CACNA1S mutation-associated dental anomalies: A calcium channelopathy

OBJECTIVES

To identify the molecular etiology of distinct dental anomalies found in eight Thai patients and explore the mutational effects on cellular functions.

MATERIALS AND METHODS

Clinical and radiographic examinations were performed for eight patients. Whole exome sequencing, mutant protein modelling, qPCR, western blot analysis, scratch assays, immunofluorescence, confocal analysis, in situ hybridization, and scanning electron micrography of teeth were done.

RESULTS

All patients had molars with multiple supernumerary cusps, single-cusped premolars, and a reduction in root number. Mutation analysis highlighted a heterozygous c.865A>G; p.Ile289Val mutation in CACNA1S in the patients. CACNA1S is a component of the slowly inactivating L-type voltage-dependent calcium channel. Mutant protein modeling suggested that the mutation might allow leakage of Ca2+ or other cations, or a tightening, to restrict calcium flow. Immunohistochemistry analysis showed expression of Cacna1s in the developing murine tooth epithelium during stages of crown and root morphogenesis. In cell culture, the mutation resulted in abnormal cell migration of transfected CHO cells compared to wildtype CACNA1S, with changes to the cytoskeleton and markers of focal adhesion.

CONCLUSIONS

The malformations observed in our patients suggest a role for calcium signaling in organization of both cusps and roots, affecting cell dynamics within the dental epithelium.

Loss of Autophagy Disrupts Stemness of Ameloblast-Lineage Cells in Aging

Autophagy is one of the intracellular degradation pathways and maintains cellular homeostasis, regulating the stress response, cell proliferation, and signal transduction. To elucidate the role of autophagy in the maintenance of dental epithelial stem cells and the subsequent enamel formation, we analyzed autophagy-deficient mice in epithelial cells (Atg7f/f;KRT14-Cre mice), focusing on the influence of aging and stress environments. We also performed in vitro cell and organ culture experiments with an autophagy inhibitor. In young Atg7f/f;KRT14-Cre mice, morphological change was not obvious in maxillary incisors, except for the remarkable cell death in the stratum intermedium of the transitional stage. However, under stress conditions of hyperglycemia, the incisor color changed to white in diabetes Atg7f/f;KRT14-Cre mice. Regarding dental epithelial stem cells, the shape of the apical bud region of the incisor became irregular with age, and odontoma was formed in aged Atg7f/f;KRT14-Cre mice. In addition, the shape of apical bud culture cells of Atg7f/f;KRT14-Cre mice became irregular and enlarged atypically, with epigenetic changes during culture, suggesting that autophagy deficiency may induce tumorigenesis in dental epithelial cells. The epigenetic change and upregulation of p21 expression were induced by autophagy inhibition in vivo and in vitro. These findings suggest that autophagy is important for the regulation of stem cell maintenance, proliferation, and differentiation of ameloblast-lineage cells, and an autophagy disorder may induce tumorigenesis in odontogenic epithelial cells.

Ift88 regulates enamel formation via involving Shh signaling

OBJECTIVES

The ciliopathies are a wide spectrum of human diseases, which are caused by perturbations in the function of primary cilia. Tooth enamel anomalies are often seen in ciliopathy patients; however, the role of primary cilia in enamel formation remains unclear.

MATERIALS AND METHODS

We examined mice with epithelial conditional deletion of the ciliary protein, Ift88, (Ift88^fl/fl ;K14Cre).

RESULTS

Ift88^fl/fl ;K14Cre mice showed premature abrasion in molars. A pattern of enamel rods which is determined at secretory stage, was disorganized in Ift88 mutant molars. Many amelogenesis-related molecules expressing at the secretory stage, including amelogenin and ameloblastin, enamelin, showed significant downregulation in Ift88 mutant molar tooth germs. Shh signaling is essential for amelogenesis, which was found to be downregulated in Ift88 mutant molar at the secretory stage. Application of Shh signaling agonist at the secretory stage partially rescued enamel anomalies in Ift88 mutant mice.

CONCLUSION

Findings in the present study indicate that the function of the primary cilia via Ift88 is critical for the secretory stage of amelogenesis through involving Shh signaling.

Juberg-Hayward syndrome is a cohesinopathy, caused by mutation in ESCO2

BACKGROUND

Juberg-Hayward syndrome (JHS; MIM 216100) is a rare autosomal recessive malformation syndrome, characterized by cleft lip/palate, microcephaly, ptosis, short stature, hypoplasia or aplasia of thumbs, and dislocation of radial head and fusion of humerus and radius leading to elbow restriction.

OBJECTIVE

To report for the first time the molecular aetiology of JHS.

PATIENT AND METHODS

Clinical and radiographic examination, whole exome sequencing, Sanger sequencing, mutant protein model construction, and in situ hybridization of Esco2 expression in mouse embryos were performed.

RESULTS

Clinical findings of the patient consisted of repaired cleft lip/palate, microcephaly, ptosis, short stature, delayed bone age, hypoplastic fingers and thumbs, clinodactyly of the fifth fingers, and humeroradial synostosis leading to elbow restriction. Intelligence is normal. Whole exome sequencing of the whole family showed a novel homozygous base substitution c.1654C>T in ESCO2 of the proband. The sister was homozygous for the wildtype variant. Parents were heterozygous for the mutation. The mutation is predicted to cause premature stop codon p.Arg552Ter. Mutations in ESCO2, a gene involved in cohesin complex formation, are known to cause Roberts/SC phocomelia syndrome. Roberts/SC phocomelia syndrome and JHS share similar clinical findings, including autosomal recessive inheritance, short stature, cleft lip/palate, severe upper limb anomalies, and hypoplastic digits. Esco2 expression during the early development of lip, palate, eyelid, digits, upper limb, and lower limb and truncated protein model are consistent with the defect.

CONCLUSIONS

Our study showed that Roberts/SC phocomelia syndrome and JHS are allelic and distinct entities. This is the first report demonstrating that mutation in ESCO2 causes JHS, a cohesinopathy.

