At the second conference of the Hydrozoan Society, a paper was presented that was so
revolutionary members of the audience did not believe it could be true.
One attendee, a respected marine biologist, stated the observation from the paper was,
in fact, totally impossible.
It was an observation made completely by mistake In the late 1980s, two laboratory students
​​collected a hydrozoan specimen that they believed to be Turritopsis nutricula
- a tiny jellyfish less than a centimeter long.
The individuals they collected were in their immature adult medusae form - meaning, they
were not sexually mature yet and unable to release eggs and sperm.
They placed the specimens in a tank, hoping to breed them for research purposes, and forgot
all about them.
When they returned, they expected to find sexually mature adults.
Instead they found fewer adult medusas than when they started - and lots of babies - in
the form of newly settled polyps on the bottom of the tank.
Had these jellyfish reproduced that quickly?
And if they did, what happened to all the adults?
To find out, the researchers started to keep a close watch on the individuals in the tank.
And what they found shocked them.
The adult medusae were not spawning and reproducing to create new baby polyps.
They were themselves reverting back into their juvenile form, completely reversing the aging
process.
What they had collected was not Turritopsis nutricula, but a different jellyfish, Turritopsis
dohrnii - one they realized is capable of Benjamin Buttoning itself, over and over again,
to the point where scientists learned they had discovered something inconceivable: immortality.
In a world obsessed with mortality and aging, the media went crazy over this news.
What is this tiny jellyfish’s secret to eternal youth?
Can it really live forever?
And if it can, how might we be able to harness this age reversing secret for ourselves?
To understand how Turritopsis dohrnii achieves its amazing feat, it’s useful to look at
its normal life cycle.
The immortal jellyfish is not a true jellyfish, but a hydrozoan, that spends most of its life
in its hydroid stage.
But for our purposes we will refer to it by its commonly used jellyfish name.
The life cycle of this jellyfish starts when adult jellyfish, in their recognizable medusae
form, swarm and release millions of eggs and sperm.
Most species of jellyfish will swarm in the hundreds or even thousands for the purpose
of reproducing.
When a sperm successfully fertilizes an egg, the fertilised egg will grow into a planula
- a tiny, floating larva.
Within a day or two, the planular will stick to a hard surface, like the sea floor, a rock,
or coral.
Once stuck they start the next phase.
The secured planula starts growing up from its perch, forming a polyp.
This looks a bit like a plant - a long stem, with a bulbous head which now has a mouth,
and long, waving fingers.
The polyp eats by sucking in food through its mouth, using its tentacles to help grab
it.
Now the polyps turn into a production line – creating a stack of cloned, nearly-jellyfish.
When the most mature clone is ready, it’s released and floats off into the water as
a tiny version of a jellyfish called an ephyra.
Now alone in the ocean, all it has to do is eat and grow, and eventually turn into the
medusa we all recognize.
And that’s the end of the line for most jellyfish.
They stay as a medusa, swimming, eating, and spawning until they die.
But Turritopsis dohrnii has a nifty hack for getting around the slight inconvenience of
death.
When this tiny jellyfish experiences high levels of stress, starvation, or physical
damage, it can send all of its cells back into a younger state.
The jellyfish shrinks and retract its tentacles, and the medusa turns into a blobby structure
called a cyst, that settles onto the ocean floor, or rock, or coral – just like its
past self.
Within three days, the blobby cyst starts growing into a polyp, and the whole process
starts over.
Start to finish, it can all be done in about a week.
It’s like a butterfly turning back into a caterpillar (and if that caterpillar could
then break apart into multiple butterflies!).
This amazing process has never actually been observed in the wild – only in the lab,
but there is no reason to think it isn’t going on throughout our oceans.
So what’s going on – how does an adult jelly turn into a baby?
Immortal jellyfish can do this amazing rejuvenation through a process called cellular transdifferentiation.
This is when a cell of one type turns into an entirely different type of cell, directly,
without turning into a neutral, intermediate form first.
Studies have shown that the medusa doesn’t seem to contain stem cells – a type of cell
that has the potential to be turned into any kind of cell – so it must be the case that
its existing cells are repurposed.
Scientists have found that the cells of the top layer of the dome shape of the medusa;
and the canal system – basically the jellyfish’s digestive system – are the most likely to
get turned into new cell types.
Of course, the cells that make up the dome of a medusa are different to the cells that
make up a polyp: they have different roles, suited to different needs.
It’s through transdifferentiation that the immortal jellyfish can get these specialised
medusa cells to turn into polyp cells.
This reversal of development goes against common ideas about aging across the animal
kingdom.
It has long been believed that sexual maturation for any animal marks a point of no return,
that cells are stuck doing what they will always do until they reached senescence – cell
death.
But Turritopsis dohrnii can turn cells back into their earlier state at any point in their
life cycle – whether they’re a newly produced medusa, to an old timer on the verge of death.
All that’s needed is a bit of a shock.
In the first experiments proving this phenomenon, a pinch with some tweezers was enough to get
them to revert.
We still don’t know exactly how Turritopsis dohrnii does it.
But, scientists have had a closer look at the cells of the cyst form of the immortal
jellyfish, and they found some interesting differences compared to its polyp state that
could tell us how the immortal jellyfish prepares for its new life.
