Myocardial phenotypes of the miR-143 morphants. (A) Phalloidin staining revealed thick actin bundles formed along the atrio-ventricular axis (blue arrowheads). (B–B′′′) In a magnified view, such bundles were pan-Cadherin-negative (blue arrowheads in B′), indicating that they were formed beyond the boundaries of cardiomyocytes. White dotted lines indicate the position of the bundles. (C to D′′′) In the miR-143 morphants, the thick longitudinal actin bundles were not formed. Rather, bundles were formed along the boundaries of cardiomyocytes, as visualized by pan-Cadherin (D′′) and DAPI staining (D′′′). Note the dot-like aggregation of the pan-Cadherin signals (D′′). (E and G) In both the WT and the miR-143 morphants, atrial phalloidin staining showed a similar mesh-like structure. (F) In the WT embryos, the amhc gene is expressed exclusively in the atrial myocardium. (H) In the miR-143 morphants, amhc is ectopically expressed in the atrium (red arrowheads). (I) Tissue stiffness of the ventricles and the atrium was measured separately by a microtensile tester. The ventricle of the WT heart was stiffer than the WT atrium (gray bars). In contrast, stiffness of the morphant ventricles decreased to the level of the WT atrium, and the morphant atrium was also affected, yet in a lesser extent (light gray bars).
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