Novel mutation in the paired box sequence of PAX9 gene in a sporadic form of oligodontia

Tooth development is regulated through a series of reciprocal interactions between the dental epithelium and mesenchyme and requires protein products of a number of genes. It has been reported that selective tooth agenesis is associated with mutations in human MSX and PAX9 genes. Mutational analysis of the two genes was performed in 25 individuals with familial or sporadic form of permanent tooth agenesis. Single-stranded conformational polymorphism analysis revealed no mutations in the entire coding sequence of the MSX1 gene. In PAX9, a novel, heterozygous G151A transition in the sequence encoding the paired domain of the PAX9 protein was detected in a patient with agenesis of third molars, second premolars and incisors, but not in her parents, the remaining patients or 162 individuals with normal dentition. This is the first de novo mutation described in PAX9. Our results support the view that mutations in PAX9 could constitute a causative factor of oligodontia. We hypothesize that the G151A transition in PAX9 might be responsible for the sporadic form of tooth agenesis in this patient.     

A screen of a large Czech cohort of oligodontia patients implicates a novel mutation in the PAX9 gene

Tooth agenesis is one of the most common developmental anomalies in humans. To date, many mutations involving paired box 9 (PAX9), msh homeobox 1 (MSX1), and axin 2 (AXIN2) genes have been identified. The aim of the present study was to perform screening for mutations and/or polymorphisms using the capillary sequencing method in the critical regions of PAX9 and MSX1 genes in a group of 270 individuals with tooth agenesis and in 30 healthy subjects of Czech origin. This screening revealed a previously unknown heterozygous g.9527G>T mutation in the PAX9 gene in monozygotic twins with oligodontia and three additional affected family members. The same variant was not found in healthy relatives. This mutation is located in intron 2, in the region recognized as the splice site between exon 2 and intron 2. We hypothesize that the error in pre‐mRNA splicing may lead to lower expression of PAX9 protein and could have contributed to the development of tooth agenesis in the affected subjects.     

MSX1, PAX9, and TGFA contribute to tooth agenesis in humans

In this study, we sought to determine the association between tooth agenesis and DNA sequence variation in the genes MSX1 and PAX9 in an ethnically diverse human population. Since cleft lip/palate is also associated with both tooth agenesis and the gene TGFA, we included TGFA in the analysis as well. Cheek swab samples were obtained for DNA analysis from 116 case/parent trios. Probands had at least one developmentally missing tooth, excluding third molars. Genotyping was performed by single-strand conformational polymorphism or kinetic polymerase chain-reaction assays. Transmission distortion of the marker alleles and DNA sequence analysis was performed. Results showed that tooth agenesis is associated with markers of the genes MSX1 and TGFA. No mutations were found in MSX1 or PAX9 coding regions. There were statistically significant data suggesting that MSX1 interacts with PAX9. These findings suggest that MSX1, PAX9, and TGFA play a role in isolated dental agenesis.     

Novel MSX1 frameshift causes autosomal-dominant oligodontia

Can kindreds with tooth agenesis caused by MSX1 or PAX9 mutations be distinguished by their phenotypes? We have identified an MSX1second bicuspids and mandibular central incisors. The dominant phenotype is apparently due to haploinsufficiency. We analyzed patterns of partial tooth agenesis in seven kindreds with defined MSX1 mutations and ten kindreds with defined PAX9 mutations. The probability of missing a particular type of tooth is always bilaterally symmetrical, but differences exist between the maxilla and mandible. MSX1-associated oligodontia typically includes missing maxillary and mandibular second bicuspids and maxillary first bicuspids. The most distinguishing feature of MSX1-associated oligodontia is the frequent (75%) absence of maxillary first bicuspids, while the most distinguishing feature of PAX9-associated oligodontia is the frequent (> 80%) absence of the maxillary and mandibular second molars.     

非综合征型先天缺牙致病基因和分子机制的研究进展

先天缺牙是牙齿发育过程中常见的牙数目发育异常,对患者的颌面部发育及美观和咀嚼功能产生严重的影响。根据有无伴发全身症状,先天缺牙可分为综合征型先天缺牙与非综合征型先天缺牙。近几年发现新的相关基因和新的突变位点及分子机制已成为目前非综合征型先天缺牙基因研究的主要方向。本文通过对近年来文献的回顾,对与非综合征型先天缺牙主要相关的Wnt/β-catenin信号通路、TGF-β/BMP信号通路、PAX9基因和MSX1基因、EDA/EDAR/NF-κb信号通路的分子机制以及相互调节的紧密联系进行综述,为未来先天缺牙的防治提供了新的理论基础。非综合征型先天缺牙致病基因的分子机制的研究目前甚少,对于其机制的精准探索将成为先天缺牙未来主要的研究方向之一。     

The role of MSX1 in human tooth agenesis

MSX1 has a critical role in craniofacial development, as indicated by expression assays and transgenic mouse phenotypes. Previously, MSX1 mutations have been identified in three families with autosomal-dominant tooth agenesis. To test the hypothesis that MSX1 mutations are a common cause of congenital tooth agenesis, we screened 92 affected individuals, representing 82 nuclear families, for mutations, using single-strand conformation analysis. A Met61Lys substitution was found in two siblings from a large family with autosomal-dominant tooth agenesis. Complete concordance of the mutation with tooth agenesis was observed in the extended family. The siblings have a pattern of severe tooth agenesis similar that in to previous reports, suggesting that mutations in MSX1 are responsible for a specific pattern of inherited tooth agenesis. Supporting this theory, no mutations were found in more common cases of incisor or premolar agenesis, indicating that these have a different etiology.     

