Planarians are tiny googly-eyed flatworms with an uncanny ability: They can regrow their entire bodies, even a new head. So how do they do it?

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Nelson Hall wants you to know that the googly-eyed flatworm he just sliced into four pieces is going to be OK.

Three of the flatworm’s four pieces have started to wriggle away from each other and its head is moving in circles under Hall’s microscope. “The head will just go off and do its own thing,” said Hall, a doctoral student of bioengineering at Stanford University.

But in three weeks, the head, as well as the other pieces, will each have grown into a complete flatworm just like the one Hall sliced up, dark brown and about a half-inch long.

Hall and researchers around the world are hard at work trying to understand how these flatworms, called planarians, use powerful stem cells to regenerate their entire bodies, an ability humans can only dream of.

Animals like starfish, salamanders and crabs can regrow a tail or a leg. Planarians, on the other hand, can regrow their entire bodies – even their heads, which only a few animals can do.

---What is the difference between healing and regeneration?
When we suffer a severe injury, the best we can hope for is that our wounds will heal. “Healing is more like closing the wound and cleaning debris. It’s too short of a process to have tissue replacement,” said Hall. “Regeneration is replacing the tissue that was lost.”

---What are pluripotent stem cells?
If planarians can regrow body parts, why can’t we? Key to planarians’ regenerative ability are powerful cells called pluripotent stem cells, which make up one-fifth of their bodies and can grow into every new body part. Humans only have pluripotent stem cells during the embryonic stage, before birth. After that, we mostly lose our ability to sprout new organs.

“We have a couple of tissues that can regenerate, like the liver, the outer layers of the skin and the inner layers of the intestine, and the bone marrow,” said Dr. Stephen Badylak, Deputy Director of the McGowan Institute for Regenerative Medicine at the University of Pittsburgh. “But the way we heal most tissues is by forming scar tissue.”

Scientists hope that studying planarians could lead to treatments for humans in which our stem cells could be coaxed one day to regrow severed limbs or sick organs.

---How to grow a fingertip.
Doctors are limited in what they can currently do to help people who lose a limb or part of one. Badylak, who doesn’t study planarians, has developed a treatment at the University of Pittsburgh that helps patients regrow their fingertips after an accident.

He applies a powder made of animal collagen and substances that stimulate cells to grow, to help form a scaffold that attracts stem cells from the parts of the nail that weren’t cut off. The stem cells regrow the fingertip, which isn’t identical to the one that was cut off, but is functional.

---+ Read the entire article on KQED Science:
www.kqed.org/science/1933246/want-a-whole-new-body…

---+ For more information:
Regeneration in Nature: Francesc Cebrià’s blog on animal regeneration: regenerationinnature.wordpress.com/

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