FMNL2 regulates actin for endoplasmic reticulum and mitochondria distribution in oocyte meiosis.

During mammalian oocyte meiosis, spindle migration and asymmetric cytokinesis are unique steps for the successful polar body extrusion. The asymmetry defects of oocytes will lead to the failure of fertilization and embryo implantation. In present study, we reported that an actin nucleating factor Formin-like 2 (FMNL2) played critical roles in the regulation of spindle migration and organelle distribution in mouse and porcine oocytes. Our results showed that FMNL2 mainly localized at the oocyte cortex and periphery of spindle. Depletion of FMNL2 led to the failure of polar body extrusion and large polar bodies in oocytes. Live-cell imaging revealed that the spindle failed to migrate to the oocyte cortex, which caused polar body formation defects, and this might be due to the decreased polymerization of cytoplasmic actin by FMNL2 depletion in the oocytes of both mice and pigs. Furthermore, mass spectrometry analysis indicated that FMNL2 was associated with mitochondria and endoplasmic reticulum (ER)-related proteins, and FMNL2 depletion disrupted the function and distribution of mitochondria and ER, showing with decreased mitochondrial membrane potential and the occurrence of ER stress. Microinjecting Fmnl2-EGFP mRNA into FMNL2-depleted oocytes significantly rescued these defects. Thus, our results indicate that FMNL2 is essential for the actin assembly, which further involves into meiotic spindle migration and ER/mitochondria functions in mammalian oocytes.

Comparison of embryo quality and pregnancy outcomes for patients with low ovarian reserve in natural cycles and mildly stimulated cycles: a cohort study.

BACKGROUND: As women with low ovarian reserve embark on the challenging journey of in-vitro fertilisation (IVF) treatment, the choice between natural and mildly stimulated cycles becomes a pivotal consideration. It is unclear which of these two regimens is superior for women with low ovarian reserve. Our study aims to assess the impact of natural cycles on embryo quality and pregnancy outcomes in women with low ovarian reserve undergoing IVF treatment compared to mildly stimulated cycles. METHODS: This retrospective study enrolled consecutive patients with low ovarian reserve who underwent IVF/intracytoplasmic sperm injection (ICSI) at Guangdong Second Provincial General Hospital between January 2017 and April 2021. The primary outcome for pregnancy rate of 478 natural cycles and 448 mild stimulated cycles was compared. Secondary outcomes included embryo quality and oocyte retrieval time of natural cycles. RESULTS: The pregnancy rate in the natural cycle group was significantly higher than that in the mildly stimulated cycle group (51.8% vs. 40.1%, p = 0.046). Moreover, natural cycles exhibited higher rates of available embryos (84.1% vs. 78.6%, p = 0.040), high-quality embryos (61.8% vs. 53.2%, p = 0.008), and utilisation of oocytes (73% vs. 65%, p = 0.001) compared to mildly stimulated cycles. Oocyte retrievals in natural cycles were predominantly performed between 7:00 and 19:00, with 94.9% occurring during this time frame. In natural cycles with high-quality embryos, 96.4% of oocyte retrievals were also conducted between 7:00 and 19:00. CONCLUSION: Natural cycles with appropriately timed oocyte retrieval may present a valuable option for patients with low ovarian reserve.

In the realm of in-vitro fertilisation (IVF) treatment, women with low ovarian reserve often face the crucial decision of opting for natural or mildly stimulated cycles. This retrospective study, conducted between January 2017 and April 2021 at Guangdong Second Provincial General Hospital, delves into the impact of these cycles on pregnancy outcomes. Examining 478 natural cycles and 448 mildly stimulated cycles, the study reveals a notably higher pregnancy rate in the natural cycle group (51.8% vs. 40.1%). Additionally, natural cycles demonstrated higher rates of available embryos, high-quality embryos, and oocyte utilisation compared to their mildly stimulated counterparts. The findings suggest that natural cycles, with proper oocyte retrieval timing, could be a favourable choice for those with low ovarian reserve seeking IVF treatment.

