Circadian rhythm in mRNA expression of the glutathione synthesis gene Gclc is controlled by peripheral glial clocks in Drosophila melanogaster

Circadian coordination of metabolism, physiology and behaviour is found in all living kingdoms. Clock genes are transcriptional regulators, and their rhythmic activities generate daily rhythms in clock-controlled genes that result in cellular and organismal rhythms. Insects provide numerous examples of rhythms in behaviour and reproduction, although less is known about control of metabolic processes by circadian clocks in insects. Recent data suggest that several pathways involved in protecting cells from oxidative stress may be modulated by the circadian system, including genes involved in glutathione (GSH) biosynthesis. Specifically, rhythmic expression of the gene encoding the catalytic subunit (Gclc) of the rate-limiting GSH biosynthetic enzyme is detected in Drosophila melanogaster heads. The present study aims to determine which clocks in the fly multi-oscillatory circadian system are responsible for Gclc rhythms. Genetic disruption of tissue-specific clocks in D. melanogaster reveals that transcriptional rhythms in Gclc mRNA levels occur independently of the central pacemaker neurones because these rhythms persist in the heads of behaviourally arrhythmic flies with a disabled central clock but intact peripheral clocks. Disrupting the clock specifically in glial cells abolishes rhythmic expression of Gclc, suggesting that glia play an important role in Gclc transcriptional regulation, which may contribute to maintaining homeostasis in the fly nervous system.