A potential role of inefficient and non-specific piRNA production from the whole transcriptome cells

Abstract

PIWI-interacting RNAs (piRNAs) are small RNAs that play a critical role in repressing transposons in the germline by guiding PIWI proteins to complementary target sequences. It is well known that the 5’ ends of piRNAs are typically defined through cleavage by PIWI proteins or by the endonuclease Zucchini, and piRNAs are amplified via reciprocal cleavage of sense and antisense transcripts by PIWI proteins. Here, we show that low levels of sense-stranded piRNAs are produced from the whole transcriptome in silkworms, flies, and mice, in a manner independent from the known biogenesis pathways. Notably, this mechanism is utilized in silkworm cultured cells for the production of piRNAs derived from the extremely abundant sub-genomic RNAs of Bombyx mori latent virus, which have been suggested to play a role in suppressing viral replication. We propose that this inefficient and non-specific piRNA-production pathway acts as a primitive sensor for aberrantly abundant transcripts in the germline, potentially seeding piRNA sequence repertoire for more efficient and established biogenesis pathways.