Different roles of Runx2 during early neural crest-derived bone and tooth development

Common and specific gene regulatory programs in zebrafish caudal fin regeneration at single-cell resolution

Following amputation, zebrafish regenerate their injured caudal fin through lineage-restricted reprogramming. Although previous studies have charted various genetic and epigenetic dimensions of this process, the intricate gene regulatory programs shared by, or unique to, different regenerating cell types remain underinvestigated. Here, we mapped the regulatory landscape of fin regeneration by applying paired snRNA-seq and snATAC-seq on uninjured and regenerating fins. This map delineates the regulatory dynamics of predominant cell populations at multiple stages of regeneration. We observe a marked increase in the accessibility of chromatin regions associated with regenerative and developmental processes at 1 dpa, followed by a gradual closure across major cell types at later stages. This pattern is distinct from that of transcriptomic dynamics, which is characterized by several waves of gene upregulation and downregulation. We identified and in vivo validated cell-type-specific and position-specific regeneration-responsive enhancers and constructed regulatory networks by cell type and stage. Our single-cell resolution transcriptomic and chromatin accessibility map across regenerative stages provides new insights into regeneration regulatory mechanisms and serves as a valuable resource for the community.

"A Friend Among Strangers" or the Ambiguous Roles of Runx2

The transcription factor Runx2 plays a crucial role in regulating osteogenic differentiation and skeletal development. This factor not only controls the expression of genes involved in bone formation, but also interacts with signaling pathways such as the Notch pathway, which are essential for body development. However, studies have produced conflicting results regarding the relationship between Runx2 and the Notch pathway. Some studies suggest a synergistic interaction between these molecules, while others suggest an inhibitory one, for example, the interplay between Notch signaling, Runx2, and vitamin D3 in osteogenic differentiation and bone remodeling. The findings suggest a complex relationship between Notch signaling and osteogenic differentiation, with ongoing research needed to clarify the mechanisms involved and resolve existing contradictions regarding role of Notch in this process. Additionally, there is increasing evidence of contradictory roles for Runx2 in various tissues and organs, both under normal conditions and in pathological states. This diversity of roles makes Runx2 a potential therapeutic target, offering new directions for research. In this review, we have discussed the mechanisms of osteogenic differentiation and the important role of Runx2 in this process. We have also examined its relationship with different signaling pathways. However, there are still many uncertainties and inconsistencies in our current understanding of these interactions. Additionally, given that Runx2 is also involved in numerous other events in various tissues, we have tried to comprehensively examine its functions outside the skeletal system.

Activation of Nuclear Factor Erythroid 2-Related Factor 2 Transcriptionally Upregulates Ectonucleotide Pyrophosphatase/Phosphodiesterase 1 Expression and Inhibits Ectopic Calcification in Mice

Calcification plays a key role in biological processes, and breakdown of the regulatory mechanism results in a pathological state such as ectopic calcification. We hypothesized that ENPP1, the enzyme that produces the calcification inhibitor pyrophosphate, is transcriptionally regulated by Nrf2, and that Nrf2 activation augments ENPP1 expression to inhibit ectopic calcification. Cell culture experiments were performed using mouse osteoblastic cell line MC3T3-E1. Nrf2 was activated by 5-aminolevulinic acid and sodium ferrous citrate. Nrf2 overexpression was induced by the transient transfection of an Nrf2 expression plasmid. ENPP1 expression was monitored by real-time RT-PCR. Because the promoter region of ENPP1 contains several Nrf2-binding sites, chromatin immunoprecipitation using an anti-Nrf2 antibody followed by real-time PCR (ChIP-qPCR) was performed. The relationship between Nrf2 activation and osteoblastic differentiation was examined by alkaline phosphatase (ALP) and Alizarin red staining. We used mice with a hypomorphic mutation in ENPP1 (ttw mice) to analyze whether Nrf2 activation inhibits ectopic calcification. Nrf2 and Nrf2 overexpression augmented ENPP1 expression and inhibited osteoblastic differentiation, as indicated by ALP expression and calcium deposits. ChIP-qPCR showed that some putative Nrf2-binding sites in the ENPP1 promoter region were bound by Nrf2. Nrf2 activation inhibited ectopic calcification in mice. ENPP1 gene expression was transcriptionally regulated by Nrf2, and Nrf2 activation augmented ENPP1 expression, leading to the attenuation of osteoblastic differentiation and ectopic calcification in vitro and in vivo. Nrf2 activation has a therapeutic potential for preventing ectopic calcification.

Single-cell multiomics decodes regulatory programs for mouse secondary palate development

Perturbations in gene regulation during palatogenesis can lead to cleft palate, which is among the most common congenital birth defects. Here, we perform single-cell multiome sequencing and profile chromatin accessibility and gene expression simultaneously within the same cells (n = 36,154) isolated from mouse secondary palate across embryonic days (E) 12.5, E13.5, E14.0, and E14.5. We construct five trajectories representing continuous differentiation of cranial neural crest-derived multipotent cells into distinct lineages. By linking open chromatin signals to gene expression changes, we characterize the underlying lineage-determining transcription factors. In silico perturbation analysis identifies transcription factors SHOX2 and MEOX2 as important regulators of the development of the anterior and posterior palate, respectively. In conclusion, our study charts epigenetic and transcriptional dynamics in palatogenesis, serving as a valuable resource for further cleft palate research.

The inhibition of mineralisation by fibroblast growth factor 2 is associated with the altered expression of genes regulating phosphate balance

The study aimed to determine whether inhibitory effects of fibroblast growth factor 2 (FGF2) on mineralisation in dental pulp (DP) cultures were associated with changes in the expression of genes regulating phosphate balance (Enpp1, Ank, Slc20a2, Alpl, Phospho1, and Xpr1). DP cultures growing under mineralisation-inducing conditions were exposed to FGF2 and inhibitors of the FGFR and MEK/ERK1/2 signaling pathways. Mineralisation, culture cellularity, and gene expression were examined at various time points. Statistical analysis was performed using analysis of variance followed by the Holm-Šídák test. Control cultures exhibited transient increases in Enpp1 and Ank, continuous increases in Alpl, Phospho1, and Xpr1, and continuous decreases in Slc20a2. FGF2 increased Enpp1, Ank, and Slc20a2 and decreased Alpl, Phospho1, and Xpr1, whereas the FGF2 withdrawal and inhibition of FGFR and MEK/ERK1/2 exerted opposite effects. These changes suggest that FGF2-mediated decreases in mineralisation could be functionally coupled to the altered regulation of phosphate formation and transport.

Amyloid-mediated remineralization for tooth hypoplasia of cleidocranial dysplasia

Introduction

Cleidocranial dysplasia (CCD) is an autosomal-dominant, heritable skeletal and dental disease, involving hypoplastic clavicles, defective ossification of the anterior fontanelle, dentin and enamel hypoplasia, and supernumerary teeth, which can seriously affect the oral and mental health of patients. Amyloid-like protein aggregation, which is established by lysozyme conjugated with polyethylene glycol (Lyso-PEG), forms a mineralized nanofilm layer on a healthy enamel surface. However, whether it can form a remineralization layer in dental tissues from CCD remains unclear.

Methods

This study evaluated deciduous teeth from healthy individuals and a patient with CCD. Because pulp and dentin are functionally closely related, stem cells from human exfoliated deciduous teeth (SHED) from CCD patients and healthy individuals were collected to compare their biological properties.

