Preimplantation and postimplantation development of rat embryos cloned with cumulus cells and fibroblasts.

In this report we demonstrate the successful in vitro culture of fertilised embryos from 1-cell to blastocyst stage, albeit in a strain-dependent fashion. We report procedures for the enucleation of rat oocytes; nuclear transfer by injection of nuclei (NT) from adult rat cumulus cells, rat primary embryonic fibroblasts and genetically modified rat fibroblasts; and activation resulting in advanced preimplantation development. Blastocyst stage rat embryos were obtained after in vitro culture of nuclear transfer zygotes at similar frequencies with each of these nuclear donor cell types. Transfer of NT embryos to surrogate mothers leads to implantation of 24% of the zygotes. These results suggest that the nuclei of cultured rat cells, even following genetic modification, can be reprogrammed to support early embryonic development, which is a prerequisite to cloning the rat.