PAPI, a novel TUDOR-domain protein, complexes with AGO3, ME31B and TRAL in the nuage to silence transposition

Abstract

SUMMARYThe nuage is a germline-specific perinuclear structure that remains functionally elusive. Recently, the nuage in Drosophila was shown to contain two of the three PIWI proteins -Aubergine and Argonaute 3 (AGO3) -that are essential for germline development. The PIWI proteins bind to PIWI-interacting RNAs (piRNAs) and function in epigenetic regulation and transposon control. Here, we report a novel nuage component, PAPI (Partner of PIWIs), that contains a TUDOR domain and interacts with all three PIWI proteins via symmetrically dimethylated arginine residues in their N-terminal domain. In adult ovaries, PAPI is mainly cytoplasmic and enriched in the nuage, where it partially colocalizes with AGO3. The localization of PAPI to the nuage does not require the arginine methyltransferase dPRMT5 or AGO3. However, AGO3 is largely delocalized from the nuage and becomes destabilized in the absence of PAPI or dPRMT5, indicating that PAPI recruits PIWI proteins to the nuage to assemble piRNA pathway components. As expected, papi deficiency leads to transposon activation, phenocopying piRNA mutants. This further suggests that PAPI is involved in the piRNA pathway for transposon silencing. Moreover, AGO3 and PAPI associate with the P body component TRAL/ME31B complex in the nuage and transposon activation is observed in tral mutant ovaries. This suggests a physical and functional interaction in the nuage between the piRNA pathway components and the mRNA-degrading P-body components in transposon silencing. Overall, our study reveals a function of the nuage in safeguarding the germline genome against deleterious retrotransposition via the piRNA pathway.

Mitochondrial protein BmPAPI modulates the length of mature piRNAs

“…In Drosophila ovaries, PAPI interacts with PIWI proteins, particularly AGO3 (Liu et al 2011). The absence of PAPI results in delocalization of AGO3 in nuage and transposon activation, implicating PAPI as a functional component in the piRNA pathway for transposon silencing (Liu et al 2011).…”

“…In Drosophila ovaries, PAPI interacts with PIWI proteins, particularly AGO3 (Liu et al 2011). The absence of PAPI results in delocalization of AGO3 in nuage and transposon activation, implicating PAPI as a functional component in the piRNA pathway for transposon silencing (Liu et al 2011). Proteomic surveys of mouse PIWI complexes have identified TDRKH/TDRD2, a mouse PAPI homolog, as a binding partner of mouse PIWI proteins Vagin et al 2009).…”

The Drosophila fragile X mental retardation protein participates in the piRNA pathway

“…Typically, the founding member of the family, Tudor, binds AGO proteins and helps them interact with specific piRNAs (Nishida et al, 2009). Among the different TDRD proteins, fs(1)Yb works in the primary pathway Saito et al, 2010;Takata et al, 2008); Krimper, Tejas, Qin/ Kumo, and PAPI work in the ping-pong pathway (Lim and Kai, 2007;Liu et al, 2011;Patil and Kai, 2010); and Vret works in both systems (Handler et al, 2011;Zamparini et al, 2011). PAPI, the only TDRD protein that has a modular structure closely related to dFmr1 (two KH domains and one TDRD), interacts with the di-methylated arginine residues of AGO3 and controls the ping-pong cycle in the nuage.…”

Caenorhabditis elegans RSD-2 and RSD-6 promote germ cell immortality by maintaining small interfering RNA populations

“…In addition to targeting 22G-RNAs, vertebrate and Drosophila Tudor domain proteins are known to target repetitive regions of the genome such as transposons (9,(30)(31)(32)(33)(34). We therefore mapped 22G-RNAs in rsd mutants against these repetitive loci.…”