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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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In situ hybridization analysis of Notch1, 2, 3, Serrate1, and lunatic fringe expression in the mandibular incisor of 2-d-old mice. (a–a′′) Notch1 is expressed in stellate reticulum in cervical loop (a) and in stratum intermedium and stellate reticulum in the zone of cell differentiation (a′′). (b–b′′) Notch2 is expressed in outer enamel epithelium and stellate reticulum in cervical loop (b) and in stratum intermedium and stellate reticulum in the zone of cell differentiation (b′′). (c–c′′) Notch3 is absent from the cervical loop (c), but is expressed in stellate reticulum and in the zone of cell differentiation (c′′). (d–d′′) Serrate1 is absent from the cervical loop (d), but is expressed in ameloblasts (d′′). (e-e′′) Lunatic fringe is expressed in basal epithelium in cervical loop continuing in the inner enamel epithelium (e′), and is downregulated in differentiated ameloblasts (e′′). Bar, 1 mm (χ). Bar, 200 μm (χ′ and χ′′).
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Figure 6: In situ hybridization analysis of Notch1, 2, 3, Serrate1, and lunatic fringe expression in the mandibular incisor of 2-d-old mice. (a–a′′) Notch1 is expressed in stellate reticulum in cervical loop (a) and in stratum intermedium and stellate reticulum in the zone of cell differentiation (a′′). (b–b′′) Notch2 is expressed in outer enamel epithelium and stellate reticulum in cervical loop (b) and in stratum intermedium and stellate reticulum in the zone of cell differentiation (b′′). (c–c′′) Notch3 is absent from the cervical loop (c), but is expressed in stellate reticulum and in the zone of cell differentiation (c′′). (d–d′′) Serrate1 is absent from the cervical loop (d), but is expressed in ameloblasts (d′′). (e-e′′) Lunatic fringe is expressed in basal epithelium in cervical loop continuing in the inner enamel epithelium (e′), and is downregulated in differentiated ameloblasts (e′′). Bar, 1 mm (χ). Bar, 200 μm (χ′ and χ′′).

Mentions: Expression of the receptors Notch1, 2, and 3 mRNA, the Notch ligand Serrate1 mRNA as well as lunatic fringe mRNA was localized in longitudinal sections through the 2-d mouse incisors. In the cervical loop, Notch1 was restricted to stellate reticulum cells and was most intense in the cells facing inner enamel epithelium. On the other hand, Notch2 was expressed in the outer enamel epithelium and the underlying stellate reticulum cells, and Notch3 was not detected in the cervical loop (Fig. 6, a–c and a′–c′′). Expression of Serrate1 was not detected in the cervical loop (Fig. 6d and Fig. d′). Interestingly, lunatic fringe was expressed in the inner enamel epithelium starting from the cervical loop (Fig. 6e and Fig. e′). This correlates closely with the distribution of BrdU incorporating cells in the enamel epithelium (Fig. 4 a). Furthermore, the localization of the slowly dividing putative stem cells in our BrdU incorporation study in the peripheral stellate reticulum cells correlates with the boundary between lunatic fringe and Notch1, suggesting that the maintenance and fate of the stem cells may be influenced by Notch signaling.


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)

In situ hybridization analysis of Notch1, 2, 3, Serrate1, and lunatic fringe expression in the mandibular incisor of 2-d-old mice. (a–a′′) Notch1 is expressed in stellate reticulum in cervical loop (a) and in stratum intermedium and stellate reticulum in the zone of cell differentiation (a′′). (b–b′′) Notch2 is expressed in outer enamel epithelium and stellate reticulum in cervical loop (b) and in stratum intermedium and stellate reticulum in the zone of cell differentiation (b′′). (c–c′′) Notch3 is absent from the cervical loop (c), but is expressed in stellate reticulum and in the zone of cell differentiation (c′′). (d–d′′) Serrate1 is absent from the cervical loop (d), but is expressed in ameloblasts (d′′). (e-e′′) Lunatic fringe is expressed in basal epithelium in cervical loop continuing in the inner enamel epithelium (e′), and is downregulated in differentiated ameloblasts (e′′). Bar, 1 mm (χ). Bar, 200 μm (χ′ and χ′′).
© Copyright Policy
Related In: Results  -  Collection

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

Figure 6: In situ hybridization analysis of Notch1, 2, 3, Serrate1, and lunatic fringe expression in the mandibular incisor of 2-d-old mice. (a–a′′) Notch1 is expressed in stellate reticulum in cervical loop (a) and in stratum intermedium and stellate reticulum in the zone of cell differentiation (a′′). (b–b′′) Notch2 is expressed in outer enamel epithelium and stellate reticulum in cervical loop (b) and in stratum intermedium and stellate reticulum in the zone of cell differentiation (b′′). (c–c′′) Notch3 is absent from the cervical loop (c), but is expressed in stellate reticulum and in the zone of cell differentiation (c′′). (d–d′′) Serrate1 is absent from the cervical loop (d), but is expressed in ameloblasts (d′′). (e-e′′) Lunatic fringe is expressed in basal epithelium in cervical loop continuing in the inner enamel epithelium (e′), and is downregulated in differentiated ameloblasts (e′′). Bar, 1 mm (χ). Bar, 200 μm (χ′ and χ′′).
Mentions: Expression of the receptors Notch1, 2, and 3 mRNA, the Notch ligand Serrate1 mRNA as well as lunatic fringe mRNA was localized in longitudinal sections through the 2-d mouse incisors. In the cervical loop, Notch1 was restricted to stellate reticulum cells and was most intense in the cells facing inner enamel epithelium. On the other hand, Notch2 was expressed in the outer enamel epithelium and the underlying stellate reticulum cells, and Notch3 was not detected in the cervical loop (Fig. 6, a–c and a′–c′′). Expression of Serrate1 was not detected in the cervical loop (Fig. 6d and Fig. d′). Interestingly, lunatic fringe was expressed in the inner enamel epithelium starting from the cervical loop (Fig. 6e and Fig. e′). This correlates closely with the distribution of BrdU incorporating cells in the enamel epithelium (Fig. 4 a). Furthermore, the localization of the slowly dividing putative stem cells in our BrdU incorporation study in the peripheral stellate reticulum cells correlates with the boundary between lunatic fringe and Notch1, suggesting that the maintenance and fate of the stem cells may be influenced by Notch signaling.

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