Morphogenetic Aspects of Mitral Valve Development

The mitral and tricuspid valves develop at the junction between the atria and ventricles from primordia known as endocardial cushions. These endocardial cushions remodel throughout foetal life and into the neonatal period to form the sculpted leaflets and support apparatus that are seen in the mature healthy valve. Although the early steps and molecular pathways involved in the early stages of mitral valve formation are fairly well understood, key gaps remain, particularly relating to remodelling of the valve leaflets from their endocardial cushion precursors. Whereas the majority of the early processes involved in mitral valve development are thought to be very similar to that for the tricuspid valve, subtle differences in embryonic cell lineage contributions, gene expression, and exposure to different haemodynamic forces may influence their differential maturation and the disorders they incur. In this chapter we focus on the molecular genetic factors that influence atrioventricular valve development, highlighting reported differences between the mitral and tricuspid valves that may account for their differential development, physiology, and function. By necessity, the majority of this experimental information comes from experiments in the mouse, and occasionally the chicken. However, the close similarity in cardiovascular development between these organisms and ourselves means that as we begin to analyse human embryos, we are finding that the same genes and processes are involved in all these higher vertebrates.