Heterotypic piRNA Ping-Pong Requires Qin, a Protein with Both E3 Ligase and Tudor Domains

Abstract

Summary piRNAs guide PIWI proteins to silence transposons in animal germ cells. Reciprocal cycles of piRNA-directed RNA cleavage—catalyzed by the PIWI proteins Aubergine (Aub) and Argonaute3 (Ago3) in Drosophila melanogaster—expand the population of antisense piRNAs in response to transposon expression, a process called the Ping-Pong cycle. Heterotypic Ping-Pong between Aub and Ago3 ensures that antisense piRNAs predominate. We show that qin, a piRNA pathway gene whose protein product contains both E3 ligase and Tudor domains, co-localizes with Aub and Ago3 in nuage, a perinuclear structure implicated in transposon silencing. In qin mutants, less Ago3 binds Aub, futile Aub:Aub homotypic Ping-Pong prevails, antisense piRNAs decrease, many families of mobile genetic elements are reactivated, and DNA damage accumulates in nurse cells and oocytes. We propose that Qin enforces heterotypic Ping-Pong between Aub and Ago3, ensuring that transposons are silenced and maintaining the integrity of the germline genome.

The HP1 Homolog Rhino Anchors a Nuclear Complex that Suppresses piRNA Precursor Splicing

“…Transposon mobilization and DNA damage are common to all piRNA pathway mutants, and could contribute to the splicing defects. We therefore analyzed cluster splicing in ovaries mutant for qin , which disrupt a component of the cytoplasmic nuage required for piRNA amplification and transposon silencing (Zhang et al, 2011). In contrast mutations in rhi, cuff and uap56 , the qin mutant combination did not increase spliced transcripts from the sox102F locus (Figure S4).…”

“…RNA isolation, small RNA library construction and sequencing data analysis, immunoblotting, immunostaining and quantitative RT-PCR were performed as described (Zhang et al, 2011). Figures were generated using Excel (Microsoft, Redmond, WA, USA), IgorPro (WaveMetrics, Lake Oswego, OR, USA), Adobe Photoshop and Illustrator (Adobe systems, San Jose CA, USA).…”

PIWI proteins and their interactors in piRNA biogenesis, germline development and gene expression

“…In addition to Aub, Ago3, and Tudor, recent studies have shown that many of the ping-pong cycle components localize to the nuage, such as the RNA helicase Armi, the DEAD-box helicase Vasa (Vas), and the HMG protein Maelstrom (Mael), as well as the TDRD proteins Spn-E, Kumo, Krimp, Vret, and Tej [40,41,67–70]. Their nuage localization suggests that the nuage is the cytoplasmic site where the ping-pong cycle takes place.…”

Posttranscriptional Regulation of Gene Expression by Piwi Proteins and piRNAs

“…The authors propose that Vasa, a conserved DEAD box RNA-helicase, promotes transfer of the target RNAs cleaved by Siwi (an Aubergine ortholog) to Ago3 for the secondary biogenesis (Xiol et al, 2014). Several proteins including Tdrd9/Spindle-E and RNF17/Kumo have been identified as factors involved in the secondary biogenesis (Anand and Kai, 2012; Malone et al, 2009; Shoji et al, 2009; Zhang et al, 2011). .…”