Skip to main content
PMC home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2016 Dec 1.
Published in final edited form as: Int Endod J. 2016 Jan 4;49(12):1124–1131. doi: 10.1111/iej.12585

Site-specific function and regulation of Osterix in tooth root formation

Y D He 1,2,†, B D Sui 2,3,†, M Li 2, J Huang 1,2,4, S Chen 1,5, L A Wu 1,2
PMCID: PMC5005108  NIHMSID: NIHMS812510  PMID: 26599722

Abstract

Congenital diseases of tooth roots, in terms of developmental abnormalities of short and thin root phenotypes, can lead to loss of teeth. A more complete understanding of the genetic molecular pathways and biological processes controlling tooth root formation is required. Recent studies have revealed that Osterix (Osx), a key mesenchymal transcriptional factor participating in both the processes of osteogenesis and odontogenesis, plays a vital role underlying the mechanisms of developmental differences between root and crown. During tooth development, Osx expression has been identified from late embryonic to postnatal stages when the tooth root develops, particularly in odontoblasts and cementoblasts to promote their differentiation and mineralization. Furthermore, the site-specific function of Osx in tooth root formation has been confirmed, because odontoblastic Osx-conditional knockout mice demonstrate primarily short and thin root phenotypes with no apparent abnormalities in the crown (Journal of Bone and Mineral Research 30, 2014 and 742, Journal of Dental Research 94, 2015 and 430). These findings suggest that Osx functions to promote odontoblast and cementoblast differentiation and root elongation only in root, but not in crown formation. Mechanistic research shows regulatory networks of Osx expression, which can be controlled through manipulating the epithelial BMP signalling, mesenchymal Runx2 expression and cellular phosphorylation levels, indicating feasible routes of promoting Osx expression postnatally (Journal of Cellular Biochemistry 114, 2013 and 975). In this regard, a promising approach might be available to regenerate the congenitally diseased root and that regenerative therapy would be the best choice for patients with developmental tooth diseases.

Keywords: dentinogenesis, odontoblast differentiation, Osterix, tooth root development

Introduction

Developmental and genetic conditions of the teeth remain a challenge (Cabay 2014). Particularly, developmental diseases of the tooth root have their distinct characteristics where only the progress of root formation is disturbed, leading to early loss of teeth postnatally (Catala et al. 1995, Apajalahti et al. 1999, Saini et al. 2004, Huang & Chai 2012). However, the mechanisms underlying the differences between tooth root and crown phenotypes in such diseases are unknown. Therefore, there is a need for a more complete understanding of the genetic molecular pathways and biological processes controlling tooth root development.

Tooth development is a complex process that is regulated precisely by several signalling pathways and transcription factors (Thesleff 2003). These developmental signals transfer indiscriminately from the dental epithelium to the mesenchyme, leaving mesenchymal differences between the root and crown to explain different developmental phenotypes (Huang & Chai 2012). Recent studies have revealed that odontoblasts, the cells that form dentine, demonstrate heterogeneity between tooth root and crown in a temporal–spatial mode of function (Bae et al. 2013). This heterogeneity is believed to be controlled by the sequential expressions and reciprocal interactions of a series of marker genes, such as Runx2 and Osx (Hirata et al. 2009, Kim et al. 2015). First recognized in bone development, these genes participate in both the processes of osteogenesis and odontogenesis that share many common characteristics in the regulation mechanisms (Nakashima et al. 2002, Matsubara et al. 2008). Therefore, comprehension of these osteogenic key transcription factors will offer new insights into the understanding of the odontoblast heterogeneity and site-specific regulation of tooth root development.

Osterix (Osx) plays an essential role in both bone and tooth formation (Nakashima et al. 2002) and is recognized to be a downstream target of Runt-related transcription factor 2 (Runx2) (Nishio et al. 2006). Recently, the critical and unique role of Osx in tooth root formation has been gradually realized. During tooth development, Runx2 and Osx are both highly expressed in the dental mesenchyme at early stages when the crown develops. However, from the bell stage to postnatally, only Osx was expressed when the root develops, whilst the expression of Runx2 declined sharply (Chen et al. 2009). The importance of Osx in tooth root formation was further demonstrated in several conditional knockout (cKO) mice, where odontoblastic Osx-cKO mice displayed short thin root phenotypes similar to those that occur in humans, further indicating the odontoblast heterogeneity (D’Souza et al. 1999, Zhang et al. 2014, Kim et al. 2015). In this review, the site-specific function and regulation of Osx in tooth root formation is summarized. These findings could be useful for root regenerative therapy based on genetic and epigenetic manipulations of Osx.

