The lamb derived recently (WILMUT et al.: Nature, February 27, 1997) from an embryo which had been cloned using adult somatic cell as nuclear donor, can revolutionize our knowledge in developmental biology. Dolly, the first mammal cloned from the tissue of a grown-up animal, proves that even the genome of highly differentiated somatic cells does not undergo irreversible modifications and retain the capability for nuclear reprogramming. Obtaining identical copies from adult animals would facilitate the exploitation of genetic potential achieved by conventional breeding. In addition to that, nuclear transfer can provide novel approaches for the genetic manipulation of mammals. However, serious ethical concern has been raised over the possibility and desirability of cloning human beings. This review article summarizes the history, current status and perspectives of cloning mammals, indicating the advantages and limitations of the different methods available today. The simplest way to clone a mammal used routinely for about 15 years is the splitting of embryos in morula stage. This method is easy to perform under practical conditions with acceptable efficacy but - due early differentiation of embryonic cells - the number of identical twins obtained by splitting is very limited. Nuclear transfer (Fig. 1) is based on the finding that nuclei from totipotent cells taken from early embryos and transferred into enucleated oocytes are able to be reprogrammed and start their development from the beginning. So far, viable offspring has been born only if the transferred nucleus derived from early stage embryos the cells of which were not yet differentiated. Although this cloning procedure resulted in several pregnancies in the last decade, its success rate is rather low and the newborn animals have an increased chance for developmental abnormalities. Now, the successful experiment of WILMUT et al. (Fig. 2) using quiescent cells from a grown-up animal confirms that - at least in sheep and probably in cattle - obtaining identical copies from adult mammals is possible. At this moment it is not clear, whether or not this method can be used in species other than the sheep.
|Translated title of the contribution||Cloning: Blessed or damned?|
|Number of pages||6|
|Journal||Magyar Allatorvosok Lapja|
|Publication status||Published - Dec 1 1997|
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