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With their squishy bodies and color-changing abilities, octopuses and other cephalopods already look like our planet’s resident aliens. But researchers have discovered yet another thing that separates them from most other animals on Earth!

Hosted by: Hank Green

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Sources:
https://doi.org/10.1016/j.cell.2017.03.025
https://doi.org/10.7554/eLife.05198
https://doi.org/10.1093/nar/gkaa172
https://doi.org/10.1038/s41587-019-0013-6
https://doi.org/10.1093/mollus/eyw052
https://doi.org/10.1126/science.1212795
https://pubmed.ncbi.nlm.nih.gov/29182635/

Image sources:
Thank you to 7Seil for the footage of an octopus opening a jar! (https://youtu.be/_xfDYs_6rUk)
https://www.istockphoto.com/vector/genetics-flat-design-baby-icon-gm915904400-252052163
https://www.istockphoto.com/photo/cuttlefish-gm139531609-667477
https://www.istockphoto.com/vector/education-icons-gm538049914-95611693
https://www.istockphoto.com/vector/cooking-class-chef-cook-stick-figure-pictogram-icons-gm496989862-78859591
https://www.istockphoto.com/vector/set-of-kitchen-utensil-icon-gm1296529250-389920253
https://www.istockphoto.com/vector/hot-pepper-flat-design-mexico-icon-with-side-shadow-gm926930526-254309654
https://www.istockphoto.com/vector/salt-or-pepper-shaker-icon-gm944153334-257926040
https://www.eurekalert.org/multimedia/pub/227559.php
https://www.istockphoto.com/photo/octopus-vulgaris-gm655094820-120552077
https://www.eurekalert.org/multimedia/pub/227560.php?from=459271
https://www.istockphoto.com/photo/a-nautilus-in-the-beautiful-blue-ocean-gm140789712-19146667
https://www.istockphoto.com/photo/octopus-tentacles-and-suckers-gm507858277-45917644
[♪ 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].