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Critical role for night blindness gene identified



Posted On: Aug. 16, 2011

Washington, August 10 (ANI): A scientist has determined how a particular gene makes night vision possible.

The study focuses on a gene called nyctalopin. Mutations in the gene result in inherited "night blindness," a loss of vision in low-light environments.

"Until now, our understanding of the role of this gene in the visual signaling pathway has been very limited," said Kirill Martemyanov, an associate professor on the Florida campus of The Scripps Research Institute.

"This is the first time we have uncovered a functional role for it-and we linked that function to a much larger molecular complex that's needed for low-light vision," added Martemyanov.

Our vision begins when photons hit light-sensitive photoreceptor cells in the retina. When excited by light, photoreceptors generate a response that needs to be rapidly transmitted to the downstream neurons (nerve cells) for the signal to be processed and sent to the brain, which then interprets the visual picture. The hand off of the information occurs at the specialized contact points called synapses.

"The proper function of a particular type of synapse between rod photoreceptors and bipolar cells is absolutely critical for the transduction of the visual signal," explained Martemyanov.

"Even if rods generate response to light but are unable to properly transmit the signal, this results in an inability to see in the dark. Without this signaling, we'd have a tough time surviving in the world where it is dark half of the time," he added.

In addition, the transmission across the synapse must occur rapidly.

"The quickness of our signaling response to light creates a clear temporal resolution of what we see," he said.

"For example, when you turn your head suddenly, you see different objects clearly, not just a blur. We couldn't drive a car without it."

In the new research, the scientists searched for proteins associated with nyctalopin in the mouse retina. Scientists had known for a decade that the gene encoding nyctalopin is one of the most frequent culprits of night blindness, but its function had remained a mystery. The results showed that the protein expressed by the gene serves as a kind of molecular glue that holds together key elements of the signal transduction machinery at the synapse, allowing for the rapid and intact transmission of these sensory signals.

In molecular terms, the study strongly suggested that nyctalopin coordinates the assembly and precise delivery to the synapse of the macromolecular complex consisting of mGluR6, a neurotransmitter receptor protein, which directly communicates with rod photoreceptors and TRPM1, a protein channel that generates the response, making vision possible.

The study was published in The Journal of Neuroscience. (ANI)

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