[Genetic analysis on methylnitrosourea (MNU) induced mouse T-cell lymphomas]

Since nonrandum chromosome changes in neoplastic cells have proven to be good indicators of gene alteration site related to transformation, the authors examined the chromosomes of T-cell lymphomas induced in mice strain RF/J with methylnitrosourea (MNU). All treated mice developed thymic lymphomas within 10 weeks after injection. Chromosomes of the thymus cells were examined at intervals before and during lymphoma development, as well as after the lymphomes were transmitted in syngeneic and nude mice for a period up to 424 days. In preparations made from the thymus and transmitted cells in both syngeneic and nude mice nonrandom quantitative and structural alterations were found involving X, 15, 14, 3, 12 chromosomes (showing in decreasing order of the frequency of alterations), suggesting that these chromosomes carry genes (oncogenes or tumor suppressor genes). MNU thus appears not only to be tissue specific but also chromosome specific in its effects. The neoplastic growth is resulted from a large number of sets of altered genes. Thus, if MNU preferentially target some of these sites, the probability of its induced transformation would be high. This may be the reason to explain its high clastogenicity.