The effects of superovulation and reproductive aging on the epigenome of the oocyte and embryo

Epigenetic modifications of gonadotropin receptors can regulate follicular development

The spatiotemporal transcription of follicle-stimulating hormone receptor (FSHR) and luteinizing hormone/human chorionic gonadotropin receptor (LHCGR) are crucial events for follicular development. However, their regulatory mechanisms are unclear. DNA methylation and histone acetylation are the main epigenetic modifications, and play important roles in transcriptional expression, which regulate cell responses including cell proliferation, senescence and apoptosis. This review will discuss the dynamic epigenetic modifications of FSHR and LHCGR that occur during the process of follicular development and their response to gonadotropins. In addition, some alteration patterns that occur during these epigenetic modifications, as well as their retrospect retrotransposons, which regulate the gene expression levels of FSHR and LHCGR will be discussed.

Transcriptome profiling reveals superovulation with the gonadotropin-releasing hormone agonist trigger impaired embryo implantation in mice

Introduction

Superovulation is a critical step in assisted reproductive technology, but the use of human chorionic gonadotropin (hCG) as a trigger for superovulation can result in ovarian hyperstimulation. Thus, the use of Gonadotropin-releasing hormone agonist (GnRHa) trigger has been increasingly adopted, although it has been associated with a higher rate of pregnancy failure compared to natural cycles. This study aimed to investigate the effect of GnRHa trigger on embryo implantation in a mouse model.

Methods

Mice in the superovulation (PG) group were administered 7.5 IU of PMSG, followed by the injection of 3.5 μg of GnRHa (Leuprorelin) 48 h later, while mice in the control group (CTR) mated naturally. We compared the number of oocytes, blastocysts, and corpus luteum between the two groups and the implantation sites after the transfer of natural blastocysts. Ovaries, uterus, and serum 2 and 4 days after mating were collected for qRT-PCR, transcriptome sequencing, and hormone assays.

Results

The PG group had more oocytes, blastocysts, and corpus luteum after superovulation than the CTR group. However, the mRNA expression of leukemia inhibitory factor (Lif) and the number of implantation sites were reduced in the PG group. The ELISA assay revealed that superovulation increased ovarian estrogen secretion. The transcriptome analysis showed that superphysiological estrogen led to a response of the uterus to a high estrogen signal, resulting in abnormal endometrium and extracellular matrix remodeling and up-regulation of ion transport and inflammation-related genes.

Conclusion

Our findings suggest that a combination of PMSG and GnRHa trigger impaired embryo implantation in mice, as the excessive uterine response to superphysiological estrogen levels can lead to the change of gene expression related to endometrial remodeling, abnormal expression of uterine ion transport genes and excessive immune-related genes.

High estrogen during ovarian stimulation induced loss of maternal imprinted methylation that is essential for placental development via overexpression of TET2 in mouse oocytes

BACKGROUND

Ovarian stimulation (OS) during assisted reproductive technology (ART) appears to be an independent factor influencing the risk of low birth weight (LBW). Previous studies identified the association between LBW and placenta deterioration, potentially resulting from disturbed genomic DNA methylation in oocytes caused by OS. However, the mechanisms by which OS leads to aberrant DNA methylation patterns in oocytes remains unclear.

METHODS

Mouse oocytes and mouse parthenogenetic embryonic stem cells (pESCs) were used to investigate the roles of OS in oocyte DNA methylation. Global 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) levels were evaluated using immunofluorescence or colorimetry. Genome-wide DNA methylation was quantified using an Agilent SureSelectXT mouse Methyl-Seq. The DNA methylation status of mesoderm-specific transcript homologue (Mest) promoter region was analyzed using bisulfite sequencing polymerase chain reaction (BSP). The regulatory network between estrogen receptor alpha (ERα, ESR1) and DNA methylation status of Mest promoter region was further detected following the knockdown of ERα or ten-eleven translocation 2 (Tet2).

RESULTS

OS resulted in a significant decrease in global 5mC levels and an increase in global 5hmC levels in oocytes. Further investigation revealed that supraphysiological β-estradiol (E2) during OS induced a notable decrease in DNA 5mC and an increase in 5hmC in both oocytes and pESCs of mice, whereas inhibition of estrogen signaling abolished such induction. Moreover, Tet2 may be a direct transcriptional target gene of ERα, and through the ERα-TET2 axis, supraphysiological E2 resulted in the reduced global levels of DNA 5mC. Furthermore, we identified that MEST, a maternal imprinted gene essential for placental development, lost its imprinted methylation in parthenogenetic placentas originating from OS, and ERα and TET2 combined together to form a protein complex that may promote Mest demethylation.

CONCLUSIONS

In this study, a possible mechanism of loss of DNA methylation in oocyte caused by OS was revealed, which may help increase safety and reduce epigenetic abnormalities in ART procedures.

The influence of environmental factors on premature ovarian insufficiency and ovarian aging

Premature ovarian insufficiency and ovarian aging are complex conditions that affect women's reproductive health and overall well-being. They are both characterized by hypergonadotropic hypogonadism and infertility, and together affect about 1 in 100 women by the age of 40. This review explores the influence of environmental factors on the development and progression of premature ovarian insufficiency and ovarian aging. When referring to environmental factors, we include a wide range of external agents and conditions, including chemicals, socioeconomic factors and lifestyle choices. Through a review of the literature, we attempt to highlight the link between environmental factors and ovarian health. We examine the impact of endocrine-disrupting chemicals, such as bisphenol A and phthalates, on ovarian function and investigate the mechanisms by which these chemicals can disrupt hormone signaling pathways, leading to alterations in ovarian reserve, oocyte quality, and folliculogenesis. Moreover, we explore lifestyle factors like obesity, stress, smoking and alcohol in relation to their effects on ovarian aging. Epigenetic changes may play a crucial role in the prevalence of premature ovarian insufficiency. Understanding the impact of environmental factors on premature ovarian insufficiency and ovarian aging is very important in public and clinical health contexts. By identifying risk factors, healthcare providers can develop targeted and strategic prevention and intervention plans. Furthermore, this knowledge can promote reproductive health and minimize exposure to harmful environmental agents.

Higher incidence of embryonic defects in mouse offspring conceived with assisted reproduction from fathers with sperm epimutations

Assisted reproductive technologies (ART) account for 1-6% of births in developed countries. While most children conceived are healthy, increases in birth and genomic imprinting defects have been reported; such abnormal outcomes have been attributed to underlying parental infertility and/or the ART used. Here, we assessed whether paternal genetic and lifestyle factors, that are associated with male infertility and affect the sperm epigenome, can influence ART outcomes. We examined how paternal factors, haploinsufficiency for Dnmt3L, an important co-factor for DNA methylation reactions, and/or diet-induced obesity, in combination with ART (superovulation, in vitro fertilization, embryo culture and embryo transfer), could adversely influence embryo development and DNA methylation patterning in mice. While male mice fed high-fat diets (HFD) gained weight and showed perturbed metabolic health, their sperm DNA methylation was minimally affected by the diet. In contrast, Dnmt3L haploinsufficiency induced a marked loss of DNA methylation in sperm; notably, regions affected were associated with neurodevelopmental pathways and enriched in young retrotransposons, sequences that can have functional consequences in the next generation. Following ART, placental imprinted gene methylation and growth parameters were impacted by one or both paternal factors. For embryos conceived by natural conception, abnormality rates were similar for WT and Dnmt3L+/- fathers. In contrast, paternal Dnmt3L+/- genotype, as compared to WT fathers, resulted in a 3-fold increase in the incidence of morphological abnormalities in embryos generated by ART. Together, the results indicate that embryonic morphological and epigenetic defects associated with ART may be exacerbated in offspring conceived by fathers with sperm epimutations.

