This study was carried out to investigate the effect of vitrification and slow freezing methods on the post-thaw developmental rate of rabbit zygotes. After exposing rabbit zygotes in EFS solution for 0.5, 1, 2, 3 and S min at room temperature, they were washed with 0.5 M sucrose solution, D-PBS and TCM-199 and then cultured in TCM-199 plus 10% FBS with bovine oviduct epithelial cells(BOEC) to examine whether the cryoprotectant induced injury during the various exposure periods. The embryo development rates to hatched blastocyst after exposing in EFS solution for 3 and 5 min(40.0 and 16.7%) were significantly lower than in 0.5, 1 and 2 min(63.0, 72.0 and 54.5%), respectively. The post-thaw development rates to hatched blastocyst were significantly(P<0.05) higher in in vivo morula with intact mucin coat(85.2%) and mucin seperated morula(77.8%) than those of in vitro morula(58.5%) and zygote(5.9%), hut no difference was shown between in vitro morulae and mucin separated morula. The cryoprotectant dilution procedures showed no effects on the post-thaw development rates to hatched blastocyst under the present culture conditions. The post-thaw development to hatched blastocyst in the rabbit zygotes was not significantly different between the slow freezing(12.8%) and vitrification(5.9%). These results indicated that the rabbit frozen zygotes could he successfully developed in vitro to hatched blastocysts, though their developmental rate was very low, compared with morula stage embryos, in either vitrification or slow freezing procedure under the present conditions.

Large scale production of cloned embryos requires the technology of multiple generational nuclear transfer(NT) by using NT embryos itself as the subsequent donor nuclei. In this work we investigated comparatively the effects of enucleated oocytes treated with ionomycin and 6-DMAP on the electrofusion rate and in vitro developmental potential in the first and second NT embryos. The embryos of 16-cell stage were collected from the mated does by flushing oviducts with Dulbecco's phosphate buffered saline(D-PBS) containing 10% fetal calf serum(FCS) at 47 hours after hCG injection. The recipient cytoplasms were obtained by removing the nucleus and the first polar body from the oocytes collected at 15 hours after hCG injection. The enucleated oocytes were pre-activated by 5 min incubation in 5M ionomycin and 2 hours incubation in 2 mM 6-DMAP at 19~20 hours post-hCG before microinjection. In the first and second generation NT, the unsynchronized 16-cell stage embryos were used as nuclear donor. The separated donor blastomeres were injected into the enucleated activated recipient oocytes by micromanipulation and were electrofused by electrical stimulation of single pulse for 60 sec at 1.25kV/cm in +, + - free 0.28 M mannitol solution. In the non-preactivation group, the electrofusion and electrical stimulation was given 3 pulses for 60 sec at 1.25 kV/cm in 100M +, + 0.28 M mannitol solution. The fused oocytes were co-cultured with a monolayer of rabbit oviductal epithelial cells in TCM-199 solution containing 10% FCS for 120 hours at 39 in a 5% incubator. The results obtained were summarized as follows: 1. In the first generational NT embryos, the electrofusion rate of preactivated and non-activated oocytes(80.4 and 87.8%) was not significantly different, but in the second generational NT embryos, the electrofusion rate was significantly(P<0.05) higher in the non-activated oocytes(85.7%) than in the preactivated oocytes(70.1%). 2) In the first and second generational NT embryos, the developmental potential to biastocyst stage was significantly(P<0.05) higher in the preactivated oocytes(39.3 and35.7%) than in the non-preactivated oocytes(16.0 and 13.3%). No significant difference in the developmental potential was shown between the first and second generational NT embryos derived from the preactivated oocytes. In conclusion, it may be efficient to use the oocytes preactivated with ionomycin and 6-DMAP for the multiple production of cloned embryos by recycling nuclear transfer.

