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

In vitro maturation of oocytes (IVM): historical landmarks, current status and future perspectives

One of the major advancements in in vitro fertilization (IVF) has been the development of culture media that enhance gamete maturation in vitro and sustain embryo development up to the blastocyst stage. The deep understanding of the mechanisms involved in gametogenesis and the complex sequence of events surrounding nuclear and cytoplasmic maturation has also enabled the development of efficient in vitro maturation (IVM) protocols. This review outlines the major landmarks in the history of in vitro maturation of oocytes, the advantages and importance of its clinical application in human, especially in patients with Polycystic Ovary Syndrome (PCOS), Resistant Ovary Syndrome, high antral follicle count or oncology patients, as well as the safety and efficacy of the technique. IVM has not been shown yet to be as effective as controlled ovarian stimulation in terms of maturation rates, fertilization rates, and clinical outcome, possibly owing to a dysfunctional or asynchronous nuclear/cytoplasmic maturation process. A confusing set of IVM clinical protocols may also have contributed to the slow incorporation of the technology into routine IVF practice. However, recent improvements have led to comparable live birth rates between IVM and IVF, in women with high antral follicle count. The current status of IVM in the Assisted Reproductive Technology (ART) laboratory and its future perspectives, aiming to provide maximum fertility care to patients will be discussed.

Transcriptomic profiling of miRNA-mRNA interactions in canine oocytes and cumulus cells during in vitro maturation: a sequencing analysis

Oocyte maturation is a critical process for successful fertilization and early embryonic development. In this study, we investigated the molecular mechanisms underlying oocyte maturation in dogs by analyzing the transcriptomic profiles of miRNAs and mRNAs in canine cumulus cells (CCs) and oocytes during in vitro maturation (IVM). RNA sequencing identified 285 miRNAs expressed in oocytes and 310 in CCs, with 282 miRNAs shared between the two cell types, highlighting the role of intercellular communication in maintaining miRNA expression equilibrium. Differential expression analysis revealed 222 mRNAs with significant differences between CCs and oocytes, including genes involved in transcriptional regulation and nuclear structure. Enrichment analyses identified pathways such as actin cytoskeleton regulation, mTOR signaling, cAMP signaling, and calcium signaling, all critical to oocyte maturation. Network analysis revealed 643 significant miRNA-mRNA coexpression relationships, suggesting miRNAs play pivotal roles in regulating mRNA expression during oocyte maturation. Notably, key miRNAs such as miR-30b, miR-375, and miR-503 were implicated in regulating genes involved in oocyte maturation pathways, while others like miR-378 and miR-21 aligned with known roles in suppressing cumulus expansion and influencing maturation. The absence of differential miRNA expression between CCs and oocytes suggests the miRNA transfer through gap junctions. These findings provide new insights into the transcriptional and post-transcriptional regulation of oocyte maturation in dogs, offering valuable knowledge to improve reproductive biotechnologies such as in vitro fertilization and embryo development in this species.

Dual-omics reveals temporal translational recovery landscapes and cryodamage repair mechanisms in vitrified mouse oocytes

PURPOSE

The efficacy of oocyte cryopreservation still requires enhancement. Current understanding of cryodamage is largely limited to the organelle level, and the impact of freezing on oocyte gene expression remains unclear.

METHODS

In this study, we employed an innovative dual-omics approach to assess the transcriptional and translational profiles of mouse metaphase II (MII) oocytes during the initial 4 h post-thaw.

RESULTS

Our mapping of the translational recovery in vitrified mouse oocytes post-thaw revealed a critical 2-h window that is optimal for recovery. We confirmed the mitochondrial damage associated with vitrification and identified the activation of autophagy and proteasomal degradation during this period. Additionally, our analysis indicates that vitrified oocytes have another repair response to counteract cryoinjury, involving spindle remodeling and membrane recycling.

CONCLUSIONS

These findings can guide future efforts to improve oocyte vitrification outcomes by improving repair processes and not focusing solely on the damage processes.

Exosomal Communication Between Cumulus-Oocyte Complexes and Granulosa Cells: A New Molecular Axis for Oocyte Competence in Human-Assisted Reproduction

Exosomal microRNAs (ex-miRs), encapsulated in extracellular vesicles (EVs), play a vital role in facilitating paracrine communication among granulosa cells (GCs), cumulus cells (CCs), and the oocyte inside follicular fluid (FF). These small non-coding RNAs are crucial for regulating folliculogenesis, oocyte maturation, and early embryonic development via modulating intracellular signaling networks. Dysregulation o has been associated with reproductive disorders such as polycystic ovarian syndrome (PCOS), diminished ovarian reserve (DOR), and inadequate ovarian response (POR), impacting oocyte quality and fertility outcomes. This narrative review consolidates molecular data from current human and animal studies regarding ex-miR expression patterns, functional targets, and pathway involvement within the context of assisted reproductive technologies (ARTs). A literature-based analysis was undertaken, focusing on signaling pathways, pathogenic processes, and clinical implications. Specifically, ex-miRs-such as miR-21, miR-34c, miR-143-3p, miR-155-5p, miR-339-5p, and miR-424-5p-were identified as regulators of critical pathways including phosphoinositide 3-kinase (PI3K)-AKT, ERK1/2, TGF-β/SMAD, and Rb-E2F1. These ex-miRs regulate apoptosis, glycolysis, mitochondrial function, and cell cycle expansion to influence oocyte competence. Pathological patterns in PCOS and POR are associated with altered ex-miR expression that disrupts metabolic and developmental signaling. Research utilizing animal models confirmed that modifications in EV-associated miRNA influence in vitro maturation (IVM) efficiency and blastocyst quality. Ex-miRs serve as intriguing non-invasive biomarkers and potential therapeutic targets for ARTs. Their mechanical involvement in oocyte and follicular physiology positions them for integration into forthcoming precision-based infertility therapies. For its implementation in reproductive medicine, EV profiling requires standardization and further functional validation in clinical environments.

Impact of Chronic Fluoxetine Exposure on Oocyte Development and Reproductive Outcomes in a Mouse Model

Selective serotonin reuptake inhibitors (SSRIs), like fluoxetine, are increasingly used by women of a reproductive age, raising concerns about their impact on oocyte quality and early embryonic development. This study investigated the effects of chronic fluoxetine exposure on oocyte maturation, ovulation, and embryonic development in a mouse model. Female mice were administered fluoxetine via drinking water, and their reproductive outcomes were compared to those of control mice. Oocyte quantity and quality were assessed following superovulation, including the analysis of spindle morphology, chromatin configuration, and maturation markers. In vitro maturation assays were conducted to evaluate the developmental competence of oocytes exposed to fluoxetine. Finally, the impact of fluoxetine on blastocyst formation, litter size, offspring growth, and ovarian reserve was examined. The results show that fluoxetine treatment reduced the number of ovulated oocytes but did not significantly affect oocyte quality or meiotic spindle formation. Fluoxetine exposure impaired cytoplasmic maturation at the germinal vesicle stage, resulting in a lower proportion of fully mature oocytes and reduced in vitro maturation efficiency. While blastocyst numbers were modestly reduced in fluoxetine-treated mice, litter size and offspring ovarian reserve were unaffected. Unexpectedly, offspring of fluoxetine-treated mothers exhibited increased body weight. These findings suggest that while fluoxetine may impair oocyte developmental competence through disruptions in cytoplasmic maturation, it does not severely compromise overall reproductive outcomes or offspring fertility.

DNA methylation landscapes of in vitro matured oocytes retrieved during endoscopic gynaecological procedures

In vitro maturation (IVM) of human oocytes offers cost efficiency and minimal invasiveness, serving as a valuable supplementary tool in assisted reproduction for fertility preservation, ovarian hyperstimulation syndrome prevention, and other reproductive strategies. Despite its availability for three decades, the clinical use of IVM remains limited due to efficacy and safety concerns. This study examines the DNA methylation profile of IVM oocytes collected during laparoscopic/hysteroscopic surgeries compared to in vivo matured oocytes via reduced representation bisulfite sequencing. Results indicate IVM oocytes exhibit a higher global methylation level. Differentially methylated regions (DMR) analysis reveals that the in vitro group displays more hypermethylated and fewer hypomethylated DMRs compared to the in vivo group. Additionally, the in vitro group exhibits a higher level of non-CpG methylation than the in vivo group. However, no significant correlation between methylation levels and transcriptional activity in these oocytes is found, especially for those specific imprinted genes or genes related to embryonic development. These findings shed light on the epigenetic landscape of IVM oocytes, contributing to the ongoing assessment of their clinical feasibility and safety in assisted reproduction.

