title: Ameloblasts require active RhoA to generate normal dental enamel.
abstract: RhoA plays a fundamental role in regulation of the actin cytoskeleton, intercellular attachment, and cell proliferation. During amelogenesis, ameloblasts (which produce the enamel proteins) undergo dramatic cytoskeletal changes and the RhoA protein level is up-regulated. Transgenic mice were generated that express a dominant-negative RhoA transgene in ameloblasts using amelogenin gene-regulatory sequences. Transgenic and wild-type (WT) molar tooth germs were incubated with sodium fluoride (NaF) or sodium chloride (NaCl) in organ culture. Filamentous actin (F-actin) stained with phalloidin was elevated significantly in WT ameloblasts treated with NaF compared with WT ameloblasts treated with NaCl or with transgenic ameloblasts treated with NaF, thereby confirming a block in the RhoA/Rho-associated protein kinase (ROCK) pathway in the transgenic mice. Little difference in quantitative fluorescence (an estimation of fluorosis) was observed between WT and transgenic incisors from mice provided with drinking water containing NaF. We subsequently found reduced transgene expression in incisors compared with molars. Transgenic molar teeth had reduced amelogenin, E-cadherin, and Ki67 compared with WT molar teeth. Hypoplastic enamel in transgenic mice correlates with reduced expression of the enamel protein, amelogenin, and E-cadherin and cell proliferation are regulated by RhoA in other tissues. Together these findings reveal deficits in molar ameloblast function when RhoA activity is inhibited.
authors.affiliation: Department of Anatomy and Cell Biology, University of Pennsylvania School of Dental Medicine, Philadelphia, PA 19104, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Xue
authors.forename: Yong
authors.initials: Y
authors.lastname: Li
authors.forename: Eric T
authors.initials: ET
authors.lastname: Everett
authors.forename: Kathleen
authors.initials: K
authors.lastname: Ryan
authors.forename: Li
authors.initials: L
authors.lastname: Peng
authors.forename: Rakhee
authors.initials: R
authors.lastname: Porecha
authors.forename: Yan
authors.initials: Y
authors.lastname: Yan
authors.forename: Anna M
authors.initials: AM
authors.lastname: Lucchese
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Kuehl
authors.forename: Megan K
authors.initials: MK
authors.lastname: Pugach
authors.forename: Jessica
authors.initials: J
authors.lastname: Bouchard
authors.forename: Carolyn W
authors.initials: CW
authors.lastname: Gibson
mesh_terms: D000565:Ameloblasts / Q000187:drug effects / Q000378:metabolism*; D000566:Amelogenesis / Q000187:drug effects*; D053523:Amelogenin / Q000378:metabolism; D000818:Animals; D003743:Dental Enamel / Q000002:abnormalities / Q000187:drug effects*; D003744:Dental Enamel Hypoplasia / Q000378:metabolism; D009050:Fluorosis, Dental / Q000378:metabolism; D015870:Gene Expression; D007180:Incisor / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D008963:Molar / Q000473:pathology; D012969:Sodium Fluoride / Q000494:pharmacology*; D014083:Tooth Germ / Q000254:growth & development*; D054460:rho-Associated Kinases / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
chemical_list: D053523:Amelogenin; D012969:Sodium Fluoride; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein
keywords: ameloblasts; dental enamel; dominant-negative RhoA; transgenic mice