Current knowledge of tooth root and crown developmental differences: emerging understanding of mesenchymal contributions

Tooth development is a consequence of sequential and reciprocal crosstalks between the dental epithelium and mesenchyme, which is also guaranteed by specific temporal–spatial expressions of a series of genes (Tummers & Thesleff 2009). Crown development is completed with the interaction between the dental lamina and the mesenchyme located in the dental papilla (Lan et al. 2014). For the root development, the extension of Hertwig’s epithelial root sheath (HERS) starts this process following crown formation (Zeichner-David et al. 2003). HERS acts as an inducer and regulator of the root formation, expressing signalling molecules to promote the differentiation of mesenchymal cells (Thomas & Kollar 1989). It is acknowledged that the crown is formed early embryonically, whereas the root is formed through the later embryonic stage to the postnatal stage, implying potential genetic differences between tooth root and crown formation (Huang & Chai 2012). Clinically, congenital crown defects are often accompanied by root defects, whilst the root development-related defects are sometimes observed independently, such as short root anomaly disease first reported by Lind (1972) and dentine dysplasia type I (Shields et al. 1973). Intensive studies on these differences and the underlying mechanisms might contribute to further understanding of diseases in tooth root development.

Many mesenchymal molecules contribute to odontoblast and cementoblast differentiation and maturation during tooth root development. It has been reported that Nfic, which belongs to the nuclear factor I family of transcriptional factors, is expressed primarily in odontoblasts (Lee et al. 2009). Recently, the special role of Nfic in postnatal root formation has been recognized (Huang et al. 2010). The homozygous Nfic-deficient mice by removal of the second exon from the Nfic gene exhibited normal crown formation, but short and abnormal root phenotypes. Furthermore, aberrant odontoblast differentiation during root formation was found in Nfic-deficient mice (Steele-Perkins et al. 2003, Park et al. 2007, Lee et al. 2009). In addition, mesenchyme-specific β-catenin- and Smad4-cKO mice also had rootless molars or short roots in mice with disorders of odontoblasts (Gao et al. 2009, Kim et al. 2013). Consequently, mesenchymal differences per se may underlie different developmental phenotypes between root and crown. In this respect, the site-specific function of osteogenic key transcription factor, Osx, in tooth root development has been disclosed.

The temporal–spatial expression pattern of Osx in tooth development

Osx is a zinc finger-containing protein, which was first discovered as a bone morphogenetic protein 2 (BMP2) inducible transcription factor in mesenchymal cells (Nakashima et al. 2002). Osx consists of 431 amino acids including a Smad-binding domain (SBD), a proline-rich domain between −552 and −839 bp from its transcription start site (Gao et al. 2004, Hatta et al. 2006, Mandal et al. 2010). Smad proteins have been shown to take part in the BMP signalling pathway and play significant roles in mediating epithelial signals in the dental mesenchyme (Qin et al. 2012). This may be the structural basis for the function of Osx (Hatta et al. 2006).

In skeleton development, Osx is a downstream target gene of Runx2, which directly binds to Runx2-binding element located in the Osx promoter and activates Osx expression (Sinha & Zhou 2013). Runx2 expresses earlier whilst Osx expression begins at around E13.5 in the perichondrium of long bones and calvaria and is strong at E15.5 in all of the skeletal components. These temporal expression patterns of Runx2 and Osx also exist in tooth development. Chen et al. (2009) reported that during embryonic tooth development, Runx2 and Osx both highly expressed in the mesenchyme at early stages. Early Osx expressions were detected at the cap stage (E14) in mesenchymal cells of the alveolar bone, enamel organ, dental papilla and follicle, but barely in the dental epithelium, which suggests that Osx provides its regulation function only in the dental mesenchyme. At the bell stage (E16), Osx expression began to be found in differentiating osteogenic mesenchyme, ameloblasts, odontoblasts and dental papilla cells. However, at E18, a sharp decline of Runx2 expression occurred in the odontoblasts, ameloblasts and dental pulp cells (Chen et al. 2005). In contrast, Osx remained consecutively intense in osteoblasts of the alveolar bone, odontoblasts and dental pulp cells from E18. At PN 8 to 14, high Osx expression was present in the cement–enamel junction and tooth roots. High expressions of Osx in tooth roots at postnatal stages highlight the importance of Osx in root formation (Chen et al. 2009). These findings suggested Runx2 functions primarily at earlier stages embryonically in tooth development, whilst Osx participates at later stages.

Site-specific function of Osx in root formation

Function of Osx in odontoblasts

Odontoblasts synthesize and secrete various kinds of proteins to form the dentine matrix (Bae et al. 2013, Jacob et al. 2014). Recent studies reveal that Osx is capable of promoting the expression and secretion of dentine sialophosphoprotein (Dspp), contributing to dentinogenesis. Dspp is the predominant component of noncollagenous dentine extracellular matrix and is critical to dentine formation (D’Souza et al. 1997). Chen et al. (2009) examined Osx and Dspp expression patterns at different stages of tooth development using in situ hybridization. The Dspp mRNA signal was strong in odontoblasts from E18, when highly expressed Osx overlapped with Dspp in primarily the developing roots, but Runx2 expression declined at this stage as mentioned above. Further experiments demonstrated that in mouse odontoblast-like cells, Osx overexpression generated a 2.7-fold Dspp mRNA upregulation compared with the control group, detected by qRT-PCR analysis. Accordingly, Osx could activate Dspp transcription independent of Runx2.

