Fig. 5. Histological analysis of altered cardiac morphology in Tbx20 knockdown embryos at E9.5. (A,D,G,J) Wild-type embryos. (B,E,H,K) Tbx20 b12 knockdown; B,E and H,K correspond to two distinct embryos. (C,F,I,L) Tbx20 a6 knockdown. The outflow tract and right ventricle (ot/rv) are combined in b12 embryos. Epithelial to mesenchymal transformation (EMT) of both the outflow and AV cushions is impaired (arrowheads in F,K; see ot in C) compared with wild-type embryos (asterisks in G, arrowhead in J). (J) Higher magnification of the atrioventricular canal in wild type compared with a b12 knockdown (K) embryo, showing the lack of EMT in the b12 embryo (arrowhead). (L,M) Higher magnification of left ventricular wall of a6 (L) and wild-type (M) embryos, showing thinned ventricular wall in a6 (compare red brackets). a, atrium; lv, left ventricle; ot, outflow tract; rv, right ventricle.