MicroRNAs regulate distal region of mandibular development through Hh signaling

Mandibular anomalies are often seen in various congenital diseases, indicating that mandibular development is under strict molecular control. Therefore, it is crucial to understand the molecular mechanisms involved in mandibular development. MicroRNAs (miRNAs) are noncoding small single-stranded RNAs that play a critical role in regulating the level of gene expression. We found that the mesenchymal conditional deletion of miRNAs arising from a lack of Dicer (an essential molecule for miRNA processing, Dicer^fl/fl ;Wnt1Cre), led to an abnormal groove formation at the distal end of developing mandibles. At E10.5, when the region forms, inhibitors of Hh signaling, Ptch1 and Hhip1 showed increased expression at the region in Dicer mutant mandibles, while Gli1 (a major mediator of Hh signaling) was significantly downregulated in mutant mandibles. These suggest that Hh signaling was downregulated at the distal end of Dicer mutant mandibles by increased inhibitors. To understand whether the abnormal groove formation inDicer mutant mandibles was caused by the downregulation of Hh signaling, mice with a mesenchymal deletion of Hh signaling activity arising from a lack of Smo (an essential molecule for Hh signaling activation, Smo^fl/fl ;Wnt1Cre) were examined. Smo^fl/fl ;Wnt1Cre mice showed a similar phenotype in the distal region of their mandibles to those in Dicer^fl/fl ;Wnt1Cre mice. We also found that approximately 400 miRNAs were expressed in wild-type mandibular mesenchymes at E10.5, and six microRNAs were identified as miRNAs with binding potential against both Ptch1 and Hhip1. Their expressions at the distal end of the mandible were confirmed by in situ hybridization. This indicates that microRNAs regulate the distal part of mandibular formation at an early stage of development by involving Hh signaling activity through controlling its inhibitor expression level.

A novel P3H1 mutation is associated with osteogenesis imperfecta type VIII and dental anomalies

OBJECTIVE

Our objective was to investigate the molecular etiology of osteogenesis imperfecta type VIII and dental anomalies in 4 siblings of a Karen tribe family.

MATERIALS AND METHODS

Four patients and their unaffected parents were studied by clinical and radiographic examination. In situ hybridization of P3h1 during early murine tooth development, whole-exome sequencing, and Sanger direct sequencing were performed.

RESULTS

A novel homozygous missense P3H1 mutation (NM_001243246.1; c.2141A>G; NP_001230175.1; p.Lys714Arg) was identified in all patients. Their unaffected parents were heterozygous for the mutation. The mutation is hypothesized to belong to isoform c of P3H1. Mutations in P3H1 are associated with autosomal recessive osteogenesis imperfecta type VIII. Hypodontia, a mesiodens, and single-rooted permanent second molars found in our patients have never been reported in patients with P3H1 mutations. Single-rooted second permanent molars or failure to form multiple roots implies effects of the P3H1 mutation on root development.

CONCLUSIONS

We report a novel P3H1 mutation as the underlying cause of osteogenesis imperfecta type VIII with dental anomalies. Our study suggests that isoform c of P3H1 is also a functional isoform of P3H1. We report, for the first time, to our knowledge, the association of P3H1 mutation and osteogenesis imperfecta type VIII with dental anomalies.

Overactivation of the NF-κB pathway impairs molar enamel formation

OBJECTIVE

Hypohidrotic ectodermal dysplasia (HED) is a hereditary disorder characterized by abnormal structures and functions of the ectoderm-derived organs, including teeth. HED patients exhibit a variety of dental symptoms, such as hypodontia. Although disruption of the EDA/EDAR/EDARADD/NF-κB pathway is known to be responsible for HED, it remains unclear whether this pathway is involved in the process of enamel formation.

EXPERIMENTAL SUBJECTS AND METHODS

To address this question, we examined the mice overexpressing Ikkβ (an essential component required for the activation of NF-κB pathway) under the keratin 5 promoter (K5-Ikkβ).

RESULTS

Upregulation of the NF-κB pathway was confirmed in the ameloblasts of K5-Ikkβ mice. Premature abrasion was observed in the molars of K5-Ikkβ mice, which was accompanied by less mineralized enamel. However, no significant changes were observed in the enamel thickness and the pattern of enamel rods in K5-Ikkβ mice. Klk4 expression was significantly upregulated in the ameloblasts of K5-Ikkβ mice at the maturation stage, and the expression of its substrate, amelogenin, was remarkably reduced. This suggests that abnormal enamel observed in K5-Ikkβ mice was likely due to the compromised degradation of enamel protein at the maturation stage.

CONCLUSION

Therefore, we could conclude that the overactivation of the NF-κB pathway impairs the process of amelogenesis.

R2TP/PAQosome as a promising chemotherapeutic target in cancer

R2TP/PAQosome (particle for arrangement of quaternary structure) is a novel multisubunit chaperone specialized in the assembly/maturation of protein complexes that are involved in essential cellular processes such as PIKKs (phosphatidylinositol 3-kinase-like kinases) signaling, snoRNP (small nucleolar ribonucleoprotein) biogenesis, and RNAP II (RNA polymerase II) complex formation. In this review article, we describe the current understanding of R2TP/PAQosome functions and characteristics as well as how the chaperone complex is involved in oncogenesis, highlighting DNA damage response, mTOR (mammalian target of rapamycin) pathway as well as snoRNP biogenesis. Also, we discuss its possible involvement in HNSCC (head and neck squamous cell carcinoma) including OSCC (oral squamous cell carcinoma). Finally, we provide an overview of current anti-cancer drug development efforts targeting R2TP/PAQosome.

Ift88 is involved in mandibular development

The mandible is a crucial organ in both clinical and biological fields due to the high frequency of congenital anomalies and the significant morphological changes during evolution. Primary cilia play a critical role in many biological processes, including the determination of left/right axis patterning, the regulation of signaling pathways, and the formation of bone and cartilage. Perturbations in the function of primary cilia are known to cause a wide spectrum of human diseases: the ciliopathies. Craniofacial dysmorphologies, including mandibular deformity, are often seen in patients with ciliopathies. Mandibular development is characterized by chondrogenesis and osteogenesis; however, the role of primary cilia in mandibular development is not fully understood. To address this question, we generated mice with mesenchymal deletions of the ciliary protein, Ift88 (Ift88^fl/fl ;Wnt1Cre). Ift88^fl/fl ;Wnt1Cre mice showed ectopic mandibular bone formation, whereas Ift88 mutant mandible was slightly shortened. Meckel's cartilage was modestly expanded in Ift88^fl/fl ;Wnt1Cre mice. The downregulation of Hh signaling was found in most of the mesenchyme of Ift88 mutant mandible. However, mice with a mesenchymal deletion of an essential molecule for Hh signaling activity, Smo (Smo^fl/fl ;Wnt1Cre), showed only ectopic mandibular formation, whereas Smo mutant mandible was significantly shortened. Ift88 is thus involved in chondrogenesis and osteogenesis during mandibular development, partially through regulating Sonic hedgehog (Shh) signaling.

