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

Effects of klotho protein or klotho knockdown in porcine oocytes at different stages

Klotho is a protein that plays different functions in female fertility. We have previously reported that klotho protein supplementation during in vitro maturation improves porcine embryo development, while klotho knockout for somatic cell cloning completely blocks full-term pregnancy in vivo. However, the effects of the microinjection of klotho protein or klotho knockdown dual vector in porcine embryos at different time points and the specific molecular mechanisms remain largely unknown. In this study, we injected the preassembled cas9 + sgRNA dual vector, for klotho knockdown, into the cytoplasm of the germinal vesicle stage of oocytes and into porcine embryos after 6-h parthenogenetic activation. Similarly, the klotho protein was inserted into the cytoplasm of germinal vesicle stage oocytes and porcine embryos after 6-h parthenogenetic activation. Compared with the controls, the microinjection of klotho dual vector markedly decreased the blastocyst formation rates in germinal vesicle stage oocytes and activated embryos. However, the efficiency of blastocyst formation when klotho protein was inserted before in vitro maturation was significantly higher than that after klotho protein insertion into parthenogenetically activated embryos. These results indicated that klotho knockdown may impair embryo development into blastocyst irrespective of injection timing. In addition, klotho protein injection timing in pig embryos may be an important factor for regulating embryo development.

The combination of rolipram and cilostamide improved the developmental competence of cloned porcine embryos

In vitro maturation of porcine oocytes is characterized by asynchronous cytoplasmic and nuclear maturation, leading to less competent oocytes supporting embryo development. The purpose of this study was to evaluate the combined effect of rolipram and cilostamide as cyclic Adenine monophosphate (cAMP) modulators to find the maximum cAMP levels that temporarily arrest meiosis. We determined the optimal time to maintain functional gap junction communication during pre-in vitro maturation to be four hours. Oocyte competence was evaluated by the level of glutathione, reactive oxygen species, meiotic progression, and gene expression. We evaluated embryonic developmental competence after parthenogenetic activation and somatic cell nuclear transfer. The combined treatment group showed significantly higher glutathione and lower reactive oxygen species levels and a higher maturation rate than the control and single treatment groups. Cleavage and blastocyst formation rates in parthenogenetic activation and somatic cell nuclear transfer embryos were higher in two-phase in vitro maturation than in the other groups. The relative levels of BMP15and GDF9 expression were increased in two-phase in vitro maturation. Somatic cell nuclear transfer blastocysts from two-phase in vitro maturation oocytes showed a lower level of expression of apoptotic genes than the control, indicating better pre-implantation developmental competence. The combination of rolipram and cilostamide resulted in optimal synchrony of cytoplasmic and nuclear maturation in porcine in vitro matured oocytes and there by enhanced the developmental competence of pre-implantation embryos.

Non-coding RNAs: emerging regulatory factors in the derivation and differentiation of mammalian parthenogenetic embryonic stem cells

Parthenogenetic embryonic stem cells (PESCs) are ESCs derived from early parthenogenetic embryos. Haploid PESCs, containing haploid DNA, originate from a single sperm or occyte, while, diploid PESCs originate from two fused occytes. Most PESC lines used so far are diploid. PESCs exhibit representative pluripotent stem cell features, such as the capacity for self-renewal and the pariticular molecular signatures. Whereas, PESCs display distinctive properties, such as differential regulation of X-chromosome inactivation (XCI) and divergent monitor of genes involved in multiple biological processes. PESCs are considered promising in the regeneration medicine and developmental biology. Non-coding RNAs (ncRNAs), especially miRNAs and lncRNAs, have garnered increasing attention over the past 2 decades. They are now known to be involved in almost all cellular processes due to their full-range regulation of gene expression. Numerous studies have indicated that embryonic stem cells (ESCs) displayed distinct signatures of ncRNA genes, which play key roles in the pluripotency and self renewal of ESCs. However, the expression pattern of ncRNAs in PESCs and their roles in the derivation and differentiation of PESCs were rarely reported. In this paper, we reviewed recent research on the derivation and differentiation of PESCs and describe the emerging role of ncRNAs in these processes.

Cilostamide and forskolin treatment during pre-IVM improves preimplantation development of cloned embryos by influencing meiotic progression and gap junction communication in pigs

