Mouse Oocyte Maturation Research Articles

Toxic effects of 4-methylimidazole on the maturation and fertilization of mouse oocytes

Individuals of all ages, including children and teenagers, consume 4-methylimidazole (4-MI) in their food. 4-MI is a caramel-colored waste product that has previously been linked to human carcinogenesis and has shown possible signs of reproductive toxicity. This study aimed to determine whether 4-MI is harmful to oocytes during meiosis and fertilization. Female mice were intragastrically administered 0, 50, or 100 mg/kg body weight of 4-MI daily for 10 days. We found that 4-MI affects the quality of oocytes by affecting their meiotic ability and fertility potential. Specifically, 4-MI rendered the meiotic spindles and chromosomes less stable, which halted oocyte maturation and resulted in aneuploidy. 4-MI also slowed the decrease in the levels of cortical granules and their component ovastacin; consequently, sperms could not be bound and fertilization could not occur. We also found that mitochondrial dysfunction was associated with oocytes deterioration. This led to reactive oxygen species accumulation and cell death. Altogether, our findings reveal that the poor condition of oocytes subjected to 4-MI is primarily attributable to mitochondrial malfunction and redox alterations.

Aberrant Expression of Mitochondrial SAM Transporter SLC25A26 Impairs Oocyte Maturation and Early Development in Mice.

The immature germinal vesicle (GV) oocytes proceed through metaphase I (MI) division, extrude the first polar body, and become mature metaphase II (MII) oocytes for fertilization which is followed by preimplantation and postimplantation development until birth. Slc25a26 is the gene encoding S-adenosylmethionine carrier (SAMC), a member of the mitochondrial carrier family. Its major function is to catalyze the uptake of S-adenosylmethionine (SAM) from cytosol into mitochondria, which is the only known mitochondrial SAM transporter. In the present study, we demonstrated that excessive SLC25A26 accumulation in mouse oocytes mimicked naturally aged oocytes and resulted in lower oocyte quality with decreased maturation rate and increased reactive oxygen species (ROS) by impairing mitochondrial function. Increased level of Slc25a26 gene impacted gene expression in mouse oocytes such as mt-Cytb which regulates mitochondrial respiratory chain. Furthermore, increased level of Slc25a26 gene in fertilized oocytes slightly compromised blastocyst formation, and Slc25a26 knockout mice displayed embryonic lethality around 10.5 dpc. Taken together, our results showed that Slc25a26 gene plays a critical role in oocyte maturation and early mouse development.

Zinc pyrithione exposure compromises oocyte maturation through involving in spindle assembly and zinc accumulation

Zinc Pyrithione (ZPT), a Food and Drug Administration (FDA) approved chemical, is widely used for topical antimicrobials and cosmetic consumer products, including anti-dandruff shampoos. ZPT and its degraded byproducts have detected in large quantities in the environment, and identified to pose healthy risks on aquatic organisms and human. However, so far, knowledge about ZPT effects on female reproduction, particularly oocyte maturation and quality, is limited. Herein, we investigated the adverse impact of ZPT on mouse oocyte maturation and quality in vitro and found exposure to ZPT significantly compromises oocyte maturation. The results revealed that ZPT disturbed the meiotic cell cycle by impairing cytoskeletal dynamics, kinetochore-microtubule attachment (K-MT), and causing spindle assembly checkpoints (SAC) continuous activation. Further, we observed the microtubule-organizing centers (MTOCs) associated proteins p-MAPK and Aurora-A were disrupted in ZPT-treated oocytes, signified by decreased expression and abnormal localization, responsible for the severe cytoskeletal defects. In addition, ZPT exposure induced a significant increase in the levels of H3K9me2, H3K9me3, H3K27me1, and H3K27me3, suggesting the alterations of epigenetic modifications. Moreover, the accumulation of zinc ions (Zn2+) was observed in ZPT-treated oocytes, which was detrimental because overmuch intracellular Zn2+ disrupted oocyte meiosis. Finally, these above alterations impaired spindle organization and chromosome alignment in metaphase-II (MII) oocytes, indicative of damaged oocytes quality. In conclusion, ZPT exposure influenced oocyte maturation and quality via involvement in MTOCs-associated proteins mediated spindle defects, altered epigenetic modifications and zinc accumulation.

