Imprinting methylation errors in ART

Sex-specific differences in head circumference of term singletons after assisted reproductive technology: a multicentre study in Japan

RESEARCH QUESTION

Does fertility treatment, specifically assisted reproductive technology (ART), affect head circumference in term singletons?

DESIGN

A total of 32,651 women who delivered at term at 12 maternity hospitals in Japan between 2010 and 2018 were included in the analysis; of these, 1941 (5.9%) and 2984 (9.1%) women conceived through ART and non-ART fertility treatments (timed intercourse, ovulation induction or artificial insemination), respectively. The study evaluated the adjusted odds ratios of head circumference ≥90th percentile stratified by infant sex and type of ART procedure after adjusting for covariates, with natural conception as the reference group.

RESULTS

ART significantly increased the risk of head circumference ≥90th percentile (adjusted odds ratio 1.56 [95% confidence interval 1.25-1.96]), whereas non-ART fertility treatment did not increase the risk (1.14 [0.92-1.42]). This increased risk of head circumference ≥90th percentile was observed exclusively in male neonates (1.73 [1.33-2.26]) and not in female neonates (1.18 [0.76-1.85]) in the ART group. Frozen embryo transfer (FET), FET in a hormone replacement cycle (HRC-FET) and blastocyst-stage embryo transfer were significantly associated with head circumference ≥90th percentile (1.60 [1.26-2.02], 1.70 [1.30-2.22] and 1.72 [1.33-2.24], respectively).

CONCLUSIONS

The use of ART, particularly FET, HRC-FET or blastocyst-stage embryo transfer, was linked with a heightened risk of head circumference ≥90th percentile compared with non-ART fertility treatment or natural conception. The increased risk was observed only in male neonates.

Exploring the effect of cryopreservation in assisted reproductive technology and potential epigenetic risk

Since the birth of the first baby by in vitro fertilization in 1978, more than 9 million children have been born worldwide using medically assisted reproductive treatments. Fertilization naturally takes place in the maternal oviduct where unique physiological conditions enable the early healthy development of the embryo. During this dynamic period of early development major waves of epigenetic reprogramming, crucial for the normal fate of the embryo, take place. Increasingly, over the past 20 years concerns relating to the increased incidence of epigenetic anomalies in general, and genomic-imprinting disorders in particular, have been raised following assisted reproduction technology (ART) treatments. Epigenetic reprogramming is particularly susceptible to environmental conditions during the periconceptional period and non-physiological conditions such as ovarian stimulation, in vitro fertilization and embryo culture, as well as cryopreservation procedure, might have the potential to independently or collectively contribute to epigenetic dysregulation. Therefore, this narrative review offers a critical reappraisal of the evidence relating to the association between embryo cryopreservation and potential epigenetic regulation and the consequences on gene expression together with long-term consequences for offspring health and wellbeing. Current literature suggests that epigenetic and transcriptomic profiles are sensitive to the stress induced by vitrification, in terms of osmotic shock, temperature and pH changes, and toxicity of cryoprotectants, it is therefore, critical to have a more comprehensive understanding and recognition of potential unanticipated iatrogenic-induced perturbations of epigenetic modifications that may or may not be a consequence of vitrification.

DNA Methylation in the Fields of Prenatal Diagnosis and Early Detection of Cancers

The central objective of the metamorphosis of discovery science into biomedical applications is to serve the purpose of patients and curtail the global disease burden. The journey from the discovery of DNA methylation (DNAm) as a biological process to its emergence as a diagnostic tool is one of the finest examples of such metamorphosis and has taken nearly a century. Particularly in the last decade, the application of DNA methylation studies in the clinic has been standardized more than ever before, with great potential to diagnose a multitude of diseases that are associated with a burgeoning number of genes with this epigenetic alteration. Fetal DNAm detection is becoming useful for noninvasive prenatal testing, whereas, in very preterm infants, DNAm is also shown to be a potential biological indicator of prenatal risk factors. In the context of cancer, liquid biopsy-based DNA-methylation profiling is offering valuable epigenetic biomarkers for noninvasive early-stage diagnosis. In this review, we focus on the applications of DNA methylation in prenatal diagnosis for delivering timely therapy before or after birth and in detecting early-stage cancers for better clinical outcomes. Furthermore, we also provide an up-to-date commercial landscape of DNAm biomarkers for cancer detection and screening of cancers of unknown origin.

Can Cryopreservation in Assisted Reproductive Technology (ART) Induce Epigenetic Changes to Gametes and Embryos?

Since the birth of Louise Brown in 1978, more than nine million children have been conceived using assisted reproductive technologies (ARTs). While the great majority of children are healthy, there are concerns about the potential epigenetic consequences of gametes and embryo manipulation. In fact, during the preimplantation period, major waves of epigenetic reprogramming occur. Epigenetic reprogramming is susceptible to environmental changes induced by ovarian stimulation, in-vitro fertilization, and embryo culture, as well as cryopreservation procedures. This review summarizes the evidence relating to oocytes and embryo cryopreservation and potential epigenetic regulation. Overall, it appears that the stress induced by vitrification, including osmotic shock, temperature and pH changes, and toxicity of cryoprotectants, might induce epigenetic and transcriptomic changes in oocytes and embryos. It is currently unclear if these changes will have potential consequences for the health of future offspring.

Considerations on staffing levels for a modern assisted reproductive laboratory

The duties recently performed in the embryology laboratory have deeply increased compared to those realized a couple of decades ago. Currently, procedures include conventional in vitro fertilization (IVF) and ICSI techniques, or processing of surgically retrieved sperm, embryo culture and time-lapse monitoring, blastocyst culture, as well as trophectoderm biopsy for preimplantation genetic testing and cryopreservation. These techniques require not only time, but also high knowledge level and acutely concentration by the embryologist team. The existing data indicate that an IVF laboratory need to have adequate staffing levels to perform the required daily duties, and to work in optimal conditions that are critical to assure a high quality service, as well as avoiding incidents and to provide the best outcomes. As a result, IVF clinics have invested in human resources, but there is still a large discrepancy between IVF centres on the number of embryologists employed. Currently there is no golden standard on the human resource requirements for assisted reproductive technology procedures; therefore, in this review paper we aim to provide arguments to take into account to determine the embryology staffing requirements in an embryology laboratory to assure optimal safety and efficiency of operations.

Risk of genetic and epigenetic alteration in children conceived following ART: Is it time to return to nature whenever possible?

Assisted reproductive technology may influence epigenetic signature as the procedures coincide with the extensive epigenetic modification occurring from fertilization to embryo implantation. However, it is still unclear to what extent ART alters the embryo epigenome. In vivo fertilization occurs in the fallopian tube, where a specific and natural environment enables the embryo's healthy development. During this dynamic period, major waves of epigenetic reprogramming, crucial for the normal fate of the embryo, take place. Over the past decade, concerns relating to the raised incidence of epigenetic anomalies and imprinting following ART have been raised by several authors. Epigenetic reprogramming is particularly susceptible to environmental conditions during the periconceptional period; therefore, unphysiological conditions, including ovarian stimulation, in vitro fertilization, embryo culture, cryopreservation of gametes and embryos, parental lifestyle, and underlying infertility, have the potential to contribute to epigenetic dysregulation independently or collectively. This review critically appraises the evidence relating to the association between ART and genetic and epigenetic modifications that may be transmitted to the offspring.

