Co-option of retroviral genes: diversity and evolution in vertebrates

Endogenous retroviruses (ERVs) are remnants of retroviral sequences that integrated into the host germline genome and are inherited across generations. Occasionally, the protein-coding genes within ERVs have been co-opted as host genes and contribute to diverse biological processes. In early studies, the identified ERV-derived genes remained taxonomically restricted to model organisms. Recently, however, the increasing availability of vertebrate genome assemblies has expanded the known repertoire of ERV-derived genes across diverse lineages. Here, I review the current knowledge of ERV-derived genes and how the era of comparative genomics is reshaping our understanding of the vertebrate ERV-derived genes. I first describe the processes of ERV endogenization, genomic expansion, and co-option. Then, I summarize the known functions of ERV-derived genes in vertebrates and the methodology of comparative genomic approaches to discover ERV-derived genes. I further discuss evolutionary models of ERV-derived genes, which will become increasingly important for understanding the broad pattern of their evolution. This review also provides a catalog of ERV-derived genes, including recently identified genes of unknown function. By integrating findings from recent comparative genomic studies, this review provides an updated view of how ERV-derived genes have contributed to vertebrate evolution.