Homeobox protein MSX‐1 inhibits expression of bone morphogenetic protein 2, bone morphogenetic protein 4, and lymphoid enhancer‐binding factor 1 via Wnt/β‐catenin signaling to prevent differentiation of dental mesenchymal cells during the late bell stage

Homeobox protein MSX‐1 (hereafter referred to as MSX‐1) is essential for early tooth‐germ development. Tooth‐germ development is arrested at bud stage in Msx1 knockout mice, which prompted us to study the functions of MSX‐1 beyond this stage. Here, we investigated the roles of MSX‐1 during late bell stage. Mesenchymal cells of the mandibular first molar were isolated from mice at embryonic day (E)17.5 and cultured in vitro. We determined the expression levels of β‐catenin, bone morphogenetic protein 2 (Bmp2), Bmp4, and lymphoid enhancer‐binding factor 1 (Lef1) after knockdown or overexpression of Msx1. Our findings suggest that knockdown of Msx1 promoted expression of Bmp2, Bmp4, and Lef1, resulting in elevated differentiation of odontoblasts, which was rescued by blocking the expression of these genes. In contrast, overexpression of Msx1 decreased the expression of Bmp2, Bmp4, and Lef1, leading to a reduction in odontoblast differentiation. The regulation of Bmp2, Bmp4, and Lef1 by Msx1 was mediated by the Wnt/β‐catenin signaling pathway. Additionally, knockdown of Msx1 impaired cell proliferation and slowed S‐phase progression, while overexpression of Msx1 also impaired cell proliferation and prolonged G1‐phase progression. We therefore conclude that MSX‐1 maintains cell proliferation by regulating transition of cells from G1‐phase to S‐phase and prevents odontoblast differentiation by inhibiting expression of Bmp2, Bmp4, and Lef1 at the late bell stage via the Wnt/β‐catenin signaling pathway.     

Exclusion of coding region mutations in MSX1, PAX9 and AXIN2 in eight patients with severe oligodontia phenotype

PURPOSE: This paper describes the screening of eight patients with severe oligodontia for PAX9 and AXIN2 mutations. SUBJECTS AND METHODS: Anamnestic data and a panoramic radiograph were collected to study the phenotype of eight patients with oligodontia and their first-degree relatives. A blood sample was taken for a mutational screening for PAX9 and AXIN2 mutations. RESULTS: No mutations were discovered, but a unique nucleotide change in a conserved 5' flanking region of PAX9 was revealed. Earlier screening of the same patients for MSX1 mutations also had a negative outcome. CONCLUSIONS: Considering the discrepancy between the high incidence rate of agenesis and the relatively small number of reported causative mutations in PAX9, MSX1 and AXIN2 genes, the genetic contribution to oligodontia probably is much more heterogeneous than expected so far. Therefore negative results, like the present exclusion data, should be published more often in order to get a better appreciation of the relative contribution of these specific mutations causing oligodontia. In this context the exact number of tested probands also should be mentioned at all cases. Recent evidence of PAX9-MSX1 protein interactions in odontogenesis as well as other genes and developmental factors should receive more attention.     

Genetic analysis: Wnt and other pathways in nonsyndromic tooth agenesis

Tooth agenesis (TA) is one of the most common developmental anomalies that affects the number of teeth. An extensive analysis of publicly accessible databases revealed 15 causative genes responsible for nonsyndromic TA, along with their signaling pathways in Wnt/β‐catenin, TGF‐β/BMP, and Eda/Edar/NF‐κB. However, genotype–phenotype correlation analysis showed that most of the causal genes are also responsible for syndromic TA or other conditions. In a total of 198 different mutations of the 15 genes responsible for nonsyndromic TA, 182 mutations (91.9%) are derived from seven genes (AXIN2, EDA, LRP6, MSX1, PAX9, WNT10A, and WNT10B) compared with the remaining 16 mutations (8.1%) identified in the remaining eight genes (BMP4, DKK1, EDAR, EDARADD, GREM2, KREMEN1, LTBP3, and SMOC2). Furthermore, specificity analysis in terms of the ratio of nonsyndromic TA mutations versus syndromic mutations in each of the aforementioned seven genes showed a 98.2% specificity rate in PAX9, 58.9% in WNT10A, 56.6% in MSX1, 41.2% in WNT10B, 31.4% in LRP6, 23.8% in AXIN2%, and 8.4% in EDA. These findings underscore an important role of the Wnt and Wnt‐associated pathways in the genetic etiology of this heterozygous disease and shed new lights on the discovery of novel molecular mechanisms associated with tooth agenesis.