Results

The results found that deciduous teeth from patients with CCD exhibited dentin hypoplasia. In addition, the proliferative ability and osteogenic potential of SHED from patients with CCD were lower than those of control individuals. Finally, Lyso-PEG was applied to dentin from the CCD and control groups, showing a similar remineralization-induced effect on the dentin surfaces of the two groups.

Conclusion

These results extend our understanding of the dentin and SHED of patients with CCD, exhibiting good caries-preventive capacity and good biocompatibility of Lyso-PEG, thus providing a novel dental therapy for CCD and patients with tooth hypoplasia.

Dental niche cells directly contribute to tooth reconstitution and morphogenesis

Mammalian teeth develop from the inductive epithelial-mesenchymal interaction, an important mechanism shared by many organs. The cellular basis for such interaction remains elusive. Here, we generate a dual-fluorescence model to track and analyze dental cells from embryonic to postnatal stages, in which Pitx2⁺ epithelium and Msx1⁺ mesenchyme are sufficient for tooth reconstitution. Single-cell RNA sequencing and spatial mapping further revealed critical cellular dynamics during molar development, where tooth germs are organized by Msx1⁺Sdc1⁺ dental papilla and surrounding dental niche. Surprisingly, niche cells are more efficient in tooth reconstitution and can directly regenerate papilla cells through interaction with dental epithelium. Finally, from the dental niche, we identify a group of previously unappreciated migratory Msx1⁺ Sox9⁺ cells as the potential cell origin for dental papilla. Our results indicate that the dental niche cells directly contribute to tooth organogenesis and provide critical insights into the essential cell composition for tooth engineering.

CK1α/RUNX2 Axis in the Bone Marrow Microenvironment: A Novel Therapeutic Target in Multiple Myeloma

Simple Summary

Multiple myeloma (MM) is an incurable disease for which novel therapeutic approaches targeting the malignant cells and the associated bone disease are urgently needed. CK1α is a protein kinase that plays a crucial role in the signaling network that sustains plasma cell (PC) survival and bone disease. This protein regulates Wnt/β-catenin signaling, which is fundamental for both MM cell survival and mesenchymal stromal cell (MSC) osteogenic differentiation. In this study, we investigated its involvement in MM–MSC cross-talk. We found that, by lowering CK1α expression levels in co-cultures of MM and MSC cells, expression of RUNX2—the master regulator of osteogenic differentiation—was regulated differently in the two cell types. Our data suggest the possibility of using a specific CK1α inhibitor as part of a novel therapeutic approach to selectively kill malignant PCs and overcome the blocking of osteogenic differentiation induced by MM cells in MSCs.

Abstract

Multiple myeloma (MM) is a malignant plasma cell (PC) neoplasm, which also displays pathological bone involvement. Clonal expansion of MM cells in the bone marrow causes a perturbation of bone homeostasis that culminates in MM-associated bone disease (MMABD). We previously demonstrated that the S/T kinase CK1α sustains MM cell survival through the activation of AKT and β-catenin signaling. CK1α is a negative regulator of the Wnt/β-catenin cascade, the activation of which promotes osteogenesis by directly stimulating the expression of RUNX2, the master gene regulator of osteoblastogenesis. In this study, we investigated the role of CK1α in the osteoblastogenic potential of mesenchymal stromal cells (MSCs) and its involvement in MM–MSC cross-talk. We found that CK1α silencing in in vitro co-cultures of MMs and MSCs modulated RUNX2 expression differently in PCs and in MSCs, mainly through the regulation of Wnt/β-catenin signaling. Our findings suggest that the CK1α/RUNX2 axis could be a potential therapeutic target for constraining malignant PC expansion and supporting the osteoblastic transcriptional program of MSCs, with potential for ameliorating MMABD. Moreover, considering that Lenalidomide treatment leads to MM cell death through Ikaros, Aiolos and CK1α proteasomal degradation, we examined its effects on the osteoblastogenic potential of MSC compartments.

BMP Signaling Pathway in Dentin Development and Diseases

BMP signaling plays an important role in dentin development. BMPs and antagonists regulate odontoblast differentiation and downstream gene expression via canonical Smad and non-canonical Smad signaling pathways. The interaction of BMPs with their receptors leads to the formation of complexes and the transduction of signals to the canonical Smad signaling pathway (for example, BMP ligands, receptors, and Smads) and the non-canonical Smad signaling pathway (for example, MAPKs, p38, Erk, JNK, and PI3K/Akt) to regulate dental mesenchymal stem cell/progenitor proliferation and differentiation during dentin development and homeostasis. Both the canonical Smad and non-canonical Smad signaling pathways converge at transcription factors, such as Dlx3, Osx, Runx2, and others, to promote the differentiation of dental pulp mesenchymal cells into odontoblasts and downregulated gene expressions, such as those of DSPP and DMP1. Dysregulated BMP signaling causes a number of tooth disorders in humans. Mutation or knockout of BMP signaling-associated genes in mice results in dentin defects which enable a better understanding of the BMP signaling networks underlying odontoblast differentiation and dentin formation. This review summarizes the recent advances in our understanding of BMP signaling in odontoblast differentiation and dentin formation. It includes discussion of the expression of BMPs, their receptors, and the implicated downstream genes during dentinogenesis. In addition, the structures of BMPs, BMP receptors, antagonists, and dysregulation of BMP signaling pathways associated with dentin defects are described.

RUNX2 Regulates Osteoblast Differentiation via the BMP4 Signaling Pathway

RUNX2 is a master osteogenic transcription factor, and mutations in RUNX2 cause the inherited skeletal disorder cleidocranial dysplasia (CCD). Studies have revealed that RUNX2 is not only a downstream target of the bone morphogenetic protein (BMP) pathway but can also regulate the expression of BMPs. However, the underlying mechanism of the regulation of BMPs by RUNX2 remains unknown. In this project, we diagnosed a CCD patient with a 7.86-Mb heterozygous deletion on chromosome 6 containing all exons of RUNX2 by multiplex ligation-dependent probe amplification (MLPA) and whole-genome sequencing (WGS). Bone marrow mesenchymal stem cells (BMSCs) were further extracted from patient alveolar bone fragments (CCD-BMSCs), an excellent natural model to explore the possible mechanism. The osteogenic differentiation ability of CCD-BMSCs was severely affected by RUNX2 heterozygous deletion. Also, BMP4 decreased most in BMP ligands, and CHRDL1, a BMP antagonist, was abnormally elevated in CCD-BMSCs. Furthermore, BMP4 treatment essentially rescued the osteogenic capacity of CCD-BMSCs, and RUNX2 overexpression reversed the abnormal expression of BMP4 and CHRDL1. Notably, we constructed CRISPR/Cas9 Runx2^+/m MC3T3-E1 cells, which simulated a variant in CCD-BMSCs, to exclude the interference of other gene deletions and the heterogeneity of the genetic background of primary cells, and verified all findings from the CCD-BMSCs. Moreover, the luciferase reporter experiment showed that RUNX2 could inhibit the transcription of CHRDL1. Through immunofluorescence, the inhibitory effect of CHRDL1 on BMP4/Smad signaling was confirmed in MC3T3-E1 cells. These results revealed that RUNX2 regulated the BMP4 pathway by inhibiting CHRDL1 transcription. We collectively identified a novel RUNX2/CHRDL1/BMP4 axis to regulate osteogenic differentiation and noted that BMP4 might be a valuable therapeutic option for treating bone diseases.

Appropriateness of standard cephalometric norms for the assessment of dentofacial characteristics in patients with cleidocranial dysplasia

OBJECTIVES

Cleidocranial dysplasia (CCD) is a rare skeletal syndrome affecting craniofacial and dental development. As a consequence, conventional cephalometric landmarks may not be valid for CCD patients, and the appropriateness of norms used for the general population should be critically discussed.

