A point mutation in Fgf9 impedes joint interzone formation leading to multiple synostoses syndrome
A point mutation in Fgf9 impedes joint interzone formation leading to multiple synostoses syndrome
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Fgf9 的点突变阻碍关节间带的形成，导致多发性骨连接综合征
DOI：
10.1093/hmg/ddx029
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发表时间：
2017-04-01
影响因子：
3.5
通讯作者：
Wang, Zhugang
中科院分区：
文献类型：
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作者：
Tang, Lingyun;Wu, Xiaolin;Wang, Zhugang
人类多发性骨结合综合征（SYNS）是一种以多关节融合为特征的常染色体显性遗传疾病。我们先前鉴定了FGF 9中导致人SYNS 3的点突变（S99 N）。然而，FGF 9在关节发育过程中的生理功能和SYNS 3的全面分子画像仍然难以捉摸。在这里，我们报告了在Fgf 9中携带S99 N突变的小鼠产生了卷曲尾表型，部分或完全融合了尾椎和肢体关节，这模拟了SYNS 3患者的主要表型。进一步的研究表明，Fgf 9中的S99 N突变通过影响关节发育早期间充质细胞的软骨形成分化来破坏关节间区的形成。因此，肢芽微团培养（LBMMC）测定显示Fgf 9通过下调Sox 6和Sox 9的表达来抑制间充质细胞向软骨细胞的分化。然而，突变蛋白不表现出相同的抑制作用。我们还表明，Fgf 9是所需的正常表达Gdf 5在未来的肘关节和膝关节，通过其激活Gdf 5启动子活性。信号转导分析表明，S99 N突变减少了发育肢体关节中的FGF信号传导。最后，我们证明了由S99 N突变引起的FGF 9构象变化破坏了FGF 9/FGFR/肝素相互作用，从而阻碍了发育关节中的FGF信号传导。综上所述，我们得出结论，Fgf 9中的S99 N突变通过干扰关节间区的形成而导致SYNS 3。这些结果进一步暗示了FGF 9在胚胎关节发育过程中的关键作用。
Human multiple synostoses syndrome (SYNS) is an autosomal dominant disorder characterized by multiple joint fusions. We previously identified a point mutation (S99N) in FGF9 that causes human SYNS3. However, the physiological function of FGF9 during joint development and comprehensive molecular portraits of SYNS3 remain elusive. Here, we report that mice harboring the S99N mutation in Fgf9 develop the curly tail phenotype and partially or fully fused caudal vertebrae and limb joints, which mimic the major phenotypes of SYNS3 patients. Further study reveals that the S99N mutation in Fgf9 disrupts joint interzone formation by affecting the chondrogenic differentiation of mesenchymal cells at the early stage of joint development. Consistently, the limb bud micromass culture (LBMMC) assay shows that Fgf9 inhibits mesenchymal cell differentiation into chondrocytes by downregulating the expression of Sox6 and Sox9. However, the mutant protein does not exhibit the same inhibitory effect. We also show that Fgf9 is required for normal expression of Gdf5 in the prospective elbow and knee joints through its activation of Gdf5 promoter activity. Signal transduction assays indicate that the S99N mutation diminishes FGF signaling in developmental limb joints. Finally, we demonstrate that the conformational change in FGF9 resulting from the S99N mutation disrupts FGF9/FGFR/heparin interaction, which impedes FGF signaling in developmental joints. Taken together, we conclude that the S99N mutation in Fgf9 causes SYNS3 via the disturbance of joint interzone formation. These results further implicate the crucial role of Fgf9 during embryonic joint development.