Making a good egg: human oocyte health, aging, and in vitro development.

Mammalian eggs (oocytes) are formed during fetal life and establish associations with somatic cells to form primordial follicles that create a store of germ cells (the primordial pool). The size of this pool is influenced by key events during the formation of germ cells and by factors that influence the subsequent activation of follicle growth. These regulatory pathways must ensure that the reserve of oocytes within primordial follicles in humans lasts for up to 50 years, yet only approximately 0.1% will ever be ovulated with the rest undergoing degeneration. This review outlines the mechanisms and regulatory pathways that govern the processes of oocyte and follicle formation and later growth, within the ovarian stroma, through to ovulation with particular reference to human oocytes/follicles. In addition, the effects of aging on female reproductive capacity through changes in oocyte number and quality are emphasized, with both the cellular mechanisms and clinical implications discussed. Finally, the details of current developments in culture systems that support all stages of follicle growth to generate mature oocytes in vitro and emerging prospects for making new oocytes from stem cells are outlined.

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.

The RNA m6A Reader YTHDF2 Is Essential for the Post-transcriptional Regulation of the Maternal Transcriptome and Oocyte Competence.

YTHDF2 binds and destabilizes N6-methyladenosine (m6A)-modified mRNA. The extent to which this branch of m6A RNA-regulatory pathway functions in vivo and contributes to mammalian development remains unknown. Here we find that YTHDF2 deficiency is partially permissive in mice and results in female-specific infertility. Using conditional mutagenesis, we demonstrate that YTHDF2 is autonomously required within the germline to produce MII oocytes that are competent to sustain early zygotic development. Oocyte maturation is associated with a wave of maternal RNA degradation, and the resulting relative changes to the MII transcriptome are integral to oocyte quality. The loss of YTHDF2 results in the failure to regulate transcript dosage of a cohort of genes during oocyte maturation, with enrichment observed for the YTHDF2-binding consensus and evidence of m6A in these upregulated genes. In summary, the m6A-reader YTHDF2 is an intrinsic determinant of mammalian oocyte competence and early zygotic development.

Unveiling the impact of DNA methylation machinery: Dnmt1 and Dnmt3a in orchestrating oocyte development and cellular homeostasis.

DNA methylation can be considered the most prominent in controlling the gene expression responsible for the balance between cell proliferation and cell death. In this study, we aimed to analyze the distinct contributions of Dnmt1 and Dnmt3a enzymes in oocyte maturation, survival, autophagy, reactive oxygen species (ROS) production, and compensation capacity of Dnmt3b and Dnmt3l enzymes in mouse oocytes. Following confirming the suppression of Dnmt1or Dnmt3a through siRNA application, the assessment involved immunofluorescence staining for Dnmts, 5mC, p62, and ROS levels. Cell death rates showed a noticeable increase while oocyte maturation rates exhibited significant reduction. Global DNA methylation showed a decline, concomitant with elevated p62 and ROS levels upon Dnmt1 or Dnmt3a knockdown. Remarkably, silencing of Dnmt1 led to an upsurge in Dnmt3a expression, whereas Dnmt3a knockdown triggered an increase in Dnmt1 levels. Furthermore, Dnmt3l expression exhibited a notable decrease after silencing of either Dnmt1 or Dnmt3a, while Dnmt3b levels remained comparable between control and siRNA-treated groups. Collectively, this study underscores the pivotal roles of Dnmt1 and Dnmt3a in orchestrating various facets of oocyte development, encompassing maturation, survival, autophagy, and ROS production. These findings offer valuable insights into the intricate regulatory network governed by DNA methylation machinery within the context of oocyte physiology.

The potential effect of melatonin on in vitro oocyte maturation and embryo development in animals.

