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Sci. STKE, 18 November 2003
[DOI: 10.1126/stke.2092003tr6]

Oscillatory Mechanisms Underlying the Drosophila Circadian Clock

Russell N. Van Gelder*

1Department of Ophthalmology and Visual Sciences, Department of Molecular Biology and Pharmacology, Washington University Medical School, 660 South Euclid Avenue, St. Louis, MO 63110, USA.


*Contact information. E-mail, vangelder{at}


This animation depicts a schematic of the Drosophila circadian clock mechanism in a single, pacemaking lateral brain neuron. Circadian clocks allow organisms to exhibit rhythmic behaviors and processes based on a nearly 24-hour cycle in the absence of any light stimulation. In the fruit fly, the basic molecular mechanism consists of two intertwined transcription-translation negative feedback loops. One loop--the "positive loop"--controls the rhythmic expression of a positive transcription factor gene, Clock. The second loop--the "negative loop"--controls the transcription of period and timeless, two genes that encode repressor proteins. The loops are intertwined because Period and Timeless repress transcription mediated by the transcription factors Clock and Cycle, whereas the Clock:Cycle heterodimer drives transcription of period and timeless, as well as that of vrille, a repressor of Clock expression. Light cycles can synchronize the Drosophila circadian pathway by directly stimulating cryptochrome-dependent degradation of Timeless.

The time of day is represented as Zeitgeber time (ZT), which is the number of hours elapsed since dawn (ZT 0), and is indicated by the travel of the sun and moon. ZT 6 corresponds to noon, ZT 12 to dusk, and ZT 18 to midnight. Within each cell, circadian clock components are shown in the cytoplasm (black) and nucleus (dark blue). Each gene's coding DNA is color coded as double helical, whereas the transcripts from that gene are shown as green curved lines. The changes in abundance and interactions of many components of the oscillatory mechanism occur simultaneously; for simplicity, only the major activities taking place at each time point are listed.

The animation accompanying each interaction can be seen individually by clicking on the green arrow. The times shown for all activities are approximate, and may vary from cell to cell within a single organism. To see the animation in continuous motion, click and hold the red double arrows at the bottom of the screen.

The animation was created by Cameron Slayden under the scientific oversight of Russell N. Van Gelder, Department of Ophthalmology and Visual Sciences, Department of Molecular Biology and Pharmacology, Washington University Medical School, 660 South Euclid Avenue, St. Louis, MO 63110, USA.

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Educational Details

Learning Resource Type: Animation

Context: Undergraduate upper division, graduate, professional (degree program)

Intended Users: Teacher, learner

Intended Educational Use: Teach, learn

Discipline: Cell Biology, Physiology

Keywords: movie, Drosophila, circadian, clock, rhythm, neurobiology

Technical Details

Format: Shockwave Flash Object (swf file)

Size: 67 kb

Requirements: Macromedia Flash 5 (

Related Resources

Connections Map: R. N. Van Gelder, Drosophila circadian pathway. Sci. STKE (as seen November 2003), [Abstract] [Specific Pathway]

Connections Map: Russell N. Van Gelder, Circadian pathway. Sci. STKE (as seen November 2003),;CMP_12992. [Abstract] [Canonical Pathway]

Review: M. P. Pando, P. Sassone-Corsi, Signaling to the mammalian circadian clocks: In pursuit of the primary mammalian circadian photoreceptor. Sci. STKE 2001, re16 (2001). [Gloss] [Abstract] [Full Text]

Virtual Journal: R. N. Van Gelder, E. D. Herzog, W. J. Schwartz, P. H. Taghert, Circadian rhythms: In the loop at last. Science 300, 1534-1535 (2003). [Abstract] [Full Text]

Limits for Use

Cost: Free

Rights: This material may be downloaded, printed, linked to, and/or redistributed without modification for noncommercial, course-teaching purposes only, provided credit to STKE is included by listing the citation for the teaching resource.


Citation: R. N. Van Gelder, Oscillatory Mechanisms Underlying the Drosophila Circadian Clock, Sci. STKE 2003, tr6 (2003).

© 2003 American Association for the Advancement of Science

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