The decapping scavenger enzyme DCS-1 controls microRNA levels in Caenorhabditis elegans.

In metazoans, microRNAs play a critical role in the posttranscriptional regulation of genes required for cell proliferation and differentiation. MicroRNAs themselves are regulated by a multitude of mechanisms influencing their transcription and posttranscriptional maturation. However, there is only sparse knowledge on pathways regulating the mature, functional form of microRNA. Here, we uncover the implication of the decapping scavenger protein DCS-1 in the control of microRNA turnover. In Caenorhabditis elegans, mutations in dcs-1 increase the levels of functional microRNAs. We demonstrate that DCS-1 interacts with the exonuclease XRN-1 to promote microRNA degradation in an independent manner from its known decapping scavenger activity, establishing two molecular functions for DCS-1. Our findings thus indicate that DCS-1 is part of a degradation complex that performs microRNA turnover in animals.

A new role for the GARP complex in microRNA-mediated gene regulation.

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.

The R148.3 Gene Modulates Caenorhabditis elegans Lifespan and Fat Metabolism.

Despite many advances, the molecular links between energy metabolism and longevity are not well understood. Here, we have used the nematode model Caenorhabditis elegans to study the role of the yet-uncharacterized gene R148.3 in fat accumulation and lifespan. In wild-type worms, a R148.3p::GFP reporter showed enhanced expression throughout life in the pharynx, in neurons, and in muscles. Functionally, a protein fusing a predicted 22 amino acid N-terminal signal sequence (SS) of R148.3 to mCherry displayed robust accumulation in coelomyocytes, indicating that R148.3 is a secreted protein. Systematic depletion of R148.3 by RNA interference (RNAi) at L1 but not at young-adult stage enhanced triglyceride accumulation, which was associated with increased food uptake and lower expression of genes involved in lipid oxidation. However, RNAi of R148.3 at both L1 and young-adult stages robustly diminished mean and maximal lifespan of wild-type worms, and also abolished the long-lived phenotypes of eat-2 and daf-2/InsR mutants. Based on these data, we propose that R148.3 is an SS that modulates fat mass and longevity in an independent manner.

Developmental characterization of the microRNA-specific C. elegans Argonautes alg-1 and alg-2.

The genes alg-1 and alg-2 (referred to as "alg-1/2") encode the Argonaute proteins affiliated to the microRNA (miRNA) pathway in C. elegans. Bound to miRNAs they form the effector complex that effects post-transcriptional gene silencing. In order to define biological features important to understand the mode of action of these Argonautes, we characterize aspects of these genes during development. We establish that alg-1/2 display an overlapping spatio-temporal expression profile and shared association to a miRNAs set, but with gene-specific predominant expression in various cells and increased relative association to defined miRNAs. Congruent with their spatio-temporal coincidence and regardless of alg-1/2 drastic post-embryonic differences, only loss of both genes leads to embryonic lethality. Embryos without zygotic alg-1/2 predominantly arrest during the morphogenetic process of elongation with defects in the epidermal-muscle attachment structures. Altogether our results highlight similarities and specificities of the alg-1/2 likely to be explained at different cellular and molecular levels.