The mammalian preimplantation embryo: Its role in the environmental programming of postnatal health and performance

During formation of the preimplantation embryo several cellular and molecular milestones take place, making the few cells forming the early embryo vulnerable to environmental stressors than can impair epigenetic reprogramming and controls of gene expression. Although these molecular alterations can result in embryonic death, a significant developmental plasticity is present in the preimplantation embryo that promotes full-term pregnancy. Prenatal epigenetic modifications are inherited during mitosis and can perpetuate specific phenotypes during early postnatal development and adulthood. As such, the preimplantation phase is a developmental window where developmental programming can take place in response to the embryonic microenvironment present in vivo or in vitro. In this review, the relevance of the preimplantation embryo as a developmental stage where offspring health and performance can be programmed is discussed, with emphasis on malnutrition and assisted reproductive technologies; two major environmental insults with important implications for livestock production and human reproductive medicine.

Factors affecting superovulation induction in goats (Capra hericus): An analysis of various approaches

Goats are generally called a "poor man's cow" because they not only provide meat and milk but also other assistance to their owners, including skins for leather production and their waste, which can be used as compost for fertilizer. Multiple ovulation and embryo transfer (MOET) is an important process in embryo biotechnology, as it increases the contribution of superior female goats to breeding operations. The field of assisted reproductive biotechnologies has seen notable progress. However, unlike in cattle, the standard use of superovulation and other reproductive biotechnologies has not been widely implemented for goats. Multiple intrinsic and extrinsic factors can alter the superovulatory response, significantly restricting the practicability of MOET technology. The use of techniques to induce superovulation is a crucial step in embryo transfer (ET), as it accelerates the propagation of animals with superior genetics for desirable traits. Furthermore, the conventional superovulation techniques based on numerous injections are not appropriate for animals and are labor-intensive as well as expensive. Different approaches and alternatives have been applied to obtain the maximum ovarian response, including immunization against inhibin and the day-0 protocol for the synchronization of the first follicular wave. While there are several studies available in the literature on superovulation in cattle, research on simplified superovulation in goats is limited; only a few studies have been conducted on this topic. This review describes the various treatments with gonadotropin that are used for inducing superovulation in various dairy goat breeds worldwide. The outcomes of these treatments, in terms of ovulation rate and recovery of transferrable embryos, are also discussed. Furthermore, this review also covers the recovery of oocytes through repeated superovulation from the same female goat that is used for somatic cell nuclear transfer (SCNT).

Epigenetic regulation in premature ovarian failure: A literature review

Premature ovarian failure (POF), or premature ovarian insufficiency (POI), is a multifactorial and heterogeneous disease characterized by amenorrhea, decreased estrogen levels and increased female gonadotropin levels. The incidence of POF is increasing annually, and POF has become one of the main causes of infertility in women of childbearing age. The etiology and pathogenesis of POF are complex and have not yet been clearly elucidated. In addition to genetic factors, an increasing number of studies have revealed that epigenetic changes play an important role in the occurrence and development of POF. However, we found that very few papers have summarized epigenetic variations in POF, and a systematic analysis of this topic is therefore necessary. In this article, by reviewing and analyzing the most relevant literature in this research field, we expound on the relationship between DNA methylation, histone modification and non-coding RNA expression and the development of POF. We also analyzed how environmental factors affect POF through epigenetic modulation. Additionally, we discuss potential epigenetic biomarkers and epigenetic treatment targets for POF. We anticipate that our paper may provide new therapeutic clues for improving ovarian function and maintaining fertility in POF patients.

Effect of Superovulation Treatment on Oocyte's DNA Methylation

Controlled ovarian stimulation is a necessary step in some assisted reproductive procedures allowing a higher collection of female gametes. However, consequences of this stimulation for the gamete or the offspring have been shown in several mammals. Most studies used comparisons between oocytes from different donors, which may contribute to different responses. In this work, we use the bovine model in which each animal serves as its own control. DNA methylation profiles were obtained by single-cell whole-genome bisulfite sequencing of oocytes from pre-ovulatory unstimulated follicles compared to oocytes from stimulated follicles. Results show that the global percentage of methylation was similar between groups, but the percentage of methylation was lower for non-stimulated oocytes in the imprinted genes APEG3, MEG3, and MEG9 and higher in TSSC4 when compared to stimulated oocytes. Differences were also found in CGI of imprinted genes: higher methylation was found among non-stimulated oocytes in MEST (PEG1), IGF2R, GNAS (SCG6), KvDMR1 ICR UMD, and IGF2. In another region around IGF2, the methylation percentage was lower for non-stimulated oocytes when compared to stimulated oocytes. Data drawn from this study might help to understand the molecular reasons for the appearance of certain syndromes in assisted reproductive technologies-derived offspring.

OXIDATIVE STRESS AND REPRODUCTIVE FUNCTION: Oxidative stress and in vitro ageing of the post-ovulatory oocyte: an update on recent advances in the field

In brief

Post-ovulatory ageing of oocytes leads to poor oocyte and embryo quality as well as abnormalities in offspring. This review provides an update on the contributions of oxidative stress to this process and discusses the current literature surrounding the use of antioxidant media to delay post-ovulatory oocyte ageing.

Abstract

Following ovulation, the metaphase II stage oocyte has a limited functional lifespan before succumbing to a process known as post-ovulatory oocyte ageing. This progressive demise occurs both in vivo and in vitro and is accompanied by a deterioration in oocyte quality, leading to a well-defined sequelae of reduced fertilisation rates, poor embryo quality, post-implantation errors, and abnormalities in the offspring. Although the physiological consequences of post-ovulatory oocyte ageing have largely been characterised, less is known regarding the molecular mechanisms that drive this process. This review presents an update on the established relationships between the biochemical changes exhibited by the ageing oocyte and the myriad of symptoms associated with the ageing phenotype. In doing so, we consider the molecular events that are potentially involved in orchestrating post-ovulatory ageing with a particular focus on the role of oxidative stress. We highlight the mounting evidence that oxidative stress acts as an initiator for a cascade of events that create the aged oocyte phenotype. Specifically, oxidative stress has the capacity to disrupt mitochondrial function and directly damage multiple intracellular components of the oocyte such as lipids, proteins, and DNA. Finally, this review addresses emerging strategies for delaying post-ovulatory oocyte ageing with emphasis placed on the promise afforded by the use of selected antioxidants to guide the development of media tailored for the preservation of oocyte integrity during in vitro fertilisation procedures.

Circular RNA expression profiles of ovarian granulosa cells in advanced-age women explain new mechanisms of ovarian aging

Aim: We aimed to determine the role of granulosa cells (GCs) circular RNA (circRNA) in ovarian aging. Methods: Nine women were recruited, including three diminished ovarian reserve young women, three advanced-aged women and three normal ovarian reserve young women. The circRNA expression profiles of GCs were characterized by CLEAR software. Key circRNA were validated by quantitative reverse transcription PCR. Results: GCs in advanced-age group females exhibited active MHC class II-related biological processes. A total of 3575 circRNAs were found in the advanced age group. Hsa-circ-0031584 appears to be one of the important molecules regulating the mitotic process of GCs. Conclusion: The expression profiles of circRNAs exhibited obvious stage specificity with age which might contribute to ovarian aging progression.