Yang et al. (2014) further used an immortalized human dental papilla cell (hDPC) line to investigate the effects of Osx on the proliferation and odontoblastic differentiation. They analysed Osx and Dspp expressions of hDPCs cultured in odontoblastic induction medium at 0, 7 and 14 days. The mRNA levels of Osx and Dspp both showed an obvious upregulation from day 7 until day 14. After overexpression of Osx in hDPCs, they confirmed that Osx retarded proliferation but promoted odontoblastic differentiation and mineralization through upregulating Dspp, dentine matrix protein 1 (DMP1), nestin and alkaline phosphatase (ALP). Therefore, Osx is considered as a key regulator for not only dentine matrix apposition but also odontoblastic differentiation and mineralization. Considering its specific temporal–spatial expression in tooth roots, it is of interest to look into the functional consequences of Osx-cKO in odontoblasts.

The short and thin root phenotypes of Osx-cKO mice

A series of reports have uncovered site-specific function of Osx in tooth root development. Zhang et al. (2014) discovered that odontoblast-Osx-cKO mice displayed short and thin root dentine phenotypes, with few dentine tubules and striking decreases in expressions of Dspp and DMP1, similar to the tooth phenotype of traditional Osx KO mice (Nakashima et al. 2002). However, no apparent changes in the crown dentine matrix and tubular structure were found, indicating that Osx is not involved in crown dentine formation (Zhang et al. 2014). Kim et al. (2015) also investigated the effects of odontoblast-specific inactivation of Osx. They confirmed that mutant mice displayed normal crowns but short molar roots and thin inter-radicular dentine; the root elongation was also disturbed by impaired odontoblastic maturation. These findings suggested that Osx participates at later stages specifically in tooth root formation. Although the expression of Osx is positive in crown regions, odontoblast-Osx-cKO mice showed no apparent changes in the crown, which may be ascribable to compensation effects of other molecules in the crown but not in the root. Conditional deletion of the downstream effector β-catenin and upstream regulators Nfic and Smad4 of Osx in dental mesenchyme also resulted in rootless molars or short roots in mice with disorders of odontoblasts, as mentioned above (Gao et al. 2009, Kim et al. 2013). Therefore, we concluded that Osx is central to only root formation by regulating odontoblast differentiation, maturation and root elongation, but not crown development.

Potential role of odontoblast heterogeneity in tooth development

Given the fact that conditional knockout of Osx in odontoblasts showed only abnormality in roots but not in crowns, odontoblast heterogeneity in functional and regulatory mechanisms might exist (Park et al. 2007, Gao et al. 2009, Kim et al. 2013, 2015, Zhang et al. 2014). This proposal was confirmed by Bae et al. (2013). They identified some low columnar odontoblasts that are essential for root initiation and elongation, but not involved in crown development. This group of odontoblasts was named ‘apical odontoblasts’ (AOds), because they were observed only in the apical region of forming dental roots. Further mechanistic studies revealed that AOds expressed Osx in root development, with related signalling Nfic and β-catenin (Bae et al. 2013). The unique morphological and functional characteristics of AOds illustrate the existence of odontoblast heterogeneity in tooth root and crown formation. In view of the temporal–spatial expression pattern of Osx and its close relationship with Nfic and β-catenin, how Osx mediates the function of AOds to underlie differences from crown odontoblasts in tooth development needs further explorations.

Function of Osx in Cementoblasts

Besides odontoblasts, different developmental phenotypes between root and crown might be attributed to cementoblasts, which are derived from dental follicle cells and form the cementum matrix. Cementoblasts possess many genetic properties similar to those of osteoblasts, including the expressions of key marker genes such as DMP1, OPN, BSP and Osx (Somerman et al. 1990, Bosshardt 2005).

