Natural selection and molecular evolution in primate PAX9 gene, a major determinant of tooth development

"Examining the link between tooth agenesis and papillary thyroid cancer: is there a risk factor?" Observational study

BACKGROUND

Mutations in one or multiple genes can lead to hypodontia and its characteristic features. Numerous studies have shown a strong genetic influence on the occurrence of hypodontia, and identified several genes, including AXIN2, EDA, FGF3, FGFR2, FGFR10, WNT10A, MSX1, and PAX9, that are directly associated with dental agenesis and carcinogenesis. The objective of this study was to investigate the occurrence and pattern of tooth agenesis, microdontia, and palatally displaced canine (PDC) in women diagnosed with papillary thyroid cancer (PTC), compared to a control group of women without any malignancy or thyroid disease.

MATERIALS AND METHODS

This case-control study was carried at the Department of Orthodontics, School of Dental Medicine University of Zagreb, and Department of Oncology and Nuclear Medicine Sestre Milosrdnice University Hospital Centre. The study involved a clinical examination and evaluation of dental status, panoramic X-ray analysis, and assessment of medical and family history of 116 female patients aged 20-40 with PTC, as well as 424 females in the control group who were of similar age.

RESULTS

The prevalence of hypodontia, microdontia, and PDC was statistically higher in women with PTC than in the control group. The prevalence rate of hypodontia was 11.3% in the experimental group and 3.5% in the control group. The experimental group showed a higher occurrence of missing upper lateral incisors, lower left central incisors, and all the third molars (except the upper left) compared to the control group. Women with PTC showed the prevalence of PDC significantly higher than the control group (3.5%, 0.7%, p = 0.002). The probability of hypodontia as a clinical finding increases 2.6 times, and microdontia occurs 7.7 times more frequently in women with PTC.

CONCLUSION

Our study suggests a possible link between odontogenesis and PTC. The absence of permanent teeth may increase the likelihood of PTC in women. Leveraging the age-7 orthopantomogram to identify women at high risk for PTC within a critical early detection window could significantly improve oral health outcomes and PTC prognosis through proactive interventions.

Genetic Factors of Teeth Impaction: Polymorphic and Haplotype Variants of PAX9, MSX1, AXIN2, and IRF6 Genes

In recent research, there has been a growing awareness of the role of genetic factors in the positioning and eruption of teeth in the maxilla and mandible. This study aimed to evaluate the potential of specific polymorphic markers of single nucleotide polymorphisms (SNPs) located within the PAX9, MSX1, AXIN2, and IRF6 genes to determine the predisposition to tooth impaction. The study participants were divided into two groups: the first group consisted of individuals with at least one impacted secondary tooth. In contrast, the second group (control group) had no impacted teeth in their jaws. To analyze the genes, real-time PCR (polymerase chain reaction) and TaqMan probes were utilized to detect the selected polymorphisms. The findings suggest that disruptions in the structure and function of the mentioned genetic factors such as polymorphic and haplotype variants of PAX9, MSX1, AXIN2, and IRF6 genes, which play a direct role in tooth and periodontal tissue development, might be significant factors in tooth impaction in individuals with genetic variations. Therefore, it is reasonable to hypothesize that tooth impaction may be influenced, at least in part, by the presence of specific genetic markers, including different allelic variants of the PAX9, AXIN2, and IRF6 genes, and especially MSX1.

Historical aspects about third molar removal versus retention and distal surface caries in the second mandibular molar adjacent to impacted third molars

This paper provides an insight into the historical recommendations regarding removal of mandibular third molars, as set out by the Royal College of Surgeons of England and the National Institutes of Health in the USA, as well as regional guidance from the National Institute for Health and Care Excellence and the controversy that surrounds surgical removal of third molars. The influences of third molar management as it developed in the UK, the historical economic evaluations, and the available evidence base on third-molar removal versus retention are described. This article seeks to address the growing concerns regarding the increasing frequency of distal surface caries (DSC) in mandibular second molar teeth when the decay is associated with asymptomatic, partially erupted, mandibular third molars, especially when they are mesially or horizontally impacted. Lastly, we illustrate radiographs of patients affected by DSC and how guidance that has been issued by a guideline institution regarding third molar surgery, even though it is based on insufficient evidence, is perceived as a strictly compulsory clinical strategy, and has been used in clinical practice in the UK for more than 20 years.

