Polar Body Research Articles

Defects in meiosis I contribute to the genesis of androgenetic hydatidiform moles.

To identify novel genes responsible for recurrent hydatidiform moles (HMs), we performed exome sequencing on 75 unrelated patients who were negative for mutations in the known genes. We identified biallelic deleterious variants in 6 genes, FOXL2, MAJIN, KASH5, SYCP2, MEIOB, and HFM1, in patients with androgenetic HMs, including a familial case of 3 affected members. Five of these genes are essential for meiosis I, and their deficiencies lead to premature ovarian insufficiency. Advanced maternal age is the strongest risk factor for sporadic androgenetic HM, which affects 1 in every 600 pregnancies. We studied Hfm1-/- female mice and found that these mice lost all their oocytes before puberty but retained some at younger ages. Oocytes from Hfm1-/- mice initiated meiotic maturation and extruded the first polar bodies in culture; however, their meiotic spindles were often positioned parallel, instead of perpendicular, to the ooplasmic membrane at telophase I, and some oocytes extruded the entire spindle with all the chromosomes into the polar bodies at metaphase II, a mechanism we previously reported in Mei1-/- oocytes. The occurrence of a common mechanism in two mouse models argues in favor of its plausibility at the origin of androgenetic HM formation in humans.

Human oocyte zona pellucida abnormalities: evaluation of clinical impact for different zona pellucida abnormalities and role of using assisted hatching.

Zona pellucida (ZP) plays an important role in oocyte development and fertilisation, as well as in early embryo development. However, there is currently no exploration of systematic categorising and clinical treatment measures for patients with abnormal ZP, especially the fast and easy method that can be used clinically. In this study, 185 patients with abnormal ZP (ZPA) and 222 patients with normal ZP (ZPN) were enrolled and analysed. Patients with ZPA exhibited altered hormone levels and lower laboratory outcomes in in vitro fertilisation (IVF), such as reduced MII rate, cleavage rate, high-quality embryo rate, and blastocyst formation rate compared to ZPN group. ZPA patients were sub-categorised into ZPA-A/B/C/D group according to the status of oocyte polar body and the width of perivitelline space (PVS). There are also differences in the degree of sperm binding to ZP derived from different ZPA patients and the elasticity of the oocyte membrane. ZPA subgroup analysis revealed further disparities in various IVF parameters and pregnancy outcomes. In addition, by performing different treatments on oocytes derived from ZPA patients, we found that ZP assisted hatching before the first oocyte cleavage on D1 of embryonic development in the ZPA-A/B groups and before blastocyst expansion on D4 of embryonic development in the ZPA-C/D groups were beneficial to improve embryonic development. The degree of the impact on clinical outcomes is correlated with the types of ZPA, and laser-assisted hatching of the ZP helps to improve embryonic development in patients with ZPA.

The NAD+ precursor nicotinamide riboside protects against postovulatory aging in vitro.

Postovulatory aging (POA) of oocytes is clinically significant as it mirrors the degeneration observed in maternally aged oocytes, leading to substantial impairments in oocyte quality and the success rates of artificial reproductive technology (ART). The molecular alterations associated with POA, such as the degeneration of the first polar body, an increase in perivitelline space, reactive oxygen species (ROS) accumulation, energy depletion, and chromosomal and DNA damage, underscore the urgency of finding interventions to mitigate these effects. This study aims to identify whether nicotinamide riboside (NR) can prevent POA during the process of in vitro culture and raise the success rates of ART. Taking advantage of an in vitro postovulatory oocyte aging model, we examined the morphological integrity and NAD+ levels of ovulated mouse MII oocytes after 24h of culturing. Following in vitro fertilization, we assessed the embryonic developmental potential of oocytes affected by POA. Using immunofluorescence and confocal microscopy, we measured the levels of ROS, mitochondrial function, and γH2AX. We also evaluated spindle assembly and chromosome alignment. Additionally, we detected the distribution of cortical granules to assess the metabolic and quality changes in POA oocytes with the supplementation of NR. To further our analysis, quantitative real-time PCR was conducted to measure the mRNA expression levels of antioxidant enzymes Sod1 and Gpx1 in the oocytes. With 200μM NR supplementation during in vitro culture for 24h, the oocytes from POA demonstrated reduced signs of aging-related decline in oocyte quality, including reduced ROS accumulation, improved mitochondrial function, and corrected mis-localization of cortical granules. This improvement in oocyte quality is likely due to the inhibition of oxidative stress via the NAD+/SIRT1 signaling pathway, which also helped to restore normal spindle assembly and chromosome alignment, as well as reduce the elevated levels of γH2AX, thereby potentially enhancing the embryonic development potential. Current research provides evidence that NR is an efficient and safe natural component that prevents the process of POA and is thus a potential ideal antiaging drug for raising the success rates of ART in clinical practice.

