Scientists restore sight to blind cave fish

[Wayne Harrison]

Last Updated: Monday, January 7, 2008 | 1:06 PM ET
CBC News

Cross-breeding blind cave fish with those from separate populations of blind cave fish can partially restore their vision, overriding half a million years of evolutionary change, say U.S. scientists.

"These fish are descended from ancestors that have been isolated in the dark for nearly one million years and most likely haven't had the capacity for vision for at least half that time," New York University biology professor Richard Borowsky, the study's lead author, said in a release.

"But by recombining the right genes through hybridization, you can partially restore vision. Not only are the structures of the eye restored to the point where they regain function, but all the connections to the brain for proper processing of information not used for that enormous length of time are restored."

The finding, which may have implications for understanding human eyes, was published in Monday's issue of the journal Current Biology.

The study suggests that genetic engineering can override, at least in part, evolutionary change in just one generation. That's because mutations in different genes are responsible for the loss of sight in separate cavefish lineages.

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Blind cave fish see the light

By mating blind fish from distant underwater caves, researchers have bred offspring that can see.

The results, published this week in Current Biology 1, show that the two populations took different evolutionary paths to blindness.

“We’ve basically shown that these different populations have converged upon the same outward appearance independently, and that they use different genes to do it,” says Richard Bolowsky of New York University.

The blind fish, called Astyanax mexicanus , live in isolated limestone caves in northeast Mexico. Over hundreds of millennia of living in darkness, the fish, which have a sighted ancestor, accumulated genetic mutations that affect eye development, and so lost their sight. Today some 29 different varieties of the blind Mexican fish live in isolated caves. Researchers have long wondered whether they all lost their sight the same way or not.

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[driggs]

A. mexicanus' blindness was once explained as a withering of sight through disuse, but may instead go fin-in-fin with the advantages of system-wide gene overexpression. This burns out A. mexicanus corneas but also gives them powerful jaws, refined taste buds and sensitivity enough to navigate by fluctuations in water pressure.

However, because A. mexicanus populations arrived at blindness separately since their mid-Pleistocene era arrival in Mexico, different populations lost their sight in different ways. Each population has its own set of blindness-producing mutations; the NYU researchers reasoned that, if crossed, the differing mutation sets would cancel each other out, producing fish that could see.

Lo and behold, it did: after a million years of increasing darkness, just a single generation of genetic intermingling sufficed to return the species' sight. Rather than scarred and stunted optical patches, the fish had eyes.

Quote from Wired Article, emphasis is mine. See these links:

Wired: Blind Fish Learn to See

Press Release: Progeny of blind cavefish can regain their sight

Current Biology Abstract: Restoring sight in blind cavefish

[driggs]

More coverage:

National Geographic News: Blind Cavefish Can Produce Sighted Offspring

Blind cavefish, despite having adapted to their lightless environment for more than a million years, can produce sighted offspring in just a single generation, a new study reveals.

The ability was discovered when researchers mated fish from distinct populations that had been isolated in separate caves.