Histone lactylation regulates early embryonic development through m6A methyltransferase METTL3 in goats

Histone lysine lactylation (Kla) is a novel epigenetic modification that plays a crucial role in cellular processes driven by glycolysis and lactate production. However, the mechanisms of histone lactylation and its interaction with m6A RNA methylation during early embryonic development remain underexplored. This study systematically investigated the effects of oxygen levels-atmospheric oxygen (atmosO2; 20% O2) and physiological oxygen (physO2; 5% O2)-on hallmark events during early embryonic development, revealing that lactylation modification regulates early goat embryonic development through the m6A methyltransferase-like 3 (METTL3). We observed that physO2 conditions significantly promote embryonic development, with higher expression levels of METTL3, global histone lactylation, and histone H3 lysine 18 lactylation (H3K18la) compared to atmosO2 exposure. Furthermore, the addition of lactate dehydrogenase inhibitors led to a decrease in global lactylation, which was accompanied by a significant reduction in METTL3 expression. Sequencing analysis of the METTL3 knockdown embryo revealed that the differentially expressed genes (DEGs) were primarily enriched in the ribosome, oxidative phosphorylation, thermogenesis, RNA degradation, and RNA polymerase pathways. These findings provide novel insights into the epigenetic regulatory mechanisms of histone lactylation during early embryonic development in livestock, highlighting potential molecular targets and strategies to enhance mammalian in vitro embryo production techniques.

Uncovering the Fluctuation of Peroxynitrite during Early Embryonic Development Using an Integrative Nanobeacon

Embryonic development is the beginning of life, and various kinds of bioactive molecules are implicated in this crucial process. Especially in its early stage, some important biochemical reactions regulating physiological balance may be resuscitated. Thus, revealing the dynamic changes of bioactive molecules during early embryonic development is crucial to the elucidation of biological phenomena. Peroxynitrite (ONOO-) is a typical signaling molecule in intercellular communication. However, up to now, no work has studied the fluctuation of ONOO- during early embryonic development due to its low content, especially in mammals. Herein, a polymeric nanobeacon that integrates an ONOO--responsive degradable scaffold and a fluorescence amplification module, named IFN, was designed to selectively sense embryonic ONOO- with high sensitivity. By virtue of the specific dye, ONOO- was sensitively detected in the range of 0-4.5 μM with a detection limit of 20.4 nM. From the attractive embryonic results, a sudden increase in ONOO- content after fertilization was observed in a mammalian model, while the level of ONOO- decreased slightly at the four-cell and eight-cell stages, finally reaching an equilibrium throughout the morula and blastocyst stages. This phenomenon is due to the resuscitation of ovotids, the activation of some life events by fertilization, and the subsequent establishment of physiological balance. This work not only suggests that ONOO- plays a positive role in normal embryonic development but also highlights the molecular events occurring at the initial phase of life. Furthermore it opens up new avenues for monitoring chemical changes during mammalian embryonic development.

Sod1 deficiency in mouse oocytes during in vitro maturation increases chromosome segregation errors with a reduced BUBR1 at kinetochore

Purpose

This study aimed to investigate the molecular mechanisms associated with chromosome segregation errors caused by intrinsic oxidative stress during in vitro oocyte maturation (IVM) using oocytes from Sod1-deficient (Sod1KO) mice.

Methods

Ovulated or in vitro matured cumulus-cells oocyte complexes (COCs) were collected from wild-type (WT) and Sod1KO mice and evaluated chromosome alignment, chromosome segregation, meiotic progression, and BUBR1 and REC8 protein expression levels.

Results

In 21% O2 IVM, the Sod1KO had significantly higher frequencies of chromosome misalignment and segregation errors compared to the WT, and they also reached Germinal Vesicle Break Down (GVBD) and M I stages peak earlier and showed a shorter M I stage residence time compared to the WT. These changes were associated with a decrease in the recruitment of BUBR1 to kinetochores at M I stage, but there were no differences in the expression of REC8 between the two genotypes. Furthermore, the addition of L-ascorbic acid (AsA) or N-acetyl-L-cysteine (NAC) during IVM reduced the frequency of chromosome segregation errors in Sod1KO oocytes.

Conclusions

Oxidative stress caused by Sod1 deficiency during IVM impairs the spindle assembly checkpoint function due to a decrease in the recruitment of BUBR1 to M I stage kinetochores, leading to abnormalities in meiotic progression and chromosome segregation.

Mitochondrial morphology, distribution and activity during oocyte development

Mitochondria have a crucial role in cellular function and exhibit remarkable plasticity, adjusting both their structure and activity to meet the changing energy demands of a cell. Oocytes, female germ cells that become eggs, undergo unique transformations: the extended dormancy period, followed by substantial increase in cell size and subsequent maturation involving the segregation of genetic material for the next generation, present distinct metabolic challenges necessitating varied mitochondrial adaptations. Recent findings in dormant oocytes challenged the established respiratory complex hierarchies and underscored the extent of mitochondrial plasticity in long-lived oocytes. In this review, we discuss mitochondrial adaptations observed during oocyte development across three vertebrate species (Xenopus, mouse, and human), emphasising current knowledge, acknowledging limitations, and outlining future research directions.

