DN1p Circadian Neurons Coordinate Acute Light and PDF Inputs to Produce Robust Daily Behavior in Drosophila

Abstract

Summary Background Daily behaviors in animals are determined by the interplay between internal timing signals from circadian clocks and environmental stimuli such as light. How these signals are integrated to produce timely and adaptive behavior is unclear. The fruit fly Drosophila exhibits clock-driven activity increases that anticipate dawn and dusk and free-running rhythms under constant conditions. Flies also respond to the onset of light and dark with acute increases in activity. Results Mutants of a novel ion channel, narrow abdomen (na), lack a robust increase in activity in response to light and show reduced anticipatory behavior and free-running rhythms, providing a genetic link between photic responses and circadian clock function. We used tissue-specific rescue of na to demonstrate a role for ∼16-20 circadian pacemaker neurons, a subset of the DN1p, in mediating the acute response to the onset of light as well as morning anticipatory behavior. Circadian pacemaker neurons expressing the neuropeptide PIGMENT DISPERSING FACTOR are especially important for morning anticipation and free-running rhythms and send projections to the DN1p. We also demonstrate that DN1p Pdfr expression is sufficient to rescue, at least partially, Pdfr morning anticipation defects as well as defects in free-running rhythms including those in DN1 molecular clocks. Additionally, these DN1 clocks in wild-type flies are more strongly reset to timing changes in PDF clocks than other pacemaker neurons, suggesting they are direct targets. Conclusion Taken together, we demonstrate that the DN1p lie at the nexus of PDF and photic signaling to produce appropriate daily behavior.

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