Local control of mRNA translation modulates neuronal development, synaptic 
plasticity, and memory formation. A poorly understood aspect of this control is 
the role and composition of ribonucleoprotein (RNP) particles that mediate 
transport and translation of neuronal RNAs. Here, we show that staufen- and 
FMRP-containing RNPs in Drosophila neurons contain proteins also present in 
somatic "P bodies," including the RNA-degradative enzymes Dcp1p and Xrn1p/Pacman 
and crucial components of miRNA (argonaute), NMD (Upf1p), and general 
translational repression (Dhh1p/Me31B) pathways. Drosophila Me31B is shown to 
participate (1) with an FMRP-associated, P body protein (Scd6p/trailer hitch) in 
FMRP-driven, argonaute-dependent translational repression in developing eye 
imaginal discs; (2) in dendritic elaboration of larval sensory neurons; and (3) 
in bantam miRNA-mediated translational repression in wing imaginal discs. These 
results argue for a conserved mechanism of translational control critical to 
neuronal function and open up new experimental avenues for understanding the 
regulation of mRNA function within neurons.