Cmu gene rearrangement of mouse immunoglobulin genes in normal B cells occurs on both the expressed and nonexpressed chromosomes.

Abstract

The organization of heavy-chain Ig genes on both the expressed and nonexpressed chromosomes of normal B lymphocytes from allotype heterozygous (BALB/c .times. C57BL/J)F1 mice. The C.mu. genes of BALB/c mice are on 12.4 kb EcoRI and 13.1 kb Kpn I restriction fragments; those of C57BL/J mice are on 13.6 kb EcoRI and 14.3 kb Kpn I restriction fragments, allowing the examination of rearrangements on each chromosome independently. B lymphocytes from spleen and Peyer''s patches expressing both IgD and IgM of the BALB/c allotype were isolated with a fluorescence-activated cell sorter. EcoRI and Kpn I restriction digests were hybridized with a C.mu. gene-containing probe. The C.mu. gene is present on both chromosomes. DNA rearrangements occur on both the expressed and nonexpressed chromosome within the 3.6 kb Kpn I/EcoRI restriction fragment containing the joining (JH) gene locus. Allelic exclusion of heavy-chain Ig gene expression is not mediated by JH-region DNA rearrangement of the expressed chromosome only. Analysis of the C.kappa. gene region from the same sorted B-cell DNA reveals a substantial quantity of germ-line context DNA. The deletions observed on the EcoRI fragment containing the C.mu. gene in myeloma cells and in C.mu. gene-containing recombinant DNA do not usually occur in normally differentiating B lymphocytes and are likely to be confined to myeloma tumor cells.