Mammalian Endogenous Retroviruses

Mammalian genomes have accumulated millions of retrotransposed sequences during evolution. This material can be divided into long terminal repeat (LTR) retrotransposons that include the endogenous retroviruses (ERVs), as well as long and short retrotransposons lacking LTRs, known as LINEs and SINEs, respectively. ERVs are defined as inherited genetic elements closely resembling the proviruses formed following exogenous retrovirus infection. In this chapter we describe the discovery, classification, and origins of ERVs in mammals, consider cellular mechanisms that have evolved to control their expression, and discuss the biological consequences, both positive and negative from the host's standpoint, of ERV inheritance.