Endogenous siRNAs Derived from Transposons and mRNAs in <i>Drosophila</i> Somatic Cells

TLDR

siRNAs mediate RNA interference in eukaryotes, and in flies, somatic cells generate siRNAs from exogenous double‑stranded RNA to defend against viral infection. The study proposes that endogenous siRNAs produced by the fly RNAi pathway silence selfish genetic elements in the soma, analogous to Piwi‑interacting RNAs in the germ line. We identified 21‑nt endogenous siRNAs derived from transposons, heterochromatic sequences, and mRNAs in Drosophila somatic cells, and demonstrated that their accumulation requires Dicer‑2 and Argonaute‑2.

Abstract

Small interfering RNAs (siRNAs) direct RNA interference (RNAi) in eukaryotes. In flies, somatic cells produce siRNAs from exogenous double-stranded RNA (dsRNA) as a defense against viral infection. We identified endogenous siRNAs (endo-siRNAs), 21 nucleotides in length, that correspond to transposons and heterochromatic sequences in the somatic cells of Drosophila melanogaster . We also detected endo-siRNAs complementary to messenger RNAs (mRNAs); these siRNAs disproportionately mapped to the complementary regions of overlapping mRNAs predicted to form double-stranded RNA in vivo. Normal accumulation of somatic endo-siRNAs requires the siRNA-generating ribonuclease Dicer-2 and the RNAi effector protein Argonaute2 (Ago2). We propose that endo-siRNAs generated by the fly RNAi pathway silence selfish genetic elements in the soma, much as Piwi-interacting RNAs do in the germ line.