Kinesin motor KIFC1 is required for tubulin acetylation and actin-dependent spindle migration in mouse oocyte meiosis.

Mammalian oocyte maturation is a unique asymmetric division, which is mainly because of actin-based spindle migration to the cortex. In the present study, we report that a kinesin motor KIFC1, which is associated with microtubules for the maintenance of spindle poles in mitosis, is also involved in actin dynamics in murine oocyte meiosis, co-localizing with microtubules during mouse oocyte maturation. Depletion of KIFC1 caused the failure of polar body extrusion, and we found that meiotic spindle formation and chromosome alignment were disrupted. This might be because of the effects of KIFC1 on HDAC6 and NAT10-based tubulin acetylation, which further affected microtubule stability. Mass spectroscopy analysis revealed that KIFC1 also associated with several actin nucleation factors and we found that KIFC1 was essential for the distribution of actin filaments, which further affected spindle migration. Depletion of KIFC1 leaded to aberrant expression of formin 2 and the ARP2/3 complex, and endoplasmic reticulum distribution was also disturbed. Exogenous KIFC1 mRNA supplement could rescue these defects. Taken together, as well as its roles in tubulin acetylation, our study reported a previously undescribed role of kinesin KIFC1 on the regulation of actin dynamics for spindle migration in mouse oocytes.

The Spontaneous Nitric Oxide Production during Mouse Oocyte Maturation and Aging Process

The Spontaneous Nitric Oxide Production during Mouse Oocyte Maturation and Aging Process

Identification of a heterozygous variant of ZP2 as a novel cause of empty follicle syndrome in humans and mice.

Is a recurrent heterozygous mutation in ZP2, c.1925G>A (p.R642Q), associated with the Empty follicle syndrome (EFS)? ZP2, c.1925G>A (p.R642Q), led to female infertility related to EFS in humans and mice and resulted in ZP2 accumulation in the cytoplasm of oocytes. EFS is a complex disease defined as a complete failure of oocyte retrieval after ovarian stimulation and after repeated aspirations and flushing of mature ovarian follicles. Furin-mediated cleavage is a post-translational modification (PTM) involved in various physiological processes, but the clear role of PTM mediated by furin cleavage of ZP2 protein on female fertility needs to be further explored. PTM is required for proteins to function in physiological conditions, and its perturbation has been linked to a growing number of human pathologies. Zona pellucida (ZP) proteins, which are important for oocyte development, are regulated post-translationally by well-characterized glycosylation events, as well as by furin-mediated cleavage. However, knowledge of the relevance of the consensus furin cleavage site of ZP proteins in female reproduction remains lacking. This was a basic medical research project to assess the pathogenicity of a heterozygous mutation in the ZP2 gene in EFS. We studied 3 families with EFS and a control group 2213 women with proven fertility. Whole-exome sequencing detected a heterozygous mutation in the ZP2 gene in all EFS patients. The mouse strain Zp2Arg635Gln/+ (ZP2R642Q) was generated by CRISPR-Cas9-mediated genome editing. RNA-sequencing was applied to investigate transcriptional changes in the ovaries of heterozygous ZP2R642Q knock-in (KI) mice compared to WT mice. We found a heterozygous mutation of ZP2, c.1925G>A (p.R642Q), in unrelated females with EFS, which was inherited in an autosomal-dominant manner. We used CRISPR-Cas9 to generate a mouse model encoding the orthologous variant of ZP2R642Q detected in humans, and the female ZP2R642Q KI mice recapitulated the human EFS phenotype. We further found the decreased expression of key genes involved in oocyte maturation in ZP2R642Q KI mice compared to WT mice by RNA-sequencing analysis. N/A. Only three families affected by EFS with the mutation were available because of its rare incidence. Although we have found different expressions of the several indispensable genes related to oocyte development between WT mice and ZP2R642Q KI mice through RNA-sequencing analysis, the specific regulatory mechanisms of the oocyte apoptosis in ZP2R642Q KI mice need to be studied further. These results are expected to open new avenues for researchers in the exploration of potential therapeutic strategies in treating EFS. This project is funded by the National Key Research and Development Program of China (2018YFC1002804, 2017YFC1001500 and 2016YFC1000200). All authors declared no competing interests. N/A.