Hybrid incompatibility emerges at the one-cell stage in interspecies Caenorhabditis embryos.

Intrinsic reproductive isolation occurs when genetic differences between populations disrupt the development of hybrid organisms, preventing gene flow and enforcing speciation. 1-4 While prior studies have examined the genetic origins of hybrid incompatibility, 5-18 the effects of incompatible factors on development remain poorly understood. Here, we investigate the mechanistic basis of hybrid incompatibility in Caenorhabditis nematodes by capitalizing on the ability of C. brenneri females to produce embryos after mating with males from several other species. Contrary to expectations, hybrid incompatibility was evident immediately after fertilization, suggesting that post-fertilization barriers to hybridization originate from physical incompatibility between sperm and oocyte-derived factors rather than from zygotic transcription, which starts after the 4-cell stage. 19-22 Sperm deliver chromatin, which expands to form a pronucleus, and a pair of centrioles, which form centrosomes that attach to the sperm-derived pronucleus and signal to establish the embryo's anterior-posterior axis. 23,24 In C. brenneri oocytes fertilized with C. elegans sperm, sperm pronuclear expansion was compromised, frequent centrosome detachment was observed, and cortical polarity was disrupted. Live imaging revealed that defective polar body extrusion contributes to defects in mitotic spindle morphology. C. brenneri oocytes fertilized with C. remanei or C. sp. 48 sperm showed similar defects, and their severity and frequency increased with phylogenetic distance. Defective expansion of the sperm-derived pronucleus and unreliable polar body extrusion immediately after fertilization generally underlie the inviability of hybrid embryos in this clade. These results indicate that physical mismatches between sperm and oocyte-derived structures may be a primary mechanism of hybrid incompatibility.

Mutation of the SUMOylation site of Aurora-B disrupts spindle formation and chromosome alignment in oocytes

Aurora-B is a kinase that regulates spindle assembly and kinetochore-microtubule (KT-MT) attachment during mitosis and meiosis. SUMOylation is involved in the oocyte meiosis regulation through promoting spindle assembly and chromosome segregation, but its substrates to support this function is still unknown. It is reported that Aurora-B is SUMOylated in somatic cells, and SUMOylated Aurora-B contributes the process of mitosis. However, whether Aurora-B is SUMOylated in oocytes and how SUMOylation of Aurora-B impacts its function in oocyte meiosis remain poorly understood. In this study, we report that Aurora-B is modified by SUMOylation in mouse oocytes. The results show that Aurora-B colocalized and interacted with SUMO-2/3 in mouse oocytes, confirming that Aurora-B is modified by SUMO-2/3 in this system. Compared with that in young mice, the protein expression of SUMO-2/3 decreased in the oocytes of aged mice, indicating that SUMOylation might be related to mouse aging. Overexpression of Aurora-B SUMOylation site mutants, Aurora-BK207R and Aurora-BK292R, inhibited Aurora-B recruitment and first polar body extrusion, disrupting localization of gamma tubulin, spindle formation and chromosome alignment in oocytes. The results show that it was related to decreased recruitment of p-HDAC6 which induces the high stability of whole spindle microtubules including the microtubules of both correct and wrong KT-MT attachments though increased acetylation of microtubules. Therefore, our results corroborate the notion that Aurora-B activity is regulated by SUMO-2/3 in oocytes, and that SUMOylated Aurora B plays an important role in spindle formation and chromosome alignment.

The Immediate Partial Removal of Cumulus-Oocyte Complexes: A Refined Approach for Rapid Observation of In Vitro Fertilization.