KAT8 functions in redox homeostasis and mitochondrial dynamics during mouse oocyte meiosis progression

As a histone acetyltransferase, lysine acetyltransferase 8 (KAT8) participates in diverse biological processes. However, the effect of KAT8 on oocyte maturation in mice remains unclear. In this study, we found that mouse oocytes overexpressing Kat8-OE induced maturation failure manifested reduced rates of GVBD and first polar body emission. In addition, immunostaining results revealed that Kat8 overexpressing oocytes showed inappropriate mitochondrial distribution patterns, overproduction of reactive oxygen species (ROS), accumulation of phosphorylated γH2AX, hyperacetylation of α-tubulin, and severely disrupted spindle/chromosome organization. Moreover, we revealed that Kat8 overexpression induced a decline in SOD1 proteins and KAT8's interaction with SOD1 in mouse ovaries via immunoprecipitation. Western blotting data confirmed that Kat8-OE induced downregulation of SOD1 expression, which is a key factor for the decline of oocyte quality in advanced maternal age. Also, the injection of Myc-Sod1 cRNA could partially rescue maternal age-induced meiotic defects in oocytes. In conclusion, our data demonstrated that high level of KAT8 inhibited SOD1 activity, which in turn induced defects of mitochondrial dynamics, imbalance of redox homeostasis, and spindle/chromosome disorganization during mouse oocyte maturation.

OXIDATIVE STRESS AND REPRODUCTIVE FUNCTION: Reactive oxygen species in the mammalian pre-implantation embryo

In brief

Reactive oxygen species are generated throughout the pre-implantation period and are necessary for normal embryo formation. However, at pathological levels, they result in reduced embryo viability which can be mediated through factors delivered by sperm and eggs at conception or from the external environment.

Abstract

Reactive oxygen species (ROS) occur naturally in pre-implantation embryos as a by-product of ATP generation through oxidative phosphorylation and enzymes such as NADPH oxidase and xanthine oxidase. Biological concentrations of ROS are required for crucial embryonic events such as pronuclear formation, first cleavage and cell proliferation. However, high concentrations of ROS are detrimental to embryo development, resulting in embryo arrest, increased DNA damage and modification of gene expression leading to aberrant fetal growth and health. In vivo embryos are protected against oxidative stress by oxygen scavengers present in follicular and oviductal fluids, while in vitro, embryos rely on their own antioxidant defence mechanisms to protect against oxidative damage, including superoxide dismutase, catalase, glutathione and glutamylcysteine synthestase. Pre-implantation embryonic ROS originate from eggs, sperm and embryos themselves or from the external environment (i.e. in vitro culture system, obesity and ageing). This review examines the biological and pathological roles of ROS in the pre-implantation embryo, maternal and paternal origins of embryonic ROS, and from a clinical perspective, we comment on the growing interest in combating increased oxidative damage in the pre-implantation embryo through the addition of antioxidants.

Lycopene Improves In Vitro Development of Porcine Embryos by Reducing Oxidative Stress and Apoptosis

In vitro culture (IVC) for porcine embryo development is inferior compared to in vivo development because oxidative stress can be induced by the production of excessive reactive oxygen species (ROS) under high oxygen tension in the in vitro environment. To overcome this problem, we investigated the effect of lycopene, an antioxidant carotenoid, on developmental competence and the mechanisms involved in mitochondria-dependent apoptosis pathways in porcine embryos. In vitro fertilized (IVF) embryos were cultured in IVC medium supplemented with 0, 0.02, 0.05, 0.1, or 0.2 μM lycopene. The results indicate that 0.1 μM lycopene significantly increased the rate of blastocyst formation and the total cell numbers, including trophectoderm cell numbers, on Day In terms of mitochondria-dependent apoptosis, IVF embryos treated with 0.1 μM lycopene exhibited significantly decreased levels of ROS, increased mitochondrial membrane potential, and decreased expression of cytochrome c on Days 2 and Furthermore, 0.1 μM lycopene significantly decreased the number and percentage of caspase 3-positive and apoptotic cells in Day-6 blastocysts. In addition, Day-2 embryos and Day-6 blastocysts treated with 0.1 μM lycopene showed significantly reduced mRNA expression related to antioxidant enzymes (SOD1, SOD2, CATALASE) and apoptosis (BAX/BCL2L1 ratio). These results indicate that lycopene supplementation during the entire period of IVC enhanced embryonic development in pigs by regulating oxidative stress and mitochondria-dependent apoptosis.