The protoconid: a key cusp in lower molars. Evidence from a recent modern human population

BACKGROUND

The molar (M) size sequence in the genus Homo is decreasing and the general pattern in Homo sapiens is M1 > M2 > M3.

AIM

To gain a better understanding of the reduction patterns of molar components (cusps), we aim to assess the area of the protoconid, the phylogenetically oldest cusp of the lower molars.

SUBJECT AND METHODS

We measured the protoconid and the total crown area in the scaled photographs of a recent modern human sample of lower molars (76 males and 39 females). The values were statistically analysed.

RESULTS

The absolute size of the protoconid increases significantly between M1 and M2/M3, whereas the relative size of this cusp increases significantly from M1 to M3. In the latter, reduction or disappearance of the cusps of the talonid is common.

CONCLUSIONS

The results can be explained in the framework of the patterning cascade model. As the first cusp to appear developmentally, the protoconid forms in response to signals from the primary enamel knot, likely contributing to its stability. Inhibitory signals emitted during the protoconid formation may lead to the reduction or disappearance of the talonid cusps, if these do not have enough time to form before the end of the molar morphogenetic process.

Testing the inhibitory cascade model in a recent human sample

The Inhibitory Cascade Model was proposed by Kavanagh and colleagues (Nature, 449, 427-433 [2007]) after their experimental studies on the dental development of murine rodent species. These authors described an activator-inhibitor mechanism that has been employed to predict evolutionary size patterns of mammalian teeth, including hominins. In the present study, we measured the crown area of the three lower permanent molars (M1, M2, and M3) of a large recent modern human sample of male and female individuals from a collection preserved at the Institute of Anthropology of the University of Coimbra (Portugal). The main aim of the present study is to test if the size molar patterns observed in this human sample fits the Inhibitory Cascade Model. For this purpose, we first measured the crown area in those individuals preserving the complete molar series. Measurements were taken in photographs, using a planimeter and following well-tested techniques used in previous works. We then plot the M3 /M1 and M2 /M1  size ratios. Our results show that the premise of the Inhibitory Cascade Model, according to which the average of the crown area of M2 is approximately one-third of the sum of the crown area of the three molars, is fulfilled. However, our results also show that the individual values of a significant number of males and females are out of the 95% confidence interval predicted by the Inhibitory Cascade Model in rodents. As a result, the present analyses suggest that neither the sample of males, nor that of females, nor the pooled sample fits the Inhibitory Cascade Model. It is important to notice that, although this model has been successfully tested in a large number of current human populations, to the best of our knowledge this is the first study in which individual data have been obtained in a recent human population rather than using the average of the sample. Our results evince that, at the individual level, some factors not yet known could interfere with this model masking the modulation of the size on the molar series in modern humans. We suggest that the considerable delay in the onset of M3 formation in modern humans could be related to a weakening of the possible activation/inhibition process for this tooth. Finally, and in support of our conclusions, we have checked that the absolute and relative size of M1 and M2 is not related to the M3 agenesis in our sample. In line with other studies in primates, our results do not support the Inhibitory Cascade Model in a recent human sample. Further research is needed to better understand the genetic basis of this mechanism and its relationship to the phenotype. In this way, we may be able to find out which evolutionary changes may be responsible for the deviations observed in many species, including Homo sapiens.

The clinical significance and correlative signaling pathways of paired box gene 9 in development and carcinogenesis

Paired box 9 (PAX9) gene belongs to the PAX family, which encodes a family of metazoan transcription factors documented by a conserved DNA binding paired domain 128-amino-acids, critically essential for physiology and development. It is primarily expressed in embryonic tissues, such as the pharyngeal pouch endoderm, somites, neural crest-derived mesenchyme, and distal limb buds. PAX9 plays a vital role in craniofacial development by maintaining the odontogenic potential, mutations, and polymorphisms associated with the risk of tooth agenesis, hypodontia, and crown size in dentition. The loss-of-function of PAX9 in the murine model resulted in a short life span due to the arrest of cleft palate formation and skeletal abnormalities. According to recent studies, the PAX9 gene has a significant role in maintaining squamous cell differentiation, odontoblast differentiation of pluripotent stem cells, deregulation of which is associated with tumor initiation, and malignant transformation. Moreover, PAX9 contributes to promoter hypermethylation and alcohol- induced oro-esophageal squamous cell carcinoma mediated by downregulation of differentiation and apoptosis. Likewise, PAX9 activation is also reported to be associated with drug sensitivity. In summary, this current review aims to understand PAX9 function in the regulation of development, differentiation, and carcinogenesis, along with the underlying signaling pathways for possible cancer therapeutics.

