The circular RNA circbabo(5,6,7,8S) regulates lipid metabolism and neuronal integrity in Drosophila

Circular RNAs (circRNAs) are widely expressed in eukaryotes. However, only a subset has been functionally characterized. Here we report that the circRNA circbabo(5,6,7,8S) regulates lipid metabolism and neuronal integrity in Drosophila. We show that circbabo(5,6,7,8S) is derived from the babo pre-mRNA by back-splicing, and is widely distributed in Drosophila tissues. Depletion of circbabo(5,6,7,8S) in the fat body and neurons, respectively, causes elevated lipid droplet (LD) accumulation, and progressive photoreceptor cell loss and shortened lifespan, phenotypes that are rescued by restoring circbabo(5,6,7,8S) expression. In addition, RNA-seq and epistasis analyses reveal that these abnormalities are caused by aberrant activation of the SREBP signaling pathway. Furthermore, circbabo(5,6,7,8S)-depleted tissues display enhanced activation of the TGF-β signaling pathway and compromised mitochondrial function, resulting in a reduction in ATP levels and upregulation of ROS. Moreover, we provide evidence that circbabo(5,6,7,8S) encodes the protein circbabo(5,6,7,8S)-p, which inhibits the TGF-β signaling pathway by interfering with the assembly of babo/put heterodimer complex. Lastly, we show that the ROS/JNK/SREBP signaling cascade is implicated in the LD accumulation, neurodegeneration, and shortened lifespan phenotypes elicited by circbabo(5,6,7,8S) depletion. Thus, our study demonstrates the physiological role of the protein-coding circRNA circbabo(5,6,7,8S) in regulating lipid metabolism and neuronal integrity. This study aims to identify RNAs that are differentially expressed upon depletion of the circular RNA circbabo(5,6,7,8S) in vivo. Flies carrying a shRNA transgene against circbabo(5,6,7,8S) or a control shRNA transgene against GFP were crossed to flies carrying the fat body expressed cg-Gal4 driver. Total RNAs were extracted from fat bodies of 3rd instar wandering larvae of cg>shGFP and cg>sh-circbabo(5,6,7,8S) flies and subjected to RNA-seq to identify genes that are impacted by circbabo(5,6,7,8S) depletion.