Agouti-signaling protein (ASIP) improves bovine in vitro matured oocyte developmental competence and modulates lipid content

PURPOSE

Bovine embryos produced in vitro are developmentally inferior compared to in vivo derived embryos due to the lack of optimization of the oocyte and embryo culture conditions in vitro. Agouti-signaling protein (ASIP), a secreted protein produced by the bovine oocyte, has been recently shown to aid in acquiring oocyte developmental competence. Therefore, in the present study, we aimed to reveal the effects of supplementation of ASIP during in vitro oocyte maturation and embryo culture on subsequent embryonic development.

METHODS

Cumulus-oocyte complexes or presumptive zygotes were placed in culture medium containing either 0, 1, 10, or 100 ng/mL of recombinant ASIP (rASIP). Effects on development, gene expression, lipid content, and blastocyst cell allocation were examined.

RESULTS

Supplementation of rASIP during oocyte maturation was found to significantly increase the blastocyst development rate (P < 0.05) and produced blastocysts with an increased inner cell mass to trophectoderm cell ratio. Addition of rASIP during oocyte maturation increased oocyte (P < 0.05) but not embryo (P > 0.05) lipid levels. The expression of genes involved in lipid metabolism, including FASN, PPAR γ , SCD, CSL1, ELOVL5, and ELOVL6, was not significantly altered in blastocysts due to treatment (P > 0.05). Supplementation of rASIP during embryo culture was not found to affect blastocyst rates.

CONCLUSIONS

The data presented in this study further support the role of ASIP in oocyte competence and suggest that the supplementation of rASIP during oocyte maturation may lead to the production of blastocyst of increased quality.

Rab32-based vesicles coordinate mitochondria and actin for spindle migration and organelle rearrangement in oocyte meiosis

INTRODUCTION

Rab32 is a part of the Rab GTPase family, which is known as the regulator of vesicle transport for an array of cellular functions including endosomal transport, autophagy, generation of melanosomes, phagocytosis and inflammatory processes.

OBJECTIVE

However, the role of Rab32 in oocyte meiosis is still not well-defined.

METHODS

We depleted Rab32 expression by knock down approach, and we also disrupted Rab32 function by exogenous Rab32Q83L/T37N mRNA injection for mutation.

RESULTS

In our current investigation, we delved into its impacts on the cytoskeleton dynamics and the functionality of organelles during the meiotic maturation process in mouse oocytes. Rab32 expressed during oocyte meiosis and deletion of Rab32 or the expression of exogenous Rab32Q83L/T37N led to oocyte polar body extrusion defects or symmetric division. We showed that Rab32 was essential for ROCK1-based actin assembly which further led to spindle migration for the asymmetry. Besides, perturbation of Rab32 affected DRP1 phosphorylation for the spatial arrangement and functionality of mitochondria in mouse oocytes. And we found that Rab32 disruption caused the miscarriage of membrane organelles such as Golgi apparatus, ER, lysosome and CGs during oocyte meiosis, leading to ER stress and autophagy.

CONCLUSIONS

In summary, our study unravels the critical functions of Rab32 for the interplay between actin and mitochondria, which further facilitates movement of the spindle apparatus and organelles arrangement in mouse oocyte meiotic development.

Late maturing oocyte rescue in poor-prognosis patients: delayed intracytoplasmic sperm injection results in more viable embryos

RESEARCH QUESTION

Can delayed intracytoplasmic sperm injection (DICSI) in late maturing oocytes improve fertilization, blastocyst formation, pregnancy and live birth rates for poor-prognosis patients?

DESIGN

Retrospective analysis of 2243 oocytes from 250 poor-prognosis patients who underwent 311 assisted reproductive technology (ART) cycles. Patients were offered DICSI to increase the number of embryos available for testing when over 50% of oocytes collected were immature on day 0, less than 50% of the injected oocytes were fertilized on day 1 or when patients were undergoing preimplantation genetic testing for aneuploidy.

RESULTS

Fertilization and blastulation rates differed depending on the original assessment of the oocyte maturation stage. Euploidy rate did not differ between blastocysts derived from fertilized oocytes originally assessed as metaphase I (MI) or metaphase II (MII). A transferred blastocyst derived from a matured oocyte originally assessed as MI was as likely to result in a live birth as one from a MII oocyte. No differences in delivery method, gestation period or birth weight were found between intracytoplasmic sperm injection and DICSI. As a result of DICSI, at least 27 cycles (8.7%), which would have otherwise been unproductive, resulted in live births, with five ongoing pregnancies.

CONCLUSIONS

Both MI and germinal vesicle oocytes can complete maturation in vitro. Blastocysts produced from these are likely to be chromosomally normal compared with oocytes originally assessed as MII, and result in similar live birth rates. With no differences in birth outcomes, and DICSI increasing overall ART cycle success, this approach has value for poor-prognosis patients.

Integrated Multi-Omics Analysis Reveals Key Regulators of Bovine Oocyte Maturation

A well-regulated metabolism is crucial for optimal oocyte development and embryonic health. However, the metabolic framework governing oocyte maturation remains poorly understood. Using bovine oocytes as a model, we examined metabolomic and transcriptomic alterations during the transition from the germinal vesicle (GV) to the metaphase II (MII) stage. Our findings reveal distinct metabolic shifts, including suppressed β-oxidation combined with the accumulation of long-chain fatty acids (LCFAs). Notably, progesterone emerged as a key regulator of meiotic resumption through its influence on cAMP levels. We also observed enhanced glycolysis, moderate activation of the citric acid cycle (TCA cycle), and suppression of oxidative phosphorylation (OXPHOS), alongside reduced urea cycle flux and shifts in amino acid metabolism favoring glutamate synthesis. Intriguingly, discrepancies between metabolic and transcriptional activities in pathways such as the TCA cycle and nucleotide metabolism suggest asynchronous regulation. These findings provide a comprehensive multi-omics resource, advancing our understanding of the dynamic metabolic and transcriptional landscape during bovine oocyte maturation.

Mitochondrial replacement techniques to resolve mitochondrial dysfunction and ooplasmic deficiencies: where are we now?

Mitochondria are the powerhouses of cell and play crucial roles in proper oocyte competence, fertilization, and early embryo development. Maternally inherited mitochondrial DNA (mtDNA) mutations can have serious implications for individuals, leading to life-threatening disorders and contribute to ovarian ageing and female infertility due to poor oocyte quality. Mitochondrial replacement techniques (MRTs) have emerged as a promising approach not only to replace defective maternal mitochondria in patients carrying mtDNA mutations, but also to enhance oocyte quality and optimize IVF outcomes for individuals experiencing infertility. There are two main categories of MRT based on the source of mitochondria. In the heterologous approach, mitochondria from a healthy donor are transferred to the recipient's oocyte. This approach includes several methodologies such as germinal vesicle, pronuclear, maternal spindle, and polar body transfer. However, ethical concerns have been raised regarding the potential inheritance of third-party genetic material and the development of heteroplasmy. An alternative approach to avoid these issues is the autologous method. One promising autologous technique was the autologous germline mitochondrial energy transfer (AUGMENT), which involved isolating oogonial precursor cells from the patient, extracting their mitochondria, and then injecting them during ICSI. However, the efficacy of AUGMENT has been debated following the results of a randomized clinical trial (RCT) that demonstrated no significant benefit over conventional IVF. Recent developments have focused on novel approaches based on autologous, non-invasively derived stem cells to address infertility. While these techniques show promising results, further RCTs are necessary to establish their effectiveness and safety for clinical use. Only after robust evidence becomes available could MRT potentially become a viable treatment option for overcoming infertility and enabling patients to have genetically related embryos. This review aims to provide an overview of the current state of MRTs in addressing low oocyte quality due to mitochondrial dysfunction.

