Paramutation-like behaviour of genic piRNA-producing loci in Drosophila virilis

Piwi-interacting RNAs (piRNAs) play a crucial role in silencing transposable elements (TEs) in the germ cells of Metazoa by acting as sequence-specific guides. Originating from distinct genomic loci, called piRNA clusters, piRNA can trigger an epigenetic conversion of TE insertions into piRNA clusters by means of paramutation-like process. However, the variability in piRNA clusters' capacity to induce such conversion remains poorly understood. Here, we investigated two Drosophila virilis strains with differing capacities to produce piRNAs from the RhoGEF3 and Adar gene loci. We found that active piRNA generation correlates with high levels of the heterochromatic mark H3K9me3 over genomic regions that give rise to piRNAs. Importantly, maternal transmission of piRNAs drives their production in the progeny, even from homologous loci previously inactive in piRNA biogenesis. The subtelomeric RhoGEF3 locus, once epigenetically converted, maintained enhanced piRNA production in subsequent generations lacking the original allele carrying the active piRNA cluster. In contrast, piRNA expression from the converted Adar locus was lost in offspring lacking the inducer allele. Our findings highlight that the paramutation-like behavior of piRNA clusters is influenced not only by piRNAs but also by structural features of chromosomal regions, providing new insights into epigenetic regulation in Drosophila. The submission includes samples from chromatin immunoprecipitation sequencing (ChIP-seq), RNA-seq and small RNA-seq from ovaries of female Drosophila virilis. The research focuses on two distinct Drosophila virilis strains: strain 9, collected from Batumi, Georgia, and the laboratory strain 140 (eb, va).