Feedback Inhibitory Mechanisms in Skeletal Development

成纤维细胞生长因子(FGFs)及其受体(FGFRs)发挥着重要作用 在发育中，包括骨骼和颅面发育。激活人类FGFR1的突变， FGFR2和FGFRs与骨骼发育不良相关，包括颅骨融合和侏儒症 综合症。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信号在骨骼发育中起着关键作用：FGFRs的信号必须是 严格监管，以实现正常发展。重要的悬而未决的问题是 在骨骼发育过程中由FGFRs激活的通路，以及这些通路如何反馈到 调节成纤维细胞生长因子信号。对果蝇和脊椎动物的研究表明， Sprouty(Spry)基因家族是FGFR信号转导的抑制因子。Spryl、SPRY2和SPRY4在 小鼠发育过程中的肢芽、上颌弓和下颌弓以及其他部位。 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 建立条件转基因小鼠模型以探讨Spry家族成员在骨骼中的作用 发展。我们发现Spryl在脑神经脊细胞中的条件性表达导致严重的 头面部缺陷，包括鼻骨和额骨的缺失。这些老鼠也表现出很大的 转录因子Msx1、Msx2和AP2在颅面原基中的表达降低。我们 假设Spry在骨骼发育中的作用是维持成纤维细胞生长因子-1之间的平衡。 介导的增殖、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)检验过度- Spry基因表达抑制骨原基成纤维细胞生长因子活性，导致成骨细胞数量减少 2)利用功能丧失的方法研究Spry在成骨细胞增殖中的作用。 体内的分化和凋亡；以及3)表征Spry影响的机制 体外颅骨培养成骨细胞的增殖、分化和凋亡。这些研究将 对颅面和骨骼中信号通路的负调控提供重要的洞察力 以及反馈信号通路中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.