Gut microbiota-bile acid-vitamin D axis plays an important role in determining oocyte quality and embryonic development.

OBJECTIVE: To reveal whether gut microbiota and their metabolites are correlated with oocyte quality decline caused by circadian rhythm disruption, and to search possible approaches for improving oocyte quality. DESIGN: A mouse model exposed to continuous light was established. The oocyte quality, embryonic development, microbial metabolites and gut microbiota were analyzed. Intragastric administration of microbial metabolites was conducted to confirm the relationship between gut microbiota and oocyte quality and embryonic development. RESULTS: Firstly, we found that oocyte quality and embryonic development decreased in mice exposed to continuous light. Through metabolomics profiling and 16S rDNA-seq, we found that the intestinal absorption capacity of vitamin D was decreased due to significant decrease of bile acids such as lithocholic acid (LCA), which was significantly associated with increased abundance of Turicibacter. Subsequently, the concentrations of anti-Mullerian hormone (AMH) hormone in blood and melatonin in follicular fluid were reduced, which is the main reason for the decline of oocyte quality and early embryonic development, and this was rescued by injection of vitamin D3 (VD3). Secondly, melatonin rescued oocyte quality and embryonic development by increasing the concentration of lithocholic acid and reducing the concentration of oxidative stress metabolites in the intestine. Thirdly, we found six metabolites that could rescue oocyte quality and early embryonic development, among which LCA of 30 mg/kg and NorDCA of 15 mg/kg had the best rescue effect. CONCLUSION: These findings confirm the link between ovarian function and gut microbiota regulation by microbial metabolites and have potential value for improving ovary function.

Insights into the adverse effects of prepubertal chronic ethanol exposure on adult female reproduction.

Heavy drinking in women is known to adversely affect pregnancy and fertility. However, pregnancy is a complex process, and the adverse effects of ethanol on pregnancy does not mean that ethanol will have adverse effects on all stages from gamete to fetal formation. Similarly, the adverse effects of ethanol before and after adolescence cannot be generalized. To focus on the effects of prepubertal ethanol on female reproductive ability, we established a mouse model of prepubertal ethanol exposure by changing drinking water to 20% v/v ethanol. Some routine detections were performed on the model mice, and details such as mating, fertility, reproductive organ and fetal weights were recorded day by day after discontinuation of ethanol exposure. Prepubertal ethanol exposure resulted in decreased ovarian weight and significantly reduced oocyte maturation and ovulation after sexual maturation, however, normal morphology oocytes with discharged polar body showed normal chromosomes and spindle morphology. Strikingly, oocytes with normal morphology from ethanol exposed mice showed reduced fertilization rate, but once fertilized they had the ability to develop to blastocysts. RNA-seq analysis showed that the gene expression of the ethanol exposed oocytes with normal morphology had been altered. These results show the adverse effects of prepubertal alcohol exposure on adult female reproductive health.

NLRP14 Safeguards Calcium Homeostasis via Regulating the K27 Ubiquitination of Nclx in Oocyte-to-Embryo Transition.

Sperm-induced Ca2+ rise is critical for driving oocyte activation and subsequent embryonic development, but little is known about how lasting Ca2+ oscillations are regulated. Here it is shown that NLRP14, a maternal effect factor, is essential for keeping Ca2+ oscillations and early embryonic development. Few embryos lacking maternal NLRP14 can develop beyond the 2-cell stage. The impaired developmental potential of Nlrp14-deficient oocytes is mainly caused by disrupted cytoplasmic function and calcium homeostasis due to altered mitochondrial distribution, morphology, and activity since the calcium oscillations and development of Nlrp14-deficient oocytes can be rescued by substitution of whole cytoplasm by spindle transfer. Proteomics analysis reveal that cytoplasmic UHRF1 (ubiquitin-like, containing PHD and RING finger domains 1) is significantly decreased in Nlrp14-deficient oocytes, and Uhrf1-deficient oocytes also show disrupted calcium homeostasis and developmental arrest. Strikingly, it is found that the mitochondrial Na+ /Ca2+ exchanger (NCLX) encoded by Slc8b1 is significantly decreased in the Nlrp14mNull oocyte. Mechanistically, NLRP14 interacts with the NCLX intrinsically disordered regions (IDRs) domain and maintain its stability by regulating the K27-linked ubiquitination. Thus, the study reveals NLRP14 as a crucial player in calcium homeostasis that is important for early embryonic development.

