Male SIRT1 insufficiency leads to sperm with decreased ability to hyperactivate and fertilize.

Deficient sperm motility is a frequent cause of the age-related male sub-/infertility. Since the protein sirtuin 1 (SIRT1) develops anti-aging action and participates in sperm motility and ATP synthesis in mitochondria, we investigated its role in the acquisition of hyperactivated motility during capacitation. For this, the dynamics of sperm subpopulations were studied, using males of Sirt1+/- heterozygous mutant mice. After 2 hr of capacitation, we observed reduced percentage of hyperactivated spermatozoa in Sirt1+/- males. Interestingly, prior to capacitation, Sirt1+/- spermatozoa showed higher mitochondrial superoxide levels, which could render mitochondrial injury and thereby motility defects. Accordingly, the fertilization rate of Sirt1+/- males after mating was decreased. We elucidated that SIRT1 male insufficiency underlies posterior sperm defects to hyperactivate during capacitation and propose Sirt1+/- males as a model for the study of the age-related infertility.

Exposure to alternative bisphenols BPS and BPF through breast milk: Noxious heritage effect during nursing associated with idiopathic infertility.

There is increasing evidence that bisphenols BPS and BPF, which are analogues of BPA, have deleterious effects on reproduction even at extremely low doses. Indirect exposure via the maternal route (i.e. across the placenta and/or by breastfeeding) is underestimated, although it can be assumed to be a cause of idiopathic female infertility. Therefore, we hypothesised the deleterious effects of exposure to BPA analogues during breastfeeding on the ovarian and oocyte quality of offspring. A 15-day exposure period of pups was designed, whilst nursing dams (N ≥ 6 per experimental group) were treated via drinking water with a low (0.2 ng/g body weight/day) or moderate (20 ng/g body weight/day) dose of bisphenol, mimicking real exposure in humans. Thereafter, female pups were bred to 60 days and oocytes were collected. Immature oocytes were used in the in-vitro maturation assay; alternatively, in-vivo-matured oocytes were isolated and used for parthenogenetic activation. Both in-vitro- and in-vivo-matured oocytes were subjected to immunostaining of spindle microtubules (α-tubulin) and demethylation of histone H3 on the lysine K27 (H3K27me2) residue. Although very low doses of both BPS and BPF did not affect the quality of ovarian histology, spindle formation and epigenetic signs were affected. Notably, in-vitro-matured oocytes were significantly sensitive to both doses of BPS and BPF. Although no significant differences in spindle-chromatin quality were identified in ovulated and in-vivo-matured oocytes, developmental competence was significantly damaged. Taken together, our mouse model provides evidence that bisphenol analogues represent a risk to human reproduction, possibly leading to idiopathic infertility in women.

Low doses of Bisphenol S affect post-translational modifications of sperm proteins in male mice.

BACKGROUND: Bisphenol S (BPS) is increasingly used as a replacement for bisphenol A in the manufacture of products containing polycarbonates and epoxy resins. However, further studies of BPS exposure are needed for the assessment of health risks to humans. In this study we assessed the potential harmfulness of low-dose BPS on reproduction in male mice. METHODS: To simulate human exposure under experimental conditions, 8-week-old outbred ICR male mice received 8 weeks of drinking water containing a broad range of BPS doses [0.001, 1.0, or 100 µg/kg body weight (bw)/day, BPS1-3] or vehicle control. Mice were sacrificed and testicular tissue taken for histological analysis and protein identification by nano-liquid chromatography/mass spectrometry (MS) and sperm collected for immunodetection of acetylated lysine and phosphorylated tyrosine followed by protein characterisation using matrix-assisted laser desorption ionisation time-of-flight MS (MALDI-TOF MS). RESULTS: The results indicate that compared to vehicle, 100 µg/kg/day exposure (BPS3) leads to 1) significant histopathology in testicular tissue; and, 2) higher levels of the histone protein γH2AX, a reliable marker of DNA damage. There were fewer mature spermatozoa in the germ layer in the experimental group treated with 1 µg/kg bw (BPS2). Finally, western blot and MALDI-TOF MS studies showed significant alterations in the sperm acetylome and phosphorylome in mice treated with the lowest exposure (0.001 µg/kg/day; BPS1), although the dose is several times lower than what has been published so far. CONCLUSIONS: In summary, this range of qualitative and quantitative findings in young male mice raise the possibility that very low doses of BPS may impair mammalian reproduction through epigenetic modifications of sperm proteins.