Melatonin prevents oocyte deterioration due to cotinine exposure in mice†.

Levels of cotinine, a major metabolite of nicotine, have been positively correlated with risks of cigarette smoking-related diseases. Melatonin is synthesized by the pineal gland and has been demonstrated to be beneficial to oocyte maturation due to its antioxidative activity. In this study, we investigated the effects of cotinine on mouse oocyte meiosis and the protective roles of melatonin in vitro and in vivo. The results showed that cotinine exposure caused defects in the first polar body extrusion and reduced parthenogenetic activation in in vitro-matured oocytes. Additionally, cotinine exposure increased the level of oxidative stress, which resulted in aberrant actin distribution, abnormal spindle morphology, chromosome misalignment, and even oocyte aneuploidy. Simultaneously, cotinine exposure decreased the mitochondrial membrane potential and antioxidant gene expression and increased apoptosis-related gene expression. However, all these toxic effects of cotinine could be reversed after the addition of melatonin, and the mechanism may be a decrease in reactive oxygen species production. In conclusion, cotinine causes poor oocyte quality, which could be rescued by melatonin supplementation during meiotic maturation in mouse oocytes.

Fyn and argonaute 2 participate in maternal-mRNA degradation during mouse oocyte maturation

ABSTRACT Fertilization triggers physiological degradation of maternal-mRNAs, which are then replaced by embryonic transcripts. Ample evidence suggests that Argonaut 2 (AGO2) is a possible post-fertilization regulator of maternal-mRNAs degradation; but its role in degradation of maternal-mRNAs during oocyte maturation remains obscure. Fyn, a member of the Src family kinases (SFKs), and an essential factor in oocyte maturation, was reported to inhibit AGO2 activity in oligodendrocytes. Our aim was to examine the role of Fyn and AGO2 in degradation of maternal-mRNAs during oocyte maturation by either suppressing their activity with SU6656 – an SFKs inhibitor; or by microinjecting DN-Fyn RNA for suppression of Fyn and BCl-137 for suppression of AGO2. Batches of fifteen mouse oocytes or embryos were analyzed by qPCR to measure the expression level of nine maternal-mRNAs that were selected for their known role in oocyte growth, maturation and early embryogenesis. We found that Fyn/SFKs are involved in maintaining the stability of at least four pre-transcribed mRNAs in oocytes at the germinal vesicle (GV) stage, whereas AGO2 had no role at this stage. During in-vivo oocyte maturation, eight maternal-mRNAs were significantly degraded. Inhibition of AGO2 prevented the degreadation of at least five maternal-mRNAs, whereas inhibition of Fyn/SFK prevented degradation of at least five Fyn maternal-mRNAs and two SFKs maternal-mRNAs; pointing at their role in promoting the physiological degradation which occurs during in-vivo oocyte maturation. Our findings imply the involvement of Fyn/SFKs in stabilization of maternal-mRNA at the GV stage and the involvement of Fyn, SFKs and AGO2 in degradation of maternal mRNAs during oocyte maturation.

Nivalenol affects spindle formation and organelle functions during mouse oocyte maturation

Oocyte maturation is essential for fertilization and early embryo development, and proper organelle functions guarantee this process to maintain high-quality oocytes. The type B trichothecene nivalenol (NIV) is a mycotoxin produced by Fusarium oxysporum and is commonly found in contaminated food. NIV intake affect growth, the immune system, and the female reproductive system. Here, we investigated NIV toxicity on mouse oocyte quality. Transcriptome analysis results showed that NIV exposure altered the expression of multiple genes involved in spindle formation and organelle function in mouse oocytes, indicating its toxicity on mouse oocyte maturation. Further analysis indicated that NIV exposure disrupted spindle structure and chromosome alignment, possibly through tubulin acetylation. NIV exposure induced aberrant mitochondria distribution and reduced mitochondria number, mitochondria membrane potential (MMP), and ATP levels. In addition, NIV caused the abnormal distribution of the Golgi apparatus and altered the expression of the vesicle trafficking protein Rab11. ER distribution was also disturbed under NIV exposure, indicating the effects of NIV on protein modification and transport in oocytes. Thus, our results demonstrated that NIV exposure affected spindle structure and organelles function in mouse oocytes.

