Electrofusion-induced intracellular Ca2+ flux and its effect on murine oocyte activation

Effect of Kisspeptin on the Developmental Competence and Early Transcript Expression in Porcine Oocytes Parthenogenetically Activated with Different Methods

Recent studies showed the modulatory effect of kisspeptin (KP) on calcium waves through the cell membrane and inside the cell. Spermatozoon can induce similar ooplasmic calcium oscillations at fertilization to trigger meiosis II. Here, we evaluated the effect of KP supplementation with 6-dimethylaminopurine (6-DMAP) for 4 h on embryonic development after oocyte activation with single electric pulse, 5 µM ionomycin, or 8% ethanol. Compared to control nonsupplemented groups, KP significantly improved embryo developmental competence electric- and ethanol-activated oocytes in terms of cleavage (75.3% and 58.6% versus 64% and 48%, respectively, p < 0.05) and blastocyst development (31.3% and 10% versus 19.3% and 4%, respectively, p < 0.05). MOS expression was increased in electrically activated oocytes in presence of KP while it significantly reduced CCNB1 expression. In ionomycin treated group, both MOS and CCNB1 showed significant increase with no difference between KP and control groups. In ethanol-treated group, KP significantly reduced CCNB1 but no effect was observed on MOS expression. The early alterations in MOS and CCNB1 mRNA transcripts caused by KP may explain the significant differences in the developmental competence between the experimental groups. Kisspeptin supplementation may be adopted in protocols for porcine oocyte activation through electric current and ethanol to improve embryonic developmental competence.

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.

Optimal concentration of calcium and electric field levels improve tetraploid embryo production by electrofusion in mice

Polyploid embryo production is an important technique in generating mice directly from embryonic stem (ES) cells. The present study was designed to assess the effect of different calcium concentrations and electric field intensities on the production of tetraploid embryos with higher developmental potential by electrofusion. Two-cell mouse embryos were electrofused in fusion solution containing different concentrations of calcium ion (0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2 and 1.4 mM). The rates of blastomere fusion, and subsequent cleavage and development of tetraploids to the blastocyst stage were highest when two-cell embryos were electrically stimulated in a fusion medium containing 1.0 mM calcium. Therefore, we tested electric field intensities (0.6, 0.8, 1.0, 1.2 and 1.4 kV/cm) for electrofusion of two-cell embryos and subsequent development to the blastocyst stage in 1.0 mM calcium. The highest rates of fusion and blastocyst formation were observed when the electric field strength was 0.8 kV/cm. The present results showed that mouse two-cell embryos stimulated with 0.8 kV/cm in a fusion medium containing 1.0 mM calcium had the highest rates of fusion and development to the blastocyst stage.

The regulation of calcium/calmodulin-dependent protein kinase II during oocyte activation in the rat

Increases in intracellular Ca2+ are required for oocyte activation and subsequent development. Calmodulin-dependent protein kinase II (CaMKII) plays a crucial role in oocyte activation. However, how CaMKII is regulated during this process is not well characterized. We show here for the first time in rat oocytes that CaMKII is phosphorylated during oocyte activation. CaMKII phosphorylation was suppressed by KN93, a CaMKII inhibitor, but not KN92, which is the inactive analogue of KN93. Electrical stimulation of rat oocytes resulted in degradation of both cyclin B and Mos, presumably due a rise in Ca2+ induced by the electrical pulse. KN93 blocked the degradation of both proteins induced by the electrical pulse. Addition of a protein phosphatase inhibitor, okadaic acid (OA), further increased the amount of CaMKII and also increased the amount of phosphorylated enzyme. Importantly, in oocytes undergoing spontaneous activation, accumulation and phosphorylation of CaMKII also occurs in a time-dependent manner. Consistent with this, addition of KN93 inhibited spontaneous activation. Collectively, our results show that CaMKII is phosphorylated during oocyte activation and that this phosphorylation is involved in inactivation of p34cdc2 kinase and somewhat involved in degradation of Mos. Furthermore, CaMKII phosphorylation is negatively regulated by a protein phosphatase.

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.

Parthenogenetic Activation of Porcine Oocytes After Nuclear Transfer

Mature porcine oocytes are arrested at metaphase II of meiosis. At fertilization, like all mammalian oocytes they exhibit a low frequency Ca(2+) oscillation lasting several hours. This oscillation is thought to be the signal that triggers resumption of meiosis and activates the developmental program of the oocyte. The signal transduction mechanism of the sperm-induced Ca(2+) signal is not known in detail, and attempts to generate the oscillation artificially have met with little success. Nevertheless, artificial activation of the oocyte is a crucial step during nuclear transfer. Methods are available to induce a transient elevation in the intracellular free Ca(2+) concentration to surpass the meiotic arrest and induce development of the constructed embryo. Further studies concentrating on the mechanism of Ca(2+) signaling during fertilization will help to improve the efficiency of the procedures used for parthenogenetic activation of the oocyte.

