Squids Offer Insight for Treating Human Eye Diseases
Madison, Wisconsin — It's hard to miss the huge eye of a squid. But now it appears that certain squids can detect light through an organ other than their eyes as well.
That's what researchers at the University of Wisconsin-Madison report in the June 2, 2009 issue of the Proceedings of the National Academy of Sciences.
The study shows that the light-emitting organ some squids use to camouflage themselves in order to avoid being seen by predators — usually fish sitting on the ocean floor — also detects light.
The findings, offering insights into the molecular mechanisms of controlling and perceiving light, may lead someday to new strategies for treating human diseases of the eye.
"Evolution has a 'toolkit' and when it needs to do a particular job, such as see light, it uses the same toolkit again and again," says lead author Margaret McFall-Ngai, PhD, a professor of medical microbiology and immunology at the UW School of Medicine and Public Health (SMPH). "In this case, the light organ, which comes from different tissues than the eye during development, uses the same proteins as the eye to see light."
In studying the squid for the past 20 years, McFall-Ngai and her colleagues have been drawn to the fact that the squid-light organ is a natural model of symbiosis — an interdependent relationship between two different species in which each benefits from the other.
In this case, the light organ is filled with luminous bacteria that emit light and provide the squid protection against predators. In turn, the squid provides housing and nourishment for the bacteria.
The UW researchers have been intrigued by the light organ's "counterillumination" ability — this capacity to give off light to make squids as bright as the ocean surface above them, so that predators below can't see them.
"Until now, scientists thought that illuminating tissues in the light organ functioned exclusively to control the intensity and direction of light output from the organ, with no role in light perception," says McFall-Ngai.
McFall-Ngai teamed up with Nansi Jo Colley, PhD, UW School of Medicine and Public Health professor of ophthalmology and visual sciences and of genetics, for a closer look. The collaboration was fostered in part through the researchers' participation in the UW Eye Research Institute, a campus entity with a mission of bringing together vision researchers from multiple disciplines.
The study demonstrated that the E. scolopes squid has additional light-detecting tissue that is an integral component of the light organ and that the organ has the molecular machinery to respond to light cues.
"We also did the molecular analysis to show that genes that produce key visual proteins are expressed in light-organ tissues, including genes similar to those that occur in the retina," says McFall-Ngai.
Then physiological work in Colley's lab provided proof that, as in the retina, these visual proteins respond to light and produce a physiological response.
"We found that the light organ is capable of sensing light as well as emitting and controlling the intensity of luminescence," Colley says.
McFall-Ngai's large research program into the relatively simple squid-light organ symbiosis aims to shed light on symbiosis affecting humans.
"We know that humans house trillions of bacteria associated with components of eight of their 10 organ systems," she says. "These communities of bacteria are stable partners that make us healthy."
Date Published: 06/02/2009