Multiple Amidated Neuropeptides Are Required for Normal Circadian Locomotor Rhythms in<i>Drosophila</i>

Abstract

In <i>Drosophila</i>, the amidated neuropeptide pigment dispersing factor (PDF) is expressed by the ventral subset of lateral pacemaker neurons and is required for circadian locomotor rhythms. Residual rhythmicity in <i>pdf</i> mutants likely reflects the activity of other neurotransmitters. We asked whether other neuropeptides contribute to such auxiliary mechanisms. We used the<i>gal4/UAS</i> system to create mosaics for the neuropeptide amidating enzyme PHM; amidation is a highly specific and widespread modification of secretory peptides in <i>Drosophila</i>. Three different <i>gal4</i> drivers restricted PHM expression to different numbers of peptidergic neurons. These mosaics displayed aberrant locomotor rhythms to degrees that paralleled the apparent complexity of the spatial patterns. Certain PHM mosaics were less rhythmic than <i>pdf</i> mutants and as severe as<i>per</i> mutants. Additional <i>gal4</i> elements were added to the weakly rhythmic PHM mosaics. Although adding<i>pdf</i>-<i>gal4</i> provided only partial improvement, adding the widely expressed<i>tim</i>-<i>gal4</i> largely restored rhythmicity. These results indicate that, in <i>Drosophila,</i> peptide amidation is required for neuropeptide regulation of behavior. They also support the hypothesis that multiple amidated neuropeptides, acting upstream, downstream, or in parallel to PDF, help organize daily locomotor rhythms.