Influence of strain difference on the karyotypic changes in N-nitroso-N-butylurea--induced mouse lymphomas

Karyotypes were analyzed in 44 cases of mouse lymphomas induced by continuous oral administration of N-nitroso-N-butylurea (NBU): 14 cases of C57BL/6JKok, 6 from LT/sv, 5 from MT/Hok, 2 from (AKR/MsHok x T1Ct)F1, 2 from (AKR/MsHok x CBA/H-T6Hok)F1, and 15 from the first backcross generation of (CBA/Hok x CBA/H-T6Hok)F1 to CBA/Hok. Thirty-six were thymic lymphomas (TLs) and the remaining 8 nonthymic lymphomas (NTLs). No chromosome abnormality was found in 8 NTLs, whereas modal cells were karyotypically changed in 13 TLs. Unlike the situation in NTLs, chromosomally abnormal cells were always present in the remaining 23 TL cases in which modal cells showed no apparent deviation from the constitutional host karyotype. A total of 31 independent karyotypic changes were identified in 26 cytogenetically abnormal major clones from 19 TLs. Although trisomy 15 was the most frequent karyotypic change, being present in 9 TLs, its incidence was substantially low compared with experimentally induced murine TLs so far reported. Furthermore, 6 of the 9 trisomy 15 clones clustered to (CBA x T6)F1 x CBA. Thus, it seems probable that the genetic background of the host animals has a profound influence upon the frequency of trisomy 15 in TLs.