Dopamine and GPCR-mediated modulation of DN1 clock neurons gates the circadian timing of sleep.

The metronome-like circadian regulation of sleep timing must still adapt to an uncertain environment. Recent studies in indicate that neuromodulation not only plays a key role in clock neuron synchronization but also affects interactions between the clock network and brain sleep centers. We show here that the targets of neuromodulators, G Protein Coupled Receptors (GPCRs), are highly enriched in the fly brain circadian clock network.

Two light sensors decode moonlight versus sunlight to adjust a plastic circadian/circalunidian clock to moon phase.

Many species synchronize their physiology and behavior to specific hours. It is commonly assumed that sunlight acts as the main entrainment signal for ∼24-h clocks. However, the moon provides similarly regular time information.

Internal state configures olfactory behavior and early sensory processing in larvae.

Animals exhibit different behavioral responses to the same sensory cue depending on their internal state at a given moment. How and where in the brain are sensory inputs combined with state information to select an appropriate behavior? Here, we investigate how food deprivation affects olfactory behavior in larvae. We find that certain odors repel well-fed animals but attract food-deprived animals and that feeding state flexibly alters neural processing in the first olfactory center, the antennal lobe.

A transcriptomic taxonomy of circadian neurons around the clock.

Many different functions are regulated by circadian rhythms, including those orchestrated by discrete clock neurons within animal brains. To comprehensively characterize and assign cell identity to the 75 pairs of circadian neurons, we optimized a single-cell RNA sequencing method and assayed clock neuron gene expression at different times of day. The data identify at least 17 clock neuron categories with striking spatial regulation of gene expression.

A Functional Clock Within the Main Morning and Evening Neurons of Is Not Sufficient for Wild-Type Locomotor Activity Under Changing Day Length.

A major challenge for all organisms that live in temperate and subpolar regions is to adapt physiology and activity to different photoperiods. A long-standing model assumes that there are morning (M) and evening (E) oscillators with different photoreceptive properties that couple to dawn and dusk, respectively, and by this way adjust activity to the different photoperiods. In the fruit fly , M and E oscillators have been localized to specific circadian clock neurons in the brain.

Entrainment of the clock by the visual system.

Circadian clocks evolved as an adaptation to the cyclic change of day and night. To precisely adapt to this environment, the endogenous period has to be adjusted every day to exactly 24 hours by a process called entrainment. Organisms can use several external cues, called zeitgebers, to adapt.

Neuron-specific knockouts indicate the importance of network communication to rhythmicity.

Animal circadian rhythms persist in constant darkness and are driven by intracellular transcription-translation feedback loops. Although these cellular oscillators communicate, isolated mammalian cellular clocks continue to tick away in darkness without intercellular communication. To investigate these issues in , we assayed behavior as well as molecular rhythms within individual brain clock neurons while blocking communication within the ca.

Light-Mediated Circuit Switching in the Drosophila Neuronal Clock Network.

The circadian clock is a timekeeper but also helps adapt physiology to the outside world. This is because an essential feature of clocks is their ability to adjust (entrain) to the environment, with light being the most important signal. Whereas cryptochrome-mediated entrainment is well understood in Drosophila, integration of light information via the visual system lacks a neuronal or molecular mechanism.

A Distinct Visual Pathway Mediates High-Intensity Light Adaptation of the Circadian Clock in .

To provide organisms with a fitness advantage, circadian clocks have to react appropriately to changes in their environment. High-intensity (HI) light plays an essential role in the adaptation to hot summer days, which especially endanger insects of desiccation or prey visibility. Here, we show that solely increasing light intensity leads to an increased midday siesta in behavior.

Allatostatin-C/AstC-R2 Is a Novel Pathway to Modulate the Circadian Activity Pattern in Drosophila.

Seven neuropeptides are expressed within the Drosophila brain circadian network. Our previous mRNA profiling suggested that Allatostatin-C (AstC) is an eighth neuropeptide and specifically expressed in dorsal clock neurons (DN1s). Our results here show that AstC is, indeed, expressed in DN1s, where it oscillates.

Cryptochrome Interacts With Actin and Enhances Eye-Mediated Light Sensitivity of the Circadian Clock in .

