Blues in the night

How can eyeless worms sense color?

Gregory Nemec

Gregory Nemec

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The tiny transparent nematode C. elegans has “elegant” in its scientific name, but it’s just a lowly worm. It has no lungs, no heart, and no eyes—not even opsins, the proteins that enable sight in birds, bees, and readers of magazines.

It’s long been known that roundworms avoid bacteria called P. aeruginosa, which secrete a deadly blue toxin. Could the worms sense the blue? The mystery intrigued biologist Dipon Ghosh ’17PhD when he worked with Professor Michael Nitabach at Yale, and he continued the work as a postdoc in the Robert Horvitz lab at MIT.

Ghosh tested 59 strains of C. elegans, collected in locations ranging from California to Madagascar to Japan. He shone various tints of blue light on a substitute toxin, keeping the total light energy constant, and he compared the worms’ responses. Different strains of worms avoided different tints of blue, and some strains did not flee blue. But Ghosh had answered his question: the worms do sense color—without eyes or opsins.

C. elegans is ubiquitous, not only in compost heaps, where the barely visible worms forage on microbes, but also in biology labs, where they serve as model organisms. And yet, says Ghosh, “People have been studying worms for decades now, and no one knew they were sensitive to the color of light in their environments.” His discovery, published in Science, suggests larger questions: do other eyeless creatures perceive color? Might human cells that lack opsins still sense color?

Ghosh and colleagues identified two genes implicated in the roundworms’ color sensitivity. Those genes are evolutionarily conserved, meaning that they have counterparts in the human genome. Scientists know that in humans, the genes affect responses to stress. Do they play a role in sight?

Ghosh has many ideas for further research, and he looks forward to seeing what other scientists will discover. “For now, we’re sharing our findings with the world, and saying, ‘Here’s some weird stuff we’ve found,’” says Ghosh. “Our work suggests that we have a lot to learn and explore about how animals can sense light.”

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