The adult ovary at single cell resolution: an expert review

The ovaries play a crucial role in both the endocrine health and fertility of adult women. The fundamental functional units of the ovaries, primordial follicles, form during fetal development and constitute the ovarian reserve. Ovaries age prematurely in comparison to other organs, with the quality of oocytes declining steeply prior to the entire reserve becoming depleted, usually around age 50. Despite the pivotal role of ovaries in women's overall health, surprisingly little is known about the mechanisms controlling follicle dormancy, growth activation, atresia, maturation, and oocyte quality. Understanding ovarian function on a cellular and molecular level is increasingly important for several reasons. First, the global trend of women delaying childbirth creates a growing population of patients wishing to conceive when the quality and quantity of their oocytes are already critically low. Second, conditions affecting the ovaries, such as polycystic ovary syndrome and endometriosis, are widespread, yet diagnosis and treatment still present challenges. Lastly, advancements in cancer therapies have increased the number of cancer survivors who contend with late complications affecting fertility and hormonal balance. Clearly, a better understanding of diseases, aging, and toxicity in ovaries is needed for the development of novel treatments, preventive therapies, and safer pharmaceuticals. Human ovaries are notoriously difficult to obtain for research due to their pivotal role in women's health, and the highly heterogeneous distribution of follicles within the tissue combined with monthly cyclical changes present further challenges. Single-cell profiling techniques are creating new opportunities, enabling the characterization of small amounts of tissue with unprecedented resolution. Here, we review the literature on single-cell characterization of adult, reproductive-age ovaries. The majority of the 46 identified studies have focused on oocytes discarded during assisted reproduction, with only a handful focusing on ovarian tissue. The overwhelming focus of the studies is on follicles and oocytes, although the somatic cell niche in the ovary undoubtedly plays an important role in endocrine function and follicle biology. Altogether, the studies reveal unexpected diversity and heterogeneity among ovarian somatic and germ cells, highlighting the prevailing knowledge gaps in basic ovarian biology. As the most common outcome for a follicle is atresia, it is possible that part of the cell diversity relates to the biology of follicles destined to degenerate. The absence of spatial coordinates in single-cell studies further complicates the interpretation of the roles and significance of the various reported cell clusters. Accomplishing a representative ovarian single-cell atlas will require merging these studies. However, direct comparisons are challenging due to nonuniform nomenclature, differing tissue sources, varying meta-data reporting, and lack of gold standards in technical approaches. Although these reports establish a single-cell draft of adult-fertile age human ovaries, more detailed metadata and better quality reporting will be essential for the development of a robust ovarian cell atlas in health and disease.

Impact of low versus high oxygen tension on human oocyte maturation during biphasic capacitation IVM (CAPA-IVM)

PURPOSE

This study investigated the impact of low versus high oxygen tension on the oocyte maturation rate in biphasic CAPA-IVM.

METHODS

A sibling oocyte pilot study of cumulus-oocyte complexes (COCs) from participants with polycystic ovary syndrome was performed at an academic IVF center in Vietnam from November 2023 to May 2024. At collection, COCs were allocated to undergo CAPA-IVM culture with low oxygen tension (5%) or high oxygen tension (20%). Culture of COCs took place in two benchtop incubators, each equipped with commercial mix-gas bottles to establish the respective oxygen conditions. The primary outcome was the oocyte maturation rate. Secondary outcomes were rates of two-pronuclei fertilization, day-3 embryos, blastocyst formation, and good-quality embryos.

RESULTS

A total of 554 COCs from 20 participants were assigned to the low oxygen (276 COCs) or high oxygen (278 COCs) tension groups. The oocyte maturation rate was significantly lower in the low oxygen tension versus high oxygen tension group (53.6% vs. 65.8%, risk ratio 0.81, 95% confidence interval 0.71-0.94; p=0.004). The two-pronuclei fertilization rate was significantly lower in the low oxygen tension versus high oxygen tension group (61.5% vs. 72.7%, p=0.03). Numbers of day-3 embryos, blastocysts, and good-quality blastocysts were slightly, but not significantly, lower in the low oxygen tension group compared with the high oxygen tension group.

CONCLUSIONS

Low oxygen tension of 5% during both steps of biphasic CAPA-IVM reduced the number of matured oocytes and 2-pronuclei fertilized oocytes compared with the use of high oxygen tension (20%) during CAPA-IVM.

Epigenetic Alterations in Ovarian Function and Their Impact on Assisted Reproductive Technologies: A Systematic Review

Background: Epigenetic modifications have an important role in controlling ovarian function, modulating ovarian response and implantation success in Assisted Reproductive Technologies (ART). The alterations, such as DNA methylation and non-coding RNA control, have been identified as key variables regulating ovarian physiology and reproductive outcomes. This systematic review investigates the significance of epigenetic pathways in ovarian function, with an emphasis on their effect on ART success rates. Methods: A thorough search of the PubMed, Scopus, and EMBASE databases was performed to find articles published between 2015 and 2024 that investigated the connection between epigenetic changes and ovarian function in ART patients. Studies that examined miRNA expression, DNA methylation, and histone changes in follicular fluid, granulosa cells, and embryos were included. The study followed the PRISMA recommendations to guarantee scientific rigor and repeatability. The data were combined into a thorough study of epigenetic markers linked to ovarian aging, ovarian reserve, and implantation success. Results: A total of 15 studies satisfied the inclusion criteria, with substantial relationships found between distinct epigenetic markers and ovarian function. Changes in miRNA expression patterns in follicular fluid and granulosa cells were associated with oocyte maturation, ovarian reserve, and implantation potential. Women with low ovarian reserve and polycystic ovary syndrome (PCOS) have different DNA methylation patterns. MiR-27a-3p and miR-15a-5p were shown to be involved with granulosa cell malfunction and poor ovarian response, whereas global DNA hypomethylation was linked to ovarian aging and ART results. Conclusions: Epigenetic alterations affect ovarian function via pathways that control hormone signaling, follicular development, and implantation success. Further study is needed to determine the practical applicability of epigenetic biomarkers in predicting ART effectiveness and enhancing patient treatment procedures.

Artificial intelligence in in-vitro fertilization (IVF): A new era of precision and personalization in fertility treatments

In-vitro fertilization (IVF) has been a transformative advancement in assisted reproductive technology. However, success rates remain suboptimal, with only about one-third of cycles resulting in pregnancy and fewer leading to live births. This narrative review explores the potential of artificial intelligence (AI), machine learning (ML), and deep learning (DL) to enhance various stages of the IVF process. Personalization of ovarian stimulation protocols, gamete selection, and embryo annotation and selection are critical areas where AI may benefit significantly. AI-driven tools can analyze vast datasets to predict optimal stimulation protocols, potentially improving oocyte quality and fertilization rates. In sperm and oocyte quality assessment, AI can offer precise, objective analyses, reducing subjectivity and standardizing evaluations. In embryo selection, AI can analyze time-lapse imaging and morphological data to support the prediction of embryo viability, potentially aiding implantation outcomes. However, the role of AI in improving clinical outcomes remains to be confirmed by large-scale, well-designed clinical trials. Additionally, AI has the potential to enhance quality control and workflow optimization within IVF laboratories by continuously monitoring key performance indicators (KPIs) and facilitating efficient resource utilization. Ethical considerations, including data privacy, algorithmic bias, and fairness, are paramount for the responsible implementation of AI in IVF. Future research should prioritize validating AI tools in diverse clinical settings, ensuring their applicability and reliability. Collaboration among AI experts, clinicians, and embryologists is essential to drive innovation and improve outcomes in assisted reproduction. AI's integration into IVF holds promise for advancing patient care, but its clinical potential requires careful evaluation and ongoing refinement.

Noninvasive characterization of oocyte deformability in microconstrictions

Oocytes naturally present mechanical defects that hinder their development after fertilization. Thus, in the context of assisted reproduction, oocyte selection based on their mechanical properties has great potential to improve the quality of the resulting embryos and the success rate of these procedures. However, using mechanical properties as a quantifiable selective criterion requires robust and nondestructive measurement tools. This study developed a constriction-based microfluidic device that monitors the deformation of mouse oocytes under controlled pressure. The device can distinguish mechanically aberrant oocyte groups from healthy control ones. On the basis of a mathematical model, we propose that deformability measurements infer both oocyte tension and elasticity, elasticity being the most discriminating factor in our geometry. Despite force transmission during oocyte deformation, no long-term damage was observed. This noninvasive characterization of mouse oocyte deformability in microconstrictions allows for a substantial advance in assessing the mechanical properties of mammalian oocytes and has potential application as a quantifiable selective criterion in medically assisted reproduction.

Pyrroloquinoline-quinone supplementation restores ovarian function and oocyte quality in a mouse model of advanced maternal age†

Natural ovarian aging is one of the major causes for declining fertility in female animals, which has become an insurmountable issue in human reproduction clinics and assisted reproductive technology procedures. Nevertheless, the molecular basis of oocyte aging remains poorly understood, and feasible improvement strategies are unavailable. In the present study, in vivo supplementation of pyrroloquinoline-quinone effectively elevated the fecundity of reproductively aged mice by balancing hormonal secretion, harmonizing the estrus cycle, and eliminating ovarian fibrosis. Moreover, oocyte quality also increased in aged mice after pyrroloquinoline-quinone administration from various aspects, including nuclear and cytoplasmic maturation competency, fertilization capacity, and pre-implantation embryonic development potential. Transcriptomic analysis identified target pathways that might mediate pyrroloquinoline-quinone's effects in aged oocytes. Specifically, it was demonstrated that pyrroloquinoline-quinone supplementation restored the mitochondrial dynamics and lysosomal function to remove excessive reactive oxygen species and suppress apoptosis in aged oocytes. Jointly, these findings demonstrate pyrroloquinoline-quinone administration is an efficacious method to restore the compromised ovary function and damaged oocyte quality in reproductively aged mice, which might be a potential clinical therapy for women of advanced maternal age with infertility.

