Nuclear and cytoplasmic maturation of sow oocytes are not synchronized by specific meiotic inhibition with roscovitine during in vitro maturation

Effects of cumulus cells on the in vitro cytoplasmic maturation of immature oocytes in pigs

The exposure of cumulus cells to nuclear matured oocytes can be regulated through the forced delay of nuclear maturation or the alteration of in vitro maturation (IVM) time in cumulus-oocyte complexes (COCs). However, to date, no evidence has been presented for the enhancement of cytoplasmic maturation by them, indicating irrelevance of cumulus cells in cytoplasmic maturation. Therefore, in order to identify the requirement of cumulus cells in achieving the cytoplasmic maturation of immature oocytes, this study investigated the effects of cumulus cells on the in vitro cytoplasmic maturation of oocytes within COCs derived from porcine medium antral follicles (MAFs) post-the completion of nuclear maturation. For these, with IVM of COCs for 44 h (control), cumulus cell-free oocytes with completed nuclear maturation were in-vitro-matured additionally for 0, 6, or 12 h, and then a variety of factors representing the cytoplasmic maturation of oocytes were analyzed and compared. As the results, the IVM of COCs for 32 h showed complete nuclear maturation and incomplete cytoplasmic maturation. Moreover, after the removal of cumulus cells from COCs with the completion of nuclear maturation, IVM for an additional 6 or 12 h resulted in significant increases in the size of the perivitelline space, the proportion of oocytes with a normal intracellular mitochondrial distribution and a normal round first polar body, and the preimplantation development into the 2-cell and blastocyst stages after parthenogenetic activation. Simultaneously, they showed significant reduction in the level of intracellular reactive oxygen species and no significant differences in the total number of blastocysts. Furthermore, oocytes obtained by this approach did not significantly differ from control oocytes produced by IVM of COCs for 44 h. Our results demonstrate that the cumulus cells enclosing COCs derived from porcine MAFs are not essential for the completion of cytoplasmic maturation after complete nuclear maturation by COCs.

Dibutyryl-cAMP and roscovitine differently affect premature meiotic resumption and embryo development of vitrified immature porcine oocytes

Vitrification and warming can trigger premature meiosis in immature porcine oocytes. Our aim was to compare the efficacies of two meiotic inhibitors, dibutyryl-cAMP and roscovitine for the meiosis synchronization during in vitro maturation (IVM) of porcine oocytes vitrified at the germinal vesicle (GV) stage. We first compared the efficacy of 1 mM dibutyryl-cAMP and 25 μM roscovitine on meiotic arrest during the first 22 h of IVM. Dibutyryl-cAMP could maintain the GV stage in 83.5% of oocytes; however, roscovitine was even more effective (96.6%), whereas only 17.4% of the oocytes remained at the GV stage without these additives. Temporal meiotic arrest for 22 h by roscovitine did not reduce the percentage of oocytes reaching the Metaphase II stage during subsequent IVM. However, after parthenogenetic stimulation or in vitro fertilization, subsequent embryo development to the blastocyst stage was compromised after roscovitine treatment, whereas dibutyryl-cAMP improved the percentage of blastocyst development. In conclusion, dibutyryl-cAMP could derogate but not completely prevent premature meiosis in vitrified oocytes, whereas roscovitine could more efficiently prevent it. However, for embryo production, the use of roscovitine was disadvantageous, whereas the use of dibutyryl-cAMP was beneficial.

The effect of copper supplementation on in vitro maturation of porcine cumulus-oocyte complexes and subsequent developmental competence after parthenogenetic activation

Copper (Cu) ions have redox activity and act as cofactors of enzymes related to respiration, radical detoxification, and iron metabolism. In this study, we aimed to examine the effects of copper (II) chloride dihydrate (CuCl2·2H2O) on porcine oocytes during in vitro maturation (IVM) and subsequent embryonic development following parthenogenetic activation (PA). Nuclear maturation, intracellular glutathione (GSH) and reactive oxygen species (ROS) levels, cumulus expansion, the mRNA expression levels of various genes, and developmental competence were analyzed. During IVM, the maturation medium was supplemented with various concentrations of Cu (0, 0.7, 1.4, and 2.8 μg/mL). After 42 h of IVM, Cu supplementation significantly increased the number of oocytes in the metaphase II stage. Further, the 1.4 μg/mL Cu group showed significantly higher intracellular GSH levels than the control group. However, Cu supplementation increased intracellular ROS levels regardless of their concentration. Additionally, the mRNA levels of Has-2, the cumulus cell expansion-related gene, were higher in all the Cu-treated groups than in the control group. The cumulus cell expansion index was higher in the 0.7 and 1.4 μg/mL Cu groups than in the other groups. In the 0.7 μg/mL Cu group, the mRNA expression levels of PCNA, Zar1, and NPM2, which are related to developmental competence, were significantly higher than those in the control group. Moreover, increased levels of Sod1 transcript, correlated with the antioxidative response, were observed in the 0.7 and 1.4 μg/mL Cu groups. The apoptosis rate in Cu-treated cumulus cells and oocytes was decreased compared to that in the corresponding control groups. Upon evaluation of subsequent embryonic development after PA, the 0.7 μg/mL Cu group showed significantly improved cleavage and blastocyst formation rate compared to the control group. In conclusion, our results suggest that Cu supplementation at appropriate concentrations in IVM medium improves porcine oocyte maturation and the subsequent embryonic potential of PA embryos by reducing oxidative stress and apoptosis.