Osx induces pre-cementoblasts to differentiate into cementoblasts and promotes cementum formation. Hirata et al. (2009) observed the immunolocalization patterns of Runx2 and Osx during rat molar tooth formation. Pre-cementoblasts expressed only Runx2, whilst mature cementoblasts expressed both Runx2 and Osx. Cao et al. (2015) further investigated the function of Osx in cementogenesis. Immunohistochemical staining showed a weak but reproducible signal of Osx in dental follicle cells but not in HERS cells at 2 weeks postnatally. Osx expressed in the cementoblasts and cementocytes at 3 weeks postnatally, and then sharply increased at 4–6 weeks postnatally, closely correlated with the formation of cellular cementum. Similar to its function and related mechanisms in osteogenesis and dentinogenesis, Osx in cementoblasts controls cementum formation via downregulating Wnt-signalling and increasing expressions of BSP, ALP and dickkopf1 (DKK1) in an inhibited cell proliferation and promoted differentiation and mineralization mode. The conditional deletion of Osx in the dental mesenchymal cells severely frustrated the formation of cellular cementum due to reductions in cementocyte number and mineralization rate (Cao et al. 2012). These findings indicate potential role of cementoblastic Osx in determining different developmental phenotypes between root and crown.

Regulatory mechanisms of Osx expression

Runx2-dependent regulatory mechanisms

Osx, as a key transcriptional factor specifically expressed and functioning in the mesenchyme, receives signals from the epithelium in tooth development. As mentioned above, Osx is a downstream target of Runx2 in the dental mesenchyme (Nakashima et al. 2002, Nishio et al. 2006). Actually, Runx2 acts as both a sensor for the epithelial signal and an effector to induce downstream changes. BMP2, identified as an important HERS signal implicated in the determination of tooth root development, functions also as an upstream of Runx2 and an inducer of Osx expression, which controls Osx indirectly through a Runx2-dependent manner via BMP2/Smad pathway (Nakashima et al. 2002). Nfic is another important factor participating in tooth root development (Liu et al. 2015). Nfic-deficient mice exhibit short and abnormal root phenotypes with normal crown formation (Steele-Perkins et al. 2003, Park et al. 2007, Lee et al. 2009). It has been shown by Lee et al. (2014) for the first time that Runx2-dependent Osx regulation in the HERS-related BMP2 signalling is mediated in part by Nfic. Nfic was proved to function as an intermediary transducer between Runx2 and Osx.

Runx2-independent regulatory mechanisms

Recent studies also suggest Runx2-independent regulatory mechanisms of Osx expression. Ulsamer et al. (2008) reported no expression of Osx in Runx2-null calvarial cells, but induced expression by BMP2 treatment. They discovered that BMP2 is capable of regulating Osx through upregulation and phosphorylation of distal-less homeobox5 (Dlx5), which further binds to the SBD in the Osx promotor. BMP2 also induces Osterix protein levels through Akt, a member of the serine/threonine-specific protein kinase (Choi et al. 2011b). Besides, PI3-kinase/Akt signalling is crucial to Smad-induced Osx expression in response to BMP2 (Mandal et al. 2010). BMP2 treatment on human mesenchymal stem cells phosphorylated and activated p38 and Erk1/2 in the MAPK signalling, which positively regulated protein stability and transcriptional activity of Osx (Ulsamer et al. 2008, Ortuno et al. 2010, Choi et al. 2011a). Moreover, inositol-requiring protein 1-α (IRE1α) and its target transcription factor X-box binding protein 1 (XBP1) have the capacity of stimulating BMP2-induced Osx expression to promote the maturation of pre-osteoblasts into osteoblasts (Tohmonda et al. 2011). In addition, Msx2 regulates Osx expression through Runx2-independent pathways in BMP2 signalling (Matsubara et al. 2008). These studies highlight the importance of BMP2 signalling in the regulation of Osx expression.

BMP4 also induces Osx expression, because the deletion of BMP4 in early odontogenesis reduced the expression of Dlx5 and Osx in odontoblasts (Gluhak-Heinrich et al. 2010). Celil & Campbell (2005) found that insulin-like growth factor I (IGF-I) mediates Osx expression via PKD and MAPK signalling in hMSC. Besides, Pax5 was reported to enhance Osx promoter activity in a manner dependent on the paired domain in MC3T3-E1 cells (Hinoi et al. 2012). Furthermore, studies have demonstrated that peptidyl-prolyl isomerase 1 (Pin1) and several kinases such as protein kinase A (PKA), glycogen synthase kinase 3-alpha (GSK3-α) and calmodulin-dependent kinase II (CaMKII) could modulate the function of Osx at posttranslational level through phosphorylation, regulation of protein stabilization and transcriptional activity (Choi et al. 2013, Li et al. 2013, He et al. 2014, Lee et al. 2015). Hosoya et al. confirmed that small ubiquitin-related modifier (SUMO) conjugation (SUMOylation) plays important roles in regulating the transcriptional activity of Osx in odontoblast lineage cells during dentine formation (Hosoya et al. 2013). Strikingly, Osx could even bind and stimulate the upstream CCACCC site in its promoter to regulate its own expression, forming a positive feedback mechanism (Barbuto & Mitchell 2013).

