DNA rearrangement causes a high rate of spontaneous mutation at the immunoglobulin heavy-chain locus of a mouse XXXX cell line.

@entity1582 @entity10986 @entity37504
The spontaneous mutation rate of immunoglobulin genes expressed in @entity1582 cells is well above that of other genes expressed in these or in other cell types. The nature of such mutations in one @entity1582 cell line, MPC11, was explored at the molecular level. Included in this study were MPC11 variants representing 24 independent and spontaneous mutations affecting immunoglobulin secretion. Of the mutants studied, 19 had ceased @entity37504 ( @entity37504 ) production (nonproducers), and 5 produced from as little as 1/1,000 to as much as 1/10 the amount of immunoglobulin produced by MPC11 (low producers). Only one of the MPC11 mutants (a nonproducer) showed no evidence of DNA rearrangement in or near the expressed @entity37504 gene. The formerly expressed @entity10986 gene had been deleted in 18 of the 19 nonproducers. All of the low producers had undergone DNA rearrangement in or near the expressed @entity37504 gene, and three of them produced immunoglobulin of a new heavy chain class. The cause for reduced heavy-chain synthesis in the low producers is not yet known. However, in several of these mutants, the defect appeared to be posttranscriptional. In these cell lines, steady-state @entity37504 mRNA levels were much lower than in the parent cell line, while the heavy-chain gene transcription rate remained unchanged.
