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

Apr 6, 2010Current biology : CB

Daily behavior in fruit flies is controlled by DN1(p) clock neurons combining immediate light and PDF signals

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Abstract

Mutants of the narrow abdomen (na) ion channel exhibit reduced anticipatory behavior and free-running rhythms.

A genetic link between light responses and circadian clock function is suggested by the na mutants' lack of robust activity increases in response to light.
Approximately 16-20 specific circadian pacemaker neurons, known as DN1(p)s, play a role in mediating the acute response to light and morning anticipatory behavior.
Neurons that express the neuropeptide PIGMENT-DISPERSING FACTOR (PDF) are particularly important for morning anticipation and maintaining free-running rhythms.
The expression of PDF in DN1(p) neurons can partially rescue defects in morning anticipation and free-running rhythms.
DN1 clocks in wild-type flies are more responsive to timing changes in PDF than those of other pacemaker neurons, indicating their role as direct targets.

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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 approximately 16-20 circadian pacemaker neurons, a subset of the posterior dorsal neurons 1 (DN1(p)s), 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 (PDF) are especially important for morning anticipation and free-running rhythms and send projections to the DN1(p)s. We also demonstrate that DN1(p)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 that they are direct targets.

CONCLUSIONS: Taking these results together, we demonstrate that the DN1(p)s lie at the nexus of PDF and photic signaling to produce appropriate daily behavior.

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

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