These mechanistic reports uncover both genetic and epigenetic regulations of Osx expression (Fig. 1). To summarize, in tooth root development, the dental epithelium (HERS) transmits signals to initiate the developmental process, whilst Osx serves as a point of signal integration for developmental signals and mesenchymal effectors. Crosstalks between HERS and Osx are multiple, involving epithelial signals such as BMP2 and BMP4 and several mesenchymal factors including Runx2, Nfic, Dlx5. The potential feedback regulation from Osx to HERS has not been documented. Thoroughly elucidating these crosstalks will be beneficial for the comprehension of the different process of tooth root and crown formation and the treatment of congenital diseases of tooth roots.

Figure 1.

Figure 1

Open in a new tab

Genetic and epigenetic regulations of Osx expression. The expression of Osx is positively regulated by both epithelial signals such as BMP and mesenchymal factors including Runx2, Nfic, Dlx5, etc. Therefore, these upstream molecules could become the targets to manipulate Osx expression. Osx is crucial to the differentiation of apical odontoblasts and cementoblasts and the expression of matrix proteins during tooth root development, which is supported by short and thin root dentine but normal crown phenotypes of odontoblastic Osx-cKO mice.

Clinical implications

Some clinical developmental diseases of the tooth root such as aberrant root formation and the anomaly of short thin roots have been reported with currently no cure (Catala et al. 1995, Apajalahti et al. 1999, Saini et al. 2004). These congenital conditions result in early loss of teeth postnatally, with the aetiology remaining unknown (Catala et al. 1995, Apajalahti et al. 1999). Given the central role of Osx in tooth root development, it will be of great benefit to investigate whether these human diseases are caused by the defect of Osx expression and/or function, as seen in Osx-deficient mice (Zhang et al. 2014, Kim et al. 2015). Furthermore, genetic treatments by the specific BMP signals (Matsubara et al. 2008, Gluhak-Heinrich et al. 2010), and epigenetic manipulations by posttranslational modifications such as phosphorylation (Ulsamer et al. 2008, He et al. 2014), may be feasible to promote Osx in the dental mesenchyme postnatally. In this regard, a promising approach might be achieved to regenerate the congenitally diseased root, and the regenerative therapy might be the best choice for patients with developmental tooth diseases.

Conclusions

  • Mesenchymal differences regarding key transcription factors underlie different developmental phenotypes between root and crown.

  • The differential temporal–spatial expression patterns of osteogenic key transcription factors in tooth development explain mesenchymal differences between root and crown. Runx2 functions primarily at earlier stages embryonically in tooth formation, whilst Osx participates at later stages specifically in tooth roots development.

  • Osx is considered as a key regulator for not only dentine matrix apposition but also odontoblast differentiation and mineralization. Furthermore, Osx is capable of inducing cementoblast differentiation and promoting cementum formation.

  • Short and thin root dentine but normal crown phenotypes of odontoblastic Osx-cKO mice support the site-specific function of Osx in promoting odontoblast and cementoblast differentiation and root elongation in tooth root development.

  • A comprehensive understanding of regulation mechanisms of Osx expression is beneficial to obtain a promising regenerative approach to clinical developmental diseases of tooth root.

Acknowledgments

This research was supported by the National Natural Science Foundation of China (81170929), and ShanXi provincial Natural Science Foundation (2014JM4114).

Footnotes

Conflict of interest

The authors have stated explicitly that there are no conflicts of interest in connection with this article.

