Our Nails Hold The Stem Cell Key to Limb Regeneration, Scientists Say

It may be annoying to have to clip and clean the nails on our digits, but a new study highlights how exactly they give our precious extremities the ability to regenerate themselves, even from a partial amputation, 40 years after the phenomenon was first documented.

A study, published in the journal Nature, explains that there is a small group of stem cells just under the base of the nail that are responsible for nail growth. These stem cells can even help a finger or a toe regenerate itself - but only if there is enough nail epithelium, the tissue found underneath the nail, is left. If too much nail epithelium is missing, then the digit cannot regrow itself.

The mechanism through which this process occurs is similar, although not as advanced, as the ones found in creatures such as salamanders, which can grow a new leg despite having no nails.

"I was amazed by the similarities," says Mayumi Ito, leader of the research team that published the study. "It suggests that we partly retain the regeneration mechanisms that operate in amphibians."

The team tested their hypothesis on mice that had lost toe tips. The scientists found out that if enough of the nail epithelium was preserved, digits were restored in as little as five weeks. The Ito-led researchers then found the exact neurological pathways activated (a Wnt pathway activating a FGF2 protein that can regrow tendon, tissue, and bone), hoping the results could provide a springboard for advances into rebuilding human limbs.

"This is encouraging because the similarities give us hope that we will be able to induce human regeneration in the not-too-distant future," says molecular biologist Ken Muneoka from Tulane University in New Orleans.

Despite the optimism surrounding the study, however, some scientists aren't convinced that mammals and amphibians share the same restorative powers.

"Amphibians can regenerate a complete digit from any amputation level and they lack a nail organ altogether," said Ashley Seifert, a regeneration biologist at the University of Kentucky in Lexington.

He went on to say that humans and amphibians "independently evolved the ability to regenerate digit tips through a mechanism dependent on the nail organ".