Screening PAX9, MSX1 and WNT10A Mutations in 4 Iranian Families with Non-Syndromic Tooth Agenesis

BACKGROUND

Tooth agenesis is one of the most common developmental anomalies in human and the main reasons for its occurrence are still unknown. Mutations of several genes such as PAX9, MSX1, AXIN2, KDF1 and WNT10A have been reported which are associated with non-syndromic tooth agenesis. However, PAX9, MSX1 and WNT10A are commonly reported in the literature. Hence, the aim of this study was to investigate the mutations of these genes in 4 Iranian families with non-syndromic tooth agenesis.

METHODS

DNA extractions from peripheral blood cells of patients with non-syndromic tooth agenesis from 4 unrelated Iranian families were performed by salting out method, and the candidate genes were amplified then followed by Sanger sequencing method.

RESULTS

One missense variant (rs4904210) and 4 Single Nucleotide Polymorphisms (SNPs) (rs2236007, rs12883298, rs12882923 and rs12883049) were found in PAX9 gene. Five variants (rs149370601, rs8670, rs186861426 and rs774949973) including a missense variant (rs36059701) were detected in MSX1 gene and no variants were found in WNT10A gene.

CONCLUSION

All variants were analyzed based on bioinformatics websites and Iranian gene databases, and as a result, it was revealed that variants of PAX9, MSX1 and WNT10A may not play a role in non-syndromic tooth agenesis among Iranian cases.

Genotyping analysis of the Pax9 Gene in patients with maxillary canine impaction

Background: Paired-box gene 9 ( PAX9) mutation is potentially associated with impaction in some patient populations. Here, we analyzed the relationship between PAX9 polymorphism and the occurrence of maxillary canine impaction. Methods: Patients with and without maxillary canine impaction were selected based on specific inclusion criteria, and samples of genomic DNA were obtained from a buccal mucosa swab. DNA was amplified by polymerase chain reaction and sequenced for further bioinformatics analysis to identify single nucleotide polymorphism (SNP) genotypes. Genotype and allele counting was performed in both case and control groups prior to conducting statistical analysis. Results: Four SNPs were identified in patients with maxillary canine impaction, with relative confidence determined based on chromatogram-peak assessment. All SNPs were located in exon 3 of PAX9 and in the region sequenced by the primer pair -197Fex3 and +28Rex3. Three of the SNPs (rs375436662, rs12881240, and rs4904210) were reported previously and are annotated in NCBI (dbSNP version 150), whereas another SNP mapped to chromosome 14 has not been reported. Patients with a CC genotype at SNP 3 [odds ratio (OR): 2.61 vs. TT; 1.28 vs. CT] and a CC genotype at SNP 4 [OR: 0.71 vs. GG; 0.79 vs. CG] were more likely to have maxillary canine impaction. Conclusions: These results demonstrated that the presence of SNPs 3 and 4 is associated with increased likelihood of suffering from maxillary canine impaction.

Mathematical Characterization of Protein Sequences Using Patterns as Chemical Group Combinations of Amino Acids

Comparison of amino acid sequence similarity is the fundamental concept behind the protein phylogenetic tree formation. By virtue of this method, we can explain the evolutionary relationships, but further explanations are not possible unless sequences are studied through the chemical nature of individual amino acids. Here we develop a new methodology to characterize the protein sequences on the basis of the chemical nature of the amino acids. We design various algorithms for studying the variation of chemical group transitions and various chemical group combinations as patterns in the protein sequences. The amino acid sequence of conventional myosin II head domain of 14 family members are taken to illustrate this new approach. We find two blocks of maximum length 6 aa as 'FPKATD' and 'Y/FTNEKL' without repeating the same chemical nature and one block of maximum length 20 aa with the repetition of chemical nature which are common among all 14 members. We also check commonality with another motor protein sub-family kinesin, KIF1A. Based on our analysis we find a common block of length 8 aa both in myosin II and KIF1A. This motif is located in the neck linker region which could be responsible for the generation of mechanical force, enabling us to find the unique blocks which remain chemically conserved across the family. We also validate our methodology with different protein families such as MYOI, Myosin light chain kinase (MLCK) and Rho-associated protein kinase (ROCK), Na+/K+-ATPase and Ca2+-ATPase. Altogether, our studies provide a new methodology for investigating the conserved amino acids' pattern in different proteins.

