Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Spontaneous mammary tumors in GR mice contain, in addition to the endogenous MMTV copies, acquired proviral sequences, which can be detected and characterized by the Southern transfer procedure. Hormone responsive and independent cell populations were selected from spontaneous GR tumors by transplanting tumor cell suspensions into pairs of hormone treated and untreated syngeneic males. Analysis of the acquired MMTV DNA copies revealed differences between hormone responsive and independent cell populations derived from the same tumor indicating that the original tumors were comprised of multiple cell populations. The hormone responsiveness of a tumor cell population could not be correlated with the presence of specific acquired proviral fragments, degree of methylation or histological type. Our results also indicated that some tumor cells may be pluripotent and are able to undergo differentiation in vivo.;The endogenous MMTV proviral copies were characterized in three genetically dissimilar mouse strains: GR, NFS, and DBA. Proviral sequences were characterized using the Southern transfer procedure in genetic crosses and somatic cell hybrids. By examining the cosegregation of Eco RI and Bam HI viral specific fragments it was possible to demonstrate that (1) the three strains carried similar endogenous MMTV proviral loci, (2) the proviral copies were heterogenous with respect to their internal restriction sites, (3) the copies were distributed on multiple chromosomes and (4) in some instances, two unlinked proviral copies gave rise to the same size restriction fragment.