Magda Babonits

Nonrandom chromosome changes involving the Ig gene-carrying chromosomes 12 and 6 in pristane-induced mouse plasmacytomas

The karyotypes of pristane-induced mouse plasmacytomas were studied by G banding. Only primary tumors or early passage generations were analyzed. In contrast to murine T cell leukemias that showed a regular trisomy of chromosome 15, all plasmacytomas showed a consistent translocation of the distal part of chromosome 15 to either chromosome 6 [rcpT(6;15)] or 12 [T(12;15)]. The specific breakpoints were at 6C, 15D3/E ro D2/3 and 12F2. Early passage generations often showed a mixed population with two different translocations, suggesting polyclonal origin. Considered together with the known karyotypic features of murine and human lymphomas, these findings support the theory that the nonrandom chromosomal changes in lymphoproliferative malignancies are associated with the type of the target cell, rather than with the etiological agent. Moreover, the involvement of the chromosomes known to carry the heavy chain (12) and the light chain (6) determinants, respectively, raises the question of whether the translocations may be related to the DNA level rearrangements known to occur during the differentiation of normal plasma cells.

Cytogenetic studies on IgA/lambda-producing murine plasmacytomas: Regular occurrence of a T(12;15) translocation

Seven IgA/lambda-producing murine plasmacytomas had the 12;15 translocation, previously found in IgA/kappa-producing plasmacytomas, and lacked the rcpT(6;15) translocation, also found in some kappa producers. The results suggest that the generation of the 12;15 translocation is an important, perhaps essential event during the genesis of plasmacytomas. The possibility that the distal region of chromosome 15 may contain a “supergene” area involved with the differentiation and/or normal responsiveness of various types of lymphoreticular cells, must be seriously considered on the basis of the present and previous evidence on plasmacytomas, as well as the extensive evidence now available on the role of chromosome 15-changes in the genesis of murine lymphomas. The involvement of chromosome 12 is of interest in view of the fact that it is known to carry the heavy-chain immunoglobulin determinants.