Expression of epicardial cell marker Wt1 in murine embryonic heart. Expression of Wt1 was confined to the epicardium (arrowheads) from E10.5 to E11.5 (a, b), but was detected within the heart (arrow) from E12.5 to E14.5 (c, d). a1, b1, c1, and d1 are sections from the VS (200×); c2 and d2 are higher-magnification views (400×) of c1 and d1, respectively. a2, b2, c3, and d3 are sections from the LV (200×). a3, b3, c4, and d4 are sections from the RV (200×); c5 and c6 are higher-magnification views (400×) of the areas within the white squares in c3 and c4, respectively. d5 and d6 are higher-magnification views (400×) of the areas within the white squares in d3 and d4, respectively. VS, ventricular septum; LA/RA, left/right atrium; LV/RV, left/right ventricle. Blue, DAPI staining of nuclei.