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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.

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Lunatic fringe mRNA expression in dental epithelium is stimulated by dental mesenchyme and by FGF-10. (a) The epithelium and mesenchyme from the apical end of the 2-d-old mouse incisor were separated and cultured as recombinants for 24 h. Stimulation of lunatic fringe expression was seen in the cervical loop epithelium and inner enamel epithelium in close contact with mesenchyme. (b) FGF-10 beads stimulated lunatic fringe expression when placed adjacent to cervical loop epithelium. (c) FGF-10 beads did not induce lunatic fringe expression when placed on the zone of differentiated ameloblasts. No specific expression was observed around BSA beads (large arrowhead). Red points in a represent the border of epithelial tissue. Green dots in b and c represent beads (the beads were detached during processing). Small arrowheads point to cervical loop epithelium. Bar, 200 μm.
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Figure 9: Lunatic fringe mRNA expression in dental epithelium is stimulated by dental mesenchyme and by FGF-10. (a) The epithelium and mesenchyme from the apical end of the 2-d-old mouse incisor were separated and cultured as recombinants for 24 h. Stimulation of lunatic fringe expression was seen in the cervical loop epithelium and inner enamel epithelium in close contact with mesenchyme. (b) FGF-10 beads stimulated lunatic fringe expression when placed adjacent to cervical loop epithelium. (c) FGF-10 beads did not induce lunatic fringe expression when placed on the zone of differentiated ameloblasts. No specific expression was observed around BSA beads (large arrowhead). Red points in a represent the border of epithelial tissue. Green dots in b and c represent beads (the beads were detached during processing). Small arrowheads point to cervical loop epithelium. Bar, 200 μm.

Mentions: The expression of lunatic fringe in the basal epithelial cells of the cervical loop suggested that it may be regulated by the underlying mesenchyme, and the close correlation of Fgf-10 and lunatic fringe expression in mesenchyme and epithelium was suggestive of a role for FGF-10 in the regulation of lunatic fringe. We examined these possibilities in vitro in isolated epithelial and mesenchymal tissues from the apical ends of 2-d-old mouse incisors. When the isolated epithelium and mesenchyme were placed in contact on the filter and cultured for 24 h, intense expression of lunatic fringe was seen in the basal epithelial cells of the cervical loop and in the inner enamel epithelium contacting the mesenchyme (Fig. 9 a). No expression was seen in the epithelium of the differentiated zone contacting mesenchyme. When the epithelium was cultured alone, lunatic fringe expression was not seen, indicating that expression had been downregulated in the absence of mesenchyme. When FGF-10 releasing beads were placed on the cervical loop epithelium and inner enamel epithelium, they caused an upregulation of lunatic fringe expression in the contacting epithelium (Fig. 9 b). When FGF-10 beads were placed on the ameloblast zone, the beads had no effect (Fig. 9 c). Control BSA beads had no effect on expression. Hence, these experiments demonstrated that the maintenance of lunatic fringe in the cervical loop epithelium depends on mesenchymal signals, and that this effect is mimicked by FGF-10.


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)

Lunatic fringe mRNA expression in dental epithelium is stimulated by dental mesenchyme and by FGF-10. (a) The epithelium and mesenchyme from the apical end of the 2-d-old mouse incisor were separated and cultured as recombinants for 24 h. Stimulation of lunatic fringe expression was seen in the cervical loop epithelium and inner enamel epithelium in close contact with mesenchyme. (b) FGF-10 beads stimulated lunatic fringe expression when placed adjacent to cervical loop epithelium. (c) FGF-10 beads did not induce lunatic fringe expression when placed on the zone of differentiated ameloblasts. No specific expression was observed around BSA beads (large arrowhead). Red points in a represent the border of epithelial tissue. Green dots in b and c represent beads (the beads were detached during processing). Small arrowheads point to cervical loop epithelium. Bar, 200 μm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2164976&req=5

Figure 9: Lunatic fringe mRNA expression in dental epithelium is stimulated by dental mesenchyme and by FGF-10. (a) The epithelium and mesenchyme from the apical end of the 2-d-old mouse incisor were separated and cultured as recombinants for 24 h. Stimulation of lunatic fringe expression was seen in the cervical loop epithelium and inner enamel epithelium in close contact with mesenchyme. (b) FGF-10 beads stimulated lunatic fringe expression when placed adjacent to cervical loop epithelium. (c) FGF-10 beads did not induce lunatic fringe expression when placed on the zone of differentiated ameloblasts. No specific expression was observed around BSA beads (large arrowhead). Red points in a represent the border of epithelial tissue. Green dots in b and c represent beads (the beads were detached during processing). Small arrowheads point to cervical loop epithelium. Bar, 200 μm.
Mentions: The expression of lunatic fringe in the basal epithelial cells of the cervical loop suggested that it may be regulated by the underlying mesenchyme, and the close correlation of Fgf-10 and lunatic fringe expression in mesenchyme and epithelium was suggestive of a role for FGF-10 in the regulation of lunatic fringe. We examined these possibilities in vitro in isolated epithelial and mesenchymal tissues from the apical ends of 2-d-old mouse incisors. When the isolated epithelium and mesenchyme were placed in contact on the filter and cultured for 24 h, intense expression of lunatic fringe was seen in the basal epithelial cells of the cervical loop and in the inner enamel epithelium contacting the mesenchyme (Fig. 9 a). No expression was seen in the epithelium of the differentiated zone contacting mesenchyme. When the epithelium was cultured alone, lunatic fringe expression was not seen, indicating that expression had been downregulated in the absence of mesenchyme. When FGF-10 releasing beads were placed on the cervical loop epithelium and inner enamel epithelium, they caused an upregulation of lunatic fringe expression in the contacting epithelium (Fig. 9 b). When FGF-10 beads were placed on the ameloblast zone, the beads had no effect (Fig. 9 c). Control BSA beads had no effect on expression. Hence, these experiments demonstrated that the maintenance of lunatic fringe in the cervical loop epithelium depends on mesenchymal signals, and that this effect is mimicked by FGF-10.

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