Primary cilia in murine palatal rugae development

Periodic patterning of iterative structures is a fundamental process during embryonic development, since these structures are diverse across the animal kingdom. Therefore, elucidating the molecular mechanisms in the formation of these structures promotes understanding of the process of organogenesis. Periodically patterned ridges, palatal rugae (situated on the hard palate of mammals), are an excellent experimental model to clarify the molecular mechanisms involved in the formation of periodic patterning of iterative structures. Primary cilia are involved in many biological events, including the regulation of signaling pathways such as Shh and non-canonical Wnt signaling. However, the role of primary cilia in the development of palatal rugae remains unclear. We found that primary cilia were localized to the oral cavity side of the interplacode epithelium of the palatal rugae, whereas restricted localization of primary cilia could not be detected in other regions. Next, we generated mice with a placodal conditional deletion of the primary cilia protein Ift88, using ShhCre mice (Ift88^fl/fl;ShhCre). Highly disorganized palatal rugae were observed in Ift88^fl/fl;ShhCre mice. Furthermore, by comparative in situ hybridization analysis, many Shh and non-canonical Wnt signaling-related molecules showed spatiotemporal expression patterns during palatal rugae development, including restricted expression in the epithelium (placodes and interplacodes) and mesenchyme. Some of these expression were found to be altered in Ift88^fl/fl;ShhCre mice. Primary cilia is thus involved in development of palatal rugae.

Bmp signaling in molar cusp formation

Tooth cusp is a crucial structure, since the shape of the molar tooth is determined by number, shape, and size of the cusp. Bone morphogenetic protein (Bmp) signaling is known to play a critical role in tooth development, including in initiation. However, it remains unclear whether Bmp signaling is also involved in cusp formation. To address this question, we examined cusp in two different transgenic mouse lines: mice with overexpression of Bmp4 (K14-Bmp4), and those with Bmp inhibitor, Noggin, (K14-Noggin) under keratin14 (K14) promoter. K14-Noggin mice demonstrated extra cusps, whereas reduced number of cusps was observed in K14-Bmp4 mice. To further understand how Bmps are expressed during cusp formation, we performed whole-mount in situ hybridisation analysis of three major Bmps (Bmp2, Bmp4, and Bmp7) in murine maxillary and mandibular molars from E14.5 to P3. The linear expressions of Bmp2 and Bmp4 were observed in both maxillary and mandibular molars at E14.5. The expression patterns of Bmp2 and Bmp4 became significantly different between the maxillary and mandibular molars at E16.5. At P3, all Bmps were expressed in all the cusp regions of the maxillary molar; however, the patterns differed. All Bmps thus exhibited dynamic temporo-spatial expression during the cusp formation. It could therefore be inferred that Bmp signaling is involved in regulating cusp formation.

Ift88 limits bone formation in maxillary process through suppressing apoptosis

OBJECTIVE

The development of the maxillary bone is under strict molecular control because of its complicated structure. Primary cilia play a critical role in craniofacial development, since defects in primary cilia are known to cause congenital craniofacial dysmorphologies as a wide spectrum of human diseases: the ciliopathies. The primary cilia also are known to regulate bone formation. However, the role of the primary cilia in maxillary bone development is not fully understood.

DESIGN

To address this question, we generated mice with a mesenchymal conditional deletion ofIft88 using the Wnt1Cre mice (Ift88^fl/fl;Wnt1Cre). The gene Ift88 encodes a protein that is required for the function and formation of primary cilia.

RESULTS

It has been shown thatIft88^fl/fl;Wnt1Cre mice exhibit cleft palate. Here, we additionally observed excess bone formation in the Ift88 mutant maxillary process. We also found ectopic apoptosis in the Ift88 mutant maxillary process at an early stage of development. To investigate whether the ectopic apoptosis is related to the Ift88 mouse maxillary phenotypes, we generated Ift88^fl/fl;Wnt1Cre;p53^-/- mutants to reduce apoptosis. The Ift88^fl/fl;Wnt1Cre;p53^-/- mice showed no excess bone formation, suggesting that the cells evading apoptosis by the presence of Ift88 in wild-type mice limit bone formation in maxillary development. On the other hand, the palatal cleft was retained in the Ift88^fl/fl;Wnt1Cre;p53^-/- mice, indicating that the excess bone formation or abnormal apoptosis was independent of the cleft palate phenotype in Ift88 mutant mice.

CONCLUSIONS

Ift88 limits bone formation in the maxillary process by suppressing apoptosis.

MicroRNAs control eyelid development through regulating Wnt signaling

BACKGROUND

The timing, location, and level of gene expression are crucial for normal organ development, because morphogenesis requires strict genetic control. MicroRNAs (miRNAs) are noncoding small single-stranded RNAs that play a critical role in regulating gene expression level. Although miRNAs are known to be involved in many biological events, the role of miRNAs in organogenesis is not fully understood. Mammalian eyelids fuse and separate during development and growth. In mice, failure of this process results in the eye-open at birth (EOB) phenotype.

RESULTS

It has been shown that conditional deletion of mesenchymal Dicer (an essential protein for miRNA processing; Dicer ^fl/fl ;Wnt1Cre) leads to the EOB phenotype with full penetrance. Here, we identified that the up-regulation of Wnt signaling resulted in the EOB phenotype in Dicer mutants. Down-regulation of Fgf signaling observed in Dicer mutants was caused by an inverse relationship between Fgf and Wnt signaling. Shh and Bmp signaling were down-regulated as the secondary effects in Dicer ^fl/fl ;Wnt1Cre mice. Wnt, Shh, and Fgf signaling were also found to mediate the epithelial-mesenchymal interactions in eyelid development.

CONCLUSIONS

miRNAs control eyelid development through Wnt. Developmental Dynamics 248:201-210, 2019. © 2019 Wiley Periodicals, Inc.