Bovine oocyte maturation: acquisition of developmental competence

Although millions of oocytes are formed during embryo and fetal development in the cow, only a small fraction of these will form a developmentally competent oocyte and be fertilised. Development to competence relies on an intimate contact between the oocyte and the surrounding somatic cells in ovarian follicles, via both direct cell-cell contact and paracrine signalling. An important aspect of oocyte maturation is the segregation of homologous chromosomes and subsequently sister chromatids to form a haploid oocyte. Furthermore, the cytoplasm needs to be prepared for the formation of pronuclei and nuclear reprogramming to form a totipotent zygote. Conditions such as high levels of fatty acids or oxidative stress constrain the developmental competence of oocytes, and a better insight into these processes may help improve in vitro and in vivo oocyte maturation success. In addition, identification of the developmentally competent oocyte is useful for the efficiency of (artificial) reproduction.

Effects of vitrification of cumulus-enclosed porcine oocytes at the germinal vesicle stage on cumulus expansion, nuclear progression and cytoplasmic maturation

Although offspring have been produced from porcine oocytes vitrified at the germinal vesicle (GV) stage, the rate of embryo development remains low. In the present study, nuclear morphology and progression, cumulus expansion, transzonal projections (TZPs), ATP and glutathione (GSH) levels were compared between vitrified cumulus-oocyte complexes (COCs) and control COCs (no cryoprotectant treatment and no cooling), as well as a toxicity control (no cooling). Vitrification was performed with 17.5% (v/v) ethylene glycol and 17.5% (v/v) propylene glycol. Vitrification at the GV stage caused premature meiotic progression, reflected by earlier GV breakdown and untimely attainment of the MII stage. However, cytoplasmic maturation, investigated by measurement of ATP and GSH levels, as well as cumulus expansion, proceeded normally despite detectable damage to TZPs in vitrified COCs. Moreover, treatment with cryoprotectants caused fragmentation of nucleolus precursor bodies and morphological changes in F-actin from which oocytes were able to recover during subsequent IVM culture. Reduced developmental competence may be explained by premature nuclear maturation leading to oocyte aging, although other mechanisms, such as initiation of apoptosis and reduction of cytoplasmic mRNA, can also be considered. Further research will be required to clarify the presence and effects of these phenomena during the vitrification of immature COCs.

Synchronization of In Vitro Maturation in Porcine Oocytes

When removed from the follicles, during the 44 h process of in vitro maturation (IVM) fully grown porcine oocytes resume meiosis spontaneously from the late diplotene stage of the first meiotic prophase and proceed to the metaphase-II (MII) stage at which they remain arrested until fertilization. However, the spontaneous resumption may start at various times causing heterogeneity in the nuclear stage and also in cytoplasmic characteristics within a population. Those oocytes that reach the MII stage earlier than others undergo an aging process which is detrimental for further embryo development. The synchronization of nuclear progression of porcine oocytes can be achieved by a transient inhibition of meiotic resumption during the first 20-22 h of IVM by the elevation of intracellular levels of cyclic adenosine monophosphate (cAMP) using the cellular membrane-permeable analog of cAMP, dibutyryl cyclic AMP. A simple and efficient protocol for such treatment is described below.

Transient Arrest of Germinal Vesicle Breakdown Improved In Vitro Development Potential of Buffalo (Bubalus Bubalis) Oocytes

Germinal vesicle breakdown (GVBD) is the first milestone that an oocyte needs to achieve toward completing the maturation and gaining potential to fertilize. Significantly lower in vitro embryo production rate in buffaloes can be attributed to heterogeneity of GVBD occurrence among oocytes obtained from abattoir derived ovaries. Evidence from our earlier work had suggested that different qualities of buffalo oocytes differ significantly in their timing of GVBD. Besides, these oocytes also differ in terms of volume of Akt phosphorylation, which initiates the process of GVBD. With objective of synchronizing the oocytes for GVBD, immature buffalo oocytes were subjected to a two-step culture protocol, initially in the presence of GVBD inhibitors and subsequently, in vitro maturation (IVM) with added SC79 (activates Akt). Expression of developmentally important genes was assessed along with embryo development rate and blastocyst health to interpret the consequences. Oocytes subjected to a short GVBD inhibition period of 6 h followed by IVM with SC79 resulted in improved cleavage and blastocyst rates. Resultant blastocysts also possessed higher ICM: TE ratio. Further, GVBD inhibited oocytes displayed a sustained cytoplasmic maturation status in terms of reorganization of cortical granules (CGs), mitochondrial membrane potential, and glutathione levels during the period of inhibition. We conclude that a temporary GVBD arrest of buffalo oocytes and modulation of Akt improves the in vitro embryo development rate as well as quality of resultant embryos. Besides, our meiotic arrest protocol does not affect the cytoplasmic maturation. J. Cell. Biochem. 119: 278-289, 2018. © 2017 Wiley Periodicals, Inc.