This study was conducted to evaluate the effects of treatment with the cAMP modulators cilostamide and/or forskolin during pre-IVM culture on meiotic progression, gap junction communication, intraoocyte cAMP level and glutathione content, embryonic development after parthenogenesis, and somatic cell nuclear transfer in pigs. Cumulus-oocyte complexes were cultured for 24 hours in unsupplemented medium or media containing 20 μM cilostamide and/or 50 μM forskolin. After pre-IVM, oocytes were cultured for 41 to 44 hours in a standard IVM medium to induce oocyte maturation. When the nuclear status of oocytes was examined after pre-IVM for 24 hours, a higher (P < 0.01) proportion of oocytes treated with forskolin (85.5%) and cilostamide + forskolin (92.6%) remained at the germinal vesicle stage compared with untreated (20.6%) and cilostamide-treated oocytes (54.7%). cAMP level in pre-IVM oocytes was significantly increased by combined treatment with cilostamide + forskolin (21.38 fmol/oocyte) relative to the no pre-IVM control, no treatment, cilostamide, and forskolin groups (2.85, 1.88, 1.74, and 8.95 fmol/oocyte, respectively). Forskolin with or without cilostamide significantly maintained open-gap junction communication relative to no treatment. Blastocyst formation in parthenogenesis was significantly (P < 0.01) improved by forskolin (65.3%) relative to other treatments (28.3% to 48.1%). Supplementation of pre-IVM with dibutyryl cAMP showed similar blastocyst formation as forskolin treatment (61.1% and 61.0%, respectively). In somatic cell nuclear transfer, simultaneous treatment with cilostamide + forskolin significantly (P < 0.05) increased embryonic development to the blastocyst stage (42.9%) relative to the no pre-IVM, control, and cilostamide groups (32.3, 28.6, and 32.8%, respectively). The glutathione contents in pre-IVM oocytes were increased by no treatment, forskolin, and cilostamide + forskolin (1.38, 1.39, and 1.27 pixels/oocyte, respectively) compared with no pre-IVM and cilostamide (1.00 and 0.99 pixels/oocyte, respectively; P < 0.05). Our results reported that the meiotic progression of immature pig oocytes could be reversibly attenuated by cAMP, whereas treatment with cilostamide and forskolin during pre-IVM had positive effects on developmental competence of oocytes in pigs, probably by improving cytoplasmic maturation.

Developmental potential of pig embryos reconstructed by use of sow versus pre-pubertal gilt oocytes after somatic cell nuclear transfer

In this study, the developmental ability of cloned embryos using gilt versus sow oocytes was evaluated under the hypothesis that the efficiency of nuclear transfer using gilt oocytes was lower than that of sow oocytes, but that it could be optimized. Five experiments were performed with routine production of cloned embryos with sow oocytes serving as the control. Results showed that: Experiment 1: Blastocyst rates of cloned embryos with gilt oocytes was about half compared with control. Experiment 2: An extended maturation time of 48 h used for gilt oocytes resulted in lower blastocyst rates after cloning. Experiment 3: Development of cloned embryos with gilt oocytes was improved by co-culture with sow oocytes. Experiment 4: After maturation of gilt oocytes using follicular fluid from gilt instead of sow, the oocytes were sorted into large and small oocytes, and after cloning, blastocyst rates were higher using large gilt oocytes compared with small oocytes; however, the rate remained lower compared with control. Experiment 5: Six sow recipients received a total of 503 morulae and blastocysts cloned from gilt oocytes (four recipients) and 190 cloned from sow oocytes (two recipients). All recipients became pregnant and went to term, resulting in 26 (gilt oocytes) and six (sow oocytes) piglets. In conclusion, results confirmed that nuclear transfer efficiency was higher using sow versus gilt oocytes, but the use of gilt oocytes can be optimized by sorting after ooplasm size following maturation and by maturing gilt and sow oocytes together.

What is the optimal condition for fertilization of IVM oocytes?

Application of in vitro maturation (IVM) is recently increasing for human infertility, especially to rescue patients of polycystic ovarian syndrome and ovarian hyperstimulation syndrome. To increase the application of IVM oocytes for embryo production and the efficiency of successful production of babies using IVM oocytes, quality control of oocytes and achievement of fertilization in the most suitable condition may be very important. In this paper, suitable conditions for fertilization of IVM oocytes will be discussed with recent knowledge about IVM and in vitro fertilization of oocytes in domestic animals. Currently, human oocytes are collected mainly from patients' ovaries 36 h following mild gonadotropin stimulation and used for IVM for 24-26 h. However, asynchronous progression of those oocytes to reach the metaphase-II stage may have occurred during the IVM culture. In the oocytes that have already progressed to the metaphase-II stage, sudden aging such as reduction in maturation promoting factor and MAP kinases will start to occur. Application of specific inhibitors of phosphodiesterase to control intracellular cAMP (cyclic adenosine monophosphate) level may be effective to synchronize timings of the germinal vesicle breakdown and consequently the meiotic progression of oocytes, and to improve the developmental competence. Furthermore, treatment of aging oocytes with caffeine appears to rescue them from reductions in maturation promoting factor and MAP kinases and to improve the developmental competence. Assessment methods to select oocytes with good quality may also be important to improve the successful rates.

MG132 treatment during oocyte maturation improves embryonic development after somatic cell nuclear transfer and alters oocyte and embryo transcript abundance in pigs

The objective of this study was to examine the effect of treating pig oocytes during in vitro maturation (IVM) with a proteasome inhibitor, MG132, on oocyte maturation and embryonic development. In one series of experiments, oocytes from medium-sized follicles (3-8 mm in diameter) were untreated (MCO) or treated with MG132 during 0-22 hr (M0-22) or 30-42 hr (M30-42) of IVM. There was no significant effect of MG132 on nuclear maturation or cytoplasmic maturation (as assessed by intracellular amounts of glutathione and p34cdc2 kinase activity). Blastocyst formation after parthenogenetic activation (PA) and somatic cell nuclear transfer (SCNT), however, was increased for M30-42 (65.2% and 27.7% for PA and SCNT, respectively) compared to MCO (42.6% and 13.6%, respectively) and M0-22 (45.3% and 19.5%, respectively; P<0.05). Expression of PCNA and ERK2 was increased in M30-42 for IVM oocytes while transcript abundance for POUF51, DNMT1, FGFR2, and PCNA was increased in M30-42 for 4-cell SCNT embryos. When oocytes derived from small follicles (<3 mm in diameter) were untreated (SCO) or treated with MG132 during 0-22 hr (S0-22), 30-42 hr (S30-42) of IVM, or 0-22 and 30-42 hr of IVM (S0-22/30-42), expression of POU5F1, DNMT1, FGFR2, and PCNA and blastocyst formation were increased for SCNT embryos derived from S30 to 42 (16.5%) and S0-22/30-42 oocytes (20.8%) as compared to embryos from SCO (8.7%) or S0-22 oocytes (8.8%; P<0.05). Results demonstrate that treatment of oocytes with MG132 during the later stage of IVM improves embryonic development and alters gene expression in pigs.