Lrp4/Wise regulates palatal rugae development through Turing-type reaction-diffusion mechanisms

Periodic patterning of iterative structures is diverse across the animal kingdom. Clarifying the molecular mechanisms involved in the formation of these structure helps to elucidate the process of organogenesis. Turing-type reaction-diffusion mechanisms have been shown to play a critical role in regulating periodic patterning in organogenesis. Palatal rugae are periodically patterned ridges situated on the hard palate of mammals. We have previously shown that the palatal rugae develop by a Turing-type reaction-diffusion mechanism, which is reliant upon Shh (as an inhibitor) and Fgf (as an activator) signaling for appropriate organization of these structures. The disturbance of Shh and Fgf signaling lead to disorganized palatal rugae. However, the mechanism itself is not fully understood. Here we found that Lrp4 (transmembrane protein) was expressed in a complementary pattern to Wise (a secreted BMP antagonist and Wnt modulator) expression in palatal rugae development, representing Lrp4 expression in developing rugae and Wise in the inter-rugal epithelium. Highly disorganized palatal rugae was observed in both Wise and Lrp4 mutant mice, and these mutants also showed the downregulation of Shh signaling, which was accompanied with upregulation of Fgf signaling. Wise and Lrp4 are thus likely to control palatal rugae development by regulating reaction-diffusion mechanisms through Shh and Fgf signaling. We also found that Bmp and Wnt signaling were partially involved in this mechanism.

Expanding the Oro-Dental and Mutational Spectra of Kabuki Syndrome and Expression of KMT2D and KDM6A in Human Tooth Germs

Kabuki syndrome is a rare genetic disorder characterized by distinct dysmorphic facial features, intellectual disability, and multiple developmental abnormalities. Despite more than 350 documented cases, the oro-dental spectrum associated with kabuki syndrome and expression of KMT2D (histone-lysine N-methyltransferase 2D) or KDM6A (lysine-specific demethylase 6A) genes in tooth development have not been well defined. Here, we report seven unrelated Thai patients with Kabuki syndrome having congenital absence of teeth, malocclusion, high-arched palate, micrognathia, and deviated tooth shape and size. Exome sequencing successfully identified that six patients were heterozygous for mutations in KMT2D, and one in KDM6A. Six were novel mutations, of which five were in KMT2D and one in KDM6A. They were truncating mutations including four frameshift deletions and two nonsense mutations. The predicted non-functional KMT2D and KDM6A proteins are expected to cause disease by haploinsufficiency. Our study expands oro-dental, medical, and mutational spectra associated with Kabuki syndrome. We also demonstrate for the first time that KMT2D and KDM6A are expressed in the dental epithelium of human tooth germs.

The Sonic Hedgehog signaling pathway regulates inferior alveolar nerve regeneration

Activation of Shh signaling is known to be observed following injury of the peripheral nerves such as the sciatic nerve. However, the precise role of Shh signaling during peripheral nerve regeneration is not fully understood. The inferior alveolar nerve (IAN) is most commonly injured during oral surgery. Unlike the sciatic nerve, the IAN is isolated from other craniofacial tissues, as it resides in a long bony canal within the mandible. The IAN is thus an excellent experimental model for investigating peripheral nerve regeneration. In this study, the role of Shh signaling in peripheral nerve regeneration was investigated using the mouse IAN transection model. During regeneration, Shh signaling was activated within the entire distal region of the IAN and proximal stumps. Inhibition of Shh signaling by cyclopamine application at the transection site led to abnormal axon growth in random directions, a reduced number of macrophages, and an increase in myelin debris within the distal region. Shh signaling is thus involved in peripheral nerve regeneration via the regulation of myelin degradation.

The effect of bone mass and architecture on mandibular condyle after mandibular distraction

OBJECTIVE

Mandibular distraction surgery is a critical treatment for jaw deformity. However, abnormal mandibular condylar bone resorption is often seen as complication after surgery. Our previous study using a rat mandibular distraction model suggested that overloading leads to mandibular condylar resorption. Host factors are also believed to influence the resorption. To understand the relationship between host factors and resorption, we investigated the effect of changing bone mass and architecture on the mandibular condyle using FK506.

STUDY DESIGN

FK506, an immunosuppressant, was used to compromise bone mass and architecture in this study. Animals were divided into 4 groups: distraction surgery (Dist), FK506 administration (FK), distraction surgery with FK506 administration (FK + Dist), and no surgery or FK506 administration (Cont).

RESULTS

The FK group showed reduced bone mass and impaired bone architecture. The Dist group exhibited abnormal bone resorption on the surface of the condyles, which was slightly exacerbated in the FK + Dist group. Bone defect length decreased over time as a result of bone apposition in the Dist group. However, in the FK + Dist group, the bone defect length remained the same.

CONCLUSIONS

These results suggest that bone mass and architecture strongly affect the tolerance to the overloading and adaptation with bone apposition in condylar resorption site.

A novel GJA1 mutation in oculodentodigital dysplasia with extensive loss of enamel

OBJECTIVE

To characterize clinical features and identify genetic causes of a patient with oculodentodigital dysplasia (ODDD).

SUBJECTS AND METHODS

Clinical, dental, radiological features were obtained. DNA was collected from an affected Thai family. Whole-exome sequencing was employed to identify the disease-causing mutation causing ODDD. The presence of the identified variant was confirmed by Sanger sequencing.

RESULTS

The proband suffered with extensive enamel hypoplasia, polysyndactyly and clinodactyly of the 3rd-5th fingers, microphthalmia, and unique facial characteristics of ODDD. Mutation analysis revealed a novel missense mutation, c. 31C>A, p.L11I, in the GJA1 gene which encodes gap junction channel protein connexin 43. Bioinformatics and structural modeling suggested the mutation to be pathogenic. The parents did not harbor the mutation.

CONCLUSIONS

This study identified a novel de novo mutation in the GJA1 gene associated with severe tooth defects. These results expand the mutation spectrum and understanding of pathologic dental phenotypes related to ODDD.

