vrille, Pdp1, and dClock form a second feedback loop in the Drosophila circadian clock.
The Drosophila circadian clock consists of two interlocked transcriptional feedback loops. In one loop, dCLOCK/CYCLE activates period expression, and PERIOD protein then inhibits dCLOCK/CYCLE activity. dClock is also rhythmically transcribed, but its regulators are unknown. vrille (vri) and Par Domain Protein 1 (Pdp1) encode related transcription factors whose expression is directly activated by dCLOCK/CYCLE. We show here that VRI and PDP1 proteins feed back and directly regulate dClock expression. Repression of dClock by VRI is separated from activation by PDP1 since VRI levels peak 3-6 hours before PDP1. Rhythmic vri transcription is required for molecular rhythms, and here we show that the clock stops in a Pdp1 null mutant, identifying Pdp1 as an essential clock gene. Thus, VRI and PDP1, together with dClock itself, comprise a second feedback loop in the Drosophila clock that gives rhythmic expression of dClock, and probably of other genes, to generate accurate circadian rhythms.
Pubmed ID: 12581523 RIS Download
Animals | Basic-Leucine Zipper Transcription Factors | Behavior, Animal | Biological Clocks | CLOCK Proteins | Circadian Rhythm | Drosophila Proteins | Drosophila melanogaster | Feedback | Female | Male | Mutation | Photoreceptor Cells, Invertebrate | RNA, Messenger | Repressor Proteins | Transcription Factors | Transcriptional Activation