July 5, 2000 CHAMPAIGN, Ill. -- A gene associated with the biological clock in many organisms has revealed yet another function. In honeybees, which live in a world with a distinct division of labor, the gene is more active in the brains of older bees, especially foragers whose jobs are outside the hive.
The new findings suggest that there are molecular connections occurring in the brain that influence the division of labor and the biological clocks of social insects, University of Illinois researchers say. The study, published June 6 in the Proceedings of the National Academy of Sciences, is the first to examine the period gene in a developmental context.
"This paper implicates a clock gene in a function that is different than the basic mechanism of the biological clock," said entomologist Gene E. Robinson, director of the UI Bee Research Facility. "This may go beyond circadian rhythms. But we have no idea yet what causes the increase in gene activity, nor do we know its function. This is the first time that such developmental changes in the activity of the period gene have ever been detected."
Robinson's team chose to examine the period gene for its possible role in the honeybees' complex, age-mediated labor system, because it had been found to be involved in time-related processes in fruit flies. Forager honeybees, Robinson said, have a highly developed internal circadian clock that guides their navigation, dancing communication and nectar gathering. In addition, he said, their division of labor is temporal -- a matter of timing and aging.
In a study published in 1998, Robinson and colleagues looked for the rhythms of life in a beehive. They found that young bees shifted randomly between rest and work regardless of time as they performed their duties of feeding the larvae, while foragers only ventured from the hive during daytime hours.
In the latest study, Robinson's team noted that levels of mRNA of the period gene, a message carrier of active DNA, rose and fell during the day in both young and old bees. This cyclic activity is a signature of all clock genes, including period. However, levels of mRNA were twice as high in older bees and in precocious foragers -- bees forced into foraging at an earlier than normal age. The latter discovery, Robinson said, suggests an association between foraging activities and high levels of period gene activity.
The elevated levels, the authors wrote, "cannot be caused solely, if at all, by increased chronological age, foraging, flight, or exposure to the sun," as foragers confined to the laboratory and isolated in darkness away from their social environment for several days also maintained high levels.
Working with Robinson were Dan Toma, a graduate student in the department of ecology, ethology and evolution who cloned the honeybee's period gene, postdoctoral researcher Guy Bloch, and Darrell Moore, a visiting biologist from East Tennessee State University. The National Institutes of Health, National Science Foundation and the UI were among the agencies that funded the research.
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