Oocyte Apoptosis Research Articles

Fumonisin B1 exposure adversely affects porcine oocyte maturation in vitro by inducing mitochondrial dysfunction and oxidative stress

Fumonisin B1 (FB1), as the most toxic fumonisin, is a common Fusarium mycotoxin contaminant of feed stuff and food, posing a potential health hazard to animals and humans. FB1 has been reported to cause hepatotoxicity, neurotoxicity, nephrotoxicity, immunotoxicity and embryotoxicity; however, little information is available on whether FB1 has toxic effects on mammalian oocytes. Herein, we adopted porcine oocytes as models to explore the effects and potential mechanisms of FB1 on mammalian oocytes during in vitro maturation. Porcine cumulus oocyte complexes (COCs) were exposed to 0, 20, 30 and 40 μM FB1 for 44 h during in vitro maturation, and the results reported that first polar body (PB1) extrusion was significantly inhibited when the FB1 concentration reached 30 (P < 0.01) or 40 μM (P < 0.001). Further cell cycle analysis revealed that meiotic progression was disrupted, with a larger proportion of the 30 μM FB1-treated oocytes being arrested at the germinal vesicle breakdown (GVBD) stage (P < 0.01). After being treated with 30 μM FB1 for 28 h, the percentage of oocytes with aberrant spindle assembly was observably increased (P < 0.01), and the distribution of actin filaments on the plasma membrane was significantly reduced (P < 0.05). Furthermore, an observably higher rate of abnormal mitochondrial distribution (P < 0.05) and significantly decreased mitochondrial membrane potential (MMP) (P < 0.05) were observed in FB1-exposed oocytes. In addition, ROS generation in FB1-treated oocytes was rapidly increased (P < 0.05), while the transcriptional levels of antioxidant-related genes (CAT, SOD2 and GSH-Px) were sharply decreased compared with those in the control group. Additionally, the incidence of early apoptosis in FB1-treated oocytes was also significantly increased (P < 0.05), suggesting that FB1 exposure induced oxidative stress and further triggered apoptosis in porcine oocytes. Thus, these results suggested that FB1 adversely affected oocyte maturation by disturbing cell cycle progression, destroying cytoskeletal dynamics and damaging mitochondrial function, which eventually induced oxidative stress and apoptosis in porcine oocytes.

Effects of tris (2-carboxyethyl) phosphine hydrochloride treatment on porcine oocyte in vitro maturation and subsequent in vitro fertilized embryo developmental capacity

Oocyte in vitro maturation (IVM) is a crucial process that determines subsequent in vitro embryo production. The present study investigated the effects of the antioxidant tris (2-carboxyethyl) phosphine hydrochloride (TCEP-HCL) on the in vitro maturation of porcine oocytes and in vitro developmental competence of fertilized embryos. Oocytes were matured in IVM medium based on four concentration groups of TCEP-HCL (0, 50, 100, and 200 μM) treatment. 100 μM TCEP-HCL treatment significantly increased the oocyte first polar body extrusion rate, monospermy rate and subsequent in vitro fertilized embryo developmental capacity (cleavage rate, blastocyst formation rate, and blastocyst total cell number) compared to those in the control group. Furthermore, 100 μM TCEP-HCL treatment significantly reduced the levels of reactive oxygen species, significantly increased glutathione levels and mitochondrial content compared to those in the control group. Moreover, 100 μM TCEP-HCL treatment significantly decreased the oocyte apoptosis, blastocyst apoptosis compared to that in the controls. In summary, these results indicate that 100 μM TCEP-HCL treatment improves the quality and developmental capacity of in vitro-fertilized embryos by decreasing oxidative stress in porcine oocytes.

Assessment of Mitochondrial Function and Developmental Potential of Mouse Oocytes after Mitoquinone Supplementation during Vitrification.

