Influence of growth hormone on the craniofacial complex of transgenic mice

Food texture and vitamin D influence mouse mandible form and molar roots

Industrialization influenced several facets of lifestyle, including softer nutrient-poor diets that contributed to vitamin D deficiency in post-industrzialized populations, with concomitantly increased dental problems. Here we simulated a post-industrialized diet in a mouse model to test the effects of diet texture and vitamin D level on mandible and third molar (M3) forms. Mice were raised on a soft diet with vitamin D (VitD) or without it (NoD), or on a hard diet with vitamin D. We hypothesized that a VitD/hard diet is optimal for normal mandible and tooth root form, as well as for timely M3 initiation. Subsets of adult NoD/soft and VitD/soft groups were bred to produce embryos that were micro-computed tomography (μCT) scanned to stage M3 development. M3 stage did not differ between embryos from mothers fed VitD and NoD diets, indicating that vitamin D does not affect timing of M3 onset. Sacrificed adult mice were μCT-scanned, their mandibles 3D-landmarked and M3 roots were measured. Principal component (PC) analysis described the largest proportion of mandible shape variance (PC1, 30.1%) related to diet texture, and nominal shape variance (PC2, 13.8%) related to vitamin D. Mice fed a soft diet had shorter, relatively narrower, and somewhat differently shaped mandibles that recapitulated findings in human populations. ANOVA and other multivariate tests found significantly wider M3 roots and larger root canals in mice fed a soft diet, with vitamin D having little effect. Altogether our experiments using a mouse model contribute new insights about how a post-industrial diet may influence human craniodental variation.

Polymorphism analysis of myosin 1H (G/A) and P561T (C/A) genes on class I, class II, and class III malocclusion

CONTEXT:

Besides environmental factors, genetic factors play an important role in the etiology of malocclusion. Polymorphisms of the Myosin 1H gene in orofacial muscle fibers are thought to influence the growth and development of the mandible. Growth hormone receptors are present on the growth of cartilage, especially the condyle of the mandible. The polymorphisms of the growth hormone receptor have an effect on the growth and development of the mandible. The potential of the Myosin 1H and P561T genes as bioindicators in aiding diagnosis of malocclusion is quite good based on the available literature. However, until now there has been no research that has observed genetic analysis on polymorphism-based malocclusion of the Myosin 1H and P561T genes in the Indonesian population.

AIMS:

To determine the relationship between polymorphisms of Myosin 1H and P561T genes, towards the growth and development of the mandible in malocclusion cases.

SETTINGS AND DESIGN:

Subjects were patients aged 17--45 years old with skeletal malocclusions who were undergoing or were about to undergo orthodontic treatment at RSGM-FKG UI (Universitas Indonesia's Dental Hospital), with 50 people in each group.

METHODS AND MATERIAL:

Malocclusions were determined based on radiographic analysis of the initial cephalometry using the Stainer method. DNA samples were extracted from buccal swabs and blood cells in Class I and II malocclusion while nail clippings and hair follicles extracts were used in Class III malocclusion. DNA sequence amplification was carried out using Polymerase Chain Reaction, while Genetic Polymorphism Analysis of Myosin 1H and P561T genes was performed with Restriction Fragment Length Polymorphism.

STATISTICAL ANALYSIS USED:

Pearson Chi-Square was used to analyze the Myosin 1H gene, while the Fisher Exact Test was used to analyze the P561T gene.

RESULTS:

A relationship between Myosin 1H gene polymorphism and Class I, II, and III skeletal malocclusion was found. There was no correlation between P561T gene polymorphism and Class I, II, and III skeletal malocclusion.

CONCLUSIONS:

Myosin 1H gene polymorphism is one of the risk factors for Class I, II, and III malocclusion. Extraction of DNA from hair follicles gave good results in terms of DNA quality and was a relatively easier sampling method compared to blood cell purification and buccal swabs.

Genetic effect of single nucleotide polymorphisms in growth hormone receptor gene on the risk of non-syndromic mandibular prognathism in the Korean population

OBJECTIVES

To evaluate the association of three single-nucleotide polymorphisms (SNPs) of growth hormone receptor (GHR) gene with mandibular prognathism (MP) and relationships between mandibular morphology and GHR gene SNPs in the Korean population.

MATERIALS AND METHODS

A total of 325 subjects were divided into two groups based on sagittal maxillomandibular relationship by the lateral cephalography: the MP and control groups. From the SNPs in the GHR gene, three SNPs (rs6180, rs6182 and rs6184) were selected. SNP genotyping was performed using direct sequencing. The craniofacial measurements of lateral cephalography were analysed.

RESULTS

We found a lack of association between GHR and MP. However, in the analysis according to the values of cephalometric measurements, rs6180 was significantly associated with ANB, SNB, effective mandibular length and SNMP in females. Additionally, rs6182 and rs6184 were significantly associated with ramal height in males.

CONCLUSION

Growth hormone receptor SNPs may affect not only the sagittal development of mandible but also the vertical development of ramal height, and GHR SNPs may gender-differently influence mandibular morphology. This finding supports that the GHR might be susceptible on mandibular morphogenesis in the Korean population.