Injection of a porcine sperm factor induces activation of mouse eggs

Injection of sperm preparations into mammalian oocytes and eggs has been shown to elicit persistent [Ca2+]i oscillations that closely resemble fertilization-associated Ca2+ release. However, the ability of these sperm fractions to initiate egg activation has not been clearly demonstrated. In the present experiments, mouse eggs injected with a porcine sperm preparation were evaluated for early and late events of activation. Events monitored included, among early events, the generation of [Ca2+]i oscillations and cortical granule exocytosis and, among late events, the decrease in histone H1 and myelin basic protein kinase activities, polar body extrusion, pronuclear formation, and cleavage to the two-cell stage. Injection of sperm fractions consistently evoked [Ca2+]i oscillations that, in turn, initiated all events of activation. Uninjected control eggs or eggs injected with buffer or heat-treated sperm fractions failed to show Ca2+ responses or activation. In addition, injection of sperm fractions into recently ovulated eggs (experiments were concluded within 15 hr after human chorionic gonadotropin administration) induced high rates of activation, while similarly aged eggs exposed to 7% ethanol for 5 min, a known parthenogenetic treatment, failed to activate. Together these results indicate that injection of sperm fractions elicits [Ca2+]i oscillations that are capable of initiating normal egg activation. These results support the hypothesis that a sperm component participates in the generation of fertilization-associated [Ca2+]i oscillations.

Factors affecting electrical activation of porcine oocyte matured in vitro

This work was undertaken to improve conditions for in vitro maturation and activation of porcine oocytes. Experiments were designed to compare: (i) electrical pulse frequency, (ii) methods of oocyte preparation, (iii) maturation conditions, and (iv) electrical poration medium on development. Oocytes were harvested by follicle dissection or aspiration, co-cultured with follicle shells in M199 based medium with or without media changes at 38.5 degrees C in 5% CO2 under non-static conditions for 48 h and electroactivated using single or multiple pulses (current strength 1.0 kV/cm for 50 microseconds in 0.28 M inositol or mannitol based media with 10 mM histidine) at different time intervals. The results showed: (i) neither the pulse frequency nor the pulse interval influenced rates of pronuclear formation but multiple pulse activation (3 pulses at 5 min intervals) induced a higher incidence of development and progression through the 4-cell block in contrast to one pulse activation; (ii) both the rate of nuclear maturation (88.6% vs. 77.6%) and post-activation cleavage (89.8% vs. 67.4%) were higher (P < 0.05) when oocytes were collected by follicle dissection rather than by aspiration; (iii) while changing to a hormone-free medium at 24 h was without effect on maturation (91.9% vs. 91.7%), rate of cleavage (81.6% vs. 72.3%, P < 0.05) at 24 h was enhanced by the medium change; and (iv) oocytes activated with 3 pulses 5 min apart in mannitol based medium at 48-49 h and at 53-54 h formed pronuclei at a comparable rate but subsequent parthenogenetic development was higher in the older eggs. By contrast, inositol-based medium supported development of young and old eggs equally well. Calcium and magnesium ions are, however, necessary in both mannitol and inositol media for activation of porcine oocytes matured in vitro. The present results suggest that optimal parthenogenetic activation and early development of IVM pig oocytes could be obtained if oocytes are harvested by dissection, cultured for 24 h in hormone-containing medium before being placed in hormone free medium and activated at 48 h in inositol based medium using a three pulse activation system.

