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Repression of C. elegans microRNA targets at the initiation level of translation requires GW182 proteins.

ABSTRACT: MicroRNAs (miRNAs) repress target genes through a poorly defined antisense mechanism. Cell-free and cell-based assays have supported the idea that miRNAs repress their target mRNAs by blocking initiation of translation, whereas studies in animal models argued against this possibility. We examined endogenous targets of the let-7 miRNA, an important regulator of stem cell fates. We report that let-7 represses translation initiation in Caenorhabditis elegans, demonstrating this mode of action for the first time in an organism. Unexpectedly, although the lin-4 miRNA was previously reported to repress its targets at a step downstream of translation initiation, we also observe repression of translation initiation for this miRNA. This repressive mechanism, which frequently but not always coincides with transcript degradation, requires the GW182 proteins AIN-1 and AIN-2, and acts on several mRNAs targeted by different miRNAs. Our analysis of an expanded set of endogenous miRNA targets therefore indicates widespread repression of translation initiation under physiological conditions and establishes C. elegans as a genetic system for dissection of the underlying mechanisms.

SUBMITTER: Ding XC

PROVIDER: S-EPMC2637332 | biostudies-literature | 2009 Feb

REPOSITORIES: biostudies-literature

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Repression of C. elegans microRNA targets at the initiation level of translation requires GW182 proteins.

Ding Xavier C XC Grosshans Helge H

The EMBO journal 20090108 3

MicroRNAs (miRNAs) repress target genes through a poorly defined antisense mechanism. Cell-free and cell-based assays have supported the idea that miRNAs repress their target mRNAs by blocking initiation of translation, whereas studies in animal models argued against this possibility. We examined endogenous targets of the let-7 miRNA, an important regulator of stem cell fates. We report that let-7 represses translation initiation in Caenorhabditis elegans, demonstrating this mode of action for t ...[more]

PMID: 19131968

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Project description:MicroRNAs are small non-coding RNA molecules mediating the translational repression and degradation of target mRNAs in the cell. Mature miRNAs are used as a template by the RNA-induced silencing complex (RISC) to recognize the complementary mRNAs to be regulated. To discern further RISC complex functions, we analyzed the activities of two RISC proteins, AGO2 and GW182, in the MCF-7 human breast cancer cell line. We performed three RIP-Chip experiments using either anti-AGO2 or anti-GW182 antibody and compiled a dataset made up of the miRNA and mRNA expression profiles of three samples for each experiment. Specifically, we analyzed the input sample, the immunoprecipitated fraction and the unbound sample resulting from the RIP experiment. We used the expression profile of the input sample to compute several variables, using formulae capable of integrating the information on predicted miRNA binding sites, both in the 3’UTR and coding regions, with miRNA and mRNA expression level profiles. We compared immunoprecipitated vs unbound samples to determine the differentially expressed genes, independently for AGO2 and GW182 related samples. For each of the two proteins, we trained and tested several support vector machine algorithms able to predict the differentially expressed genes that were experimentally detected. The most efficient algorithm for predicting the over-expressed genes in AGO2 immunoprecipitated samples was trained by using variables involving the number of binding sites in both the 3’UTR and coding region, integrated with the miRNA expression profile, as expected for miRNA targets. On the other hand, we found that the best variable for predicting over-expressed genes in the GW182 immunoprecipitated sample was the length of the coding region. Due to the major role of GW182 in GW/P-bodies, our data suggests that the AGO2-GW182 RISC complex recruits genes based on miRNA binding sites in the 3’UTR and coding region, but only the longer mRNAs remain sequestered in GW/P-bodies, functioning as a repository for translationally silenced RNAs.

Dataset Information

Repression of C. elegans microRNA targets at the initiation level of translation requires GW182 proteins.

Publications

Repression of C. elegans microRNA targets at the initiation level of translation requires GW182 proteins.

Similar Datasets

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