RET signalling provides tumorigenic mechanism and tissue specificity for AIP-related somatotrophinomas

It is unclear how loss-of-function germline mutations in the widely-expressed co-chaperone AIP, result in young-onset growth hormone secreting pituitary tumours. The RET receptor, uniquely co-expressed in somatotrophs with PIT1, induces apoptosis when unliganded, while RET supports cell survival when it is bound to its ligand. We demonstrate that at the plasma membrane, AIP is required to form a complex with monomeric-intracellular-RET, caspase-3 and PKCδ resulting in PIT1/CDKN2A-ARF/p53-apoptosis pathway activation. AIP-deficiency blocks RET/caspase-3/PKCδ activation preventing PIT1 accumulation and apoptosis. The presence or lack of the inhibitory effect on RET-induced apoptosis separated pathogenic AIP variants from non-pathogenic ones. We used virogenomics in neonatal rats to demonstrate the effect of mutant AIP protein on the RET apoptotic pathway in vivo. In adult male rats altered AIP induces elevated IGF-1 and gigantism, with pituitary hyperplasia through blocking the RET-apoptotic pathway. In females, pituitary hyperplasia is induced but IGF-1 rise and gigantism are blunted by puberty. Somatotroph adenomas from pituitary-specific Aip-knockout mice overexpress the RET-ligand GDNF, therefore, upregulating the survival pathway. Somatotroph adenomas from patients with or without AIP mutation abundantly express GDNF, but AIP-mutated tissues have less CDKN2A-ARF expression. Our findings explain the tissue-specific mechanism of AIP-induced somatotrophinomas and provide a previously unknown tumorigenic mechanism, opening treatment avenues for AIP-related tumours.

The Role of GH/IGF Axis in Dento-Alveolar Complex from Development to Aging and Therapeutics: A Narrative Review

The GH/IGF axis is a major regulator of bone formation and resorption and is essential to the achievement of normal skeleton growth and homeostasis. Beyond its key role in bone physiology, the GH/IGF axis has also major pleiotropic endocrine and autocrine/paracrine effects on mineralized tissues throughout life. This article aims to review the literature on GH, IGFs, IGF binding proteins, and their respective receptors in dental tissues, both epithelium (enamel) and mesenchyme (dentin, pulp, and tooth-supporting periodontium). The present review re-examines and refines the expression of the elements of the GH/IGF axis in oral tissues and their in vivo and in vitro mechanisms of action in different mineralizing cell types of the dento-alveolar complex including ameloblasts, odontoblasts, pulp cells, cementoblasts, periodontal ligament cells, and jaw osteoblasts focusing on cell-specific activities. Together, these data emphasize the determinant role of the GH/IGF axis in physiological and pathological development, morphometry, and aging of the teeth, the periodontium, and oral bones in humans, rodents, and other vertebrates. These advancements in oral biology have elicited an enormous interest among investigators to translate the fundamental discoveries on the GH/IGF axis into innovative strategies for targeted oral tissue therapies with local treatments, associated or not with materials, for orthodontics and the repair and regeneration of the dento-alveolar complex and oral bones.

Impact of the endocannabinoid system on murine cranial and alveolar bone phenotype

PURPOSE

The endocannabionoid signaling system has been demonstrated to be present in the skeleton, with involvement in the regulation of skeletal homeostasis. However, investigations substantiating these findings in cranial and alveolar bones are missing to date. The aim of our study was to investigate a potential impact of the endocannabinoid system on cranial and alveolar bone structures and phenotypes.

BASIC PROCEDURES

CB1^-/-, CB2^-/- and WT mice (n = 5) were scanned via μCT. Reconstructed datasets were processed for analyses. Cranial cephalometric measurements were performed with OnyxCeph^3TMsoftware. Alveolar bone densities were determined via mean grey value measurements with Mimics research 18.0. Alveolar bone heights around teeth in upper and lower jaws were morphometrically analyzed. Alveolar osteoclasts were quantified via TRAP staining of paraffin-embedded histologies. Bone-marrow derived macrophages isolated from murine hind legs were analyzed for CD40 and MMR expression via flow cytometry.

MAIN FINDINGS

CB2^-/- mice exhibited significantly higher bone densities with mean grey values of 138.3 ± 22.6 compared to 121.9 ± 9.3 for WT for upper jaws, and 134.6 ± 22.9 compared to 116.1 ± 12.9 for WT 134.6 ± 22.9. Concurrently, CB2 receptor knockout entailed reduced alveolar bone heights of about 50% compared to WT mice. Antigen-presenting cell marker expression of MMR was significantly diminished in bone-marrow derived macrophages of CB2^-/- mice. Cranium dimensions as much as alveolar osteoclasts were unaffected by receptor knockouts.CB1 receptor knockout did not involve statistically significant alterations in the parameters investigated compared to WT mice.

PRINCIPAL CONCLUSIONS

The endoncannabinoid system, and particularly CB2 receptor strongly affects murine alveolar bone phenotypes. These observations suggest CB2 as promising target in the modulation of oral bone phenotypes, probably by impact on bone dynamics via osteal immune cells.

Possible association between craniofacial dimensions and genetic markers in ESR1 and ESR2

OBJECTIVE

To investigate the association of genetic markers in ESR1 and ESR2 with craniofacial measurements.

DESIGN

Cross-sectional study.

SETTING

School of Dentistry of Ribeirão Preto, University of São Paulo.

PARTICIPANTS

A total of 146 biologically unrelated, self-reported Caucasian Brazilians with no syndromic conditions were included.

