Activation of pig oocytes using calcium ionophore: effect of protein synthesis inhibitor cycloheximide

Design of novel oocyte activation methods: The role of zinc

Oocyte activation occurs at the time of fertilization and is a series of cellular events initiated by intracellular Ca2+ increases. Consequently, oocytes are alleviated from their arrested state in meiotic metaphase II (MII), allowing for the completion of meiosis. Oocyte activation is also an essential step for somatic cell nuclear transfer (SCNT) and an important tool to overcome clinical infertility. Traditional artificial activation methods aim to mimic the intracellular Ca2+ changes which occur during fertilization. Recent studies emphasize the importance of cytoplasmic Zn2+ on oocyte maturation and the completion of meiosis, thus suggesting artificial oocyte activation approaches that are centered around the concentration of available Zn2+in oocytes. Depletion of intracellular Zn2+ in oocytes with heavy metal chelators leads to successful oocyte activation in the absence of cellular Ca2+ changes, indicating that successful oocyte activation does not always depends on intracellular Ca2+ increases. Current findings lead to new approaches to artificially activate mammalian oocytes by reducing available Zn2+ contents, and the approaches improve the outcome of oocyte activation when combined with existing Ca2+ based oocyte activation methods. Here, we review the important role of Ca2+ and Zn2+ in mammalian oocyte activation and development of novel oocyte activation approaches based on Zn2+ availability.

Molecular triggers of egg activation at fertilization in mammals

In mammals, the sperm activates the development of the egg by triggering a series of oscillations in the cytosolic-free Ca(2+) concentration (Ca(2+) i). The sperm triggers these cytosolic Ca(2+i) oscillations after sperm-egg membrane fusion, as well as after intracytoplasmic sperm injection (ICSI). These Ca(2+) i oscillations are triggered by a protein located inside the sperm. The identity of the sperm protein has been debated over many years, but all the repeatable data now suggest that it is phospholipase Czeta (PLCζ). The main downstream target of Ca(2+) i oscillations is calmodulin-dependent protein kinase II (CAMKII (CAMK2A)), which phosphorylates EMI2 and WEE1B to inactivate the M-phase promoting factor protein kinase activity (MPF) and this ultimately triggers meiotic resumption. A later decline in the activity of mitogen-activated protein kinase (MAPK) then leads to the completion of activation which is marked by the formation of pronuclei and entry into interphase of the first cell cycle. The early cytosolic Ca(2+) increases also trigger exocytosis via a mechanism that does not involve CAMKII. We discuss some recent developments in our understanding of these triggers for egg activation within the framework of cytosolic Ca(2+) signaling.

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.

The effect of protein kinase C activator and nitric oxide donor on oocyte activation and cortical granule exocytosis in porcine eggs

Nitric oxide (NO) and protein kinase C (PKC) are involved in the activation of mammalian oocytes, although their role in the exit from the metaphase II stage and cortical granule (CG) exocytosis is still not fully understood. The aim of this study was to verify whether the NO-donor together with specific PKC-activators induce the complete activation of porcine oocytes assessed as meiosis resumption and a cortical reaction. Pig maturated oocytes were treated with the NO-donor S-nitroso-N-acetylpenicillamine (SNAP, 2 mM) or PKC-activators such as phorbol-12-myristate-13-acetate (PMA, 100 nM), 1-oleoyl-2-acetyl-sn-glycerol (OAG, 400 μM) and l-α-phosphatidylinositol-3,4,5-trisphosphate dipalmitoyl heptaammonium salt (DPAM, 2 μM). To study the combined effect of NO-donor and PKC-activators, aliquots of oocytes were also incubated with SNAP (0.5 mM) together with PKC-activators at the same concentration as above (SNAP-DPAM, SNAP-OAG and SNAP-PMA groups). After in vitro maturation, an aliquot of oocytes was placed in a fresh medium without NO-donor or PKC-activators (Control group). Another aliquot of oocytes was activated by calcium ionophore A23187 (25 μM, 5 min). The results showed that 0% of the control oocytes reassumed meiosis. However, both the PKC-activators (DPAM 44.0 ± 10.0%, OAG 63.3 ± 1.0% and PMA 45.0 ± 16.5%) as well as the NO-donor alone (48.7 ± 21.0%) significantly induced exit from MII. Interestingly, the combination of PKC-activators and SNAP mainly restrained to the meiosis resumption (SNAP-OAG 0, SNAP-DPAM 17.4 ± 2.5% and SNAP-PMA 38.4 ± 8.5%). Control oocytes did not show a cortical reaction and the area occupied by CG reached 25.9 ± 1.7%, whereas CGs were partially released after Ca2+ ionophore treatment (13.0 ± 3.2%). Treatment with PKC-activators induced a cortical reaction compared with the control group (8.6 ± 2.5, 6.7 ± 1.9 and 0.7 ± 0.4%, respectively, for DPAM, OAG and PMA groups). However, treatment with the NO-donor alone (SNAP group 17.2 ± 2.2%) or combined with any PKC-activator prevented cortical reaction (SNAP-DPAM 20.7 ± 2.6%, SNAP-OAG 16.7 ± 2.9% or SNAP-PMA 20.0 ± 2.4%). Besides, meiosis resumption was not always accompanied by a cortical reaction, indicating that these two activation events are independent. In conclusion, PKC-activators alone induce CG exocytosis to the same degree as calcium ionophore. However, an NO-donor alone or combined with PKC-activators is not able to induce a cortical reaction in pig oocytes.

