A field guide to endogenous retrovirus regulatory networks

Germ cells are subject to exogenous retrovirus infections occasionally resulting in the genomic integration of retroviral gene sequences. These endogenized retroviruses (ERVs) are found throughout mammalian genomes. Initially thought to be inert, it is now appreciated that ERVs have often been co-opted for complex physiological processes. However, unregulated ERV transposition and expression are a threat to cellular fitness and genomic integrity, and so mammalian cells must control ERVs through pre- and post-transcriptional mechanisms. Here, we provide a field guide to the molecular machinery that identifies and silences ERVs.