Effect of Oocyte Age on Electrofusion and In Vitro Development of Nuclear Transplant Embryos in Rabbits

토끼에서 난자의 성숙도가 전기융합 및 핵이식 수정란의 체외발달에 미치는 영향

The long term goal of this research is to develop an efficient procedure for large scale production of genetically identical or cloned animals. To improve nuclear transpalntation efficiency in the rabbit, this study evaluated the age of nuclear recipient oocytes on the different steps of nuclear transplantation. The ovulated oocytes in different ages were collected from the superovulated does by flushing oviducts with Dulbecco's phosphate buffered saline(D-PBS) supplemented with 10% fetal calf serum(FCS) from 13 to 15, 17 to 20 and 23 to 26 hours after hCG 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 enucleated oocytes receiving a blastomere in the perivitteline space were fused in the 0.28 M mannitol solution at 1.5 kV/cm, 60 sec for three times. The fused oocytes were co-cultured with the monolayered rabbit oviductal epithelial cells in TGM-199 solution with 10% FCS for 72 hours at 37$^{\circ}C$ in a 5% $CO_2$ incubator. The cultured nuclear transplant embryos and in vivo developed embryos collected at 72 hours after hCG injection were stained with Hoechst 33342 dye. Their cell numbers were counted under a fluorescent microscope. The results obtained were summarized as follows ; 1. The aged oocytes(20 hrs. post hCG) showed significantly(P<0.05) higher fusionrates(70 ~ 90%) than the recently ovulated oocytes(30.8%) 2. The aged oocytes which were electrically activated and fused at 20 hours developed to blastocyst at significantly(P<0.05) high rate, while none of the recently ovulated oocytes developed to blastocyst. 3. Even though the aged oocytes at 23~26 hours showed higher fusion rate(85.7%), not only they were inadequate to manipulate but also their developmental potential to blastocyst was highly impaired. 4. The developmental potential in vitro of nuclear transplant embryos was significantly retarded than in vivo deveolped embryos.