Activity of LINE-1 as a promoter in adult rat hippocampus. (a–d) We examined the activity and specificity of the LINE-1–based promoter in adult rat hippocampus. EGFP-expressing lentivirus, under the control of the LINE-1–based promoter, was stereotactically microinjected into the dentate gyrus of adult rats and the population of GFP-positive cells (green) was analyzed by immunohistochemistry using an antibody to NeuroD1 (red, a). Comparisons of the LINE-GFP population (green) to TUJ1 staining (red, b), NeuN staining (red, c) and Sox2 staining (magenta, d) are also shown.