Fig. 3. Generation of Nkx2.5::Cre mice. (A,B) X-gal stained embryos showing staining in the linear heart tube (arrowhead) at E8.0 (A) and throughout the ventricular myocardium at E8.5 (B). (C,D) Nuclear Fast Red counterstained serial sections through the embryo in B. There are high levels of ß-gal staining throughout the ventricular myocardium and in a subset of endocardial cells. (E) X-gal stained E12.5 embryo showing efficient ventricular recombination and minimal recombination in the outflow tract (oft) and atria (a). lv, left ventricle; rv, right ventricle; la, left atria; ra, right atria.