The serine protease inhibitors and SERPINE1/2 disrupt prostaglandin E2 production and hyaluronic acid retention in FSH-stimulated pig cumulus-oocyte complexes.

The serine proteases, tissue- and urokinase-type plasminogen activators (PLAT and PLAU) and their inhibitors SERPINE1/2 are regulators of plasminogen to plasmin conversion. They are widely expressed in ovarian tissues, including granulosa and cumulus cells, and their expression is regulated by gonadotropins. The aim of this work was to assess the effect of serine protease inhibitors (aprotinin and AEBSF) and SERPINE1/2 on FSH-induced cumulus cell expansion, the production of prostaglandin E2 (PGE2) and retention of hyaluronic acid (HA) in expanding cumulus. The serine protease activity proved to be essential for the production of PGE2 and also for the retention of HA; the inhibition of plasminogen activators by SERPINE1/2 had the same effect. Collectively, these data indicate that plasmin is required for proper function of expanding cumulus cells in vitro and presumably also in vivo in the pre-ovulatory follicles.

Long-term exposure to very low doses of bisphenol S affects female reproduction.

Bisphenols belong to the endocrine disruptors, affecting reproduction even in extremely low doses. Bisphenol S (BPS) has become widely used as a substitute for the earlier-used bisphenol A; however, its harmlessness is questionable. The aim of this study was to evaluate the effect of BPS on folliculogenesis and oocyte quality after in vivo exposure to low doses of BPS. Four-week-old ICR females (n = 16 in each experimental group) were exposed to vehicle control (VC), BPS1 (0.001 ng BPS.g/bw/day), BPS2 (0.1 ng.g/bw/day), BPS3 (10 ng.g/bw/day) and BPS4 (100 ng.g/bw/day) for 4 weeks. Ovaries were subjected to stereology and nano liquid chromatography-mass spectrometry (LC/MS). Simultaneously, metaphase II oocytes were obtained after pregnant mare serum gonadotrophin and human chorionic gonadotrophin administration, followed by immunostaining. In particular, mating and two-cell embryo flushing were performed. We observed that BPS decreases the amount of ovarian follicles and BPS2 (0.1 ng.g/bw/day) affects the volume of antral follicles. Accordingly, ovarian proteome is affected after BPS2 treatment. While BPS2 dosing results mainly in cytoskeletal damage in matured oocytes, the effects of BPS3 and BPS4 seem to be due instead to epigenetic alterations in oocytes. Arguably, these changes lead to observed affection of in vivo fertilization rate after BPS3 and BPS4 treatment. BPS significantly affects female reproduction astoundingly in extremely low doses. These findings underline the necessity to assess the risk of ongoing BPS exposure for public health.

Involvement of K+ATP and Ca2+ channels in hydrogen sulfide-suppressed ageing of porcine oocytes.

BACKGROUND: Hydrogen sulfide has been shown to improve the quality of oocytes destined for in vitro fertilization. Although hydrogen sulfide is capable of modulating ion channel activity in somatic cells, the role of hydrogen sulfide in gametes and embryos remains unknown. Our observations confirmed the hypothesis that the KATP and L-type Ca2+ ion channels play roles in porcine oocyte ageing and revealed a plausible contribution of hydrogen sulfide to the modulation of ion channel activity. RESULTS: We confirmed the benefits of the activation and suppression of the KATP and L-type Ca2+ ion channels, respectively, for the preservation of oocyte quality. CONCLUSIONS: Our experiments identified hydrogen sulfide as promoting the desired ion channel activity, with the capacity to protect porcine oocytes against cell death. Further experiments are needed to determine the exact mechanism of hydrogen sulfide in gametes and embryos.

Prostaglandin E2 stimulates the expression of cumulus expansion-related genes in pigs: the role of protein kinase B.