Dynamic changes of intracellular zinc ion level during maturation, fertilization, activation, and development in mouse oocytes.

Although it is well known that calcium oscillations are required for fertilization in all mammalian species studied to date, recent studies also showed the ejection of zinc into the extracellular milieu in a series of coordinated events, called "zinc spark," during mammalian fertilization. These results led us to the hypothesis that a zinc ion-dependent signal is important for oocyte maturation, fertilization (activation), and further embryonic development. In this study, we evaluated the amounts and localization of intracellular zinc ions during maturation, fertilization, activation, and embryonic development in mouse oocytes. Our results show that abundant zinc ions are present in both immature and mature oocytes. After in vitro fertilization, the amounts of zinc ions were dramatically decreased at the pronuclear (PN) stage. Artificial activation by cycloheximide, SrCl2 , and TPEN also reduced the amounts of zinc ions in the PN stage. On the other hand, PN embryos derived from sperm injection still showed high level of zinc ions. However, the amounts of zinc ions rapidly increased at the blastocysts regardless of activation method. We showed here that the amounts of zinc ions dramatically changed during maturation, fertilization, activation, and development in mouse oocytes.

Correlation between CDK1 protein and CDK1 mRNA during oocyte maturation in mouse.

The aim of this study was to investigate the correlation between CDK1 protein and CDK1 mRNA during oocyte maturation in vivo in mouse. GV, GVBD, MI and MII oocytes were obtained from mice, respectively. Western blot validated that the CDK1 protein expression increased continuously and significantly with oocyte maturation in vivo (P<0.05). Real-time qRT-PCR showed that CDK1 mRNA expression was down-regulated significantly during transformation from GV to MI stages (P<0.05), and up-regulated significantly during transformation from MI to MII stages (P<0.05). The level of CDK1 mRNA peaked at MII stages. Spearman correlation analysis indicated that CDK1 protein expression was poor correlation with CDK1 mRNA expression during oocyte maturation in vivo (R=0.200). This finding suggested that the increase of CDK1 protein during oocyte maturation in vivo was not entirely caused by the change of transcription level. The results provide new food for thought for further research on the molecular mechanism of oocyte maturation in vivo.

Lycopene Improves Maturation Rate and Antioxidant Status of in vitro Matured Mouse Oocytes

The present study aimed to investigate the effect of lycopene supplementation to the in vitro maturation (IVM) medium of mouse oocytes on their maturation rate and oxidative biomarkers levels. Lycopene concentrations of 50, 100, 200, and 400nM were tested. The effects of lycopene on maturation rate of mouse oocytes under in vitro oxidative and heat stress conditions were also explored. Cumulus-oocyte complexes (COCs) were collected from ovaries of super-ovulated mice via puncturing technique and incubated in the IVM medium for 17h. To simulate oxidative stress, COCs were incubated in an IVM medium containing 100µM hydrogen peroxide (H2O2) with or without lycopene. Additionally, to mimic heat stress, COCs were in vitro matured at 40℃ with or without lycopene. Among the four tested lycopene concentrations, the 200nM lycopene achieved the highest improvement in oocyte maturation. The oocyte concentrations of H2O2, malondialdehyde (MDA), total antioxidant capacity (TAC), reduced glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD) were altered by lycopene treatment: H2O2 and MDA were significantly decreased, meanwhile TAC, GSH, CAT and SOD were increased. IVM rates of mouse oocytes revealed a significant decline following their exposure to heat and oxidative stresses. Interestingly, lycopene supplementation rescued the IVM rate of the oxidative stressed or the thermally challenged mouse oocytes as they appeared comparable to those of the control oocytes. Taken together, our data report beneficial effects of lycopene on mouse oocytes and suggest lycopene as a candidate factor for improving the quality of mammalian oocytes and embryos.

