Acquisition of oocyte competence to develop as an embryo: integrated nuclear and cytoplasmic events

Maternal spindle transfer overcomes embryo developmental arrest caused by ooplasmic defects in mice

The developmental potential of early embryos is mainly dictated by the quality of the oocyte. Here, we explore the utility of the maternal spindle transfer (MST) technique as a reproductive approach to enhance oocyte developmental competence. Our proof-of-concept experiments show that replacement of the entire cytoplasm of oocytes from a sensitive mouse strain overcomes massive embryo developmental arrest characteristic of non-manipulated oocytes. Genetic analysis confirmed minimal carryover of mtDNA following MST. Resulting mice showed low heteroplasmy levels in multiple organs at adult age, normal histology and fertility. Mice were followed for five generations (F5), revealing that heteroplasmy was reduced in F2 mice and was undetectable in the subsequent generations. This pre-clinical model demonstrates the high efficiency and potential of the MST technique, not only to prevent the transmission of mtDNA mutations, but also as a new potential treatment for patients with certain forms of infertility refractory to current clinical strategies.

MicroRNA-21 as a regulator of human cumulus cell viability and its potential influence on the developmental potential of the oocyte

MicroRNA-21 is expressed in bovine, murine, and human cumulus cells with its expression in murine and bovine cumulus cells correlated with oocyte developmental potential. The aim of this study was to assess the relationship between cumulus cell MIR-21 and human oocyte developmental potential. These studies revealed that both the immature and mature forms of MicroRNA-21 (MIR-21-5p) were elevated in cumulus cells of oocytes that developed into blastocysts compared to cumulus cells of oocytes that arrested prior to blastocyst formation. This increase in MicroRNA-21 was observed regardless of whether the oocytes developed into euploid or aneuploid blastocysts. Moreover, MIR-21-5p levels in cumulus cells surrounding oocytes that either failed to mature or matured to metaphase II but failed to fertilize, were ≈50% less than the MIR-21-5p levels associated with oocytes that arrested prior to blastocyst formation. Why cumulus cells associated with oocytes of reduced developmental potential expressed less MIR-21-5p is unknown. It is unlikely due to reduced expression of either the receptors of growth differentiation factor 9 or rosha Ribonuclease III (DROSHA) and Dicer Ribonuclease III (DICER) which sequentially promote the conversion of immature forms of MicroRNA-21 to mature MicroRNA-21. Furthermore, cultured cumulus cells treated with a MIR-21-5p inhibitor had an increase in apoptosis and a corresponding increase in the expression of PTEN, a gene known to inhibit the AKT-dependent survival pathway in cumulus cells. These studies provide evidence for a role of MicroRNA-21 in human cumulus cells that influences the developmental potential of human oocytes.

Recent progress in bovine in vitro-derived embryo cryotolerance: Impact of in vitro culture systems, advances in cryopreservation and future considerations

Cryopreservation of in vitro-derived bovine embryos is a crucial step for the widespread reproduction and conservation of valuable high-merit animals. Given the current popularity of bovine in vitro embryo production (IVP), there is a demand for a highly efficient ultra-low temperature storage method in order to maximize donor ovum pickup (OPU) turn-over, recipient availability/utilization and domestic/overseas commercial trading opportunities. However, IVP bovine embryos are still very sensitive to chilling and cryopreservation, and despite recent progress, a convenient (simple and robust) protocol has not yet been developed. At the moment, there are two methods for bovine IVP embryo cryopreservation: slow programmable freezing and vitrification. Both of the aforementioned techniques have pros and cons. While controlled-rate slow cooling can easily be adapted for direct transfer (DT), ice crystal formation remains an issue. On the other hand, vitrification solved this problem but the possibility of successful DT commercial incorporation remains to be determined. Moreover, simplification of the vitrification protocol (including warming) through the use of an in-straw dilution without the use of a microscope is a prerequisite for its use under farm conditions. This review summarizes the bovine IVP embryo cryopreservation achievements, strengths and limitations of both freezing systems and prospective improvements to enhance cryosurvival, as well as perspectives on future directions of this assisted reproductive technology.

