Generation of healthy cloned mice using enucleated cryopreserved oocytes.

The successful generation of cloned animals and the establishment of embryonic stem (ES) cell lines from somatic cells suggest that these techniques may be used in human regenerative medicine. However, the fact that oocytes must be donated by women undergoing infertility treatment remains a fundamental ethical objection, as they might be concerned about the potential exploitation of their genome. Here, we investigated the reprogramming potential of enucleated and cryopreserved oocytes for the development of full-term cloned mice. BDF1 strain mouse oocytes were cryopreserved at metaphase II, before and after enucleation. After thawing, cumulus cell nuclei were microinjected to generate clones. Although the rate of development of cloned embryos to the blastocyst stage using the treated oocytes was lower than that obtained using fresh oocytes, three live pups were delivered after embryo transfer into pseudopregnant females (0.4% of the oocytes used). Thus, although cryopreservation reduces the potential of oocytes, these cells retain the ability to support the full-term development of cloned embryos. In addition, the removal of DNA from human oocytes may alleviate the ethical and psychological problems for women who are undergoing infertility treatment and are considering oocyte donation for research or therapeutic purposes.