Zinc (Zn) is an essential trace element and it plays indispensable roles in cellular processes for embryonic and postnatal development in mammals. Zn deficiency causes growth retardation, reduced bone volume, dental decay, skin diseases, and other conditions. Zn homeostasis is tightly controlled by the action of Zn transporters and metallothioneins, which together intricately regulate the Zn concentration and distribution in cells. We recently investigated the role of the Zn transporter Slc39a13/Zip13 in mice and humans. Mice deficient in Zip13 show changes in the tooth, bone, and connective tissues, and impairments in BMP and TGF-β signaling. A unique variant of Ehlers-Danlos syndrome (EDS) with hypodontia was found, in which Zip13 possesses a loss-of-function mutation, indicating that Zip13-mediated Zn homeostasis is crucial for tooth, bone and connective tissue development in mice and humans. In this review, we describe how Zn affects biological events especially in tooth development, with recent progress uncovering the roles of the Zn transporter Zip13 in mammalian health and diseases.

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Neurotrophic factors are soluble growth factors predominantly expressed in vertebrate nervous systems and have been well-characterized for their critical roles in neural tissues. Recent studies have revealed that neurotrophin factors and their receptors are also expressed in multiple non-neural tissues, and play a role in a wide range of biological functions, such as regulation of cellular proliferation, survival, migration, and differentiation. The neurotrophic factor family is defined by its structural and functional similarities to 4 ligands; nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4, also known as NT-5). They activate 2 different receptors, trk tyrosine kinase and p75, the latter of which is a member of the tumor necrosis factor receptor superfamily. During tooth development, observations of dynamic changes of specific expression patterns of neurotrophic factors and their receptors imply their important functions in odontogenic processes. In addition, our recent study demonstrated that NT-4 regulates proliferation and differentiation of dental epithelium, and promotes the production of enamel matrixes. In this review, we describe the expression patterns and functions of neurotrophic factors in the tooth germ, and discuss the relationships with tooth development.

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The developing tooth is a good model for studying the mechanism of organogenesis. Tooth development begins as the placode formation with the thickening and invaginating of the oral ectoderm into the dental mesenchyme. A series of reciprocal interactions between these two cell types give rise to differentiation into various cell types including epithelial-derived enamel-secreting ameloblasts and neural crest-derived dentin-secreting odontoblasts. A number of transcription factors control tooth development in order to form unique structures specialized for tooth function with optimized shapes and sizes. We identified Epiprofin (Epfn) as a transcription factor preferentially expressed in teeth. Epfn KO mice display profound embryonic and postnatal growth retardation and develop impaired hair follicle and whisker formation. The drastic phenotypes of Epfn KO are supernumerary tooth formation and lack of enamel in teeth. These observations suggest that Epiprofin plays critical roles in ectodermal organ development and regulates the number of teeth. This review summarizes the roles of Epiprofin in tooth development.

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As societies age, the number of people complaining of dry mouth is increasing; an estimated 30,000,000 people suffer from dry mouth in Japan. The mouth fulfills many basic human appetites, such as eating, drinking, tasting, and talking, and a core component of these functions is saliva. In this paper we will; (1) Explain what dry mouth is; (2) Introduce Niigata University Medical and Dental Hospital’s dry mouth outpatient clinic; (3) Describe a new diagnostic method using ultrasonic waves; and (4) Describe salivary protein analysis in patients suffering from Sjögren’s syndrome (SS).

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The salivary glands are innervated by autonomic nerves. Upon activation of M₃-muscarinic acetylcholine receptors or a₁-adrenergic receptors, cytosolic aquaporin-5 (AQP5) is translocated from intracellular endosomes to the apical plasma membrane (APM) together with lipid rafts in the parotid acinar and duct cells. Some AQP5 is dissociated from the lipid rafts to non-rafts in the APM and the dissociated AQP5 is released into the saliva from the APM. Other AQP5 associated with lipid rafts is internalized and recycled together with the lipid rafts. The subcellular distribution of AQP5 in the salivary glands and its release into the saliva are regulated by autonomic nerves. This review focuses on autonomic nerve-regulated AQP5 trafficking in the parotid glands and AQP5 release into the saliva.

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Ca²⁺ responses in salivary acinar cells are mostly homogeneous and synchronous, whereas the timing and magnitude of Ca²⁺ responses in salivary ductal cells are variable. Imaging analysis using multiphoton microscopy revealed the heterogeneity of salivary ductal cell sensitivity to Ca²⁺-mobilizing agonists. Stimulation of isolated rat parotid ducts with a low concentration (0.1 μM) of epinephrine (Epi) elevated the intracellular Ca²⁺ levels ( [Ca²⁺] _i) in ∼30% of the ductal cells. Similarly, threshold concentrations (0.5 or 1 μM) of phenylephrine (PhL), carbachol (CCh), or ATP induced responses in∼20% of the ductal cells. Sequential stimulation with threshold concentrations of PhL, CCh, and ATP suggested that low concentrations of PhL, CCh, and ATP activate different subpopulations of parotid ductal cells. In addition, certain rat parotid ductal cells exhibit spontaneous oscillations in [Ca²⁺] _i. Electron microscopic analysis indicated that spontaneously oscillating ducts contained numerous granules on the luminal side, which is characteristic of granular ducts. These Ca²⁺ oscillations were completely blocked by the purinergic receptor inhibitors, PPADS and suramin. Differential interference contrast images and a plasma membrane fluorescence probe, synaptogreen C4, revealed that the spontaneous elevations in [Ca²⁺] _i were closely correlated with spontaneous swelling of ductal cells. The present findings suggest that purinergic receptors mediate spontaneous Ca²⁺ oscillations in parotid ductal cells and regulate electrolyte reabsorption from the primary saliva under resting conditions.

