A New Hypersensitive Site, HS10, and the Enhancers, E3′ and Ed, Differentially Regulate Igκ Gene Expression

Abstract

The mouse Igκ gene locus has three known transcriptional enhancers: an intronic enhancer (Ei), a 3′ enhancer (E3′), and a further downstream enhancer (Ed). We previously discovered, using the chromosome conformation-capture technique, that Ei and E3′ interact with a novel DNA sequence near the 3′ end of the Igκ locus, specifically in B cells. In the present investigation, we examined the function of this far downstream element. The sequence is evolutionarily conserved and exhibits a plasmacytoma cell-specific DNase I-hypersensitive site in chromatin, henceforth termed HS10 in the locus. HS10 acts as a coactivator of E3′ in transient transfection assays. Although HS10−/− mice exhibited normal patterns of B cell development, they were tested further along with E3′−/− and Ed−/− mice for their Igκ expression levels in plasma cells, as well as for both allelic and isotype exclusion in splenic B cells. HS10−/− and Ed−/−, but not E3′−/−, mice exhibited 2.5-fold lower levels of Igκ expression in antigenically challenged plasma cells. E3′−/− mice, but not HS10−/− mice, exhibited impaired IgL isotype and allelic exclusion in splenic B cells. We have suggestive results that Ed may also weakly participate in these processes. In addition, HS10−/− mice no longer exhibited regional chromosome interactions with E3′, and they exhibited modestly reduced somatic hypermutation in the Jκ-Cκ intronic region in germinal center B cells from Peyer’s patches. We conclude that the HS10, E3′, and Ed differentially regulate Igκ gene dynamics.