Sp6/Epiprofin is a master regulator in the developing tooth

Tooth development involves the coordinated transcriptional regulation of extracellular matrix proteins produced by ameloblasts and odontoblasts. In this study, whole-genome ChIP-seq analysis was applied to identify the transcriptional regulatory gene targets of Sp6 in mesenchymal cells of the developing tooth. Bioinformatic analysis of a pool of Sp6 target peaks identified the consensus nine nucleotide binding DNA motif CTg/aTAATTA. Consistent with these findings, a number of enamel and dentin matrix genes including amelogenin (Amelx), ameloblastin (Ambn), enamelin (Enam) and dental sialophosphoprotein (Dspp), were identified to contain Sp6 target sequences. Sp6 peaks were also found in other important tooth genes including transcription factors (Dlx2, Dlx3, Dlx4, Dlx5, Sp6, Sp7, Pitx2, and Msx2) and extracellular matrix-related proteins (Col1a2, Col11a2, Halpn1). Unsupervised UMAP clustering of tooth single cell RNA-seq data confirmed the presence of Sp6 transcripts co-expressed with many of the identified target genes within ameloblasts and odontoblasts. Lastly, transcriptional reporter assays using promoter fragments from the Hapln1 and Sp6 gene itself revealed that Sp6 co-expression enhanced gene transcriptional activity. Taken together these results highlight that Sp6 is a major regulator of multiple extracellular matrix genes in the developing tooth.

Altered miRNA expression profiling in enamel organ of fluoride affected rat embryos

Evidence has shown that miRNAs could play a role in dental fluorosis, but there is no study has investigated the global expression miRNA profiles of fluoride-exposed enamel organ. In this study, we analysed the differentially expressed (DE) miRNAs between fluoride-treated and control enamel organ for the first time and found several candidate miRNAs and signaling pathways worthy of further research. Thirty Wistar rats were randomly distributed into three groups and exposed to drinking water with different fluoride contents for 10 weeks and during the gestation. The three groups were a control group (distilled water), medium fluoride group (75 mg/L NaF), and high fluoride group (150 mg/L NaF). On the embryonic day 19.5, the mandible was dissected for histological analysis, and the enamel organ of the mandibular first molar tooth germ was collected for miRNA sequencing (miRNA-seq) and quantitative real-time PCR analysis (qRT-PCR). Typical dental fluorosis was observed in the incisors of the prepregnant rats. In addition to the disorganized structure of enamel organ cells, 39 DE miRNAs were identified in the fluoride groups compared with the control group, and good agreement between the miRNA-seq data and qRT-PCR data was found. The functional annotation of the target genes of 39 DE miRNAs showed significant enrichment in metabolic process, cell differentiation, calcium signaling pathway, and mitogen-activated protein kinase(MAPK) signaling pathway terms. This study provides a theoretical reference for an extensive understanding of the mechanism of fluorosis and potential valuable miRNAs as therapeutic targets in fluorosis.

Single nucleotide polymorphism rs4284505 in microRNA17 and risk of dental fluorosis

OBJECTIVES

The aim of this study is to evaluate the association between the single nucleotide polymorphism (SNP) rs4284505 within the gene that codifies microRNA17 (miRNA17) and dental fluorosis (DF) in a group of children.

METHODS

Children living in a city with fluoridation of public water supplies were included. DF was assessed in erupted permanent teeth by Dean's modified index. The miR-SNP rs4284505 was selected in miRNA17 and genotyping was carried out by real-time PCR. Genotype and allelic distributions between DF and control, and between DF phenotypes (mild, moderate and severe) and control were analysed.

RESULTS

Among a total of 527 children enrolled for the study, 383 were DF free and 144 presented DF. In the dominant model analysis (AA + AG vs. GG) the miR-SNP rs4284505 was associated with moderate DF, with carriers of the GG genotype having an increased risk of more than two times for DF (p = 0.031; Odds Ratio = 2.26, Confidence Interval 95%= 1.04-4.73). Allelic distribution showed borderline statistical significance for moderate DF with the carriers of G allele having an increased risk for DF (p = .050; Odds Ratio = 1.75, Confidence Interval 95%= 1.00-3.12).