METHODS

Five patients 9- to 22-year-old (three females, two males) with CCD were included. Lateral-cephalograms, orthopantomographies, and intra-oral photos were retrospectively analysed. Lateral-cephalograms of 50 normal controls (ten for each CCD patient) matched for age and sex were selected from an online database. Cephalometric measurements of each CCD patients were compared with average values of matched controls using Wilcoxon signed-rank test for paired values (α = 0.05).

RESULTS

In CCD patients, a shortening of the cranial base was present (ΔSN = -17.1 mm, p = 0.043). Thus, the mandible (ΔSNPg = +9.5°, p = 0.043) and the maxilla (ΔSNA = +11.2°, p = 0.043) showed protrusion compared to the cranial base, despite a reduced maxillary (ΔCo-A = -15.1 mm, p = 0.043) and mandibular (ΔCo-Gn = -15.2 mm, p = 0.080) length. The mandibular divergence was reduced (ΔSN/GoGn = -6.4°, p = 0.043), a reduced overbite was present (ΔOverbite = -2.9 mm, p = 0.043), and the interincisal angle was increased (ΔInterincisalAngle = +13.7°, p = 0.043), mainly due to retro-inclination of lower incisors.

CONCLUSIONS

Standard cephalometric norms for the assessment of horizontal jaw position may not be applicable to CCD patients because of a reduced anterior cranial base length compared to normal subjects. Vertical relationships may not be affected, and mandibular hypodivergency was confirmed.

The Human Genetics of Dental Anomalies

The development of tooth is a highly complex procedure and mastered by specific genetic programs. Genetic alterations, environmental factors, and developmental timing can disturb the execution of these programs, and result in various dental anomalies like hypodontia/oligodontia, and supernumerary teeth, which are commonly seen in our clinical practice. Advances in molecular research enabled the identification of various genes involved in the pathogenesis of dental anomalies. In the near future, it will help provide a more accurate diagnosis and biological-based treatment for these anomalies. In this article, we present the molecular phenomenon of tooth development and the genetics of various dental anomalies.

Runx2 deficiency in junctional epithelium of mouse molars decreases the expressions of E-cadherin and junctional adhesion molecule 1

Junctional epithelium (JE) attaching to the enamel surface seals gaps around the teeth, functioning as the first line of gingival defense. Runt-related transcription factor 2 (Runx2) plays a role in epithelial cell fate, and the deficiency of Runx2 in JE causes periodontal destruction, while its effect on the barrier function of JE remains largely unexplored. In the present study, hematoxylin-eosin (H&E) staining revealed the morphological differences of JE between wild-type (WT) and Runx2 conditional knockout (cKO) mice. We speculated that these changes were related to the down-regulation of E-cadherin (E-cad), junctional adhesion molecule 1 (JAM1), and integrin β6 (ITGB6) in JE. Moreover, immunohistochemistry (IHC) was conducted to assess the expressions of these proteins. To verify the relationship between Runx2 and the three above-mentioned proteins, human gingival epithelial cells (HGEs) were cultured for in vitro experiment. The expression of Runx2 in HEGs was depleted by lentivirus. Quantitative real-time PCR (qRT-PCR) and Western blotting analysis were adopted to analyze the differences in mRNA and protein expressions. Taken together, Runx2 played a crucial role in maintaining the structure and function integrality of JE via regulating the expressions of E-cad and JAM1.

Runx2-Twist1 interaction coordinates cranial neural crest guidance of soft palate myogenesis

Cranial neural crest (CNC) cells give rise to bone, cartilage, tendons, and ligaments of the vertebrate craniofacial musculoskeletal complex, as well as regulate mesoderm-derived craniofacial muscle development through cell-cell interactions. Using the mouse soft palate as a model, we performed an unbiased single-cell RNA-seq analysis to investigate the heterogeneity and lineage commitment of CNC derivatives during craniofacial muscle development. We show that Runx2, a known osteogenic regulator, is expressed in the CNC-derived perimysial and progenitor populations. Loss of Runx2 in CNC-derivatives results in reduced expression of perimysial markers (Aldh1a2 and Hic1) as well as soft palate muscle defects in Osr2-Cre;Runx2fl/fl mice. We further reveal that Runx2 maintains perimysial marker expression through suppressing Twist1, and that myogenesis is restored in Osr2-Cre;Runx2fl/fl;Twist1fl/+ mice. Collectively, our findings highlight the roles of Runx2, Twist1, and their interaction in regulating the fate of CNC-derived cells as they guide craniofacial muscle development through cell-cell interactions.

Evolution and expansion of the RUNX2 QA repeat corresponds with the emergence of vertebrate complexity

Runt-related transcription factor 2 (RUNX2) is critical for the development of the vertebrate bony skeleton. Unlike other RUNX family members, RUNX2 possesses a variable poly-glutamine, poly-alanine (QA) repeat domain. Natural variation within this repeat is able to alter the transactivation potential of RUNX2, acting as an evolutionary 'tuning knob' suggested to influence mammalian skull shape. However, the broader role of the RUNX2 QA repeat throughout vertebrate evolution is unknown. In this perspective, we examine the role of the RUNX2 QA repeat during skeletal development and discuss how its emergence and expansion may have facilitated the evolution of morphological novelty in vertebrates.

Functional Effects of WNT10A Rare Variants Associated with Tooth Agenesis

Mutations in WNT10A have frequently been reported as etiologic for tooth agenesis (TA). However, the effects of WNT10A variation on gene/protein function and contribution to TA phenotypes remain poorly understood. Here, we performed bioinformatic and functional characterization analysis of WNT10A variants. In silico prediction of variant function was performed with VIPUR for all WNT10A missense variants reported in the Exome Aggregation Consortium database. Functional characterization experiments were then performed for selected WNT10A variants previously associated with TA. Expression vectors for wild-type and mutant WNT10A were made and transfected into stem cells from human exfoliated deciduous teeth (SHED) for evaluation of gene/protein function, WNT signaling activity, and effects on expression of relevant genes. While 75% of WNT10A variants were predicted neutral, most of the TA-associated variants received deleterious scores by potentially destabilizing or preventing the disulfide bond formation required for proper protein function. WNT signaling was significantly decreased with 8 of 13 variants tested, whereas wild-type-like activity was retained with 4 of 13 variants. WNT10A-mutant cells (T357I, R360C, and R379C mutants) showed reduced or impaired binding affinity to FZD5, suggesting a potential mechanism for the decreased WNT signaling. Mutant cells also had decreased WNT10A protein expression in comparison to wild-type cells. mRNA expression of PAX9, MSX1, AXIN2, and RUNX2 (known tooth development genes) was perturbed in mutant cells and quite significantly for PAX9 and RUNX2. Transcriptome analysis of wild-type and T357I-mutant cells identified 36 differentially expressed genes (26 downregulated, 10 upregulated) involved in skeletal system development and morphogenesis and pattern specification. WNT10A variants deemed pathogenic for TA likely affect protein folding and/or stabilization, leading to decreased WNT signaling and concomitant dysregulated expression of relevant genes. These findings may allow for improved interpretation of TA phenotypes upon clinical diagnosis while providing important insights toward the development of future tooth replacement therapies.

