DAVIS, Calif. — While human eyes, once damaged, can’t regrow, golden apple snails can replace an entire eye within a month. Researchers at the University of California, Davis, discovered that snail and human eyes share similar structures and developmental genes. This finding, combined with new gene-editing tools, creates a system to study eye regeneration. This could lead to therapies for vision loss in humans.
A Pest Becomes a Pioneer in Eye Regeneration Research
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Golden apple snails can regrow complex eyes, offering insights into human vision repair.
Molecular and cellular biologist Alice Accorsi and her team at UC Davis are studying the *Pomacea canaliculata* snail, native to South America but now invasive in tropical regions. These snails reproduce rapidly, thrive in captivity, and possess stalk-mounted eyes with lenses.
“Apple snails are resilient, their generation time is very short, and they have a lot of babies,” Accorsi said. These traits make them ideal for regenerative biology studies, overcoming challenges faced in previous research.
Unlike planarians, which regrow simple light sensors, or salamanders, which regenerate retinas but not whole eyes, apple snails rebuild every component of their camera-type eyes. This includes the cornea, lens, retina, and optic nerve. This structure mirrors the human eye, facilitating comparison.
Accorsi’s research used high-resolution histology and gene sequencing to identify similarities between snail and human eye development. “We did a lot of work to show that many genes that participate in human eye development are also present in the snail,” she stated.
Key genes like pax6, sox2, otx, and six are found in the snail’s genome and are active during eye formation. Once regenerated, the new snail eye’s structure and gene activity are nearly identical to the original.
When an eye stalk is removed, the snail begins regeneration within 24 hours. Undifferentiated cells migrate to the site, and by approximately 15 days, the new eye shows recognizable lens fibers, retinal layers, and a reconnecting optic nerve. The tissue continues maturing for several more weeks, with gene expression changes indicating late-stage remodeling.
CRISPR Unlocks Gene Function in Snail Eye Regeneration
The team developed a method to edit apple snail genes using CRISPR-Cas9. This allows them to test the function of specific genes in regeneration. “The idea is that we mutate specific genes and then see what effect it has on the animal,” Accorsi explained.
As a test, they deactivated the *pax6* gene. Snails with two inactive copies were born without eyes, confirming *pax6*’s essential role in eye formation, similar to its function in vertebrates and flies. This method can now be used to determine if *pax6* and other genes are also crucial for adult eye regrowth.
The Process of Rebuilding a Snail’s Eye
Imaging reveals that regeneration starts with cell migration and growth at the site of injury. Accorsi suggests that stem-like cells at the eye stalk base may contribute, along with cells from the surrounding skin or blood. Future research will focus on tracing these cell lineages and understanding the signals that guide them to become lens or retina cells.
Behavioral tests are also planned. “We still don’t have conclusive evidence that they can see images, but anatomically, they have all the components that are needed to form an image,” Accorsi noted. Observing behaviors like moving towards shade will confirm functional recovery and provide benchmarks for genetic manipulation experiments.
From Snail Regeneration to Restoring Human Sight
Humans possess similar developmental genes, but they are largely inactive after embryonic development. Identifying signals that reactivate these genes could provide methods to encourage human eye tissue self-repair.
“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. Bridging evolutionary differences is a challenge, but the apple snail offers a rare model for full organ regeneration in a complex eye.
The snail’s accessible genetics, life cycle, and regenerative capabilities make it a powerful research tool. It holds promise for advancing ophthalmology, stem cell research, and understanding scar-free healing.
Accorsi’s project highlights how exploring unexpected organisms can advance biomedical research. What was once considered a pest could become a key to restoring human vision as scientists continue to map the genetic pathways of eye regrowth.
The study is published in the journal *Nature Communications*.
