Another case of imprinting defect in a girl with Angelman syndrome who was conceived by intracytoplasmic semen injection

Ovulation induction and epigenetic anomalies

In this systematic review of ovulation induction and epigenetic control, studies mainly done in the mouse model highlight how hormone treatments may be prejudicial to the epigenetic reprogramming of gametes as well as early embryos. Moreover, the hormone protocols used in assisted reproduction may also modify the physiologic environment of the uterus, a potential link to endometrial epigenetic disturbances. At present, the few available data in humans are insufficient to allow us to independently determine the impact of a woman's age and infertility problems and treatment protocols and hormone doses on such processes as genomic imprinting.

Effects of embryonic manipulation and epigenetics

Embryonic manipulation techniques, such as in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), are widely used in assisted reproductive technology (ART), livestock propagation and application in other fields. Fertilization with IVF and ICSI have been shown to be highly effective, and the mice produced by these techniques develop healthily and with a normal appearance. However, there remains a possibility of epigenetic changes being induced by these techniques. The early stage of mammalian development from fertilization to implantation is a period in which global changes in the epigenetic landscape take place. The sperm and oocyte epigenetic profiles are very different from each other, and the epigenetic remodeling process after fertilization exhibits allelic differences. It is during this period that embryonic manipulation is performed. In this review, I discuss the effects of embryonic manipulation procedures in relation to the epigenetic asymmetry that is present in mammalian early development. Such regulation in the preimplantation embryo provides an important insight into epigenetics.

Embryo manipulation via assisted reproductive technology and epigenetic asymmetry in mammalian early development

The early stage of mammalian development from fertilization to implantation is a period when global and differential changes in the epigenetic landscape occur in paternally and maternally derived genomes, respectively. The sperm and egg DNA methylation profiles are very different from each other, and just after fertilization, only the paternally derived genome is subjected to genome-wide hydroxylation of 5-methylcytosine, resulting in an epigenetic asymmetry in parentally derived genomes. Although most of these differences are not present by the blastocyst stage, presumably due to passive demethylation, the maintenance of genomic imprinting memory and X chromosome inactivation in this stage are of critical importance for post-implantation development. Zygotic gene activation from paternally or maternally derived genomes also starts around the two-cell stage, presumably in a different manner in each of them. It is during this period that embryo manipulation, including assisted reproductive technology, is normally performed; so it is critically important to determine whether embryo manipulation procedures increase developmental risks by disturbing subsequent gene expression during the embryonic and/or neonatal development stages. In this review, we discuss the effects of various embryo manipulation procedures applied at the fertilization stage in relation to the epigenetic asymmetry in pre-implantation development. In particular, we focus on the effects of intracytoplasmic sperm injection that can result in long-lasting transcriptome disturbances, at least in mice.

Cytoplasmic inheritance redux

Since the early twentieth century, inheritance was seen as the inheritance of genes. Concurrent with the acceptance of the genetic theory of inheritance was the rejection of the idea that the cytoplasm of the oocyte could also play a role in inheritance and a corresponding devaluation of embryology as a discipline critical for understanding human development. Development, and variation in development, came to be viewed solely as matters of genetic inheritance and genetic variation. We now know that inheritance is a matter of both genetic and cytoplasmic inheritance. A growing awareness of the centrality of the cytoplasm in explaining both human development and phenotypic variation has been promoted by two contemporaneous developments: the continuing elaboration of the molecular mechanisms of epigenetics and the global rise of artificial reproductive technologies. I review recent developments in the ongoing elaboration of the role of the cytoplasm in human inheritance and development.

Genomic imprints as a model for the analysis of epigenetic stability during assisted reproductive technologies

Gamete and early embryo development are important stages when genome-scale epigenetic transitions are orchestrated. The apparent lack of remodeling of differential imprinted DNA methylation during preimplantation development has lead to the argument that epigenetic disruption by assisted reproductive technologies (ARTs) is restricted to imprinted genes. We contend that aberrant imprinted methylation arising from assisted reproduction or infertility may be an indicator of more global epigenetic instability. Here, we review the current literature on the effects of ARTs, including ovarian stimulation,in vitrooocyte maturation, oocyte cryopreservation, IVF, ICSI, embryo culture, and infertility on genomic imprinting as a model for evaluating epigenetic stability. Undoubtedly, the relationship between impaired fertility, ARTs, and epigenetic stability is unquestionably complex. What is clear is that future studies need to be directed at determining the molecular and cellular mechanisms giving rise to epigenetic errors.

Semen samples showing an increased rate of spermatozoa with imprinting errors have a negligible effect in the outcome of assisted reproduction techniques

The topic of imprinting defects present in the sperm of infertile patients has been addressed by several reports in the last few years. However, whether methylation abnormalities at one or few CpGs within an imprinted locus are pathological is a matter of debate. Moreover, whether imprinting anomalies in sperm could interfere with fertility treatment outcomes is still unknown. In this report we analyze the sperm DNA methylation profile of H19-ICR, KvDMR, SNRPN-ICR, IG-DMR and MEG3-DMR by pyrosequencing in 107 infertile men series and a control population of 30 proven fertile males. DNA methylation was statistically evaluated from two points of view: first, the methylation of each CpG was analyzed in the control population and the mean, standard deviation and range were determined and compared with infertile population data; second, in order to define altered methylation patterns for each region, a hierarchical cluster analysis was performed by which individuals were grouped in different clusters according to the degree of similarity of their methylation pattern. Two pieces of data supported the results obtained in the multi-variate analysis: the classification of the vast majority of control individuals in clusters with normal methylation patterns and the significant differences in methylation levels found between individuals within the normal and abnormal clusters. Individuals included in normal and abnormal methylation clusters were compared according to seminal parameters as well as to the outcome of assisted reproduction.