Effect of cyanocobalamin on oocyte maturation, in vitro fertilization, and embryo development in mice

The aim of this study was to investigate the effect of cyanocobalamin supplementation on in vitro maturation (IVM), in vitro fertilization (IVF), and subsequent embryonic development competence to the blastocyst stage, and in vitro development of mouse 2-cell embryos. Cumulus cells were prepared from mouse cumulus-oocyte complexes (COCs) and incubated for 24 h in an in vitro culture (IVC) medium that contained different concentrations of cyanocobalamin (100, 200, 300 or 500 pM). We collected 2-cell embryos from superovulated NMRI mice and cultured them in the same concentrations of cyanocobalamin (100, 200, 300 or 500 pM). After 42 h of IVM, we observed significantly increased oocyte maturation in the 200 pM cyanocobalamin-treated group compared with the control group (P < 0.0001). Mature oocytes cultured in 200 pM cyanocobalamin were fertilized and cultured in IVC medium with cyanocobalamin (100, 200, 300 or 500 pM) during early embryogenesis. The matured oocytes that were cultured in 200 pM cyanocobalamin had significantly higher 2-cell development rates compared with the control oocytes (P < 0.01). Embryos obtained from in vitro mature oocytes and in vivo fertilized oocytes that were cultured in 200 pM cyanocobalamin had significantly greater frequencies of development to the blastocyst stage and a significant reduction in 2-cell blocked and degenerated embryos compared with the control embryos (P < 0.0001). Embryos derived from oocytes fertilized in vivo with 200 pM cyanocobalamin had a higher percentage of blastocyst embryos compared with those derived from matured oocytes cultured in vitro (P < 0.0001). These finding demonstrated that the effects of cyanocobalamin on oocyte maturation, fertilization, and embryo development in mice depend on the concentration used in IVC medium.

Testis-specific peroxiredoxin 4 variant is not absolutely required for spermatogenesis and fertility in mice

PRDX4, a member of peroxiredoxin family, is largely concentrated in the endoplasmic reticulum (ER) and plays a pivotal role in the redox relay during oxidative protein folding as well as in peroxidase reactions. A testis-specific PRDX4 variant transcript (PRDX4t) lacks the conventional exon 1, which encodes the signal peptide that is required for entry into the ER lumen, but instead carries alternative exon 1, which is transcribed from the upstream promoter in a testis-specific manner and results in the PRDX4t protein being localized in the cytosol. However, the potential roles of PRDX4t in male genital action remain unknown. Using a CRISPR/Cas9 system, we first disrupted the testis-specific promoter/exon 1 and generated mice that were specifically deficient in PRDX4t. The resulting PRDX4t knockout (KO) mice underwent normal spermatogenesis and showed no overt abnormalities in the testis. Mating PRDX4t KO male mice with wild-type (WT) female mice produced normal numbers of offspring, indicating that a PRDX4t deficiency alone had no effect on fertility in the male mice. We then generated mice lacking both PRDX4 and PRDX4t by disrupting exon 2, which is communal to these variants. The resulting double knockout (DKO) mice were again fertile, and mature sperm isolated from the epididymis of DKO mice exhibited a normal fertilizing ability in vitro. In the meantime, the protein levels of glutathione peroxidase 4 (GPX4), which plays an essential role in the disulfide bond formation during spermatogenesis, were significantly increased in the testis and caput epididymis of the DKO mice compared with the WT mice. Based on these results, we conclude that the disruption of the function of PRDX4t in the spermatogenic process appears to be compensated by other factors including GPX4.

The Anti-oxidative Effects of Encapsulated Cysteamine During Mice In Vitro Matured Oocyte/Morula-Compact Stage Embryo Culture Model: a Comparison of High-Efficiency Nanocarriers for Hydrophilic Drug Delivery-a Pilot Study

Although it is well-recognized that antioxidant nano-encapsulation has many benefits such as minimizing side effects (e.g., high-dose toxicity), the most attention was paid to the hydrophobic antioxidant not hydrophilic. In this regard, we sought to compare two hydrophilic model nanocarriers to deliver the optimal dose of cystamine (Cys) into the in vitro matured oocyte and the first cleavage stages until morula-compact stage embryonic cells. The formation of Cys-loaded solid self-emulsifying lipid (Cys + SLN) and Cys-loaded chitosan shell (Cys-CS-NC) were confirmed by FT-IR and UV-Vis spectrophotometry, dynamic light scattering (DLS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) technologies. In two experiments, the oocytes/presumptive zygotes were cultured under various concentrations of Cys-SLN and Cys-CS-NC. The results of nuclear staining (aceto-orcein and Hoechst 33342), H2DCFDA fluorescent staining, chemiluminescence test, and quantitative reverse transcription-PCR (qRT-PCR) technique as in vitro toxicity studies demonstrated that adding the lowest dose of Cys-encapsulated in both nanocarriers [Cys-SLN (5 μM) and Cys-CS-NC (10 μM)] to maturation or culture medium could accumulate a strong anti-oxidative effect in oocyte/embryo by controlled release and enhanced intracellular penetration of Cys. In comparison, Cys-SLN (5 μM) is more effective than Cys-CS-NC (10 μM) groups to improve the expression of antioxidant genes (SOD, CAT, GPx) or anti-apoptotic (BCL-2) gene and decreased apoptosis (BAX and caspase-3) or intra-/extracellular ROS levels. In a nutshell, both nanocarriers (CS-NC or SLN) can deliver the lowest dose of Cys into the oocyte/embryo, thus encouraging a better expansion of antioxidant genes and enhancing the development of in vitro oocyte/embryo.