Elevated N-glycosylated cathepsin L impairs oocyte function and contributes to oocyte senescence during reproductive aging

Age-related declines in oocyte quality and ovarian function are pivotal contributors to female subfertility in clinical settings. Yet, the mechanisms driving ovarian aging and oocyte senescence remain inadequately understood. The present study evaluated the alterations in N-glycoproteins associated with ovarian aging and noted a pronounced elevation in N221 glycopeptides of cathepsin L (Ctsl) in the ovaries of reproductive-aged mice (8-9 months and 11-12 months) compared to younger counterparts (6-8 weeks). Subsequent analysis examined the involvement of Ctsl in oocyte aging and demonstrated a significant elevation in Ctsl levels in aged oocytes. Further, it was revealed that the overexpression of Ctsl in young oocytes substantially diminished their quality, while oocytes expressing an N221-glycosylation mutant of Ctsl did not suffer similar quality degradation. This finding implies that the N221 glycosylation of Ctsl is pivotal in modulating its effect on oocyte health. The introduction of a Ctsl inhibitor into the culture medium restored oocyte quality in aged oocytes by enhancing mitochondrial function, reducing accumulated reactive oxygen species (ROS), lowering apoptosis, and recovering lysosome capacity. Furthermore, the targeted downregulation of Ctsl using siRNA microinjection in aged oocytes enhanced fertilization capability and blastocyst formation, affirming the role of Ctsl knockdown in fostering oocyte quality and embryonic developmental potential. In conclusion, these findings underscore the detrimental effects of high expression of N-glycosylated Ctsl on oocyte quality and its contribution to oocyte senescence, highlighting it as a potential therapeutic target to delay ovarian aging and enhance oocyte viability.

The chromatin accessibility landscape of mouse oocytes during configuration transition

The transition of chromatin configuration in mammalian oocytes from a non-surrounded nucleolus (NSN) to a surrounded nucleolus (SN) is critical for acquiring the developmental competence. However, the genomic and epigenomic features underlying this process remain poorly understood. In the present study, we first establish the chromatin accessibility landscape of mouse oocytes from NSN to SN stage. Through the integrative analysis of multi-omics, we find that the establishment of DNA methylation in oocytes is independent of the dynamics of chromatin accessibility. In contrast, histone H3K4me3 status is closely associated with the dynamics of accessible regions during configuration transition. Furthermore, by focusing on the actively transcribed genes in NSN and SN oocytes, we discover that chromatin accessibility coupled with histone methylation (H3K4me3 and H3K27me3) participates in the transcriptional control during phase transition. In sum, our data provide a comprehensive resource for probing configuration transition in oocytes, and offer insights into the mechanisms determining chromatin dynamics and oocyte quality.

Effects of pentoxifylline on mouse oocytes maturation and quality in vitro

Objectives

To investigate the impact of Pentoxifylline (PTX) on the in vitro maturation (IVM) of mouse oocytes and its effect on oocyte quality.

Materials and Methods

This experimental study involved culturing mouse oocytes in an IVM medium with varying PTX concentrations (0-100 μM). Post-culture, oocytes were assessed for nuclear and cytoplasmic maturation and quality indicators, including germinal vesicle breakdown (GVBD), first polar body extrusion (PB1E), cortical granules (CGs) distribution, spindle structure, chromosome alignment, and intracellular reactive oxygen species (ROS) levels.

Results

Treatment with PTX at 10, 25, and 50 μM concentrations significantly enhanced the nuclear maturation rates of oocytes. The optimal concentration was found to be 10 μM, as it resulted in the most favorable cytoplasmic maturation, characterized by improved distribution of CGs, spindle structure, and chromosome alignment. Additionally, treatment with 10 μM PTX effectively reduced reactive oxygen species (ROS) levels.

Conclusion

PTX supplementation at specific concentrations enhances mouse oocyte maturation and quality, potentially by facilitating CG distribution, spindle integrity, and chromosome alignment and by reducing ROS production.

Which Side of the Coin Are You on Regarding Possible Postnatal Oogenesis?

It is well known that oocytes are produced during fetal development and that the total number of primary follicles is determined at birth. In humans, there is a constant loss of follicles after birth until about two years of age. The number of follicles is preserved until the resumption of meiosis at puberty and there is no renewal of the oocytes; this dogma was maintained in the last century because there were no suitable techniques to detect and obtain stem cells. However, following stem cell markers, several scientists have detected them in developing and adult human ovarian tissues, especially in the ovarian surface epithelial cells. Furthermore, many authors using different methodological strategies have indicated this possibility. This evidence has led many scientists to explore this hypothesis; there is no definitive consensus to accept this idea. Interestingly, oocyte retrieval from mature ovaries and other tissue sources of stem cells has contributed to the development of strategies for the retrieval of mature oocytes, useful for assisted reproductive technology. Here, we review the evidence and controversies on oocyte neooogenesis in adult women; in addition, we agree with the idea that this process may occur in adulthood and that its alteration may be related to various pathologies in women, such as polycystic ovary syndrome, premature ovarian insufficiency, diminished ovarian reserve and several infertility and genetic disorders.

O-GlcNAc participates in the meiosis of aging oocytes by mediating mitochondrial function

IN BRIEF

O-GlcNAc plays an important role in many age-related diseases. This study shows that O-GlcNAc participates in oocyte aging and that reducing O-GlcNAc levels in aging oocytes improves oocyte quality.

ABSTRACT

With an increase in the mean age at parturition worldwide, female reproductive aging has become a key health problem. Advanced maternal age is reflected by decreased oocyte quality; however, the molecular mechanisms of oocyte aging are uncharacterized. O-linked N-acetylglucosamine (O-GlcNAc), a dynamic posttranslational modification, plays a critical role in the development of many age-related diseases; yet, it remains unclear whether and how O-GlcNAc participates in oocyte aging. Here, we found that global O-GlcNAc was elevated in normal biological aging mice oocytes (9 months), which were characterized by meiotic maturation failure and impaired mitochondrial function. Specifically, O-GlcNAc targeted the mitochondrial fission protein dynamic-related protein 1 to mediate mitochondrial distribution in the process of aging. Using the O-GlcNAcase (OGA) pharmacological inhibitor Thiamet-G and Oga knockdown (Oga-KD) to mimic the age-related high O-GlcNAc in young oocytes from 6-8 week-old mice mimicked the phenotype of oocyte aging. Moreover, reducing O-GlcNAc levels in aging oocytes restored spindle organization to improve oocyte quality. Our results demonstrate that O-GlcNAc is a key regulator of meiotic maturation that participates in the progression of oocyte aging.

Ultra-fast vitrification and rapid elution of human oocytes: part I. germinal vesicle model validation

RESEARCH QUESTION

Can GV-oocytes serve as an effective model to test the efficacy of ultra-fast vitrification (UFV)/ rapid elution (RE) treatments to support reliable, high survival rates and sustained functionality?

DESIGN

Prospective pilot cohort studies were performed to investigate the feasibility of non-equilibration, UFV to sustain cellular integrity and development in contrast to control vitrification (CV: 10-15min ES/ 1min VS). In Phase 1, we applied a 2 × 2 factorial design (n=25-30 eggs/group) to evaluate post-warming dilution treatments: conventional multi-step (CD) versus rapid elution (RE; one-step), including an apriori fresh egg control group. Phase 1/2 focused on survival and maturation assessments, including meiotic spindle formation (Phase 2).

RESULTS

The survival of EG/DMSO treated UFV oocytes in Phase 1 and 2 was not different to spontaneous degeneration seen in the fresh IVM control groups (3.2%) but was higher than CV treated oocytes immediately post-warming (p<0.03). Of the intact GVs, no difference in IVM-MII development was detected (52.6 -58.3%) at +48h IVM across all groups. Meiotic spindle integrity of MII oocytes was normal in all treatment groups.

CONCLUSIONS

As originally reported by Gallardo (2019), non-equilibrated dehydrated human oocytes can effectively vitrify after UFV/CD treatment. We further verified the resiliency of oocytes to withstand RE treatment and continue to develop normally, like fresh GV-matured oocytes. Furthermore, we confirmed that the meiotic spindle formation and density of UFV/RE-treated GV oocytes was similar to fresh controls. Overall, the GV-model proved to be a useful resource to substantiate the promising potential of UFV technology to reliably achieve high survival and normal developmental competence in a more time efficient manner.

