Aspects of somatic cloning in mammalian species: achievements, opportunities, and obstacles (review)

He analysis on a somatic cloning productivity in different animal species is submitted. The data are summarized on molecular and genetic events involved in cloning and cell reprogramming, chimerism on mitochondrial DNA under intra- and interspecific cloning. The essential problems connected with methodical difficulties, low efficiency, and big losses during embryonic, pre- and postnatal development are in the focus. The somatic cloning is now mainly considered as an opportunity for rapid and durable fixation of the unique valuable traits of an individual, which can be lost due to recombination under normal reproduction or resulting from the threat of extinction. The method allows to combine different breeding and transgenic technologies, i.e. the targeted in vitro insertions, cell selection, and cell nuclear transfer. An agriculture is considered as the main area in which this approach should be used. But, despite of expected advantages and the increased number of successful cloning and clones, reported all over the world, a commercial use of the method in animal husbandry is strictly limited by the extremely low efficacy, high costs, and big losses of the initial material. At the same time, the specific molecular and cell mechanisms, involved in somatic cloning, should be further studied. That is why the more effective alternative approaches are forced to be sought, and the cloning technique must be improved. Nevertheless, despite the still low efficiency (3-5 %) and a lower use compared with forecasts, the cloned animals gradually become an integral part of agriculture in the U.S. and Europe. Somatic cloning is also prospective for fundamental genetics, particularly in studying genome expression, cell differentiation, etc. The ethic aspects of cloning in agriculture and medicine must be also discussed and estimated to prevent speculations both of opponents and supporters of the method.