The endonuclease activity of Mili fuels piRNA amplification that silences LINE1 elements

Serena De Fazio, Nenad Bartonicek, Monica Di Giacomo, Cei Abreu-Goodger, Aditya Sankar, Charlotta Funaya, Claude Antony, Pedro N. Moreira, Anton J. Enright, Donal O'Carroll*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Piwi proteins and Piwi-interacting RNAs (piRNAs) have conserved functions in transposon silencing(1). The murine Piwi proteins Mili and Miwi2 (also called Piwil2 and Piwil4, respectively) direct epigenetic LINE1 and intracisternal A particle transposon silencing during genome reprogramming in the embryonic male germ line(2-4). Piwi proteins are proposed to be piRNA-guided endonucleases that initiate secondary piRNA biogenesis(5-7); however, the actual contribution of their endonuclease activities to piRNA biogenesis and transposon silencing remain unknown. To investigate the role of Piwi-catalysed endonucleolytic activity, we engineered point mutations in mice that substitute the second aspartic acid to an alanine in the DDH catalytic triad of Mili and Miwi2, generating the Mili(DAH) and Miwi2(DAH) alleles, respectively. Analysis of Mili-bound piRNAs from homozygous Mili(DAH) fetal gonadocytes revealed a failure of transposon piRNA amplification, resulting in the marked reduction of piRNA bound within Miwi2 ribonuclear particles. We find that Mili-mediated piRNA amplification is selectively required for LINE1, but not intracisternal A particle, silencing. The defective piRNA pathway in Mili(DAH) mice results in spermatogenic failure and sterility. Surprisingly, homozygous Miwi2(DAH) mice are fertile, transposon silencing is established normally and no defects in secondary piRNA biogenesis are observed. In addition, the hallmarks of piRNA amplification are observed in Miwi2-deficient gonadocytes. We conclude that cycles of intra-Mili secondary piRNA biogenesis fuel piRNA amplification that is absolutely required for LINE1 silencing.

Original languageEnglish
Pages (from-to)259-263
Number of pages5
JournalNature
Volume480
Issue number7376
Early online date23 Oct 2011
DOIs
Publication statusPublished - 8 Dec 2011

Keywords

  • DNA METHYLATION
  • FAMILY-MEMBERS
  • PIWI PROTEINS
  • GERM-CELLS
  • MICE
  • PATHWAY
  • GENE
  • MIRNA
  • RISC
  • RNAS
  • DNA transposable elements
  • Gene silencing
  • Piwi RNAs
  • Spermatogenesis

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