title: Control of chicken CR1 retrotransposons is independent of Dicer-mediated RNA interference pathway.
abstract: BACKGROUND
  Dicer is an RNase III-ribonuclease that initiates the formation of small interfering RNAs as a defence against genomic parasites such as retrotransposons. Despite intensive characterization in mammalian species, the biological functions of Dicer in controlling retrotransposable elements of the non-mammalian vertebrate are poorly understood. In this report, we examine the role of chicken Dicer in controlling the activity of chicken CR1 retrotransposable elements in a chicken-human hybrid DT40 cell line employing a conditional loss-of-Dicer function.
  
  
  RESULTS
  Retrotransposition is detrimental to host genome stability and thus eukaryotic cells have developed mechanisms to limit the expansion of retrotransposons by Dicer-mediated RNAi silencing pathways. However, the mechanisms that control the activity and copy numbers of transposable elements in chicken remain unclear. Here, we describe how the loss of Dicer in chicken cells does not reactivate endogenous chicken CR1 retrotransposons with impaired RNAi machinery, suggesting that the control of chicken CR1 is independent of Dicer-induced RNAi silencing. In contrast, upon introduction of a functionally active human L1 retrotransposable element that contains an active 5' UTR promoter, the Dicer-deficient chicken cells show a strong increase in the accumulation of human L1 transcripts and retrotransposition activity, highlighting a major difference between chicken CR1 and other mammalian L1 retrotransposons.
  
  
  CONCLUSIONS
  Our data provide evidence that chicken CR1 retrotransposons, unlike their mammalian L1 counterparts, do not undergo retrotransposition because most CR1 retrotransposons are truncated or mutated at their 5'UTR promoters and thus are not subjected to Dicer-mediated RNAi-silencing control.
authors.affiliation: The John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory 2601, Australia. Sunghun.Lee@anu.edu.au
authors.forename: Sung-Hun
authors.initials: SH
authors.lastname: Lee
authors.forename: Preethi
authors.initials: P
authors.lastname: Eldi
authors.forename: Soo-Young
authors.initials: SY
authors.lastname: Cho
authors.forename: Danny
authors.initials: D
authors.lastname: Rangasamy
mesh_terms: D020121:5' Untranslated Regions; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002645:Chickens / Q000235:genetics*; D018628:Gene Dosage; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D016678:Genome; D006801:Humans; D020084:Long Interspersed Nucleotide Elements / Q000235:genetics*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000502:physiology*; D034622:RNA Interference / Q000502:physiology*; D034741:RNA, Small Interfering; D018626:Retroelements / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D043244:Ribonuclease III / Q000172:deficiency / Q000378:metabolism*; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D019076:Transgenes
chemical_list: D020121:5' Untranslated Regions; D034741:RNA, Small Interfering; D018626:Retroelements; D043244:Ribonuclease III
references.citation: Trends Ecol Evol. 2000 Mar;15(3):95-99
references.pmid: 10675923
references.citation: Dev Cell. 2007 Apr;12(4):503-14
references.pmid: 17395546
references.citation: Mol Cell Biol. 2005 May;25(9):3793-801
references.pmid: 15831483
references.citation: Genetics. 2008 Jan;178(1):573-81
references.pmid: 17947446
references.citation: Biochem Biophys Res Commun. 2006 Aug 18;347(1):36-43
references.pmid: 16815300
references.citation: Nature. 2003 Nov 20;426(6964):310-4
references.pmid: 14628056
references.citation: Gene. 2007 Jun 15;395(1-2):116-24
references.pmid: 17434692
references.citation: Cell. 1999 Oct 15;99(2):133-41
references.pmid: 10535732
references.citation: Nucleic Acids Res. 2005 Feb 08;33(3):846-56
references.pmid: 15701756
references.citation: Nucleic Acids Res. 2003 Jul 1;31(13):3576-9
references.pmid: 12824369
references.citation: Nat Cell Biol. 2004 Aug;6(8):784-91
references.pmid: 15247924
references.citation: Mol Biol Evol. 1994 Nov;11(6):886-98
references.pmid: 7815928
references.citation: Nucleic Acids Res. 2002 May 1;30(9):e36
references.pmid: 11972351
references.citation: Proc Natl Acad Sci U S A. 1993 Sep 1;90(17):8199-203
references.pmid: 8396264
references.citation: Biochem Genet. 2007 Apr;45(3-4):239-43
references.pmid: 17265138
references.citation: Cell. 1996 Nov 29;87(5):917-27
references.pmid: 8945518
references.citation: Genome Res. 2005 Jan;15(1):126-36
references.pmid: 15256510
references.citation: Nat Struct Mol Biol. 2006 Sep;13(9):763-71
references.pmid: 16936727
references.citation: Nucleic Acids Res. 2005 Mar 14;33(5):1564-73
references.pmid: 15767281
references.citation: Nucleic Acids Res. 2006 Jan 1;34(Database issue):D108-10
references.pmid: 16381825
references.citation: Cell. 2004 Apr 2;117(1):69-81
references.pmid: 15066283
references.citation: Nature. 2004 Dec 9;432(7018):695-716
references.pmid: 15592404
references.citation: Trends Cell Biol. 2008 Mar;18(3):136-48
references.pmid: 18282709
references.citation: Gene. 1999 Feb 18;227(2):169-79
references.pmid: 10023050
references.citation: Nature. 2004 Jul 22;430(6998):471-6
references.pmid: 15269773
references.citation: Genetics. 2005 Feb;169(2):607-17
references.pmid: 15545645
references.citation: Cell. 2006 Feb 10;124(3):495-506
references.pmid: 16469697
references.citation: Cell. 2007 Mar 23;128(6):1089-103
references.pmid: 17346786
references.citation: Nat Rev Genet. 2003 Feb;4(2):87-98
references.pmid: 12560806
references.citation: Curr Biol. 2001 Jul 10;11(13):1017-27
references.pmid: 11470406
references.citation: Nat Struct Mol Biol. 2006 Sep;13(9):758-9
references.pmid: 16955095
references.citation: Cell. 1990 Dec 21;63(6):1267-76
references.pmid: 2124518
references.citation: Science. 2006 Jul 21;313(5785):320-4
references.pmid: 16809489
references.citation: Gene. 2001 Mar 7;265(1-2):175-83
references.pmid: 11255020
references.citation: RNA. 2003 Feb;9(2):187-92
references.pmid: 12554861
references.citation: Mol Biol Evol. 1997 Dec;14(12):1206-17
references.pmid: 9402732
references.citation: Nat Cell Biol. 2004 Aug;6(8):696-7
references.pmid: 15303098
references.citation: J Biomed Biotechnol. 2006;2006(1):29049
references.pmid: 16877812
references.citation: Mol Cell Biol. 2004 Mar;24(6):2536-45
references.pmid: 14993290
references.citation: Nature. 2008 May 22;453(7194):539-43
references.pmid: 18404146
references.citation: Genes Dev. 1998 Dec 1;12(23):3715-27
references.pmid: 9851978