putzig safeguards genome integrity by contributing to the Piwi-mediated repression of transposon activity in the female germline of Drosophila in a two-tiered fashion
Genome integrity in the germline is jeopardized by the activity of transposable elements (TEs). Transposon activity is kept in check by the Piwi-piRNA pathway, which silences TEs post-transcriptionally in the cytoplasm as well as co-transcriptionally in the nucleus. piRNAs derive from long precursor transcripts originating at piRNA-loci by non-conventional transcription. They are processed in the cytoplasm and loaded into Piwi-piRNA complexes that then enter the nucleus to bind to target RNAs and direct local heterochromatin formation at TE loci, involving several downstream effectors. In this work, we have analyzed the role of Putzig (Pzg) in Piwi-mediated TE silencing in the female germline. Pzg has multi-facetted roles during Drosophila development and is important for DNA integrity, germ cell differentiation and survival. Here, we provide evidence for a two-tier activity of Pzg by serving as a hub for various Piwi-pathway members. Firstly, Pzg assists transcription initiation at piRNA clusters by coupling the Trf2-Moonshiner transcription initiation complex to the Rhino-Deadlock-Cutoff complex, thereby promoting formation of piRNA-precursor transcripts. Secondly, in the context of co-transcriptional gene silencing, Pzg licences heterochromatin formation by linking the Piwi-piRNA silencing machinery and the histone demethylase Lsd1, involved in promoter inactivation.