Opg, Rank, and Rankl in Tooth Development: Co-ordination of Odontogenesis and Osteogenesis

Osteoprotegerin (OPG), receptor activator of nuclear factor-κB (RANK), and RANK ligand (RANKL) are mediators of various cellular interactions, including bone metabolism. We analyzed expression of these three genes during murine odontogenesis from epithelial thickening to cytodifferentiation stages. Opg showed expression in the thickening and bud epithelium. Expression of Opg and Rank was observed in both the internal and the external enamel epithelium as well as in the dental papilla mesenchyme. Although Rankl expression was not detected in tooth epithelium or mesenchyme, it was expressed in pre-osteogenic mesenchymal cells close to developing tooth germs. All three genes were detected in developing dentary bone at P0. The addition of exogenous OPG to explant cultures of tooth primordia produced a delay in tooth development that resulted in reduced mineralization. We propose that the spatiotemporal expression of these molecules in early tooth and bone primordia cells has a role in co-ordinating bone and tooth development.

Expression of Sox genes in tooth development

Members of the Sox gene family play roles in many biological processes including organogenesis. We carried out comparative in situ hybridization analysis of seventeen sox genes (Sox1-14, 17, 18, 21) during murine odontogenesis from the epithelial thickening to the cytodifferentiation stages. Localized expression of five Sox genes (Sox6, 9, 13, 14 and 21) was observed in tooth bud epithelium. Sox13 showed restricted expression in the primary enamel knots. At the early bell stage, three Sox genes (Sox8, 11, 17 and 21) were expressed in pre-ameloblasts, whereas two others (Sox5 and 18) showed expression in odontoblasts. Sox genes thus showed a dynamic spatio-temporal expression during tooth development.

Spatio-temporal expression of Sox genes in murine palatogenesis

Members of the Sox gene family play critical roles in many biological processes including organogenesis. We carried out comparative in situ hybridisation analysis of seventeen Sox genes (Sox1-14, 17, 18 and 21) during murine palatogenesis from initiation to fusion of the palatal shelves above the dorsal side of the tongue. At palatal shelf initiation (E12.5), the localized expression of six Sox genes (Sox2, 5, 6, 9, 12 and 13) was observed in the shelves, whereas Sox4 and Sox11 showed ubiquitious expression. During the down-growth of palatal shelves (E13.5), Sox4, Sox5, and Sox9 exhibited restricted expression to the interior side of the palatal shelves facing the tongue. Following elevation of the palatal shelves (E14.5), Sox2, Sox11 and Sox21 expression was present in the midline epithelial seam. We thus identify dynamic spatio-temporal expression of Sox gene family during the process of palatogenesis.

Disrupted mitochondrial function in the Opa3L122P mouse model for Costeff Syndrome impairs skeletal integrity

Mitochondrial dysfunction connects metabolic disturbance with numerous pathologies, but the significance of mitochondrial activity in bone remains unclear. We have, therefore, characterized the skeletal phenotype in the Opa3^L122P mouse model for Costeff syndrome, in which a missense mutation of the mitochondrial membrane protein, Opa3, impairs mitochondrial activity resulting in visual and metabolic dysfunction. Although widely expressed in the developing normal mouse head, Opa3 expression was restricted after E14.5 to the retina, brain, teeth and mandibular bone. Opa3 was also expressed in adult tibiae, including at the trabecular surfaces and in cortical osteocytes, epiphyseal chondrocytes, marrow adipocytes and mesenchymal stem cell rosettes. Opa3^L122P mice displayed craniofacial abnormalities, including undergrowth of the lower mandible, accompanied in some individuals by cranial asymmetry and incisor malocclusion. Opa3^L122P mice showed an 8-fold elevation in tibial marrow adiposity, due largely to increased adipogenesis. In addition, femoral length and cortical diameter and wall thickness were reduced, the weakening of the calcified tissue and the geometric component of strength reducing overall cortical strength in Opa3^L122P mice by 65%. In lumbar vertebrae reduced vertebral body area and wall thickness were accompanied by a proportionate reduction in marrow adiposity. Although the total biomechanical strength of lumbar vertebrae was reduced by 35%, the strength of the calcified tissue (σ_max) was proportionate to a 38% increase in trabecular number. Thus, mitochondrial function is important for the development and maintenance of skeletal integrity, impaired bone growth and strength, particularly in limb bones, representing a significant new feature of the Costeff syndrome phenotype.

Contribution of synovial lining cells to synovial vascularization of the rat temporomandibular joint

The lining layer of the synovial membrane in the temporomandibular joint (TMJ) contains two types of lining cells: macrophage-like type A and fibroblast-like type B cells. The type B cells are particularly heterogeneous in their morphology and immunoreactivity, so that details of their functions remain unclear. Some of the type B cells exhibit certain resemblances in their ultrastructure to those of an activated capillary pericyte at the initial stage of the angiogenesis. The articular surface, composed of cartilage and the disc in the TMJ, has few vasculatures, whereas the synovial lining layer is richly equipped with blood capillaries to produce the constituent of synovial fluid. The present study investigated at both the light and electron microscopic levels the immunocytochemical characteristics of the synovial lining cells in the adult rat TMJ, focusing on their contribution to the synovial vascularization. It also employed an intravascular perfusion with Lycopersicon esculentum (tomato) lectin to identify functional vessels in vivo. Results showed that several type B cells expressed desmin, a muscle-specific intermediate filament which is known as the earliest protein to appear during myogenesis as well as being a marker for the immature capillary pericyte. These desmin-positive type B cells showed immunoreactions for vimentin and pericyte markers (neuron-glial 2; NG2 and PDGFRβ) but not for the other markers of myogenic cells (MyoD and myogenin) or a contractile apparatus (αSMA and caldesmon). Immunoreactivity for RECA-1, an endothelial marker, was observed in the macrophage-like type A cells. The arterioles and venules inside the synovial folds extended numerous capillaries with RECA-1-positive endothelial cells and desmin-positive pericytes to distribute densely in the lining layer. The distal portion of these capillaries showing RECA-1-immunoreactivity lacked lectin-staining, indicating a loss of blood-circulation due to sprouting or termination in the lining layer. The desmin-positive type B and RECA-1-positive type A cells attached to this portion of the capillaries. Some capillaries in the lining layer also expressed ninein, a marker for sprouting endothelial cells, called tip cells. Since an activated pericyte, macrophage and tip cell are known to act together at the forefront of the vessel sprout during angiogenesis, the desmin-positive type B cell and RECA-1-positive type A cell might serve as these angiogenic cells in the synovial lining layer. Tomato lectin perfusion following decalcification would be a highly useful tool for research on the vasculature of the mineralized tissue. Use of this technique combined with immunohistochemistry should permit future extensive investigations on the presence of the physiological angiogenesis and on the function of the lining cells in the synovial membrane.