Stereological study of organelle distribution in human oocytes at metaphase I

We have previously presented a stereological analysis of organelle distribution in human prophase I oocytes. In the present study, using a similar stereological approach, we quantified the distribution of organelles in human metaphase I (MI) oocytes also retrieved after ovarian stimulation. Five MI oocytes were processed for transmission electron microscopy and a classical manual stereological technique based on point-counting with an adequate stereological grid was used. Kruskal-Wallis and Mann-Whitney U-tests with Bonferroni correction were used to compare the means of relative volumes (Vv) occupied by organelles. In all oocyte regions, the most abundant organelles were mitochondria and smooth endoplasmic reticulum (SER) elements. No significant differences were observed in Vv of mitochondria, dictyosomes, lysosomes, or SER small and medium vesicles, tubular aggregates and tubules. Significant differences were observed in other organelle distributions: cortical vesicles presented a higher Vv (P = 0.004) in the cortex than in the subcortex (0.96% vs 0.1%) or inner cytoplasm (0.96% vs 0.1%), vesicles with dense granular contents had a higher Vv (P = 0.005) in the cortex than in the subcortex (0.1% vs 0%), and SER large vesicles exhibited a higher Vv (P = 0.011) in the inner cytoplasm than in the subcortex (0.2% vs 0%). Future stereological analysis of metaphase II oocytes and a combined quantitative data of mature and immature oocytes, will enable a better understanding of oocyte organelle distribution during in vivo maturation. Combined with molecular approaches, this may help improve stimulation protocols and in vitro maturation methods.

Diversity of RNA-Binding Proteins Modulating Post-Transcriptional Regulation of Protein Expression in the Maturing Mammalian Oocyte

The oocyte faces a particular challenge in terms of gene regulation. When oocytes resume meiosis at the end of the growth phase and prior to ovulation, the condensed chromatin state prevents the transcription of genes as they are required. Transcription is effectively silenced from the late germinal vesicle (GV) stage until embryonic genome activation (EGA) following fertilisation. Therefore, during its growth, the oocyte must produce the mRNA transcripts needed to fulfil its protein requirements during the active period of meiotic completion, fertilisation, and the maternal-to zygote-transition (MZT). After meiotic resumption, gene expression control can be said to be transferred from the nucleus to the cytoplasm, from transcriptional regulation to translational regulation. Maternal RNA-binding proteins (RBPs) are the mediators of translational regulation and their role in oocyte maturation and early embryo development is vital. Understanding these mechanisms will provide invaluable insight into the oocyte's requirements for developmental competence, with important implications for the diagnosis and treatment of certain types of infertility. Here, we give an overview of post-transcriptional regulation in the oocyte, emphasising the current knowledge of mammalian RBP mechanisms, and develop the roles of these mechanisms in the timely activation and elimination of maternal transcripts.

The 5.8S pre-rRNA maturation factor, M-phase phosphoprotein 6, is a female fertility factor required for oocyte quality and meiosis

Objectives

M‐phase phosphoprotein 6 (MPP6) is important for 5.8S pre‐rRNA maturation in somatic cells and was screened as a female fertility factor. However, whether MPP6 functions in oocyte meiosis and fertility is not yet known. We aimed to address this.

Materials and Methods

Mouse oocytes with surrounded nucleus (SN) or non‐surrounded nucleus (NSN) were used for all experiments. Peptide nanoparticle‐mediated antibody transfection was used to deplete MPP6. Immunofluorescence staining, immunohistochemistry and live tracker staining were used to examine MPP6 localization and characterize phenotypes after control or MPP6 depletion. High‐fidelity PCR and fluorescence in situ hybridization (FISH) were used to examine the localization and level of 5.8S rRNAs. Western blot was used to examine the protein level. MPP6‐EGFP mRNA microinjection was used to do the rescue.