The Role of Redox Dysregulation in the Effects of Prenatal Stress on Embryonic Interneuron Migration

Maternal stress during pregnancy is associated with increased risk of psychiatric disorders in offspring, but embryonic brain mechanisms disrupted by prenatal stress are not fully understood. Our lab has shown that prenatal stress delays inhibitory neural progenitor migration. Here, we investigated redox dysregulation as a mechanism for embryonic cortical interneuron migration delay, utilizing direct manipulation of pro- and antioxidants and a mouse model of maternal repetitive restraint stress starting on embryonic day 12. Time-lapse, live-imaging of migrating GAD67GFP+ interneurons showed that normal tangential migration of inhibitory progenitor cells was disrupted by the pro-oxidant, hydrogen peroxide. Interneuron migration was also delayed by in utero intracerebroventricular rotenone. Prenatal stress altered glutathione levels and induced changes in activity of antioxidant enzymes and expression of redox-related genes in the embryonic forebrain. Assessment of dihydroethidium (DHE) fluorescence after prenatal stress in ganglionic eminence (GE), the source of migrating interneurons, showed increased levels of DHE oxidation. Maternal antioxidants (N-acetylcysteine and astaxanthin) normalized DHE oxidation levels in GE and ameliorated the migration delay caused by prenatal stress. Through convergent redox manipula-tions, delayed interneuron migration after prenatal stress was found to critically involve redox dysregulation. Redox biology during prenatal periods may be a target for protecting brain development.

Application of extracellular flux analysis for determining mitochondrial function in mammalian oocytes and early embryos

Mitochondria provide the major source of ATP for mammalian oocyte maturation and early embryo development. Oxygen Consumption Rate (OCR) is an established measure of mitochondrial function. OCR by mammalian oocytes and embryos has generally been restricted to overall uptake and detailed understanding of the components of OCR dedicated to specific molecular events remains lacking. Here, extracellular flux analysis (EFA) was applied to small groups of bovine, equine, mouse and human oocytes and bovine early embryos to measure OCR and its components. Using EFA, we report the changes in mitochondrial activity during the processes of oocyte maturation, fertilisation, and pre-implantation development to blastocyst stage in response to physiological demands in mammalian embryos. Crucially, we describe the real time partitioning of overall OCR to spare capacity, proton leak, non-mitochondrial and coupled respiration – showing that while activity changes over the course of development in response to physiological demand, the overall efficiency is unchanged. EFA is shown to be able to measure mitochondrial function in small groups of mammalian oocytes and embryos in a manner which is robust, rapid and easy to use. EFA is non-invasive and allows real-time determination of the impact of compounds on OCR, facilitating an assessment of the components of mitochondrial activity. This provides proof-of-concept for EFA as an accessible system with which to study mammalian oocyte and embryo metabolism.

Ascorbic acid and CoQ10 ameliorate the reproductive ability of superoxide dismutase 1-deficient female mice†

Superoxide dismutase 1 suppresses oxidative stress within cells by decreasing the levels of superoxide anions. A dysfunction of the ovary and/or an aberrant production of sex hormones are suspected causes for infertility in superoxide dismutase 1-knockout mice. We report on attempts to rescue the infertility in female knockout mice by providing two antioxidants, ascorbic acid and/or coenzyme Q10, as supplements in the drinking water of the knockout mice after weaning and on an investigation of their reproductive ability. On the first parturition, 80% of the untreated knockout mice produced smaller litter sizes compared with wild-type mice (average 2.8 vs 7.3 pups/mouse), and supplementing with these antioxidants failed to improve these litter sizes. However, in the second parturition of the knockout mice, the parturition rate was increased from 18% to 44–75% as the result of the administration of antioxidants. While plasma levels of progesterone at 7.5 days of pregnancy were essentially the same between the wild-type and knockout mice and were not changed by the supplementation of these antioxidants, sizes of corpus luteum cells, which were smaller in the knockout mouse ovaries after the first parturition, were significantly ameliorated in the knockout mouse with the administration of the antioxidants. Moreover, the impaired vasculogenesis in uterus/placenta was also improved by ascorbic acid supplementation. We thus conclude that ascorbic acid and/or coenzyme Q10 are involved in maintaining ovarian and uterus/placenta homeostasis against insults that are augmented during pregnancy and that their use might have positive effects in terms of improving female fertility.

