[♪ INTRO]
Octopuses and their cephalopod kin are unique creatures.
They can change their color and shape at a moment’s notice,
there’s the whole business with the inking…
But this uniqueness continues all the way to the DNA level.
They have a completely wild way of adapting
that researchers didn’t think was really possible.
Instead of relying on permanent changes to their genome,
they edit their genetic instructions on the fly!
The more I learn about octopuses, the more I’m like...okay, are they from Earth?
Are they definitely from Earth?
Now, to understand why that’s so weird,
it helps to know how cells make the proteins they need.
In the nucleus of an animal cell, you have your DNA,
which contains the genes that act as blueprints for all the proteins the cell makes.
But to actually make those proteins,
those instructions have to be taken out of that compartment.
And that is where messenger or mRNA comes in.
To make something from a gene, the cell first creates an RNA copy of
that section of DNA. And that mRNA is the instruction material that it sends
out of the nucleus to the cell’s protein-making factories.
Only so many proteins can be made from one mRNA instruction manual
before it gets recycled, though.
So if a cell needs lots of a protein or a constant supply, it makes more mRNAs.
Now, we usually think of organisms adapting through mutations to their genomes.
Those changes to the DNA mean changes to the mRNA copies, and therefore,
a slight change in the proteins that are made from them.
And if that new version of the protein helps the critter survive and reproduce,
then more of the population will have it in the next generation.
That is evolution in a nutshell.
But researchers think that cephalopods in the subclass Coleoidea —
which includes octopus, squid, and cuttlefish —
can adapt by editing their mRNA instead.
That changes proteins a lot faster than DNA mutations. But... it can get a bit messy.
Think of it like cooking. DNA is the recipe, mRNA is the chef following the recipe,
and the proteins produced by the cell — they’re the meal.
When DNA mutates, the recipe changes — permanently.
But when mRNA is edited, it’s more like the chef just deciding to put
salt in place of sugar because they felt like it that day.
And as you can imagine, these kinds of edits typically do more harm than good.
There’s always more potential to break things than to make them better.
So RNA editing often leads to diseases and disorders.
Which is why, even though a lot of creatures can do it,
they edit their RNAs extremely sparingly!
We humans, for instance, edit only three percent of our mRNAs.
Meanwhile, in 2015, researchers discovered that the longfin inshore squid
edits more than 60 percent of the mRNA in its nervous system!
That’s a lot more than anyone had seen in any other animal.
And the researchers were able to show that cephalopods have hung onto ancient
versions of their genes that code for the enzymes that actually do this mRNA editing.
So, evolutionarily speaking, they have cultivated the ability
to make these on-the-fly edits!
Why risk the collateral damage? Well, it might be all about flexibility.
For starters, these changes are more temporary.
Not only are they not passed on to the next generation like changes to DNA are,
they also don’t have to happen to every mRNA that’s made from that gene.
And that might mean the animals can use different versions of a protein
as it suits them, without changing the DNA.
For example, thanks to RNA editing, octopuses are able to produce different proteins
depending on the temperature of the water around them.
Cold temperatures slow proteins down, which could mean that
everything a cold-water octopus tried to do would be really slow!
But, researchers have found that while cold and warm-water octopuses
share nearly identical DNA, the ones living in colder waters
edit the mRNA for certain neuronal proteins more.
And those edits tweak the structure of them just enough
that they work faster when they’re cold!
So with just one gene, they can do well in warm and cold water.
Also: there’s no rule that it has to be just one edit to an mRNA.
If there are lots of potential editing sites,
then an animal could make lots of different proteins from the same gene!
And researchers think the ability to generate that level of protein complexity
might explain one of cephalopods’ most notable features: their smarts.
Octopuses and their relatives are known for their intellect.
Do a quick YouTube search, and you will find videos of them opening jars,
escaping from aquariums, even taking photographs!
And across the board, these species have very complex nervous systems,
including brain lobes dedicated to learning and memory.
Well, it turns out that a lot of the mRNA editing they do is to the proteins
that make and stimulate connections in their brains.
And most occur in the axons of neurons —
the parts responsible for passing information between cells.
Scientists think that’s evidence that RNA editing
plays a big role in how their brains work!
This theory tracks when you compare the coleoids
to their distant cousins, the nautiloids.
Nautiloids don’t edit their mRNA to the same extent.
And their brains are much simpler!
All of this rampant RNA editing isn’t without consequence, though.
It may limit their ability to adapt the old fashioned way —
through DNA mutation and natural selection.
Because they need to keep all the pieces in place to make these edits happen,
the actual genomes of these creatures change very slowly.
And that may mean that it’s much harder for them
to come up with a totally new thing that could help them survive better.
We still have a lot to learn about why these creatures do things differently
than every other animal on our planet.
But one thing we do know is that studying these wonderfully weird creatures
is expanding our ideas of how life works and what living things can do.
And that is just one reason why we love them.
Speaking of “love”, before I go, I’d like to give a little love
to today’s President of Space, Matthew Brant!
Matthew: we’re very lucky to have you as a patron!
We could not do this show without the support of patrons like you.
So thank you, for being a part of our awesomely nerdy community!
And if you’re not Matthew Brant, but want to learn more about being a patron —
including how you, too, can become President of Space —
you might want to head on over to Patreon.com/SciShow.
[♪ OUTRO]