Fluorosed Mouse Ameloblasts Have Increased SATB1 Retention and Gαq Activity

Dental fluorosis is characterized by subsurface hypomineralization and increased porosity of enamel, associated with a delay in the removal of enamel matrix proteins. To investigate the effects of fluoride on ameloblasts, A/J mice were given 50 ppm sodium fluoride in drinking water for four weeks, resulting serum fluoride levels of 4.5 µM, a four-fold increase over control mice with no fluoride added to drinking water. MicroCT analyses showed delayed and incomplete mineralization of fluorosed incisor enamel as compared to control enamel. A microarray analysis of secretory and maturation stage ameloblasts microdissected from control and fluorosed mouse incisors showed that genes clustered with Mmp20 appeared to be less downregulated in maturation stage ameloblasts of fluorosed incisors as compared to control maturation ameloblasts. One of these Mmp20 co-regulated genes was the global chromatin organizer, special AT-rich sequence-binding protein-1 (SATB1). Immunohistochemical analysis showed increased SATB1 protein present in fluorosed ameloblasts compared to controls. In vitro, exposure of human ameloblast-lineage cells to micromolar levels of both NaF and AlF3 led to a significantly increase in SATB1 protein content, but not levels of Satb1 mRNA, suggesting a fluoride-induced mechanism protecting SABT1 from degradation. Consistent with this possibility, we used immunohistochemistry and Western blot to show that fluoride exposed ameloblasts had increased phosphorylated PKCα both in vivo and in vitro. This kinase is known to phosphorylate SATB1, and phosphorylation is known to protect SATB1 from degradation by caspase-6. In addition, production of cellular diacylglycerol (DAG) was significantly increased in fluorosed ameloblasts, suggesting that the increased phosphorylation of SATB1 may be related to an effect of fluoride to enhance Gαq activity of secretory ameloblasts

Contributions To the Development of human Deciduous Tooth Primordia

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Gènes, forces et formes : aspects mécaniques du développement cranio-facial prénatal

La connaissance actuelle de la signalisation moléculaire au cours du développement cranio-facial progresse rapidement. Nous savons que les cellules peuvent répondre aux stimuli mécaniques par une signalisation biochimique. Ainsi, le lien entre les stimuli mécaniques et l'expression génétique est devenu un domaine nouveau et important des sciences morphologiques. Ce thème de recherche semble être la reprise d'une ancienne approche de la mécanique du développement, remontant aux embryologistes His [Unsere Körperform und das physiologische Problem ihrer Entstehung. Leipzig: FCW Vogel, 1874.], Carey [J Gen Physiol 1920;2:357–372. et J Gen Physiol 1920;3:61–83.], et Blechschmidt [Mechanische Genwirkungen Funktionentwicklung I. Göttingen: Musterschmidt, 1948.]. Pour ces chercheurs, les forces jouent un rôle fondamental dans la différenciation tissulaire et dans la morphogenèse. Ils conçoivent la morphogenèse comme un système fermé, les cellules vivantes en constituant la part active, ses règles relevant des lois de la biologie, de la chimie et de la physique. Cette revue de la littérature porte sur les liens reliant les aspects mécaniques de la biologie du développement avec les connaissances actuelles de la différenciation tissulaire. Nous faisons le point sur la formation du cartilage (en rapport avec la pression), de l'os (en rapport avec les forces de cisaillement), et des muscles (en rapport avec les forces de dilatation). La cascade de molécules peut être déclenchée par les forces qui apparaissent au cours de l'interaction physique cellulaire et tissulaire. Préciser l'emplacement exact et la chronologie des régions où ces forces s'exercent requiert une connaissance morphologique détaillée. Cette conclusion restant également valable pour la chronologie et l'emplacement exacts des signaux, une meilleure connaissance 3D des processus du développement s'impose. Une recherche complémentaire s'impose également pour développer des méthodes de mesure des forces au sein d'un tissu. Les molécules dont nous vérifions la présence et la nécessité indispensable paraissent plus médiatrices que créatrices de la forme

Tooth-bone morphogenesis during postnatal stages of mouse first molar development

The first mouse molar (M1) is the most common model for odontogenesis, with research particularly focused on prenatal development. However, the functional dentition forms postnatally, when the histogenesis and morphogenesis of the tooth is completed, the roots form and the tooth physically anchors into the jaw. In this work, M1 was studied from birth to eruption, assessing morphogenesis, proliferation and apoptosis, and correlating these with remodeling of the surrounding bony tissue. The M1 completed crown formation between postnatal (P) days 0–2, and the development of the tooth root was initiated at P4. From P2 until P12, cell proliferation in the dental epithelium reduced and shifted downward to the apical region of the forming root. In contrast, proliferation was maintained or increased in the mesenchymal cells of the dental follicle. At later stages, before tooth eruption (P20), cell proliferation suddenly ceased. This withdrawal from the cell cycle correlated with tooth mineralization and mesenchymal differentiation. Apoptosis was observed during all stages of M1 postnatal morphogenesis, playing a role in the removal of cells such as osteoblasts in the mandibular region and working together with osteoclasts to remodel the bone around the developing tooth. At more advanced developmental stages, apoptotic cells and bodies accumulated in the cell layers above the tooth cusps, in the path of eruption. Three-dimensional reconstruction of the developing postnatal tooth and bone indicates that the alveolar crypts form by resorption underneath the primordia, whereas the ridges form by active bone growth between the teeth and roots to form a functional complex