%0 Journal Article
%T Epigenetic histone modifications of human transposable elements: genome defense versus exaptation
%A Ahsan Huda
%A Leonardo Mari£¿o-Ram¨ªrez
%A I King Jordan
%J Mobile DNA
%D 2010
%I BioMed Central
%R 10.1186/1759-8753-1-2
%X We evaluated several predictions generated by the genome defense hypothesis versus the exaptation hypothesis using recently characterized epigenetic histone modification data for the human genome. To this end, we mapped chromatin immunoprecipitation sequence tags from 38 histone modifications, characterized in CD4+ T cells, to the human genome and calculated their enrichment and depletion in all families of human TEs. We found that several of these families are significantly enriched or depleted for various histone modifications, both active and repressive. The enrichment of human TE families with active histone modifications is consistent with the exaptation hypothesis and stands in contrast to previous analyses that have found mammalian TEs to be exclusively repressively modified. Comparisons between TE families revealed that older families carry more histone modifications than younger ones, another observation consistent with the exaptation hypothesis. However, data from within family analyses on the relative ages of epigenetically modified elements are consistent with both the genome defense and exaptation hypotheses. Finally, TEs located proximal to genes carry more histone modifications than the ones that are distal to genes, as may be expected if epigenetically modified TEs help to regulate the expression of nearby host genes.With a few exceptions, most of our findings support the exaptation hypothesis for the role of TE epigenetic modifications when vetted against the genome defense hypothesis. The recruitment of epigenetic modifications may represent an additional mechanism by which TEs can contribute to the regulatory functions of their host genomes.Transposable elements (TEs) are mobile DNA sequences that can replicate to extremely high genomic copy numbers. TEs are also widely distributed; they have been found within genomes representing all major eukaryotic lineages. Accordingly, TEs have had a profound impact on the structure, function and evolution of
%U http://www.mobilednajournal.com/content/1/1/2