A heterozygous deficiency in protein phosphatase Ppm1b results in an altered ovulation number in mice

Ppm1b, a metal‑dependent serine/threonine protein phosphatase, catalyzes the dephosphorylation of a variety of phosphorylated proteins. Ppm1b‑/‑ mouse embryos die at the fertilized oocyte stage, whereas Ppm1b+/‑ mice with a C57BL/6 background exhibit no phenotypic abnormalities. Because the C57BL/6 strain produces a limited number of pups, in an attempt to produce Ppm1b‑/‑ mice, congenic Ppm1b+/‑ mice with an ICR background were established, which are more fertile and gave birth to more pups. As a result, however, no Ppm1b‑/‑ offspring were obtained when pairs of Ppm1b+/‑ ICR mice were bred again. Ppm1b+/‑ male and female ICR mice were analyzed from the viewpoint of fecundity. The Ppm1b haploinsufficiency had no effect on testicular weight or the number of sperm in male mice. Despite the fact that the levels of Ppm1b protein in the ovaries of sexually mature Ppm1b+/‑ mice were decreased compared with those of Ppm1b+/+ mice, there appeared to be no significant difference in the histological appearance of the ovaries, litter sizes or plasma progesterone levels at the estrous stage. When superovulation was induced by stimulation using a hormone treatment, the number of ovulated oocytes were the same for Ppm1b+/‑ and Ppm1b+/+ mice at 4 weeks of age when the estrous cycle did not proceed, however, the number of ovulated oocytes was lower in sexually mature Ppm1b+/‑ mice at 11 weeks of age compared with Ppm1b+/+ mice in the first and the second superovulation cycles. These collective results suggest that follicle development is excessive in Ppm1b+/‑ mice, and that this leads to a partial depletion of matured follicles and a corresponding decrease in the number of ovulated oocytes.

Impact of Oxidative Stress on Age-Associated Decline in Oocyte Developmental Competence

Reproductive capacity in women starts to decline beyond their mid-30s and pregnancies in older women result in higher rates of miscarriage with aneuploidy. Age-related decline in fertility is strongly attributed to ovarian aging, diminished ovarian reserves, and decreased developmental competence of oocytes. In this review, we discuss the underlying mechanisms of age-related decline in oocyte quality, focusing on oxidative stress (OS) in oocytes. The primary cause is the accumulation of spontaneous damage to the mitochondria arising from increased reactive oxygen species (ROS) in oocytes, generated by the mitochondria themselves during daily biological metabolism. Mitochondrial dysfunction reduces ATP synthesis and influences the meiotic spindle assembly responsible for chromosomal segregation. Moreover, reproductively aged oocytes produce a decline in the fidelity of the protective mechanisms against ROS, namely the ROS-scavenging metabolism, repair of ROS-damaged DNA, and the proteasome and autophagy system for ROS-damaged proteins. Accordingly, increased ROS and increased vulnerability of oocytes to ROS lead to spindle instability, chromosomal abnormalities, telomere shortening, and reduced developmental competence of aged oocytes.

Developmental and molecular responses of buffalo (Bubalus bubalis) cumulus–oocyte complex maturedin vitrounder heat shock conditions

To investigate the effects of physiologically relevant heat shock during oocyte maturation, buffalo cumulus–oocyte complexes (COCs) were cultured at 38.5°C (control) or were exposed to 39.5°C (T1) or 40.5°C (T2) for the first 6 h ofin vitromaturation (IVM), followed by 38.5°C through the next 18 h/IVM and early embryonic development up to the blastocyst stage. Gene expression analysis was performed on selected target genes (HSF-1,HSF-2,HSP-70,HSP-90,BAX,p53,SOD1,COX1,MAPK14) in denuded oocytes and their isolated cumulus cells resulting from control COCs as well as from COCs exposed to a temperature of 39.5°C (T1). The results indicated that heat shock significantly (P< 0.01) decreased the maturation rate in T1 and T2 cells compared with the control. Afterin vitrofertilization (IVF), cleavage rate was lower (P< 0.01) for oocytes exposed to heat stress, and the percentage of oocytes arrested at the 2- or 4-cell stage was higher (P< 0.01) than that of the control. The percentage of oocytes that developed to the 8-cell, 16-cell or blastocyst stage was lower (P< 0.01) in both T1 and T2 groups compared with the control group. mRNA expression levels for the studied genes were decreased (P< 0.05) in treated oocytes (T1) except forHSP-90andHSF-1, which were increased. In cumulus cells isolated from COCs (T1), the expression for the target genes was upregulated except forBAX, which was downregulated. The results of this study demonstrated that exposure of buffalo oocytes to elevated temperatures for 6 h severely compromised their developmental competence and gene expression.

C-Phycocyanin protects against mitochondrial dysfunction and oxidative stress in parthenogenetic porcine embryos

C-Phycocyanin (CP) is a biliprotein enriched in blue-green algae that is known to possess antioxidant, anti-apoptosis, anti-inflammatory, and radical-scavenging properties in somatic cells. However, the protective effect of CP on porcine embryo developmental competence in vitro remains unclear. In the present study, we investigated the effect of CP on the development of early porcine embryos as well as its underlying mechanisms. Different concentrations of CP (2, 5, 8, 10 μg/mL) were added to porcine zygote medium 5 during in vitro culture. The results showed that 5 μg/mL CP significantly increased blastocyst formation and hatching rate. Blastocyst formation and quality were significantly increased in the 50 μM H₂O₂ treatment group following 5 μg/mL CP addition. CP prevented the H₂O₂-induced compromise of mitochondrial membrane potential, release of cytochrome c from the mitochondria, and reactive oxygen species generation. Furthermore, apoptosis, DNA damage level, and autophagy in the blastocysts were attenuated by supplementation of CP in the H₂O₂-induced oxidative injury group compared to in controls. These results suggest that CP has beneficial effects on the development of porcine parthenotes by attenuating mitochondrial dysfunction and oxidative stress.