Results

MPP6 was enriched within ovaries and oocytes. MPP6 depletion significantly impeded oocyte meiosis. MPP6 depletion increased 5.8S pre‐rRNA. The mRNA levels of MPP6 and 5.8S rRNA decreased within ageing oocytes, and MPP6 mRNA injection partially increased 5.8S rRNA maturation and improved oocyte quality.

Conclusions

MPP6 is required for 5.8S rRNA maturation, meiosis and quality control in mouse oocytes, and MPP6 level might be a marker for oocyte quality.

Luteinizing Hormone Action in Human Oocyte Maturation and Quality: Signaling Pathways, Regulation, and Clinical Impact

The ovarian follicle luteinizing hormone (LH) signaling molecules that regulate oocyte meiotic maturation have recently been identified. The LH signal reduces preovulatory follicle cyclic nucleotide levels which releases oocytes from the first meiotic arrest. In the ovarian follicle, the LH signal reduces cyclic nucleotide levels via the CNP/NPR2 system, the EGF/EGF receptor network, and follicle/oocyte gap junctions. In the oocyte, reduced cyclic nucleotide levels activate the maturation promoting factor (MPF). The activated MPF induces chromosome segregation and completion of the first and second meiotic divisions. The purpose of this paper is to present an overview of the current understanding of human LH signaling regulation of oocyte meiotic maturation by identifying and integrating the human studies on this topic. We found 89 human studies in the literature that identified 24 LH follicle/oocyte signaling proteins. These studies show that human oocyte meiotic maturation is regulated by the same proteins that regulate animal oocyte meiotic maturation. We also found that these LH signaling pathway molecules regulate human oocyte quality and subsequent embryo quality. Remarkably, in vitro maturation (IVM) prematuration culture (PMC) protocols that manipulate the LH signaling pathway improve human oocyte quality of cultured human oocytes. This knowledge has improved clinical human IVM efficiency which may become a routine alternative ART for some infertile patients.

Prolonged ovarian storage of mature Drosophila oocytes dramatically increases meiotic spindle instability

Human oocytes frequently generate aneuploid embryos that subsequently miscarry. In contrast, Drosophila oocytes from outbred laboratory stocks develop fully regardless of maternal age. Since mature Drosophila oocytes are not extensively stored in the ovary under laboratory conditions like they are in the wild, we developed a system to investigate how storage affects oocyte quality. The developmental capacity of stored mature Drosophila oocytes decays in a precise manner over 14 days at 25°C. These oocytes are transcriptionally inactive and persist using ongoing translation of stored mRNAs. Ribosome profiling revealed a progressive 2.3-fold decline in average translational efficiency during storage that correlates with oocyte functional decay. Although normal bipolar meiotic spindles predominate during the first week, oocytes stored for longer periods increasingly show tripolar, monopolar and other spindle defects, and give rise to embryos that fail to develop due to aneuploidy. Thus, meiotic chromosome segregation in mature Drosophila oocytes is uniquely sensitive to prolonged storage. Our work suggests the chromosome instability of human embryos could be mitigated by reducing the period of time mature human oocytes are stored in the ovary prior to ovulation.

Oocyte meiotic spindle morphology is a predictive marker of blastocyst ploidy-a prospective cohort study

OBJECTIVE

To evaluate oocyte meiotic spindle (OMS) morphology at intracytoplasmic sperm injection (ICSI) as a predictor of blastocyst ploidy and whether OMS morphology could aid standard morphology-based blastocyst selection.

DESIGN

Prospective cohort study.

SETTING

In vitro fertilization clinic.

PATIENT(S)

Patients undergoing ICSI cycles with an intention to perform preimplantation genetic testing for aneuploidy (PGT-A) from October 2014 to December 2017.

