Feedback Inhibitory Mechanisms in Skeletal Development

成纤维细胞生长因子（FGF）和成纤维细胞生长因子受体（FGFRs）在肿瘤的发生发展中起着重要的作用 包括骨骼和颅面的发育。人FGFR 1中的激活突变， FGFR 2和FGFRS与包括颅缝早闭和侏儒的骨骼发育不良有关 综合征这些突变影响成骨细胞和软骨细胞的增殖和分化。 这些数据表明FGFR信号传导在骨骼发育中的关键作用： 严格控制正常发育。重要的未决问题是查明 骨骼发育过程中FGFRs激活的通路，以及这些通路如何反馈到 调节FGF信号传导。对果蝇和脊椎动物的研究表明， Sprouty（Spry）基因家族是FGFR信号传导的抑制剂。Spry 1、Spry 2和Spry 4在 肢芽，上颌和下颌弓，以及小鼠发育过程中的其他部位。 逆转录病毒介导的Spryl在鸡肢芽中的过度表达导致软骨发育不良。我们有 开发了一种条件性转基因小鼠模型，以探索Spry家族成员在骨骼肌中的作用。 发展我们发现，脑神经嵴细胞中Spryl的条件性表达导致严重的脑损伤。 包括鼻骨和额骨缺失在内的颅面缺陷。这些老鼠还表现出 降低颅面原基中转录因子Msx 1、Msx 2和AP 2的表达。我们 假设Spry在骨骼发育中的功能是维持FGF-1之间的平衡， 它介导了细胞增殖、分化和凋亡，而Spry的表达水平决定了这一点。 平衡因此，我们提出了以下三个具体目标：1）检验假设，过度- Spry的表达抑制了骨原基中FGF的活性，导致成骨细胞的总体减少， 2）使用功能丧失方法研究Spry在成骨细胞增殖中的作用， 分化和凋亡; 3）表征Spry影响细胞凋亡的机制。 成骨细胞增殖、分化和凋亡。这些研究将 提供了重要的洞察信号通路的负调控颅面和骨骼 发育以及这种反馈信号通路的扰动如何导致骨骼发育不良。

The fibroblast growth factors (FGFs) and the fibroblast growth factor receptors (FGFRs) play important roles in development, including skeletal and craniofacial development. Activating mutations in human FGFR1, FGFR2, and FGFRS are associated with skeletal dysplasias including craniosynostosis and dwarfing syndromes. These mutations affect the proliferation and differentiation of osteoblasts and chondrocytes. These data indicate a pivotal role for FGFR signaling in skeletal development: signaling by FGFRs must be tightly regulated for normal development. Important unresolved issues are the identification of pathways activated by FGFRs during skeletal development, and how these pathways feedback to regulate FGF signaling. Studies in Drosophila and vertebrates have demonstrated that members of the Sprouty (Spry) gene family are inhibitors of FGFR signaling. Spryl, Spry2, and Spry4 are expressed in the limb buds, and maxillary and mandibular arches, as well as other sites during mouse development. Retroviral-mediated over-expression of Spryl in chick limb buds results in chondrodysplasia. We have developed a conditional transgenic mouse model to explore the role of Spry family members in skeletal development. We show that conditional expression of Spryl in cranial neural crest cells results in severe craniofacial defects including the absence of the nasal and frontal bones. These mice also exhibit greatly reduced expression of the transcription factors Msx1, Msx2, and AP2 in craniofacial primordia. We hypothesize that the function of Spry in skeletal development is to maintain a balance between FGF- mediated proliferation, differentiation, and apoptosis, and that the level of Spry expression determines this balance. Accordingly, we propose the following three specific aims: 1) to test the hypothesis that over- expression of Spry inhibits FGF activity in bone primordia, leading to decreased overall osteoblast development; 2) to use loss-of-function approaches to investigate the role of Spry in osteoblast proliferation, differentiation, and apoptosis in vivo; and 3) to characterize the mechanisms by which Spry affects osteoblast proliferation, differentiation, and apoptosis using calvarial cultures in vitro. These studies will provide significant insight into the negative regulation of signaling pathways in craniofacial and skeletal development and how perturbations in this feedback signaling pathway lead to skeletal dysplasias.