Oxidative Stress Delays Prometaphase/Metaphase of the First Cleavage in Mouse Zygotes via the MAD2L1-Mediated Spindle Assembly Checkpoint

In zygotes, DNA damage delays the first cleavage to enable repair. Our previous study found that 0.03 mM hydrogen peroxide (H₂O₂) was the minimum concentration required for induction of oxidative DNA damage in mouse zygotes and that this represented the most similar situation to the clinical phenomenon. In this study, we quantified the cleavage rates of cells in blastocysts at different developmental stages, followed by immunofluorescence to detect activation of γ-H2A histone family member X (a marker of DNA damage) in zygotes to confirm that oxidative DNA damage was induced in H₂O₂-treated zygotes. Monitoring H3S10P (phosphorylation of Ser10 on histone H3; a prometaphase/metaphase marker) levels at different hour postinsemination revealed that treatment of zygotes with 0.03 mM H₂O₂ resulted in a prometaphase/metaphase delay. Furthermore, immunofluorescence staining for mitotic arrest deficient 2-like 1 and the protein kinase TTK, components of the spindle assembly checkpoint (SAC), suggested that this delay possibly involved SAC activation. These studies of the relationships between oxidative stress and SAC can promote the success rate of in vitro fertilization.

Oxidative stress-induced DNA damage of mouse zygotes triggers G2/M checkpoint and phosphorylates Cdc25 and Cdc2

In vitro fertilized (IVF) embryos show both cell cycle and developmental arrest. We previously showed oxidative damage activates the ATM → Chk1 → Cdc25B/Cdc25C cascade to mediate G2/M cell cycle arrest for repair of hydrogen peroxide (H2O2)-induced oxidative damage in sperm. However, the mechanisms underlying the developmental delay of zygotes are unknown. To develop a model of oxidative-damaged zygotes, we treated mouse zygotes with different concentrations of H2O2 (0, 0.01, 0.02, 0.03, 0.04, 0.05 mM), and evaluated in vitro zygote development, BrdU incorporation to detect the duration of S phase. We also examined reactive oxygen species level and used immunofluorescence to detect activation of γH2AX, Cdc2, and Cdc25. Oxidatively damaged zygotes showed a delay in G2/M phase and produced a higher level of ROS. At the same time, γH2AX was detected in oxidatively damaged zygotes as well as phospho-Cdc25B (Ser323), phospho-Cdc25C (Ser216), and phospho-Cdc2 (Tyr15). Our study indicates that oxidative stress-induced DNA damage of mouse zygotes triggers the cell cycle checkpoint, which results in G2/M cell cycle arrest, and that phospho-Cdc25B (Ser323), phospho-Cdc25C (Ser216), and phospho-Cdc2 (Tyr15) participate in activating the G2/M checkpoint.

Paradoxical Roles of Antioxidant Enzymes: Basic Mechanisms and Health Implications

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate "paradoxical" outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of "antioxidant" nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that "paradoxical" roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways.

Discovery of porcine maternal factors related to nuclear reprogramming and early embryo development by proteomic analysis

Background

Differentiated cell nuclei can be reprogrammed to a pluripotent state in several ways, including incubation with oocyte extracts, transfer into enucleated oocytes, and induced pluripotent stem cell technology. Nuclear transfer-mediated reprogramming has been proven to be the most efficient method. Maternal factors stored in oocytes have critical roles on nuclear reprogramming and early embryo development, but remain elusive.

Results

In this study, we showed most of porcine oocytes became nuclear matured at 33 h of IVM and the rate had no significant difference with oocytes at 42 h of IVM (p > 0.05). Moreover, the cleavage and blastocyst rates of SCNT and PA embryos derived from 42O were significantly higher than that of 33O (p < 0.05). But 33O could sustain IVF embryo development with higher cleavage and blastocyst rates comparing to 42O (p < 0.05). To clarify the development potential difference between 33O and 42O, 18 differentially expressed proteins were identified by proteomic analysis, and randomly selected proteins were confirmed by Western blot. Bioinformatic analysis of these proteins revealed that 33O highly synthesized proteins related to fertilization, and 42O was rich in nuclear reprogramming factors.

Conclusions

These results present a unique insight into maternal factors related to nuclear reprogramming and early embryo development.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-015-0074-5) contains supplementary material, which is available to authorized users.