A Nonsyndromic Autosomal Dominant Oligodontia with A Novel Mutation of PAX9-A Clinical and Genetic Report

Oligodontia is congenital absence of one or more teeth which has familial abnormality and attributable to various mutations or polymorphisms of genes often associated with malformative syndromes. The present case reports a rare case of non syndromic oligodontia in an 8-year-old girl with missing 14 permanent teeth excluding third molars in mixed dentition. It is a rare finding which has not been frequently documented in Indian children. Mutations in MSX1 and PAX9 have been described in families in which inherited oligodontia characteristically involves permanent incisors, lateral incisors, premolars and molars. Our study analysed one large family with dominantly inherited oligodontia clinically and genetically. This phonotype is distinct from oligodontia phenotypes associated with mutations in PAX9. Sequencing of the PAX9 revealed a novel mutation in the paired domain of the molecule. The multiple sequence alignment and SNP analysis of the PAX9 exon 2 revealed two mutations.

Complex analysis of multiple single nucleotide polymorphisms as putative risk factors of tooth agenesis in the Hungarian population

OBJECTIVES

The role was studied of multiple single nucleotide polymorphisms in tooth agenesis in the Hungarian population using a complex approach.

METHODS

Eight SNPs, PAX9 -912 C/T, PAX9 -1031 A/G, MSX1 3755 A/G, FGFR1 T/C rs881301, IRF6 T/C rs764093, AXIN2-8150 A/G, AXIN2-8434 A/G and AXIN2-30224 C/T, were studied in 192 hypodontia and 17 oligodontia cases and in 260 healthy volunteers. Case-control analysis was performed to test both allelic and genotypic associations as well as associations at the level of haplotypes. Multivariate exploratory Bayesian network-based multi-level analysis of relevance (BN-BMLA) as well as logistic regression analysis were performed.

RESULTS

Conventional statistics showed that PAX9 SNP -912 C/T and the MSX1 SNP changed the incidence of hypodontia, although after Bonferroni correction for multiple hypothesis testing, the effects were only borderline tendencies. Using a statistical analysis better suited for handling multiple hypotheses, the BN-BMLA, PAX9 SNPs clearly showed a synergistic effect. This was confirmed by other multivariate analyses and it remained significant after corrections for multiple hypothesis testing (p < 0.0025). The PAX9-1031-A-PAX9-912-T haplotype was the most relevant combination causing hypodontia. Interaction was weaker between PAX9 and MSX1, while other SNPs had no joint effect on hypodontia.

CONCLUSION

This complex analysis shows the important role of PAX9 and MSX1 SNPs and of their interactions in tooth agenesis, while IRF6, FGFR1 and AXIN2 SNPs had no detectable role in the Hungarian population. These results also reveal that risk factors in hypodontia need to be identified in various populations, since there is considerable variability among them.