Calcium ionophore-induced egg activation and apoptosis are associated with the generation of intracellular hydrogen peroxide

The present study was designed to investigate whether calcium ionophore-induced activation and apoptosis are associated with the generation of hydrogen peroxide (H(2)O(2)) in rat eggs cultured in vitro. Culture of metaphase-II (M-II) arrested eggs in Ca(2+)/Mg(2+)-deficient medium did not induce egg activation, while a second polar body was observed in 20% of eggs when cultured in Ca(2+)/Mg(2+)-supplemented medium. In Ca(2+)/Mg(2+)-deficient medium, lower concentrations of calcium ionophore (0.2,0.4 and 0.8 microm) not only induced egg activation in a dose-dependent manner but also generation of intracellular H(2)O(2) (84.40+/-0.50 ng/egg) when compared to control eggs (80.46+/-1.34 ng/egg). The higher concentration of calcium ionophore (1.6 microm) induced apoptosis and pronounced generation of intracellular H(2)O(2) (92.43+/-0.93 ng/egg) in treated eggs. Conversely, cell-permeant antioxidant such as 2(3)-tert-butyl-4-hydroxyanisole (BHA) reduced intracellular H(2)O(2) level (81.20+/-1.42 ng/egg) and protected against calcium ionophore-induced morphological changes characteristics of egg activation and apoptosis. These results clearly suggest that calcium ionophore-induced activation and apoptosis are associated with the generation of intracellular H(2)O(2) in rat eggs.

Effect of different parthenogenetic activation methods on the developmental competence of in vitro matured porcine oocytes

