Effects of microRNA regulation on locomotor behaviour in Drosophila melanogaster

MicroRNAs (miRNAs) are small non-coding RNA molecules that repress expression of target genes. As a result, miRNAs mould the protein complement of the cell, altering cellular function. Here, we use the fruitfly Drosophila melanogasterto explore the roles of miRNAs in the nervous system. We developed a large-scale screen that establishes the impact of loss-of-function mutations affecting different miRNAs on an innate Drosophila larval behaviour, self-righting (SR). This can be quantified as the time required by the larva to return to normal (‘dorsal-up’) position when turned upside-down (‘ventral-up’). We analysed 83 Drosophila miRNA mutants representing 96% of all miRNAs expressed at this stage. Remarkably, we found that miRNA regulation of this behaviour is extremely pervasive, with 41% of mutants showing delays in SR compared to the wild-type population. Moreover, the magnitude of the behavioural effects observed is not correlated with miRNA expression level or overlapping targeting, suggesting distinct molecular mechanisms. To further characterise behavioural differences between these miRNAs, we performed detailed analysis of the self-righting struggle and other larval behaviours. The diversity of behavioural profiles observed suggests a network of miRNA-dependent regulation of behaviour. The Hox gene, Ultrabithoraxhas been previously shown to modulate SR under miR-iab-4 regulation (Picao-Osorio et al., 2015). We therefore considered the developmental family of Hox genes as potential downstream effectors of this behaviour under regulation by other SR-miRNAs. Our data suggests that Abd-Bis also a SR modulator under miRNA-regulation. Finally, we selected a miRNA with an effect on SR through its action in the nervous system, miR-980, to explore miRNA function in this tissue. Through a combination of RNA-sequencing, genetic and behavioural tests, we identified two potential downstream effectors of miR-980 with SR modulatory functions. Altogether, our work hints at a complex molecular network, affecting different mechanisms, which modulates behaviour under miRNA-mediated gene regulation.