Effects of putrescine on the quality and epigenetic modification of mouse oocytes during in vitro maturation

CONTEXT

Low ovarian putrescine levels and decreased peak values following luteinising hormone peaks are related to poor oocyte quantity and quality in ageing women.

AIMS

To investigate the effects of putrescine supplementation in in vitro maturation (IVM) medium on oocyte quality and epigenetic modification.

METHODS

Germinal vesicle oocytes retrieved from the ovaries of 8-week-old and 9-month-old mice were divided into four groups (the young, young+difluoromethylornithine (DFMO), ageing and ageing+putrescine groups) and cultured in IVM medium with or without 1mM putrescine or DFMO for 16h. The first polar body extrusion (PBE), cleavage and embryonic development were evaluated. Spindles, chromosomes, mitochondria and reactive oxygen species (ROS) were measured. The expression levels of SIRT1, H3K9ac, H3K9me2, H3K9me3, and 5mC levels were evaluated. Sirt1 and imprinted genes were detected.

RESULTS

The PBE was higher in the ageing+putrescine group than in the ageing group. Putrescine increased the total and inner cell mass cell numbers of blastocysts in ageing oocytes. Putrescine decreased aberrant spindles and chromosome aneuploidy, increased the mitochondrial membrane potential and decreased ROS levels. Putrescine increased SIRT1 expression and attenuated the upregulation of H3K9ac levels in ageing oocytes. Putrescine did not affect 5mC, H3K9me2 or H3K9me3 levels or imprinted gene expression.

CONCLUSIONS

Putrescine supplementation during IVM improved the maturation and quality of ageing oocytes and promoted embryonic development by decreasing ROS generation, maintaining mitochondrial and spindle function and correcting aberrant epigenetic modification.

IMPLICATIONS

Putrescine shows application potential for human-assisted reproduction, especially for IVM of oocytes from ageing women.

Conception by fertility treatment and cardiometabolic risk in middle childhood

OBJECTIVE

To evaluate whether children conceived using assisted reproductive technology (ART) or ovulation induction (OI) have greater cardiometabolic risk than children conceived without treatment.

DESIGN

Clinical assessments in 2018-2019 in the Upstate KIDS cohort.

SETTING

Clinical sites in New York.

PATIENT(S)

Three hundred thirty-three singletons and 226 twins from 448 families.

INTERVENTION(S)

Mothers reported their use of fertility treatment and its specific type at baseline and approximately 4 months after delivery. High validity of the self-reported use of ART was previously confirmed. The children were followed up from infancy through 8-10 years of age. A subgroup was invited to participate in clinic visits.

MAIN OUTCOME MEASURE(S)

The measurements of blood pressure (BP), arterial stiffness using pulse wave velocity, anthropometric measures, and body fat using bioelectrical impedance analysis were performed (n = 559). The levels of plasma lipids, C-reactive protein, and hemoglobin A1c were measured using blood samples obtained from 263 children.

RESULT(S)

The average age of the children was 9.4 years at the time of the clinic visits Approximately 39% were conceived using fertility treatment (18% using ART and 21% using OI). Singletons conceived using fertility treatment (any type or using ART or OI specifically) did not statistically differ in systolic or diastolic BP, heart rate, or pulse wave velocity. Singletons conceived using OI were smaller than singletons conceived without treatment, but the average body mass index of the latter was higher (z-score: 0.41 [SD, 1.24]) than the national norms. Twins conceived using either treatment had lower BP than twins conceived without treatment. However, twins conceived using OI had significantly higher arterial stiffness (0.59; 95% CI, 0.03-1.15 m/s), which was attenuated after accounting for maternal BP (0.29; 95% CI, -0.03 to 0.46 m/s). Twins did not significantly differ in size or fat measures across the groups. The mode of conception was not associated with the levels of lipids, C-reactive protein, or glycosylated hemoglobin.

CONCLUSION(S)

Clinical measures at the age of 9 years did not indicate greater cardiometabolic risk in children conceived using ART or OI compared with that in children conceived without treatment.

CLINICAL TRIAL REGISTRATION NUMBER

ClinicalTrials.gov #NCT03106493.

An Interplay between Epigenetics and Translation in Oocyte Maturation and Embryo Development: Assisted Reproduction Perspective

Germ cell quality is a key prerequisite for successful fertilization and early embryo development. The quality is determined by the fine regulation of transcriptomic and proteomic profiles, which are prone to alteration by assisted reproduction technology (ART)-introduced in vitro methods. Gaining evidence shows the ART can influence preset epigenetic modifications within cultured oocytes or early embryos and affect their developmental competency. The aim of this review is to describe ART-determined epigenetic changes related to the oogenesis, early embryogenesis, and further in utero development. We confront the latest epigenetic, related epitranscriptomic, and translational regulation findings with the processes of meiotic maturation, fertilization, and early embryogenesis that impact the developmental competency and embryo quality. Post-ART embryo transfer, in utero implantation, and development (placentation, fetal development) are influenced by environmental and lifestyle factors. The review is emphasizing their epigenetic and ART contribution to fetal development. An epigenetic parallel among mouse, porcine, and bovine animal models and human ART is drawn to illustrate possible future mechanisms of infertility management as well as increase the awareness of the underlying mechanisms governing oocyte and embryo developmental complexity under ART conditions.

Comprehensive analysis of miRNA-mRNA interactions in ovaries of aged mice

Advanced maternal age and ovarian aging are deleterious to the quantity and quality of oocytes and epigenetic modifications, which can affect the health of offspring. However, relatively little is known about the regulation of microRNA-mediated transcription during ovarian aging. We therefore aimed to identify age-related mRNA and microRNA changes and their interactions in the ovaries of aged mice. We performed QuantSeq 3'mRNA and small RNA sequencing to compare their expression patterns in post-ovulation ovaries from young (12-week-old) and old (44-week-old) mice. Functional annotation and integrative analyses were performed to identify the potential functions of differentially expressed genes and identify binding sites for critical microRNAs. We found 343 differentially expressed genes and 9 microRNAs in our comparison of the two mouse groups, with fold changes >2.0 (P < 0.01). Furthermore, we identified possible direct interactions between 24 differentially expressed mRNAs and 8 microRNAs. The differentially expressed genes are involved in fat digestion and absorption, the PI3K-Akt signaling pathway, serotonergic synapse, and ovarian steroidogenesis, which are important for folliculogenesis and oocyte growth. During ovarian aging, changes in gene expression induce alterations in folliculogenesis, oocyte growth, and steroidogenesis, resulting in decreased oocyte quality and reproductive outcomes.

Transcriptome-wide N6-methyladenine methylation in granulosa cells of women with decreased ovarian reserve

Background

The emerging epitranscriptome plays an essential role in female fertility. As the most prevalent internal mRNA modification, N6-methyladenine (m6A) methylation regulate mRNA fate and translational efficiency. However, whether m6A methylation was involved in the aging-related ovarian reserve decline has not been investigated. Herein, we performed m6A transcriptome-wide profiling in the ovarian granulosa cells of younger women (younger group) and older women (older group).

Results

m6A methylation distribution was highly conserved and enriched in the CDS and 3’UTR region. Besides, an increased number of m6A methylated genes were identified in the older group. Bioinformatics analysis indicated that m6A methylated genes were enriched in the FoxO signaling pathway, adherens junction, and regulation of actin cytoskeleton. A total of 435 genes were differently expressed in the older group, moreover, 58 of them were modified by m6A. Several specific genes, including BUB1B, PHC2, TOP2A, DDR2, KLF13, and RYR2 which were differently expressed and modified by m6A, were validated using qRT-PCR and might be involved in the decreased ovarian functions in the aging ovary.

