Daedalus and Gasz recruit Armitage to mitochondria, bringing piRNA precursors to the biogenesis machinery

Abstract

The Piwi-interacting RNA (piRNA) pathway is a small RNA-based immune system that silences mobile genetic elements in animal germlines. piRNA biogenesis requires a specialized machinery that converts long singlestranded precursors into small RNAs of ∼25-nucleotides in length. This process involves factors that operate in two different subcellular compartments: the nuage/Yb body and mitochondria. How these two sites communicate to achieve accurate substrate selection and efficient processing remains unclear. Here, we investigate a previously uncharacterized piRNA biogenesis factor, Daedalus (Daed), that is located on the outer mitochondrial membrane. Daed is essential for Zucchini-mediated piRNA production and the correct localization of the indispensable piRNA biogenesis factor Armitage (Armi). We found that Gasz and Daed interact with each other and likely provide a mitochondrial "anchoring platform" to ensure that Armi is held in place, proximal to Zucchini, during piRNA processing. Our data suggest that Armi initially identifies piRNA precursors in nuage/Yb bodies in a manner that depends on Piwi and then moves to mitochondria to present precursors to the mitochondrial biogenesis machinery. These results represent a significant step in understanding a critical aspect of transposon silencing; namely, how RNAs are chosen to instruct the piRNA machinery in the nature of its silencing targets.

Armitage determines Piwi−piRISC processing from precursor formation and quality control to inter‐organelle translocation

“…The probe used was for idefix-piRNA arising from the flam locus. These findings corroborated the notion that Gasz acts in conjunction with Daed as the platform for Zuc-dependent piRNA maturation from piRNA precursors [20]. Without Gasz, mature idefix-piRNA almost disappeared but the piRNA precursors strongly accumulated, as was the case upon Zuc depletion (Fig 1A).…”

“…These results suggest that, without Gasz, regardless of the presence or absence of Zuc, Armi no longer remains on the mitochondrial surface and so returns to Yb bodies while leaving Piwi in the cytosol. Previous studies showed that Gasz loss perturbs mitochondrial morphology in OSCs [17,20], which was also observed but to a lesser extent in this study ( Fig EV1E). Previous studies showed that Gasz loss perturbs mitochondrial morphology in OSCs [17,20], which was also observed but to a lesser extent in this study ( Fig EV1E).…”

“…These factors can be classified into two groups by their apparent cellular localization in OSCs. In contrast, Zuc, Mino, Daed, and Gasz are localized at the outer membrane of mitochondria via their own transmembrane targeting signals (TMs) [17,18,20,21,26]. In contrast, Zuc, Mino, Daed, and Gasz are localized at the outer membrane of mitochondria via their own transmembrane targeting signals (TMs) [17,18,20,21,26].…”

Epigenetic Requirements for Triggering Heterochromatinization and Piwi-Interacting RNA Production from Transgenes in the Drosophila Germline

“…Analysis of ovarian transcription profiles suggests that regions facilitating convergent transcription favor the formation of transgenic piRNA clusters.Cells 2020, 9, 922 2 of 19 piRNA clusters [3][4][5]. In germ cells, in contrast to protein-coding mRNAs, piRNA precursors are delivered to the piRNA processing machinery localized in the specialized cytoplasmic structure, "nuage", and on the outer mitochondrial membrane [6][7][8][9]. piRNA-mediated silencing is a potent mechanism of expression control realized through transcriptional [10,11] and co-transcriptional [12] repression of target loci.…”

Assembly and Function of Gonad-Specific Non-Membranous Organelles in Drosophila piRNA Biogenesis

“…Female sterile (1) Yb (Yb), Armitage (Armi), Sister of Yb (SoYb), Vreteno (Vret), and Shutdown (Shu) are detected at Yb bodies, while Zucchini (Zuc), Gasz, Minotaur (Mino), and Daedalus (Daed) are detected on mitochondria (for details, see Sections 4 and 5) [60][61][62][63][64][65][66][67][68]. Armi, Vret, and Zuc are also expressed in germ cells [48,63,[67][68][69][70][71][72][73][74][75][76]. Germ-specific factors include Brother of Yb (BoYb), Spindle-E/Homeless (Spn-E), and Qin/Kumo (Qin) [64,[77][78][79].…”