Germ-line MuLV reintegrations in AKR/J mice

Abstract

AKR mice are viraemic from birth¹ and contract leukaemia at high incidence at 6–9 months of age². They express, in all tissues studied, the ecotropic (mouse infectious) retrovirus AKV¹. Rowe^3,4 showed, by crossing AKR mice with the low-viraemia, non-leukaemic NIH/Swiss mice, that viraemia and the leukaemic phenotype are linked and carried at two independent loci (Akv-1 and Akv-2). These two loci were shown to represent integrated ecotropic proviruses^5,6. As part of a study of the structure of proviruses which arise in the leukaemic thymus of AKR mice, we identified ecotropic-specific hybridization probes from different regions of the AKV genome⁷. Initial Southern hybridization⁸ analyses showed that individual leukaemic AKR/Jackson mice, which have been sibling inbred for over 140 generations, had differing numbers of ecotropic proviruses⁹. We now report analyses showing that AKR/J mice had three common proviruses; however, two additional ecotropic loci were scattered throughout the Jackson Laboratory AKR population. These loci probably arose through reinfection of the germ line and represent a currently occurring amplification of ecotropic proviruses in these inbred mice.