Causal biology of Chd8 haploinsufficiency in complex brain disorders

摘要 在绘制神经发育障碍（NDD）的遗传原因方面取得了重大进展。在 自闭症谱系障碍 (ASD) 和智力障碍 (ID)，聚合网络的从头突变 编码染色质重塑因子（CRF）的基因已成为最强的组成部分之一 遗传风险。该领域目前面临的一个主要挑战是确定基因组机制并 与 NDD 相关 CRF 突变相关的神经发育后果。 CRF基因 在 ASD 和 ID 队列中观察到，CHD8 的从头功能丧失突变率最高。 精神分裂症和强迫症病例中也描述了突变，以及 CHD8 突变 携带者也经常被诊断患有巨头畸形。我们的工作和其他人的工作已经证实 小鼠 Chd8 种系杂合突变导致 NDD 相关病理变化 基因组、神经解剖学和行为领域。网络分析具有 CHD8 的链接功能和 发育中大脑中其他与 NDD 相关的 CRF，提高了理解 CHD8- 神经发育过程中相关的病理机制将揭示普遍的因果路径 由 CRF 单倍体不足介导。然而，CHD8 与早期大脑发育中的作用无关， 以及其他 NDD 相关 CRF，在神经元中表达，突变可能驱动行为病理学 通过产后大脑中神经元的特异性影响。因此，解决发育与神经元的因果关系是 对于理解 NDD 的 CRF 相关机制至关重要。我们将利用有条件的 Chd8 /- 小鼠模型在体内剖析 Chd8 突变导致 NDD 相关的机制 病理学。我们的初步数据表明，大头畸形和认知缺陷是相互依赖的 Chd8 /- 小鼠早期大脑发育过程中的病理学，以及相关的分子机制 Chd8 介导的染色质相关 RNA 加工。我们将应用互补组学、细胞 检测和小鼠研究来测试这个模型，具体来说，我们将：1）建立机制 Chd8 单倍体不足影响胚胎大脑中的染色质和转录，2) 表征细胞类型 Chd8 单倍体不足对大脑发育过程中神经发生的具体影响，以及 3) 定义 Chd8 单倍体不足引起的行为、脑电图和突触病理学，并测试是否存在此类病理学 是通过发育机制与神经元机制驱动的。这项研究将绘制 Chd8 的作用图谱 体内单倍体不足，阐明了 CHD8 剂量敏感性导致 NDD 的机制 病理学以及将分子和细胞机制与行为和系统水平联系起来。重要的是，这些 关键研究不能使用体外模型进行，此类对 NDD 风险基因的高度关注的研究是 对于连接遗传关联和机制理解来说是必要的。通过揭示最高风险的因果关系 基因，如 CHD8，我们将确定致病因素并确定新的治疗方法，以改善 NDD 的护理。

SUMMARY Major gains have been in made in mapping the genetic causes of neurodevelopmental disorders (NDDs). In autism spectrum disorder (ASD) and intellectual disability (ID), de novo mutations to a convergent network of genes encoding chromatin remodeling factors (CRFs) has emerged as one of the strongest components of genetic risk. A major challenge now facing the field is identifying the genomic mechanisms and neurodevelopmental consequences associated with mutations of NDD-associated CRFs. The CRF gene CHD8 has among the highest rates of de novo loss-of-function mutations observed in ASD and ID cohorts with mutations also described in schizophrenia and obsessive compulsive disorder cases, and CHD8 mutation carriers frequently also are diagnosed with macrocephaly. Our work and the work of others have confirmed that Chd8 germline heterozygous mutation in mice causes NDD-relevant pathological changes across genomic, neuroanatomical, and behavioral domains. Network analyses have linked functionality of CHD8 and other NDD-associated CRFs in the developing brain, raising the possibility that understanding CHD8- associated pathological mechanisms during neurodevelopment will reveal generalizable causal pathways mediated by CRF haploinsufficiency. However, independent of a role in early brain development, CHD8, as well as other NDD-associated CRFs, are expressed in neurons and mutation may drive behavioral pathology via neuron-specific impacts in postnatal brain. Thus, resolving developmental versus neuronal causality is essential for understanding CRF-associated mechanisms of NDDs. We will leverage conditional Chd8+/- mice model to dissect in vivo the mechanisms by which Chd8 mutations cause NDD-associated pathology. Our preliminary data suggests that macrocephaly and cognitive deficits are interdependent on pathology during early brain development in Chd8+/- mice, and that the molecular mechanisms are associated with chromatin-associated RNA processing mediated by Chd8. We will apply complementary -omics, cellular assays, and mouse studies to test this model, specifically, we will: 1) establish the mechanisms through which Chd8 haploinsufficiency impacts chromatin and transcription in embryonic brain, 2) characterize cell-type specific impacts of Chd8 haploinsufficiency on neurogenesis during brain development, and 3) define behavioral, EEG, and synaptic pathology caused by Chd8 haploinsufficiency and test whether such pathology is driven via developmental versus neuronal mechanism. This research will map the effect of Chd8 haploinsufficiency in vivo, illuminating mechanisms via which CHD8 dosage-sensitivity contributes to NDD pathology and linking molecular and cellular mechanisms to behavioral and systems level. Importantly, these critical studies cannot be done using in vitro models and such studies of high interest NDD risk genes is necessary to bridge genetic association and mechanistic understanding. By revealing causality for top risk genes such as CHD8, we will establish causal factors and identify novel treatments to improve care of NDDs.