A long-acting recombinant FSH supports high-quality mouse follicle development and oocyte maturation in vitro by coordinating somatic and germ cell transcriptomes.

Strategies to maximize individual fertility chances are constant requirements of ART. In vitro folliculogenesis may represent a valid option to create a large source of immature ovarian follicles in ART. Efforts are being made to set up mammalian follicle culture protocols with suitable FSH stimuli. In this study, a new type of recombinant FSH (KN015) with a prolonged half-life is proposed as an alternative to canonical FSH. KN015 supports the in vitro development of mouse follicles from primary to preovulatory stage with higher efficiency than canonical FSH and enhanced post-fertilization development rates of the ovulated oocytes. The use of KN015 also allows us to compare the dynamic transcriptome changes in oocytes and granulosa cells at different stages, in vivo and in vitro. In particular, KN015 facilitates mRNA accumulation in growing mouse oocytes and prevents spontaneous luteinization of granulosa cells in vitro. Novel analyses of transcriptome changes in this study reveal that the in vivo oocytes were more efficient than in vitro oocytes in terms of maternal mRNA clearing during meiotic maturation. KN015 promotes the degradation of maternal mRNA during in vitro oocyte maturation, improves cytoplasmic maturation and, therefore, enhances embryonic developmental potential. These findings establish new transcriptome data for oocyte and granulosa cells at the key stages of follicle development, and should help to widen the use of KN015 as a valid and commercially available hormonal support enabling optimized in vitro development of follicles and oocytes.

Dynamic of centromere associated RNAs and the centromere loading of DNA repair proteins in growing oocytes.

Mammalian centromeres are generally composed of dispersed repeats and the satellites such as α-satellites in human and major/minor satellites in mouse. Transcription of centromeres by RNA polymerase II is evolutionary conserved and critical for kinetochore assembly. In addition, it has been found that the transcribed satellite RNAs can bind DNA repair proteins such as MRE11 and PRKDC, and excessively expressed satellite RNAs could induce genome instability and facilitate tumorigenesis. During the maturation of female oocyte, centromeres are critical for accurate segregation of homologous chromosomes and sister chromatids. However, the dynamics of oocyte centromere transcription and whether it associated with DNA repair proteins are unknown. In this study, we found the transcription of centromeres is active in growing oocytes but it is silenced when oocytes are fully grown. DNA repair proteins like Mlh1, Mre11 and Prkdc are found associated with the minor satellites and this association can be interfered by RNA polymerase II inhibitor α-amanitin. When the growing oocyte is in vitro matured, Mlh1/Mre11/Prkdc foci would release from centromeres to the ooplasm. If the oocytes are treated with Mre11 inhibitor Mirin, the meiosis resumption of growing oocytes with Mre11 foci can be suppressed. These data revealed the dynamic of centromeric transcription in oocytes and its potential association with DNA repair proteins, which provide clues about how oocytes maintain centromere stability and assemble kinetochores.

USP7 reduction leads to developmental failure of mouse early embryos.

