Loss of circRNAs from the crh-1 gene extends the mean lifespan in Caenorhabditis elegans

Abstract

Accumulation of circular RNAs (circRNAs) during aging occurs on a genome-wide level for multiple organisms, but its significance is unknown. Generating circRNA loss-of-function mutants is difficult because the vast majority of these RNAs are comprised of exons shared with protein-coding mRNAs. In Caenorhabditis elegans, most circRNAs were previously found to accumulate during aging. Two of the most abundant, age-accumulating circRNAs are generated from exon 4 of the crh-1 gene (circ-crh-1). Here, we found that the biogenesis of circ-crh-1 was regulated by the double-stranded RNA-binding protein ADR-1. We identified Reverse Complementary Match (RCM) sequences in introns flanking circ-crh-1. Using CRISPR-Cas9, we deleted the downstream RCM and found that this completely eliminated expression of the circRNA without affecting linear mRNA expression from the crh-1 gene. Remarkably, worms lacking circ-crh-1 exhibited a significantly longer mean lifespan. Lifespan was partially restored to wild type by expression of circ-crh-1 in neural tissues. Widespread transcriptome alterations in circ-crh-1 mutants were identified using RNA-Seq. Moving forward, intronic RCM deletion using CRISPR should be a widely applicable method to identify lifespan-regulating circRNAs in C. elegans.

Keywords: Caenorhabditis elegans; crh-1; aging; circRNA; reverse complementary match.