How to improve the clinical outcome of round spermatid injection (ROSI) into the oocyte: Correction of epigenetic abnormalities

Background

First successful human round spermatid injection (ROSI) was conducted by Tesarik et al. in 1996 for the sole treatment of nonobstructive azoospermic men whose most advanced spermatogenic cells were elongating round spermatids. Nine offsprings from ROSI were reported between 1996 and 2000. No successful deliveries were reported for 15 years after that. Tanaka et al. reported 90 babies born after ROSI and their follow-up studies in 2015 and 2018 showed no significant differences in comparison with those born after natural conception in terms of physical and cognitive abilities. However, clinical outcomes remain low.

Method

Clinical and laboratory data of successful cases in the precursor ROSI groups and those of Tanaka et al. were reviewed.

Results

Differences were found between the two groups in terms of identification of characteristics of round spermatid and oocyte activation. Additionally, epigenetic abnormalities were identified as underlying causes for poor ROSI results, besides correct identification of round spermatid and adequate oocyte activation. Correction of epigenetic errors could lead to optimal embryonic development.

Conclusion

Correction of epigenetic abnormalities has a probability to improve the clinical outcome of ROSI.

Sperm cryopreservation and DNA methylation: possible implications for ART success and the health of offspring

Despite the beneficial effects of sperm cryopreservation, increased reactive oxygen species (ROS) production during this process can affect spermatozoon structure and function. Moreover, ROS production is associated with elevated DNA damage and alterations in DNA methylation. There is little information about the effects of cryopreservation on epigenetic modulation in sperm and the health of children born with frozen spermatozoa. Considering the potential consequences of cryopreservation in ART-conceived children, it is necessary to assure that cryopreservation does not modify sperm DNA methylation status. This review summarizes reports on epigenetic modifications of spermatozoa during cryopreservation and the probable effects of this process on offspring health. Contradictory results have reported the influence of sperm cryopreservation on DNA methylation in imprinted genes. Multiclinical studies with larger sample sizes under the same conditions of cryopreservation and DNA methylation analysis are needed to make any definitive conclusion about the effect of the cryopreservation process on sperm DNA methylation.

Epigenetic Risks of Medically Assisted Reproduction

Since the birth of Louise Joy Brown, the first baby conceived via in vitro fertilization, more than 9 million children have been born worldwide using assisted reproductive technologies (ART). In vivo fertilization takes place in the maternal oviduct, where the unique physiological conditions guarantee the healthy development of the embryo. During early embryogenesis, a major wave of epigenetic reprogramming takes place that is crucial for the correct development of the embryo. Epigenetic reprogramming is susceptible to environmental changes and non-physiological conditions such as those applied during in vitro culture, including shift in pH and temperature, oxygen tension, controlled ovarian stimulation, intracytoplasmic sperm injection, as well as preimplantation embryo manipulations for genetic testing. In the last decade, concerns were raised of a possible link between ART and increased incidence of imprinting disorders, as well as epigenetic alterations in the germ cells of infertile parents that are transmitted to the offspring following ART. The aim of this review was to present evidence from the literature regarding epigenetic errors linked to assisted reproduction treatments and their consequences on the conceived children. Furthermore, we provide an overview of disease risk associated with epigenetic or imprinting alterations in children born via ART.

Contemporary Use of ICSI and Epigenetic Risks to Future Generations

Since the birth of Louise Brown in 1978 via IVF, reproductive specialists have acquired enormous knowledge and refined several procedures, which are nowadays applied in assisted reproductive technology (ART). One of the most critical steps in this practice is the fertilization process. In the early days of IVF, a remarkable concern was the unpleasant outcomes of failed fertilization, overtaken by introducing intracytoplasmic sperm injection (ICSI), delineating a real breakthrough in modern ART. ICSI became standard practice and was soon used as the most common method to fertilize oocytes. It has been used for severe male factor infertility and non-male factors, such as unexplained infertility or advanced maternal age, without robust scientific evidence. However, applying ICSI blindly is not free of potential detrimental consequences since novel studies report possible health consequences to offspring. DNA methylation and epigenetic alterations in sperm cells of infertile men might help explain some of the adverse effects reported in ICSI studies on reproductive health in future generations. Collected data concerning the health of ICSI children over the past thirty years seems to support the notion that there might be an increased risk of epigenetic disorders, congenital malformations, chromosomal alterations, and subfertility in babies born following ICSI compared to naturally conceived children. However, it is still to be elucidated to what level these data are associated with the cause of infertility or the ICSI technique. This review provides an overview of epigenetic mechanisms and possible imprinting alterations following the use of ART, in particular ICSI. It also highlights the sperm contribution to embryo epigenetic regulation and the risks of in vitro culture conditions on epigenetic dysregulation. Lastly, it summarizes the literature concerning the possible epigenetic disorders in children born after ART.

ImprintSeq, a novel tool to interrogate DNA methylation at human imprinted regions and diagnose multilocus imprinting disturbance

PURPOSE

Disruptions of genomic imprinting are associated with congenital imprinting disorders (CIDs) and other disease states, including cancer. CIDs are most often associated with altered methylation at imprinted differentially methylated regions (iDMRs). In some cases, multiple iDMRs are affected causing multilocus imprinting disturbances (MLIDs). The availability of accurate, quantitative, and scalable high-throughput methods to interrogate multiple iDMRs simultaneously would enhance clinical diagnostics and research.

METHODS

We report the development of a custom targeted methylation sequencing panel that covered most relevant 63 iDMRs for CIDs and the detection of MLIDs. We tested it in 70 healthy controls and 147 individuals with CIDs. We distinguished loss and gain of methylation per differentially methylated region and classified high and moderate methylation alterations.

RESULTS

Across a range of CIDs with a variety of molecular mechanisms, ImprintSeq performed at 98.4% sensitivity, 99.9% specificity, and 99.9% accuracy (when compared with previous diagnostic testing). ImprintSeq was highly sensitive for detecting MLIDs and enabled diagnostic criteria for MLID to be proposed. In a child with extreme MLID profile a probable genetic cause was identified.

CONCLUSION

ImprintSeq provides a novel assay for clinical diagnostic and research studies of CIDs, MLIDs, and the role of disordered imprinting in human disease states.

Placental Dysfunction in Assisted Reproductive Pregnancies: Perinatal, Neonatal and Adult Life Outcomes

Obstetric and newborn outcomes of assisted reproductive technology (ART) pregnancies are associated with significative prevalence of maternal and neonatal adverse health conditions, such as cardiovascular and metabolic diseases. These data are interpreted as anomalies in placentation involving a dysregulation of several molecular factors and pathways. It is not clear which extent of the observed placental alterations are the result of ART and which originate from infertility itself. These two aspects probably act synergically for the final obstetric risk. Data show that mechanisms of inappropriate trophoblast invasion and consequent altered vascular remodeling sustain several clinical conditions, leading to obstetric and perinatal risks often found in ART pregnancies, such as preeclampsia, fetal growth restriction and placenta previa or accreta. The roles of factors such as VEGF, GATA3, PIGF, sFLT-1, sEndoglin, EGFL7, melatonin and of ART conditions, such as short or long embryo cultures, trophectoderm biopsy, embryo cryopreservation, and supraphysiologic endometrium preparation, are discussed. Inflammatory local conditions and epigenetic influence on embryos of ART procedures are important research topics since they may have important consequences on obstetric risk. Prevention and treatment of these conditions represent new frontiers for clinicians and biologists involved in ART, and synergic actions with researchers at molecular levels are advocated.