The production of prostaglandin E2 (PGE2) seems to play an important role in the ovulation process. PGE2 was found to induce cumulus expansion and meiosis resumption in mice, but little is known about its role in pigs. The goals of this study were (a) to assess the effect of PGE2 on the expression levels of cumulus expansion-related genes, (b) to define the signaling pathways that drive the PGE2-stimulated expression of cumulus expansion-related genes, (c) to measure the effect of PGE2 on the activation of key signaling molecules (MAPK3/1, PKB) and on hyaluronan production in cumulus cells, and (d) to assess the effect of PGE2 on meiosis resumption. We documented that PGE2 is able to induce the expression of cumulus expansion-related genes (HAS2, TNFAIP6) as well as genes involved in steroidogenesis (CYP11A1) or prostaglandin production (PTGS2). PGE2 is able to activate PKB and MAPK3/1 and induce mild cumulus expansion and meiosis resumption, but less efficiently than FSH.

Non-Invasive Approaches to Epigenetic-Based Sperm Selection.

Since sperm size and form do not necessarily provide information on internal sperm structures, novel sperm markers need to be found in order to conduct assisted reproductive therapies (ART) successfully. Currently, the priority of andrologists is not only to select those sperm able to fertilize the oocyte, but also a high quality of sperm that will guarantee a healthy embryo. Evidence of this shows us the importance of studying sperm intensively on genetic and epigenetic levels, because these could probably be the cause of a percentage of infertility diagnosed as idiopathic. Thus, more attention is being paid to posttranslational modifications as the key for better understanding of the fertilization process and its impact on embryo and offspring. Advances in the discovery of new sperm markers should go hand in hand with finding appropriate techniques for selecting the healthiest sperm, guaranteeing its non-invasiveness. To date, most sperm selection techniques can be harmful to sperm due to centrifugation or staining procedures. Some methods, such as microfluidic techniques, sperm nanopurifications, and Raman spectroscopy, have the potential to make selection gentle to sperm, tracking small abnormalities undetected by methods currently used. The fact that live cells could be analyzed without harmful effects creates the expectation of using them routinely in ART. In this review, we focus on the combination of sperm epigenetic status (modifications) as quality markers, with non-invasive sperm selection methods as novel approaches to improve ART outcomes.

Nitric oxide donor s-nitroso-n-acetyl penicillamine (SNAP) alters meiotic spindle morphogenesis in Xenopus oocytes.

Nitric Oxide (NO) has been involved in both intra- and extra-cellular signaling pathways in a wide range of organisms, and can be detected in some reproductive tissues. Based upon previous results reporting that NO-donor SNAP (s-nitroso-n-acetyl penicillamine) promoted the release from the metaphase II-anaphase II block in amphibian eggs, the aim of the present study was to assess the influence of SNAP on the activation of the molecular mechanisms triggering meiotic resumption of Xenopus oocytes, analogous to G2/M transition of the cell cycle. A high concentration of SNAP (2.5 mM) was found to inhibit the appearance of the white spot (meiotic resumption) and promoted alteration of spindle morphogenesis leading to atypical structures lacking bipolarity and correct chromosomes equatorial alignment. The medium acidification (pH = 4) promoted by SNAP specifically impacted the white spot occurrence. However, even when pH was restored to 7.4 in SNAP medium, observed spindles remained atypical (microtubule disorganization), suggesting SNAP impacted spindle assembly regardless of the pH. n-Acetyl-d,l-penicillamine disulfide, a degradation product of SNAP with the same molecular characteristics, albeit without release of NO, yielded spindle assemblies typical of metaphase II suggesting the specificity of NO action on meiotic spindle morphogenesis in Xenopus oocytes.

Endogenously produced hydrogen sulfide is involved in porcine oocyte maturation in vitro.

Hydrogen sulfide, one of three known gasotransmitters, is involved in physiological processes, including reproductive functions. Oocyte maturation and surrounding cumulus cell expansion play an essential role in female reproduction and subsequent embryonic development. Although the positive effects of exogenous hydrogen sulfide on maturing oocytes are well known, the role of endogenous hydrogen sulfide, which is physiologically released by enzymes, has not yet been described in oocytes. In this study, we observed the presence of Cystathionine ß-Synthase (CBS), Cystathionine γ-Lyase (CTH) and 3-Mercaptopyruvate Sulfurtransferase (3-MPST), hydrogen sulfide-releasing enzymes, in porcine oocytes. Endogenous hydrogen sulfide production was detected in immature and matured oocytes as well as its requirement for meiotic maturation. Individual hydrogen sulfide-releasing enzymes seem to be capable of substituting for each other in hydrogen sulfide production. However, meiosis suppression by inhibition of all hydrogen sulfide-releasing enzymes is not irreversible and this effect is a result of M-Phase/Maturation Promoting Factor (MPF) and Mitogen-Activated Protein Kinase (MAPK) activity inhibition. Futhermore, cumulus expansion expressed by hyaluronic acid (HA) production is affected by the inhibition of hydrogen sulfide production. Moreover, quality changes of the expanded cumuli are indicated. These results demonstrate hydrogen sulfide involvement in oocyte maturation as well as cumulus expansion. As such, hydrogen sulfide appears to be an important cell messenger during mammalian oocyte meiosis and adequate cumulus expansion.