Conclusions

Hence, our finding revealed the transcriptional significance of m6A modifications and provide potential therapeutic targets to promote fertility reservation for aging women.

Oocyte aging: looking beyond chromosome segregation errors

The age-associated decline in female fertility is largely ascribable to a decrease in oocyte quality. This phenomenon is multifaceted and influenced by numerous interconnected maternal and environmental factors. An increase in the rate of meiotic errors is the major cause of the decline in oocyte developmental competence. However, abnormalities in the ooplasm accumulating with age - including altered metabolism, organelle dysfunction, and aberrant gene regulation - progressively undermine oocyte quality. Stockpiling of maternal macromolecules during folliculogenesis is crucial, as oocyte competence to achieve maturation, fertilization, and the earliest phases of embryo development occur in absence of transcription. At the same time, crucial remodeling of oocyte epigenetics during oogenesis is potentially exposed to interfering factors, such as assisted reproduction technologies (ARTs) or environmental changes, whose impact may be enhanced by reproductive aging. As the effects of maternal aging on molecular mechanisms governing the function of the human oocyte remain poorly understood, studies in animal models are essential to deepen current understanding, with translational implications for human ARTs. The present mini review aims at offering an updated and consistent view of cytoplasmic alterations occurring in oocytes during aging, focusing particularly on gene and epigenetic regulation. Appreciation of these mechanisms could inspire solutions to mitigate/control the phenomenon, and thus benefit modern ARTs.

Ribosomal DNA methylation in human and mouse oocytes increases with age

An age-dependent increase in ribosomal DNA (rDNA) methylation has been observed across a broad spectrum of somatic tissues and the male mammalian germline. Bisulfite pyrosequencing (BPS) was used to determine the methylation levels of the rDNA core promoter and the rDNA upstream control element (UCE) along with two oppositely genomically imprinted control genes (PEG3 and GTL2) in individual human germinal vesicle (GV) oocytes from 90 consenting women undergoing fertility treatment because of male infertility. Apart from a few (4%) oocytes with single imprinting defects (in either PEG3 or GTL2), the analyzed GV oocytes displayed correct imprinting patterns. In 95 GV oocytes from 42 younger women (26-32 years), the mean methylation levels of the rDNA core promoter and UCE were 7.4±4.0% and 9.3±6.1%, respectively. In 79 GV oocytes from 48 older women (33-39 years), methylation levels increased to 9.3±5.3% (P = 0.014) and 11.6±7.4% (P = 0.039), respectively. An age-related increase in oocyte rDNA methylation was also observed in 123 mouse GV oocytes from 29 4-16-months-old animals. Similar to the continuously mitotically dividing male germline, ovarian aging is associated with a gain of rDNA methylation in meiotically arrested oocytes. Oocytes from the same woman can exhibit varying rDNA methylation levels and, by extrapolation, different epigenetic ages.

Plane of nutrition and FSH-induced superovulation affect the expression of steroid hormone receptors and growth factors in caruncular tissue of non-pregnant sheep

Implantation is a critical step in the establishment of pregnancy and an important part of embryo-maternal contact. Uterine receptivity can be affected by changes in body condition and the maternal endocrine milieu, including those caused by the use of exogenous gonadotropins in controlled ovarian hyperstimulation to induce the development of multiple follicles. This study demonstrates the effects of FSH-mediated ovarian hyperstimulation on the caruncles of ewes under various feeding regimes. Sheep were classified into 3 categories: control fed (CF), overfed (OF), or underfed (UF). In each group, animals were superovulated with FSH or injected with a saline solution (non-treated control). Uterine caruncles were collected at the early (d 5) and mid-luteal phase (d 10) of the estrous cycle. The transcript levels of steroid hormone receptors (ESR1, ESR2, PGR) and growth factors (IGF1, IGF2, VEGFA) were investigated and their expression localized by immunohistochemical staining. As for the main findings, day of the estrous cycle affected expression of ESR1, IGF1 and IGF2, but not of ESR2, PGR and VEGFA; both feeding and superovulation had modulatory effects, with feeding (UF/OF) stimulating expression of all genes studied, and superovulation altering expression of some genes, eg IGF1, PGR and ESR1 and ESR2, in CF animals. Similarly, feeding (UF/OF) altered responsiveness to superovulation for PGR on d 5 and ESR1/ESR2 on d 5 and/or 10. Our data emphasize possible effects of dietary and/or hormonal stimuli on uterine physiology, which may affect pregnancy outcomes by disrupting uterine functionality.

Association Between Type of Infertility and Live Birth in Couples With a Single Intrauterine Insemination Resulting in Pregnancy: A Propensity Score Matching Cohort Study

BACKGROUND

Few studies have described the relationship between the type of infertility and live birth in patients treated with intrauterine insemination (IUI). We focused on this issue and attempted to explore it.

METHODS

This retrospective study enrolled 2,256 infertile patients who underwent their first IUI cycle and were subsequently diagnosed with a clinical pregnancy at Ji'an Women and Child Health Care Hospital between 2007 and 2018. Inductees were divided into primary infertility (1,680 patients) and secondary infertility groups (876 patients). Following 1:1 propensity score matching to obtain balanced data, the COX proportional hazards model, landmark analysis, and subgroup analysis were used to assess the association between infertility types and live birth rates. Subsequently, a sensitivity analysis was employed to evaluate the potential effect of unmeasured confounding on outcomes.

RESULTS

Of the 1,486 patients who were identified as a matched cohort, 743 were in the primary infertility group and the remaining patients were in another group. A total of 1,143 patients had live births during 431,009 person-days of follow-up (average 290.0 days). Throughout the follow-up period, patients with secondary infertility demonstrated more live births than patients with primary infertility (hazard ratio [HR], 1.16; 95% confidence interval [CI], 1.04 to 1.30; P = .007). More details were observed in the landmark analysis. Live birth rates were similar in both groups within 316 days of follow-up (HR, 0.84; 95% CI, 0.62 to 1.14; P = .269), whereas the opposite was found between 316 days of follow-up and delivery day (HR, 1.19; 95% CI, 1.06 to 1.34; P = .004). This was also obtained in a subgroup analysis of patients younger than 35 years old and patients treated with natural cycles (NCs) and IUIs.

CONCLUSION

Among the infertile patients who underwent a single natural or stimulated cycle followed by IUI and had later pregnancies, full-term young secondary infertility mothers (<35 years of age) had a greater chance of having viable babies than the primary infertility ones. The latter may get more benefits when undergoing ovarian stimulation and IUI rather than NC-IUI.

The proteome, not the transcriptome, predicts that oocyte superovulation affects embryonic phenotypes in mice

Superovulation is the epitome for generating oocytes for molecular embryology in mice, and it is used to model medically assisted reproduction in humans. However, whether a superovulated oocyte is normal, is an open question. This study establishes for the first time that superovulation is associated with proteome changes that affect phenotypic traits in mice, whereas the transcriptome is far less predictive. The proteins that were differentially expressed in superovulated mouse oocytes and embryos compared to their naturally ovulated counterparts were enriched in ontology terms describing abnormal mammalian phenotypes: a thinner zona pellucida, a smaller oocyte diameter, increased frequency of cleavage arrest, and defective blastocyst formation, which could all be verified functionally. Moreover, our findings indicate that embryos with such abnormalities are negatively selected during preimplantation, and ascribe these abnormalities to incomplete ovarian maturation during the time of the conventional superovulation, since they could be corrected upon postponement of the ovulatory stimulus by 24 h. Our data place constraints on the common view that superovulated oocytes are suitable for drawing general conclusions about developmental processes, and underscore the importance of including the proteins in a modern molecular definition of oocyte quality.

