A minimal ankyrin promoter linked to a human gamma-globin gene demonstrates erythroid specific copy number dependent expression with minimal positionor enhancer dependence in transgenic mice

In red blood cells ankyrin (ANK-1) provides the primary linkage between the erythrocyte membrane skeleton and the plasma membrane. We have previously demonstrated that a 2-71-bp 5'-flanking region of the ANK-1 gene has promot er activity in erythroid, but not non-erythroid, cell lines. To determine w hether the ankyrin promoter could direct erythroid-specific expression in v ivo, we analyzed transgenic mice containing the ankyrin promoter fused to t he human (A)gamma-globin gene. Sixteen of 17 lines expressed the transgene in erythroid cells indicating nearly position-independent expression. We al so observed a significant correlation between the level of Ank/(A)gamma-glo bin mRNA and transgene copy number. The level of Ank/(A)gamma mRNA averaged 11% of mouse alpha-globin mRNA per gene copy at all developmental stages. The addition of the HS2 enhancer from the beta-globin locus control region to the Ank/(A)gamma-globin transgene resulted in Ank/(A)gamma-globin mRNA e xpression in embryonic and fetal erythroid cells in six of eight lines but resulted in absent or dramatically reduced levels of Ank/(A)gamma-globin mR NA in adult erythroid cells in eight of eight transgenic lines. These data indicate that the minimal ankyrin promoter contains all sequences necessary and sufficient for erythroid-specific, copy number-dependent, position-ind ependent expression of the human (A)gamma-globin gene.