The influence of cryopreservation of donor embryos on the in vitro developmental potential in the nuclear transplant rabbit embryos was evaluated. The embryos of 16-cell stage were collected and cryopreserved with EFS solution by vitrification method. The frozen embryos were thawed and synchronized to S and G phase of 32-cell stage. The recipient/ cytoplasms were obtained by removing the first polar body and chromosome mass from the oocytes collected by non-disruptive microsurgery procedure. The separated S and G phase blastomeres of 32-cell stage were injected into enucleated recipient cytoplasms by micromanipulation. After culture until 20 hrs post-hCG injection, the nuclear transplant oocytes were electrofused and activated by electrical stimulation. The fused nuclear transplant embryos were co-cultured with rabbit oviduct epithelial cells. After in vitro culture for 120 hrs, the nuclear transplant embryos developed to blastocyst stage were stained with Hoechst 33342 dye and their blastomeres were counted. The electrofusion rate was significantly (P<0.05) reduced in the frozen nuclear donor,compared with fresh donor nuclei as 80.0 vs 62.8% in S phase and 81.7 vs 64.8% in Gphase, respectivley. The in vitro developmental rate to blastocyst stage with the S and Gphase of fresh embryos(26.3 and 61.1%, respectively) was found significantly (P<0.05) higher, compared to the S and G]phase of frozen embryos(11.9 and 34.6%, respectively). When frozen as well as fresh donor embryos were synchronized to G phase, the in vitro developmental rate to blastocyst stage was significantly (P<0.05) higher, compared with S phase donor nuclei. The cell counts of nuclear transplant embryos developed to blastosyst stage were significantly (P<0.05) more in G phase of fresh or frozen embryos (180.1 and 125.7 cells, respectively), compared with S phase nuclear donor (145.1 and 103.7 cells, respectively). From the above results it was concluded that the rabbit embryos cryo- preserved by vitrification might be available as nuclear donor, though the developmentalpotential and cell counts of nuclear transplant rabbit embryos were decreased significantly.

The present study was conducted to investigate the influence of embryo cell stage at 18h post-fusion and oocyte preactivation on sebsequent in vitro developmental potential in the nuclear transplant rabbit embryos. The embryos of 16-cell stage were collected and synchronized to G phase of 32-cell stage. The recipient cytoplasms were obtained by removing the first polar body and chromosome rnass from the oocytes collected by non-dis-ruptive microsurgery procedure. The separated G phase blastomeres of 32-cell stage were injected into non-preactivated recipient cytoplasms. Otherwise, the enucleated recipient cytoplasms were preactivated by electrical stimulation at 18h post-hCG injection and the separated G phase blastomeres of 32-cell stage were injected. Mter culture until 20h post-hOG injection, the nuclear transplant oocytes were electrofused by electrical stimulation. The fused nuclear transplant embryos were classified into 3~4-cell, 2-cell and 1-cell stage at 18 hrs post-fusion and cultured until the embryos reached blastocyst stage. The developmental rate to blastocyst stage was significantly (P <0.05) higher in all the reconstituted embryos of 3~4-cell stage(58.0%) than in 2 and icell stage. The developmental rate to blastocyst stage in the embryos of 3~4-cell stage at 18 hrs post-fusion was significantly (P<0.05) higher in the reconstituted without oocyte preactivation(77.8%) than in the oocyte-preactivated embryos (33.3%). These results indicated that the higher rate of in the in vitro development to blastocyst stage might be obtained form the embryos which were reconstituted with nuclear donor of G phase and non-preactivated oocyte, and developed more rapidly for 18 hrs post-fusion.

The present experirnents on cryopreservation were carried out to investigate effect of solution toxicity, equilibration time and cell stages on the post-thaw survival of mouse morulae and blastocyst embryos cryopreserved by vitrification in EFS solution. The mouse embryos were exposed to the EFS solution in one step at room temperature, kept in the EFS solution during different period for toxicity test, vitrified in liquid nitrogen and thawed rapidly. After the mouse morulae embryos were exposed to EFS solution for 2 and 5 ruin. at room temperature and then they were washed in 0.5 M sucrose solution and basal mediurn(D-PBS + 10% FCS), they were cultured to examined cryoprotectant toxicity induced injury during exposure, most of embryos developed to expanded blastocysts(100 and 90.0%). However, when the exposure time was extended to 10 and 20 min, these development rates dropped dramatically in 10 ruin. (75.0%) and 20 ruin. (4.5%), respectively. When the compacted morulae were vitrified in EFS solution after equilibration for 2 and 5 min, the embryos have developed to normal blastocyst following thawing, washing and culture processes was 89.3 and 89.6%. However, when the exposure time was expanded to 10 ruin, this survival rate dropped to 68.8%. When the blastocyst were vitrified in EFS solution after equilibration for 2, 5 and 10 minutes, the survival rate of embryos which developed to normal blastocyst following thawing and culture processing were 58.5, 46.7 and 22.4%, respectively. The optimal time of equilibration of mouse morula and blastocysts in EFS solution seemed o be 2 and 5 ruin.

This experiment was carried out to produce cloned aniraals by nuclear transplantation in rabbits. The ovulated oocytes were collected from the oviducts between 14 and 15 hours after hGG injection. The denuded oocytes were used as nuclear recipient cytoplasm following enucleation by micromanipulation. The blastomeres separated from the 8-cell embryos were used as nuclear donor. The nucleated oocytes receiving a blastomere in the perivitelline space were electrically fused in the 0.28 M mannitol solution at 1.5 kV /cm, 60sec for three times. The nuclear transplant embryos which were used and developed to 2- to 4-cell stage in vitro were transferred into the oviducts of synchronized recipient does. A total of 64 nuclear transplant embryos were transferred to 7 recipient does and produced three offspring(4.7%) from a foster mother 31 days after embryo transfer.

