LTR Retroelement-Derived Protein-Coding Genes and Vertebrate Evolution

Abstract

During evolution, many cellular protein-coding genes have been formed from genes carried by long terminal repeat (LTR) retroelements (retroviruses and LTR retrotransposons). This phenomenon, called molecular domestication, has significantly impacted the emergence and diversification of the vertebrate lineage. LTR retroelements have contributed different types of coding regions to the gene repertoire of their host, including gag, envelope, integrase and protease genes. Genes derived from gag and envelope sequences are particularly well represented in vertebrate genomes. Retroelement-derived genes fulfil functions in important ­biological processes, particularly placenta formation and immunity against retro­elements, as well as cell proliferation and apoptosis. Of particular interest is the recurrent molecular domestication of retrovirus envelope genes, which has taken place several times independently in different mammalian sublineages to generate new genes involved in placenta formation. The function of most retroelement-derived genes remains unknown, and additional new genes are still to be identified particularly in “lower” vertebrates.