Despite the rapid advancements in clinical and laboratory technologies for in vitro fertilization (IVF), a significant proportion (10%-15%) of patients continue to experience fertilization disorders, leading to low fertilization rates and the production of nonviable embryos. Short-term fertilization involves the early removal of granulosa cells to observe the extrusion of the second polar body, enabling the assessment of fertilization and early remedial measures to address low fertilization rates and complete fertilization failure. However, the observation of short-term fertilization in IVF is impeded by challenges such as excessively large unprocessed clusters of cumulus-oocyte complexes and adhesion between eggs, necessitating complex external procedures for granulosa cell removal, and prolonged observation duration. To tackle this issue, this study proposes a method of immediate partial removal of granulosa cells post egg retrieval. This approach streamlines subsequent stages of short-term fertilization and traditional fertilization monitoring, reduces the time needed for oocyte extrusion, minimizes the likelihood of external environmental impacts on the oocytes, and decreases the risk of missing the critical fertilization observation window. Consequently, the study yields novel clinical evidence aimed at enhancing the operational efficiency of embryonic laboratories in IVF.

Melatonin decreases excessive polyspermy for single oocyte in pigs through the MT2 receptor

Melatonin supplementation during in vitro maturation (IVM) improves porcine oocyte maturation and embryonic development by exerting antioxidative effects. Nevertheless, the mechanism by which melatonin prevents polyspermy after in vitro fertilization (IVF) remains unclear. Here, we examined the effects of melatonin on cytoplasmic maturation and the incidence of polyspermic penetration in porcine oocytes. No statistically significant difference was observed in the rate of first polar body formation between the groups (Control, Melatonin, Melatonin + Luzindole, and Melatonin + 4-P-PDOT). Interestingly, melatonin supplementation significantly improved the cytoplasmic maturation of porcine oocytes by enhancing the normal distribution of organelles (Golgi apparatus, endoplasmic reticulum and mitochondria) and upregulating organelle-related gene expressions (P < 0.05). However, these promotional effects were counteracted by melatonin antagonists, suggesting that melatonin enhances cytoplasmic maturation through its receptors in porcine oocytes. Melatonin supplementation also significantly improved the rate of diploid and blastocyst formation after IVF by promoting the normal distribution of cortical granules (P < 0.05). In conclusion, melatonin supplementation during in vitro maturation of porcine oocyte improves fertilization efficiency and embryonic developmental competence by enhancing cytoplasmic maturation.

Bisphenol AP inhibits mouse oocyte maturation in vitro by disrupting cytoskeleton architecture and cell cycle processes

Bisphenol A (BPA) is among the extensively researched environmental endocrine-disrupting chemicals (EDCs), and its utilization is restricted owing to the detrimental impacts it has on human health. Bisphenol AP (BPAP) is one of the alternatives to BPA, but the influence of BPAP on human health has not been elucidated. The objective of the current research was to determine the influence of BPAP exposure on the in vitro maturation of mouse oocytes and to explore its potential reproductive toxicity. BPAP exposure was found to inhibit polar body extrusion during mouse oocyte maturation, resulting in an arrest at the metaphase I stage of meiosis. Exposure to BPAP led to sustained activation of BubR1, preventing the degradation of both Securin and Cyclin B1. Mechanistically, BPAP exposure disrupts spindle assembly and chromosome alignment. Levels of acetylated α-tubulin were significantly elevated in BPAP-treated oocytes, reflecting decreased spindle stability. Exposure to BPAP also induced DNA damage and impaired DNA damage repair. In addition, BPAP exposure altered histone modification levels. In summary, this investigation suggests that exposure to BPAP can influence cytoskeletal assembly, interfere with cell cycle progression, induce DNA damage, alter histone modifications, and ultimately impede oocyte meiotic maturation. This investigation enhances understanding of the impact of bisphenol analogs on female gametes, underscoring that BPAP cannot be considered a reliable replacement for BPA.

Deoxynivalenol exposure disturbs the cytoplasmic maturation in porcine oocytes

Deoxynivalenol (DON) is a secondary metabolite of Fusarium fungi and belonged to trichothecenes, and it widely presents in various food commodities. Previous studies have highlighted its potent toxicity, adversely affecting the growth, development, and reproductive in both humans and animals. However, the potential impact of DON on porcine oocyte organelles remains elusive. In present study, we delved into the toxic effects of DON on mitochondria, endoplasmic reticulum, Golgi during the porcine oocyte maturation. Our findings revealed that DON exposure significantly impeded granulosa cell diffusion and the expulsion of the first polar body. Additionally, mitochondrial fluorescence intensity and membrane potential underwent notable alterations under DON exposure. Notably, lysosomal fluorescence intensity decreased significantly, suggesting protein degradation and potential autophagy, which was further corroborated by the enhanced fluorescence intensity of LC3. Furthermore, endoplasmic reticulum fluorescence intensity declined, and DON exposure elevated endoplasmic reticulum stress levels, evident from the upregulated expression of GRP78. Concurrently, we observed disruption in the fusiform cortex distribution of the Golgi apparatus, characterized by reduced Golgi apparatus fluorescence intensity and GM130 expression. Collectively, our results indicate that DON exposure profoundly affects the fundamental functions of porcine oocyte organelles during meiosis and maturation.

