Fig. 8. Lack of detectable transgene expression in cephalic mesenchyme by in situ hybridization with a human-specific Psen1 cRNA. Shown are horizontal sections through the telencephalon of an E12.5 nestin-Psen1 transgenic embryo from line 9 (A,B,D) or a non-transgenic littermate control (C,E) embryo hybridized with a human specific Psen1 probe. (A) A section through the anterior telencephalon. The lateral ventricle (LV) and interhemispheric fissure (IH) are indicated. There is prominent hybridization in the brain parenchyma. Hybridization in the ventricular zone from a transgenic (Tg) and non-transgenic (+/+) embryo is shown in B and C. The transgenic embryo is strongly hybridized. (D) Hybridization at the juncture between the brain parenchyma and the overlying cephalic mesenchyme in the interhemispheric fissure from a transgenic embryo. (E) A comparable region from a non-transgenic embryo (+/+) is shown to indicate the level of background staining. An arrow indicates the border between the brain parenchyma (showing hybridization product in D but not in E) and the cephalic mesenchyme. Scale bar: 20 µm for A; 50 µm for B-E.