In eukaryotic cells degradation of bulk mRNA in the 5' to 3' direction requires 
the consecutive action of the decapping complex (consisting of DCP1 and DCP2) 
and the 5' to 3' exonuclease XRN1. These enzymes are found in discrete 
cytoplasmic foci known as P-bodies or GW-bodies (because of the accumulation of 
the GW182 antigen). Proteins acting in other post-transcriptional processes have 
also been localized to P-bodies. These include SMG5, SMG7, and UPF1, which 
function in nonsense-mediated mRNA decay (NMD), and the Argonaute proteins that 
are essential for RNA interference (RNAi) and the micro-RNA (miRNA) pathway. In 
addition, XRN1 is required for degradation of mRNAs targeted by NMD and RNAi. To 
investigate a possible interplay between P-bodies and these post-transcriptional 
processes we depleted P-body or essential pathway components from Drosophila 
cells and analyzed the effects of these depletions on the expression of reporter 
constructs, allowing us to monitor specifically NMD, RNAi, or miRNA function. We 
show that the RNA-binding protein GW182 and the DCP1:DCP2 decapping complex are 
required for miRNA-mediated gene silencing, uncovering a crucial role for P-body 
components in the miRNA pathway. Our analysis also revealed that inhibition of 
one pathway by depletion of its key effectors does not prevent the functioning 
of the other pathways, suggesting a lack of interdependence in Drosophila.