Melatonin is a hormone mainly secreted by the pineal gland during the circadian cycle, with low levels during the daytime and prominent levels during the night. It is involved in numerous physiological functions including the immune system, circadian rhythm, reproduction, fertilization, and embryo development. In addition, melatonin exerts anti-inflammatory and antioxidant effects inside the body by scavenging reactive oxygen and reactive nitrogen species, increasing antioxidant defenses, and blocking the transcription factors of pro-inflammatory cytokines. Its protective activity has been reported to be effective in various reproductive biotechnological processes, including in vitro maturation, embryo development, and survival rates. In this comprehensive review, our objective is to summarize and debate the potential mechanism and impact of melatonin on oocyte maturation and embryo development through various developmental routes in different mammalian species.

Role of miRNAs in glucose metabolism of mouse cumulus cells†.

It is known that the oocyte has a limited capacity to acquire and metabolize glucose, and it must rely on cumulus cells (CCs) to take up glucose and produce pyruvate for use to produce ATP through oxidative phosphorylation. We therefore propose that miRNAs might regulate glucose metabolism (GM) in CCs and might be used as markers for oocyte quality assessment. Here, mouse CC models with impaired glycolysis or pentose phosphate pathway (PPP) were established, and miRNAs targeting the key enzymes in glycolysis/PPP were predicted using the miRNA target prediction databases. Expression of the predicted miRNAs was compared between CCs with normal and impaired glycolysis/PPP to identify candidate miRNAs. Function of the candidate miRNAs was validated by transfecting CCs or cumulus-oocyte-complexes (COCs) with miRNA inhibitors and observing effects on glucose metabolites of CCs and on competence of oocytes. The results validated that miR-23b-3p, let-7b-5p, 34b-5p and 145a-5p inhibited glycolysis, and miR-24-3p, 3078-3p,183-5p and 7001-5p inhibited PPP of CCs. Our observation using a more physiologically relevant model (intact cultured COCs) further validated the four glycolysis-targeting miRNAs we identified. Furthermore, miR-let-7b-5p, 34b-5p and 145a-5p may also inhibit PPP, as they decreased the production of glucose-6-phosphate. In conclusion, miRNAs play critical roles in GM of CCs and may be used as markers for oocyte quality assessment. Summary sentence:  We identified and validated eight new miRNAs that inhibit glycolysis and/or pentose phosphate pathways in cumulus cells (CCs) suggesting that miRNAs play critical roles in glucose metabolism of CCs and may be used for oocyte quality markers.

Antioxidant sericin averts the disruption of oocyte-follicular cell communication triggered by oxidative stress.

Antioxidants are free radical scavengers that increase oocyte quality and improve female fertility by suppressing oxidative stress. However, the related mechanisms remain unclear. The present study was designed to examine whether a reduction of oxidative stress from using the antioxidant sericin led to expanded cumulus cell (CC)-oocyte communication and oocyte developmental acquisition in a bovine model. We found that cumulus-oocyte complexes (COCs) matured in the presence of sericin showed a significantly increased oocyte meiotic maturation rate (P < 0.01) and accelerated subsequent blastocyst formation, as more blastocysts were found at the hatched stage (P < 0.05) compared to that in the control group. In contrast to the control group, sericin suppressed H2O2 levels in COCs, resulting in a markedly enhanced CC-oocyte gap junction communication index and number of transzonal projections, which were preserved until 18 h of oocyte maturation. These findings indicate that sericin reduces disruption of oocyte-follicular cell communication induced by oxidative stress. Sericin consistently increased intra-oocyte glutathione (GSH) levels and reduced oocyte H2O2 levels (P < 0.05), both of which were ablated when GSH synthesis was inhibited by buthionine sulfoximide (an inhibitor of GSH synthesis). Furthermore, the inhibition of GSH synthesis counteracted the positive effects of sericin on subsequent embryo developmental competence (P < 0.01). Intra-oocyte GSH levels were positively associated with blastocyst development and quality. These outcomes demonstrate new perspectives for the improvement of oocyte quality in assisted reproductive technology and may contribute to developing treatment strategies for infertility and cancer.

Addition of rapamycin or co-culture with cumulus cells from younger reproductive age women does not improve rescue in vitro oocyte maturation or euploidy rates in older reproductive age women.