INTERVENTION(S)

The OMS was visualized with the use of polarized light microscopy at the time of ICSI and the morphology classified as normal, dysmorphic, translucent, not visible, or in telophase. Blastocyst biopsy for PGT-A was performed on embryos with suitable development.

MAIN OUTCOME MEASURE(S)

The association of OMS morphology with the resulting blastocyst ploidy was evaluated on an "intention-to-treat" (ITT) and an "as-treated analysis" (ATA) basis.

RESULT(S)

The morphology of 2,056 OMSs were classified. A strong association of OMS morphology with fertilization, cleavage to at least 6 cells on day 3, and good/top-quality blastocyst formation was present. Normal OMS was positively associated with blastocyst euploidy compared with all other OMS types combined, per either ITT or ATA. Even after controlling for female age, blastocyst quality, and developmental stage, the presence of a normal OMS was strongly associated with the probability of blastocyst euploidy.

CONCLUSION(S)

OMS morphology is a predictive marker of blastocyst ploidy and can potentially aid standard morphology-based blastocyst selection.

Artificial intelligence in reproductive medicine

Artificial intelligence (AI) has experienced rapid growth over the past few years, moving from the experimental to the implementation phase in various fields, including medicine. Advances in learning algorithms and theories, the availability of large datasets and improvements in computing power have contributed to breakthroughs in current AI applications. Machine learning (ML), a subset of AI, allows computers to detect patterns from large complex datasets automatically and uses these patterns to make predictions. AI is proving to be increasingly applicable to healthcare, and multiple machine learning techniques have been used to improve the performance of assisted reproductive technology (ART). Despite various challenges, the integration of AI and reproductive medicine is bound to give an essential direction to medical development in the future. In this review, we discuss the basic aspects of AI and machine learning, and we address the applications, potential limitations and challenges of AI. We also highlight the prospects and future directions in the context of reproductive medicine.

Melatonin promotes human oocyte maturation and early embryo development by enhancing clathrin-mediated endocytosis

Embryo development potential and reproductive clinical outcomes are all deeply rooted in oocyte maturation. Melatonin has been reported to promote oocyte maturation as an antioxidant in nonprimate species. Its antioxidative functions also help reduce plasma membrane rigidity, which facilitates clathrin-mediated endocytosis (CME). Whether melatonin has effects on human oocyte maturation by regulating CME is worthy of exploration. In this study, we found that the optimal melatonin concentration for human oocyte maturation was 10^-11  M, and the maturation rate of this group was 71.9% (P = .03). The metaphase II (MII) stage oocytes obtained by in vitro maturation with 10^-11  M melatonin had a significantly higher fertilization rate (81.4% vs 61.4%, respectively, P = .017) and blastocyst rate (32.2% vs 15.8%, respectively, P = .039) compared to controls. During maturation, antioxidative melatonin greatly enhanced CME and decreased intra-oocyte cAMP level. The former was evidenced by the increasing numbers of coated pits and vesicles, and the upregulated expression of two major CME markers-clathrin and adaptor protein-2 (AP2). CME inhibitor dynasore increased intra-oocyte cAMP level and blocked oocyte maturation, and melatonin could partly rescue oocyte maturation and significantly elevate the expression of clathrin and AP2 in the presence of dynasore. Therefore, we conclude that melatonin could promote human oocyte maturation and early embryo development through enhancing CME.

Circular RNA profiling in the oocyte and cumulus cells reveals that circARMC4 is essential for porcine oocyte maturation

Thousands of circular RNAs (circRNAs) have been recently discovered in cumulus cells and oocytes from several species. However, the expression and function of circRNA during porcine oocyte meiotic maturation have been never examined. Here, we separately identified 7,067 and 637 circRNAs in both cumulus cells and oocytes via deep sequencing and bioinformatic analysis. Further analysis revealed that a faction of circRNAs is differentially expressed (DE) in a developmental stage-specific manner. The host genes of DE circRNAs are markedly enriched to multiple signaling pathways associated with cumulus cell function and oocyte maturation. Additionally, most DE circRNAs harbor several miRNA targets, suggesting that these DE circRNAs potentially act as miRNA sponge. Importantly, we found that maternal circARMC4 knockdown by siRNA microinjection caused a severely impaired chromosome alignment, and significantly inhibited first polar body extrusion and early embryo development. Taken together, these results demonstrate for the first time that circRNAs are abundantly and dynamically expressed in a developmental stage-specific manner in cumulus cells and oocytes, and maternally expressed circARMC4 is essential for porcine oocyte meiotic maturation and early embryo development.