6-Gingerol and Astaxanthin Mitigate the Effects of Stearic Acid in Pig Oocyte Maturation

Elevated non-esterified fatty acids (NEFAs), particularly stearic acid (SA), have a deleterious effect on oocyte maturation, leading to developmental damage and reproductive issues. High SA levels disrupt metabolic processes, inducing lipotoxicity that impairs oocyte quality and contributes to reproductive failures through early embryonic losses. This research investigates the lipotoxic effects of SA and assesses the protective potential of 6-Gingerol (6-G) and Astaxanthin (AX) on porcine oocytes during in vitro maturation (IVM). Herein, 6100 cumulus-oocyte complexes (COCs) were exposed to various concentrations of SA (25-250 μM) to elucidate the concentration-dependent effect on oocyte viability, polar body extrusion (PBE) and cumulus cell expansion index (CCEI). However, the efficacy of 6-G (5-15 μM) and AX (2.5 μM) in combination with SA at 150 μM (SA6) concentration was evaluated to mitigate these adverse effects. The results indicated that SA6 substantially reduced oocyte viability, PBE and CCEI, demonstrating its toxic impact on oocyte developmental competence (p < 0.0001). Moreover, treatment with antioxidants such as SA6 + 6-G (10 μM) and SA6 + AX showed a considerable increase in viability and PBE compared to SA6 alone (p < 0.05). These findings demonstrate the importance of lipid metabolism in oocyte health, where dysregulation impairs reproductive capacity. Both 6-G and AX protected against lipotoxicity induced by SA6 while enhancing lipid homeostasis and the anti-oxidative defences necessary for maintaining cellular integrity. This study finds substantial evidence that optimising the microenvironment with specific antioxidants can improve oocyte quality and provide invaluable knowledge in reproductive technologies and fertility treatments.

Cryopreservation, cryoprotectants, and potential risk of epigenetic alteration

The cryopreservation of gametes and embryos has increased notably over the past 20 years and is now an essential part of assisted reproductive technologies (ARTs). However, because the cryopreservation process is un-physiological for human cells, gametes, and embryos, cryobiologists have suggested diverse methods to successfully cryopreserve human gametes and embryos in order to maintain their viability and assure successful pregnancy. During the first period of early development, major waves of epigenetic reprogramming-crucial for the fate of the embryo-occur. Recently, concerns relating to the increased incidence of epigenetic anomalies and genomic-imprinting disorders have been reported after ARTs and cryopreservation. Epigenetic reprogramming is particularly susceptible to environmental and un-physiological conditions such as ovarian stimulation, embryo culture, and cryopreservation that might collectively affect epigenetics dysregulation. Additionally, recent literature suggests that epigenetic and transcriptomic profiles are sensitive to the stress induced by vitrification, osmotic shock, oxidative stress, rapid temperature and pH changes, and cryoprotectants; it is therefore critical to have a more comprehensive understanding of the potential induced perturbations of epigenetic modifications that may be associated with vitrification. The aim of this paper is to present a critical evaluation of the association of gamete and embryo cryopreservation, use of cryoprotectants, and epigenetic dysregulations with potential long-term consequences for offspring health.

Stereological study of organelle distribution in human mature oocytes

The ultrastructure of human oocytes has been described only qualitatively. To offer a precise organelle spatial distribution and organelle volume during the main maturation stages, we previously conducted stereological studies on prophase-I (GV) and metaphase-I (MI) oocytes, and here we present results on metaphase-II (MII) oocytes. Five donor oocytes from different donors were processed for transmission electron microscopy, and quantification of organelle distribution was performed using point-counting stereology. Statistical tests compared the means of the relative volumes occupied by organelles among oocyte regions. The most abundant organelles were elements of the smooth endoplasmic reticulum (SER), such as SER small vesicles, SER medium vesicles, SER large vesicles and SER isolated tubules, along with mitochondria, followed by SER tubular aggregates, cortical vesicles and lysosomes. Significant differences between oocyte regions were found for lysosomes, cortical vesicles and SER large vesicles. Comparisons of MII oocytes to previous findings in GV and MI oocytes evidenced specific patterns of organelle distribution and relative volumes. This final evaluation thus enables to track organelle spatial reorganization across oocyte stages, which, in addition to gathered knowledge, may be useful to assist in improvements of stimulation protocols, in-vitro maturation media and cryopreservation techniques.

Improved low-invasive mRNA electroporation method into immature mouse oocytes visualizes protein dynamics during development†

One of the major causes of oocyte quality deterioration, chromosome segregation abnormalities manifest mainly during meiosis I, which occurs before and during ovulation. However, currently, there is a technical limitation in the introduction of mRNA into premature oocytes without impairing embryonic developmental ability. In this study, we established a low-invasive electroporation (EP) method to introduce mRNA into pre-ovulatory, germinal vesicle (GV) mouse oocytes in an easier manner than the traditional microinjection method. The EP method with an optimized impedance value resulted in the efficient introduction of mRNAs encoding enhanced green fluorescent protein (EGFP) into the GV oocytes surrounded by cumulus cells at a survival rate of 95.0%. Furthermore, the introduction of histone H2B-EGFP mRNA into the GV oocytes labeled most of the oocytes without affecting the blastocyst development rate, indicating the feasibility of the visualization of oocyte chromosomal dynamics that enable us to assay chromosomal integrity in oocyte maturation and cell count in embryonic development. The establishment of this EP method offers extensive assays to select pre-implantation embryos and enables the surveying of essential factors for mammalian oocyte quality determination.

Beyond simple tails: poly(A) tail-mediated RNA epigenetic regulation

The poly(A) tail is an essential structural component of mRNA required for the latter's stability and translation. Recent technologies have enabled transcriptome-wide profiling of the length and composition of poly(A) tails, shedding light on their overlooked regulatory capacities. Notably, poly(A) tails contain not only adenine but also uracil, cytosine, and guanine residues. These findings strongly suggest that poly(A) tails could encode a wealth of regulatory information, similar to known reversible RNA chemical modifications. This review aims to succinctly summarize our current knowledge on the composition, dynamics, and regulatory functions of RNA poly(A) tails. Given their capacity to carry rich regulatory information beyond the genetic code, we propose the concept of 'poly(A) tail epigenetic information' as a new layer of RNA epigenetic regulation.

New insights into oocyte cytoplasmic lattice-associated proteins

Oocyte maturation and preimplantation embryo development are critical to successful pregnancy outcomes and the correct establishment and maintenance of genomic imprinting. Thanks to novel technologies and omics studies in human patients and mouse models, the importance of the proteins associated with the cytoplasmic lattices (CPLs), highly abundant structures found in the cytoplasm of mammalian oocytes and preimplantation embryos, in the maternal to zygotic transition is becoming increasingly evident. This review highlights the recent discoveries on the role of these proteins in protein storage and other oocyte cytoplasmic processes, epigenetic reprogramming, and zygotic genome activation (ZGA). A better comprehension of these events may significantly improve clinical diagnosis and pave the way for targeted interventions aiming to correct or mitigate female fertility issues and genomic imprinting disorders.

Oocyte Competence, Embryological Outcomes and miRNA Signature of Different Sized Follicles from Poor Responder Patients

Poor ovarian response (POR) patients often face the risk of not having enough competent oocytes. Then, aspirating small follicles could serve as a strategy to increase their number. Many efforts have been addressed to associate follicular size with oocyte competence, but results are controversial. Therefore, our study aimed to evaluate oocyte maturation and developmental competence, along with a non-invasive oocyte-maturation-related miRNA signature in oocytes retrieved from both large and small follicles. A total of 178 follicles, from 31 POR patients, were aspirated and measured on the day of ovarian puncture. Follicular diameters, oocyte collection, oocyte maturation, fertilization, blastocysts, and good-quality blastocyst rates were recorded. Simultaneously, follicular fluids were collected to quantify their miRNA expression. The efficacy of oocyte retrieval along with oocyte maturation, fertilization, and blastulation rates tended to increase with follicular size, but few significant differences were found. Despite there being significantly more collected oocytes from follicles > 11.5 mm compared to follicles ≤ 11.5 mm (p < 0.05), oocytes from the latter were also mature, with no significant differences in the miRNA signature, but only those > 13.5 mm demonstrated developmental competence. In conclusion, 11.5 mm follicles can produce mature oocytes, but only those larger than 13.5 mm yielded transferable embryos.

