Nuclear RNA export factor variant initiates piRNA‐guided co‐transcriptional silencing

Abstract

The PIWI-interacting RNA (piRNA) pathway preserves genomic integrity by repressing transposable elements (TEs) in animal germ cells. Among PIWI-clade proteins in Drosophila, Piwi transcriptionally silences its targets through interactions with cofactors, including Panoramix (Panx) and forms heterochromatin characterized by H3K9me3 and H1. Here, we identified Nxf2, a nuclear RNA export factor (NXF) variant, as a protein that forms complexes with Piwi, Panx, and p15. Panx-Nxf2-P15 complex formation is necessary in the silencing by stabilizing protein levels of Nxf2 and Panx. Notably, ectopic targeting of Nxf2 initiates co-transcriptional repression of the target reporter in a manner independent of H3K9me3 marks or H1. However, continuous silencing requires HP1a and H1. In addition, Nxf2 directly interacts with target TE transcripts in a Piwidependent manner. These findings suggest a model in which the Panx-Nxf2-P15 complex enforces the association of Piwi with target transcripts to trigger co-transcriptional repression, prior to heterochromatin formation in the nuclear piRNA pathway. Our results provide an unexpected connection between an NXF variant and small RNA-mediated co-transcriptional silencing. The EMBO JournalKensaku Murano et al F Density plots for normalized H3K9me3 ChIP-seq signals over the consensus sequence from mdg1, gypsy (targeted by Piwi-piRNA, orange), and roo (not targeted by Piwi-piRNA, blue) TEs in EGFP-, Piwi-, Panx-, and Nxf2-KD OSCs. G Boxplots as in (D) showing fold changes in the H3K9me3 levels of Piwi-piRNA-targeted and un-targeted TEs upon the indicated KD. H Northern blotting for Idefix-piRNA, traffic jam (tj)-piRNA, and esiRNA sl-1 (control) on total RNA isolated from OSCs with the indicated KD.

Asterix/Gtsf1 links tRNAs and piRNA silencing of retrotransposons

“…Asterix/Gtsf1 links tRNAs and piRNA silencing of retrotransposons Jonathan J. 15 N NOE values of the near zero or negative indicate substantial disorder in the Nand C-terminal regions flanking the zinc fingers. The linker between the two zinc fingers also have relaxation data compatible with an ordered backbone.…”

“…Recent work on several of these proteins (including, but not limited to, Panoramix 12 , Nxf2, and Nxt1 [13][14][15] ) has provided a framework for linking the piRNA pathway to deposition of heterochromatic silencing marks. However, many of the molecular and mechanistic underpinnings that govern these connections remain obscure.…”

RDC complex executes a dynamic piRNA program duringDrosophilaspermatogenesis to safeguard male fertility

“…piRNA pathway factors appear to be expressed during all stages of oogenesis from GSCs to late-stage nurse cells. Recent studies reported several new factors involved in piRNA pathway in ovary, such as Moon, Boot, Nxf3, Panx, Arx and Nxf2 (Andersen et al, 2017;Batki et al, 2019;Dönertas et al, 2013;ElMaghraby et al, 2019;Fabry et al, 2019;Kneuss et al, 2019;Muerdter et al, 2013;Murano et al, 2019;Ohtani et al, 2013;Sienski et al, 2015;Yu et al, 2015;Zhao et al, 2019). These proteins are expressed at a low level in testis and their functions during spermatogenesis have not yet been reported.…”

The piRNA pathway in <i>Drosophila</i> ovarian germ and somatic cells

“…Nxf2 has two LRR regions, an NTF2-like domain, and a UBA domain at the C-terminus. 80) Nxf2 within the complex interacts directly with target RNA transcripts via the first LRR. 80) Asterix/Gametocyte-specific factor 1 (Gtsf1) can also be found in the vicinity of PPNP.…”