Dynamics and necessity of SIRT1 for maternal-zygotic transition.

Dynamic changes in maternal‒zygotic transition (MZT) require complex regulation of zygote formation, maternal transcript decay, embryonic genome activation (EGA), and cell cycle progression. Although these changes are well described, some key regulatory factors are still elusive. Sirtuin-1 (SIRT1), an NAD+-dependent histone deacetylase, is a versatile driver of MZT via its epigenetic and nonepigenetic substrates. This study focused on the dynamics of SIRT1 in early embryos and its contribution to MZT. A conditional SIRT1-deficient knockout mouse model was used, accompanied by porcine and human embryos. Embryos across mammalian species showed the prominent localization of SIRT1 in the nucleus throughout early embryonic development. Accordingly, SIRT1 interacts with histone H4 on lysine K16 (H4K16) in both mouse and human blastocysts. While maternal SIRT1 is dispensable for MZT, at least one allele of embryonic Sirt1 is required for early embryonic development around the time of EGA. This role of SIRT1 is surprisingly mediated via a transcription-independent mode of action.

The bisphenol S contamination level observed in human follicular fluid affects the development of porcine oocytes.

Bisphenol S (BPS), the main replacement for bisphenol A (BPA), is thought to be toxic, but limited information is available on the effects of Bisphenol S on ovarian follicles. In our study, we demonstrated the presence of Bisphenol S in the follicular fluid of women at a concentration of 22.4 nM. The effect of such concentrations of Bisphenol S on oocyte maturation and subsequent embryo development is still unknown. Therefore, we focused on the effect of Bisphenol S on in vitro oocyte maturation, fertilization, and embryo development. As a model, we used porcine oocytes, which show many physiological similarities to human oocytes. Oocytes were exposed to Bisphenol S concentrations similar to those detected in female patients in the ART clinic. We found a decreased ability of oocytes to successfully complete meiotic maturation. Mature oocytes showed an increased frequency of meiotic spindle abnormalities and chromosome misalignment. Alarming associations of oocyte Bisphenol S exposure with the occurrence of aneuploidy and changes in the distribution of mitochondria and mitochondrial proteins were demonstrated for the first time. However, the number and quality of blastocysts derived from oocytes that successfully completed meiotic maturation under the influence of Bisphenol S was not affected.

Non-invasive method of obtaining milk from mice using carbetocin, a synthetic analogue of oxytocin.

INTRODUCTION: The mouse is an important laboratory animal in pharmacological and toxicological research. However, there is a limited ability to analyse the penetration of tested substances in mouse breastmilk, which is technically difficult to obtain in sufficient quantities. The aim of the study is to verify the use of carbetocin for this purpose. METHODS: The effect of carbetocin (20 and 40 µg per animal) was tested in nursing ICR females that had milk collected for 15 min, started 1.5 min after administration. At a higher dose, carbetocin was also tested with a 20-min collection, started 7 min after application. Oxytocin (2 IU per animal) and saline were used as positive and negative controls, respectively. RESULTS: Milk yield using a lower dose of carbetocin was comparable to oxytocin. However, the duration of action of carbetocin was longer than that of oxytocin. A higher doses of carbetocin resulted in significantly higher milk volumes. DISCUSSION: The use of carbetocin has proven to be an effective non-invasive method to obtain up to 0.89 g of milk from one mouse in 20 min.

Nursing Exposure to Bisphenols as a Cause of Male Idiopathic Infertility.

