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J Dent Res 85(5):427-431, 2006
© 2006 International and American Associations for Dental Research

RESEARCH REPORT
Biological

Sonic Hedgehog Signaling is Important in Tooth Root Development

M. Nakatomi1,3, I. Morita2,3, K. Eto1, and M.S. Ota1,*

1 Section of Molecular Craniofacial Embryology,
2 Section of Cellular Physiological Chemistry, Department of Maxillofacial Biology, Graduate School, Tokyo Medical and Dental University, and
3 21st Century Center of Excellence (COE) Program for Frontier Research on Molecular Destruction and Reconstruction of Tooth and Bone, Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8549, Japan

* corresponding author, seijin.emb{at}tmd.ac.jp


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS & METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Hertwig’s epithelial root sheath (HERS) is important for tooth root formation, but the molecular basis for the signaling of root development remains uncertain. We hypothesized that Sonic hedgehog (Shh) signaling is involved in the HERS function, because it mediates epithelial-mesenchymal interactions during embryonic odontogenesis. We examined the gene expression patterns of Shh signaling in murine developing molar roots. Shh and Patched2 transcripts were identified in the HERS, whereas Patched1, Smoothened, and Gli1 were expressed in the proliferative dental mesenchyme in addition to the HERS. To confirm whether Shh signaling physiologically functions in vivo, we analyzed mesenchymal dysplasia (mes) mice carrying an abnormal C-terminus of the PATCHED1 protein. In the mutant, cell proliferation was repressed around the HERS at 1 wk. Moreover, the molar eruption was disturbed, and all roots were shorter than those in control littermates at 4 wks. These results indicate that Shh signaling is important in tooth root development. Abbreviations used: BrdU, 5-bromo-2'-deoxyuridine; HERS, Hertwig’s epithelial root sheath; NFI-C/CTF, nuclear factor Ic/CAAT box transcription factor; PCNA, proliferating cell nuclear antigen; Ptc, patched; Shh, sonic hedgehog; Smo, smoothened.

KEY WORDS: Sonic hedgehog • Patched • mesenchymal dysplasia • tooth root development • Hertwig’s epithelial root sheath


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS & METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Sonic hedgehog (Shh), a member of the vertebrate Hedgehog family, plays key roles in the growth and morphogenesis of several organs during development (Ingham and McMahon, 2001; Cohen, 2003; McMahon et al., 2003). In the absence of SHH, Patched (PTC), a 12-pass transmembrane protein and a putative receptor for SHH, represses the signaling activity of a seven-pass transmembrane protein, Smoothened (SMO). Binding of SHH to PTC relieves this inhibitory effect and allows a zinc-finger-type transcription factor GLI to enter the nucleus, where it regulates transcription. Previous studies reported that Ptc1 and Gli1 are themselves targets of Shh signaling in vertebrates, and identification of Ptc1 and Gli1 transcripts indicates functional activation of Shh signaling (Marigo et al., 1996a,b).

Murine tooth morphogenesis involves a series of epithelial-mesenchymal interactions mediated by several growth factors and signaling molecules, including Shh (Jernvall and Thesleff, 2000; Tucker and Sharpe, 2004). Shh is characteristically expressed at each stage of tooth development: in the presumptive tooth-forming area at the epithelial thickening stage (Bitgood and McMahon, 1995); in the enamel knot, which is considered to be a signaling center, during the early cap stage (Vaahtokari et al., 1996); and throughout the inner enamel epithelium at the late cap and bell stages (Bitgood and McMahon, 1995). Recent reports have indicated that tooth size and ameloblast polarization are affected in the absence of Shh signaling in the enamel epithelium (Dassule et al., 2000; Gritli-Linde et al., 2002). As for other components, Ptc2 expression, like Shh, is restricted to the enamel epithelium (Motoyama et al., 1998; Hardcastle et al., 1999), whereas Ptc1, Smo, and Gli1 are widely expressed in both the enamel epithelium and throughout the dental mesenchyme, except for the enamel knot (Hardcastle et al., 1998, 1999).