Mutational analysis of AXIN2, MSX1, and PAX9 in two Mexican oligodontia families

The genes for axin inhibition protein 2 (AXIN2), msh homeobox 1 (MSX1), and paired box gene 9 (PAX9) are involved in tooth root formation and tooth development. Mutations of the AXIN2, MSX1, and PAX9 genes are associated with non-syndromic oligodontia. In this study, we investigated phenotype and AXIN2, MSX1, and PAX9 gene variations in two Mexican families with non-syndromic oligodontia. Individuals from two families underwent clinical examinations, including an intra-oral examination and panoramic radiograph. Retrospective data were reviewed, and peripheral blood samples were collected. The exons and exon-intronic boundaries of the AXIN2, MSX1, and PAX9 genes were sequenced and analyzed. Protein and messenger RNA structures were predicted using bioinformative software programs. Clinical and oral examinations revealed isolated non-syndromic oligodontia in the two Mexican families. The average number of missing teeth was 12. The sequence analysis of exons and exon-intronic regions of AXIN2, MSX1, and PAX9 revealed 11 single-nucleotide polymorphisms (SNPs), including seven in AXIN2, two in MSX1, and three in PAX9. One novel SNP of MSX1, c.476T>G (Leu159Arg), was found in all of the studied patients in the families. MSX1 Leu159Arg and PAX9 Ala240Pro change protein and messenger RNA structures. Our findings suggested that a combined reduction of MSX1 and PAX9 gene dosages increased the risk for oligodontia in the Mexican families, as in vivo investigation has indicated that interaction between Msx1 and Pax9 is required for tooth development.

MSX1 and PAX9 investigation in monozygotic twins with variable expression of tooth agenesis

Non-syndromic agenesis of permanent teeth is one of the most common anomalies in human development, a multifactorial characteristic caused by genetic and environmental factors. We describe a pair of monozygotic twins who showed second premolar and third molar agenesis, albeit with different expressions. We studied the DNA of two genes, paired domain box gene 9 (PAX9) and muscle segment homeodomain-homeobox1 (MSX1), encoding transcription factors that earlier studies found were involved in the manifestation of this condition. No specific causative mutation was found. However, we detected a C→T change in MSX1 exon 2 in both twins, suggesting that this polymorphism might be involved in the trait's expression.

Contrasting evolutionary dynamics of the developmental regulator PAX9, among bats, with evidence for a novel post-transcriptional regulatory mechanism

Morphological evolution can be the result of natural selection favoring modification of developmental signaling pathways. However, little is known about the genetic basis of such phenotypic diversity. Understanding these mechanisms is difficult for numerous reasons, yet studies in model organisms often provide clues about the major developmental pathways involved. The paired-domain gene, PAX9, is known to be a key regulator of development, particularly of the face and teeth. In this study, using a comparative genetics approach, we investigate PAX9 molecular evolution among mammals, focusing on craniofacially diversified (Phyllostomidae) and conserved (Vespertilionidae) bat families, and extend our comparison to other orders of mammal. Open-reading frame analysis disclosed signatures of selection, in which a small percentage of residues vary, and lineages acquire different combinations of variation through recurrent substitution and lineage specific changes. A few instances of convergence for specific residues were observed between morphologically convergent bat lineages. Bioinformatic analysis for unknown PAX9 regulatory motifs indicated a novel post-transcriptional regulatory mechanism involving a Musashi protein. This regulation was assessed through fluorescent reporter assays and gene knockdowns. Results are compatible with the hypothesis that the number of Musashi binding-elements in PAX9 mRNA proportionally regulates protein translation rate. Although a connection between morphology and binding element frequency was not apparent, results indicate this regulation would vary among craniofacially divergent bat species, but be static among conserved species. Under this model, Musashi's regulatory control of alternative human PAX9 isoforms would also vary. The presence of Musashi-binding elements within PAX9 of all mammals examined, chicken, zebrafish, and the fly homolog of PAX9, indicates this regulatory mechanism is ancient, originating basal to much of the animal phylogeny.

Relation between agenesis and shape anomaly of maxillary lateral incisors and canine impaction

OBJECTIVE: The purpose was to obtain information about the relation between agenesis and shape anomaly of maxillary lateral incisors and canine impaction. METHODS: Seventy-three patients with canine impaction and 73 control patients, without canine impaction, were evaluated. The mesiodistal distances of the maxillary lateral incisors adjacent to the impacted canines and the correspondent mandibular lateral incisors were measured. The adjacent lateral incisors were classified in: 1 - absent, 2 - small, 3 - peg-shaped, 4 - standard. RESULTS: The results showed that among the patients with impacted canines, there were 21 anomalous teeth (small and peg-shaped) and among the control patients there were only three small and peg-shaped teeth, with a statistically significant difference (p = 0.001). No patients were found with impacted canines and absent lateral incisors. CONCLUSION: It was concluded that in patients with anomalous lateral incisors (small and peg-shaped) there is a probability to present impacted canines and this must be considered.

