Characterization of the endogenous feline leukemia virus-related DNA sequences in cats and attempts to identify exogenous viral sequences in tissues of virus-negative leukemic animals

Abstract

We analyzed DNA from tissues of different cats (normal virus negative and normal virus positive; leukemic virus negative and leukemic virus positive) using the techniques of restriction enzyme digestion and blot hybridization to (i) characterize the endogenous, feline leukemia virus (FeLV)-related DNA sequences in normal cats and (ii) attempt to identify exogenously acquired FeLV sequences in leukemic cats, particularly ones that are virus negative. The results suggest that the endogenous FeLV-related sequences (FeLV 0) are arranged as multiple (8–12 copies), discrete genetic elements in a nontandem fashion. The loci of FeLV 0 are conserved from tissue to tissue within the same animal but vary among different animals. They appear to be segregated as stable genetic elements that were probably introduced into the cat species by independent infection events sometime during evolution. Although extra bands can be detected in feline cells deliberately infected with FeLV of different subgroups and in some tissues of viremic cats, we were unable to identify any exogenous sequence in tumor tissues of virus-negative leukemic cats. Possible indirect mechanisms for the role of FeLV in leukemogenesis in these virus-negative animals are discussed.