Molecular factors resulting in tooth agenesis and contemporary approaches for regeneration: a review

Unraveling the Connection between Fibroblast Growth Factor and Bone Morphogenetic Protein Signaling

Ontogeny of higher organisms as well the regulation of tissue homeostasis in adult individuals requires a fine-balanced interplay of regulating factors that individually trigger the fate of particular cells to either stay undifferentiated or to differentiate towards distinct tissue specific lineages. In some cases, these factors act synergistically to promote certain cellular responses, whereas in other tissues the same factors antagonize each other. However, the molecular basis of this obvious dual signaling activity is still only poorly understood. Bone morphogenetic proteins (BMPs) and fibroblast growth factors (FGFs) are two major signal protein families that have a lot in common: They are both highly preserved between different species, involved in essential cellular functions, and their ligands vastly outnumber their receptors, making extensive signal regulation necessary. In this review we discuss where and how BMP and FGF signaling cross paths. The compiled data reflect that both factors synchronously act in many tissues, and that antagonism and synergism both exist in a context-dependent manner. Therefore, by challenging a generalization of the connection between these two pathways a new chapter in BMP FGF signaling research will be introduced.

Colorectal Cancer-Associated Genes Are Associated with Tooth Agenesis and May Have a Role in Tooth Development

Previously reported co-occurrence of colorectal cancer (CRC) and tooth agenesis (TA) and the overlap in disease-associated gene variants suggest involvement of similar molecular pathways. Here, we took an unbiased approach and tested genome-wide significant CRC-associated variants for association with isolated TA. Thirty single nucleotide variants (SNVs) in CRC-predisposing genes/loci were genotyped in a discovery dataset composed of 440 individuals with and without isolated TA. Genome-wide significant associations were found between TA and ATF1 rs11169552 (P = 4.36 × 10-10) and DUSP10 rs6687758 (P = 1.25 × 10-9), and positive association found with CASC8 rs10505477 (P = 8.2 × 10-5). Additional CRC marker haplotypes were also significantly associated with TA. Genotyping an independent dataset consisting of 52 cases with TA and 427 controls confirmed the association with CASC8. Atf1 and Dusp10 expression was detected in the mouse developing teeth from early bud stages to the formation of the complete tooth, suggesting a potential role for these genes and their encoded proteins in tooth development. While their individual contributions in tooth development remain to be elucidated, these genes may be considered candidates to be tested in additional populations.

A review on non-syndromic tooth agenesis associated with PAX9 mutations

Tooth agenesis in the reduction of tooth number which includes hypodontia, oligodontia and anodontia is caused by disturbances and gene mutations that occur during odontogenesis. To date, several genetic mutations that unlock the causes of non-syndromic tooth agenesis are being discovered; these have been associated with certain illnesses because tooth development involves the interaction of several genes for tooth epithelium and mesenchyme odontogenesis. Mutation of candidate genes PAX9 and MSX1 have been identified as the main causes of hypodontia and oligodontia; meanwhile, AXIN2 mutation is associated with anodontia. Previous study using animal models reported that PAX9-deficient knockout mice exhibit missing molars due to an arrest of tooth development at the bud stage. PAX9 frameshift, missense and nonsense mutations are reported to be responsible; however, the most severe condition showed by the phenotype is caused by haploinsufficiency. This suggests that PAX9 is dosage-sensitive. Understanding the mechanism of genetic mutations will benefit clinicians and human geneticists in future alternative treatment investigations.

Radiographic Assessment of Dental Maturation in Children With Dental Agenesis

BACKGROUND

Dental agenesis is the most common developmental anomaly in humans, frequently associated with disorders in dental development and maturation.

AIM

The purpose of this study is to determine radiographic variations in dental maturation in a group of Venezuelan children with dental agenesis.

