The effects of delayed activation and MG132 treatment on nuclear remodeling and preimplantation development of embryos cloned by electrofusion are correlated with the age of recipient cytoplasts

Oocyte Aging: The Role of Cellular and Environmental Factors and Impact on Female Fertility

Female aging is one of the most important factors that impacts human reproduction. With aging, there is a natural decline in female fertility. The decrease in fertility is slow and steady in women aged 30-35 years; however, this decline is accelerated after the age of 35 due to decreases in the ovarian reserve and oocyte quality. Human oocyte aging is affected by different environmental factors, such as dietary habits and lifestyle. The ovarian microenvironment contributes to oocyte aging and longevity. The immediate oocyte microenvironment consists of the surrounding cells. Crosstalk between the oocyte and microenvironment is mediated by direct contact with surrounding cells, the extracellular matrix, and signalling molecules, including hormones, growth factors, and metabolic products. In this review, we highlight the different microenvironmental factors that accelerate human oocyte aging and decrease oocyte function. The ovarian microenvironment and the stress that is induced by environmental pollutants and a poor diet, along with other factors, impact oocyte quality and function and contribute to accelerated oocyte aging and diseases of infertility.

Chemically assisted somatic cell nuclear transfer without micromanipulator in the goat: effects of demecolcine, cytochalasin-B, and MG-132 on the efficiency of a manual method of oocyte enucleation using a pulled Pasteur pipette

The present study aimed to facilitate widespread application of a previously described manual method of somatic cell nuclear transfer (SCNT) by investigating the effects of demecolcine (a microtubule-depolymerizing chemical), cytochalasin-B (a microfilament-depolymerizing chemical: 2.5μg/ml for 15min) and MG-132 (a proteasome inhibitor chemical) on the (i) incidence of cytoplasmic protrusion of MII chromosomes, (ii) improvement of manual oocyte enucleation, and (iii) in vitro and in vivo developmental competence of SCNT embryos in the goat. Following in vitro maturation, around 65% of goat oocytes contained a characteristic cytoplasmic protrusion of MII-chromosomes. Treatment with demecolcine (0.4μg/ml for 30min) significantly increased this rate to 92.2±4.5%. Treatment with MG-132 (2μM for 30min) could not improve this rate when used alone (61.4±11.5%), but when combined with demecolcine (86.4±8.1%). Treatment with cytochalasin-B completely suppressed this rate whenever used, either alone (7.7±5.1%) or in combination with demecolcine (3.9±1.3%). In a direct comparison, there was no significant difference in quantity and quality of embryos propagated by the manual vs. micromanipulation-based methods of SCNT (cleavage: 85.3±4.5 vs. 89.5±8.9%, blastocyst: 19.5±4.3 vs. 24.3±4.4%, grade 1 and 2 blastocyst: 33.8±7.1 vs. 29.5±6.3%, total cell count: 125±11.1 vs. 122±10.5, respectively). Furthermore, development to live kids at term was not significant between the two SCNT methods. From both technical and economical points of view, the overall in vitro and in vivo efficiency of this manual method of SCNT proved it a simple, fast and efficient alternative for large scale production of cloned goats.

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. We found that oocytes expressed stable levels of Fas receptors up to 24 h of in vitro aging. Moreover, culture of cumulus-denuded oocytes in CCs-conditioned CZB medium (CM), in CZB supplemented with recombinant sFasL, or in CM containing sFasL neutralizing antibodies all showed that sFasL impaired the developmental potential of the oocytes whereas facilitating activation and fragmentation of aging oocytes. Furthermore, CCs from the FasL-defective gld mice did not accelerate oocyte aging due to the lack of functional FasL. In conclusion, we propose that CCs surrounding aging oocytes released sFasL in an apoptosis-related manner, and the released sFasL accelerated oocyte aging by binding to Fas receptors.

Effect of addition of FSH, LH and proteasome inhibitor MG132 to in vitro maturation medium on the developmental competence of yak (Bos grunniens) oocytes

BACKGROUND

The competence for embryonic development after IVF is low in the yak, therefore, we investigated the effects of supplementation of FSH, LH and the proteasome inhibitor MG132 in IVM media on yak oocyte competence for development after IVF.

METHODS

In Experiment 1, yak cumulus-oocyte complexes (COCs) were in vitro matured (IVM) in TCM-199 with 20% fetal calf serum (FCS), 1 microg/mL estradiol-17beta, and different combinations of LH (50 or 100 IU/mL) and FSH (0, 1, 5, 10 microg/mL) at 38.6 degrees C, 5% CO2 in air for 24 h. Matured oocytes were exposed to frozen-thawed, heparin-capacitated yak sperm. Presumptive zygotes were cultured in SOF medium containing 6 mg/ml BSA, 0.5 mg/mL myoinositol, 3% (v/v) essential amino acids, 1% nonessential amino acids and 100 μg/mL L-glutamine (48 h, 38.5 degrees C, 5% CO2, 5% O2, and 90% N2). In Experiment 2, cumulus cells were collected at the end of IVM to determine FSHR and LHR mRNA expression by real-time PCR. In Experiment 3 and 4, COCs were cultured in the presence or absence of the proteasomal inhibitor MG132 from either 0-6 h or 18-24 h after initiation of maturation.

