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Many groups in the animal kingdom have the remarkable ability to regenerate their eyes, but mammals are not one of them—at least, not yet.
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A new study analyzed the genetic mechanisms behind the ocular regenerative ability of the golden apple snail to see if a similar technique could be used in human eyes.
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Although separated by hundreds of millions of years of evolution, human eyes and apple snail eyes retain remarkable similarities, both physically and genetically.
Talk to most freshwater biologists, and you likely won’t find much love for the golden apple snail. An invasive species outside of South America, this freshwater snail (Pomacea canaliculata) is both extremely resilient and what is known as a prolific organism, meaning it makes a lot of babies. This is a one-two punch of bad news for conservationists.
But in a strange twist of fate, these particular attributes of the golden apple snail—along with its impressive ability to regenerate its eyes when damaged—made it the perfect test subject for Alice Accorsi, an assistant professor of molecular and cellular biology at the University of California (UC) Davis. So much so, in fact, that Accorsi was surprised no other study had yet detailed exactly how these snails wield such impressive powers of regeneration.
“When I started reading about this, I was asking myself, why isn’t anybody already using snails to study regeneration?” Accorsi, the lead author of the new study, said in a press statement. “I think it’s because we just hadn’t found the perfect snail to study, until now. A lot of other snails are difficult or very slow to breed in the lab, and many species also go through metamorphosis, which presents an extra challenge.”
In the experiment, Accorsi and her team developed methods to tweak the apple snail’s genome, hoping to better understand why it can regrow its eyes—an enviable ability that vertebrates (including humans) can’t seem to achieve. Although separated by more than 600 million years of evolution, humans and apple snails both have camera-type eyes that make use of a system of corneas, lens, and retinas. Accorsi also said that many of the genes that participate in human eye development can be found in these snails as well.
An apple snail’s ocular regeneration process takes a month from start to finish. In the first 24 hours, the amputated wound heals and unspecialized cells congregate in the area before building new ocular hardware. By day 15, all parts of the eye’s structure (including the optic nerve) are present, but the snail requires a few more weeks to fully mature. During this incredible process, scientists analyzed gene expression in the snail’s genome, and found that immediately upon amputation, 9,000 genes expressed themselves at different rates than they did in a normal apple snail. The team then used CRISPR/Cas9 techniques to edit a snail embryo’s genome—specifically, a gene known as Pax6, which is also known to control the development of the brain and eye in humans.
“The idea is that we mutate specific genes and then see what effect it has on the animal, which can help us understand the function of different parts of the genome,” Accorsi said in a press statement.
When the snail embryo had two non-functional copies of the gene—one from each parent—eyes didn’t develop at all once the snail reached maturation. Future studies will investigate if the manipulation of the gene in adult snails similarly impacts regeneration.
“If we find a set of genes that are important for eye regeneration, and these genes are also present in vertebrates, in theory we could activate them to enable eye regeneration in humans,” Accorsi said in a press statement.
The idea of regenerating human eyes isn’t new. A study published earlier this year in the journal Nature Communications showed evidence of the “first successful induction of long-term neural regeneration in mammalian retinas,” according to the researchers, by inhibiting the PROX1 protein that can block retinal cell types in animals, including ones that could help restore vision to those suffering from retinitis pigmentosa. Similarly, this research was inspired by the amazing eye-regenerating abilities of the zebrafish.
We humans may be the one with the big brains of the animal kingdom, but the varied biology of Earth’s incredible creatures still has so much to teach us.
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