The epigenomic landscape of transposable elements across normal human development and anatomy

Transposable elements (TEs) have deposited functional regulatory elements throughout the human genome. Although most are silenced, certain TEs have been co-opted by the host. However, a comprehensive, multidimensional picture of the contribution of TEs to normal human gene regulation is still lacking. Here, we quantify the epigenomic status of TEs across human anatomy and development using data from the Roadmap Epigenomics Project. We find that TEs encompass a quarter of the human regulatory epigenome, and 47% of elements can be in an active regulatory state. We demonstrate that SINEs are enriched relative to other classes for active and transcribed marks, that TEs encompass a higher proportion of enhancer states in the hematopoietic lineage, and that DNA methylation of Alu elements decreases with age, corresponding with a loss of CpG islands. Finally, we identify TEs that may perform an evolutionarily conserved regulatory function, providing a systematic profile of TE activity in normal human tissue.