METHODS

Sagittal and vertical measurements (ANB, S-N, Ptm'-A', Co-Gn, Go-Pg, N-Me, ANS-Me, S-Go and Co-Go) from lateral cephalograms were examined for craniofacial evaluation. DNA was extracted from saliva and genetic markers in ESR1 (rs2234693 and rs9340799) and in ESR2 (rs1256049 and rs4986938) were analysed by real-time polymerase chain reaction. Hardy-Weinberg equilibrium was evaluated using the Chi-square test within each marker. The associations between craniofacial dimensions and genotypes were analysed by linear regression and adjusted by sex and age. The established alpha was 5%.

RESULTS

Individuals carrying CC in ESR1 rs2234693 had a decrease of -3.146 mm in ANS-Me (P = 0.044). In addition, rs4986938 in ESR2 was associated with S-N measurement (P = 0.009/ ß = -3.465). This marker was also associated with Go-Pg measurement, in which the CC genotype had a decrease of -3.925 mm in the length of the mandibular body (P = 0.043).

CONCLUSION

The present study suggests that in ESR1 and ESR2 are markers for variations in the craniofacial dimensions. However, further research should confirm the results.

Association analysis between rs6184 and rs6180 polymorphisms of growth hormone receptor gene regarding skeletal-facial profile in a Colombian population

Background/Objective

There is strong evidence that genetic factors may affect the craniofacial morphology. This study aimed to examine the association between the rs6184 and rs6180 polymorphic variants of the growth hormone receptor (GHR) gene and skeletal-facial profile in a Colombian population.

Subjects/Methods

Saliva samples from 306 individuals ranging in age from 15 to 53 (mean 24.33) years were collected. Cephalometric parameters were used to categorize the participants as Class I, Class II, or Class III skeletal-facial profile. The polymerase chain reaction-restriction fragment length polymorphism method was used to identify genotypes of the rs6184 and rs6180 single nucleotide polymorphisms (SNPs). The association of polymorphisms with the skeletal-facial profile was assessed separately and adjusted for confounding using a multivariate binary logistic regression model, alongside with analysis of linkage disequilibrium and haplotype associations.

Results

Although individuals carrying the CA genotype of the rs6184 SNP showed both significantly decreased values for ANB angle and increased measures concerning mandibular body length and mandibular length, no significant differences amongst genotype groups of rs6180 SNP were observed. Moreover, chi-square test and logistic regression analysis revealed that the CA genotype of rs6184 SNP and the A-A haplotype were highly associated with Class III skeletal-facial profile.

Conclusions

Although these results do not support that rs6180 SNP could be identified as a predictor for skeletal-facial profile, they suggest that the allele A of rs6184 SNP alone or in combination with other SNPs in the GHR gene yields significant horizontal and longitudinal variations of the mandibular morphology and might be a strong/independent prognostic indicator for Class III skeletal-facial profile in the present population.

Upper jaw development in the absence of teeth: New insights for craniodental evo-devo integration

In p63-null mice (p63^-/- ), teeth fail to form but the mandible forms normally; conversely, the upper jaw skeleton is malformed. Here we explored whether lack of dental tissues contributed to midfacial dysmorphologies in p63^-/- mice by testing if facial prominence defects appeared before odontogenesis failed. We also investigated gene dose effects by testing if one wild type (WT) p63 allele (p63^+/- ) was sufficient for normal upper jaw skeleton formation. We micro-CT scanned PFA-fixed p63^-/- , p63^+/- , and WT (p63^+/+ ) adult and embryonic mice aged E10-E14. Next, we landmarked mandibular (MdP), maxillary (MxP) and nasal prominences (NPs), and facial bones. 3D landmark data were assessed using Principal Component, Canonical Variate, Partial Least Squares, and other statistical analyses. The p63^-/- embryos showed MxP and NP malformations by E12, despite the presence of dental tissues. MdP shape was comparable among p63^-/- , p63^+/- , and p63^+/+ embryos. Upper jaw shape was comparable between p63^+/+ and p63^+/- adults. The upper jaw and its dentition both require p63 signaling, but not each other's presence, to form properly. One WT p63 allele enables normal midfacial morphogenesis; gene dose may be a target for jaw macroevolution. Jaw-specific genetic mechanisms likely integrate the evo-devo of dentitions with upper versus lower jaws.

Multimethod Approach to the Early Postnatal Growth of the Mandible in Mice from a Zone of Robertsonian Polymorphism

The western European house mouse (Mus musculus domesticus) shows high karyotypic diversity owing to Robertsonian translocations. Morphometric studies conducted with adult mice suggest that karyotype evolution due to these chromosomal reorganizations entails variation in the form and the patterns of morphological covariation of the mandible. However, information is much scarcer regarding the effect of these rearrangements on the growth pattern of the mouse mandible over early postnatal ontogeny. Here we compare mandible growth from the second to the eighth week of postnatal life between two ontogenetic series of mice from wild populations, with the standard karyotype and with Robertsonian translocations respectively, reared under the same conditions. A multi-method approach is used, including bone histology analyses of mandible surfaces and cross-sections, as well as geometric morphometric analyses of mandible form. The mandibles of both standard and Robertsonian mice display growth acceleration around weaning, anteroposterior direction of bone maturation, a predominance of bone deposition fields over ontogeny, and relatively greater expansion of the posterior mandible region correlated with the ontogenetic increase in mandible size. Nevertheless, differences exist between the two mouse groups regarding the timing of histological maturation of the mandible, the localization of certain bone remodeling fields, the temporospatial patterns of morphological variation, and the organization into two main modules. The dissimilarities in the process of mandible growth between the two groups of mice become more evident around sexual maturity, and could arise from alterations that Robertsonian translocations may exert on genes involved in the bone remodeling mechanism. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc.

