QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

doi: 10.1242/10.1242/dev.00332

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Tummers, M. Articles by Thesleff, I. Search for Related Content PubMed PubMed Citation Articles by Tummers, M. Articles by Thesleff, I.

Root or crown: a developmental choice orchestrated by the differential regulation of the epithelial stem cell niche in the tooth of two rodent species

Institute of Biotechnology, Viikki Biocenter, FIN-00014 University of Helsinki, Finland

View larger version (56K): [in a new window]   Fig. 1. Coronal and sagittal sections of the vole molar show a distinct and complex morphology. The general appearance of the sagittal section is dependent on the position it is taken, unlike most of the coronal sections. Here we used the particular sagittal section as shown that runs through the middle of the molar. The developmental histories of the vole and mouse molar start similarly and are almost identical until cap stage. After this, the actions of the enamel knots result in a different folding pattern of the epithelium. This results in the intercuspal folds or loops in the vole molar that reach almost down to the base. In the mouse molar the cervical loop epithelium loses its crown fate, i.e. it loses the stellate reticulum, and switches to root. In the vole molar most cervical loop epithelium retains the crown fate except for three small areas that are converted to root fate. After completion of root formation the mouse molar has no functional cervical loop epithelium left (i.e. it is missing stellate reticulum) unlike the vole molar, where most of the cervical loop continues to generate crown. ERM, epithelial cell rests of Malassez; HERS, Hertwig's epithelial root sheath; bl, basal lamina; icl, intercuspal loop; iee, inner enamel epithelium; oee, outer enamel epithelium; si, stratum intermedium; sr, stellate reticulum; dashed circles indicate the cervical loop area.

View larger version (158K): [in a new window]   Fig. 2. Hematoxylin and eosin staining of sagittal (A-C) and coronal (D-F) sections of the vole molar. (A) Sagittal section of entire first vole molar (B) Higher magnification of the posterior cervical loop area of the vole molar. (C) Higher magnification of the anterior region showing the anterior root domain. (D) Coronal section of the vole molar showing the location of the three root domains (boxed). (E-G) Higher magnifications of the root domains. a, anterior; p, posterior; am, ameloblasts; pod, preodontoblasts; od, odontoblasts; pdl, periodontal ligament; cem, cementum; hers, hertwig's epithelial root sheath; en, enamel; dn, dentin; mes, mesenchyme; sr, stellate reticulum; si, stratum intermedium; iee, inner enamel epithelium; oee, outer enamel epithelium. Arrows in A indicate the intercuspal loops. Asterisk in C indicates Hertwig's epithelial root sheath. A and C are from 5 dpn tissue, B,D,E,F,G are from 14 dpn tissue. Scale bars are 0.2 mm. The boxes in A indicate the areas magnified in B and C and the boxes in D indicate those in E-G.

View larger version (124K): [in a new window]   Fig. 3. Localization of Notch1 (A,B), Notch2 (C,D), Notch3 (E,F), Lfng (G,H) and Jag1 (I,J) in anterior and posterior sagittal sections of 2 dpn vole molars. Scale bar is 0.2 mm.

View larger version (147K): [in a new window]   Fig. 5. Localization of Notch1 (A,B), Notch3 (C,D), Lfng (E,F) and Jag1 (G,H) in anterior and posterior sagittal sections of 5 dpn vole molars. Scale bar is 0.2 mm.

View larger version (111K): [in a new window]   Fig. 4. Localization of delta (A,B), Hes1 (C,D), Fgf10 (E,F) and Bsp1 (G-I) in anterior and posterior sagittal sections of 2 dpn vole molars. Scale bar is 0.2 mm.

View larger version (122K): [in a new window]   Fig. 6. Localization of delta1 (A,B), Hes1 (C,D), Fgf10 (E,F), Bmp4 (G,H) and Bsp1 (I,J) in anterior and posterior sagittal sections of 5 dpn vole molars. Scale bar is 0.2 mm.

View larger version (108K): [in a new window]   Fig. 7. Localization of Notch1 (A,B), Notch2 (C,D), Notch3 (E,F), Lfng (G,H) Hes1 (I,J) and Fgf10 (K,L) in sagittal sections of 14 dpn mouse molars. B,D,F,H,J,L, higher magnification of anterior cervical loop regions in A,C,E,G,I,K, respectively. The arrows in D and H indicate the expression of Notch2 and Lfng in Hertwig's epithelial root sheath. Scale bars are 0.2 mm.

View larger version (44K): [in a new window]   Fig. 8. Schematic representation of the epithelial stem cell compartment in mouse incisor and vole molar and the similar distribution of activities of some of the proposed key Notch signaling genes. The stellate reticulum and stratum intermedium are areas of high Notch expression and the putative locations of the adult stem cells. The progeny of the stem cells migrate to the inner enamel epithelium and form a population of transit-amplifying cells characterized by Lfng expression. The cells then start to differentiate into ameloblasts and enter the next domain characterized by Jag1 expression. The proliferation and the stem cells are maintained by the mesenchymal Fgf10 expression near the cervical and intercuspal loop. The identical expression of Bmp4 and Fgf10 indicate that BMP4 might work together with FGF10 in the modulation of the stem cells and their progeny. The main difference between vole molar and mouse incisor is the presence of intercuspal folds in the vole molar, which possess an identical distribution of the key regulators as in the cervical loop area.