MicroRNA-378 Suppressed Osteogenesis of MSCs and Impaired Bone Formation via Inactivating Wnt/β-Catenin Signaling

MicroRNAs (miRNAs) have been reported to serve as silencers to repress gene expression at post-transcriptional levels. Multiple miRNAs have been demonstrated to play important roles in osteogenesis. MicroRNA (miR)-378, a conserved miRNA, was reported to mediate bone metabolism and influence bone development, but the detailed function and underlying mechanism remain obscure. In this study, the miR-378 transgenic (TG) mouse was developed to study the role of miR-378 in osteogenic differentiation as well as bone formation. The abnormal bone tissues and impaired bone quality were displayed in the miR-378 TG mice, and a delayed healing effect was observed during bone fracture of the miR-378 TG mice. The osteogenic differentiation of mesenchymal stem cells (MSCs) derived from this TG mouse was also inhibited. We also found that miR-378 mimics suppressed, whereas anti-miR-378 promoted osteogenesis of human MSCs. Two Wnt family members, Wnt6 and Wnt10a, were identified as bona fide targets of miR-378, and their expression was decreased by this miRNA, which eventually induced the inactivation of Wnt/β-catenin signaling. Finally, the short hairpin (sh)-miR-378-modified MSCs were locally injected into the fracture sites in an established mouse fracture model. The results indicated that miR-378 inhibitor therapy could promote bone formation and stimulate the healing process in vivo. In conclusion, miR-378 suppressed osteogenesis and bone formation via inactivating Wnt/β-catenin signaling, suggesting that miR-378 may be a potential therapeutic target for bone diseases.

CHD9 upregulates RUNX2 and has a potential role in skeletal evolution

BACKGROUND

Changes in gene regulation are widely recognized as an important driver of adaptive phenotypic evolution. However, the specific molecular mechanisms that underpin such changes are still poorly understood. Chromatin state plays an essential role in gene regulation, by influencing the accessibility of coding loci to the transcriptional machinery. Changes in the function of chromatin remodellers are therefore strong candidates to drive changes in gene expression associated with phenotypic adaptation. Here, we identify amino acid homoplasies in the chromatin remodeller CHD9, shared between the extinct marsupial thylacine and eutherian wolf which show remarkable skull convergence. CHD9 is involved in osteogenesis, though its role in the process is still poorly understood. We examine whether CHD9 is able to regulate the expression of osteogenic target genes and examine the function of a key substitution in the CHD9 DNA binding domain.

RESULTS

We examined whether CHD9 was able to upregulate its osteogenic target genes, RUNX2, Osteocalcin (OC) and ALP in HEK293T cells. We found that overexpression of CHD9 upregulated RUNX2, the master regulator of osteoblast cell fate, but not the downstream genes OC or ALP, supporting the idea that CHD9 regulates osteogenic progenitors rather than terminal osteoblasts. We also found that the evolutionary substitution in the CHD9 DNA binding domain does not alter protein secondary structure, but was able to drive a small but insignificant increase in RUNX2 activation. Finally, CHD9 was unable to activate an episomal RUNX2 promoter-reporter construct, suggesting that CHD9 requires the full chromatin complement for its function.

CONCLUSIONS

We provide new evidence to the role of CHD9 in osteogenic differentiation through its newly observed ability to upregulate the expression of RUNX2. Though we were unable to identify significant functional consequences of the evolutionary substitution in HEK293T cells, our study provides important steps forward in the functional investigation of protein homoplasy and its role in developmental processes. Mutations in coding genes may be a mechanism for driving adaptive changes in gene expression, and their validation is essential towards determining the functional consequences of evolutionary homoplasy.

Dual-Functionalized Apatite Nanocomposites with Enhanced Cytocompatibility and Osteogenesis for Periodontal Bone Regeneration

The development of biomimetic bone graft materials for periodontal tissue engineering is a field of topical interest. In this study, we designed a dual-functionalized apatite nanocomposite, which could integrate multiple molecular cues for manipulating the fate of periodontal ligament stem cells (PDLSCs). Briefly, inspired by mussels, a biomimetic nanohydroxyapatite was fabricated using a polydopamine structure as a template (named as tHA) and then surface-modified with bone-forming peptide-1 (BFP-1) and vascular endothelial growth factor-mimicking peptide (QK) via a single step of catechol chemistry. Our study showed that the biofunctions of tethered peptides were not compromised on the surface of apatite nanoparticles. Because of the synergistic effect of BFP-1 and QK peptides, the dual-functionalized apatite nanocomposite showed improved cytocompatibility compared to controls. Moreover, it can boost the proliferation and osteogenic differentiation of PDLSCs, indicating excellent bioactivity of tHA-BFP/QK nanoparticles on cell fate decision. More importantly, animal experiments showed that dual-functionalized apatite nanocomposites could dramatically promote the regeneration of periodontal bone. It is concluded that our work provides an instructive insight into the design of biomimetic apatite nanocomposites, which holds a great potential for applications in periodontal bone repair.

Complex Interplay between the RUNX Transcription Factors and Wnt/β-Catenin Pathway in Cancer: A Tango in the Night

Cells are designed to be sensitive to a myriad of external cues so they can fulfil their individual destiny as part of the greater whole. A number of well-characterised signalling pathways dictate the cell's response to the external environment and incoming messages. In healthy, well-ordered homeostatic systems these signals are tightly controlled and kept in balance. However, given their powerful control over cell fate, these pathways, and the transcriptional machinery they orchestrate, are frequently hijacked during the development of neoplastic disease. A prime example is the Wnt signalling pathway that can be modulated by a variety of ligands and inhibitors, ultimately exerting its effects through the β-catenin transcription factor and its downstream target genes. Here we focus on the interplay between the three-member family of RUNX transcription factors with the Wnt pathway and how together they can influence cell behaviour and contribute to cancer development. In a recurring theme with other signalling systems, the RUNX genes and the Wnt pathway appear to operate within a series of feedback loops. RUNX genes are capable of directly and indirectly regulating different elements of the Wnt pathway to either strengthen or inhibit the signal. Equally, β-catenin and its transcriptional co-factors can control RUNX gene expression and together they can collaborate to regulate a large number of third party co-target genes.

Regulation of terminal hypertrophic chondrocyte differentiation in Prmt5 mutant mice modeling infantile idiopathic scoliosis

Idiopathic scoliosis (IS) is the most common type of musculoskeletal defect affecting children worldwide, and is classified by age of onset, location and degree of spine curvature. Although rare, IS with onset during infancy is the more severe and rapidly progressive form of the disease, associated with increased mortality due to significant respiratory compromise. The pathophysiology of IS, in particular for infantile IS, remains elusive. Here, we demonstrate the role of PRMT5 in the infantile IS phenotype in mouse. Conditional genetic ablation of PRMT5 in osteochondral progenitors results in impaired terminal hypertrophic chondrocyte differentiation and asymmetric defects of endochondral bone formation in the perinatal spine. Analysis of these several markers of endochondral ossification revealed increased type X collagen (COLX) and Ihh expression, coupled with a dramatic reduction in Mmp13 and RUNX2 expression, in the vertebral growth plate and in regions of the intervertebral disc in the Prmt5 conditional mutant mice. We also demonstrate that PRMT5 has a continuous role in the intervertebral disc and vertebral growth plate in adult mice. Altogether, our results establish PRMT5 as a critical promoter of terminal hypertrophic chondrocyte differentiation and endochondral bone formation during spine development and homeostasis.

This article has an associated First Person interview with the first author of the paper.

Summary: Loss of Prmt5 in osteochondral progenitors impairs terminal hypertrophic chondrocyte differentiation, leading to defects in endochondral bone formation and models infantile idiopathic scoliosis in mouse.