Growth hormone receptor gene is related to root length and tooth length in human teeth

OBJECTIVES

To examine the relationship between tooth length and growth hormone receptor (GHR) gene variants in a healthy Japanese population.

MATERIALS AND METHODS

The subjects consisted of 193 Japanese adults (69 men, 124 women), aged 13 to 56 years. Genomic DNA was extracted from saliva and genotyped GHR rs6184 and rs6180 variants using the Taqman genotyping. Computed tomography (CT) images were acquired using a dental cone-beam CT scanner and reconstructed using open-source OsiriX medical image processing software. The maxillary (upper; U) and mandibular (lower, L) central incisors (1), lateral incisors (2), canines (3), first premolars (4), second premolars (5), first molars (6), and second premolars (7) were evaluated. Teeth were assessed for crown height (CH), root length (RL), overall tooth length (C+R), and crown to root ratio (C/R). The relationships between GHR variants and CH, RL, C+R, and C/R were statistically examined.

RESULTS

The GHR variant rs6184 was associated with the root lengths and tooth length for the upper and lower lateral incisors and upper canines (U2 RL; U3 RL, C+R; L2 RL [ P < .05]).

CONCLUSIONS

The results indicate that the GHR rs6184 variant is associated with tooth length and ratio dimensions in a Japanese cohort. Further studies utilizing a larger sample size are needed to confirm this finding.

The correlation between growth hormone receptor (GHR) polymorphism and obstructive sleep apnea syndrome among the Han and Hani population in China

Obstructive sleep apnea syndrome (OSAS) is a common health problem that is associated with abnormality in craniofacial morphology. The growth hormone receptor (GHR) belongs to the cytokine receptor superfamily and mediates the majority of growth hormone signaling, which, among other functions, determines mandibular growth and development. The aim of this study was to determine if correlations exist between single nucleotide polymorphisms (SNPs) in the GHR gene and OSAS in the Han or Hani ethnic groups in China. A total of 274 Han subjects (106 with OSAS and 168 without OSAS) and a total of 270 Hani subjects (64 with OSAS and 206 without OSAS) were enrolled in our study. Genomic DNA was extracted from peripheral blood obtained from all subjects. Genotyping was undertaken for eight SNPs in the GHR gene (rs3756416, rs7727047, rs2910875, rs12153009, rs2972781, rs12518414, rs4410646, and rs6451620) using PCR amplification and Sanger sequencing. The genotype frequency of rs12518414 was associated with OSAS in both the Han and Hani groups, and the A allele frequency was remarkably lower in Hani OSAS patients compared with Hani controls (16.7 vs 29.9%). In addition, the G allele frequency of the rs3756416 SNP was significantly lower in OSAS patients compared with normal controls in the Hani ethnic group (12.5 vs 24.6%). In a comparison between ethnic groups, genotype frequencies of four SNPs (rs2972781, rs6451620, rs12518414, and rs7727047) differed between Han and Hani OSAS patients, with the A allele frequency of the rs12518414 and G allele frequency of the rs7727047 were significantly higher in the Han OSAS patients. In conclusion, significant associations were detected between some SNPs in the GHR gene and OSAS occurrence while others appeared to be ethnicity-dependent.

The effect of the physical consistency of the diet on the bone quality of the mandibular condyle in rats

OBJECTIVE

This study aimed to analyze how the physical consistency of the diet affects the bone quality at the mandibular condyle.

DESIGN

Sixty-three Wistar rats were randomly assigned to three groups. Twenty-two animals composed each group and they were fed with either a liquid, soft or hard diet. Seven animals were sacrificed from each group at days 7, 20, and 40 respectively. Their mandibles were removed and scanned at the postero-superior area of the condyle with a micro-CT scan.

RESULTS

showed a statistically significant difference for the bone mineral density (p<0.01) and total mineral density (p<0.01), when comparing the hard against the liquid group after seven days. After 20days both, the soft and the liquid diet groups, computed a statistically significant difference demonstrating a significant decrease in the measured values for bone mineral density, bone mineral content, total mineral density, and total mineral content. At day 40, the values stayed lower for the soft and liquid diets, even though they did not reach a significant difference.

CONCLUSIONS

This study supports the idea that a soft or liquid diet has a negative impact on the bone quality of the mandible, particularly during the periods of more active growing.

Growth hormone receptor gene variant and three-dimensional mandibular morphology

OBJECTIVE

To examine the relationship between three-dimensional mandibular morphology and growth hormone receptor (GHR) gene variants in a healthy Japanese population.

MATERIALS AND METHODS

The subjects, who were unrelated Japanese orthodontic patients, consisted of 64 men and 114 women. Using the Taqman genotyping assay, GHR gene rs6184 and rs6180 variants were detected in genomic DNA extracted from saliva. Mandibular volume and length were measured from cone-beam computed tomography images that were analyzed using Analyze image-processing software. The relationship between GHR gene variants and three-dimensional mandibular morphology was statistically examined.

RESULTS

Statistical significance for the relationship between the distance between the left and right coronoid processes and rs6180 was noted (P < .05).

CONCLUSION

Our results indicate that the GHR variant rs6180 is associated with the distance between the left and right coronoid process in the Japanese subjects.