The suitable electric stimulation is essential for activation and fusion of oocytes before or after nuclear transplantation The present study was undertaken to determine the optirnal condition for the parthenogenetic activation of in vitro rnatured(IVM) bovine oocytes by electric stimulation. Different direct current(DC) electric voltage of 1.0, 1.5 and 2.0 kV/cm and pulse duration of 30, 60 and 120 sec were applied to the JVM nocytes in 0.3 M mannitol solution containing each 100 M CaCl and MgCl. IVM occytes at 24, 28 and 32 hours Post-maturation(hpm) were also electrically stimulated at 1.5 kV /cm, for 60 sec. The stimulated nocytes were then co-cultured in TCM-199 solution containing 10% fetal calf serum with bovine oviductal epithelial cells for 7~9 days in a 5% incubator at 39 ~ Their activation and in vitro development to morula and blastocyst were assessed under an inverted microscope. The higher activation rates 62.8 and 63.4% and in vitro de- velopment rates to morula and blastocyst 5.1 and 10.9% were shown in the oocytes stimulated at the voltage of 1.0 and 1.5 kV/cm than 2.0 kV/cm, respectively. No signifi- cantly(P<0.05) different activation rate was shown in JVM oocytes stimulated for 30, 60 and 120 sec, but developmental rates to morula and blastocyst was significantly(P<0.05) higher in the oocytes stimulated for 30 sec(6~3%) and 60 sec(10~0%) than 120 sec(0~ 0%). The aged oocytes at 28 and 30 hpm showed significantly(P<0.05) higher activation rates(72~7 and 79.7%) than the oocytes at 24 hpm(50~9%)~ Also, their developmental rates to morula and blastocyst were significantly(P<0.05) higher in the nocytes at 28(14.3%) and 32 hpm(15.9%) than 24 hpm(3.6%). From these results, it can be suggested that the optimal electric stimulation for IVM bovine occytes is a DC voltage between 1.0 and 1.5 kV/cm, pulse duration of 30 or 60 sec, and the optimal age of IVM oocytes for electric activation is at 32 hpm.

This experiment was investigated the effect of cell stage of embryos at 48 hours post-insemination On in vitro development of IVF embryos. The ovaries of Korean native cows or heifers were obtained from an abattoir and kept on 25 to 28 and transported to laboratorty within 2 hrs. The oocytes were matured in vitro(IVM) for 24 hrs. in TGM-199 supplemented with 35 g/ FSH, 10 g/ LH, 1 g/ estradiol-17 and granulosa cells at 39 under 5% in air. They were fertilized in vitro(IVF) by epididymal spermatozoa treated with heparin for 24 hrs. , and then the zygotes were co-cultured in vitro(IVC) with bovine oviductal epithelial cells for 7 to 9 days. At 48 hrs. post-insemination, the embryos were classfied into 5 to 8-cell, 3 to 4-cell or 2-cell stage and then were co-cultured in vitro(IVC) with bovine oviductal epithelial cells until the embyos reached blastocyst stage. Embryos developed to blastocyst stage were stained with Hoechst 33342 for cell counting. The embryos of 5 to 8-cell stage at 48 hrs. post-insemination with grade I oocytes were significantly (P<0.05) better developed to blastocysts(63.0%) than 3 to 4-cell(42.0%) and 2-cell stage(2.7%) embryos which delayed in the early cleavage, and those embryos cleaved faster in the very early stage seemed to develop to blastocysts earlier. These results indicate that the embryos cleaved faster at 48 hrs. post-insemination seemed to develop to blastocysts earlier.