Vitrification negatively affects the mitochondrial membrane potential (ΔΨm) in oocytes while also leading to increased reactive oxygen species (ROS), ATP depletion and induction of apoptosis in oocytes. Mitoquinone (MitoQ) is an antioxidant that protects mitochondrial membrane integrity from ROS. This study examined the effect of adding MitoQ to vitrification medium on mitochondrial function and embryo development in vitrified oocytes. Metaphase II (MII) stage oocytes were collected from NMRI mouse ovaries and preincubated for 20 min in a medium containing 0.02 μM of MitoQ. Next, oocytes were vitrified in medium supplemented with 0.02μM of MitoQ (treatment group). The control group was processed in the same way but without exposure to MitoQ. After warming, oocyte survival rate, ΔΨm, cytoplasmic ROS and glutathione (GSH) levels and gene expression levels (Bcl2, BAX, and caspase3) were measured. In addition, the vitrified oocytes were fertilized in-vitro to assess developmental competence. The results showed that MitoQ improved survival and ΔΨm in treated vitrified oocytes. Treated oocytes showed lower ROS levels and higher GSH levels than did the control group. Furthermore, mRNA expression of the Bax/ Bcl2 ratio and caspase3 were significantly lower in treated oocytes. These findings indicate that medium supplementation with 0.02 μM of MitoQ during vitrification can improve oocyte survival and developmental competency in mouse oocytes.

Melatonin Alleviates the Toxicity of High Nicotinamide Concentrations in Oocytes: Potential Interaction with Nicotinamide Methylation Signaling.

Despite the numerous studies on melatonin and nicotinamide (NAM, the active form of vitamin B3), the linkage between these two biomolecules in the context of signaling pathways regulating preimplantation embryo development has not yet been investigated. In this study, we used bovine oocyte model to elucidate the effect of melatonin on the developmental competence of oocytes under the stress of high NAM concentrations. Results showed that NAM (20 mM) administration during in vitro maturation (IVM) significantly reduced oocyte maturation and actin distribution, while induced reactive oxygen species (ROS) accumulation and mitochondrial dysfunction, the multiple deleterious effects that were alleviated by melatonin (10−7 M). The RT-qPCR and/or immunofluorescence showed upregulation of the apoptosis (Caspase-3, Caspase-9, and BAX), autophagy (Beclin-1, LC3A, LC3B, ATG7, LAMP1, and LAMP2), cell cycle (P21, P27, and P53), and DNA damage (COX2 and 8-OxoG) specific markers in oocytes matured under NAM treatment, compared to NAM-melatonin dual-treated and the untreated ones. In addition, the total cleavage and blastocyst development rate, as well as the total number of cells and the inner cell mass (ICM) per blastocyst, were reduced, while DNA fragmentation was induced, in the group of NAM sole treatment than NAM-melatonin cotreatment and control. Inspecting the underlying mechanisms behind NAM-associated toxicity revealed an increase in transcription pattern of NAM methylation (NNMT and AHCY) genes in NAM-treated oocytes while the opposite profile was observed upon melatonin supplementation. In conclusion, to our knowledge, this is the first study reporting that melatonin can protect oocytes and embryos from NAM-induced injury through its ROS-scavenging activity together with potential interaction with NAM methylation signaling.

Invivo zearalenone exposure dose-dependently compromises mouse oocyte competence by impairing chromatin configuration and gene transcription.

Although invivo and invitro zearalenone (ZEN) exposure impaired oocyte quality, the mechanisms by which ZEN damages oocytes and the lowest observed effect level remain unclear. Furthermore, although it is known that premature chromatin condensation may occur in oocytes under proapoptotic conditions, whether ZEN exposure compromises oocyte competence by impairing gene transcription by causing premature chromatin condensation remains to be investigated. This study tested the toxic concentrations of invivo ZEN exposure that impair oocyte preimplantation developmental potential (PIDP) and the hypothesis that ZEN exposure compromises oocyte competence by increasing oxidative stress and changing chromatin configuration and the transcription of related genes. We found that invivo treatment of mice (Kunming strain, 8 weeks after birth) with 0.5-1mg kg-1 ZEN daily for 5 days, impaired the PIDP of mouse oocytes, increased oxidative stress, disturbed spindle assembly and chromosome segregation, caused premature chromatin condensation, impaired global gene transcription and disturbed the expression of genes related to oocyte competence, spindle assembly, redox potential and apoptosis. In conclusion, ZEN dose-dependently compromised the competence of mouse oocytes by causing oxidative stress and impairing chromatin configuration and gene transcription.