The role of Rho-GEF Trio in regulating tooth root development through the p38 MAPK pathway

Trio, the Rho guanine nucleotide exchange factor (Rho-GEF), plays diverse roles in cell migration, cell axon guidance and cytoskeleton reorganization. Conserved during evolution, Trio encodes two guanine nucleotide exchange factor domains (GEFs) and activates small GTPases. The Rho-family small GTPases RhoA and Rac1, which are target molecules of Trio, have been described to engage in craniofacial development and tooth formation. However, the exact role of Trio in tooth development remains elusive. In this study, we generated Wnt1-cre;Trio^fl/fl mice to address the potential function of Trio in tooth development. Wnt1-cre;Trio^fl/fl mice showed short root deformity as well as decreased expression of odontogenic makers such as RUNX2, OSX, OCN, and OPN. In vitro, Trio was silenced in human stem cells of dental papilla (SCAPs). Compared with the control group, the proliferation and migration ability in the experimental group was disrupted. After knocking down Trio in SCAPs, the cells showed phenotypes of poor odontogenic differentiation and weak mineralized nodules. To study the underlying mechanism, we investigated the p38 MAPK pathway and found that loss of Trio blocked the cascade transduction of p38 MAPK signaling. In conclusion, we identified Trio as a novel coordinator in regulating root development and clarified its relevant molecular events.

FGF2 Enhances Odontoblast Differentiation by αSMA+ Progenitors In Vivo

The goal of this study was to examine the effects of early and limited exposure of perivascular cells expressing α (αSMA) to fibroblast growth factor 2 (FGF2) in vivo. We performed in vivo fate mapping by inducible Cre-loxP and experimental pulp injury in molars to induce reparative dentinogenesis. Our results demonstrate that early delivery of exogenous FGF2 to exposed pulp led to proliferative expansion of αSMA-tdTomato+ cells and their accelerated differentiation into odontoblasts. In vivo lineage-tracing experiments showed that the calcified bridge/reparative dentin in FGF2-treated pulps were lined with an increased number of Dspp+ odontoblasts and devoid of BSP+ osteoblasts. The increased number of odontoblasts derived from αSMA-tdTomato+ cells and the formation of reparative dentin devoid of osteoblasts provide in vivo evidence for the stimulatory effects of FGF signaling on odontoblast differentiation from early progenitors in dental pulp.

Mesenchymal Wnt/β-catenin signaling limits tooth number

Tooth agenesis is one of the predominant developmental anomalies in humans, usually affecting the permanent dentition generated by sequential tooth formation and, in most cases, caused by mutations perturbing epithelial Wnt/β-catenin signaling. In addition, loss-of-function mutations in the Wnt feedback inhibitor AXIN2 lead to human tooth agenesis. We have investigated the functions of Wnt/β-catenin signaling during sequential formation of molar teeth using mouse models. Continuous initiation of new teeth, which is observed after genetic activation of Wnt/β-catenin signaling in the oral epithelium, was accompanied by enhanced expression of Wnt antagonists and a downregulation of Wnt/β-catenin signaling in the dental mesenchyme. Genetic and pharmacological activation of mesenchymal Wnt/β-catenin signaling negatively regulated sequential tooth formation, an effect partly mediated by Bmp4. Runx2, a gene whose loss-of-function mutations result in sequential formation of supernumerary teeth in the human cleidocranial dysplasia syndrome, suppressed the expression of Wnt inhibitors Axin2 and Drapc1 in dental mesenchyme. Our data indicate that increased mesenchymal Wnt signaling inhibits the sequential formation of teeth, and suggest that Axin2/Runx2 antagonistic interactions modulate the level of mesenchymal Wnt/β-catenin signaling, underlying the contrasting dental phenotypes caused by human AXIN2 and RUNX2 mutations.

Embryonic Explant Culture: Studying Effects of Regulatory Molecules on Gene Expression in Craniofacial Tissues

The ex vivo culture of embryonic tissue explants permits the continuous monitoring of growth and morphogenesis at specific embryonic stages. The functions of soluble regulatory molecules can be analyzed by introducing them into culture medium or locally with beads to the tissue. Gene expression in the manipulated tissue explants can be analyzed using in situ hybridization, quantitative PCR, and reporter constructs combined to organ culture to examine the functions of the signaling molecules.

Cleidocranial Dysplasia: A Clinico-radiographic Spectrum with Differential Diagnosis

INTRODUCTION

Cleidocranial dysplasia (CCD) is characterized by aplasia or hypoplasia of the clavicles, characteristic craniofacial malformations, and the presence of numerous supernumerary and unerupted teeth. It affects bones derived from both intra-membranous and endochondral ossification. Incidence has been reported as 1 in 10,00,000. It is caused by mutation in the gene encoding transcription factor Core Binding Factor Subunit Alpha l (CBFAl) or Runt related transcription factor 2 (RUNX2).

CASE REPORT

This presentation discusses the clinical and radiographic features of a familial case of cleidocranial dysplasia occurring in a father and a child. All the clinical and radiographic features, except that of the chest x-ray, were more prominent in the child than the father. This supports the fact that CCD is transmitted by an autosomal-dominant mode of inheritance with high penetrance and variable expressivity. It is sporadic in about 40% of cases. Each child of an individual with CCD has a 50% chance of in heriting the mutation.

CONCLUSION

Diagnosis is mostly made on the basis of clinical and radiographic features. Molecular genetic testing such as sequence analysis or deletion analysis can be used in cleidocranial dysplasia. Some cases are diagnosed through incidental findings by physicians, treating patients for unrelated conditions. Treatment of these patients requires a multidisciplinary approach which includes orthopaedic and dental corrections along with management of any complications of cleidocranial dysplasia.

Does prenatal restraint stress change the craniofacial growth pattern of rat offspring?

A major and frequently encountered condition underlying the long-term programming effects of the intrauterine environment is exposure to stress. Gestational stress is an environmental factor that induces physical and behavioral alterations in offspring. Seventy female virgin Wistar rats were mated with one male rat for a maximum of four times, after which 52 pregnant rats were divided into two groups. In the experimental group the rats were exposed to restraint stress during pregnancy, whereas the control group did not receive the stress protocol. One male litter was randomly chosen from the offspring of each rat with 8-13 pups. A total of 40 male rat offspring were available for analysis. Thirty-one linear and angular measurements were analyzed in both study groups to investigate whether prenatal restraint stress changes the craniofacial growth pattern of rat offspring. In the prenatally stressed group, anterior cranial base length and viscerocranium measures were significantly increased compared with the control group, whereas cranial width, mandibular dimensions, and posterior cranial height and length remained unchanged. Furthermore, the prenatally stressed group showed backward rotation of the midface and decreased flattening of the cranial vault. It was concluded that prenatal chronic stress can induce alterations in the craniofacial growth pattern by promoting endochondral growth in the cranial base and nasal septum.

Suppression of epithelial differentiation by Foxi3 is essential for molar crown patterning

Epithelial morphogenesis generates the shape of the tooth crown. This is driven by patterned differentiation of cells into enamel knots, root-forming cervical loops and enamel-forming ameloblasts. Enamel knots are signaling centers that define the positions of cusp tips in a tooth by instructing the adjacent epithelium to fold and proliferate. Here, we show that the forkhead-box transcription factor Foxi3 inhibits formation of enamel knots and cervical loops and thus the differentiation of dental epithelium in mice. Conditional deletion of Foxi3 (Foxi3 cKO) led to fusion of molars with abnormally patterned shallow cusps. Foxi3 was expressed in the epithelium, and its expression was reduced in the enamel knots and cervical loops and in ameloblasts. Bmp4, a known inducer of enamel knots and dental epithelial differentiation, downregulated Foxi3 in wild-type teeth. Using genome-wide gene expression profiling, we showed that in Foxi3 cKO there was an early upregulation of differentiation markers, such as p21, Fgf15 and Sfrp5. Different signaling pathway components that are normally restricted to the enamel knots were expanded in the epithelium, and Sostdc1, a marker of the intercuspal epithelium, was missing. These findings indicated that the activator-inhibitor balance regulating cusp patterning was disrupted in Foxi3 cKO. In addition, early molar bud morphogenesis and, in particular, formation of the suprabasal epithelial cell layer were impaired. We identified keratin 10 as a marker of suprabasal epithelial cells in teeth. Our results suggest that Foxi3 maintains dental epithelial cells in an undifferentiated state and thereby regulates multiple stages of tooth morphogenesis.

