Briefing Chat: Stressed mitochondria spawn new 'organelles' in cells

Hi Benjamin here, welcome to the Nature Briefing podcast.

The Friday show where we talk about a couple of stories we've read about in the Nature Briefing

which is of course nature's daily email round up of the latest science stories.

And joining me today to chat is another than Sharmini Bundel, Sharmini, thank you for

being here.

I am actually really excited about today's story.

Why don't we start with you then in that case and tell me what you've got.

Look, I'll give you the preview.

It's got mitochondria, we all love mitochondria, it's got parasites, it's got evolution, I love

evolution.

Ding, ding, ding, ding.

This is a preprint from bioarchive so not a peer-reviewed paper but I read an article

in Nature where they've covered it and yes it's about mitochondria, the powerhouse of

the cell, little organelles found in eukaryotic cells producing energy and it's kind of about

how our cells got to be, how they are.

Right.

But it came from an experiment with a parasite.

Okay, parasite biology often very strange, tell me what's going on here.

So a group of researchers infected human cancer cells with a parasite called toxoplasma

gondii.

This is the parasite that causes toxoplasmosis which if you've ever gotten pregnant they

tell you to stay away from cat poos you don't get toxoplasmosis.

Right.

It's a really common parasite and it's also his little side tour, it's the one that

changes the behavior of rodents to make them more likely to get eaten by cats.

They stopped being scared.

Yeah, that's a whole other story but go look it up, it's great, mind controlling parasite.

So anyway these researchers are there infecting these human cancer cells with some toxoplasma

and what happened was that these little parasites in the cell started having an effect on the

mitochondria in the cell, these membrane bound organelles and these mitochondria started

to shed their outer membranes and that membrane then formed its own little bubbly structure.

They call them spots, structures positive out of mitochondrial membrane spots.

And those little spots went engulfed some other little organelles, little things in the

cells called lysosomes which do sort of waste disposal jobs in the cell.

And it turns out that this weird change was actually helpful to the parasite.

And they stopped this from happening, the parasite didn't do as well.

So something about this process that's triggered by the parasite is benefiting the parasite.

So let me get this straight.

So parasite infects cells, something that you would expect is a defense mechanism, isn't.

So the mitochondria loses its membrane, that joins with another organelle, but instead

of defeating a parasite, this helps the parasite.

Yeah, you make an interesting point because quite possibly this kind of reaction from the

mitochondria, this ability to shed some of their membranes and form new organelles, that

could well be usually a benefit, that could be an adaptation to maybe help the cell adapt

to different stresses by creating new structures.

That is possible, but yes, certainly in this one specific case, which is a very narrow

thing that they were looking at, this one particular situation.

But yeah, in this situation, the toxoplasma gondii is definitely doing well from this

and the implication here is that this is an adaptation by this parasite to benefit it

by manipulating these mitochondria.

And also, you mentioned that this is a new organelle and that's super interesting too.

Well, so here is where it gets much broader.

We're going to step away from infecting cancer cells with a specific parasite and we're

going to start asking questions about how our cells evolved.

Okay.

You might know that the prevailing theory is that back in the mists of time, there were

two different types of cell and one of the bigger types absorbed one of the little smaller

bacterial types and instead of eating it, dissolving it, consuming it, kept it around.

And that is the origin we think of, what's called eukaryotic cells, the complex cells in

animals and plants that have organelles in.

So the idea is we got organelles by essentially eating a bacteria and keeping it.

Mitechondria have their own little DNA in them and it's not the same as the nuclear DNA,

it's kind of like bacterial DNA.

Right, so mitochondria are thought to originally have been a bacterial cell or a pro-carion.

But other organelles, then, are they thought to have come from somewhere else as well?

Well, there's a kind of big gap in our understanding of eukaryotic cells because there's loads of

differences between us and the ancestors that would have been maybe absorbing little bacteria

and turning them into mitochondria.

We have nuclear membrane, we have other organelles as well and I don't think it's super

clear where they all came from, but this observation that the mitochondria can in some circumstances

shed some outer membrane and kind of make new organelles, that's really fascinating

because that could be a possible route for making other organelles.

This is a very new idea, but the suggestion here is that it could well be that other organelles

came from mitochondria, that them shedding their membranes made some of the other organelles

we find in ourselves.

Oh, so that's the evolution aspect that you mentioned.

Then obviously it's hard to know exactly what went on, what happens now.

This is an unusual finding like where the researchers take it.

Yeah, and it supports a particular theory, ideas that have been shared about how eukaryotic

cells and their organelles might have developed.

It's one little clue, it may be backs up an older paper that people were really skeptical

of, that maybe suggested the same thing, but now they might go and we look at that and

think, oh yeah, maybe there was something in that and maybe spur some new avenues of investigation.

I just think it's really interesting that such a niche look at the behavior of this strange

little parasite could give us this potential clue to this grand evolutionary question.

Well, that is a fascinating one and a strange finding that potentially opens up some broader

questions.

Let's move on to our second story today that also I guess opens up some questions, but

I think we need to hop into our absolutely real time machine for this.

We need to head back to the Lake Cretaceous period, like from about 100 to about 70 million

years ago.

I'd love a bit of Lake Cretaceous, yeah.

Well, we're going to meet an extinct creature that was potentially absolutely enormous

and a top underwater predator.

Now, this is a story that I read in nature and it's based on a paper in science.

Oh, underwater.

