PRG-1 and 21U-RNAs Interact to Form the piRNA Complex Required for Fertility in C. elegans

Abstract

In metazoans, Piwi-related Argonaute proteins have been linked to germline maintenance, and to a class of germline-enriched small RNAs termed piRNAs. Here we show that an abundant class of 21 nucleotide small RNAs (21U-RNAs) are expressed in the C. elegans germline, interact with the C. elegans Piwi family member PRG-1, and depend on PRG-1 activity for their accumulation. The PRG-1 protein is expressed throughout development and localizes to nuage-like structures called P granules. Although 21U-RNA loci share a conserved upstream sequence motif, the mature 21U-RNAs are not conserved and, with few exceptions, fail to exhibit complementarity or evidence for direct regulation of other expressed sequences. Our findings demonstrate that 21U-RNAs are the piRNAs of C. elegans and link this class of small RNAs and their associated Piwi Argonaute to the maintenance of temperature-dependent fertility.

mRNP granules

“…14,15 Notably, various mRNA degradative enzymes are found in mRNP granules besides P-bodies, such as Xrn1 in stress granules 11 and Drosophila/mouse spermatid nuage, 65 Dcp1/ Dcp2 in various germ granules, [66][67][68] and several Argonaute proteins with endonuclease activity in stress granules, 69 and various germ granules. [70][71][72][73] Whether mRNA degradation occurs in mRNP granules besides P-bodies remains poorly studied.…”

Evolution, biogenesis and function of promoter-associated RNAs

“…To test this, we analyzed wild type, mutant, and various life-cycle stage small RNA deep sequencing libraries from Arabidopsis 21 and C. elegans. 22 None of the Arabidopsis deep sequencing libraries revealed evidence of 18 nt RNA species proximal to TSSs, including wild type flowers (Fig. 3A).…”

“…3B). After removing highly abundant PIWIassociated 21U sequences 22,23 we observed a peak of sense and antisense small RNAs immediately downstream of TSSs. Small RNAs from both strands show peaks at 18 nt, although these are less abundant than 22 and 26 nt endogenous small interfering RNAs (siRNAs).…”

“…In the inset bar chart both sense (red bars) and antisense (purple bars) small RNAs are dominantly 24 nt. (B) Small RNAs from wild type adult worms (GEO series ID GSE11738, sample ID GSM297751, 22 ) were mapped to the C. elegans genome (UCSC genome browser ce6, wormbase build WS190, 53 ) and plotted against TSSs of RefGenes (annotations obtained from a local mirror of the UCSC Genome Browser). Light red and light purple lines indicate the density abundance of the subset of 18 and 19 nt sense and antisense small RNAs, respectively.…”

High-throughput sequencing reveals extraordinary fluidity of miRNA, piRNA, and siRNA pathways in nematodes

“…elegans piRNAs (also called 21U-RNAs) are 21 nt long and contain a uracil at their 59 termini (Ruby et al 2006;Batista et al 2008;Das et al 2008). piRNAs bind to the two PIWI-clade Argonautes PRG-1 and PRG-2.…”