Reporter gene expression driven by mHS−25/6 in transgenic mice. (A) Diagram of the reporter gene expression vector 5′3′LacZ to which a DNA fragment encompassing mHS−25/6 was attached. 5′3′LacZ consists of a genomic fragment that includes 2.3 kb of sequence upstream of the hematopoietic-specific IE promoter, IE (gray box), and 6 Gata1 exons (black boxes) and intervening introns. mHS+3.5 within the first intron is shown (red box). β-Galactosidase gene is fused in frame with the initiator ATG of the Gata1 gene. (B) Percentage of β-galactosidase expressing (%FDG+ve) TER-119⁺ erythroid cells (left) and CD61⁺Mac1⁻ megakaryocytes (right) in F0 transgenic fetal livers (FL), F0 transgenic bone marrow (BM), and bone marrow for lines of mice heterozygous for the transgene (Het BM; black dots). Gray dots show percentage of FDG-positive cells in nontransgenic controls. (C) Representative FACS plots of FDG staining, demonstrating β-galactosidase expression, in erythroid populations from E14.5 transgenic F0 fetal liver (FL), transgenic F0 bone marrow (BM), and bone marrow for lines of mice heterozygous for the transgene (Het BM; black histogram). The gray histogram is from nontransgenic controls.