Following tooth crown formation, tooth roots develop to generate the final tooth shape (Ten Cate, 1996). During early root morphogenesis, the inner and outer enamel epithelia fuse to form a bilayered tissue called Hertwig’s epithelial root sheath. The Hertwig’s epithelial root sheath is thought to be important for the initiation of mesenchymal cell proliferation and differentiation into odontoblasts during root development, but little is known about the molecular mechanisms of root morphogenesis. The aim of this study was to investigate the role of Shh signaling in post-natal tooth root development by examining its gene expression patterns and the root phenotypes of mesenchymal dysplasia (mes) mice carrying an abnormal C-terminus of PTC1 protein.


   MATERIALS & METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS & METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Mice and Processing of Tissues
All experimental procedures were approved by the Animal Welfare Committee of Tokyo Medical and Dental University. C57BL/6 wild-type and heterozygous Ptcmes mutant (Makino et al., 2001) mice were purchased from Sankyo Labo Service Corporation (Tokyo, Japan) and RIKEN Bioresource Center (Tsukuba, Japan), respectively. As previously reported, the heterozygous Ptcmes mutant has no phenotype (Sweet et al., 1996). Thus, wild-type and heterozygous littermates were used as controls. The day on which a pregnant mouse gave birth was designated as post-natal day (P) 0. For whole-mount analyses, the lower first molars of pups were extracted, fixed overnight in 4% paraformaldehyde, dehydrated, and stored in 100% methanol until use. For section analyses, whole heads or mandibles were dissected, fixed overnight in Bouin’s fixative, and decalcified with Morse’s solution (10% w/v sodium citrate and 22.5% v/v formic acid) for 1 or 2 days, depending on the developmental stage, with moderate stirring at 4°C. The specimens were then dehydrated, embedded in paraffin, and cut into 7-µm frontal sections.

Whole-mount and Section in situ Hybridizations
Whole-mount and section in situ hybridizations were carried out according to standard protocols (Xu and Wilkinson, 1999), with some modifications. Digoxigenin-labeled probes for Shh (Dassule and McMahon, 1998), Ptc2 (Motoyama et al., 1998), Ptc1, Smo, and Gli1 (kindly provided by Dr. J. Motoyama) were prepared according to the manufacturer’s protocol. In section in situ hybridization, sections were stained with 4-nitro-blue-tetrazolium (NBT)/5-bromo-4-chloro-3-indolyl-phosphate (BCIP) (Roche Diagnostics Corporation, Indianapolis, IN, USA) dissolved in a solution containing 10% w/v polyvinyl alcohol (Sigma-Aldrich, St. Louis, MO, USA), 100 mM Tris-HCl (pH 9.6), 100 mM NaCl, and 5 mM MgCl2.

Immunohistochemistry
To examine cell proliferation, we injected post-natal pups intraperitoneally with 250 µg of BrdU (Roche) dissolved in PBS 4 or 24 hrs before death. Immunohistochemistry was carried out essentially according to the manufacturer’s instructions (Roche), with anti-PCNA rabbit polyclonal antibody (1:200; Santa Cruz Biotechnology, Santa Cruz, CA, USA) and anti-BrdU mouse monoclonal antibody (1:200; Roche). Biotinylated secondary antibody against rabbit IgG (1:200; Vector Laboratories, Burlingame, CA, USA) and mouse IgG (1:200; Vector) was applied and detected by means of a Vectastain ABC kit (Vector) and 3,3'-diaminobenzidine (Sigma-Aldrich). As a negative control, no staining was observed when the primary antibody was omitted. Photomicrographs were processed with Adobe Photoshop CS software (Adobe Systems, San Jose, CA, USA).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS & METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Shh and Downstream Target Genes in the Developing Root
Tooth crown morphogenesis was almost completed at P5, and it was followed by root formation. We removed developing lower first molars at P6, P8, and P10 to investigate whether Shh signaling is involved in root formation. We identified Shh transcripts in the outline of the epithelial edge of the developing medial and distal roots of lower molars at P8 (Fig. 1AGo). Moreover, transcripts of the SHH target genes Ptc1 and Gli1 overlapped with Shh expression at the same stage (Figs. 1B, 1CGo). Similar expression patterns were also observed at P6 and P10 (data not shown).


