Quantitatively increased somatic transposition of transposable elements in Drosophila strains compromised for RNAi.

Weiwu Xie,James A Birchler,Ryan C Donohue

doi:10.1371/journal.pone.0072163

Abstract

In Drosophila melanogaster, small RNAs homologous to transposable elements (TEs) are of two types: piRNA (piwi-interacting RNA) with size 23-29nt and siRNA (small interfering RNA) with size 19-22nt. The siRNA pathway is suggested to silence TE activities in somatic tissues based on TE expression profiles, but direct evidence of transposition is lacking. Here we developed an efficient FISH (fluorescence in Situ hybridization) based method for polytene chromosomes from larval salivary glands to reveal new TE insertions. Analysis of the LTR-retrotransposon 297 and the non-LTR retroposon DOC shows that in the argonaut 2 (Ago2) and Dicer 2 (Dcr2) mutant strains, new transposition events are much more frequent than in heterozygous strains or wild type strains. The data demonstrate that the siRNA pathway represses TE transposition in somatic cells. Nevertheless, we found that loss of one functional copy of Ago2 or Dcr2 increases somatic transpositions of the elements at a lower level depending on the genetic background, suggesting a quantitative role for RNAi core components on mutation frequency.

Highlights

The genome of Drosophila melanogaster contains over 100 families of transposable elements (TEs)
Studies of the TEs are mostly focused on the genetic consequences of their activities; most attention has centered on germline transposition events
Salivary glands are dissected from 3rd instar larvae in saline solution (0.7% Sodium Chloride), and Element expected Deletions

Summary

Introduction

The genome of Drosophila melanogaster contains over 100 families of transposable elements (TEs). The majority of them have potentially functional copies [1]. Studies of the TEs are mostly focused on the genetic consequences of their activities; most attention has centered on germline transposition events. The DNA transposon P and non-LTR retroelement I normally transpose only in the germline [2,3]. Other TEs are active in somatic tissues. New transpositions of hobo (a DNA transposon) were detected in salivary glands by FISH [4]; and R2 (non-LTR) has been demonstrated to transpose in various tissues by a PCR-based assay [5]

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Results

Conclusion