Cryptochromes (CRYs) are a class of flavoproteins that sense blue light. In animals, CRYs are expressed in the eyes and in the clock neurons that control sleep/wake cycles and are implied in the generation and/or entrainment of circadian rhythmicity. Moreover, CRYs are sensing magnetic fields in insects as well as in humans.

A New Rhodopsin Influences Light-dependent Daily Activity Patterns of Fruit Flies.

Rhodopsin 7 ( Rh7), a new invertebrate Rhodopsin gene, was discovered in the genome of Drosophila melanogaster in 2000, but its function has remained elusive. We generated an Rh7 null mutant ( Rh7) by P element-mediated mutagenesis and found that an absence of Rh7 had significant effects on fly activity patterns during light-dark (LD) cycles: Rh7 mutants exhibited less morning activity and a longer siesta than wild-type controls. Consistent with these results, we found that Rh7 appears to be expressed in a few dorsal clock neurons that have been previously implicated in the control of the siesta.

Adaptation of Circadian Neuronal Network to Photoperiod in High-Latitude European Drosophilids.

The genus Drosophila contains over 2,000 species that, stemming from a common ancestor in the Old World Tropics, populate today very different environments [1, 2] (reviewed in [3]). We found significant differences in the activity pattern of Drosophila species belonging to the holarctic virilis group, i.e.

A Neural Network Underlying Circadian Entrainment and Photoperiodic Adjustment of Sleep and Activity in Drosophila.

Unlabelled: A sensitivity of the circadian clock to light/dark cycles ensures that biological rhythms maintain optimal phase relationships with the external day. In animals, the circadian clock neuron network (CCNN) driving sleep/activity rhythms receives light input from multiple photoreceptors, but how these photoreceptors modulate CCNN components is not well understood. Here we show that the Hofbauer-Buchner eyelets differentially modulate two classes of ventral lateral neurons (LNvs) within the Drosophila CCNN.

Normal vision can compensate for the loss of the circadian clock.

Circadian clocks are thought to be essential for timing the daily activity of animals, and consequently increase fitness. This view was recently challenged for clock-less fruit flies and mice that exhibited astonishingly normal activity rhythms under outdoor conditions. Compensatory mechanisms appear to enable even clock mutants to live a normal life in nature.

Twilight dominates over moonlight in adjusting Drosophila's activity pattern.

Light is the most important zeitgeber for the synchronization of the Drosophila melanogaster circadian clock. In nature, there is twilight, and the nights are rarely completely dark, a fact that is usually disregarded in lab experiments. Recent studies showed contrary effects of simulated twilight and moonlight on fly locomotor activity, with twilight shifting morning and evening activity into the day and moonlight shifting it into the night.

Photic entrainment in Drosophila assessed by locomotor activity recordings.

Light is the most important Zeitgeber to entrain the circadian clock of the fruit fly Drosophila melanogaster to the 24-h cycle on earth. The fruit fly's circadian clock is very light sensitive, mainly because about half of the 150 clock neurons in the fly's brain express the blue-light photopigment, Cryptochrome, which provokes an immediate degradation of the clock protein Timeless upon activation by light. Consequently, Drosophila's molecular clock can reset very fast to measure the changes in environmental-lighting conditions.

Moonlight detection by Drosophila's endogenous clock depends on multiple photopigments in the compound eyes.

Many organisms change their activity on moonlit nights. Even the fruit fly Drosophila melanogaster responds to moonlight with a shift of activity into the night, at least under laboratory conditions. The compound eyes have been shown to be essential for the perception of moonlight, but it is unknown which of the 5 rhodopsins in the eyes are responsible for the observed moonlight effects.

Fly cryptochrome and the visual system.

Cryptochromes are flavoproteins, structurally and evolutionarily related to photolyases, that are involved in the development, magnetoreception, and temporal organization of a variety of organisms. Drosophila CRYPTOCHROME (dCRY) is involved in light synchronization of the master circadian clock, and its C terminus plays an important role in modulating light sensitivity and activity of the protein. The activation of dCRY by light requires a conformational change, but it has been suggested that activation could be mediated also by specific "regulators" that bind the C terminus of the protein.