UC San Diego

The production of diverse antibodies in B cells is the end result of the combinatorial rearrangement of immunoglobulin genes. However, given the choice of two immunoglobulin heavy or light chain alleles, a functional rearrangement occurs only on one allele at a given time, and B cells subsequently express surface receptors with a single specificity, a phenomenon termed allelic exclusion. Although it has been a subject of intensive research, the exact mechanisms for the establishment of allelic exclusion are yet to be fully understood. In this study, we provide evidence suggesting that E47 might be involved in the differential accessibility of two immunoglobulin kappa light chain alleles. Using the combination of biarsenical-tetracysteine (TC) labeling system and 3D fluorescence in situ hybridization (3D FISH) to visualize E47 and the IgK locus, we demonstrate that the association of E47 with the IgK intronic/3ʹ enhancers in pro-B and pre -B cells is predominantly monoallelic. Furthermore, the analysis of the spatial distances between the distal VK region and the IgK enhancers among pro-B and pre-B cells showing monoallelic E47 binding revealed that the E47- bound IgK alleles are in a more compact state than the non -E47-bound IgK alleles. In addition, E47 association correlates with a more central subnuclear localization of the IgK locus. Hence, our findings suggest that the monoallelic interaction of trans-acting factors such as E47 and cis-acting regulatory DNA elements might contribute to the establishment of allelic exclusion at the IgK locus by creating differential locus environments. These findings may provide valuable insight into the potential universal mechanism for allelic exclusion during lymphocyte development in general