Disproportionate Dwarfism in the Mouse Mutant Rhizomelia

描述（由申请人提供）：脊椎动物骨骼是一个重要的解剖学系统，为能动的身体提供结构支撑，为重要的内脏器官提供保护，并为造血系统提供适宜的环境。这些骨结构发育的一系列过程被称为骨骼形态发生。骨骼形态发生的缺陷表现为骨软骨发育不良，这是一大组影响5000人中超过1人的身体状况障碍，并在近1%的围产期死亡中观察到。这些情况的严重程度从相对轻微到严重不等。较温和的条件可能会影响这些生活质量的问题，如身高，流动性，活动和性。中度疾病可能包括神经和骨科并发症。最严重的病例可导致围产期死亡。 本研究的目的是研究在携带rhizomelia（rzm）突变的小鼠中观察到的不成比例侏儒症的分子遗传学基础，rzm是一种新的转基因诱导突变，其导致中轴和无骨骨骼的骨骼生长异常，包括肱骨和股骨缩短、胸腔狭窄、尾巴缩短和颅面缺陷。这项建议的具体目标是集中在了解rzm表型的分子遗传基础。首先，将进行实验以确定rzm表型是否由功能获得（GoF）或功能丧失（LoF）机制引起。使用基于胚胎干（ES）细胞的方法，将构建跨越rzm基因座的缺失（δ）。在创建携带缺失的小鼠后，将使用遗传杂交将rzm反式放置到包含缺失（rzm/A）。评估所产生的表型应该允许一个区分GoF和LoF的假设。第二，将进行分子研究，以克隆基因组区域侧翼的转基因插入，并评估表达的候选基因和其他关键球员牵连骨骼形态。这项研究和后续研究的最终目标是使用这种独特的动物和转基因本身提供的分子标签作为进入协调骨骼发育的结构和调控基因网络的手段。

DESCRIPTION (provided by applicant): The vertebrate skeleton is an important anatomical system providing structural support for a motile body, protection for vital internal organs, and a hospitable environment for the hematopoetic system. The set of processes by which these bony structures develop is known as skeletal morphogenesis. Defects in skeletal morphogenesis are manifested as osteochondrodysplasias, a large group of statural disorders affecting more than 1 person in 5000 in the human population and observed in nearly one percent of perinatal deaths. These conditions range in seriousness from relatively mild to severe. The more mild conditions may affect such quality of life issues as stature, mobility, activity and sexuality. Moderate conditions may include neurological and orthopedic complications. The most severe cases can result in perinatal lethality. The purpose of this proposal is to study the molecular genetic basis of disproportionate dwarfism seen in mice carrying the rhizomelia (rzm) mutation, rzm is a novel, transgene-induced mutation that causes skeletal growth aberrations in both the axial and appendicular skeleton including shortened humeri and femora, narrowed thoracic cavity, shortened tail, and craniofacial defects. The specific aims of this proposal are focused at understanding the molecular genetic basis of the rzm phenotype. First, experiments will be performed to determine whether the rzm phenotype results from a gain-of-function (GoF) or loss-of-function (LoF) mechanism. Using an embryonic stem (ES) cell-based approach, a deletion (delta) will be constructed which spans the rzm locus. After creating deletion-bearing mice, genetic crosses will be used to place rzm in trans to the encompassing deletion (rzm/A). Assessment of the resulting phenotype should allow one to discriminate between the GoF and LoF hypotheses. Second, molecular studies will be performed to clone the genomic region flanking the transgene insertion and to assess the expression of linked candidate genes and other critical players implicated in skeletal morphogenesis. The ultimate goal of this and subsequent studies is to use this unique animal and the molecular tag provided by the transgene itself as a means of entry into the network of structural and regulatory genes that coordinate skeletal development.