Moonlight shifts the endogenous clock of Drosophila melanogaster

Abstract

The ability to be synchronized by light-dark cycles is a fundamental property of circadian clocks. Although there are indications that circadian clocks are extremely light-sensitive and that they can be set by the low irradiances that occur at dawn and dusk, this has not been shown on the cellular level. Here, we demonstrate that a subset of Drosophila's pacemaker neurons responds to nocturnal dim light. At a nighttime illumination comparable to quartermoonlight intensity, the flies increase activity levels and shift their typical morning and evening activity peaks into the night. In parallel, clock protein levels are reduced, and clock protein rhythms shift in opposed direction in subsets of the previously identified morning and evening pacemaker cells. No effect was observed on the peripheral clock in the eye. Our results demonstrate that the neurons driving rhythmic behavior are extremely light-sensitive and capable of shifting activity in response to the very low light intensities that regularly occur in nature. This sensitivity may be instrumental in adaptation to different photoperiods, as was proposed by the morning and evening oscillator model of Pittendrigh and Daan. We also show that this adaptation depends on retinal input but is independent of cryptochrome.circadian rhythm ͉ dual-oscillator model ͉ PERIOD ͉ synchronization ͉ TIMELESS E ndogenous circadian clocks prepare organisms according to the most reliable and predictable of environmental changes, the cycle of day and night. To function as reliable timers, circadian clocks themselves are synchronized to the 24-h cycle. This synchronization is accomplished mainly by light. Whereas light during the day has little effect on circadian clocks, they are most susceptible to light in the early and late night. Bright light pulses applied during the early night delay the phase of the clock; light pulses during the late night advance it (1). Stable synchronization occurs when the delaying and advancing effects of light on the clock in the early (at dusk) and late night (at dawn) are of equal strength. In nature, stable synchronization is a challenging task, because irradiances during dawn and dusk can vary largely from day to day because of the weather. Bünning (2) measured irradiances systematically throughout day and night and found that day-to-day fluctuations are smallest during early dawn and late dusk, when the irradiances are still Ͻ10 lux. Therefore, he proposed that organisms time their clocks to the very low irradiances occurring during early dawn and late dusk and thus must be very light-sensitive. Indeed, he found that bean plants synchronize to light of moonlight intensity (0.6-0.8 lux) and that artificial moonlight applied during the night phase shifted the rhythm of leaf movement (2). Bean plants lower their leaves during the night, and Bünning suggested that they need to do so to decrease the moonlight reaching the leaf surface to avoid their light-sensitive clocks interpreting the moonlight as the coming dawn (2).In animals, it is under deb...

Pigment Dispersing Factor-Dependent and -Independent Circadian Locomotor Behavioral Rhythms

“…In NaChBac flies the fifth sLNv peak is out-of-phase in comparison with the manipulated sLNv and the LNd. These results are consistent with those of some recent studies that indicate that the period and phase of molecular oscillation in the fifth sLNv is altered by environmental inputs independent of the other LNvs (Rieger et al, 2006;Bachleitner et al, 2007). However, the results of a recent study suggest that the fifth sLNv has similar projections as the other four sLNv and is therefore is likely to make intimate connections with the later .…”

Regulation of Drosophila circadian rhythms by miRNA let-7 is mediated by a regulatory cycle

“…All experiments were imaged on a Nikon ECLIPSE TE2000-E and a Nikon D-ECLIPSE confocal microscope (Nikon, Japan). Confocal images were obtained at an optical section thickness of 1-2 mm and finally analysed with Image J. Staining intensity of PER was calculated and normalized as described 60 .…”

Chronobiology by moonlight

“…The locomotor activity of fruitflies can be easily entrained to moonlight-dark cycles, and when artificial moonlight is given during the dark period of a 12 L : 12 D cycle, the flies' usual crepuscular activity patterns turn more nocturnal: the flies shift their activity largely into the night [98]. Fruitflies seems to be active at dim light [99]; thus, part of their nocturnality is due to moonlight-stimulated activity without shifting the circadian clock [100].…”

“…Thus, moonlight is capable of shifting the clock and can act as significant zeitgeber in fruitflies. Interestingly, the bluelight photopigment cryptochrome (CRY1) seems to be dispensible for the phase-shifting capability of the clock, since flies without functional CRY1 can still shift activity into the night, whereas eyeless flies cannot [98]. Notably, the effect of moonlight on Drosophila's activity rhythm was entirely studied in the laboratory at constant moderate temperatures.…”

“…Such responses are also called masking effects (see below). Nevertheless, a significant part of the flies' nocturnal activity is caused by a phase shift of the molecular clock in response to moonlight [98]. Thus, moonlight is capable of shifting the clock and can act as significant zeitgeber in fruitflies.…”