Stimulation of repetitive calcium transients in mouse eggs

1. We have combined cell membrane electroporation by electrical field (EF) stimulation with a rapid perfusion system in order to stimulate repetitive increases in cytoplasmic free [Ca2+] ([Ca2+]i) in mouse eggs. [Ca2+]i was monitored by ratio fluorescent measurements of intracellular indo-1 on individual eggs. The conditions required to cause different types of [Ca2+]i increases were established and the effects of these [Ca2+]i changes upon egg activation examined. 2. The rapid perfusion of non-ionic medium caused a single [Ca2+]i increase. However, to generate repetitive [Ca2+]i increases, eggs were exposed to EF pulses in the presence of Ca2+ and then washed rapidly with culture medium. Sequential EF pulse application led to prolonged elevation of [Ca2+]i levels and eventual cell lysis unless rapid reperfusion with culture medium was achieved. Transient increases in [Ca2+]i in eggs could also be generated by EF pulses in the presence of inositol 1,4,5-trisphosphate (InsP3). 3. In response to EF stimulation fertilized eggs showed [Ca2+]i increases that were enhanced relative to unfertilized eggs. The responses in these fertilized eggs were often followed by repetitive [Ca2+]i oscillations, despite the fact that the [Ca2+]i oscillations associated with sperm penetration had ceased by this stage. 4. In unfertilized mouse eggs the [Ca2+]i increases appeared to be due to direct cation influx since repeated EF pulses caused repeated influx of Mn2+ as monitored by quenching of fluorescence of fura-2 loaded eggs. 5. Under conditions that stimulated reproducible patterns of [Ca2+]i transients we found that a single large [Ca2+]i transient did not cause significant egg activation, but that inducing repetitive [Ca2+]i transients was effective in activating eggs. The speed of activation as judged by the rate of pronuclear formation was also dependent upon the frequency of pulse application. 6. These data show that combining EF pulses with a rapid and precise sequential perfusion system can be used to manipulate [Ca2+]i levels in mammalian eggs. This provides a means of artificial mimicry of the [Ca2+]i transients seen after fertilization. It appears that Ca2+ influx during EF pulses does not cause significant Ca2+ release from internal stores in unfertilized eggs, but after fertilization Ca2+ influx does induce Ca2+ release. It is also apparent that mouse eggs are more successfully activated by repetitive [Ca2+]i increases than by single large [Ca2+]i rises. We suggest that our data provide direct evidence for the hypothesis that a cellular response to oscillations of intracellular [Ca2+]i can be distinct from that to monotonic rises in [Ca2+]i.

Parthenogenetic development of bovine oocytes matured in vitro for 24 hr and activated by ethanol and cycloheximide

This research was undertaken to improve development of parthenogenetic embryos following various combined treatments of ethanol and cycloheximide. In Experiment 1 in vitro matured oocytes (IVM, 24 hr) were treated with 7% ethanol for 5 min followed by incubation in 10 micrograms/ml cycloheximide in Medium 199 for 0 (control), 5, 10, and 20 hr. Development to 2-8 cells following culture for 3 days was similar among treated groups (32-41%; P > 0.05), which was higher than that of controls (6%; P < 0.05). Experiment 2 compared pre-ethanol exposures for 0, 1, 2.5, and 5 min, followed by 5 hr cycloheximide treatment on activation development. One- to 5-min groups resulted in 42-44% cleavage contrasted to 1-12% for controls (P < 0.05). Experiment 3 examined the effect on oocyte development of ethanol and different concentrations of cycloheximide (0, 1, 5, and 10 micrograms/ml). Cleavage to 2-8 cells was similar among the 5 and 10 micrograms/ml cycloheximide groups (36% and 42%, P > 0.05) but lower (P < 0.05) for the 1 micrograms/ml group (24%) and the controls (2-13%). When 5 micrograms/ml cycloheximide was used (Experiment 4), pre-exposure to ethanol (1, 2.5, and 5 min) resulted in more oocytes cleaved (38-41%) than in the cycloheximide alone group (0%) or the control (0%, P < 0.05). Experiment 5 tested blastocyst development of the activated oocytes with or without cytochalasin B treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Diacylglycerol-enhanced electrical activation of porcine oocytes matured in vitro

This study was undertaken to examine the effect of second messengers added to the electroporation medium on electric pulse-induced artificial activation of meiotic Metaphase II porcine oocytes. Six separate experiments evaluated second messengers added to electroporation medium. When added to electroporation medium, neither phospholipase C (PLC: 0 to 2.5 Units/ml), D-myo-inositol triphosphate (IP(3): 0 to 10,000 muM), nor guanosine 5'-O-(3-thiotriphosphate; GTP-gamma-S: 0 to 100 muM) had any effect (P> 0.05) on activation rates. However, addition of 1,2-dioctanoyl-sn-glycerol (DiC(8)) increased activation rates in a dose-dependent response. At a level of 1,000 muM, DiC(8) resulted in a higher activation rate (P< 0,05) than 0.0, 0.1, 1 or 10 muM of DiC(8) with a pulse, and the 1,000 and 10,000 muM of DiC(8) no-pulse control groups. Effects of DiC(8) (1,000 muM) and IP(3) (100 muM) in combination or individually were investigated. At 1,000 muM, DiC(8) caused a higher rate of activation (P< 0.05) than 100 muM IP(3), but the result was not different from DiC(8) + IP(3). In another experiment, no difference (P> 0.05) was observed between DiC(8), GTP-gamma-S and IP(3), but DiC(8) + GTP-gamma-S + IP(3) + PLC yielded a higher (P< 0.05) activation rate than PLC or the rate of the controls. No significant development (blastocyst) was observed after 5 days of culture in any of the experiments. Protein profiles of activated oocytes, determined by 1D SDS-PAGE, were characteristic of pronuclear-stage embryos. These data indicate that the addition of DiC(8) to the electroporation medium synergistically enhances the rate of activation of electrically stimulated in vitro-matured porcine oocytes.

