Magazine article Science News

Oddities in Rod Cells May Help with Night Sight: Nocturnal Mammals Invert Retinal DNA Arrangement

Magazine article Science News

Oddities in Rod Cells May Help with Night Sight: Nocturnal Mammals Invert Retinal DNA Arrangement

Article excerpt

Mice and cats don't usually agree, but both animals have the same bright idea about night vision. Cats, rats, mice and other nocturnal mammals arrange DNA in some eye cells to form miniature lenses that help focus light, a new study shows.

Scientists at the Ludwig-Maximilians University Munich in Germany and colleagues discovered the unusual DNA arrangement while investigating genes in the rod cells of mouse eyes, says Boris Joffe, one of the authors of the new study, which appears in the April 17 Cell. Rod cells are light-gathering cells in the retina of the eye. They operate under low-light conditions, while cone cells perform the light-gathering duty when it is bright.

Usually, active genes are located in the part of DNA at the center of a cell's nucleus. There, the genes have easy access to the cellular machinery that rewrites instructions encoded in the DNA into RNA. Inactive DNA is pushed to the periphery of the nucleus, where it is out of the way.

But rod cells in the mouse retina shove active genes to the outside of the nucleus, the researchers found. The center of the nucleus is instead occupied by densely packed inactive DNA called heterochromatin. Mice give this type of DNA center stage in their rod cells.

"Everything that must be inside is outside, and everything that should be outside is inside," Joffe says. "It was an absolutely heretic finding."

The team decided to examine retinas from more than a dozen different species of mammals and found that animals active in low-light conditions, including cats, rats, deer, opossum, rabbits and ferrets, had the inside-out arrangement in rod cells. …

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