Nuclear Transplantation and Cloning in Mammals

Nuclear transplantation has been used for many years as an investigative tool with which to study the interactions between the nucleus and cytoplasm in early embryos and with which to characterize the developmental potency of embryonic and adult cell nuclei. As reviewed in a recent book on the subject by Professor Marie DiBerardino (1 ), nuclear transplantation has been accomplished in a variety of organisms, both unicellular and multicellular, and both vertebrate and invertebrate. Nuclear transplantations were first accomplished in mammals during the early 1980s, using techniques developed originally by James McGrath and Davor Solter in studies using laboratory mice (2 ). That methodology has since been used to improve our understanding of many interesting aspects of mammalian biology, including genomic imprinting, postfertili- zation epigenetic modifications of the parental chromosomes, embryonic genome activation, and nuclear reprogramming. The majority of these studies have involved nuclear transplantations into enucleated fertilized one-cell-stage recipients. Cloning in mice has not been possible using one-cell-stage embryos as recipients, but some studies have employed oocytes or two-cell-stage embryos as recipients to produce live offspring (e.g., 3-6). With oocyte recipients, the greatest success has been achieved using serial transplantation protocols.