C-myc-S mu rearrangement in a murine plasmacytoma without visible chromosomal translocations.

We report here that one murine plasmacytoma (DCPC 21) arising in a Balb/c mouse implanted i.p. with a Millipore diffusion chamber lacks any known chromosomal translocations. In situ molecular hybridization analysis of the metaphase spreads of DCPC 21, however, revealed that the c-myc gene has moved to the IgH locus on the chromosome 12. Further, an Ig switch region-mediated recombination was detected. The DNA sequencing analysis demonstrated that the c-myc gene has juxtaposed directly to S mu 5'-flanking sequence in a 'head-to-tail' orientation. The results strongly support our notion that the c-myc rearrangement is an essential step in the genesis of murine plasmacytomas, whether or not they have visible chromosomal translocations.