Molecular markers of cardiac endocardial cushion development.

Endocardial cushions are precursors of mature heart valves. They form within the looped heart tube as discrete swellings and develop into thin, pliable leaflets that prevent regurgitation of blood. The embryonic origins of cardiac valves include endothelial, myocardial, and neural crest cells. Recently, an increasing number of animal models derived from mutational screens, gene inactivation, and transgenic studies have identified specific molecules required for normal development of the cardiac valves, and critical molecular pathways are beginning to emerge. To further this process, we have sought to assemble a diverse set of molecular markers encompassing all stages of cardiac valve development. Here, we provide a detailed comparative gene expression analysis of thirteen endocardial cushion markers. We identify endocardial cushion expression of the transcription factor Fog1, and we demonstrate active Wnt/beta-catenin signaling in developing endocardial cushions suggesting pathways that have not been previously appreciated to participate in cardiac valve formation.