BLOCKING ENDOCYTOSIS INDROSOPHILA'SCIRCADIAN PACEMAKER NEURONS INTERFERES WITH THE ENDOGENOUS CLOCK IN A PDF-DEPENDENT WAY

Nov 18, 2009Chronobiology international

Stopping cell intake in fruit fly's internal clock neurons disrupts their daily rhythm through PDF signaling

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Abstract

Blocking Shibire function in PDF neurons slowed the behavioral rhythm of fruit flies by 3 hours.

The neuropeptide pigment-dispersing factor (PDF) is important for regulating the circadian clock in fruit flies.
Interference with PDF signaling was achieved by inhibiting the GTPase Shibire in PDF neurons.
Shibire is essential for processes that recycle neurotransmitters and terminate signals in neurons.
The slowed behavioral rhythm effect was not observed in PDF receptor null mutants, suggesting PDF receptor involvement.
Increased PDF levels near PDF neurons produced similar effects on behavioral rhythms, indicating prolonged PDF signaling.
Terminating PDF signaling through receptor-mediated endocytosis is crucial for determining the period of behavioral rhythms.

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The neuropeptide pigment-dispersing factor (PDF) plays an essential role in the circadian clock of the fruit fly Drosophila melanogaster, but many details of PDF signaling in the clock network are still unknown. We tried to interfere with PDF signaling by blocking the GTPase Shibire in PDF neurons. Shibire is an ortholog of the mammalian Dynamins and is essential for endocytosis of clathrin-coated vesicles at the plasma membrane. Such endocytosis is used for neurotransmitter reuptake by presynaptic neurons, which is a prerequisite of synaptic vesicle recycling, and receptor-mediated endocytosis in the postsynaptic neuron, which leads to signal termination. By blocking Shibire function via overexpression of a dominant negative mutant form of Shibire in PDF neurons, we slowed down the behavioral rhythm by 3 h. This effect was absent in PDF receptor null mutants, indicating that we interfered with PDF receptor-mediated endocytosis. Because we obtained similar behavioral phenotypes by increasing the PDF level in regions close to PDF neurons, we conclude that blocking Shibire did prolong PDF signaling in the neurons that respond to PDF. Obviously, terminating the PDF signaling via receptor-mediated endocytosis is a crucial step in determining the period of behavioral rhythms.

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BLOCKING ENDOCYTOSIS INDROSOPHILA'SCIRCADIAN PACEMAKER NEURONS INTERFERES WITH THE ENDOGENOUS CLOCK IN A PDF-DEPENDENT WAY

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