Bovine oocyte cytoplasm supports development of embryos produced by nuclear transfer of somatic cell nuclei from various mammalian species

The transfer of nuclei from one cell to another provides a powerful tool fo r studying the interactions between the cytoplasm of one cell and the nucle us of another. This study was designed to examine the ability of the bovine metaphase oocyte cytoplasm to support mitotic cell cycles under the direct ion of differentiated somatic cell nuclei of various mammalian species. Ski n fibroblast cells from cows, sheep, pigs, monkeys, and rats were used as s ources of donor nuclei. Nuclear transfer units produced by fusion of enucle ated bovine oocytes and individual fibroblasts from all species examined un derwent transition to interphase accompanied by nuclear swelling, further p rogression through the cell cycle, and completion of the first mitosis. Reg ardless of the species of donor fibroblasts used, some cleaving units progr essed further and developed to advanced stages, as evidenced by continuatio n of cell proliferation and formation of a blastocoele cavity at the time a ppropriate for the donor fibroblast species. Although no pregnancies have b een carried to term after transfer of embryos into surrogate animals, these observations suggest that mechanisms regulating early embryonic developmen t may be conserved among mammalian species and that bovine oocyte cytoplasm can support the introduced differentiated nucleus regardless of chromosome number, species, or age of the donor fibroblast.