Link to Pubmed [PMID] – 31679813
Link to DOI – 10.1016/j.it.2019.09.003S1471-4906(19)30191-7
Trends Immunol 2019 Nov; 40(11): 998-1010
Eukaryotic genomes contain virus-derived sequences called endogenous virus elements (EVEs). The majority of EVEs are related to retroviruses, which integrate into the host genome in order to replicate. Some retroviral EVEs encode a function; for example, some produce proteins that block infection by related viruses. EVEs derived from nonretroviral viruses – also recently found in many eukaryotic genomes – are more enigmatic. Here, we summarize the evidence that EVEs can act as templates to generate Piwi-interacting RNAs (piRNAs), whose canonical function is sequence-specific silencing of transposable elements (TEs) to maintain genomic integrity. We argue that EVEs may thus enable heritable, sequence-specific antiviral immune memory in eukaryotes – analogous to CRISPR-Cas immunity in prokaryotes.