high level of sensitivity. Sperm fluorescent in situ hybridization (i.e., FISH) and several different tests for deoxyribonucleic acid (DNA) fragmentation have been used infrequently in clinical assessment. Animal models of chemotherapy-induced testicular damage are currently being used to identify potential molecular biomarkers that may be translatable to humans-these include sperm messenger RNAs, microRNAs, histone modifications, and DNA methylation patterns. Changes in these molecular measurements are quantitative and sensitive, potentially making them important clinical biomarkers of testicular function after chemotherapy treatment.

The current status of biomarkers for predicting toxicity

INTRODUCTION

There are significant rates of attrition in drug development. A number of compounds fail to progress past preclinical development due to limited tools that accurately monitor toxicity in preclinical studies and in the clinic. Research has focused on improving tools for the detection of organ-specific toxicity through the identification and characterization of biomarkers of toxicity.

AREAS COVERED

This article reviews what we know about emerging biomarkers in toxicology, with a focus on the 2012 Northeast Society of Toxicology meeting titled 'Translational Biomarkers in Toxicology.' The areas covered in this meeting are summarized and include biomarkers of testicular injury and dysfunction, emerging biomarkers of kidney injury and translation of emerging biomarkers from preclinical species to human populations. The authors also provide a discussion about the biomarker qualification process and possible improvements to this process.

EXPERT OPINION

There is currently a gap between the scientific work in the development and qualification of novel biomarkers for nonclinical drug safety assessment and how these biomarkers are actually used in drug safety assessment. A clear and efficient path to regulatory acceptance is needed so that breakthroughs in the biomarker toolkit for nonclinical drug safety assessment can be utilized to aid in the drug development process.

SOT Symposium Highlight: Translatable Indicators of Testicular Toxicity: Inhibin B, MicroRNAs, and Sperm Signatures

Testicular toxicity is an important safety endpoint in drug development and risk assessment, but reliable and translatable biomarkers for predicting injury have eluded researchers. However, this area shows great potential for improvement, with several avenues currently being pursued. This was the topic of a symposium session during the 2013 Society of Toxicology Annual Meeting in San Antonio, TX, entitled "Translatable Indicators of Testicular Toxicity: Inhibin B, MicroRNAs, and Sperm Signatures." This symposium brought together stakeholders from academia, government, and industry to present the limitations and drawbacks of currently used indicators of injury and discussed the ongoing efforts in developing more predictive biomarkers of injury. The presentations highlighted the early challenges of using circulating inhibin B and microRNA levels, and sperm messenger RNA transcript abundance and DNA methylation profiles, as novel biomarkers of testicular toxicity.

Epigenetic consequences of a changing human diet

The human diet has undergone profound changes over recent generations and this trend is likely to accelerate in the 21st century. Innovations in food technology, new ways of producing and processing foods and the increasing use of artificial vitamins and novel ingredients are changing the human diet in ways that our dietary monitoring systems struggle to keep pace with. There is a growing awareness of the importance of diet, but little understanding of how these changes may affect the health of current and future generations. Epigenetic programming, and specifically the persistence of functional epigenetic states following nutritional exposure, is particularly relevant to the issue of dietary change. Epigenetics is emerging as perhaps the most important mechanism through which diet and nutrition can directly influence the genome and there is now considerable evidence for nutritional epigenetic programming of health and the response to diet itself. A number of nutrients and food components that are changing in the human diet have been shown to produce epigenetic states that are stable across different timescales. We need to better understand the nutritional programming of epigenetic states, the persistence of these marks in time and their effect on biological function and the response to diet.

DNA methyltransferase candidate polymorphisms, imprinting methylation, and birth outcome

Background

Birth weight and prematurity are important obstetric outcomes linked to lifelong health. We studied a large birth cohort to look for evidence of epigenetic involvement in birth outcomes.

