Mitochondrial Daed disambiguates Zuc endonucleolysis in Piwi-piRISC production to optimize its function in transposon repression

In Drosophila ovarian somatic cells, Piwi and piRNA assemble Piwi-piRISC and protect the genome against transposons. The Piwi-piRISC precursor is produced in Yb bodies and translocates with Armi to mitochondria for Zuc-dependent maturation. Daed features in this maturation phase, but the details remain unclear. Here, we show that Daed stabilizes its partner Gasz through protein?protein interaction, and tethers Armi to mitochondria to allow Zuc to process substrates. Daed binds to Armi through two regions: the first ?-helix in the extended coiled-coil domain, which interacts with Armi?s N-terminus, and the SAM domain, which interacts with Armi?s UPF1-like helicase domain. Inhibition of the former interaction abolishes Piwi-piRISC generation. When the latter interaction is disrupted, Zuc obscures cleavage positions and Piwi-bound piRNAs elongate atypically. Consequently, Piwi-piRISC?s level is reduced, leading to transposon derepression. Thus, it is Daed that disambiguates Zuc cleavage in orchestrating with Gasz and Armi to optimize Piwi-piRISC production and its function. 12 smRNA-seq libraries (4 different samples with triplicates): PIWI-associated small RNA libraries were prepared from small RNAs associated with Piwi immunoprecipitates.