Expression profiling and function analysis identified new genes regulating cumulus expansion and cumulus cell apoptosis in mouse oocytes.

In Brief: Genes expressed in cumulus cells might be used as markers for competent oocytes/embryos. This study identified and validated a new group of cumulus expansion and/or apoptosis-regulating genes, which may be used for selection of quality oocytes/embryos.

Abstract: Studies on the mechanisms behind cumulus expansion and cumulus cell (CC) apoptosis are essential for understanding the mechanisms for oocyte maturation.

Postovulatory Aging of Mouse Oocytes Impairs Offspring Behavior by Causing Oxidative Stress and Damaging Mitochondria.

Information on long-term effects of postovulatory oocyte aging (POA) on offspring is limited. Whether POA affects offspring by causing oxidative stress (OS) and mitochondrial damage is unknown. Here, in vivo-aged (IVA) mouse oocytes were collected 9 h after ovulation, while in vitro-aged (ITA) oocytes were obtained by culturing freshly ovulated oocytes for 9 h in media with low, moderate, or high antioxidant potential.

Role and action mechanisms of miR-149 and miR-31 in regulating function of pig cumulus cells and oocytes.

Understanding the mechanisms for oocyte maturation and optimizing the protocols for in vitro maturation (IVM) are greatly important for improving developmental potential of IVM oocytes. The miRNAs expressed in cumulus cells (CCs) play important roles in oocyte maturation and may be used as markers for selection of competent oocytes/embryos. Although a recent study from our group identified several new CCs-expressed miRNAs that regulate cumulus expansion (CE) and CC apoptosis (CCA) in mouse oocytes, validation of these findings and further investigation of mechanisms of action in other model species was essential before wider applications.

Role of miRNAs in glucose metabolism of mouse cumulus cells†.

It is known that the oocyte has a limited capacity to acquire and metabolize glucose, and it must rely on cumulus cells (CCs) to take up glucose and produce pyruvate for use to produce ATP through oxidative phosphorylation. We therefore propose that miRNAs might regulate glucose metabolism (GM) in CCs and might be used as markers for oocyte quality assessment. Here, mouse CC models with impaired glycolysis or pentose phosphate pathway (PPP) were established, and miRNAs targeting the key enzymes in glycolysis/PPP were predicted using the miRNA target prediction databases.

Role of calcium-sensing receptor in regulating activation susceptibility of postovulatory aging mouse oocytes.

The mechanisms underlying postovulatory oocyte aging (POA) remain largely unknown. The expression of the calcium-sensing receptor (CaSR) in mouse oocytes and its role in POA need to be explored. Our objective was to observe CaSR expression and its role in the susceptibility to activating stimuli (STAS) in POA mouse oocytes.

Role of tPA in Corticosterone-Induced Apoptosis of Mouse Mural Granulosa and Oviductal Epithelial Cells.

Although studies indicate that female stress-increased secretion of glucocorticoids impairs oocyte competence and embryo development, by inducing apoptosis of ovarian and oviductal cells, respectively, the mechanisms by which glucocorticoids induce apoptosis of ovarian and oviductal cells are largely unclear. Tissue plasminogen activator (tPA) has been involved in apoptosis of different cell types. However, while some studies indicate that tPA is proapoptotic, others demonstrate its antiapoptotic effects.

Restraint stress of female mice during oocyte development facilitates oocyte postovulatory aging.

Studies suggest that psychological stress on women can impair their reproduction and that postovulatory oocyte aging (POA) might increase the risk of early pregnancy loss and affect offspring's reproductive fitness and longevity. However, whether psychological stress during oocyte development would facilitate POA is unknown but worth exploring to understand the mechanisms by which psychological stress and POA damage oocytes. This study observed effects of female restraint stress during oocyte development (FRSOD) on oocyte resistance to POA.

Glucocorticoid Exposure of Preimplantation Embryos Increases Offspring Anxiety-Like Behavior by Upregulating miR-211-5p Trpm1 Demethylation.

