If a salamander loses its leg, it can grow a new one. Humans and other mammals are not so fortunate, but we can regenerate the tips of our digits, as long as enough of the nail remains. This was first shown some 40 years ago; today researchers finally reveal why it is that nails are necessary. Working with mice, researchers led by Mayumi Ito at New York University have identified a population of stem cells lying beneath the base of the nail that can orchestrate the restoration of a partially amputated digit. However, the cells can do so only if sufficient nail epithelium — the tissue that lies immediately below the nail — remains. The results are published on Nature's website today1.
The process is limited compared with the regenerative powers of amphibians, but the two share many features, from the molecules that are involved to the fact that nerves are necessary. “I was amazed by the similarities,” says Ito. “It suggests that we partly retain the regeneration mechanisms that operate in amphibians.” By labelling groups of nail cells so that all the daughter cells they produced were blue, Ito, together with Makoto Takeo and others, showed that the nail base contains a small population of self-renewing stem cells, which sustain the nail’s continuous growth. This ongoing growth depends on signals carried by the Wnt family of proteins — if this signalling pathway is disrupted, mouse nails cannot form.