Sodium nitrite negatively affects reproductive ability and offspring survival in female mice

Sodium nitrite (NaNO₂) is an industrial chemical that is frequently used as a food additive to prevent botulism and enhance glossiness, such as curing meat. In addition, in some regions, water source NaNO₂ concentrations exceed standard regulatory levels. Whether the excessive intake of NaNO₂ has toxic effects on female fertility and fetal development remain unknown. In this study, we administered ICR mice control saline, low-dose NaNO₂ (60 mg/kg/day), or high-dose NaNO₂ (120 mg/kg/day) by intragastric gavage for 21 days. We then assessed oocyte morphology, spindle-chromosome dynamics, mitochondrial distribution, ATP content, apoptotic cell numbers, DNA damage levels, histone modifications, reactive oxygen species (ROS) levels, and offspring survival. Results showed that NaNO₂ treatment decreased oocyte number, impaired polar body extrusion, and increased zona pellucida thickness in oocytes. Furthermore, NaNO₂ disrupted MII spindle integrity, caused abnormal mitochondrial distribution, decreased ATP content, and increased levels of ROS and H3K4me2. Moreover, the number of oocytes in early stages of apoptosis and with levels of DNA damage increased in NaNO₂-treated mice along with decreased offspring numbers and survival rates. We demonstrated the negative effects of NaNO₂ on female reproductive abilities in mice.

Ovine oocytes display a similar germinal vesicle configuration and global DNA methylation at prepubertal and adult ages

Epigenetic mechanisms are thought to be involved in the reduced developmental capacity of early prepubertal ewe oocytes compared to their adult counterparts. In this study, we have analyzed the global DNA methylation pattern and in vitro meiotic and developmental competence of oocytes at the germinal vesicle (GV) stage obtained from adult and 3-month-old donors. All oocytes were aspirated from antral follicles with a diameter ≥3 mm, and DNA methylation on 5-methylcytosine was detected by immunofluorescence using an anti-methyl cytosine antibody. The main global chromatin configuration pattern shown by both prepubertal and adult ovine oocytes corresponded to condensed chromatin localized close to the nuclear envelope (the SNE pattern). Immunofluorescence showed that a global bright nuclear staining of 5-methylcytosine (5-mC) occurred in all germinal vesicle stage oocytes and matched the propidium iodide staining pattern. The total fluorescence intensity values of lamb GVs were not lower than those observed in adult GVs. The meiotic competence and cleavage rates were similar in adult and prepubertal oocytes, however, the developmental competence of embryos to reach blastocysts was higher for adult oocytes than lamb oocytes (p<0.0001). In conclusion, our results indicate that adult-size oocytes derived from 3 to 4 month old prepubertal ewes show similar GV morphology and DNA methylation staining patterns to those obtained from adult animals, despite exhibiting a lower developmental competence.