Effects of recipient oocyte age and interval from fusion to activation on development of buffalo (Bubalus bubalis) nuclear transfer embryos derived from fetal fibroblasts

The objective was to investigate the effect of recipient oocyte age and the interval from activation to fusion on developmental competence of buffalo nuclear transfer (NT) embryos. Buffalo oocytes matured in vitro for 22 h were enucleated by micromanipulation under the spindle view system, and a fetal fibroblast (pretreated with 0.1 μg/mL aphidicolin for 24 h, followed by culture for 48 h in 0.5% fetal bovine serum) was introduced into the enucleated oocyte, followed by electrofusion. Both oocytes and NT embryos were activated by exposure to 5 μM ionomycin for 5 min, followed by culture in 2 mM 6-dimethyl-aminopurine for 3 h. When oocytes matured in vitro for 28, 29, 30, 31, or 32 h were activated, more oocytes matured in vitro for 30 h developed into blastocysts in comparison with oocytes matured in vitro for 32 h (31.3 vs 19.9%, P < 0.05). When electrofusion was induced 27 h after the onset of oocyte maturation, the cleavage rate (78.0%) was higher than that of electrofusion induced at 28 h (67.2%, P < 0.05), and the blastocyst yield (18.1%) was higher (P < 0.05) than that of electrofusion induced at 25 or 26 h (7.4 and 8.5%, respectively). A higher proportion of NT embryos activated at 3 h after electrofusion developed to the blastocyst stage (18.6%) in comparison with NT embryos activated at 1 h (6.0%), 2 h (8.3%), or 4 h (10.6%) after fusion (P < 0.05). No recipient was pregnant 60 d after transfer of blastocysts developed from NT embryos activated at 1 h (0/8), 2 h (0/10), or 4 h (0/9) after fusion. However, 3 of 16 recipients were pregnant following transfer of blastocysts developed from the NT embryos activated at 3 h after fusion, and two of these recipients maintained pregnancy to term. We concluded that the developmental potential of buffalo NT embryos was related to recipient oocyte age and the interval from fusion to activation.

Early metaphase II oocytes treated with dibutyryl cyclic adenosine monophosphate provide suitable recipient cytoplasm for the production of miniature pig somatic cell nuclear transfer embryos

We investigated the effects of in vitro maturation duration and treatment with dibutyryl cyclic adenosine monophosphate (dbcAMP) on the blind enucleation efficiency and developmental competence of miniature pig somatic cell nuclear transfer (SCNT) embryos. Oocytes were cultured for 22 h in NCSU-23 medium with or without 1 mM dbcAMP and then additionally cultured in dbcAMP-free NCSU-23 for 14, 18, or 22 h. Regardless of dbcAMP treatment, the rate of nuclear maturation reached a plateau at 36 and 40 h. However, mitochondrial distribution, a marker for cytoplasmic maturation, differed between the dbcAMP-untreated oocytes at 36 h and dbcAMP-treated oocytes at 40 h. The metaphase II chromosomes were adjacent to the first polar body in 68.8% and 63.5% of the dbcAMP-untreated oocytes at 36 h and dbcAMP-treated oocytes at 40 h, respectively. Furthermore, the blind enucleation efficiency by removing a small volume of cytoplasm was significantly higher in the dbcAMP-untreated oocytes at 36 h (82.9%) and dbcAMP-treated oocytes at 40 h (89.9%) than other groups. The rate of blastocyst formation was highest in the dbcAMP-treated oocytes at 40 h. Hence, this study demonstrated that dbcAMP-treated early metaphase II oocytes are suitable for the production of miniature pig SCNT embryos.

Effects of different oocyte activation procedures on development and gene expression of porcine pre-implantation embryos

Among the factors that affect the efficiency of somatic cell nuclear transfer (SCNT) in pigs, the activation protocol is the most variable among the current SCNT procedures. The aim of this study is focused on defining an efficient activation treatment of porcine oocytes. In Experiment 1, we studied the effects of nine different oocyte activation procedures (including chemical- and electrical-based treatments) on parthenogenetic embryo development. In Experiment 2, we studied the effect of the more efficient activation procedures on the gene expression profile of Oct4 and Igf2r in parthenogenetic blastocysts. In conclusion, ionomycin as a first calcium stimulus is not able to activate porcine oocytes efficiently in comparison with electric procedures. Electrical treatments with 6-DMAP significantly increased the level of Oct4 expression, whereas the single and double pulse treatments alone maintained the same profile as the IVF group.

