Functional Analysis of Circadian Pacemaker Neurons inDrosophila melanogaster

Abstract

The molecular mechanisms of circadian rhythms are well known, but how multiple clocks within one organism generate a structured rhythmic output remains a mystery. Many animals show bimodal activity rhythms with morning (M) and evening (E) activity bouts. One long-standing model assumes that two mutually coupled oscillators underlie these bouts and show different sensitivities to light. Three groups of lateral neurons (LN) and three groups of dorsal neurons govern behavioral rhythmicity of Drosophila. Recent data suggest that two groups of the LN (the ventral subset of the small LN cells and the dorsal subset of LN cells) are plausible candidates for the M and E oscillator, respectively. We provide evidence that these neuronal groups respond differently to light and can be completely desynchronized from one another by constant light, leading to two activity components that free-run with different periods. As expected, a long-period component started from the E activity bout. However, a short-period component originated not exclusively from the morning peak but more prominently from the evening peak. This reveals an interesting deviation from the original Pittendrigh and Daan (1976) model and suggests that a subgroup of the ventral subset of the small LN acts as "main" oscillator controlling M and E activity bouts in Drosophila.

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 .…”

“…This could be a reflection of an autonomous oscillation in DN2 occurring in addition to strong rhythmic inputs from LNv as a result of NaChBac expression. An association between the long-period bout and peak in PER levels in sLNv and short-period bout and fifth sLNv and one of the LNd was observed in another study using cry b mutants, which also exhibit two bouts of activity each with a different period under constant light (LL) (Rieger et al, 2006). Based on these associations, we expect that the phase relationship of molecular oscillation among different neuronal subgroups will be internally consistent if measured at time points other than 15 d in DD, with the exception of the special circumstance when long and short behavior bouts converge.…”

Even a stopped clock tells the right time twice a day: circadian timekeeping in Drosophila

“…Similarly, the s-LN v s display a short period, fitting their role as the M cells. The splitting of the evening peak in LL into both a short and long component suggests that the M cells also contribute to the evening peak of activity, an addition to the original model, suggesting that these cells should be named 'Main' rather than 'Morning' neurons [53].…”

“…Pittendrigh and Dann's [73] model predicted that in constant light, the M oscillator will free run with a short period and the E oscillator a long period. cry b flies show a weak morning and a strong evening activity peak in LL [53]. After a few days, the evening peak splits into a long (25.2 h) and a short (22.5 h) period component; the short component has a similar period to the weak morning activity peak.…”

“…Strangely, Drosophila cry b mutants show both molecular and behavioural rhythms in LL. This is surprising given that cry b flies can still detect light via the visual system and can entrain to LD cycles [51][52][53], but is probably partly due to increased TIM stability in cry b mutants in some clock neurons.…”