What if humans could regrow an amputated arm or leg, or completely restore nervous system function after a spinal cord injury?
a whole, live acorn worm
An intact, live acorn worm. The head is on the far left, and the worm will be cut in the middle.Shawn Luttrell/University of Washington
A new study of one of our closest invertebrate relatives, the acorn worm, reveals that this feat might one day be possible. Acorn worms burrow in the sand around coral reefs, but their ancestral relationship to chordates means they have a genetic makeup and body plan surprisingly similar to ours.
A study led by the University of Washington and published in the December issue of the journal Developmental Dynamics has shown that acorn worms can regrow every major body part — including the head, nervous system and internal organs — from nothing after being sliced in half. If scientists can unlock the genetic network responsible for this feat, they might be able to regrow limbs in humans through manipulating our own similar genetic heritage.
“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,” said lead author Shawn Luttrell, a UW biology doctoral student based at Friday Harbor Laboratories. “This could have implications for central nervous system regeneration in humans if we can figure out the mechanism the worms use to regenerate.”
The new study finds that when an acorn worm — one of the few living species of hemichordates — is cut in half, it regrows head or tail parts on each opposite end in perfect proportion to the existing half. Imagine if you cut a person in half at the waist, the bottom half would grow a new head and the top half would grow new legs.
After three or four days, the worms start growing a proboscis and mouth, and five to 10 days after being cut the heart and kidneys reappear. By day 15, the worms had regrown a completely new neural tube, the researchers showed. In humans, this corresponds to the spinal cord and brain.
After being cut, each half of the worm continues to thrive, and subsequent severings also produce vital, healthy worms once all of the body parts regrow.
“Regeneration gives animals or populations immortality,” said senior author Billie Swalla, director of Friday Harbor Laboratories and a UW biology professor. “Not only are the tissues regrown, but they are regrown exactly the same way and with the same proportions so that at the end of the process, you can’t tell a regenerated animal from one that has never been cut.”