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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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Localization of stem cells by BrdU pulse–chase analysis and by anti-adenovirus receptor antibody (anti-CVADR). 3 h BrdU labeling was followed by 7 d chase period. (a and b) Labeled cells were detected in the cervical loop at the border between basal epithelium and stellate reticulum. (a and c) Labeled cells represent ameloblasts derived from the last cell division of inner enamel epithelial cells. Stellate reticulum cells in cervical loop expressed CVADR strongly (d and e). The expression in basal epithelium was at lower level. The staining at the border of the frozen section is due to nonspecific binding of antibodies. m, mesenchyme; be, basal epithelium; sr, stellate reticulum; black dots, basement membrane. Bars: (a and d) 200 μm; (b) 100 μm; (c and e) 50 μm.
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Figure 5: Localization of stem cells by BrdU pulse–chase analysis and by anti-adenovirus receptor antibody (anti-CVADR). 3 h BrdU labeling was followed by 7 d chase period. (a and b) Labeled cells were detected in the cervical loop at the border between basal epithelium and stellate reticulum. (a and c) Labeled cells represent ameloblasts derived from the last cell division of inner enamel epithelial cells. Stellate reticulum cells in cervical loop expressed CVADR strongly (d and e). The expression in basal epithelium was at lower level. The staining at the border of the frozen section is due to nonspecific binding of antibodies. m, mesenchyme; be, basal epithelium; sr, stellate reticulum; black dots, basement membrane. Bars: (a and d) 200 μm; (b) 100 μm; (c and e) 50 μm.

Mentions: To analyze kinetics of cell division, we cultured the explants for 7 d after they had been incubated for 3 h with BrdU. The rapidly proliferating cells were, thereby, given time to dilute the label. After the 7-d chase period, very few labeled cells were seen in the inner enamel epithelium area, indicating that the vast majority of cells had diluted the label by repeated divisions or differentiated into ameloblasts after their last divisions. BrdU-labeled ameloblasts were present near the inner enamel epithelium zone, and they were grouped into clusters. Hence, they appeared as clones of cells that presumably were descendants of individual inner enamel epithelial cells, which had undergone their last cell divisions and incorporated BrdU during the 3-h labeling period (Fig. 5, a and c). Similarly, clusters of labeled cells were seen in the epithelial cells overlying the labeled ameloblasts, suggesting that they had differentiated from precursor cells that had been labeled during the first 3 h of culture.


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)

Localization of stem cells by BrdU pulse–chase analysis and by anti-adenovirus receptor antibody (anti-CVADR). 3 h BrdU labeling was followed by 7 d chase period. (a and b) Labeled cells were detected in the cervical loop at the border between basal epithelium and stellate reticulum. (a and c) Labeled cells represent ameloblasts derived from the last cell division of inner enamel epithelial cells. Stellate reticulum cells in cervical loop expressed CVADR strongly (d and e). The expression in basal epithelium was at lower level. The staining at the border of the frozen section is due to nonspecific binding of antibodies. m, mesenchyme; be, basal epithelium; sr, stellate reticulum; black dots, basement membrane. Bars: (a and d) 200 μm; (b) 100 μm; (c and e) 50 μm.
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Related In: Results  -  Collection

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Figure 5: Localization of stem cells by BrdU pulse–chase analysis and by anti-adenovirus receptor antibody (anti-CVADR). 3 h BrdU labeling was followed by 7 d chase period. (a and b) Labeled cells were detected in the cervical loop at the border between basal epithelium and stellate reticulum. (a and c) Labeled cells represent ameloblasts derived from the last cell division of inner enamel epithelial cells. Stellate reticulum cells in cervical loop expressed CVADR strongly (d and e). The expression in basal epithelium was at lower level. The staining at the border of the frozen section is due to nonspecific binding of antibodies. m, mesenchyme; be, basal epithelium; sr, stellate reticulum; black dots, basement membrane. Bars: (a and d) 200 μm; (b) 100 μm; (c and e) 50 μm.
Mentions: To analyze kinetics of cell division, we cultured the explants for 7 d after they had been incubated for 3 h with BrdU. The rapidly proliferating cells were, thereby, given time to dilute the label. After the 7-d chase period, very few labeled cells were seen in the inner enamel epithelium area, indicating that the vast majority of cells had diluted the label by repeated divisions or differentiated into ameloblasts after their last divisions. BrdU-labeled ameloblasts were present near the inner enamel epithelium zone, and they were grouped into clusters. Hence, they appeared as clones of cells that presumably were descendants of individual inner enamel epithelial cells, which had undergone their last cell divisions and incorporated BrdU during the 3-h labeling period (Fig. 5, a and c). Similarly, clusters of labeled cells were seen in the epithelial cells overlying the labeled ameloblasts, suggesting that they had differentiated from precursor cells that had been labeled during the first 3 h of culture.

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