Normalized Ploidy Following 20 Consecutive Blastocysts with Chromosomal Error: Healthy 46, XY Pregnancy with IVF after Intraovarian Injection of Autologous Enriched Platelet-derived Growth Factors

One explanation for why downstream gonadotropin protocol changes during IVF commonly arrive too late to have significant effects is that embryo development actually begins during oogenesis. Thus, efforts to modify the chromosomal status of blastocysts must address the ovarian milieu well in advance of follicular recruitment. A 42 year old woman with primary infertility of 3 year duration attended with her partner. Five previous IVF cycles had produced 20 embryos, but all had genetic abnormalities and no embryo transfer was performed. Karyotypes and all lab tests were normal for both partners. 3 months before her IVF here, she received isolated platelet-derived growth factors injected into both ovaries as a cell-free, enriched substrate. Genetic assessments were via whole genome amplification and DNA tagmentation and PCR adapter sequences. Comprehensive chromosomal screening was carried out by dual-indexed sequencing of pooled libraries on the MiSeq™ platform. From this IVF cycle one euploid 46, XY blastocyst was produced and vitrified on the day of trophectoderm biopsy. 9 days after frozen embryo transfer, serum human chorionic gonadotropin was 250 mIU/ml and a transvaginal ultrasound at 6 week gestation confirmed a single intrauterine pregnancy with fetal heart at 153/min. A healthy male infant was delivered by c-section at 39 weeks' gestation. While cellular and molecular events directing the oocyte-to-embryo transition are incompletely characterized, processes related to ovarian stem cell differentiation, mitochondrial dynamics, and mRNA storage, translation, and degradation likely are relevant. It appears that intraovarian application of autologous platelet-derived growth factors, when used before IVF, can impact oocyte integrity and facilitate euploid blastocyst development. Although research on intraovarian injection of autologous activated platelet rich plasma has already shown improved quantitative IVF responses, this is the first description of qualitative improvements in embryo genetics after intraovarian injection of autologous platelet-derived growth factors.

Participation of EML6 in the regulation of oocyte meiotic progression in mice

The generation of a high-quality egg for reproduction requires faithful segregation of chromosome during oocyte meiosis. Here, we report that echinoderm microtubule-associated protein like 6 (EML6) is highly expressed in oocytes, and responsible for accurate segregation of homologous chromosomes in mice. Quantitative real-time RT-PCR and immunohistochemistry analyses revealed that EML6 was predominantly expressed by oocytes in the ovaries. Whole mount immunofluorescent staining showed that EML6 was colocalized with spindle microtubules in oocytes at various stages after meiotic resumption. This specialized localization was disrupted by nocodazole, the microtubule destabilizer, while enhanced by Taxol, a microtubule stabilizing reagent. In vivo knockdown of Eml6 expression by the specific siRNA resulted in chromosome misalignment and alteration in spindle dimension at both metaphase Ⅰ and Ⅱ stages, as well as the increased aneuploidy in the mature oocytes. Thus, these data suggest that EML family proteins participate in the control of oocyte meiotic division.

Individualization of FSH Doses in Assisted Reproduction: Facts and Fiction

The art of ovarian stimulation for IVF/ICSI treatment using exogenous FSH should be balanced against the relative contribution of other steps of the ART process such as the IVF-lab-phase and the Embryo-Transfer. The aim of ovarian stimulation is to obtain a certain number of oocytes, that will enable the best probability of achieving a live birth. It has been suggested that more oocytes will create a better prospect for pregnancy, but studies on the question whether the retrieval of a few oocytes less or more will make the difference are not clearly supportive for this mantra. Personalization strategies have been the subject of many studies over the past 20 years. Creating the optimal response in a patient in terms of live birth prognosis as well as OHSS risks may be based on information from the Ovarian Reserve testing using the Antral Follicle Count or Anti-Mullerian Hormone, the patient's bodyweight, the ovarian response in a previous cycle, and the dosage level of FSH. Taken together, steering the ovarian response into a supposed optimal range may appear difficult as the interrelation for each of these factors with the egg number is weak. Using OR testing for choosing FSH dosage, compared to a standard normal dosage of 150 IU, has been studied in several trials. Dosage individualization, in general, does not appear to improve the prospects for live birth, but the reduction in OHSS risk may be substantial. This implies that the use of high dosages of FSH in predicted LOW responders lacks any cost-benefit for the patient and may be abandoned, while in predicted HIGH responders, reduction of the usual dosage level of 150 IU may create better safety, provided that in case of an unexpected LOW response cancelation of the cycle is refrained from. In view of recent developments in using GnRH agonist triggering of final oocyte maturation, the trend could be that with the Antagonist co-medication system and a standard dosage of 150 IU of FSH, prior ovarian reserve testing may become futile, as safety can be managed well in actual HIGH responders by replacing the high dose hCG trigger.