GREMLIN 2 Mutations and Dental Anomalies

Isolated or nonsyndromic tooth agenesis or hypodontia is the most common human malformation. It has been associated with mutations in MSX1, PAX9, EDA, AXIN2, EDAR, EDARADD, and WNT10A. GREMLIN 2 (GREM2) is a strong bone morphogenetic protein (BMP) antagonist that is known to regulate BMPs in embryogenesis and tissue development. Bmp4 has been shown to have a role in tooth development. Grem2(-/-) mice have small, malformed maxillary and mandibular incisors, indicating that Grem2 has important roles in normal tooth development. Here, we demonstrate for the first time that GREM2 mutations are associated with human malformations, which include isolated tooth agenesis, microdontia, short tooth roots, taurodontism, sparse and slow-growing hair, and dry and itchy skin. We sequenced WNT10A, WNT10B, MSX1, EDA, EDAR, EDARADD, AXIN2, and PAX9 in all 7 patients to rule out the effects of other ectodermal dysplasias and other tooth-related genes and did not find mutations in any of them. GREM2 mutations exhibit variable expressivity even within the same families. The inheritance is autosomal dominant with incomplete penetrance. The expression of Grem2 during the early development of mouse teeth and hair follicles and the evaluation of the likely effects of the mutations on the protein structure substantiate these new findings.

Excess NF-κB induces ectopic odontogenesis in embryonic incisor epithelium

Nuclear factor kappa B (NF-κB) signaling plays critical roles in many physiological and pathological processes, including regulating organogenesis. Down-regulation of NF-κB signaling during development results in hypohidrotic ectodermal dysplasia. The roles of NF-κB signaling in tooth development, however, are not fully understood. We examined mice overexpressing IKKβ, an essential component of the NF-κB pathway, under keratin 5 promoter (K5-Ikkβ). K5-Ikkβ mice showed supernumerary incisors whose formation was accompanied by up-regulation of canonical Wnt signaling. Apoptosis that is normally observed in wild-type incisor epithelium was reduced in K5-Ikkβ mice. The supernumerary incisors in K5-Ikkβ mice were found to phenocopy extra incisors in mice with mutations of Wnt inhibitor, Wise. Excess NF-κB activity thus induces an ectopic odontogenesis program that is usually suppressed under physiological conditions.

R-spondins/Lgrs expression in tooth development

BACKGROUND

Tooth development is highly regulated in mammals and it is regulated by networks of signaling pathways (e. g. Tnf, Wnt, Shh, Fgf and Bmp) whose activities are controlled by the balance between ligands, activators, inhibitors and receptors. The members of the R-spondin family are known as activators of Wnt signaling, and Lgr4, Lgr5, and Lgr6 have been identified as receptors for R-spondins. The role of R-spondin/Lgr signaling in tooth development, however, remains unclear.

RESULTS

We first carried out comparative in situ hybridization analysis of R-spondins and Lgrs, and identified their dynamic spatio-temporal expression in murine odontogenesis. R-spondin2 expression was found both in tooth germs and the tooth-less region, the diastema. We further examined tooth development in R-spondin2 mutant mice, and although molars and incisors exhibited no significant abnormalities, supernumerary teeth were observed in the diastema.

CONCLUSIONS

R-spondin/Lgr signaling is thus involved in tooth development.

A mathematical model for mechanotransduction at the early steps of suture formation

Growth and patterning of craniofacial sutures is subjected to the effects of mechanical stress. Mechanotransduction processes occurring at the margins of the sutures are not precisely understood. Here, we propose a simple theoretical model based on the orientation of collagen fibres within the suture in response to local stress. We demonstrate that fibre alignment generates an instability leading to the emergence of interdigitations. We confirm the appearance of this instability both analytically and numerically. To support our model, we use histology and synchrotron X-ray microtomography and reveal the fine structure of fibres within the sutural mesenchyme and their insertion into the bone. Furthermore, using a mouse model with impaired mechanotransduction, we show that the architecture of sutures is disturbed when forces are not interpreted properly. Finally, by studying the structure of sutures in the mouse, the rat, an actinopterygian (Polypterus bichir) and a placoderm (Compagopiscis croucheri), we show that bone deposition patterns during dermal bone growth are conserved within jawed vertebrates. In total, these results support the role of mechanical constraints in the growth and patterning of craniofacial sutures, a process that was probably effective at the emergence of gnathostomes, and provide new directions for the understanding of normal and pathological suture fusion.

The buccohypophyseal canal is an ancestral vertebrate trait maintained by modulation in sonic hedgehog signaling

Background

The pituitary gland is formed by the juxtaposition of two tissues: neuroectoderm arising from the basal diencephalon, and oral epithelium, which invaginates towards the central nervous system from the roof of the mouth. The oral invagination that reaches the brain from the mouth is referred to as Rathke’s pouch, with the tip forming the adenohypophysis and the stalk disappearing after the earliest stages of development. In tetrapods, formation of the cranial base establishes a definitive barrier between the pituitary and oral cavity; however, numerous extinct and extant vertebrate species retain an open buccohypophyseal canal in adulthood, a vestige of the stalk of Rathke’s pouch. Little is currently known about the formation and function of this structure. Here we have investigated molecular mechanisms driving the formation of the buccohypophyseal canal and their evolutionary significance.

Results

We show that Rathke’s pouch is located at a boundary region delineated by endoderm, neural crest-derived oral mesenchyme and the anterior limit of the notochord, using CD1, R26R-Sox17-Cre and R26R-Wnt1-Cre mouse lines. As revealed by synchrotron X-ray microtomography after iodine staining in mouse embryos, the pouch has a lobulated three-dimensional structure that embraces the descending diencephalon during pituitary formation. Polaris^fl/fl; Wnt1-Cre, Ofd1^-/- and Kif3a^-/- primary cilia mouse mutants have abnormal sonic hedgehog (Shh) signaling and all present with malformations of the anterior pituitary gland and midline structures of the anterior cranial base. Changes in the expressions of Shh downstream genes are confirmed in Gas1^-/- mice. From an evolutionary perspective, persistence of the buccohypophyseal canal is a basal character for all vertebrates and its maintenance in several groups is related to a specific morphology of the midline that can be related to modulation in Shh signaling.