Effects of the E1 activating enzyme UBA2 on porcine oocyte maturation, apoptosis, and embryonic development in vitro.

The purpose of this study was to investigate the effect of the E1 activating enzyme UBA2 on the expression of the SUMO-1 protein during in vitro maturation (IVM) of pig oocytes and embryonic development. In the 5μg/ml UBA2 treatment group, the expression of the anti-apoptotic gene Bcl-2 and the embryo cleavage rate was significantly increased, while the proapoptotic gene Bax was significantly reduced. When 10μg/ml UBA2 was added, the in vitro maturation rate, blastocyst rate, and SUMO-1 protein content of oocytes increased significantly (p<.05), and the expression of proapoptotic gene Caspase3 was significantly decreased (p<.05), while the viability of cumulus cells was extremely significantly reduced (p<.01). In summary, UBA2 can regulate the content of the SUMO-1 protein in mature pig oocytes in vitro, which in turn affects the maturation rate of oocytes, expression of apoptosis genes, cumulus cell viability, and the development of embryos after fertilization.

Design and Microfabrication of An On-Chip Oocyte Maturation System for Reduction of Apoptosis.

Objective:In customary assisted reproductive technology (ART), oocyte culture occurs in static micro drops of Petri dishes with vast media volume; while, the in vivo condition is dynamic. In this study, we aimed to improve the maturation efficiency of mammalian oocytes by designing an optimal microchamber array to obtain the integration of oocyte trapping and maturation within a microfluidic device and evaluate the role of microfluidic culture condition in lipid peroxidation level of the culture medium, in vitro matured oocytes apoptosis, and its comparison with the conventional static system.Materials and Methods:In this experimental research, immature oocytes were collected from ovaries of the Naval Medical Research Institute (NMRI) mice. Oocytes were randomly laid in static and dynamic (passive < active)in vitro maturation culture medium for 24 hours. The lipid peroxidation level in oocyte culture media was assessed by measuring the concentration of malondialdehyde (MDA), and the rate of apoptosis in in vitro matured oocytes was assessed by the TUNEL assay after a-24 hour maturation period.Results:The MDA concentration in both dynamic oocyte maturation media were significantly lower than the static medium (0.003 and 0.002 vs. 0.13 µmol/L, P<0.01). Moreover, the rate of apoptosis in matured oocytes after a-24 hour maturation period was significantly lower in passive dynamic and active dynamic groups compared with the static group (16%, 15% vs. 35%, P<0.01).Conclusion:The dynamic culture for in vitro oocyte maturation (IVM) improves the viability of IVM oocytes in comparison with the static culture condition.

Vitrification-induced apoptosis and pan-caspase inhibition in domestic cat immature oocytes

Vitrification-induced apoptosis and pan-caspase inhibition in domestic cat immature oocytes

Procyanidin B1 promotes in vitro maturation of pig oocytes by reducing oxidative stress.

Oxidative stress negatively affects the in vitro maturation (IVM) of oocytes. Procyanidin B1 (PB1) is a natural polyphenolic compound that has antioxidant properties. In this study, we investigated the effect of PB1 supplementation during IVM of porcine oocytes. Treatment with 100 μM PB1 significantly increased the MII oocytes rate (p <0.05), the parthenogenetic (PA) blastocyst rate (p <0.01) and the total cell number in the PA blastocyst (p < 0.01) which were cultured in regular in vitro culture (IVC) medium. The PA blastocyst rate of regular MII oocytes activated and cultured in IVC medium supplemented with 100 and 150 μM PB1 significantly increased compared with control (p < 0.01 and p < 0.05). We also evaluated the reactive oxygen species (ROS) levels, mitochondrial membrane potential (Δψm) levels, glutathione (GSH) levels, and apoptotic levels in MII oocytes and cumulus cells following 100 μM PB1 treatment. The results showed that the PB1 supplementation decreased ROS production and apoptotic levels. In addition, PB1 was found to increase Δψm levels and GSH levels. In conclusion, PB1 inhibited apoptosis of oocytes and cumulus cells by reducing oxidative stress. Moreover, PB1 improved the quality of oocytes and promoted PA embryo development. Taken together, our results suggest that PB1 is a promising antioxidant additive for IVM of oocytes.

