Figure 3. Heart valve leaflets in Sox9^flox/flox;Col2a1-cre mice are abnormal with reduced Alcian blue staining.

Col2a1-cre recombination (A) is observed in a subset of cells on the atrial (A) and ventricular (V) surfaces of the valve leaflets at E18.5 in Col2a1-cre mice bred with Rosa26R. (B) At this time, Sox9 expression is detected by in situ hybridization throughout the valve leaflet structures (arrows). (C) Compared to Sox9^flox/+;Col2a1-cre control mice, nuclear Sox9 protein expression is diminished on the ventricular aspect of valve leaflets of Sox9^flox/flox;Col2a1-cre mice (arrow) (D), although expression remains on the atrial surface where recombination has not taken place (arrowhead). Heart valve leaflets of Sox9^flox/flox;Col2a1-cre mice (F) are abnormal at E18.5 and Alcian blue staining is reduced compared to Sox9^flox/+;Col2a1-cre control mice (E). IVS, interventricular septum; mv, mitral valve; tv, tricuspid valve.