Teaching Resource

Oscillatory Mechanisms Underlying the Drosophila Circadian Clock

Science's STKE  18 Nov 2003:
Vol. 2003, Issue 209, pp. tr6
DOI: 10.1126/stke.2092003tr6


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.