Compromised fertility disrupts Peg1 but not Snrpn and Peg3 imprinted methylation acquisition in mouse oocytes

Growth and maturation of healthy oocytes within follicles requires bidirectional signaling and intercellular gap junctional communication. Aberrant endocrine signaling and loss of gap junctional communication between the oocyte and granulosa cells leads to compromised folliculogenesis, oocyte maturation, and oocyte competency, consequently impairing fertility. Given that oocyte-specific DNA methylation establishment at imprinted genes occurs during this growth phase, we determined whether compromised endocrine signaling and gap junctional communication would disrupt de novo methylation acquisition using ERβ and connexin37 genetic models. To compare mutant oocytes to control oocytes, DNA methylation acquisition was first examined in individual, 20-80 μm control oocytes at three imprinted genes, Snrpn, Peg3, and Peg1. We observed that each gene has its own size-dependent acquisition kinetics, similar to previous studies. To determine whether compromised endocrine signaling and gap junctional communication disrupted de novo methylation acquisition,individual oocytes from Esr2- and Gja4-deficient mice were also assessed for DNA methylation establishment. We observed no aberrant or delayed acquisition of DNA methylation at Snrpn, Peg3, or Peg1 in oocytes from Esr2-deficient females, and no perturbation in Snrpn or Peg3de novo methylation in oocytes from Gja4-null females. However, Gja4 deficiency resulted in a loss or delay in methylation acquisition at Peg1. One explanation for this difference between the three loci analyzed is the late establishment of DNA methylation at the Peg1 gene. These results indicate that compromised fertility though impaired intercellular communication can lead to imprinting acquisition errors. Further studies are required to determine the effects of subfertility/infertility originating from impaired signaling and intercellular communication during oogenesis on imprint maintenance during preimplantation development.

Characterization of DNA methylation errors in patients with imprinting disorders conceived by assisted reproduction technologies

BACKGROUND

There is an increased incidence of rare imprinting disorders associated with assisted reproduction technologies (ARTs). The identification of epigenetic changes at imprinted loci in ART infants has led to the suggestion that the techniques themselves may predispose embryos to acquire imprinting errors and diseases. However, it is still unknown at what point(s) these imprinting errors arise, or the risk factors.

METHODS

In 2009 we conducted a Japanese nationwide epidemiological study of four well-known imprinting diseases to determine any association with ART. Using bisulfite sequencing, we examine the DNA methylation status of 22 gametic differentially methylated regions (gDMRs) located within the known imprinted loci in patients with Beckwith-Wiedemann syndrome (BWS, n=1) and also Silver-Russell syndrome (SRS, n= 5) born after ART, and compared these with patients conceived naturally.

RESULTS

We found a 10-fold increased frequency of BWS and SRS associated with ART. The majority of ART cases showed aberrant DNA methylation patterns at multiple imprinted loci both maternal and paternal gDMRs (5/6), with both hyper- and hypomethylation events (5/6) and also mosaic methylation errors (5/6). Although our study may have been limited by a small sample number, the fact that many of the changes were mosaic suggested that they occurred after fertilization. In contrast, few of the patients who were conceived naturally exhibited a similar pattern of mosaic alterations. The differences in methylation patterns between the patients who were conceived naturally or after ART did not manifest due to the differences in the disease phenotypes in these imprinting disorders.

CONCLUSION

A possible association between ART and BWS/SRS was found, and we observed a more widespread disruption of genomic imprints after ART. The increased frequency of imprinting disorders after ART is perhaps not surprising given the major epigenetic events that take place during early development at a time when the epigenome is most vulnerable.

Obstetric outcome and long-term follow up of children conceived through assisted reproduction

Most children born after assisted reproduction techniques are healthy. The most important risk associated with in-vitro fertilisation is the higher multiple birth rate, which may result in increased child morbidity because several embryos are transferred at each cycle. Single-embryo transfer reduces this risk dramatically. Large registry studies and meta-analyses have indicated a small but statistically significantly increased risk of congenital malformations among children born after in-vitro fertilisation. Other risks, such as preterm birth and low birth weight seem to be associated more with parental characteristics than the in-vitro fertilisation technique. All knowledge about children conceived through in-vitro fertilisation is based on observational studies, with risks of bias and confounders. It is possible that pregnancies and children resulting from in-vitro fertilisation are more carefully monitored and seek health care more frequently, resulting in more health problems being discovered. Continuous follow up of children after in-vitro fertilisation is of great importance, particularly as new techniques are constantly being introduced.

Methylation levels at imprinting control regions are not altered with ovulation induction or in vitro fertilization in a birth cohort

STUDY QUESTION

Do fertility treatments, including ovulation induction (OI), alter epigenetic mechanisms such as DNA methylation at imprinted loci?

SUMMARY ANSWER

We observed small but statistically significant differences in certain imprinting control regions (ICRs) based on the method of conception, however, these small changes in methylation did not correlate to the overall transcriptional levels of the genes adjacent to the ICRs (such as KCNQ1 and SNRPN).

WHAT IS KNOWN AND WHAT THIS PAPER ADDS

Assisted reproductive technology (ART) has been associated with an increase in the risk of rare childhood disorders caused by loss of imprinting (LOI). This study provides novel epigenetic analyses on infants conceived by OI and examines how methylation levels correlate with gene expression.

DESIGN

Data and biospecimens used in this study were from 147 participants of the Epigenetic Birth Cohort comprising 1941 mother-child dyads recruited between June 2007 and June 2009 at the Department of Obstetrics, Gynecology and Reproductive Biology at Brigham and Women's Hospital (BWH) in Boston, MA, USA. Wilcoxon rank-sum tests were used to examine the differences in median percent methylation at each differentially methylated region (DMR) between the spontaneous conception control group and the fertility treatment groups (OI and IVF).

PARTICIPANTS AND SETTING

For each woman who reported IVF we selected a woman who conceived spontaneously matched on age (± 2 years). To increase efficiency, we matched the same controls from the spontaneously conceived group to participants who reported OI. If an appropriate control was not identified that had been previously matched to an IVF participant, a new control was selected. The final analytic sample consisted of 61 spontaneous, 59 IVF and 27 OI conceptions.

