Leaving the Past Behind

E Jean Finnegan,Emma Whitelaw

doi:10.1371/journal.pgen.1000248

Abstract

There is considerable interest from the wider scientific community in the heritability of epigenetic states across generations, and this has arisen as a result of a series of studies in mice [1],[2], flies [3], plants [4],[5], and yeast [6] over the past decade. These studies have identified genetic elements at which epigenetic states appear to be inherited through meiosis. The Lamarckian implications of these findings are hard to avoid. Transgenes, transposons, and other “foreign DNA” appear to be particularly prone to transgenerational epigenetic inheritance (reviewed in [7]). In this issue of PLoS Genetics, Singh et al. [8] describe the identification of a locus in the genome of maize at which a transposon, silenced by an RNAi-based mechanism, becomes reactivated over subsequent generations. This article reports an activating “position effect,” i.e., an integration site that is associated with the reversal of a previously established silent state in plants.

Highlights

The authors have devised a clever system for studying position effects that involves a single transposon, MuDR, and a variant of MuDR, called Mu killer (Muk) [8]
When MuDR and Muk are both present in one plant, the MuDR elements become epigenetically silenced as a result of a long hairpin RNA molecule produced from Muk that acts in trans to initiate DNA methylation of MuDR elements (Figure 1)
Once the MuDR has been silenced, it generally remains so even after Muk segregates away in subsequent generations (Figure 1A). This is consistent with observations made by others studying the activity of endogenous genes or transgenes that have been silenced by RNA-directed mechanisms in plants [5,9,10] and with transgenes in mice [11]

Summary

Introduction

The authors have devised a clever system for studying position effects that involves a single transposon, MuDR, and a variant of MuDR, called Mu killer (Muk) [8]. When MuDR and Muk are both present in one plant, the MuDR elements become epigenetically silenced as a result of a long hairpin RNA molecule produced from Muk that acts in trans to initiate DNA methylation of MuDR elements (Figure 1). Once the MuDR has been silenced, it generally remains so even after Muk segregates away in subsequent generations (Figure 1A).

Results

Conclusion