Neuronal influence on peripheral circadian oscillators in pupal Drosophila prothoracic glands

Rhythmic expression of period (per) and timeless (tim) genes in central circadian pacemaker neurons and prothoracic gland cells, part of the peripheral circadian oscillators in flies, may synergistically control eclosion rhythms, but their oscillatory profiles remain unclear. Here we show differences and interactions between peripheral and central oscillators using per-luciferase and cytosolic Ca²⁺ reporter (yellow cameleon) imaging in organotypic prothoracic gland cultures with or without the associated central nervous system. Isolated prothoracic gland cells exhibit light-insensitive synchronous per-transcriptional rhythms. In prothoracic gland cells associated with the central nervous system, however, per transcription is markedly amplified following 12-h light exposure, resulting in the manifestation of day-night rhythms in nuclear PER immunostaining levels and spontaneous Ca²⁺ spiking. Unlike PER expression, nuclear TIM expression is associated with day-night cycles that are independent of the central nervous system. These results demonstrate that photoreception and synaptic signal transduction in/from the central nervous system coordinate molecular 'gears' in endocrine oscillators to generate physiological rhythms.