Reduced β-globin gene expression in adult mice containing deletions of locus control region 5′ HS-2 or 5′ HS-3

To gain insights into the functions or individual DNA'se hypersensitive sites within the β globin locus control region (LCR), we deleted the endogenous 5′ HS-2 and HS-3 regions from the mouse germline using homologous recombination techniques. We demonstrated that the deletion of either murine 5′ HS-2 or 5′ HS-3 reduced the expression of the embryonic εγ and βh1 globin genes minimally in yolk sac-derived erythrocytes, but that both knockouts reduced the output of the adult β (β-Major + β-Minor) globin genes by approximately 30% in adult erythrocytes. When the selectable marker PGK-Neo cassette was retained within either the HS-2 or HS-3 region, a much more severe reduction in globin gene expression was observed at all developmental stages. PGK-Neo was shown to be expressed in an erythroid-specific fashion when it was retained in the HS-3 position. These results show that neither 5′ HS-2 nor HS-3 is required for the activity of embryonic globin genes, nor are these sites required for correct developmental switching. However, each site is required for approximately 30% of the total LCR activity associated with adult β-globin gene expression in adult red blood cells. Each site therefore contains some non-redundant information that contributes to adult globin gene function.