Figure 1
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  		Figure 1. Expression of Shh and its target genes, Ptc1 and Gli1, in the developing tooth root. Whole-mount in situ hybridization revealed that Shh (A), Ptc1 (B), and Gli1 (C) were expressed at P8 in the outline of the epithelial edge of the growing medial and distal roots in the lower first molar. Tooth buds are oriented with the bottom side up and the medial side on the left. Original color images were digitally converted to gray scale. Scale bar: 200 µm.

 
Localization of Shh Signaling Genes during Root Formation
At P1, Shh was expressed throughout the inner enamel epithelium except for the tooth cusp region, where epithelial cells began to differentiate into ameloblasts, and the cervical loop area (Figs. 2A, 2AGo*). Ptc2 expression was identified in the apical end of the inner enamel epithelium (Figs. 2B, 2BGo*). In contrast to Shh and Ptc2, which were restricted to the epithelium, the expression of Ptc1 (Figs. 2C, 2CGo*) was mainly observed in the dental mesenchyme, whereas Smo (Figs. 2D, 2DGo*) and Gli1 (Figs. 2E, 2EGo*) transcripts were identified in both the enamel epithelium and the dental mesenchyme. As odontogenesis proceeded, the expression of Shh signaling genes became gradually localized in and around the apical end of the inner enamel epithelium at P5 and the Hertwig’s epithelial root sheath at P9, particularly in the epithelial diaphragm, while it disappeared from other areas, such as well-differentiated ameloblasts and odontoblasts. At both P5 and P9, as in P1, Shh (Figs. 2H, 2HGo*, 2O, 2O*) and Ptc2 (Figs. 2I, 2I*, 2P, 2P*Go) transcripts were restricted to the epithelium, whereas Ptc1 (Figs. 2J, 2J*, 2Q, 2Q*Go), Smo (Figs. 2K, 2K*, 2R, 2R*Go), and Gli1 (Figs. 2L, 2L*, 2S, 2S*Go) were expressed not only in the apical end of the epithelium, but also in the surrounding dental mesenchyme, which is called the pulp proliferation zone. Notably, areas that were positive for the proliferation markers PCNA (Figs. 2F, 2F*, 2M, 2M*, 2T, 2T*Go) and BrdU (Figs. 2G, 2G*, 2N, 2N*, 2U, 2U*Go) overlapped extensively with the areas expressing transcripts for Shh signaling molecules.


Figure 2
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  		Figure 2. Localization of Shh signaling genes in the developing lower molar. The buccal side is to the left. P1 (A-G*), P5 (H-N*), and P9 (O-U*). In situ hybridization of Shh (A, A*, H, H*, O, O*), Ptc2 (B, B*, I, I*, P, P*), Ptc1 (C, C*, J, J*, Q, Q*), Smo (D, D*, K, K*, R, R*), and Gli1 (E, E*, L, L*, S, S*). Immunohistochemistry for PCNA (F, F*, M, M*, T, T*) and BrdU (G, G*, N, N*, U, U*). (A*-U*) Higher magnification of boxed areas in (A-U). The expression of Shh signaling genes gradually became localized to the proliferating apical end of the tooth root. Ptc1 and Gli1 transcripts were found in areas overlapping extensively with the cell proliferation markers PCNA and BrdU. AB, ameloblast; B, bone; D, dentin; DM, dental mesenchyme; E, enamel; HERS, Hertwig’s epithelial root sheath; IEE, inner enamel epithelium; IR, incisor root; OB, odontoblast; SR, stellate reticulum; T, tongue; WF, whisker follicle. Scale bars: 200 µm in (A) for (A-U) and 50 µm in (A*) for (A*-U*).

