Abstract
An endogenous retrovirus (ERV) is a remnant of an ancient retroviral infection in the host genome. Although most ERVs have lost their viral productivity, a few ERVs retain their replication capacity. In addition, partially inactivated ERVs can present a potential risk to the host via their encoded virulence factors or the generation of novel viruses by viral recombination. ERVs can also eventually acquire a biological function, and this ability has been a driving force of host evolution. Therefore, the presence of an ERV can be harmful or beneficial to the host. Various reports about paleovirology have revealed each event in ERV evolution, but the continuous processes of ERV evolution over millions of years are mainly unknown. A unique ERV family, ERV-DC, is present in the domestic cat (Felis silvestris catus) genome. ERV-DC proviruses are phylogenetically classified into three genotypes, and the specific characteristics of each genotype have been clarified: their capacity to produce infectious viruses; their recombination with other retroviruses, such as feline leukemia virus or RD-114; and their biological functions as host antiviral factors. In this review, we describe ERV-DC-related phenomena and discuss the continuous changes in the evolution of this ERV in the domestic cat.
Highlights
Retroviruses can integrate into the host genome through a DNA intermediate in the viral life cycle
These results indicate that endogenous retrovirus (ERV)-DC7 and ERV-DC16, belonging to ERV-DC genotype II (GII), have been domesticated as Refrex-1 to protect the host from viral infection
The rearrangement of ERV-DC-related phenomena suggests a scenario of ERV-DC evolution and raises new questions
Summary
Retroviruses can integrate into the host genome through a DNA intermediate in the viral life cycle. Paleovirology is the study of ancient viruses, including ERVs, to clarify the processes of viral evolution in the long term [5,6,7]. Various paleovirological studies have clarified the events of ancestral virus evolution, including interspecies viral transmission [8,9], virus–host evolutionary arms races [10,11], and the acquisition of host functional genes through ERV domestication [12,13,14,15]. Because ERV-DC2 and ERV-DC6 have been identified as partial genomes, their virus productivity is still unknown (?); 3 surface unit in the env gene (SU). The GII proviruses encode an antiviral factor, Refrex-1, that inhibits ERV-DC GI and FeLV-D infections [20].
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