Lanosterol influences cytoplasmic maturation of pig oocytes in vitro and improves preimplantation development of cloned embryos

Lanosterol is a precursor of meiosis-activating sterols in the cholesterol biosynthetic pathway and induces a physiological signal that instructs the oocyte to reinitiate meiosis. In this study, we examined the effect of lanosterol on IVM of porcine oocytes, specifically on nuclear maturation, cytoplasmic maturation by investigating intracellular glutathione (GSH) levels and lipid content, embryonic development after parthenogenetic activation and somatic cell nuclear transfer (SCNT), and on gene expression in cumulus cells, oocytes, and SCNT-derived blastocysts. There was no significant difference in nuclear maturation rates between the control and treatment groups (10, 50, and 100 μM of lanosterol added to IVM culture medium). Supplementation with 50-μM lanosterol significantly increased lipid content and GSH levels and decreased reactive oxygen species levels compared with the control. In addition, oocytes treated with 50 μM of lanosterol exhibited significantly increased blastocyst formation rates and total cell numbers after parthenogenetic activation (30.3% and 63.9 vs. 21.6% and 36.5, respectively) and SCNT (18.2% and 53.7 vs. 12.6% and 37.5, respectively), when compared with the control group. Cumulus cells treated with 50 μM of lanosterol showed significantly increased 14α-demethylase, Δ14-reductase, and Δ7-reductase mRNA transcript levels. Significantly increased PPARγ, SREBF1, GPX1, and Bcl-2 and decreased Bax transcript levels were observed in mature oocytes treated with 50 μM of lanosterol compared with the control. SCNT blastocysts derived from 50-μM lanosterol-treated oocytes had significantly higher POU5F1, FGFR2, and Bcl-2 transcript levels than control SCNT-derived blastocysts. In conclusion, supplementation with 50 μM of lanosterol during IVM improves preimplantation development of SCNT embryos by elevating lipid content of oocytes, increasing GSH levels, decreasing reactive oxygen species levels, and regulating genes related to the cholesterol biosynthetic pathway in cumulus cells, to lipid metabolism and apoptosis in oocytes, and their developmental potential and apoptosis in blastocysts.

Time course of the meiotic arrest in sheep cumulus-oocyte complexes treated with roscovitine

Temporary meiosis arrest with cyclin-dependent kinases inhibitors has been proposed in order to improve the quality of in vitro matured oocytes. In sheep, however, this phenomenon has been rarely investigated. Therefore, the present study aimed to evaluate the effect of different incubation times with roscovitine on nuclear maturation and cumulus cell expansion of sheep cumulus-oocyte complexes (COCs). For this, COCs were cultured for 0, 6, 12 or 20 h in basic maturation medium (Control) containing 75 μM roscovitine (Rosco). After, they were in vitro matured (IVM) for 18 h in the presence of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). At the end of each treatment, cumulus cell expansion and nuclear maturation were assessed under a stereomicroscope and by Hoechst 33342 staining, respectively. In the Control and Rosco groups, the absence of cumulus cell expansion prevailed at 0, 6, 12 and 20 h. After IVM for 18 h, total cumulus cell expansion in the Rosco treatments was dependent on the exposure time to roscovitine. A significantly high percentage of oocytes treated with roscovitine for 6 h (87%), 12 h or 20 h (65%) were arrested at the germinal vesicle (GV) stage. In contrast, 23% GVBD, 54% metaphase I (MI) and 61% MII oocytes were observed in the Control groups at 6, 12 and 20 h, respectively. In all treatments, a significant percentage of oocytes reached MII after IVM for 18 h. Therefore, roscovitine reversibly arrested the meiosis of sheep oocytes during different culture times with the maximal efficiency of meiotic inhibition reached at 6 h. In addition, reversibility of its inhibitory action on cumulus cells was exposure-time dependent.

The evolution of porcine embryo in vitro production

The in vitro production of porcine embryos has presented numerous challenges to researchers over the past four decades. Some of the problems encountered were specific to porcine gametes and embryos and needed the concerted efforts of many to overcome. Gradually, porcine embryo in vitro production systems became more reliable and acceptable rates of blastocyst formation were achieved. Despite the significant improvements, the problem of polyspermic fertilization has still not been adequately resolved and the embryo in vitro culture conditions are still considered to be suboptimal. Whereas early studies focused on increasing our understanding of the reproductive processes involved, the technology evolved to the point where in vitro-matured oocytes and in vitro-produced embryos could be used as research material for developing associated reproductive technologies, such as SCNT and embryo cryopreservation. Today, the in vitro procedures used to mature oocytes and culture embryos are integral to the production of transgenic pigs by SCNT. This review discusses the major achievements, advances, and knowledge gained from porcine embryo in vitro production studies and highlights the future research perspectives of this important technology.

