Two research reports published Friday offer novel approaches to the age-old dream of regenerating the body from its own cells. 

Animals like newts and zebra fish can regenerate limbs, fins, even part of the heart. If only people could do the same, amputees might grow new limbs and stricken hearts be coaxed to repair themselves. 

But humans have very little regenerative capacity, probably because of an evolutionary trade-off: suppressing cell growth reduced the risk of cancer, enabling humans to live longer. A person can renew his liver to some extent, and regrow a fingertip while very young, but not much more. 

In the first of the two new approaches, a research group at Stanford University led by Helen M. Blau, Jason H. Pomerantz and Kostandin V. Pajcini has taken a possible first step toward unlocking the human ability to regenerate. By inactivating two genes that work to suppress tumors, they got mouse muscle cells to revert to a younger state, start dividing and help repair tissue. 

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