[Chromosome translocations and the activation of C-myc oncogene in mouse plasmacytomas]

Plasmacytomas can be induced in BALB/c mice by three different agents: (1) Mineral oil, (2) Solid plastics such as diffusion chambers, and (3) Abelson murine leukemia virus plus pristane. We examined chromosome aberrations in mouse plasmacytomas induced by each of the three agents. Most of plasmacytomas showed the specific translocations of chromosomes between either No. 12 and No. 15 or No. 6 and No. 15. These chromosome translocations were common to all plasmacytomas induced by different agents. The specific breakpoints were at 12F2 where IgH genes appear to locate, and 6C2 where kappa light chain genes might be located, and 15D2/3 where c-myc oncogene appears to locate. However, we have found very recently a few plasmacytomas which have no translocations of chromosomes. The subregion (s) of one copy of chromosome 15 which is called D1:D2 appears to be deleted in these plasmacytomas. In the next study, we examined the relationship of chromosomal aberrations to the activation of c-myc oncogene. Not only the plasmacytomas with chromosome translocations, but also the translocation-negative plasmacytomas showed the either rearrangement or germline type of c-myc DNA. Rearranged c-myc transcript was found only in plasmacytomas with the 12;15 translocation. However, not all plasmacytomas belonging to this group expressed the altered c-myc RNA transcript. Our experiments indicated that the germline type c-myc RNA was 2.4 kb and the rearranged c-myc RNA was mostly 1.8 kb in length. Concerning the c-myc DNA, the germline type was 21 kb and the rearranged type of c-myc DNA was estimated, mostly, to be 14 kb by EcoRI digestion.