Genome-Wide Analysis of DNA Methylation in Buccal Cells of Children Conceived through IVF and ICSI

Early life periconceptional exposures during assisted reproductive technology (ART) procedures could alter the DNA methylation profiles of ART children, notably in imprinted genes and repetitive elements. At the genome scale, DNA methylation differences have been reported in ART conceptions at birth, but it is still unclear if those differences remain at childhood. Here, we performed an epigenome-wide DNA methylation association study using Illumina InfiniumEPIC BeadChip to assess the effects of the mode of conception on the methylome of buccal cells from 7- to 8-year-old children (48 children conceived after ART or naturally (control, CTL)) and according to the embryo culture medium in which they were conceived. We identified 127 differentially methylated positions (DMPs) and 16 differentially methylated regions (DMRs) (FDR < 0.05) with low delta beta differences between the two groups (ART vs. CTL). DMPs were preferentially located inside promoter proximal regions and CpG islands and were mostly hypermethylated with ART. We highlighted that the use of distinct embryo culture medium was not associated with DNA methylation differences in childhood. Overall, we bring additional evidence that children conceived via ART display limited genome-wide DNA methylation variation compared with those conceived naturally.

A comparison study of superovulation strategies for C57BL/6J and B6D2F1 mice in CRISPR-Cas9 mediated genome editing

Reproductive techniques such as superovulation and in vitro fertilisation (IVF) have been widely used in generating genetically modified animals. The current gold standard for superovulation in mice is using coherent treatments of equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG). An alternative method using inhibin antiserum (IAS) instead of eCG has been recently reported. Here, we evaluate different superovulation strategies in C57BL/6J and B6D2F1 mice. Firstly, we found that using 5-week-old C57BL/6J and 4-week-old B6D2F1 donors could achieve better superovulation outcomes. Then, we compared eCG-hCG, IAS-hCG and eCG-IAS-hCG with different dosages in both mouse strains. Significantly increased numbers of oocytes were obtained by using IAS-hCG and eCG-IAS-hCG methods. However, low fertilisation rates (36.3-38.8%) were observed when natural mating was applied. We then confirmed that IVF could dramatically ameliorate the fertilisation rates up to 89.1%. Finally, we performed CRISPR-Cas9 mediated genome editing targeting Scn11a and Kcnh1 loci, and successfully obtained mutant pups using eCG-hCG and IAS-hCG induced zygotes, which were fertilised by either natural mating or IVF. Our results showed that IAS is a promising superovulation reagent, and the efficiency of genome editing is unlikely to be affected by using IAS-induced zygotes.

Obstetric and neonatal outcomes of pregnancies resulting from preimplantation genetic testing: a systematic review and meta-analysis

BACKGROUND

Preimplantation genetic testing (PGT) includes methods that allow embryos to be tested for severe inherited diseases or chromosomal abnormalities. In addition to IVF/ICSI and repeated freezing and thawing of the embryos, PGT requires a biopsy to obtain embryonic genetic material for analysis. However, the potential effects of PGT on obstetric and neonatal outcomes are currently uncertain.

OBJECTIVE AND RATIONALE

This study aimed to investigate whether pregnancies conceived after PGT were associated with a higher risk of adverse obstetric and neonatal outcomes compared with spontaneously conceived (SC) pregnancies or pregnancies conceived after IVF/ICSI.

SEARCH METHODS

PubMed, EMBASE, MEDLINE, Web of Science and The Cochrane Library entries from January 1990 to January 2021 were searched. The primary outcomes in this study were low birth weight (LBW) and congenital malformations (CMs), and the secondary outcomes included gestational age, preterm delivery (PTD), very preterm delivery (VPTD), birth weight (BW), very low birth weight (VLBW), neonatal intensive care unit (NICU) admission, hypertensive disorders of pregnancy (HDP), gestational diabetes, placenta previa and preterm premature rupture of membranes (PROM). We further pooled the results of PGT singleton pregnancies. Subgroup analyses included preimplantation genetic diagnosis (PGD), preimplantation genetic screening (PGS), cleavage-stage biopsy combined with fresh embryo transfer (CB-ET) and blastocyst biopsy combined with frozen-thawed embryo transfer (BB-FET).

OUTCOMES

This meta-analysis included 15 studies involving 3682 babies born from PGT pregnancies, 127 719 babies born from IVF/ICSI pregnancies and 915 222 babies born from SC pregnancies. The relative risk (RR) of LBW was higher in PGT pregnancies compared with SC pregnancies (RR = 3.95, 95% confidence interval [CI]: 2.32-6.72), but the risk of CMs was not different between the two groups. The pooled results for the risks of LBW and CMs were similar in PGT and IVF/ICSI pregnancies. The risks of PTD (RR = 3.12, 95% CI: 2.67-3.64) and HDP (RR = 3.12, 95% CI: 2.18-4.47) were significantly higher in PGT pregnancies compared with SC pregnancies. Lower gestational age (mean difference [MD] = -0.76 weeks, 95% CI -1.17 to -0.34) and BW (MD = -163.80 g, 95% CI: -299.35 to -28.24) were also noted for PGT pregnancies compared with SC pregnancies. Nevertheless, compared with IVF/ICSI pregnancies, the risks of VPTD and VLBW in PGT pregnancies were significantly decreased by 41% and 30%, respectively, although the risk of HDP was still significantly increased by 50% in PGT pregnancies compared with IVF/ICSI pregnancies. The combined results of obstetric and neonatal outcomes of PGT and IVF/ICSI singleton pregnancies were consistent with the overall results. Further subgroup analyses indicated that both PGD and PGS pregnancies were associated with a higher risk of PTD and a lower gestational age compared with SC pregnancies.

WIDER IMPLICATIONS

This meta-analysis showed that PGT pregnancies may be associated with increased risks of LBW, PTD and HDP compared with SC pregnancies. The overall obstetric and neonatal outcomes of PGT pregnancies are favourable compared with those of IVF/ICSI pregnancies, although PGT pregnancies were associated with a higher risk of HDP. However, because the number of studies that could be included was limited, more randomised controlled trials and prospective cohort studies are needed to confirm these conclusions.

Understanding Reproductive Aging in Wildlife to Improve Animal Conservation and Human Reproductive Health

Similar to humans and laboratory animals, reproductive aging is observed in wild species-from small invertebrates to large mammals. Aging issues are also prevalent in rare and endangered species under human care as their life expectancy is longer than in the wild. The objectives of this review are to (1) present conserved as well as distinctive traits of reproductive aging in different wild animal species (2) highlight the value of comparative studies to address aging issues in conservation breeding as well as in human reproductive medicine, and (3) suggest next steps forward in that research area. From social insects to mega-vertebrates, reproductive aging studies as well as observations in the wild or in breeding centers often remain at the physiological or organismal scale (senescence) rather than at the germ cell level. Overall, multiple traits are conserved across very different species (depletion of the ovarian reserve or no decline in testicular functions), but unique features also exist (endless reproductive life or unaltered quality of germ cells). There is a broad consensus about the need to fill research gaps because many cellular and molecular processes during reproductive aging remain undescribed. More research in male aging is particularly needed across all species. Furthermore, studies on reproductive aging of target species in their natural habitat (sentinel species) are crucial to define more accurate reproductive indicators relevant to other species, including humans, sharing the same environment. Wild species can significantly contribute to our general knowledge of a crucial phenomenon and provide new approaches to extend the reproductive lifespan.