MAIN RESULTS AND THE ROLE OF CHANCE

No functionally relevant differences in methylation levels were observed across five (out of six) imprinted DMRs in either the placenta or cord blood of infants conceived with OI or IVF compared with infants conceived spontaneously. While KCNQ1, SNRPN and H19 DMRs demonstrated small but statistically significant differences in methylation based on the method of conception, expression levels of the genes related to these control regions only correlated with the methylation levels of H19.

BIAS, CONFOUNDING AND OTHER REASONS FOR CAUTION

Limitations of our study include the limited sample size, lack of information on OI medication used and culture medium for the IVF procedures and underlying reasons for infertility among OI and IVF patients. We did not perform allele-specific expression analyses and therefore cannot make any inferences about LOI.

GENERALIZABILITY TO OTHER POPULATIONS

These results are likely to be generalizable to non-Hispanic white individuals in populations with similar ART and fertility treatments.

Loss of genomic imprinting in mouse embryos with fast rates of preimplantation development in culture

Currently, the stage of embryo development has been proposed as one of many criteria for identifying healthy embryos in infertility clinics with the fastest embryos being highlighted as the healthiest. However the validity of this as an accurate criterion with respect to genomic imprinting is unknown. Given that embryo development in culture generally requires an extra day compared to in vivo development, we hypothesized that loss of imprinting correlates with slower rates of embryonic development. To evaluate this, embryos were recovered at the 2-cell stage, separated into four groups based on morphological stage at two predetermined time points, and cultured to blastocysts. We examined cell number, embryo volume, embryo sex, imprinted Snrpn and H19 methylation, imprinted Snrpn, H19, and Cdkn1c expression, and expression of genes involved in embryo metabolism-Atp1a1, Slc2a1, and Mapk14-all within the same individual embryo. Contrary to our hypothesis, we observed that faster developing embryos exhibited greater cell numbers and embryo volumes as well as greater perturbations in genomic imprinting and metabolic marker expression. Embryos with slower rates of preimplantation development were most similar to in vivo derived embryos, displaying similar cell numbers, embryo volumes, Snrpn and H19 imprinted methylation, H19 imprinted expression, and Atp1a1 and Slc2a1 expression. We conclude that faster development rates in vitro are correlated with loss of genomic imprinting and aberrant metabolic marker expression. Importantly, we identified a subset of in vitro cultured embryos that, according to the parameters evaluated, are very similar to in vivo derived embryos and thus are likely most suitable for embryo transfer.

Role of ART in imprinting disorders

Assisted reproductive technologies (ART) offer revolutionary infertility treatments for millions of childless couples around the world. Currently, ART accounts for 1 to 3% of annual births in industrialized countries and continues to expand rapidly. Except for an increased incidence of premature births, these technologies are considered safe. However, new evidence published during the past decade has suggested an increased incidence of imprinting disorders in children conceived by ART. Specifically, an increased risk was reported for Beckwith-Wiedemann syndrome (BWS), Angelman syndrome (AS), Silver-Russell syndrome, and retinoblastoma. In contrast, some studies have found no association between ART and BWS, AS, Prader-Willi syndrome, transient neonatal diabetes mellitus, and retinoblastoma. The variability in ART protocols and the rarity of imprinting disorders complicate determining the causative relationship between ART and an increased incidence of imprinting disorders. Nevertheless, compelling experimental data from animal studies also suggest a link between increased imprinting disorders and ART. Further comprehensive, appropriately powered studies are needed to better address the magnitude of the risk for ART-associated imprinting disorders. Large longitudinal studies are particularly critical to evaluate long-term effects of ART not only during the perinatal period but also into adulthood. An important consideration is to determine if the implicated association between ART and imprinting disorders is actually related to the procedures or to infertility itself.

Epigenetic programming by maternal nutrition: shaping future generations

Within the Western world's aging and increasingly overweight population, we are seeing an increasing prevalence of adult-onset, lifestyle-related disease such as diabetes, hypertension and atherosclerosis. There is significant evidence that suboptimal nutrition in pregnancy can lead to an increased risk of these diseases developing in offspring, and that this increased risk can be heritable. Thus, poor in utero nutrition may be a major contributor to the current cycle of obesity. While the molecular basis of this phenomenon is unknown, available evidence suggests that it can be mediated by epigenetic changes to gene expression. Here, we discuss epigenetics as a mediator of disease risk in response to nutritional cues. The potential for maternal nutrition to heritably alter epigenetic states may have implications for population health and adaptive evolution.

DNA methylation profiling highlights the unique nature of the human placental epigenome

As the 'gateway' to the fetus, the placenta is subject to a myriad of environmental factors, each with the potential to alter placental epigenetic and gene expression profile. This can have direct consequences for the developing fetus and potentially even long-term health implications. As a result, interest in placental epigenetics generally, and changes occurring in placenta-associated disease, has intensified over recent years. This article will discuss the general features of placental DNA methylation and will describe current technologies for profiling genome-wide DNA methylation patterns in this tissue, the approaches to data analysis and some of the major findings from recent studies.

The effect of nutrition during early life on the epigenetic regulation of transcription and implications for human diseases

Epigenetic processes which include DNA methylation, histone modification and miRNAs are integral in determining when and where specific genes are expressed. There is now increasing evidence that the epigenome is susceptible to a variety of environmental cues, such as nutrition, during specific periods of development. The changes induced by early-life nutrition may reflect an adaptive response of the foetus to environmental cues acting through the process of developmental plasticity. This may allow an organism to adjust its developmental programme resulting in long-term changes in its metabolism and physiology in order to be better matched to the future environment. However, when the future environment lies outside the anticipated range, metabolic and homoeostatic capacity will be mismatched with the environment and that individual will be at increased risk of developing a range of non-communicable diseases. Thus the environmental regulation of epigenetic processes is a central component in the developmental origins of non-communicable diseases and our understanding of these processes is, therefore, critical both for the identification of individuals at risk and for the development of new intervention strategies.

