The Ion Transport Peptide Is a New Functional Clock Neuropeptide in the Fruit Fly Drosophila melanogaster

Jul 18, 2014The Journal of neuroscience : the official journal of the Society for Neuroscience

The ion transport peptide is a new brain chemical that helps control the internal clock in fruit flies

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Abstract

The ion transport peptide (ITP) may play a significant role in regulating behavioral rhythms in Drosophila melanogaster.

ITP is expressed in specific neurons associated with the circadian clock and in a few nonclock cells in the brain.
Immunocytochemical analyses suggest that ITP is released rhythmically in the dorsal protocerebrum, controlled by the biological clock.
A reduction in ITP expression was observed in the Clk(AR) mutant, indicating regulation by the CLOCK protein.
Knockdown of ITP in clock cells resulted in reduced evening activity and increased nocturnal activity in flies.
Overexpression of ITP disrupted behavioral rhythms while only slightly affecting the cycling of a key clock protein.
Simultaneous knockdown of ITP and PDF led to hyperactivity and near-complete arrhythmia in constant conditions.

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The clock network of Drosophila melanogaster expresses various neuropeptides, but a function in clock-mediated behavioral control was so far only found for the neuropeptide pigment dispersing factor (PDF). Here, we propose a role in the control of behavioral rhythms for the ion transport peptide (ITP), which is expressed in the fifth small ventral lateral neuron, one dorsal lateral neuron, and in only a few nonclock cells in the brain. Immunocytochemical analyses revealed that ITP, like PDF, is most probably released in a rhythmic manner at projection terminals in the dorsal protocerebrum. This rhythm continues under constant dark conditions, indicating that ITP release is clock controlled. ITP expression is reduced in the hypomorph mutant Clk(AR), suggesting that ITP expression is regulated by CLOCK. Using a genetically encoded RNAi construct, we knocked down ITP in the two clock cells and found that these flies show reduced evening activity and increased nocturnal activity. Overexpression of ITP with two independent timeless-GAL4 lines completely disrupted behavioral rhythms, but only slightly dampened PER cycling in important pacemaker neurons, suggesting a role for ITP in clock output pathways rather than in the communication within the clock network. Simultaneous knockdown (KD) of ITP and PDF made the flies hyperactive and almost completely arrhythmic under constant conditions. Under light-dark conditions, the double-KD combined the behavioral characteristics of the single-KD flies. In addition, it reduced the flies' sleep. We conclude that ITP and PDF are the clock's main output signals that cooperate in controlling the flies' activity rhythms.

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The Ion Transport Peptide Is a New Functional Clock Neuropeptide in the Fruit Fly Drosophila melanogaster

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