Epigenetic clock and methylation study of oocytes from a bovine model of reproductive aging

Cattle are an attractive animal model of fertility in women due to their high degree of similarity relative to follicle selection, embryo cleavage, blastocyst formation, and gestation length. To facilitate future studies of the epigenetic underpinnings of aging effects in the female reproductive axis, several DNA methylation-based biomarkers of aging (epigenetic clocks) for bovine oocytes are presented. One such clock was germane to only oocytes, while a dual-tissue clock was highly predictive of age in both oocytes and blood. Dual species clocks that apply to both humans and cattle were also developed and evaluated. These epigenetic clocks can be used to accurately estimate the biological age of oocytes. Both epigenetic clock studies and epigenome-wide association studies revealed that blood and oocytes differ substantially with respect to aging and the underlying epigenetic signatures that potentially influence the aging process. The rate of epigenetic aging was found to be slower in oocytes compared to blood; however, oocytes appeared to begin at an older epigenetic age. The epigenetic clocks for oocytes are expected to address questions in the field of reproductive aging, including the central question: how to slow aging of oocytes.

Association between peak serum estradiol level during controlled ovarian stimulation and neonatal birthweight in freeze-all cycles: a retrospective study of 8501 singleton live births

STUDY QUESTION

Is there an association between peak serum estradiol (E2) level during controlled ovarian stimulation (COS) and neonatal birthweight in freeze-all cycles?

SUMMARY ANSWER

Peak serum E2 level during ovarian stimulation is not associated with neonatal birthweight in freeze-all cycles.

WHAT IS KNOWN ALREADY

Supraphysiologic E2 levels during COS have been demonstrated to generate a suboptimal peri-implantation endometrial environment and thus lead to adverse neonatal outcomes in fresh embryo transfer cycles. Previous experimental studies also suggested a potential influence of superovulation on oocyte epigenetic programming, but whether it translates into altered phenotypes of fetal growth and development remains unclear in clinical practice. By segmenting the process of COS and embryo transfer, the freeze-all policy provides a novel model to investigate the sole impact of ovarian stimulation on oocytes after ruling out the effects of hyperestrogenic milieu on endometrium in fresh cycles.

STUDY DESIGN, SIZE, DURATION

A retrospective cohort study of 8501 patients who underwent their first COS cycles with a freeze-all strategy and delivered live-born singletons in subsequent frozen-thawed embryo transfer cycles from January 2007 to December 2016 at a tertiary-care academic medical center.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Patients were categorized into six groups according to E2 level on trigger day in regular increments of 1000 pg/mL: <1000, 1000-1999, 2000-2999, 3000-3999, 4000-4999 and ≥5000 pg/mL. Univariable and multivariable linear regression and logistic regression analysis were performed to assess the independent association between peak E2 level and measures of neonatal birthweight including absolute birthweight, Z-score, low birthweight (LBW) and small-for-gestational age (SGA).

MAIN RESULTS AND THE ROLE OF CHANCE

The six groups did not differ significantly in birthweight, Z-score or the incidence of LBW and SGA. Compared with the E2 <1000 pg/mL group, the adjusted mean difference (95% confidence interval [CI]) of stratified higher E2 groups was 17.2 (-31.0-65.5), 12.3 (-35.9-60.5), -4.1 (-51.9-43.7), -0.6 (-48.9-47.8) and -3.6 (-50.0-42.8) g for birthweight, and 0 (-0.11-0.10), 0.02 (-0.08-0.12), 0.04 (-0.06-0.14), -0.01 (-0.11-0.10) and -0.04 (-0.14-0.06) for Z-score, respectively. Regarding the outcomes of LBW and SGA, no increased risks were observed in each E2 category, with the adjusted odds ratio (95% CI) being 1.21 (0.68-2.16), 1.0 (0.58-1.90), 0.90 (0.50-1.63), 0.93 (0.51-1.69) and 1.08 (0.61-1.90) for LBW, and 0.97 (0.58-1.64), 1.06 (0.63-1.77), 0.77 (0.46-1.31), 0.71 (0.41-1.22) and 1.00 (0.60-1.65) for SGA, respectively.

LIMITATIONS, REASONS FOR CAUTION

The study was retrospective in design, and other unknown confounding factors may not be included for adjustment. Furthermore, the generalization of the study finding could be limited to some extent by the majority of double cleavage-stage embryo transfer and difference in birthweight reference percentiles between Chinese and other populations.

WIDER IMPLICATIONS OF THE FINDINGS

Our observations suggest that the hyperestrogenic milieu during COS does not seem to pose adverse effects on neonatal birthweight after frozen-thawed embryo transfer, which provides reassuring information for high ovarian responders in freeze-all cycles concerning their offspring's health.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by the National Key Research and Development Program of China (SQ2018YFC100163) and National Natural Science Foundation of China (81571397, 81771533). The authors declare no conflict of interest.

Oocyte Spontaneous Activation: An Overlooked Cellular Event That Impairs Female Fertility in Mammals

In mammals, including humans, mature oocytes are ovulated into the oviduct for fertilization. Normally, these oocytes are arrested at metaphase of the second meiosis (MII), and this arrest can be maintained for a certain period, which is essential for fertilization in vivo and oocyte manipulations in vitro, such as assisted reproduction in clinics and nuclear/spindle transfer in laboratories. However, in some species and under certain circumstances, exit from MII occurs spontaneously without any obvious stimulation or morphological signs, which is so-called oocyte spontaneous activation (OSA). This mini-review summarizes two types of OSA. In the first type (e.g., most rat strains), oocytes can maintain MII arrest in vivo, but once removed out, oocytes undergo OSA with sister chromatids separated and eventually scattered in the cytoplasm. Because the stimulation is minimal (oocyte collection itself), this OSA is incomplete and cannot force oocytes into interphase. Notably, once re-activated by sperm or chemicals, those scattered chromatids will form multiple pronuclei (MPN), which may recapitulate certain MPN and aneuploidy cases observed in fertility clinics. The second type of OSA occurs in ovarian oocytes (e.g., certain mouse strains and dromedary camel). Without ovulation or fertilization, these OSA-oocytes can initiate intrafollicular development, but these parthenotes cannot develop to term due to aberrant genomic imprinting. Instead, they either degrade or give rise to ovarian teratomas, which have also been reported in female patients. Last but not the least, genetic models displaying OSA phenotypes and the lessons we can learn from animal OSA for human reproduction are also discussed.

Different response of embryos originating from control and obese mice to insulin in vitro

The aim of the present work was to investigate the impact of maternal obesity on DNA methylation in ovulated oocytes, and to compare the response of in vitro-developing preimplantation embryos originating from control and obese mice to insulin. An intergenerational, diet-induced obesity model was used to produce outbred mice with an increased body weight and body fat. Two-cell and eight-cell embryos recovered from obese and control mice were cultured in a medium supplemented with 1 or 10 ng/ml insulin until blastocyst formation. In the derived blastocysts, cell proliferation, differentiation, and death rates were determined. The results of immunochemical visualization of 5-methylcytosine indicated a slightly higher DNA methylation in ovulated metaphase II oocytes recovered from obese females; however, the difference between groups did not reach statistical significance. Expanded blastocysts developed from embryos provided by control dams showed increased mean cell numbers (two and eight-cell embryos exposed to 10 ng/ml), an increased inner-cell-mass/trophectoderm ratio (two-cell embryos exposed to 1 ng/ml and eight-cell embryos exposed to 10 ng/ml), and a reduced level of apoptosis (two and eight-cell embryos exposed to 10 ng/ml). In contrast, embryos originating from obese mice were significantly less sensitive to insulin; indeed, no difference was recorded in any tested variable between the embryos exposed to insulin and those cultured in insulin-free medium. Real-time RT-PCR analysis showed a significant increase in the amount of insulin receptor transcripts in blastocysts recovered from obese dams. These results suggest that maternal obesity might modulate the mitogenic and antiapoptotic responses of preimplantation embryos to insulin.

