Substitution of the Human β-Spectrin Promoter for the Human Aγ-Globin Promoter Prevents Silencing of a Linked Human β-Globin Gene in Transgenic Mice

摘要

During development, changes occur in both the sites of erythropoiesis and the globin genes expressed at each developmental stage. Previous work has shown that high-level expression of human β-like globin genes in transgenic mice requires the presence of the locus control region (LCR). Models of hemoglobin switching propose that the LCR and/or stage-specific elements interact with globin gene sequences to activate specific genes in erythroid cells. To test these models, we generated transgenic mice which contain the human Aγ-globin gene linked to a 576-bp fragment containing the human β-spectrin promoter. In these mice, the β-spectrin Aγ-globin (βsp/Aγ) transgene was expressed at high levels in erythroid cells throughout development. Transgenic mice containing a 40-kb cosmid construct with the micro-LCR, βsp/Aγ-, ψβ-, δ-, and β-globin genes showed no developmental switching and expressed both human γ- and β-globin mRNAs in erythroid cells throughout development. Mice containing control cosmids with the Aγ-globin gene promoter showed developmental switching and expressed Aγ-globin mRNA in yolk sac and fetal liver erythroid cells and β-globin mRNA in fetal liver and adult erythroid cells. Our results suggest that replacement of the γ-globin promoter with the β-spectrin promoter allows the expression of the β-globin gene. We conclude that the γ-globin promoter is necessary and sufficient to suppress the expression of the β-globin gene in yolk sac erythroid cells.