 
Repressed Cell Proliferation around the HERS in Homozygous Ptcmes Mutants
To examine the physiological function of Shh signaling in vivo, we observed the tooth root phenotypes of homozygous Ptcmes mutant mice. Although multiple mesenchymal defects of the mutant were previously described (Sweet et al., 1996), the effects on the tooth root were not reported. At P7, several BrdU-positive cells were identified in the dental mesenchyme adjacent to the Hertwig’s epithelial root sheath in control littermates (arrows in Fig. 3AGo), but not in mutants (Fig. 3BGo). At P9, the distance between the cemento-enamel junction and the apical end of root dentin was noticeably shorter in mutants (double-headed arrows in Fig. 3DGo) than in controls (double-headed arrows in Fig. 3CGo).


Figure 3
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  		Figure 3. Repressed cell proliferation around the HERS of homozygous Ptcmes mutants. The buccal side is to the left. (A,B) BrdU incorporation (four-hour labeling) in the apical end of the developing lower first molar of a control littermate (A) and a mutant (B) at P7. Several BrdU-positive cells were identified along the HERS in the control (arrows in A), but not in the mutant. (C,D) Hematoxylin and eosin staining of a control littermate (C) and a mutant (D) at P9. Double-headed arrows indicate the distance between the cemento-enamel junction and the apical end of root dentin. AB, ameloblast; B, bone; Ctrl, control; D, dentin; DF, dental follicle; E, enamel; HERS, Hertwig’s epithelial root sheath; MN, mandibular nerve; OB, odontoblast. Scale bars: 50 µm in (A) and 100 µm in (C).

 
Disturbance of Tooth Eruption and Root Formation in Homozygous Ptcmes Mutants
All lower molars had finished eruption in control littermates by P28 (Fig. 4AGo; n = 11/11), whereas in homozygous mutants, all molars showed delayed eruption (Fig. 4BGo; n = 7/7). In particular, the third molars had not reached the occlusal plane in mutants (white arrowhead in Fig. 4BGo), and their cervical line could not be observed (black arrow in Fig. 4BGo). In addition, all tooth roots of mutants (right tooth in Figs. 4C-4E) were shorter than those in controls (left tooth in Figs. 4C-4EGo), especially the third molars (white arrow in Fig. 4EGo). To evaluate the root development, we measured the length and width of the middle part of the tooth roots (indicated by lines in Figs. 4C-4EGo). The length of all tooth roots (asterisks in Fig. 4FGo; P < 0.001) and the width of the third molar roots (asterisk in Fig. 4GGo; P < 0.001) were significantly different between controls (n = 11) and mutants (n = 7). BrdU labeling in the apical radicular region of all molars of controls and the first and second molars of mutants were virtually absent (Fig. 4HGo; data not shown), whereas many BrdU-positive cells were identified in the third molars of mutants (arrowhead in Fig. 4IGo). In all cases, the basal layer of the gingival epithelium showed BrdU incorporation (inset in Fig. 4HGo; data not shown). Analysis of these data indicates delayed root development in the third molars of mutants. Moreover, almost no cementum was deposited in the third molars of mutants (Fig. 4IGo), whereas it was thickly deposited around the apical end of root dentin in controls (double-headed arrow in Fig. 4HGo). Because the cementum layer is gradually formed in response to the stress of biting under normal circumstances, these results indicate a disturbance of tooth eruption in mutants.


