Genetic mapping and comparative genomics show the lncRNA ANTSR multiallelic locus in Aculeata directs female development via heterozygosity despite lacking sequence homology.
0:00Welcome to Base by Base, the papercast that brings genomics to you wherever you are. Thanks for listening, and don't forget to follow and rate us in your podcast app. It's great to be here. So today, we're doing a deep dive into a study that, honestly, it kind of challenges how we even think about finding important stuff in the genome.
0:17It really does. I think to start, it helps to frame the problem. Think about how nature decides male or female. In mammals, like us, it's, well, it's pretty stable. Very stable. You have the Y chromosome, the strygene.
0:33It's a master switch. Exactly, a master switch. And it's been doing that same job for something like 160000000 years. You can look across different mammals and you find it. The sequence is recognizable.
0:43Right. It's a classic example of conservation. The function is critical. So the DNA sequence itself stays pretty similar over time. But then you look at insects. And everything you read suggests it's just chaos.
0:55It's the Wild West of genetics. That is absolutely the prevailing view. Yeah. The standard model, the Wilkins model, basically says sex determination evolves from the bottom up. Meaning the genes at the end of the process are old and stable.
1:08Right, genes like double sex. They're ancient. But the master triggers at the very top of that cascade. They're supposed to be changing all the time. Constantly, evolution just swaps them out. A fly does it one way, a B another, a beetle a 3rd way.
1:23It's like they're all disposable. So the assumption has been, okay, there is no single ancient sex determining system for insects, but the paper we're looking at today just throws that out the window. It says, no, it exists.
1:36just couldn't see it. We couldn't see it because we were looking for the wrong thing. We were stuck on this idea that to have a conserved function, you must have a conserved sequence. We were looking for matching letters.
1:45And this study finds a master switch in ants, bees, and wasps that's been doing the exact same job since, what, the time of the dinosaurs. And yet. And yet the DNA sequence has 0 similarity between them.
1:58It's a functional ghost. It's there, it does the job, but it's invisible to our usual tools. It makes you wonder then how much else we're missing. I mean, a vital control switch can hide in plain sight for 150000000 years, just because the sequence has changed.
2:12How much of the so-called junk DNA is actually doing something essential? It's a huge question. It is. Okay, so let's get into the source material for this deep dive. The paper is titled deep evolutionary conservation of a sex determining locust without sequence homology.
2:28It's a bit of a mouthful, but it really nails that paradox, doesn't it? Deep conservation without the sequence homology you'd expect. And we should give us special recognition here. This is a massive undertaking.
2:39You're talking about the work of Twang Sinu, Dean Hodap, Safira Mug, and a whole team of colleagues. A huge collaboration. It brought together the Max Planck Institute for Biology in Germany, Johannes Gutenberg University, the University of Tours in France, just a major international effort.
2:55And what I love is that they didn't just sit at a computer. This wasn't only bioinformatics. Not at all They knew that to solve this, they had to get their hands dirty. They combine these huge genomic comparisons with actual real world breeding of bees and hornets.
3:09They had to connect the digital model to living animals. So before we get into how they found this invisible gene, Let's set the stage. The biological context here is hymenoptera. So that's the group that includes all the ants, bees, and wasps, and their sex determination system is, well, it's pretty unusual.
3:28haplo deploidy. Right. So put simply fertilized eggs. They get DNA from both mom and dad. They're deployed, and they become females. And the unfertilized eggs, they only get DNA from the mother, so they're haploid.
3:42And they become males. So males don't have fathers. It's a weird thought. But the paper points out that this system has a really big flaw. It's not just about counting chromosomes. No, it's more subtle than that.
3:51It all comes down to a specific spot in the genome, the complementary sex determiner or CSD locus. And the rule is, what you need 2 different versions to be female. Exactly. It's called a lyic complementarity.
4:04For the cell to trigger the female development pathway, it needs to see 2 different versions or allelies of this gene. One from the mother, one from the father. So if the 2 copies are different, the switch flips to female.
