Elucidating the regulation and function of circRNAs

Circular RNAs (circRNAs) are a newly appreciated class of RNAs that are expressed in a wide range of organisms, tissues, and disease states. The factors regulating circRNA biogenesis are poorly understood. CircRNAs are typically produced from exons of protein-coding genes through a process termed backsplicing. CircRNAs are enriched in the brain compared to other tissues in humans, and increase globally in expression during neuronal differentiation. In Chapter 2, we discovered that the neural-enriched splicing factor NOVA2 positively regulates hundreds of circRNAs in the developing mouse brain. We found that this regulation occurs through NOVA2 binding within introns flanking circRNA loci. This work identified the first RNA binding protein that facilitates circRNA enrichment in the mammalian brain.CircRNAs accumulate during aging across various organisms, especially in the brain. What functions, if any, do these age-related circRNAs have? A considerable roadblock to studying circRNA function has been the difficulty to establish circRNA-specific mutants. In Chapter 3 we identified sequences in introns that were important for circularization of two age-regulated circRNAs expressed from the crh-1 gene in the nematode C. elegans. Using CRISPRCas9, we generated intronic deletions that completely abolished crh-1 circRNAs without interrupting linear crh-1 mRNA expression. Remarkably, we found thatelimination of these circRNAs increased mean lifespan in C. elegans, suggesting that they contribute to age-related decline