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In Drosophila, two intersecting molecular loops constitute an autoregulatory mechanism that oscillates with a period close to 24 hr. These loops touch when proteins from one loop, PERIOD (PER) and TIMELESS (TIM), repress the transcription of their parent genes, period (per) and timeless (tim), by blocking positive transcription factors from the other loop. The arrival of PER and TIM into the nucleus of a clock cell marks the timing of this interaction between the two loops; thus, control of PER:TIM nuclear accumulation is a central component of the molecular model of clock function. If a light pulse occurs early in the night as the heterodimer accumulates in the nucleus of clock cells, TIM is degraded, PER is destabilized, and clock time is delayed. Alternatively, if TIM is degraded during the later part of the night, after peak accumulation, clock time advances. Current models state that the effect of a light pulse depends on the state of the PER:TIM oscillation, which turns on the changing levels of TIM. However, previous studies have shown that light:dark (LD) regimes mimicking seasonal changes cause behavioral adjustments while altering clock gene expression. This should be reflected in the adjustment of PER and TIM dynamics. We manipulated LD cycles to assess the effects of altered day length on PER and TIM dynamics in clock cells within the central brain as well as light-induced resetting of locomotor rhythms.

We examined the locomotor activity ofDrosophila melanogaster for the existence of circadian rhythms, using the wild type and two mutants of theperiod (per) gene,pero andpers. This was accomplished using a newly described apparatus for the recording and measurement of larval path lengths over a 96-h test period. None of the larvae examined exhibited appreciable diel rhythms under cycling conditions of light or temperature. Larvae were also not rhythmic under free-running conditions. Our results suggest that theper gene does not influence an observable locomotor behavioral phenotype in the larval stage of development.

In Drosophila, two intersecting molecular loops constitute an autoregulatory mechanism that oscillates with a period close to 24 hr. These loops touch when proteins from one loop, PERIOD (PER) and TIMELESS (TIM), repress the transcription of their parent genes, period (per) and timeless (tim), by blocking positive transcription factors from the other loop. The arrival of PER and TIM into the nucleus of a clock cell marks the timing of this interaction between the two loops; thus, control of PER:TIM nuclear accumulation is a central component of the molecular model of clock function. If a light pulse occurs early in the night as the heterodimer accumulates in the nucleus of clock cells, TIM is degraded, PER is destabilized, and clock time is delayed. Alternatively, if TIM is degraded during the later part of the night, after peak accumulation, clock time advances. Current models state that the effect of a light pulse depends on the state of the PER:TIM oscillation, which turns on the changing levels of TIM. However, previous studies have shown that light:dark (LD) regimes mimicking seasonal changes cause behavioral adjustments while altering clock gene expression. This should be reflected in the adjustment of PER and TIM dynamics. We manipulated LD cycles to assess the effects of altered day length on PER and TIM dynamics in clock cells within the central brain as well as light-induced resetting of locomotor rhythms.

Phosphorylation is an important feature of pacemaker organization inDrosophila. Genetic and biochemical evidence suggests involvement of the casein kinase I homologdoubletime(dbt) in theDrosophilacircadian pacemaker. We have characterized two noveldbtmutants. Both cause a lengthening of behavioral period and profoundly alterperiod(per) andtimeless(tim) transcript and protein profiles. The PER profile shows a major difference from the wild-type program only during the morning hours, consistent with a prominent role for DBT during the PER monomer degradation phase. The transcript profiles are delayed, but there is little effect on the protein accumulation profiles, resulting in the elimination of the characteristic lag between the mRNA and protein profiles. These results and others indicate that light and post-transcriptional regulation play major roles in defining the temporal properties of the protein curves and suggest that this lag is unnecessary for the feedback regulation ofperandtimprotein onperandtimtranscription.