The human EDAR 370V/A polymorphism affects tooth root morphology potentially through the modification of a reaction-diffusion system

Critical Considerations in Calling Disease-Causing EDAR Mutations in Nonsyndromic Oligodontia

Background/Objectives: Oligodontia, the absence of six or more teeth excluding third molars, is a rare genetic condition, unlike hypodontia (missing one or more teeth), which is a relatively common human disease. Methods: To identify the genetic etiology of nonsyndromic oligodontia (NSO) families, we performed mutational analysis and investigated the functional effects of identified EDAR mutations. Whole-exome sequencing was conducted on recruited families with NSO. Bioinformatic analysis identified mutations in oligodontia-causing candidate genes, which were confirmed by Sanger sequencing and segregation within families. The impact of EDAR mutations on the EDA signaling pathway was assessed using luciferase activity analysis. Results:EDAR mutations were identified in three NSO families. A homozygous missense EDAR mutation (NM_022336.4: c.319A>G p.(Met107Val)) was found in the singleton proband of family 1. The proband of family 2 carried compound heterozygous EDAR mutations: a maternal missense mutation (c.319A>G p.(Met107Val)) and a paternal missense variant (c.1270G>A p.(Val424Met)). The proband of family 3 had heterozygous EDAR mutations: a maternal missense mutation (c.389T>A p.(Ile130Asn)) and paternal intronic variants in cis (c.[357-4G>A;440+50C>T]). Luciferase assays confirmed reduced transcriptional activity for all identified missense mutations, while splicing assays revealed altered splicing patterns. Conclusions: In conclusion, recessive EDAR mutations, including novel ones, were identified in NSO families, and their pathological mechanism was explored through transcriptional activity measurements.

Bioclimatic and masticatory influences on human cranial diversity verified by analysis of 3D morphometric homologous models

This study analyzes the effects of bioclimate and masticatory factors on the regional variability of human cranial forms across 150 ethnic groups worldwide. Morphometric variables were generated using principal component analysis applied to 3D homologous models. Relationships between cranial form and bioclimate (temperature and precipitation) and masticatory factors (infratemporal space) were tested considering sampling bias due to past population movements during the late Pleistocene and/or early- to mid-Holocene. Cranial size correlated with thermal conditions, consistent with Bergmann's rule. The length/breadth proportion of the neurocranium aligned with Allen's rule for thermal adaptation, while no relationship with masticatory stress was found. Facial form responded to either climate or masticatory conditions, although the primary factor was unclear due to the high correlation between stresses. However, masticatory stress was identified as an equally significant factor behind facial flatness in cold regions, else than the effect of Allen's rule. High narrowness of nasal and orbital openings correlated significantly with cold temperatures and cranial size, suggesting not only functional but also allometric effect. This study demonstrated the complexity of environmental influences on cranial form diversity, nonetheless suggested reduction of selective pressure on cranial form caused by natural environmental stress due to the development of civilization.

Molecular basis and genetics of hypohidrotic ectodermal dysplasias

Ectodermal dysplasia (ED) is a heterogeneous group of hereditary diseases of the skin and its appendages, which are characterized by impaired development and/or homeostasis of two or more ectoderm derivatives, including: hair, teeth, nails, sweat glands and their modifications (mammary glands, for instance). The overall prevalence of ectodermal dysplasia remains precisely unknown not only in Russia, but also in the world, nor is known the contribution of individual genes to its structure. This complicates the DNA diagnosis establishment of this disease due to the lack of an accurate diagnostic algorithm and a universal cost-effective method of analysis. To date, the most highly-researched genes involved in the development of anhydrous or hypohidrotic forms of ED are EDA, EDAR, EDARADD and WNT10A. The ectodysplasin A (EDA) gene is the cause of the most common X-linked form of ED, a gene from the Wnt family (WNT10A) is responsible for the autosomal recessive form of the disease, and two other genes (EDAR and EDARADD) can cause both autosomal recessive and autosomal dominant forms. This review provides the characteristics of the genes involved in ED, their mutation spectra, the level of their expression in human tissues, as well as the interrelation of the aforementioned genes. The domain structures of the corresponding proteins are considered, as well as the molecular genetic pathways in which they are involved. Animal models for studying this disorder are also taken into consideration. Due to the cross-species genes conservation, their mutations cause the disruption of the development of ectoderm derivatives not only in humans, but also in mice, cows, dogs, and even fish. It can be exploited for a better understanding of the etiopathogenesis of ectodermal dysplasias. Moreover, this article brings up the possibility of recurrent mutations in the EDA and WNT10A genes. The review also presents data on promising approaches for intrauterine ED treatment.