Methylation: An Ineluctable Biochemical and Physiological Process Essential to the Transmission of Life

Methylation is a universal biochemical process which covalently adds methyl groups to a variety of molecular targets. It plays a critical role in two major global regulatory mechanisms, epigenetic modifications and imprinting, via methyl tagging on histones and DNA. During reproduction, the two genomes that unite to create a new individual are complementary but not equivalent. Methylation determines the complementary regulatory characteristics of male and female genomes. DNA methylation is executed by methyltransferases that transfer a methyl group from S-adenosylmethionine, the universal methyl donor, to cytosine residues of CG (also designated CpG). Histones are methylated mainly on lysine and arginine residues. The methylation processes regulate the main steps in reproductive physiology: gametogenesis, and early and late embryo development. A focus will be made on the impact of assisted reproductive technology and on the impact of endocrine disruptors (EDCs) via generation of oxidative stress.

Does the elevated estradiol level on the day of human chorionic gonadotropin administration affect embryo quality among women undergoing in vitro fertilization?

OBJECTIVE

To evaluate the association between estradiol (E₂ ) levels on the day of human chorionic gonadotropin (hCG) administration and embryo quality during in vitro fertilization (IVF) cycles.

METHODS

A retrospective study of 6676 IVF cycles among women treated at the Reproductive Center of The First Affiliated Hospital of USTC, Hefei, China, from June 2014 to May 2017. E₂ levels on hCG day were divided into four groups by 25th percentile: 0-1763 pg/mL (group I), 1763-3692 pg/mL (group II), 3692-4800 pg/mL (group III), and higher than 4800 pg/mL (group IV). Analysis of variance and multiple linear regression were used to test associations.

RESULTS

There were significant differences in the frequency of high-quality embryos between group I (51.6 ± 1.1%) and groups II (65.6 ± 0.8%), III (62.1 ± 0.7%), and IV (62.3 ± 0.7%). Using E₂ as a dummy variable and group II as a control, multiple linear regression showed that E₂ levels were associated with the frequency of high-quality embryos obtained (P < 0.05).

CONCLUSION

Serum E₂ on hCG day had an impact on embryo quality. Higher E₂ levels did not produce the most high-quality embryos; the highest frequencies were achieved for E₂ levels within 1763-3692 pg/mL.

Increased transcriptome variation and localised DNA methylation changes in oocytes from aged mice revealed by parallel single-cell analysis

Advancing maternal age causes a progressive reduction in fertility. The decline in developmental competence of the oocyte with age is likely to be a consequence of multiple contributory factors. Loss of epigenetic quality of the oocyte could impair early developmental events or programme adverse outcomes in offspring that manifest only later in life. Here, we undertake joint profiling of the transcriptome and DNA methylome of individual oocytes from reproductively young and old mice undergoing natural ovulation. We find reduced complexity as well as increased variance in the transcriptome of oocytes from aged females. This transcriptome heterogeneity is reflected in the identification of discrete sub‐populations. Oocytes with a transcriptome characteristic of immature chromatin configuration (NSN) clustered into two groups: one with reduced developmental competence, as indicated by lower expression of maternal effect genes, and one with a young‐like transcriptome. Oocytes from older females had on average reduced CpG methylation, but the characteristic bimodal methylation landscape of the oocyte was preserved. Germline differentially methylated regions of imprinted genes were appropriately methylated irrespective of age. For the majority of differentially expressed transcripts, the absence of correlated methylation changes suggests a post‐transcriptional basis for most age‐related effects on the transcriptome. However, we did find differences in gene body methylation at which there were corresponding changes in gene expression, indicating age‐related effects on transcription that translate into methylation differences. Interestingly, oocytes varied in expression and methylation of these genes, which could contribute to variable competence of oocytes or penetrance of maternal age‐related phenotypes in offspring.

Single-cell DNA methylation sequencing reveals epigenetic alterations in mouse oocytes superovulated with different dosages of gonadotropins

BACKGROUND

Epigenetic abnormalities caused by superovulation have recently attracted increasing attention. Superovulation with exogenous hormones may prevent oocytes from establishing an appropriate epigenetic state, and this effect may extend to the methylation programming in preimplantation embryos, as de novo DNA methylation is a function of developmental stage of follicles and oocyte size. Follicle-stimulating hormone (FSH) and human menopausal gonadotropin (hMG) are common gonadotropins used for superovulation, and appropriate concentrations of these gonadotropins might be necessary. However, no systematic study on the effects of DNA methylation alterations in oocytes associated with superovulation with different dosages of FSH/hMG at the single-cell level has yet been reported. In the current study, different dosages of FSH/hMG combined with human chorionic gonadotropin (hCG) were used in female mice to generate experimental groups, while naturally matured oocytes and oocytes superovulated with only hCG were respectively used as controls. Single-cell level DNA methylation sequencing was carried out on all these matured oocytes.

RESULTS

In this study, we revealed that the genome-wide methylation pattern and CG methylation level of the maternal imprinting control regions of all mature oocytes were globally conserved and stable. However, methylation alterations associated with superovulation were found at a specific set of loci, and the differentially methylated regions (DMRs) mainly occurred in regions other than promoters. Furthermore, some of the annotated genes in the DMRs were involved in biological processes such as glucose metabolism, nervous system development, cell cycle, cell proliferation, and embryo implantation and were altered in all dosages of FSH/hMG group (for example, Gfod2 and SYF2). Other genes were impaired only after high gonadotropin dosages (for instance, Sox17 and Phactr4).

CONCLUSIONS

In conclusion, the current study addressed the effects of superovulation on DNA methylation from the perspective of different dosages of gonadotropins at the single-cell level. We found that the genome-wide DNA methylation landscape was globally preserved irrespective of superovulation or of the kind and dosage of gonadotropins used, whereas the methylation alterations associated with superovulation occurred at a specific set of loci. These observed effects reflect that superovulation recruits oocytes that would not normally be ovulated or that have not undergone complete epigenetic maturation. Our results provide an important reference for the safety assessment of superovulation with different dosages of gonadotropins. However, it should be noted that this study has some limitations, as the sample number and library coverage of analyzed oocytes were relatively low. Future studies with larger sample sizes and high-coverage libraries that examine the effects of superovulation on embryo development and offspring health as well as the underlying mechanisms are still needed.

Developmental Plasticity in Response to Embryo Cryopreservation: The Importance of the Vitrification Device in Rabbits

Simple Summary

This study was conducted to demonstrate how embryo manipulation techniques incur phenotypic changes throughout life. This study reports the first evidence demonstrating that the vitrification device used is not a trivial decision, providing valuable information about how the cooling–warming rates during vitrification can be partly responsible of the postnatal phenotypic variations.