Methods

We investigated the association between birth weight, length, placental weight and duration of gestation and four candidate variants in 1,236 mothers and 1,073 newborns; DNMT1 (rs2162560), DNMT3A (rs734693), DNMT3B (rs2424913) and DNMT3L (rs7354779). We measured methylation of LINE1 and the imprinted genes, PEG3, SNRPN, and IGF2, in cord blood.

Results

The minor DNMT3L allele in the baby was associated with higher birth weight (+54 95% CI 10,99 g; p = 0.016), birth length (+0.23 95% CI 0.04,0.42 cm; p = 0.017), placental weight, (+18 95% CI 3,33 g; p = 0.017), and reduced risk of being in the lowest birth weight decile (p = 0.018) or requiring neonatal care (p = 0.039). The DNMT3B minor allele in the mother was associated with an increased risk of prematurity (p = 0.001). Placental size was related to PEG3 (p<0.001) and IGF2 (p<0.001) methylation. Birth weight was related to LINE1 and IGF2 methylation but only at p = 0.052. The risk of requiring neonatal treatment was related to LINE1 (p = 0.010) and SNRPN (p = 0.001) methylation. PEG3 methylation was influenced by baby DNMT3A genotype (p = 0.012) and LINE1 by baby 3B genotype (p = 0.044). Maternal DNMT3L genotype was related to IGF2 methylation in the cord blood but this effect was only seen in carriers of the minor frequency allele (p = 0.050).

Conclusions

The results here suggest that epigenetic processes are linked birth outcome and health in early life. Our emerging understanding of the role of epigenetics in health and biological function across the lifecourse suggests that these early epigenetic events could have longer term implications.

Folate in pregnancy and imprinted gene and repeat element methylation in the offspring

BACKGROUND

Epigenetic regulation of imprinted genes and transposable elements has been implicated in human disease and may be affected by maternal diet.

OBJECTIVE

The objective was to determine the effect on offspring epigenetic status of nutritional and genetic factors that influence folate exposure in pregnancy.

DESIGN

We measured folate intake from diet, the use of folic acid supplements and the period of consumption, maternal and cord red blood cell (RBC) folate, and genotypes for 5 methylation cycle enzymes in a prospective cohort study of pregnancies in the United Kingdom between 2000 and 2006. We related these to offspring methylation status within 3 maternally methylated imprinted genes: paternally expressed gene 3 (PEG3), insulin-like growth factor 2 (IGF2), and small nuclear ribonucleoprotein polypeptide N, and the long interspersed nuclear element 1 (LINE-1) in genomic DNA extracted from whole blood in 913 pregnancies.

RESULTS

Supplement use after 12 wk of gestation was associated with a higher level of methylation in IGF2 (+0.7%; 95% CI: 0.02, 1.4; P = 0.044) and reduced methylation in both PEG3 (-0.5%; 95% CI: -0.9, -0.1; P = 0.018) and LINE-1 (-0.3%; 95% CI: -0.6, -0.04; P = 0.029). The same pattern was observed in relation to RBC folate in the cord blood at birth: IGF2 (P = 0.038), PEG3 (P < 0.001), and LINE-1 (P < 0.001). LINE-1 methylation was related to maternal RBC folate (P = 0.001) at 19 wk. No effect of supplement use up to 12 wk (current recommendation) was found.

CONCLUSIONS

Folic acid use after 12 wk of gestation influences offspring repeat element and imprinted gene methylation. We need to understand the consequences of these epigenetic effects.

Abnormal DNA methylation in oocytes could be associated with a decrease in reproductive potential in old mice

PURPOSE

This study was designed to evaluate DNA methylation and the expression of DNA methyltransferases (Dnmt1, Dnmt3a, Dnmt3b and Dnmt3L) in metaphaseII (MII) oocytes and the DNA methylation of pre-implantation embryos during mouse aging to address whether such aging-related changes are associated with decreased reproductive potential in aged mice.

