Roles and regulation of endogenous retroviruses in pluripotency and early development

Abstract Endogenous retroviruses (ERVs) represent abundant retrotransposon families that have coevolved in the mammalian genome for millions of years. Although long considered junk DNA, it is becoming increasingly evident that ERVs are likely to play important roles during normal development. Retroviral sequences have been coopted to create new regulatory elements, used by cells to rewire their gene expression patterns. On the other hand, ERVs are capable of retrotransposition into new genomic locations, thus carrying mutagenic potential. As a result, specialized host regulatory mechanisms have evolved to control ERV expression and activity. In this review, we discuss the exquisite regulation of ERVs in pluripotent cells and throughout early development in human and mouse.