The nuage, a perinuclear structure of unknown function, is present in the germline cells of many organisms. Now, on p. , Haifan Lin and colleagues reveal a function for the Drosophila germline nuage. This structure contains Aubergine and Argonaute 3 (AGO3), two of the three PIWI proteins that are essential for germline development. PIWI proteins bind to PIWI-interacting RNAs (piRNAs) and function in transposon silencing. The researchers report that Partner of PIWIs (PAPI), a novel nuage component, is a TUDOR-domain protein that interacts with all three PIWI proteins through symmetrically dimethylated arginines in their N-terminal domains. This interaction is essential for AGO3 recruitment to the nuage and for transposon silencing. Importantly, the AGO3-PAPI complex associates with the P-body component TRAL/ME31B complex in the nuage and transposon activation occurs in tral mutant ovaries. Thus, the interaction in the nuage between the piRNA pathway and mRNA-degrading P-body components is involved in transposon silencing. The researchers suggest, therefore, that the nuage safeguards the germline genome against deleterious retrotransposition.