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.

Sexual maturity and reproductive phase of oocyte donor influence the developmental ability and apoptosis of cloned and parthenogenetic porcine embryos

This study investigated the influence of the sexual maturity and reproductive phase of oocyte donor on the developmental ability and quality of porcine embryos produced by somatic cell nuclear transfer (SCNT) or parthenogenesis (PA). Blastocyst quality was evaluated in terms of hatching ability, total nuclei number and types of apoptosis. Results revealed that maturation rate was not influenced by the reproductive status of the oocyte donor. However, when subjected to PA or SCNT, embryos derived from sexually mature sow oocytes developed to blastocysts at higher rates and had higher cell number than those derived from immature gilt oocytes (p<0.05). Significant effect of reproductive phase, luteal versus follicular, was also noted with luteal stage oocytes yielding higher (p<0.05) rate of blastocyst formation (PA: 54.3+/-1.3% versus 44.8+/-0.3%; SCNT: 29.4+/-0.2% versus 22.7+/-0.1%). Blastocysts derived from luteal phase oocytes also had higher (p<0.05) hatching ability (PA: 44.2+/-1.1%; SCNT: 39.6+/-4.7%) and cell number (PA: 77.4+/-4.9; SCNT: 54.9+/-2.4) than those derived from follicular phase oocytes (PA: 34.9+/-0.9%, 67.2+/-3.9; SCNT: 34.6+/-2.7%, 47.5+/-2.9). TUNEL assay and Hoechst 33342 staining revealed that percentage of blastocysts showing total apoptosis did not differ among the groups. However, luteal phase oocyte-derived blastocysts had the highest incidence of nuclear fragmentation. Among cloned blastocysts that showed the signs of apoptosis, the highest index of total apoptosis was observed in prepubertal oocyte-derived blastocysts (5.2+/-0.7). Blastocysts derived from luteal phase oocytes showed the lowest TUNEL index (2.0+/-0.5). The present study therefore, indicates that the sexual maturity and reproductive phase of cytoplast donor significantly influences the developmental ability, apoptosis and quality of blastocysts produced by SCNT or PA. Oocytes from sexually mature sows in luteal phase of their reproductive cycle may be better cytoplast recipients for SCNT.

Production of viable cloned miniature pig embryos using oocytes derived from domestic pig ovaries

For production of viable somatic cell nuclear transferred (SCNT) miniature pig embryos, in vitro condition for controlling the quality of recipient oocytes derived from domestic pig ovaries should be evaluated. In the present study, to get information on optimal in vitro maturation (IVM) condition of oocytes, we investigated the effect of IVM duration of recipient oocytes on subsequent development of SCNT miniature pig embryos, the maturation-promoting factor (MPF) activity in recipient oocytes before and after SCNT, and the occurrence of premature chromosome condensation (PCC) and spindle morphologies of donor nuclei following SCNT. The optimal window of the IVM period in terms of in vitro developmental ability of SCNT embryos was determined to be 36-40 h after the start of IVM. The use of recipient oocytes matured for 36 and 40 h resulted in a high level of MPF activity before and after SCNT, and increased the occurrence of PCC in transferred nuclei compared to the use of oocytes matured for 44 and 52 h. The proportion of abnormal spindle-like structures increased as the IVM period was prolonged. In addition, SCNT embryos constructed from recipient cytoplasts obtained after 40 h of maturation by using fetal fibroblasts of miniature pigs were transferred to surrogate miniature pigs, and developed to full term. These results suggest that recipient oocytes matured for 36 h and 40 h effectively induce PCC with a normal cytoskeletal structure because of a high level of MPF activity; furthermore, the 40-h IVM period improves in vitro development of SCNT embryos to the blastocyst stage, resulting in the production of viable cloned miniature pigs.

Defined system for in vitro production of porcine embryos using a single basic medium

We have previously indicated that porcine blastocysts can be produced by in vitro fertilization (IVF) and culture (IVC) in chemically defined porcine gamete medium (PGM) and porcine zygote medium (PZM)-5, respectively, In the present study, the effects of basic media and macromolecular components on in vitro maturation (IVM) were investigated to develop a defined system for in vitro embryo production using a single basic medium through IVM, IVF and IVC. Porcine immature oocytes were matured in porcine oocyte medium (POM) or modified North Carolina State University (mNCSU) 37, which were supplemented with either 10% (v/v) porcine follicular fluid (pFF) or 3 mg/ml polyvinyl alcohol (PVA) as a macromolecular component (designated POM+pFF, POM+PVA, mNCSU37+pFF and mNCSU37+PVA). In the maturation with mNCSU37+PVA, the percentages of oocytes that reached the metaphase II stages were significantly lower than those in the other treatments. Following IVM with the above media, oocytes were treated with an electrical stimulus and cycloheximide for parthenogenetic activation and were cultured in PZM-5 for 5 days. The rates of cleavage and blastocyst formation of parthenogenetic oocytes were significantly lowered for maturation with mNCSU37+PVA compared with the other treatments, while there were no significant differences in the total numbers of cells in blastocysts among the treatments. Following IVF and IVC, the rates of penetration, male pronucleus formation, cleavage and blastocyst formation were significantly lower when oocytes were matured in mNCSU37+PVA than in other maturation media. The normal fertilization rate was significantly higher in POM+PVA compared with the other treatments, although the total number of cells in blastocysts was reduced with the addition of PVA to both POM and mNCSU37 compared with pFF supplementation. These results demonstrate that porcine blastocysts can be produced by the defined system using a single basic medium.

