Organization of the Drosophila Circadian Control Circuit

Abstract

Molecular genetics has revealed the identities of several components of the fundamental circadian molecular oscillator - an evolutionarily conserved molecular mechanism of transcription and translation that can operate in a cell-autonomous manner. Therefore, it was surprising when studies of circadian rhythmic behavior in the fruit fly Drosophila suggested that the normal operations of circadian clock cells, which house the molecular oscillator, in fact depend on non-cell-autonomous effects - interactions between the clock cells themselves. Here we review several genetic analyses that broadly extend that viewpoint. They support a model whereby the approximately 150 circadian clock cells in the brain of the fly are sub-divided into functionally discrete rhythmic centers. These centers alternatively cooperate or compete to control the different episodes of rhythmic behavior that define the fly's daily activity profile.

Dispensable, Redundant, Complementary, and Cooperative Roles of Dopamine, Octopamine, and Serotonin inDrosophila melanogaster

“…Although both defects are likely to contribute to a decrease in rhythmicity, the defect in morning activity appears to be more severe. A relatively selective effect on morning vs. evening activity is of interest because different groups of clock neurons are postulated to control the two bouts of activity (Nitabach and Taghert 2008), although there is still ongoing debate about the precise composition of the evening and morning circadian oscillators (e.g., Shafer and Taghert 2009;Sheeba et al 2010). In addition to the LD phenotype, most dVMAT individuals-even those that exhibit bimodal activity in LD-are weakly rhythmic or arrhythmic in freerunning DD conditions ( Figure 6, Table 2), consistent with the idea that biogenic amines are also essential for free-running rhythmicity.…”

The hormonal and circadian basis for insect photoperiodic timing

“…The circadian clock of almost all living organisms, from bacteria to mammals [132][133][134][135] drives endogenous oscillations in anticipation of the regular daily changes of light, temperature and other cycling environmental parameters, and D. melanogaster has led the way in the molecular and neurogenetic dissection of these oscillators [136,137]. It is indeed fortunate that such a genetically tractable organism also shows a photoperiodic reproductive diapauses in females, albeit a shallow one, at least in European populations [7,138].…”

“…Light signals are also transduced by the compound eye photoreceptors that can entrain circadian pacemaker neurons [136,137]. Natural light-dark cycles change gradually through the seasons and as a consequence, the circadian clock should synchronize to seasonal changes.…”

Circadian Control of Membrane Excitability in Drosophila melanogaster Lateral Ventral Clock Neurons

“…Drosophila circadian rhythms are governed by ϳ150 autonomously oscillating clock neurons, which include a number of anatomically and functionally distinct cell groups (HelfrichForster, 2003;Shafer et al, 2006;Nitabach and Taghert, 2008). Transcriptional feedback loops essential for cellular oscillation of clock neurons have been studied extensively and are well understood (for review, see Harmer et al, 2001;Hardin, 2005;Rosato et al, 2006).…”