CONCLUSION

The miR-SNP rs4284505 in miRNA17 was associated with an increased risk of DF.

ACTN2 (rs6656267) and MPPED2 (rs11031093 and rs536007) polymorphisms in primary dentition caries: A case-control study

BACKGROUND

Dental caries represents one of the most common human diseases which can lead to pulpitis, pain, and tooth loss and can negatively affect growth and well-being. Although dietary and environmental factors have been extensively studied towards their contribution of the disease, genetic factors that contribute one's susceptibility over caries development remain rather clouded.

AIM

To investigate the possible contribution of ACTN2 (rs6656267) and MPPED2 (rs11031093 and rs536007) polymorphisms in primary dentition caries.

DESIGN

Samples from children (5-12 years old) were collected and genotyped for ACTN2 (rs6656267) and MPPED2 (rs11031093 and rs536007) polymorphisms. With regard to dmfs index and socio-economic status, an association between these polymorphisms and primary dentition caries was investigated.

RESULTS

ACTN2 (rs6655267) and MPPED2 (rs536007) are not associated with primary dentition caries. MPPED2 (rs11031093, G Allele) is marginally associated.

CONCLUSIONS

MPPED2 (rs11031093, G Allele) is marginally associated with caries susceptibility on primary dentition.

Transcriptomic analysis of MicroRNA expression in enamel-producing cells

There is little evidence for the involvement of microRNAs (miRNAs) in the regulation of circadian rhythms during enamel development. Few studies have used ameloblast-like cell line LS8 to study the circadian rhythm of gene activities related to enamel formation. However, the transcriptomic analysis of miRNA expression in LS8 cells has not been established yet. In this study, we analyze the oscillations of miRNAs in LS8 cells during one-day cycle of 24 h by next generation deep sequencing. After removal of low quality reads, contaminants, and ligation products, we obtained a high number of clean reads in all 12 samples from four different time points. The length distribution analysis indicated that 77.5% of clean reads were between 21 and 24 nucleotides (nt), of which 35.81% reads exhibited a length of 22 nt. In total, we identified 1471 miRNAs in LS8 cells throughout all four time-points. 1330 (90.41%) miRNAs were identified as known miRNA sequences, whereas 139 (9.59%) were unannotated and classified as novel miRNA sequences. The differential expression analysis showed that 191 known miRNAs exhibited significantly (P-value < 0.01) different levels of expression across three time-points investigated (T6, T12, and T18) compared to T0. Verification of sequencing data using qRT-PCR on six selected miRNAs suggested good correlation between the two methods. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed significant enrichment of predicted target genes of differentially expressed miRNAs. The present study shows that miRNAs are highly expressed in LS8 cells and that a significant number of them oscillate during one-day cycle of 24 h. This is the first transcriptomic analysis of miRNAs in ameloblast-like cell line LS8 that can be potentially used to further characterize the epigenetic regulation of miRNAs during enamel formation.

[Expression and function of microRNAs in enamel development]

microRNAs (miRNAs) are endogenous short, noncoding RNAs that can negatively regulate gene expression post-transcriptionally. miRNAs are involved in multiple developmental events in various tissues and organs, including dental enamel development. Any disruption during enamel development may result in inherited enamel malformations. This article reviews the expression and function of miRNAs in enamel development.