Idiopathic infertility is a serious problem, which can be caused and explained by exposure to endocrine disruptors, such as bisphenols. In our study, we studied transactional exposure to bisphenol and its effects on newborn male mice throughout their reproductive life. Newborn male mice were exposed to bisphenol S and bisphenol F through maternal milk from post-natal day 0 to post-natal day 15 at concentrations of 0.1 ng.g/bw/day and 10 ng.g/bw/day, respectively. Although there were minimal differences between the control and experimental groups in testicular tissue quality and spermatozoa quality, we discovered an interesting influence on early embryonic development. Moderate doses of bisphenol negatively affected cleavage of the early embryo and subsequently, the blastocyst rate, as well as the number of blastomeres per blastocyst. In our study, we focused on correlations between particular stages from spermatogenesis to blastocyst development. We followed epigenetic changes such as dimethylation of histone H3 and phosphorylation of histone H2 from germ cells to blastocysts; we discovered the transfer of DNA double-strand breaks through the paternal pronucleus from spermatozoa to blastomeres in the blastocyst. We elucidated the impact of sperm DNA damage on early embryonic development, and our results indicate that idiopathic infertility in adulthood may have causes related to the perinatal period.

Effect of Bisphenol S on testicular tissue after low-dose lactation exposure.

Exposure to endocrine disruptors such as bisphenols, can lead to and be the explanation for idiopathic infertility. In our study, we assessed the effect of exposure to bisphenol S (BPS) via breast milk on the testicular tissue health of adult male mice. Lactating dams were exposed to BPS through drinking water (0.216 ng g bw/day and 21.6 ng g bw/day) from post-natal day 0-15. Although there was no significant difference in testicular histopathology between the control and experimental groups, we observed an increase in the number of tight and gap junctions in the blood-testis barrier (BTB) of adult mice after lactation BPS exposure. Moreover, there was an increase in oxidative stress markers in adult testicular tissue of mice exposed via breast milk. Our lactation model indicates that breast milk is a route of exposure to an endocrine disruptor that can be responsible for idiopathic male infertility through the damage of the BTB and weakening of oxidative stress resistance in adulthood.

Evidence of endogenously produced hydrogen sulfide (H2S) and persulfidation in male reproduction.

Persulfidation contributes to a group of redox post-translational modifications (PTMs), which arise exclusively on the sulfhydryl group of cysteine as a result of hydrogen sulfide (H2S) action. Redox-active molecules, including H2S, contribute to sperm development; therefore, redox PTMs represent an extremely important signalling pathway in sperm life. In this path, persulfidation prevents protein damage caused by irreversible cysteine hyperoxidation and thus maintains this signalling pathway. In our study, we detected both H2S and its production by all H2S-releasing enzymes (cystathionine γ-lyase (CTH), cystathionine ß-synthase (CBS), and 3-mercaptopyruvate sulfurtransferase (MPST)) in male reproduction, including spermatozoa. We provided evidence that sperm H2S leads to persulfidation of proteins, such as glyceraldehyde-3-phosphate dehydrogenase, tubulin, and anchor protein A-kinase. Overall, this study suggests that persulfidation, as a part of the redox signalling pathway, is tightly regulated by enzymatic H2S production and is required for sperm viability.

H3K4me2 accompanies chromatin immaturity in human spermatozoa: an epigenetic marker for sperm quality assessment.

Chromatin remodeling, including histone post-translational modifications, during spermatogenesis can affect sperm quality and fertility, and epigenetic marks may therefore be useful for clinical evaluations of sperm. Together with histone hyperacetylation, the dimethylation of histone H3 on lysine K4 (H3K4me2) is also required during protamination. Accordingly, we evaluated the utilization of this epigenetic mark for the identification of sperm with decrease quality and immature chromatin. In this study, 99 semen samples, including 22 normozoospermic (N), 63 asthenozoospermic (A), and 14 oligoasthenozoospermic (OA) samples, were comprehensively analyzed with respect to H3K4me2 levels, DNA damage (DNA fragmentation index, DFI), and sperm immaturity (high DNA stainability, %HDS), as determined by a sperm chromatin structure assay using flow cytometry. We detected a significant relationship between H3K4me2 and %HDS (r = 0.47; p < 0.001). Furthermore, we observed negative correlations between H3K4me2 and sperm concentration, motility, and mitochondrial activity (p < 0.05). The increase in immaturity as semen quality decreased (N > A > OA) indicates the importance of chromatin immaturity and histone code deviations in sperm evaluations. Using various approaches, our study elucidated H3K4me2 as a molecular marker of sperm quality with potential use in reproductive medicine.Abbreviations: A: asthenozoospermic; AO: acridine orange; ART: assisted reproductive therapy; BWW: Biggers-Whitten Whittingham; DAPI: 4',6' -diamidino-2-phenylindole; DFI: DNA fragmentation index; H3K4me2: dimethylation of lysine K4 on histones H3; HDS: high DNA stainability; HRP: horseradish peroxidase; MACS: magnetic-activated cell sorting; N: normospermic; NGS: normal goat serum; OA: oligoasthenozoospermic; PTM: post-translational modification; SCSA: sperm chromatin structure assay; SUTI: sperm ubiquitin tag assay; TBS-T: TBS with 0.5% Tween-20.

