A new hypersensitive site, HS10, and the enhancers, E3′ and ED, differentially regulate IGκ gene expression

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 cellspecific 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.