Cmu gene rearrangement of mouse immunoglobulin genes in normal B cells occurs on both the expressed and nonexpressed chromosomes.
We have examined the organization of heavy-chain immunoglobulin genes on both the expressed and nonexpressed chromosomes of normal B lymphocytes from allotype heterozygous (BALB/c X C57BL/J)F1 mice. The C mu genes of BALB/c mice are on 12.4-kilobase EcoRI and 13.1-kilobase Kpn I restriction fragments, whereas those of C57BL/J mice are on 13.6-kilobase EcoRI and 14.3-kilobase 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-kilobase Kpn I/EcoRI restriction fragment containing the joining (JH) gene locus. We conclude that allelic exclusion of heavy-chain immunoglobulin gene expression is not mediated by JH-region DNA rearrangement of the expressed chromosome only. In contrast, analysis of the C kappa gene region from the same sorted B-cell DNA reveals a substantial quantity of germ-line context DNA. We also demonstrate that the deletions observed on the Eco RI fragment containing the C mu gene in myeloma cells and in C mu gene-containing recombinant DNAs do not usually occur in normally differentiating B lymphocytes and are likely to be confined to myeloma tumor cells.
D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology*; D002874:Chromosome Mapping; D002875:Chromosomes / Q000378:metabolism; D004247:DNA / Q000235:genetics; D004262:DNA Restriction Enzymes; D006579:Heterozygote; D007126:Immunoglobulin Allotypes / Q000235:genetics; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D007145:Immunoglobulin kappa-Chains / Q000235:genetics; D007148:Immunoglobulin mu-Chains / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL
D007126:Immunoglobulin Allotypes; D007143:Immunoglobulin Heavy Chains; D007145:Immunoglobulin kappa-Chains; D007148:Immunoglobulin mu-Chains; D004247:DNA; D004262:DNA Restriction Enzymes