Conclusion

These results provide insight into a poorly understood ancestral vertebrate structure. It appears that the opening of the buccohypophyseal canal depends upon Shh signaling and that modulation in this pathway most probably accounts for its persistence in phylogeny.

Multiple postnatal craniofacial anomalies are characterized by conditional loss of polycystic kidney disease 2 (Pkd2)

Polycystin 2 (Pkd2), which belongs to the transient receptor potential family, plays a critical role in development. Pkd2 is mainly localized in the primary cilia, which also function as mechanoreceptors in many cells that influence multiple biological processes including Ca(2+) influx, chemical activity and signalling pathways. Mutations in many cilia proteins result in craniofacial abnormalities. Orofacial tissues constantly receive mechanical forces and are known to develop and grow through intricate signalling pathways. Here we investigate the role of Pkd2, whose role remains unclear in craniofacial development and growth. In order to determine the role of Pkd2 in craniofacial development, we located expression in craniofacial tissues and analysed mice with conditional deletion of Pkd2 in neural crest-derived cells, using Wnt1Cre mice. Pkd2 mutants showed many signs of mechanical trauma such as fractured molar roots, distorted incisors, alveolar bone loss and compressed temporomandibular joints, in addition to abnormal skull shapes. Significantly, mutants showed no indication of any of these phenotypes at embryonic stages when heads perceive no significant mechanical stress in utero. The results suggest that Pkd2 is likely to play a critical role in craniofacial growth as a mechanoreceptor. Pkd2 is also identified as one of the genes responsible for autosomal dominant polycystic kidney disease (ADPKD). Since facial anomalies have never been identified in ADPKD patients, we carried out three-dimensional photography of patient faces and analysed these using dense surface modelling. This analysis revealed specific characteristics of ADPKD patient faces, some of which correlated with those of the mutant mice.

Oral lining mucosa development depends on mesenchymal microRNAs

The oral mucosa plays critical roles in protection, sensation, and secretion and can be classified into masticatory, lining, and specialized mucosa that are known to be functionally, histologically, and clinically distinct. Each type of oral mucosa is believed to develop through discrete molecular mechanisms, which remain unclear. MicroRNAs (miRNAs) are 19 to 25nt non-coding small single-stranded RNAs that negatively regulate gene expression by binding target mRNAs. miRNAs are crucial for fine-tuning of molecular mechanisms. To investigate the role of miRNAs in oral mucosa development, we examined mice with mesenchymal (Wnt1Cre;Dicer(fl/fl)) conditional deletion of Dicer. Wnt1Cre;Dicer(fl/fl) mice showed trans-differentiation of lining mucosa into an epithelium with masticatory mucosa/ skin-specific characteristics. Up-regulation of Fgf signaling was found in mutant lining mucosal epithelium that was accompanied by an increase in Fgf7 expression in mutant mesenchyme. Mesenchyme miRNAs thus have an indirect effect on lining mucosal epithelial cell growth/differentiation.

Histological analysis of the embryonic and adult tooth

Histology is the study of the microscopic anatomy of tissues by examining a thin slice of the tissue under the microscope. Prior to slicing/sectioning, most tissues require some form of solidifying to allow thin sections to be cut. However, since the tooth is the hardest substance in the vertebrate body, it is one of the most difficult tissues to process for histology. This chapter describes the methods used for making histological sections of tooth from different embryonic stages through to adulthood.

The origin of the stapes and relationship to the otic capsule and oval window

BACKGROUND

The stapes, an ossicle found within the middle ear, is involved in transmitting sound waves to the inner ear by means of the oval window. There are several developmental problems associated with this ossicle and the oval window, which cause hearing loss. The developmental origin of these tissues has not been fully elucidated.

RESULTS

Using transgenic reporter mice, we have shown that the stapes is of dual origin with the stapedial footplate being composed of cells of both neural crest and mesodermal origin. Wnt1cre/Dicer mice fail to develop neural crest-derived cartilages, therefore, have no middle ear ossicles. We have shown in these mice the mesodermal stapedial footplate fails to form and the oval window is induced but underdeveloped.

CONCLUSIONS

If the neural crest part of the stapes fails to form the mesodermal part does not develop, indicating that the two parts are interdependent. The stapes develops tightly associated with the otic capsule, however, it is not essential for the positioning of the oval window, suggesting that other tissues, perhaps within the inner ear are needed for oval window placement.

Distinct roles of microRNAs in epithelium and mesenchyme during tooth development

BACKGROUND

Tooth development is known to be mediated by the cross-talk between signaling pathways, including Shh, Fgf, Bmp, and Wnt. MicroRNAs (miRNAs) are 19- to 25-nt noncoding small single-stranded RNAs that negatively regulate gene expression by binding target mRNAs, which is believed to be important for the fine-tuning signaling pathways in development. To investigate the role of miRNAs in tooth development, we examined mice with either mesenchymal (Wnt1Cre/Dicer(fl/fl)) or epithelial (ShhCre/Dicer(fl/fl)) conditional deletion of Dicer, which is essential for miRNA processing.

RESULTS

By using a CD1 genetic background for Wnt1Cre/Dicer(fl/fl), we were able to examine tooth development, because the mutants retained mandible and maxilla primordia. Wnt1Cre/Dicer(fl/fl) mice showed an arrest or absence of teeth development, which varied in frequency between incisors and molars. Extra incisor tooth formation was found in ShhCre/Dicer(fl/fl) mice, whereas molars showed no significant anomalies. Microarray and in situ hybridization analysis identified several miRNAs that showed differential expression between incisors and molars.

CONCLUSION

In tooth development, miRNAs thus play different roles in epithelium and mesenchyme, and in incisors and molars.

Dyschromatosis symmetrica hereditaria with long hair on the forearms, hypo/hyperpigmented hair, and dental anomalies: report of a novel ADAR1 mutation

We report on a father and his two children who are affected with dyschromatosis symmetrica hereditaria (DSH). Mutation analysis of ADAR1 gene demonstrated a novel splice acceptor site mutation in intron 10, IVS10-2A>C. The hair on the forearm of the affected father became longer, larger in diameter, and hypopigmented (white) after age 40 years. Hyperpigmented hair was also found in normal and hypopigmented skin. The colors of the hair and the skin did not correlate. Transmission electron micrography of cortical keratinocytes of the hair follicles showed that normal hair contained more keratinocytes than those of hyperpigmented and hypopigmented hair. The keratinocytes of the hyperpigmented hair were larger than those of normal and hypopigmented hair and those of the normal hair were larger than those of the hypopigmented hair. The affected daughter had dens evaginatus of the mandibular right second premolar and the son had dens invaginatus of the maxillary permanent lateral incisors. Expression of Adar1 gene during mouse tooth development is demonstrated.