The aim of this study was to investigate the effect of electrical pulse, ethanol, and ionomycin combined with cycloheximide (CHX), cytochalasin B (CB), and 6-dimethylaminopurine (6-DMAP) on parthenogenetic developmental competence of in vitro matured porcine oocytes. In experiment 1, oocytes were treated with direct current electrical pulse (DC pulse) and then incubated in the NCSU-23 medium supplemented with CHX, 6-DMAP, CB + CHX, and CB + 6-DMAP for 6 h, respectively. The rate of blastocyst development in DC pulse + CB + 6-DMAP group was significantly higher than those in other groups (42.4% vs 23.9% approximately 35.8%; P < 0.05); however, there were no differences in both of the cleavage rate and the cell number of blastocysts among four groups. In experiment 2, oocytes were treated with NCSU-23 medium containing 20 muM ionomycin for 40 min and then incubated in the NCSU-23 medium supplemented with CHX, 6-DMAP, CB + CHX and CB + 6-DMAP for 6 h, respectively. The rates of cleavage and blastocyst development in ionomycin + 6-DMAP group were higher than those obtained in other groups (66.2% vs 46.3% approximately 57.3%; 22.3% vs 7.4% approximately 16.1%; P < 0.05). In experiment 3, the activation effects of ethanol combined with 6-DMAP, CHX, CB + 6-DMAP and CB + CHX were investigated. The rates of cleavage and blastocyst development in ethanol + CB + 6-DMAP group were significantly higher than those in other groups (55.5% vs 42% approximately 46.2%; 18.0% vs 7.1% approximately 11.9%; P < 0.05). In experiment 4, the optimal activation protocols in each group plus DC pulse + ionomycin + 6-DMAP were compared. The results showed the rates of cleavage in DC pulse + CB + 6-DMAP group and ionomycin + 6-DMAP were higher than those in ethanol + CB + 6-DMAP and DC pulse + ionomycin + 6-DMAP (73.8-74.4% vs 56.5-57.5%; P < 0.05), but the blastocyst development only in DC pulse + CB + 6-DMAP group was significantly higher than that in other groups (34.1% vs 13.4% approximately 22.3%; P < 0.05). Total cell number of blastocysts in the group of DC pulse + ionomycin + 6-DMAP was higher than that in other groups (34.1 vs 25.3-27.2; P < 0.05). In conclusion, DC pulse, ethanol, CB, and 6-DMAP all affected the parthenogenesis of porcine oocytes matured in vitro, but their combination of DC pulse + CB + 6-DMAP showed the best result in both of cleavage and blastocyst development.

Brief exposure to cycloheximide prior to electrical activation improves in vitro blastocyst development of porcine parthenogenetic and reconstructed embryos

To investigate the effects of cycloheximide exposure before electrical activation of in vitro-matured porcine oocytes on the subsequent development of parthenogenetic embryos, cumulus-free mature oocytes were exposed to NCSU-23 medium containing cycloheximide (10 microg/mL) for 0, 5, 10, 20, 30 and 60 min, activated by electrical pulse treatment (1.5 kV/cm, 100 micros) and then cultured in PZM-3 for 7 days. To evaluate the effects of cycloheximide on the activation of nuclear transfer embryos, reconstructed embryos were electrically activated by two DC pulses (1.2 kV/cm, 30 micros) before or after exposure to cycloheximide. The reconstructed embryos were allocated into four groups: electrical pulse treatment alone (Ele); exposure to cycloheximide for 10 min followed by electrical activation (CHX+Ele); electrical activation followed by exposure to cycloheximide for 6h (Ele+CHX); exposure to cycloheximide for 10 min, followed by electrical activation and a further exposure to cycloheximide for 6h (CHX+Ele+CHX). The activated reconstructed embryos were cultured in PZM-3 for 6 days. Oocytes treated with 10 min exposure to cycloheximide followed by electrical activation had a significantly higher percentage of blastocyst formation compared to control oocytes and oocytes exposed for > or =30 min. In the reconstructed embryos, the blastocyst development rates of embryos exposed to cycloheximide (CHX+Ele, Ele+CHX and CHX+Ele+CHX) were significantly higher than those of the control group (Ele). Among the cycloheximide-treated groups, the CHX+Ele group had increased development rate and total blastocyst cell number, though these values were not significantly different from those observed in the other cycloheximide-treated groups. To evaluate the quality of NT embryos treated with cycloheximide, apoptosis in blastocysts was analyzed by TUNEL assay. The 10 min exposure to cycloheximide prior to electrical activation significantly reduced cell death compared with longer exposure to cycloheximide after electrical fusion. In conclusion, brief exposure to cycloheximide prior to electrical activation may increase the subsequent blastocyst development rates in porcine parthenogenetic and reconstructed embryos.

Effect of Activation Treatments on Actin Filament Distribution and In Vitro Development of Miniature Pig Somatic Cell Nuclear Transfer Embryos