References

  1. Apajalahti S, Arte S, Pirinen S. Short root anomaly in families and its association with other dental anomalies. European Journal of Oral Sciences. 1999;107:97–101. doi: 10.1046/j.0909-8836.1999.eos107204.x. [DOI] [PubMed] [Google Scholar]
  2. Bae CH, Kim TH, Chu JY, Cho ES. New population of odontoblasts responsible for tooth root formation. Gene Expression Patterns. 2013;13:197–202. doi: 10.1016/j.gep.2013.04.001. [DOI] [PubMed] [Google Scholar]
  3. Barbuto R, Mitchell J. Regulation of the osterix (Osx, Sp7) promoter by osterix and its inhibition by parathyroid hormone. Journal of Molecular Endocrinology. 2013;51:99–108. doi: 10.1530/JME-12-0251. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Bosshardt DD. Are cementoblasts a subpopulation of osteoblasts or a unique phenotype? Journal of Dental Research. 2005;84:390–406. doi: 10.1177/154405910508400501. [DOI] [PubMed] [Google Scholar]
  5. Cabay RJ. An overview of molecular and genetic alterations in selected benign odontogenic disorders. Archives of Pathology & Laboratory Medicine. 2014;138:754–8. doi: 10.5858/arpa.2013-0057-SA. [DOI] [PubMed] [Google Scholar]
  6. Cao Z, Zhang H, Zhou X, et al. Genetic evidence for the vital function of Osterix in cementogenesis. Journal of Bone Mineral Research. 2012;27:1080–92. doi: 10.1002/jbmr.1552. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Cao Z, Liu R, Zhang H, et al. Osterix controls cementoblast differentiation through downregulation of Wnt-signaling via enhancing DKK1 expression. International Journal of Biological Sciences. 2015;11:335–44. doi: 10.7150/ijbs.10874. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Catala M, Zaragoza A, Estrela F, Valdemoro C. Unusual case of rootless premolar. Pediatric Dentistry. 1995;17:127–8. [PubMed] [Google Scholar]
  9. Celil AB, Campbell PG. BMP-2 and insulin-like growth factor-I mediate Osterix (Osx) expression in human mesenchymal stem cells via the MAPK and protein kinase D signaling pathways. The Journal of Biological Chemistry. 2005;280:31353–9. doi: 10.1074/jbc.M503845200. [DOI] [PubMed] [Google Scholar]
  10. Chen S, Rani S, Wu Y, et al. Differential regulation of dentin sialophosphoprotein expression by Runx2 during odontoblast cytodifferentiation. The Journal of Biological Chemistry. 2005;280:29717–27. doi: 10.1074/jbc.M502929200. [DOI] [PubMed] [Google Scholar]
  11. Chen S, Gluhak-Heinrich J, Wang YH, et al. Runx2, osx, and dspp in tooth development. Journal of Dental Research. 2009;88:904–9. doi: 10.1177/0022034509342873. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Choi YH, Gu YM, Oh JW, Lee KY. Osterix is regulated by Erk1/2 during osteoblast differentiation. Biochemical and Biophysical Research Communications. 2011a;415:472–8. doi: 10.1016/j.bbrc.2011.10.097. [DOI] [PubMed] [Google Scholar]
  13. Choi YH, Jeong HM, Jin YH, Li H, Yeo CY, Lee KY. Akt phosphorylates and regulates the osteogenic activity of Osterix. Biochemical and Biophysical Research Communications. 2011b;411:637–41. doi: 10.1016/j.bbrc.2011.07.009. [DOI] [PubMed] [Google Scholar]
  14. Choi YH, Choi JH, Oh JW, Lee KY. Calmodulin-dependent kinase II regulates osteoblast differentiation through regulation of Osterix. Biochemical and Biophysical Research Communications. 2013;432:248–55. doi: 10.1016/j.bbrc.2013.02.005. [DOI] [PubMed] [Google Scholar]
  15. D’Souza RN, Cavender A, Sunavala G, et al. Gene expression patterns of murine dentin matrix protein 1 (Dmp1) and dentin sialophosphoprotein (DSPP) suggest distinct developmental functions in vivo. Journal of Bone and Mineral Research. 1997;12:2040–9. doi: 10.1359/jbmr.1997.12.12.2040. [DOI] [PubMed] [Google Scholar]
  16. D’Souza RN, Aberg T, Gaikwad J, et al. Cbfa1 is required for epithelial-mesenchymal interactions regulating tooth development in mice. Development. 1999;126:2911–20. doi: 10.1242/dev.126.13.2911. [DOI] [PubMed] [Google Scholar]
  17. Gao Y, Jheon A, Nourkeyhani H, Kobayashi H, Ganss B. Molecular cloning, structure, expression, and chromosomal localization of the human Osterix (SP7) gene. Gene. 2004;341:101–10. doi: 10.1016/j.gene.2004.05.026. [DOI] [PubMed] [Google Scholar]
  18. Gao Y, Yang G, Weng T, et al. Disruption of Smad4 in odontoblasts causes multiple keratocystic odontogenic tumors and tooth malformation in mice. Molecular and Cellular Biology. 2009;29:5941–51. doi: 10.1128/MCB.00706-09. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Gluhak-Heinrich J, Guo D, Yang W, et al. New roles and mechanism of action of BMP4 in postnatal tooth cytodifferentiation. Bone. 2010;46:1533–45. doi: 10.1016/j.bone.2010.02.024. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Hatta M, Yoshimura Y, Deyama Y, Fukamizu A, Suzuki K. Molecular characterization of the zinc finger transcription factor, Osterix. International Journal of Molecular Medicine. 2006;17:425–30. [PubMed] [Google Scholar]