I was going to say, oh, is it dinosaurs or love dinosaurs, but underwater, so I guess

not.

There were some marine reptiles swimming around, a reckon Cretaceous times, at the Moser

Saws.

Maybe is that where we're going with this?

Absolutely.

That is the right sort of time.

Moser Saws, yes.

Giant aquatic reptiles, like 12 meters long, that's about 40 feet long.

Pleasier sores.

I know you're nice.

Pleasier sores.

Long neck many times.

Yeah.

And that's in the ocean.

And on land, of course, we've got T-Rex, that sort of time.

So this was a period of giant vertebrates, right?

These are big, old animals.

And it's often thought that invertebrates were kind of like, basically, dinner, essentially

for the other animals, quite small things.

But there may have been an animal that outstripped all these vertebrates.

It was an invertebrate, an octopus, in fact, and an absolutely gargantuan.

Wow.

But octopuses, I mean, octopuses can grow quite big today, but we're not talking shark

size.

Well, maybe we are.

So let me give you some facts.

So you're right, cephalopods more generally, so that includes octopuses, can get quite

big, right?

The giant squid can be like 10 meters long.

But this octopus is thought to be, well, about the length of a tennis court, so 19 meters

long, like 60 feet long.

So it would have potentially massively outstripped the most of the sores and things like that.

Now these animals have been identified from kightenous jaw fossils, right?

So octopuses have got kind of a beak that's made out of kighten.

And it's the only bit that survives the fossilisation period, really, because soft-bodied animals

don't preserve very well.

It's very unusual to find a soft-bodied animal.

So not much has been known about the size of these octopuses and their lifestyle and so

forth.

And that's what this new work has tried to maybe open the door on a little bit.

So are they essentially just guessing from the beaks, because the beak is all we have?

Everything else is an extrapolation.

Pretty much.

That's exactly right.

So the team re-analyzed 15 large fossil octopus jaws, and they found 12 new fossils as

well by looking at some carbonate rocks, and they worked with AI here to try and find

these things.

And they divided these animals into two species.

Now apparently these belong to the same evolutionary group as modern dombo octopuses.

You know these ones, they have got the little deer.

They flap along and they live quite deep.

That's right.

They actually fins to help them swim to the water.

Anyway, on the basis of the anatomy of modern octopuses, right, they've had to do some comparisons.

They reckon that one of the species, Nanomatithus Higatai, or Hagatai, I hope I'm pronouncing

that correctly, could have been, say, 19 meters long, potentially, although a lot of that

would have been its arms, right, the head part would potentially only have been a mere

four meters long.

Only four meters, right?

Yeah.

Ah!

I'm imagining that.

I feel like this is ripe territory for a horror movie of some kind, with a terrifying

giant quotation's octopus in.

Yeah.

Well, of course, the Kraken, that mythological cephalopod, that terrified sailors for centuries,

right?

That was potentially based on giant squids, which is, I say, about 10 meters long.

This one is twice as long as that, but not everyone, I have to say, is convinced.

A lot of this work, as we've said, is based on extrapolating and looking at modern octopus

species.

And there is a lot of variability in modern octopuses between the sort of headbit, I suppose,

and the arm length, right?

Some focus saying that maybe this octopus would have been at the lower end of the team's

estimates, putting it around just six and a half meters long.

Pretty small.

It's kind of hard to know, but the team have also made some other inferences as well about

the lives of these massive creatures.

Did they eat mosaules for breakfast?

Maybe not mosaules, but these beaks were pretty chipped, and they showed signs of

wear.

Now, the biggest one of these animals, they're reckon that maybe 10% of the jaw had been

worn down, maybe by crushing things like crustaceans and, you know, bivalves, smaller, hard

prey, which could chip this jaw.

And the author's reckon that the pattern of wear suggests that these animals were essentially

apex predators in the ocean during the Cretaceous period.

And what's kind of weird is that there's an asymmetric wear pattern.

So one side was maybe more worn down than the other.

And the author's reckon that this shows that these animals had a preference for kind

of how they ate, which suggests that maybe they were capable of complex behavior, if

they favoured one side over the other, suggesting that maybe these animals were pretty smart.

Now, we know that modern octopuses are very intelligent animals.

We've covered that on the podcast a lot.

But folk are cautious to kind of give these extinct animals an entire backstory based

on one bit of them.

It's hard to find out unless we use our obviously very real time machine, Germany, but I guess

this work does give us a little window into a lost past.

Like, there's so little that remains of these extinct soft-bodied animals, and I guess

hard to get a sense of what they were really like, find stomach content.

This sort of thing, but I do think these animals are absolutely fascinating.

These giant cephalopods, that whenever we see a video of what I'm like, right, must watch

that right now.

I want to see what it's all about, you know?

Yeah, you know, it's amazing how you can get so much information from sometimes just

such faint markings on a rock.

And I love that how it brings to life in my imagination this crack-and-like intelligent

giant octopus.

I love that.

Agreed.

A wonderful story.

And we'll put a link to it in the show notes, along with a link to the story you've

talked about today, Sharmini, listeners, I think that's probably all we've got time

for this week.

If you'd like to sign up to the Nature Briefing to get even more stories like this delivered

directly to your inbox, then look out for a link in the show notes.

Otherwise, all that remains to be said is Sharmini Bundel, thank you as always for being

with me today.

Thanks very much.

And thanks for listening everyone.

We'll see you next time.