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Developmentally regulated piRNA clusters implicate MILI in transposon control

Alexei A Aravin1, Ravi Sachidanandam, Angelique Girard

  • 1Watson School of Biological Sciences, Cold Spring Harbor Laboratory, Howard Hughes Medical Institute (HHMI), 1 Bungtown Road, Cold Spring Harbor, NY 11724, USA.

Science (New York, N.Y.)
|April 21, 2007
PubMed

Insights

Mammalian PIWI proteins, MIWI and MILI, suppress transposons through piRNAs. Mili mutants show derepressed LINE-1 elements and loss of DNA methylation, confirming PIWI proteins

Area of Science:

  • Genomics and Molecular Biology
  • Epigenetics and Transposon Regulation

Background:

  • Approximately 50% of mammalian genomes consist of repetitive sequences, including transposons.
  • Piwi proteins are known to control transposons in Drosophila, but their role in mammals is unclear due to piRNAs lacking repeat sequences.

Purpose of the Study:

  • To investigate the role of mammalian Piwi proteins (MIWI and MILI) in transposon suppression.
  • To identify small RNAs that program Piwi proteins for transposon control in mice.

Main Methods:

  • Bioinformatic analysis of murine small RNAs to identify piRNA loci.
  • Characterization of piRNA loci for similarities to Drosophila transposon control elements.
  • Analysis of Mili mutant mice for transposon derepression and DNA methylation changes.

Main Results:

  • Discovery of developmentally regulated piRNA loci in mice, some resembling Drosophila transposon master control loci.
  • Evidence for an adaptive amplification loop involving MILI in piRNA 5' end formation.
  • Mili mutants exhibit derepression of LINE-1 and intracisternal A particle elements, with associated loss of L1 DNA methylation.

Conclusions:

  • Mammalian PIWI proteins, particularly MILI, play a crucial role in transposon suppression.
  • An evolutionarily conserved mechanism of PIWI-mediated transposon control exists in mammals.
  • The findings highlight the importance of piRNAs and PIWI proteins in maintaining genome stability.

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