The Molecular Circuit Regulating Tooth Development in Crocodilians

Alligators have robust regenerative potential for tooth renewal. In contrast, extant mammals can either renew their teeth once (diphyodont dentition, as found in humans) or not at all (monophyodont dentition, present in mice). Previously, the authors used multiple mitotic labeling to map putative stem cells in alligator dental laminae, which contain quiescent odontogenic progenitors. The authors demonstrated that alligator tooth cycle initiation is related to β-catenin/Wnt pathway activity in the dental lamina bulge. However, the molecular circuitry underlying the developmental progression of polyphyodont teeth remains elusive. Here, the authors used transcriptomic analyses to examine the additional molecular pathways related to the process of alligator tooth development. The authors collected juvenile alligator dental laminae at different developmental stages and performed RNA-seq. This data shows that Wnt, bone morphogenetic protein (BMP), and fibroblast growth factor (FGF) pathways are activated at the transition from pre-initiation stage (bud) to initiation stage (cap). Intriguingly, the activation of Wnt ligands, receptors and co-activators accompanies the inactivation of Wnt antagonists. In addition, the authors identified the molecular circuitry at different stages of tooth development. The authors conclude that multiple pathways are associated with specific stages of tooth development in the alligator. This data shows that Wnt pathway activation may play the most important role in the initiation of tooth development. This result may offer insight into ways to modulate the genetic controls involved in mammalian tooth renewal.

Regulating Craniofacial Development at the 3' End: MicroRNAs and Their Function in Facial Morphogenesis

Defects in craniofacial development represent a majority of observed human birth defects, occurring at a rate as high as 1:800 live births. These defects often occur due to changes in neural crest cell (NCC) patterning and development and can affect non-NCC-derived structures due to interactions between NCCs and the surrounding cell types. Proper craniofacial development requires an intricate array of gene expression networks that are tightly controlled spatiotemporally by a number of regulatory mechanisms. One of these mechanisms involves the action of microRNAs (miRNAs), a class of noncoding RNAs that repress gene expression by binding to miRNA recognition sequences typically located in the 3' UTR of target mRNAs. Recent evidence illustrates that miRNAs are crucial for vertebrate facial morphogenesis, with changes in miRNA expression leading to facial birth defects, including some in complex human syndromes such as 22q11 (DiGeorge Syndrome). In this review, we highlight the current understanding of miRNA biogenesis, the roles of miRNAs in overall craniofacial development, the impact that loss of miRNAs has on normal development and the requirement for miRNAs in the development of specific craniofacial structures, including teeth. From these studies, it is clear that miRNAs are essential for normal facial development and morphogenesis, and a potential key in establishing new paradigms for repair and regeneration of facial defects.

Mutations in the latent TGF-beta binding protein 3 (LTBP3) gene cause brachyolmia with amelogenesis imperfecta

Inherited dental malformations constitute a clinically and genetically heterogeneous group of disorders. Here, we report on four families, three of them consanguineous, with an identical phenotype, characterized by significant short stature with brachyolmia and hypoplastic amelogenesis imperfecta (AI) with almost absent enamel. This phenotype was first described in 1996 by Verloes et al. as an autosomal recessive form of brachyolmia associated with AI. Whole-exome sequencing resulted in the identification of recessive hypomorphic mutations including deletion, nonsense and splice mutations, in the LTBP3 gene, which is involved in the TGF-beta signaling pathway. We further investigated gene expression during mouse development and tooth formation. Differentiated ameloblasts synthesizing enamel matrix proteins and odontoblasts expressed the gene. Study of an available knockout mouse model showed that the mutant mice displayed very thin to absent enamel in both incisors and molars, hereby recapitulating the AI phenotype in the human disorder.

