Sokolova O A, Iakushev E Iu, Stoliarenko A D, Mikhaleva E A, Gvozdev V A, Klenov M S
Mol Biol (Mosk). 2011 Jul-Aug;45(4):633-41.
Complexes of Piwi proteins and Piwi-interacting RNAs (piRNAs) carry out the repression of transposable elements in animal gonads. The Piwi protein clade is represented in D. melanogaster by three members: Piwi, Aub and Ago3. Piwi protein functions in the nuclei of somatic and germinal ovarian cells, whereas Aub and Ago3 are cytoplasmic proteins of germinal cells. Aub and Ago3 interact with each other in the perinuclear nuage organelle to perform piRNA amplification via the ping-pong mechanism. Previously, derepression of several transposable elements as a result of mutations in the piRNA silencing system was shown. Here we quantify the increase in expression level of an enlarged number of retrotransposons due to the mutations in the piwi gene, nuage components coding aub, mael and spn-E genes and the RNA helicase armi gene mutation that impairs Piwi nuclear localization, but not the ping-pong cycle. We reveal that piwi, armi, aub, spn-E and mael genes participate together in the repression of several transposons (HMS-Beagle, Gate and HeT-A), whereas silencing of land G elements requires the same genes except piwi. We suggest that Armi has other functions besides the localizing of Piwi protein in the nuclei. Our data suggest also a role of cytoplasmic Aub, Spn-E and Mael nuage proteins in Piwi-mediated repression of Gate and HMS-Beagle transposons in the germline nuclei. As a whole, our results corroborate the idea that genome stabilization in the germline is realized by different silencing strategies specific for different transposable elements. At the same time, our data suggest the existence of yet unknown mechanisms of interplay between nuclear and cytoplasmic components of the piRNA machinery in the germline.
Piwi蛋白与Piwi相互作用RNA（piRNA）的复合物在动物性腺中对转座元件进行抑制。在黑腹果蝇中，Piwi蛋白家族由三个成员代表：Piwi、Aub和Ago3。Piwi蛋白在体细胞和生殖卵巢细胞的细胞核中发挥作用，而Aub和Ago3是生殖细胞的细胞质蛋白。Aub和Ago3在核周的核仁细胞器中相互作用，通过乒乓机制进行piRNA扩增。此前，已表明piRNA沉默系统中的突变会导致几种转座元件的去抑制。在这里，我们量化了由于piwi基因、编码aub、mael和spn - E基因的核仁成分以及损害Piwi核定位但不影响乒乓循环的RNA解旋酶armi基因突变，导致大量逆转座子表达水平的增加。我们发现piwi、armi、aub、spn - E和mael基因共同参与了对几种转座子（HMS - Beagle、Gate和HeT - A）的抑制，而对land G元件的沉默除了piwi外需要相同的基因。我们认为Armi除了将Piwi蛋白定位在细胞核中之外还有其他功能。我们的数据还表明细胞质中的Aub、Spn - E和Mael核仁蛋白在Piwi介导的生殖系细胞核中对Gate和HMS - Beagle转座子的抑制中发挥作用。总体而言，我们的结果证实了这样一种观点，即生殖系中的基因组稳定是通过针对不同转座元件的不同沉默策略实现的。同时，我们的数据表明生殖系中piRNA机制的核成分和细胞质成分之间存在尚未知的相互作用机制。
