| Research Abstract |
The present study was conducted to establish cloning techniques for genetic improvement and multiplication of animals. The following results were obtained : 1.Embryonic loss, retardation of development, decrease in size and subsequent regulation of development were demonstrated after transfer of mouse bisected embryos. A decrease in the number of embryonic cells at the morula stage affects trophoblast outgrowth, endoderm formation and development to the egg cylinder stage in vitro, 2.Offspring with coat color chimera were obtained after transfer of mouse aggregated embryos from 2-, 4- and 8-cell stage parthenogenetic embryos and 4-cell stage blastomeres, 3.Cytoplasm of unfertilized mature oocytes was demonstrated to have the ability of reprogramming the nuclei of mouse 2-to 8-cell embryos. Interaction between the nucleus and cytoplasm is required for reprogramming in the nuclear transferred embryos. The nucleus of the embryo at the early cell-cycle-stage should be transferred to cytoplasm of enucleated unfertilized mature oocyte, 4.Bovine oocytes derived from in vitro fertilization were successfully cultured to the blastocyst stage in chemically defined medium. Developmental rate of the nuclear transferred embryos to the blastocyst stage was improved when nuclear donor embryos were treated with nocodazole and recipient oocytes were treated with ethanol and cycloheximide. Offspring was obtained after transfer of bovine nuclear transferred embryos.
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