Origins of Brain Somatic Mosaicism in Developmental Brain Disease

摘要 脑体细胞嵌合现象（BSM）是指脑中数十亿个细胞中任何一个细胞内突变的积累， 人类大脑，从胚胎发育到成年都可能发生。范围、影响和 BSM对脑部疾病的作用机制仍知之甚少。Brain Somatic的前期工作 PI服务的马赛克网络（BSMN）在马赛克的可靠性方面取得了重大突破 检测，但也提出了新的问题，包括BSM存在于健康大脑中的程度， BSM突变解释疾病的机制。 局灶性皮质发育不良（FCD）与实质性神经精神障碍相关，是神经精神障碍的主要原因。 儿童期顽固性癫痫的最常见原因。15 - 59%的患者有神经精神病学特征， 患者5 - 7，并且神经病理学上显示神经发生、迁移、分化被破坏，并且改变 神经兴奋性我们和其他人先前在少数人中发现了mTOR通路中的嵌合突变。 FCD的案件，但大多数案件仍然没有解决，缺乏基本的机制。 我们假设：1] FCD突变的模式与中性体细胞突变相似， 分布，由发育过程决定，但在功能效果上有所不同。2]BSM模式，等位基因 细胞之间的等位基因共享和片段（AF）可以重建细胞谱系和迁移历史。三、 对FCD切除组织的研究可以揭示疾病的新原因，如果存在于 每个细胞4]小鼠BSM模型可以解开复杂嵌合突变的中断信号网络。 我们的初步数据显示：1]从死后对照尸体，我们验证了259个体细胞 使用300X基因组测序的变体，并开始使用这些变体作为“条形码”来重建 血统历史2]314例FCD患者脑切除术的深度测序确定了12个新候选者 基因，突出信号传导和突触功能障碍，以及一种新的“两击”疾病机制。3]我们 建立子宫内小鼠电穿孔模型以评估推定的FCD变体作为功能的获得或丧失， 并评估"单次打击"和"两次打击"突变的影响。 我们提出了三个目标：1]从对照尸体，我们将重建细胞谱系跨解剖 使用BSM作为条形码的域。2]有了这些血统信息，我们将研究BSM的起源 通过招募新患者，进行靶向和无偏测序， 找出新的原因。3]我们将在动物模型中对假定的有害等位基因进行功能验证， "一击"和"两击"的原因。目标是实现对 BSM在控制个体中的程度，重建神经谱系并确定新的机制， 发育性脑疾病

Abstract Brain somatic mosaicism (BSM) refers to the accumulation of mutations within any of the billions of cells in the human brain, which can occur from embryogenesis through adulthood. The extent, impact and mechanisms of BSM on brain disease remain poorly understood. Prior work from the Brain Somatic Mosaicism Network (BSMN), on which the PI served, made critical breakthroughs in reliability of mosaicism detection, but also raised new questions, including the degree to which BSM exists in the healthy brain, and the mechanisms by which BSM mutations explain disease. Focal cortical dysplasia (FCD) is associated with substantial neuropsychiatric disability, and is the most common cause of intractable epilepsy in childhood. Neuropsychiatric features are seen in 15-59% of patients 5-7, and neuropathologically shows disrupted neurogenesis, migration, differentiation, and altered neural excitability. We and others previously identified mosaic mutations in the mTOR pathway in a minority of FCD cases, but most cases remain unsolved, and fundamental mechanisms are lacking. We hypothesize that: 1] FCD mutations are similar to neutral somatic mutations in their patterns and distributions, dictated by developmental processes, but differ in their functional effect. 2] BSM patterns, allelic fractions (AFs) and allele sharing between cells can reconstruct cellular lineages and migratory histories. 3] Study of FCD resected tissue can uncover novel causes of disease that would not be tolerated if present in every cell. 4] BSM modeling in mouse can unravel disrupted signaling networks of complex mosaic mutations. Our preliminary data shows: 1] From a post-mortem control cadaver, we validated 259 somatic variants using 300X genome sequencing, and started to use these variants as ‘barcodes’ to reconstruct lineage histories. 2] Deep sequencing from 314 FCD patient brain resections identified 12 new candidate genes, highlighting signaling and synaptic dysfunction, and a novel ‘two-hit’ disease mechanisms. 3] We established in utero mouse electroporation models to assess putative FCD variants as gain or loss of function, and to assess effects of ‘single-hit’ and ‘two-hit’ mutations. We propose three aims: 1] From control cadavers, we will reconstruct cell lineage across anatomical domains using BSM as barcodes. 2] With this lineage information, we will study the origins of BSM mutations in FCD, by recruiting new patients, performing both targeted and unbiased sequencing, and identifying novel causes. 3] We will functionally validate putative deleterious alleles in animal models for both ‘single-hit’ and ‘two-hit’ causes. The goal is to achieve a mechanistic understanding of the extent of BSM in control individuals, to reconstruct neural lineages and to identify novel mechanisms in developmental brain disease.