Effects of Thyroxine on the Craniosynostotic Phenotype

描述（由申请人提供）：颅缝闭合（CS）是颅骨的一个或多个纤维关节过早融合，通常允许扩张的神经颅骨生长。在美国，CS的发病率是每2500个活产婴儿中有一个。CS的病因是多因素的，对于大多数临床病例来说，是遗传的还是环境的往往是未知的。一般基因-环境模型认为，如果一种遗传易感性与某种环境暴露相结合，其影响可能是加性的，甚至是倍增性的，从而导致严重异常的表型。遗传变异和环境暴露之间的相互作用已经研究了几种颅面异常，包括口面裂。然而，目前，关于基因-环境相互作用在调节CS表型中的作用知之甚少。疾病控制中心国家出生缺陷预防研究已经确定了几个与CS相关的环境因素，包括甲状腺激素的循环水平。虽然这些药物在流行病学上与CS有关，但其机制尚不清楚。我们建议在具有已知突变的CS小鼠模型中探索这些外源因子的细胞，分子和形态学影响。Twist-1靶向突变小鼠与对照C57BL小鼠杂交时产生类似于Saethre- Chotzen CS综合征的表型。与人类的情况类似，性状表达是高度可变的，这使得它对如何修改因素建模很有用

DESCRIPTION (provided by applicant): Craniosynostosis (CS) is the premature fusion of one or more of the fibrous joints of the skull, which normally allow for the growth of the expanding neurocranium. In the United States, the incidence of CS is one in every 2500 live births. The etiology of CS is multifactorial, and whether genetic or environmental is often unknown for the majority of clinical cases. The general gene-environment model proposes that if a genetic predisposition is coupled with certain environmental exposures, the effects can be additive or even multiplicative, resulting in severely abnormal phenotypes. The interaction between genetic variants and environmental exposures has been studied for several craniofacial anomalies, including orofacial clefting. However, at present, very little is known about the role of gene-environment interactions in modulating CS phenotypes. The Centers for Disease Control National Birth Defects Prevention Study has identified several environmental factors associated with CS, including circulating levels of thyroid hormone. Although these agents have been epidemiologically associated with CS, the mechanism is not understood. We propose to explore the cell, molecular, and morphological effects of these exogenous factors in a CS mouse model with a known mutation. The Twist-1 targeted mutation mouse when bred with control C57BL mice produces a phenotype similar to Saethre- Chotzen CS syndrome. Similar to the human condition, trait expression is highly variable, making it useful for modeling how modifying factors might relate to the range of CS phenotypes. Because of the range of expression in timing and severity of CS, we can specifically study the effects of the insults on cellular morphology, molecular expression, presence of certain active proteins in the tissues, and development of the organism. In Aim #1 we propose to determine the downstream effects of teratogenic challenges to cell morphology, protein, epigenetic and molecular expression in the Twist-1 CS mouse model primary cells. Specifically, we will subject cells to traditional liquid-phase stimulation wih thyroxine and various markers of osteogenesis will be evaluated for expression via q-PCR. In addition, genome wide microarrays will be analyzed for targets downstream of TWIST and for pathways linked to aberrant bone formation or CS under these conditions. In Aim #2 we propose to determine the in-vivo morphological effects of in utero exposure to thyroxine in the Twist-1 model. Outcome measures will be assessed by a combination of 3D imaging for bone and suture microarchitecture, craniofacial morphometrics, immunohistochemistry, suture histomorphometry and whole mount calvaria analysis. By determination of the specific pathway of teratogenic action upon the gene, the proposed studies will provide a better understanding of the genetic-epigenetic-environment interaction for CS and aid in the diagnosis and management of craniofacial anomalies. This paradigm can then be applied to other teratogens with known interaction with CS, e.g. selective serotonin reuptake inhibitors, hypoxia, or ovulation stimulatin drugs.