Immature Oocyte for Fertility Preservation

In vitro maturation (IVM) of human immature oocytes has been offered to women who are at risk of developing ovarian hyperstimulation syndrome (OHSS) caused by gonadotropin stimulation, such as PCO(S) patients or who have poor ovarian reserve. Cryopreservation of oocytes matured in vivo obtained in IVF cycles has improved after implementing the vitrification method and many successful results have been reported. Now, this procedure can be successfully offered to fertility preservation programs for patients who are in danger of losing their ovarian function due to medical or social reasons, and to oocyte donation programs. This vitrification technique has also been applied to cryopreserve oocytes obtained from IVM program. Some advantages of oocytes vitrification related with IVM are: (1) eliminating costly drugs and frequent monitoring; (2) completing treatment within 2 to 10 days (3) avoiding the use of hormones in cancer patients with hormone-sensitive tumors; and (4) retrieving oocytes at any point in menstrual cycle, even in the luteal phase. In addition, immature oocytes can also be collected from extracorporeal ovarian biopsy specimens or ovaries during caesarian section. Theoretically, there are two possible approaches for preserving immature oocytes: oocyte cryopreservation at the mature stage (after IVM) and oocyte cryopreservation at the Germinal Vesicle (GV)-stage (before IVM). Both vitrification of immature oocyte before/after IVM is not currently satisfactory. Nevertheless, many IVF centers worldwide are doing IVM oocyte cryopreservation as one of the options to preserve fertility for female cancer. Therefore, more studies are urgently required to improve IVM- and vitrification method to successfully preserve oocytes collected from cancer patients. In this review, present oocyte maturation mechanisms and recent progress of human IVM cycles will be discussed first, followed by some studies of the vitrification of human IVM oocyte.

Can peri-ovulatory putrescine supplementation improve egg quality in older infertile women?

The aging-related decline in fertility is an increasingly pressing medical and economic issue in modern society where women are delaying family building. Increasingly sophisticated, costly, and often increasingly invasive, assisted reproductive clinical protocols and laboratory technologies (ART) have helped many older women achieve their reproductive goals. Current ART procedures have not been able to address the fundamental problem of oocyte aging, the increased rate of egg aneuploidy, and the decline of developmental potential of the eggs. Oocyte maturation, which is triggered by luteinizing hormone (LH) in vivo or by injection of human chorionic gonadotropin (hCG) in an in vitro fertilization (IVF) clinic, is the critical stage at which the majority of egg aneuploidies arise and when much of an egg's developmental potential is established. Our proposed strategy focuses on improving egg quality in older women by restoring a robust oocyte maturation process. We have identified putrescine deficiency as one of the causes of poor egg quality in an aged mouse model. Putrescine is a biogenic polyamine naturally produced in peri-ovulatory ovaries. Peri-ovulatory putrescine supplementation has reduced egg aneuploidy, improved embryo quality, and reduced miscarriage rates in aged mice. In this paper, we review the literature on putrescine, its occurrence and physiology in living organisms, and its unique role in oocyte maturation. Preliminary human data demonstrates that there is a maternal aging-related deficiency in ovarian ornithine decarboxylase (ODC), the enzyme responsible for putrescine production. We argue that peri-ovulatory putrescine supplementation holds great promise as a natural and effective therapy for infertility in women of advanced maternal age, applicable in natural conception and in combination with current ART therapies.