Normal epigenetic inheritance in mice conceived by in vitro fertilization and embryo transfer

An association between assisted reproductive technology (ART) and neurobehavioral imprinting disorders has been reported in many studies, and it seems that ART may interfere with imprint reprogramming. However, it has never been explored whether epigenetic errors or imprinting disease susceptibility induced by ART can be inherited transgenerationally. Hence, the aim of this study was to determine the effect of in vitro fertilization and embryo transfer (IVF-ET) on transgenerational inheritance in an inbred mouse model. Mice derived from IVF-ET were outcrossed to wild-type C57BL/6J to obtain their female and male line F2 and F3 generations. Their behavior, morphology, histology, and DNA methylation status at several important differentially methylated regions (DMRs) were analyzed by Morris water maze, hematoxylin and eosin (H&E) staining, and bisulfite genomic sequencing. No significant differences in spatial learning or phenotypic abnormality were found in adults derived from IVF (F1) and female and male line F2 and F3 generations. A borderline trend of hypomethylation was found in H19 DMR CpG island 3 in the female line-derived F3 generation (0.40±0.118, P=0.086). Methylation status in H19/Igf2 DMR island 1, Igf2 DMR, KvDMR, and Snrpn DMR displayed normal patterns. Methylation percentage did not differ significantly from that of adults conceived naturally, and the expression of the genes they regulated was not disturbed. Transgenerational integrity, such as behavior, morphology, histology, and DNA methylation status, was maintained in these generations, which indicates that exposure of female germ cells to hormonal stimulation and gamete manipulation might not affect the individuals and their descendents.

Assisted reproduction treatment and epigenetic inheritance

BACKGROUND

The subject of epigenetic risk of assisted reproduction treatment (ART), initiated by reports on an increase of children with the Beckwith–Wiedemann imprinting disorder, is very topical. Hence, there is a growing literature, including mouse studies.

METHODS

In order to gain information on transgenerational epigenetic inheritance and epigenetic effects induced by ART, literature databases were searched for papers on this topic using relevant keywords.

RESULTS

At the level of genomic imprinting involving CpG methylation, ART-induced epigenetic defects are convincingly observed in mice, especially for placenta, and seem more frequent than in humans. Data generally provide a warning as to the use of ovulation induction and in vitro culture. In human sperm from compromised spermatogenesis, sequence-specific DNA hypomethylation is observed repeatedly. Transmittance of sperm and oocyte DNA methylation defects is possible but, as deduced from the limited data available, largely prevented by selection of gametes for ART and/or non-viability of the resulting embryos. Some evidence indicates that subfertility itself is a risk factor for imprinting diseases. As in mouse, physiological effects from ART are observed in humans.

In the human, indications for a broader target for changes in CpG methylation than imprinted DNA sequences alone have been found. In the mouse, a broader range of CpG sequences has not yet been studied. Also, a multigeneration study of systematic ART on epigenetic parameters is lacking.

CONCLUSIONS

The field of epigenetic inheritance within the lifespan of an individual and between generations (via mitosis and meiosis, respectively) is growing, driven by the expansion of chromatin research. ART can induce epigenetic variation that might be transmitted to the next generation.

Embryo culture and epigenetics

During preimplantation development, major epigenetic reprogramming occurs, erasing gametic modifications, and establishing embryonic epigenetic modifications. Given the plasticity of these modifications, they are susceptible to disruption by assisted reproductive technologies, including embryo culture. The current state of evidence is presented for the effects of embryo culture on global DNA methylation and histone modifications, retroviral silencing, X-inactivation, and genomic imprinting. Several salient points emerge from the literature; that culture in the absence of other procedures can lead to epigenetic perturbations; that all media are suboptimal; and that embryo response to in vitro culture is stochastic. We propose that embryos adapt to the suboptimal environment generated by embryo culture, including epigenetic adaptations, and that "quiet" embryos may be the least epigenetically compromised by in vitro culture.

Defects in imprinting and genome-wide DNA methylation are not common in the in vitro fertilization population

OBJECTIVE

To examine an IVF cohort for imprinted and genome-wide DNA methylation abnormalities.

DESIGN

Retrospective study.

SETTING

Research laboratory.

PATIENT(S)

DNA samples from a previously described IVF cohort that comprised 66 IVF-conceived prepubertal children (IVF, n = 34; intracytoplasmic sperm injection, n = 32) and 69 matched naturally conceived controls.

INTERVENTION(S)

DNA methylation was examined at four imprinted gene loci (H19, SNRPN, KCNQ1OT1, and IGF2) and satellite 2 using methylation-sensitive quantitative polymerase chain reaction (MSQ-PCR) followed by bisulfite sequencing at H19, SNRPN, and KCNQ1OT1. Methylated DNA immunoprecipitation (MeDIP) microarray with validation using the Sequenom MassARRAY EpiTYPER(®) platform was also used.

MAIN OUTCOME MEASURE(S)

Percentage of DNA methylation by MSQ-PCR, differential methylation based on microarray signal intensity, and percentage DNA methylation as determined by Sequenom MassARRAY EpiTYPER were compared.

RESULT(S)

No differences in percentage of methylation between the IVF and control group were observed at H19, KCNQ1OT1, SNRPN, or IGF2. Absence of aberrant imprinting was confirmed using bisulfite sequencing. Methylation of satellite 2 repeats (a surrogate for global methylation) showed no difference between the IVF and control groups. MeDIP was used to screen for differences in promoter methylation. Subsequent quantification of methylation of eight candidate genes using the Sequenom MassARRAY EpiTYPER system did not reveal any differential methylation.

CONCLUSION(S)

Low-level imprinting errors are not common in the IVF population.

