Discovery Could Help Humans Regrow Limbs

(March 17) -- Humans could one day regrow limbs, much like flatworms, sponges and newts, simply by flicking the off switch on a single gene.

Researchers at the Wistar Institute in Philadelphia have pinpointed p21 as the gene that prevents most species from regenerating tissue, bone, organs and body parts.

When most creatures -- humans included -- suffer a wound, their bodies heal by producing scar tissue. Regenerative organisms, like newts, respond by creating a blastema: a clump of undifferentiated cells that can create diverse body parts, including muscle, tissue and bone.

The Wistar team, whose findings are published in this week's Proceedings of the National Academy of Sciences, tested their p21 theory on mice with damaged ears.

When p21 was turned off, the mice started producing blastema to regrow the ear, rather than creating scar tissue, which would simply repair the damage.

"Much like a newt that has lost a limb, these mice will replace missing or damaged tissue with healthy tissue that lacks any sign of scarring," lead researcher Ellen Heber-Katz said in a statement.

Of course, studies in mice don't necessarily translate successfully to humans. But Heber-Katz expressed optimism about the initial discovery.

"While we are just beginning to understand the repercussions of these findings, perhaps one day we'll be able to accelerate healing in humans by temporarily inactivating the p21 gene," she said.

But p21 does have a logical function: By preventing damaged DNA from replicating, it helps ward off the uncontrolled cell replication that's a hallmark of cancer. It's also linked to another gene, p53, that plays a role in almost every type of the disease.

If the science were to be applied to humans, researchers would need to use carefully localized, and short-term, genetic therapy to prevent side effects.

The idea of regeneration in humans is rapidly becoming a realistic possibility. DARPA, the military's advanced research agency, has been funding ambitious tissue regeneration projects for nearly a decade.

Already, DARPA-funded researchers have created blastemas out of adult human cells. The next step is turning those clumps into new body parts, and flicking off p21 might make the process much easier.