STUDY DESIGN

1,188 panoramic radiographs, from healthy patients ages 5 to 12 years old were studied for agenesis of permanent teeth. Dental maturation was assessed by relative eruption and dental age according to Nolla, comparing children affected with dental agenesis to a stratified control group selected from the same population, excluding children with premature loss of primary teeth in the left quadrants and unclear radiographs. Descriptive analysis, and differences between means and medians (Student t test, Kruskall-Wallis p=0.05) were performed.

RESULTS

Medians for Nolla stages were similar between groups, with delay in tooth formation in the agenesis group for second molars (p<0.05) and maxillary lateral incisors and second premolars. Dental age was significantly underestimated for both groups, -0.89 (±0.78) for the control group and -1.20 (±0.95) for the study group. Tooth eruption was similar between groups.

CONCLUSION

Dental age was significantly delayed in Venezuelan children with dental agenesis, with variable significance for tooth formation of studied teeth.

Prevalence of delayed tooth development and its relation to tooth agenesis in Korean children

OBJECTIVE

The aim of this study was to investigate the epidemiology of delayed tooth development (DTD) and the link between DTD and tooth agenesis (TA).

DESIGN

The dental maturity of all of the developing permanent teeth of 4611 children (2417 males and 2194 females) was evaluated from panoramic radiographs. The prevalence of DTD and TA was analyzed, and gender difference for DTS and TA was investigated. The correlation of DTD and TA was investigated in intra-fields and inter-fields.

RESULTS

The total prevalence of DTD among the 4611 children was 3.40%. The maxillary second premolar was the most frequently delayed tooth (1.02%), followed by the maxillary second molar (0.88%) and the mandibular second premolar (0.74%). DTD significantly correlated with TA in both intra-fields and inter-fields (p<0.05).

CONCLUSIONS

The field of delayed development exhibited a significant correlation with that of TA.

Axis inhibition protein 2 polymorphisms may be a risk factor for families with isolated oligodontia

The objective of the present study was to search for Msh homeobox 1 (MSX1), paired box gene 9 (PAX9), ectodysplasin‑A (EDA) and axis inhibition protein 2 (AXIN2) variants in a family with isolated oligodontia and analyse the pathogenesis of mutations that result in oligodontia phenotypes. Members of a single family (but of different descent) with oligodontia and unrelated healthy controls were enrolled in our study. Genomic DNA was isolated from blood samples. Mutation analysis was performed by amplifying MSX1, PAX9, EDA and AXIN2 exons as well as their exon‑intron boundaries and sequencing the products. DNA sequencing of the AXIN2 gene revealed three mutations in the two patients with oligodontia: a homozygotic silent mutation c.1365A>G (p.Pro455=) in exon 3, two c.956+16A>G mutations (II‑1: homozygosis; III‑1: heterozygosis) and c.1200+71A>G (homozygosis) in the intron, which possibly contributed to structural and functional changes in proteins. The heterozygotic mutations c.1365A>G and c.1200+71A>G were identified in the proband's mother (II‑2). No mutations were detected in the MSX1, PAX9 and EDA genes of oligodontia patients. The findings suggest that the c.956+16A>G, c.1365A>G and c.1200+71A>G mutations of AXIN2 may be responsible for the oligodontia phenotype in this family, but these findings require further study.

Delivery of plasmid DNA into dental tissues of developing rat teeth by electroporation

Gene transfer by electroporation is a versatile technique that can effectively deliver DNA or RNA into almost all types of cells or tissues. As a widely used nonviral approach, electroporation possesses several advantages over viral methods including non-immunogenicity and local tissue transfection. We have successfully transferred plasmid DNA and siRNA into the dental tissues of rat developing and unerupted molars using electroporation. This chapter presents a step-by-step electroporation method for transferring plasmid DNA into dental tissues. The parameters and factors affecting transfection efficiency are discussed in Subheading 4 of the chapter for aiding others in designing their experimental protocols. This dental tissue transfection technique provides a useful tool to overexpress the genes of interest to study their functions in tooth development and eruption. It can be used to deliver nucleic acids into dental tissues for development of gene-based therapies to treat dental disorders.