Hydrogen Sulfide Impairs Meiosis Resumption in Xenopuslaevis Oocytes.

The role of hydrogen sulfide (H2S) is addressed in Xenopuslaevis oocytes. Three enzymes involved in H2S metabolism, cystathionine ß-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate sulfurtransferase, were detected in prophase I and metaphase II-arrested oocytes and drove an acceleration of oocyte meiosis resumption when inhibited. Moreover, meiosis resumption is associated with a significant decrease in endogenous H2S. On another hand, a dose-dependent inhibition was obtained using the H2S donor, NaHS (1 and 5 mM). NaHS impaired translation. NaHS did not induce the dissociation of the components of the M-phase promoting factor (MPF), cyclin B and Cdk1, nor directly impacted the MPF activity. However, the M-phase entry induced by microinjection of metaphase II MPF-containing cytoplasm was diminished, suggesting upstream components of the MPF auto-amplification loop were sensitive to H2S. Superoxide dismutase and catalase hindered the effects of NaHS, and this sensitivity was partially dependent on the production of reactive oxygen species (ROS). In contrast to other species, no apoptosis was promoted. These results suggest a contribution of H2S signaling in the timing of amphibian oocytes meiosis resumption.

Acute low-dose bisphenol S exposure affects mouse oocyte quality.

Bisphenol S (BPS) is widely used to replace the known endocrine disruptor BPA in various products. We evaluated the effect of acute in vivo BPS exposure on oocyte quality, simulating the oral route of exposure via oral gavage. Eight-week-old ICR female mice (N = 15 per experimental group) were exposed to vehicle or BPS1-BPS4 (0.001, 0.1, 10, and 100 ng BPS x g bw-1 day-1, respectively) for seven days. Oocytes were isolated and matured in vitro. We observed that BPS exposure increased aberrant spindle formation in mature oocytes and induced DNA damage. Moreover, BPS3 significantly increased the chromatin repressive marks 5-methyl cytosine (5meC) and H3K27me2 in immature oocytes. In the BPS2 group, the increase in 5meC occurred during oocyte maturation. Transcriptome analysis revealed differential expression of early embryonic development transcripts in BPS2-exposed oocytes. These findings indicate that the biological effect of BPS is non-monotonic, affecting oocyte quality even at concentrations that are orders of magnitude below those measured in humans.

Epigenetic and non-epigenetic mode of SIRT1 action during oocyte meiosis progression.

BACKGROUND: SIRT1 histone deacetylase acts on many epigenetic and non-epigenetic targets. It is thought that SIRT1 is involved in oocyte maturation; therefore, the importance of the ooplasmic SIRT1 pool for the further fate of mature oocytes has been strongly suggested. We hypothesised that SIRT1 plays the role of a signalling molecule in mature oocytes through selected epigenetic and non-epigenetic regulation. RESULTS: We observed SIRT1 re-localisation in mature oocytes and its association with spindle microtubules. In mature oocytes, SIRT1 distribution shows a spindle-like pattern, and spindle-specific SIRT1 action decreases α-tubulin acetylation. Based on the observation of the histone code in immature and mature oocytes, we suggest that SIRT1 is mostly predestined for an epigenetic mode of action in the germinal vesicles (GVs) of immature oocytes. Accordingly, BML-278-driven trimethylation of lysine K9 in histone H3 in mature oocytes is considered to be a result of GV epigenetic transformation. CONCLUSIONS: Taken together, our observations point out the dual spatiotemporal SIRT1 action in oocytes, which can be readily switched from the epigenetic to non-epigenetic mode of action depending on the progress of meiosis.