Analysis of developmental switching in transgenic mice with 5' and 3' deletions in the human beta globin gene.

Our interest in the cis-acting elements that promote the up-regulation of the beta globin gene has led to a systematic deletion analysis of portions of the beta globin gene in the context of the HS2 and gamma globin gene using transgenic mice. In constructs that delete the 5' region to only 265 bp, high-level, erythroid-specific expression was observed. Further deletion to 122 bp, however, results in significantly reduced expression levels. A substitution of a minilocus control region for the single HS2 site was also produced, resulting in increased beta globin expression over that seen with the HS2 alone. These results are consistent with the presence of an enhancer-like element between -122 and -265. In addition, a construct in which the entire beta globin gene promoter was replaced by a thymidine kinase promoter was tested. Interestingly, no expression was detected in these transgenic mice. This may indicate the requirement for an erythroid-specific promoter to drive this gene. Finally, the 3' region of the beta globin gene was deleted in order to examine the effect of a previously defined 3' enhancer region. With deletion of this region, the expression of the human beta globin gene in transgenic mice is unchanged relative to the parental constructs.