Innovations in 3D ovarian and follicle engineering for fertility preservation and restoration

In-vitro maturation (IVM) is the process of cultivating early-stage follicles from the primordial to the antral stage and facilitating the maturation of oocytes outside the body within a supportive environment. This intricate procedure requires the careful coordination of various factors to replicate the natural ovarian conditions. Advanced techniques for IVM are designed to mimic the natural ovarian environment and enhance the development of follicles. Three-dimensional (3D) culture systems provide a more biologically relevant setting for follicle growth compared to traditional two-dimensional (2D) cultures. Traditional culture systems, often fail to support the complex process of follicle development effectively. However, modern engineered reproductive tissues and culture systems are making it possible to create increasingly physiological in-vitro models of folliculogenesis. These innovative methods are enabling researchers and clinicians to better replicate the dynamic and supportive environment of the ovary, thereby improving the outcomes of IVM offering new hope for fertility preservation and treatment. This paper focuses on the routine 3D culture, and innovative 3D culture of ovary and follicles, including a tissue engineering scaffolds, microfluidic (dynamic) culture system, organ-on-chip models, EVATAR system, from a clinical perspective to determine the most effective approach for achieving in-vitro maturation of follicles. These techniques provide critical support for ovarian function in various ovarian-associated disorders, including primary ovarian insufficiency (POI), premature ovarian failure (POF), ovarian cancer, and age-related infertility.

Ketoconazole blocks progesterone production without affecting other parameters of cumulus-oocyte complex maturation

Ketoconazole (KTZ) is widely used as a fungicide, but it is also known to target steroid hormone formation which may affect female reproductive health. Our study aims to investigate the effects of KTZ on in vitro matured bovine cumulus-oocyte complexes (COCs), as a model for female reproductive toxicity. Cumulus cells of in vitro maturing COCs produce progesterone and pregnenolone, but exposure to 10-6 M KTZ effectively blocked the synthesis of these hormones. Exposure to lower concentrations of KTZ (i.e. 10-7 M and 10-8 M) had no such effect on steroidogenesis compared to the 0.1 % v/v DMSO vehicle control. Classical parameters of in vitro COC maturation, such as oocyte nuclear maturation to the metaphase II stage and expansion of the cumulus investment, were not affected by any KTZ concentration tested. Apoptosis and necrosis levels were also not altered in cumulus cells or oocytes exposed to KTZ. Moreover, oocytes exposed to KTZ during maturation showed normal cleavage and early embryo development up to day 8 post fertilization; albeit a statistically significant decrease was observed in day 8 blastocysts produced from oocytes exposed to the lowest concentration of 10-8 M KTZ. When unexposed mature oocytes were fertilized, followed by embryo culture for 8 days under KTZ exposure, no adverse effects in embryo cleavage and blastocyst formation were observed. In conclusion, KTZ has no major impact on in vitro bovine oocyte maturation and blastocyst formation in our study, even at concentrations blocking steroidogenesis.

Assessing the developmental competence of oocytes matured following rescue in vitro maturation: a systematic review and meta-analysis

PURPOSE

To assess the developmental competence of oocytes matured following rescue in vitro maturation (IVM).

METHODS

PubMed, EmBASE, and SCOPUS were systematically searched for peer-reviewed original papers using relevant keywords and Medical Subject Heading terms. Study quality was assessed using the Newcastle-Ottawa Scale. Odds ratios with a 95% confidence interval were calculated by applying a random effects model. The primary outcomes were fertilization and blastulation rates. Secondary outcomes included abnormal fertilization, cleavage, euploidy, clinical pregnancy, and live-birth rates.

RESULT

Twenty-four studies were included in the meta-analysis. The oocytes matured following rescue IVM showed significantly reduced fertilization, cleavage, blastulation, and clinical pregnancy rates compared to sibling in vivo-matured oocytes. No significant differences were found for the euploidy and live-birth rates in euploid blastocyst transfer. In poor responders, a reduced fertilization rate was observed using in vitro-matured GV but not with in vitro-matured MI. A reduced cleavage rate in MI matured overnight compared to < 6 incubation hours was found.

CONCLUSION

Our results showed compromised developmental competence in oocytes matured following rescue IVM. However, in poor responders, rescue IVM could maximize the efficiency of the treatment. Notably, our data suggests using in vitro MI matured within 6 incubation hours.

CLINICAL TRIAL REGISTRATION NUMBER

CRD42023467232.

MIB2 Functions in Oocyte Meiosis by Modulating Chromatin Configuration

Chromatin configuration serves as a principal indicator of GV (germinal vesicle)-stage oocyte quality. However, the underlying mechanisms governing the chromatin configuration transition from NSN (non-surrounded nucleolus) to SN (surrounded nucleolus) remain unclear. In this study, by conducting a quantitative proteomic analysis, we identified an increased expression of the MIB2 (MIB E3 ubiquitin protein ligase 2) protein in SN oocytes. Specific depletion of MIB2 in SN oocytes not only leads to severe disruption of the meiotic apparatus and a higher incidence of aneuploidy but also adversely affects meiotic maturation and early embryo development. Notably, overexpression of MIB2 in NSN oocytes facilitates the chromatin configuration transition. Meantime, we observed that forced expression of MIB2 in NSN oocytes significantly mitigates spindle/chromosome disorganization and aneuploidy. In summary, our results suggest that chromatin configuration transition regulated by MIB2 is crucial for oocytes to acquire developmental competence.

Maternal mRNA deadenylation is defective in in vitro matured mouse and human oocytes

Oocyte in vitro maturation is a technique in assisted reproductive technology. Thousands of genes show abnormally high expression in in vitro maturated metaphase II (MII) oocytes compared to those matured in vivo in bovines, mice, and humans. The mechanisms underlying this phenomenon are poorly understood. Here, we use poly(A) inclusive RNA isoform sequencing (PAIso-seq) for profiling the transcriptome-wide poly(A) tails in both in vivo and in vitro matured mouse and human oocytes. Our results demonstrate that the observed increase in maternal mRNA abundance is caused by impaired deadenylation in in vitro MII oocytes. Moreover, the cytoplasmic polyadenylation of dormant Btg4 and Cnot7 mRNAs, which encode key components of deadenylation machinery, is impaired in in vitro MII oocytes, contributing to reduced translation of these deadenylase machinery components and subsequently impaired global maternal mRNA deadenylation. Our findings highlight impaired maternal mRNA deadenylation as a distinct molecular defect in in vitro MII oocytes.

An Update on Physiopathological Roles of Akt in the ReprodAKTive Mammalian Ovary

The phosphoinositide 3-kinase (PI3K)/Akt pathway is a key signaling cascade responsible for the regulation of cell survival, proliferation, and metabolism in the ovarian microenvironment. The optimal finetuning of this pathway is essential for physiological processes concerning oogenesis, folliculogenesis, oocyte maturation, and embryo development. The dysregulation of PI3K/Akt can impair molecular and structural mechanisms that will lead to follicle atresia, or the inability of embryos to reach later stages of development. Due to its pivotal role in the control of cell proliferation, apoptosis, and survival mechanisms, the dysregulation of this molecular pathway can trigger the onset of pathological conditions. Among these, we will focus on diseases that can harm female fertility, such as polycystic ovary syndrome and premature ovarian failure, or women's general health, such as ovarian cancer. In this review, we report the functions of the PI3K/Akt pathway in both its physiological and pathological roles, and we address the existing application of inhibitors and activators for the balancing of the molecular cascade in ovarian pathological environments.

Multiple intersecting pathways are involved in CPEB1 phosphorylation and regulation of translation during mouse oocyte meiosis

The RNA-binding protein cytoplasmic polyadenylation element binding 1 (CPEB1) plays a fundamental role in regulating mRNA translation in oocytes. However, the specifics of how and which protein kinase cascades modulate CPEB1 activity are still controversial. Using genetic and pharmacological tools, and detailed time courses, we have re-evaluated the relationship between CPEB1 phosphorylation and translation activation during mouse oocyte maturation. We show that both the CDK1/MAPK and AURKA/PLK1 pathways converge on CPEB1 phosphorylation during prometaphase of meiosis I. Only inactivation of the CDK1/MAPK pathway disrupts translation, whereas inactivation of either pathway alone leads to CPEB1 stabilization. However, CPEB1 stabilization induced by inactivation of the AURKA/PLK1 pathway does not affect translation, indicating that destabilization and/or degradation is not linked to translational activation. The accumulation of endogenous CCNB1 protein closely recapitulates the translation data that use an exogenous template. These findings support the overarching hypothesis that the activation of translation during prometaphase in mouse oocytes relies on a CDK1/MAPK-dependent CPEB1 phosphorylation, and that translational activation precedes CPEB1 destabilization.