Effect of trans-ε-viniferin on in vitro porcine oocyte maturation and subsequent developmental competence in preimplantation embryos

Trans-ε-viniferin is a naturally occurring polyphenol belonging to the stilbenoid family that has been isolated from Vitis amurensis, one of the most common wild grapes in Asia. We investigated the effects of trans-ε-viniferin on in vitro maturation (IVM) and developmental competence after in vitro fertilization (IVF) or parthenogenesis (PA). We observed that trans-ε-viniferin treatment during IVM did not improve nuclear maturation rates of oocytes in any group, but significantly increased (P<0.05) intracellular glutathione (GSH) levels and reduced reactive oxygen species (ROS) levels in the 0.5 µM treatment group. Trans-ε-viniferin treatment during IVM of recipient oocytes promoted higher (P<0.05) expression of DNA methyltransferase-1 (DNMT1) mRNA in the 0.5 µM treatment group as compared with the control group. However, the expression of essential transcriptional and apoptosis-related genes did not significantly differ from that of the control. In cumulus cells, pro-apoptosis gene expressions were changed as apoptosis decreased. Oocytes treated with trans-ε-viniferin during IVM did not have significantly different cleavage rates or blastocyst formation rates after PA, but total cell numbers were significantly higher (P<0.05) in the 0.5 and 5.0 µM treatment groups compared with those in the control group. IVF embryos showed similar results. In conclusion, these results indicate that trans-ε-viniferin treatment during porcine IVM increased the total cell number of blastocysts, possibly by increasing intracellular GSH synthesis, reducing ROS levels, increasing DNMT1 gene expression of oocytes and decreasing pro-apoptosis gene expressions of cumulus cells.

Roscovitine is a novel agent that can be used for the activation of porcine oocytes reconstructed with adult cutaneous or fetal fibroblast cell nuclei

The present study was undertaken to investigate the preimplantation developmental competence of cloned pig embryos that were derived from fibroblast cell nuclei by different methods for the activation of reconstructed oocytes. In subgroups IA and IB, nuclear-transferred (NT) oocytes derived from either adult cutaneous or fetal fibroblast cells that had been classified as nonapoptotic by intra vitam analysis for programmed cell death using the YO-PRO-1 DNA fluorochrome underwent sequential physical (i.e., electrical) and chemical activation (SE-CA). This novel method of SE-CA, which was developed and optimized in our laboratory, involves treatment of reconstituted oocytes with direct current pulses and subsequent exposure to 7.5 μM calcium ionomycin, followed by incubation with 30 μM R-roscovitine (R-RSCV), 0.7 mM 6-dimethylaminopurine and 3.5 μg/mL cycloheximide. In subgroups IIA and IIB, NT oocytes were subjected to the standard method of simultaneous fusion and activation mediated by direct current pulses. The proportion of cloned embryos in subgroup IA that reached the morula and blastocyst stages was 145/248 (58.5%) and 78/248 (31.5%), respectively. The proportions of cloned embryos in subgroup IB that reached the morula and blastocyst stages were 186/264 (70.5%) and 112/264 (42.4%), respectively. In turn, subgroup IIA yielded proportions at the morula and blastocyst stages of 110/234 (47.0%) and 49/234 (20.9%), respectively. Subgroup IIB yielded proportions at the morula and blastocyst stages of 144/243 (59.3%) and 74/243 (30.5%), respectively. In summary, the SE-CA of NT oocytes reconstructed from either type of nonapoptotic/nonnecrotic (i.e., YO-PRO-1-negative) fibroblast cell resulted in porcine cloned embryos with considerably better in vitro developmental outcomes than those of cloned embryos generated using the simultaneous fusion and activation approach. To our knowledge, this is the first report of the successful stimulation of porcine NT oocytes using electric pulses followed by an additional activation with a higher dose (1.5 times) of calcium ionomycin and subsequent exposure to a combination of 30 μM R-RSCV and lower concentrations (by 3 times) of 6-dimethylaminopurine and cycloheximide. Moreover, we report here the first use of R-RSCV, a novel meiosis-promoting factor-related p34(cdc2) kinase inhibitor, in the oocyte activation protocol for the somatic cell cloning of pigs.

Roscovitine in combination with calcium ionophore induces oocyte activation through reduction of M-phase promoting factor activity in mice

The aim of the present study was to determine oocyte activation and change in M-phase promoting factor (MPF) activity induced by treatment with calcium ionophore and roscovitine in comparison with those induced by treatment with roscovitine alone and treatment with calcium ionophore and puromycin in mice. Freshly ovulated oocytes obtained from 6–8-week-old mice were divided into five groups (no activation treatment; 5 μM calcium ionophore A23187; 50 μM roscovitine; 5 μM calcium ionophore and 10 μg/ml puromycin; and 5 μM calcium ionophore and 50 μM roscovitine) and were incubated for 6 h. Oocyte activation, assessed by morphological changes, and changes in MPF activity in the five groups at 0, 2, 4 and 6 h of incubation were examined. Activated oocytes were defined as oocytes with at least one pronucleus. Oocytes treated with roscovitine alone were not activated during the 6-h incubation period. All of the oocytes in the calcium ionophore with puromycin group and in the calcium ionophore with roscovitine group were activated. The percentage activity of MPF in oocytes treated with roscovitine alone was decreased after 2 h and increased after 4 h of incubation. The percentage activity of MPF in oocytes treated with calcium ionophore and roscovitine was significantly decreased with suppression of MPF activity being maintained for 6 h, and this change was similar to that in oocytes treated with calcium ionophore and puromycin. Roscovitine with calcium ionophore is effective for induction of oocyte activation through suppression of MPF activity in mice.

