The Aγ-globin 3′ element provides no unique function(s) for human β-globin locus gene regulation

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Abstract
The human β-globin locus is activated transcriptionally by a complex series of events that culminate in appropriate temporal and tissue-specific control over five separate genes during embryonic and early postnatal development. One cis-regulatory element in the locus, originally identified as an enhancer 3′ to the Aγ-globin gene, more recently has been suggested to harbor alternative or additional properties, including stage-specific silencer, insulator, nuclear matrix, or chromosome scaffold attachment activities. We have re-evaluated the activity during erythropoiesis that is conferred by this element by deleting it from a yeast artificial chromosome (YAC) containing the entire human β-globin locus and then assaying for the expression of each gene at each developmental stage after incorporation of the mutant YAC into the mouse germline. The data show that loss of the Aγ-globin 3′ element confers no phenotype in six independent lines of intact YAC mutant transgenic mice, thus demonstrating (minimally) that any activities attributable to this element are fully compensated by other DNA sequences within the β-globin locus.