Dynamic changes in accessibility, nuclear positioning, recombination, and transcription at the Igκ locus

The 3-megabase Ig kappa locus undergoes differentially controlled nuclear positioning events and chromatin structural changes during the course of B cell development. The temporal association of chromatin structural changes, transcription, and recombination at the Ig kappa locus was determined in a marine pre-B cell line that can be induced to recombine at the Ig kappa locus and in ex vivo-cultured murine pre-B cells. Additionally, the timing of nuclear positioning relative to the temporal order of chromatin structural changes and recombination and transcription was determined. We demonstrate that before induction, the Ig kappa locus was poised for recombination; both alleles were in a contracted state, and the enrichment of histone modifications and germline transcripts of specific V kappa genes were observed. Histone modifications of the V kappa genes did not vary upon induction but the levels of modifications correlated with the levels of germline V kappa gene transcripts and recombination. Upon induction, but before V kappa J kappa recombination, centromeric recruitment of single Ig kappa alleles occurred. DNase I sensitivity of the entire locus increased gradually over the course of differentiation while the enrichment of histone modifications downstream of the V kappa genes was increased in the silencer regions upstream of J kappa 1, within the Ig kappa sterile transcript, the kappa constant region, the E kappa i and E kappa 3 ' enhancers, and the recombining sequence. The ex vivo pre-B cells showed similar patterns of histone modifications across the locus except at the V kappa genes. In this study, H3 acetylation correlated with levels of germline transcripts while H3 methylation correlated with levels of recombination.