Deciphering the role of the MOF complex and H4K16ac in the regulation of neuronal enhancers

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Histone proteins package DNA into a compact DNA-protein structure termed chromatin. Accessibility of compacted DNA for transcription is regulated by enzymatic complexes that add covalent modifications like acetyl and methyl groups to histones. Covalent modifications on the histones including acetylation play essential roles in many aspects of cellular function, including normal development of complex organs including the brain. Genes encoding histone-modifying protein complexes are frequently mutated in developmental disorders. Severe neurodevelopmental disorders are most commonly caused by new mutations in genes important for normal development of the central nervous system, with a wide range of phenotypes such as global developmental delay, severe intellectual disability and autism. It is estimated that about 1 in 220 children in the UK have severe neurodevelopmental impairments as a result of new mutations. Clear and early diagnosis and a better understanding of disease mechanism will improve the stratification of neurodevelopmental disorder patients for personalized therapy and support. Genes encoding epigenetic modifiers are frequently mutated in patients with developmental disorders. Male specific lethal 3 (MSL3) gene encoding a component of histone acetyltransferase complex (MSL/MOF) is mutated in a neurodevelopmental disorder called MSL3 syndrome. The MSL/MOF protein complex is responsible for acetylation of histone H4 at lysine 16 (H4K16ac), which is known to increase gene expression. However, a specific role of MSL/MOF complex in the development of the nervous system and how mutations in MSL3 contribute to a specific neurodevelopmental phenotype is not known.Only about 42% of patients with severe developmental disorders have detectable mutations that affect the protein coding regions of genes. Sequence variants found in non-coding distal regulatory elements called enhancers points contribution of enhancer dysfunction in developmental disorders. Enhancers are scattered around 98% of the genome that is non-coding and can regulate genes from large distances, hence it is challenging to delineate disease mechanism due to sequence variation in the enhancer DNA. Genome-wide profiling of acetylation of histone H3 at lysine 27 (H3K27ac) is widely method to identify active enhancers in the genome. We have previously discovered a new class of active enhancers based on the presence of H4K16ac that lack H3K27ac. In this project, we will identify genes and enhancers regulated by MOF and H4K16ac, then compare the activity of enhancers identified based on histone acetylation. Furthermore, we will investigate the mechanism through which histone acetyltransferase complex function to regulate gene expression. We will also investigate how mutations in genes encoding proteins in histone acetylation pathway leads to a specific neuronal phenotype. Finally, we will test if we can rescue altered cellular and gene expression phenotype by treating with drugs that increases histone acetylation levels.Overall, we will use state-of-the-art functional genomics and genome editing methods to comprehensively understand the mechanism through which MSL/MOF and H4K16ac regulate genes. Importantly, this work will provide important insights into the disease mechanism which results from mutations that leads to altered level of histone acetylation. This work will improve our understanding of the mechanisms through which mutations in MSL3 and enhancers contribute to neurodevelopmental disorders and, in addition, provide afunctional criterion on which to stratify patients for therapeutic intervention.