In order to survive, starfish cut off their body parts to escape from predators. They will also eventually regenerate those lost limbs, but how this biological process works remains a mystery. Now, a team of scientists has identified the type of neurohormone responsible for limb amputation in the common starfish (Asterias is sad). The findings are detailed in a study published on August 29 in the journal Current Biology.
What is Autotomy?
Autotomy is the ability of an animal to withdraw a body part—and still be alive—as a way to escape from an animal that is trying to eat it. Lizards can extend their tails to escape and newts can regenerate their limbs, eyes, jaws, spine and more. Starfish – or sea stars – will cut off one or more arms and grow back his lost limbs over time.
Maurice R. Elphick, co-author and biologist at Queen Mary University of London (QMUL), says: “Cells in the area where autotomy occurs are pre-programmed to facilitate rapid regeneration.” Normal Science. “It’s as if starfish are built to expect that rebirth after making a corpse will happen at some point in their life, that is, they will be attacked by a predator or their hands will be trapped under a stone and they go away.”
[Related: The sea star’s whole body is a head.]
According to Elphick, when scientists collect starfish on the beach, they often find many parasites that have clearly lost an arm or two at some point in their lives.
Elphick says: “You can tell when the adaptation is made because the regenerated hand is smaller than the other hands and probably doesn’t reach the same size as the original hands.”
Although autotomy was first described scientifically three decades ago, the molecules and hormones behind it remain elusive. Understanding what actually causes this process at the molecular level could have implications for regenerative medicine in the future.
The stars, they’re just like us (kind of)
Initially, the team in this new study looked at a mammalian neurohormone called cholecystokinin (CCK). They were curious about how the same neurohormone in starfish works.
“One of its natural actions [in humans] is to stimulate the contraction of the gallbladder and that contraction of the gallbladder forces the bile into the intestine and this shows its role in facilitating digestion,” says Elphick.
CCK also inhibits feeding behavior. When the stomach is full and food is transferred to the intestines, CCK is one of the hormones that sends a message to the brain that it is time to stop eating.
Because of CCK’s role in feeding behavior in mammals, Elphick and co-author Ana Tinoco from QMUL and the University of Cadiz in Spain looked at how a cholecystokinin-type neurohormone called ArSK/CCK1 works. How do starfish eat? While testing the neurohormone in the laboratory, they noticed that it did indeed induce independence in some starfish, but not all.
Elphick says: “In some animals only one arm was lost, but in several animals four out of five arms grew on their own.
They found that at the molecular level, cholecystokinin-type neurohormones work the same way in starfish and humans. They bind to a specific receptor protein on the cell surface of the target cells. The binding triggers a signal that ultimately changes some of the properties of the target cells.
[Related: Antlion larvae can ‘play dead’ for more than an hour–then, things get random.]
One of these changes is muscle contraction. In humans, it causes the gallbladder to clog. For starfish, the contractions produced by these neurohormones appear to be related to autotomy.
“We have evidence that the process of autotomy is facilitated by the release of this peptide, which we think causes muscle contraction in the starfish arm,” says Elphick. “This helps close the arm and close the wound after the autotomy.”
The team is still providing detailed information on how this process works, but it is out of place for further study.
Future treatments
Although the way cholecystokinin-type neurohormones work in starfish and humans is very similar, both organisms have evolved to use them differently. However, the similarity means that further study can advance our understanding of human tissue regeneration and better treatments for limb injuries.
“The process of self-renewal is complex, like many biological processes, and is likely to be controlled by many factors and we would like to identify other molecules involved in controlling the process,” says Elphick. of independent starfish.
[Related: The blueprints for early organs may be hiding in sea stars.]
It also provides a lesson in how scientists can start with one question or project that turns into something completely different.
“I think the most important take-home message from this study is the importance of being able to do experiments where you don’t know what the outcome is going to be and you don’t really have to be hypocritical,” says Elphick. . “You just look at things and sometimes you’ll find something really interesting and interesting”
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