Possible involvement of Class III phosphatidylinositol-3-kinase in meiotic progression of porcine oocytes beyond germinal vesicle stage

Phosphatidylinositol-3-kinases (PI3Ks) play pivotal roles in meiotic progression of oocytes from metaphase I to metaphase II stage. Using a Class III-specific inhibitor of PI3K, 3-methyladenine (3MA), this study shows that Class III PI3K may be essential for meiotic progression of porcine oocytes beyond germinal vesicle (GV) stage. Treatment of immature porcine oocytes with 3MA for 22-42 h arrested them at the GV stage, irrespective of the presence or absence of cumulus cells. Furthermore, a significantly high proportion (60.9 ± 13.8%) of 3MA-treated oocytes acquired a nucleolus completely surrounded by a rim of highly condensed chromatin (GV-II stage). The GV-arresting effect of 3MA was, however, completely reversible upon their further culture in the absence of 3MA for 22 h. When cumulus-oophorus-complexes (COCs), arrested at the GV stage for 22 h by 3MA, were further cultured for 22 h in the absence of 3MA, 96.1 ± 1.5% of oocytes reached the MII stage at 42 h of IVM and did not differ from non-treated control oocytes with respect to their ability to fertilize, cleave and form blastocyst (P > 0.05) upon in vitro fertilization (IVF) or parthenogenetic activation (PA). These data suggest that 3MA efficiently blocks and synchronizes the meiotic progression of porcine oocytes at the GV stage without affecting their ooplasmic maturation in terms of post-fertilization/activation in vitro embryonic development. Our data also provide indirect evidence for the likely participation of Class III PI3K in meiotic maturation of porcine oocyte beyond the GV stage.

The effects of roscovitine on cumulus cell apoptosis and the developmental competence of domestic cat oocytes

The developmental competence of cat oocytes matured in vitro is relatively poor when compared with that of in vivo oocytes. The study aimed to investigate the effect of roscovitine on the developmental competence of cat Felis catus oocytes matured in vitro. Cumulus-oocyte complexes (COCs) were classified as Grade I and II to III. Groups of COCs were cultured in 0, 12.5, 25, 50, 100, and 200 microM roscovitine for 24h and were either fixed to assess the stages of nuclear maturation (Experiment 1) or additionally matured in vitro for 24h before fixation (Experiment 2). In Experiment 3, cumulus cells from the COCs treated with roscovitine were examined for apoptosis. Experiment 4 examined the developmental competence of cat oocytes after roscovitine treatment and in vitro fertilization in terms of cleavage and morula and blastocyst formation rates. Roscovitine reversibly arrested cat oocytes at an immature stage in a dose-dependent manner. Roscovitine at 12.5 and 25 microM demonstrated less efficiency compared with that of other doses. However, higher doses of roscovitine induced cumulus cell apoptosis and resulted in a high number of degenerated oocytes after in vitro maturation. Roscovitine at 12.5 and 25 microM were therefore used to evaluate their effect on embryo development. Pretreatment with 12.5 and 25 microM roscovitine prior to in vitro maturation decreased the developmental competence of cat oocytes compared with that of non-roscovitine-treated controls. In conclusion, roscovitine reversibly maintained cat oocytes at the germinal vesicle stage without detrimental effect on nuclear maturation. However, it negatively affected cumulus cell viability and developmental competence.

CDC2/SPDY transiently associates with endoplasmic reticulum exit sites during oocyte maturation

BACKGROUND

Mammalian oocytes acquire competence to be fertilized during meiotic maturation. The protein kinase CDC2 plays a pivotal role in several key maturation events, in part through controlled changes in CDC2 localization. Although CDC2 is involved in initiation of maturation, a detailed analysis of CDC2 localization at the onset of maturation is lacking. In this study, the subcellular distribution of CDC2 and its regulatory proteins cyclin B and SPDY in combination with several organelle markers at the onset of pig oocyte maturation has been investigated.

RESULTS

Our results demonstrate that CDC2 transiently associates with a single domain, identified as a cluster of endoplasmic reticulum (ER) exit sites (ERES) by the presence of SEC23, in the cortex of maturing porcine oocytes prior to germinal vesicle break down. Inhibition of meiosis resumption by forskolin treatment prevented translocation of CDC2 to this ERES cluster. Phosphorylated GM130 (P-GM130), which is a marker for fragmented Golgi, localized to ERES in almost all immature oocytes and was not affected by forskolin treatment. After removal of forskolin from the culture media, the transient translocation of CDC2 to ERES was accompanied by a transient dispersion of P-GM130 into the ER suggesting a role for CDC2 in redistributing Golgi components that have collapsed into ERES further into the ER during meiosis. Finally, we show that SPDY, rather than cyclin B, colocalizes with CDC2 at ERES, suggesting a role for the CDC2/SPDY complex in regulating the secretory pathway during oocyte maturation.

