Fig. 2. Morphological and histological defects induced by NICD1-activation. (A,B) Sections stained with Hematoxylin and Eosin show normal EMT in the AV cushion (brackets) and trabecular development in wild-type hearts (A), whereas the trabeculae are not formed normally in NICD1-activated hearts (B). Ectopic cell masses were also evident (arrowheads in B), the interventricular septum is right-shifted (arrow) and trabeculation occurs in the AV myocardium (asterisk in B) in NICD1-activated hearts. (C,D) Bmp10 expression was observed in the trabecular cells in both the wild-type (C) and NICD1-activated (D) ventricles. (E-J,O,P) Immunohistochemistry using anti-myosin (E,F,O), anti--smooth muscle actin (Sma) (G,H,P) and anti-Pecam (I,J) antibodies reveal that ectopic cell masses (arrowheads) are present in the cushion tissue in NICD1-activated hearts (F,H,J,O,P), but are never observed in wild-type hearts (E,G,I). (M,N) Hematoxylin and Eosin staining at E9.5 also shows ectopic cell masses in the cushion of NICD1-activated heart (arrowheads in N) but not in wild-type heart (M). (K,L) In wild-type myocardium (K), myofibrils with sarcomere structures (Z bands are indicated by black arrowheads) are observed by transmission electron microscopy, but only thin myofibrils without a proper sarcomere structure (no Z band indicated by while arrowheads) are formed in NICD1-activated hearts (L). Embryo samples were prepared at either E10.5 (A-L) or E9.5 (M-P). Serial sections were used for E,G,I (wild-type), F,H,J (NICD1-activated) and N-P (NICD1-activated). Abbreviations: LA, left atrium; RA, right atrium; LV, left ventricle; RA, right ventricle; Nu, nucleus. Scale bars: 200 µm in A-J,M-P; 1 µm in K,L.