Elucidating the Relationship Between Notch and WNT Signaling in Bone Formation

描述（由申请人提供）：在胚胎发生过程中，Notch/RBPjk 和 Wnt/2-catenin 信号通路调节不同的细胞命运决定。成骨细胞是负责产生骨基质的主要细胞类型，不仅对于骨骼发育而且对于骨重塑和体内平衡都是必需的。成骨细胞分化缺陷会导致骨质疏松症，这是一种以骨量显着减少为特征的疾病。在成骨细胞发育过程中，Notch/RBPjk 信号通过抑制成骨细胞分化来维持骨髓间充质祖细胞。相反，Wnt/2-连环蛋白信号传导促进成骨细胞分化。这两种途径的不同作用是显而易见的，Notch 抑制分化，而 Wnt 促进分化。然而，Notch 抑制成骨细胞发育的确切阶段尚未确定，尽管我们的初步研究表明 Notch 可能阻碍 Runx2 阳性细胞的进一步进展。此外，成骨细胞分化过程中Wnt和Notch通路之间的遗传关系尚不清楚。因此，本提案的目的是检验以下假设：Notch 抑制 Runx2 阳性细胞的进一步分化，并且 Notch 至少部分通过抑制 Wnt/-连环蛋白信号传导发挥作用。为了检验这个假设，我制定了两个具体目标。目标 1. 确定成骨细胞分化过程中 Runx2 阳性细胞中 Notch/RBPjk 信号传导的作用 我将使用新型小鼠品系以强力霉素诱导的方式删除 Runx2 阳性细胞中的 RBPjk，并评估潜在的骨表型。这项研究将提供有关 Notch/RBPjk 信号传导对成骨细胞分化的阶段特异性调节的遗传证据。目标 2. 评估成骨细胞发育过程中 RBPjk 和 -catenin 之间的遗传关系 我将检查 -catenin 去除（单个或两个等位基因）对间充质祖细胞中 RBPjk 缺失引起的高骨量表型的影响。本研究将检验以下假设：Notch/RBPjk 在成骨细胞分化过程中在 Wnt/-连环蛋白信号传导上游发挥遗传作用。 总体而言，这些研究将增强目前对Notch抑制成骨细胞分化的认识，并阐明成骨细胞发育过程中两个相反信号Notch和Wnt之间的功能关系。

DESCRIPTION (provided by applicant): During embryogenesis, the Notch/RBPjk and Wnt/2-catenin signaling pathways regulate diverse cell fate decisions. Osteoblasts are the primary cell type responsible for producing bone matrix and are necessary not only for bone development but also bone remodeling and homeostasis. Deficiency in osteoblast differentiation results in osteoporosis, a disease characterized by significant decreases in bone mass. During osteoblast development, Notch/RBPjk signaling maintains bone marrow mesenchymal progenitors by suppressing osteoblast differentiation. Conversely, Wnt/2-catenin signaling promotes osteoblast differentiation. The disparate effects of these two pathways are clear, with Notch inhibiting differentiation while Wnt promoting it. However, the exact stage at which Notch inhibits osteoblast development has not been defined, although our preliminary studies indicate that Notch likely impedes further progression of Runx2- positive cells. Moreover, the genetic relationship between Wnt and Notch pathways during osteoblast differentiation is not known. As such, the goal of this proposal is to test the hypothesis that Notch suppresses further differentiation of Runx2-positive cells and that Notch functions at least in part by inhibiting Wnt/ -catenin signaling. To test this hypothesis I have developed two specific aims. Aim 1. Determine the role of Notch/RBPjk signaling in Runx2-positive cells during osteoblast differentiation I will use a novel mouse line to delete RBPjk in Runx2-positive cells in a doxycycline-inducible manner and to assess the potential bone phenotype. This study will provide genetic evidence about the stage-specific regulation of osteoblast differentiation by Notch/RBPjk signaling. Aim 2. Evaluate the genetic relationship between RBPjk and -catenin during osteoblast development I will examine the effect of -catenin removal (single or both alleles) on the high-bone-mass phenotype caused by RBPjk deletion in mesenchymal progenitors. This study will test the hypothesis that Notch/RBPjk functions genetically upstream of Wnt/ -catenin signaling during osteoblast differentiation. Overall, these studies will enhance the current understanding about Notch inhibition of osteoblast differentiation, and shed light on the functional relationship between two opposing signals, Notch and Wnt, during osteoblast development.