Circadian locomotor activity-rest rhythm in <i>Drosophila</i> is regulated by microRNA-275

The circadian clock in Drosophila generates the 24 hour (h) rhythmicity in its behaviour. MicroRNAs are essential post-transcriptional regulators that can influence circadian rhythms by modulating clock mRNA expression or by aiding in the rhythmic oscillation of gene transcripts and their protein products. Previous studies identified around 27 miRNAs robustly expressed in Drosophila clock neurons. We conducted a genetic screen of 21 of these relatively underexplored miRNAs to investigate their effects on circadian clock properties. Each miRNA was downregulated in circadian clock neurons using specific sponge lines, and the impact on free running period and rhythm robustness was analyzed through locomotor activity-rest assessments. We observed that downregulation of two miRNAs shortened the free running period, while two miRNAs reduced rhythm robustness. Our findings reveal that miR-275 modulates locomotor activity-rest rhythm, circadian rhythmicity, and the transcript levels of the circadian neuropeptide PIGMENT DISPERSING FACTOR (PDF). Overexpression of Pdf in miR-275 overexpressed flies partially rescued the altered circadian rhythm parameters under 12h light: 12h dark cycles and constant darkness. Overall, this study identifies miR-275 as a critical regulator of circadian locomotor activity-rest rhythm.