The tiny eyeless C. elegans roundworm, one of the most widely used animals in biological research, can detect flashes of light and responds to them by quickly wriggling away, a biologist and his colleagues have discovered.
The finding should lead to an expanded research role for C. elegans, already one of the mainstay model organisms of biology, says Shawn Xu, a research assistant professor at the Life Sciences Institute (LSI).
“Though this animal lacks the specialized light-sensing organs we call eyes, it can still see light,” says Xu, also an assistant professor of molecular and integrative physiology at the Medical School. “We now have a new model that can be used to study the building blocks of the visual system and the causes of human eye diseases.”
Researchers long have assumed that the soil-dwelling worm, about the size of this comma, lacks any visual system whatsoever.
Xu suspects the worm’s primitive visual system serves a protective function. It tells the worm when it is nearing the surface, enabling it to avoid damaging sunlight. Ultraviolet-A radiation in sunlight is harmful to C. elegans worms, and prolonged exposure to it kills them.
The new C. elegans finding suggests that other eyeless animals living in dark environments, such as soil or caves, also can sense light.
Xu and his colleagues found that humans and the C. elegans worm rely on many of the same chemical reactions to convert light energy into electrical signals, a process called phototransduction. That means the worm can be used to study the building blocks of human vision, as well as how disrupting the phototransduction pathway can lead to eye disease.
The Xu team’s findings appear online in the July 6 Nature Neuroscience. Co-lead authors of the paper are Alex Ward and Jie Liu of LSI.
Since the 1970s the
C. elegans roundworm has been used to study the genetic control of animal development, as well as sensory physiology. Because it is one of the simplest organisms with a nervous system (302 nerve cells versus about 100 billion in the human brain), it is widely used to probe the neural mechanisms behind various behaviors.
Scientists have known for years that the rudimentary C. elegans nervous system provides the worm with the senses of touch, taste and smell. Two years ago the Xu lab, which studies C. elegans full time, reported in the journal Nature that the worms possess a fourth sense, an awareness of body posture known as proprioception.
“Now we’ve added a fifth sense: the ability to sense light,” Xu says.