Figure 4
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  		Figure 4. Disturbance of tooth eruption and root formation in homozygous Ptcmes mutants at P28. The medial side is to the left in (A-E). (A,B) Lingual view of the lower molars of a control littermate (A) and a mutant (B). Soft tissues were carefully removed. Eruption of all molars of the mutant was delayed, especially the third molar (black arrow in B), which had not reached the occlusal plane (white arrowhead in B). (C-E) Lingual view of the extracted first (C), second (D), and third (E) molars. In each panel, the tooth on the left is from the control, and the one on the right is from the mutant. All roots were shorter in the mutant than in the control, especially the third molar (white arrow in E). Lines indicate the measured position. (F,G) Mean root length (F) and width (G) ± SD of medial (M) and distal (D) roots of the lower first (M1) and second (M2) molars and single root of the third (M3) molar of controls (n = 11) and mutants (n = 7). Asterisks (*) indicate values significantly different from controls according to Student’s t test (P < 0.001). (H,I) BrdU incorporation (24-hour labeling) was detected inside the apical region of the lower third molar of the mutant (arrowhead in I), whereas it was not observed in the control (H). The basal layer of the oral mucosa in the same section was observed as a positive control (inset in H). Almost no cementum was deposited in the mutant in contrast to the control (double-headed arrow in H). AF, apical foramen; BL, basal layer; C, cementum; Ctrl, control; D, dentin; DL, dermal layer; P, dental pulp; PL, periodontal ligament. Scale bars: 600 µm in (A) for (A-E) and 50 µm in (H).

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS & METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
In this study, we examined the expression patterns of Shh signaling genes and cell proliferation markers in developing molar roots. The SHH target genes, Ptc1 and Gli1, were identified in the PCNA- and BrdU-positive mesenchyme of the pulp proliferation zone adjacent to the Hertwig’s epithelial root sheath, strongly suggesting that Shh signaling is involved in the regulation of tooth root elongation. Recently, insulin-like growth factor-I (Fujiwara et al., 2005) and NFI-C/CTF (Steele-Perkins et al., 2003) were reported to be essential factors for root development, but the relationship between Shh signaling and these factors remains unknown.

Accumulated evidence suggests that signaling molecules—including bone morphogenetic protein (BMP), fibroblast growth factor (FGF), Hedgehog, and Wnt—are involved at multiple steps in embryonic odontogenesis (Jernvall and Thesleff, 2000). Our results, together with those form a previous report on the expression of Bmp (Yamashiro et al., 2003), indicate that the same signaling cascades are probably involved in post-natal tooth root development. This possibility could be directly examined by the observation of single or compound mutants of these genes. However, it is very difficult to analyze post-natal tooth development in these mutants because of early lethality of currently available strains. Shh signaling genes also have a similar problem: Shh-null embryos die at birth (Chiang et al., 1996); both Ptc1- (Goodrich et al., 1997) and Smo- (Zhang et al., 2001) null embryos die around embryonic day 9; and both Shh (Dassule et al., 2000) and Smo (Gritli-Linde et al., 2002) conditional knockout mice die within 1 day after birth. Since homozygous Ptcmes mutants are viable after delivery, they have great advantages for the functional analysis of Shh signaling in post-natal development.

It is generally accepted that SHH acts as a mitogen in several developing tissues, including the embryonic tooth germ (Cobourne et al., 2001), while PTC1 antagonistically acts to inhibit cell proliferation (Barnes et al., 2001). In fact, PTC is the gene responsible for the human nevoid basal cell carcinoma syndrome (Hahn et al., 1996), and several mutations in human PTC1 have been reported to be involved in tumorigenesis (Cohen, 2003; McMahon et al., 2003). Here, we demonstrated the repression of cell proliferation in the dental mesenchyme adjacent to the Hertwig’s epithelial root sheath in the developing tooth roots of Ptcmes mutants. In addition, distinctive growth retardation was observed in Ptcmes mutants until weaning (data not shown), as previously reported (Sweet et al., 1996), and a similar phenotype was reported in Ptc1 transgenic mice (Milenkovic et al., 1999). Analysis of these data suggests that Ptcmes is a gain-of-function-type allele.

