The CRYPTOCHROME Photoreceptor Gates PDF Neuropeptide Signaling to Set Circadian Network Hierarchy in Drosophila

Nov 17, 2009Current biology : CB

The light-sensing protein controls PDF neuropeptide signals to set the daily rhythm system order in fruit flies

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Abstract

Flies lacking both the PDF receptor and the circadian photoreceptor show altered molecular oscillations in E cells.

E cells in mutant flies exhibit molecular oscillations that are out of sync with those of wild-type flies.
PDF neuropeptide signaling influences the timing of evening behavior, particularly when CRY is absent.
In short days, M cells dictate the timing of morning behavior, while E cells take over in long days.
The resetting of evening behavioral phase is more pronounced when PDF(+) M cells are present without CRY.
These findings suggest that CRY regulates how PDF signaling affects behavior and the overall hierarchy of the circadian network.

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Circadian clocks in the brain are organized as coupled oscillators that integrate seasonal cues such as light and temperature to time daily behaviors. In Drosophila, the PIGMENT DISPERSING FACTOR (PDF) neuropeptide-expressing morning (M) and non-PDF evening (E) cells are coupled cell groups important for morning and evening behavior, respectively. Depending on day length, either M cells (short days) or E cells (long days) dictate both the morning and the evening phase, a phenomenon that we term network hierarchy. To examine the role of PDF in light-dark conditions, we examined flies lacking both the PDF receptor (PDFR) and the circadian photoreceptor CRYPTOCHROME (CRY). We found that subsets of E cells exhibit molecular oscillations antiphase to those of wild-type flies, single cry mutants, or single Pdfr mutants, demonstrating a potent role for PDF in light-mediated entrainment, specifically in the absence of CRY. Moreover, we find that the evening behavioral phase is more strongly reset by PDF(+) M cells in the absence of CRY. On the basis of our findings, we propose that CRY can gate PDF signaling to determine behavioral phase and network hierarchy.

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The CRYPTOCHROME Photoreceptor Gates PDF Neuropeptide Signaling to Set Circadian Network Hierarchy in Drosophila

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