Comparison of maturational and developmental parameters of oocytes recovered from prepubertal and adult pigs

To clarify the cause(s) of the differences between the developmental competence of prepubertal and adult porcine oocytes, the following were examined: (i) the meiotic progression, p34(cdc2) kinase activity, ooplasm diameter and response to activation stimuli of the oocytes; and (ii) the development of parthenotes and nuclear transfer (NT) embryos obtained using oocytes recovered from prepubertal and adult pigs. Oocytes were recovered from 4- to 8-mm follicles of abattoir-derived ovaries. There were no apparent differences in the morphology of the germinal vesicle, nuclear maturation rate, activity of p34(cdc2) kinase or response to parthenogenetic stimulation between prepubertal and adult oocytes. Before and after maturation culture, the ooplasm diameters of prepubertal oocytes were smaller than those of adult oocytes. Parthenotes and NT embryos derived from prepubertal gilt oocytes showed a lower rate of development to the blastocyst stage than those derived from adult oocytes. These results suggest that lower developmental competence of prepubertal oocytes may be caused by their inability to complete ooplasmic maturation, and that this is not because of altered oocyte maturation kinetics and/or p34(cdc2) kinase activity. Furthermore, the smaller diameter of the ooplasm of prepubertal oocytes indicates that most oocytes that have routinely recovered from prepubertal gilt ovarian follicles are still in the growing phase and have immature ooplasm.

Modification of maturation condition improves oocyte maturation and in vitro development of somatic cell nuclear transfer pig embryos

This study examined effects on the developmental competence of pig oocytes after somatic cell nuclear transfer (SCNT) or parthenogenetic activation (PA) of : 1) co-culturing of oocytes with follicular shell pieces (FSP) during in vitro maturation (IVM); 2) different durations of maturation; and 3) defined maturation medium supplemented with polyvinyl alcohol (PVA; control), pig follicular fluid (pFF), cysteamine (CYS), or beta-mercaptoethanol (beta-ME). The proportion of metaphase II oocytes was increased (p < 0.05) by co-culturing with FSP compared to control oocytes (98% vs. 94%). However, blastocyst formation after SCNT was not improved by FSP coculture (9% vs. 12%). Nuclear maturation of oocytes matured for 39 or 42 h was higher (p < 0.05) than that of oocytes matured for 36 h (95-96% vs. 79%). Cleavage (83%) and blastocyst formation (26%) were significantly higher (p < 0.05) in oocytes matured for 42 h than in other groups. Supplementation of a defined maturation medium with 100 microM CYS or 100 microM beta-ME showed no stimulatory effect on oocyte maturation, embryo cleavage, or blastocyst formation after PA. beta-ME treatment during IVM decreased embryo cleavage after SCNT compared to pFF or PVA treatments, but no significant difference was found in blastocyst formation (7-16%) among the four treatment groups. The results indicated that maturation of oocytes for 42 h was beneficial for the development of SCNT embryos. Furthermore, the defined maturation system used in this study could support in vitro development of PA or SCNT embryos.

Spindle formation and microtubule organization during first division in reconstructed rat embryos produced by somatic cell nuclear transfer

The present study was conducted to demonstrate the spindle formation and behavior of chromosomes and microtubules during first division in reconstructed rat embryos produced by somatic cell nuclear transfer (SCNT) with cumulus cell nuclei. To demonstrate the effect of oocyte aging after ovulation on the cleavage of SCNT embryos, micromanipulation was carried out 11, 15 and 18 h after injection of hCG. SCNT oocytes were activated by incubation in culture medium supplemented with 5 microM ionomycin for 5 min followed by treatment with 2 mM 6-dimethylaminopurine (6-DMAP) in mR1ECM for 2-3 h. For immunocytochemical observation, the SCNT embryos were incubated with monoclonal anti-alpha-tubulin antibody and then fluorescein isothiocyanate (FITC)-conjugated goat anti-mouse IgG. Cleavage rates were significantly higher for oocytes collected after 15 and 18 h rather than for those collected 11 h after injection of hCG (56 and 53%, respectively vs. 28%; P<0.05). Premature chromosome condensation occurred before activation of the SCNT oocytes, but adequate spindle formation was only rarely observed. The distribution of microtubules in SCNT embryos after activation was different from those of fertilized and parthenogenic oocytes, i.e., a dense microtubule organization shaped like a ring was observed. Eighteen to 20 h post-activation, most SCNT embryos were in the 2-cell stage, but no nucleoli were clearly visible, which was quite different from the fertilized oocytes. In addition, first division with and without small cellular bodies containing DNA was observed in the rat SCNT embryos in some cases. The present study suggests that reorganization of transferred nuclei in rat SCNT embryos may be inadequate in terms of formation of the mitotic assembly and nucleolar reorganization.