Inhibitory effects of astaxanthin on postovulatory porcine oocyte aging in vitro

Mammalian oocytes represent impaired quality after undergoing a process of postovulatory aging, which can be alleviated through various effective ways such as reagent treatment. Accumulating evidences have revealed the beneficial effects of astaxanthin (Ax) as a potential antioxidant on reproductive biology. Here, porcine matured oocytes were used as a model to explore whether Ax supplement can protect against oocyte aging in vitro and the underlying mechanism, and therefore they were cultured with or without 2.5 μM Ax for an additional 24 h. Aged oocytes treated with Ax showed improved yield and quality of blastocysts as well as recovered expression of maternal genes. Importantly, oxidative stress in aged oocytes was relieved through Ax treatment, based on reduced reactive oxygen species and enhanced glutathione and antioxidant gene expression. Moreover, inhibition in apoptosis and autophagy of aged oocyte by Ax was confirmed through decreased caspase-3, cathepsin B and autophagic activities. Ax could also maintain spindle organization and actin expression, and rescue functional status of organelles including mitochondria, endoplasmic reticulum, Golgi apparatus and lysosomes according to restored fluorescence intensity. In conclusion, Ax might provide an alternative for ameliorating the oocyte quality following aging in vitro, through the mechanisms mediated by its antioxidant properties.

Melatonin Reverses 10-Hydroxycamptothecin-Induced Apoptosis and Autophagy in Mouse Oocyte.

10-Hydroxycamptothecin (HCPT) is a widely used anticancer drug that induces cytotoxicity by triggering the cell apoptotic pathway. Studies have shown that HCPT has harmful effects on normal cells, but whether HCPT affects the development of mouse oocytes in vitro has not been reported. First, this study investigated the development of oocytes exposed to 60μM HCPT in vitro. In the HCPT-treated group, the first polar body extrusion (PBE) rate of oocytes decreased, spindle morphology was abnormal, DNA double-strand break, oxidative stress level increased, and mitochondrial distribution was abnormal. The apoptosis and autophagy levels of oocytes in the HCPT-treated group were detected by qRT-PCR and western blot. Compared with the control group, the expressions of key regulators of oocyte apoptosis (bax, caspase-3) and autophagy (lc3, beclin, ATG12) pathway were increased in the HCPT-treated group. HCPT treatment induced apoptosis and autophagy in oocytes. Melatonin (MT) can protect cell structure, prevent DNA damage, and reduce the content of peroxides. So we wondered whether MT could ameliorate the harmful effects of mouse oocytes induced by HCPT. Interestingly, the addition of 1mM MT can protect oocytes from HCPT toxicity to some extent. Compared with the HCPT group, the addition of 1mM MT increased the PBE ratio of oocytes, decreased ROS levels, and decreased spindle abnormalities and DNA breakage ratio. In summary, these results revealed that HCPT exhibited adverse effects on mouse oocyte maturation and quality, and MT administration alleviated the negative influence of HCPT.

Glutathione Ethyl Ester Protects In Vitro-Maturing Bovine Oocytes against Oxidative Stress Induced by Subsequent Vitrification/Warming.

This study aimed to examine whether the addition of glutathione ethyl ester (GSH-OEt) to the in vitro maturation (IVM) medium would improve the resilience of bovine oocytes to withstand vitrification. The effects of GSH-OEt on spindle morphology, levels of reactive oxygen species (ROS), mitochondrial activity and distribution, and embryo developmental potential were assessed together with the expression of genes with a role in apoptosis (BAX, BCL2), oxidative-stress pathways (GPX1, SOD1), water channels (AQP3), implantation (IFN-τ) and gap junctions (CX43) in oocytes and their derived blastocysts. Vitrification gave rise to abnormal spindle microtubule configurations and elevated ROS levels. Supplementation of IVM medium with GSH-OEt before vitrification preserved mitochondrial distribution pattern and diminished both cytoplasmic and mitochondrial ROS contents and percentages of embryos developing beyond the 8-cell stage were similar to those recorded in fresh non-vitrified oocytes. Although not significantly different from control vitrified oocytes, vitrified oocytes after GSH-OEt treatment gave rise to similar day 8-blastocyst and hatching rates to fresh non-vitrified oocytes. No effects of GSH-OEt supplementation were noted on the targeted gene expression of oocytes and derived blastocysts, with the exception of GPX1, AQP3 and CX43 in derived blastocysts. The addition of GSH-OEt to the IVM medium before vitrification may be beneficial for embryo development presumably as the consequence of additional anti-oxidant protection during IVM.

