IMMUNOGLOBULIN GENE EXPRESSION IN A MOUSE MYELOMA CELL LINE (SOMATIC MUTATION, DNA REARRANGEMENTS, SEQUENCING, SECRETION)

Abstract

The variable region confers antigen-binding capability on the immunoglobulin molecule. I have been studying the molecular basis of processes that alter the variable region and may affect antigen binding. One such process is somatic mutation of the variable region genes. Somatic mutation has been putatively linked to immunoglobulin heavy chain class switching, the process by which an antibody-producing cell switches from the production of one heavy chain constant region to a different isotype while retaining the original antigen-binding specificity. The IgG2b-producing MPC11 mouse myeloma gives rise to a number of variants in vitro that produce different isotypes, providing an opportunity to test the linkage of somatic mutation and isotype switching. DNA sequence analysis of the V(,H) gene of MPC11 and a number of variants shows identical sequences with no evidence of somatic mutation in either coding or flanking sequences. We conclude that somatic mutation of variable regions and isotype switching are not tightly coupled and may be independent processes.;A second process that may affect antibody variable regions is DNA rearrangement. DNA rearrangements are required to assemble a functional variable region from component V, D and J gene segments. Using Southern blot analysis, I have detected novel DNA rearrangements near the variable region of the heavy chain gene in two independent short heavy chain-producing variants. Restriction mapping documents the presence of DNA of unknown origin, unique to each variant, that is 5' to identifiable sequences. The "new" DNAs may extend into the V(,H) gene and are possibly chromosomal translocations involving oncogenes, or may reflect a novel mechanism of generating diversity in the immune response by recombination among variable region genes.