This ASU researcher is looking at the sex chromosomes of Gila monsters
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A team of scientists at Arizona State University has become the first to fully sequence the genome of the Gila monster. The work also allowed the researchers to gain insights into the evolution of sex chromosomes. And, they were able to do it thanks to a crowdfunding effort that raised more than $10,000.
Melissa Wilson is an associate professor of genomics, evolution and bioinformatics at ASU joined The Show to talk more about the project and how sex is determined in the lizards.
Full interview
MARK BRODIE: Why is it important to know how sex is determined in Gila monsters?
MELISSA WILSON: I think particularly thinking about our understanding of sex determination can be important for understanding species history and how species might respond to changes in climate or changes in environment, whether that be humans building over their homes or just changes in precipitation that might affect how they interact with each other.
So, we know in squamate reptiles, so that's snakes and lizards, they have pretty much every form of sex determination imaginable. That means that they can have genetic sex determination, which is the thing that we are most familiar with. Or they can have environmental sex determination. There are some species like the whiptail lizard also here in Arizona that are parthogenic. So they are just females that will make an egg that makes arguably a clone of herself. And so trying to understand why there's such a wide range of sex determination mechanisms across squamate reptiles is a more fundamentally interesting question.
And then when it comes to the Gila monster, we'd like to know how is sex determined and how might that change with changing environments for the Gila monsters?
BRODIE: So what have you learned about sex determination in Gila monsters?
WILSON: So we, we know, and we knew a little bit, we knew from imaging, or we thought we knew from imaging, that their sex chromosomes are the opposite of ours. So in humans, people may be familiar with genetic females, typically having two X chromosomes and genetic males typically having an X and a Y chromosome. And that means the individuals that have testes and make sperm can make a sperm with either an X or a Y typically.
But in Gila monsters, it's the opposite. It's the female Gila monsters that lay an egg that can make an egg with either a large Z chromosome or a small W chromosome. And so it's entirely swapped from our sex determination system. And, and one, I think that's pretty cool. And, and then we further went on to try to study what are the consequences of that in humans and mammals?
For example, because half of the population has two X chromosomes and half of the population typically has a single X chromosome, there is a process called dosage compensation where you actually get silencing of one of the two X chromosomes so that you have roughly one X chromosome expressed in individuals with two X chromosomes and roughly one X chromosome expressed in individuals with one. So you have equal gene dosage between everybody across everyone. It turns out Gila monsters don't do that. They actually, we, we were able to as part of this project, not only study their genome, but also study the genes that are expressed or turned on and off and how much they are on the Z and Z chromosome. And they don't compensate for having two Z chromosomes or a single Z chromosome at all. And I find that really exciting. Why, why do we do this process of compensating genes and Gila monsters do not?
BRODIE: So, what are the consequences of that? Like, what kind of impact does that have on the sexes in Gila monsters?
WILSON: Yeah. I, we don't know yet. I think one of the most exciting pieces of this project is that it's opened up a lot more questions for us to investigate. So we don't know why or what the consequences are of ZZ males having more expression on the Z chromosome than ZW females. And I think that's one of the areas that we'd like to go into in the future.
BRODIE: Yeah. So how does this relate back to humans? Like, are you able to learn, are you able to apply what you've learned, at least so far, with sex determination to heal a monsters to help understand anything more about humans?
WILSON: I'd say, in particular, in this case, we're, we're much more removed from humans. Usually the research in my lab relates back to humans in many ways. In this particular case, it is all about the monster. It's, it's literally everything trying to understand what is going on in this particular critter. And, and because its mode of sex determination is so very different from our own, I can say at least that it, it's a good reminder of how very far removed the process of sex determination is from the actual organism being male or female.
BRODIE: Well, are there other reptiles or other non reptile species that do it this way like Gila monsters do or are they entirely unique in the animal kingdom?
WILSON: Oh, they, they're not unique in the animal kingdom but — well, man, I'll take that back. Gila monsters are so cool. They are, they are unique in the animal kingdom, but their mode, so using this mode called ZZZW where it's the egg producers that can produce an egg with a Z or W, the two different kinds of sex chromosomes. That's been observed in in birds, actually, in all birds that we've, we've looked at including hummingbirds and ostriches, right? Every bird uses this ZZZW mechanism. Also, also butterflies use this ZZZW mechanism. So it's been observed in very different kinds of species but still a very limited number of species that exist. So we still as a, as humans, we don't know the sex determination mechanism for most species that exist.
BRODIE: Is it fair to assume then that if there are other animals you mentioned birds and others that have this ZZZW chromosome makeup like Gila monsters, is it fair to assume that there might be other similarities between those animals? Or could it just be that, that their sex determination is the same, and that's it?
WILSON: That's a really excellent question. And what we understand from doing comparative genomics is that when we call something ZZZW, it actually doesn't mean it's the exact same genes or even the same chromosomes. All that ZZZW means is that it's the egg producers that can make an egg with a large or a small sex chromosome.
And it's, it's like if you, you went around the world and you asked everyone to show you a hammer, right? And the hammer might look very different. So you might have a very large hammer with a large metal head or maybe someone's using a mallet that's made of wood, but it all does the job. It's a hammer, it will hammer and a nail. But we don't necessarily think that those hammers are exactly the same and we still call it a hammer, right. But it, it has a slightly different origin or maybe a completely different origin. And that's the same way with the sex determination with ZZ or ZW. We think that different chromosomes got looped into the role or roped into the role of being a sex chromosome.
And sometimes it happens that it's the egg havers that can make two different kinds of eggs, and sometimes it's the sperm producers that can make two different kinds of sperm. But, but it just gets picked up independently over and over throughout life, which is, is pretty cool.
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