Genomic imprinting in human placentation

Background

Genomic imprinting (GI) is a mammalian-specific epigenetic phenomenon that has been implicated in the evolution of the placenta in mammals.

Methods

Embryo transfer procedures and trophoblast stem (TS) cells were used to re-examine mouse placenta-specific GI genes. For the analysis of human GI genes, cytotrophoblast cells isolated from human placental tissues were used. Using human TS cells, the biological roles of human GI genes were examined.

Main findings

(1) Many previously identified mouse GI genes were likely to be falsely identified due to contaminating maternal cells. (2) Human placenta-specific GI genes were comprehensively determined, highlighting incomplete erasure of germline DNA methylation in the human placenta. (3) Human TS cells retained normal GI patterns. (4) Complete hydatidiform mole-derived TS cells were characterized by aberrant GI and enhanced trophoblastic proliferation. The maternally expressed imprinted gene p57KIP2 may be responsible for the enhanced proliferation. (5) The primate-specific microRNA cluster on chromosome 19, which is a placenta-specific GI gene, is essential for self-renewal and differentiation of human TS cells.

Conclusion

Genomic imprinting plays diverse and important roles in human placentation. Experimental analyses using TS cells suggest that the GI maintenance is necessary for normal placental development in humans.

Epigenetic Mechanisms of ART-Related Imprinting Disorders: Lessons From iPSC and Mouse Models

The rising frequency of ART-conceived births is accompanied by the need for an improved understanding of the implications of ART on gametes and embryos. Increasing evidence from mouse models and human epidemiological data suggests that ART procedures may play a role in the pathophysiology of certain imprinting disorders (IDs), including Beckwith-Wiedemann syndrome, Silver-Russell syndrome, Prader-Willi syndrome, and Angelman syndrome. The underlying molecular basis of this association, however, requires further elucidation. In this review, we discuss the epigenetic and imprinting alterations of in vivo mouse models and human iPSC models of ART. Mouse models have demonstrated aberrant regulation of imprinted genes involved with ART-related IDs. In the past decade, iPSC technology has provided a platform for patient-specific cellular models of culture-associated perturbed imprinting. However, despite ongoing efforts, a deeper understanding of the susceptibility of iPSCs to epigenetic perturbation is required if they are to be reliably used for modelling ART-associated IDs. Comparing the patterns of susceptibility of imprinted genes in mouse models and IPSCs in culture improves the current understanding of the underlying mechanisms of ART-linked IDs with implications for our understanding of the influence of environmental factors such as culture and hormone treatments on epigenetically important regions of the genome such as imprints.

Association of assisted reproductive technology with autism spectrum disorder in the offspring: an updated systematic review and meta-analysis

This study aims to provide an up-to-date meta-analysis of data from studies investigating the risk of bearing a child with autism spectrum disorder (ASD) after being conceived by assisted reproductive technology (ART). The study was conducted according to the PRISMA Statement. PubMed and Scopus databases were searched up to August 2, 2020. Observational studies using a type of conception of assisted reproductive technology and examined as outcome offspring with ASD were included. A random effect model was applied due to the heterogeneity of the studies. Statistical analysis was performed with Stata 13 software. The Newcastle-Ottawa scale was used to assess the methodological quality of the included studies. The search strategy identified 587 potentially relevant studies. A total of 15 studies provided adequate data for statistical comparisons and, therefore, were included in the meta-analysis. Analysis of the subset of studies that examined all offspring and controlled for confounder factors revealed that the use of ART is associated with a higher risk of ASD (RR = 1.11, 95% CI = 1.03-1.19, p < 0.009), while in the case of studies that focused on singletons, a statistically significant association between ART and ASD was not observed (RR = 0.96, 95% CI = 0.82-1.13, p = 0.654).Conclusion: The present meta-analysis confirmed the existing positive correlation between ART and ASD in offspring, suggesting that ART is correlated with a higher risk for bearing a child with ASD. In contrast, this relationship is not confirmed in singletons. High quality prospective studies with a larger number of participants are still required. What is Known: • Studies that investigated the association between ART and ASD in offspring have shown conflicting results. • A previous meta-analysis showed that offspring conceived by ART are 1.35 times more likely to develop ASD than offspring spontaneously conceived. What is New: • This investigation separately considered studies with and without adjustment for confounders. • The findings from the two analyses were similar.

Alteration of Genomic Imprinting after Assisted Reproductive Technologies and Long-Term Health

Assisted reproductive technologies (ART) are the treatment of choice for some infertile couples and even though these procedures are generally considered safe, children conceived by ART have shown higher reported risks of some perinatal and postnatal complications such as low birth weight, preterm birth, and childhood cancer. In addition, the frequency of some congenital imprinting disorders, like Beckwith-Wiedemann Syndrome and Silver-Russell Syndrome, is higher than expected in the general population after ART. Experimental evidence from animal studies suggests that ART can induce stress in the embryo and influence gene expression and DNA methylation. Human epigenome studies have generally revealed an enrichment of alterations in imprinted regions in children conceived by ART, but no global methylation alterations. ART procedures occur simultaneously with the establishment and maintenance of imprinting during embryonic development, so this may underlie the apparent sensitivity of imprinted regions to ART. The impact in adulthood of imprinting alterations that occurred during early embryonic development is still unclear, but some experimental evidence in mice showed higher risk to obesity and cardiovascular disease after the restriction of some imprinted genes in early embryonic development. This supports the hypothesis that imprinting alterations in early development might induce epigenetic programming of metabolism and affect long-term health. Given the growing use of ART, it is important to determine the impact of ART in genomic imprinting and long-term health.

The L1-dependant and Pol III transcribed Alu retrotransposon, from its discovery to innate immunity

The 300 bp dimeric repeats digestible by AluI were discovered in 1979. Since then, Alu were involved in the most fundamental epigenetic mechanisms, namely reprogramming, pluripotency, imprinting and mosaicism. These Alu encode a family of retrotransposons transcribed by the RNA Pol III machinery, notably when the cytosines that constitute their sequences are de-methylated. Then, Alu hijack the functions of ORF2 encoded by another transposons named L1 during reverse transcription and integration into new sites. That mechanism functions as a complex genetic parasite able to copy-paste Alu sequences. Doing that, Alu have modified even the size of the human genome, as well as of other primate genomes, during 65 million years of co-evolution. Actually, one germline retro-transposition still occurs each 20 births. Thus, Alu continue to modify our human genome nowadays and were implicated in de novo mutation causing diseases including deletions, duplications and rearrangements. Most recently, retrotransposons were found to trigger neuronal diversity by inducing mosaicism in the brain. Finally, boosted during viral infections, Alu clearly interact with the innate immune system. The purpose of that review is to give a condensed overview of all these major findings that concern the fascinating physiology of Alu from their discovery up to the current knowledge.