The molecular basis of hereditary enamel defects in humans

The formation of human enamel is highly regulated at the molecular level and involves thousands of genes. Requisites for development of this highly mineralized tissue include cell differentiation; production of a unique extracellular matrix; processing of the extracellular matrix; altering of cell function during different stages of enamel formation; cell movement and attachment; regulation of ion and protein movement; and regulation of hydration, pH, and other conditions of the microenvironment, to name just a few. Not surprising, there is a plethora of hereditary conditions with an enamel phenotype. The objective of this review was to identify the hereditary conditions listed on Online Mendelian Inheritance in Man (OMIM) that have an associated enamel phenotype and whether a causative gene has been identified. The OMIM database was searched with the terms amelogenesis, enamel, dental, and tooth, and all results were screened by 2 individuals to determine if an enamel phenotype was identified. Gene and gene product function was reviewed on OMIM and from publications identified in PubMed. The search strategy revealed 91 conditions listed in OMIM as having an enamel phenotype, and of those, 71 have a known molecular etiology or linked genetic loci. The purported protein function of those conditions with a known genetic basis included enzymes, regulatory proteins, extracellular matrix proteins, transcription factors, and transmembrane proteins. The most common enamel phenotype was a deficient amount of enamel, or enamel hypoplasia, with hypomineralization defects being reported less frequently. Knowing these molecular defects allows an initial cataloging of molecular pathways that lead to hereditary enamel defects in humans. This knowledge provides insight into the diverse molecular pathways involved in enamel formation and can be useful when searching for the genetic etiology of hereditary conditions that involve enamel.

Root-like enamel pearl: a case report

Introduction

In general, enamel pearls are found in maxillary molars as a small globule of enamel. However, this case report describes an enamel pearl with a prolate spheroid shape which is 1.8mm wide and 8mm long. The different type of enamel pearl found in my clinic has significantly improved our understanding of enamel pearl etiology and pathophysiology.

Case presentation

A 42-year-old Han Chinese woman with severe toothache received treatment in my Department of Endodontics. She had no significant past medical history. A dental examination revealed extensive distal decay in her left mandibular first molar, tenderness to percussion and palpation of the periradicular zone, and found a deep periodontal pocket on the buccal lateral. Vitality testing was negative. Periapical radiographic images revealed radiolucency around the mesial apex. Cone beam computed tomography detected an opaque enamel pearl in the furcation area with a prolate spheroid shape of 1.8mm wide and 8mm long.

Conclusion

The enamel pearl described in this case report is like a very long dental root. Cone beam computed tomography may be used for evaluating enamel pearls.

Genetic Association of MPPED2 and ACTN2 with Dental Caries

The first genome-wide association study of dental caries focused on primary teeth in children aged 3 to 12 yr and nominated several novel genes: ACTN2, EDARADD, EPHA7, LPO, MPPED2, MTR, and ZMPSTE24. Here we interrogated 156 single-nucleotide polymorphisms (SNPs) within these candidate genes for evidence of association with dental caries experience in 13 race- and age-stratified samples from 6 independent studies (n = 3600). Analysis was performed separately for each sample, and results were combined across samples via meta-analysis. MPPED2 was significantly associated with caries via meta-analysis across the 5 childhood samples, with 4 SNPs showing significant associations after gene-wise adjustment for multiple comparisons (p < .0026). These results corroborate the previous genome-wide association study, although the functional role of MPPED2 in caries etiology remains unknown. ACTN2 also showed significant association via meta-analysis across childhood samples (p = .0014). Moreover, in adults, genetic association was observed for ACTN2 SNPs in individual samples (p < .0025), but no single SNP was significant via meta-analysis across all 8 adult samples. Given its compelling biological role in organizing ameloblasts during amelogenesis, this study strengthens the hypothesis that ACTN2 influences caries risk. Results for the other candidate genes neither proved nor precluded their associations with dental caries.

Deoxyoligonucleotide microarrays for gene expression profiling in murine tooth germs

The use of deoxyoligonucleotide microarrays facilitates rapid expression profiling of gene expression using samples of about 1 μg of total RNA. Here are described practical aspects of the procedures involved, including essential reagents. Analysis of results is discussed from a practical, experimental, point of view together with software required to carry out the required statistical analysis to isolate populations of differentially expressed genes.

