Limits...
Localization of putative stem cells in dental epithelium and their association with Notch and FGF signaling.

Harada H, Kettunen P, Jung HS, Mustonen T, Wang YA, Thesleff I - J. Cell Biol. (1999)

Bottom Line: It is known from tissue recombination studies that in the mouse incisor the mesenchyme regulates the continuous growth of epithelium.When FGF-10 protein was applied with beads on the cultured cervical loop epithelium it stimulated cell proliferation as well as expression of lunatic fringe.We present a model in which FGF signaling from the mesenchyme regulates the Notch pathway in dental epithelial stem cells via stimulation of lunatic fringe expression and, thereby, has a central role in coupling the mitogenesis and fate decision of stem cells.

View Article: PubMed Central - PubMed

Affiliation: Developmental Biology Programme, Institute of Biotechnology, Viikki Biocenter, University of Helsinki, 00014 Helsinki, Finland.

ABSTRACT
The continuously growing mouse incisor is an excellent model to analyze the mechanisms for stem cell lineage. We designed an organ culture method for the apical end of the incisor and analyzed the epithelial cell lineage by 5-bromo-2'-deoxyuridine and DiI labeling. Our results indicate that stem cells reside in the cervical loop epithelium consisting of a central core of stellate reticulum cells surrounded by a layer of basal epithelial cells, and that they give rise to transit-amplifying progeny differentiating into enamel forming ameloblasts. We identified slowly dividing cells among the Notch1-expressing stellate reticulum cells in specific locations near the basal epithelial cells expressing lunatic fringe, a secretory molecule modulating Notch signaling. It is known from tissue recombination studies that in the mouse incisor the mesenchyme regulates the continuous growth of epithelium. Expression of Fgf-3 and Fgf-10 were restricted to the mesenchyme underlying the basal epithelial cells and the transit-amplifying cells expressing their receptors Fgfr1b and Fgfr2b. When FGF-10 protein was applied with beads on the cultured cervical loop epithelium it stimulated cell proliferation as well as expression of lunatic fringe. We present a model in which FGF signaling from the mesenchyme regulates the Notch pathway in dental epithelial stem cells via stimulation of lunatic fringe expression and, thereby, has a central role in coupling the mitogenesis and fate decision of stem cells.

Show MeSH
Development of the apical end of mouse incisor in organ culture. (a) Schematic appearance of the incisor tooth in a sagittal section through the mouse mandible. Enamel (red) is covered by odontogenic epithelium (blue) that forms the cervical loop in the apical end of the tooth. Dentin is shown in green. (b) The appearance of the dissected incisor tooth of a 2-d-old mouse in stereomicroscope. (c and d) Histology of the apical end of the incisor showing the different epithelial layers in the cervical loop and the gradual differentiation from the apical to incisal direction of epithelial ameloblasts and mesenchymal odontoblasts depositing enamel (red) and dentin (green), respectively. (e–i) Development of the dissected apical end of a 2-d-old mouse incisor in organ culture for 7 d as seen in stereomicroscope. (j) H-E–stained section of the explant in i, and (m) higher magnification of ameloblasts and enamel. (k) Whole mount alizarin red staining of an explant (l) cultured for 5 d shows mineralization of the extracellular matrices formed in vitro. Abbreviations: a, ameloblast; be, basal epithelium; d, dentin; e, enamel; iee, inner enamel epithelium; o, odontoblast; p, pulp cell; si, stratum intermedium; sr, stellate reticulum. Bars: (b) 1 mm; (d and i) 500 μm; (j) 200 μm; (l) 700 μm; and (m) 100 μm.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2164976&req=5

