Scientists eye secrets of retinal re...(o the eye to switch particular cellular ...)

After a variety of these and other types of experiments, the team discovered that the new light-sensing discs are formed by the fusion, at the base of the outer segment, of rhodopsin vesicles.

"This fusion makes a kind of preliminary disc, and then this disc matures and grows until it joins the hundreds of other discs on the rod cell's outer segment," Dr. Sung says. "All of this happens with the help of a regulating protein called the 'Smad Anchor for Receptor Activation' (SARA)," she adds. "It's a central player in the disc-fusion process, allowing new growth to occur."

Besides rewriting the ophthalmology textbooks on retinal growth, the discovery should greatly enhance research into eye disease, the experts say.

"There are currently more than 100 retinal eye diseases in human populations, and problems with rhodopsin trafficking or outer segment development are thought to play a role in many of these potentially blinding conditions," Dr. Sung notes. "In fact, we got interested in this type of research because we knew that breakdowns in rhodopsin trafficking were crucial to a common eye disease, retinitis pigmentosa."

Retinitis pigmentosa, a genetic disorder affecting about 100,000 Americans, is caused by the gradual death of rods and cones, triggering a progressive loss of vision.

Until now, however, little was known about rod cell regeneration, especially when it came to replacing rhodopsin-bearing discs.

"Our discovery now lays the groundwork for people to study just how many of these retinal diseases occur," Dr. Sung says. "That's why it's so important from a clinical point of view."

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