PMC:521203 / 958-3282
Annnotations
{"target":"http://pubannotation.org/docs/sourcedb/PMC/sourceid/521203","sourcedb":"PMC","sourceid":"521203","source_url":"https://www.ncbi.nlm.nih.gov/pmc/521203","text":"Introduction\nSomatic cell cloning (cloning or nuclear transfer) is a technique in which the nucleus (DNA) of a somatic cell is transferred into an enucleated metaphase-II oocyte for the generation of a new individual, genetically identical to the somatic cell donor (Figure 1). The success of cloning an entire animal, Dolly, from a differentiated adult mammary epithelial cell [1] has created a revolution in science. It demonstrated that genes inactivated during tissue differentiation can be completely re-activated by a process called nuclear reprogramming: the reversion of a differentiated nucleus back to a totipotent status. Somatic cloning may be used to generate multiple copies of genetically elite farm animals, to produce transgenic animals for pharmaceutical protein production or xeno-transplantation [2-5], or to preserve endangered species. With optimization, it also promises enormous biomedical potential for therapeutic cloning and allo-transplantation [6]. In addition to its practical applications, cloning has become an essential tool for studying gene function [7], genomic imprinting [8], genomic re-programming [9-12], regulation of development, genetic diseases, and gene therapy, as well as many other topics.\nFigure 1 Schematic diagram of the somatic cloning process. Cells are collected from donor (a) and cultured in vitro (b). A matured oocyte (c) is then enucleated (d) and a donor cell is transferred into the enucleated oocyte (e). The somatic cell and the oocyte is then fused (f) and the embryos is allowed to develop to a blastocyst in vitro (g). The blastocyst can then be transferred to a recipient (h) and cloned animals are born after completion of gestation (i). One of the most difficult challenges faced, however, is cloning's low efficiency and high incidence of developmental abnormalities [13-19]. Currently, the efficiency for nuclear transfer is between 0–10%, i.e., 0–10 live births after transfer of 100 cloned embryos. Developmental defects, including abnormalities in cloned fetuses and placentas, in addition to high rates of pregnancy loss and neonatal death have been encountered by every research team studying somatic cloning. It has been proposed that low cloning efficiency may be largely attributed to the incomplete reprogramming of epigenetic signals [20-23].","divisions":[{"label":"title","span":{"begin":0,"end":12}},{"label":"p","span":{"begin":13,"end":1237}},{"label":"figure","span":{"begin":1238,"end":1706}},{"label":"label","span":{"begin":1238,"end":1246}},{"label":"caption","span":{"begin":1248,"end":1706}},{"label":"p","span":{"begin":1248,"end":1706}}],"tracks":[]}