Argonaute proteins affect siRNA levels and accumulation of a novel extrachromosomal DNA from the Dictyostelium retrotransposon DIRS-1

J Biol Chem. 2014 Dec 19;289(51):35124-38. doi: 10.1074/jbc.M114.612663. Epub 2014 Oct 28.

Abstract

The retrotransposon DIRS-1 is the most abundant retroelement in Dictyostelium discoideum and constitutes the pericentromeric heterochromatin of the six chromosomes in D. discoideum. The vast majority of cellular siRNAs is derived from DIRS-1, suggesting that the element is controlled by RNAi-related mechanisms. We investigated the role of two of the five Argonaute proteins of D. discoideum, AgnA and AgnB, in DIRS-1 silencing. Deletion of agnA resulted in the accumulation of DIRS-1 transcripts, the expression of DIRS-1-encoded proteins, and the loss of most DIRS-1-derived secondary siRNAs. Simultaneously, extrachromosomal single-stranded DIRS-1 DNA accumulated in the cytoplasm of agnA- strains. These DNA molecules appear to be products of reverse transcription and thus could represent intermediate structures before transposition. We further show that transitivity of endogenous siRNAs is impaired in agnA- strains. The deletion of agnB alone had no strong effect on DIRS-1 transposon regulation. However, in agnA-/agnB- double mutant strains strongly reduced accumulation of extrachromosomal DNA compared with the single agnA- strains was observed.

Keywords: Argonaute; Gene Silencing; RNA Interference (RNAi); Small Interfering RNA (siRNA); Transposable Element (TE).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Argonaute Proteins / genetics*
  • Argonaute Proteins / metabolism
  • Blotting, Western
  • DNA, Protozoan / genetics*
  • DNA, Protozoan / metabolism
  • DNA, Single-Stranded / genetics
  • DNA, Single-Stranded / metabolism
  • Dictyostelium / genetics*
  • Dictyostelium / metabolism
  • Gene Deletion
  • Gene Expression
  • Mutation
  • Protozoan Proteins / genetics*
  • Protozoan Proteins / metabolism
  • RNA Interference
  • RNA, Small Interfering / genetics*
  • RNA, Small Interfering / metabolism
  • Retroelements / genetics*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Transformation, Genetic

Substances

  • Argonaute Proteins
  • DNA, Protozoan
  • DNA, Single-Stranded
  • Protozoan Proteins
  • RNA, Small Interfering
  • Retroelements