Superoxide dismutase 1 loss disturbs intracellular redox signaling, resulting in global age-related pathological changes

Aging is characterized by increased oxidative stress, chronic inflammation, and organ dysfunction, which occur in a progressive and irreversible manner. Superoxide dismutase (SOD) serves as a major antioxidant and neutralizes superoxide radicals throughout the body. In vivo studies have demonstrated that copper/zinc superoxide dismutase-deficient (Sod1(-/-)) mice show various aging-like pathologies, accompanied by augmentation of oxidative damage in organs. We found that antioxidant treatment significantly attenuated the age-related tissue changes and oxidative damage-associated p53 upregulation in Sod1(-/-) mice. This review will focus on various age-related pathologies caused by the loss of Sod1 and will discuss the molecular mechanisms underlying the pathogenesis in Sod1(-/-) mice.

Mitochondrial membrane potential in 2-cell stage embryos correlates with the success of preimplantation development

Hormonal stimulation in superovulation induces female mice to ovulate more oocytes than spontaneous ovulation. Because the superovulated oocytes contain a number of oocytes that normally regress before spontaneous ovulation or immature oocytes, the development of some embryos that derive from these oocytes by IVF is prevented. Therefore, the quality of superovulated oocytes should differ from that of spontaneously ovulated oocytes. In this study, we evaluated the quality of superovulated oocytes, by examining 1- and 2-cell stage embryos, in which the development mainly depends on the maternal mRNA, proteins, and mitochondria that are contained in the oocytes, and we then measured the mitochondrial membrane potential (ΔΨm) of the 1- and 2-cell stage,in vivo-fertilized, and IVF embryos. The ΔΨmof 1-cell stage IVF embryos was lower than that ofin vivo-fertilized embryos; however, there was no difference between IVF embryos. During the developmental process from 1- to 2-cell stage, the ΔΨmofin vivo-fertilized embryos was highly upregulated, whereas a number of IVF embryos remained unchanged. As a result, 2-cell stage embryos were divided into two groups: high- and low- ΔΨm2-cell stage IVF embryos. The development of low-ΔΨm2-cell stage IVF embryos tended to be arrested after the 2-cell stage. These results indicated that the upregulation of ΔΨmduring the 1- to 2-cell stage was important in the development of early preimplantation embryos; there were some defects in the mitochondria of superovulated oocytes, which prevented their development.

Protective effect of quercetin on the development of preimplantation mouse embryos against hydrogen peroxide-induced oxidative injury

Quercetin, a plant-derived flavonoid in Chinese herbs, fruits and wine, displays antioxidant properties in many pathological processes associated with oxidative stress. However, the effect of quercetin on the development of preimplantation embryos under oxidative stress is unclear. The present study sought to determine the protective effect and underlying mechanism of action of quercetin against hydrogen peroxide (H₂O₂)-induced oxidative injury in mouse zygotes. H₂O₂ treatment impaired the development of mouse zygotes in vitro, decreasing the rates of blastocyst formation and hatched, and increasing the fragmentation, apoptosis and retardation in blastocysts. Quercetin strongly protected zygotes from H₂O₂-induced oxidative injury by decreasing the reactive oxygen species level, maintaining mitochondrial function and modulating total antioxidant capability, the activity of the enzymatic antioxidants, including glutathione peroxidase and catalase activity to keep the cellular redox environment. Additionally, quercetin had no effect on the level of glutathione, the main non-enzymatic antioxidant in embryos.

Oxidative stress and redox regulation of gametogenesis, fertilization, and embryonic development

Oxidative stress caused by elevated reactive oxygen species (ROS) is one of the predominant causes of both male and female infertility. Oxidative stress conditions cause either cell death or senescence by oxidation of cellular molecules including nucleic acid, proteins, and lipids. It is particularly important to minimize oxidative stress when in vitro fertilization is performed for the purpose of assisted reproduction. The problems associated with assisted reproductive technology are becoming evident, and it is now the time to clarify its mechanisms and cope with them. On the other hand, the beneficial roles of ROS, such as intracellular signaling, have become evident. The antithetical functions of ROS make it more difficult to overcome the problems caused by oxidative stress. Despite the difficulty in understanding mammalian reproduction, the mechanisms and problems can be gradually unveiled by advanced technology such as genetic modification of animals.

Cryotolerance of in vitro-produced porcine blastocysts is improved when using glucose instead of pyruvate and lactate during the first 2 days of embryo culture

