Dr. Elisa Izaurrralde and colleagues (EMBL; Max-Planck-Institute for Developmental Biology-Tuebingen) provide new mechanistic insight into gene silencing by miRNAs.

Their paper will be featured on the cover of the July 15th issue of G&D, and also will be made available online in advance on 7/3.

MicroRNAs (miRNAs) are a novel class of small regulatory RNAs that silence the expression of complementary mRNA targets.

Dr. Izaurralde and colleagues demonstrate that the P-body protein, GW182, interacts with the miRNA effector Argonaute proteins as well as mRNA degradation enzymes, to promote target mRNA decay. The authors establish that GW182 functions downstream of the Argonaute-1 protein in the miRNA pathway, targeting transcripts for decay via a deadenylation and decapping reaction.

The question of whether miRNAs silence gene expression without affecting mRNA levels has been controversial, and conflicting results have been reported in the literature. Dr. Izaurralde explains that, "Our findings reveal that miRNAs silencing gene expression by at least two independent mechanisms: by repression of translation and/or by induction of mRNA degradation. This provides an explanation for changes in mRNA levels observed at least for a subset of miRNA targets."