In the developmental process, Shh signaling is known to play a critical role in determining digit number and identity in the developing limb bud (Tickle, 2003). Overexpression of Ptc1 causes a reduced number of digits, whereas Ptc1-null mice, which are partially rescued by the insertion of a Ptc1 transgene to overcome its early lethality, show polydactyly (Milenkovic et al., 1999). The fact that Ptcmes mutants show pre-axial polydactyly with perfect penetrance (Sweet et al., 1996; Makino et al., 2001) paradoxically suggests that Ptcmes is a loss-of-function-type allele. The understanding of these contradictory tissue-specific phenomena at the molecular level requires further investigation.

In conclusion, our results suggest that Shh signaling is involved in post-natal tooth development, as well as in embryonic odontogenesis, and that its precise regulation is required for proper tooth root formation.


   ACKNOWLEDGMENTS
 
We thank Dr. T. Shiroishi for permission to use heterozygous Ptcmes mutant mice and RIKEN Bioresource Center for providing them; Dr. A.P. McMahon and Dr. J. Motoyama for providing riboprobes; and Dr. D.A.F. Lobel for critical reading of the manuscript and helpful discussion. This work was supported by Grants-in-Aid from the Japanese Society for the Promotion of Science (15390554 to M.O. and 13357015 to K.E.) and the Japanese Ministry of Education, 21st Century Center of Excellence (COE) Program for Frontier Research on Molecular Destruction and Reconstruction of Tooth and Bone.

Received September 1, 2005; Last revision December 16, 2005; Accepted December 19, 2005


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS & METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Barnes EA, Kong M, Ollendorff V, Donoghue DJ (2001). Patched1 interacts with cyclin B1 to regulate cell cycle progression. EMBO J 20:2214–2223.[ISI][Medline]

Bitgood MJ, McMahon AP (1995). Hedgehog and Bmp genes are coexpressed at many diverse sites of cell-cell interaction in the mouse embryo. Dev Biol 172:126–138.[ISI][Medline]

Chiang C, Litingtung Y, Lee E, Young KE, Corden JL, Westphal H, et al. (1996). Cyclopia and defective axial patterning in mice lacking Sonic hedgehog gene function. Nature 383:407–413.[Medline]

Cobourne MT, Hardcastle Z, Sharpe PT (2001). Sonic hedgehog regulates epithelial proliferation and cell survival in the developing tooth germ. J Dent Res 80:1974–1979.[Abstract/Free Full Text]

Cohen MM Jr (2003). The hedgehog signaling network. Am J Med Genet A 123:5–28.[Medline]

Dassule HR, McMahon AP (1998). Analysis of epithelial-mesenchymal interactions in the initial morphogenesis of the mammalian tooth. Dev Biol 202:215–227.[ISI][Medline]

Dassule HR, Lewis P, Bei M, Maas R, McMahon AP (2000). Sonic hedgehog regulates growth and morphogenesis of the tooth. Development 127:4775–4785.[Abstract]

Fujiwara N, Tabata MJ, Endoh M, Ishizeki K, Nawa T (2005). Insulin-like growth factor-I stimulates cell proliferation in the outer layer of Hertwig’s epithelial root sheath and elongation of the tooth root in mouse molars in vitro. Cell Tissue Res 320:69–75.[ISI][Medline]

Goodrich LV, Milenkovic L, Higgins KM, Scott MP (1997). Altered neural cell fates and medulloblastoma in mouse patched mutants. Science 277:1109–1113.[Abstract/Free Full Text]

Gritli-Linde A, Bei M, Maas R, Zhang XM, Linde A, McMahon AP (2002). Shh signaling within the dental epithelium is necessary for cell proliferation, growth and polarization. Development 129:5323–5337.[Abstract/Free Full Text]

Hahn H, Wicking C, Zaphiropoulos PG, Gailani MR, Shanley S, Chidambaram A, et al. (1996). Mutations of the human homolog of Drosophila patched in the nevoid basal cell carcinoma syndrome. Cell 85:841–851.[ISI][Medline]