The Dnmt3b splice variant is specifically expressed in in vitro-manipulated blastocysts and their derivative ES cells

Manipulation of preimplantation embryos in vitro, such as in vitro fertilization (IVF), in vitro culture (IVC), intracytoplasmic sperm injection (ICSI), somatic cell nuclear transfer (SCNT) and other assisted reproduction technologies (ART), has contributed to the development of infertility treatment and new animal reproduction methods. However, such embryos often exhibit abnormal DNA methylation patterns in imprinted genes and centromeric satellite repeats. These DNA methylation patterns are established and maintained by three DNA methyltransferases: Dnmt1, Dnmt3a and Dnmt3b. Dnmt3b is responsible for the creation of methylation patterns during the early stage of embryogenesis and consists of many alternative splice variants that affect methylation activity; nevertheless, the roles of these variants have not yet been identified. In this study, we found an alternatively spliced variant of Dnmt3b lacking exon 6 (Dnmt3bΔ6) that is specific to mouse IVC embryos. Dnmt3bΔ6 also showed prominent expression in embryonic stem (ES) cells derived from in vitro manipulated embryos. Interestingly, IVC blastocysts were hypomethylated in centromeric satellite repeat regions that could be susceptible to methylation by Dnmt3b. In vitro methylation activity assays showed that Dnmt3bΔ6 had lower activity than normal Dnmt3b. Our findings suggest that Dnmt3bΔ6 could induce a hypomethylation status especially in in vitro manipulated embryos.

DNA methylation at H19/IGF2 ICR1 in the placenta of pregnancies conceived by in vitro fertilization and intracytoplasmic sperm injection

DNA methylation at H19 ICR1 was investigated in the placenta from pregnancies conceived by in vitro fertilization, intracytoplasmic sperm injection, and from natural conception. Our results showed that there were no significant differences in mean methylation between all pregnancy groups; therefore, assisted reproductive technology may not affect proper imprinting of H19 and IGF2.

Analysis of H19 methylation in control and abnormal human embryos, sperm and oocytes

ART is suspected to generate increased imprinting errors in the lineage. Following an intra cytoplasmic sperm injection (ICSI) procedure, a certain number of embryos fail to develop normally and imprinting disorders may be associated to the developmental failure. To evaluate this hypothesis, we analysed the methylation profile of H19DMR, a paternally imprinting control region, in high-graded blastocysts, in embryos showing developmental anomalies, in the matching sperm and in oocytes of the concerned couples when they were available. Significant hypomethylation of the paternal allele was observed in half of the embryos, independently of the stage at which they were arrested (morula, compacted morula, pre blastocyst or BC-graded blastocysts). Conversely, some embryos showed significant methylation on the maternal allele, whereas few others showed both hypomethylation of the paternal allele and abnormal methylation of the maternal allele. The matching sperm at the origin of the embryos exhibited normal methylated H19 patterns. Thus, hypomethylation of the paternal allele in the embryos does not seem inherited from the sperm but likely reflects instability of the imprint during the demethylating process, which occurred in the early embryo. Analysis of a few oocytes suggests that the defect in erasure of the paternal imprint in the maternal germ line may be responsible for the residual methylation of the maternal allele in some embryos. None of these imprinting alterations could be related to a particular stage of developmental arrest; compared with high-grade blastocysts, embryos with developmental failure are more likely to have abnormal imprinting at H19 (P<0.05).

Genome-wide DNA methylation patterns in IVF-conceived mice and their progeny: a putative model for ART-conceived humans

The aim of this study was to use a mouse model to gain an understanding of the safety of reproduction between humans conceived through assisted reproductive technology (ART). Mice derived from in vitro fertilization and embryo transfer (IVF-ET) were crossed. Their behavior, morphology, histology and genome-wide DNA methylation status in the brain were examined by the Morris water maze, H&E staining and methylated DNA immunoprecipitation coupled with DNA methylation microarrays. Although no significant differences in behavior or morphology were observed, we did find small clusters of CpG islands and promoters that were aberrantly methylated. Hypermethylation was more common than hypomethylation in each of the two generations. Some of the aberrant methylated promoters were validated by bisulfite sequencing. Our results show that IVF may slightly modify the somatic methylation pattern and that some of this aberrant methylation might be inherited by the following generation.

Quantitative analysis of DNA methylation of imprinted genes in single human blastocysts by pyrosequencing

We report the first quantitative assessment of DNA methylation for any gene in the human preimplantation embryo to reveal that imprints exist at KvDMR1, RB1, SNRPN, and GRB10 in the human blastocyst. For comparison, in two human embryonic stem cell lines, imprints were also observed at KvDMR1, SNRPN, GRB10, and other imprinted loci, whereas RB1 and MEG3 were hypermethylated.

Child health, developmental plasticity, and epigenetic programming

Plasticity in developmental programming has evolved in order to provide the best chances of survival and reproductive success to the organism under changing environments. Environmental conditions that are experienced in early life can profoundly influence human biology and long-term health. Developmental origins of health and disease and life-history transitions are purported to use placental, nutritional, and endocrine cues for setting long-term biological, mental, and behavioral strategies in response to local ecological and/or social conditions. The window of developmental plasticity extends from preconception to early childhood and involves epigenetic responses to environmental changes, which exert their effects during life-history phase transitions. These epigenetic responses influence development, cell- and tissue-specific gene expression, and sexual dimorphism, and, in exceptional cases, could be transmitted transgenerationally. Translational epigenetic research in child health is a reiterative process that ranges from research in the basic sciences, preclinical research, and pediatric clinical research. Identifying the epigenetic consequences of fetal programming creates potential applications in clinical practice: the development of epigenetic biomarkers for early diagnosis of disease, the ability to identify susceptible individuals at risk for adult diseases, and the development of novel preventive and curative measures that are based on diet and/or novel epigenetic drugs.

Integrity of human sperm DNA assessed by the neutral comet assay and its relationship to semen parameters and clinical outcomes for the IVF-ET program

Objective

To explore potential relationships between sperm DNA integrity and both semen parameters and clinical outcomes.

Methods

Semen analysis of 498 samples was performed according to the 2010 criteria of the World Health Organization. The sperm DNA fragmentation Index (DFI) of the semen samples was assessed using a neutral comet assay.

