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. Rowe3,4 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 proviruses5,6. 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.