The endogenous siRNA pathway is involved in heterochromatin formation in Drosophila.
A new class of small RNAs (endo-siRNAs) produced from endogenous double-stranded RNA (dsRNA) precursors was recently shown to mediate transposable element (TE) silencing in the Drosophila soma. These endo-siRNAs might play a role in heterochromatin formation, as has been shown in S. pombe for siRNAs derived from repetitive sequences in chromosome pericentromeres. To address this possibility, we used the viral suppressors of RNA silencing B2 and P19. These proteins normally counteract the RNAi host defense by blocking the biogenesis or activity of virus-derived siRNAs. We hypothesized that both proteins would similarly block endo-siRNA processing or function, thereby revealing the contribution of endo-siRNA to heterochromatin formation. Accordingly, P19 as well as a nuclear form of P19 expressed in Drosophila somatic cells were found to sequester TE-derived siRNAs whereas B2 predominantly bound their longer precursors. Strikingly, B2 or the nuclear form of P19, but not P19, suppressed silencing of heterochromatin gene markers in adult flies, and altered histone H3-K9 methylation as well as chromosomal distribution of histone methyl transferase Su(var)3-9 and Heterochromatin Protein 1 in larvae. Similar effects were observed in dcr2, r2d2, and ago2 mutants. Our findings provide evidence that a nuclear pool of TE-derived endo-siRNAs is involved in heterochromatin formation in somatic tissues in Drosophila.
Fagegaltier
Delphine
D
Centre National de la Recherche Scientifique, Unité de Recherche Associée 2578, Institut Pasteur, 25 rue du Dr Roux, F75015 Paris, France. fagegalt@cshl.edu
Bougé
Anne-Laure
AL
Berry
Bassam
B
Poisot
Emilie
E
Sismeiro
Odile
O
Coppée
Jean-Yves
JY
Théodore
Laurent
L
Voinnet
Olivier
O
Antoniewski
Christophe
C
D000818:Animals; D030801:Animals, Genetically Modified; D002875:Chromosomes; D004251:DNA Transposable Elements / Q000235:genetics; D004330:Drosophila; D020868:Gene Silencing; D005819:Genetic Markers; D006570:Heterochromatin / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D008745:Methylation; D034741:RNA, Small Interfering / Q000037:antagonists & inhibitors / Q000502:physiology*
D004251:DNA Transposable Elements; D005819:Genetic Markers; D006570:Heterochromatin; D006657:Histones; D034741:RNA, Small Interfering