In Drosophila, Piwi-interacting RNAs (piRNAs) preserve genome integrity in the germline by silencing mobile genetic elements, such as transposons. On , Ruth Lehmann and co-workers report the identification of Vreteno, a novel gonad-specific protein that is essential for germline development and primary piRNA biogenesis in Drosophila. The researchers demonstrate that vreteno (vret), which was identified in a screen for maternal-effect mutations affecting oocyte polarity, is essential for germline development. They further show that Vret, which contains two Tudor domains, interacts with Piwi and Aubergine to regulate their stability and subcellular localisation. Using microarray analyses, they confirm that vret regulates transposon silencing in both the germline and somatic tissues of the Drosophila gonad. Finally, the authors report, in the absence of Vret, Piwi-bound piRNAs are lost, whereas piRNAs can engage in Aubergine- and Argonaute 3-dependent `ping-pong' amplification. The authors thus suggest that Vreteno regulates transposon silencing by acting at the early stages of primary piRNA processing.
