Nocturnal Mammals Use Special DNA Lenses to See in the Dark

By Eliza Strickland | April 17, 2009 5:55 pm

racoonsA group of geneticists has peered into the eyes of nocturnal animals, and say they may have found the secret to these animals’ keen night vision: light-sensing cells with unusually structured DNA that turns each cell’s nucleus into a tiny lens.

The researchers were examining mice’s rod cells, the cells in the retina of the eye that operate under low light. Usually, they say, active genes are clustered in the center of each cell’s nucleus for convenient access to cellular machinery. 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 put this type of DNA front and center in their rod cells. “Everything that must be inside is outside, and everything that should be outside is inside,” [lead researcher Boris] Joffe says. “It was an absolutely heretic finding” [Science News].

In the study, published in the journal Cell, researchers note that placing densely packed inactive DNA raises the refractivity index — the degree to which the material decreases the speed of light traveling through it. The photons travel faster through the loosely packed DNA containing active genes, called euchromatin, and slower through the dense heterochromatin. Slowing down the photons creates a lens to focus light in the center of the cell. Rod cells form columns in the retina of nocturnal animals, so that many little lenses are stacked on top of each other. The DNA lenses form a chain that acts a bit like fiber-optic cables [Science News], the researchers suggest.

The researchers then mapped the nuclear architecture of nearly 40 mammal species and found that all the nocturnal animals had the same inverted pattern as mice, also a nocturnal species, whereas all the diurnal animals had the conventional arrangement [The Scientist]. The nocturnal animal’s inverted arrangement with the useful genes scattered around the nucleus’s edges probably comes with disadvantages, the researchers note. They suggest that as soon as certain animals didn’t need the light-focusing advantage, they dumped the backwards system.

Related Content:
80beats: Marine Worm’s Light-Sensitive Cells Are the Earliest Vision System
DISCOVER: Eye of the Beast ponders the marvels in animals’ eyes

Image: flickr / striatic

CATEGORIZED UNDER: Living World
MORE ABOUT: genetics, senses, vision
  • http://clubneko.net Nick

    Here’s to hoping we can one day incorporate this technology into our own eyes.

  • Grant H

    @ Nick: Well, I guess it would save on power for those who like to stay up late reading books ;)

    “The nocturnal animal’s inverted arrangement with the useful genes scattered around the nucleus’s edges probably comes with disadvantages, the researchers note. They suggest that as soon as certain animals didn’t need the light-focusing advantage, they dumped the backwards system.”

    That sounds like reasonable logic to me. I wonder what that disadvantage would be though. It would be interesting to know.

  • Fo Twenny

    We’ll have to wait for a miltary application.
    Maybe enlistments would go up if you get to keep your super vision after serving 4 years in a desert! Get me the general!

  • patrick

    I want gorilla strength and raccoon vision.

    For now, I’ll have to settle for being good-lookin’.

  • http://charleszigmund.com Charles Zigmund

    “The nocturnal animal’s inverted arrangement with the useful genes scattered around the nucleus’s edges probably comes with disadvantages, the researchers note. They suggest that as soon as certain animals didn’t need the light-focusing advantage, they dumped the backwards system.”

    Translation: The animals’ habitat or competition changed so they now needed daylight-sensitive vision more than night-sensitive vision. Sometime after this, a mutation or several mutations appeared that satisfied this need. The lineages without the mutaton(s) died out and were replaced by others descended from the mutant(s).

    The wordings “as soon as” and “dumped” suggests that 1. the animals decided to get rid of the maladaption, and 2. The mutation(s) appeared immediately. Neither of which is true, definitely in the first case, and probably in the second.

  • Michael C

    That type of adaptation would give you great vision in low light levels but, would be a disadvantage in bright light. The cells would “over load” on the extreme light captured. The over load could happen even with the iris closed.

    Also, a bright light beam (at night) could “blind” the animal for a while – allowing capture.

    Better stick with the night vision goggles, you’ll have the best of both visual worlds.

  • http://TwoSistersArtandSoul Lisette Root

    This seems like a strong case for proving Darwins’ theory of evolution to me!

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