Results

Sperm DFI showed a significant correlation with semen parameters, including the patient's age, sperm viability, motility, morphology, and number of leukocytes (p<0.05). The sperm DFI values for asthenozoospermic (15.2%), oligoteratozoospermic (18.3%), asthenoteratozoospermic (17.5%), and oligoasthenoteratozoospermic semen samples (21.3%) were significantly higher than that observed in normozoospermic semen samples (10.5%, p<0.05). A sperm DFI value of 14% was used as a threshold of sperm DFI in assessing whether DNA was highly damaged. In 114 IVF-ET cycles, the fertilization rate of the sperm DFI <14% group (70 cycles, 61.7%) was significantly higher than that observed for the ≥14% group (44 cycles, 55.3%), but there was no difference in the other clinical outcomes between the two groups. In the ≥14% group, the pregnancy rates of the ICSI cycles (40.0%) and half-ICSI (44.0%) were higher than conventional IVF cycles (30.7%), but the difference was not statistically significant.

Conclusion

Along with the conventional semen analysis, the sperm DFI assessed using the comet assay was shown to improve the quality of the semen evaluation. To evaluate the precise effect of ICSI on pregnancy rates in the patients who demonstrate high sperm DFI values, further study is necessary.

Epigenetic differences between embryonic stem cells generated from blastocysts developed in vitro and in vivo

Embryonic stem (ES) cells constitute a very important tool for regenerative medicine today. These ES cells, and human ES cells in particular, are almost all derived from embryos obtained by in vitro fertilization (IVF) and from in vitro culture (IVC); however, such in vitro manipulated embryos often show abnormal genomic imprinting, which can lead to the development of various diseases. Nevertheless, several reports have evaluated ES cells derived from in vitro manipulated embryos. In this study, we established ES cells derived from both in vivo and in vitro developed blastocysts (Vivo ES cells and Vitro ES cells, respectively) to compare the methylation status of imprinted genes and gene expression patterns. At very early passages, Vitro ES cells showed an increase in abnormal genomic imprinting compared to Vivo ES cells. In addition, we found that the gene expression patterns of several methylation related-genes frequently shifted to promote demethylation and to inhibit methylation in early-passage Vitro ES cells. In contrast, at later passages, we found no significant differences between Vivo and Vitro ES cells. In conclusion, it is advisable to use early passage Vivo ES cells whenever feasible, or to select ES cell lines with a normal epigenotype.

Effect of maternal diet on the epigenome: implications for human metabolic disease

The rapid increase in the incidence of chronic non-communicable diseases over the past two decades cannot be explained solely by genetic and adult lifestyle factors. There is now considerable evidence that the fetal and early postnatal environment also strongly influences the risk of developing such diseases in later life. Human studies have shown that low birth weight is associated with an increased risk of CVD, type II diabetes, obesity and hypertension, although recent studies have shown that over-nutrition in early life can also increase susceptibility to future metabolic disease. These findings have been replicated in a variety of animal models, which have shown that both maternal under- and over-nutrition can induce persistent changes in gene expression and metabolism within the offspring. The mechanism by which the maternal nutritional environment induces such changes is beginning to be understood and involves the altered epigenetic regulation of specific genes. The demonstration of a role for altered epigenetic regulation of genes in the developmental induction of chronic diseases raises the possibility that nutritional or pharmaceutical interventions may be used to modify long-term cardio-metabolic disease risk and combat this rapid rise in chronic non-communicable diseases.

Relationship of folate, vitamin B12 and methylation of insulin-like growth factor-II in maternal and cord blood

BACKGROUND/OBJECTIVE

One of the speculated mechanisms underlying fetal origin hypothesis of breast cancer is the possible influence of maternal environment on epigenetic regulation, such as changes in DNA methylation of the insulin-like growth factor-2 (IGF2) gene. The aim of the study is to investigate the relationship between folate, vitamin B(12) and methylation of the IGF2 gene in maternal and cord blood.

SUBJECTS/METHODS

We conducted a cross-sectional study to measure methylation patterns of IGF2 in promoters 2 (P2) and promoters 3 (P3).

RESULTS

The percentage of methylation in IGF2 P3 was higher in maternal blood than in cord blood (P<0.0001), whereas the methylation in P2 was higher in cord blood than in maternal blood (P=0.016). P3 methylation was correlated between maternal and cord blood (P<0.0001), but not P2 (P=0.06). The multivariate linear regression model showed that methylation patterns of both promoters in cord blood were not associated with serum folate levels in either cord or maternal blood, whereas the P3 methylation patterns were associated with serum levels of vitamin B(12) in mother's blood (mean change (MC)=-0.22, P=0.0014). Methylation patterns in P2 of maternal blood were associated with serum levels of vitamin B(12) in mother's blood (MC=-0.23, P=0.012), exposure to passive smoking (MC=0.46, P=0.034) and mother's weight gain during pregnancy (MC=0.23, P=0.019).

CONCLUSIONS

The study suggests that environment influences methylation patterns in maternal blood, and then the maternal patterns influence the methylation status and levels of folate and vitamin B(12) in cord blood.

Generation of mtDNA homoplasmic cloned lambs

Generally in mammals, individual animals contain only maternally inherited mitochondrial DNA (mtDNA), as paternal (sperm)-derived mitochondria are usually eliminated during early development. Somatic cell nuclear transfer (SCNT) bypasses the normal routes of mtDNA inheritance and introduces not only a different nuclear genome into the recipient cytoplast (in general an enucleated oocyte) but also somatic mitochondria. Differences in mtDNA genotype between recipient oocytes and potential mtDNA heteroplasmy due to persistence and replication of somatic mtDNA means that offspring generated by SCNT are not true clones. However, more importantly, the consequences of the presence of somatic mtDNA, mtDNA heteroplasmy, or possible incompatibility between nuclear and mtDNA genotypes on subsequent development and function of the embryo, fetus and offspring are unknown. Following sexual reproduction, mitochondrial function requires the biparental control of maternally inherited mtDNA, whereas following SCNT incompatibility between the recipient cell mitochondrial and transplanted nuclear genomes, or mtDNA heteroplasmy, may result in energy imbalance and initiate the onset of mtDNA-type disease, or disruption of normal developmental events. To remove the potentially adverse effects of somatic mtDNA following SCNT we have previously produced embryos using donor cells depleted to residual levels of mtDNA (mtDNA). We now report that these cells support development to term and produced live lambs in which no donor somatic mtDNA was detected, the lambs being homoplasmic for recipient oocyte DNA.

