Floating Harbor Syndrome as a paradigm for understanding the role of chromatin perturbation in human craniofacial disorders

 描述(申请人提供)：由于各种染色质重构体在人类早期发育中的重要性已经变得明显，为什么这些重构体的扰动会影响特定的发育过程，特别是头面部的发育，这一生物学解释仍然是一个谜。事实上，许多染色质重构体，包括Snf2相关的CREBBP激活蛋白(SRCAP)，与人类颅面部疾病有关。最近，SRCAP基因的截断突变被证明是一种被称为浮港综合征(FHS)的疾病的致病突变。有趣的是，FHS的许多症状可以用单个细胞群--神经脊的扰动来解释。神经脊是在胚胎发育的三到六周内从神经管的背部长出的一群暂时的微细胞，这使得在人类胚胎中研究这些细胞变得非常困难。为了解决这一问题，我们实验室建立了人类神经脊分化的体外模型，该模型与动物模型一起，可以有效地用于研究神经脊的生物学。然而，由于神经脊细胞对包括头面部结构在内的各种组织和器官的贡献，它们必须表现出显著的发育可塑性和迁移潜力，这需要仔细执行转录程序。事实上，神经脊细胞对即使是轻微的转录干扰也高度敏感，因为许多染色质重构体的突变在神经脊衍生的颅面结构的畸形中表现出来。众所周知，SRCAP在转录程序的精确调控中发挥着重要作用，作为 一种蛋白质复合体，通过在转录起始点和增强子上用组蛋白变体H_2A.Z取代规范的H_2A-H_2B组蛋白二聚体来促进活性转录。FHS导致头面部缺陷的细胞起源尚未确定，体外神经脊分化模型和高通量的非洲爪哇动物模型的结合使我们能够从多个水平研究这种疾病，从分子机制到细胞缺陷再到疾病状态。我们概述了SRCAP FHS截断，既有显示出与该综合征一致的颅面畸形的体内胚胎学模型，也有体外细胞模型。拟议的研究将利用这些模型来确定FHS的潜在分子、细胞和发育原因，从而提供潜在的治疗靶点。最终，我们的研究将有助于从生物学上解释为什么染色质重构体的扰动对头面部发育有如此显著的影响。

 DESCRIPTION (provided by applicant): As the importance of various chromatin remodelers during early human development has become apparent, the biological explanation of why perturbations of these remodelers impact particular developmental process- es, specifically craniofacial development, remains a mystery. In fact, a number of chromatin remodelers, in- cluding Snf2-related CREBBP activator protein (SRCAP), are associated with human craniofacial disorders. Truncation mutations in the SRCAP gene have recently been shown to be the causative mutations in a disor- der called Floating-Harbor syndrome (FHS). Intriguingly, the many symptoms of FHS could be explained by the perturbation of a single population of cells - the neural crest. The neural crest is a transient population of mi- gratory cells arising from the dorsal part of the neural tube during weeks three to six of embryogenesis, making it exceeding difficult to study these cells in a human embryo. To address this issue, our lab has established an in vitro model of human neural crest differentiation, which, together with animal models, can be effectively used to study the biology of the neural crest. However, because neural crest cells contribute to such diverse tissues and organs, including craniofacial structures, they must demonstrate remarkable developmental plasticity and migratory potential, which requires careful execution of transcriptional programs. Indeed, neural crest cells ap- pear highly sensitive to even modest transcriptional perturbations, as mutations in many chromatin remodelers manifest in malformations of neural crest-derived craniofacial structures. SRCAP is known to play a significant role in the precise regulation of transcriptional programs as a part of a protein complex that facilitates active transcription by replacing the canonical H2A-H2B histone dimer with histone variant H2A.Z at transcription start sites and enhancers. The cellular origin of FHS leading to craniofacial defects has not previously been established, and the combination of an in vitro neural crest differentiation model and a high-throughput Xenopus lelvels animal model allows us to study this disorder at multiple levels, from molecular mechanism to cellular defects to disease state. We have recapitulated SRCAP FHS truncations both an in vivo embryological model that displays craniofacial dysmorphology consistent with the syndrome, as well as an in vitro cellular model. Proposed research will take advantage of these models to identify the underlying molecular, cellular, and developmental causes of FHS, thus providing potential targets for treatment. Ultimately, our research will contribute to a biological explanation for why perturbations of chromatin remodelers have such a pronounced impact on craniofacial development.