Fibroblast growth factor receptor 1 (FGFR1) variants and craniofacial variation in Amerindians and related populations

OBJECTIVES

The polymorphic site rs4647905 of the FGFR1 gene was previously associated with a decrease in cephalic index (CI). Here, we evaluate the relationships between genotypes and cephalometric measurements and indices in one Mexican Native and two mestizo Mexican populations using two haplotype-tag SNPs (rs4647905 and rs3213849) that represent >85% of the FGFR1 variability, plus three other SNPs (rs2293971, rs2304000, and rs930828) situated nearby. In addition, we genotyped five South American natives, two European, one African, and one Siberian populations to evaluate their intra and intercontinental population diversity.

METHODS

The five SNPs were tested and the craniofacial measurements and indices were collected using standardized procedures. Principal Component Analysis was used to verify individual/population comparisons. Associations were performed through the generalized linear model (GLM), coefficient of determination R(2) and linear regression tests.

RESULTS

We found a tendency for a decrease in CI in individuals homozygous for allele rs4647905C, regardless of the population to which they belong, though the effect is more pronounced in mestizo. When the GLM analyses were performed using the absolute/linear cephalometric measurements, a statistically significant association was found between four SNPs and head length in the mestizo population.

CONCLUSIONS

FGFR1 polymorphisms, especially rs4647905, can have an important role in the normal human skull variation, primarily due to their influence in head length, which would affect other cephalometric absolute/linear measures as well as indices like CI as a result of the pervasive nature of the morphological integration that characterizes the human skull.

Multidisciplinary treatment of non-syndromic oligodontia

Oligodontia is the agenesis of 6 or more teeth, excluding third molars. The etiology of congenital absence of teeth is believed to be rooted in heredity or developmental anomalies. The absence of teeth in patients can cause aesthetic, functional, and psychological problems, particularly if the anterior region is involved. This case report describes the multidisciplinary treatment approach toward a patient 17 years of age with non-syndromic oligodontia, with absence of 11 permanent teeth. Genetic counseling revealed non-syndromic, autosomal-recessive-linked oligodontia. The objectives of the first phase of therapy were pre-prosthetic orthodontic space opening for proper positioning of the missing teeth and correction of inter-maxillary relations, as a prerequisite for proper prosthetic restoration. The second phase of therapy was prosthetic restoration of the missing teeth and provision of occlusion with full-mouth porcelain fused to metal crowns and bridges after increasing occlusal vertical dimension by 2 mm.

Is the human species still evolving?: to where?

The questions of the title have been considered in several ways. First, indications of the traits which make us humans were considered. Then the behavior and culture concepts were examined, and the biology and culture interactions discussed, with an emphasis on the similarities and differences between the genetic and cultural transmissions. Next diverse types of selective pressures were reviewed, and finally pessimistic and optimistic views of our future contrasted. Vigorous action against acts which lead to exclusion and discriminatory policies against human subjects is needed.

Sequence analysis of PAX9, MSX1 and AXIN2 genes in a Chinese oligodontia family

OBJECTIVES

The goal of our research was to look into the clinical traits and genetic mutations in nonsyndromic oligodontia in a Chinese family and to gain insight into the role of mutations of PAX9, MSX1 and AXIN2 in oligodontia phenotypes.

MATERIALS AND METHODS

6 subjects from a family underwent complete oral examination, including panoramic radiographs. Retrospective data were reviewed and blood samples were collected. PCR primers for PAX9, MSX1, and AXIN2 were designed through the Oligo Primer Analysis Software. PCR products were purified and sequenced using the BigDye Terminator Kit and analysed by the 3730 DNA Analyzer.

RESULTS

The proband missed 4 permanent canines, 2 permanent maxillary lateral incisors, 2 permanent mandibular lateral incisors, and 2 permanent mandibular central incisors, whilst his maternal grandfather lacked only 2 permanent mandibular central incisors. Moreover, the size of some permanent teeth appeared smaller than normal values of crown width of Chinese people. Oligodontia and abnormalities of teeth were not present in other family members. Radiographic examination showed that the proband and the rest of family members retained all germs of the third molars. There was one known mutation A240P (rs4904210) of PAX9 in the coding region in the proband and the maternal family members (II-2, II-3, and II-4), which possibly contributed to structural and functional changes of proteins. No mutations were identified in MSX1 and AXIN2.