Novel Concepts for Inducing Final Oocyte Maturation in In Vitro Fertilization Treatment

Infertility affects one in six of the population and increasingly couples require treatment with assisted reproductive techniques. In vitro fertilization (IVF) treatment is most commonly conducted using exogenous FSH to induce follicular growth and human chorionic gonadotropin (hCG) to induce final oocyte maturation. However, hCG may cause the potentially life-threatening iatrogenic complication "ovarian hyperstimulation syndrome" (OHSS), which can cause considerable morbidity and, rarely, even mortality in otherwise healthy women. The use of GnRH agonists (GnRHas) has been pioneered during the last two decades to provide a safer option to induce final oocyte maturation. More recently, the neuropeptide kisspeptin, a hypothalamic regulator of GnRH release, has been investigated as a novel inductor of oocyte maturation. The hormonal stimulus used to induce oocyte maturation has a major impact on the success (retrieval of oocytes and chance of implantation) and safety (risk of OHSS) of IVF treatment. This review aims to appraise experimental and clinical data of hormonal approaches used to induce final oocyte maturation by hCG, GnRHa, both GnRHa and hCG administered in combination, recombinant LH, or kisspeptin. We also examine evidence for the timing of administration of the inductor of final oocyte maturation in relationship to parameters of follicular growth and the subsequent interval to oocyte retrieval. In summary, we review data on the efficacy and safety of the major hormonal approaches used to induce final oocyte maturation in clinical practice, as well as some novel approaches that may offer fresh alternatives in future.

Oocyte related factors impacting on embryo quality: relevance for in vitro embryo production

The outcome of pregnancy is closely linked to early events that occur during the onset of embryogenesis. The first stages in embryonic development are mainly governed by the storage of maternal factors present in the oocyte at the time of fertilisation. In this review, we outline the different classes of oocyte transcripts that may be involved in activation of the embryonic genome as well as those associated with epigenetic reprogramming, imprinting maintenance or the control of transposon mobilisation during preimplantation development. We also report the influence of cumulus-oocyte crosstalk during the maturation process on the oocyte transcriptome and how in vitro procedures can affect these interactions.

GDNF-Induced Downregulation of miR-145-5p Enhances Human Oocyte Maturation and Cumulus Cell Viability

CONTEXT

Although glial cell line-derived neurotrophic factor (GDNF) and microRNAs (miRNAs) have been shown to regulate mammalian oocyte maturation, little is known about their effects on human oocyte maturation and the underlying molecular mechanisms.

OBJECTIVES

To examine the effects of GDNF on both nuclear and cytoplasmic maturation in cultured immature human oocytes and to investigate the involvement of miRNAs in GDNF-induced oocyte maturation.

DESIGN

A total of 200 human immature oocytes were used to evaluate the effects of GDNF on oocyte maturation. The involvement of miRNAs in GDNF-induced oocyte maturation was identified by comparing the miRNA expression profiles of cumulus cells (CCs) either with or without GDNF stimulation.

SETTING

An in vitro fertilization center at the Women's Hospital, Zhejiang University School of Medicine.

METHODS

Agilent human miRNA (8*60K) arrays were used to examine the miRNA expression patterns of human CCs either with or without GDNF stimulation. miR-145-5p inhibitor and mimic transfections were performed to study downstream gene expression in human CCs.

RESULTS

During the in vitro maturation process, GDNF significantly increased the percentage of metaphase II-stage oocytes and downregulated the expression of miR-145-5p in cultured human CCs. Expression of miR-145-5p in CCs is negatively correlated with oocyte maturation. miR-145-5p mimic significantly decreased the expression of GDNF family receptor-α1, ret proto-oncogene, and epidermal growth factor receptor, whereas miR-145-5p inhibitor reversed these effects. GDNF treatment inhibited cell apoptosis in cultured CCs, and this suppressive effect was reversed by transfection with the miR-145-5p mimic.

CONCLUSION

Downregulation of miR-145-5p may contribute to GDNF-induced enhancement of oocyte maturation and of cell viability against cell apoptosis.