Both spontaneously conceived pregnancies and those achieved using assisted reproduction decline with advancing maternal age. In this study, we tested if rapamycin and/or cumulus cells (CCs) from young donors could improve oocyte maturation and euploidy rates of germinal vesicle (GV) stage oocytes obtained from older women of reproductive age. A total of 498 GVs from 201 women >38 years (40.6 ± 1.8, mean ± SD) were included. GVs were randomly assigned into five groups for rescue IVM: control (with no CCs and no rapamycin); with autologous CCs; with autologous CCs and rapamycin; with CCs from young women (<35 years); and with CCs from young women and rapamycin. After 24 h of culture, the first polar body (PB) was biopsied in metaphase II oocytes, and the cytogenetic constitution was assessed using next-generation sequencing for both oocytes and PBs. Comparable maturation rates were found (56.2%, 60.0%, 46.5%, 51.7%, and 48.5% for groups 1-5, respectively; P = 0.30). Similarly, comparable euploidy rates were observed in the five groups (41.5%, 37.8%, 47.2%, 43.6%, and 47.8% for Groups 1-5, respectively; P = 0.87). Our findings indicate that rescue IVM is effective for obtaining mature euploid oocytes in older women of reproductive age, and that incubation with rapamycin or CCs obtained from young donors does not improve the maturation or euploidy rate.

How Do Environmental Toxicants Affect Oocyte Maturation Via Oxidative Stress?

In mammals, oogenesis initiates before birth and pauses at the dictyate stage of meiotic prophase I until luteinizing hormone (LH) surges to resume meiosis. Oocyte maturation refers to the resumption of meiosis that directs oocytes to advance from prophase I to metaphase II of meiosis. This process is carefully modulated to ensure a normal ovulation and successful fertilization. By generating excessive amounts of oxidative stress, environmental toxicants can disrupt the oocyte maturation. In this review, we categorized these environmental toxicants that induce mitochondrial dysfunction and abnormal spindle formation. Further, we discussed the underlying mechanisms that hinder oocyte maturation, including mitochondrial function, spindle formation, and DNA damage response.

Gonadotropin elevation is ootoxic to ovulatory oocytes and inhibits oocyte maturation, and activin decoy receptor ActRIIB:Fc therapeutically restores maturation.

BACKGROUND: Elevated FSH often occurs in women of advanced maternal age (AMA, age ≥ 35) and in infertility patients undergoing controlled ovarian stimulation (COS). There is controversy on whether high endogenous FSH contributes to infertility and whether high exogenous FSH adversely impacts patient pregnancy rates. METHODS: The senescence-accelerated mouse-prone-8 (SAMP8) model of female reproductive aging was employed to assess the separate impacts of age and high FSH activity on the percentages (%) of viable and mature ovulated oocytes recovered after gonadotropin treatment. Young and midlife mice were treated with the FSH analog equine chorionic gonadotropin (eCG) to model both endogenous FSH elevation and exogenous FSH elevation. Previously we showed the activin inhibitor ActRIIB:Fc increases oocyte quality by preventing chromosome and spindle misalignments. Therefore, ActRIIB:Fc treatment was performed in an effort to increase % oocyte viability and % oocyte maturation. RESULTS: The high FSH activity of eCG is ootoxic to ovulatory oocytes, with greater decreases in % viable oocytes in midlife than young mice. High FSH activity of eCG potently inhibits oocyte maturation, decreasing the % of mature oocytes to similar degrees in young and midlife mice. ActRIIB:Fc treatment does not prevent eCG ootoxicity, but it restores most oocyte maturation impeded by eCG. CONCLUSIONS: FSH ootoxicity to ovulatory oocytes and FSH maturation inhibition pose a paradox given the well-known pro-growth and pro-maturation activities of FSH in the earlier stages of oocyte growth. We propose the FOOT Hypothesis ("FSH OoToxicity Hypothesis), that FSH ootoxicity to ovulatory oocytes comprises a new driver of infertility and low pregnancy success rates in DOR women attempting spontaneous pregnancy and in COS/IUI patients, especially AMA women. We speculate that endogenous FSH elevation also contributes to reduced fecundity in these DOR and COS/IUI patients. Restoration of oocyte maturation by ActRIB:Fc suggests that activin suppresses oocyte maturation in vivo. This contrasts with prior studies showing activin A promotes oocyte maturation in vitro. Improved oocyte maturation with agents that decrease endogenous activin activity with high specificity may have therapeutic benefit for COS/IVF patients, COS/IUI patients, and DOR patients attempting spontaneous pregnancies.

