Silencing-associated and meiosis-specific small RNA pathways in Paramecium tetraurelia

Nucleic Acids Res. 2009 Feb;37(3):903-15. doi: 10.1093/nar/gkn1018. Epub 2008 Dec 22.


Distinct small RNA pathways are involved in the two types of homology-dependent effects described in Paramecium tetraurelia, as shown by a functional analysis of Dicer and Dicer-like genes and by the sequencing of small RNAs. The siRNAs that mediate post-transcriptional gene silencing when cells are fed with double-stranded RNA (dsRNA) were found to comprise two subclasses. DCR1-dependent cleavage of the inducing dsRNA generates approximately 23-nt primary siRNAs from both strands, while a different subclass of approximately 24-nt RNAs, characterized by a short untemplated poly-A tail, is strictly antisense to the targeted mRNA, suggestive of secondary siRNAs that depend on an RNA-dependent RNA polymerase. An entirely distinct pathway is responsible for homology-dependent regulation of developmental genome rearrangements after sexual reproduction. During early meiosis, the DCL2 and DCL3 genes are required for the production of a highly complex population of approximately 25-nt scnRNAs from all types of germline sequences, including both strands of exons, introns, intergenic regions, transposons and Internal Eliminated Sequences. A prominent 5'-UNG signature, and a minor fraction showing the complementary signature at positions 21-23, indicate that scnRNAs are cleaved from dsRNA precursors as duplexes with 2-nt 3' overhangs at both ends, followed by preferential stabilization of the 5'-UNG strand.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cloning, Molecular
  • Meiosis / genetics*
  • Membrane Proteins / genetics
  • Paramecium tetraurelia / genetics*
  • Paramecium tetraurelia / metabolism
  • Polyadenylation
  • Protozoan Proteins / genetics
  • RNA Interference*
  • RNA, Small Interfering / chemistry*
  • RNA, Small Interfering / classification
  • RNA, Small Interfering / metabolism
  • Ribonuclease III / genetics


  • Membrane Proteins
  • ND7 protein, Protozoa
  • Protozoan Proteins
  • RNA, Small Interfering
  • Ribonuclease III