Expression and DNA Methylation Status of the Imprinted Genes PEG10 and L3MBTL1 in the Umbilical Cord Blood and Placenta of the Offspring of Assisted Reproductive Technology

The aim of this study is to investigate the expression and DNA methylation status of the imprinted genes PEG10 and L3MBTL1 in the offspring of assisted reproductive technology (ART). The ART group consists of 30 cases of placenta and umbilical cord blood from ART full-term, uncomplicated singleton pregnancy progeny, and the normal control group consists of 30 cases of placenta and umbilical cord blood from natural full-term, uncomplicated singleton pregnancy progeny. The imprinted genes PEG10 and L3MBTL1 are analyzed, and the expression and methylation status of the two genes are detected using real-time quantitative polymerase chain reaction (QRT-PCR), immunohistochemistry (IHC), Western blotting (WB), and methylation-specific polymerase chain reaction (MSP). Compared with the normal control group, the PEG10 mRNA relative quantity (RQ) value in the placenta is 0.994 ± 0.458, with its RQ value up-regulated (P = 0.015). The PEG10 mRNA RQ value in the umbilical cord blood is 0.875 ± 0.452, with its RQ value up-regulated (P = 0.002). However, the L3MBTL1 mRNA RQ value in the placenta is 0.404 ± 0.234, with its RQ value down-regulated (P = 0.024). The L3MBTL1 mRNA RQ value in the umbilical cord blood is 0.337 ± 0.213, and there is no difference in the umbilical cord blood (P = 0.081). Compared with the normal control group, the expression of PEGl0 protein in the placenta of the ART progeny is up-regulated (P = 0.000), while the expression of L3MBTLl protein is down-regulated (P = 0.000). The methylation status of the PEGl0 promoter region in the placenta in the ART group is lower than that in the normal control group (P = 0.037), and that of the promoter region of the umbilical cord blood is lower than that of the natural pregnancy group (P = 0.032). The methylation status of the L3MBTLl promoter region is higher in the placenta than in the normal control group (P = 0.038), and there is no difference between the two groups in the umbilical cord blood (P = 0.301). In the ART group, the values of PEGl0 and L3MBTLl RQ in the placenta and the umbilical cord blood of the hypermethylated group are lower than in those of the hypomethylated group. ART may increase the risk of the abnormal expression of PEG10 and L3MBTL1 in offspring imprinted genes. The methylation of the promoter region may be the mechanism that regulates the expression of PEGl0 and L3MBTL1.

Assisted reproductive technology represents a possible risk factor for development of epimutation-mediated imprinting disorders for mothers aged ≥ 30 years

Backgrounds

The proportion of assisted reproductive technology (ART)-conceived livebirths of patients with imprinting disorders (IDs) is higher than that of the general population. Whether this is due to ART or confounding effects of advanced parental age was not investigated. We examined the association of ART and parental ages at childbirth for the development of eight epimutation-mediated imprinting disorders (epi-IDs).

Results

We enrolled 136 patients with epi-IDs and obtained general population ART data from the Japanese robust nationwide registry. We compared the proportion of ART-conceived livebirths and maternal childbearing ages between patients with epi-IDs and the general population. The proportion of ART-conceived livebirths in patients with epi-IDs was higher than that in mothers aged ≥ 30 years, the age group in which more than 90% of ART procedures performed. The maternal childbearing ages of patients with epi-IDs were widely distributed from 19 to 45 (median: 32) within the approximate 2.5th to 97.5th percentiles of maternal childbearing ages of the general population. In addition, we compared the proportion of ART-conceived livebirths and parental ages at childbirth across patients with eight epi-IDs. We demonstrated that more than 90% of ART-conceived patients with epi-IDs were found in Silver-Russell syndrome (SRS) and Beckwith-Wiedemann syndrome (BWS) patients, and parental ages were almost consistent in patients with eight epi-IDs, except Prader-Willi syndrome.

Conclusions

According to the prerequisite that most of the ART procedures in Japan are performed on mothers aged ≥ 30 years, ART can be a risk factor for the development of epi-IDs, particularly SRS and BWS, for mothers aged ≥ 30 years.

In-utero stress and mode of conception: impact on regulation of imprinted genes, fetal development and future health

BACKGROUND

Genomic imprinting is an epigenetic gene regulatory mechanism; disruption of this process during early embryonic development can have major consequences on both fetal and placental development. The periconceptional period and intrauterine life are crucial for determining long-term susceptibility to diseases. Treatments and procedures in assisted reproductive technologies (ART) and adverse in-utero environments may modify the methylation levels of genomic imprinting regions, including insulin-like growth factor 2 (IGF2)/H19, mesoderm-specific transcript (MEST), and paternally expressed gene 10 (PEG10), affecting the development of the fetus. ART, maternal psychological stress, and gestational exposures to chemicals are common stressors suspected to alter global epigenetic patterns including imprinted genes.

OBJECTIVE AND RATIONALE

Our objective is to highlight the effect of conception mode and maternal psychological stress on fetal development. Specifically, we monitor fetal programming, regulation of imprinted genes, fetal growth, and long-term disease risk, using the imprinted genes IGF2/H19, MEST, and PEG10 as examples. The possible role of environmental chemicals in genomic imprinting is also discussed.

SEARCH METHODS

A PubMed search of articles published mostly from 2005 to 2019 was conducted using search terms IGF2/H19, MEST, PEG10, imprinted genes, DNA methylation, gene expression, and imprinting disorders (IDs). Studies focusing on maternal prenatal stress, psychological well-being, environmental chemicals, ART, and placental/fetal development were evaluated and included in this review.

OUTCOMES

IGF2/H19, MEST, and PEG10 imprinted genes have a broad developmental effect on fetal growth and birth weight variation. Their disruption is linked to pregnancy complications, metabolic disorders, cognitive impairment, and cancer. Adverse early environment has a major impact on the developing fetus, affecting mostly growth, the structure, and subsequent function of the hypothalamic-pituitary-adrenal axis and neurodevelopment. Extensive evidence suggests that the gestational environment has an impact on epigenetic patterns including imprinting, which can lead to adverse long-term outcomes in the offspring. Environmental stressors such as maternal prenatal psychological stress have been found to associate with altered DNA methylation patterns in placenta and to affect fetal development. Studies conducted during the past decades have suggested that ART pregnancies are at a higher risk for a number of complications such as birth defects and IDs. ART procedures involve multiple steps that are conducted during critical windows for imprinting establishment and maintenance, necessitating long-term evaluation of children conceived through ART. Exposure to environmental chemicals can affect placental imprinting and fetal growth both in humans and in experimental animals. Therefore, their role in imprinting should be better elucidated, considering the ubiquitous exposure to these chemicals.

WIDER IMPLICATIONS

Dysregulation of imprinted genes is a plausible mechanism linking stressors such as maternal psychological stress, conception using ART, and chemical exposures with fetal growth. It is expected that a greater understanding of the role of imprinted genes and their regulation in fetal development will provide insights for clinical prevention and management of growth and IDs. In a broader context, evidence connecting impaired imprinted gene function to common diseases such as cancer is increasing. This implies early regulation of imprinting may enable control of long-term human health, reducing the burden of disease in the population in years to come.

