Glial microRNAs Regulate Circadian Behavior in Drosophila

Circadian rhythms are highly conserved, endogenous 24-hour oscillations. Disruption of these rhythms can result in pathophysiological states such as sleep and mood disorders. Previous work from the Jackson Lab demonstrated a role for glia, specifically astrocytes, in the regulation of rhythmic behavior via the clock neuronal circuitry. Those studies demonstrated that disruption of glia-to-neuron communication results in altered neuronal signaling and circadian behavior.  We hypothesize that factors released by glia function as important signals for proper neuronal circadian signaling, but their identity is unknown. In addition to screening genes known to be expressed in glia, we are using a microRNA (miRNA)-based approach to identify glia-to-neuron signaling components. There is emerging literature on the function of miRNAs in circadian biology – certain miRNAs exhibit daily cycles in abundance and/or target clock mRNAs. Generally, miRNAs target RNAs by binding at 3’ untranslated regions (UTR) to inhibit translation and/or degrade the target RNA(s). To identify novel glial miRNAs that regulate circadian behavior, we employed a collection of 146 miRNA-inhibitors called “miR-sponges”. miR-sponges have complementary binding sites to the miRNA of interest, and thus inhibit its binding to its RNA targets. From our initial screen, we identified twenty-one miRNAs whose inhibition in glia resulted in at least a 30% decrease in rhythmicity. Inhibition of 11 of these miRNAs in astrocytes also decreased rhythmicity. To determine whether these miRNAs have a relevant physiological role, as opposed to a developmental one, we restricted miR-sponge expression to adulthood and identified six miRNAs that may have relevant physiological functions. Experiments are currently underway to identify the mRNA targets of these miRNAs that may be functionally relevant for maintaining circadian behavior. These experiments will provide insight into the mechanisms underlying glial regulation of circadian behavior.