Evaluation of telomere length and telomerase activity on predicting in vitro fertilization treatment outcomes

The current article is a literature review aiming to provide an overview of the existing knowledge on the association between telomere length and telomerase activity and in vitro fertilization. Recently, telomeres have been used as an effective biomarker to determine biological age, which may differ from chronological age due to genetic, lifestyle, and environmental factors. Cellular senescence, along with other exogenous and mainly environmental factors, can enhance telomere wear, further shortening their ends and may also affect reproductive aging. IVF is a common fertility treatment caused by female reasons (age, ovulation disorders, damaged or blocked fallopian tubes, endometriosis), male reasons (low sperm quantity or quality), or unexplained infertility. A growing number of studies have proposed a relationship between telomere length and telomerase activity and IVF success and have suggested their use as candidate biomarkers for IVF outcome. Nevertheless, additional studies are necessary to be conducted, in order to clarify the possible implication of telomeres in IVF and to evaluate their possible role as valuable predictors of IVF result.

FGF2, LIF, and IGF-1 supplementation improves mouse oocyte in vitro maturation via increased glucose metabolism†

Chemically defined oocyte maturation media supplemented with FGF2, LIF, and IGF-1 (FLI medium) enabled significantly improved oocyte quality in multiple farm animals, yet the molecular mechanisms behind such benefits were poorly defined. Here, we first demonstrated that FLI medium enhanced mouse oocyte quality assessed by blastocyst formation after in vitro fertilization and implantation and fetal development after embryo transfer. We then analyzed the glucose concentrations in the spent media; reactive oxygen species concentrations; mitochondrial membrane potential; spindle morphology in oocytes; and the abundance of transcripts of endothelial growth factor-like factors, cumulus expansion factors, and glucose metabolism-related genes in cumulus cells. We found that FLI medium enabled increased glucose metabolism through glycolysis, pentose phosphate pathway, and hexosamine biosynthetic pathway, as well as more active endothelial growth factor-like factor expressions in cumulus cells, resulting in improved cumulus cell expansion, decreased spindle abnormality, and overall improvement in oocyte quality. In addition, the activities of MAPK1/3, PI3K/AKT, JAK/STAT3, and mTOR signaling pathways in cumulus cells were assessed by the phosphorylation of MAPK1/3, AKT, STAT3, and mTOR downstream target RPS6KB1. We demonstrated that FLI medium promoted activations of all these signaling pathways at multiple different time points during in vitro maturation.

Impact of oxygen tension during in vitro maturation: a sibling-oocyte prospective double-blinded study

OBJECTIVE

To determine whether oxygen (O2) tension (20% vs. 5%) has an impact on oocyte maturation rates and morphology during in vitro maturation (IVM).

DESIGN

A prospective, observational, monocentric, sibling-oocyte study.

SETTING

University Hospital.

PATIENTS

A total of 143 patients who underwent IVM for fertility preservation purposes from November 2016 to April 2021 were analyzed. Patients were included when ≥2 cumulus-oocyte complexes (COCs) were retrieved. The cohort of COCs obtained for each patient was randomly split into two groups: group 20% O2 and group 5% O2.

INTERVENTION

Cumulus-oocyte complexes were incubated for 48 hours either under 5% O2 or 20% O2. After 24 and 48 hours of culture, every oocyte was assessed for maturity and morphology, to estimate oocyte quality. Morphology was evaluated considering six parameters (shape, size, ooplasm, perivitelline space, zona pellucida, and polar body characteristics), giving a total oocyte score ranging from -6 to +6.

MAIN OUTCOME MEASURES

Maturation rates and total oocyte scores were compared using paired-sample analysis between group 20% O2 and group 5% O2.

RESULTS

Patient median age was 31.4 [28.1-35.2] years-old. The mean serum antimüllerian hormone levels and antral follicle count were 3.2 ± 2.3 ng/mL and 27.2 ± 16.0 follicles, respectively. A mean of 10.7 COCs per cycle were retrieved, leading to 6.1 ± 2.4 metaphase II oocytes vitrified (total maturation rate = 57.3%; 991 metaphase II oocytes/1,728 COCs). A total of 864 COCs were included in each group. Oocyte maturation rates were not different between the two groups (group 20% O2: 56.82% vs. group 5% O2: 57.87%, respectively). Regarding oocyte morphology, the mean total oocyte score was significantly higher in group 5% O2 compared with group 20% O2 (3.44 ± 1.26 vs. 3.16 ± 1.32, P=.014).

CONCLUSION

As culture under low O2 tension (5% O2) improves oocyte morphology IVM, our results suggest that culture under hypoxia should be standardized. Additional studies are warranted to assess the impact of O2 tension on oocyte maturation and the benefit of IVM under low O2 tension for embryo culture after utilization of frozen material.

Meiotic and developmental competence of growing pig oocytes derived from small antral follicles is enhanced in culture medium containing FGF2, LIF, and IGF1 (FLI medium)

BACKGROUND

Oocytes of large animal species isolated from small ovarian follicles (< 2 mm) are less competent to support early embryonic development after in vitro maturation and fertilization than their counterparts isolated from medium-sized and preovulatory follicles. This study aimed to assess the effect of a new maturation medium containing FGF2, LIF, and IGF1 (FLI medium) on the meiotic and developmental competence of pig cumulus-oocytes complexes (COCs) derived from the small and medium-sized follicles.

METHODS

The growing oocytes were isolated from 1 to 2 (small follicle; SF) and the fully-grown ones from 3 to 6 (large follicle; LF) mm follicles and matured in a control M199 medium with gonadotropins and EGF and the FLI medium enriched by the triplet of growth factors. The matured oocytes were parthenogenetically activated and cultured to the blastocyst stage. Chromatin configuration before and during the culture and MAP kinase activity were assessed in the oocytes. Finally, the expression of cumulus cell genes previously identified as markers of oocyte quality was assessed.

RESULTS

The maturation and blastocyst rates of oocytes gained from LF were significantly higher than that from SF in the control medium. In contrast, similar proportions of oocytes from LF and SF completed meiosis and developed to blastocysts when cultured in FLI. Most of the oocytes freshly isolated from SF possessed germinal vesicles with fine filaments of chromatin (GV0) or chromatin surrounding the nucleolus (GVI; 30%); the oocytes from LF were mainly in GVI (or GVII) exhibiting a few small lumps of chromatin beneath the nuclear membrane. When cultured in the FLI medium for 16 h, an acceleration of the course of maturation in oocytes both from SF and LF compared to the control medium was observed and a remarkable synchrony in the course of chromatin remodeling was noticed in oocytes from SF and LF.

CONCLUSIONS

This work demonstrates that the enrichment of culture medium by FGF2, LIF, and IGF1 can enhance the meiotic and developmental competence of not only fully-grown, but also growing pig oocytes and significantly thus expanding the number of oocytes available for various assisted reproductive technology applications.

The role of zygotic genome activation in genetic-related reproductive medicine: Technological perspective, religious and bioethical concerns, challenges and benefits

Zygotic Genome Activation (ZGA) is a crucial developmental milestone in early embryogenesis, marking the transition from maternal to embryonic control of development. This process, which varies in timing across species, involves the activation of the embryonic genome, paving the way for subsequent cell differentiation and organismal development. Recent advances in genomics and reproductive medicine have highlighted the potential of ZGA in the realm of genetic screening, providing a window into the genetic integrity of the developing embryo at its earliest stages. The intersection of ZGA and genetic screening primarily emerges in the context of preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS). These techniques, often employed during assisted reproductive technologies, aim to detect potential genetic abnormalities or chromosomal imbalances before embryo implantation. Given that ZGA represents the onset of embryonic gene expression, understanding its intricacies can significantly enhance the accuracy and predictive power of these screening processes. With the advent of next-generation sequencing and other high-throughput genomic techniques, detailed mapping of the transcriptomic changes during ZGA has become feasible. Such advancements have deepened our insights into the dynamics of early embryonic development and the onset of genetic disorders. As our knowledge in this realm expands, it promises to revolutionize our capabilities in detecting, understanding, and potentially rectifying genetic anomalies at the earliest stages of human life, thereby optimizing reproductive outcomes.

A genome-wide perspective of the maternal mRNA translation program during oocyte development

Transcriptional and post-transcriptional regulations control gene expression in most cells. However, critical transitions during the development of the female gamete relies exclusively on regulation of mRNA translation in the absence of de novo mRNA synthesis. Specific temporal patterns of maternal mRNA translation are essential for the oocyte progression through meiosis, for generation of a haploid gamete ready for fertilization and for embryo development. In this review, we will discuss how mRNAs are translated during oocyte growth and maturation using mostly a genome-wide perspective. This broad view on how translation is regulated reveals multiple divergent translational control mechanisms required to coordinate protein synthesis with progression through the meiotic cell cycle and with development of a totipotent zygote.