Disrupted mitochondrial function in the Opa3L122P mouse model for Costeff Syndrome impairs skeletal integrity

Mitochondrial dysfunction connects metabolic disturbance with numerous pathologies, but the significance of mitochondrial activity in bone remains unclear. We have, therefore, characterized the skeletal phenotype in the Opa3^L122P mouse model for Costeff syndrome, in which a missense mutation of the mitochondrial membrane protein, Opa3, impairs mitochondrial activity resulting in visual and metabolic dysfunction. Although widely expressed in the developing normal mouse head, Opa3 expression was restricted after E14.5 to the retina, brain, teeth and mandibular bone. Opa3 was also expressed in adult tibiae, including at the trabecular surfaces and in cortical osteocytes, epiphyseal chondrocytes, marrow adipocytes and mesenchymal stem cell rosettes. Opa3^L122P mice displayed craniofacial abnormalities, including undergrowth of the lower mandible, accompanied in some individuals by cranial asymmetry and incisor malocclusion. Opa3^L122P mice showed an 8-fold elevation in tibial marrow adiposity, due largely to increased adipogenesis. In addition, femoral length and cortical diameter and wall thickness were reduced, the weakening of the calcified tissue and the geometric component of strength reducing overall cortical strength in Opa3^L122P mice by 65%. In lumbar vertebrae reduced vertebral body area and wall thickness were accompanied by a proportionate reduction in marrow adiposity. Although the total biomechanical strength of lumbar vertebrae was reduced by 35%, the strength of the calcified tissue (σ_max) was proportionate to a 38% increase in trabecular number. Thus, mitochondrial function is important for the development and maintenance of skeletal integrity, impaired bone growth and strength, particularly in limb bones, representing a significant new feature of the Costeff syndrome phenotype.

Relationship between P561T and C422F polymorphisms in growth hormone receptor gene and mandibular prognathism

OBJECTIVE

To evaluate the allele and genotype frequencies of the P561T and C422F polymorphic sites of the growth hormone receptor (GHR) gene and the relationship between mandibular prognathism (MP) and these two single-nucleotide polymorphisms (SNPs).

MATERIALS AND METHODS

A total of 99 subjects with severe skeletal Class III MP who planned to undergo orthognathic surgery and 99 subjects with Class I occlusion were examined in this study to evaluate the relationship between MP and two SNPs in exon 10 of the GHR gene. GHR was chosen as a candidate gene because growth hormone plays an important role in cartilage growth. A blood sample was used to extract genomic DNA, and the polymerase chain reaction-restriction fragment length polymorphism method was used to determine genotypes of P561T and C422F. The Minitab 14.0 packet program was used to perform statistical analysis.

RESULTS

Allele frequencies of the C422F and P561T variants were determined. Because of the low allele frequency of the control group, statistical analysis could not be performed to test the difference between MP and control groups. Therefore, the data were combined to determine the association between the P561T polymorphism and craniofacial measurements. Effective mandibular length (condylion-gnathion) and lower face height (anterior nasal spina-menton) were associated with the P561T variant.

CONCLUSION

This finding supports that the GHR might be a candidate gene for mandibular morphogenesis in this population.

Shape covariation between the craniofacial complex and first molars in humans

The occurrence of mutual genetic loci in morphogenesis of the face and teeth implies shape covariation between these structures. However, teeth finalize their shape at an early age, whereas the face grows and is subjected to environmental influences for a prolonged period; it is therefore conceivable that covariation might modulate with age. Here we investigate the extent of this covariation in humans by measuring the 3D shape of the occlusal surface of the permanent first molars and the shape of the craniofacial complex from lateral radiographs, at two maturations stages. A sample of Greek subjects was divided into two groups (110 adult, 110 prepubertal) with equally distributed gender. The occlusal surfaces of the right first molars were 3D scanned from dental casts; 265 and 274 landmarks (including surface and curve semilandmarks) were digitized on the maxillary and mandibular molars, respectively. The corresponding lateral cephalometric radiographs were digitized with 71 landmarks. Geometric morphometric methods were used to assess shape variation and covariation. The vertical dimension of the craniofacial complex was the main parameter of shape variation, followed by anteroposterior deviations. The male craniofacial complex was larger (4.0-5.7%) and was characterized by a prominent chin and clockwise rotation of the cranial base (adult group only). Allometry was weak and statistically significant only when examined for the sample as a whole (percent variance explained: 2.1%, P = 0.0002). Covariation was statistically significant only between the lower first molar and the craniofacial complex (RV = 14.05%, P = 0.0099, and RV = 12.31%, P = 0.0162, for the prepubertal and adult groups, respectively). Subtle age-related covariation differences were noted, indicating that environmental factors may influence the pattern and strength of covariation. However, the main pattern was similar in both groups: a class III skeletal pattern (relative maxillary retrusion and mandibular protrusion), hyperdivergency, forward rotation of the posterior cranial base and upward rotation of the anterior cranial base were associated with mesiodistal elongation of the lower molars and height reduction of their distal cusps. This pattern mimics phylogeny in humans, where flexion and counterclockwise rotation of the cranial base, considered advantageous to survival, co-occur with tooth reductions that cannot be easily explained in evolutionary terms. The similarity of the phylogenetic and covariation patterns seems to support the pleiotropic gene hypothesis.

