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Moon jellyfish regains its symmetry after losing limbs

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Posted June 18, 2015

Ability to repair itself is very important to all living organisms. Injuries are inevitable and body has to find a way to survive by healing the wound or, in some cases, even regrowing lost part. Example of a lizard, which can regrow its lost tail, shows that such self-repair properties differ quite significantly between different species. And now scientists at California Institute of Technology have discovered a previously unknown self-repair mechanism in a certain species of jellyfish – the reorganization of existing anatomy to regain symmetry of the body.

Example of how jellyfish with removed arms regain its symmetry. This process is driven by muscle contractions and the viscoelastic jellyfish body material, instead of usual cell proliferation and cell death, seen in other organisms. Image credit: Michael Abrams and Ty Basinger/Caltech

Example of how jellyfish with removed arms regain its symmetry. This process is driven by muscle contractions and the viscoelastic jellyfish body material, instead of usual cell proliferation and cell death, seen in other organisms. Image credit: Michael Abrams and Ty Basinger/Caltech

Regenerating tissues in case of injury is an important mechanism of survival. It has been known previously that jellyfish can rapidly heal themselves. However, now scientists have noticed that the moon jellyfish (Aurelia aurita) has a unique self-repair mechanism. Scientists started researching this animal to see if the moon jellyfish would respond to injuries in the same manner as an injured hydra. It is a jellyfish-like animal, which is a very commonly used model organism in studies of regeneration.

Scientists focused on the jellyfish’s juvenile (or ephyra) stage, because its disk-shaped body with eight symmetrical arms would make any tissue regeneration clearly visible. Researchers performed amputations on anesthetized ephyra, leaving it with two, three, four, five, six, or seven arms, instead of usual eight. Wounds healed as rapidly as it was expected, it only took a few hours. However, scientists also noticed something they did not anticipate – the jellyfish were not regenerating tissues to replace the lost arms. Instead, the animal had reorganized its existing arms to be symmetrical and evenly spaced around the body.

This process was observed regardless of how many arms jellyfish had left. It was also observed in three additional species of jellyfish ephyra. Radial symmetry is essential is crucially important for jellyfish as well as variety of other marine animals such as sea urchins, sea stars, and sea anemones. Michael Abrams, one of the lead authors of the research, said that this is important because of how jellyfish move – they flap their arms, which not only pushes animal forward, but also moves water and food past the mouth of the jellyfish. Abrams said – “As they are swimming, a boundary layer of viscous—that is, thick—fluid forms between their arms, creating a continuous paddling surface. And you can imagine how this paddling surface would be disturbed if you have a big gap between the arms.”

Researchers also noticed that those jellyfish that did not succeed to symmetrize (only about 15 % of the studied animals), could not develop into normal adult jellyfish, called medusa. Scientists also found that this repair mechanism is unusual in another sense as well. Usually such processes involve cell proliferation and cell death, but in this case jellyfish were neither making new cells nor killing existing cells as they redistributed their existing arms around their bodies.

Arms are redistributed by mechanical forces created by the jellyfish’s own muscle contractions and the viscoelastic jellyfish body material. It was proved by a simple experiment – scientists added muscle relaxants to the water and repair process slowed down. Magnesium sped up the process, because it sped up the muscle contractions. Scientists say, that when one or several arms are missing, mechanical forces in the body of the jellyfish are unbalanced, ant they push arm into symmetry again. This discovery is already giving scientists ideas about its practical application.

Scientists say that there may be application for such mechanism in healing wounds and injuries. Researchers will try to create new biomaterials that would be designed to heal by regaining functional geometry rather than regenerating precise shapes. Scientists say that mechanical forces, needed for such self-repair, are easier to apply than controlling process of cell proliferation and cell death.

This is just another great example how small discoveries in nature can have a practical applications for humans. Even though it will take many years for results of researches like this to find ways into therapies of drug treatments, it is still an interesting knowledge about jellyfish as well as hope for innovative healing compounds in the future.

Source: Caltech

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