As a member of Ubiquitin-specific protease subfamily, ubiquitin specific protease 7 (USP7) has been reported to participate in a variety of cellular processes, including cell cycle, apoptosis, DNA damage response, and epigenetic modification. However, its function in preimplantation embryos is still obscure. To investigate the functions of USP7 during preimplantation embryo development, we used siRNA to degrade endogenous USP7 messenger RNA. We found that USP7 knockdown significantly decreased the development rate of mouse early embryos. Moreover, depletion of USP7 induced the accumulation of the DNA lesions and apoptotic blastomeres in early embryos. In addition, USP7 knockdown caused an abnormal H3K27me3 modification in 2-cell embryos. Overall, our results indicate that USP7 maintains genome stability perhaps via regulating H3K27me3 and DNA damage, consequently controlling the embryo quality.

Continuous light exposure influences luteinization and luteal function of ovary in ICR mice.

With the rapid change of people's lifestyle, more childbearing couples live with irregular schedules (i.e., staying up late) and suffer from decreased fertility and abortion, which can be caused by luteal phase defect (LPD). We used continuous light-exposed mice as a model to observe whether continuous light exposure may affect luteinization and luteal function. We showed that the level of progesterone in serum reduced (p < .001), the number of corpus luteum (CL) decreased (p < .01), and the expressions of luteinization-related genes (Lhcgr, Star, Ptgfr, and Runx2), clock genes (Clock and Per1), and Mt1 were downregulated (p < .05) in the ovaries of mice exposed to continuous light, suggesting that continuous light exposure induces defects in luteinization and luteal functions. Strikingly, injection of melatonin (3 mg/kg) could improve luteal functions in continuous light-exposed mice. Moreover, we found that, after 2 h of hCG injection, the level of pERK1/2 in the ovary decreased in the continuous light group, but increased in the melatonin administration group, suggesting that melatonin can improve LPD caused by continuous light exposure through activating the ERK1/2 pathway. In summary, our data demonstrate that continuous light exposure affects ovary luteinization and luteal function, which can be rescued by melatonin.

Maternal exposure to 4-vinylcyclohexene diepoxide during pregnancy induces subfertility and birth defects of offspring in mice.

4-vinylcyclohexene diepoxide (VCD), widely used in industry, is a hazardous compound that can cause premature ovarian failure, but whether maternal VCD exposure affects the health and reproduction of offspring is unknown. Here we focused on the effects of VCD on fertility and physical health of F1 and F2 offspring in mice. The pregnant mice were injected intraperitoneally with different dosages of VCD once every day from 6.5 to 18.5 days post-coitus (dpc). We showed that maternal exposure to VCD during pregnancy significantly reduced the litter size and ovarian reserve, while increasing microtia occurrences of F1 mice. The cytospread staining showed a significant inhibition of meiotic prophase I progression from the zygotene stage to the pachytene stage. Mechanistically, the expression level of DNA damage marker (γ-H2AX) and BAX/BCL2 ratios were significantly increased, and RAD51 and DMC1 were extensively recruited to DNA double strand breaks sites in the oocytes of offspring from VCD-exposed mothers. Overall, our results provide solid evidence showing that maternal exposure to VCD during pregnancy has intergenerational deleterious effects on the offspring.

Maternal EHMT2 is essential for homologous chromosome segregation by regulating Cyclin B3 transcription in oocyte meiosis.

During oocyte growth, various epigenetic modifications are gradually established, accompanied by accumulation of large amounts of mRNAs and proteins. However, little is known about the relationship between epigenetic modifications and meiotic progression. Here, by using Gdf9-Cre to achieve oocyte-specific ablation of Ehmt2 (Euchromatic-Histone-Lysine-Methyltransferase 2) from the primordial follicle stage, we found that female mutant mice were infertile. Oocyte-specific knockout of Ehmt2 caused failure of homologous chromosome separation independent of persistently activated SAC during the first meiosis. Further studies revealed that lacking maternal Ehmt2 affected the transcriptional level of Ccnb3, while microinjection of exogenous Ccnb3 mRNA could partly rescue the failure of homologous chromosome segregation. Of particular importance was that EHMT2 regulated ccnb3 transcriptions by regulating CTCF binding near ccnb3 gene body in genome in oocytes. In addition, the mRNA level of Ccnb3 significantly decreased in the follicles microinjected with Ctcf siRNA. Therefore, our findings highlight the novel function of maternal EHMT2 on the metaphase I-to-anaphase I transition in mouse oocytes: regulating the transcription of Ccnb3.

