title: Multiple roles for Piwi in silencing Drosophila transposons.
abstract: Silencing of transposons in the Drosophila ovary relies on three Piwi family proteins--Piwi, Aubergine (Aub), and Ago3--acting in concert with their small RNA guides, the Piwi-interacting RNAs (piRNAs). Aub and Ago3 are found in the germ cell cytoplasm, where they function in the ping-pong cycle to consume transposon mRNAs. The nuclear Piwi protein is required for transposon silencing in both germ and somatic follicle cells, yet the precise mechanisms by which Piwi acts remain largely unclear. We investigated the role of Piwi by combining cell type-specific knockdowns with measurements of steady-state transposon mRNA levels, nascent RNA synthesis, chromatin state, and small RNA abundance. In somatic cells, Piwi loss led to concerted effects on nascent transcripts and transposon mRNAs, indicating that Piwi acts through transcriptional gene silencing (TGS). In germ cells, Piwi loss showed disproportionate impacts on steady-state RNA levels, indicating that it also exerts an effect on post-transcriptional gene silencing (PTGS). Piwi knockdown affected levels of germ cell piRNAs presumably bound to Aub and Ago3, perhaps explaining its post-transcriptional impacts. Overall, our results indicate that Piwi plays multiple roles in the piRNA pathway, in part enforcing transposon repression through effects on local chromatin states and transcription but also participating in germ cell piRNA biogenesis.
authors: Watson School of Biological Sciences, Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA.
authors: Nikolay V
authors: NV
authors: Rozhkov
authors: Molly
authors: M
authors: Hammell
authors: Gregory J
authors: GJ
authors: Hannon
mesh_terms: D000818:Animals; D060565:Argonaute Proteins / Q000235:genetics* / Q000378:metabolism; D004251:DNA Transposable Elements / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics* / Q000378:metabolism; D004331:Drosophila melanogaster / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D055785:Gene Knockdown Techniques; D010053:Ovary / Q000378:metabolism; D010448:Peptide Initiation Factors / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism
chemical_list: C518392:AGO3 protein, Drosophila; D060565:Argonaute Proteins; D004251:DNA Transposable Elements; D029721:Drosophila Proteins; D010448:Peptide Initiation Factors; D034741:RNA, Small Interfering; C436124:aub protein, Drosophila; C116498:piwi protein, Drosophila
references: Cell. 2011 Dec 23;147(7):1628-39
references: 22196736
references: Nat Rev Genet. 2011 Aug 18;12(9):615-27
references: 21850042
references: Cell. 2011 Dec 23;147(7):1551-63
references: 22196730
references: Mol Cell. 2008 Sep 26;31(6):785-99
references: 18922463
references: Genetics. 1998 Aug;149(4):1857-66
references: 9691042
references: Science. 1980 Feb 8;207(4431):606-11
references: 6766221
references: Genes Dev. 2010 Nov 15;24(22):2499-504
references: 20966049
references: Genes Dev. 2012 Nov 1;26(21):2361-73
references: 23124062
references: Cell. 2009 May 1;137(3):522-35
references: 19395010
references: PLoS Genet. 2010 Mar 12;6(3):e1000880
references: 20300658
references: Mol Cell Biol. 2002 May;22(9):3204-18
references: 11940677
references: Genetics. 2008 Sep;180(1):121-31
references: 18723888
references: Genetics. 2003 Jun;164(2):501-9
references: 12807771
references: Genetics. 1977 Aug;86(4):813-33
references: 17248751
references: Genetics. 1995 Feb;139(2):697-711
references: 7713426
references: Proc Natl Acad Sci U S A. 2011 Dec 27;108(52):21164-9
references: 22160707
references: Nature. 2012 Nov 8;491(7423):284-7
references: 23064230
references: Curr Biol. 2011 Aug 23;21(16):1373-9
references: 21820311
references: Science. 2008 Dec 19;322(5909):1845-8
references: 19056941
references: Nucleic Acids Res. 2005 Apr 07;33(6):2052-9
references: 15817569
references: Genes Dev. 2006 Aug 15;20(16):2214-22
references: 16882972
references: Nat Rev Genet. 2009 Feb;10(2):94-108
references: 19148191
references: Genetics. 2007 Apr;175(4):1615-24
references: 17277359
references: Development. 2000 Feb;127(3):503-14
references: 10631171
references: Cell. 2007 Mar 23;128(6):1089-103
references: 17346786
references: Nat Rev Genet. 2007 Apr;8(4):272-85
references: 17363976
references: RNA. 2012 Aug;18(8):1446-57
references: 22753781
references: RNA. 2012 Dec;18(12):2128-34
references: 23086923
references: Science. 2007 Nov 2;318(5851):761-4
references: 17975059
references: Nature. 2009 Oct 29;461(7268):1296-9
references: 19812547
references: Nucleic Acids Res. 2011 Nov 1;39(20):8703-11
references: 21764773
references: Genes Dev. 2006 Feb 1;20(3):345-54
references: 16452506
references: Mol Biol Evol. 2013 Feb;30(2):397-408
references: 23079419
references: Cell. 2009 May 1;137(3):509-21
references: 19395009
references: Proc Natl Acad Sci U S A. 2011 Nov 15;108(46):18760-5
references: 22065765
references: Genetica. 1997;100(1-3):29-37
references: 9440256
references: Cell. 2009 Feb 20;136(4):656-68
references: 19239887
references: Nat Genet. 2010 Nov;42(11):920-1; author reply 921
references: 20980983
references: EMBO J. 2010 Oct 6;29(19):3301-17
references: 20818334
references: Nat Methods. 2012 Mar 04;9(4):357-9
references: 22388286
references: Nat Genet. 2011 Feb;43(2):153-8
references: 21186352
references: Nature. 2007 Nov 8;450(7167):304-8
references: 17952056
references: Nature. 2012 Oct 4;490(7418):112-5
references: 22922650
references: Mol Cell. 2011 Sep 16;43(6):1015-22
references: 21925389
references: Science. 2010 May 14;328(5980):916-9
references: 20395474
references: Bioinformatics. 2009 Aug 1;25(15):1952-8
references: 19505939
references: Science. 2008 Nov 28;322(5906):1387-92
references: 19039138
references: Science. 2007 Mar 16;315(5818):1587-90
references: 17322028
references: PLoS Genet. 2007 Sep;3(9):1633-43
references: 17941712
references: Genome Biol. 2011;12(1):R1
references: 21205303
references: EMBO J. 1994 Sep 15;13(18):4401-11
references: 7925283
references: J Virol. 2007 Feb;81(4):1951-60
references: 17135323
references: Cell. 2012 Nov 21;151(5):964-80
references: 23159368
references: Cell Rep. 2012 Oct 25;2(4):1025-35
references: 23062713
references: Mol Biol (Mosk). 2011 Jul-Aug;45(4):633-41
references: 21954595
references: Genes Dev. 1998 Dec 1;12(23):3715-27
references: 9851978
references: Mol Cell. 2004 Aug 13;15(3):467-76
references: 15304225
references: Nature. 2012 Nov 8;491(7423):279-83
references: 23064227
references: Nucleic Acids Res. 2007;35(16):5430-8
references: 17702759
references: Genes Dev. 2008 Apr 1;22(7):908-17
references: 18381894
references: Genes Dev. 2010 Nov 15;24(22):2493-8
references: 20966047
references: Cell. 2009 Sep 18;138(6):1137-49
references: 19732946
references: Genes Dev. 2007 Sep 15;21(18):2300-11
references: 17875665