Southern blotting shows monoclonal integrations in Sox4/Sfpi1 leukemias. Southern blotting analyses of genomic DNA prepared from leukemic spleens of the Sox4/Sfpi1 cohort (A) and the Sox4/Wt cohort (B) using an MSCV specific probe. Samples were digested with HindIII, which cuts a single time within the vector; thus, each band represents an independent integration event. Lanes are marked by pathology identification numbers.