Biological clocks fly into view.

Clocks are ubiquitous in today's society. In addition to their traditional homes on mantles, nightstands, and wrists, timepieces now appear on VCRs, computer screens, TVs, microwave ovens, and much more. Nature's fondness for clocks may be even more impressive, however. Scientists report in the Nov. 28 Science that the fruit fly harbors biological clocks in its head, thorax, abdomen, leg bristles, wings, antennae, and proboscis. "We were really shocked there were these light-resettable clocks throughout the animal," says Steve A. Kay of the Scripps Research Institute in La Jolla, Calif.

Biological clocks are the internal timekeepers; that generate circadian rhythms, the day-long cycles of activities. One clock has been well documented in the brains of many animals. Its rhythm governs several easily observable behaviors such as sleeping, and it has been considered the body's master clock. Yet investigators have found that other tissues seem to maintain their own biological clocks. For example, Jadwiga M. Giebultowicz of Oregon State University in Corvallis and her colleagues have found biological clocks in the testes of moths and in the fruit fly's Malpighian tubules, excretory organs similar to kidneys.

By linking the activity of per, a gene that acts as a gear in the fly's biological clock, to genes encoding fluorescent markers, Kay and his colleagues obtained striking visual evidence of daily cyclical activity in almost every fruit fly tissue studied. They could reset each clock by exposing isolated tissues to a new light-dark cycle. Rather than being controlled by the clock in the fly's brain, the other clocks may be governed independently by the day-night cycle, suggests Kay. "The master clock for the fruit fly is sunlight," he proposes.

The new work is "mind-boggling. It suggests that there are circadian oscillators all over," says Michael Menaker of the University of Virginia in Charlottesville, who discovered that the mammalian retina has its own biological clock (SN: 4/20/96, p. 245). Unfortunately, adds Menaker, scientists still have few clues to why most of these clocks exist and whether they indeed act independently or form a hierarchy.

Kay and his colleagues now plan to repeat their fruit fly work in mammals by creating transgenic mice in which clock genes are linked to genes encoding fluorescent markers. They will also explore how the individual fly clocks perceive light. "It looks like the circadian photoreceptor is not going to be a known visual pigment," says Kay.