Elisa Izaurralde Memorial Lecture: Roles of microRNAs in animal development: lessons from C. elegans

The long-term goal of our lab is to understand gene regulatory mechanisms that enable the development of a single cell zygote into a multicellular organism. A large focus of our work has been on the roles of post-transcriptional repression by microRNAs. MicroRNAs (miRNAs) repress target genes, controlling their protein output in time and space. They provide an essential layer of regulation during development, evidenced in the fact that loss of the machinery that processes these short RNAs causes embryonic lethality in every animal examined. Moreover, mutations in the miRNA biogenesis or effector machinery in humans causes syndromic diseases. Individual miRNAs have also been linked to essential functions in model organisms as well as disease in humans (e.g. mutation in a single miRNA causes progressive deafness in humans). Although the number of miRNAs has increased during animal evolution, a set of 32 miRNAs were present in the last common ancestor of bilaterian animals and have been conserved over hundreds of millions of years. However, with few exceptions, the functional targets of these highly conserved miRNAs remain unknown due to a number of technical challenges associated with: i) the short nature of miRNAs that has made their profiling more difficult than longer mRNAs, ii) the fact that miRNAs exert quantitative, often modest, repression on their targets, and iii) the fact that target predictions that largely rely on short sequence information, produce an excess of false positives.

Our research program systematically tackles the roles of conserved miRNAs during animal development. We have developed experimental strategies that leverage the use of the nematode C. elegans, with state-of-the-art molecular biology and genetics approaches. We have focused on the rigorous identification of functionally relevant targets of miRNAs. Knowledge of these targets has allowed us to begin to address how changes in their dosage, even if modest, affect cellular processes and ultimately development and physiology. Our findings in C. elegans are also guiding investigation of these conserved miRNAs in mammalian cell models.