Cytogenetic studies on rat thymic lymphomas induced by N-propyl-N-nitrosourea.

N-Propyl-N-nitrosourea (PNU) was proved to be a strong leukemogen, which induces myelogenous leukemia or thymic lymphoma in rats. BUF/Mna rats and F344 rats were the strain most susceptible to thymic lymphomagenic activity of PNU. In addition, F1 rats between BUF/Mna and WKY rats were also susceptible to PNU-lymphomagenic activity. In the present experiment, karyotypes of 31 thymic lymphomas induced by PNU in BUF/Mna rats and in F1 rats between BUF/Mna and WKY rats were analysed for chromosomal abnormalities. Although no specific chromosomal abnormalities were observed throughout all lymphomas, del(11q) and dup(2q) were observed frequently in BUF/Mna rat lymphomas. Breakpoints and/or fusion-points were frequently observed in chromosome 11, followed by chromosomes 2, 5 and 6. Trisomy of chromosome 7, on which c-myc oncogene is mapped, was observed in seven cases, and monosomy of chromosomes 12, 18, 19, 20 and X was seen in seven or eight cases each, though these changes were generally observed in minor cell population in each case.