RNAi-dependent Polycomb repression controls transposable elements in Tetrahymena

Genes Dev. 2019 Mar 1;33(5-6):348-364. doi: 10.1101/gad.320796.118. Epub 2019 Feb 26.


RNAi and Polycomb repression play evolutionarily conserved and often coordinated roles in transcriptional silencing. Here, we show that, in the protozoan Tetrahymena thermophila, germline-specific internally eliminated sequences (IESs)-many related to transposable elements (TEs)-become transcriptionally activated in mutants deficient in the RNAi-dependent Polycomb repression pathway. Germline TE mobilization also dramatically increases in these mutants. The transition from noncoding RNA (ncRNA) to mRNA production accompanies transcriptional activation of TE-related sequences and vice versa for transcriptional silencing. The balance between ncRNA and mRNA production is potentially affected by cotranscriptional processing as well as RNAi and Polycomb repression. We posit that interplay between RNAi and Polycomb repression is a widely conserved phenomenon, whose ancestral role is epigenetic silencing of TEs.

Keywords: Polycomb repression; RNAi; transposable elements.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • DNA Transposable Elements / genetics*
  • Epigenesis, Genetic
  • Gene Silencing
  • Mutation
  • Polycomb-Group Proteins / genetics*
  • Protozoan Proteins / genetics*
  • RNA Interference*
  • RNA, Messenger / genetics
  • RNA, Untranslated / genetics
  • Tetrahymena thermophila / genetics*
  • Transcriptional Activation / genetics*


  • DNA Transposable Elements
  • Polycomb-Group Proteins
  • Protozoan Proteins
  • RNA, Messenger
  • RNA, Untranslated