The incidence of aneuploidy after single pulse electroactivation of mouse oocytes

A brief electric pulse often produces a high rate of activation of recently ovulated oocytes. Some other efficient parthenogenetic stimuli, such as alcohol, however, disrupt the spindle apparatus and increase the incidence of aneuploidy. In this paper, we have determined whether electroactivation per se increases the incidence of chromosomal segregation errors in haploid parthenogenones as evidenced at first cleavage mitosis. Superovulated F1 hybrid female mice were killed at 15.5, 18.5, 22.5, and 25 h after the HCG injection. Batches of 10-12 cumulus-denuded oocytes were transferred to an electroactivation chamber containing mannitol which was connected to a high voltage pulse stimulator and the pulse was triggered once. A high proportion of oocytes activated following this treatment, but only the single-pronuclear haploid parthenogenones were incubated overnight in medium containing colcemid, to determine the incidence of aneuploidy as evidenced at first cleavage mitosis. "Sham" electroactivation groups were also examined for evidence of activation and aneuploidy as described above. In these cases, cumulus-denuded oocytes were put through the electroactivation chamber but the pulse was not triggered. A further group of oocytes was studied to determine the effect of handling and exposure to hyaluronidase on activation frequency and parthenogenetic pathways. Finally, the spontaneous rate of aneuploidy was examined in fertilised embryos of F1 hybrid female mice x Rb(1.3)1Bnr male mice at first cleavage mitosis. The results show that single pulse electroactivation does not increase the level of aneuploidy in single-pronuclear parthenogenous compared to the "sham" group or the spontaneous rate observed in 1-cell fertilised embryos, nor does aneuploidy appear to increase with postovulatory age.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrically induced calcium elevation, activation, and parthenogenetic development of bovine oocytes

The influence of electrical stimulation on the level of intracellular Ca2+ in bovine oocytes, as well as activation and extent of parthenogenetic development, was investigated. Mature oocytes were electrically stimulated at 29 hr of maturation, and intracellular Ca2+ concentration was determined with the Ca2+ indicator fura-2 dextran (fura-2 D). The Ca2+ response of oocytes to a given electrical pulse was variable. Oocytes responded with either no Ca2+ rise from baseline (approximately 12 nM), a short-duration Ca2+ rise (from 12 nM to 300 nM) that returned to baseline within 2 min of the pulse, or a long-duration Ca2+ rise (from 12 nM to 1,000-2,000 nM) that never returned to baseline during the 8 min period over which the oocytes were monitored. In these oocytes, Ca2+ level returned to baseline when oocytes were removed from 0.30 M mannitol and placed in an ionic medium. Increasing field strength or pulse duration tended to increase the proportion of oocytes displaying a Ca2+ rise, and at 1.0 kVcm-1 for 40 microseconds, all oocytes displayed a long-duration Ca2+ elevation. Direct transfer of oocytes from culture medium to mannitol also triggered a Ca2+ rise. Multiple stimulations, either electrical or by transferring to mannitol, produced multiple Ca2+ rises. This mannitol-induced Ca2+ rise could be inhibited by first washing the oocytes in medium containing equal parts of 0.30 M mannitol and phosphate buffered saline (PBS). The level of Ca2+ stimulation affected activation and development of oocytes. Insufficient, or, conversely, excessive Ca2+ stimulation impaired development. Optimum development was obtained with 1) three pulses of 0.2 kVcm-1 for 20 microseconds, each pulse 22 min apart, after direct transfer of oocytes from culture medium to mannitol (22% blastocysts) or 2) three pulses of 1.0 kVcm-1 for 20 microseconds after transfer of oocytes from culture medium to medium containing equal parts mannitol and PBS, then to mannitol (24% blastocysts). This procedure avoided induction of a Ca2+ rise prior to the pulse. The results indicate that the level of Ca2+ stimulation can be regulated by incubation conditions prior to the pulse and, to some extent, by field strength and pulse duration. The level of electrical stimulation influenced oocyte Ca2+ response, activation, and parthenogenetic development.