RESULTS

The optimum concentration of FSH and LH in IVM media was 5 microg/mL FSH and 50 IU/mL LH which resulted in the greatest cleavage (79.1%) and blastocyst rates (16.1%). Both FSHR and LHR mRNA were detected in yak cumulus cells after IVM. Treatment with MG132 early in maturation reduced (P<0.05) cleavage and blastocyst rates. Conversely, treatment with MG132 late in maturation improved (P<0.05) blastocyst rate. Optimal results with MG132 were achieved at a concentration of 10 microM.

CONCLUSIONS

An optimum concentration of FSH and LH in IVM medium, and treatment with MG132 late in maturation can improve yak oocytes competence for development after IVF.

Role of Na+/Ca2+ exchanger (NCX) in modulating postovulatory aging of mouse and rat oocytes

We studied the role of the Na+/Ca2+ exchanger (NCX) in modulating oocyte postovulatory aging by observing changes in NCX contents and activities in aging mouse and rat oocytes. Whereas the NCX activity was measured by observing oocyte activation following culture with NCX inhibitor or activator, the NCX contents were determined by immunohistochemical quantification. Although NCX was active in freshly-ovulated rat oocytes recovered 13 h post hCG injection and in aged oocytes recovered 19 h post hCG in both species, it was not active in freshly-ovulated mouse oocytes. However, NCX became active when the freshly-ovulated mouse oocytes were activated with ethanol before culture. Measurement of cytoplasmic Ca2+ revealed Ca2+ increases always before NCX activation. Whereas levels of the reactive oxygen species (ROS) and the activation susceptibility increased, the density of NCX member 1 (NCX1) decreased significantly with oocyte aging in both species. While culture with H2O2 decreased the density of NCX1 significantly, culture with NaCl supplementation sustained the NCX1 density in mouse oocytes. It was concluded that (a) the NCX activity was involved in the modulation of oocyte aging and spontaneous activation; (b) ROS and Na+ regulated the NCX activity in aging oocytes by altering its density as well as functioning; and (c) cytoplasmic Ca2+ elevation was essential for NCX activation in the oocyte.

Human embryonic stem cells derived by somatic cell nuclear transfer

Reprogramming somatic cells into pluripotent embryonic stem cells (ESCs) by somatic cell nuclear transfer (SCNT) has been envisioned as an approach for generating patient-matched nuclear transfer (NT)-ESCs for studies of disease mechanisms and for developing specific therapies. Past attempts to produce human NT-ESCs have failed secondary to early embryonic arrest of SCNT embryos. Here, we identified premature exit from meiosis in human oocytes and suboptimal activation as key factors that are responsible for these outcomes. Optimized SCNT approaches designed to circumvent these limitations allowed derivation of human NT-ESCs. When applied to premium quality human oocytes, NT-ESC lines were derived from as few as two oocytes. NT-ESCs displayed normal diploid karyotypes and inherited their nuclear genome exclusively from parental somatic cells. Gene expression and differentiation profiles in human NT-ESCs were similar to embryo-derived ESCs, suggesting efficient reprogramming of somatic cells to a pluripotent state.

An insufficient increase of cytosolic free calcium level results postovulatory aging-induced abortive spontaneous egg activation in rat

PURPOSE

The present study was aimed to find out whether postovulatory aging-induced abortive spontaneous egg activation (SEA) is due to insufficient increase of cytosolic free Ca(2+) level.

METHODS

Immature female rats (22-24 days old) were subjected to superovulation induction protocol. Eggs were collected 14, 17 and 19 h post-hCG surge to induce in vivo egg aging. The eggs were collected 14 h post-hCG surge and cultured in vitro for 3, 5 and 7 h to induce in vitro egg aging. The morphological changes, rate of abortive SEA, chromosomal status and cytosolic free Ca(2+) levels were analyzed.

RESULTS

Postovulatory aging induced morphological features characteristics of abortive SEA in a time-dependent manner in vivo as well as in vitro. The extracellular Ca(2+) increased rate of abortive SEA during initial period of culture, while co-addition of a nifedipine (L-type Ca(2+) channel blocker) protected against postovulatory aging-induced abortive SEA. However, CI induced morphological features characteristics of egg activation (EA) in a dose-dependent manner. As compare to control, an increase of cytosolic free Ca(2+) level (1.42 times) induced abortive SEA, while further increase of cytosolic free Ca(2+) level (2.55 times) induced EA.