Reduction of mtDNA heteroplasmy in mitochondrial replacement therapy by inducing forced mitophagy.

Mitochondrial replacement therapy (MRT) has been used to prevent maternal transmission of disease-causing mutations in mitochondrial DNA (mtDNA). However, because MRT requires nuclear transfer, it carries the risk of mtDNA carryover and hence of the reversion of mtDNA to pathogenic levels owing to selective replication and genetic drift. Here we show in HeLa cells, mouse embryos and human embryos that mtDNA heteroplasmy can be reduced by pre-labelling the mitochondrial outer membrane of a donor zygote via microinjection with an mRNA coding for a transmembrane peptide fused to an autophagy receptor, to induce the degradation of the labelled mitochondria via forced mitophagy. Forced mitophagy reduced mtDNA carryover in newly reconstructed embryos after MRT, and had negligible effects on the growth curve, reproduction, exercise capacity and other behavioural characteristics of the offspring mice. The induction of forced mitophagy to degrade undesired donor mtDNA may increase the clinical feasibility of MRT and could be extended to other nuclear transfer techniques.

Correction: Chromosomal variants accumulate in genomes of the spontaneous aborted fetuses revealed by chromosomal microarray analysis.

[This corrects the article DOI: 10.1371/journal.pone.0259518.].

Metabolomic and transcriptomic responses of mouse testis to the dextran sulfate sodium induced colitis.

Inflammatory bowel diseases (IBDs), including Crohn's disease (CD) and ulcerative colitis, are widespread in developed countries and gradually increasing in developing countries. Evidences showed that man with CD has a decrease of serum testosterone, but how IBD take effects on testicular testosterone synthesis is not well elucidated. To investigate the effects of IBD on testis, we analyzed testicular metabolome and transcriptome data of the dextran sulfate sodium (DSS) induced IBD mice. As a result, metabolomic data showed that DSS indeed induced androgen decrease in mouse testis. Correspondingly, androgen synthesis associated genes, especially Lhcgr, were down-regulated in DSS testis. From the metabolomic data, we found vitamin intake associated metabolites vitamin B2 and pyridoxamine were significantly decreased, whereas fatty acid metabolism associated molecules N-lauroylglycine and N-decanoylglycine were increased in DSS testis. In addition, we found 8-hydroxy-deoxyguanosine, a DNA oxidative damage marker, and 8-oxoguanine, a molecule responsible for DNA damage repair, were also changed in DSS testis. Simultaneously, our data also showed that DSS up-regulated the expression of meiosis initiation associated gene Stra8 and oxygen transport associated genes in testis. In summary, these results depicted the complex effects of colitis on testis. These metabolites and transcripts changed in DSS testis could be used as potential targets for IBD treatment or symptom relieve.

Chromosomal variants accumulate in genomes of the spontaneous aborted fetuses revealed by chromosomal microarray analysis.