While in its cyst form Turritopsis dohrnii spends a good amount of its energy on internal
upkeep, in particular, looking after its DNA.
The jellyfish seems to be able to protect and repair its telomeres.
Telomeres are strands of DNA found at the end of chromosomes, and - a bit like the plastic
bits on our shoelaces - they protect the rest of our DNA from damage, especially during
cell replication.
Every time a cell replicates, a little DNA is lost from the telomeres, but because they
are super long, there’s a lot to lose before any of the important stuff is affected.
But eventually, telomeres are ground down to nothing, and DNA is more prone to damage
– this leads to cell death, and, ultimately, the death of an organism.
This is what happens in humans.
Telomere shortening, as its known, is a key element of aging.
But in Turritopsis dohrnii cysts, there seem to be a particularly high number of genes
expressed that promote telomerase – an enzyme that repairs telomeres.
With large amounts of this enzyme, the immortal jellyfish could be protecting the cells from
naturally aging by simply elongating the telomeres, and protecting the jellyfish’s DNA.
On top of this, when in its cyst stage, the jellyfish spends little effort on replication
or cell differentiation, which makes sense - it is actively trying to prevent cells from
specializing.
The cysts also don’t respond to external stimuli, ensuring that they are focusing all
of their energy on DNA repair and maintenance until its ready to become a polyp once more.
This has worked well for Turritopsis dohrnii.
It’s fast taking over the world’s oceans.
Originally from the Meditteranean, it is believed that they have hitchhiked on boats and are
now found almost everywhere.
Their resilience has probably helped contribute to their ability to survive across long distances
and lots of environments.
Researchers have found that in the lab, a single Turritopsis dohrnii is able to regenerate
10 times, at intervals as short as one month.
In the wild, this could go on for much longer - possibly forever - in an eternal loop of
back and forth transdifferentiations.
So, can we learn anything from this that might help us age better, or not at all?
We’re not going to be able to Benjamin button ourselves, but there are things we can learn
from the Turritopsis dohrnii that could help us stave off some of the diseases that plague
us in later life.
Transdifferentiation is an interesting field for scientists.
Being able to turn one cell into another in few to no steps, and over a short period of
time, could open the doors to treatments for things like Parkinson’s – imagine if we
could turn skin cells into neuronal cells to replace lost or damaged cells in the brain.
Understanding how the immortal jellyfish does this could help us work out how to do it ourselves.
Another area that Turritopsis dohrnii could shed light on is microRNAs.
These are short strands of genetic material that regulate our DNA.
They can switch genes on and off, and are involved in DNA repair.
We know that a lot of DNA repair is happening in a regenerating Turritopsis dohrnii, and
finding out more about how microRNAs act to regulate DNA repair in the little jellys could
help us do the same for our own cells.
Having said that, humans and jellyfish, while pretty similar in terms of their DNA when
you consider how different we appear, still split apart on the tree of life some time
ago, and there are genes in jellyfish that aren’t expressed in humans, and vice versa,
so there may be some limitations to what is applicable.
Even though Turritopsis dohrnii was first discovered in 1883, we only found out it might
be immortal in the 1980s.
And we are also learning that there may be other ‘immortal’ creatures out there.
The natural world, from organisms large and small, from jellies, to trees, to microbes,
to fungi, likely hold answers that we can’t even conceive of right now.
But as we discover more biodiversity, and as our scientific technology becomes increasingly
sophisticated, we are likely to find out more, and it may mean new avenues for treatments
for degenerative diseases and cancer.
And while the immortal jellyfish may not hold the answer to a never-ending life for us,
it may at least give us a little longer.
To fill our increasingly long lives, it’s important to continuously fill our minds.
And if you are like me, entertaining but educational documentaries are one of the best ways to
fill both.
YouTube can be a treasure trove of content, and finding a binge-able channel or series
that is also educational is one of the greatest feelings.
One of the worst feelings is when you are out of ideas of what to watch, especially
when you have your lunch sitting in front of you and you can’t eat it until you find
something good.
This happens to me when I’ve already seen nearly all the videos made by my favorite
creators.
If you’ve ever felt this lack-of-content-induced despair, now is the best time ever to sign
up to Nebula - the streaming platform me and several other educational content creators
made together, which is a gold mine of new, original content.
To dive deep into history, the brand new series Battle of Britain, made by the team behind
this channel and Real Engineering, is of such high quality I can’t believe it's not made
for TV.
It’s a series that will take you through the key moments of the first major military
campaign fought entirely by air forces.
The 3D animations are out of this world, and the storytelling will leave you captivated,
all while learning about one of the most important moments in modern history.
There are so many original series like this on Nebula, with more coming in all the time.
And right now is the single best time to sign up.
Nebula has partnered with CuriosityStream to offer you both streaming services for just
$11.59 for the entire year - that’s 42% off the usual price - meaning you get both
services for less than a dollar per month.
And with this subscription, you are also supporting us in the best way possible.
Every signup helps us to hire more animators, take on bigger projects, and keep the lights
on and machines running.
So go to curiositystream.com/realscience to get both Nebula and CuriosityStream for just
$11.59 for the entire year.
And if you are looking for something else to watch right now, you can watch our previous
video about the incredible harpy eagle, or watch Real Engineering’s latest video about
the unusual fuel SpaceX is exploring for its upcoming missions.