Search

Although endogenous siRNAs (endo-siRNAs) have been described in many species, still little is known about their endogenous utility. Here, we show that Drosophila hairpin RNAs (hpRNAs) generate an endo-siRNA class with predominant expression in testes. Although hpRNAs are universally recently evolved, we identify highly complementary protein-coding targets for all hpRNAs. Importantly, we find broad evidence for evolutionary divergences that preferentially maintain compensatory pairing between hpRNAs and targets, serving as first evidence for adaptive selection for siRNA-mediated target regulation in metazoans. We demonstrate organismal impact of hpRNA activity, since knockout of hpRNA1 derepresses its target ATP synthase-β in testes and compromises spermatogenesis and male fertility. Moreover, we reveal surprising male-specific impact of RNAi factors on germ cell development and fertility, consistent with testis-directed function of the hpRNA pathway. Finally, the collected hpRNA loci chronicle an evolutionary timeline that reflects their origins from prospective target genes, mirroring a strategy described for plant miRNAs., (Copyright © 2015 Elsevier Inc. All rights reserved.)

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.