In Vitro Fertilization Technology and Child Health

BACKGROUND

Just under 3% of children in Germany, and approximately 6% of children in some other countries, such as Denmark, are now being conceived with the aid of in vitro fertilization (IVF) technology. Alongside the increased risk of organ malformation, there is now evidence for functional abnormalities due to epigenetic modifications.

METHODS

This review is based on pertinent publications retrieved by a literature search on currently known associations of IVF therapy with malformations and functional abnormalities. The potential implications for the treatment of infertility are discussed.

RESULTS

The risk of congenital malformations is approximately one-third higher in children conceived with the aid of IVF technology than in other children; specifically, there is an odds ratio (OR) of 1.29 (95% confidence interval, [1.03; 1.60]) for cardiac malformations, and there is a relative risk (RR) of 1.35 ([1.12; 1.64]) for musculo- skeletal malformations and 1.58 ([1.28; 1.94]) for genitourinary malformations. The risks of preterm birth and low birth weight are, respectively, 1.7 and 1.5 times higher in IVF singleton pregnancies than in non-IVF pregnancies. Cardiovascular changes are the main type of functional disturbance. Some of the risks associated with IVF have decreased in recent years. An association has been revealed between cardiovascular abnormalities and epigenetic modifications; the causes are thought to include not only maternal and paternal factors, but also the IVF techniques that are used. A modification of IVF therapies might lower the risks, but might also lower the success rate.

CONCLUSION

For the well-being of the children to be conceived, IVF therapy should hat cannot be treated by any other means, as the precise causes of the risks of IVF to child health are unclear.

The effect of cryopreservation on DNA methylation patterns of the chromosome 15q11-q13 region in human spermatozoa

Human sperm cryopreservation is a common technique which is used in assisted reproductive technologies. Despite the existence of evidence supporting the production of ROS and DNA fragmentation during sperm cryopreservation, there is little and equivocal information about the cryopreservation effects on methylation of imprinted genes and imprinting control regions. In this study, we have investigated the effects of cryopreservation on DNA methylation in promoter regions of SNURF-SNRPN and UBE3A imprinted genes, PWS-ICR and AS-ICR in the chromosome 15q11-q13 region. Semen samples from 10 healthy normozoospermic men were collected and each sample was divided into four equal aliquots: fresh, cryoprotectant, cryopreservation, and H₂O₂. We measured the ROS levels and DNA fragmentation using DCFH-DA and TUNEL assay respectively by flow cytometry. DNA methylation in promoter regions of SNURF-SNRPN and UBE3A imprinted genes, PWS-ICR and AS-ICR in the chromosome 15q11-q13 region were evaluated by quantitative methylation-specific PCR technique. Intracellular levels of ROS and percentage of TUNEL-positive spermatozoa significantly increased in cryopreservation group compared to fresh group. Exposure to cryoprotectant had no significant effect on ROS levels and DNA fragmentation. Neither cryopreservation nor exposure to cryoprotectant significantly affected DNA methylation of the selected gene regions. However, DNA fragmentation had positive correlation with DNA methylation of AS-ICR. In conclusion, based on our study, clinical use of sperm cryopreservation for fertility treatments appear to be safe in regard to DNA methylation in the chromosome 15q11-q13 region.

Epigenetic Regulation and Risk Factors During the Development of Human Gametes and Early Embryos

Drastic epigenetic reprogramming occurs during human gametogenesis and early embryo development. Advances in low-input and single-cell epigenetic techniques have provided powerful tools to dissect the genome-wide dynamics of different epigenetic molecular layers in these processes. In this review, we focus mainly on the most recent progress in understanding the dynamics of DNA methylation, chromatin accessibility, and histone modifications in human gametogenesis and early embryo development. Deficiencies in remodeling of the epigenomes can cause severe developmental defects, infertility, and long-term health issues in offspring. Aspects of the external environment, including assisted reproductive technology procedures, parental diets, and unhealthy parental habits, may disturb the epigenetic reprogramming processes and lead to an aberrant epigenome in the offspring. Here, we review the current knowledge of the potential risk factors of aberrant epigenomes in humans.

In the human sperm nucleus, nucleosomes form spatially restricted domains consistent with programmed nucleosome positioning

In human sperm, a fraction of its chromatin retains nucleosomes that are positioned on specific sequences containing genes and regulatory units essential for embryonic development. This nucleosome positioning (NP) feature provides an inherited epigenetic mark for sperm. However, it is not known whether there is a structural constraint for these nucleosomes and, if so, how they are localized in a three-dimensional (3D) context of the sperm nucleus. In this study, we examine the 3D organization of sperm chromatin and specifically determine its 3D localization of nucleosomes using structured illumination microscopy. A fraction of the sperm chromatin form nucleosome domains (NDs), visible as microscopic puncta ranging from 40 μm to 700 μm in diameter, and these NDs are precisely localized in the post acrosome region (PAR), outside the sperm's core chromatin. Further, NDs exist mainly in sperm from fertile men in a pilot survey with a small sample size. Together, this study uncovers a new spatially-restricted sub-nuclear structure containing NDs that are consistent with NPs of the sperm, which might represent a novel mark for healthy sperm in human.

Association of four imprinting disorders and ART

Background

Human-assisted reproductive technologies (ART) are a widely accepted treatment for infertile couples. At the same time, many studies have suggested the correlation between ART and increased incidences of normally rare imprinting disorders such as Beckwith-Wiedemann syndrome (BWS), Angelman syndrome (AS), Prader-Willi syndrome (PWS), and Silver-Russell syndrome (SRS). Major methylation dynamics take place during cell development and the preimplantation stages of embryonic development. ART may prevent the proper erasure, establishment, and maintenance of DNA methylation. However, the causes and ART risk factors for these disorders are not well understood.

Results

A nationwide epidemiological study in Japan in 2015 in which 2777 pediatrics departments were contacted and a total of 931 patients with imprinting disorders including 117 BWS, 227 AS, 520 PWS, and 67 SRS patients, were recruited. We found 4.46- and 8.91-fold increased frequencies of BWS and SRS associated with ART, respectively. Most of these patients were conceived via in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), and showed aberrant imprinted DNA methylation. We also found that ART-conceived SRS (ART-SRS) patients had incomplete and more widespread DNA methylation variations than spontaneously conceived SRS patients, especially in sperm-specific methylated regions using reduced representation bisulfite sequencing to compare DNA methylomes. In addition, we found that the ART patients with one of three imprinting disorders, PWS, AS, and SRS, displayed additional minor phenotypes and lack of the phenotypes. The frequency of ART-conceived Prader-Willi syndrome (ART-PWS) was 3.44-fold higher than anticipated. When maternal age was 37 years or less, the rate of DNA methylation errors in ART-PWS patients was significantly increased compared with spontaneously conceived PWS patients.

Conclusions

We reconfirmed the association between ART and imprinting disorders. In addition, we found unique methylation patterns in ART-SRS patients, therefore, concluded that the imprinting disorders related to ART might tend to take place just after fertilization at a time when the epigenome is most vulnerable and might be affected by the techniques of manipulation used for IVF or ICSI and the culture medium of the fertilized egg.

