Proteins of the PIWI subfamily Aub and AGO3 associated with the 
germline-specific perinuclear granules (nuage) are involved in the silencing of 
retrotransposons and other selfish repetitive elements in the Drosophila genome. 
PIWI proteins and their 25- to 30-nt PIWI-interacting RNA (piRNAs) are 
considered as key participants of the piRNA pathway. Using immunostaining, we 
found a large, nuage-associated organelle in the testes, the piNG-body (piRNA 
nuage giant body), which was significantly more massive than an ordinary nuage 
granule. This body contains known ovarian nuage proteins, including Vasa, Aub, 
AGO3, Tud, Spn-E, Bel, Squ, and Cuff, as well as AGO1, the key component of the 
microRNA pathway. piNG-bodies emerge at the primary spermatocyte stage of 
spermatogenesis during the period of active transcription. Aub, Vasa, and Tud 
are located at the periphery of the piNG-body, whereas AGO3 is found in its 
core. Mutational analysis revealed that Vasa, Aub, and AGO3 were crucial for 
both the maintenance of the piNG-body structure and the silencing of selfish 
Stellate repeats. The piNG-body destruction caused by csul mutations that 
abolish specific posttranslational symmetrical arginine methylation of PIWI 
proteins is accompanied by strong derepression of Stellate genes known to be 
silenced via the piRNA pathway.