Xenotropic Mouse Gammaretroviruses Isolated from Pre-Leukemic Tissues Include a Recombinant

Distribution of endogenous gammaretroviruses and variants of the Fv1 restriction gene in individual mouse strains and strain subgroups

Inbred laboratory mouse strains carry endogenous retroviruses (ERVs) classed as ecotropic, xenotropic or polytropic mouse leukemia viruses (E-, X- or P-MLVs). Some of these MLV ERVs produce infectious virus and/or contribute to the generation of intersubgroup recombinants. Analyses of selected mouse strains have linked the appearance of MLVs and virus-induced disease to the strain complement of MLV E-ERVs and to host genes that restrict MLVs, particularly Fv1. Here we screened inbred strain DNAs and genome assemblies to describe the distribution patterns of 45 MLV ERVs and Fv1 alleles in 58 classical inbred strains grouped in two ways: by common ancestry to describe ERV inheritance patterns, and by incidence of MLV-associated lymphomagenesis. Each strain carries a unique set of ERVs, and individual ERVs are present in 5–96% of the strains, often showing lineage-specific distributions. Two ERVs are alternatively present as full-length proviruses or solo long terminal repeats. High disease incidence strains carry the permissive Fv1ⁿ allele, tested strains have highly expressed E-ERVs and most have the Bxv1 X-ERV; these three features are not present together in any low-moderate disease strain. The P-ERVs previously implicated in P-MLV generation are not preferentially found in high leukemia strains, but the three Fv1 alleles that restrict inbred strain E-MLVs are found only in low-moderate leukemia strains. This dataset helps define the genetic basis of strain differences in spontaneous lymphomagenesis, describes the distribution of MLV ERVs in strains with shared ancestry, and should help annotate sequenced strain genomes for these insertionally polymorphic and functionally important proviruses.