Imprinting disorders and assisted reproductive technology

PURPOSE OF REVIEW

To summarize current evidence in the association of imprinting disorders and assisted reproductive technology.

RECENT FINDINGS

The worldwide usage of assisted reproductive technology (ART) has continued to increase since the first successful birth of a human after IVF. Since 2002, several reports have raised concerns that children conceived by ART are at increased risk of having imprinting disorders. The majority of published studies have examined DNA methylation in children conceived by ART, but results are conflicting. Beckwith-Wiedemann syndrome and Angelman syndrome are the most extensively studied imprinting disorders and multiple case series and reports have been published on ART-conceived children with these syndromes. Overall the majority of reports suggest that ART might be associated with Beckwith-Wiedermann syndrome and Angelman syndrome, but larger collaborative studies need to be performed.

SUMMARY

The current data suggest an association between imprinting disorders and ART although the absolute risk appears to be low. However, animal studies have established biologic plausibility and there is continuing concern about the possibility of epigenetic changes resulting from ART.

Side-by-side comparison of five commercial media systems in a mouse model: suboptimal in vitro culture interferes with imprint maintenance

Assisted reproductive technologies (ARTs) are becoming increasingly prevalent and are generally considered to be safe medical procedures. However, evidence indicates that embryo culture may adversely affect the developmental potential and overall health of the embryo. One of the least studied but most important areas in this regard is the effects of embryo culture on epigenetic phenomena, and on genomic imprinting in particular, because assisted reproduction has been linked to development of the human imprinting disorders Angelman and Beckwith-Wiedemann syndromes. In this study, we performed side-by-side comparisons of five commercial embryo culture systems (KSOMaa, Global, Human Tubal Fluid, Preimplantation 1/Multiblast, and G1v5PLUS/G2v5PLUS) in relation to a best-case (in vivo-derived embryos) and a worst-case (Whitten culture) scenario. Imprinted DNA methylation and expression were examined at three well-studied loci, H19, Peg3, and Snrpn, in mouse embryos cultured from the 2-cell to the blastocyst stage. We show that embryo culture in all commercial media systems resulted in imprinted methylation loss compared to in vivo-derived embryos, although some media systems were able to maintain imprinted methylation levels more similar to those of in vivo-derived embryos in comparison to embryos cultured in Whitten medium. However, all media systems exhibited loss of imprinted H19 expression comparable to that using Whitten medium. Combined treatment of superovulation and embryo culture resulted in increased perturbation of genomic imprinting, above that from culture alone, indicating that multiple ART procedures further disrupt genomic imprinting. These results suggest that time in culture and number of ART procedures should be minimized to ensure fidelity of genomic imprinting during preimplantation development.

Epigenetic regulatory mechanisms associated with infertility

Infertility is a complex human condition and is known to be caused by numerous factors including genetic alterations and abnormalities. Increasing evidence from studies has associated perturbed epigenetic mechanisms with spermatogenesis and infertility. However, there has been no consensus on whether one or a collective of these altered states is responsible for the onset of infertility. Epigenetic alterations involve changes in factors that regulate gene expression without altering the physical sequence of DNA. Understanding these altered epigenetic states at the genomic level along with higher order organisation of chromatin in genes associated with infertility and pericentromeric regions of chromosomes, particularly 9 and Y, could further identify causes of idiopathic infertility. Determining the association between DNA methylation, chromatin state, and noncoding RNAs with the phenotype could further determine what possible mechanisms are involved. This paper reviews certain mechanisms of epigenetic regulation with particular emphasis on their possible role in infertility.

Autism spectrum disorders and epigenetics

OBJECTIVE

Current research suggests that the causes of autism spectrum disorders (ASD) are multifactorial and include both genetic and environmental factors. Several lines of evidence suggest that epigenetics also plays an important role in ASD etiology and that it might, in fact, integrate genetic and environmental influences to dysregulate neurodevelopmental processes. The objective of this review is to illustrate how epigenetic modifications that are known to alter gene expression without changing primary DNA sequence may play a role in the etiology of ASD.

METHOD

In this review, we summarize current knowledge about epigenetic modifications to genes and genomic regions possibly involved in the etiology of ASD.

RESULTS

Several genetic syndromes comorbid with ASD, which include Rett, Fragile X, Prader-Willi, Angelman, and CHARGE (Coloboma of the eye, Heart defects, Atresia of the nasal choanae, Retardation of growth and/or development, Genital and/or urinary abnormalities, and Ear abnormalities and deafness), all demonstrate dysregulation of epigenetic marks or epigenetic mechanisms. We report also on genes or genomic regions exhibiting abnormal epigenetic regulation in association with either syndromic (15q11-13 maternal duplication) or nonsyndromic forms of ASD. Finally, we discuss the state of current knowledge regarding the etiologic role of environmental factors linked to both the development of ASD and epigenetic dysregulation.

CONCLUSION

Data reviewed in this article highlight a variety of situations in which epigenetic dysregulation is associated with the development of ASD, thereby supporting a role for epigenetics in the multifactorial etiologies of ASD.

