Chromosomal evolution in secretory and nonsecretory subline of MOPC 21

Murine myeloma cell lines are noted for the instability of their immunoglobulin genes and the production of nonsynthesizing variants. In this study, the synthesizing line P3-X63-Ag8 (P3) and its nonsynthesizing subline X63-Ag8-653 (653) were karyotyped and rearrangements of the immunoglobulin carrying chromosomes were investigated. Loss of immunoglobulin synthesis was associated with a reduction in the number of immunoglobulin-carrying chromosomes. When these findings were analyzed in light of published molecular data, it appeared that loss of immunoglobulin synthesis in 653 probably occurred as a result of immunoglobulin gene loss. An unusual finding was the absence of the t(12;15) chromosome in both P3 and 653 cell lines. It was concluded that the t(12;15) chromosome, carried by MOPC 21, has evolved into an unrecognizable form.