The mammalian tooth forms by a series of reciprocal epithelial-mesenchymal interactions. Although several signaling pathways and transcription factors have been implicated in regulating molar crown development, relatively little is known about the regulation of root development. Four genes encoding nuclear factor I (NFI) transcription-replication proteins are present in the mouse genome: Nfia, Nfib, Nfic, and Nfix. In order to elucidate its physiological role(s), we disrupted the Nfic gene in mice. Heterozygous animals appear normal, whereas Nfic ؊/؊ mice have unique tooth pathologies: molars lacking roots, thin and brittle mandibular incisors, and weakened abnormal maxillary incisors. Feeding in Nfic ؊/؊ mice is impaired, resulting in severe runting and premature death of mice reared on standard laboratory chow. However, a soft-dough diet mitigates the feeding impairment and maintains viability. Although Nfic is expressed in many organ systems, including the developing tooth, the tooth root development defects were the prominent phenotype. Indeed, molar crown development is normal, and well-nourished Nfic ؊/؊ animals are fertile and can live as long as their wild-type littermates. The Nfic mutation is the first mutation described that affects primarily tooth root formation and should greatly aid our understanding of postnatal tooth development.Tooth formation is a complex developmental process that is mediated through a series of epithelial-mesenchymal interactions (29). Several signaling pathways required for early molar tooth development have been identified, including the BMP (31), FGF (13, 27), SHH (5, 10), and WNT (25, 33) pathways. In addition, targeted disruption of a number of transcription factors, including Msx1 and -2 (1), Dlx1 and -2 (22), Pax-9 (21) and others, severely disrupts early tooth development. In contrast, only one pathway regulating late tooth developement has been identified. The Tabby (Ta), Downless (Dl), and Crinkled (Cr) mouse mutations each cause similar defects of postnatal development (32) by disrupting different components of the Ectodysplasin-A hormone signaling system.The nuclear factor I (NFI) family of transcription-replication factors is encoded by four genes in mammals (NFI-A, -B, -C, and -X) and a single gene in Drosophila melanogaster and Caenorhabditis elegans (8,14,23). Prokaryotic homologues of the NFI genes have not been identified. NFI was discovered as a protein required for adenovirus DNA replication in vitro (19,20), but it is now clear that NFI proteins play an important role in the expression of many cellular genes (reviewed in reference 8). NFI-C/CTF was the initial NFI gene cloned (24) and contains a prototypical proline-rich transcriptional activation domain, as well as a heptamer repeat homologous to the C-terminal domain of RNA polymerase II (18). Because products of the four NFI genes are often coexpressed (3) and bind to similar DNA sequences (15), it has been difficult to determine the roles of individual NFI family members in gene expression during deve...

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. Developmental Dynamics 228:651-663, 2003.

Destruction of the periodontium is normally associated with periodontal disease, although many other factors, such as trauma, aging, infections, orthodontic tooth movement and systemic and genetic diseases, can contribute to this process. Strategies (such as guided tissue regeneration) have been developed to guide and control regeneration using bioresorbable membranes and bone grafts. Although effective to a certain point, these strategies have the problem that they are not predictable and do not completely restore the architecture of the original periodontium. To achieve complete repair and regeneration it is necessary to recapitulate the developmental process with complete formation of cementum, bone and periodontal ligament fibers. Detailed knowledge of the biology of cementum is key for understanding how the periodontium functions, identifying pathological issues and for developing successful therapies for repair and regeneration of damaged periodontal tissue. It is the purpose of this review to focus on the role of cementum and its specific components in the formation, repair and regeneration of the periodontium. As cementum is a matrix rich in growth factors that could influence the activities of various periodontal cell types, this review will examine the characteristics of cementum, its composition and the role of cementum components, especially the cementum protein-1, during the process of cementogenesis, and their potential usefulness for regeneration of the periodontal structures in a predictable therapeutic manner.

A mouse cDNA encoding a 180 amino acid amelogenin was subcloned into the pET expression plasmid (Novagen, Madison, WI) for production in Escherichia coli. A simple growth and purification protocol yields 20-50 mg of 95-99% pure recombinant amelogenin from a 4.5-liter culture. This is the first heterologous expression of an enamel protein. The expressed protein was characterized by partial Edman sequencing, amino acid composition analysis, SDS-PAGE, Western blotting, laser desorption mass spectrometry, and hydroxyapatite binding. The recombinant amelogenin is 179 amino acids in length, has a molecular weight of 20,162 daltons, and hydroxyapatite binding properties similar to the porcine 173 residue amelogenin. Solubility analyses showed that the bacterially expressed protein is only sparingly soluble in the pH range of 6.4-8.0 or in solutions 20% saturated with ammonium sulfate. The purified protein was used to generate rabbit polyclonal anti-amelogenin antibodies which show specific reaction to amelogenins in both Western blot analyses of enamel extracts and in immunostaining of developing mouse molars.

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