Figure 1: Development of the apical end of mouse incisor in organ culture. (a) Schematic appearance of the incisor tooth in a sagittal section through the mouse mandible. Enamel (red) is covered by odontogenic epithelium (blue) that forms the cervical loop in the apical end of the tooth. Dentin is shown in green. (b) The appearance of the dissected incisor tooth of a 2-d-old mouse in stereomicroscope. (c and d) Histology of the apical end of the incisor showing the different epithelial layers in the cervical loop and the gradual differentiation from the apical to incisal direction of epithelial ameloblasts and mesenchymal odontoblasts depositing enamel (red) and dentin (green), respectively. (e–i) Development of the dissected apical end of a 2-d-old mouse incisor in organ culture for 7 d as seen in stereomicroscope. (j) H-E–stained section of the explant in i, and (m) higher magnification of ameloblasts and enamel. (k) Whole mount alizarin red staining of an explant (l) cultured for 5 d shows mineralization of the extracellular matrices formed in vitro. Abbreviations: a, ameloblast; be, basal epithelium; d, dentin; e, enamel; iee, inner enamel epithelium; o, odontoblast; p, pulp cell; si, stratum intermedium; sr, stellate reticulum. Bars: (b) 1 mm; (d and i) 500 μm; (j) 200 μm; (l) 700 μm; and (m) 100 μm.

Mentions: We have used the mouse incisor tooth as a model to analyze certain aspects of stem cell regulation and functions. The mouse incisor differs from mouse molars as well as from all human teeth in that it erupts continuously throughout the life of the animal. Cells in the apical end of the tooth proliferate and differentiate into the various tooth forming cells including the mesenchyme-derived odontoblasts producing dentin and the epithelium-derived ameloblasts producing enamel. The epithelial tissue at the labial aspect of the incisor apex forms the cervical loop, which consists of a core of stellate reticulum cells surrounded by basal epithelial cells contacting the dental mesenchyme (see Fig. 1, a–d). The cells in the apex of the tooth divide rapidly as compared with the more incisal region, and there is a gradient of cell differentiation from the apex towards the incisal direction (Smith and Warshawsky 1975, Smith and Warshawsky 1977). Hence, it is generally thought that the apex is the reservoir for the cells producing the enamel and dentin of the erupting tooth. There is no evidence of stem cells among the differentiated ameloblasts (Nataatmadja et al. 1990). Therefore, the epithelial stem cells presumably reside within the cervical loop, but this has not been demonstrated directly and their identity has remained completely unknown.


Localization of putative stem cells in dental epithelium and their association with Notch and FGF signaling.

Harada H, Kettunen P, Jung HS, Mustonen T, Wang YA, Thesleff I - J. Cell Biol. (1999)

Development of the apical end of mouse incisor in organ culture. (a) Schematic appearance of the incisor tooth in a sagittal section through the mouse mandible. Enamel (red) is covered by odontogenic epithelium (blue) that forms the cervical loop in the apical end of the tooth. Dentin is shown in green. (b) The appearance of the dissected incisor tooth of a 2-d-old mouse in stereomicroscope. (c and d) Histology of the apical end of the incisor showing the different epithelial layers in the cervical loop and the gradual differentiation from the apical to incisal direction of epithelial ameloblasts and mesenchymal odontoblasts depositing enamel (red) and dentin (green), respectively. (e–i) Development of the dissected apical end of a 2-d-old mouse incisor in organ culture for 7 d as seen in stereomicroscope. (j) H-E–stained section of the explant in i, and (m) higher magnification of ameloblasts and enamel. (k) Whole mount alizarin red staining of an explant (l) cultured for 5 d shows mineralization of the extracellular matrices formed in vitro. Abbreviations: a, ameloblast; be, basal epithelium; d, dentin; e, enamel; iee, inner enamel epithelium; o, odontoblast; p, pulp cell; si, stratum intermedium; sr, stellate reticulum. Bars: (b) 1 mm; (d and i) 500 μm; (j) 200 μm; (l) 700 μm; and (m) 100 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2164976&req=5