Most studies on mechanisms by which prenatal stress affects offspring behavior were conducted during late pregnancy using models; studies on the effect of preimplantation stress are rare. models do not allow accurate specification of the roles of different hormones and cells within the complicated living organism, and cannot verify whether hormones act directly on embryos or indirectly to alter progeny behavior. Furthermore, the number of anxiety-related miRNAs identified are limited.

Topoisomerase II dysfunction causes metaphase I arrest by activating Aurora B, SAC and MPF and prevents PB1 abscission in mouse oocytes†.

Oocyte aneuploidy is caused mainly by chromosome nondisjunction and/or unbalanced sister chromatid pre-division. Although studies in somatic cells have shown that topoisomerase II (TOP2) plays important roles in chromosome condensation and timely separation of centromeres, little is known about its role during oocyte meiosis. Furthermore, because VP-16, which is a TOP2 inhibitor and induces DNA double strand breaks, is often used for ovarian cancer chemotherapy, its effects on oocytes must be studied for ovarian cancer patients to recover ovarian function following chemotherapy.

A next-generation sequencing study on mechanisms by which restraint and social instability stresses of male mice alter offspring anxiety-like behavior.

Pathophysiological mechanisms for depression/anxiety are largely unknown. Evidence for transgenerational transmission of acquired epigenetic marks remains limited. We bred unstressed (US) female mice with adolescently restraint-stressed (RS), social instability-stressed (SI) or US males to produce RS, SI and control F1 offspring, respectively.

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.

Role of AMP-activated protein kinase during postovulatory aging of mouse oocytes†.

Studies suggested that postovulatory oocyte aging might be prevented by maintaining a high maturation-promoting factor (MPF) activity. Whether AMP-activated protein kinase (AMPK) plays any role in postovulatory oocyte aging is unknown. Furthermore, while activation of AMPK stimulates meiotic resumption in mouse oocytes, it inhibits meiotic resumption in pig and bovine oocytes.

Meiotic block with roscovitine improves competence of porcine oocytes by fine-tuning activities of different cyclin-dependent kinases.

Successful use of oocytes from small follicles (SFs) is of great importance for animal embryo production and human in vitro fertilization with reduced hormone-related side effects. How in vitro meiotic arrest maintenance (MAM) increases the competence of oocytes is not clear. In this study, pig oocytes recovered from SF of 1-2 mm and medium-follicles (MF) of 3-6 mm in diameter from abattoir ovaries were treated by various MAM treatments to improve their competence.

Restraint stress of male mice triggers apoptosis in spermatozoa and spermatogenic cells via activating the TNF-α system.

Studies have indicated that psychological stress impairs human fertility and that various stressors can induce apoptosis of testicular cells. However, the mechanisms by which psychological stress on males reduces semen quality and stressors induce apoptosis in testicular cells are largely unclear. Using a psychological (restraint) stress mouse model, we tested whether male psychological stress triggers apoptosis of spermatozoa and spermatogenic cells through activating tumour necrosis factor (TNF)-α signalling.

Cumulus cell-released tumor necrosis factor (TNF)-α promotes post-ovulatory aging of mouse oocytes.

Although previous studies indicated that cumulus cells (CCs) accelerate oocyte aging by releasing soluble factors, the factors have yet to be characterized. While demonstrating that CCs promoted oocyte aging by releasing soluble Fas ligand (sFasL), our recent study suggested that CCs might secrete other factors to mediate oocyte aging as well. This study tested whether CCs accelerate oocyte aging by secreting tumor necrosis factor (TNF)-α.

Glucose metabolism during in vitro maturation of mouse oocytes: An study using RNA interference.

In previous studies on glucose metabolism during in vitro maturation, intact cumulus-oocyte complexes (COCs) were treated with enzyme inhibitors/activators. Because inhibitors/activators may have non-specificity and/or toxicity, and culture of COCs cannot differentiate whether glucose metabolism of cumulus cells (CCs) or that of the oocyte supports oocyte maturation, results from the previous studies must be verified by silencing genes in either CCs or cumulus-denuded oocytes (DOs). In this study, RNAi was adopted to specify the effects of glucose metabolism in CCs or DOs on oocyte maturation.

