Friendly Viruses

The Special Relationship between Endogenous Retroviruses and Their Host

Authors

  • Mariana Varela,

    1. Institute of Comparative Medicine, University of Glasgow Veterinary School, Glasgow, Scotland, UK
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    • cCurrent address: Department of Veterinary Medicine, University of Cambridge, Madingley Road, CB3 0ES, Cambridge, England, UK

  • Thomas E. Spencer,

    1. Laboratory for Uterine Biology and Pregnancy, Department of Animal Science, Texas A&M University, College Station, Texas, USA
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  • Massimo Palmarini,

    1. Institute of Comparative Medicine, University of Glasgow Veterinary School, Glasgow, Scotland, UK
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  • Frederick Arnaud

    1. Institute of Comparative Medicine, University of Glasgow Veterinary School, Glasgow, Scotland, UK
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Address for correspondence: Frederick Arnaud, Institute of Comparative Medicine, University of Glasgow Veterinary School, 464 Bearsden Road, Glasgow, G61 1QH, Scotland, UK. Voice: +44-(0)141-3306288; fax: +44-(0)141-3302271. f.arnaud@vet.gla.ac.uk

Abstract

Endogenous retroviruses (ERVs) are present in the genome of all vertebrates and have coevolved with their hosts for millions of years. Some ERVs play a critical role in placental development, contribute to genome plasticity, and protect the host against infection of related pathogenic and exogenous retroviruses, thus some ERVs have been positively selected and maintained in the host genome. The sheep genome contains 27 endogenous retroviruses (enJSRVs) related to the pathogenic Jaagsiekte sheep retrovirus (JSRV), the causative agent of a transmissible lung cancer in sheep. enJSRVs are able to protect their host against JSRV infection by blocking different steps of the viral replication cycle. In addition, enJSRVs are absolutely required for sheep placental development. Thus, enJSRVs-JSRV provides a unique and interesting model to study the symbiotic relationship and interplay between host ERVs and evolution. This review will provide some examples of the biological functions of ERVs. In particular, the role of ERVs in reproductive biology and in protecting the host against pathogenic retrovirus infections will be emphasized using enJSRVs/JSRV and the sheep as a model.

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