A circular RNA Edis-Relish-castor axis regulates neuronal development in Drosophila

Abstract

Circular RNAs (circRNAs) are a new group of noncoding/regulatory RNAs that are particularly abundant in the nervous system, however, their physiological functions are underexplored. Here we report that the brain-enriched circular RNAEdis(Ect4-derivedimmunesuppressor) plays an essential role in neuronal development inDrosophila. We show that depletion ofEdis in vivocauses defects in axonal projection patterns of mushroom body (MB) neurons in the brain, as well as impaired locomotor activity and shortened lifespan of adult flies. In addition, we find that thecastorgene, which encodes a transcription factor involved in neurodevelopment, is upregulated inEdisknockdown neurons. Notably,castoroverexpression phenocopiesEdisknockdown, and reducingcastorlevels suppresses the neurodevelopmental phenotypes inEdis-depleted neurons. Furthermore, chromatin immunoprecipitation analysis reveals that the transcription factor Relish, which plays a key role in regulating innate immunity signaling, occupies a pair of sites at thecastorpromoter, and that both sites are required for optimalcastorgene activation by either immune challenge orEdisdepletion. Lastly,Relishmutation and/or depletion can rescue both thecastorgene hyperactivation phenotype and neuronal defects inEdisknockdown animals. We conclude that the circular RNAEdisacts through Relish andcastorto regulate neuronal development.