Roles of KAT8 complexes in governing histone acylation and mouse cerebral development

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Epigenetic regulation is a natural process fundamental to all eukaryotic organisms. We have taken a mouse genetic approach to understand three lysine (K) acetyltranferases (KATs) and their activators (JBC 2015A, 2015B; PLoS Genet 2015; JBC 2016; JCI 2016). The enzymes belong to the MYST family of acetyltransferases and acetylate two specific lysine residues of histone H3 in vivo. As an independent line of research, we have analyzed mammalian KAT8 (a.k.a. MOF), another member of the MYST family. It is an ortholog of fly Mof (males absent on the first), which is so named due to its crucial role in governing gene dosage compensation in male flies. Like fly Mof, mammalian KAT8 does not acetylate histone H3 but specifically targets histone H4 at lysine (K) 16 (H4K16). KAT8 is the major acetyltransferase acetylating this residue in vivo, so it has a distinct substrate specificity to confer H4K16 acetylation. This epigenetic mark is of fundamental importance from yeasts and plants to humans. An important question is what roles KAT8 has in animal and human development. Disruption of the mouse gene led to embryonic lethality at a very early stage, and conditional inactivation of the gene in Purkinje neurons of the mouse cerebellum causes ataxia. Little is known about the role of KAT8 in mammalian forebrain development. We have recently generated cerebrum-specific Kat8 knockout mice and found severe cerebral defects (to be submitted to Nat Genet). ******Hypothesis***We hypothesize that KAT8 regulates cerebral development through acylating histone H4K16. With this hypothesis, we will pursue 3 specific aims by combining molecular and genetic approaches.******Specific Aims***1) Elucidate how KAT8 catalyzes histone H4K16 propionylation. Our published data indicate that KAT8 is critical for histone H4K16 propionylation in vivo. To substantiate this, we will analyze H4K16 propionylation in vitro by KAT8 and its complexes. ******2) Investigate how KAT8 regulates mouse cerebral development. Using the Cre-LoxP system, we have generated cerebrum-specific knockouts. They display striking cerebral defects, starting at E12.5. To substantiate this, we will utilize an inducible Cre line to confer time-dependent cerebrum-specific inactivation to investigate the role of KAT8 at different stages of cerebral development.******3) Determine the role of MSL1 in mouse cerebral development. KAT8 is the catalytic subunit of two multisubunit complexes, but it is unclear how the non-catalytic subunits such as MSL1 contribute to the functions of KAT8 in vivo. We will perform inducible cerebrum-specific inactivation Msl1 to assess its role at different stages of cerebral development.******Significance***The program will address how KAT8 and its complexes regulate brain development. As histone H4 acetylation is conserved from yeasts, flies and plants to humans, the knowledge will shed light on natural processes in diverse organisms, thus contributing directly to the NSERC's mission in discovery and innovation.**