Table of Contents
International Journal of Evolutionary Biology
Volume 2012, Article ID 436196, 13 pages
http://dx.doi.org/10.1155/2012/436196
Review Article

Transposon Invasion of the Paramecium Germline Genome Countered by a Domesticated PiggyBac Transposase and the NHEJ Pathway

1CNRS, Centre de Génétique Moléculaire, UPR3404, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
2CNRS, Centre de Recherches de Gif-sur-Yvette, FRC3115, 91198 Gif-sur-Yvette Cedex, France
3Université Paris-Sud, Département de Biologie, 91405 Orsay, France
4Université Paris Diderot, Sorbonne Paris Cité, Sciences du Vivant, 75205 Paris Cedex 13, France

Received 20 March 2012; Accepted 7 May 2012

Academic Editor: Frédéric Brunet

Copyright © 2012 Emeline Dubois et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Sequences related to transposons constitute a large fraction of extant genomes, but insertions within coding sequences have generally not been tolerated during evolution. Thanks to their unique nuclear dimorphism and to their original mechanism of programmed DNA elimination from their somatic nucleus (macronucleus), ciliates are emerging model organisms for the study of the impact of transposable elements on genomes. The germline genome of the ciliate Paramecium, located in its micronucleus, contains thousands of short intervening sequences, the IESs, which interrupt 47% of genes. Recent data provided support to the hypothesis that an evolutionary link exists between Paramecium IESs and Tc1/mariner transposons. During development of the macronucleus, IESs are excised precisely thanks to the coordinated action of PiggyMac, a domesticated piggyBac transposase, and of the NHEJ double-strand break repair pathway. A PiggyMac homolog is also required for developmentally programmed DNA elimination in another ciliate, Tetrahymena. Here, we present an overview of the life cycle of these unicellular eukaryotes and of the developmentally programmed genome rearrangements that take place at each sexual cycle. We discuss how ancient domestication of a piggyBac transposase might have allowed Tc1/mariner elements to spread throughout the germline genome of Paramecium, without strong counterselection against insertion within genes.