Department of Molecular Biology, Keio University School of Medicine, Shinjuku-ku, Tokyo 160-8582, Japan.
Curr Opin Genet Dev. 2011 Aug;21(4):484-90. doi: 10.1016/j.gde.2011.05.001. Epub 2011 Jul 18.
RNA silencing pathways are now recognized to participate in essential cellular functions ranging from the regulation of mRNA turnover to the suppression of the activity of potentially deleterious transposable elements (TEs). Piwi-interacting RNAs (piRNAs) are germline-specific, small silencing RNAs that suppress TE activity and maintain genome integrity during germline development. In Drosophila ovarian somatic cells, piRNAs are processed from long single-stranded RNAs by a Dicer-independent pathway and are loaded onto Piwi in the cytoplasm. The Piwi-piRNA complexes are then transported into the nucleus to exert TE silencing. This mechanism involves gatekeepers for a functional Piwi-piRNA complex to be imported, which parallels with the Tetrahymena Twi1p-scan RNA pathway used to carry out the programmed DNA elimination.
RNA 沉默途径现在被认为参与了许多重要的细胞功能，从调节 mRNA 的周转，到抑制潜在有害转座元件（TEs）的活性。Piwi 相互作用 RNA（piRNAs）是生殖系特异性的小沉默 RNA，可抑制 TE 活性并在生殖系发育过程中维持基因组完整性。在果蝇卵巢体细胞中，piRNAs 通过一种非 Dicer 依赖的途径从长的单链 RNA 中加工而来，并在细胞质中加载到 Piwi 上。然后，Piwi-piRNA 复合物被运送到细胞核中以发挥对 TE 的沉默作用。这种机制涉及到功能性 Piwi-piRNA 复合物导入的门控因子，这与用于进行程序性 DNA 消除的四膜虫 Twi1p-scan RNA 途径相似。
