Chromosome alteration and the development of tumors. XXIII. Banding karyotype analyses of methylcholanthrene-induced tumors in the Indian spiny mouse, Mus platythrix, with special regard to the anomalies of chromosomes with nucleolar organizer regions.

In the Indian spiny mouse, Mus platythrix (2n = 26), six tumors were induced by 3-methylcholanthrene, and their karyotypes were analyzed in the primary state by G-banding. The chromosome numbers of these tumors were widely distributed ranging from diploid to tetraploid, but the frequency of cells exhibiting diploidy was the highest. Among these cells, the frequency of the cells with a normal diploid karyotype was only 27%, but the remaining cells (73%) showed pseudo- or near-diploid karyotypes. Although several numerical and structural anomalies of the chromosomes were observed in these tumor cells, centric fusion and translocation was most commonly seen, and that of trisomy and monosomy ranked second. Among 13 chromosome pairs, higher frequencies of chromosome anomalies were observed in the chromosomes No. 5, 8, and 12. Anomalies of the other autosomes were related primarily to centric fusion with chromosomes No, 5, 8, or 12, those of the X chromosome were mainly numerical changes. Taking into account the nucleolar organizer regions (NORs), which always occurred in chromosome pairs No. 5, 8 and 12 in this species, a possible relationship between the anomalies of those chromosomes containing NORs and the malignant transformation of cells is proposed.