Whole transcriptome screening for novel genes involved in meiosis and fertility in Drosophila melanogaster

Reproductive success requires the development of viable oocytes and the accurate segregation of chromosomes during meiosis. Failure to segregate chromosomes properly can lead to infertility, miscarriages, or developmental disorders. A variety of factors contribute to accurate chromosome segregation and oocyte development, such as spindle assembly and sister chromatid cohesion. However, many proteins required for meiosis remain unknown. In this study, we aimed to develop a screening pipeline for identifying novel meiotic and fertility genes using the genome of Drosophila melanogaster. To accomplish this goal, genes upregulated within meiotically active tissues were identified. More than 240 genes with no known function were silenced using RNA interference (RNAi) and the effects on meiosis and fertility were assessed. We identified 94 genes that when silenced caused infertility and/or high levels of chromosomal nondisjunction. The vast majority of these genes have human and mouse homologs that are also poorly studied. Through this screening process, we identified novel genes that are crucial for meiosis and oocyte development but have not been extensively studied in human or model organisms. Understanding the function of these genes will be an important step towards the understanding of their biological significance during reproduction.

Alternative cleavage and polyadenylation of the Ccnb1 mRNA defines accumulation of cyclin protein during the meiotic cell cycle

Progression through the mitotic and meiotic cell cycle is driven by fluctuations in the levels of cyclins, the regulatory subunits controlling the localization and activity of CDK1 kinases. Cyclin levels are regulated through a precise balance of synthesis and degradation. Here we demonstrate that the synthesis of Cyclin B1 during the oocyte meiotic cell cycle is defined by the selective translation of mRNA variants generated through alternative cleavage and polyadenylation (APA). Using gene editing in mice, we introduced mutations into the proximal and distal polyadenylation elements of the 3' untranslated region (UTR) of the Ccnb1 mRNA. Through in vivo loss-of-function experiments, we demonstrate that the translation of mRNA with a short 3' UTR specifies Cyclin B1 protein levels that set the timing of meiotic re-entry. In contrast, translation directed by a long 3' UTR is necessary to direct Cyclin B1 protein accumulation during the MI/MII transition. These findings establish that the progression through the cell cycle is dependent on the selective translation of multiple mRNA variants generated by APA.

Multiple intersecting pathways are involved in the phosphorylation of CPEB1 to activate translation during mouse oocyte meiosis

The RNA-binding protein cytoplasmic polyadenylation element binding 1 (CPEB1) plays a fundamental role in the regulation of mRNA translation in oocytes. However, the nature of protein kinase cascades modulating the activity of CPEB1 is still a matter of controversy. Using genetic and pharmacological tools and detailed time courses, here we have reevaluated the relationship between CPEB1 phosphorylation and the activation of translation during mouse oocyte maturation. We show that both the CDK1/MAPK and AURKA/PLK1 pathways converge on the phosphorylation of CPEB1 during prometaphase. Only inactivation of the CDK1/MAPK pathway disrupts translation, while inactivation of either pathway leads to CPEB1 stabilization. However, stabilization of CPEB1 induced by inactivation of the AURKA/PLK1 does not affect translation, indicating that destabilization/degradation can be dissociated from translational activation. The accumulation of the endogenous CCNB1 protein closely recapitulates the translation data. These findings support the overarching hypothesis that the activation of translation in prometaphase in mouse oocytes relies on a CDK1-dependent CPEB1 phosphorylation, and this translational activation precedes CPEB1 destabilization.

Maturation and culture affect the metabolomic profile of oocytes and follicular cells in young and old mares

Introduction: Oocytes and follicular somatic cells within the ovarian follicle are altered during maturation and after exposure to culture in vitro. In the present study, we used a nontargeted metabolomics approach to assess changes in oocytes, cumulus cells, and granulosa cells from dominant, follicular-phase follicles in young and old mares. Methods: Samples were collected at three stages associated with oocyte maturation: (1) GV, germinal vesicle stage, prior to the induction of follicle/oocyte maturation in vivo; (2) MI, metaphase I, maturing, collected 24 h after induction of maturation in vivo; and (3) MIIC, metaphase II, mature with collection 24 h after induction of maturation in vivo plus 18 h of culture in vitro. Samples were analyzed using gas and liquid chromatography coupled to mass spectrometry only when all three stages of a specific cell type were obtained from the same mare. Results and Discussion: Significant differences in metabolite abundance were most often associated with MIIC, with some of the differences appearing to be linked to the final stage of maturation and others to exposure to culture medium. While differences occurred for many metabolite groups, some of the most notable were detected for energy and lipid metabolism and amino acid abundance. The study demonstrated that metabolomics has potential to aid in optimizing culture methods and evaluating cell culture additives to support differences in COCs associated with maternal factors.

Transient suppression of Wnt signaling in poor-quality buffalo oocytes improves their developmental competence

Introduction

One of the most evolutionary conserved communication systems, the Wnt signaling pathway is a major gene regulatory pathway that affects the developmental competence of oocytes and regulates most embryonic developmental processes. The present study was undertaken to modulate the canonical Wnt (Wingless/integration) signaling pathway in the poor-quality (colorless cytoplasm after Brilliant Cresyl Blue staining, BCB-) buffalo cumulus-oocyte complexes (COCs) to improve their in vitro maturation (IVM) and embryo production (IVEP) rates.

Methods

The expression of key Wnt pathway genes was initially assessed in the good (blue cytoplasm after Brilliant Cresyl Blue staining, BCB+) and poor quality (BCB-) buffalo COCs to establish a differential activity of the Wnt pathway. The BCB- COCs were supplemented with the Wnt pathway inhibitor, Dickkopf-related protein 1 (DKK1) and later subjected to IVM and IVEP along with the BCB+ and BCB- controls. The cumulus expansion index (CEI), rate of nuclear maturation (mean percentage of oocytes in the MII stage) and embryo production, and the expression of developmentally important genes were evaluated to assess the effect of Wnt pathway inhibition on the development competence of these poor-quality oocytes.

Results

The Wnt pathway genes exhibited a significantly higher expression (p < 0.05) in the poor-quality BCB- oocytes compared to the good-quality BCB+ oocytes during the early maturation stages. The supplementation of BCB- COCs with 100 ng/mL DKK1 effectively inhibited the expression of the key mediators of the Wnt pathway (β-catenin and dishevelled homolog 1, DVL1). DKK1 supplemented BCB- COCs exhibited significantly improved cytoplasmic and nuclear maturation indices, development rates and significantly elevated expression (p < 0.05) of genes implicated in germinal vesicle breakdown (GVBD) and embryonic genome activation (EGA) vis-à-vis BCB- control COCs.

Conclusion

These data indicate that inhibition of the Wnt pathway during the initial course of oocyte maturation can improve the development competence of poor-quality buffalo oocytes.

Single-Cell Transcriptome Analysis Reveals Development-Specific Networks at Distinct Synchronized Antral Follicle Sizes in Sheep Oocytes

The development of the ovarian antral follicle is a complex, highly regulated process. Oocytes orchestrate and coordinate the development of mammalian ovarian follicles, and the rate of follicular development is governed by a developmental program intrinsic to the oocyte. Characterizing oocyte signatures during this dynamic process is critical for understanding oocyte maturation and follicular development. Although the transcriptional signature of sheep oocytes matured in vitro and preovulatory oocytes have been previously described, the transcriptional changes of oocytes in antral follicles have not. Here, we used single-cell transcriptomics (SmartSeq2) to characterize sheep oocytes from small, medium, and large antral follicles. We characterized the transcriptomic landscape of sheep oocytes during antral follicle development, identifying unique features in the transcriptional atlas, stage-specific molecular signatures, oocyte-secreted factors, and transcription factor networks. Notably, we identified the specific expression of 222 genes in the LO, 8 and 6 genes that were stage-specific in the MO and SO, respectively. We also elucidated signaling pathways in each antral follicle size that may reflect oocyte quality and in vitro maturation competency. Additionally, we discovered key biological processes that drive the transition from small to large antral follicles, revealing hub genes involved in follicle recruitment and selection. Thus, our work provides a comprehensive characterization of the single-oocyte transcriptome, filling a gap in the mapping of the molecular landscape of sheep oogenesis. We also provide key insights into the transcriptional regulation of the critical sizes of antral follicular development, which is essential for understanding how the oocyte orchestrates follicular development.