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Mutant hamsters: running a little early.

Mutant hamsters: Running a little early

A family of hamsters with oddly timed biological clocks is providing new clues about the genetics of circadian rhythms. The restless rodents may someday help explain why some people seem to need more sleep than others, or prefer to be more active at different times of the day.

The pattern of inheritance observed in the animals suggests the behavioral abnormality -- which leaves the affected hamsters living 20-hour instead of 24-hour days -- is the result of a single mutant gene. If confirmed, it would be the first such gene discovered in a vertebrate animal.

Michael Menaker and Martin R. Ralph, then at the University of Oregon in Eugene, charted activity periods for the nocturnal rodents by recording the time spent on exercise wheels, and traced the inheritance of abnormal patterns through numerous breeding experiments. Normal hamsters, even when reared in total darkness, spontaneously start exercising every 24 hours and stay active for several hours. But the researchers' purebred mutants showed 20-hour cycles, and hybrids became active every 22 hours. "It's a textbook case of a semi-dominant gene," says Menaker. The researchers, now at the University of Virginia in Charlottesville, report their results in the Sept. 2 SCIENCE.

Scientists already have identified a handful of genes that affect daily behavioral rhythms and mating-call frequencies in lower organisms such as fruit flies. In mammals, daily biological rhythms have long been recognized, and brain areas regulating them have been identified. But the genetics of these phenomena have remained a mystery.

"The value of [the mutant hamsters] is that you can start getting at the genes and the proteins and the actual building blocks involved in making this clock run -- what the gears are," says Mitchell Dushay, a circadian-rhythm researcher at Brandeis University in Waltham, Mass. With a genetic defect now identified in a mammal, he adds, "I think the field is going to take off."

"There are some people who have trouble synchronizing to the day/night cycle, and we have no idea why," Menaker says. "The clock is no doubt a very complicated mechanism, and we are not going to fully understand it by figuring out what this gene makes. But it may give us a handle that we can use for further exploration."
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Title Annotation:research on circadian rhythms
Author:Weiss, Rick
Publication:Science News
Date:Sep 3, 1988
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