Molecular effects of transposable element sequences in mammalian cells

Transposable elements (TEs) are often epigenetically repressed in eukaryotic cells, but still affect the molecular state of the cell in certain contexts. A flurry of recent studies have elucidated new effects of TE sequences in eukaryotic cells. We review these emerging molecular effects of TEs, including a variety of new mechanisms by which TE sequences affect the cell, including pre- and post-transcriptional regulation of gene expression; cell-to-cell transmission of genes within a multicellular organism through virus-like activity; and RNA-guided DNA insertion. Recent demonstration of TE-guided genome editing underscores the importance of these investigations for both basic and translational research. Future work is needed to continue to unravel the molecular effects of TE sequences across developmental stages, across cell types, and in various diseases.