Abstract

In this study, we evaluated the effect of embryo vitrification using two different devices on adulthood phenotype in rabbits. In vitro development, prenatal embryo survival, body weight, growth performance, haematological and biochemical peripheral blood analysis, reproductive performance, and lactation performance traits were compared between the experimental groups. They derived from naturally-conceived embryos (NC), fresh-transferred embryos (FT), vitrified-transferred embryos using mini-straw (VTs), or vitrified-transferred embryos using Cryotop (VTc). Straw-vitrified embryos exhibited lower in vitro developmental rates and in vivo survival rates following embryo transfer compared to its Cryotop-vitrified counterparts. Moreover, the VTs group exhibited higher foetal losses than VTc, FT, and NC groups. Independently of the vitrification device, vitrified-transferred (VT) offspring showed a skewed sex ratio in favour of males, and an increased birth bodyweight. In contrast, postnatal daily growth was diminished in all ART (i.e., FT and VT) animals. In adulthood, significant differences in body weight between all groups was founded—all ART progenies weighed less than NC animals and, within ART, VT animals weighed less than FT. For VT groups, weight at adulthood was higher for the VTs group compared with the VTc group. Peripheral blood parameters ranged between common values. Moreover, no differences were found in the fertility rates between experimental groups. Furthermore, similar pregnancy rates, litter sizes, and the number of liveborns were observed, regardless of the experimental group. However, decreased milk yield occurred for VTc and FT animals compared to VTs and NC animals. A similar trend was observed for the milk composition of dry matter and fat. Concordantly, reduced body weight was found for suckling kits in the VTc and FT groups compared to VTs and NC animals. Our findings reveal that developmental changes after the embryo vitrification procedure could be associated with an exhibition of the embryonic developmental plasticity. Moreover, to our best knowledge, this study reports the first evidence demonstrating that the vitrification device used is not a trivial decision, providing valuable information about how the cooling–warming rates during vitrification can be partly responsible of the postnatal phenotypic variations.

Genome-wide assessment of DNA methylation in mouse oocytes reveals effects associated with in vitro growth, superovulation, and sexual maturity

Background

In vitro follicle culture (IFC), as applied in the mouse system, allows the growth and maturation of a large number of immature preantral follicles to become mature and competent oocytes. In the human oncofertility clinic, there is increasing interest in developing this technique as an alternative to ovarian cortical tissue transplantation and to preserve the fertility of prepubertal cancer patients. However, the effect of IFC and hormonal stimulation on DNA methylation in the oocyte is not fully known, and there is legitimate concern over epigenetic abnormalities that could be induced by procedures applied during assisted reproductive technology (ART).

Results

In this study, we present the first genome-wide analysis of DNA methylation in MII oocytes obtained after natural ovulation, after IFC and after superovulation. We also performed a comparison between prepubertal and adult hormonally stimulated oocytes. Globally, the distinctive methylation landscape of oocytes, comprising alternating hyper- and hypomethylated domains, is preserved irrespective of the procedure. The conservation of methylation extends to the germline differential methylated regions (DMRs) of imprinted genes, necessary for their monoallelic expression in the embryo. However, we do detect specific, consistent, and coherent differences in DNA methylation in IFC oocytes, and between oocytes obtained after superovulation from prepubertal compared with sexually mature females. Several methylation differences span entire transcription units. Among these, we found alterations in Tcf4, Sox5, Zfp521, and other genes related to nervous system development.

Conclusions

Our observations show that IFC is associated with altered methylation at specific set of loci. DNA methylation of superovulated prepubertal oocytes differs from that of superovulated adult oocytes, whereas oocytes from superovulated adult females differ very little from naturally ovulated oocytes. Importantly, we show that regions other than imprinted gDMRs are susceptible to methylation changes associated with superovulation, IFC, and/or sexual immaturity in mouse oocytes. Our results provide an important reference for the use of in vitro growth and maturation of oocytes, particularly from prepubertal females, in assisted reproductive treatments or fertility preservation.

Identification and characterization of human ovary-derived circular RNAs and their potential roles in ovarian aging

Circular RNAs (circRNAs) have recently been shown to exert effects on multiple pathological processes by acting as miRNA sponges. However, the roles of circRNAs in ovarian senescence are largely unknown. The objective of this study was to identify the circRNAs involved in ovarian aging and predict their potential biological functions. We first performed RNA-sequencing to generate ovarian circRNA expression profiles from young (n = 3) and aging (n = 3) groups. In total, 48,220 circRNAs were identified, of which 194 circRNAs were significantly up-regulated and 207 circRNAs were down-regulated during aging (fold change > 2, P < 0.05). Bioinformatics analysis demonstrated that the metabolic process, regulated secretory pathway, oxidation-reduction process, steroid hormone biosynthesis, and insulin secretion pathways, which may be associated with ovarian aging, were significantly enriched (P < 0.05). The biological characteristics of ovary-derived circRNA, such as back-splicing, RNase R resistance, stability, and alternative splicing, were further validated. Bioinformatics predicted that most of the circRNAs harboured miRNA binding sites, of which circDDX10-miR-1301-3p/miR-4660-SIRT3 axis may be involved in the regulation of ovarian function. Our study indicates that circRNAs are aberrantly expressed in the aging ovary and may play potential roles in the development of ovarian senescence.

Advances in research into gamete and embryo-fetal origins of adult diseases

The fetal and infant origins of adult disease hypothesis proposed that the roots of adult chronic disease lie in the effects of adverse environments in fetal life and early infancy. In addition to the fetal period, fertilization and early embryonic stages, the critical time windows of epigenetic reprogramming, rapid cell differentiation and organogenesis, are the most sensitive stages to environmental disturbances. Compared with embryo and fetal development, gametogenesis and maturation take decades and are more vulnerable to potential damage for a longer exposure period. Therefore, we should shift the focus of adult disease occurrence and pathogenesis further back to gametogenesis and embryonic development events, which may result in intergenerational, even transgenerational, epigenetic re-programming with transmission of adverse traits and characteristics to offspring. Here, we focus on the research progress relating to diseases that originated from events in the gametes and early embryos and the potential epigenetic mechanisms involved.

Antioxidant hesperetin improves the quality of porcine oocytes during aging in vitro

The citrus flavonoid hesperetin has a variety of pharmacological actions, including antioxidant, antiinflammatory, and anticancer activities. This study investigated whether hesperetin prevents aging of oocytes in vitro in which it determined the maturation of nuclear and cytoplasm and the developmental capacity of embryo by modulating the reactive oxygen species (ROS) level. Porcine oocytes were matured in vitro for 44 hr (control) and for an additional 24 hr in the presence of 0, 1, 10, 100, and 250 μM hesperetin (aging, H-1, H-10, H-100, and H-250, respectively). Although there was no difference in the rate of maturation among all the groups, both the control and H-100 groups significantly increased in the rate of cleavage and blastocyst formation compared to the aging group. The H-100 group significantly decreased ROS activity and increases the level of glutathione (GSH) and expression of the antioxidant genes (PRDX5, NFE2L, SOD1, and SOD2) compared with the aging group. The H-100 groups prevented aberrant spindle organization and chromosomal misalignment, blocked the decrease in the level of phosphorylated-p44/42 mitogen-activated protein kinase and increased the messenger RNA expression of cytoplasmic maturation factor genes (GDF9, CCNB1, BMP15, and MOS). Subsequently, both the control and H-100 groups significantly increased the total cell number and decreased the apoptosis cells at the blastocyst stage compared with aging group. The results indicate that hesperetin improves the quality of porcine oocytes by protecting them against oxidative stress during aging in vitro.