Think of a reptile that's been genetically mutated, and Godzilla springs to mind. Or maybe ninja turtles.
But the real thing is here, and it's neither hell-bent on destroying Tokyo nor eating pizza in the sewers. Instead, it's a pale, finger-sized lizard — the world's first gene-edited reptile, researchers at the University of Georgia reported this week.
In a paper published in the journal Cell Reports, Douglas B. Menke and his colleagues described how they made an albino version of the brown anole (Anolis sagrei), a species of lizard native to Cuba and the Bahamas.
"Instead of performing gene-editing on fertilized eggs or single-cell embryos, we performed gene-editing on unfertilized eggs while they are still physically attached to the ovary of adult female lizards," said Menke, a geneticist and developmental biologist.
The first genetically modified animal was a transgenic mouse, created in 1974. But it was only seven years later that researchers could edit genes that were passed on to future generations. In the case of the albino lizard, the changes are inheritable.
Though gene editing has been around for decades and the advent of CRISPR technology makes it easier and is more efficient to carry out, doing so in reptilian zygotes is particularly challenging. Researchers consider it best to make an edit when the embryo is newly formed. For animals that reproduce sexually, the target is usually a single cell at this stage.
In reptiles, it's difficult to pin down when fertilization actually happens, in large part due to internal fertilization and sperm storage, where females can store sperm for extended periods. In A. sagrei lizards, the females can store sperm for more than two months.
The Anolis genus, which includes more than 400 species, is native to Central and South America and the Caribbean islands. Brown anole lizards are widely distributed beyond their native Cuba and Bahamas because they're a highly invasive species. The lizards used in the experiment were caught from the wild in Orlando, Florida.
The scientists performed surgery to insert gene-editing reagents into 146 unfertilized eggs of 21 adult female lizards. The females were then mated with adult males. A fraction of the resulting offspring carried the mutation, which manifested as albinism. The edit is unlikely to be lethal to the animals.
The downside of manipulating the egg and not the embryo is that it doesn't host the paternal DNA, reducing the chances that the edit will manifest in the offspring. For their study, the authors had to wait for three months for the lizard eggs to hatch to verify whether their editing method had induced the desired mutation.
Only about 6 to 9 percent of the eggs in which the edit was introduced produced mutant lizards. This is low when compared to other methods that report efficiencies of 80 percent or more. However, being able to produce the change in those few individuals is itself a breakthrough. The authors say the efficiency can be boosted by targeting larger eggs (more than 0.75 mm in diameter), which had the highest success rate in this experiment.
Editing genes is one of the key ways to deduce what role they play and which traits they're associated with. The University of Georgia researchers are already exploring different gene functions in Anolis lizards and say they hope this will aid in the study of genetic defects in humans. For example, people with albinism are also likely to have poor eyesight due to defects in a part of the eye called the fovea. Mice that are widely used for genetic studies don't have a fovea and so studying in albinism in mice may not shed light on the link between albinism and impaired vision.
Gene editing can also be used to curb invasive species populations. Its most widely known application is to control mosquito populations, but with advances in gene editing this could be extended to invasive reptiles as well.
"There are over 10,000 described species of reptile, and the genome of each species contains around 25,000 protein-coding genes. There is a whole universe of unstudied biology in these animals," Menke said. "We hope that other research groups will adapt our gene-editing method to investigate gene function in additional reptile species."