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The heart is one of the first organs to develop in a vertebrate embryo. The intricate design of the asymmetric four-chambered organ is reflected in both its structures and mechanics. A healthy functional heart is an amalgamation of precisely aligned great vessels, continuous sheets of trilayered tissues that form the chamber walls and septum, a coordinated conduction system, and an uninterrupted supply of oxygenated blood from the coronary vasculature. At a cellular level, heart morphogenesis is a remarkable feat of tightly regulated cell proliferation, apoptosis, migration and differentiation. These events are driven by spatially and temporally coordinated gene expressions. Post-translational modifications of histone proteins such as acetylation and deacetylation are central to gene expression and repression. The genome site-specific activities of enzymes responsible for acetylation and/or deacetylation rely on protein domains that can recognize and bind to modified histone residues. These protein domains are present in either the histone modifying enzyme itself or adaptor proteins that are present within the histone modifying complex, known as histone ‘reader’ proteins. In this thesis, I have used knockout mice to investigate the roles of two histone reader proteins – ING4 and ING5, both present in histone acetyltransferase complexes in vivo, demonstrating the consequences of loss of these histone reader proteins in the patterning and structural development of the heart. In the first part of my thesis, I have demonstrated that loss of both Ing5 alleles alone did not incur any haematopoietic defects, unlike loss of the proposed histone acetyltransferase enzyme subunit present in the ING5 protein complex. Subsequently, I characterised the survival and appearances of mice with deletion of a combination of Ing4 and Ing5 alleles. I showed that ING4 and ING5 are functionally redundant, as mice died in mid-gestation in the absence of both proteins, whereas mice lacking o

The INhibitor of Growth (ING) family of tumor suppressors regulates the transcriptional state of chromatin by recruiting remodeling complexes to sites with histone H3 trimethylated at lysine 4 (H3K4me3). This modification is recognized by the plant homeodomain (PHD) present at the C-terminus of the five ING proteins. ING5 facilitates histone H3 acetylation by the HBO1 complex, and also H4 acetylation by the MOZ/MORF complex. We show that ING5 forms homodimers through its N-terminal domain, which folds independently into an elongated coiled-coil structure. The central region of ING5, which contains the nuclear localization sequence, is flexible and disordered, but it binds dsDNA with micromolar affinity. NMR analysis of the full-length protein reveals that the two PHD fingers of the dimer are chemically equivalent and independent of the rest of the molecule, and they bind H3K4me3 in the same way as the isolated PHD. We have observed that ING5 can form heterodimers with the highly homologous ING4, and that two of three primary tumor-associated mutants in the N-terminal domain strongly destabilize the coiled-coil structure. They also affect cell proliferation and cell cycle phase distribution, suggesting a driver role in cancer progression.