In Vivo Occupancy of the κ Light Chain Enhancers in Primary Pro- and Pre-B Cells: A Model for κ Locus Activation

AbstractThe immunoglobulin κ light chain locus has two enhancer elements: the intronic enhancer, which lies between the Jκ cluster and the Cκ exon, and the 3′κ enhancer, which is located downstream of Cκ. To address the contribution of these elements to the developmentally regulated activation of germline κ locus transcription and rearrangement, we purified primary pro- and pre-B cells and determined by in vivo footprinting the sites within each enhancer that were occupied. We found that the κ intronic enhancer NF-κB site is occupied in both pro- and pre-B cells, while CRE, BSAP, and PU.1/pip sites within the 3′κ enhancer undergo changes in occupancy as cells progress from the pro-B to the pre-B cell stage. These findings suggest that regulation of the κ locus in primary pre-B cells may be mediated by factors that bind the 3′κ enhancer