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Fig. 2 | Cell Communication and Signaling

Fig. 2

From: PIWI-interacting RNAs and PIWI proteins in glioma: molecular pathogenesis and role as biomarkers

Fig. 2

Epigenetic silencing by Piwi–piRNA in Drosophila. a Piwi, a Drosophila PIWI protein, is localized to the nucleus and can epigenetically silence target genes. Transcripts of piRNA clusters, which contain numerous sequences complementary to transposons, serve as precursors to piRNAs. piRNA precursors are processed into piRNA intermediates and exported to the cytoplasm. Intermediates are processed by the endonuclease Zuc near the mitochondria, localized to granules termed Flam bodies, and then to Yb bodies, where factors such as Yb, Armi, Vret, and Shut are localized. Armi is recruited to mitochondria by Gasz. Here, piRNAs are processed and loaded onto Piwi. Then, piRNAs are 3′trimmed and 2′-O-methylated by Hen1 and then transferred into the nucleus. Within the nucleus, Piwi–piRNA complexes regulate their target genes by modifying histones and affecting the association of Pol II with target genes. Several factors, such as DmGTSF1, Mael, and HP1a, are involved in this process, but the regulatory mechanism remains to be completely understood. Abbreviations: Armi, Armitage; Mael, Maelstrom; Mito, mitochondria; N, nucleus; piRNA, PIWI-interacting RNA; Pol II, RNA polymerase II; Shut, Shutdown; TE, transposable element; Vret, Vreteno; Yb, fs (1) Yb; Zuc, Zucchini. Scale bar, 0.2 μm

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