CONCLUSION

Our results show that an insufficient cytosolic free Ca(2+) level is associated with postovulatory aging -induced abortive SEA, while furthermore increase is required to induce EA in rat.

Treatment with the proteasome inhibitor MG132 during the end of oocyte maturation improves oocyte competence for development after fertilization in cattle

Maturation of the oocyte involves nuclear and cytoplasmic changes that include post-translational processing of proteins. The objective was to investigate whether inhibition of proteasomes during maturation would alter competence of the bovine oocyte for fertilization and subsequent development. Cumulus-oocyte complexes were cultured in the presence or absence of the proteasomal inhibitor MG132 from either 0-6 h or 16-22 h after initiation of maturation. Treatment with MG132 early in maturation prevented progression to meiosis II and reduced fertilization rate and the proportion of oocytes and cleaved embryos that became blastocysts. Conversely, treatment with MG132 late in maturation improved the percentage of oocytes and cleaved embryos that became blastocysts without affecting nuclear maturation or fertilization rate. Optimal results with MG132 were achieved at a concentration of 10 µM - effects were generally not observed at lower or higher concentrations. Using proteomic analysis, it was found that MG132 at the end of maturation increased relative expression of 6 proteins and decreased relative expression of 23. Among those increased by MG132 that are potentially important for oocyte competence are GAPDH, involved in glycolysis, TUBA1C, needed for organellar movement, and two proteins involved in protein folding (P4HB and HYOU1). MG132 decreased amounts of several proteins that exert anti-apoptotic actions including ASNS, HSP90B1, PDIA3 and VCP. Another protein decreased by MG132, CDK5, can lead to apoptosis if aberrantly activated and one protein increased by MG132, P4HB, is anti-apoptotic. Finally, the pregnancy rate of cows receiving embryos produced from oocytes treated with MG132 from 16-22 h of maturation was similar to that for control embryos, suggesting that use of MG132 for production of embryos in vitro does not cause a substantial decrease in embryo quality.

Offspring from intracytoplasmic sperm injection of aged mouse oocytes treated with caffeine or MG132

Postovulatory mammalian oocytes age significantly in culture. B6D2F1 or ICR strain mouse oocytes were collected 16 h after hCG injection and then cultured for up to 40 h post hCG at 37 °C under 5% CO(2) in air. After intracytoplasmic sperm injection (ICSI), B6D2F1 and ICR oocytes lost full-term developmental potential by 30 h and 26 h after hCG administration, respectively. However, using supplementation with 10 mM caffeine or 1-5 μM of MG132, we could obtain live offspring from oocytes at 34 h (BDF1, 5%-21%) or 28 h (ICR, 5%-18%), whereas none were obtained from untreated aged oocytes. Caffeine maintained normal meiotic spindle morphology, whereas MG132 maintained maturation-promoting factor activity. These treatments did not affect the potential of fresh oocytes for fertilization and subsequent development. Thus, it should be safe to use these chemicals in routine in vitro fertilization and offspring could be generated by ICSI of aged fertilization failed oocytes.

Post-fusion treatment with MG132 increases transcription factor expression in somatic cell nuclear transfer embryos in pigs

The objective of this study was to examine the effect of post-fusion treatment of somatic cell nuclear transfer (SCNT) oocytes with the proteasomal inhibitor MG132 on maturation promoting factor (MPF) activity, nuclear remodeling, embryonic development, and gene expression of cloned pig embryos. Immediately after electrofusion, SCNT oocytes were treated with MG132 and/or caffeine for 2 hr, vanadate for 0.5 hr, or vanadate for 0.5 hr followed by MG132 for 1.5 hr. Of the MG132 concentrations tested (0-5 microM), the 1 microM concentration showed a higher rate of blastocyst formation (25.9%) than 0 (14.2%), 0.5 (16.9%), and 5 microM (16.9%). Post-fusion treatment with MG132, caffeine, and both MG132 and caffeine improved blastocyst formation (22.1%, 21.4%, and 24.4%, respectively), whereas vanadate treatment inhibited blastocyst formation (6.5%) compared to the control (11.1%). When examined 2 hr after fusion and 1 hr after activation, MPF activity remained at a higher (P < 0.05) level in SCNT oocytes that were treated post-fusion with caffeine and/or MG132, but it was decreased by vanadate. The rate of oocytes showing premature chromosome condensation was not altered by MG132 but was decreased by vanadate treatment. In addition, formation of single pronuclei was increased by MG132 compared to control and vanadate treatment. MG132-treated embryos showed increased expression of POU5F1, DPPA2, DPPA3, DPPA5, and NDP52l1 genes compared to control embryos. Our results demonstrate that post-fusion treatment of SCNT oocytes with MG132 prevents MPF degradation and increases expression of transcription factors in SCNT embryos, which are necessary for normal development of SCNT embryos.

