Piwi Induces PiRNA-guided Transcriptional Silencing and Establishment of a Repressive Chromatin State

Overview

Journal Genes Dev

Specialty Molecular Biology

Date 2013 Feb 9

PMID 23392610

Citations 266

Authors

Adrien Le Thomas

Alicia K Rogers

Alexandre Webster

Georgi K Marinov

Susan E Liao

Edward M Perkins

Junho K Hur

Alexei A Aravin

Katalin Fejes Toth

Affiliations

Soon will be listed here.

Abstract

In the metazoan germline, piwi proteins and associated piwi-interacting RNAs (piRNAs) provide a defense system against the expression of transposable elements. In the cytoplasm, piRNA sequences guide piwi complexes to destroy complementary transposon transcripts by endonucleolytic cleavage. However, some piwi family members are nuclear, raising the possibility of alternative pathways for piRNA-mediated regulation of gene expression. We found that Drosophila Piwi is recruited to chromatin, colocalizing with RNA polymerase II (Pol II) on polytene chromosomes. Knockdown of Piwi in the germline increases expression of transposable elements that are targeted by piRNAs, whereas protein-coding genes remain largely unaffected. Derepression of transposons upon Piwi depletion correlates with increased occupancy of Pol II on their promoters. Expression of piRNAs that target a reporter construct results in a decrease in Pol II occupancy and an increase in repressive H3K9me3 marks and heterochromatin protein 1 (HP1) on the reporter locus. Our results indicate that Piwi identifies targets complementary to the associated piRNA and induces transcriptional repression by establishing a repressive chromatin state when correct targets are found.

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