Dicer-2 promotes mRNA activation through cytoplasmic polyadenylation

Abstract

Cytoplasmic polyadenylation is a widespread mechanism to regulate mRNA translation. In vertebrates, this process requires two sequence elements in target 3' UTRs: the U-rich cytoplasmic polyadenylation element and the AAUAAA hexanucleotide. In <i>Drosophila melanogaster</i>, cytoplasmic polyadenylation of <i>Toll</i> mRNA occurs independently of these canonical elements and requires a machinery that remains to be characterized. Here we identify Dicer-2 as a component of this machinery. Dicer-2, a factor previously involved in RNA interference (RNAi), interacts with the cytoplasmic poly(A) polymerase Wispy. Depletion of Dicer-2 from polyadenylation-competent embryo extracts and analysis of <i>wispy</i> mutants indicate that both factors are necessary for polyadenylation and translation of <i>Toll</i> mRNA. We further identify <i>r2d2</i> mRNA, encoding a Dicer-2 partner in RNAi, as a Dicer-2 polyadenylation target. Our results uncover a novel function of Dicer-2 in activation of mRNA translation through cytoplasmic polyadenylation.