Fig. 9

Inhibition of fetal compact myocardial expansion results in prominent trabeculae and thin compacted layer of postnatal heart. a Schematic figure showing generation of Yap1 gene deletion in Hey2⁺ cells by tamoxifen injection at embryonic stage. b Immunostaining for YAP1 and TNNI3 on postnatal day 7 (P7) control and mutant heart sections. Although YAP1 is detected in the inner myocardial wall (IMW) of both control and mutant hearts, YAP1 is reduced in the outer myocardial wall (OMW) of mutant heart compared with that in the control heart. c Hematoxylin and eosin (H&E) staining of heart sections from P7 control (left) and mutant (right) mice. Inserts indicate whole-mount images of hearts. d Immunostaining for TNNI3 and pHH3 or EdU on control and mutant heart sections. Yellow arrowheads indicate proliferating cardiomyocytes in the magnified inserts. e Quantification on the percentage of pHH3⁺ or EdU⁺ cardiomyocytes is shown on the right panel. f Echocardiographic analysis of heart function showed a significant reduction of ejection fraction and fractional shortening in the mutant, compared with the control. *P < 0.05; n = 4 for mutant and n = 5 for control. g Cartoon image showing hybrid myocardial zone in the postnatal heart derived from trabecular layer and compact myocardium. The hybrid zone (yellow) is interposed between the inner myocardial wall (blue) produced mainly by trabecular coalescence and the outer myocardial wall (red) produced by compact myocardial expansion. RV right ventricle, LV left ventricle, VS ventricular septum; Pa. papillary muscle. Scale bars, 1 mm (black or yellow); 100 µm (white)