METHODS

Oocytes (MII) from 6 to 8 weeks old female mice are referred to as the 'young group'; oocytes from the same group that were maintained until 35-40 weeks old are referred to as the 'old group.' The oocytes were fertilized both in vitro and in vivo to obtain embryos. The DNA methylation levels in the oocytes (MII) and pre-implantation embryos were assessed using fluorescence staining. The expression levels of the Dnmt genes in the oocytes (MII) were assessed using Western blotting.

RESULTS

The DNA methylation levels in the oocytes and pre-implantation embryos (in vivo and in vitro) decreased significantly during the aging of the mice. The expression levels of all of the examined Dnmt proteins in the old group were lower than young group. Both the cleavage and blastocyst rate were significantly lower in the oocytes of the older mice (69.9 % vs. 80.9 %, P < 0.05; 33.9 % vs. 56.4 %, P < 0.05). The pregnancy rate of the old mice was lower than that of the young mice (46.7 % vs. 100 %, P < 0.05). The stillbirth and fetal malformation rate was significantly higher in the old group than in the young group (17.2 % vs. 2.9 %, P < 0.05).

CONCLUSIONS

The decreased expression of Dnmt1, Dnmt3a, Dnmt3b and Dnmt3L in oocytes (MII) and the change of genome-wide DNA methylation in oocytes and pre-implantation embryos due to aging may be related to lower reproductive potential in old female mice.

Genetic polymorphisms of DNMT3L involved in hypermethylation of chromosomal ends are associated with greater risk of developing ovarian endometriosis

Endometrioma is a common ovarian cyst associated with pain and infertility, but its pathogenesis remains enigmatic. Demonstration of the subtelomeric location of hypermethylation in endometrioma has been reported by genome-wide profiling of methylated promoters. Recently, rs113593938, a polymorphism in the DNA methyltransferase 3-like (DNMT3L) gene has been associated with subtelomeric hypomethylation. We investigated the association between endometrioma and rs113593938, rs8129776, rs7354779, and rs2276248, which were chosen for thoroughly covering the locus of interest. We enrolled 127 patients with histologically proved endometrioma and no associated deep endometriotic lesions and 317 healthy subjects for a case-control genetic association study. Genotyping was performed after PCR amplification of the region encompassing the polymorphisms, restriction enzyme digestion, and detection of fragments on an agarose gel. Differences in genotype and allele distributions between cases and controls were tested for each polymorphism separately using the χ(2) test. The rs8129776 was significantly associated with endometrioma (P = 0.003). Haplotype analysis showed a higher risk for the patients carrying the ACCC+T haplotypes for rs8129776, rs7354779, rs113593938, and rs2276248 (odds ratio, 7.15; 95% CI, 2.63 to 19.44). We report, for the first time to our knowledge, the association of DNMT3L genetic variants and endometrioma; DNMT3L expression itself was not modified. Our study constitutes a first milestone toward a plausible role of DNMT3L in the establishment of specific DNA methylation patterns in endometrioma.

Can the partial deletion in the Y chromosome of male mice affect the reproductive efficiency of their daughters?

It has been previously shown that cumuli oophori around ovulated oocytes of B10.BR-Y(del) female mice (sired by males with the deleted Y chromosome) are more resistant to enzymatic treatment than cumuli oophori around eggs of control B10.BR females (having fathers with the intact Y chromosome). This can imply that some genes which influence the establishment of the imprinting pattern in male gametes are located in the region covered by the deletion. We hypothesize that the Y-dependent imprinting pattern, inherited by female offspring, affects stability of periovum layers within them. In the present study, cumulus-oocyte complexes ovulated by females from consomic strains: DBA, DBA-Y(BR), DBA-Y(del), and CBA, CBA-Y(BR), CBA-Y(del) were tested for their susceptibility to hyaluronidase digestion. The mean times for dispersal of cumulus cells surrounding oocytes of females from the backcross lines were convergent with the times typical for oocytes from strains being the donors of the Y chromosome (B10.BR or B10.BR-Y(del)) and differed clearly from pure DBA and CBA strains. It confirmed previous findings that Y chromosomes of fathers influence the properties of cumulus-oocyte complexes ovulated by their daughters. This influence is definitely stronger than the influence of the genetic background. Additionally, it was demonstrated that the cumuli oophori surrounding oocytes of B10.BR-Y(del) females exhibit increased resistance to penetration by spermatozoa in vitro, in comparison to the control B10.BR strain. This regularity was reflected in the decreased proportion of fertilized ova recovered from oviducts of B10.BR-Y(del) females mated with B10.BR-Y(del) males and in the lower litter sizes recorded for these pairs. The excessive stability of cumuli oophori typical for oocytes of females having Y(del) fathers may negatively affect their fertility, if they have partners producing poor quality sperm.

