Mechanisms of miRNA function

Dr. Elisa Izaurralde

Project Summary:

MicroRNAs (miRNAs) represent a novel class of genome-encoded eukaryotic regulatory RNAs that silence gene expression post-transcriptionally. Although the proteins mediating miRNA biogenesis and function have been identified, the precise mechanism by which miRNAs regulate the expression of target mRNAs remains unclear. Recent work from our laboratory has demonstrated that miRNAs silence gene expression by at least two independent mechanisms: by repressing translation and/or by promoting mRNA degradation. In Drosophila melanogaster, both mechanisms require Argonaute 1 (AGO1) and the P-body component GW182. Moreover, mRNA degradation by miRNAs is effected by the enzymes involved in general mRNA decay, including deadenylases and decapping enzymes, which localize to P-bodies. Our findings suggest a model for miRNA function in which AGO1 associates with miRNA targets through miRNA:mRNA base-pairing interactions. GW182 interacts with AGO1 and recruits deadenylases and decapping enzymes, leading to mRNA degradation. However, not all miRNA-targets are degraded:  some stay in a translationally silent state, from which they may eventually be released. The aim of this project is to understand how the final outcome of miRNA regulation (i.e. degradation versus translational repression) is specified and potentially influenced by other RNA-binding proteins interacting with the targeted mRNA and/or by the spatial confinement of targets into P-bodies.

Selected publications (2007-09):
1. Eulalio, A., Behm-Ansmant, I., Schweizer, D., Iand zaurralde, E. 2007. P-body formation is a consequence, not the cause of RNA-mediated gene silencing. Mol. Cell. Biol., 27:3970–81

2. Eulalio, A., Rehwinkel, J., Stricker, M., Huntzinger, E., Yang, S.F., Doerks, T., Dorner, S., Bork, P., Boutros, M., and Izaurralde, E. 2007. Target-specific requirements for enhancers of decapping in miRNA-mediated gene silencing. Genes & Dev., 21:2558–70

3. Eulalio, A, Huntzinger, E, and Izaurralde, E. 2008. GW182 interaction with Argonaute is essential for miRNA-mediated translational repression and mRNA decay. Nat. Struct. Mol. Biol., 15:346–53

4. Eulalio, A., Huntzinger, E., Nishihara, T., Rehwinkel, J., Fauser, M., and Izaurralde E. 2009. Deadenylation is a widespread effect of miRNA regulation. RNA, 15:21–32.

5. Eulalio, A., Tritschler, F., Büttner, R., Weichenrieder, O., Izaurralde, E., and Truffault, V. 2009. The RRM domain in GW182 proteins contributes to miRNA-mediated gene silencing. Nucleic Acids Res., 37:2974–83

6. Lazzaretti, D., Tournier, I., and Izaurralde, E. 2009. The C-terminal domains of human TNRC6A, TNRC6B, and TNRC6C silence bound transcripts independently of Argonaute proteins. RNA, 15:1059–1066

7. Eulalio, A., Helms, S., Fritzsch, C., Fauser, M., and Izaurralde, E. 2009. A C-terminal silencing domain in GW182 is essential for miRNA function. RNA, 15:1067–1077