A 5' control region of the human epsilon-globin gene is sufficient for embryonic specificity in transgenic mice

When introduced as part of DNA constructions containing the human beta-globin locus control region (LCR), the human embryonic beta-globin gene, epsilon, is expressed in primitive but not definitive erythroid cells of recipient transgenic mice. In contrast to this pattern, the human fetal beta-globin gene, gamma, has been shown to be expressed in both primitive and definitive erythroid cells of transgenic mice when introduced in similar LCR-containing constructions. To begin to identify the minimal sequence(s) necessary for the epsilon expression pattern, we have fused a DNA fragment that contains the human epsilon-globin gene promoter region, and 13.7-kilobase (kb) of contiguous upstream flanking sequence containing super-hypersensitive (HS) sites 5'HS-2 and 5'HS-1 of the globin LCR, to the structural portion and near 3'-flanking region of the human gamma-globin gene. This construction, and one containing an intact human gamma-globin gene with the same 3'-flanking sequence and 383 base pairs of 5'-flanking sequence linked to LCR DNA from -0.86 to -13.7 kb upstream of epsilon, were each microinjected to produce transgenic mice. While the construction containing the intact gamma-globin gene is transcriptionally active in primitive and definitive erythroid cells of the transgenic mice, the fusion construction, in which the gamma-globin gene promoter and promoter proximal region is essentially replaced by that of epsilon, is not active in definitive erythroid cells and expresses with the same pattern as an intact epsilon gene. These results indicate that the promoter and near 5'-flanking region of epsilon, when linked to the LCR, is sufficient for embryonic-specific expression in transgenic mice. The level of expression of the fusion construction in primitive erythroid cells of transgenic mice is similar to that previously observed for the intact epsilon gene when identically cloned. This suggests that the epsilon 5'-region of the fusion construction also contains all the sequence necessary for the LCR-dependent activation of epsilon in transgenic mice.