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Epithelial-mesenchymal transition (EMT) plays crucial roles in appropriate embryonic development, and in adults during wound healing, organ fibrosis and cancer progression. Many secreted polypeptides are implicated in the EMT process and act in a sequential or cooperative manner. Transforming growth factor (TGF)-β can initiate and maintain EMT by activating intracellular signaling pathways and transcriptional factors. Recent studies have provided new insights into the molecular mechanisms underlying TGF-β-induced EMT, crosstalk between TGF-β/Smad and Ras signaling, and the signals that control transcriptional factors for EMT induction.

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To generalise the effect of bolus (tea) volume on the piezoelectric sensor (PES) signals during pharyngeal swallowing by general linear models (GLMs), laryngeal movement PES data were recorded from eleven healthy adults while they swallowed one of a wide range of volumes. A PES was attached to the front of the neck to record a laryngeal mechanogram, and then each subject was asked to swallow one of six volumes (10 to 32 mL) of tea after a command. For each swallow, four characteristic points on each PES record were defined and four intervals that spanned these points were measured. GLM-ANOVA analysis revealed statistically significant linear regression coefficients for two ‘volume’ effects and four main ‘subject’ effects. The two linear coefficients of the ‘volume’ effect were 2.5 and 2.7, which suggests that a 10-mL increase in tea volume lengthens these intervals by 25 and 27 ms, respectively.

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Proteoglycans and their constituent glycosaminoglycan (GAG) have been proposed to be involved in the inhibition of mineralization in unmineralized tissue, predentin. Among the proteoglycans secreted by odontoblasts, we focused on the large chondroitin sulfate proteoglycan, versican, for its large binding capacity for calcium ions. The aims of this study were the determination of the full-length sequence and splicing variants of the porcine versican, and the detection of versican in the porcine predentin. The complete coding sequence of the porcine versican mRNA was cloned to be 11,775 nucleotides long and encode 3,924 amino acids, and four splicing variants, V0, V1, V2 and V3, were characterized in the isolated porcine cartilage cells. The number of potential GAG attachment sites was 15 in the V0 variant, 13 in the V1 variant, 2 in the V2 variant and 0 in the V3 variant. They were deposited in DDBJ. The V1 variant was determined by RT-PCR in the odontoblasts, dental papilla cells, dental follicle cells, periodontal ligament cells, dental pulp cells, and gingival cells of pigs, although a small amount of the V0 valiant was found in the dental papilla cells. The predentin was prepared from developing porcine permanent incisor tooth germs and its soluble proteins were extracted in order to be partially characterized by protein and proteinase profiles. The versican V1 cleavage products were detected in the predentin extract by Western blotting analysis. These results suggested that the versican splice variant V1 implicates both the control of the mineralization and the activities of the predentin metalloproteinases, because it has 13 GAG chains that bind a large amount of calcium.

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The aim of this study was to evaluate inhibition of adherence of oral streptococci by addition of funoran to xylitol-containing chewing gum or tablets. The inhibitory effect by addition of funoran on adherence was evaluated by scintillation counting using ³H-labeled oral streptococci and saliva-coated hydroxyapatite beads. In samples containing more than 0.1% funoran, the number of attached bacteria was significantly reduced in all tested microorganisms compared with funoran-free samples. This reduction in adherence was also observed by scanning electron microscopy. The results indicate that addition of funoran to xylitol chewing gum or tablets inhibits colonization by oral streptococci, including Streptococcus mutans.

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Antibacterial activity of sodium citrate against tongue bacteria, especially hydrogen-sulfide (H₂S) producers, was examined. Based on 16s rDNA partial sequences analysis, 691 isolates from 6 subjects were identified. In the present study, Prevotella histicola, P. melaninogenica, Veillonella atypica and V. dispar/V. parvula were detected as predominant H₂S producing bacteria. Antibacterial assay showed that sodium citrate inhibited the growth of the representative strains of H₂S producers at low concentrations although it similarly inhibited that of commensal bacteria, viz., Streptococcus parasanguinis and S. salivarius. When the effects of several pH conditions on antibacterial activity of sodium citrate against P. melaninogenica JCM6325^T were examined, the activity was effective under neutral pH as well as under acidic conditions.

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