Cut off part of an amphibian, and it'll regrow. But humans and other mammals can only regrew the very tips of our fingers and toes, if they're cut off. But the mechanism that makes that small feat happen could be the key to unlocking the secret of full limb regeneration in humans.
How come we can regrow fingertips, but not fingers? Researchers looked at mice, and discovered that stem cells beneath the nail were crucial to digit regrowth in mice, acting as coordinating centers for the regenerative processes. And that, in turn, could mean that nail stem cells could provide the key to human limb regeneration.