Loss of Runx2 in committed osteoblasts impairs postnatal skeletogenesis

The Runx2 transcription factor is critical for commitment to the osteoblast lineage. However, its role in committed osteoblasts and its functions during postnatal skeletogenesis remain unclear. We established a Runx2-floxed line with insertion of loxP sites around exon 8 of the Runx2 gene. The Runx2 protein lacking the region encoded by exon 8 is imported into the nucleus and binds target DNA but exhibits diminished transcriptional activity. We specifically deleted the Runx2 gene in committed osteoblasts using 2.3-kb col1a-Cre transgenic mice. Surprisingly, the homozygous Runx2 mutant mice were born alive. The Runx2 heterozygous and homozygous null were grossly indistinguishable from wild-type littermates at birth. Runx2 deficiency did not alter proliferative capacity of osteoblasts during embryonic development (E18). Chondrocyte differentiation and cartilage growth in mutants was similar to wild-type mice from birth to 3 months of age. Analysis of the embryonic skeleton revealed poor calcification in homozygous mutants, which was more evident in bones formed by intramembranous ossification. Runx2 mutants showed progressive retardation in postnatal growth and exhibited significantly low bone mass by 1 month of age. Decreased bone formation was associated with decreased gene expression of osteoblast markers and impaired collagen assembly in the extracellular matrix. Consequently, Runx2 mutant bones exhibited decreased stiffness and structural integrity. By 3 months of age, bone acquisition in mutant mice was roughly half that of wild-type littermates. In addition to impaired osteoblast function, mutant mice showed markedly decreased osteoclast number and postnatal bone resorption. Taken together, functional deficiency of Runx2 in osteoblasts does not result in failed embryonic skeletogenesis but disrupts postnatal bone formation.

Derivation of mesenchymal stromal cells from pluripotent stem cells through a neural crest lineage using small molecule compounds with defined media

Neural crest cells (NCCs) are an embryonic migratory cell population with the ability to differentiate into a wide variety of cell types that contribute to the craniofacial skeleton, cornea, peripheral nervous system, and skin pigmentation. This ability suggests the promising role of NCCs as a source for cell-based therapy. Although several methods have been used to induce human NCCs (hNCCs) from human pluripotent stem cells (hPSCs), such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), further modifications are required to improve the robustness, efficacy, and simplicity of these methods. Chemically defined medium (CDM) was used as the basal medium in the induction and maintenance steps. By optimizing the culture conditions, the combination of the GSK3β inhibitor and TGFβ inhibitor with a minimum growth factor (insulin) very efficiently induced hNCCs (70-80%) from hPSCs. The induced hNCCs expressed cranial NCC-related genes and stably proliferated in CDM supplemented with EGF and FGF2 up to at least 10 passages without changes being observed in the major gene expression profiles. Differentiation properties were confirmed for peripheral neurons, glia, melanocytes, and corneal endothelial cells. In addition, cells with differentiation characteristics similar to multipotent mesenchymal stromal cells (MSCs) were induced from hNCCs using CDM specific for human MSCs. Our simple and robust induction protocol using small molecule compounds with defined media enabled the generation of hNCCs as an intermediate material producing terminally differentiated cells for cell-based innovative medicine.

Dual role of the Trps1 transcription factor in dentin mineralization

TRPS1 (tricho-rhino-phalangeal syndrome) is a unique GATA-type transcription factor that acts as a transcriptional repressor. TRPS1 deficiency and dysregulated TRPS1 expression result in skeletal and dental abnormalities implicating TRPS1 in endochondral bone formation and tooth development. Moreover, patients with tricho-rhino-phalangeal syndrome frequently present with low bone mass indicating TRPS1 involvement in bone homeostasis. In addition, our previous data demonstrated accelerated mineralization of the perichondrium in Trps1 mutant mice and impaired dentin mineralization in Col1a1-Trps1 transgenic mice, implicating Trps1 in the mineralization process. To understand the role of Trps1 in the differentiation and function of cells producing mineralized matrix, we used a preodontoblastic cell line as a model of dentin mineralization. We generated both Trps1-deficient and Trps1-overexpressing stable cell lines and analyzed the progression of mineralization by alkaline phosphatase and alizarin red staining. As predicted, based on our previous in vivo data, delayed and decreased mineralization of Trps1-overexpressing odontoblastic cells was observed when compared with control cells. This was associated with down-regulation of genes regulating phosphate homeostasis. Interestingly, Trps1-deficient cells lost the ability to mineralize and demonstrated decreased expression of several genes critical for initiating the mineralization process, including Alpl and Phospho1. Based on these data, we have concluded that Trps1 serves two critical and context-dependent functions in odontoblast-regulated mineralization as follows: 1) Trps1 is required for odontoblast maturation by supporting expression of genes crucial for initiating the mineralization process, and 2) Trps1 represses the function of mature cells and, consequently, restricts the extent of extracellular matrix mineralization.

Wnt signaling regulates pulp volume and dentin thickness

Odontoblasts, cementoblasts, ameloblasts, and osteoblasts all form mineralized tissues in the craniofacial complex, and all these cell types exhibit active Wnt signaling during postnatal life. We set out to understand the functions of this Wnt signaling, by evaluating the phenotypes of mice in which the essential Wnt chaperone protein, Wntless was eliminated. The deletion of Wls was restricted to cells expressing Osteocalcin (OCN), which in addition to osteoblasts includes odontoblasts, cementoblasts, and ameloblasts. Dentin, cementum, enamel, and bone all formed in OCN-Cre;Wls(fl/fl) mice but their homeostasis was dramatically affected. The most notable feature was a significant increase in dentin volume and density. We attribute this gain in dentin volume to a Wnt-mediated misregulation of Runx2. Normally, Wnt signaling stimulates Runx2, which in turn inhibits dentin sialoprotein (DSP); this inhibition must be relieved for odontoblasts to differentiate. In OCN-Cre;Wls(fl/fl) mice, Wnt pathway activation is reduced and Runx2 levels decline. The Runx2-mediated repression of DSP is relieved and odontoblast differentiation is accordingly enhanced. This study demonstrates the importance of Wnt signaling in the homeostasis of mineralized tissues of the craniofacial complex.