Quality of IVM ovarian tissue oocytes: impact of clinical, demographic, and laboratory factors.

To determine how clinical, demographic, and laboratory characteristics influence ovarian tissue oocyte quality. Immature cumulus-oocyte complexes were isolated from removed ovaries and cultured for 48-52h in either monophasic standard or biphasic CAPA media for fertility preservation. A total of 355 MII oocytes from 53 patients were described for intracytoplasmic and extracytoplasmic anomalies. Multiple clinical, laboratory, and demographic characteristics were analyzed. Statistically significant differences between independent groups in qualitative variables were identified using Pearson's χ2 and Fisher's exact tests. The diagnostic value of quantitative variables was assessed using the ROC curve analysis. Factors associated with the development of dysmorphism, taking patient age into account, were identified using the binary logistic regression analysis. Dysmorphisms were observed in 245 oocytes (69.0%), with a median number of dysmorphisms of 2. Oocyte dysmorphisms were found to be 2.211 times more likely to be detected in patients with ovarian cancer, while the presence of dark-colored cytoplasm was associated with gynecologic surgery in the anamnesis (p = 0.002; OR 16.652; 95% CI, 1.977-140.237; Cramer's V 0.187). Small polar bodies developed 2.717 times more often (95% CI, 1.195-6.18) in patients older than 35. In the case of ovarian transportation on ice at 4 ℃, the chances of development of cytoplasmic granularity increased 2.569 times (95% CI, 1.301-5.179). The use of biphasic CAPA IVM media contributed to a decrease in the probability of large polar body formation (p = 0.034) compared to the standard monophasic IVM media. Both patients' characteristics and laboratory parameters have an impact on the quality of IVM ovarian tissue oocytes.

Oleanolic acid promotes porcine oocyte maturation by activating the Nrf2/HO-1 signalling pathway

This study investigated the potential role and underlying mechanisms of oleanolic acid (OA), a pentacyclic triterpene with antioxidant and anti-inflammatory properties, in porcine oocytes during in vitro maturation (IVM). The results showed that supplementation with 5 μM OA during IVM resulted in a greater percentage of mature oocytes, parthenogenetically activated embryos and somatic cell nuclear-transferred embryos. This was evidenced by significant increases in the rate of first polar body expulsion, the expansion of cumulus granulosa cells and the total cell number in blastocysts. Further analysis revealed that OA promoted fatty acid accumulation and upregulated the mRNA expression of genes involved in fatty acid β-oxidation. OA significantly increased the intracellular mitochondrial membrane potential and ATP levels and effectively inhibited BAX/BCL2 and Cleaved Caspase3 protein expression. Notably, OA increased the protein levels of intracellular Nrf2 and HO-1, and the GSH levels and the activities of the antioxidant enzymes SOD and catalase (CAT), while reducing ROS levels. Mechanistically, OA activated the Nrf2/HO-1 signalling pathway, which is crucial for regulating the expression of antioxidant-related targets in IVM porcine oocytes. Our findings indicated that OA improved antioxidant capacity by activating the Nrf2/HO-1 signalling pathway, thereby promoting porcine oocyte maturation.