CONCLUSIONS

Our findings may imply that the PAX9 A240P mutation is a risk factor for oligodontia in the Chinese population. A240P is likely to be a genetic cause of oligodontia though previous literature suggested it as a polymorphism only.

Genetic variation among major human geographic groups supports a peculiar evolutionary trend in PAX9

A total of 172 persons from nine South Amerindian, three African and one Eskimo populations were studied in relation to the Paired box gene 9 (PAX9) exon 3 (138 base pairs) as well as its 5'and 3'flanking intronic segments (232 bp and 220 bp, respectively) and integrated with the information available for the same genetic region from individuals of different geographical origins. Nine mutations were scored in exon 3 and six in its flanking regions; four of them are new South American tribe-specific singletons. Exon3 nucleotide diversity is several orders of magnitude higher than its intronic regions. Additionally, a set of variants in the PAX9 and 101 other genes related with dentition can define at least some dental morphological differences between Sub-Saharan Africans and non-Africans, probably associated with adaptations after the modern human exodus from Africa. Exon 3 of PAX9 could be a good molecular example of how evolvability works.

PAX9 and MSX1 transcription factor genes in non-syndromic dental agenesis

OBJECTIVE

The molecular variation of paired domain box gene 9 (PAX9) was previously investigated by our research group and a high degree of evolutionary conservation in coding and non-coding regions was observed except in exon 3. PAX9 is a transcription factor important in tooth development, and we wanted to verify its role in dental agenesis in detail. Since dental development is a complex trait we also decided to examine the influence of another transcription factor, muscle segment homeodomain-homeobox 1 (MSX1) on it.

DESIGN

A total of 360 consecutively ascertained patients seeking orthodontic treatment were screened for tooth agenesis and 33% of them were found to have it. Thirty-five of those with agenesis and 15 controls had their DNA studied for PAX9 exons 2, 3, 4 and adjacent regions (total of 1476 base pairs, bp) as well as MSX1 exon 2 (698bp). A trio (a proband and her parents) was also studied.

RESULTS

Six polymorphic sites were found, three in PAX9 exon 3 and three in MSX1 exon2. MSX1 rs1095 derived allele occurred in individuals with agenesis only, and two other mutations in this gene had been earlier associated with tooth agenesis. Homozygosity for the PAX9 Ala240Pro mutation was studied in a family (proband and her parents), suggesting recessive inheritance with variable expressivity for the dental agenesis found.

CONCLUSION

Common variants located out of the DNA binding domain of the two PAX9 and MSX1 genes can also be related to tooth agenesis.

Mutations in the PAX9 gene in sporadic oligodontia

OBJECTIVES

Oligodontia, a congenital lack of six or more teeth, is often associated with mutations in the PAX9 gene; therefore, we searched for mutations in this gene.

DESIGN

In the present work, we sequenced fragments of the PAX9 gene in individuals with sporadic oligodontia. Next, we genotyped some mutations we found in patients with oligodontia and individuals without tooth agenesis.

SETTING AND SAMPLE POPULATION

DNA sequencing was performed in the material isolated from peripheral blood lymphocytes of six unrelated patients with sporadic, non-syndromic oligodontia. These patients were selected based upon explorative cluster analysis. Genotyping was performed in 38 patients with oligodontia and 100 control individuals.

MATERIAL AND METHODS

Direct sequencing and restriction fragment length polymorphism PCR were employed.

RESULTS

We detected two homozygotic substitutions, IVS2-109G>C and IVS2-54A>G, in intron 2 in three patients. Another homozygotic substitution in intron 2, IVS2-41A>G, was revealed in two patients. Two patients had an IVS3+40G>A homozygotic change in intron 3 and 4 patients displayed a 717C>T transition in exon 4 (silent mutation). One patient had a heterozygotic 718G>C transversion, resulting in a missense Ala240Pro substitution. We detected also several other intronic substitutions. Further genotyping of the IVS2-54A>G, IVS2-109G>C, and IVS2-41A>G mutations suggested that they can display polymorphic changes.

CONCLUSION

The IVS2-54A>G, IVS2-109G>C, and IVS2-41A>G mutations of the PAX9 gene may represent polymorphism associated with sporadic oligodontia.