Electroporation of inositol 1,4,5-triphosphate induces repetitive calcium oscillations in murine oocytes

The purpose of these experiments was to determine the effect of electroporation of IP3 into the cytosol of murine secondary oocytes and evaluate any alterations in [Ca2+]i resulting from Ca2+ release from intracellular stores. In addition, we evaluated the effect of ethanol (ETOH) on the release of Ca2+ from intracellular stores. Oocytes were loaded with the Ca2+ indicator fluo-3 by incubation in 100 microliters drops of medium containing 2 microM fluo-3/AM for 60 min at 37 degrees C. Changes in fluorescence were monitored by use of an inverted microscope which had been connected to a spectrofluorometer. Fluorescent intensity measurements were acquired for a minimum of 416 sec time span or up to 1,248 sec, with integration readings of 1 sec duration obtained every 2 sec throughout the measurement period. The experimental design consisted of comparing the rise in [Ca2+]i of fluo-3 loaded secondary oocytes subjected to electroporation in PBS and Ca(2+)-free PBS, each containing 25 microM IP3, to that elicited by PBS and Ca(2+)-free PBS containing a final concentration of 7% ETOH. Non-pulsed control secondary oocytes were placed in PBS + 25 microM IP3 during monitoring of [Ca2+]i fluorescence. Pulsed control secondary oocytes were placed in Ca(2+)-free PBS, subjected to electroporation pulse, and monitored for [Ca2+]i fluorescence. Electroporation of IP3 was accomplished by placing fluo-3 loaded secondary oocytes between the electrodes of a glass slide fusion chamber which had been overlaid with 300 microliters of PBS + 25 microM IP3 or Ca(2+)-free PBS + 25 microM IP3.(ABSTRACT TRUNCATED AT 250 WORDS)

Micromanipulation of mammalian embryos: Principles, progress and future possibilities

Numerous advances in development of techniques for manipulating mammalian embryos outside the maternal environment have been made over the past decade. Some techniques were developed primarily for use in research; others were developed in response to problems of practical livestock production but have proven useful in research as well. Embryo micromanipulation procedures are used often in conjunction with embryo transfer, and interest in these procedures was stimulated by growth of the embryo transfer industry. Included in this review are discussions of procedures for manipulation of gametes and embryos, including sperm injection into oocytes, pronuclear and nuclear transfer, embryo biopsy and splitting, experimental chimera production and isolation of embryonic stem cells.

Effect of electrofusion pulse in either electrolyte or nonelectrolyte fusion medium on subsequent murine embryonic development

This study was designed to determine what effect electropulse parameters would have on rate of fusion, lysis, and embryo viability when embryos were subjected to electrofusion treatment in nonelectrolyte or electrolyte pulse media. Previous experiments have shown electrolyte medium (i.e., phosphate-buffered saline; PBS) to have a positive effect on electric pulse-induced murine oocyte activation. In addition, these results also indicated that pulse media containing 0.9 mM Ca2+ induced a dramatic increase in the rate of murine oocyte activation compared with oocytes pulsed in media containing 0.0 or 0.05 mM Ca2+. Pronuclear or two-cell-stage embryos were obtained from superovulated prepubertal randomly bred Swiss (albino) female mice. Embryos were randomly assigned to three nonelectrolyte and three electrolyte treatment media. Nonelectrolyte media consisted of 0.3 M mannitol (T1), 0.3 M mannitol + 0.05 mM CaCl2 (T2), and 0.3 M mannitol + 0.9 mM CaCl2 (T3). Electrolyte media consisted of Ca(2+)-free PBS (T4), PBS containing 0.05 mM CaCl2 (T5), and PBS containing 0.9 mM CaCl2 (T6). Three experiments were carried out; the objective of the first was to determine the rate of fusion and rate of lysis in murine two-cell embryos placed in the two types of (0.3 M mannitol, T1-T3; and PBS, T4-T6) fusion media and subjected to a fusion procedure (3 V, 5 sec AC alignment pulse, followed by a 1.56 kV.cm-1, 99 microsec DC fusion pulse). Control two-cell embryos were placed in T1 for 2 min and did not receive a fusion pulse.(ABSTRACT TRUNCATED AT 250 WORDS)