The effects of plasma-derived extracellular vesicles on cumulus expansion and oocyte maturation in mice

Cumulus cell expansion is required for the ovulation of a fertilizable oocyte. Extracellular vesicles (EVs) are bilayer-lipid membrane vesicles that may be found in a variety of bodily fluids and play an important role in biological processes. This study aimed to examine the effects of plasma-derived EVs on cumulus expansion and in vitro maturation (IVM) of the oocyte. EVswere isolated using ultracentrifugation from the plasma of female mice. The morphology and size of EVs were analyzed by transmission electron microscopy (TEM) and dynamic light scattering (DLS). Western blotting allowed us to identify CD63, CD81, CD9, and HSP70 protein markers of EVs; the expression of the genes related to cumulus cell expansion, including hyaluronan synthase 2 (Has2) and prostaglandinendoperoxide synthase 2 (Ptgs2), were assessed using real-time polymerase chain reaction. Plasma-derived EVs labeled with Dil dye were successfully incorporated with cumulus cells during IVM. Plasma-derived EVs significantly induced cumulus expansion and maturation of oocytes. The percentage of oocytes that reached the MII stage was significantly greater in the EVs treatment group compared with other groups. Although treatment with epidermal growth factor (EGF) significantly increased cumulus expansion in cumulus-oocyte complexes (COCs), the impact was less than that seen with plasma-derived EVs. Furthermore, EVs generated from plasma substantially enhanced Has2 and Ptgs2 mRNA expression in the cumulus-oocyte complex. This research indicates that EVs derived from plasma are capable of promoting cumulus expansion and oocyte maturation.

A primary effect of palmitic acid on mouse oocytes is the disruption of the structure of the endoplasmic reticulum.

Exposure of mouse oocytes to saturated fatty acids (FAs) such as palmitic acid (PA) has been shown to increase lipid content and cause an endoplasmic reticulum (ER) stress response and changes in the mitochondrial redox state. PA can also disrupt Ca2+ stores in other cell types. The links between these intracellular changes, or whether they are prevented by mono-unsaturated FAs such as oleic acid (OA), is unclear. Here, we have investigated the effects of FAs on mouse oocytes, that are maturated in vitro, using coherent anti-Stokes Raman scattering and two-photon fluorescence microscopy. When oocytes were matured in the presence of PA, there were changes in the aggregation pattern and size of lipid droplets that were mitigated by co-incubation in OA. Maturation in PA alone also caused a distinctive disruption of the ER structure. This effect was prevented by incubation of OA with PA. In contrast, maturation of mouse oocytes in medium containing PA was not associated with any significant change in the redox state of mitochondria or the Ca2+ content of intracellular stores. These data suggest that a primary effect of saturated FAs such as PA on oocytes is to disrupt the structure of the ER and this is not due to an effect on the mitochondria or Ca2+ stores.

The N501Y Mutation of SARS-CoV-2 Spike Protein Impairs Spindle Assembly in Mouse Oocytes.

The COVID-19 pandemic has been continuing for one and a half year and caused a profound effect on human health. Although advanced researches and literatures are gathered, the influences of SARS-CoV-2 on the reproduction systems are largely unknown, especially on the female reproductive functions. The purpose of this study was to investigate the effect of N501Y mutant spike protein of SARS-Cov-2 on oocyte maturation. We demonstrated that the N501Y mutant of SARS-CoV-2 spike protein impaired the mouse oocyte maturation accompanied by abnormal spindle assembly. Furthermore, the mean spindle length and the plate width were significantly increased in the N501Y-treated group compared to the control group. These results indicated the potential impairment of maturation of the oocytes caused by the infection of SARS-CoV-2, albeit current results were derived from mouse oocytes. The present study provided a theoretical basis for the attention of female reproductive health during the COVID-19 pandemic and shed light on the potential risk of SARS-CoV-2 in the successful rate of assisted reproduction.Supplementary InformationThe online version contains supplementary material available at 10.1007/s43032-021-00809-7.

