Biology

Why can’t humans regenerate body parts? We’ve got the genes

Why can’t humans regenerate bo...
This acorn worm has grown a new head, internal organs and neural tube within fifteen days after being cut in half. Scientists believe humans have nearly all the genes needed to regenerate in a similar way, if the process is unlocked
This acorn worm has grown a new head, internal organs and neural tube within fifteen days after being cut in half. Scientists believe humans have nearly all the genes needed to regenerate in a similar way, if the process is unlocked
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This acorn worm has grown a new head, internal organs and neural tube within fifteen days after being cut in half. Scientists believe humans have nearly all the genes needed to regenerate in a similar way, if the process is unlocked
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This acorn worm has grown a new head, internal organs and neural tube within fifteen days after being cut in half. Scientists believe humans have nearly all the genes needed to regenerate in a similar way, if the process is unlocked
Five days after being cut - a rudimentary head, including the mouth and proboscis, has formed
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Five days after being cut - a rudimentary head, including the mouth and proboscis, has formed
A close-up view of the cut site and tail end of the worm the day it was cut
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A close-up view of the cut site and tail end of the worm the day it was cut
The tail end of the worm after being cut - the boxed area indicates where the worm will grow a new head
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The tail end of the worm after being cut - the boxed area indicates where the worm will grow a new head
An intact, live acorn worm - the head is on the far left, and the worm will be cut in the middle
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An intact, live acorn worm - the head is on the far left, and the worm will be cut in the middle

Some of our closest invertebrate cousins, like this Acorn worm, have the ability to perfectly regenerate any part of their body that's cut off - including the head and nervous system. Humans have most of the same genes, so scientists are trying to work out whether human regeneration is possible, too.

Regeneration – now that'd be a nice superpower to have. Injure an arm? Chop it off and wait for it to grow back. Dicky knee? Ingrown toenail? Lop off your leg and get two for one!

It sounds ridiculous, but there's a growing number of scientists that believe body part regeneration is not only possible, but achievable in humans. After all, not only are there plenty of animals that can do it, we can do it ourselves for our skin, nails, and bits of other organs.

What's more, we've got a lot of the genes for it. "I really think we as humans have the potential to regenerate, but something isn't allowing that to happen," says Billie Swalla, director of Friday Harbor Laboratories and and a Biology professor at the University of Washington, and part of a team that's closely studying regeneration in some of our invertebrate relatives. "I believe humans have these same genes, and if we can figure out how to turn on these genes, we can regenerate."

An intact, live acorn worm - the head is on the far left, and the worm will be cut in the middle
An intact, live acorn worm - the head is on the far left, and the worm will be cut in the middle

Swalla and research partner Shawn Luttrell, also from the University of Washington, have been looking at the acorn worm; a small aquatic worm that burrows in the sand around coral reefs.

Acorn worms are interesting for two reasons. Firstly, they have the ability to regenerate every part of their body, including the head, nervous system and internal organs. Cut one in half, and within 15 days each half will regenerate into a whole worm so perfectly you couldn't distinguish it from one that had never been cut.

But secondly, they're also remarkably similar to humans, both genetically and in terms of how their body structure is laid out. In fact, thanks to their ancestral relationship with chordates like ourselves, acorn worms have a lot of DNA in common with us.

A close-up view of the cut site and tail end of the worm the day it was cut
A close-up view of the cut site and tail end of the worm the day it was cut

"We share thousands of genes with these animals, and we have many, if not all, of the same genes they are using to regenerate their body structures," says Luttrell, "This could have implications for central nervous system regeneration in humans if we can figure out the mechanism the worms use to regenerate."

Through DNA, every cell in our bodies contains the roadmap to build or re-build the entire machine. But for some evolutionary reason, this process has been blocked off. Perhaps we're flat out too big for it to be worthwhile from an energy perspective, as opposed to smaller amphibians and fish. Maybe our immune systems spoil the party by building up scar tissue around cuts.

Thus, the researchers have been trying to figure out the gene expression patterns that happen when these Acorn worms are regenerating. They suspect there's some sort of "master control" gene that starts the process off, because once it begins, it follows the same steps in every worm.

Five days after being cut - a rudimentary head, including the mouth and proboscis, has formed
Five days after being cut - a rudimentary head, including the mouth and proboscis, has formed

They're also trying to work out exactly which types of cells the worms use as the building blocks of a regeneration – be they stem cells, or other cells that could be repurposed for regrowth.

The eventual goal is to learn how to activate the process in other animals, including humans, through gene editing or activation, and supply the necessary materials to let it work.

It's a complex problem, but genetically we're working from a strong starting point. And if it's possible to regenerate tissue the same way as an Acorn worm does, that will include the nervous system, heart and other internal organs. A pretty amazing process to think about, but could this be an accepted medical reality in 100 years?

Source: University of Washington

14 comments
VincentWolf
I would love to try that with my left foot which has made me suffer from pinched nerves and incredible persistent electrical pain for 4 years now. I guess I'll just chop it off now and see if my genes are up to the task! Kidding.
Augure
Too bad the human mind, not brain, body, cells or gens, the human mind has a maximum tolerable length of life past which you just slowly become a zombie even if your body and organs are in best shapes. Imagine living in eternity. Any eternity. Yup eventually you'd reach a point where anything in any scenario becomes hells. Well that point is usually reach when you live past a hundred of years or so depending on what you live, because ultimately you've seen, felt and experiences it "all", and no new technology or events could make you feel "alive".
myale
All they need to do is read spiderman vs the lizard and hey presto.
GeorgeWade
The acorn worm tries to live in unpolluted water: lets watch its future as pollution spreads. How well does it cope with our industrial cocktail !
Gmayle
I can already see a huge problem with this science. As with the worm, wouldn't another you be created as the severed limb begins to grow into another you. I guess you could somehow dispose of the severed limb to keep it from regrowing, but couldn't that be construed as murder. You see that there are a number of issues that would have to be worked out before taking such a step. It never ceases to amaze me how, as we always do, people love the potential newly discovered science brings, but they don't consider the consequences it's implementation would bring.
Buellrider
Gmayle, I'm pretty sure you'd need your internal organs working to allow your body to regenerate an arm. The severed appendage would just rot without a blood supply. Now if you could keep that severed arm alive with some outside source of blood then I could see where you are coming from with your worry of the arm growing another body. That would be a pretty good horror movie.
Leo Baldwin
Let's not forget the time scales here people. Let's say you did cut off your limb. You have a tiny infant limb in about 1 year, a juvenile limb for about another 12 years and then finally some kind of Adolescent and teenager limb. Your full adult limb would not be there for about 17 years. It would appear pristine and much younger than your other leg. With this long waiting time and this mismatch to the limb would it be worth it?
BobM
BobM Best guess, it will start will Stem Cell regeneration. And, yes a modified method to speed up the growth process will be necessary to make it feasible for immediate medical attention. IMO
habakak
Gmayle....relax. This is bogus and will not happen. Most likely ever and definitely not in our life time. And if it does, it will cost an arm and a leg!
Racqia Dvorak
First, genetics are not the full information that forms organisms, especially in cellular construction of organs. Internal Cellular Matrixes have been implicated in vastly complex activities previously thought to be the domain of DNA. There's two halves to the puzzle and we don't even know how to read half of it right now. SO I wouldn't hold your breath that they'll be able to tackle this without the full picture. Second, they should look closer to humans first. As in mammalian. Much higher chance that the African spiny mice (particularly Acomys kempi and Acomys percivali) will be able to help us regenerate than something that doesn't even have a backbone.