In the present study, we investigated the effect of activation treatments on the actin filament distribution and in vitro development of somatic cell nuclear transfer (SCNT) embryos in miniature pigs. We combined three activation methods, ionomycin (ION), electrical stimulation (ES), and cycloheximide treatment (CH), to prepare seven activation treatments (ION, ES, CH, ION + CH, ION + ES, ES + CH and ION + ES + CH). First, we investigated the activation rate of oocytes and in vitro development of parthenotes. The activation rates of the oocytes in the ION, ES, CH, ION + CH, ION + ES, ES + CH, and ION + ES + CH groups were 42.9, 51.3, 0.0, 82.1, 80.6, 78.1 and 78.6%, respectively, showing that the rates of the combined treatment groups were significantly higher (P<0.05) than those of the single treatment groups. Although there were no significant differences in the activation rates of the combined treatment groups, the developmental rate to blastocysts in the ION + CH treatment group (36.1%) was significantly higher (P<0.05) than the other combined treatment groups (14.6-24.7%). Subsequently, we investigated the in vitro development and distribution of microfilaments in SCNT embryos. The developmental rate to blastcysts of the SCNT embryos in the ION + CH treatment group (11.3%) was significantly higher (P<0.05) than in the ES and ION + ES + CH treatment groups (4.5 and 5.2%, respectively). The rate of normal actin filament distribution in the SCNT embryos activated with ION + CH was significantly higher (P<0.05) than those activated with ES or ION + ES + CH treatment (63.3 vs. 46.8 or 46.4%). In addition, the fragmentation rate of the SCNT embryos activated with ION + CH was significantly lower (P<0.05) than those activated with ION + ES + CH (14.9 vs. 26.1%). The present results suggest that an activation treatment of ionomycin combined with cycloheximide may avoid physical damage to microfilaments and result in improved subsequent development of miniature pig SCNT embryos.

Activation of pig oocytes using nitric oxide donors

Nitric oxide (NO) plays an important role in intracellular signaling, but its role during the activation of mammalian oocytes is little understood. In our study, in vitro matured pig oocytes were cultured with NO-donors-S-nitroso-N-acetylpenicillamine (SNAP) or sodium nitropruside (SNP). These treatments were able to induce parthenogenetic activation of pig oocytes matured in vitro. The specificity of this effect was confirmed by the activation of oocytes by exogenous endothelial nitric oxide synthase (eNOS) microinjected in the oocyte with its activator calmodulin. Relatively long exposure (10 hr) is needed for activation of pig oocytes with 2.0 mM SNAP. An active NOS is necessary for the NO-dependent activation of pig oocytes because NOS inhibitors L-NMMA or L-NAME are able to inhibit activation of oocytes with NO-donor SNAP. On the basis of our data, we conclude that the NO-dependent activating stimulus seems inadequate because it did not induce the exocytosis of cortical granules. Also, the cleavage of parthenogenetic embryos was very low, and embryos did not develop beyond the stage of eight blastomeres.

Induction and activation of meiosis and subsequent parthenogenetic development of growing pig oocytes using calcium ionophore A23187

The pig ovary contains a large number of growing oocytes, which do not mature in vitro and cannot be readily used in various biotechnologies. This study was conducted to determine the possibility of inducing meiotic maturation in growing pig oocytes with an internal diameter of 110 microm, which had developed partial meiotic competence. Most of these oocytes spontaneously stopped maturation at the metaphase I stage (68%); a limited number proceeded to the metaphase II stage (26%). Treatment with calcium ionophore A23187 (50 microM for 5 or 10 min) after 24h in vitro culture overcame the block at the metaphase I stage, and treated growing pig oocytes matured to the metaphase II stage (66%). Oocytes in which maturation had been induced by calcium ionophore were again treated with calcium ionophore. Up to 58% of the treated oocytes were activated. Parthenogenetic development in oocytes treated with ionophore for meiosis induction and activation was very limited. The portion which reached morula stage did not exceed 8% and at most 3% developed to the blastocyst stage.

Developmental Potential of Bovine Androgenetic and Parthenogenetic Embryos: A Comparative Study1