Melatonin Attenuates Peroxynitrite-Induced Meiosis Dysfunction in Porcine Oocytes.

A high level of reactive oxygen species (ROS) is widely considered one of the major causes of oocyte quality decline. Peroxynitrite is known as a powerful oxidant, which could induce multiple physical diseases. Recently, emerging pieces of evidences indicate that melatonin effectively promotes the development of oocytes, although the specific work mechanism remains to be further clarified. In this study, it was shown that peroxynitrite increased the level of ROS in porcine oocytes, which induced the apoptosis of oocytes, thereby leading to the obstruction of spindle assembly, depolymerization of actin, and decrease of polar body expulsion. These negative effects contributed to the failure of meiosis and ultimately blocked the maturation of porcine oocytes. As expected, it was found that melatonin effectively removed the accumulated ROS in oocytes, preventing oocytes from peroxynitrite-induced oocyte maturation failure, which might provide a novel approach to improve female livestock reproduction and cure female infertility in clinical practice.

Genetics of premature ovarian insufficiency and the association with X-autosome translocations.

Premature ovarian insufficiency (POI) is the cessation of menstruation before the age of 40 and can result from different etiologies, including genetic, autoimmune, and iatrogenic. Of the genetic causes, single-gene mutations and cytogenetic alterations, such as X-chromosome aneuploidies and chromosome rearrangements, can be associated with POI. In this review, we summarize the genetic factors linked to POI and list the main candidate genes. We discuss the association of these genes with the ovarian development, the functional consequences of different mutational mechanisms and biological processes that are frequently disrupted during POI pathogenesis. Additionally, we focus on the high prevalence of X-autosome translocations involving the critical regions in Xq, known as POI1 and POI2, and ddiscuss in depth the main hypotheses proposed to explain this association. Although the incorrect pairing of chromosomes during meiosis could lead to oocyte apoptosis, the reason for the prevalence of X-chromosome breakpoints at specific regions remains unclear. In most cases, studies on genes disrupted by balanced structural rearrangements cannot explain the ovarian failure. Thus, the position effect has emerged as a putative explanation for genetic mechanisms as translocations possibly result in changes in overall chromatin topology due to chromosome repositioning. Given the tremendous impact of POI on women's quality of life, we highlight the value of investigations in to the interplay between ovarian function and gene regulation to deepen our understanding of the molecular mechanisms related to this disease, with the ultimate goal of improving patients' care and assistance.

Microcystin-LR exposure results in aberrant spindles and induces apoptosis in porcine oocytes

Microcystin-LR (MC-LR), as a well-known hepatotoxin, was recently found to accumulate in gonads and induce a variety of reproductive damages in zebrafish, mice and other model organisms, however, little information is available on whether MC-LR has toxic effects on the mammalian oocytes, especially in livestock species. In this study, the effects of MC-LR on meiotic maturation of porcine oocytes were investigated, and the potential mechanism of MC-LR toxicity was explored. Germinal vesicle (GV)-stage oocytes were exposed to 0, 20, 40 and 60 μM MC-LR, respectively, during the in vitro maturation for 44 h, and the results showed that the first polar body (PbI) extrusion rate of the oocytes decreased significantly when the MC-LR concentration reached 40 (P < 0.01) or 60 μM (P < 0.001). After treated with 60 μM MC-LR for 44 h, a significant higher percentage of the oocytes arrested at anaphase-telophase I (ATI) stage (P < 0.01). Laser scanning confocal results further confirmed that a significantly larger proportion of the 60 μM MC-LR-treated oocytes exhibited aberrant spindles and misaligned chromosomes, suggesting a failure of spindle assembly and homologous chromosome segregation during the ATI stage. Furthermore, the ROS levels in the 60 μM MC-LR-exposed oocytes were significantly higher than the control group (P < 0.01), while the expression of antioxidant related genes (SOD1, CAT and GPX) were much lower compared with control group, indicating that oxidative stress was induced and the antioxidant capacity of oocytes was depleted by 60 μM MC-LR treatment. Additionally, markedly decreased mitochondrial membrane potential (MMP) (P < 0.01) and significantly higher incidence of early apoptosis (P < 0.01) were observed in the 60 μM MC-LR-treated oocytes, suggesting that MC-LR exposure induced apoptosis in porcine oocytes. Moreover, the protein expression of PP2A was remarkably inhibited, whereas the expression of p53, BAX, Caspase3 and Cleaved-caspase3 were prominently increased in the 60 μM MC-LR-exposed oocytes. Together, these results suggested that 60 μM of MC-LR exposure can induce oxidative stress, and lead to aberrant spindles, impaired MMP, and trigger apoptosis, which eventually result in failure of porcine oocyte maturation.

