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ERC

Micromecca Report Summary

Project ID: 282460
Funded under: FP7-IDEAS-ERC
Country: Denmark

Mid-Term Report Summary - MICROMECCA (Molecular mechanisms underlying plant miRNA action)

The MICROMECCA project aims to unravel fundamental aspects of how microRNAs (miRNAs) regulate gene expression using the plant Arabidopsis thaliana as a model system. miRNAs associate with proteins of the ARGONAUTE (AGO) family that are recruited to complementary mRNA via base pairing. Targeted mRNA is post-transcriptionally repressed either by AGO-catalyzed endonucleolysis (slicing) or by translational repression that may be coupled to mRNA decay. It is not clear what determines whether one or the other mode of repression is used, and the molecular mechanism underlying each mode of repression also remains ill-defined, particularly in plants. AGO localizes in part to endomembrane systems, but its membrane recruitment and functions in these compartments is not fully understood. In addition, there are still many unknowns regarding the biogenesis and degradation of miRNAs. The MICROMECCA project has made progress to provide answers to several questions regarding these important unknown parts of the mechanism by which miRNA regulates eukaryotic genes.
We have identified a small family of highly conserved proteins that are required for presence of AGO1 in endomembrane compartments. The proteins are post-translationally modified by a lipid, and we have shown that their lipidation is required for miRNA activity. We have also identified a separate set of endoplasmic reticulum-localized, plant-specific proteins that interact directly with a binding site in AGO that may distinguish RNA-bound from non-RNA bound AGO. These proteins are required for regulated degradation of AGO1.
A third major outcome at this stage is the identification of highly conserved proteins that associate with AGO1, and have domains with clear, established roles in translational regulation. It is too early to say whether these proteins really are core components of the mechanism of translational repression, but their in-depth characterization constitutes a major objective of the remaining period of the project.
Progress has also been made on understanding the mechanism and biological relevance of AGO catalyzed slicing. A conditional loss-of-function system has been set up to study slicer-deficient ago1 alleles in post-embryonic tissues, and we are in the process of completing the molecular analyses to determine precise molecular consequences of loss of slicer activity. We find no evidence for nuclear activity of non-coding RNA generated by slicing – as hypothesized in the proposal – but we do find a series of nuclear non-coding RNAs whose presence correlates with DNA methylation of loci encoding miRNA targets.
Finally, our genetic analyses have identified a cytoplasmic RNA degradation pathway that is responsible for removal of cleavage fragments generated by slicing. We are currently following up on interesting preliminary results that suggest an implication of this pathway not only in degradation of cleavage fragments, but also in accelerated decay of mRNAs targeted by miRNAs.

Contact

Poul PETERSEN, (Head of Department)
Tel.: +4535322810
Fax: +45 35324612
E-mail
Record Number: 179805 / Last updated on: 2016-04-21
Information source: SESAM
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