MiR-29b inhibits COC expansion and oocyte in vitro maturation via induction of ROS by targeting CYCS

Cumulus-oocyte complex (COC) expansion and oocyte maturation are crucial processes for embryo development and fertility across species. Although miR-29b has been detected in porcine ovarian granulosa cells, its specific role in regulating oocyte maturation remains largely unknown. In this study, using the pig as a model, we report that over-expression of miR-29b lead to a decrease of COC expansion area and inhibits oocyte maturation (P<0.05). This suppression correlated with a decrease expression of COC-expansion-associated genes, including SHAS2, ADAMTS1, ADAMTS2, ADAMTS17 and PTX 3 in both mural granulosa cells (mGCs) and cumulus granulosa cells (cGCs). Further investigation revealed that miR-29b over-expression induces reactive oxygen species (ROS) accumulation in both mGCs and cGCs, conversely, knock-down of miR-29b reverses all these effects. Treatment with the antioxidant β-mercaptoethanol alleviates ROS accumulation, rescues COC expansion and restores oocyte polar body formation impaired by miR-29b mimics. Computational analysis predicted CYCS, the gene encoding cytochrome C, as a potential target of miR-29b. Subsequent examination demonstrated that miR-29b downregulates CYCS at both mRNA and protein levels. Dual-luciferase reporter assays further confirmed that miR-29b interacts with the 3’-untranslated region (3’UTR) of CYCS. Over-expression of CYCS decreases ROS accumulation and promotes COC expansion (P<0.05). These results indicate that miR-29b regulates COC expansion and oocyte maturation in vitro by inducing ROS, likely through targeting of CYCS. This study sheds light on the role of miR-29b in oocyte maturation and provides insight into the regulatory function of miRNAs in ovarian physiology.

Use of time-lapse technology on fertilization verification, embryo evaluation, and utilization: A national survey in Japan

BackgroundTime-lapse technology (TLT) has emerged as a significant advancement in the field of assisted reproductive technology (ART), providing continuous observation of embryos. However, limited information exists on the adoption of TLT across ART facilities and the clinical implications of its application in embryo evaluation and fertilization verification. The existing literature has not yet comprehensively examined how TLT data are utilized to optimize ART outcomes, particularly in Japan, where ART practices are highly prevalent. ObjectivesThis study aimed to investigate the adoption rate of TLT and its clinical effects on fertilization verification, embryo evaluation, and utilization of ART in Japan. Study DesignAn online survey was conducted from December 23, 2022, to January 16, 2023, in 616 ART facilities with both email and mailed notices. The survey investigated the utilization of TLT in each facility's evaluation of oocyte morphology, fertilization, embryo culture, and morphology. ResultsOverall, 345 responses were analyzed. Of these, only 42.6% confirmed fertilization at 16 to 18 hours after insemination. Most facilities defined normally fertilized eggs as 2 pronuclei (2PN; 53.3%) or a combination of a second polar body extrusion and 2PN (44.9%). Overall, 54.6% of the facilities had adopted TLT, and 76.9% to 96.9% of these facilities used TLT images for fertilization verification. At these centers, the use of 0PN embryos decreased, whereas the use of 2.1PN embryos increased. The rates of culture medium supplemented with antioxidants and hyaluronan were significantly higher in facilities with TLT than in those without TLT. TLT images were used for embryo evaluation in 94.3% of the facilities, while 31.0% used a combination of TLT images and artificial intelligence-based scoring systems. ConclusionsWhile TLT use is widespread in Japan, its application in evaluating fertilization and embryo development stages varies across facilities. Reaching a consensus on the optimal use of the TLT system will enhance the effectiveness, safety, and efficiency of ARTs.

Rescue ICSI Improved Cumulative Live Birth Rate for Cycles with Second Polar Body Extrusion Rate

ObjectiveTo determine the indications for early rescue intracytoplasmic sperm injection (ICSI) application. DesignA retrospective cohort study SubjectsThe study included 19,808 patients who underwent conventional in vitro fertilization (IVF) or rescue ICSI for their first cycles between February 2017 and December 2021. ExposureRescue ICSI cycles constituted the study group, where oocytes that had not extruded the second polar body 4-6 hours after insemination were rescued by ICSI. The control group consisted of conventional IVF cycles with no interventions to rescue oocytes without the second polar body. Generalized additive models (GAMs) were constructed to describe the relationship between the second polar body extrusion rate and cumulative live birth rate in conventional IVF and rescue ICSI cycles, respectively. The cutoff value of the second polar body extrusion rate guiding rescue ICSI application was determined from the intersection point of GAMs. Maternal age range applicable to rescue ICSI was further analyzed using the same method. Clinical outcomes were compared between conventional IVF and rescue ICSI cycles across different second polar body extrusion rate and maternal age subgroups. Main outcome measuresThe second polar body extrusion rate and maternal age range for rescue ICSI application, normal fertilization rate, and cumulative live birth rate. ResultsGAMs showed that the cutoff value for the second polar body extrusion rate about rescue ICSI application was 50%. When the rate <50%, normal fertilization rate and cumulative live birth rate (63.7% vs. 46.1%, OR: 1.609, 95% CI: 1.276-2.030) were significantly higher in rescue ICSI cycles than conventional IVF cycles. When the rate ≥50%, rescue ICSI cycles had similar normal fertilization rate and cumulative live birth rate compared to conventional IVF cycles. Further analysis on maternal age in cycles with second polar body extrusion rate <50% released that rescue ICSI cycles showed a higher cumulative live birth rate (67.7% vs. 48.3%, OR: 1.732, 95% CI: 1.361-2.202) than conventional IVF cycles for women aged < 38 years. ConclusionIVF cycles with second polar body extrusion rate <50% in women aged < 38 years was applicable to early rescue ICSI.