Role of calcium-sensing receptor in regulating spontaneous activation of postovulatory aging rat oocytes.

Mechanisms for postovulatory aging (POA) of oocytes and for spontaneous activation (SA) of rat oocytes are largely unknown. Expression of calcium-sensing receptor (CaSR) in rat oocytes and its role in POA remain unexplored. In this study, expression of CaSR in rat oocytes aging for different times was detected by immunofluorescence microscopy, and western blotting and the role of CaSR in POA was determined by observing the effects of regulating its activity on SA susceptibility and cytoplasmic calcium levels.

Mechanisms for the species difference between mouse and pig oocytes in their sensitivity to glucorticoids.

Although in vitro exposure to physiological concentrations of glucorticoids did not affect maturation of mouse oocytes, it significantly inhibited nuclear maturation of pig oocytes. Studies on this species difference in oocyte sensitivity to glucocorticoids will contribute to our understanding of how stress/glucocorticoids affect oocytes. We showed that glucorticoid receptors (NR3C1) were expressed in both oocytes and cumulus cells (CCs) of both pigs and mice; however, while cortisol inhibition of oocyte maturation was overcome by NR3C1 inhibitor RU486 in pigs, it could not be relieved by RU486 in mice.

Expression profiles and function analysis of microRNAs in postovulatory aging mouse oocytes.

In this study, microRNA (miRNA) profiles in postovulatory aging mouse oocytes were analyzed by microarray screening and RT-qPCR. Hierarchical cluster analysis on the microarray data and KEGG pathway enrichment analysis on the mRNAs targeted by differentially expressed (DE) miRNAs between two adjacent egg-ages suggest that while only a mild alteration in miRNA expression occurred from 13 to 18 h, a great change took place from 18 to 24 h post hCG injection. Theoretical exploration on functions of the predicted target genes suggest that KEGG pathways enriched by 13-18 h DE miRNAs are correlated with early events of oocyte aging while pathways most enriched by 18-24 h or 24-30 h DE miRNAs are correlated with the late symptoms of aged oocytes.

Stresses on Female Mice Impair Oocyte Developmental Potential: Effects of Stress Severity and Duration on Oocytes at the Growing Follicle Stage.

Aim: Although previous studies found that 1-time acute stress applied during follicle maturation impaired oocyte competence, it is unknown whether repeated chronic stress, which is known to cause animal behavioral adaptation, would damage oocytes when applied during follicle growth.

Methods And Results: In this study, female mice were exposed to repeated restraint stress (RRS) or unpredictable stress (UPS) for different days before equine chorionic gonadotropin injection to initiate oocyte prematuration development and to observe effects of different stressors on oocytes in the growing follicles. The results showed that although oocyte pre- and postimplantation development was unaffected when mice were exposed to RRS or UPS once a day for 4 days, development was impaired when mice were exposed to RRS for 8 or more days or to UPS twice a day for 4 days (4 × 2).

Effects of pH during liquid storage of goat semen on sperm viability and fertilizing potential.

A specific problem in goat semen preservation is the detrimental effect of seminal plasma on sperm viability in extenders containing yolk or milk. Thus, the use of chemically defined extenders will have obvious advantages. Although previous studies indicate that the initial pH of an extender is crucial to sustain high sperm motility, changes in extender pH during long-term semen storage have not been observed.

Cumulus cells accelerate oocyte aging by releasing soluble Fas ligand in mice.

Although previous studies have suggested that cumulus cells (CCs) accelerate oocyte aging by secreting soluble and heat-sensitive paracrine factors, the factors involved are not well characterized. Because Fas-mediated apoptosis represents a major pathway in induction of apoptosis in various cells, we proposed that CCs facilitate oocyte aging by releasing soluble Fas ligand (sFasL). In this study, we reported that when the aging of freshly ovulated mouse oocytes were studied in vitro, both the apoptotic rates of CCs and the amount of CCs produced sFasL increased significantly with the culture time.