[A new study followed as a Turritopsis dohrnii rejuvenated itself,
uncovering developmental patterns for further inquiry.]
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THIS JELLYFISH CAN LIVE FOREVER. ITS GENES MAY TELL US HOW.  
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Veronique Greenwood
September 6, 2022
New York Times
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_ A new study followed as a Turritopsis dohrnii rejuvenated itself,
uncovering developmental patterns for further inquiry. _

A juvenile medusa-stage specimen of the Turritopsis dohrnii
jellyfish., Maria Pascual-Torner

 

Fleets of tiny translucent umbrellas, each about the size of a lentil,
waft through the waters of the Mediterranean Sea. These miniature
jellyfish, known as Turritopsis dohrnii_,_ wave and grasp with their
pale tentacles, bringing plankton to their mouths like many other
jellyfish species adrift in the glowing water.

But they have a secret that sets them apart from the average sea
creature: When their bodies are damaged, the mature adults, known as
medusas, can turn back the clock and transform back into their
youthful selves. They shed their limbs, become a drifting blob and
morph into polyps, twiggy growths that attach to rocks or plants.
Gradually, the medusa buds off the polyp once again, rejuvenated.
While a predator or an injury can kill T. dohrnii, old age does not.
They are, effectively, immortal.

Now, in a paper published Monday in The Proceedings of the National
Academy of Sciences
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have taken a detailed look at the jellyfish’s genome, searching for
the genes that control this remarkable process. By examining the genes
active at different phases of the life cycle, the researchers got a
glimpse of the delicate orchestration of the jellyfish’s
rejuvenation.

Gathering enough T. dohrnii to study their genomes can be difficult.
Only one scientist, Shin Kubota at Kyoto University in Japan, has
successfully maintained a colony in the lab over the long term. (He
has also written
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subjects.)

When it comes to living in an aquarium, “they are very picky,”
said Maria Pascual-Torner, a scientist at Universidad de Oviedo in
Spain who studies the jellyfish. “And they are very, very small,
which also makes them difficult to identify and sample in the
field.”

To get enough material for the new paper, Dr. Pascual-Torner and a
colleague drove a specially equipped camper van to a coast in Italy
and went diving to gather wild jellyfish. They then rushed them back
to the lab.

When they and their colleagues sequenced the creatures’ genomes, the
researchers noticed that the jellyfish had extra copies of certain
genes, a sign that these might be important for the creatures’
survival. The researchers found many of the duplicated genes among
them, including some that protect and repair the jellyfish’s DNA, as
DNA is often eroded with age in animals.

A Turritopsis dohrnii polyp. Credit...Maria Pascual-Torner

To trigger rejuvenation, the researchers put the jellyfish under
stress by letting them go hungry, among other regimens. As the medusas
shrank into little balls, sprouted polyps and began remaking their
adult bodies, the scientists took snapshots of what genes they were
using in each phase of their development. They took some jellyfish in
each phase, froze them and turned them to mush to extract their mRNA,
giving a record of which genes were actively being used to make
proteins.

As the jellyfish transformed, the scientists were interested to see a
marked change in the use of genes linked to DNA storage. In adults,
these genes were active or expressed at a high level — that is, they
were being used frequently to make proteins. But as the animals began
their descent back into polyps, the genes became quieter, with their
proteins reaching their lowest levels in the floating ball form.

Genes related to pluripotency, or a cell’s ability to grow into a
variety of fully developed forms, did the opposite. They were quiet in
the adult form but leaped into action as a jellyfish broke its body
down and started to build it back up. The pluripotency genes then
returned to dormancy when the process was complete.

What this suggests, Dr. Pascual-Torner said, is that DNA that’s
normally in storage is brought out during the transformation, and
genes that coax cells to reset go into overdrive.

The paper’s findings corroborate what her group of researchers
saw in a similar study last year
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Maria Miglietta, a marine biology professor at Texas A&M University at
Galveston who also studies T. dohrnii. Her team saw that genes related
to DNA repair and protection were involved in the jellyfish’s
rejuvenation.

Both sets of research suggest when and how much the jellyfish’s
genes are expressed matters just as much as the genes themselves in
giving an old body new life. In other words, there is no gene for
immortality, but there is certainly a procedure for it.

The researchers hope to understand more about this dance of unfurling
DNA. If the storage proteins were tweaked to stay active, would the
jellyfish be able to start over? Or would they be trapped, like the
rest of us, able only to move forward in time?

Still, we are unlikely to be able to make use of the T. dohrnii’s
process.

“Our goal is not to find the formula of human immortality,” Dr.
Pascual-Torner said. “Jellyfish are very different from humans.
It’s not just about one gene or complex. It’s about the whole
mechanism we found that works together.”

Whether any of these processes in T. dohrnii’s body have a parallel
in the human body is an open question. But for the foreseeable future,
this fountain of youth is just for jellyfish.

_VERONIQUE GREENWOOD is a science writer and essayist. Her work has
appeared in The New York Times Magazine, Smithsonian,
Discover, Aeon, Quanta and other publications._

_A version of this article appears in print on Sept. 13, 2022,
Section D, Page 2 of the New York edition of the NEW YORK TIMES
with the headline: Rejuvenation Process: This Jellyfish Can Live
Forever. Its Genes May Tell Us How.. Subscribe
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* Science
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* genetics
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* DNA
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* mRNA
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* protein
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