PARIS: Researchers say they have identified a key enzyme that triggers eye development, in a discovery that could one day lead to "eye in a dish" replacement tissue for the visually impaired.

Writing in 'Nature', a team from the University of Warwick, central England, say the switch, called E-NTPDase2, is a so-called ectoenzyme, which is normally found on the outside surface of cells. E-NTPDase2 initiates a molecular cascade that cause the eye to grow, they believe.

The researchers, experimenting on eight-cell frog embryos, introduced the enzyme into cells that would form the head area of the tadpole, and found that multiple eyes appeared to be created. When the enzyme was introduced to some cells that would form parts of the body, eye-like structures began to grow there, too, leading to tadpoles with an additional eye in their side, abdomen or even along their tail.

The researchers believe that E-NTPDase2 latches onto an important signal - and energy-carrying molecule called ATP and converts it into another molecule, ADP. Previous research has identified the genes that initiate and direct eye development, but what has hitherto been unknown are the triggers to turn them on.