Role of histone ubiquitination in neurodevelopment and disease

在皮质发育过程中，神经祖细胞（NPC）以确定的方式产生成熟的神经元亚型。 时间顺序NPC多能性的限制决定了六层皮层神经元的组成 皮质，并由NPC染色质的变化控制。皮质后代的异常产生是 具有自闭症特征的神经发育障碍的病理学。染色质重塑基因通常 因此，在自闭症谱系障碍（ASD）中发现，神经元表观遗传机制可能是 对皮质生成至关重要。跨染色质景观的组蛋白修饰的发育重塑 允许限制NPC多能性的转录回路的空间和时间调节。一个染色质 组蛋白H2 A赖氨酸119单泛素化（H2 AUb 1）是一种进化上保守的抑制性蛋白， Polycomb Group（PcG）蛋白的组蛋白修饰。我们最近发现人类的新优势 PcG蛋白ASXL 3（额外性梳样3）中的致病性变体作为 具有自闭症和智力残疾的综合征特征的神经发育障碍。ASXL 3显然发挥 在哺乳动物大脑功能中起着核心作用。我们提出实验来描绘ASXL 3的机制， 调节皮质生成。我们已经证明ASXL 3是Polycomb抑制蛋白的一个组成部分， 去泛素化酶复合物（PR-DUB），其去泛素化H2 AUb 1。致病性人类ASXL 3变体改变了 全基因组H2 AUb 1水平，并影响患者来源的细胞中的转录调控。我们已经证实 并在小鼠和人类神经祖细胞（NPC）中扩展了这一发现。虽然H2 AUb 1被描述为 三十多年前，它在转录调控和表观遗传抑制中的功能还不太好， 比其他组蛋白修饰更容易理解。我们假设ASXL 3依赖的去泛素化活性 在指定NPC转录程序中起着关键作用，这些程序有助于神经元的多样性。 皮层，最终，高级大脑功能我们将定义皮质发育机制调节 通过ASXL 3和H2 AUb 1：（目的1）使用现有的Asxl 3突变小鼠，（目的2）确定基因组范围内的 过量H2 AUb 1在NPC中的分布和皮质生成的表观基因组机制， （目的3）测试人中ASXL 3病理学和PR-DUB活性的保守性 神经发育的脑类器官模型。我们的实验策略将建立 皮质发育的基础，确定NPC中皮质神经发生的范例，并最终揭开 导致ASD病理的失调机制。

During cortical development, neural progenitor cells (NPCs) produce mature neuronal subtypes in a defined temporal order. Restriction of NPC multipotency determines the cortical neuron composition of the six-layer cortex and is governed by changes to NPC chromatin. Abnormal production of cortical progeny underlies the pathology of neurodevelopmental disorders with features of autism. Chromatin remodeling genes are often identified in autism spectrum disorder (ASD), therefore, neuronal epigenetic mechanisms are likely to be essential for corticogenesis. Developmental remodeling of histone modifications across the chromatin landscape permits spatial and temporal regulation of transcription circuitry that restricts NPC multipotency. One chromatin modification is histone H2A lysine 119 mono-ubiquitination (H2AUb1), an evolutionarily conserved repressive histone modification of the Polycomb group (PcG) proteins. We recently identified human de novo dominant pathogenic variants in the PcG protein ASXL3 (Additional sex comb-like 3) as the genetic basis of neurodevelopmental disorders with syndromic features of autism and intellectual disability. ASXL3 clearly plays a central role in mammalian brain function. We propose experiments to delineate mechanisms of ASXL3 regulation in corticogenesis. We have shown that ASXL3 is a component of the Polycomb repressive deubiquitinase complex (PR-DUB), which deubiqutinates H2AUb1. Pathogenic human ASXL3 variants alter the genome-wide H2AUb1 levels and affect transcriptional regulation in patient-derived cells. We have confirmed and extended this finding in mouse and human neural progenitor cells (NPCs). Although H2AUb1 was described more than three decades ago, its functions in transcriptional regulation and epigenetic repression are less well understood than other histone modifications. We hypothesize that ASXL3-dependent deubiquitination activity plays a critical role in specifying NPC transcriptional programs that contribute to the neuronal diversity of the cortex, and, ultimately, higher brain function. We will define the cortical developmental mechanisms regulated by ASXL3 and H2AUb1 by: (Aim 1) using an existing Asxl3 mutant mice, (Aim 2) determining the genome-wide distribution of excess H2AUb1 in NPCs and the epigenomic mechanisms of corticogenesis using genetically- engineered mice, and (Aim 3) testing the conservation of ASXL3 pathology and PR-DUB activity in human cerebral organoid models of neural development. Our experimental strategy will establish the epigenetic foundation of cortical development, identify paradigms for cortical neurogenesis in NPCs, and, ultimately, unveil the mechanisms of dysregulation that leads to ASD pathology.