Genome-wide association scan for childhood caries implicates novel genes

Dental caries is the most common chronic disease in children and a major public health concern due to its increasing incidence, serious health and social co-morbidities, and socio-demographic disparities in disease burden. We performed the first genome-wide association scan for dental caries to identify associated genetic loci and nominate candidate genes affecting tooth decay in 1305 US children ages 3-12 yrs. Affection status was defined as 1 or more primary teeth with evidence of decay based on intra-oral examination. No associations met strict criteria for genome-wide significance (p < 10E-7); however, several loci (ACTN2, MTR, and EDARADD, MPPED2, and LPO) with plausible biological roles in dental caries exhibited suggestive evidence for association. Analyses stratified by home fluoride level yielded additional suggestive loci, including TFIP11 in the low-fluoride group, and EPHA7 and ZMPSTE24 in the sufficient-fluoride group. Suggestive loci were tested but not significantly replicated in an independent sample (N = 1695, ages 2-7 yrs) after adjustment for multiple comparisons. This study reinforces the complexity of dental caries, suggesting that numerous loci, mostly having small effects, are involved in cariogenesis. Verification/replication of suggestive loci may highlight biological mechanisms and/or pathways leading to a fuller understanding of the genetic risks for dental caries.

The physiology and pathobiology of human kallikrein-related peptidase 6 (KLK6)

The human kallikrein-related peptidase 6 (KLK6) gene belongs to the 15-member kallikrein (KLK) gene family mapping to chromosome 19q13.3-13.4. Encoding for an enzyme with trypsin-like properties, KLK6 can degrade components of the extracellular matrix. The successful utilisation of another KLK member (KLK3/PSA) for prostate cancer diagnosis has led many to evaluate KLK6 as a potential biomarker for other cancer and diseased states. The observed dysregulated expression in cancers, neurodegenerative diseases and skin conditions has led to the discovery that KLK6 participates in other cellular pathways including inflammation, receptor activation and regulation of apoptosis. Moreover, the improvements in high-throughput genomics have not only enabled the identification of sequence polymorphisms, but of transcript variants, whose functional significances have yet to be realised. This comprehensive review will summarise the current findings of KLK6 pathophysiology and discuss its potential as a viable biomarker.

Effects of in vivo transfection with anti-miR-214 on gene expression in murine molar tooth germ

MicroRNAs (miRNAs) are an abundant class of noncoding RNAs that are believed to be important in many biological processes through regulation of gene expression. Little is known of their function in tooth morphogenesis and differentiation. MicroRNA-214 (miR-214), encoded by the polycistronic Dnm30os gene, is highly expressed during development of molar tooth germ and was selected as a target for silencing with anti-miR-214. Mandibular injection of 1–100 pmol of anti-miR-214 close to the developing first molar in newborn mice resulted in significant decrease in expression of miR-214, miR-466h, and miR-574-5p in the tooth germ. Furthermore, levels of miR-199a-3p, miR-199a-5p, miR-690, miR-720, and miR-1224 were significantly increased. Additionally, the expression of 863 genes was significantly increased and the expression of 305 genes was significantly decreased. Among the genes with increased expression was Twist-1 and Ezh2, suggested to regulate expression of miR-214. Microarray results were validated using real-time RT-PCR and Western blotting. Among genes with decreased expression were Amelx, Calb1, Enam, and Prnp; these changes also being reflected in levels of corresponding encoded proteins in the tooth germ. In the anti-miR-214-treated molars the enamel exhibited evidence of hypomineralization with remnants of organic material and reduced surface roughness after acid etching, possibly due to the transiently decreased expression of Amelx and Enam. In contrast, several genes encoding contractile proteins exhibited significantly increased expression. mRNAs involved in amelogenesis ( Ambn, Amelx, Enam) were not found among targets of miRNAs that were differentially expressed following treatment with anti-miR-214. It is therefore suggested that effects of miR-214 on amelogenesis are indirect, perhaps mediated by the observed miR-214-dependent changes in levels of expression of numerous transcription factors.