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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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Analysis of cell division in the dental epithelium by BrdU labeling. (a–c) After 3 h labeling, BrdU incorporating cells are located in the cervical loop (c) and inner enamel epithelium extending to the zone of terminal ameloblast differentiation (b). (d–i) After 24 (d–f) and 72 h of labeling (g–i), BrdU incorporation is seen also among the newly differentiated ameloblasts (arrows). Particularly high incorporation was evident in the zone of inner enamel epithelium (arrowheads). Bars: (a, d, and g) 200 μm; (b, c, e, f, h, and i) 100 μm.
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Figure 4: Analysis of cell division in the dental epithelium by BrdU labeling. (a–c) After 3 h labeling, BrdU incorporating cells are located in the cervical loop (c) and inner enamel epithelium extending to the zone of terminal ameloblast differentiation (b). (d–i) After 24 (d–f) and 72 h of labeling (g–i), BrdU incorporation is seen also among the newly differentiated ameloblasts (arrows). Particularly high incorporation was evident in the zone of inner enamel epithelium (arrowheads). Bars: (a, d, and g) 200 μm; (b, c, e, f, h, and i) 100 μm.

Mentions: The kinetics of epithelial cell division was examined by labeling the apical ends of the incisors with BrdU for various times and examining the BrdU incorporating cells in tissue sections after culture. When the explants were labeled for 3 h and immediately fixed, labeled cells were seen throughout the cervical loop epithelium extending to the inner enamel epithelium zone (Fig. 4, a–c). Presumably both stem cells and transit-amplifying cells were labeled with BrdU during this period, as recently shown for skin keratinocytes in vitro (Jensen et al. 1999). When the explants were cultured for 24 h in the presence of BrdU, labeled cells were observed in the same locations as in the 3-h cultures and in the ameloblast zone, indicating that the inner enamel epithelium, which had undergone their last divisions during the culture, had differentiated into ameloblasts (Fig. 4d and Fig. f). When the labeling period was extended to 72 h, BrdU incorporation was seen to extend further to the zone of differentiated, postmitotic ameloblasts (Fig. 4 i). These results are in line with the observations on DiI-labeled explants, indicating that proliferating cells in the apical region of the incisor give rise to ameloblasts.


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)

Analysis of cell division in the dental epithelium by BrdU labeling. (a–c) After 3 h labeling, BrdU incorporating cells are located in the cervical loop (c) and inner enamel epithelium extending to the zone of terminal ameloblast differentiation (b). (d–i) After 24 (d–f) and 72 h of labeling (g–i), BrdU incorporation is seen also among the newly differentiated ameloblasts (arrows). Particularly high incorporation was evident in the zone of inner enamel epithelium (arrowheads). Bars: (a, d, and g) 200 μm; (b, c, e, f, h, and i) 100 μm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2164976&req=5

Figure 4: Analysis of cell division in the dental epithelium by BrdU labeling. (a–c) After 3 h labeling, BrdU incorporating cells are located in the cervical loop (c) and inner enamel epithelium extending to the zone of terminal ameloblast differentiation (b). (d–i) After 24 (d–f) and 72 h of labeling (g–i), BrdU incorporation is seen also among the newly differentiated ameloblasts (arrows). Particularly high incorporation was evident in the zone of inner enamel epithelium (arrowheads). Bars: (a, d, and g) 200 μm; (b, c, e, f, h, and i) 100 μm.
Mentions: The kinetics of epithelial cell division was examined by labeling the apical ends of the incisors with BrdU for various times and examining the BrdU incorporating cells in tissue sections after culture. When the explants were labeled for 3 h and immediately fixed, labeled cells were seen throughout the cervical loop epithelium extending to the inner enamel epithelium zone (Fig. 4, a–c). Presumably both stem cells and transit-amplifying cells were labeled with BrdU during this period, as recently shown for skin keratinocytes in vitro (Jensen et al. 1999). When the explants were cultured for 24 h in the presence of BrdU, labeled cells were observed in the same locations as in the 3-h cultures and in the ameloblast zone, indicating that the inner enamel epithelium, which had undergone their last divisions during the culture, had differentiated into ameloblasts (Fig. 4d and Fig. f). When the labeling period was extended to 72 h, BrdU incorporation was seen to extend further to the zone of differentiated, postmitotic ameloblasts (Fig. 4 i). These results are in line with the observations on DiI-labeled explants, indicating that proliferating cells in the apical region of the incisor give rise to ameloblasts.

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