Characteristics of Wt1 in murine embryonic heart. Expression of Wt1 was confined to the epicardium (arrowheads) from E10.5 to E11.5 and was also detected within the heart from E12.5 to E14.5 (arrow). 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, and c3, d3 are sections from the LV (200×). a3, b3, and c4, d4 are sections from the RV (200×). c5,6 and d5,6 are higher-magnification views of the white squares in c3,4 and d3,4 respectively; they highlight that some Wt1-expressing cells are located within the heart but are not cardiomyocytes. Blue, DAPI staining of nuclei.