EDA ligand triggers plasma membrane trafficking of its receptor EDAR via PKA activation and SNAP23-containing complexes

BACKGROUND

Ectodysplasin-A (EDA), a skin-specific TNF ligand, interacts with its membrane receptor EDAR to trigger EDA signaling in skin appendage formation. Gene mutations in EDA signaling cause Anhidrotic/Hypohidrotic Ectodermal Dysplasia (A/HED), which affects the formation of skin appendages including hair, teeth, and several exocrine glands.

RESULTS

We report that EDA triggers the translocation of its receptor EDAR from a cytosolic compartment into the plasma membrane. We use protein affinity purification to show that upon EDA stimulation EDAR associates with SNAP23-STX6-VAMP1/2/3 vesicle trafficking complexes. We find that EDA-dependent PKA activation is critical for the association. Notably, either of two HED-linked EDAR mutations, T346M and R420W, prevents EDA-induced EDAR translocation; and both EDA-induced PKA activation and SNAP23 are required for Meibomian gland (MG) growth in a skin appendage model.

CONCLUSIONS

Overall, in a novel regulatory mechanism, EDA increases plasma membrane translocation of its own receptor EDAR, augmenting EDA-EDAR signaling in skin appendage formation. Our findings also provide PKA and SNAP23 as potential targets for the intervention of HED.

Supernumerary roots in maxillary deciduous canines: A rare anomaly with a long history

OBJECTIVE

To describe two maxillary deciduous bi-rooted canines, one archeological and one modern, and examine the possible etiology of this condition.

DESIGN

Two cases of bi-rooted canines were described and compared to published examples. Both specimens were radiographed and measured and compared to one-rooted samples. The archeological specimen was scanned using CBCT to facilitate detailed examination of the deciduous teeth. The extracted modern tooth was embedded in epoxy resin and two coronal sections were cut, one through the crown and one through the roots and examined with a light microscope.

RESULTS

The bi-rooted canines were larger than the control samples. They showed none of the features commonly associated with gemination. The radiographs and scans showed that the canine roots in the archeological case diverged mesio-distally like the buccal roots in the adjacent first deciduous molar. In the clinical case, the root trunk was elongated mesio-distally and the furcation was located very close to the apex with a C-shaped root canal.

CONCLUSIONS

Both variants of the condition described above are rare in deciduous canines. They do not seem to be associated with fusion or gemination. However, as the teeth are relatively flattened bucco-lingually and we tentatively propose that this form results from spatial constraints during the early stages of crown development that have contributed to the development of additional roots. The megadont dimension of the recent bi-rooted deciduous canine may affect root development and the necessity of two mesio-distally located roots for anchorage in the maxilla.

Variation in Middle Stone Age mandibular molar enamel-dentine junction topography at Klasies River Main Site assessed by diffeomorphic surface matching

The morphology and variability of the Middle Stone Age (MSA) hominin fossils from Klasies River Main Site have been the focus of investigation for more than four decades. The mandibular remains have figured prominently in discussions relating to robusticity, size dimorphism, and symphyseal morphology. Variation in corpus size between the robust SAM-AP 6223 and the diminutive SAM-AP 6225 mandibles is particularly impressive, and the difference between the buccolingual diameters of their M₂s significantly exceeds recent human sample variation. SAM-AP 6223 and SAM-AP 6225 are the only Klasies specimens with homologous teeth (M₂ and M₃) that permit comparisons of crown morphology. While the differences in dental trait expression at the outer enamel surfaces of these molars are slight, diffeomorphic surface analyses of their underlying enamel-dentine junction (EDJ) topographies reveal differences that are well beyond the means of pairwise differences among comparative samples of Later Stone Age (LSA) Khoesan and recent African homologues. The EDJs of both SAM-AP 6225 molars and the SAM-AP 6223 M₃ fall outside the envelopes that define the morphospace of these two samples. Although the radiocarbon dated LSA individuals examined here differ by a maximum of some 7000 years, and the two Klasies jaws may differ by perhaps as much as 18,000 years, it is difficult to ascribe their differences to time alone. With reference to the morphoscopic traits by which the SAM-AP 6223 and SAM-AP 6225 EDJs differ, the most striking is the expression of the protoconid cingulum. This is very weakly developed on the SAM-AP 6223 molars and distinct in SAM-AP 6225. As such, this diminutive fossil exhibits a more pronounced manifestation of what is likely a plesiomorphic feature, thus adding to the morphological mosaicism that is evident in the Klasies hominin assemblage. Several possible explanations for the variation and mosaicism in this MSA sample are discussed.