The ability to grow a new limb may seem like something straight out of science fiction, but new research shows exactly how animals like salamanders and zebrafish perform this stunning feat—and how humans may share the biological machinery that lets them do it. Scientists have long known of the regenerative powers of some species of fish and amphibians: To recreate a limb or fin lost to a hungry predator, they can regrow everything from bone to muscle to blood vessels with stem cells that form at the site of the injury. But just how they do it at the genetic level is a mystery. To figure out what might be happening, scientists amputated the appendages of two ray-finned fish—zebrafish and bichir—and a salamander known as the axolotl, all of which can regrow their legs and fins. They then compared RNA from the site of the amputation. They found 10 microRNAs—small pieces of RNA that regulate gene expression—that were the same in all three species. What’s more, they seemed to function in the same way, despite the structural difference between the axolotl (pictured above) and the fishes. The finding supports an existing idea that the three master limb-replacers last shared a common ancestor about 420 million years ago, and it suggests that the evolutionary process of growing limbs is saved over time, not developed independently in separate species, the researchers report today in PLOS ONE. What does this mean for humans? If these microRNAs can be programmed to work like they do in salamanders and fish, humans could enhance their ability to heal from serious injuries. But don’t expect to get Wolverine-like powers just yet—scientists say such modifications are still a long way off.
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