Abstract Congenital heart disease (CHD) remains the most common congenital malformation. Therefore, attaining a mechanistic understanding of cardiomyocyte formation is crucial for improving outcomes to structural heart disease. Post-translational modifications of histones act to regulate cardiac chromatin structure and hence, the temporal and spatial program of gene regulation during cardiac development. We have found that SMYD1, a cardiomyocyte essential histone methyltransferase interacts with the chromatin remodeling MLL4 class of Complex of Proteins ASsociated with Set1 (COMPASS) complex. SMYD1 has been shown to be essential for cardiac development and as we show here, causes CHD. Like SMYD1, two of the core components of the MLL4-COMPASS complex, KMT2D/MLL4 and KDM6a are essential for cardiac development and cause CHD. The goal of the current application is to test the central hypothesis that SMYD1 acts within the MLL4-COMPASS complex to clear histones at cardiac enhancers prior to gene activation. This will be achieved by: 1) 2) Determining the function of SMYD1 in the assembly and function of the cardiac MLL4- COMPASS complex and, 2) Establishing the requirement for KDM6a in MLL4- COMPASS activity. Collectively, these studies will provide a detailed mechanistic understanding of the tissue specific role for SMYD1 and MLL4-COMPASS complex in cardiac development and heart disease.

Congenital malformations, or structural birth defects, are now the leading cause of infant mortality in the US. Of the congenital malformations, congenital heart disease (CHD) is the most common. We have recently developed genetic and biochemical platforms that will enable a systems based approach to uncover the essential protein and protein complexes that in mammalian heart development and in parallel, a patient driven approach to understanding the function of these proteins in human homeostasis and disease.