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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 the cell fate of cervical loop epithelial cells. DiI was injected in the center of the cervical loop and the explants were cultured for 5 d. (a) Appearance of the explant in phase-contrast and (b) fluorescent microscope. DiI-labeled cells have extended from the point of injection incisally, and the highest intensity of fluorescence is in the inner enamel epithelium corresponding to the location of rapidly dividing cells. Arrowheads show the point of injection of DiI at the onset of culture. Bar, 250 μm.
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Figure 2: Analysis of the cell fate of cervical loop epithelial cells. DiI was injected in the center of the cervical loop and the explants were cultured for 5 d. (a) Appearance of the explant in phase-contrast and (b) fluorescent microscope. DiI-labeled cells have extended from the point of injection incisally, and the highest intensity of fluorescence is in the inner enamel epithelium corresponding to the location of rapidly dividing cells. Arrowheads show the point of injection of DiI at the onset of culture. Bar, 250 μm.

Mentions: To visualize the fate of the cervical loop cells, they were labeled with the fluorescent DiI stain at the onset of culture, and the labeled cells were examined after 5 d of culture. Care was taken to microinject DiI to the central cells in the cervical loop, and the restriction of the dye was checked at the onset of culture (not shown). After 5 d of culture, fluorescent cells were seen to extend from the cervical loop to the differentiated ameloblasts (Fig. 2, a and b). The original site of DiI injection could still be seen (Fig. 2, a and b, arrows), but, interestingly, the highest intensity of fluorescence was observed at some distance incisally from the original site. These presumably represent daughter cells, which proliferated rapidly. Extending incisally from this site were labeled cells that had entered the stage of ameloblast differentiation. In conclusion, the DiI injection experiments showed that the cells in the cervical loop give rise to the differentiated dental epithelial cells, in particular the 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 the cell fate of cervical loop epithelial cells. DiI was injected in the center of the cervical loop and the explants were cultured for 5 d. (a) Appearance of the explant in phase-contrast and (b) fluorescent microscope. DiI-labeled cells have extended from the point of injection incisally, and the highest intensity of fluorescence is in the inner enamel epithelium corresponding to the location of rapidly dividing cells. Arrowheads show the point of injection of DiI at the onset of culture. Bar, 250 μm.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 2: Analysis of the cell fate of cervical loop epithelial cells. DiI was injected in the center of the cervical loop and the explants were cultured for 5 d. (a) Appearance of the explant in phase-contrast and (b) fluorescent microscope. DiI-labeled cells have extended from the point of injection incisally, and the highest intensity of fluorescence is in the inner enamel epithelium corresponding to the location of rapidly dividing cells. Arrowheads show the point of injection of DiI at the onset of culture. Bar, 250 μm.
Mentions: To visualize the fate of the cervical loop cells, they were labeled with the fluorescent DiI stain at the onset of culture, and the labeled cells were examined after 5 d of culture. Care was taken to microinject DiI to the central cells in the cervical loop, and the restriction of the dye was checked at the onset of culture (not shown). After 5 d of culture, fluorescent cells were seen to extend from the cervical loop to the differentiated ameloblasts (Fig. 2, a and b). The original site of DiI injection could still be seen (Fig. 2, a and b, arrows), but, interestingly, the highest intensity of fluorescence was observed at some distance incisally from the original site. These presumably represent daughter cells, which proliferated rapidly. Extending incisally from this site were labeled cells that had entered the stage of ameloblast differentiation. In conclusion, the DiI injection experiments showed that the cells in the cervical loop give rise to the differentiated dental epithelial cells, in particular the 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