title: Role of Hertwig's epithelial root sheath cells in tooth root development.
abstract: During tooth development, after the completion of crown formation, the apical mesenchyme forms the developing periodontium while the inner and outer enamel epithelia fuse below the level of the crown cervical margin to produce a bilayered epithelial sheath termed Hertwig's epithelial root sheath (HERS). The role of HERS cells in root formation is widely accepted; however, the precise function of these cells remains controversial. Functions suggested have ranged from structural (subdivide the dental ectomesenchymal tissues into dental papilla and dental follicle), regulators of timing of root development, inducers of mesenchymal cell differentiation into odontoblasts and cementoblasts, to cementoblast cell precursors. The characterization of the HERS phenotype has been hindered by the small amount of tissue present at a given time during root formation. In this study, we report the establishment of an immortal HERS-derived cell line that can be maintained in culture and then induced to differentiate in vitro. Characterization of the HERS phenotype using reverse transcriptase-polymerase chain reaction and Western blot immunostaining suggests that HERS cells initially synthesize and secrete some enamel-related proteins such as ameloblastin, and then these cells appear to change their morphology and produce a mineralized extracellular matrix resembling acellular cementum. These studies suggest that the acellular and cellular cementum are synthesized by two different types of cells, the first one by HERS-derived cementoblasts and the later by neural crest-derived cementoblasts.
authors.affiliation: Center for Craniofacial Molecular Biology, University of Southern California School of Dentistry, Los Angeles, California 90033, USA. zeichner@usc.edu
authors.forename: Margarita
authors.initials: M
authors.lastname: Zeichner-David
authors.forename: Keiji
authors.initials: K
authors.lastname: Oishi
authors.forename: Zhengyan
authors.initials: Z
authors.lastname: Su
authors.forename: Vassili
authors.initials: V
authors.lastname: Zakartchenko
authors.forename: Li-Sha
authors.initials: LS
authors.lastname: Chen
authors.forename: Higinio
authors.initials: H
authors.lastname: Arzate
authors.forename: Pablo
authors.initials: P
authors.lastname: Bringas
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D002478:Cells, Cultured; D017931:DNA Primers / Q000494:pharmacology; D003739:Dental Cementum / Q000502:physiology; D003746:Dental Enamel Proteins / Q000096:biosynthesis; D004847:Epithelial Cells; D004848:Epithelium / Q000473:pathology*; D005109:Extracellular Matrix / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D017403:In Situ Hybridization; D051379:Mice; D009432:Neural Crest / Q000378:metabolism; D009805:Odontogenesis; D015675:Osteocalcin / Q000378:metabolism; D010641:Phenotype; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014092:Tooth Root / Q000196:embryology*
chemical_list: C490890:Ambn protein, mouse; D017931:DNA Primers; D003746:Dental Enamel Proteins; D015675:Osteocalcin; D000469:Alkaline Phosphatase