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0623-3) contains supplementary material, which is available to authorized users.

Epigenetic regulation in development: is the mouse a good model for the human?

BACKGROUND

Over the past few years, advances in molecular technologies have allowed unprecedented mapping of epigenetic modifications in gametes and during early embryonic development. This work is allowing a detailed genomic analysis, which for the first time can answer long-standing questions about epigenetic regulation and reprogramming, and highlights differences between mouse and human, the implications of which are only beginning to be explored.

OBJECTIVE AND RATIONALE

In this review, we summarise new low-cell molecular methods enabling the interrogation of epigenetic information in gametes and early embryos, the mechanistic insights these have provided, and contrast the findings in mouse and human.

SEARCH METHODS

Relevant studies were identified by PubMed search.

OUTCOMES

We discuss the levels of epigenetic regulation, from DNA modifications to chromatin organisation, during mouse gametogenesis, fertilisation and pre- and post-implantation development. The recently characterised features of the oocyte epigenome highlight its exceptionally unique regulatory landscape. The chromatin organisation and epigenetic landscape of both gametic genomes are rapidly reprogrammed after fertilisation. This extensive epigenetic remodelling is necessary for zygotic genome activation, but the mechanistic link remains unclear. While the vast majority of epigenetic information from the gametes is erased in pre-implantation development, new insights suggest that repressive histone modifications from the oocyte may mediate a novel mechanism of imprinting. To date, the characterisation of epigenetics in human development has been almost exclusively limited to DNA methylation profiling; these data reinforce that the global dynamics are conserved between mouse and human. However, as we look closer, it is becoming apparent that the mechanisms regulating these dynamics are distinct. These early findings emphasise the importance of investigations of fundamental epigenetic mechanisms in both mouse and humans.

WIDER IMPLICATIONS

Failures in epigenetic regulation have been implicated in human disease and infertility. With increasing maternal age and use of reproductive technologies in countries all over the world, it is becoming ever more important to understand the necessary processes required to establish a developmentally competent embryo. Furthermore, it is essential to evaluate the extent to which these epigenetic patterns are sensitive to such technologies and other adverse environmental exposures.

Overrepresentation of pregnancies conceived by artificial reproductive technology in prenatally identified fetuses with Beckwith-Wiedemann syndrome

OBJECTIVES

In vitro fertilization (IVF) has been linked to an increased risk for imprinting disorders in offspring. The data so far have predominantly been retrospective, comparing the rate of IVF conceptions in affected patients with controls. We describe a series of fetuses with omphalocele that were tested for Beckwith-Wiedemann syndrome (BWS) and subsequently ascertained as to whether pregnancies were conceived by assisted reproductive technologies (ART).

METHODS

Fetuses were tested for BWS by Southern blot, PCR based methods, and methylation analysis to identify the imprinting status at primarily the IC2 locus, KCNQ1OT1, as well as IC1, H19/IGF-2. Some fetuses were also tested for uniparental disomy of chromosome 11p.

RESULTS

We tested 301 fetuses with omphalocele for BWS. Forty samples were positive. Sixteen were from IVF pregnancies, for an overall rate of 40%. Such as high proportion of IVF pregnancies in a series of BWS-positive fetuses has not been described previously. Possible factors such as twinning and ascertainment bias are discussed.

CONCLUSION

We found about a 20-fold overrepresentation of IVF cases in fetuses with BWS/omphalocele when compared with the rate of ART pregnancies in the USA (p < .0001). Our series provides support for an association of IVF and BWS. Patients should be counseled about these risks and made aware of the availability of prenatal diagnosis for detection.

Pseudohypoparathyroidism type 1B in a patient conceived by in vitro fertilization: another imprinting disorder reported with assisted reproductive technology

Pseudohypoparathyroidism type 1B (PHP1B) is characterized by renal tubular resistance to parathyroid hormone (PTH) leading to hyperphosphatemia, hypocalcemia, elevated PTH, and hyperparathyroid bone changes. PHP1B is an imprinting disorder that results from loss of methylation at the maternal GNAS gene, which suppresses transcription of the alpha subunit of the stimulatory G protein of the PTH receptor. Emerging evidence supports an association between assisted reproductive technologies (ART) and imprinting disorders; however, there is currently little evidence linking PHP1B and ART. We present a twin boy conceived by ART to parents with no history of subfertility who presented at age 12 with bilateral slipped capital femoral epiphysis and bilateral genu valgum deformity. Clinical and laboratory investigation revealed markedly elevated PTH, low ionized calcium, elevated phosphorus, TSH resistance, and skeletal evidence of hyperparathyroidism, leading to the diagnosis of PHP1B. A partial loss of methylation at the GNAS exon A/B locus was observed. The patient's dizygotic twin sibling was asymptomatic and had normal laboratory evaluation. This is the second reported case of a child with PHP1B conceived by ART, further supporting the possibility that ART may lead to an increased risk for imprinting defects.

Beckwith Wiedemann syndrome: A population-based study on prevalence, prenatal diagnosis, associated anomalies and survival in Europe

Beckwith Wiedemann syndrome is a complex developmental disorder characterized by somatic overgrowth, macroglossia, abdominal wall defects, neonatal hypoglycemia, and predisposition to embryonal tumors. We present epidemiological and clinical aspects of patients with Beckwith Wiedemann syndrome diagnosed prenatally or in the early years of life, using data from EUROCAT (European Surveillance of Congenital Anomalies) registries. The study population consisted of 371 cases identified between January 1990 and December 2015 in 34 registries from 16 European countries. There were 15 (4.0%) terminations of pregnancy after prenatal detection of severe anomaly/anomalies, 10 fetal deaths (2.7%), and 346 (93.3%) live-births. Twelve (3.6%) of the 330 live-births with available information on survival died in the first week of life, of those eleven (91.6%) were preterm. First-year survival rate was 90.9%. Prematurity was present in 40.6% of males and 33.9% of females. Macrosomia was found in 49.2% and 43.3% of preterm males and females, respectively. Of term newborns, 41.1% of males and 24% of females were macrosomic. Out of 353 cases with known time of diagnosis, 39.9% were suspected prenatally, 36.3% at birth, 7.6% were diagnosed in the first week of life, and 16.2% in the first year of life. The mean gestational age at prenatal diagnosis by obstetric ultrasound was 19.8 ± 6.2 (11-39) gestational weeks. The mean prenatal diagnosis of cases where parents opted for termination of pregnancy was 15.3 ± 2.4 (11-22) gestational weeks, and the mean gestational age at termination was 19.3 ± 4.1 (13-26) gestational weeks. The prenatal detection rate was 64.1% (141/220) with no significant change over time. There were 12.7% of familial cases. The study confirmed the association of assisted reproductive technologies with Beckwith Wiedemann syndrome, as 7.2% (13/181) of patients were conceived by one of the methods of assisted reproductive technologies, which was three times higher compared to the general population of the countries included in the study. Twin pregnancies of undetermined zygosity were recorded in 5.7% (21/365) cases, and were on average three to four times more common than in European countries that participated in the study. The estimated mean prevalence of classical Beckwith Wiedemann syndrome in Europe was 3.8 per 100,000 births or 1:26,000 births.

