Abstract
Follicular oocytes of Grade I and II were collected from 2~6 mm ovarian follicles and matured in vitro (IVM) for 24 hrs in TCM-199 su, pp.emented with 35$\mu\textrm{g}$/ml FSH, 10$\mu\textrm{g}$/ml LH, and 1$\mu\textrm{g}$/ml estradiol-17$\beta$ at 39$^{\circ}C$ under 5% CO2 in air. They were fretilized in vitro (IVF) by epididymal spermatozoa capacitated with heparin for 12 hrs. The zygotes were then co-cultured in vitro with bovine oviducted epithelial cells (BOEC) for 7 to 9 days. The optimal time for IVM, the successful enucleation of IVM oocytes by micromanipulation at different oocyte ages after IVM, and the ideal culture system for IVM for effective IVF and in vitro development of IVM-IVF embryos was examined for in vitro production of nuclear recipient oocytes and nuclear donor embryos. To improve the efficiency of nuclear transplantation (NT) of IVF embryo into IVM follicular oocytes, this study evaluated the optimal electric condition and oocytes age for activation of IVM oocytes and in vitro development of NT embryos. In vitro development of NT embryos with preactivation or non-preactivation in enucleation oocytes, cell number of IVN-IVF embryos, and NT embryos wre also examined. The results obtained were as follows; 1. The most suitable enucleation time was at 24 hpm (83.3%) rather than that of 28 hpm(69.6%) and 32 hpm(50.0%). 2. There was no difference among the fusion rates of NT embryos at the voltages of 0.75, 1.0 and 1.5 kV/cm, but the in vitro development rates to morule and blastocyst were significantly (P<0.05) higher at the voltage of 0.75(12.5%) and 1.0kV/cm (12.6%) compared to 1.5kV/cm(0%). 3. No significant difference in activation rates were seen in NT embryos stimulated for 30, 60 and 120 $\mu$sec (71.7, 85.2 and 71.9%, respectively), but the in vitro development rates to morulae and blastocyst were significantly (P<0.05) higher in the oocytes stimulated for 30 $\mu$sec (11.6%) and 60 $\mu$sec(10.7%) than 120 $\mu$sec(0.0%). 4. The fusion rates (71.0 and 87.3%) and the in vitro development rates (9.1 and 12.7%) to morula and blastocyst were seen in the NT embryos stimulated at 28 and 32 hpm under the condition of 1.0 kV/ml, 60 $\mu$sec. However, at 24 hpm the fusion rates were 64.8% and the in vitro development to morula and blastocyst were not seen. 5. The fusion rates between the 8~12, 13~17 and 18~22-cell stage of IVM-IVF embryos were not significantly different. The in vitro development rates of the fused embryos to morula and blastocyst which were received from a blastomere of 8~12, 13~17 and 18~22-cell stages of IVM-IVF embryos were 14.9, 8.3 and 6.5%, respectively. 6. The in vitro development rate of the enucleated recipient oocytes with preactivation (24.2%) to morula and blastocyst was significantly (P<0.05) higher than that of non-preactivation (12.8%). 7. The cell numbers of NT blastocyst and IVM-IVF blastocyst cultured during 7~9 days were 63$\pm$11 and 119$\pm$23, and then their the mean cell cycle number were 5.98 and 6.89, respectively.
