Alfonso-Gonzalez, C.; Holec, S.; Gorey, S.; Shi, M.; Rauer, M.; Carrasco, J.; Tsagkris, S.; Hilgers, V.

Circular RNAs (circRNAs) arise from back-splicing of precursor RNAs and accumulate in the nervous system of animals, where they are thought to regulate gene expression and synaptic function. Here, we show that neuronal circRNA biosynthesis is mediated by the pan-neuronal RNA-binding protein ELAV. In Drosophila embryos, we characterize the circRNA landscape in normal and elav mutant neurons. We find that neuronal circRNAs are globally (>75%) depleted upon ELAV knockout, and induction of ELAV expression drives ectopic RNA circularization. In brain tissue, ELAV binds to pre-mRNA introns flanking putative circRNAs and decreases efficiency of linear splicing in favor of intron pairing at reverse complementary matches, inducing circularization. Together, our data demonstrate that ELAV directly modulates splicing decisions to generate the neuronal circRNA landscape.