Gregory M. Cahill, associate professor of biology and biochemistry at UH, and Maki Kaneko, a fellow UH researcher who is now at the University of California-San Diego, presented their findings in a paper titled "Light-dependent Development of Circadian Gene Expression in Transgenic Zebrafish," appearing Feb. 1 in the Public Library of Science's PLoS Biology, an online journal that, along with PLoS Medical, is committed to making scientific and medical literature a public resource.
"By injecting the luc gene that makes fireflies glow into our zebrafish, our bottom-line finding goes back to nature versus nurture," Cahill said. "We found that these per3-luc zebrafish contain something in their genetic makeup that gets their clocks ticking without parental influence, however, we determined that it does take some sort of environmental input for the clock to start. In this case it was exposure to light/dark cycles after the fourth day of development, about the age when the fish start to swim and feed."
The researchers used zebrafish (danio rerio) because they yield such a high output of spawn, with hundreds of eggs being laid by each female per week. This gives the scientists a better chance of identifying mutant fish whose biological clocks run fast or slow, providing the ability to trace the specific genes that create the anomaly. Putting UH a bit ahead of other institutions engaged in this type of research, Cahill and his team will be able to analyze more than 2,000 zebrafish per week. The per3-luc zebrafish is the first vertebrate system available for this level of high-throughput measurement.
"Because we can test so many zebrafish at a time, the one in a thousand odds of finding a mutant are more easily and efficiently attainable," Cahill said. "Ultimately, this type of research can help with tracing why humans develop such things as sleep disorders or mental illnesses like depression."
Per3 is the naturally occurring clock-regulated gene. The protein that it encodes is produced at highest levels near dawn, and when the luc gene is inserted into it, the luciferase protein is produced in a similar way. The result is that these fish glow rhythmically, emitting more light during the day than during the night. The amount of light is below the level of detection by the human eye, but it is easily measured with an instrument called a luminometer.
"This has given us the tool we need to find other parts of systems that influence biological clocks," Cahill said. "We are optimistic that this will shed light upon such things as reproduction in other light-dependent animals."
These findings have laid the groundwork for further study along these lines. With a team now built, UH graduate students who assisted with this project are now trained to work with Cahill to implement the next steps of this research.
Prior to coming to UH in 1994, Cahill was a research assistant professor in the Department of Anatomy and Cell biology at the University of Kansas Medical Center in Kansas City and received his postdoctoral training at Emory University. He received his doctorate in biology and neuroscience from the University of Oregon in Eugene, where he studied the mechanisms of circadian responses to light. He graduated with his bachelor of science from the College of Biological Sciences at the University of Minnesota in Minneapolis/St. Paul. His research interests include molecular, cellular and physiological mechanisms of vertebrate circadian rhythmicity, photoreceptor cell and molecular biology, and neurobiology. He is a member of the Society for Research on Biological Rhythms and the Society for Neuroscience and is currently funded under a $1.2 million National Institutes of Health grant through 2007 as the principal investigator on "Genetic analysis of zebrafish circadian rhythmicity," under which this latest study falls.