Bioengineered 3D ovarian model for long-term multiple development of preantral follicle: bridging the gap for poly(ε-caprolactone) (PCL)-based scaffold reproductive applications.

BACKGROUND: Assisted Reproductive Technologies (ARTs) have been validated in human and animal to solve reproductive problems such as infertility, aging, genetic selection/amplification and diseases. The persistent gap in ART biomedical applications lies in recapitulating the early stage of ovarian folliculogenesis, thus providing protocols to drive the large reserve of immature follicles towards the gonadotropin-dependent phase. Tissue engineering is becoming a concrete solution to potentially recapitulate ovarian structure, mostly relying on the use of autologous early follicles on natural or synthetic scaffolds. Based on these premises, the present study has been designed to validate the use of the ovarian bioinspired patterned electrospun fibrous scaffolds fabricated with poly(ε-caprolactone) (PCL) for multiple preantral (PA) follicle development. METHODS: PA follicles isolated from lamb ovaries were cultured on PCL scaffold adopting a validated single-follicle protocol (Ctrl) or simulating a multiple-follicle condition by reproducing an artificial ovary engrafted with 5 or 10 PA (AO5PA and AO10PA). The incubations were protracted for 14 and 18 days before assessing scaffold-based microenvironment suitability to assist in vitro folliculogenesis (ivF) and oogenesis at morphological and functional level. RESULTS: The ivF outcomes demonstrated that PCL-scaffolds generate an appropriate biomimetic ovarian microenvironment supporting the transition of multiple PA follicles towards early antral (EA) stage by supporting follicle growth and steroidogenic activation. PCL-multiple bioengineering ivF (AO10PA) performed in long term generated, in addition, the greatest percentage of highly specialized gametes by enhancing meiotic competence, large chromatin remodeling and parthenogenetic developmental competence. CONCLUSIONS: The study showcased the proof of concept for a next-generation ART use of PCL-patterned scaffold aimed to generate transplantable artificial ovary engrafted with autologous early-stage follicles or to advance ivF technologies holding a 3D bioinspired matrix promoting a physiological long-term multiple PA follicle protocol.

Oocyte in-vitro maturation primed with letrozole-HCG versus FSH-HCG in women with oocyte maturation abnormalities: a retrospective study.

RESEARCH QUESTION: Are there differences between in-vitro maturation (IVM) primed with letrozole-human chorionic gonadotrophin (HCG) and IVM primed with FSH-HCG in women with oocyte maturation abnormalities (OMAs), defined as at least two failed IVF cycles where immature oocytes were retrieved? DESIGN: This retrospective study was conducted at a private fertility clinic from January 2009 to April 2023. The final analysis included 75 women in Group 1 (IVM primed with FSH-HCG) and 52 women in Group 2 (IVM primed with letrozole-HCG). RESULTS: A significantly higher median number of oocytes was obtained in Group 1 compared with Group 2 {9 [interquartile range (IQR) 1-5] versus 5 (IQR 1-18); P < 0.001}. However, no differences in oocyte maturation stage at collection were found between the groups (P > 0.05). At the end of IVM, Group 1 had 73/666 mature oocytes and Group 2 had 106/322 mature oocytes, and the median metaphase II oocyte rate per patient was higher in Group 2 [33.3% (IQR 66.7-100.0%) versus 0.0% (IQR 0.0-22.2%); P < 0.001]. Moreover, Group 2 demonstrated a higher median fertilization rate [66.7% (IQR 50.0-100.0%) versus 50.0% (IQR 0.0-66.7%); P = 0.027]. Group 2 had a higher proportion of Grade 2 embryos (58.5% versus 6.3%), and Group 1 had a higher proportion of Grade 3 embryos (93.8% vs 24.4%; P < 0.001). Notably, all pregnancies obtained in the study were in Group 2 (5 versus 0; P = 0.042). CONCLUSIONS: IVM primed with letrozole-HCG in women with prior failed IVF cycles due to OMAs may result in mature oocytes, clinical pregnancies and live births. The effectiveness of letrozole priming for the subtypes of OMAs needs further investigation, with studies including greater numbers of cases.

