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

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0:51Hi, 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 roundup of the latest science stories and joining me today to chat is none other than sharmony bundell sharmony 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 tell me what you've got look i'll give you the preview it's got mitochondria we all love mitochondria ding it's got parasites ding it's got evolution I love evolution. Ding, ding, ding, ding, ding.

1:24This 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. 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 poo so you don't get toxoplasmosis right but it's actually a really common parasite and it's also here's a little side tour it's the one that changes the behavior of rodents to make them more likely to get eaten by cats they stop being scared.

2:20Yeah, that's a whole nother 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 for outer mitochondrial membrane spots. And those little spots went and engulfed some other little organelles, little things in the cells called lysosomes, which do sort of waste disposal jobs in the cell.

3:01And it turns out that this weird change was actually helpful to the parasite. When 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. Yes. Something that you would expect is a defence 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 And the implication here is that this is an adaptation by this parasite to benefit it by manipulating these mitochondria.

4:13And 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. So 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.

5:00So the idea is we got organelles by essentially eating a bacteria and keeping it. Mitochondria 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, so are prokaryotic. 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.

5:33You know, 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 our cells. Oh, so that's the evolution aspect that you mentioned then.

6:14Obviously, it's hard to know exactly what went on. What happens now? This is an unusual finding. Like, where do researchers take it? Yeah, and it supports a particular theory, ideas that have been shared about how eukaryotic cells in their organelles might have developed. It's one little clue. It maybe backs up an older paper that people were really sceptical of that maybe suggested the same thing, but now they might go and re-look at that and think, oh yeah, maybe there was something in that, and maybe spur some new avenues of investigation. but I just think it's really interesting that such a niche look at the behaviour of this strange little parasite could give us this potential clue to this grand evolutionary question.

6:55Well that is a fascinating one and a strange finding that potentially opens up some broader questions but 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 late Cretaceous period, like from about 100 to about 70 million years ago. I'd love a bit of late 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.

7:31Oh, underwater. I was going to say, oh, is it dinosaurs? I love dinosaurs. But underwater, so I guess not. There were some marine reptiles swimming around, I reckon, Cretaceous times, mosasaurs ichthyosaurs maybe is that where we're going with this absolutely right that is the right sort of time so mosasaurs yes giant aquatic reptiles like 12 meters long yeah it's about 40 feet long plesiosaurs i know you and i have spoken about plesiosaurs with their 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 one 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 metres long.

8:38But this octopus is thought to be, well, about the length of a tennis court. So 19 metres long, like 60 feet long. So it would have potentially massively outstripped the mosasaurs and things like that. Now, these animals have been identified from chitinous jaw fossils, right? So octopuses have got kind of a beak that's made out of chitin. 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.

9:17And 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 reanalyzed 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 Dumbo octopuses. You know these ones that have the little ears?

9:53And they flap along and they live quite deep. That's right. They're actually fins to help them swim to the water. Anyway, on the basis of the anatomy of modern octopuses, rights they've had to do some comparisons they reckon that one of the species nanomotithis haegati or hageti 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 i'm imagining that i feel like this is ripe territory for a horror movie of some kind with a terrifying giant cretaceous octopus in Yeah, well, of course, the kraken, that mythological cephalopod that terrified sailors for centuries, right?

10:39That was potentially based on giant squids, which, as I say, about 10 metres 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 head bit I suppose and the arm length right some folk are 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 mosasaurs for breakfast maybe not mosasaurs but these beaks were pretty chipped and they showed signs of wear now the biggest one of these animals they reckon maybe 10 of the jaw had been worn down maybe by crushing things like crustaceans and you know valves smaller hard prey which could chip this jaw and the authors 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 authors 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 favored 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 yeah but i guess this work does give us a little window into a lost past like there's so little the remains of these extinct soft-bodied animals and i guess hard to get a sense of what they were really like fine stomach contents this sort of thing but i do think these animals are absolutely fascinating these giant cephalopods like whenever we see a video of one i'm like right must watch that right now i want to see what it's all about 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 how it brings to life in my imagination this kraken 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 shalmany 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.

13:36Otherwise, all that remains to be said is Shalmany Bundel, thank you as always for being with me today. Thanks very much. And thanks for listening, everyone. We'll see you next time. If you work in university maintenance, Grainger considers you an MVP because your playbook ensures your arena is always ready for tip-off. And Grainger is your trusted partner, offering the products you need all in one place, from HVAC and plumbing supplies to lighting and more, and all delivered with plenty of time left on the clock, so your team always gets the win. Call 1-800-GRAINGER, visit grainger.com, or just stop by.

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