Why Fingertips Might Grow Back But Entire Limbs Won’t
If a salamander or newt loses its leg, it can just grow another one. Humans aren’t so lucky. If you cut off my arm, it won’t grow back. (Note: please don’t do that.)
But back in the 1970s, scientists showed that children can sometimes regrow the tip of an amputated finger, as long as there’s a bit of nail left over and the wound isn’t stitched up. Later, we discovered that mice have the same ability. But why is the nail important, and why can’t a finger grow back without it? A new study provides an answer to this longstanding mystery. As I wrote in Nature News:
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 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.”
You can find out more details about this process over at Nature. Meanwhile, you might also enjoy this long piece I posted a few months back, about whether we’ll ever regenerate limbs. It covers what happens in salamanders, why we can’t do the same, why these abilities have been so difficult for scientists to study, and whether we’ll ever be able to duplicate a salamander’s prowess to heal amputees. Here’s a taster:
Despite these hurdles, we know the basic steps that a regenerating limb must go through. After an amputation, cells from the outermost layer of skin climb over to seal the wound. At this point, humans would lay down lots of scar tissue, and that would be that. But in salamanders, the new cells transform into a structure called the wound epidermis, which sends chemical instructions to those below it. In response, nerves in the stump to start to grow again, while mature cells such as muscles and connective tissues revert to an immature mass called a blastema. This is what restores the limb. Regeneration is about taking a few steps back to take many steps forward.
“Somehow, the cells know their positions, and they’ll only regenerate what’s missing,” says Enrique Amaya, developmental biologist at the University of Manchester. If the limb is amputated at the shoulder or hip, the blastema creates the full leg. If it’s amputated at the wrist, the blastema makes just a hand and digits. As they grow and divide, the cells take up specific positions, so they know up from down, or left from right. They fashion a miniature version of the full limb, which eventually grows to full size.
The basic outline is there, but the details have been hard to fill. Why does the wound epidermis form, and what does it do to the cells beneath it? The limb won’t regenerate if the nerves inside don’t start growing, but what exactly do the nerves do? When cells in the stump rewind their fates to become a blastema, how far back to they go?
Go Further
Animals
- Soy, skim … spider. Are any of these technically milk?Soy, skim … spider. Are any of these technically milk?
- This pristine piece of the Amazon shows nature’s resilienceThis pristine piece of the Amazon shows nature’s resilience
- Octopuses have a lot of secrets. Can you guess 8 of them?
- Animals
- Feature
Octopuses have a lot of secrets. Can you guess 8 of them? - This biologist and her rescue dog help protect bears in the AndesThis biologist and her rescue dog help protect bears in the Andes
Environment
- This pristine piece of the Amazon shows nature’s resilienceThis pristine piece of the Amazon shows nature’s resilience
- Listen to 30 years of climate change transformed into haunting musicListen to 30 years of climate change transformed into haunting music
- This ancient society tried to stop El Niño—with child sacrificeThis ancient society tried to stop El Niño—with child sacrifice
- U.S. plans to clean its drinking water. What does that mean?U.S. plans to clean its drinking water. What does that mean?
- Food systems: supporting the triangle of food security, Video Story
- Paid Content
Food systems: supporting the triangle of food security
History & Culture
- Heard of Zoroastrianism? The religion still has fervent followersHeard of Zoroastrianism? The religion still has fervent followers
- Strange clues in a Maya temple reveal a fiery political dramaStrange clues in a Maya temple reveal a fiery political drama
- How technology is revealing secrets in these ancient scrollsHow technology is revealing secrets in these ancient scrolls
- Pilgrimages aren’t just spiritual anymore. They’re a workout.Pilgrimages aren’t just spiritual anymore. They’re a workout.
- This ancient society tried to stop El Niño—with child sacrificeThis ancient society tried to stop El Niño—with child sacrifice
Science
- Soy, skim … spider. Are any of these technically milk?Soy, skim … spider. Are any of these technically milk?
- Can aspirin help protect against colorectal cancers?Can aspirin help protect against colorectal cancers?
- The unexpected health benefits of Ozempic and MounjaroThe unexpected health benefits of Ozempic and Mounjaro
- Do you have an inner monologue? Here’s what it reveals about you.Do you have an inner monologue? Here’s what it reveals about you.
- Jupiter’s volcanic moon Io has been erupting for billions of yearsJupiter’s volcanic moon Io has been erupting for billions of years
Travel
- This chef is taking Indian cuisine in a bold new directionThis chef is taking Indian cuisine in a bold new direction
- On the path of Latin America's greatest wildlife migrationOn the path of Latin America's greatest wildlife migration
- Everything you need to know about Everglades National ParkEverything you need to know about Everglades National Park
- Spend a night at the museum at these 7 spots around the worldSpend a night at the museum at these 7 spots around the world