Although you may not know it, mammals (even humans!) can regrow small portions of amputated digits like fingers and toes. This remarkable ability has perplexed scientists for some time, as they pondered whether it was due to the presence of already-existing adult stem cells in each of the various tissues that make up the end of a finger (blood vessels, bone, skin and tendons, for example), or if specialized cells near the site of injury were somehow able to regress developmentally and gain the capacity to become many different tissue types. As described in our release today:

[The researchers...] have shown that damage to a digit tip is repaired by specialized adult stem cells that spend their lives quietly nestled in each tissue type. Like master craftsmen, these cells spring into action at the first sign of damage, working independently yet side-by-side to regenerate bone, skin, tendon, vessels and nerves. But just as you wouldn’t ask a mason to wire your house, or an electrician to put on a new roof, the division of labor among these stem cells is strict. Each is responsible solely for its own tissue type. In contrast, the blastema theory invokes a new pluripotent cell type formed out of urgency from previously specialized cells. This jack-of-all-trades cell discards its former profession and instead jumps in to indiscriminately regenerate all the tissue types of the limb.

The work was performed by postdoctoral scholar Yuval Rinkevich, PhD, in the laboratory of Irving Weissman, MD. Weissman had this to say about the findings:

We’ve shown conclusively that what was thought to be a blastema is instead simply resident stem cells that are already committed to become specific tissue types. The controversy about limb regeneration in mammals should be over.

According to Weissman, the study is particularly important because, in the past, some scientists and national media reports have championed the idea that money allotted by the California Institute for Regenerative Medicine for stem cell studies would have been better funneled to blastema research.

Photo by Yuval Rinkevich