Changes in Histone Acetylation Are Associated with Differences in Accessibility of VH Gene Segments to V-DJ Recombination during B-Cell Ontogeny and Development

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Abstract
Although V(D)J recombination is thought to be regulated by changes in the accessibility of chromatin to the recombinase machinery, the mechanisms responsible for establishing “open” chromatin are poorly understood. We performed a detailed study of the acetylation status of histones associated with 11 VH gene segments, their flanking regions, and various intergenic elements during B-cell development and ontogeny, when V(D)J recombination is highly regulated. Histone H4 shows higher and more-regulated acetylation than does histone H3 in the VH locus. In adult pro-B cells, VH gene segments are acetylated prior to V(D)J rearrangement, with higher acetylation associated with JH-distal VH gene segments. While large regions of the VH locus have similar patterns of histone acetylation, acetylation is narrowly confined to the gene segments, their flanking promoters, and recombinase signal sequence elements. Thus, histone acetylation in the VH locus is both locally and globally regulated. Increased histone acetylation accompanies preferential recombination of JH-proximal VH gene segments in early B-cell ontogeny, and decreased histone acetylation accompanies inhibition of V-DJ recombination in a transgenic model of immunoglobulin heavy-chain allelic exclusion. Thus, changes in histone acetylation appear to be important for both promotion and inhibition of V-DJ rearrangement during B-cell ontogeny and development.