4:18Okay, but what happens if, by chance, an egg gets the exact same version from both parents? And that's the fatal glitch in the system. If it's homozygous, meaning it has 2 identical copies, the whole mechanism fails.
4:31It doesn't recognize femaleness. So even though the egg was fertilized and is deployed, it develops as a male. A deployed male. And these are usually sterile, right? A total dead end. Almost always sterile, yeah.
4:43They're a huge drain on the colony. They eat resources but can't reproduce. So natural selection is pushing really hard to avoid making them. Okay, so that's the gap the researchers were looking at. Scientists knew about this mechanism, and they'd even found a possible location in the Argentine ant called ANTSR.
4:59Right. But the big question was, is NTSR just some weird thing that only ants do? Or is it something much, much older? The ancestral switch for all stinging insects. And the problem was, when they used the standard tool, blast, to look for NTSR in, say, a B or a WASP.
5:16They found nothing, not a sausage, no matches at all, which, you know, for years supported the idea that these genes just don't last. Which brings us to their method. And I thought this was so clever. When you can't find something by its name, you look for it on a map, they use Synony.
5:32Centony is just such a powerful tool for looking across deep time. It's um, think of it this way. Imagine you're looking for a specific kind of shop. The name of the shop changes in every city. The building looks totally different.
5:43So you can't recognize it just by looking at it. Exactly. But what if you knew that this shop was always located right between the post office and the fire station? Ah, you'd look for the neighbors, the landmark.
5:54You look for the landmarks. symphony. They analyzed 41 different genomes of ants, bees, and wasps. They stopped trying to find the sequence of the sex gene itself, and instead looked for the protein coating genes around it that are conserved.
6:08And they found a pair of landmarks. Two genes, creled 2, and Thumbi 3. And like clockwork, in almost every species, these 2 genes were sitting there. And sandwiched right between them was this, this genomic interval, something was always there.
6:24But the sequence of that something was completely different every time. Utterly different. So now they have a suspect location, but that's just a correlation. They had to prove that this specific block of DNA actually controls sex.
6:36Which is where they move from the computer to the lab. They had to force the system to break. They had to make those deployed males on purpose. So they started with bumblebees, Bombas terrestrious. They set up brother sister crosses.
6:49Which is a really fast way to get inbreeding and increase the chances of getting too identical allel. Absolutely. So they did that. They got colonies that were producing these sterile, deployed males. And then they sequenced everyone, the normal females, the deployed males.
7:03They were testing a very specific prediction. If their theory is right, the females have to be heterozygis at that spot. different copies. Yeah. And the diploid males have to be homozygous, identical copies.
7:15And that is precisely what they found. In 9 different colonies that they tested, the pattern was perfect. Every single deployed male was homozygous, right there, in that little window between Krilled 2 and thumb B 3.
7:29And they didn't stop there. They did the same thing with the Asian hornet, Vesto Volutina. Yeah, and this was really cool. They didn't even have to breed them in the lab. The invasive hornet population in Europe is basically a giant, uncontrolled, inbreeding experiment.
7:42Because it started from just a few individuals. A tiny number of founders. Yeah, so they're naturally inbred. The researchers just had to go out, collect wild, deployed males and sequence them, and they found the exact same signature.
7:54A chunk of DNA on chromosome 23, homazygus in the males, heterozygus in the females. So the proof is solid. We have the location, we have the function confirmed in ants, bees, and hornets. So what is this gene?
8:07It's not a normal protein coating gene, is it? No, and this is the real key to the whole mystery of the invisible sequence. The locust produces a long non-coding RNA, a elm CRNA. Okay, let's untack that.
8:19Why does it being an LNCRNA matter so much for this conservation paradox? Well, think about a normal gene that codes for a protein. The DNA sequence is under really strict constraints. If you change the DNA letters too much.
8:34You change the amino acids, the protein misfolds, and it stops working. That's purifying selection. It keeps the sequence stable. But LNCRNAs are different. Very different. They don't make proteins. Their function isn't in their translation.
8:48It's in their shape. The RNA molecule itself folds up into a complex 3D structure, and that structure is what does the job. So you can change a lot of the letters, the primary sequence, as long as the final folded shape stays more or less the same.
