GSE59965
A trans-generational epigenetic process defines piRNA biogenesis in Drosophila virilis
Piwi interacting (pi)RNAs repress diverse transposable elements in the germ cells of metazoans and are essential for fertility in both invertebrates and vertebrates. The precursors of piRNAs are transcribed from distinct genomic regions, the so-called piRNA clusters; however, how piRNA clusters are differentiated from the rest of the genome is not known. To address this question, we studied piRNA biogenesis in two Drosophila  virilis strains that show differential ability to generate piRNAs from several genomic regions. We found that active piRNA biogenesis correlates with high levels of histone 3 lysine 9 trimethylation (H3K9me3) over genomic regions that give rise to piRNAs. Furthermore, piRNA biogenesis in the progeny requires the trans-generational inheritance of an epigenetic signal, presumably in form of homologous piRNAs that are generated in the maternal germline and deposited into the oocyte. The inherited piRNAs enhance piRNA biogenesis by installment of H3K9me3 mark on piRNA clusters and by promoting ping-pong processing of homologous transcripts into mature piRNAs. We submitted the resequencing data together with the functional genomic datasets because it was generated with the sole purpose of supporting those. The SRA accession numbers are SRR1536176 and SRR1536175. Overall design: ChIP-seq against H3K9me3 and Pol2, Total RNA-seq, in Drosophila virilis Strain9 and Strain160 as well as crosses between them