The complex ontogenetic trajectory of mandibular shape in a laboratory mouse

The mouse mandible is a popular model system that continues to be the focus of studies in evo-devo and other fields. Yet, little attention has been given to the role of postnatal growth in producing the adult form. Using cleared and stained specimens, we describe the timing of tooth and jaw development and changes in jaw size and shape from postnatal day 1 (p1) through weaning to adulthood. We found that tooth development is relatively advanced at birth, and that the functional adult dentition is in place by p15 (just before the start of weaning). Shape analysis showed that the trajectory of mandible shape changes direction at least twice between birth and adulthood, at p7 and p15. At each stage there are changes in shape to all tooth- and muscle-bearing regions and, at each change of direction, all of these regions change their pattern of growth. The timing of the changes in direction in Mus suggests there are signals that redirect growth patterns independently of changes in function and loading associated with weaning and jaw muscle growth. A better understanding of these signals and how they produce a functionally integrated mandible may help explain the mechanisms guiding evolutionary trends and patterns of plasticity and may also provide valuable clues to therapeutic manipulation of growth to alleviate the consequences of trauma or disease.

Jaw growth in the absence of teeth: the developmental morphology of edentulous mandibles using the p63 mouse mutant

Mammalian tooth and jaw development must be coordinated well enough that these systems continue to function together properly throughout growth, thus optimizing an animal's survival and fitness, as well as a species' success. The persistent question is how teeth and jaws remain developmentally and functionally viable despite sometimes monumental evolutionary changes to tooth and jaw shape and size. Here we used the p63 mouse mutant to test the effect of tooth development - or the lack thereof - on normal mandible developmental morphology. Using 3D geometric morphometrics, we compared for the first time mandible shape among mice with normal tooth and jaw development against p63 double knock-out mice, with failed tooth development but apparently normal jaw development. Mandible shape differed statistically between toothless (p63(-/-) ) and toothed (p63(+/-) , p63(+/+) ) mice as early as embryonic day (E) 18. As expected, most of the shape difference in the p63(-/-) mandibles was due to underdeveloped alveolar bone related to arrested odontogenesis in these E18-aged mice. Mandible shape did not differ statistically between p63(+/-) and p63(+/+) adult mice, which showed normal tooth development. Our results support the idea of a gene regulatory network that is exclusive to the mandible and independent of the dentition. This study also underscores the biomechanical impact of the teeth on the developing alveolar bone. Importantly, this work shows quantitatively that the p63 mutant is an apt model with which to study mandible morphogenesis in isolation of odontogenesis to clarify developmental relationships between the teeth and jaws.

Growth hormone therapy and craniofacial bones: a comprehensive review

Growth hormone (GH) has significant effects on linear bone growth, bone mass and bone metabolism. The primary role of GH supplementation in children with GH deficiency, those born small for gestational age or with other types of disorders in somatic development is to increase linear growth. However, GH therapy seems to elicit varying responses in the craniofacial region. Whereas the effects of GH administration on somatic development are well documented, comparatively little is known of its effects on the craniofacial region. The purpose of this review was to search the literature and compile results from both animal and human studies related to the impact of GH on craniofacial growth.

Growth of functional cranial components in rats with intrauterine growth retardation after treatment with growth hormone

The goal of this study was to analyse the effect of growth hormone (GH) on catch-up growth of functional facial (splanchnocranial) and neurocranial components in rats with intrauterine growth retardation (IUGR). Wistar rats were divided into the following groups: control (C), sham-operated (SH), IUGR, and IUGR + GH. IUGR was surgically induced and GH was administered between 21 and 60 days of age. Radiographs were obtained at 1, 21, 42, 63, and 84 days of age in order to measure length, width, and height of neurocranium (NL, NW, and NH) and face length, width, and height (FL, FW, and FH). Analysis of variance was performed at 1 day of age and a principal components analysis (PCA) at 84 days of age. Neurocranial and facial volumetric indexes were calculated as NVI = (3)√NL × NW × NH and FVI = (3)√FL × FW × FH, respectively, and adjusted by non-linear regression analysis. On postnatal day 1, there were significant differences between SH and IUGR (P < 0.01). Also, in both genders, final neurocranial volume was similar between SH and IUGR + GH groups, while the IUGR group had the lower value (P < 0.01). Final facial volume was similar among the three groups. In both genders, facial growth rates were SH = IUGR > IUGR + GH (P < 0.01). The first axis of the PCA exhibited size effect and the second axis showed shape effect. Reductions of placental blood flow modify cranial growth. The functional neurocranial and facial components in rats with IUGR presented different recovery strategies through modular behaviour, mainly related to modifications of growth rate as response to GH administration.

The effects of testosterone on craniosynostotic calvarial cells: a test of the gene/environmental model of craniofacial anomalies

INTRODUCTION

The gene-environmental interaction model for craniofacial development proposes that if a genetic predisposition for an anomaly is coupled with an environmental factor that can exacerbate this predisposition, more severe phenotypes will result. Here, we utilize cells derived from our non-syndromic rabbit model of craniosynostosis to test the hypothesis that an insult, testosterone (TP) administration (exogenous source) will alter the osteogenic activity of these cells.

DESIGN

Calvarial cells from wild-type (WT) (N=13) or craniosynostotic (CS) rabbits (N=11) were stimulated with TP, an androgen receptor blocker, flutamide, and combined treatments. Proliferation and differentiation assays were conducted after 7 days. anova and t-tests were used to determine differences in stimulation and cell type.

RESULTS

The CS cells had significantly greater proliferation after TP administration compared to WT. There were no appreciable changes in differentiation after TP stimulation. Flutamide administration or combined TP and flutamide administration decreased both proliferation and differentiation for both cell types similarly.