Spontaneous abortion is an impeding factor for the success rates of human assistant reproductive technology (ART). Causes of spontaneous abortion include not only the pregnant mothers' health conditions and lifestyle habits, but also the fetal development potential. Evidences had shown that fetal chromosome aneuploidy is associated with fetal spontaneous abortion, however, it is still not definite that whether other genome variants, like copy number variations (CNVs) or loss of heterozygosity (LOHs) is associated with the spontaneous abortion. To assess the relationship between the fetal genome variants and abortion during ART, a chromosomal microarray data including chromosomal information of 184 spontaneous aborted fetuses, 147 adult female patients and 78 adult male patients during ART were collected. We firstly analyzed the relationship of fetal aneuploidy with maternal ages and then compared the numbers and lengths of CNVs (< 4Mbp) and LOHs among adults and aborted fetuses. In addition to the already known association between chromosomal aneuploidy and maternal ages, from the chromosomal microarray data we found that the numbers and the accumulated lengths of short CNVs and LOHs in the aborted fetuses were significantly larger or longer than those in adults. Our findings indicated that the increased numbers and accumulated lengths of CNVs or LOHs might be associated with the spontaneous abortion during ART.

High-Survival Rate After Microinjection of Mouse Oocytes and Early Embryos With mRNA by Combining a Tip Pipette and Piezoelectric-Assisted Micromanipulator.

Utilizing microinjection to introduce biological molecules such as DNA, mRNA, siRNA, and proteins into the cell is well established to study oocyte maturation and early embryo development in vitro. However, microinjection is an empirical technology. The cellular survival after microinjection is mainly dependent on the operator, and an experienced operator should be trained for a long time, from several months to years. Optimizing the microinjection to be highly efficient and quickly learned should be helpful for new operators and some newly established laboratories. Here, we combined the tip pipette and piezo-assisted micromanipulator to microinject the oocyte and early embryos at different stages of mouse. The results showed that the survival rate after microinjection was more than 85% for cumulus-oocyte complex, germinal vesicle oocyte, two-cell, and four-cell embryos, and close to 100% for MII oocyte and zygotes. The high-rate survival of microinjection can save many experimental samples. Thus, it should be helpful in studying some rare animal models such as aging and conditional gene knockout mice. Furthermore, our protocol is much easier to learn for new operators, who can usually master the method proficiently after several training times. Therefore, we would like to publicly share this experience, which will help some novices master microinjection skillfully and save many laboratory animals.

Single-cell RNA sequencing analysis of mouse follicular somatic cells†.

Within the development of ovarian follicle, in addition to cell proliferation and differentiation, sophisticated cell-cell cross talks are established among follicular somatic cells such as granulosa cells (GCs) and theca cells. To systematically reveal the cell differentiation and signal transductions in follicular somatic cells, we collected the mouse follicular somatic cells from secondary to ovulatory stage, and analyzed the single cell transcriptomes. Having data filtered and screened, we found 6883 high variable genes in 4888 single cells. Then follicular somatic cells were clustered into 26 cell clusters, including 18 GC clusters, 4 theca endocrine cell (TEC) clusters, and 4 other somatic cell clusters, which include immune cells and Acta2 positive theca externa cells. From our data, we found there was metabolic reprogramming happened during GC differentiation. We also found both Cyp19a1 and Cyp11a1 could be expressed in TECs. We analyzed the expression patterns of genes associated with cell-cell interactions such as steroid hormone receptor genes, insulin signaling genes, and cytokine/transformation growth factor beta associated genes in all cell clusters. Lastly, we clustered the highly variable genes into 300 gene clusters, which could be used to search new genes involved in follicle development. These transcriptomes of follicular somatic cells provide us potential clues to reveal how mammals regulating follicle development and could help us find targets to improve oocyte quality for women with low fertility.

Double-strand breaks induce short-scale DNA replication and damage amplification in the fully grown mouse oocytes.

