Germline deletion of Igh 3′ regulatory region elements hs5-7 affects B cell specific regulation rearrangement and insulation of the Igh locus

摘要

Regulatory elements located within a ~28 kb region 3′ of the Igh gene cluster (3′ regulatory region, 3′ RR) are required for class switch recombination and for high levels of IgH expression in plasma cells. We previously defined novel DNase I hypersensitive (hs) sites, i.e. hs5-7, immediately downstream of this region. Hs5-7 contains a high density of binding sites for CTCF, a zinc finger protein associated with mammalian insulator activity and is an anchor for interactions with CTCF sites flanking the DH region. To test the function of hs5-7, we have generated mice with an 8 kb deletion encompassing all three hs elements. B cells from hs5-7 KO mice showed a modest increase in expression of the nearest downstream gene. In addition, Igh alleles in hs5-7 KO mice were in a less contracted configuration compared to WT Igh alleles and showed a two-fold increase in the usage of proximal VH7183 gene families. Hs5-7 KO mice were essentially indistinguishable from wild type mice in B cell development, allelic regulation, class switch recombination, and chromosomal looping. We conclude that hs5-7--a high-density CTCF binding region at the 3′ end of the Igh locus--impacts usage of VH regions as far as 500 kb away.