  21. He S, Choi YH, Choi JK, Yeo CY, Chun C, Lee KY. Protein kinase A regulates the osteogenic activity of Osterix. Journal of Cellular Biochemistry. 2014;115:1808–15. doi: 10.1002/jcb.24851. [DOI] [PubMed] [Google Scholar]
  22. Hinoi E, Nakatani E, Yamamoto T, et al. The transcription factor paired box-5 promotes osteoblastogenesis through direct induction of Osterix and Osteocalcin. Journal of Bone and Mineral Research. 2012;27:2526–34. doi: 10.1002/jbmr.1708. [DOI] [PubMed] [Google Scholar]
  23. Hirata A, Sugahara T, Nakamura H. Localization of runx2, osterix, and osteopontin in tooth root formation in rat molars. The Journal of Histochemistry and Cytochemistry. 2009;57:397–403. doi: 10.1369/jhc.2008.952192. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Hosoya A, Yukita A, Ninomiya T, et al. Localization of SUMOylation factors and Osterix in odontoblast lineage cells during dentin formation and regeneration. Histochemistry and Cell Biology. 2013;140:201–11. doi: 10.1007/s00418-013-1076-y. [DOI] [PubMed] [Google Scholar]
  25. Huang XF, Chai Y. Molecular regulatory mechanism of tooth root development. International Journal of Oral Science. 2012;4:177–81. doi: 10.1038/ijos.2012.61. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Huang X, Xu X, Bringas P, Jr, Hung YP, Chai Y. Smad4-Shh-Nfic signaling cascade-mediated epithelial-mesenchymal interaction is crucial in regulating tooth root development. Journal of Bone and Mineral Research. 2010;25:1167–78. doi: 10.1359/jbmr.091103. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Jacob A, Zhang Y, George A. Transcriptional regulation of dentin matrix protein 1 (DMP1) in odontoblasts and osteoblasts. Connective Tissue Research. 2014;55(Suppl 1):107–12. doi: 10.3109/03008207.2014.923850. [DOI] [PubMed] [Google Scholar]
  28. Kim TH, Bae CH, Lee JC, et al. beta-catenin is required in odontoblasts for tooth root formation. Journal of Dental Research. 2013;92:215–21. doi: 10.1177/0022034512470137. [DOI] [PubMed] [Google Scholar]
  29. Kim TH, Bae CH, Lee JC, et al. Osterix regulates tooth root formation in a site-specific manner. Journal of Dental Research. 2015;94:430–8. doi: 10.1177/0022034514565647. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Lan Y, Jia S, Jiang R. Molecular patterning of the mammalian dentition. Seminars in Cell & Developmental Biology. 2014;25–26:61–70. doi: 10.1016/j.semcdb.2013.12.003. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Lee DS, Park JT, Kim HM, et al. Nuclear factor I-C is essential for odontogenic cell proliferation and odontoblast differentiation during tooth root development. The Journal of Biological Chemistry. 2009;284:17293–303. doi: 10.1074/jbc.M109.009084. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Lee DS, Choung HW, Kim HJ, et al. NFI-C regulates osteoblast differentiation via control of osterix expression. Stem Cells. 2014;32:2467–79. doi: 10.1002/stem.1733. [DOI] [PubMed] [Google Scholar]
  33. Lee SH, Jeong HM, Han Y, Cheong H, Kang BY, Lee KY. Prolyl isomerase Pin1 regulates the osteogenic activity of Osterix. Molecular and Cellular Endocrinology. 2015;400:32–40. doi: 10.1016/j.mce.2014.11.017. [DOI] [PubMed] [Google Scholar]
  34. Li H, Jeong HM, Choi YH, et al. Glycogen synthase kinase 3 alpha phosphorylates and regulates the osteogenic activity of Osterix. Biochemical and Biophysical Research Communications. 2013;434:653–8. doi: 10.1016/j.bbrc.2013.03.137. [DOI] [PubMed] [Google Scholar]
  35. Lind V. Short root anomaly. Scandinavian Journal of Dental Research. 1972;80:85–93. doi: 10.1111/j.1600-0722.1972.tb00268.x. [DOI] [PubMed] [Google Scholar]
  36. Liu Y, Feng J, Li J, Zhao H, Ho TV, Chai Y. An Nfic-hedgehog signaling cascade regulates tooth root development. Development. 2015;142:3374–82. doi: 10.1242/dev.127068. [DOI] [PMC free article] [PubMed] [Google Scholar]