CONCLUSION

Our data demonstrate the presence of a novel structure in the cortex of porcine oocytes that comprises ERES and transiently accumulates CDC2 prior to germinal vesicle breakdown. In addition, we show that SPDY, but not cyclin B, localizes to this ERES cluster together with CDC2.

The use of R-roscovitine to fit the ‘time frame’ on in vitro porcine embryo production by intracytoplasmic sperm injection

Micromanipulation of oocytes is time consuming during ICSI experiments; however the ‘time frame’ to manipulate oocytes without a drop in efficiency is not very wide due to the use of not completely matured and/or aged MII oocytes. Therefore, the aim of this work was to study the effect of a short roscovitine pretreatment for 5 h and two different IVM periods (5R + 40IVM or 5R + 45IVM) and a prolonged IVM time from 45 h (45IVM) to 50 h (50IVM) on parthenogenetic and ICSI embryo development, in order to fit the time frame to manipulate pig oocytes to the whole labour day session. In the first experiment, oocytes, pretreated with roscovitine and IVM cultured for 5 h, showed a similar nuclear stage as non-cultured oocytes and a significantly higher percentage of GVI-GVII oocytes compared with non-roscovitine treated oocytes cultured for 5 h in IVM conditions. When COC were cultured under the 5R + 40IVM system, nuclear maturation and cleavage rates after electrical activation were significantly lower than when COC were cultured under the 45IVM, 50IVM and 5R + 45IVM culture systems (54.2% vs. 72.6–76.8% and 58.8% vs. 81.4–88.3%, respectively). However, this difference was not statistically significant for parthenogenote blastocyst rate. No differences were observed in MII and in parthenogenote and ICSI embryo development among 45IVM, 50IVM and 5R + 45IVM experimental groups. In conclusion, under our conditions and using parthenogenetic and ICSI embryos, we observed that it is feasible to prolong the pig oocyte manipulation ‘time frame’ by at least 5 h with no significant drop in blastocyst rate.

Exposure to human chorionic gonadotropin during in vitro maturation does not improve the maturation rate and developmental potential of immature oocytes from patients with polycystic ovary syndrome

OBJECTIVE

To investigate the effects of human chorionic gonadotropin (hCG) in culture medium on the in vitro maturation (IVM) and subsequent developmental potential of human immature oocytes.

DESIGN

Prospective, randomized study.

SETTING

Reproductive Medicine Center, First Affiliated Hospital of Wenzhou Medical College, People's Republic of China.

PATIENT(S)

62 women with polycystic ovary syndrome (PCOS) undergoing IVM treatment.

INTERVENTION(S)

Immature oocytes were retrieved from unstimulated ovaries of women with PCOS. We tried three different culture systems in this experiment. In group A, oocytes were cultured in the medium containing M199 + 20% fetal bovine serum (FBS) + 75 mIU/mL recombinant follicle-stimulating hormone (FSH) + 0.5 IU/mL recombinant hCG. In group B, oocytes were cultured in hCG-free IVM medium (M199 + 20% FBS + 75 mIU/mL recombinant FSH) for 10 hours, then transferred to the same medium as used for group A. In group C, oocytes were cultured only in hCG-free IVM medium. After the oocytes had matured in vitro, fertilization and embryo transfer were performed.

MAIN OUTCOME MEASURE(S)

Rates of maturation, fertilization, cleavage, implantation, clinical pregnancy, miscarriage, and live birth.

RESULT(S)

For groups A, B, and C, the maturation rates at 32 and 48 hours were 46.02% and 69.25%; 43.72% and 64.51%; and 51.87% and 67.51%, respectively. Relatively satisfactory clinical results and implantation rates were obtained in all three groups. No statistically significant differences among groups A, B, and C were found in the rates of maturation, fertilization, cleavage, implantation, clinical pregnancy, miscarriage, or live birth.

CONCLUSION(S)

The results of our study indicated that the addition of hCG to in vitro culture medium did not improve the maturation rate or development potential of immature oocytes. For the IVM and development of immature oocytes from women with PCOS, hCG appears to be unnecessary.

Exposure of Oocytes to the Fusarium Toxins Zearalenone and Deoxynivalenol Causes Aneuploidy and Abnormal Embryo Development in Pigs1

Fungi of the Fusarium species can infect food and feed commodities and produce the mycotoxins zearalenone (ZEA) and deoxynivalenol (DON). Since both toxins have been reported to reduce fertility, the mechanisms of ZEA and DON on inhibition of oocyte maturation were examined. Pig oocytes were matured in the presence of ZEA (a mycotoxin with estrogenlike activity), 17beta-estradiol, and DON (all 3.12 micromol/L). Zearalenone, 17beta-estradiol, and DON inhibited oocyte maturation and caused approximately 34% of the oocytes to form an aberrant spindle. Different ratios of ZEA:DON did not lead to a more severe inhibition of oocyte maturation. Both mycotoxins caused abnormal formation of the meiotic spindle. The developmental competence of oocytes matured in the presence of mycotoxins was further investigated after in vitro fertilization. Presence of ZEA (3.12 micromol/L) during maturation reduced the percentages of oocytes that cleaved and formed a blastocyst to about 12%, compared with 25% of control oocytes. Maturation in the presence of equimolar concentrations of DON was not compatible with development. The ploidy of blastomeres from blastocysts derived from mycotoxin-exposed oocytes was analyzed with fluorescent in situ hybridization. All blastocysts, even those from the control group, contained at least one blastomere with abnormal ploidy, but the variation in the percentages of aneuploid blastomeres was significantly larger in embryos from oocytes exposed to mycotoxins. It is concluded that ZEA and DON can lead to abnormal spindle formation, leading to less fertile oocytes and embryos with abnormal ploidy, and that the effects of ZEA and DON are not synergistic.

