Generation of fertile and diploid fish, medaka (Oryzias latipes), from nuclear transplantation of blastula and four-somite-stage embryonic cells into nonenucleated unfertilized eggs

In two experimental series of transplantation of embryonic cell nuclei into nonenucleated unfertilized eggs in medaka (Oryzias latipes), fertile and diploid nuclear transplants were successfully generated. In the first experiment, nuclei from blastula cells of a medaka stock with the wild-type body color were transplanted into 1722 eggs from the orange-red variety. Of 26 adult nuclear transplants with the wild-type body color, 22 were, as expected, triploid and sterile, but the other four were fertile. Three of the four were diploid, and the last one was tetraploid. They transmitted the wild-type body color to the F1 and F2 progenies in a Mendelian fashion. In the second experiment, cell nuclei from four-somite-stage embryos of the orangered variety carrying the green fluorescent protein (GFP) transgene were transplanted into 1688 recipients of the same strain. Three adult nuclear transplants expressing GFP were obtained. Two of them were triploid and sterile, but the remaining one was fertile and diploid. The transgene of the donor nuclei was transmitted to the F(1) and F(2) offspring in a Mendelian fashion. These observations that diploid and fertile nuclear transplants could be obtained without enucleation of the recipient eggs may have important implications for future nuclear transplantation in medaka.