Abstract
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. Here, we show that a single photoreceptor subtype is essential for long-day adaptation. These cells activate key circadian neurons, namely the large ventral-lateral neurons (lLNvs), which release the neuropeptide pigment-dispersing factor (PDF). RNAi and rescue experiments show that PDF from these cells is necessary and sufficient for delaying the timing of the evening (E) activity in long-day conditions. This contrasts to PDF that derives from the small ventral-lateral neurons (sLNvs), which are essential for constant darkness (DD) rhythmicity. Using a cell-specific CRISPR/Cas9 assay, we show that lLNv-derived PDF directly interacts with neurons important for E activity timing. Interestingly, this pathway is specific for long-day adaptation and appears to be dispensable in equinox or DD conditions. The results therefore indicate that external cues cause a rearrangement of neuronal hierarchy, which contributes to behavioral plasticity.
•Receptor cell 8 of the compound eyes is essential for long-day adaptation•PDF from the lLNvs is necessary and sufficient for long-day adaptation•Disruption of the PDF receptor suggests a direct connection between lLNvs and LNds•The targets of PDF neurons change depending on environmental conditions
Schlichting et al. describe the contribution of a single photoreceptor subtype to long-day adaptation in Drosophila melanogaster. Light information from this receptor is integrated into the clock network by PDF release from the lLNvs, suggesting a shift of neuronal dominance in the network, depending on environmental conditions.