Comparison of luteal phase and follicular phase in-vitro maturation in women with oocyte maturation abnormalities.

RESEARCH QUESTION: Are there differences in immature oocyte retrieval following luteal phase in-vitro maturation (IVM) compared with follicular phase IVM in women with oocyte maturation abnormalities (OMAs). DESIGN: From January 2019 to May 2023, a retrospective cohort study at a private IVF centre included 36 women with 53 IVM cycles in Group 1 (follicular phase) and 24 women with 32 IVM cycles in Group 2 (luteal phase). Additionally, nine women had both follicular and luteal phase IVM cycles for intracycle variability analysis. RESULTS: There were no differences in oocyte maturation stages between the groups at collection. Group 1 and Group 2 exhibited comparable median metaphase II oocyte rates per patient at 48 h after collection [40.0%, interquartile range (IQR) 0.0-66.7% versus 22.5%, IQR 0.0-52.9%] (P = 0.53). The median fertilization rate in Group 1 (66.7%, IQR 50.0-66.7%) was found to be comparable with that in Group 2 (66.7%, IQR 50.0-66.7%). There were no significant differences in the yielded embryo grades and pregnancy rates between the groups. Comparing follicular and luteal phase IVM within the same menstrual cycle in nine patients, no differences were observed in metaphase II oocyte maturation rates (P > 0.05). CONCLUSIONS: This study found no significant differences in oocyte maturation, fertilization rate, embryo quality or pregnancy outcomes between luteal phase and follicular phase IVM in women with OMAs. These findings suggest that luteal phase IVM can be used similarly to follicular phase IVM, offering a potential avenue to enhance embryo yield for women with OMAs.

Should the trigger to oocyte retrieval interval be different in progestin-primed ovarian stimulation cycles?

RESEARCH QUESTION: Does the trigger to oocyte retrieval interval (TORI) affect oocyte maturation rates differently in progestin-primed ovarian stimulation (PPOS) and gonadotrophin-releasing hormone (GnRH) antagonist cycles? DESIGN: This was a retrospective cohort study. The interaction between the stimulation protocol and TORI was assessed in a linear mixed effects multivariable regression analysis with oocyte maturation rate as the dependent variable, and stimulation protocol (GnRH antagonist or PPOS), age (continuous), gonadotrophin type (FSH or human menopausal gonadotrophin), trigger (human chorionic gonadotrophin [HCG] or GnRH agonist), TORI (continuous) and days of stimulation (continuous) as the independent variables. Oocyte maturation rate was defined as number of metaphase II oocytes/number of cumulus-oocyte complexes retrieved. The maturation rate was calculated per cycle and treated as a continuous variable. RESULTS: A total of 473 GnRH antagonist and 205 PPOS cycles (121 conventional PPOS and 84 flexible PPOS) were analysed. The median (quartiles) female age was 36 (32-40) years. Of these cycles, 493 were triggered with HCG and 185 with a GnRH agonist. The TORI ranged between 33.6 and 39.1 h, with a median (quartiles) of 36.2 (36-36.4) hours. Maturation rates were similar between fixed PPOS, flexible PPOS and antagonist cycles (median 80%, 75% and 75%, respectively, P = 0.15). There was no significant interaction between the stimulation protocols and TORI for oocyte maturation. CONCLUSIONS: PPOS cycles do not seem to require a longer TORI than GnRH antagonist cycles.

Plasma-derived extracellular vesicles improve mice embryo development.

