Project 3 - Tabin

项目总结（见说明）：分泌的蛋白质指导发育中的骨骼元素的起始、生长和模式化。印度刺猬（Ihh）就是一个重要的例子。像许多诱导信号一样，Ihh除了与靶细胞上的受体外，还与细胞外基质成分发生物理相互作用。这种细胞外相互作用可以隔离信号，影响组织中的形态发生体运动和/或介导配体-受体相互作用。Hedgehog蛋白先前已显示与硫酸肝素蛋白聚糖（HSPG）特异性相互作用。虽然这还没有直接探索，特别是Ihh，突变的两个基因参与HSPG链延长，Ext 1和Ext 2，导致骨骼发育不良称为外生糖和Ihh信号是受损的Ext 1突变体。为了直接说明HSPG相互作用对Ihh功能的重要性，我们将构建缺乏可结合HSPG的Cardin-Weintraub（C-W）结构域的Ihh等位基因。Ihh通过直接作用于增殖的软骨细胞，也通过包被膜间接作用于骨骼发育，包被膜是包裹骨骼生长原的扁平细胞的膜鞘。事实上，已知骨膜在调节下颌骨骨骼成分分化的许多方面发挥重要作用。我们最近发现了一系列标志物，表明这种组织的复杂程度令人惊讶。我们将构建转基因小鼠，其中cre重组酶被置于驱动不同软骨膜结构域表达的启动子的转录控制下。这些将被用来绘制软骨膜不同层细胞的命运图，并测试骨骼调节因子在该组织中的作用，包括Ihh和Hox基因。

PROJECT SUMMARY (See instructions): Secreted proteins direct the initiation, growth and patterning of the developing skeletal elements. Indian hedgehog (Ihh) is an important example of such a factor. Like many inductive signals, Ihh physically interacts with extracellular matrix components in addition to receptors on it's target cells. Such extracellular interactions can sequester the signals, influence morphogen movement across tissues and/or mediate ligand-receptor interactions. Hedgehog proteins have previously been shown to specifically interact with Heparin Sulfate Proteoglycans (HSPGs). While this has not been directly explored for Ihh in particular, mutations in two genes involved in HSPG chain elongation, Ext1 and Ext2, cause skeletal dysplasias known as exotoses and Ihh signaling is compromised in Ext1 mutants. To directly address the importance of HSPG interacting for Ihh function, we will construct an allelle of Ihh that lacks the puttaive HSPG-binding Cardin- Weintraub (C-W) domain. Ihh acts on skeletal development through direct effects on prolioferating chondrocytes, and also through indirect effects via the perchondrium a membrous sheath of flattened cells encapsulating the skeletal aniagen. Indeed, the perchondrium is known to play important roles in a number of aspects of regulating the differentiation of subjacent skeletal elements. We recently identified a series of markers indicating a surprising level of complexity in the organization of this tissue. We will construct transgenic mice in which cre-recombinase is placed under the transcriptional control of promoters driving expression in different perichondrial domains. These will be used to fate-map the cells in different layers of the perichondrium and to test the roles of skeletal regulators in this tissue, including Ihh and Hox genes.