Ancient Evolutionary Origin and Positive Selection of the Retroviral Restriction Factor Fv1 in Muroid Rodents.

The laboratory mouse Fv1 gene encodes a retroviral restriction factor that mediates resistance to murine leukemia viruses (MLVs). Sequence similarity between Fv1 and the gag protein of the murine endogenous retrovirus L (MuERV-L) family of ERVs suggests that Fv1 was coopted from an ancient provirus. Previous evolutionary studies found Fv1 orthologs only in the genus Mus Here, we describe identification of orthologous Fv1 sequences in several species belonging to multiple families of rodents outside the genus Mus We show that these Fv1 orthologs are in the same region of conserved synteny, between the genes Miip and Mfn2, suggesting a minimum insertion time of 45 million years for the ancient progenitor of Fv1 Our analysis also revealed that Fv1 was not detectable or heavily mutated in some lineages in the superfamily Muroidea, while, in concert with previous findings in the genus Mus, we found strong evidence of positive selection of Fv1 in the African clade in the subfamily Muridae Residues identified as evolving under positive selection include those that have been previously found to be important for restriction of multiple retroviral lineages. Taken together, these findings suggest that the evolutionary origin of Fv1 substantially predates Mus evolution, that the rodent Fv1 has been shaped by lineage-specific differential selection pressures, and that Fv1 has long been evolving under positive selection in the rodent family Muridae, supporting a defensive role that significantly antedates exposure to MLVs.IMPORTANCE Retroviruses have adapted to living in concert with their hosts throughout vertebrate evolution. Over the years, the study of these relationships revealed the presence of host proteins called restriction factors that inhibit retroviral replication in host cells. The first of these restriction factors to be identified, encoded by the Fv1 gene found in mice, was thought to have originated in the genus Mus In this study, we utilized genome database searches and DNA sequencing to identify Fv1 copies in multiple rodent lineages. Our findings suggest a minimum time of insertion into the genome of rodents of 45 million years for the ancestral progenitor of Fv1 While Fv1 is not detectable in some lineages, we also identified full-length orthologs showing signatures of a molecular "arms race" in a family of rodent species indigenous to Africa. This finding suggests that Fv1 in these species has been coevolving with unidentified retroviruses for millions of years.

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