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.
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—+ For more information:
Regeneration in Nature: Francesc Cebrià’s blog on animal regeneration:
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thanks to curiosity stream for supporting PBS Digital Studios this goofy little guy is called a planarian sure it's just a flatworm at the bottom of a pond but it has a very special superpower one that scientists would love to harness to show you well it's gonna get a little bit slasher movie here okay don't worry it's going to be okay seriously I promise it doesn't even hurt that would be curtains for most organisms I mean this piece here is just a chunk with no head and no tail but watch you can see under a microscope that overnight its wound heals closed ok maybe we could do that more slowly of course but then it starts to regenerate growing new tissue it's that white part called the blastema in a week see those tiny little spots there new eyes grown from scratch but the planarian can I call it that yet it still kind of looks like a blob by day 12 it's starting to look like a proper planarian it's got a head an entirely new one and a new tail and it's doing its regular planarian things like pooping that's because one of the first things that started regrowing was a tube called the pharynx which is how things go in and out it sucks up food like this beef liver that scientists are feeding it after three weeks it looks totally normal from that one planarian you get four other animals like this newt can regrow a toe or a tail but planarians are practically the only animal that can regrow a head so why can't we do that well it all comes down to powerful cells known as stem cells they're the green dots here and they make up 1/5 of a planarian body they can turn into different kinds of cells and make every new body part we only have stem cells to act like these when were embryos once we grow up we pretty much lose this ability though doctors have been able to get us to grow back a fingertip but what if we could grow ourselves a new a whole arm or a liver scientists are trying to figure out exactly how planarians do it and maybe one day these humble flatworms could inspire new ways to heal our injuries hi it's Lauren again this kind of planarian is from San Francisco those aren't ears they're Oracle's it uses them to feel around you can tune in to more deep look by following us over to patreon you'll get special members-only benefits like behind-the-scenes peeks and how we make our show link in the description thanks and see you soon thank you to curiosity stream for supporting PBS Digital Studios curiosity stream is a subscription streaming service that offers documentaries and nonfiction titles from a variety of filmmakers including curiosity stream originals age of big cats is the untold story of the seven major species of big cats who clawed their way to the top and came to dominate the land you can learn more at curiosity stream dot-com slash deep look and use the code deep look during the signup process