BACKGROUND: To investigate the effect of plasma-derived extracellular vesicles (EVs) or conventional medium in fertilization and early embryo development rate in mice. METHODS AND RESULTS: MII oocytes (matured in vivo or in vitro conditions) were obtained from female mice. The extracellular vesicles were isolated by ultracentrifugation of plasma and were analyzed and measured for size and morphology by dynamic light scattering (DLS) and transmission electron microscopy (TEM). By western blotting analysis, the EVs proteins markers such as CD82 protein and heat shock protein 90 (HSP90) were investigated. Incorporating DiI-labeled EVs within the oocyte cytoplasm was visible at 23 h in oocyte cytoplasm. Also, the effective proteins in the early reproductive process were determined in isolated EVs by western blotting. These EVs had a positive effect on the fertilization rate (P < 0.05). The early embryo development (8 cell, morula and blastocyst stages) was higher in groups supplemented with EVs (P < 0.01). CONCLUSION: Our findings showed that supplementing in vitro maturation media with EVs derived- plasma was beneficial for mice's embryo development.

Do women with severely diminished ovarian reserve undergoing modified natural-cycle in-vitro fertilization benefit from earlier trigger at smaller follicle size?

OBJECTIVE: To evaluate whether trigger and oocyte collection at a smaller follicle size decreases the risk of premature ovulation while maintaining the reproductive potential of oocytes in women with a severely diminished ovarian reserve undergoing modified natural-cycle in-vitro fertilization. METHODS: This was a retrospective cohort study including women who had at least one unsuccessful cycle (due to no response) of conventional ovarian stimulation with a high dosage of gonadotropins and subsequently underwent a modified natural cycle with a solitary growing follicle (i.e. only one follicle > 10 mm at the time of trigger). The association between follicle size at trigger and various cycle outcomes was tested using regression analyses. RESULTS: A total of 160 ovarian stimulation cycles from 110 patients were included in the analysis. Oocyte pick-up (OPU) was performed in 153 cycles and 7 cycles were canceled due to premature ovulation. Patients who received their trigger at smaller follicle sizes (≤ 15 mm) had significantly lower rates of premature ovulation and thus higher rates of OPU (98.9% vs 90.8%; odds ratio, 9.56 (95% CI, 1.58-182.9); P = 0.039) compared with those who received their trigger at larger follicle sizes (> 15 mm). On multivariable analysis, smaller follicle sizes at trigger (> 10 to 13 mm, > 13 to 15 mm, > 15 mm to 17 mm) were not associated significantly with a lower rate of cumulus-oocyte complex (COC) retrieval, metaphase-II (MII) oocytes or blastulation when compared to the > 17-mm group. On sensitivity analysis including only the first cycle of each couple, the maturity rate among those with COC retrieval was highest in follicle sizes > 15 to 17 mm (92.3%) and > 13 to 15 mm (91.7%), followed by > 10 to 13 mm (85.7%) and lowest in the > 17-mm group (58.8%). During the study period, five euploid blastocysts developed from 48 fertilized MII oocytes with follicle sizes of 12 mm (n = 3), 14 mm (n = 1) and 16 mm (n = 1) at trigger. Of those, four were transferred and resulted in two live births, both of which developed from follicles with a size at trigger of 12 mm. CONCLUSIONS: The ideal follicle size for triggering oocyte maturation may be smaller in women with a severely diminished ovarian reserve managed on a modified natural cycle when compared to conventional cut-offs. The risk of OPU cancellation was significantly higher in women triggered at follicle size > 15 mm and the yield of mature oocytes was not adversely affected in women triggered at follicle size > 13 to 15 mm compared with > 15 to 17 mm. Waiting for follicles to reach sizes > 17mm may be detrimental to achieving optimal outcome. © 2024 International Society of Ultrasound in Obstetrics and Gynecology.

Characterization of insulin-like growth factor 3 and its potential role in the spotted steed Hemibarbus maculatus ovary development.