Extracellular matrix of dental pulp stem cells: applications in pulp tissue engineering using somatic MSCs

Dental Caries affects approximately 90% of the world's population. At present, the clinical treatment for dental caries is root canal therapy. This treatment results in loss of tooth sensitivity and vitality. Tissue engineering can potentially solve this problem by enabling regeneration of a functional pulp tissue. Dental pulp stem cells (DPSCs) have been shown to be an excellent source for pulp regeneration. However, limited availability of these cells hinders its potential for clinical translation. We have investigated the possibility of using somatic mesenchymal stem cells (MSCs) from other sources for dental pulp tissue regeneration using a biomimetic dental pulp extracellular matrix (ECM) incorporated scaffold. Human periodontal ligament stem cells (PDLSCs) and human bone marrow stromal cells (HMSCs) were investigated for their ability to differentiate toward an odontogenic lineage. In vitro real-time PCR results coupled with histological and immunohistochemical examination of the explanted tissues confirmed the ability of PDLSCs and HMSCs to form a vascularized pulp-like tissue. These findings indicate that the dental pulp stem derived ECM scaffold stimulated odontogenic differentiation of PDLSCs and HMSCs without the need for exogenous addition of growth and differentiation factors. This study represents a translational perspective toward possible therapeutic application of using a combination of somatic stem cells and extracellular matrix for pulp regeneration.

Gene signature of the embryonic meniscus

The meniscus is a fibrocartilagenous disc in the knee that protects the joint from damage. Meniscal injuries are common, however repair efforts are largely unsuccessful and are not able to prevent the degenerative changes that result in development of osteoarthritis. Tissue regeneration in adults often recapitulates events of embryonic development, suggesting the regulatory pathways controlling morphogenesis are candidate repair signals. Here we use laser capture microdissection to collect mouse embryonic day 16 (E16) meniscus, articular cartilage, and cruciate ligaments. RNA isolated from these tissues was then used to perform genome-wide microarray analysis. We found 38 genes were differentially expressed between E16 meniscus and articular cartilage and 43 genes were differentially expressed between E16 meniscus and cruciate ligaments. Included in our data set were extracellular matrix proteins, transcription factors, and growth factors, including TGF-β modulators (Lox, Dpt) and IGF-1 pathway members (Igf-1, Igfbp2, Igfbp3, Igfbp5). Ingenuity Pathway Analysis revealed that IGF-1 signaling was enriched in the meniscus compared to the other joint structures, while qPCR showed that Igf-1, Igfbp2, and Igfbp3 expression declined with age. We also found that several meniscus-enriched genes were expressed either in the inner or outer meniscus, establishing that regionalization of the meniscus occurs early in development.

FGF signaling sustains the odontogenic fate of dental mesenchyme by suppressing β-catenin signaling

Odontoblasts and osteoblasts develop from multipotent craniofacial neural crest cells during tooth and jawbone development, but the mechanisms that specify and sustain their respective fates remain largely unknown. In this study we used early mouse molar and incisor tooth germs that possess distinct tooth-forming capability after dissociation and reaggregation in vitro to investigate the mechanism that sustains odontogenic fate of dental mesenchyme during tooth development. We found that after dissociation and reaggregation, incisor, but not molar, mesenchyme exhibits a strong osteogenic potency associated with robustly elevated β-catenin signaling activity in a cell-autonomous manner, leading to failed tooth formation in the reaggregates. Application of FGF3 to incisor reaggregates inhibits β-catenin signaling activity and rescues tooth formation. The lack of FGF retention on the cell surface of incisor mesenchyme appears to account for the differential osteogenic potency between incisor and molar, which can be further attributed to the differential expression of syndecan 1 and NDST genes. We further demonstrate that FGF signaling inhibits intracellular β-catenin signaling by activating the PI3K/Akt pathway to regulate the subcellular localization of active GSK3β in dental mesenchymal cells. Our results reveal a novel function for FGF signaling in ensuring the proper fate of dental mesenchyme by regulating β-catenin signaling activity during tooth development.

Ameloblastin upstream region contains structural elements regulating transcriptional activity in a stromal cell line derived from bone marrow

Ameloblastin (AMBN) was originally described as a tooth-specific extracellular matrix protein, but current data have shown that AMBN is present in many different tissues of mesenchymal origin. The identification of regulatory elements in the promoter region of the Ambn gene would assist in identifying potential mesenchymal-specific transcriptional factors. In this study we subcloned a 3,788-bp region upstream (and a 54-bp region downstream) of the mouse Ambn transcriptional start site into a LacZ reporter construct and called this construct 3788-Ambn-lacZ. In silico analysis of the 3,788-bp Ambn promoter region identified 50 potential cis-regulatory elements, 29 of which are known to be functional in cell populations of mesenchymal origin. The reporter construct was activated in transfected bone marrow cells, and the promoter activity was induced in cell cultures following addition of recombinant AMBN, interferon-γ, serotonin, or dexamethasone. We discuss the relative significance of the potential cis-acting gene-regulatory elements of Ambn in relation to bone morphogenesis. Knowledge of Ambn gene-regulatory elements will be of importance when developing strategies for bone repair and replacement in a clinical surgical setting.

Insulin-like growth factor 1 can promote the osteogenic differentiation and osteogenesis of stem cells from apical papilla

Insulin-like growth factor 1 (IGF-1) plays an important role in the regulation of tooth root development, and stem cells from apical papilla (SCAPs) are responsible for the formation of root pulp and dentin. To date, it remains unclear whether IGF-1 can regulate the function of SCAPs. In this study, SCAPs were isolated and purified from human immature root apex, and stimulated by 100 ng/mL exogenous IGF-1. The effects of IGF-1 on the proliferation and differentiation of SCAPs were subsequently investigated. IGF-1 treated SCAPs presented the morphological and ultrastructural changes. Cell proliferation, alkaline phosphatase (ALP) activity and mineralization capacity of SCAPs were increased by IGF-1. Western blot and quantitative RT-PCR analyses further demonstrated that the expression of osteogenic-related proteins and genes (e.g., alkaline phosphatase, runt-related transcription factor 2, osterix, and osteocalcin) was significantly up-regulated in IGF-1 treated SCAPs, whereas the expression of odontoblast-specific markers (e.g., dentin sialoprotein and dentin sialophosphoprotein) was down-regulated by IGF-1. In vivo results revealed that IGF-1 treated SCAPs mostly gave birth to bone-like tissues while untreated SCAPs mainly generated dentin-pulp complex-like structures after transplantation. The present study revealed that IGF-1 can promote the osteogenic differentiation and osteogenesis capacity of SCAPs, but weaken their odontogenic differentiation and dentinogenesis capability, indicating that IGF-1 treated SCAPs can be used as a potential candidate for bone tissue engineering.

Signaling networks regulating tooth organogenesis and regeneration, and the specification of dental mesenchymal and epithelial cell lineages

Teeth develop as ectodermal appendages from epithelial and mesenchymal tissues. Tooth organogenesis is regulated by an intricate network of cell-cell signaling during all steps of development. The dental hard tissues, dentin, enamel, and cementum, are formed by unique cell types whose differentiation is intimately linked with morphogenesis. During evolution the capacity for tooth replacement has been reduced in mammals, whereas teeth have acquired more complex shapes. Mammalian teeth contain stem cells but they may not provide a source for bioengineering of human teeth. Therefore it is likely that nondental cells will have to be reprogrammed for the purpose of clinical tooth regeneration. Obviously this will require understanding of the mechanisms of normal development. The signaling networks mediating the epithelial-mesenchymal interactions during morphogenesis are well characterized but the molecular signatures of the odontogenic tissues remain to be uncovered.

