Yale Stem Cell Center and Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06509, USA.
Development. 2011 May;138(9):1863-73. doi: 10.1242/dev.059287. Epub 2011 Mar 29.
The 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.
云雾是一种生殖系特异性的核周结构，其功能仍然难以捉摸。最近，果蝇中的云雾被证明包含三种 PIWI 蛋白中的两种——Aubergine 和 Argonaute 3（AGO3）——它们对生殖系发育至关重要。PIWI 蛋白与 PIWI 相互作用的 RNA（piRNA）结合，并在表观遗传调控和转座子控制中发挥作用。在这里，我们报告了一种新的云雾成分，PAPI（PIWIs 的伙伴），它含有一个 TUDOR 结构域，并通过其 N 端结构域中对称二甲基化的精氨酸残基与所有三种 PIWI 蛋白相互作用。在成年卵巢中，PAPI 主要位于细胞质中，并在云雾中富集，在那里它与 AGO3 部分共定位。PAPI 向云雾的定位不需要精氨酸甲基转移酶 dPRMT5 或 AGO3。然而，AGO3 从云雾中大部分定位，并在没有 PAPI 或 dPRMT5 的情况下变得不稳定，这表明 PAPI 将 PIWI 蛋白招募到云雾中以组装 piRNA 途径成分。正如预期的那样，papi 缺陷导致转座子激活，表型类似于 piRNA 突变体。这进一步表明 PAPI 参与了转座子沉默的 piRNA 途径。此外，AGO3 和 PAPI 在云雾中与 P 体成分 TRAL/ME31B 复合物相关，并且在 tral 突变体卵巢中观察到转座子激活。这表明在云雾中，piRNA 途径成分与 mRNA 降解的 P 体成分在转座子沉默中存在物理和功能相互作用。总的来说，我们的研究揭示了云雾在通过 piRNA 途径保护生殖系基因组免受有害逆转录转座中的作用。