In Vitro Maturation with Leukemia Inhibitory Factor Prior to the Vitrification of Bovine Oocytes Improves Their Embryo Developmental Potential and Gene Expression in Oocytes and Embryos.

Oocyte cryopreservation has a significant impact on subsequent embryonic development. Herein, we investigated whether supplementing in vitro maturation medium with Leukemia Inhibitory Factor (LIF) prior to vitrification affects embryo development and gene expression at different embryo developmental stages. A panel of genes including maternal effect, epigenetics, apoptosis and heat stress was relatively quantified. The results show reduced cleavage rates after vitrification, regardless of the LIF treatment. Although not statistically different from control-vitrified oocytes, oocyte apoptosis and the blastocyst yield of LIF-vitrified oocytes were similar to their non-vitrified counterparts. Vitrification increased oocyte ZAR1, NPM2 and DPPA3 gene expression while its expression decreased in LIF-vitrified oocytes to similar or close levels to those of non-vitrified oocytes. With a few gene-specific exceptions, vitrification significantly increased the expression of DNMT3A, HDAC1, KAT2A, BAX and BCL2L1 in oocytes and most stages of embryo development, while comparable expression patterns for these genes were observed between LIF-vitrified and non-vitrified groups. Vitrification increased HSPA1A expression in oocytes and HSP90AA1 in 2-cell embryos. Our data suggest that vitrification triggers stage-specific changes in gene expression throughout embryonic development. However, the inclusion of LIF in the IVM medium prior to vitrification stimulates blastocyst development and several other developmental parameters and induces oocytes and embryos to demonstrate gene expression patterns similar to those derived from non-vitrified oocytes.

The toxic effects and possible mechanisms of decabromodiphenyl ethane on mouse oocyte

Decabromodiphenyl ethane (DBDPE), a widely used new brominated flame retardant, is added into flammable materials to achieve fire retardation. As it is continuously detected in the environment, it has become an emerging environmental pollutant. However, the effects of DBDPE exposure on oocyte maturation and its underlying mechanisms remain unknown. This study found that DBDPE exposure inhibited the rate of germinal vesicle breakdown (GVBD), first polar body extrusion (PBE) and fertilization of mouse oocytes. After 14 h of exposure to DBDPE, metaphase II (MII) oocytes showed that the hardness of zona pellucida (ZP) markedly increased and that the spindle morphology was abnormal. Moreover, DBDPE exposure induced abnormal mitochondrial distribution, mitochondrial dysfunction, and ATP deficiency. Simultaneously, DBDPE exposure down-regulated the expression of antioxidant-related genes (Sod2, Gpx1) and increased the level of reactive oxygen species (ROS) in oocytes. The results of immunofluorescence and qRT-PCR revealed that autophagy occurred in DBDPE-treated oocytes with high expression of autophagy-related protein (LC3) and genes (Lc3, Beclin1). Meanwhile, DBDPE significantly up-regulated the protein (Bax) and mRNA (Bax, Caspase3) levels of pro-apoptosis genes. However, the protein and mRNA expression of anti-apoptosis genes Bcl-2 was dramatically down-regulated in DBDPE-exposed oocytes. Collectively, DBDPE exposure impaired mitochondrial function, causing oxidative damage, autophagy and apoptosis in oocytes.