Osteoblasts derived from induced pluripotent stem cells form calcified structures in scaffolds both in vitro and in vivo

Reprogramming somatic cells into an ESC-like state, or induced pluripotent stem (iPS) cells, has emerged as a promising new venue for customized cell therapies. In this study, we performed directed differentiation to assess the ability of murine iPS cells to differentiate into bone, cartilage, and fat in vitro and to maintain an osteoblast phenotype on a scaffold in vitro and in vivo. Embryoid bodies derived from murine iPS cells were cultured in differentiation medium for 8–12 weeks. Differentiation was assessed by lineage-specific morphology, gene expression, histological stain, and immunostaining to detect matrix deposition. After 12 weeks of expansion, iPS-derived osteoblasts were seeded in a gelfoam matrix followed by subcutaneous implantation in syngenic imprinting control region (ICR) mice. Implants were harvested at 12 weeks, histological analyses of cell and mineral and matrix content were performed. Differentiation of iPS cells into mesenchymal lineages of bone, cartilage, and fat was confirmed by morphology and expression of lineage-specific genes. Isolated implants of iPS cell-derived osteoblasts expressed matrices characteristic of bone, including osteocalcin and bone sialoprotein. Implants were also stained with alizarin red and von Kossa, demonstrating mineralization and persistence of an osteoblast phenotype. Recruitment of vasculature and microvascularization of the implant was also detected. Taken together, these data demonstrate functional osteoblast differentiation from iPS cells both in vitro and in vivo and reveal a source of cells, which merit evaluation for their potential uses in orthopedic medicine and understanding of molecular mechanisms of orthopedic disease.

Ectonucleotide pyrophosphatase/phosphodiesterase-1 (ENPP1) protein regulates osteoblast differentiation

ENPP1 (ectonucleotide pyrophosphatase/phosphodiesterase-1) is an established regulator of tissue mineralization. Previous studies demonstrated that ENPP1 is expressed in differentiated osteoblasts and that ENPP1 influences matrix mineralization by increasing extracellular levels of inorganic pyrophosphate. ENPP1 is also expressed in osteoblastic precursor cells when stimulated with FGF2, but the role of ENPP1 in preosteoblastic and other precursor cells is unknown. Here we investigate the function of ENPP1 in preosteoblasts. We find that ENPP1 expression is critical for osteoblastic differentiation and that this effect is not mediated by changes in extracellular concentration levels of phosphate or pyrophosphate or ENPP1 catalytic activity. MC3T3E1(C4) preosteoblastic cells, in which ENPP1 expression was suppressed by ENPP1-specific shRNA, and calvarial cells isolated from Enpp1 knock-out mice show defective osteoblastic differentiation upon stimulation with ascorbate, as indicated by a lack of cellular morphological change, a lack of osteoblast marker gene expression, and an inability to mineralize matrix. Additionally, MC3T3E1(C4) cells, in which wild type or catalytic inactive ENPP1 expression was increased, exhibited an increased tendency to differentiate, as evidenced by increased osteoblast marker gene expression and increased mineralization. Notably, treatment of cells with inorganic phosphate or pyrophosphate inhibited, as opposed to enhanced, expression of multiple genes that are expressed in association with osteoblast differentiation, matrix deposition, and mineralization. Our results indicate that ENPP1 plays multiple and distinct roles in the development of mineralized tissues and that the influence of ENPP1 on osteoblast differentiation and gene expression may include a mechanism that is independent of its catalytic activity.

Association of ALPL and ENPP1 gene polymorphisms with bone strength related skeletal traits in a Chuvashian population

Mineralization of the extracellular matrix of bone is an essential element of bone development, maintenance and repair. ALPL and ENPP1 genes and their products are known to be central in local regulation of bone mineralization. The present study investigates potential associations of ENPP1 and ALPL polymorphisms with several phenotypes reflecting bone size and hand BMD. The study sample included 310 Caucasian nuclear families. Forty SNPs in ALPL and 14 SNPs in ENPP1 genetic loci as well as pairwise haplotypes were tested for association with bone strength related traits. Our findings suggest that the region corresponding to exons 7 through 9 of the ALPL gene harbors functional polymorphism affecting both bone size at various skeletal sites (p-value ranged from 0.01 to 0.0001) and hand bone mineral density (p-value=0.0007). The other important finding of consistent association between bone size phenotypes and the 3' untranslated region of ENPP1 gene (p-value ranged from 0.01 to 0.001) imply functional significance of this region to bone growth. The considered anthropometric and radiographic bone phenotypes are closely related to bone fragility thus suggesting a role for both genes in osteoporosis. Further research is required to validate the relevancy of the potentially functional regions identified by our and other studies to normal and pathologic bone development as well as to determine the relevancy of the polymorphisms in ALPL and ENPP1 gene loci to clinical practice.

Patterns of Wnt pathway activity in the mouse incisor indicate absence of Wnt/beta-catenin signaling in the epithelial stem cells

The Wnt pathway is crucial for tooth development as shown by dental defects caused by impaired Wnt signaling in mouse and human. We investigated Wnt signaling in continuously growing mouse incisors focusing on epithelial stem cells. Ten Wnt ligands were expressed both in the dental epithelium and mesenchyme, and were associated mainly with odontoblast and ameloblast differentiation. Wnt/beta-catenin activity was detected in mesenchyme in BATgal and TOPgal reporter mice while Axin2, also a reporter of Wnt/beta-catenin signaling, was expressed additionally in the epithelium. Axin2 was, however, excluded from the epithelial stem cells in the cervical loop. Interestingly, these cells expressed specifically Lgr5, a Wnt target gene and stem cell marker in the intestine, suggesting that Lgr5 is a marker of incisor stem cells but is not regulated by Wnt signaling in the incisor. We conclude that epithelial stem cells in the mouse incisors are not regulated directly by Wnt/beta-catenin signaling.

The significance of RUNX2 in postnatal development of the mandibular condyle

OBJECTIVE

RUNX2, in the Runt gene family, is one of the most important transcription factors in the development of the skeletal system. Research in recent decades has shown that this factor plays a major role in the development, growth and maturation of bone and cartilage. It is also important in tooth development, mechanotransduction and angiogenesis, and plays a significant role in various pathological processes, i.e. tumor metastasization. Mutations in the RUNX2 gene correlate with the cleidocranial dysplasia (CCD) syndrome, important to dentistry, particularly orthodontics because of its dental and orofacial symptoms. Current research on experimentally-induced mouse mutants enables us to study the etiology and pathogenesis of these malformations at the cellular and molecular biological level. This study's aim is to provide an overview of the RUNX2 gene's function especially in skeletal development, and to summarize our research efforts to date, which has focused on investigating the influence of RUNX2 on mandibular growth, which is slightly or not at all altered in many CCD patients.

MATERIALS AND METHODS

Immunohistochemical analyses were conducted to reveal RUNX2 in the condylar cartilage of normal mice and of heterozygous RUNX2 knockout mice in early and late growth phases; we also performed radiographic and cephalometric analyses.

RESULTS

We observed that RUNX2 is involved in normal condylar growth in the mouse and probably plays a significant role in osteogenesis and angiogenesis. The RUNX2 also has a biomechanical correlation in relation to cartilage compartmentalization. At the protein level, we noted no differences in the occurrence and distribution of RUNX2 in the condyle, except for a short phase during the 4th and 6th postnatal weeks, so that one allele might suffice for largely normal growth; other biological factors may have compensatory effects. However, we did observe small changes in a few cephalometric parameters concerning the mandibles of heterozygous knockout animals. We discuss potential correlations to our findings by relating them to the most current knowledge about the RUNX2 biology.

Explant culture of embryonic craniofacial tissues: analyzing effects of signaling molecules on gene expression

The in vitro culture of embryonic tissue explants allows the continuous monitoring of growth and morphogenesis at specific embryonic stages. The functions of soluble regulatory molecules can be examined by adding them into culture medium or by introducing them with beads to specific locations in the tissue. Gene expression analysis using in situ hybridization, quantitative PCR, and reporter constructs can be combined with organ culture to examine the functions of the regulatory molecules.