Assisted Reproductive Technologies and imprinting disorders: Results of a study from a French congenital malformations registry

INTRODUCTION

Assisted Reproductive Technologies (ART) is increasingly used to help infertile couples to have children around the world. A number of studies have been published reporting an increased risk of major malformations in children born following ART, especially an increased incidence of epigenetic diseases (ED). This study aimed to assess the incidence of epigenetic diseases with affected imprinting genes in infants or children from pregnancies obtained through IVF/ICSI compared to infants or children from pregnancies obtained spontaneously.

PATIENT DATA

This is a monocentric retrospective epidemiological study based on data from a French congenital malformations registry called REMERA (Registre des Malformations en Rhône-Alpes) which exhaustively monitors all pregnancies in Rhone-Alpes region, whatever their nature of onset (spontaneous pregnancies or pregnancies from ART). This registry collects all malformations, except minor malformations (EUROCAT), and all polymalformative syndromes concerning all fetuses and children born alive or not, from 20 weeks of pregnancy (or 22 weeks of amenorrhea) and all medical termination of pregnancy whatever the term. Inclusion criteria are all diagnoses of epigenetic diseases (ED) related to parental imprinting recorded in the period January 2006 to December 2015.

METHODS

For each year, the total number of births (including stillbirths) was collected from the annual activity reports of the registry. The exhaustive number of cases of epigenetic diseases was known in the registry. Were collected the number of births resulting from ART pregnancies in the study population. This incidence of ED was compared between births from spontaneous pregnancies and those obtained through ART (IVF/ICSI) with a generalized linear model (GLM: binomial regression).

RESULTS

In total, 46 cases of epigenetic diseases were analyzed on the REMERA registry files from 2006 to 2015. 4 cases from the 46 analyzed cases were from pregnancies induced by ART. ART was a risk factor for epigenetic disease (OR = 2.9 [1.06-8.22] (p = .039)). In ART-pregnancies there were 2 diagnoses: Beckwith-Wiedemann syndrome (BWS) (3 cases out of 4) and Silver-Russell syndrome (SRS) (1 out of 4).

DISCUSSION

Infants and children obtained through IVF/ICSI appear to be related to a higher risk of epigenetic diseases compared to naturally conceived children. The perspectives of this study are to raise awareness about the creation of registries of congenital malformations and genetic and epigenetic syndromes with systematic and strict reports of all the cases on all the French territory and thus to widen this study with a bigger cohort.

[Culture conditions for gametes and embryos: Which culture medium? Which impact on newborn?]

Many studies have examined the impact of cell/embryo culture media on the development of human embryo during IVF process, but few studies have followed up and compared the effects of these culture media on the developmental outcome of children conceived by IVF. As recurrent experimental evidence from animal studies suggests potential long-term effects of embryo culture media on the health outcome of IVF-conceived children, more studies are needed to clarify the role of the culture media and mechanisms underlying such effects. In human, however, the effects of culture media are difficult to pinpoint due to complications stem from both the influence of maternal nutrition during the gestational period and the parental genetic. Based on a simple review of the literature integrating animal experimentations and human clinic studies, we suggest that the composition of culture medium should be considered beyond the character of unique or sequential medium, corresponding to "let embryo choose" or "back to nature" respectively. Instead, we suggest that the main components of embryo culture media should be considered from the point of view of metabolic consequences and potential epigenetic effects. Given that energetic metabolites can regulate epigenetic machinery, we hypothesize that metabolic abnormalities linked to morphological abnormalities could reveal epigenetic defects in embryos.

The safety of intracytoplasmic sperm injection and long-term outcomes

The pioneering of intracytoplasmic sperm injection (ICSI) approximately 25 years ago revolutionized the treatment of infertile couples. Today, ICSI remains an indispensable part of assisted reproductive treatments (ART) and has resulted in the birth of millions of babies. The 25th anniversary of ICSI marks a chronologic landmark in its evolving history. This landmark also serves as an opportunity to thoroughly appraise the safety of ICSI and analyze the long-term outcomes of ICSI-conceived children. In this review, we collate and analyze salient data accrued over the past 25 years pertaining to the long-term safety of ICSI and ICSI conceptions. We also evaluate the effects of ICSI on the perinatal outcomes, congenital malformation rates, cognitive development and reproductive health of ICSI-conceived neonates, children, adolescents and adults, respectively. In doing so, we also highlight the existence of potential confounders and biases that frequently obscure the interpretation of clinical follow-up studies.

Non-Invasive Approaches to Epigenetic-Based Sperm Selection

Since sperm size and form do not necessarily provide information on internal sperm structures, novel sperm markers need to be found in order to conduct assisted reproductive therapies (ART) successfully. Currently, the priority of andrologists is not only to select those sperm able to fertilize the oocyte, but also a high quality of sperm that will guarantee a healthy embryo. Evidence of this shows us the importance of studying sperm intensively on genetic and epigenetic levels, because these could probably be the cause of a percentage of infertility diagnosed as idiopathic. Thus, more attention is being paid to posttranslational modifications as the key for better understanding of the fertilization process and its impact on embryo and offspring. Advances in the discovery of new sperm markers should go hand in hand with finding appropriate techniques for selecting the healthiest sperm, guaranteeing its non-invasiveness. To date, most sperm selection techniques can be harmful to sperm due to centrifugation or staining procedures. Some methods, such as microfluidic techniques, sperm nanopurifications, and Raman spectroscopy, have the potential to make selection gentle to sperm, tracking small abnormalities undetected by methods currently used. The fact that live cells could be analyzed without harmful effects creates the expectation of using them routinely in ART. In this review, we focus on the combination of sperm epigenetic status (modifications) as quality markers, with non-invasive sperm selection methods as novel approaches to improve ART outcomes.

Time to re-evaluate ART protocols in the light of advances in knowledge about methylation and epigenetics: an opinion paper

DNA methylation is a biochemical process that modifies gene expression without changing the underlying DNA sequence, and this represents the molecular basis for imprinting and epigenetics. Recent reports have revealed alterations in DNA methylation profiles in the placenta of babies born from assisted reproductive technologies (ART). This supports several previous observations that suggested an increase in the prevalence of imprinting diseases following ART treatment, and also fits our observations regarding the metabolism and requirements of early human embryos. Human embryo culture media (HECM) are currently formulated according to requirements based on the mouse embryo model, and in fact need to pass the Mouse Embryo Assay test in order to be accepted by the relevant authorities, despite the fact that physiological (especially the time necessary to reach genomic activation) and biochemical requirements of mouse and human embryos are quite different. This commentary aims to explain some of the discrepancies, and emphasize why human embryo metabolism tells us that the composition of HECM, as well as the role of the MEA as a unique model, should be re-evaluated.

Oviduct: roles in fertilization and early embryo development

Animal oviducts and human Fallopian tubes are a part of the female reproductive tract that hosts fertilization and pre-implantation development of the embryo. With an increasing understanding of roles of the oviduct at the cellular and molecular levels, current research signifies the importance of the oviduct on naturally conceived fertilization and pre-implantation embryo development. This review highlights the physiological conditions within the oviduct during fertilization, environmental regulation, oviductal fluid composition and its role in protecting embryos and supplying nutrients. Finally, the review compares different aspects of naturally occurring fertilization and assisted reproductive technology (ART)-achieved fertilization and embryo development, giving insight into potential areas for improvement in this technology.