The objective of the present study was to determine the effects of replacing glucose with pyruvate and lactate during the first 48 h of in vitro culture (IVC) in NCSU-23 medium on embryo development, embryo quality and survival of porcine blastocysts after vitrification. To this end, in vitro-produced (IVP) porcine oocytes were cultured with either glucose for 6 days (IVC-Glu) or pyruvate–lactate from Day 0 to Day 2 and then with glucose until Day 6 (IVC-PyrLac). Blastocysts were vitrified on Day 6 using the Cryotop device and, after warming, survival rate and the apoptosis index were evaluated after 24 h incubation in NCSU-23 medium. No significant differences were observed between IVC-Glu and IVC-PyrLac in terms of cleavage rate, blastocyst yield, total number of cells per blastocyst or the apoptosis index (1.82 ± 0.75% vs 3.18 ± 0.88%, respectively) of non-vitrified embryos. However, a significant increase was seen in hatching/hatched blastocysts in the IVC-PyrLac compared with IVC-Glu treatment group (12.71 ± 1.20% vs 3.54 ± 0.47%, respectively). Regardless of treatment, vitrification impaired the survival rate and the apoptosis index. When comparing both treatments after warming, the percentage of apoptotic cells was significantly higher for blastocysts in the IVC-PyrLac compared with IVC-Glu group (18.55 ± 3.49% vs 9.12 ± 2.17%, respectively). In conclusion, under the conditions of the present study, replacement of glucose with pyruvate–lactate during the first 48 h of culture resulted in a lower cryotolerance of IVP porcine embryos.

Release of superoxide dismutase-1 by day 3 embryos of varying quality and implantation potential

PURPOSE

To determine if the antioxidant superoxide dismutase-1 (SOD1 or Cu,Zn-SOD) is released by cultured human cleavage-stage embryos and to assess any link between SOD1 and implantation potential.

METHODS

Women (n = 91; ≤40 years old) undergoing IVF treatment with transfer of one or two 8-cell embryos that resulted in 0 or 100% implantation were included. Following individual embryo culture, spent medium samples (n = 122) were collected and levels of SOD1 protein were measured by an enzyme-linked immunosorbent assay. SOD1 detection and concentration in embryo spent medium were analyzed in relation to embryo fragmentation and symmetry scores, and implantation (viable fetus at >12 weeks).

RESULTS

Cleavage-stage embryos release SOD1 protein into the spent culture medium. Neither detection nor concentration of SOD1 was related to implantation. There was a positive relationship between increased embryo fragmentation scores and SOD1 release, with no apparent association with symmetry. In non-pregnant cycles, the release of SOD1 decreased with increasing maternal age.

CONCLUSIONS

While SOD1 does not predict implantation potential of select good-quality embryos, our data support the need to evaluate the biological significance of released SOD1 by embryos of varying quality and from patients of varying age.

Oxidative stress induced carbonylation in human plasma

The focus of this study was on the assessment of technology that might be of clinical utility in identification, quantification, characterization of carbonylation in human plasma proteins. Carbonylation is widely associated with oxidative stress diseases. Breast cancer patient samples were chosen as a stress positive case based on the fact that oxidative stress has been reported to be elevated in this disease. Measurements of 8-isoprostane in plasma confirmed that breast cancer patients in this study were indeed experiencing significant oxidative stress. Carbonyl groups in proteins from freshly drawn blood were derivatized with biotin hydrazide after which the samples were dialyzed and the biotinylated proteins subsequently selected, digested and labeled with iTRAQ™ heavy isotope coding reagent(s). Four hundred sixty proteins were identified and quantified, 95 of which changed 1.5 fold or more in concentration. Beyond confirming the utility of the analytical method, association of protein carbonylation was examined as well. Nearly one fourth of the selected proteins were of cytoplasmic, nuclear, or membrane origin. Analysis of the data by unbiased knowledge assembly methods indicated the most likely disease associated with the proteins was breast neoplasm. Pathway analysis showed the proteins which changed in carbonylation were strongly associated with Brca1, the breast cancer type-1 susceptibility protein. Pathway analysis indicated the major molecular functions of these proteins are defense, immunity and nucleic acid binding.

A missense mutation in the transcription factor Foxo3a causes teratomas and oocyte abnormalities in mice

An N-ethyl-N-nitrosourea random mutation screen was used to identify recessive modifiers of gene silencing in the mouse using an epigenetically sensitive reporter transgene. One of the mutant lines, MommeR1, was identified as a suppressor of variegation and it showed female-specific age-associated infertility in homozygotes. Linkage analysis identified a region on chromosome 10, containing the Foxo3a gene, previously shown to play a critical role in female gametogenesis. Foxo3a is a transcription factor with roles in cell cycle control, apoptosis, neural and hematopoietic cell differentiation, and DNA repair. Sequencing of the Foxo3a gene in MommeR1 mice revealed a point mutation that causes an amino acid substitution in the highly conserved Forkhead DNA-binding domain. In vitro transcription assays showed that the point mutation causes loss of FOXO3a transactivation activity. Compound heterozygotes made with Foxo3a-null mice (carrying the targeted deletion of exon 2) displayed complementation with respect to both the activation of the reporter transgene and defects in folliculogenesis similar to those seen in MommeR1 homozygotes, supporting the conclusion that this is the causative mutation. Approximately one in six female MommeR1 homozygotes develop teratomas, a phenotype not reported in Foxo3a-null mice. Ovulated oocytes from MommeR1 homozygotes display a number of abnormalities. The MommeR1 mice provide a novel platform to investigate teratocarcinogenesis and link Foxo3a with parthenogenesis and ovarian cancer. The finding of Foxo3a as a modifier of epigenetic reprogramming is discussed.