Transplantation of blastula nuclei to non-enucleated eggs in the medaka, Oryzias latipes

Studies of nuclear transplantation were conducted to establish methods for the production of clones of fish, using a small laboratory fish, medaka, Or yzias latipes. As the first step of the study, single-blastula nuclei of an inbred strain with the wild-type body color were transplanted into non-enu cleated unfertilized eggs of an outbred orange-red strain. Of 845 operated eggs, 45 hatched into fry exhibiting the wild-type body color, one of the d onor markers. Twenty-seven of these nuclear transplants grew to the adult s tage and clearly exhibited external secondary sexual characteristics. Fourt een were females and 13 were males. The allozyme analysis of phosphoglucomu tase, measurements of relative DNA content by microfluorometry and chromoso me counts consistently indicated that the nuclear transplants were triploid s that originated from both the diploid donor nuclei and the haploid recipi ent pronuclei. In the crossing experiments between the nuclear transplants and the orange-red strain, most of the male nuclear transplants were steril e, whereas one male produced a viable offspring with wild-type body color. All of the female nuclear transplants were sterile. Macroscopic observation s of their gonads showed that the testes appeared normal and the ovaries ap peared degenerated. These features of the reproductive potential and the mo rphology of gonads also indicated that the nuclear transplants were triploi ds. These results demonstrated that a basic technique for nuclear transplan tation in medaka was established.