A New Role for the GARP Complex in MicroRNA-Mediated Gene Regulation

Alejandro Vasquez-Rifo,Martin J Simard,Evelyne L Rondeau,Alexandra Dallaire,Guillaume Jannot,Gabriel D Bossé,Amy E Pasquinelli

doi:10.1371/journal.pgen.1003961

Abstract

Many core components of the microRNA pathway have been elucidated and knowledge of their mechanisms of action actively progresses. In contrast, factors with modulatory roles on the pathway are just starting to become known and understood. Using a genetic screen in Caenorhabditis elegans, we identify a component of the GARP (Golgi Associated Retrograde Protein) complex, vps-52, as a novel genetic interactor of the microRNA pathway. The loss of vps-52 in distinct sensitized genetic backgrounds induces the enhancement of defective microRNA-mediated gene silencing. It synergizes with the core microRNA components, alg-1 Argonaute and ain-1 (GW182), in enhancing seam cell defects and exacerbates the gene silencing defects of the let-7 family and lsy-6 microRNAs in the regulation of seam cell, vulva and ASEL neuron development. Underpinning the observed genetic interactions, we found that VPS-52 impinges on the abundance of the GW182 proteins as well as the levels of microRNAs including the let-7 family. Altogether, we demonstrate that GARP complex fulfills a positive modulatory role on microRNA function and postulate that acting through GARP, vps-52 participates in a membrane-related process of the microRNA pathway.

Highlights

The microRNA pathway is a gene regulatory system that uses small non-coding RNAs to target messenger RNAs for post-transcriptional regulation
The gene vps-52 is a genetic interactor of the microRNA pathway Argonaute alg-1
In order to gain insights into the steps at which vps-52 regulate miRNA activity, we investigated the physical association of VPS52 with components of the microRNA pathway in C. elegans

Summary

Introduction

The microRNA (miRNA) pathway is a gene regulatory system that uses small non-coding RNAs to target messenger RNAs (mRNAs) for post-transcriptional regulation. In the canonical form of miRNA biogenesis, miRNA-containing transcripts are processed through sequential cleavage operated by the Drosha and Dicer enzymes into mature miRNA species (21–23 nucleotides long) that associate with an Argonaute protein (reviewed in [1]). The miRNA-loaded Argonaute, as part of the core miRNA-induced silencing complex (miRISC), regulates target mRNAs through binding sites in their 39UTRs. The most detailed repressive effector function of this complex is mediated by its association to GW182 proteins (reviewed in [2]). All miRISC components would be subjected to degradation, nucleases have been shown to degrade miRNAs (reviewed in [8]), and autophagy mediates the degradation of Dicer, Argonaute [9,10] and GW182 [11]

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Conclusion