Proto-oncogene expression profiles in MSH2 ^−/− mice and human LBL by RT-PCR (A-F). Results of RBTN-2, TAL-1, and HOX-11 expression in 10 representative MSH2 ^−/− thymic tumors are shown in (A), (B), and (C), respectively. Lane 1 in (A) and (B) represent amplification from MSH2 ^−/− thymic tissue before the development of lymphoma (negative control) and lane 1 in (C) represents a positive control with amplification using cDNA from day 9 ES cells. RBTN-2 expression is detected in all MSH2 ^−/− thymic tumors, TAL-1 is detected in 40%, while none express HOX-11. (D), (E), and (F) show the expression profiles of RBTN-2, TAL-1, and HOX-11, respectively, in 10 cases of human LBL. Lane 1 in (D) and (E) represent amplification using normal human lymphocyte cDNA (negative control). Lane 1 in (F) is a positive control from SiL-1, a human T-cell acute lymphoblastic leukemia (ALL) cell line. Expression of RBTN-2, TAL-1, and HOX-11 is detected in 100%, 70%, and 0% of the cases, respectively.