Ectopic expression of the neuropeptide pigment-dispersing factor alters behavioral rhythms in Drosophila melanogaster

To study the function of the neuropeptide pigment-dispersing factor (PDF) i n the circadian system of Drosophila, we misexpressed the pdf gene from the grasshopper Romalea in the CNS of Drosophila and investigated the effect o f this on behavioral rhythmicity. pdf was either ectopically expressed in d ifferent numbers of neurons in the brain or the thoracical nervous system o r overexpressed in the pacemaker neurons alone. We found severe alterations in the activity and eclosion rhythm of several but not all lines with ecto pic pdf expression. Only ectopic pdf expression in neurons that projected i nto the dorsal central brain severely influenced activity rhythms. Therefor e, we conclude that PDF acts as a neuromodulator in the dorsal central brai n that is involved in the rhythmic control of behavior. Overexpression of p df in the pacemaker neurons alone or in the other neurons that express the clock genes period ( per) and timeless (tim) did not disturb the activity r hythm. Such flies still showed a rhythm in PDF accumulation in the central brain terminals. This rhythm was absent in the terminals of neurons that ex pressed PDF ectopically. Probably, PDF is rhythmically processed, transport ed, or secreted in neurons expressing per and tim, and additional PDF expre ssion in these cells does not influence this rhythmic process. In neurons l acking per and tim, PDF appears to be continuously processed, leading to a constant PDF secretion at their nerve terminals. This may lead to conflicti ng signals in the rhythmic output pathway and result in a severely altered rhythmic behavior.