Modulatory subdomains of the HS2 enhancer differentially regulate enhancer activity in erythroid cells at different developmental stages.

The HS2 enhancer in the locus control region of human beta-like globin genes displays developmental-stage-independent enhancer function. The mechanism by which it regulates the transcription of the globin genes in erythroid cells throughout development is not fully understood. In this paper we dissect the HS2 enhancer into an enhancer core and five modulatory subdomains M1 to M5. The enhancer core possesses developmental-stage-independent enhancer activity. The modulatory subdomains by themselves do not possess such enhancer activity, but they apparently respond to environmental signals and modulate enhancer core activity in a developmental-stage specific manner. M1 located 5' of the core strongly stimulates core activity in K562 cells at the embryonic stage. M2 and M3 located 3' of the core strongly stimulate core activity in MEL cells at the adult stage. Moreover, M3 suppresses core activity at the embryonic stage and exhibits an adult-stage-selector activity. These findings indicate that the apparent developmental-stage-independence of the HS2 enhancer is a result of multiple interactions between the core and the modulatory subdomains located both near and far from the core.