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ASU researchers first to fully sequence Gila monster genome, thanks to crowd-funding campaign

Findings enable new insights into genome structure, sex chromosome evolution

A gila monster is perched next to a cactus with its mouth open.

Only 1.2% of squamates, or scaled reptile species — such as the Gila monster — have had their genomes sequenced, compared with 15% of all mammal species, according to Brendan Pinto, who leads the ASU Sex Chromosome Lab’s ongoing research on the Gila monster. Photo by kwiktor/iStock

February 28, 2024

The Sonoran Desert is full of wild creatures, from sharp-tailed scorpions that glow under black light to desert toads that secrete hallucinogenic toxins from their skin. Perhaps no creature, though, is more unique –– or beloved –– than the venomous and elusive black-and-orange Gila monster: the largest lizard in the United States, which lives exclusively in the Sonoran Desert. 

Arizonans take great pride in their Gila monster, so much so that in 2016, when Arizona State University evolutionary biologist Melissa Wilson launched a crowd-funding campaign to sequence the creature’s genome, she raised over $10,000 in donations. Now, years later, Wilson’s team has at last accomplished that long-awaited goal: They recently announced that they are the first to assemble the complete genome of the Gila monster in a new study in Genome Biology and Evolution. 

“It feels incredible to be able to deliver on our promise to the community,” Wilson says. 

The researchers weren’t just interested in the Gila monster for its beloved status, though. Wilson, who runs the Sex Chromosome Lab at ASU, explains that sequencing the Gila monster has allowed her lab to learn “new and exciting things about genome structure and sex chromosome evolution.” 

Many vertebrate species have a pair of sex chromosomes, which carry instructions related to sexual development, like what reproductive system an organism will have. Mammals have a relatively consistent sex chromosome system: Females tend to have two X chromosomes, while males typically have an X and a Y. Reptiles, though, are much more diverse. Some have an XX/XY system that works similarly to mammals, while others like the Gila monster are entirely different: Males typically have two Z chromosomes, while females typically have one Z and one W. And even between reptiles that have the same chromosome system, the genes on their chromosomes can still vary. 

That diversity among reptiles’ genomes can give researchers insight into how and why different chromosome systems evolved. But reptiles are incredibly understudied. Only 1.2% of squamates, or scaled reptile species, have had their genomes sequenced, compared with 15% of all mammal species, according to Brendan Pinto, who leads the Sex Chromosome Lab’s ongoing research on the Gila monster.  

Pinto says that filling that knowledge gap is “super important. ... These (less studied) systems are going to tell us far more about how evolution works. ... In vertebrates, this is sort of the front lines on ... saying something conclusive about how sex chromosome evolution works.” 

To get the Gila monster DNA, the researchers drew a blood sample from a male Gila monster. Dale Denardo, an environmental physiologist and ASU’s resident veterinarian, is a huge Gila monster fan, having spent 20 years studying how the reptiles are adapted to survive in the desert, with characteristics like hunting for food at night and “lumbering” rather than sprinting to conserve energy when they move. Gila monsters even store water in their urinary bladder that allows them to survive for up to 90 days without drinking, Denardo says –– the bladder “serves as a canteen.”  

Denardo believes having a full genome sequence for the Gila monster will be useful to future Gila monster research beyond studying sex chromosomes.

“This is just one application of the genome,” he said. “We can do a lot of comparison as we get more and more genomes across species. ... We can sequence them all and then look at differences ... and see what drives these evolutionary processes.” 

For now, though, the researchers at the Sex Chromosome Lab are focusing on the genes that exist along, well, the sex chromosomes. Because the Gila monster studied is a male, the researchers only know the sequence of the Z chromosome for now. That’s why Pinto is leading a project to sequence a female’s genome next, which should help the team understand the differences between what genes males and females have, and how they are expressed. While the initial sequencing project took six years, Pinto expects further sequencing projects to happen much quicker.  

“We’re still in the early stages. ... Once we start picking up, I think (the results) are going to be pretty exponential.” 

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