UC San Diego

MicroRNAs (miRNAs) are small non-coding RNAs that negatively regulate gene expression through the binding of an Argonaute (AGO) protein to facilitate the translational repression and degradation of a target messenger RNA (mRNA). In Caenorhabditis elegans, Argonaute-like Gene 1 (ALG-1) and ALG-2 act as the main AGOs in the miRNA-silencing pathway (He and Hannon, 2004; Jonas and Izaurralde, 2015). ALG-1 and ALG-2 were previously thought to function redundantly during development, but loss of these AGO proteins in adulthood results in opposing lifespan phenotypes with alg-1 and alg-2 mutants reducing or increasing longevity, respectively (Aalto & Nicastro et al., 2017). The divergent lifespans observed in alg-1 and alg-2 mutants were shown to be associated with the misregulation of several aging-associated miRNAs, such as lin-4 and miR-239a/b, which differentially regulate longevity through the IGF-1/Insulin signaling (IIS) pathway (Boehm and Slack, 2005; de Lencastre et al., 2010; Aalto & Nicastro et al., 2017). Since there are several hundred annotated miRNAs in the C. elegans genome, I hypothesized that there are likely many more miRNAs that contribute to the differential lifespans of alg-1 and alg-2 mutants. — To identify these miRNAs, I performed Small RNA profiling on alg-1 and alg-2 mutants during adulthood. Through smRNA profiling, I was able to identify 51 and 19 significantly misregulated miRNAs in alg-1 and alg-2 backgrounds, respectively. Target prediction analysis of several misregulated miRNA was able to identify many gene targets known to regulate longevity though in the IIS pathway. For instance, miR-355-5p was found to be differentially expressed in alg-1 and alg-2 mutants and was predicted to target 102 longevity suppressing genes in the IIS pathway; these observations are consistent with the differential lifespans observed in alg-1 and alg-2 mutants. miRNA-mediated regulation of aging-associated pathways, such as the IIS pathway, is a highly conserved phenomenon in many eukaryotes, including humans (Lopez-Otin C, 2013; Guarente L & Kenyon C, 2000; Kenyon CJ, 2010). By understanding how perturbation of ALG-1 and ALG-2 differentially regulates aging in C. elegans, we can further our understanding of the molecular basis of aging as a whole.