Developmental competence of porcine parthenogenetic embryos relative to embryonic chromosomal abnormalities

Parthenogenetically activated (PA) embryos exhibit delayed development, a lower blastocyst rate, and less successful development in vitro compared to in vitro fertilized (IVF) embryos. To investigate the possible mechanisms for unsuccessful parthenogenetic development, this study analyzed the chromosome abnormalities and developmental potential of porcine PA embryos. Mature oocytes were electrically activated and cultured in Porcine Zygote Medium-3 (PZM3) supplemented with 3 mg/ml BSA for 6, 7, or 8 days. The percentage of PA blastocysts was lower than that of IVF embryos on days 6 and 7 (16.4 +/- 7.4 vs. 28.7 +/- 3.7; 10.9 +/- 2.8 vs. 21.5 +/- 4.7, P < 0.05; respectively), and the PA blastocysts had significantly fewer nuclei than IVF blastocysts (23.2 +/- 1.8 vs. 29.7 +/- 0.8; 29.7 +/- 3.3 vs. 32.0 +/- 2.4, P < 0.05). The percentage of abnormal PA embryos (including embryos with condensed nuclei, arrested embryos and fragmented embryos) was higher than that of IVF embryos (PA: 52.9 +/- 12.8 vs. 16.4 +/- 7.4 on day 6), and increased with culture time (71.9 +/- 12.1 vs. 10.9 +/- 2.8. on day 7,and 75.0 +/- 22.6 vs. 12.1 +/- 2.3 on day 8, P < 0.05). The Day-6 PA blastocysts (n = 147) were divided into three classes according to the total number of nuclei (<20, 20-39, >40) and into three groups according to the morphological diameter (<150, 150-180, >180 microm). Of the haploid blastocysts, 56.1% had less than 20 nuclei, and 71.5% were less than 150 microm in diameter. Of all (114) blastocysts suitable for analysis, 55.5% displayed chromosomal abnormalities. Among chromosomal abnormalities in PA blastocysts, haploid blastocysts were most prevalent (43.6%), while polyploidy (4.4%) and mixoploidy (7.7%) embryos were less prevalent. Chromosomal abnormalities of porcine PA embryos might contribute to a higher rate of abnormal embryonic development. We suggest that a careful consideration should be given when using the blastocysts with smaller size, and establishing the optimum culture condition for PA embryos development in vitro.

Characterization of calcium oscillation patterns in caprine oocytes induced by IVF or an activation technique used in nuclear transfer

Routine activation of nuclear transfer (NT) eggs involves the application of a single intracellular calcium [Ca2+]i rise, stimulated by an electrical pulse, as opposed to [Ca2+]i oscillations, which is the natural mode of sperm-induced activation at fertilization in all mammalian species tested to date. It has yet to be shown that caprine oocytes exhibit an increase in calcium at fertilization in a manner similar to other mammals. The objective of the present study was to evaluate and characterize the ([Ca2+]i) oscillation patterns of caprine metaphase II (MII) oocytes during IVF and during an activation techniques used in nuclear transfer. Additionally, the effect of cytochalasin B (cyto B) in the NT process was evaluated for its impact on [Ca2+]i oscillations and subsequent embryo development. Mature in vitro and in vivo derived caprine oocytes were activated by 5 microM ionomycin, an electrical pulse(s), or IVF. The intracellular Ca2+ response was determined using the [Ca2+]i indicator Fura-2 dextran (Fura-2D). Ova treated with ionomycin or stimulated by an electrical pulse exhibited a single [Ca2+]i rise, whereas IVF-derived oocytes showed oscillations. IVF [Ca2+]i showed some variation, with 62% of in vitro matured oocytes exhibiting oscillations, whereas 8% of in vivo matured oocytes exhibited oscillations demonstrating a correlation between [Ca2+]i responses and maturation technique. Knowing the [Ca2+]i profile of activated eggs, one may be able to optimize the activation methodology used in a production nuclear transfer setting which could potentially improve development to term for NT embryos.

Development and apoptosis of pre-implantation porcine nuclear transfer embryos activated with different combination of chemicals

Artificial activation of oocytes is a pre-requisite for successful cloning by nuclear transfer (NT). This study investigated effect of different combination of activation chemicals such as electric pulse (E), thimerosal (Thi) + dithiothreitol (DTT), 6-dimethylaminopurine (6-DMAP), or cycloheximide (CH) on the developmental ability and the frequency of apoptosis of porcine NT embryos during the culture in vitro. NT embryos activated with chemicals showed significantly higher developmental rate to blastocyst stage compared to embryos activated with E alone (21.5%-26.6% vs. 15.7%, respectively). Of chemicals, Thi + DTT supported higher development to blastocyst stage as compared to 6-DMAP or CH (26.6% vs. 21.5%-23.4%, respectively). Apoptosis of NT embryos were analyzed by using a terminal deoxynucleatidyl transferase-mediated deoxyuridine 5-triphosphate nick-end labeling (TUNEL) assay. The onset of apoptosis of embryos activated E alone was on Day 4, whereas embryos activated with chemicals showed apoptosis on Day 3 post-activation NT embryos exposed to chemicals for activation had higher frequency of apoptosis compared to that of embryos exposed to E alone from Day 3 to Day 7 during the culture. In conclusion, this study shows that chemical activation after fusion could increase not only the developmental ability of porcine NT embryos but also the mean cell number with an increased ratio of inner cell mass (ICM) to trophectoderm (TE) cells. However, the chemical activation also could increase the frequency of apoptosis and induced apoptosis earlier in porcine NT embryos.

