T cell–specific cis-acting elements in enhancer D. (A) Areas of sequence conservation (D1-D7) within the 1.7-kb enhancer D are shown as rectangles. Horizontal lines below the D region depict the two 500-bp DI and DIII subregions used in transgenic reporters. (B) Comparison of reporter expression between the B-p-GFP-DI, B-p-GFP-DIII, B-p-GFP, and B-p-GFP-D founder lines. The reporter constructs used to generate these founder lines are depicted on the left. The number of GFP-expressing founders is displayed over the total number of founders generated. The statistical significance of the difference (increase or decrease) in the proportion of GFP-expressing founder compared with the parental B-p-GFP line (a) or B-p-GFP-D (b) was provided by χ² analysis and is shown as a P value. The percentage of GFP-positive PBLs is depicted for each founder line (circle). The average percentage of GFP⁺ PBLs for each transgenic reporter was calculated for either all GFP-expressing founders (black bar) or all founders (gray bar). The cell type specificity of each reporter is depicted on the right. (C) The MFI of GFP⁺ PBLs from B-p-GFP-D, B-p-GFP-D-I, and B-p-GFP-D-III transgenic lines was calculated for each founder (gray diamonds). Gray lines indicate the average MFI among all founders, and black lines denote the average MFI among the GFP-expressing founders. (D) Lineage-specific GFP expression in the PBLs from B-p-GFP-D, B-p-GFP-DI, and B-p-GFP-DIII founders. The average percentage of GFP⁺ cells within peripheral blood B cells (B), T cells (T), and myeloid cells (My) is shown. The significance in the difference of expression among GFP reporters was assessed by Student t test; *P < 5 × 10⁻²; **P < 5 × 10⁻³. Error bars (standard deviation) indicate variegation of GFP expression among the different founder lines made by each enhancer-based reporter.