In this study, we compared the developmental capacity of bovine haploid and diploid androgenetic and parthenogenetic embryos obtained by different methods. Androgenetic embryos were produced by piezo-intracytoplasmic sperm injection (ICSI) or in vitro fertilization (IVF) of enucleated oocytes with or without subsequent pronuclear transfer from one haploid zygote to another. Parthenogenetic embryos were obtained by activation of matured oocytes by ionomycin combined with cycloheximide or 6-dimethylaminopurine (DMAP) treatment. Only few cleaved androgenetic haploid embryos were able to compact (2.7%) and to form blastocysts (1.8%), while significantly more haploid parthenogenotes underwent compaction (24-37%) and a minority developed to blastocysts at different rates, depending on the activation procedure (cycloheximide 3%, 6-DMAP 14.5%). By contrast, development to blastocyst of diploid androgenotes, cloned androgenetic embryos, and parthenogenotes (31%, 39%, and 43%, respectively) was similar to IVF control embryos (35%). Cell number on Day 7 was higher for IVF blastocysts and decreased in consecutive order in diploid androgenotes, diploid parthenogenotes, and haploid uniparental embryos. Following transfer of diploid androgenetic embryos, a pregnancy was established and maintained up to Day 28.

Development of cloned pig embryos by nuclear transfer following different activation treatments

This study compared the effects of activation treatments on the development and ploidy of nuclear transferred (NT) pig embryos. After in vitro maturation of oocytes collected from the slaughterhouse, oocytes were enucleated and reconstructed by transfer of donor cells and fusion with three DC pulses (1.4 kV/cm, 20 musec). Oocytes were pulsed thrice electrically with 1.4 kV/cm for 20 musec and NT eggs were divided into three treatment groups: Group 1 (no further treatment), Group 2 (10 mug/mL cycloheximide [CHX], 3 hr), and Group 3 (1.9 mM 6-dimethylaminopurine [DMAP], 3 hr). All the eggs were cultured in sets of 30 in 60 muL drops of NCSU-23 supplemented with 4 mg/mL fatty acid free BSA, and compared for the rates of development and ploidy. The rates of cleavage, development, and total cell number of parthenotes in Group 3 were significantly (P < 0.05) higher than those in Groups 1 and 2. Cleavage rates of NT embryos in Group 1 were significantly (P < 0.05) lower than those in Groups 2 and 3 (73% vs. 81% and 82%, respectively). Development into blastocyst stage and total cell number of NT embryos in Group 3 were significantly (P < 0.05) higher than those in Groups 1 and 2. Although the embryos in Group 3 had higher development, approximately 58% of NT embryos evaluated were abnormal ploidy (6% haploidy, 9% polyploidy, and 42% mixoploid). The results suggested that although DMAP enhanced development and higher cell number, due attention should be paid to abnormal ploidy in pig NT embryos.

Roles of PLC-γ2 and PKCα in TPA-induced apoptosis of gastric cancer cells

AIM: To investigate the roles of PLCγ2 and PKCα in TPA-induced apoptosis of gastric cancer cells.

METHODS: Human gastric cancer cell line MGC80-3 was used. Protein expression levels of PLCγ2 and PKCα were detected by Western blot. Protein localization of PLCγ2 and PKCα was shown by immunofluoscence analysis under laser-scanning confocal microscope. Apoptotic morphology was observed by DAPI fluorescence staining, and apoptotic index was counted among 1000 cells randomly.

RESULTS: Treatment of gastric cancer cells MGC80-3 with TPA not only up-regulated expression of PLC-γ2 protein, but also induced PLC-γ2 translocation from the cytoplasm to the nucleus. However, this process was not directly associated with apoptosis induction. Further investigation showed that PKCα translocation from the cytoplasm to the nucleus was correlated with initiation of apoptosis. To explore the inevitable linkage between PLC-γ2 and PKCα during apoptosis induction, PLC inhibitor U73122 was used to block PLC-γ2 translocation, in which neither stimulating PKCα translocation nor inducing apoptosis occurred in MGC80-3 cells. However, when U73122-treated cells were exposed to TPA, not only PLC-γ2, but also PKCα was redistributed. On the other hand, when cells were treated with PKC inhibitor alone, PLC-γ2 protein was still located in the cytoplasm. However, redistribution of PLC-γ2 protein occurred in the presence of TPA, no matter whether PKC inhibitor existed or not.

CONCLUSION: PLC-γ2 translocation is critical in transmitting TPA signal to its downstream molecule PKCα. As an effector, PKCα directly promotes apoptosis of MGC80-3 cells. Therefore, protein translocation of PLCγ2 and PKCα is critical event in the process of apoptosis induction.