IVF and retinoblastoma revisited

OBJECTIVE

To evaluate the suggested association between IVF, retinoblastoma, and tumor methylation characteristics.

DESIGN

Laboratory analysis.

SETTING

National Retinoblastoma Center in the Netherlands.

PATIENT(S)

Retinoblastoma tumors from seven children conceived by IVF or intracytoplasmic sperm injection (ICSI).

INTERVENTION(S) AND MAIN OUTCOME MEASURE(S)

DNA from frozen retinoblastoma tumors was tested for mutations in the RB1 gene and for methylation status of the RB1 promoter.

RESULT(S)

For all tumors two causative RB1 mutations were found. None of the tumors showed hypermethylation of the RB1 promoter.

CONCLUSION(S)

Examination of retinoblastoma tumors of seven children conceived by IVF or ICSI did not show hypermethylation of the RB1 promoter. This demonstrates that an association between IVF or ICSI and retinoblastoma through this epigenetic mechanism is unlikely.

Epigenetic mechanisms in developmental programming of adult disease

Adverse insults during intrauterine life can result in permanent changes in the physiology and metabolism of the offspring, which in turn leads to an increased risk of disease in adulthood. This is an adaptational response by the fetus to changes in the environmental signals that it receives during early life to ensure its survival and prepare itself for postnatal life. Increasing evidence suggests that the epigenetic regulation of gene expression patterns has a crucial role in the developmental programming of adult disease. This review summarizes recent studies of epigenetic mechanisms and focuses particularly on studies that explore identifiable epigenetic biomarkers in the promoters of specific disease-associated genes. Such biomarkers would enable early recognition of children who might be at risk of developing adult disease with fetal origins.

Epigenetics in women's health care

Epigenetics refers to structural modifications to genes that do not change the nucleotide sequence itself but instead control and regulate gene expression. DNA methylation, histone modification, and RNA regulation are some of the mechanisms involved in epigenetic modification. Epigenetic changes are believed to be a result of changes in an organism's environment that result in fixed and permanent changes in most differentiated cells. Some environmental changes that have been linked to epigenetic changes include starvation, folic acid, and various chemical exposures. There are periods in an organism's life cycle in which the organism is particularly susceptible to epigenetic influences; these include fertilization, gametogenesis, and early embryo development. These are also windows of opportunity for interventions during the reproductive life cycle of women to improve maternal-child health. New data suggest that epigenetic influences might be involved in the regulation of fetal development and the pathophysiology of adult diseases such as cancer, diabetes, obesity, and neurodevelopmental disorders. Various epigenetic mechanisms may also be involved in the pathogenesis of preeclampsia and intrauterine growth restriction. Additionally, environmental exposures are being held responsible for causing epigenetic changes that lead to a disease process. Exposure to heavy metals, bioflavonoids, and endocrine disruptors, such as bisphenol A and phthalates, has been shown to affect the epigenetic memory of an organism. Their long-term effects are unclear at this point, but many ongoing studies are attempting to elucidate the pathophysiological effects of such gene-environment interactions.

