Leopard geckos, native to the Middle East and Asia, are the most common reptiles kept as pets. The lizards are easily bred in captivity, and breeders often create morphs, or variants, with unique color patterns that occasionally sell for thousands of dollars.
When reptile breeder Steve Sykes saw two leopard gecko morphs with an unusual, lemon-sorbet hue and small, black dots at an auction in 2015, he purchased them on the spot, reports Christie Wilcox for The Scientist. (The pair sold for a whopping $10,000.)
Sykes named the reptiles Mr. and Ms. Frosty because they belong to a rare variety of so-called “lemon frost” leopard geckos. When observing their offspring, Sykes noticed small, white lumps growing on some of baby lizards’ bodies, reports Maddie Bender for Scientific American.
As Sykes bred Mr. Frosty with other female lizards, he soon created a colony of more than 900 babies, reports Maria Temming for Science News. Out of all Mr. Frosty’s offspring, 80 percent developed tumors before they were five years old.
Then, Sykes received an email from Longhua Guo, a geneticist at the University of California, Los Angeles. Guo and his team were interested in learning more about the genetics behind color variations in geckos. Instead, Sykes immediately suggested that Guo’s team investigate what was going on with his lemon frost geckos, The Scientists reports.
Now, in a new study published in this month in PLOS Genetics, the researchers found a gene linked to melanoma in humans is also responsible for both the lemon frost leopard geckos' buttery hue and their deadly tumors. With further research, Mr. Frosty and his descendants may help scientists better understand skin cancer progression in humans and design future treatment methods, The Scientist reports.
Through genetic testing, the researchers found that the lizards had developed a mutation on one copy of the gene SPINT1, which has previously been linked to cancer in humans, The Scientist reports.
"It turns out that SPINT1 can explain what is going on here because SPINT1 has been reported in zebrafish, in mice, and humans. [Mutations in the gene] are associated with skin-cell tumors," Guo tells Scientific American.
The mutated gene causes an overproduction of iridophores, or pigment-producing cells in lizard scales, Scientific American reports. Iridophore overproduction gives the lizards their unique pastel color, but seems to cause tumors.
However, one mystery remains: some lizards developed large tumors that quickly grew within months, while others had slow-growing, small tumors that developed over the course of several years. (And some, like Mr. Frosty himself, never develop visible tumors at all.) Guo and his team suspect other genes may influence the more rapid form of tumor progression, reports The Scientist.
Per Scientific American, a tumor suppressor gene may be preventing the spread of cancer in some cases, which could be an intriguing avenue for future study, says conservation genomics expert Lara Urban of the University of Otago in New Zealand, who was not involved with the study.
"I do think it will have an impact on cancer research, in that we understand the conservedness of this [SPINT1 genetic] pathway a little bit better now," Urban tells Scientific American. "It will also be a potential new model organism for studying the development of skin cancer and contributing to actual therapeutic development."
To further study the tumors and possible treatments, Guo hopes to culture cancerous iridophores in the lab, The Scientist reports.
As for Mr. Frosty and his lineage, Sykes donated the geckos to science and no longer breeds lemon frost leopard geckos as pets.
“We’ve stopped breeding lemon frosts, and we have no intentions to start it up again in the future,” Sykes tells Scientific American. “My goal is to produce beautiful, perfect, healthy geckos. And it doesn’t appear that it’s possible to separate the lemon frost gene from this tumor phenotype.”