Fig. 5. Developmental expression profile of IM-lacZ-SB. Transgenic mice bearing IM-lacZ-SB (line 40 for A, B, C1 and C2; line 28 for D, E, F and G) were examined at gastrula (A, B, C1 and C2; C1 a frontal view, C2 a lateral view), E8.5 (D), E9.5 (E) and adult stages (F and G). Blue staining was first detected in emerging mesodermal cells during gastrulation (A is earliest, B is in the middle and C1, C2 are the latest) and continued in the blood islands (arrowheads in D) and in blood cells in yolk sac vessels (E). β-gal expression started in heart primordium at E8.5 (arrow in D). In adult mice, blood cells in the spleen are stained (F). In the adult heart, only the endocardium is stained, but myocardial staining is not observed (G). The scale bar corresponds to 100 µm (F) or 200 µm (G).