title: The ERI-6/7 helicase acts at the first stage of an siRNA amplification pathway that targets recent gene duplications.
abstract: Endogenous small interfering RNAs (siRNAs) are a class of naturally occuring regulatory RNAs found in fungi, plants, and animals. Some endogenous siRNAs are required to silence transposons or function in chromosome segregation; however, the specific roles of most endogenous siRNAs are unclear. The helicase gene eri-6/7 was identified in the nematode Caenorhabditis elegans by the enhanced response to exogenous double-stranded RNAs (dsRNAs) of the null mutant. eri-6/7 encodes a helicase homologous to small RNA factors Armitage in Drosophila, SDE3 in Arabidopsis, and Mov10 in humans. Here we show that eri-6/7 mutations cause the loss of 26-nucleotide (nt) endogenous siRNAs derived from genes and pseudogenes in oocytes and embryos, as well as deficiencies in somatic 22-nucleotide secondary siRNAs corresponding to the same loci. About 80 genes are eri-6/7 targets that generate the embryonic endogenous siRNAs that silence the corresponding mRNAs. These 80 genes share extensive nucleotide sequence homology and are poorly conserved, suggesting a role for these endogenous siRNAs in silencing of and thereby directing the fate of recently acquired, duplicated genes. Unlike most endogenous siRNAs in C. elegans, eri-6/7-dependent siRNAs require Dicer. We identify that the eri-6/7-dependent siRNAs have a passenger strand that is ∼19 nt and is inset by ∼3-4 nts from both ends of the 26 nt guide siRNA, suggesting non-canonical Dicer processing. Mutations in the Argonaute ERGO-1, which associates with eri-6/7-dependent 26 nt siRNAs, cause passenger strand stabilization, indicating that ERGO-1 is required to separate the siRNA duplex, presumably through endonucleolytic cleavage of the passenger strand. Thus, like several other siRNA-associated Argonautes with a conserved RNaseH motif, ERGO-1 appears to be required for siRNA maturation.
authors.affiliation: Department of Molecular Biology, Massachusetts General Hospital, Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America.
authors.forename: Sylvia E J
authors.initials: SE
authors.lastname: Fischer
authors.forename: Taiowa A
authors.initials: TA
authors.lastname: Montgomery
authors.forename: Chi
authors.initials: C
authors.lastname: Zhang
authors.forename: Noah
authors.initials: N
authors.lastname: Fahlgren
authors.forename: Peter C
authors.initials: PC
authors.lastname: Breen
authors.forename: Alexia
authors.initials: A
authors.lastname: Hwang
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Sullivan
authors.forename: James C
authors.initials: JC
authors.lastname: Carrington
authors.forename: Gary
authors.initials: G
authors.lastname: Ruvkun
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics* / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000235:genetics* / Q000378:metabolism; D004265:DNA Helicases / Q000235:genetics* / Q000378:metabolism; D020440:Gene Duplication / Q000235:genetics*; D005786:Gene Expression Regulation; D020868:Gene Silencing; D009154:Mutation; D009865:Oocytes / Q000378:metabolism*; D011544:Pseudogenes / Q000235:genetics; D012330:RNA, Double-Stranded / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics* / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D043244:Ribonuclease III / Q000235:genetics
chemical_list: D029742:Caenorhabditis elegans Proteins; C548334:ERGO-1 protein, C elegans; D012330:RNA, Double-Stranded; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D043244:Ribonuclease III; C532532:ERI-6 protein, C elegans; D004265:DNA Helicases
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