UC San Diego

MicroRNAs (miRNA) are critical regulators of many different biological processes, including cellular differentiation, development, response to stress, and aging. These small (~22 nucleotides) RNA molecules, post-transcriptionally regulate their targets in a sequence dependent manner but to exert their regulatory influence, a miRNA must be bound by an Argonaute (AGO) protein. A critical factor in miRNA targeting is base-pairing of nucleotides 2-7 of the miRNA, the seed, to the target RNA. Due to the importance of the seed sequence in targeting, miRNAs who share their seed sequence are grouped into families. Yet, in Chapter 2, I review recent studies on non-canonical miRNA regulation, including miRNA targeting that is not seed dependent, such as the role of the miRNA’s 3’ end in targeting as well as miRNA overall expression. Thus, despite the importance of miRNAs, predicting the targets and biological roles is very challenging. This outstanding problem in determining miRNAs targets and function, is especially acute for miRNAs that belong to the same family. MiRNAs in the same family, because they share a seed sequence, are often presumed to be redundant. As reviewed in Chapter 4, I explore how the miR-238, miR-239a, and miR-239b family regulate aging in C. elegans. I find that these miRNAs have distinct roles in aging, that loss of miR-238 leads to a reduced lifespan and many genes misergulated in adult, while loss of either miR-239a or miR-239b has no effect lifespan and leads to the misregultion of only a handful of non-overlapping genes. Interestingly, miR-239a or miR-239b can rescue the loss of miR-238 when they expressed from the miR-238 genetic locus suggesting that expression, not sequence, underlies the differential roles of this miRNA family in C. elegans aging. In Chapter 3, I investigated how individual miRNAs contribute to the divergent roles of the somatic C. elegans miRNA AGOs, AGO-like-gene (ALG)-1 and ALG-2, in aging. I immunoprecipitated miRNAs bound by ALG-1 and ALG-2 and analyze miRNA misregulation upon the loss of these AGOs. Some of the miRNAs I identified as contributing to these phenotypes are already known regulators of aging while others may be novel aging regulators.