  37. Mandal CC, Drissi H, Choudhury GG, Ghosh-Choudhury N. Integration of phosphatidylinositol 3-kinase, Akt kinase, and Smad signaling pathway in BMP-2-induced osterix expression. Calcified Tissue International. 2010;87:533–40. doi: 10.1007/s00223-010-9419-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Matsubara T, Kida K, Yamaguchi A, et al. BMP2 regulates Osterix through Msx2 and Runx2 during osteoblast differentiation. The Journal of Biological Chemistry. 2008;283:29119–25. doi: 10.1074/jbc.M801774200. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Nakashima K, Zhou X, Kunkel G, et al. The novel zinc finger-containing transcription factor osterix is required for osteoblast differentiation and bone formation. Cell. 2002;108:17–29. doi: 10.1016/s0092-8674(01)00622-5. [DOI] [PubMed] [Google Scholar]
  40. Nishio Y, Dong Y, Paris M, O’Keefe RJ, Schwarz EM, Drissi H. Runx2-mediated regulation of the zinc finger Osterix/Sp7 gene. Gene. 2006;372:62–70. doi: 10.1016/j.gene.2005.12.022. [DOI] [PubMed] [Google Scholar]
  41. Ortuno MJ, Ruiz-Gaspa S, Rodriguez-Carballo E, et al. p38 regulates expression of osteoblast-specific genes by phosphorylation of osterix. The Journal of Biological Chemistry. 2010;285:31985–94. doi: 10.1074/jbc.M110.123612. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Park JC, Herr Y, Kim HJ, Gronostajski RM, Cho MI. Nfic gene disruption inhibits differentiation of odontoblasts responsible for root formation and results in formation of short and abnormal roots in mice. Journal of Periodontology. 2007;78:1795–802. doi: 10.1902/jop.2007.060363. [DOI] [PubMed] [Google Scholar]
  43. Qin W, Yang F, Deng R, et al. Smad 1/5 is involved in bone morphogenetic protein-2-induced odontoblastic differentiation in human dental pulp cells. Journal of Endodontics. 2012;38:66–71. doi: 10.1016/j.joen.2011.09.025. [DOI] [PubMed] [Google Scholar]
  44. Saini TS, Kimmes NS, Westerman GH. Aberrant root formation: review of root genesis and three case reports. Pediatric Dentistry. 2004;26:261–5. [PubMed] [Google Scholar]
  45. Shields ED, Bixler D, el-Kafrawy AM. A proposed classification for heritable human dentine defects with a description of a new entity. Archives of Oral Biology. 1973;18:543–53. doi: 10.1016/0003-9969(73)90075-7. [DOI] [PubMed] [Google Scholar]
  46. Sinha KM, Zhou X. Genetic and molecular control of osterix in skeletal formation. Journal of Cellular Biochemistry. 2013;114:975–84. doi: 10.1002/jcb.24439. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. Somerman MJ, Shroff B, Agraves WS, et al. Expression of attachment proteins during cementogenesis. Journal de Biologie Buccale. 1990;18:207–14. [PubMed] [Google Scholar]
  48. Steele-Perkins G, Butz KG, Lyons GE, et al. Essential role for NFI-C/CTF transcription-replication factor in tooth root development. Molecular and Cellular Biology. 2003;23:1075–84. doi: 10.1128/MCB.23.3.1075-1084.2003. [DOI] [PMC free article] [PubMed] [Google Scholar]
  49. Thesleff I. Epithelial-mesenchymal signalling regulating tooth morphogenesis. Journal of Cell Science. 2003;116:1647–8. doi: 10.1242/jcs.00410. [DOI] [PubMed] [Google Scholar]
  50. Thomas HF, Kollar EJ. Differentiation of odontoblasts in grafted recombinants of murine epithelial root sheath and dental mesenchyme. Archives of Oral Biology. 1989;34:27–35. doi: 10.1016/0003-9969(89)90043-5. [DOI] [PubMed] [Google Scholar]
  51. Tohmonda T, Miyauchi Y, Ghosh R, et al. The IRE1alpha-XBP1 pathway is essential for osteoblast differentiation through promoting transcription of Osterix. EMBO Reports. 2011;12:451–7. doi: 10.1038/embor.2011.34. [DOI] [PMC free article] [PubMed] [Google Scholar]
  52. Tummers M, Thesleff I. The importance of signal pathway modulation in all aspects of tooth development. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution. 2009;312B:309–19. doi: 10.1002/jez.b.21280. [DOI] [PubMed] [Google Scholar]
  53. Ulsamer A, Ortuno MJ, Ruiz S, et al. BMP-2 induces Osterix expression through up-regulation of Dlx5 and its phosphorylation by p38. The Journal of Biological Chemistry. 2008;283:3816–26. doi: 10.1074/jbc.M704724200. [DOI] [PubMed] [Google Scholar]
  54. Yang G, Li X, Yuan G, Liu P, Fan M. The effects of osterix on the proliferation and odontoblastic differentiation of human dental papilla cells. Journal of Endodontics. 2014;40:1771–7. doi: 10.1016/j.joen.2014.04.012. [DOI] [PubMed] [Google Scholar]
  55. Zeichner-David M, Oishi K, Su Z, et al. Role of Hertwig’s epithelial root sheath cells in tooth root development. Developmental Dynamics. 2003;228:651–63. doi: 10.1002/dvdy.10404. [DOI] [PubMed] [Google Scholar]
  56. Zhang H, Jiang Y, Qin C, Liu Y, Ho SP, Feng JQ. Essential role of Osterix for tooth root but not crown dentin formation. Journal of Bone and Mineral Research. 2014;30:742–6. doi: 10.1002/jbmr.2391. [DOI] [PMC free article] [PubMed] [Google Scholar]

RESOURCES