Maternal high-fat diet effects on third-generation female body size via the paternal lineage

The health consequences of in utero exposure to maternal obesity on future generations are concerning because they contribute to increased rates of diabetes, cardiovascular disease, and metabolic syndrome. We previously reported that maternal high-fat diet exposure in mice resulted in an increase in body size and reduced insulin sensitivity that persisted across two generations via both maternal and paternal lineages. However, because the first generation's primordial germ cells may be affected by gestational exposure, analysis of phenotype transmission into a third generation (F3) is necessary to determine whether stable epigenetic programming has occurred. Therefore, we have examined the body size and insulin sensitivity of male and female F3 offspring. We found that only females displayed the increased body size phenotype, and this effect was only passed on via the paternal lineage. The finding of a paternally transmitted phenotype to F3 female offspring supports a stable germline-based transgenerational mode of inheritance; thus we hypothesized that imprinted genes may be involved in this epigenetic programming. Using a quantitative TaqMan Array for imprinted genes to examine paternally or maternally expressed loci in F3 female livers, we detected a potential dynamic pattern of paternally expressed genes from the paternal lineage that was not noted in the maternal lineage. These findings suggest that the environmental influence on developmental regulation of growth and body size may be the result of broad programming events at imprinted loci, thereby providing sex specificity to both the transmission and inheritance of traits related to disease predisposition.

Detection of DNA damage in oocytes of small ovarian follicles following phosphoramide mustard exposures of cultured rodent ovaries in vitro

Healthy oocytes are critical for producing healthy children, but little is known about whether or not oocytes have the capacity to identify and recover from injury. Using a model ovotoxic alkylating drug, cyclophosphamide (CPA), and its active metabolite, phosphoramide mustard (PM), we previously showed that PM (≥3μM) caused significant follicle loss in postnatal day 4 (PND4) mouse ovaries in vitro. We now investigate whether PM induces DNA damage in oocytes, examining histone H2AX phosphorylation (γH2AX), a marker of DNA double-strand breaks (DSBs). Exposure of cultured PND4 mouse ovaries to 3 and 0.1μM PM induced significant losses of primordial and small primary follicles, respectively. PM-induced γH2AX was observed predominantly in oocytes, in which foci of γH2AX staining increased in a concentration-dependent manner and peaked 18-24h after exposure to 3-10μMPM. Numbers of oocytes with ≥5 γH2AX foci were significantly increased both 1 and 8days after exposure to ≥1μMPM compared to controls. Inhibiting the kinases that phosphorylate H2AX significantly increased follicle loss relative to PM alone. In adult mice, CPA also induced follicle loss in vivo. PM also significantly decreased primordial follicle numbers (≥30μM) and increased γH2AX foci (≥3μM) in cultured PND4 Sprague-Dawley rat ovaries. Results suggest oocytes can detect PM-induced damage at or below concentrations which cause significant follicle loss, and there are quantitative species-specific differences in sensitivity. Surviving oocytes with DNA damage may represent an increased risk for fertility problems or unhealthy offspring.

Idiopathic male infertility is strongly associated with aberrant methylation of MEST and IGF2/H19 ICR1

Aberrant imprinting in spermatozoa in a subset of infertile men has been postulated to be a risk factor for congenital diseases in children conceived via assisted reproduction techniques (ART). Studies in clinically well characterized large cohorts, however, have been missing. Using bisulfite sequencing, we determined the degree of methylation of the IGF2/H19 imprinting control region 1 (ICR1) and MEST differentially methylated regions in swim-up purified spermatozoa from 148 idiopathic infertile men and 33 normozoospermic controls. All control individuals had a high degree of IGF2/H19 ICR1 and a low degree of MEST methylation. Low sperm counts were clearly associated with IGF2/H19 ICR1 hypomethylation and, even stronger, with MEST hypermethylation. MEST hypermethylation, but not IGF2/H19 ICR1 hypomethylation was found in idiopathic infertile men with progressive sperm motility below 40% and bad sperm morphology below 5% normal spermatozoa. Ageing could be ruled out as a cause for the observed methylation defects. Sequence analysis of the CTCFL gene in peripheral blood DNA from 20 men with severe methylation defects revealed several polymorphisms, but no bona fide mutation. We conclude that idiopathic male infertility is strongly associated with imprinting defects at IGF2/H19 ICR1 and MEST, with aberrant MEST methylation being a strong indicator for sperm quality. The male germ cell thus represents a potential source for aberrant epigenetic features in children conceived via ART.

