Seeing Light Without Eyes

. Sunday, August 3, 2008
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Many of the ground breaking discoveries in molecular developmental biology were made with the help of simple organisms that can be grown in laboratories with ease. Caenorhabditis elegans is one among them. Measuring about a millimeter in length, these organisms had been a good friend for molecular biologists and neuroscientists for decades. One reason why a common man may find this kind of round worm interesting is that they managed to survive the historic Columbia space Shuttle disaster. (Find more information here.)

These survivors are continuing to surprise their masters and challenging the claim that their physiology is well-studied. Not many would have expected these underground creatures to show any interest in light. Shawn Xu, a neurobiologist from University of Michigan proved just that. Upon observing that these creatures shy away from bright light while he viewed them under the microscope, he set out to explain how these eye-less worms see light.

Further investigations by Xu and his team revealed that four pairs of sensory neurons of C.elegans were responsible for its sensitivity to light. And, these neurons made them reverse their course as soon as the light is switched on.

(Find a more detailed article in ScienceNOW)

It was also found that these worms were more sensitive to the harmful UV-A radiations. This gives a clue to why evolution had gifted these simple organisms with this ability. Without these four neurons and hence the perception of light, the organisms may wander out into the light and get exposed to the harmful radiations. Such behavioral responses to light in such simpler organisms is more crucial to an evolutionary biologist, trying to understand the how higher vertebrates evolved sight.