Mechanisms of Parathyroid Hormone Receptor Signaling in Mouse Salivary Gland Development.

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This study has focused on clarifying the roles of Parathyroid hormone receptor (PTHR) signaling in salivary gland development.Expression of PTHR and its ligand, Parathyroid hormone related peptide (PTHrP), in developing mouse salivary gland, was examined by qualitative PCR, in situ hybridization and immunohistochemistry. Expression level of PTHrP was peaked at E13.5,and then gradually decreased in developing mouse submandibular gland. On the other hand, expression level of PTHR peaked at E14.5 to E15.5, and then gradually decreased. PTHrP and PTHR were dominantly expressed in epithelial cells rather than mesenchymal cells. Intracellular signaling of PTHR utilizes 2 G-protein pathways, Gs and Gq. Both Gs and Gq subunit were expressed in epithelial cells of salivary gland.To assess the roles of PTHR signaling in salivary gland development, we have analyzed the salivary glands of PTHR-null mice. Submandibular glands in PTHR-null mice developed normally during E12.5 to E15.5,and then faile … More d to develop buds, as compared to those of litter mate wild-type mice. Furthermore, BrdU incorporation into cellular nuclei was decreased in salivary gland epithelial cells of PTHR-null mice at E15.0, compared to that of wild type mice, when assessed by BrdU staining. These findings suggest that inhibited cellular proliferation of salivary gland epithelial cells resulted in reduced bud development.To examine which intracellular signaling pathway, Gs-cascade or Gq-cascade, stimulate budding development of salivary gland, we have stimulated those secondary messenger in salivary glands explants culture by those specific stimulating analogs. Stimulation of Gq-phospholipase C stimulated bud development of salivary glands in a dowse dependent manner. On the other hand, stimulation of Gs-adenylcyclase-cAMP reduced bud development and stimulated duct development. These findings suggest that PTHR signaling stimulate bud development of salivary glands via Gq-PKC cascade.In salivary gland development, receptor tyrosine kinase receptor signaling, i.e. EGF, FGF and HGF, activate PKC signaling and stimulate bud development. However, there was no effect of PTHR ligands on EGF or FGF induced-bud development, suggesting that PTHR use distinct PKC-signaling pathway from receptor tyrosine kinase signaling. Less