As a new member of the insulin-like growth factors (Igfs), Igf3 was reported to play a vital role in fish reproduction. However, in spotted steed, the function of Igf3 remains largely unknown. In the present study, we identified and characterized Igf3 gene in spotted steed. Structural analysis showed that Igf3 contained five domains (B, C, A, D, E) and six conserved cysteine residues. The expression of Igf3 mRNA and protein were increased during ovary development and peaked in the maturation stage. The subcellular localization of IGF3 was highly expressed in granulosa cells and theca cells. Furthermore, recombinant IGF3 protein was produced and in vitro treatment with ovarian follicles significantly promoted the germinal vesicle breakdown (GVBD) rates of spotted steed follicles. The mRNA expression of cdc2 and cyclinB genes were significantly increased after IGF3 treatment, which were main components of maturation promoting factor (MPF). In addition, transcription levels of 3ß-hsd, 20ß-hsd, Cyp17a and Cyp19a1a were also changed. Taken together, these findings suggest that Igf3 is essential for ovary steroidogenesis and maturation in spotted steed.

Gene mutations impede oocyte maturation, fertilization, and early embryonic development.

Reproductive diseases are a long-standing problem and have become more common in the world. Currently, 15% of the world's population suffers from infertility, and half of them are women. Maturation of oocytes, successful fertilization, and high-quality embryos are prerequisites for pregnancy. With the development of assisted reproductive technology and advanced genetic assays, we have found that infertility in many young female patients is caused by mutations in various developmental regulators. These pathogenic factors may result in impediment of oocyte maturation, failure of fertilization or early embryonic development arrest. In this review, we categorize these clinically-identified, mutated genetic factors by their molecular characteristics: nuclear factors (PALT2, TRIP13, WEE2, TBPL2, REC114, MEI1 and CDC20), cytoplasmic factors (TLE6, PADI6, NLRP2/5, FBXO43, MOS and BTG4), a factor unique to primates (TUBB8), cell membrane factor (PANX1), and zona pellucida factors (ZP1-3). We compared discrepancies observed in phenotypes between human and mouse models to provide clues for clinical diagnosis and treatment of related reproductive diseases.

Single-Cell Quantitative Proteomic Analysis of Human Oocyte Maturation Revealed High Heterogeneity in In Vitro-Matured Oocytes.

Oocyte maturation is pertinent to the success of in vitro maturation (IVM), which is used to overcome female infertility, and produced over 5000 live births worldwide. However, the quality of human IVM oocytes has not been investigated at single-cell proteome level. Here, we quantified 2094 proteins in human oocytes during in vitro and in vivo maturation (IVO) by single-cell proteomic analysis and identified 176 differential proteins between IVO and germinal vesicle oocytes and 45 between IVM and IVO oocytes including maternal effect proteins, with potential contribution to the clinically observed decreased fertilization, implantation, and birth rates using human IVM oocytes. IVM and IVO oocytes showed separate clusters in principal component analysis, with higher inter-cell variability among IVM oocytes, and have little correlation between mRNA and protein changes during maturation. The patients with the most aberrantly expressed proteins in IVM oocytes had the lowest level of estradiol per mature follicle on trigger day. Our data provide a rich resource to evaluate effect of IVM on oocyte quality and study mechanism of oocyte maturation.

A polysaccharide gel made of gellan gum improves oocyte maturation and embryonic development in pigs.

Gellan gum (GG) is a soft, tractable,　and natural polysaccharide substrate used for cell incubation. In this study, we examined the effects of GG on porcine oocyte maturation. Cumulus cells and oocyte complexes (COCs) were collected from slaughterhouse-derived porcine ovaries and cultured on plastic plates containing 0.05% or 0.1% GG gels. The 0.1% GG gel improved the maturation rate and quality of blastocysts, as determined by the total cell number and the rate of abnormally condensed nuclei. GG gels have antioxidant abilities and oocytes cultured on GG gels (0.05% and 0.1%) have reduced reactive oxygen species (ROS) content. Furthermore, GG gels (0.05% and 0.1%) increased F-actin formation, whereas treatment of oocytes with H2O2 reduced F-actin levels. GG gels increased the ATP content in oocytes but did not affect the mitochondrial DNA copy number or mitochondrial membrane potential. In addition, the medium cultured on 0.05% GG increased the glucose consumption of COCs. In conclusion, GG gel reduced ROS content, increased energy content, and improved subsequent embryonic development in pigs.