Somatic cell nuclear transfer in pigs: recent achievements and future possibilities

During the past 6 years, considerable advancement has been achieved in experimental embryology of pigs. This process was mainly generated by the rapidly increasing need for transgenic pigs for biomedical research purposes, both for future xenotransplantation to replace damaged human organs or tissues, and for creating authentic animal models for human diseases to study aetiology, pathogenesis and possible therapy. Theoretically, among various possibilities, an established somatic cell nuclear transfer system with genetically engineered donor cells seems to be an efficient and reliable approach to achieve this goal. However, as the result of unfortunate coincidence of known and unknown factors, porcine embryology had been a handicapped branch of reproductive research in domestic animals and a very intensive and focused research was required to eliminate or minimise this handicap. This review summarises recent achievements both in the background technologies (maturation, activation, embryo culture) and the actual performance of the nuclear replacement. Recent simplified methods for in vivo development after embryo transfer are also discussed. Finally, several fields of potential application for human medical purposes are discussed. The authors conclude that although in this early phase of research no direct evidence can be provided about the practical use of transgenic pigs produced by somatic cell nuclear transfer as organ donors or disease models, the future chances even in medium term are good, and at least proportional with the efforts and sums that are invested into this research area worldwide.

Fertilization, embryo development, and clinical outcome of immature oocytes from stimulated intracytoplasmic sperm injection cycles

OBJECTIVE

To evaluate the fertilization and developmental potential of immature oocytes obtained from controlled ovarian hyperstimulated cycles of patients undergoing intracytoplasmic sperm injection (ICSI).

DESIGN

Retrospective study.

SETTING

Academic assisted reproductive technology program.

PATIENT(S)

Two hundred patients with at least one mature oocyte and one immature oocyte (study 1), and 44 patients with no mature oocytes (study 2) at time of oocyte denudation.

INTERVENTION(S)

Oocyte denudation was performed immediately after retrieval. Oocytes were cultured in vitro for 4-6 hours before ICSI and then categorized into four groups: group I, metaphase II (MII) oocytes at denudation; group II, in vitro matured MII oocytes; group III, metaphase I (MI) oocytes that did not progress to MII; and group 4, germinal-vesicle (GV) oocytes that converted to MI.

MAIN OUTCOME MEASURE(S)

Fertilization and embryo development were compared among groups in study 1. Pregnancy and implantation rates were evaluated in study 2.

RESULT(S)

Although the fertilization rate in group III was significantly lower than in groups I and II, no significant difference was found between groups I and II. Day 3 embryos in group I had the highest mean number of blastomeres, proportions of good embryos, and blastocyst formation rate when compared with groups II and III. Two clinical pregnancies were achieved from 26 transfer cycles in study 2, resulting in pregnancy and implantation rates of 7.7% and 4% per transfer cycle, respectively.

CONCLUSION(S)

Although our results show that immature oocytes from stimulated cycles can be normally fertilized and used to increase the number of embryos available for transfer, the increase in number of embryos derived from immature oocytes cannot be efficiently translated into pregnancies and live births. The clinical significance of using immature oocytes in stimulated cycles needs further investigation.

Effect of roscovitine on nuclear maturation, MPF and MAP kinase activity and embryo development of prepubertal goat oocytes

The low number of embryos obtained from IVM-IVF-IVC of prepubertal goat oocytes could be due to an incomplete cytoplasmic maturation. Roscovitine (ROS) inhibits MPF and MAP kinase activity and maintains the oocyte at Germinal Vesicle (GV) stage. The aim of this study was to determine if meiotic activity is arrested in prepubertal goat oocytes cultured with 0, 12.5, 25, 50 and 100 microM of ROS for 24 h. A group of oocytes from adult goats was cultured with 25 microM of ROS to compare the effect of ROS on prepubertal and adult goat oocytes. A sample of oocytes was stained to evaluate the nuclear stage at oocyte collection time and after ROS incubation. IVM-oocytes not exposed to ROS formed the control group. Prepubertal goat IVM-oocytes were inseminated and cultured for 8 days. The percentage of oocytes at GV stage, after exposition to ROS was significantly higher in adult goat oocytes (64.5%) than in prepubertal goat oocytes. No differences were found among 25, 50 and 100 microM ROS concentrations (29, 23 and 26%, oocytes at GV stage, respectively). After 8 days of culture, no differences in total embryos were observed between control oocytes and oocytes treated with 12.5 and 25 microM (45.2, 36.1 and 39.4%, respectively), however the percentage of blastocysts was higher in the control group. Western blot for the MAPK and p34(cdc2) showed that both enzymes were active in prepubertal goat oocytes after 24h of ROS exposition. In conclusion, a low percentage of prepubertal goat oocytes reached GV stage after ROS incubation; possibly because most of them had reinitiated the meiosis inside the follicle. ROS did not affect fertilization or total embryos but ROS showed a negative effect on blastocyst development.