Degradation of retinoid X receptor α by TPA through proteasome pathway in gastric cancer cells

AIM: To investigate and determine the mechanism and signal pathway of tetradecanoylphorbol-1, 3-acetate (TPA) in degradation of RXRα.

METHODS: Gastric cancer cell line, BGC-823 was used in the experiments. The expression level of RXRα protein was detected by Western blot. Nuclear and cytoplasmic protein fractions were prepared through lysis of cell and centrifugation. Localization and translocation of RXRα were observed under laser-scanning confocal microscope through labeling specific anti-RXRα antibody and corresponding immunofluorescent antibody as secondary antibody. Different inhibitors were used as required.

RESULTS: In BGC-823 cells, RXRα was expressed in the nucleus. When cells were treated with TPA, expression of RXRα was repressed in a time-dependent and TPA-concentration-dependent manner. Meanwhile, translocation of RXRα from the nucleus to the cytoplasm occurred, also in a time-dependent manner. When cells were pre-incubated with proteasome inhibitor MG132 for 3 hrs, followed by TPA for another 12 hrs, TPA-induced RXRα degradation was inhibited. Further observation of RXRα translocation in the presence of MG132 showed that MG-132 could block TPA-induced RXRα redistribution. Conversely, when RXRα translocation was inhibited by LMB, an inhibitor for blocking protein export from the nucleus, TPA could not repress expression of RXRα.

CONCLUSION: TPA could induce the degradation of RXRα protein in BGC-823 cells, and this degradation is time- and TPA-concentration-dependent. Furthermore, the degradation of RXRα by TPA is via a proteasome pathway and associated with RXRα translocation from the nucleus to the cytoplasm.

Parthenogenetic activation and subsequent development of rat oocytes in vitro

Studies were undertaken to determine whether electrical stimulation, or ethanol treatment alone or in combination with 6-dimethylaminopurine (6-DMAP) influenced the rate of parthenogenetic activation of rat oocytes. The percentages of activated oocytes with pronuclei (89-91%) and those developed to the two-cell stage (68-72%) were significantly higher after electrical stimulation with direct current (DC) at 100 V/mm, 99 microsec once or twice, than when other DC voltages (75, 150, and 200) were applied or when ethanol or 6-DMAP treatment was given alone. However, none of the activated oocytes developed beyond the four-cell stage. The percentages of activated oocytes with pronuclei (100%) that developed to the two-cell (100%), eight-cell (89%) and blastocyst stages (50%) were significantly higher when electrical stimulation was followed by treatment with 2 mM 6-DMAP for 4 hr than when other combined procedures were applied. In conclusion, the results of the present study clearly showed that combined treatment of electrical stimulation or ethanol with 6-DMAP induces parthenogenetic activation and subsequent development of rat oocytes in vitro.

Effects of maturational age of porcine oocytes on the induction of activation and development in vitro following somatic cell nuclear transfer

To determine the effect of maturational age of porcine oocytes on the induction of activation and development following nuclear transfer, we investigated maturation rate and efficacy of oocyte activation treatment with an electrical stimulus (ES) and cycloheximide (CHX) at various timing of maturation culture. Most oocytes developed to the metaphase II (MII) stage after 32 hr of maturation culture. Both in newly matured (32 and 36 hr of age) and MII-arrested (42 and 48 hr of age) oocytes, ES followed by exposure to CHX for 6 hr caused higher rates of pronuclear formation than ES alone. Effect of maturational age of oocytes on the development of parthenotes activated with ES and CHX was then examined. The highest percentage of parthenotes developed to blastocysts was obtained when ES was added at 42 hr of culture. Finally, newly matured (33 hr of age) and MII-arrested oocytes (44 hr of age) were enucleated, fused with serum-starved pig fetal fibroblasts and activated with ES and CHX around suitable timing (39 to 40 hr of age) or later (50 to 51 hr of age), respectively. The frequencies of cleavage (58.8%) and blastocyst formation (13.6%) of newly matured oocytes were significantly (P<0.05) higher than those of MII-arrested oocytes (38.9 and 1.8%, respectively). These results demonstrated that the development of porcine nuclear transfer embryos can be improved by using complete matured oocytes as cytoplasts and activation treatment with ES followed by CHX treatment.