Effects of E2 binding enzyme UBC9 on porcine oocyte maturation, apoptosis and embryo development.

SUMOylation is a dynamic post-translational modification process. However, the function of small ubiquitin-like modifiers (SUMOs) in the maturation of porcine oocytes and embryo growth is not well known. Therefore, the aim of this study was to investigate the effect of E2 binding enzyme UBC9 on the expression of SUMO-1 protein during the in vitro maturation of porcine oocytes and embryo development after in vitro fertilization. Four groups were used: 0 (Control), 5, 10 and 15µg/ml UBC9. Western blotting, flow cytometry and RT-qPCR were used to detect the in vitro maturation of porcine oocytes, SUMO-1 content, viability and the expression of apoptotic genes. Compared to those in the control treatment, the maturation rate (p<.05) and viability (p<.01) of oocytes in the 5μg/ml treatment group decreased significantly. SUMO-1 protein markers appeared at 59 and 71kDa and the content of SUMO-1 protein in the 10µg/ml treatment group decreased significantly (p<.05). In the expression of apoptosis-related genes, Bcl-2 gene expression was significantly downregulated in the 10μg/ml treatment group (p<.05). However, Bax and Caspase-3 were significantly upregulated in the 5μg/ml treatment group (p<.05). During embryonic development, the cleavage rate of oocytes in the 10µg/ml treatment group was significantly reduced (p<.05), whereas blastocyst formation rate in the 5µg/ml treatment group was significantly reduced. UBC9 regulates SUMO-1 content in mature pig oocytes in vitro, which affects oocyte maturation rate, viability, apoptotic genes expression and embryo development after fertilization.

Mutation of rat Zp2 causes ROS-mediated oocyte apoptosis.

In this study, we investigated a gene-edited (Zp2MT/MT) rat model of infertility caused by the failure to express the zona pellucida glycoprotein 2 (ZP2) due to the significant reduction of mRNA amount. We examined the defects in the zona pellucida (ZP) caused by ZP2 nullification and the influence of these defects on aspects of oocyte development, including apoptosis and fertilization ability. To investigate the cause of the influence to the oocytes' development, we evaluated the morphology of follicular transzonal projections (TZPs), known as 'bridges', which mediate the bidirectional signaling between the oocyte and surrounding granulosa cells and the level of reactive oxygen species (ROS) in ovulated eggs. Our results showed that two types of ZP defects were generated in the Zp2MT/MT rat,that is, ZP intact but thinned and ZP cracked (or even absent). The fertilization rate of the ovulated eggs reduced in both types, while increased oocyte apoptosis was observed only in the latter type. Moreover, the increased oocyte apoptosis rate correlated closely with the reduction in follicular TZPs and increased ROS levels in ovulated egg. In conclusion, nullification of rat ZP2 destroyed the integrity of the ZP, impaired the bidirectional signaling between the oocyte and surrounding granulosa cells. Therefore, the resulting infertility likely occurs via elevation of oxidative stress and oocytes apoptosis.

Constant light exposure causes oocyte meiotic defects and quality deterioration in mice

Artificial light at night (ALAN) exposes us to prolonged illumination, that adversely affects female reproduction. However, it remains to be clarified how prolonged light exposure affects oocyte meiotic maturation and quality. To this end, we exposed female mice to a constant light (CL) of 250 lux for different durations. Our findings showed that CL exposure for 7 weeks reduced the oocyte maturation rate. Meanwhile, CL exposure caused greater abnormalities in spindle assembly and chromosome alignment and a higher rate of oocyte aneuploidy than the regular light dark cycle. CL exposure also induced oxidative stress and caused mitochondrial dysfunction, which resulted in oocyte apoptosis and autophagy. Notably, our results showed that CL exposure reduced the levels of α-tubulin acetylation, DNA methylation at 5 mC, RNA methylation at m6A and histone methylation at H3K4me2 but increased the levels of histone methylation at H3K27me2 in oocytes. In summary, our findings demonstrate that constant bright light exposure causes oocyte meiotic defects and reduces cytoplasmic quality. These results extend the current understanding of ALAN-mediated defects in female reproduction.