by
Brendon Nafziger, DOTmed News Associate Editor | August 31, 2009
To test their eyesight, Dr. Viczian exploited a little-known quirk of the tadpole personality. Light-skinned tadpoles, the ones Dr. Viczian used, have an inborn preference to swim toward light. "They have these diapers on these lab benches," Dr. Viczian says. "And the diapers are white." She put one of these under the tank, to create two sections, one light and one dark. The tadpoles with the induced "eyes" swam to the light, she says. As a control, Dr. Viczian also tested blind tadpoles that had their eyes removed, but never had EFTF-expressed stem cells grafted onto them. These tadpoles swam around at random, showing no preference for the light side of the tank, she says. "They were happy tadpoles," she adds, but they moved about "aimlessly," indicating they were, indeed, completely blind.
Dr. Viczian says an optic nerve connected the new, induced "eye" to the brain. "Because the eye is in the right place," she says," "the guidance cues are there so it directs [the nerve] to where it's supposed to go." The results indicate that the tadpole can at least detect light, though Dr. Viczian cautions they do not yet know if the tadpole's vision is normal.
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But Dr. Viczian believes the experiment that showed the true effectiveness of her technique was to grow a new eye on the tadpole's flank. Dr. Viczian and colleagues grafted the new tissue onto the skin on the side of the frog embryo, well away from its eye field. "The cells formed what looked like a retina," she says. These "eyes" could not generate vision, however, as they were too far from the brain to project nerve tissue into it.
Dr. Goldberg believes the next critical step will be seeing if this study is possible with mammalian eyes. "Because in mammals, getting a new eye to connect to an old brain is a considerably tougher proposition," he says.
Dr. Viczian has similar caveats. "The confounding problem with human cells is that the embryo is providing matrices, or structural components," she says, which are hard to re-create in the lab.
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