Characteristics of Tbx18 in murine embryonic heart. Expression of Tbx18 was expressed in the epicardium (arrowheads) and was also detected in cardiomyocytes in the VS and the LV (white arrow) from E10.5 to E14.5. a1, b1, c1 and d1 are sections from the VS (200×); a2, b2, c2 and d2 are higher-magnification views (400×) of a1, b1, c1 and d1, respectively; a3, b3, c3 and d3 are sections from the LV (200×); a4, b4, c4 and d4 are sections from the RV (200×). d5-7 are higher-magnification views of the white square in d2-4, respectively; they highlight that most of Tbx18-expressing cells are cardiomyocytes, except for a few cells at E14.5 (blue arrow). VS, ventricular septum; LA/RA, left/right atrium; LV/RV, left/right ventricle.