X centromeric drive may explain the prevalence of polycystic ovary syndrome and other conditions: Genomic structure of the human X chromosome pericentromeric region is consistent with meiotic drive associated with PCOS and other conditions.

X chromosome centromeric drive may explain the prevalence of polycystic ovary syndrome and contribute to oocyte aneuploidy, menopause, and other conditions. The mammalian X chromosome may be vulnerable to meiotic drive because of X inactivation in the female germline. The human X pericentromeric region contains genes potentially involved in meiotic mechanisms, including multiple SPIN1 and ZXDC paralogs. This is consistent with a multigenic drive system comprising differential modification of the active and inactive X chromosome centromeres in female primordial germ cells and preferential segregation of the previously inactivated X chromosome centromere to the polar body at meiosis I. The drive mechanism may explain differences in X chromosome regulation in the female germlines of the human and mouse and, based on the functions encoded by the genes in the region, the transmission of X pericentromeric genetic or epigenetic variants to progeny could contribute to preeclampsia, autism, and differences in sexual differentiation.

CtIP regulates G2/M transition and bipolar spindle assembly during mouse oocyte meiosis

CtBP-interacting protein (CtIP) is known for its multifaceted roles in DNA repair and genomic stability, directing the homologous recombination-mediated DNA double-stranded break (DSBs) repair pathway via DNA end resection, an essential error-free repair process vital for genome stability. Mammalian oocytes are highly prone to DNA damage accumulation due to prolonged G2/prophase arrest. Here, we explore the functions of CtIP in meiotic cell cycle regulation via a mouse oocyte model. Depletion of CtIP by siRNA injection results in delayed germinal vesicle breakdown and failed polar body extrusion. Mechanistically, CtIP deficiency increases DNA damage and decreases the expression and nuclear entry of CCNB1, resulting in marked impairment of meiotic resumption, which can be rescued by exogenous CCNB1 overexpression. Furthermore, depletion of CtIP disrupts MTOCs coalescence at spindle poles as indicated by failed accumulation of γ-tubulin, p-Aurora kinase A, Kif2A, and TPX2, leading to abnormal spindle assembly and prometaphase arrest. These results provide valuable insights into the important roles of CtIP in the G2/M checkpoint and spindle assembly in mouse oocyte meiotic cell cycle regulation.

Premeiotic endoreplication is the mechanism of obligate parthenogenesis in rock lizards of the genus Darevskia.

Among vertebrates, obligate parthenogenesis occurs exclusively in squamate reptiles. Premeiotic endoreplication in a small subset of developing oocytes has been documented as the mechanism of production of unreduced eggs in minutely explored obligate parthenogenetic lineages, namely in teiids and geckos. The situation in the lacertid genus Darevskia has been discussed for decades. Certain observations suggested that the ploidy level is restored during egg formation through a fusion of egg and polar body nuclei in Darevskia unisexualis and D. armeniaca. In this study, we re-evaluated the fusion hypothesis by studying diplotene chromosomes in adult females of sexual species D. raddei nairensis and obligate parthenogens D. armeniaca, D. dahli and D. unisexualis. We revealed 19 bivalents in the sexual species and 38 bivalents in the diploid obligate parthenogens, which uncovers premeiotic endoreplication as the mechanism of the production of non-reduced eggs in parthenogenetic females. The earlier contradicting reports can likely be attributed to the difficulty in identifying mispairing of chromosomes in pachytene, and the fact that in parthenogenetic reptiles relying on premeiotic endoreplication only a small subset of developing oocytes undergo genome doubling and overcome the pachytene checkpoint. This study highlights co-option of premeiotic endoreplication for escape from sexual reproduction in all independent hybrid origins of obligate parthenogenesis in vertebrates studied to date.

