Control of gene conversion and somatic hypermutation by immunoglobulin promoter and enhancer sequences.
It is thought that gene conversion (GCV) and somatic hypermutation (SHM) of immunoglobulin (Ig) genes occur in two steps: the generation of uracils in DNA by activation-induced cytidine deaminase, followed by their subsequent repair by various DNA repair pathways to generate sequence-diversified products. It is not known how either of the two steps is targeted specifically to Ig loci. Because of the tight link between transcription and SHM, we have investigated the role of endogenous Ig light chain (IgL) transcriptional control elements in GCV/SHM in the chicken B cell line DT40. Promoter substitution experiments led to identification of a strong RNA polymerase II promoter incapable of supporting efficient GCV/SHM. This surprising finding indicates that high levels of transcription are not sufficient for robust GCV/SHM in Ig loci. Deletion of the IgL enhancer in a context in which high-level transcription was not compromised showed that the enhancer is not necessary for GCV/SHM. Our results indicate that cis-acting elements are important for Ig gene diversification, and we propose that targeting specificity is achieved through the combined action of several Ig locus elements that include the promoter.
Yang
Shu Yuan
SY
Section of Immunobiology and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06520, USA.
Fugmann
Sebastian D
SD
Schatz
David G
DG
D000199:Actins / Q000235:genetics; D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism; D017123:Bacteriophage T7 / Q000235:genetics; D045744:Cell Line, Tumor; D003564:Cytidine Deaminase / Q000235:genetics; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D005785:Gene Conversion / Q000235:genetics*; D017353:Gene Deletion; D015870:Gene Expression; D050439:Genes, Immunoglobulin Light Chain / Q000235:genetics*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D007075:Immunoglobulin M / Q000235:genetics; D009154:Mutation; D020648:Peptide Elongation Factor 1 / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011947:Receptors, Antigen, B-Cell / Q000235:genetics; D027041:Somatic Hypermutation, Immunoglobulin / Q000235:genetics*; D014158:Transcription, Genetic; D014162:Transfection; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
D000199:Actins; D007143:Immunoglobulin Heavy Chains; D007075:Immunoglobulin M; D020648:Peptide Elongation Factor 1; D011947:Receptors, Antigen, B-Cell; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase