Paramutation-Like Behavior of Genic piRNA-Producing Loci in .

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 a paramutation-like process. However, the variability in piRNA clusters' capacity to induce such conversions remains poorly understood. Here, we investigated two strains with differing capacities to produce piRNAs from the subtelomeric and gene loci. We found that active piRNA generation correlates with high levels of the heterochromatic mark histone 3 lysine 9 trimethylation (H3K9me3) over genomic regions that give rise to piRNAs. Importantly, the maternal transmission of piRNAs drives their production in the progeny, even from homologous loci previously inactive in piRNA biogenesis. The 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 locus was lost in offspring lacking the inducer allele. The present findings suggest that the paramutation-like behavior of piRNA clusters may be influenced not only by piRNAs but also by structural features and the chromatin environment in the proximity to telomeres, providing new insights into the epigenetic regulation of the Drosophila genome.