Small RNA profile in fully grown mammalian oocytes

We aim to comprehensively characterize the small RNA population in oocytes Pseudogenes populate the mammalian genome as remnants of artifactual incorporation of coding mRNAs into transposon pathways 1. Here, we show that a subset of pseudogenes generates endogenous small interfering RNAs (endo-siRNAs) in mouse oocytes. In these cases, endo-siRNAs are often processed from double-stranded RNAs formed by hybridization of spliced transcripts from protein coding genes to antisense transcripts from homologous pseudogenes. In at least one case, an inverted repeat pseudogene gives rise to abundant small RNAs directly. A second class of endo-siRNAs may enforce repression of mobile genetic elements, acting in concert with piwi-interacting RNAs (piRNAs). Loss of Dicer increases expression of endo-siRNA targets, demonstrating the regulatory activity of these small RNAs. Our findings provide a function for pseudogenes in regulating gene expression via the RNAi pathway and may, in part, explain the evolutionary pressure to conserve Argonaute-mediated catalysis in mammals. Keywords: small RNAs profile Overall design: Total RNA was isolated and size-fractionated by PAGE either into 19-24nt and 24-30nt, or 19-30nt. These were independently processed and sequenced on Illumina 1G platform.