Imprinting status of Galpha(s), NESP55, and XLalphas in cell cultures derived from human embryonic germ cells: GNAS imprinting in human embryonic germ cells

GNAS is a complex gene that through use of alternative first exons encodes signaling proteins Galpha(s) and XLalphas plus neurosecretory protein NESP55. Tissue-specific expression of these proteins is regulated through reciprocal genomic imprinting in fully differentiated and developed tissue. Mutations in GNAS account for several human disorders, including McCune-Albright syndrome and Albright hereditary osteodystrophy, and further knowledge of GNAS imprinting may provide insights into variable phenotypes of these disorders. We therefore analyzed expression of Galpha(s), NESP55, and XLalphas prior to tissue differentiation in cell cultures derived from human primordia germ cells. We found that the expression of Galpha(s) was biallelic (maternal allele: 52.6%+/- 2.5%; paternal allele: 47.2%+/- 2.5%; p= 0.07), whereas NESP55 was expressed preferentially from the maternal allele (maternal allele: 81.9%+/- 10%; paternal allele: 18.1%+/- 10%; p= 0.002) and XLalphas was preferentially expressed from the paternal allele (maternal allele: 2.7%+/- 0.3%; paternal allele: 97.3%+/- 0.3%; p= 0.007). These results demonstrate that imprinting of NESP55 occurs very early in development, although complete imprinting appears to take place later than 5-11 weeks postfertilization, and that imprinting of XLalphas occurs very early postfertilization. By contrast, imprinting of Galpha(s) most likely occurs after 11 weeks postfertilization and after tissue differentiation.

Epigenetic effects of endocrine-disrupting chemicals on female reproduction: an ovarian perspective

The link between in utero and neonatal exposure to environmental toxicants, such as endocrine-disrupting chemicals (EDCs) and adult female reproductive disorders is well established in both epidemiological and animal studies. Recent studies examining the epigenetic mechanisms involved in mediating the effects of EDCs on female reproduction are gathering momentum. In this review, we describe the developmental processes that are susceptible to EDC exposures in female reproductive system, with a special emphasis on the ovary. We discuss studies with select EDCs that have been shown to have physiological and correlated epigenetic effects in the ovary, neuroendocrine system, and uterus. Importantly, EDCs that can directly target the ovary can alter epigenetic mechanisms in the oocyte, leading to transgenerational epigenetic effects. The potential mechanisms involved in such effects are also discussed.

Identification and resolution of artifacts in the interpretation of imprinted gene expression

Genomic imprinting refers to genes that are epigenetically programmed in the germline to express exclusively or preferentially one allele in a parent-of-origin manner. Expression-based genome-wide screening for the identification of imprinted genes has failed to uncover a significant number of new imprinted genes, probably because of the high tissue- and developmental-stage specificity of imprinted gene expression. A very large number of technical and biological artifacts can also lead to the erroneous evidence of imprinted gene expression. In this article, we focus on three common sources of potential confounding effects: (i) random monoallelic expression in monoclonal cell populations, (ii) genetically determined monoallelic expression and (iii) contamination or infiltration of embryonic tissues with maternal material. This last situation specifically applies to genes that occur as maternally expressed in the placenta. Beside the use of reciprocal crosses that are instrumental to confirm the parental specificity of expression, we provide additional methods for the detection and elimination of these situations that can be misinterpreted as cases of imprinted expression.

Epigenetic transmission of the impact of early stress across generations

BACKGROUND

Traumatic experiences in early life are risk factors for the development of behavioral and emotional disorders. Such disorders can persist through adulthood and have often been reported to be transmitted across generations.