Caffeine promotes premature chromosome condensation formation and in vitro development in porcine reconstructed embryos via a high level of maturation promoting factor activity during nuclear transfer

When the nucleus in G0/G1 phase is transferred to an enucleated oocyte by nuclear transfer (NT), its nuclear envelope is broken, followed by condensation of chromosome structure by maturation promoting factor (MPF). This morphological remodeling of the transferred interphase nucleus seems to be essential for subsequent development of NT embryos. In this study, we treated porcine NT embryos with caffeine, which has been reported to increase MPF activity, to keep their MPF level high during NT. When 2.5 mM caffeine was added to the handling medium, the proportion of NT embryos showing condensed chromosome increased significantly (P < 0.05). In NT embryos treated with caffeine, the activity of p34cdc2 kinase was significantly (P < 0.05) higher than in those without caffeine at 3 h post-injection. In addition, the rate of development to the blastocyst stage after activation was significantly (P < 0.05) higher in NT embryos treated with caffeine. These results indicate that caffeine treatment can increase not only the rate of chromosome condensation but also the developmental rate to the blastocyst stage of porcine NT embryos. This action is most likely due to the support/increase of MPF activity throughout the process of NT.

Changes in ovarian, follicular, and oocyte morphology immediately after the onset of puberty are not accompanied by an increase in oocyte developmental competence in the pig

This study was conducted to determine whether ovarian morphology and developmental competence of in vitro-matured (IVM) oocytes is immediately affected by the onset of puberty in the pig. Ovaries of peri-pubertal pigs were sorted into two groups according to the presence or absence of corpora lutea presence (CL and NCL, respectively. Ovary dimensions, follicle diameter and number, and oocyte diameter (with and without zona pellucidae) were determined. The developmental competence of in vitro-matured oocytes from these two groups was evaluated following parthenogenetic activation and culture in vitro. CL ovaries were significantly (P<0.01) larger than NCL ovaries (width: 22.3+/-0.9 mm versus 15.9+/-0.4 mm, length: 33.2+/-1 mm versus 24.1+/-0.4 mm). Although CL ovaries had fewer antral follicles in total compared with NCL ovaries (21.1+/-1.8 mm versus 46.8+/-2.2 mm), they had a similar number of follicles 3-8mm in diameter. The mean diameter of follicles that were aspirated was greater for CL ovaries than for NCL ovaries (4.5+/-0.1 mm versus 3.3+/-0.02 mm). Oocytes from CL ovaries were greater in diameter compared with those from NCL ovaries (zona retained: 159+/-1.3 microm versus 146.1+/-1.5 microm, zona free: 124.7+/-1.8 microm versus 113.1+/-1.6 microm). No differences were found between oocytes from CL and NCL ovaries for rates of meiotic maturation (91.6+/-3.2% versus 92.4+/-3.2%), cleavage (88.4+/-11% versus 90.7+/-2.6%) and blastocyst formation (21.0+/-3.7% versus 23.7+/-5.7%). Therefore, the onset of puberty coincides with immediate changes in ovarian morphology, increased ovary size, follicle and oocyte diameter, but not with improved oocyte developmental competence. This suggests that the higher developmental competence usually observed in adult oocytes is acquired gradually and requires exposure to multiple estrus cycles.

Parthenogenetic activation and subsequent development of porcine oocytes activated by a combined electric pulse and butyrolactone I treatment

This study was designed to evaluate the parthenogenetic activation of porcine oocytes matured in vitro for a varied period after combined electric pulse (EP; 1500 V/cm, 100 microsec) and Butyrolactone I (BL I). After 36 h of maturation culture, the rates of activated oocytes and oocytes with two pronuclei were significantly lower than those of oocytes cultured for 42 and 48 h after EP. However, when treated by a combined EP and BL I (150 microM), these rates increased to the same level as 42 and 48 h oocytes. When oocytes cultured for 48 h and activated by a combined EP and BL I treatment were subsequently cultured in mNCSU37 medium, the rates of embryos cleaved and developed to the blastocyst stage were significantly higher than those in Whitten's medium. In contrast, when activated oocytes were cultured in mNCSU37 medium under two oxygen environments (5% vs 20% O(2)), there was no difference in the rates of cleavage, blastocyst formation and nuclear numbers per blastocyst. Our results demonstrated that the combined EP and BL I treatment of porcine oocytes matured in vitro is capable of producing high rates of good quality blastocysts when cultured in a suitable in vitro condition.

Improved developmental competence of cloned porcine embryos with different energy supplements and chemical activation

