Previous studies of serial cloning in animals showed a decrease in efficiency over repeated iterations and a failure in all species after a few generations. This limitation led to the suggestion that repeated recloning might be inherently impossible because of the accumulation of lethal genetic or epigenetic abnormalities. However, we have now succeeded in carrying out repeated recloning in the mouse through a somatic cell nuclear transfer method that includes a histone deacetylase inhibitor. The cloning efficiency did not decrease over 25 generations, and, to date, we have obtained more than 500 viable offspring from a single original donor mouse. The reprogramming efficiency also did not increase over repeated rounds of nuclear transfer, and we did not see the accumulation of reprogramming errors or clone-specific abnormalities. Therefore, our results show that repeated iterative recloning is possible and suggest that, with adequately efficient techniques, it may be possible to reclone animals indefinitely.
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