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.
Vasale
Jessica J
JJ
Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, MA 01605, USA.
Gu
Weifeng
W
Thivierge
Caroline
C
Batista
Pedro J
PJ
Claycomb
Julie M
JM
Youngman
Elaine M
EM
Duchaine
Thomas F
TF
Mello
Craig C
CC
Conte
Darryl
D
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