9:02Exactly. The sequence is fluid, but the structure is frozen in time. That's why Blast couldn't find it. The letters had changed so much over 150000000 years that the conservation scores were, well, they were basically zero.
9:13Zero. That just that blows my mind. It is the same genetic element, doing the same critical job in the same genomic location, but it looks totally alien when you compare the sequence for one species to another.
9:24It completely flips the script on how we define conservation. We're trained to think that if a sequence isn't conserved, it must not be important. This proves a sequence can be hyper variable and still be absolutely essential.
9:35Now, some of our listeners might be thinking about honeybees. They're probably the most famous hymenopteran. Do they use this ancient ANTSR system? That's a great question, and surprisingly, no. Honeybees, the genus apis, are the exception that proves the rule.
9:50They actually lost this system. They lost it. Yeah, somewhere in their evolution, they discarded this ancient LNCRNA switch and evolved a completely new one, a protein coding gene called CSD. So the ANTSR system we're talking about is the ancestral state, the original.
10:06The Honey BCSD is a much more recent invention. Wow, so ANTSR is the ancient standard. Okay, so let's shift to the implications. This is obviously huge for evolutionary biology, but does it have any, you know, practical uses?
10:18You mentioned the Asian hornet. It does, yeah. The Asian hornet is a massive invasive pest in Europe. It's devastating for native pollinators, especially honeybees, and this study found a potential Achilles heel.
10:29An Achilles heel. When they looked at the ANTSR locus in that invasive French population, they found incredibly low genetic diversity, just a handful of different alleles. How low are we talking? They only found 4 distinct versions?
10:43Four Hablo types in all the hornets they sampled. In a healthy native population back in Asia, you'd expect to find dozens and dozens. And because of that rule that you need 2 different alleles to make a female worker low diversity is a huge problem for them.
10:58It's a disaster. If there are only 4 keys floating around in the population, the chances of a queen mating with a male that has a matching key skyrockets, and every time that happens. You get a sterile deployed male instead of useful female workers.
11:11Exactly. It weakens the colony, it stifles its growth. This genetic bottleneck is a major vulnerability that we can now track. We can monitor the diversity at this one spot to predict how healthy or dangerous an invasive population is.
11:26But we could flip that around, couldn't we? Use it to monitor the health of NATO pollinators, like bumblebees. Absolutely. Many bumblebee populations are in decline, and inbreeding is a big concern. We could sample a population, sequence this one locus.
11:40And if we see that the number of alleles is dropping. an early warning sign. It's a canary in the coal mine for inbreeding depression. It gives conservationists a tool to act before population collapses.
11:51So this deep evolutionary research has very real, very immediate applications. That's fantastic. Okay, so let's boil this all down. What is the one take home message you want our listeners to walk away with?
12:03I think the central insight is that this one locus, ANTSR, is a 150 million-year-old master switch that completely defies our standard definition of conservation. It proves that function can be locked in for eons, even while the underlying sequence is totally rewritten.
12:20It's not about the letters, it's about the structure. Exactly. Sequence does not always equal function. The genome is way more flexible and yet more stable than we give it credit for. And that leaves me to the thought I want to leave you with.
12:31We only found this ancient essential switch because the researchers had the insight to stop looking at the code and start looking at the map, the centony. So it makes you wonder. What does this mean for the rest of the genome?
12:46If such a vital mechanism can hide in plain sight all this time, how many other ancient essential switches are we missing? How many are out there hidden in what we call junk DNA, just because our tools are designed to read a language that they no longer speak?
12:59It feels like we might have to go back and learn a whole new language. This episode was based on an open access article under the CCBY4.0 license. You can find a direct link to the paper and the license in our episode description.
13:12If you enjoyed this, follow or subscribe in your podcast app and leave a 5 star rating. If you'd like to support our work, use the donation link in the description. Now stay with us for an original track created especially for this episode and inspired by the article you've just heard about.
13:26Thanks for listening and join us next time as we explore more science, base by base.
