Ectopic Expression of the Neuropeptide Pigment-Dispersing Factor Alters Behavioral Rhythms inDrosophila melanogaster

Abstract

To study the function of the neuropeptide pigment-dispersing factor (PDF) in the circadian system ofDrosophila, we misexpressed thepdfgene from the grasshopperRomaleain the CNS ofDrosophilaand investigated the effect of this on behavioral rhythmicity.pdfwas either ectopically expressed in different numbers of neurons in the brain or the thoracical nervous system or overexpressed in the pacemaker neurons alone. We found severe alterations in the activity and eclosion rhythm of several but not all lines with ectopicpdfexpression. Only ectopicpdfexpression in neurons that projected into the dorsal central brain severely influenced activity rhythms. Therefore, we conclude that PDF acts as a neuromodulator in the dorsal central brain that is involved in the rhythmic control of behavior. Overexpression ofpdfin the pacemaker neurons alone or in the other neurons that express the clock genesperiod(per) andtimeless(tim) did not disturb the activity rhythm. Such flies still showed a rhythm in PDF accumulation in the central brain terminals. This rhythm was absent in the terminals of neurons that expressed PDF ectopically. Probably, PDF is rhythmically processed, transported, or secreted in neurons expressingperandtim, and additional PDF expression in these cells does not influence this rhythmic process. In neurons lackingperandtim, PDF appears to be continuously processed, leading to a constant PDF secretion at their nerve terminals. This may lead to conflicting signals in the rhythmic output pathway and result in a severely altered rhythmic behavior.