Hardcastle Z, Mo R, Hui CC, Sharpe PT (1998). The Shh signalling pathway in tooth development: defects in Gli2 and Gli3 mutants. Development 125:2803–2811.[Abstract]

Hardcastle Z, Hui CC, Sharpe PT (1999). The Shh signalling pathway in early tooth development. Cell Mol Biol (Noisy-le-grand) 45:567–578.[ISI][Medline]

Ingham PW, McMahon AP (2001). Hedgehog signaling in animal development: paradigms and principles. Genes Dev 15:3059–3087.[Free Full Text]

Jernvall J, Thesleff I (2000). Reiterative signaling and patterning during mammalian tooth morphogenesis. Mech Dev 92:19–29.[ISI][Medline]

Makino S, Masuya H, Ishijima J, Yada Y, Shiroishi T (2001). A spontaneous mouse mutation, mesenchymal dysplasia (mes), is caused by a deletion of the most C-terminal cytoplasmic domain of patched (ptc). Dev Biol 239:95–106.[ISI][Medline]

Marigo V, Johnson RL, Vortkamp A, Tabin CJ (1996a). Sonic hedgehog differentially regulates expression of GLI and GLI3 during limb development. Dev Biol 180:273–283.[ISI][Medline]

Marigo V, Scott MP, Johnson RL, Goodrich LV, Tabin CJ (1996b). Conservation in hedgehog signaling: induction of a chicken patched homolog by Sonic hedgehog in the developing limb. Development 122:1225–1233.[Abstract]

McMahon AP, Ingham PW, Tabin CJ (2003). Developmental roles and clinical significance of hedgehog signaling. Curr Top Dev Biol 53:1–114.[ISI][Medline]

Milenkovic L, Goodrich LV, Higgins KM, Scott MP (1999). Mouse patched1 controls body size determination and limb patterning. Development 126:4431–4440.[Abstract]

Motoyama J, Takabatake T, Takeshima K, Hui CC (1998). Ptch2, a second mouse Patched gene is co-expressed with Sonic hedgehog. Nat Genet 18:104–106.[ISI][Medline]

Steele-Perkins G, Butz KG, Lyons GE, Zeichner-David M, Kim HJ, Cho MI, et al. (2003). Essential role for NFI-C/CTF transcription-replication factor in tooth root development. Mol Cell Biol 23:1075–1084.[Abstract/Free Full Text]

Sweet HO, Bronson RT, Donahue LR, Davisson MT (1996). Mesenchymal dysplasia: a recessive mutation on chromosome 13 of the mouse. J Hered 87:87–95.[Abstract/Free Full Text]

Ten Cate AR (1996). The role of epithelium in the development, structure and function of the tissues of tooth support. Oral Dis 2:55–62.[Medline]

Tickle C (2003). Patterning systems—from one end of the limb to the other. Dev Cell 4:449–458.[ISI][Medline]

Tucker A, Sharpe P (2004). The cutting-edge of mammalian development; how the embryo makes teeth. Nat Rev Genet 5:499–508.[ISI][Medline]

Vaahtokari A, Åberg T, Jernvall J, Keränen S, Thesleff I (1996). The enamel knot as a signaling center in the developing mouse tooth. Mech Dev 54:39–43.[ISI][Medline]

Xu Q, Wilkinson DG (1999). In situ hybridization of mRNA with hapten labelled probes. In: In situ hybridization: a practical approach. 2nd ed. Wilkinson DG, editor. Oxford: Oxford University Press, pp. 87–106.

Yamashiro T, Tummers M, Thesleff I (2003). Expression of bone morphogenetic proteins and Msx genes during root formation. J Dent Res 82:172–176.[Abstract/Free Full Text]

Zhang XM, Ramalho-Santos M, McMahon AP (2001). Smoothened mutants reveal redundant roles for Shh and Ihh signaling including regulation of L/R asymmetry by the mouse node. Cell 105:781–792.[ISI][Medline]




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