Vitrification at Day3 stage appears not to affect the methylation status of H19/IGF2 differentially methylated region of in vitro produced human blastocysts

One of the most widely used assisted reproductive technology (ART) is vitrification. The aim of this study is to evaluate DNA methylation of H19/IGF2 differentially methylation region (DMR) in in vitro produced human blastocysts derived from non-vitrified and vitrified day3 embryos. Day3 embryos derived from ICSI cycles from fertile couples referring for family balancing program were either biopsied or vitrified/warmed and subsequently biopsied. Following biopsy, embryos were cultured to day 5. Day5 blastocysts with desired sex were transferred or vitrified for future use. Blastocysts with un-desired sex were donated for research. The assessment of the embryos was performed in two non-vitrified and vitrified groups. Methylation level of H19/IGF2 DMR was analysed by bisulfite conversion and sequencing at 18 CpG sites (CpGs) located in this region. Results showed that the overall methylated CpGs percentages of this region in the vitrified and non-vitrified groups were 35.3% ± 3.6 and 38.27 ± 4.1%, respectively. The difference between the two groups was not significant. Vitrification of day3 embryo appears to have no adverse effect on DNA methylation status of H19/IGF2 DMR of embryos cultured in vitro to blastocyst stage. These data may have implications for performing frozen embryo cycles transfer instead of fresh embryo transfer cycles, owing to the naturally synchronized uterus and subsequently improved endometrial receptivity in frozen embryo transfer instead of imbalanced hormonal milieu in fresh embryo transfer cycles.

Methylation Status of H19/IGF2 Differentially Methylated Region in in vitro Human Blastocysts Donated by Healthy Couples

BACKGROUND

Imprinted genes are a unique subset of few genes that have been differentially methylated region (DMR) in a parental origin-dependent manner during gametogenesis, and these genes are highly protected during pre-implantation epigenetic reprogramming. Several studies have shown that the particular vulnerability of imprinting genes during suboptimal pre- and peri-conception micro-environments often is occurred by assisted reproduction techniques (ART). This study investigated the methylation status of H19/IGF2 DMR at high-quality expanding/expanded human blastocysts donated by healthy individuals to evaluate the risks linked to ART.

METHODS

Methylation levels of H19/IGF2 DMR were analyzed by bisulfite conversion and sequencing at 18 CpG sites (CpGs) located in this region.

RESULTS

The overall percentage of methylated CpGs and the proportion of hyper-methylated clones of H19/IGF2 DMR in analyzed blastocysts were 37.85±4.87% and 43.75±5.1%, respectively. For validation of our technique, the corresponding methylation levels of peripheral human lymphocytes were defined (49.52±1.86% and 50%, respectively).

CONCLUSIONS

Considering the absence of in vivo- produced human embryos, it is not possible to conclude that the methylation found in H19/IGF2 DMR is actually normal or abnormal. Regarding the possible risks associated with ART, the procedures should be optimized in order to at least reduce some of the epigenetic risks.

Beckwith-Wiedemann syndrome prenatal diagnosis by methylation analysis in chorionic villi

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder that can be prenatally suspected or diagnosed based on established clinical guidelines. Molecular confirmation is commonly performed on amniocytes. The possibility to use fresh (CVF) and cultured (CVC) chorionic villi has never been investigated. To verify whether CVF and CVC are reliable sources of DNA to study fetal methylation, we used pyrosequencing to test the methylation level of a number of differentially methylated regions (DMRs) at several imprinted loci (ICR1, ICR2, H19, PWS/AS-ICR, GNASXL, GNAS1A, ZAC/PLAGL1, and MEST) and at non-imprinted MGMT and RASSF1A promoters. We analyzed these regions in 19 healthy pregnancies and highlighted stable methylation levels between CVF and CVC at ICR1, ICR2, GNASXL, PWS/AS-ICR, and MEST. Conversely, the methylation levels at H19 promoter, GNAS1A and ZAC/PLAGL1 were different in CVC compared to fresh CV. We also investigated ICR1 and ICR2 methylation level of CVF/CVC of 2 BWS-suspected fetuses (P1 and P2). P1 showed ICR2 hypomethylation, P2 showed normal methylation at both ICR1 and ICR2. Our findings, although limited to one case of BWS fetus with an imprinting defect, can suggest that ICR1 and ICR2, but not H19, could be reliable targets for prenatal BWS diagnosis by methylation test in CVF and CVC. In addition, PWS/AS-ICR, GNASXL, and MEST, but not GNAS1A and ZAC/PLAGL1, are steadily hemimethylated in CV from healthy pregnancies, independently from culture. Thus, prenatal investigation of genomic imprinting in CV needs to be validated in a locus-specific manner.

Epigenetic effects of chromatin remodeling agents on organotypic cultures

BACKGROUND

Tumor epigenetic defects are of increasing relevance to clinical practice, because they are 'druggable' targets for cancer therapy using chromatin-remodeling agents (CRAs). New evidences highlight the importance of the microenvironment on the epigenome regulation and the need to use culture models able to preserve tissue morphology, to better understand the action of CRAs. Methods & methods: We studied the epigenetic response induced by culturing and CRAs in a preclinical model, preserving ex vivo the original tissue microenvironment and morphology, assessing different epigenetic signatures. Our overall findings suggest that culturing and CRAs cause heterogeneous effects on the genes methylation; CRAs affect the global DNA methylation and can trigger an active DNA demethylation; the culture induces alterations in the histone deacetylase expression.

CONCLUSION

Despite the limited number of cases, these findings can be considered a proof of concept of the possibility to test CRAs epigenetic effects on ex vivo tissues maintained in their native tissue architecture.

On the origin of sperm epigenetic heterogeneity

The influence of epigenetic modifications on reproduction and on the function of male germ cells has been thoroughly demonstrated. In particular, aberrant DNA methylation levels in sperm have been associated with abnormal sperm parameters, lower fertilization rates and impaired embryo development. Recent reports have indicated that human sperm might be epigenetically heterogeneous and that abnormal DNA methylation levels found in the sperm of infertile men could be due to the presence of sperm populations with different epigenetic quality. However, the origin and the contribution of different germ cell types to this suspected heterogeneity remain unclear. In this review, we focus on sperm epigenetics at the DNA methylation level and its importance in reproduction. We take into account the latest developments and hypotheses concerning the functional significance of epigenetic heterogeneity coming from the field of stem cell and cancer biology and discuss the potential importance and consequences of sperm epigenetic heterogeneity for reproduction, male (in)fertility and assisted reproductive technologies (ART). Based on the current information, we propose a model in which spermatogonial stem cell variability, either intrinsic or due to external factors (such as endocrine action and environmental stimuli), can lead to epigenetic sperm heterogeneity, sperm epimutations and male infertility. The elucidation of the precise causes for epimutations, the conception of adequate therapeutic options and the development of sperm selection technologies based on epigenetic quality should be regarded as crucial to the improvement of ART outcome in the near future.