METHODS

To investigate the transgenerational effect of early stress, mice were exposed to chronic and unpredictable maternal separation from postnatal day 1 to 14.

RESULTS

We show that chronic and unpredictable maternal separation induces depressive-like behaviors and alters the behavioral response to aversive environments in the separated animals when adult. Most of the behavioral alterations are further expressed by the offspring of males subjected to maternal separation, despite the fact that these males are reared normally. Chronic and unpredictable maternal separation also alters the profile of DNA methylation in the promoter of several candidate genes in the germline of the separated males. Comparable changes in DNA methylation are also present in the brain of the offspring and are associated with altered gene expression.

CONCLUSIONS

These findings highlight the negative impact of early stress on behavioral responses across generations and on the regulation of DNA methylation in the germline.

Human intelligence and polymorphisms in the DNA methyltransferase genes involved in epigenetic marking

Epigenetic mechanisms have been implicated in syndromes associated with mental impairment but little is known about the role of epigenetics in determining the normal variation in human intelligence. We measured polymorphisms in four DNA methyltransferases (DNMT1, DNMT3A, DNMT3B and DNMT3L) involved in epigenetic marking and related these to childhood and adult general intelligence in a population (n = 1542) consisting of two Scottish cohorts born in 1936 and residing in Lothian (n = 1075) or Aberdeen (n = 467). All subjects had taken the same test of intelligence at age 11yrs. The Lothian cohort took the test again at age 70yrs. The minor T allele of DNMT3L SNP 11330C>T (rs7354779) allele was associated with a higher standardised childhood intelligence score; greatest effect in the dominant analysis but also significant in the additive model (coefficient = 1.40_additive; 95%CI 0.22,2.59; p = 0.020 and 1.99_dominant; 95%CI 0.55,3.43; p = 0.007). The DNMT3L C allele was associated with an increased risk of being below average intelligence (OR 1.25_additive; 95%CI 1.05,1.51; p = 0.011 and OR 1.37_dominant; 95%CI 1.11,1.68; p = 0.003), and being in the lowest 40^th (p_additive = 0.009; p_dominant = 0.002) and lowest 30^th (p_additive = 0.004; p_dominant = 0.002) centiles for intelligence. After Bonferroni correction for the number variants tested the link between DNMT3L 11330C>T and childhood intelligence remained significant by linear regression and centile analysis; only the additive regression model was borderline significant. Adult intelligence was similarly linked to the DNMT3L variant but this analysis was limited by the numbers studied and nature of the test and the association was not significant after Bonferroni correction. We believe that the role of epigenetics in the normal variation in human intelligence merits further study and that this novel finding should be tested in other cohorts.

Generation of histocompatible androgenetic embryonic stem cells using spermatogenic cells

Androgenetic embryonic stem (aES) cells, produced by pronuclear transplantation, offer an important autologous pluripotent stem cell source. However, the isolation of aES cells, particularly individual-specific aES cells, with the use of fertilized embryos has limited the practical applications of this technology in humans. In this study, we applied a new approach, essentially described as somatic cell nuclear transfer, and generated three aES cell line types with the use of spermatogenic cells including primary spermatocytes, round spermatids, and mature spermatozoa as donor cells, omitting the need to use fertilized embryos. Although abnormality of chimeras and absent germline competency indicated that all three types of aES cells exhibited limited pluripotency, the epigenetic status of the aES cell lines tended to resemble normal ES cells during long-term culture, and some parental-specific imprinted genes were expressed at levels comparable to those of normal ES cells. Furthermore, the histocompatibility of the aES cells was investigated by transplanting the differentiation progenies of the aES cells into major histocompatibility (MHC)-matched and -mismatched recipient mice. The results indicated that these aES cells were histocompatible with MHC-matched mice after transplantation. Our study provides evidence that MHC-competent autologous aES cells could be generated from different spermatogenic cells using nuclear transfer into oocytes, a process that could avoid the use of fertilized embryos.