Erythroid-specific expression of human beta-globin genes in transgenic mice

Transgenic mice carrying human beta-globin genes were produced by microinjecting linear DNA molecules containing cloned beta-globin genes with up to 4300 bp of 5'-flanking sequence and 1700 bp of 3'-flanking sequence. Most (15 of 20) of these transgenic mice expressed the human beta-globin genes in blood cells and the level of expression in some mice was comparable with that obtained from endogenous beta-globin genes. Human beta-globin gene expression appeared to be restricted to cells of the erythroid lineage and was first detected between 11 and 14 days of development, in parallel with mouse beta-globin. Constructs with as little as 48 bp of 5'-flanking sequence also appeared to be expressed appropriately. The mRNA transcripts had correct 5' ends and directed human beta-globin synthesis in reticulocyte lysates. Human beta-globin protein was detectable in mature erythrocytes from progeny of one of these mice. The frequency and extent of expression was severely depressed when the procaryotic vector DNA was not removed prior to microinjection.