Maintenance of Meiotic Arrest and Developmental Potential of Porcine Oocytes after Parthenogenetic Activation and Somatic Cell Nuclear Transfer

Several studies report that meiotic maturation of porcine oocytes can be reversibly preserved. The present study examined how long meiotic maturation can be suppressed. The first experiment determined the preservation medium suitable for reversibly suppressing meiotic maturation of porcine oocytes. The second experiment examined the in vitro developmental potential of oocytes maintained in meiotic arrest after parthenogenetic activation and nuclear transfer of somatic cells. Preservation of cumulus-oocyte complexes with NCSU-37 medium containing 10% follicular fluid, 1 mM dibutyryl cyclic AMP, and follicular shell pieces for 24-96 h at 39 degrees C did not affect oocyte maturation compared with controls (94-98% vs. 98%). The potential of parthenogenetically activated and nuclear-transferred oocytes maintained in meiotic arrest for 24-48 h to develop into blastocysts was not significantly different from that of controls (20-25% vs. 18% and 8-11% vs. 9%, respectively). The present study demonstrated that meiotic maturation of porcine oocytes can be suppressed after preservation for 48 h at 39 degrees C without decreasing oocyte maturation competence or the ability of oocytes to develop to at least the blastocyst stage.

In vitro maturation and fertilization of porcine oocytes after a 48 h culture in roscovitine, an inhibitor of p34cdc2/cyclin B kinase

Maintaining oocytes at the germinal vesicle (GV) stage in vitro may permit enhanced acquisition of the developmental competence. The objective of the current study was to evaluate the nuclear and cytoplasmic maturation in vitro of porcine oocytes after pretreatment with S-roscovitine (ROS). Cumulus oocyte complexes (COC) were treated with 50 microM ROS for 48 h and then matured for various lengths of time in a conventional step-wise in vitro maturation (IVM) system by using dibutyryl cyclic AMP. The COC that were matured in the same system for 44 h without pretreatment with ROS were used as the control group. At various periods after the start of IVM, oocytes were assessed for the meiotic stages and subjected to in vitro fertilization (IVF) with fresh spermatozoa. The ROS treatment inhibited GV breakdown of 94.4% oocytes, with the majority arrested at the GV-I stage (67.4%). Maximum maturation rate to the metaphase-II stage after ROS treatment was achieved by 44 h of IVM (92.1%) and no differences were observed with control oocytes (95.0%). Penetration rate was correlated to the maturation rate. The duration of IVM had no effects on polyspermy and male pronuclear (MPN) formation rates at 8 h post insemination (hpi), whereas both rates increased at 22 hpi. Direct comparison with controls assessed at 22 hpi confirmed a lesser MPN formation in ROS-treated oocytes (73.7% compared with 53.6%). Glutathione (GSH) concentrations were less in oocytes treated with ROS than in control oocytes (5 compared with 7.7 pmol/oocyte) as well as blastocyst rate (22.0% compared with 38.1%, respectively). These results demonstrate that cytoplasmic maturation in porcine oocytes pretreated with ROS for 48 h did not equal that of control oocytes in the current IVM system.

Effects of roscovitine on the nuclear and cytoskeletal components of calf oocytes and their subsequent development

Roscovitine, a potent inhibitor of M-phase promoting factor kinase activity, was used to maintain calf oocytes at the germinal vesicle stage for a 24h culture period. Cumulus-oocyte complexes were first prematured for 24h in the presence of different levels of roscovitine (12.5, 25, 50 and 100 microM). Roscovitine was shown to block germinal vesicle breakdown in calf oocytes in a concentration dependent manner. Significantly greater inhibitory effect was observed at 50 and 100 microM with 64.6% and 63.2% oocytes being blocked in the germinal vesicle stage when compared to the control (0.0%) and the 12.5 microM (2.9%) and 25 microM (18.8%) groups. However, this inhibitory effect of roscovitine was fully reversible since a substantial number of the oocytes resumed meiosis and reached the metaphase II stage after a further 24h of culture in a permissive medium. Cleavage rates and blastocyst yields were not significantly different for oocytes cultured under 50 microM roscovitine inhibition compared to oocytes not subjected to prematuration culture (rates of 76.7% cleavage and 8.7% blastocysts for control oocytes compared to 69.8% and 6.3%, respectively, for oocytes pretreated with 50 microM roscovitine). The morphology of the meiotic spindle was typical of metaphase II in 75.8% and 82.1% of the oocytes reaching the metaphase II stage after pretreatment with 50 microM roscovitine compared to control, respectively. A normal distribution of actin filaments was observed in 97.0% and 98.2% of oocytes exposed to 50 microM roscovitine compared to control, respectively. These results demonstrate the feasibility of maintaining calf oocytes in artificial meiotic arrest without compromising their subsequent developmental competence.