A trans-piRNA network and transcriptional antagonism shape piRNA cluster function.

Area of Science:

• * Molecular Biology
• * Genetics
• * Epigenetics

Background:

• * PIWI-interacting RNAs (piRNAs) are essential for silencing transposable elements (TEs) in animal germlines.
• * In *Drosophila*, piRNAs are transcribed from piRNA clusters (piCs) via a non-canonical machinery involving the protein Rhino.
• * The dependence of native piC function on trans-generational piRNA transmission was previously unknown.

Purpose of the Study:

• * To investigate the necessity of cytoplasmic piRNA inheritance for piRNA biogenesis in native piRNA clusters.
• * To elucidate the network dynamics connecting individual piCs.
• * To re-evaluate the transposon trap model in light of new findings on TE integration and piC regulation.

Main Methods:

• * Experimental analysis of piRNA biogenesis using two distinct approaches.
• * Investigation of the interconnectedness of piRNA clusters via trans-acting piRNAs.
• * Assessment of the impact of promoter integration within piCs on Rhino binding and non-canonical transcription.

Main Results:

• * Cytoplasmic inheritance of cognate piRNAs is critical for piRNA biogenesis.
• * Individual piCs are interconnected by trans-acting piRNAs, forming a robust network that reinforces piRNA biogenesis.
• * Transcription from integrated promoters within piCs antagonizes Rhino-dependent piRNA precursor transcription, disrupting local piRNA biogenesis.

Conclusions:

• * piRNA biogenesis relies on the trans-generational transmission of piRNAs.
• * piRNA clusters form a dynamic, interconnected network regulated by transcriptional competition.
• * The findings necessitate a revision of the transposon trap model, highlighting potential TE-mediated suppression of piRNA production prior to domestication.