Sequential rounds of RNA-dependent RNA transcription drive endogenous small-RNA biogenesis in the ERGO-1/Argonaute pathway.
Argonaute (AGO) proteins interact with distinct classes of small RNAs to direct multiple regulatory outcomes. In many organisms, including plants, fungi, and nematodes, cellular RNA-dependent RNA polymerases (RdRPs) use AGO targets as templates for amplification of silencing signals. Here, we show that distinct RdRPs function sequentially to produce small RNAs that target endogenous loci in Caenorhabditis elegans. We show that DCR-1, the RdRP RRF-3, and the dsRNA-binding protein RDE-4 are required for the biogenesis of 26-nt small RNAs with a 5' guanine (26G-RNAs) and that 26G-RNAs engage the Piwi-clade AGO, ERGO-1. Our findings support a model in which targeting by ERGO-1 recruits a second RdRP (RRF-1 or EGO-1), which in turn transcribes 22G-RNAs that interact with worm-specific AGOs (WAGOs) to direct gene silencing. ERGO-1 targets exhibit a nonrandom distribution in the genome and appear to include many gene duplications, suggesting that this pathway may control overexpression resulting from gene expansion.
Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, MA 01605, USA.
Jessica J
JJ
Vasale
Weifeng
W
Gu
Caroline
C
Thivierge
Pedro J
PJ
Batista
Julie M
JM
Claycomb
Elaine M
EM
Youngman
Thomas F
TF
Duchaine
Craig C
CC
Mello
Darryl
D
Conte
D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D004722:Endoribonucleases / Q000378:metabolism; D020868:Gene Silencing; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000096:biosynthesis* / Q000235:genetics; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D012324:RNA-Dependent RNA Polymerase / Q000378:metabolism*; D043244:Ribonuclease III; D014158:Transcription, Genetic
D029742:Caenorhabditis elegans Proteins; C548334:ERGO-1 protein, C elegans; C461645:RDE-4 protein, C elegans; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; C406772:EGO-1 protein, C elegans; D012324:RNA-Dependent RNA Polymerase; C472756:RNA-directed RNA polymerase RRF-3, C elegans; D004722:Endoribonucleases; C118116:dcr-1 protein, C elegans; D043244:Ribonuclease III