Mariner Transposons Contain a Silencer: Possible Role of the Polycomb Repressive Complex 2

PLoS Genetics, Public Library of Science, 2016, 12 (3), pp.1-38

Solenne Bire 1, 2, Sophie Casteret 1, Benoit Piegu 1, Linda Beauclair 1, Nathalie Moiré 3, Peter Arensbuger 4, Yves Bigot 1

1 PRC - Physiologie de la reproduction et des comportements, UMR INRA-CNRS 7247, Nouzilly, France
2 Institute of Biotechnology, Center for Biotechnology, University of Lausanne, Switzerland
3 UMR ISP - Infectiologie et Santé Publique, UMR INRA 1282, Tours, France
4 Department of Biological Sciences, California State Polytechnic University, USA


Transposable elements are driving forces for establishing genetic innovations such as transcriptional regulatory networks in eukaryotic genomes. Here, we describe a silencer situated in the last 300 bp of the Mos1 transposase open reading frame (ORF) which functions in vertebrate and arthropod cells. Functional silencers are also found at similar locations within three other animal mariner elements, i.e. IS630-Tc1-mariner (ITm) DD34D elements, Himar1, Hsmar1 and Mcmar1. These silencers are able to impact eukaryotic promoters monitoring strong, moderate or low expression as well as those of mariner elements located upstream of the transposase ORF. We report that the silencing involves at least two transcription factors (TFs) that are conserved within animal species, NFAT-5 and Alx1. These cooperatively act with YY1 to trigger the silencing activity. Four other housekeeping transcription factors (TFs), neuron restrictive silencer factor (NRSF), GAGA factor (GAF) and GTGT factor (GTF), were also found to have binding sites within mariner silencers but their impact in modulating the silencer activity remains to be further specified. Interestingly, an NRSF binding site was found to overlap a 30 bp motif coding a highly conserved PHxxYSPDLAPxD peptide in mariner transposases. We also present experimental evidence that silencing is mainly achieved by co-opting the host Polycomb Repressive Complex 2 pathway. However, we observe that when PRC2 is impaired another host silencing pathway potentially takes over to maintain weak silencer activity. Mariner silencers harbour features of Polycomb Response Elements, which are probably a way for mariner elements to self-repress their transcription and mobility in somatic and germinal cells when the required TFs are expressed. At the evolutionary scale, mariner elements, through their exaptation, might have been a source of silencers playing a role in the chromatin configuration in eukaryotic genomes.


Transposable elements
Polycomb Repressive Complex 2
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