Bmp signalling in filiform tongue papillae development

OBJECTIVE

Tongue papillae are critical organs in mastication. There are four different types of tongue papillae; fungiform, circumvallate, foliate, and filiform papillae. Unlike the other three taste papillae, non-gustatory papillae, filiform papillae cover the entire dorsal surface of the tongue and are important structures for the mechanical stress of sucking. Filiform papillae are further classified into two subtypes with different morphologies, depending on their location on the dorsum of the tongue. The filiform papillae at the intermolar eminence have pointed tips, whereas filiform papillae with rounded tips are found in other regions (anterior tongue). It remains unknown how the shape of each type of filiform papillae are determined during their development. Bmp signalling pathway has been known to regulate mechanisms that determine the shapes of many ectodermal organs. The aim of this study was to investigate the role of Bmp signalling in filiform papillae development.

DESIGN

Comparative in situ hybridization analysis of six Bmps (Bmp2-Bmp7) and two Bmpr genes (Bmpr1a and Bmpr1b) were carried out in filiform papillae development. We further examined tongue papillae in mice over-expressing Noggin under the keratin14 promoter (K14-Noggin).

RESULTS

We identified a dynamic temporo-spatial expression of Bmps in filiform papillae development. The K14-Noggin mice showed pointed filiform papillae in regions of the tongue normally occupied by the rounded type.

CONCLUSIONS

Bmp signalling thus regulates the shape of filiform papillae.

Periodic stripe formation by a Turing mechanism operating at growth zones in the mammalian palate

We present direct evidence of an activator-inhibitor system in the generation of the regularly spaced transverse ridges of the palate. We show that new ridges, or rugae, marked by stripes of Sonic hedgehog (Shh) expression, appear at two growth zones where the space between previously laid-down rugae increases. However, inter-rugal growth is not absolutely required: new stripes still appear when growth is inhibited. Furthermore, when a ruga is excised new Shh expression appears, not at the cut edge but as bifurcating stripes branching from the neighbouring Shh stripe, diagnostic of a Turing-type reaction-diffusion mechanism. Genetic and inhibitor experiments identify Fibroblast Growth Factor (FGF) and Shh as an activator-inhibitor pair in this system. These findings demonstrate a reaction-diffusion mechanism likely to be widely relevant in vertebrate development.

Wnt signaling in the murine diastema

The correct number and shape of teeth are critical factors for an aesthetic and functional dentition. Understanding the molecular mechanisms regulating tooth number and shape are therefore important in orthodontics. Mice have only one incisor and three molars in each jaw quadrant that are divided by a tooth-less region, the diastema. Although mice lost teeth in the diastema during evolution, the remnants of the evolutionary lost teeth are observed as transient epithelial buds in the wild-type diastema during early stages of development. Shh and Fgf signaling pathways that are essential for tooth development have been shown to be repressed in the diastema. It remains unclear however how Wnt signaling, that is also required for tooth development, is regulated in the diastema. In this study we found that in the embryonic diastema, Wnt5a expression was observed in mesenchyme, whereas Wnt4 and Wnt10b were expressed in epithelium. The expression of Wnt6 and Wnt11 was found in both tissues. The Wnt co-receptor, Lrp6, was weakly expressed in the diastema overlapping with weak Lrp4 expression, a co-receptor that inhibits Wnt signaling. Secreted Wnt inihibitors Dkk1, Dkk2, and Dkk3 were also expressed in the diastema. Lrp4 mutant mice develop supernumerary teeth in the diastema that is accompanied by upregulation of Wnt signaling and Lrp6 expression. Wnt signaling is thus usually attenuated in the diastema by these secreted and membrane bound Wnt inhibitors.

Delayed re-epithelialization in periostin-deficient mice during cutaneous wound healing

Background

Matricellular proteins, including periostin, are important for tissue regeneration.

Methods and Findings

Presently we investigated the function of periostin in cutaneous wound healing by using periostin-deficient (−/−) mice. Periostin mRNA was expressed in both the epidermis and hair follicles, and periostin protein was located at the basement membrane in the hair follicles together with fibronectin and laminin γ2. Periostin was associated with laminin γ2, and this association enhanced the proteolytic cleavage of the laminin γ2 long form to produce its short form. To address the role of periostin in wound healing, we employed a wound healing model using WT and periostin−/− mice and the scratch wound assay in vitro. We found that the wound closure was delayed in the periostin−/− mice coupled with a delay in re-epithelialization and with reduced proliferation of keratinocytes. Furthermore, keratinocyte proliferation was enhanced in periostin-overexpressing HaCaT cells along with up-regulation of phosphorylated NF-κB.

Conclusion

These results indicate that periostin was essential for keratinocyte proliferation for re-epithelialization during cutaneous wound healing.

Lrp4: A novel modulator of extracellular signaling in craniofacial organogenesis

The low-density lipoprotein (LDL) receptor family is a large evolutionarily conserved group of transmembrane proteins. It has been shown that LDL receptor family members can also function as direct signal transducers or modulators for a broad range of cellular signaling pathways. We have identified a novel mode of signaling pathway integration/coordination that occurs outside cells during development that involves an LDL receptor family member. Physical interaction between an extracellular protein (Wise) that binds BMP ligands and an Lrp receptor (Lrp4) that modulates Wnt signaling, acts to link these two pathways. Mutations in either Wise or Lrp4 in mice produce multiple, but identical abnormalities in tooth development that are linked to alterations in BMP and Wnt signaling. Teeth, in common with many other organs, develop by a series of epithelial-mesenchymal interactions, orchestrated by multiple cell signaling pathways. In tooth development, Lrp4 is expressed exclusively in epithelial cells and Wise mainly in mesenchymal cells. Our hypothesis, based on the mutant phenotypes, cell signaling activity changes and biochemical interactions between Wise and Lrp4 proteins, is that Wise and Lrp4 together act as an extracellular mechanism of coordinating BMP and Wnt signaling activities in epithelial-mesenchymal cell communication during development.