Apple snails regrow their eyes - and may help humans do the same

Human eyes are masterpieces of biological engineering, but once damaged, they cannot rebuild themselves. Golden apple snails, by contrast, routinely replace an entire camera-type eye within a month.

In a new study, molecular and cellular biologist Alice Accorsi and colleagues at the University of California, Davis, show that snail and human eyes share both anatomical architecture and many of the genes that guide development.

By pairing those insights with new CRISPR-Cas9 genome-editing tools, the team has created a tractable system for probing the genetic logic of whole-eye regeneration. This knowledge could ultimately inform therapies for people who lose vision through injury or disease.

Invasion becomes inspiration

Pomacea canaliculata, native to South America but now invasive across the tropics, breeds fast, thrives in captivity, and possesses large, lens-bearing eyes mounted on stalks.

“Apple snails are resilient, their generation time is very short, and they have a lot of babies,” Accorsi said.

Those practical advantages overcome many of the hurdles that have deterred previous attempts to use gastropods in regenerative biology.

“When I started reading about this, I was asking myself, why isn’t anybody already using snails to study regeneration? I think it’s because we just hadn’t found the perfect snail to study – until now,” she explained.

Unlike planarians, which can regrow primordial light-sensing spots, or salamanders, which regenerate a functional retina but not an entire globe, the apple snail rebuilds every element of a complex camera-type eye. These include the transparent cornea, refractive lens, layered retina, and optic nerve.

That layout mirrors the vertebrate eye and sets the stage for meaningful cross-species comparisons.

Snail eyes mirror ours

Accorsi’s group combined high-resolution histology with transcriptome sequencing to map the similarities.

“We did a lot of work to show that many genes that participate in human eye development are also present in the snail,” she noted.

Canonical regulators such as the pax6, sox2, otx, and six gene families appear in the mollusc’s genome and activate during eye formation. Once regeneration is complete, “the morphology and gene expression of the new eye is pretty much identical to the original one.”

From the moment an eye stalk is amputated, the snail initiates replacement through coordinated phases. Wound closure seals the cut within 24 hours. Proliferating undifferentiated cells then invade the site, and by about day 15 the nascent organ shows recognizable lens fibers, retinal layers, and a reconnecting optic nerve.

Although fully formed, the tissue continues to mature for several more weeks. RNA profiling captured this transition: roughly 9,000 genes change expression early, but 1,175 remain different after 28 days, suggesting late-stage remodeling.

Editing snail genes for answers

To test gene function directly, the researchers established CRISPR-Cas9 mutagenesis in apple snail embryos.

“The idea is that we mutate specific genes and then see what effect it has on the animal,” Accorsi said.

As proof of principle, they knocked out pax6. Hatchlings carrying two inactive copies lacked eyes altogether. This demonstrates that, as in vertebrates and flies, pax6 is indispensable for initial eye assembly in snails.

The lab can now deploy the same strategy to explore whether pax6 or other regulators are also critical during regrowth in adults.

Rebuilding eyes from scratch

Imaging shows that regeneration begins with a burst of cell migration and proliferation near the stump. Accorsi hypothesizes that some of those cells originate from a reserve of stem-like cells at the base of the eye stalk. Others may derive from the surrounding epidermis or even blood-borne hemocytes.

Unraveling their lineage, and what signals tell them to adopt lens versus retina fates, will be a next challenge. With CRISPR, the team can tag cells or block signals to observe how regeneration stalls or progresses.

Behavioral tests are also on the agenda. “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 said.

Designing assays that reveal light-guided behavior – perhaps tracking movement toward shaded refuges – will confirm functional recovery. These tests will also set benchmarks for comparing successful and failed genetic manipulations.

From snails to human sight

Humans carry the same developmental genes, but in mammals they’re mostly silenced after embryogenesis ends. Identifying reactivation signals may reveal molecular switches to coax human eye tissues into 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 remarked.

That long-term vision will require bridging vast evolutionary and physiological gaps, yet the new model provides a rare example of full organ restoration in a complex eye.

Because the apple snail’s genetics, life cycle, and regenerative capacity are now accessible, it offers a powerful research model. It promises to illuminate not only ophthalmology but also broader questions of stem-cell plasticity, immune modulation, and scar-free healing.

A pest becomes a pioneer

Accorsi’s project also illustrates how curiosity-driven exploration can expand the experimental repertoire of biomedicine.

A problem that seems intractable in standard lab rodents may yield to an unexpected organism with the right combination of traits.

As Accorsi’s lab continues to map the genetic circuitry of eye regrowth – and perhaps inspire other groups to adopt the apple snail – what began as an invasive pest could become a luminous guide to restoring sight.

The study is published in the journal Nature Communications.

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