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

表观遗传调控是所有真核生物的基本自然过程。我们采用小鼠遗传学方法来了解三种赖氨酸(K)乙酰转移酶（KATs）及其激活剂（JBC 2015A, 2015B; PLoS gene 2015; JBC 2016; JCI 2016）。这些酶属于MYST乙酰转移酶家族，并在体内乙酰化组蛋白H3的两个特异性赖氨酸残基。作为一个独立的研究方向，我们分析了哺乳动物KAT8（又名MOF）， MYST家族的另一个成员。它是果蝇Mof的同源物，因其在控制雄性果蝇的基因剂量补偿中起关键作用而得名。与蝇类一样，哺乳动物的KAT8并不乙酰化组蛋白H3，而是特异性靶向组蛋白H4的赖氨酸(K) 16 （H4K16）位点。在体内，KAT8是使该残基乙酰化的主要乙酰转移酶，因此它具有独特的底物特异性来赋予H4K16乙酰化。这种表观遗传标记从酵母和植物到人类都具有重要意义。一个重要的问题是KAT8在动物和人类的发展中起什么作用。小鼠基因的破坏导致胚胎早期死亡，小鼠小脑浦肯野神经元基因的条件失活导致共济失调。人们对KAT8在哺乳动物前脑发育中的作用知之甚少。我们最近培育了大脑特异性Kat8基因敲除小鼠，发现了严重的大脑缺陷（待提交给Nat Genet）。

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.