Monoallelic demethylation and rearrangement control allelic exclusion of the immunoglobulin κ-chain locus (Igk locus) in B cells. Here, through the introduction of pre-rearranged Igk genes into their physiological position, the critical rearrangement step was bypassed, thereby generating mice producing B cells simultaneously expressing two different immunoglobulin-κ light chains. Such 'double-expressing' B cells still underwent monoallelic demethylation at the Igk locus, and the demethylated allele was the 'preferred' substrate for somatic hypermutation in each cell. However, methylation itself did not directly inhibit the activation-induced cytidine-deaminase reaction in vitro. Thus, it seems that the epigenetic mechanisms that initially bring about monoallelic variable-(diversity)-joining rearrangement continue to be involved in the control of antibody diversity at later stages of B cell development.
Bibliographical noteFunding Information:
We thank I. Keshet for experimental assistance, S. Casola for scientific advice and cell sorting; C. Goettlinger for cell sorting; C. Koenigs, C. Uthoff-Hachenberg and A. Egert for technical help; R. Grützmann (University of Cologne) for anti–mouse k (R33-18.10) and anti-IgM (R33-24.12). Supported by the National Institutes of Health (H.C., K.R. and Y.B.), the Israel Academy of Sciences (Y.B), the German Israel Foundation (Y.B.), the European Community 5th Framework Quality of Life Program (Y.B.), the Israel Cancer Research Fund (H.C.) and the Volkswagen Foundation (K.R.).