Pyruvate prevents aging of mouse oocytes

Inhibiting oocyte aging is important not only for healthy reproduction but also for the success of assisted reproduction techniques. Although our previous studies showed that cumulus cells accelerated aging of mouse oocytes, the underlying mechanism is unknown. The objective of this paper was to study the effects of pyruvate and cumulus cells on mouse oocyte aging. Freshly ovulated mouse cumulus-oocyte complexes (COCs) or cumulus-denuded oocytes (DOs) were cultured in Chatot-Ziomek-Bavister (CZB) medium or COC-conditioned CZB medium supplemented with different concentrations of pyruvate before being examined for aging signs and developmental potential. Pyruvate supplementation to CZB medium decreased rates of ethanol-induced activation in both COCs and DOs by maintaining their maturation-promoting factor activities, but more pyruvate was needed for COCs than for DOs. Addition of pyruvate to the COC-conditioned CZB also alleviated aging of DOs. Observations on cortical granules, level of BCL2 proteins, histone acetylation, intracellular concentration of glutathione, and embryo development all confirmed that pyruvate supplementation inhibited aging of mouse oocytes. It is concluded that the aging of mouse oocytes, facilitated by culture in COCs, can be partially prevented by the addition of pyruvate to the culture medium.

Efficient production of nuclear transferred rat embryos by modified methods of reconstruction

In this study we investigated spontaneous oocyte activation and developmental ability of rat embryos of the SD-OFA substrain. We also tried to improve the somatic cell nuclear transfer (SCNT) technique in the rat by optimizing methods for the production of reconstructed embryos. About 20% of oocytes extruded the second polar body after culture for 3 hr in vitro and 84% of oocytes were at the MII stage. MG132 blocked spontaneous activation but decreased efficiency of parthenogenetic activation. Pronuclear formation was more efficient in strontium-activated oocytes (66.1-80.9%) compared to roscovitine activation (24.1-54.5%). Survival rate after enucleation was significantly higher (89.4%) after slitting the zona pellucida and then pressing the oocyte with a holding pipette in medium without cytochalasin B (CB) compared to the conventional protocol using aspiration of the chromosomes after CB treatment (67.7%). Exposure of rat ova to UV light for 30 sec did not decrease their in vitro developmental capacity. Intracytoplasmic cumulus cell injection dramatically decreased survival rate of oocytes (42%). In contrast, 75.9% of oocytes could be successfully electrofused. Development to the 2-cell stage was reduced after SCNT (24.6% compared 94.6% in controls) and none from 244 reconstructed embryos developed in vitro beyond this stage. After overnight in vitro culture, 74.4% of the SCNT embryos survived and 56.1% formed pronuclei. The pregnancy rate of 33 recipients after the transfer of 695 of these cloned embryos was, however, very low (18.2%) and only six implantation sites could be detected (0.9%) without any live fetuses and offspring.

Treatment with proteasome inhibitor MG132 during cloning improves survival and pronuclear number of reconstructed rat embryos

In several mammalian species including rats, successfully cloned animals have been generated using somatic cell nuclear transfer (SCNT). However, in the case of rats, additional treatment with MG132, a proteasome inhibitor, before enucleation of oocytes seems to be required for successful cloning because ovulated rat oocytes are spontaneously activated, and hence, their suppression is the key to successful cloning. A previous study on rats demonstrated that matured oocytes potentially possess lower cytostatic factor (CSF) activity compared to mouse oocytes, resulting in a low incidence of premature chromosome condensation in the reconstructed embryos after SCNT. It is known that mice having more than two pronuclei are generally observed in nuclear-transferred oocytes after induction of premature chromosome condensation, which implies successful reprogramming. This leads us to the hypothesis that MG132 treatment affects not only the inhibition of spontaneous activation but also the reprogramming and developmental ability of reconstructed rat embryos. If so, prolonged MG132 treatment during and/or after SCNT may further improve the survivability. However, the effect of MG132 treatment on reconstructed embryos after SCNT has been very limited in rats and other species. We show here that prolonged MG132 treatment during and after SCNT improves survival and the number of pronuclei in reconstructed rat embryos after activation. These reconstructed embryos treated before, during, and after SCNT showed significantly higher p34(cdc2) kinase activity involving CSF activity compared to that of the control embryos. On the other hand, p34(cdc2) kinase activity was not recovered in nuclear-transferred oocytes without MG132, which suggested that the enucleation had detrimental effects on the development of reconstructed oocytes. Taken together, MG132 treatment during SCNT increases survival and pronuclear numbers in reconstructed rat embryos via maintenance of high CSF activity. The data suggest that MG132 treatment is indispensable for at least rat SCNT.