title: FGFR2b signaling regulates ex vivo submandibular gland epithelial cell proliferation and branching morphogenesis.
abstract: Branching morphogenesis of mouse submandibular glands is regulated by multiple growth factors. Here, we report that ex vivo branching of intact submandibular glands decreases when either FGFR2 expression is downregulated or soluble recombinant FGFR2b competes out the endogenous growth factors. However, a combination of neutralizing antibodies to FGF1, FGF7 and FGF10 is required to inhibit branching in the intact gland, suggesting that multiple FGF isoforms are required for branching. Exogenous FGFs added to submandibular epithelial rudiments cultured without mesenchyme induce distinct morphologies. FGF7 induces epithelial budding, whereas FGF10 induces duct elongation, and both are inhibited by FGFR or ERK1/2 signaling inhibitors. However, a PI3-kinase inhibitor also decreases FGF7-mediated epithelial budding, suggesting that multiple signaling pathways exist. We immunolocalized FGF receptors and analyzed changes in FGFR, FGF and MMP gene expression to identify the mechanisms of FGF-mediated morphogenesis. FGFR1b and FGFR2b are present throughout the epithelium, although FGFR1b is more highly expressed around the periphery of the buds and the duct tips. FGF7 signaling increases FGFR1b and FGF1 expression, and MMP2 activity, when compared with FGF10, resulting in increased cell proliferation and expansion of the epithelial bud, whereas FGF10 stimulates localized proliferation at the tip of the duct. FGF7- and FGF10-mediated morphogenesis is inhibited by an MMP inhibitor and a neutralizing antibody to FGF1, suggesting that both FGF1 and MMPs are essential downstream mediators of epithelial morphogenesis. Taken together, our data suggests that FGFR2b signaling involves a regulatory network of FGFR1b/FGF1/MMP2 expression that mediates budding and duct elongation during branching morphogenesis.
authors.affiliation: Matrix and Morphogenesis Unit, Craniofacial Developmental Biology and Regeneration Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, 30 Convent Drive, MSC 4370, Bethesda, MD 20892-4370, USA.
authors.forename: Zachary
authors.initials: Z
authors.lastname: Steinberg
authors.forename: Christopher
authors.initials: C
authors.lastname: Myers
authors.forename: Vernon M
authors.initials: VM
authors.lastname: Heim
authors.forename: Colin A
authors.initials: CA
authors.lastname: Lathrop
authors.forename: Ivan T
authors.initials: IT
authors.lastname: Rebustini
authors.forename: Julian S
authors.initials: JS
authors.lastname: Stewart
authors.forename: Melinda
authors.initials: M
authors.lastname: Larsen
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Hoffman
mesh_terms: D000818:Animals; D002455:Cell Division / Q000502:physiology*; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology*; D005346:Fibroblast Growth Factors / Q000378:metabolism; D008024:Ligands; D051379:Mice; D009024:Morphogenesis / Q000502:physiology*; D009924:Organ Culture Techniques; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D051496:Receptor, Fibroblast Growth Factor, Type 1; D051497:Receptor, Fibroblast Growth Factor, Type 2; D017468:Receptors, Fibroblast Growth Factor / Q000378:metabolism*; D013363:Submandibular Gland / Q000166:cytology / Q000196:embryology*; D013997:Time Factors
chemical_list: D008024:Ligands; D017468:Receptors, Fibroblast Growth Factor; D005346:Fibroblast Growth Factors; C496349:Fgfr1 protein, mouse; D020794:Receptor Protein-Tyrosine Kinases; D051496:Receptor, Fibroblast Growth Factor, Type 1; D051497:Receptor, Fibroblast Growth Factor, Type 2