The present experiments on cryopreservation were designed to examine the effects of solution toxicity, equilibration time and cell stages on the post-thaw survival of bovine IVF embryos. The oocytes were matured in vitro(IVM) for 24 hrs. in TCM-199 supplemented with 35 g /ml FSH, 10 g /ml LH, 1 g /ml estradiol-17 and granulosa cells at 39 under 5% in air. They were fertilized in vitro(IVF) by epididymal spermatozoa treated with heparin for 24 hrs., and then the zygotes were co-cultured in vitro(IVC) with bovine oviductal epithelial cells for 7 to 9 days. The bovine IVF embryos were exposed to the EFS solution in one step at room temperature, kept in the EFS solution during different period for toxicity test, vitrified in liquid nitrogen, and thawed rapidly. 1. after the bovine blastocysts were exposed to EFS solution for 2 min. at room temperature and then they were washed in 0.5 M sucrose solution and TCM-199, they were cultured to examined cryoprotectant induced injury during exposure, Most of the embryos(95.0%) developed to reexpanded blastocoels. However, when the exposure time was extended to 5 and 10 min, these development rates dropped dramatically in 5 min. (69.5%) and 10 min. (47.4%), respectively, 2. When the bovine IVF embryos were vitrified in EFS solution after the equilibration for 1 and 2 min. exposure, The embryos to have reexpanded blastocoels following thawing, washing and culture processes were found to he 82.6 and 73.9%, respectively. However, when the exposure time was extended to 3 min, this survival rate dropped to 18.2%. The optimal time for equilibration of bovine IVF blastocysts in EFS solution seemed to he 1~2 min. 3. When the bovine IVF embryos were equilibrated for 1 min. the significantly (P<0. 05) higher post-thaw survival rates were obtained from the embryos of blastocyst stage(81.3%) than morulae stage(5. 1%). The optimal cell stage for viterification with EFS solution proven to he blastocyst stage in bovine IVF embryos. 4. The number of blastomeres of blastocyst stage was examined with nuclear staining with Hoechst 33342 during 7 to 9 days post-insemination. The cell counts of frozen bovine IVF embryos were found significantly(P7.5 and those of the fresh embryos 76.67. 1, which were cultured in the sarne period and conditions as frozen embryos.

This experiment was investigated the effect of presence of granulosa cells from follicles of different size on bovine oocyte maturation, cleavage and development to late stage. The nuclear and cytoplasmic maturation of oocytes in the IVM-IVF system are critical for subsequent embryo development. Granulosa cells when the co-cultured with oocytes may interact with cumulus-oocytes complexes and influence the development competence of the oocytes. Granulosa cells from medium (2~6 mm) and large(>1O mm) size follicles were recovered by aspiration, washed 3 times by centrifugation at 500 x g for 5 min. and used for co-culture at a concentration of 2~3 x 106 cells/mi. The oocytes were matured in vitro (IVM) for 24 hrs. in TCM-199 supplemented with 35 g/ml FSH, 10 g/ml LH, 1 g/ml estradiol-17 and granulosa cells at 39 under 5% in air. They were fertilized in vitro (IVF) by epididymal spermatozoa treated with heparin for 24 hrs., and then the zygotes were co-cultured in vitro (I VC) with bovine oviductal epithelial cells for 7 to 9 days. The assessment of maturation revealed that Grade J oocytes showed significantly(P

The post-thaw survival of mouse embryos of the various developmental stages was determined after cryopreservation by vitrification in a solution containing ethylene glycol, Ficoll and sucrose (EFS). All the embryos were equilibrated for 2 minutes just prior to freezing. The number of blastomeres during in vitro development was counted by nuclei higher rates of post-thaw survival were obtained from the embryos of 2-cell(92.2%), 8-cell(77.2%) or morula stage(90.0%) than those of blastocyst stage(62.7%). The number of blastomeres per embryo following in vitro culture for 24 hours was significantly(P<0.05) smaller as 66.0f22.3 in vitrified and thawed morulae than fresh morulae(91.712.2).

The nudear changes of bovine oocytes during 24 hrs. of culture for mejotic maturation were examined. Bovine oocytes were collected from small(<2 mm), medium(2~6 mm) and large(>6mm) follicles and classified into three grades by their morphological characteristics. A total of 242 oocytes collected were obtained:from 184 small, 157 medium and 1 large follicles, respectively and were classified into 95 grade I, 155 grade H and 92 grade III oocytes. All the bovine oocytes collected and graded were washed with a basal medium and incubated in groups of 10 for 24 hrs in 5% and 39. The basal medium used was composed of TCM-199 supplemented with sodium bicarbonate, sodium pyruvate, streptomycin, penicillin G and 10% FCS. The oocytes were cultured in drops of 50,l basal medium supplemented with 35g /ml FSH, 10g /ml LH and 1g /ml estradiol-17. The oocytes were fixed and examined on their chromosomal status by 1% acetorcein staining in the interval of 3 hrs. Most of the grade I oocytes developed to germinal vesicule stage at 0 to 3 hrs., germinal vesicle breakdown at 6 hrs., metaphase I at 9 to 15 hrs., anaphase I and telophase I at 18 hrs., and metaphase II and the first polar body at 24 hrs. after culture for meiotic maturation. However, it was found that compared to grade I oocytes, grade H and W oocytes reached earlier to germinal vesicle breakdown and most of them developed earlier to M II stage at 21 hrs. after culture.