Sterigmatocystin declines mouse oocyte quality by inducing ferroptosis and asymmetric division defects

BackgroundSterigmatocystin (STE) is a mycotoxin widely found in contaminated food and foodstuffs, and excessive long-term exposure to STE is associated with several health issues, including infertility. However, there is little information available regarding the effects of STE toxin on the female reproductive system, particularly concerning oocyte maturation.MethodsIn the present study, we investigated the toxic effects of STE on mouse oocyte maturation. We also used Western blot, immunofluorescence, and image quantification analyses to assess the impact of STE exposure on the oocyte maturation progression, mitochondrial distribution, oxidative stress, DNA damages, oocyte ferroptosis and asymmetric division defects.ResultsOur results revealed that STE exposure disrupted mouse oocyte maturation progression. When we examined the cellular changes following 100 µM STE treatment, we found that STE adversely affected polar body extrusion and induced asymmetric division defects in oocytes. RNA-sequencing data showed that STE exposure affects the expression of several pathway-correlated genes during oocyte meiosis in mice, suggesting its toxicity to oocytes. Based on the RNA-seq data, we showed that STE exposure induced oxidative stress and caused DNA damage in oocytes. Besides, ferroptosis and α-tubulin acetylation were also found in STE-exposed oocytes. Moreover, we determined that STE exposure resulted in reduced RAF1 protein expression in mouse oocytes, and inhibition of RAF1 activity also causes defects in asymmetric division of mouse oocytes.ConclusionsCollectively, our research provides novel insights into the molecular mechanisms whereby STE contributes to abnormal meiosis.

Polar body-based PGT-A: not dead yet? A step forward back to the roots of PGT-A

Trophectoderm-based preimplantation genetic testing for aneuploidies (PGT-A) is used worldwide as a means of selecting embryos with high potential for achieving a live birth. However, trophectoderm analysis may be impaired through embryonic mosaicism, leading to genetically healthy embryos being falsely discarded, and thus even reducing cumulative live birth rates. Polar body biopsy, a technique applied since the early days of preimplantation testing, has been abandoned by most IVF centres. In comparison to trophectoderm analysis, however, polar body biopsy might even have certain advantages over trophectoderm PGT-A. This Countercurrent contribution discusses the newest clinical evidence, as well as ethical and cost-efficiency considerations, and argue that polar body analysis should be reconsidered.

Impact of the near-physiological temperature on the in vitro maturation of bovine oocytes: A comparative proteomic approach

In vivo, the temperature inside preovulatory follicles of cows is approximately 1 °C lower than rectal temperature. However, standard bovine oocyte in vitro maturation (IVM) protocols use 38.5 °C based on rectal temperature. This study evaluated the effect of reducing IVM temperature to 37.5 °C on the proteomic profile of oocytes compared to the routine 38.5 °C. Nuclear maturation rate and cumulus cell (CC) expansion (30 COCs per group, 21 replicates) were assessed by observing the first polar body and using a subjective scoring method (0–4). Total nitrite concentrations in the culture medium were measured using the Griess method. Differential proteomics was performed using LC-MS/MS on pooled oocyte samples (500 matured oocytes per group, three replicates), followed by gene ontology enrichment, protein-protein interaction, and putative miRNA target analyses. No significant differences were observed between the groups in nuclear maturation, CC expansion, or nitrite concentration (P > 0.05). A total of 806 proteins were identified, with 7 up-regulated and 12 down-regulated in the treatment group compared to the control. Additionally, 12 proteins were unique to the control group, and 8 were unique to the treatment group. IVM at 37.5 °C resulted in the upregulation of proteins involved in protein folding and GTP binding, and the downregulation of enzymes with oxidoreductase activity and proteins involved in cytoskeletal fiber formation. Furthermore, 43 bovine miRNAs potentially regulating these genes (DES, HMOX2, KRT75, FARSA, IDH2, CARHSP1) were identified. We conclude that IVM of bovine oocytes at 37.5 °C induces significant proteomic changes without impacting nuclear maturation, cumulus cell expansion, or nitrite concentration in the IVM medium.