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Nuclear reprogramming requires the removal of epigenetic modifications imposed on the chromatin during cellular differentiation and division. The mammalian oocyte can reverse these alterations to a state of totipotency, allowing the production of viable cloned offspring from somatic cell nuclei. To determine whether nuclear reprogramming is complete in cloned animals, we assessed the telomerase activity and telomere length status in cloned embryos, fetuses, and newborn offspring derived from somatic cell nuclear transfer. In this report, we show that telomerase activity was significantly (P 0.05). These results demonstrate that cloned embryos inherit genomic modifications acquired during the donor nuclei's in vivo and in vitro period but are subsequently reversed during development of the cloned animal.
Betts et al. (Tue,) studied this question.