Figure 1: Development of the apical end of mouse incisor in organ culture. (a) Schematic appearance of the incisor tooth in a sagittal section through the mouse mandible. Enamel (red) is covered by odontogenic epithelium (blue) that forms the cervical loop in the apical end of the tooth. Dentin is shown in green. (b) The appearance of the dissected incisor tooth of a 2-d-old mouse in stereomicroscope. (c and d) Histology of the apical end of the incisor showing the different epithelial layers in the cervical loop and the gradual differentiation from the apical to incisal direction of epithelial ameloblasts and mesenchymal odontoblasts depositing enamel (red) and dentin (green), respectively. (e–i) Development of the dissected apical end of a 2-d-old mouse incisor in organ culture for 7 d as seen in stereomicroscope. (j) H-E–stained section of the explant in i, and (m) higher magnification of ameloblasts and enamel. (k) Whole mount alizarin red staining of an explant (l) cultured for 5 d shows mineralization of the extracellular matrices formed in vitro. Abbreviations: a, ameloblast; be, basal epithelium; d, dentin; e, enamel; iee, inner enamel epithelium; o, odontoblast; p, pulp cell; si, stratum intermedium; sr, stellate reticulum. Bars: (b) 1 mm; (d and i) 500 μm; (j) 200 μm; (l) 700 μm; and (m) 100 μm.
Mentions: We have used the mouse incisor tooth as a model to analyze certain aspects of stem cell regulation and functions. The mouse incisor differs from mouse molars as well as from all human teeth in that it erupts continuously throughout the life of the animal. Cells in the apical end of the tooth proliferate and differentiate into the various tooth forming cells including the mesenchyme-derived odontoblasts producing dentin and the epithelium-derived ameloblasts producing enamel. The epithelial tissue at the labial aspect of the incisor apex forms the cervical loop, which consists of a core of stellate reticulum cells surrounded by basal epithelial cells contacting the dental mesenchyme (see Fig. 1, a–d). The cells in the apex of the tooth divide rapidly as compared with the more incisal region, and there is a gradient of cell differentiation from the apex towards the incisal direction (Smith and Warshawsky 1975, Smith and Warshawsky 1977). Hence, it is generally thought that the apex is the reservoir for the cells producing the enamel and dentin of the erupting tooth. There is no evidence of stem cells among the differentiated ameloblasts (Nataatmadja et al. 1990). Therefore, the epithelial stem cells presumably reside within the cervical loop, but this has not been demonstrated directly and their identity has remained completely unknown.

Bottom Line: It is known from tissue recombination studies that in the mouse incisor the mesenchyme regulates the continuous growth of epithelium.When FGF-10 protein was applied with beads on the cultured cervical loop epithelium it stimulated cell proliferation as well as expression of lunatic fringe.We present a model in which FGF signaling from the mesenchyme regulates the Notch pathway in dental epithelial stem cells via stimulation of lunatic fringe expression and, thereby, has a central role in coupling the mitogenesis and fate decision of stem cells.

View Article: PubMed Central - PubMed

Affiliation: Developmental Biology Programme, Institute of Biotechnology, Viikki Biocenter, University of Helsinki, 00014 Helsinki, Finland.

ABSTRACT
The continuously growing mouse incisor is an excellent model to analyze the mechanisms for stem cell lineage. We designed an organ culture method for the apical end of the incisor and analyzed the epithelial cell lineage by 5-bromo-2'-deoxyuridine and DiI labeling. Our results indicate that stem cells reside in the cervical loop epithelium consisting of a central core of stellate reticulum cells surrounded by a layer of basal epithelial cells, and that they give rise to transit-amplifying progeny differentiating into enamel forming ameloblasts. We identified slowly dividing cells among the Notch1-expressing stellate reticulum cells in specific locations near the basal epithelial cells expressing lunatic fringe, a secretory molecule modulating Notch signaling. It is known from tissue recombination studies that in the mouse incisor the mesenchyme regulates the continuous growth of epithelium. Expression of Fgf-3 and Fgf-10 were restricted to the mesenchyme underlying the basal epithelial cells and the transit-amplifying cells expressing their receptors Fgfr1b and Fgfr2b. When FGF-10 protein was applied with beads on the cultured cervical loop epithelium it stimulated cell proliferation as well as expression of lunatic fringe. We present a model in which FGF signaling from the mesenchyme regulates the Notch pathway in dental epithelial stem cells via stimulation of lunatic fringe expression and, thereby, has a central role in coupling the mitogenesis and fate decision of stem cells.

Show MeSH