CONCLUSIONS

Testosterone exposure caused an increase in cell proliferation for CS osteoblast cells. However, a therapy targeted to mitigate this response (flutamide therapy) similarly affected CS and WT cells, suggesting that the administration of flutamide or TP in the presence of flutamide decreases osteogenesis of these cells. Thus, although our data support a mechanism of gene-environmental interaction, these results would not support a therapeutic intervention based on this interaction.

Endocrine parameters and phenotypes of the growth hormone receptor gene disrupted (GHR-/-) mouse

Disruption of the GH receptor (GHR) gene eliminates GH-induced intracellular signaling and, thus, its biological actions. Therefore, the GHR gene disrupted mouse (GHR-/-) has been and is a valuable tool for helping to define various parameters of GH physiology. Since its creation in 1995, this mouse strain has been used by our laboratory and others for numerous studies ranging from growth to aging. Some of the most notable discoveries are their extreme insulin sensitivity in the presence of obesity. Also, the animals have an extended lifespan, which has generated a large number of investigations into the roles of GH and IGF-I in the aging process. This review summarizes the many results derived from the GHR-/- mice. We have attempted to present the findings in the context of current knowledge regarding GH action and, where applicable, to discuss how these mice compare to GH insensitivity syndrome in humans.

The effect of the Botulinum toxin-A on craniofacial development: an experimental study

In this study, we developed a novel experimental model to evaluate muscular action on bone formation and remodeling by the help of Botulinum toxin-A (BTX). Forty-nine 15-day-old male Wistar rats were put into 4 groups randomly. Group 1 was the control group. BTX 0.4 IU (0.05 mL) was injected into the right masseter muscle in group 2 and into right temporalis muscle in group 3. The same volume of sterile saline was given into the both above-mentioned muscles in group 4. At the end of the fourth month, all animals were killed. Histology and weight of the masseter and temporalis muscles were studied. Thirty different osteometric measurements were also taken from skulls. Significant atrophy in BTX injected muscles was observed in groups 2 and 3. In group 4 (saline injection), only few osteometric measurements were significantly reduced, indicating the effect of the injection itself. Both groups 2 and 3 have apparent decrease in nasal bone, premaxilla, maxilla, and zygomatic dimensions on the injected side. When masseter group was compared with control and saline groups, no significant difference was found in skull base dimensions and mandibular length. In contrast, temporal group has also shown significant decrease in skull base dimensions. Our conclusions are as follows: (1) With this model, it is possible to study muscular action on bone formation and modeling without any surgical intervention, that is, by avoiding surgical artifacts, such as scar and contracture; (2) denervation of the skeletal muscles with BTX during the growing phase does effect bone development in a negative way; (3) pediatric use of the BTX deserves reevaluation under the light of these findings.

The significance of RUNX2 in postnatal development of the mandibular condyle

OBJECTIVE

RUNX2, in the Runt gene family, is one of the most important transcription factors in the development of the skeletal system. Research in recent decades has shown that this factor plays a major role in the development, growth and maturation of bone and cartilage. It is also important in tooth development, mechanotransduction and angiogenesis, and plays a significant role in various pathological processes, i.e. tumor metastasization. Mutations in the RUNX2 gene correlate with the cleidocranial dysplasia (CCD) syndrome, important to dentistry, particularly orthodontics because of its dental and orofacial symptoms. Current research on experimentally-induced mouse mutants enables us to study the etiology and pathogenesis of these malformations at the cellular and molecular biological level. This study's aim is to provide an overview of the RUNX2 gene's function especially in skeletal development, and to summarize our research efforts to date, which has focused on investigating the influence of RUNX2 on mandibular growth, which is slightly or not at all altered in many CCD patients.

MATERIALS AND METHODS

Immunohistochemical analyses were conducted to reveal RUNX2 in the condylar cartilage of normal mice and of heterozygous RUNX2 knockout mice in early and late growth phases; we also performed radiographic and cephalometric analyses.

RESULTS

We observed that RUNX2 is involved in normal condylar growth in the mouse and probably plays a significant role in osteogenesis and angiogenesis. The RUNX2 also has a biomechanical correlation in relation to cartilage compartmentalization. At the protein level, we noted no differences in the occurrence and distribution of RUNX2 in the condyle, except for a short phase during the 4th and 6th postnatal weeks, so that one allele might suffice for largely normal growth; other biological factors may have compensatory effects. However, we did observe small changes in a few cephalometric parameters concerning the mandibles of heterozygous knockout animals. We discuss potential correlations to our findings by relating them to the most current knowledge about the RUNX2 biology.

Association of the growth hormone receptor gene polymorphisms with mandibular height in a Korean population

