title: Euchromatic transposon insertions trigger production of novel Pi- and endo-siRNAs at the target sites in the drosophila germline.
abstract: The control of transposable element (TE) activity in germ cells provides genome integrity over generations. A distinct small RNA-mediated pathway utilizing Piwi-interacting RNAs (piRNAs) suppresses TE expression in gonads of metazoans. In the fly, primary piRNAs derive from so-called piRNA clusters, which are enriched in damaged repeated sequences. These piRNAs launch a cycle of TE and piRNA cluster transcript cleavages resulting in the amplification of piRNA and TE silencing. Using genome-wide comparison of TE insertions and ovarian small RNA libraries from two Drosophila strains, we found that individual TEs inserted into euchromatic loci form novel dual-stranded piRNA clusters. Formation of the piRNA-generating loci by active individual TEs provides a more potent silencing response to the TE expansion. Like all piRNA clusters, individual TEs are also capable of triggering the production of endogenous small interfering (endo-si) RNAs. Small RNA production by individual TEs spreads into the flanking genomic regions including coding cellular genes. We show that formation of TE-associated small RNA clusters can down-regulate expression of nearby genes in ovaries. Integration of TEs into the 3' untranslated region of actively transcribed genes induces piRNA production towards the 3'-end of transcripts, causing the appearance of genic piRNA clusters, a phenomenon that has been reported in different organisms. These data suggest a significant role of TE-associated small RNAs in the evolution of regulatory networks in the germline.
authors: Institute of Molecular Genetics, Russian Academy of Sciences, Moscow, Russia.
authors: Sergey
authors: S
authors: Shpiz
authors: Institute of Molecular Genetics, Russian Academy of Sciences, Moscow, Russia.
authors: Sergei
authors: S
authors: Ryazansky
authors: Institute of Molecular Genetics, Russian Academy of Sciences, Moscow, Russia.
authors: Ivan
authors: I
authors: Olovnikov
authors: Institute of Molecular Genetics, Russian Academy of Sciences, Moscow, Russia.
authors: Yuri
authors: Y
authors: Abramov
authors: Institute of Molecular Genetics, Russian Academy of Sciences, Moscow, Russia.
authors: Alla
authors: A
authors: Kalmykova
mesh_terms: D000818:Animals; D004251:DNA Transposable Elements / Q000235:genetics*; D004330:Drosophila / Q000235:genetics; D022041:Euchromatin / Q000235:genetics*; D005260:Female; D053263:Gene Regulatory Networks; D005854:Germ Cells / Q000378:metabolism; D010053:Ovary / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics*
chemical_list: D004251:DNA Transposable Elements; D022041:Euchromatin; D034741:RNA, Small Interfering