Inter- and intra-individual variation in allele-specific DNA methylation and gene expression in children conceived using assisted reproductive technology

Epidemiological studies have reported a higher incidence of rare disorders involving imprinted genes among children conceived using assisted reproductive technology (ART), suggesting that ART procedures may be disruptive to imprinted gene methylation patterns. We examined intra- and inter-individual variation in DNA methylation at the differentially methylated regions (DMRs) of the IGF2/H19 and IGF2R loci in a population of children conceived in vitro or in vivo. We found substantial variation in allele-specific methylation at both loci in both groups. Aberrant methylation of the maternal IGF2/H19 DMR was more common in the in vitro group, and the overall variance was also significantly greater in the in vitro group. We estimated the number of trophoblast stem cells in each group based on approximation of the variance of the binomial distribution of IGF2/H19 methylation ratios, as well as the distribution of X chromosome inactivation scores in placenta. Both of these independent measures indicated that placentas of the in vitro group were derived from fewer stem cells than the in vivo conceived group. Both IGF2 and H19 mRNAs were significantly lower in placenta from the in vitro group. Although average birth weight was lower in the in vitro group, we found no correlation between birth weight and IGF2 or IGF2R transcript levels or the ratio of IGF2/IGF2R transcript levels. Our results show that in vitro conception is associated with aberrant methylation patterns at the IGF2/H19 locus. However, very little of the inter- or intra-individual variation in H19 or IGF2 mRNA levels can be explained by differences in maternal DMR DNA methylation, in contrast to the expectations of current transcriptional imprinting models. Extraembryonic tissues of embryos cultured in vitro appear to be derived from fewer trophoblast stem cells. It is possible that this developmental difference has an effect on placental and fetal growth.

We have screened a population of children conceived in vitro for epigenetic alterations at two loci that carry parent-of-origin specific methylation marks. We made the observation that epigenetic variability was greater in extraembryonic tissues than embryonic tissues in both groups, as has also been demonstrated in the mouse. The greater level of intra-individual variation in extraembryonic tissues of the in vitro group appears to result from these embryos having fewer trophoblast stem cells. We also made the unexpected observation that variability in parental origin-dependent epigenetic marking was poorly correlated with gene expression. In fact, there is such a high level of inter-individual variation in IGF2 transcript level that the presumed half-fold reduction in IGF2 mRNA accounted for by proper transcriptional imprinting versus complete loss of imprinting would account for less than 5% of the total population variance. Given this level of variability in the expression of an imprinted gene, the presumed operation of “parental conflict” as the selective force acting to maintain imprinted gene expression at the IGF2/H19 locus in the human should be revisited.

Evaluation of epigenetic marks in human embryos derived from IVF and ICSI

BACKGROUND

It has long been appreciated that environmental cues may trigger adaptive responses. Many of these responses are a result of changes in the epigenetic landscape influencing transcriptional states and consequently altering phenotypes. In the context of human reproductive health, the procedures necessary for assisted reproduction may result in altered phenotypes by primarily influencing DNA methylation. Among the well-documented effects of assisted reproduction technologies (ART), imprinted genes appear to be frequently altered, likely owing to their reliance on DNA methylation to impose parent-specific monoallelic expression. However, the generality of the potential deregulation of DNA methylation in ART-derived human embryos has not been evaluated.

METHODS

In this study, we evaluate the genome-wide DNA methylation together with chromatin organisation in human embryos derived by either IVF (n = 89) or ICSI (n = 76). DNA methylation was assessed using an antibody against 5-methyl-cytidine, and chromatin organisation by DNA staining.

RESULTS

Irrespective of the ART procedure, similar errors were observed in both groups and abnormal chromatin was positively correlated (P < 0.001) with inappropriate DNA methylation. Development up to the blastocyst stage was consistent with normal DNA methylation and chromatin organisation, reinforcing the importance of epigenetic regulation to form the early lineages of the blastocyst. Most importantly, we found no evidence that ICSI blastocysts were more severely affected than those derived by IVF.

CONCLUSIONS

We conclude that ICSI does not lead to an increased incidence of epigenetic errors (DNA methylation and chromatin) compared with IVF.

Effects of assisted reproduction technology on placental imprinted gene expression

We used placental tissue to compare the imprinted gene expression of IGF2, H19, KCNQ1OT1, and CDKN1C of singletons conceived via assisted reproduction technology (ART) with that of spontaneously conceived (SC) singletons. Of 989 singletons examined (ART n = 65; SC n = 924), neonatal weight was significantly lower (P < .001) in the ART group than in the SC group, but placental weight showed no significant difference. Gene expression analyzed by real-time PCR was similar for both groups with appropriate-for-date (AFD) birth weight. H19 expression was suppressed in fetal growth retardation (FGR) cases in the ART and SC groups compared with AFD cases (P < .02 and P < .05, resp.). In contrast, CDKN1C expression was suppressed in FGR cases in the ART group (P < .01), while KCNQ1OT1 expression was hyperexpressed in FGR cases in the SC group (P < .05). As imprinted gene expression patterns differed between the ART and SC groups, we speculate that ART modifies epigenetic status even though the possibilities always exist.

Sex and reproduction: an evolving relationship

BACKGROUND

Although sexual activity has, until very recently, been essential to reproduction, this did not preclude the non-reproductive importance of sexual relationships and non-conceptive copulations. Technological advances, however, now allow for both sex without reproduction and reproduction without sex. This review summarizes social and ethical commentaries on the new relationship between sex and reproduction.

METHODS

For each main area discussed, a systematic search was made using (depending on the subject) PubMed, Medline, ScienceDirect, classic books, Google and/or religious websites. The search focused on publications between 1975 and 2009, although some materials from the first part of the 20th century were also utilized.

RESULTS

The classic picture of sex for reproduction and bonding between mating partners is increasingly being replaced by reproduction separate from sexual activity. Although not every advance in assisted reproduction produced, per se, a further separation from sexual intercourse, these two fundamental human activities are today increasingly carried out independently, as reproduction is possible, not only without sex, but even through the intervention of more than two partners. The possibility of reproduction with only one or even no gametes, although highly controversial and not yet feasible, is nonetheless being investigated.

CONCLUSIONS

Technological advances in the field of reproductive biology have enabled couples considered infertile to conceive and have healthy babies, causing a revolution in culture and customs. Today the independence of sex and reproduction is established and in the future human reproduction may move even further away from the sexual act, an option definitely unacceptable to some ethicists.