Transcriptional and evolutionary basis of piRNA mediated transposon silencing in Drosophila eugracilis

Abstract

Piwi-interacting RNAs (piRNAs) are small, non-coding RNA molecules known to perform epigenetic and post-transcriptional silencing of the transposable elements. Biogenesis of piRNAs, generally, involves two mechanisms known as "phasing" and "ping-pong cycle". These mechanisms are conserved in most of the existing species. The absence of one of these negatively affects the species' fitness due to transposon overexpression that can lead to genome instability, change in epigenetic landscape and/or loss of fertility. Drosophila eugracilis lacks the "ping-pong cycle" mode of biogenesis, but does not face the abovementioned challenges. It produces primarily antisense piRNAs to partly compensate for the absence of "ping-pong cycle", but the mechanism is still not completely understood. The study is mainly focused on contributing to setting up Drosophila eugracilis as a model organism and understanding the transcriptional and evolutionary basis of piRNA biogenesis. This involves the generation of high-quality piRNA libraries and genome assemblies and analysing the interaction of transcription machinery with the piRNA clusters in different strains of Drosophila eugracilis. Further, the study provides some preliminary insights into the evolution of antisense sense bias of piRNA biogenesis in Drosophila eugracilis.