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Scientists used to believe that a differentiated cell could never return to a less mature state, much less revert into an embryonic state. Yet, nuclear transfer experiments in animals have shown that the nucleus of a differentiated adult cell can be reprogrammed by the egg into which it is inserted, creating an early embryo containing embryonic stem cells. However, the creation of a human embryo by this technique has not been accomplished and would raise ethical issues for some.
Several research groups now report that they have transformed fibroblasts from the skin of adult mice into cells with all the qualities and potential of embryonic stem cells. Investigators used viral vectors to insert four genes into the fibroblasts. The genes reprog…