The present study investigated the effect of lactate/pyruvate supplement in culture medium and of chemical activation after electric stimulus on in vitro development of porcine somatic cell nuclear transfer (SCNT) embryos. In vitro matured gilt oocytes were enucleated, reconstructed with fetal fibroblasts, and simultaneously fused/activated using a single pulse of 2.0 kV/cm for 30 microsec. In Experiment 1, reconstructed embryos were cultured in North Carolina State University (NCSU)-23 medium supplemented with either 5.5 mM glucose (Group A) or lactate (5.0 mM)/pyruvate (0.5 mM) (Group B). Compared to Group A, cleavage rate (64% vs. 47%) was higher and more blastocysts developed in Group B (17% vs. 6% at Day 6, 21% vs.11% at Day 7). Experiment 2, embryos reconstructed by electric stimulus (2.0 kV/cm for 30 microsec) were subjected to three activation protocols: (1) no chemical activation (Group C), (2) 7.5 microg/ml cytochalasin B treatment at 2 hr after electric stimulus (Group D), and (3) 5 microg/ml 6-dimethylaminopurine (Group E) treatment at 2 hr after electric stimulus. The reconstructed embryos were cultured for 7 days in NCSU-23 medium supplemented with lactate (5.0 mM)/pyruvate (0.5 mM). The rates of blastocyst formation on Day 6 and Day 7 in Group C (17 and 20%, respectively) or Group D (15, 20%, respectively) were higher than in Group E (9 and 12%, respectively). The percentage of two pseudo-pronucleus (PPN) formations in Group D (88%) was significantly higher than in Group C (71%) and Group E (72%). Mean cell numbers of blastocysts in Group D (63.4 +/- 15.8) were higher than in Group C (43.9 +/- 16.5) and Group E (32.9 +/- 17.9), due to increased trophectoderm (TE) cell numbers. Our results indicate that supplementing NCSU-23 medium with lactate/pyruvate and exposure of cytochalasin B after electrical stimulus can improve in vitro developmental competence of porcine SCNT embryos.

Improvement of a porcine somatic cell nuclear transfer technique by optimizing donor cell and recipient oocyte preparations

This study was conducted to improve a porcine somatic cell nuclear transfer (SCNT) technique by optimizing donor cell and recipient oocyte preparations. Adult and fetal fibroblasts, and cumulus and oviduct cells were used as donor cells, and in vivo- and in vitro-matured oocytes were employed as recipient oocytes. The percentages of fusion and development to the blastocyst stage, the ratio of blastocysts to 2-cell embryos, and cell number of blastocysts were monitored as experimental parameters. In Experiment 1, donor cells of four different types were transferred to enucleated oocytes matured in vitro, and more (P < 0.05) blastocysts were derived from SCNT of fetal fibroblasts than from that of other cells (15.9% versus 3.1-7.9%). For SCNT using fetal fibroblasts, increasing the number of subcultures up to 15 times did not improve developmental competence to the blastocyst stage (12.2-16.7%). In Experiment 2, fetal fibroblasts were transferred to enucleated oocytes that matured in vivo or in vitro. When parthenogenetic activation of both types of oocytes was conducted as a preliminary control treatment, a significant increase in blastocyst formation was found for in vivo-matured compared with in vitro-matured oocytes (36.4% versus 29.5%). However, no improvement was achieved in SCNT using in vivo-matured oocytes. In conclusion, the type of donor somatic cell is important for improving development after porcine SCNT, and fetal fibroblasts were the most effective among examined cells. A system with good reproducibility has been established using fetal fibroblasts as the donor karyoplast after subculturing 1-10 times, and using both in vivo and in vitro-matured oocytes as the recipient cytoplast.

Improvements in cloning efficiencies may be possible by increasing uniformity in recipient oocytes and donor cells

The low efficiency of somatic cell cloning is the major obstacle to widespread use of this technology. Incomplete nuclear reprogramming following the transfer of donor nuclei into recipient oocytes has been implicated as a primary reason for the low efficiency of the cloning procedure. The mechanisms and factors that affect the progression of the nuclear reprogramming process have not been completely elucidated, but the identification of these factors and their subsequent manipulation would increase cloning efficiency. At present, many groups are studying donor nucleus reprogramming. Here, we present an approach in which the efficiency of producing viable offspring is improved by selecting recipient oocytes and donor cells that will produce cloned embryos with functionally reprogrammed nuclei. This approach will produce information useful in future studies aimed at further deciphering the nuclear reprogramming process.

Utility of rapidly matured oocytes as recipients for production of cloned embryos from somatic cells in the pig

The present study was conducted to examine the utility of rapidly matured oocytes as recipients for production of porcine embryos reconstituted with adult skin fibroblasts and whether arrest of meiotic resumption of recipient oocytes at the germinal vesicle (GV) stage by dibutyryl cyclic AMP (dbcAMP) improves in vitro developmental rates after reconstruction. At 24 h of maturation in the medium, 36.3% of oocytes reached the metaphase II (MII) stage. At 30 h of maturation, the percentage (71.4%) of MII oocytes did not significantly differ from that (78.0%) at 42 h of maturation. When MII oocytes recovered at 24 h of maturation were used as recipients, 22/156 (14.1%) cloned embryos developing to the blastocyst stage was significantly (P < 0.05) higher than those of embryos reconstituted with oocytes collected at 30 h (5/168; 3.0%) and 42 h (13/217; 6.0%) of maturation. Culture of oocytes in medium containing 1 mM dbcAMP for 20 h maintained 72.9% in the GV stage, whereas only 15.0% of nontreated oocytes were in the GV stage (P < 0.05). The effect of dbcAMP was reversible. However, the treatment of recipient oocytes with dbcAMP did not affect the development of reconstructed embryos when compared with nontreated oocytes. These results indicate that rapidly matured oocytes are superior in their ability to support development of porcine reconstructed embryos; however, arrest of meiotic resumption of recipient oocytes at the GV stage by dbcAMP does not improve reconstructed embryo developmental rates.