Clockwork orange encodes a transcriptional repressor important for circadian-clock amplitude in Drosophila.

Gene transcription is a central timekeeping process in animal clocks. In Drosophila, the basic helix-loop helix (bHLH)-PAS transcription-factor heterodimer, CLOCK/CYCLE (CLK/CYC), transcriptionally activates the clock components period (per), timeless (tim), Par domain protein 1 (Pdp1), and vrille (vri), which feed back and regulate distinct features of CLK/CYC function. Microarray studies have identified numerous rhythmically expressed transcripts, some of which are potential direct CLK targets. Here we demonstrate a circadian function for one such target, a bHLH-Orange repressor, CG17100/CLOCKWORK ORANGE (CWO). cwo is rhythmically expressed, and levels are reduced in Clk mutants, suggesting that cwo is CLK activated in vivo. cwo mutants display reduced-amplitude molecular and behavioral rhythms with lengthened periods. Molecular analysis suggests that CWO acts, in part, by repressing CLK target genes. We propose that CWO acts as a transcriptional and behavioral rhythm amplifier.

A dynamic role for the mushroom bodies in promoting sleep in Drosophila.

The fruitfly, Drosophila melanogaster, exhibits many of the cardinal features of sleep, yet little is known about the neural circuits governing its sleep. Here we have performed a screen of GAL4 lines expressing a temperature-sensitive synaptic blocker shibire(ts1) (ref. 2) in a range of discrete neural circuits, and assayed the amount of sleep at different temperatures. We identified three short-sleep lines at the restrictive temperature with shared expression in the mushroom bodies, a neural locus central to learning and memory. Chemical ablation of the mushroom bodies also resulted in reduced sleep. These studies highlight a central role for the mushroom bodies in sleep regulation.

The ion channel narrow abdomen is critical for neural output of the Drosophila circadian pacemaker.

Circadian clocks consist of transcriptional feedback loops housed in interdependent pacemaker neurons. Yet little is known about the neuronal output components essential for rhythmic behavior. Drosophila mutants of a putative ion channel, narrow abdomen (na), exhibit poor circadian rhythms and suppressed daylight activity. We find that NA is expressed in pacemaker neurons and induced expression within circadian neurons is sufficient to rescue these mutant phenotypes. Selective na rescue in distinct pacemaker neurons influences rhythmicity and timing of behavior. Oscillations of the clock protein PERIOD are intact in na mutants, indicating an output role. Pore residues are required for robust rescue consistent with NA action as an ion channel. In na mutants, expression of potassium currents and the key neuropeptide PDF are elevated, the latter consistent with reduced release. These data implicate NA and the pacemaker neural network in controlling phase and rhythmicity.