Break-induced replication (BIR) is essential for the repair of DNA double-strand breaks (DSBs) with single ends. DSBs-induced microhomology-mediated BIR (mmBIR) and template-switching can increase the risk of complex genome rearrangement. In addition, DSBs can also induce the multi-invasion-mediated DSB amplification. The mmBIR-induced genomic rearrangement has been identified in cancer cells and patients with rare diseases. However, when and how mmBIR is initiated have not been fully and deeply studied. Furthermore, it is not well understood about the conditions for initiation of multi-invasion-mediated DSB amplification. In the G2 phase oocyte of mouse, we identified a type of short-scale BIR (ssBIR) using the DNA replication indicator 5-ethynyl-2'-deoxyuridine (EdU). These ssBIRs could only be induced in the fully grown oocytes but not the growing oocytes. If the DSB oocytes were treated with Rad51 or Chek1/2 inhibitors, both EdU signals and DSB marker γH2A.X foci would decrease. In addition, the DNA polymerase inhibitor Aphidicolin could inhibit the ssBIR and another inhibitor ddATP could reduce the number of γH2A.X foci in the DSB oocytes. In conclusion, our results showed that DNA DSBs in the fully grown oocytes can initiate ssBIR and be amplified by Rad51 or DNA replication.

Maturation conditions, post-ovulatory age, medium pH, and ER stress affect [Ca2+]i oscillation patterns in mouse oocytes.

Insufficiency of oocyte activation impairs the subsequent embryo development in assisted reproductive technology (ART). Intracellular Ca2+ concentration ([Ca2+]i) oscillations switch the oocytes to resume the second meiosis and initiate embryonic development. However, the [Ca2+]i oscillation patterns in oocytes are poorly characterized. In this study, we investigated the effects of various factors, such as the oocytes age, pH, cumulus cells, in vitro or in vivo maturation, and ER stress on [Ca2+]i oscillation patterns and pronuclear formation after parthenogenetic activation of mouse oocytes. Our results showed that the oocytes released to the oviduct at 17 h post-human chorionic gonadotrophin (hCG) displayed a significantly stronger [Ca2+]i oscillation, including higher frequency, shorter cycle, and higher peak, compared with oocytes collected at earlier or later time points. [Ca2+]i oscillations in acidic conditions (pH 6.4 and 6.6) were significantly weaker than those in neutral and mildly alkaline conditions (pH from 6.8 to 7.6). In vitro-matured oocytes showed reduced frequency and peak of [Ca2+]i oscillations compared with those matured in vivo. In vitro-matured oocytes from the cumulus-oocyte complexes (COCs) showed a significantly higher frequency, shorter cycle, and higher peak compared with the denuded oocytes (DOs). Finally, endoplasmic reticulum stress (ER stress) severely affected the parameters of [Ca2+]i oscillations, including elongated cycles and lower frequency. The pronuclear (PN) rate of oocytes after parthenogenetic activation was correlated with [Ca2+]i oscillation pattern, decreasing with oocyte aging, cumulus removal, acidic pH, and increasing ER stress. These results provide fundamental but critical information for the mechanism of how these factors affect oocyte activation.

Effects of various calcium transporters on mitochondrial Ca2+ changes and oocyte maturation.

Ca2+ participates in many important cellular processes, but the underlying mechanisms are still poorly understood, especially during oocyte maturation. First, we confirmed that calcium in the culture medium was essential for oocyte maturation. Next, various inhibitors of Ca2+ channels were applied to investigate their roles in mitochondrial Ca2+ changes and oocyte maturation. Our results showed that Trmp7, Orai, T-type Ca2+ channels and Na+ /Ca2+ exchanger complex (NCLX) were important for oocyte maturation. Trmp7 inhibition delayed germinal vesicle breakdown. Orai and NCLX inhibition significantly weakened the distribution of mitochondrial Ca2+ around the nucleus compared to the Ctrl group. Interestingly, even T-type Ca2+ channels-specific inhibitor Mibefradil blocked germinal vesicle breakdown; mitochondrial Ca2+ surrounding the nucleus still was maintained at a high level without spindle formation. Two calcium transporter inhibitors, Thapsigargin and Ruthenium Red, which have been confirmed to inhibit oocyte activation, did not significantly affect oocyte maturation. Increasing the knowledge of calcium transport may provide a basis to build on for improving oocyte in vitro maturation in human assisted reproduction clinics.