Deletion of PAX9 and oligodontia: a third family and review of the literature

OBJECTIVE

This study was conducted to report a family affected by benign hereditary chorea in which a large deletion including TTF1, PAX9, and other genes was identified and results in oligodontia.

METHODS

Clinical and radiological studies of the two affected members (mother and daughter) were used to describe the oligodontia present in both of them.

RESULTS

The missing teeth in both patients are described in detail, and these data are compared with the dental anomalies observed in the only two other families with deletions of PAX9 and with the data available for 12 previously reported families carrying different types of PAX9 mutations.

CONCLUSIONS

There is a clinical relevance for recognizing such families, and offering available therapies since childhood is stressed. Some genotype-phenotype correlations between PAX9 mutations and dental anomalies can be drawn.

Dental agenesis: genetic and clinical perspectives

Dental agenesis is the most common developmental anomaly in humans and is frequently associated with several other oral abnormalities. Whereas the incidence of missing teeth may vary considerably depending on dentition, gender, and demographic or geographic profiles, distinct patterns of agenesis have been detected in the permanent dentition. These frequently involve the last teeth of a class to develop (I2, P2, M3) suggesting a possible link with evolutionary trends. Hypodontia can either occur as an isolated condition (non-syndromic hypodontia) involving one (80% of cases), a few (less than 10%) or many teeth (less than 1%), or can be associated with a systemic condition or syndrome (syndromic hypodontia), essentially reflecting the genetically and phenotypically heterogeneity of the condition. Based on our present knowledge of genes and transcription factors that are involved in tooth development, it is assumed that different phenotypic forms are caused by different genes involving different interacting molecular pathways, providing an explanation not only for the wide variety in agenesis patterns but also for associations of dental agenesis with other oral anomalies. At present, the list of genes involved in human non-syndromic hypodontia includes not only those encoding a signaling molecule (TGFA) and transcription factors (MSX1 and PAX9) that play critical roles during early craniofacial development, but also genes coding for a protein involved in canonical Wnt signaling (AXIN2), and a transmembrane receptor of fibroblast growth factors (FGFR1). Our objective was to review the current literature on the molecular mechanisms that are responsible for selective dental agenesis in humans and to present a detailed overview of syndromes with hypodontia and their causative genes. These new perspectives and future challenges in the field of identification of possible candidate genes involved in dental agenesis are discussed.

Tooth agenesis: from molecular genetics to molecular dentistry

Tooth agenesis may originate from either genetic or environmental factors. Genetically determined hypodontic disorders appear as isolated features or as part of a syndrome. Msx1, Pax9, and Axin2 are involved in non-syndromic hypodontia, while genes such as Shh, Pitx2, Irf6, and p63 are considered to participate in syndromic genetic disorders, which include tooth agenesis. In dentistry, artificial tooth implants represent a common solution to tooth loss problems; however, molecular dentistry offers promising solutions for the future. In this paper, the genetic and molecular bases of non-syndromic and syndromic hypodontia are reviewed, and the advantages and disadvantages of tissue engineering in the clinical treatment of tooth agenesis are discussed.

Evidence for positive selection on the E2 gene of bovine viral diarrhoea virus type 1

Despite the growing interest in the molecular epidemiology of pestivirus, there have been few attempts to determine which regions of the pestivirus genome are subject to positive selection, although this may be a key indicator of the nature of the interaction between host and virus. By using likelihood-based methods for phylogenetic inference, the positive selection pressure of BVDV-1 E2 gene were assessed and a site-by-site analysis of the dN/dS ratio was performed, to identify specific codons undergoing diversifying positive selection. The overall omega was 0.20, indicating that most sites were subject to strong purifying selection and five positively selected sites (886, 888, 905, 944, and 946) were identified. It is surprising to find that all the potential positively selected sites fall within the C-terminal of E2, and out of the N-terminal of E2 which is thought to be surface-exposed and therefore prime targets for host antibody response. In conclusion, these results suggest that selection favoring avoidance of antibody recognition has not been a major factor in the history of BVDV-1. Further analysis is necessary to see if amino acid substitutions in the BVDV-1 positively selected sites can lead to change of host tropism or\and escape from epitope-specific CD8 T-cell response.