Toxic effects of methomyl on mouse oocytes and its possible mechanisms.

Methomyl is a broad-spectrum carbamate insecticide that has a variety of toxic effects on humans and animals. However, there have been no studies on the toxicity of methomyl in female mammalian oocytes. This study investigated the toxic effects of environmental oestrogen methomyl exposure on mouse oocyte maturation and its possible mechanisms. Our results indicated that methomyl exposure inhibited polar body extrusion in mouse oocytes. Compared with that in the control group, in the methomyl treatment group, superoxide anion free radicals in oocytes were significantly increased. In addition, the mitochondrial membrane potential of metaphase II stage oocytes in the methomyl treatment group was significantly decreased, resulting in reduced mouse oocyte quality. After 8.5 h of exposure to methomyl, metaphase I stage mouse oocytes displayed an abnormal spindle morphology. mRNA expression of the pro-apoptotic genes Bax and Caspase-3 in methomyl-treated oocytes increased, which confirmed the apoptosis. Collectively, our results indicated that mouse oocyte maturation is defective after methomyl treatment at least through disruption of spindle morphology, mitochondrial function and by induction of oxidative stress.

Pervasive 3'-UTR Isoform Switches During Mouse Oocyte Maturation.

Oocyte maturation is the foundation for developing healthy individuals of mammals. Upon germinal vesicle breakdown, oocyte meiosis resumes and the synthesis of new transcripts ceases. To quantitatively profile the transcriptomic dynamics after meiotic resumption throughout the oocyte maturation, we generated transcriptome sequencing data with individual mouse oocytes at three main developmental stages: germinal vesicle (GV), metaphase I (MI), and metaphase II (MII). When clustering the sequenced oocytes, results showed that isoform-level expression analysis outperformed gene-level analysis, indicating isoform expression provided extra information that was useful in distinguishing oocyte stages. Comparing transcriptomes of the oocytes at the GV stage and the MII stage, in addition to identification of differentially expressed genes (DEGs), we detected many differentially expressed transcripts (DETs), some of which came from genes that were not identified as DEGs. When breaking down the isoform-level changes into alternative RNA processing events, we found the main source of isoform composition changes was the alternative usage of polyadenylation sites. With detailed analysis focusing on the alternative usage of 3′-UTR isoforms, we identified, out of 3,810 tested genes, 512 (13.7%) exhibiting significant switches of 3′-UTR isoforms during the process of moues oocyte maturation. Altogether, our data and analyses suggest the importance of examining isoform abundance changes during oocyte maturation, and further investigation of the pervasive 3′-UTR isoform switches in the transition may deepen our understanding on the molecular mechanisms underlying mammalian early development.

YTHDF2 is essential for spermatogenesis and fertility by mediating a wave of transcriptional transition in spermatogenic cells.

The dynamic and reversible regulation roles of m6A modification and the characterization of m6A readers have provided new insights into spermatogenesis at the post-transcriptional level. YTHDF2, as an m6A reader, has been reported to mediate the m6A-containing transcript decay during the mouse oocyte maturation, embryonic stem cell differentiation, neural development, and zebrafish maternal-to-zygotic transition. However, the roles of YTHDF2 in mammalian spermatogenesis are uncertain. Here, we generated germ cell-specific Ythdf2 mutants (Ythdf2-vKO) at a C57BL/6J background and demonstrated that YTHDF2 is essential for mouse spermatogenesis and fertility. Ythdf2-vKO provides oligoasthenoteratozoospermia phenotype with increased apoptosis in germ cells. High-throughput RNA-seq analysis showed that a group of mRNAs is upregulated in Ythdf2-vKO mouse testis; further analysis and MeRIP-qPCR data showed that most of the upregulated genes in Ythdf2-vKO mouse testis are modified with m6A and are YTHDF2 candidate binding genes. Interestingly, RNA-seq analysis combined with our previous single-cell transcriptomics data of mouse spermatogenesis pointed out the failure of a wave of transcript transition during the spermatogenesis of Ythdf2-vKO mice, which was confirmed by gene expression analysis using qPCR of diplotene spermatocytes and round spermatids obtained through fluorescence-activated cell sorting. Our study demonstrates the fundamental role of YTHDF2 during mouse spermatogenesis and provides a potential candidate for the diagnosis of male infertility with the oligoasthenoteratozoospermia syndrome.

