TALL-het tumors are generated through a distinct genetic mechanism from TALL-homo tumors. (A) Flow cytomytric analysis of TALL-het and -homo tumor cells with T-cell markers expressed at different developmental stages. Two representative tumors of 5 for each tumor type are shown. (B) Western blot analysis of TdT expression levels in control cells, oncogenic Nras mutation-initiated TALL-het and -homo tumors (top panels), and oncogenic Kras mutation-initiated TALL-KrasG12D tumors (bottom panels). (C) Western blot analysis of total Nras expression levels in control, TALL-het, and -homo thymocytes. (D) Direct sequencing of RT-PCR amplified products in TALL-het and -homo tumors at the Nras G12 codon. Results are representative of 5 animals for each tumor type.