Growth hormone receptor gene (GHR) is one of the likely candidates for determining morphological traits, because GH is a key regulator of bone growth. The genetic association of GHR in exon 10 with mandibular ramus height has been found in different populations, Japanese and Chinese. On the other hand, two common isoforms of GHR, one full-length (fl-GHR) and the other lacking the extracellular domain encoded by exon 3 (d3-GHR), are associated with differences in responsiveness to GH. The purpose of this study involving 159 Korean subjects was to study the associations between a GHR polymorphism (d3/fl-GHR) that results in genomic deletion of exon 3 and craniofacial morphology, and to study the associations between GHR genotypes in exon 10 and craniofacial morphology. Moreover, the allelic frequencies in a multi-ethnic population (24 Han Chinese, 24 African-Americans, 24 European-Americans, and 24 Hispanics) in a GHR polymorphism (d3/fl-GHR) were compared in this study. The five craniofacial linear measurements (cranial base length, maxillary length, overall mandibular length, mandibular corpus length, and mandibular ramus height) obtained from lateral cephalograms were examined as craniofacial morphology. We found that the d3/fl-GHR polymorphism had no association for any measurements, and a statistically significant association (P=0.024) between the GHR polymorphisms P561T and C422F in exon 10 and mandibular ramus height. Neither SNPs besides P561T and C422F polymorphisms in exon 10 nor the measurements besides mandibular ramus height have statistically significances. Both derived alleles at P561T and C422F SNPs were highly associated with only one haplotype, haplotype-4 in Korean population. As quantitative haplotype association, the results showed a significant difference in mandibular ramus height between individuals having one haplotype-4 and others without haplotype-4 (P=0.028). Moreover, we found that the d3/fl-GHR polymorphism showed diverse frequency in different population. Regarding GHR genotypes in exon 10, the present study mostly reflected the results obtained for a Japanese population, although our current study does not replicate the correlation between the I526L polymorphism of GHR and mandibular ramus height as was reported in a previous study of Han Chinese. The results of the present study suggest that the GHR exon 10 SNPs, not d3/fl-GHR, contribute to changes in the mandibular ramus height of Koreans.

Dento-craniofacial phenotypes and underlying molecular mechanisms in hypohidrotic ectodermal dysplasia (HED): a review

The hypohidrotic ectodermal dysplasias (HED) belong to a large and heterogeneous nosological group of polymalfomative syndromes characterized by dystrophy or agenesis of ectodermal derivatives. Molecular etiologies of HED consist of mutations of the genes involved in the Ectodysplasin (EDA)-NF-kappaB pathway. Besides the classic ectodermal signs, craniofacial and bone manifestations are associated with the phenotypic spectrum of HED. The dental phenotype of HED consists of various degrees of oligodontia with other dental abnormalities, and these are important in the early diagnosis and identification of persons with HED. Phenotypic dental markers of heterozygous females for EDA gene mutation-moderate oligodontia, conical incisors, and delayed dental eruption-are important for individuals giving reliable genetic counseling. Some dental ageneses observed in HED are also encountered in non-syndromic oligodontia. These clinical similarities may reflect possible interactions between homeobox genes implicated in early steps of odontogenesis and the Ectodysplasin (EDA)-NF-kappaB pathway. Craniofacial dysmorphologies and bone structural anomalies are also associated with the phenotypic spectrum of persons with HED patients. The corresponding molecular mechanisms involve altered interactions between the EDA-NF-kappaB pathway and signaling molecules essential in skeletogenic neural crest cell differentiation, migration, and osteoclastic differentiation. Regarding oral treatment of persons with HED, implant-supported prostheses are used with a relatively high implant survival rate. Recently, groundbreaking experimental approaches with recombinant EDA or transgenesis of EDA-A1 were developed from the perspective of systemic treatment and appear very promising. All these clinical observations and molecular data allow for the specification of the craniofacial phenotypic spectrum in HED and provide a better understanding of the mechanisms involved in the pathogenesis of this syndrome.

Short-faced mice and developmental interactions between the brain and the face

The length of the face represents an important axis of variation in mammals and especially in primates. Mice with mutations that produce variation along this axis present an opportunity to study the developmental factors that may underlie evolutionary change in facial length. The Crf4 mutant, obtained from the C57BL/6J (wt/wt) background by chemical mutagenesis by the Baylor Mouse Mutagenesis Resource, is reported to have a short-faced phenotype. As an initial step towards developing this model, we performed 3D geometric morphometric comparisons of Crf4 mice to C57BL/6J wild-type mice focusing on three stages of face development and morphology--embryonic (GD 9.5-12), neonatal, and adult. Morphometric analysis of adult Crf4 mutants revealed that in addition to a shortened face, these mice exhibit a significant reduction in brain size and basicranial length. These same features also differ at the neonatal stage. During embryonic face formation, only dimensions related to brain growth were smaller, whereas the Crf4 face actually appeared advanced relative to the wild-type at the same somite stage. These results show that aspects of the Crf4 phenotype are evident as early as embryonic face formation. Based on our anatomical findings we hypothesize that the reduction in facial growth in Crf4 mice is a secondary consequence of reduction in the growth of the brain. If correct, the Crf4 mutant will be a useful model for studying the role of epigenetic interactions between the brain and face in the evolutionary developmental biology of the mammalian craniofacial complex as well as human craniofacial dysmorphology.

Hierarchies of Extracellular Matrix and Mineral Organization in Bone of the Craniofacial Complex and Skeleton

Structural hierarchies are common in biologic systems and are particularly evident in biomineralized structures. In the craniofacial complex and skeleton of vertebrates, extracellular matrix and mineral of bone are structurally ordered at many dimensional scales from the macro level to the nano level. Indeed, the nanocomposite texture of bone, with nanocrystals of apatitic mineral embedded within a crosslinked matrix of fibrillar and nonfibrillar proteins, imparts to bone the very mechanical properties and toughness it needs to function in vital organ protection, musculoskeletal movement and mastication. This article focuses on how hierarchies of extracellular matrix protein organization influence bone cell behavior, tissue architecture and mineralization. Additional attention is given to recent work on the molecular determinants of mineral induction in bone, and how the mineralization process is subsequently regulated by inhibitory proteins.