CDC26 is a key factor in human oocyte aging.

Is CDC26 a key factor in human oocyte aging? The lack of CDC26 disrupts the oocytes maturation process, leading to oocyte aging, but these defects could be partially rescued by overexpression of the CDC26 protein. Age-related oocyte aging is the main cause of female fertility decline. In mammalian oocytes, aberrant meiosis can cause chromosomal abnormalities that might lead to infertility and developmental disorders. CDC26 participates in the meiosis process. Differential gene expression in young and old women oocytes were screened by single-cell RNA-seq technology, and the functions of differentially genes were verified on mouse oocytes. Finally, transfection technology was used to evaluate the effect of a differentially expressed gene in rescuing human oocyte from aging. Discarded human oocytes were collected for single-cell RNA-seq, q-PCR and immunocytochemical analyses to screen for and identify differential gene expression. Female KM mice oocytes were collected for IVM of oocytes, q-PCR and immunocytochemical analyses to delineate the relationships between oocyte aging and differential gene expression. Additionally, recombinant lentiviral vectors encoding CDC26 were transfected into the germinal vesicle oocytes of older women, to investigate the effects of the CDC26 gene expression on oocyte development. Many genes were found to be differentially expressed in the oocytes of young versus old patients via RNA-seq technology. CDC26 mRNA and protein levels in aged oocytes were severely decreased, when compared with the levels observed in young oocytes. Moreover, aged oocytes lacking CDC26 were more prone to aneuploidy. These defects in aged oocytes could be partially rescued by overexpression of the CDC26 protein. N/A. Our study delineated key steps in the oocyte aging process by identifying the key role of CDC26 in the progression of oocyte maturation. Future studies are required to address whether other signaling pathways play a role in regulating oocyte maturation via CDC26 and which genes are the direct molecular targets of CDC26. Our results using in vitro systems for both mouse and human oocyte maturation provide a proof of principle that CDC26 may represent a novel therapeutic approach against maternal aging-related spindle and chromosomal abnormalities. This work was supported by grants from the National Natural Science Foundation of China (81571442 and 81170571), the outstanding Talent Project of Shanghai Municipal Commission of Health (XBR2011067) and Clinical Research and Cultivation Project in Shanghai Municipal Hospitals (SHDC12019X32). The authors declare no conflict of interest.

Perfluorooctane sulfonate affects mouse oocyte maturation in vitro by promoting oxidative stress and apoptosis induced bymitochondrial dysfunction

Perfluorooctane sulphonate (PFOS), as a surfactant, is widely applied in the agricultural production activities and has become a potential menace to human health. The mechanism of its effect on the maturation of mammalian oocytes is unclear. This study explored the toxic effect of PFOS on mouse oocyte maturation in vitro. The results revealed that PFOS under a concentration of 600 μM could significantly reduce the polar body extrusion rate (PBE) of mouse oocytes and cause symmetrical cell division. Further experiments showed that PFOS resulted in the abnormal cytoskeleton of the oocytes, causing the abnormal spindles and misplaced chromosomes, as well as the impaired dynamics of actin. Moreover, PFOS exposure inhibited the process of oocyte meiosis, which reflected in the slower spindle migration and continuous activation of spindle assembly checkpoint (SAC), then ultimately increased the probability of aneuploidy. Most importantly, PFOS exposure reduced the quality of oocytes, specifically by disrupting the function of mitochondria, inducing cell oxidative stress, and triggering early apoptosis. Furthermore, the level of methylation of histones is additionally influenced. In summary, our findings showed that PFOS exposure interfered with the maturation of mouse oocytes through affecting cytoskeletal dynamics, meiotic progression, oocyte quality, and histone modifications.