Yuan Guohua, Yang Guobin, Zheng Yuqian, Zhu Xiaojing, Chen Zhi, Zhang Zunyi, Chen YiPing
The State Key Laboratory Breeding Base of Basic Science of Stomatology & Key Laboratory for Oral Biomedicine of Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan 430079, China Department of Cell and Molecular Biology, Tulane University, New Orleans, LA 70118, USA.
Department of Cell and Molecular Biology, Tulane University, New Orleans, LA 70118, USA Department of Periodontology, College of Stomatology, Fujian Medical University, Fuzhou 350002, China.
Development. 2015 Jan 1;142(1):128-39. doi: 10.1242/dev.117887. Epub 2014 Nov 26.
BMP and Wnt signaling pathways play a crucial role in organogenesis, including tooth development. Despite extensive studies, the exact functions, as well as if and how these two pathways act coordinately in regulating early tooth development, remain elusive. In this study, we dissected regulatory functions of BMP and Wnt pathways in early tooth development using a transgenic noggin (Nog) overexpression model (K14Cre;pNog). It exhibits early arrested tooth development, accompanied by reduced cell proliferation and loss of odontogenic fate marker Pitx2 expression in the dental epithelium. We demonstrated that overexpression of Nog disrupted BMP non-canonical activity, which led to a dramatic reduction of cell proliferation rate but did not affect Pitx2 expression. We further identified a novel function of Nog by inhibiting Wnt/β-catenin signaling, causing loss of Pitx2 expression. Co-immunoprecipitation and TOPflash assays revealed direct binding of Nog to Wnts to functionally prevent Wnt/β-catenin signaling. In situ PLA and immunohistochemistry on Nog mutants confirmed in vivo interaction between endogenous Nog and Wnts and modulation of Wnt signaling by Nog in tooth germs. Genetic rescue experiments presented evidence that both BMP and Wnt signaling pathways contribute to cell proliferation regulation in the dental epithelium, with Wnt signaling also controlling the odontogenic fate. Reactivation of both BMP and Wnt signaling pathways, but not of only one of them, rescued tooth developmental defects in K14Cre;pNog mice, in which Wnt signaling can be substituted by transgenic activation of Pitx2. Our results reveal the orchestration of non-canonical BMP and Wnt/β-catenin signaling pathways in the regulation of early tooth development.
骨形态发生蛋白（BMP）和Wnt信号通路在包括牙齿发育在内的器官发生过程中起着至关重要的作用。尽管进行了广泛的研究，但这两条信号通路的确切功能，以及它们是否协同作用以及如何协同作用来调节早期牙齿发育，仍然不清楚。在本研究中，我们使用转基因noggin（Nog）过表达模型（K14Cre;pNog）剖析了BMP和Wnt信号通路在早期牙齿发育中的调控功能。该模型表现出早期牙齿发育停滞，伴有细胞增殖减少以及牙上皮中牙源性命运标记物Pitx2表达缺失。我们证明，Nog过表达破坏了BMP非经典活性，导致细胞增殖率显著降低，但不影响Pitx2表达。我们进一步通过抑制Wnt/β-连环蛋白信号通路鉴定出Nog的一种新功能，导致Pitx2表达缺失。免疫共沉淀和TOPflash分析揭示了Nog与Wnts直接结合，从而在功能上阻止Wnt/β-连环蛋白信号通路。对Nog突变体进行的原位邻近连接分析（PLA）和免疫组化证实了内源性Nog与Wnts在牙胚中的体内相互作用以及Nog对Wnt信号通路的调节。基因拯救实验表明，BMP和Wnt信号通路均参与牙上皮细胞增殖的调控，其中Wnt信号通路还控制牙源性命运。同时激活BMP和Wnt信号通路，而不是仅激活其中之一，可挽救K14Cre;pNog小鼠的牙齿发育缺陷，其中Wnt信号通路可通过转基因激活Pitx2来替代。我们的研究结果揭示了非经典BMP和Wnt/β-连环蛋白信号通路在早期牙齿发育调控中的协同作用。
