Otsu Keishi, Ida-Yonemochi Hiroko, Fujiwara Naoki, Harada Hidemitsu
Division of Developmental Biology and Regenerative Medicine, Department of Anatomy, Iwate Medical University, Iwate, Japan.
Division of Anatomy and Cell Biology of the Hard Tissue, Department of Tissue Regeneration and Reconstruction, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan.
J Bone Miner Res. 2016 Nov;31(11):1943-1954. doi: 10.1002/jbmr.2876. Epub 2016 Oct 26.
During tooth development, oral epithelial cells differentiate into ameloblasts in order to form the most mineralized tissue in the vertebrate body: enamel. During this process, ameloblasts directionally secrete enamel matrix proteins and morphologically change from low columnar cells to polarized tall columnar cells, both of which are essential for the proper formation of enamel. In this study, we elucidated the molecular mechanism that integrates ameloblast function and morphology. Immunohistochemistry revealed that the restricted expression of semaphorin 4D (Sema4D) and RhoA activation status are closely associated with ameloblast differentiation in mouse incisors. In addition, in vitro gain-of-function and loss-of-function experiments demonstrated that Sema4D acts upstream of RhoA to regulate cell polarity and amelogenin expression via the Plexin B1/Leukemia-associated RhoGEF (LARG) complex during ameloblast differentiation. Experiments in transgenic mice demonstrated that expression of a dominant-negative form of RhoA in dental epithelium hindered ameloblast differentiation and subsequent enamel formation, as well as perturbing the establishment of polarized cell morphology and vectorial amelogenin expression. Finally, we showed that spatially restricted Akt mediates between Sema4D-RhoA signaling and these downstream cellular events. Collectively, our results reveal a novel signaling network, the Sema4D-RhoA-Akt signal cascade, that coordinates cellular function and morphology and highlights the importance of specific spatiotemporally restricted components of a signaling pathway in the regulation of ameloblast differentiation. © 2016 American Society for Bone and Mineral Research.
在牙齿发育过程中，口腔上皮细胞分化为成釉细胞，以形成脊椎动物体内矿化程度最高的组织：牙釉质。在此过程中，成釉细胞定向分泌牙釉质基质蛋白，形态上从低柱状细胞转变为极化的高柱状细胞，这两者对于牙釉质的正常形成均至关重要。在本研究中，我们阐明了整合成釉细胞功能与形态的分子机制。免疫组织化学显示，信号素4D（Sema4D）的限制性表达和RhoA激活状态与小鼠切牙中的成釉细胞分化密切相关。此外，体外功能获得和功能丧失实验表明，在成釉细胞分化过程中，Sema4D通过Plexin B1/白血病相关Rho鸟嘌呤核苷酸交换因子（LARG）复合体作用于RhoA上游，以调节细胞极性和釉原蛋白表达。转基因小鼠实验表明，在牙上皮中表达显性负性形式的RhoA会阻碍成釉细胞分化及随后的牙釉质形成，同时扰乱极化细胞形态的建立和釉原蛋白的定向表达。最后，我们表明空间受限的Akt在Sema4D-RhoA信号传导与这些下游细胞事件之间起介导作用。总体而言，我们的结果揭示了一个新的信号网络，即Sema4D-RhoA-Akt信号级联，它协调细胞功能和形态，并突出了信号通路中特定时空受限成分在调节成釉细胞分化中的重要性。© 2016美国骨与矿物质研究学会。
