The Semaphorin 4D-RhoA-Akt Signal Cascade Regulates Enamel Matrix Secretion in Coordination With Cell Polarization During Ameloblast Differentiation

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.


MeSH terms

  • Ameloblasts / cytology*
  • Ameloblasts / metabolism
  • Amelogenin / metabolism
  • Animals
  • Antigens, CD / metabolism*
  • Cell Differentiation*
  • Cell Polarity*
  • Cell Proliferation
  • Dental Enamel / metabolism*
  • Dental Enamel Proteins / metabolism*
  • Humans
  • Mice
  • Models, Biological
  • Nerve Tissue Proteins / metabolism
  • Phenotype
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Receptors, Cell Surface / metabolism
  • Rho Guanine Nucleotide Exchange Factors / metabolism
  • Semaphorins / metabolism*
  • Signal Transduction
  • Tooth / metabolism
  • rhoA GTP-Binding Protein / metabolism*


  • Amelogenin
  • Antigens, CD
  • Arhgef12 protein, mouse
  • CD100 antigen
  • Dental Enamel Proteins
  • Nerve Tissue Proteins
  • Plxnb1 protein, mouse
  • Receptors, Cell Surface
  • Rho Guanine Nucleotide Exchange Factors
  • Semaphorins
  • enamel matrix proteins
  • Proto-Oncogene Proteins c-akt
  • rhoA GTP-Binding Protein