The hypersensitive sites of the murine β-globin locus control region act independently to affect nuclear localization and transcriptional elongation

The beta-globin locus control region (LCR) is necessary for high-level beta-globin gene transcription and differentiation-dependent relocation of the beta-globin locus from the nuclear periphery to the central nucleoplasm and to foci of hyperphosphorylated Pol II transcription factories (TFys). To determine the contribution of individual LCR DNasel hypersensitive sites (HSs) to transcription and nuclear location, in the present study, we compared beta-globin gene activity and location in erythroid cells derived from mice with deletions of individual HSs, deletions of 2 HSs, and deletion of the whole LCR and found all of the HSs had a similar spectrum of activities, albeit to different degrees. Each HS acts as an independent module to activate expression in an additive manner, and this is correlated with relocation away from the nuclear periphery. In contrast, HSs have redundant activities with respect to association with TFys and the probability that an allele is actively transcribed, as measured by primary RNA transcript FISH. The limiting effect on RNA levels occurs after beta-globin genes associate with TFys, at which time HSs contribute to the amount of RNA arising from each burst of transcription by stimulating transcriptional elongation. (Blood. 2012;119(16):3820-3827)