The GdC region is required for Gata1 gene activation in the hematopoietic system. (A) Structure of the intact Gata1 BAC, endogenous Gata1 locus, and a series of modified BAC reporters. The 3 regulatory elements are shown as black (G1HE), gray (dbG), and white rectangles (CACCC). The horizontal arrows depict the 3.7-kb GdC-region and the 659-bp minigene. The number of GFP-positive transgenic lines among the total transgenic lines (GFP/Tg) is indicated. (B) GFP histograms of whole bone marrow cells from G1B-GFP mouse (line 392; 2 copies) showed 25.4% of GFP-positive cells. GFP-positive cell population is significantly diminished (0.3%) in the ΔGdC-GFP mice (line 32; 2 copies), whereas the GFP-positive cell population is restored to a normal level (23.6%) in the MG-GFP mice (line 19; 2 copies). (C) Fluorescence images of E14.5 whole embryos. ΔGdC-GFP embryos rarely show GFP fluorescence, whereas the GFP fluorescence is recovered in the MG-GFP embryos (line 19; 2 copies), as observed in the G1B-GFP embryo (line 392; 2 copies).