Fig. 8. AV valve remodeling requires Gata4 expression in endocardium and its derivatives. Gata4^T2del/Ki (Gata4^Ki/flox; Tie2Cre⁺) embryos are deficient for Gata4-Fog interaction in the endocardium and its derivatives. (A-D) AV cushions were normally populated by mesenchymal cells at E12.5 (asterisks, C,D), indicating that the Gata4-Fog interaction is not essential for EMT. The liver (L) was normal in size and morphology. Boxed regions of A,B are enlarged in C,D. (E,F) A common atrioventricular canal (asterisk) was present in all Gata4^T2del/Ki embryos at E14.5, whereas in control embryos the AVC was septated by the fusion of the superior and inferior cushions. (G) Decreased proliferation of cushion mesenchyme in Gata4^T2del/Ki embryos. Proliferation was measured as the percentage of nuclei that stained positive for BrdU (red). Nuclei were stained with DAPI. Myocyctes were labeled with desmin (green). Three sections from three different E12.5 embryos were examined per group by a blinded observer (^*P<0.05).