Prenatal craniofacial development: new insights on normal and abnormal mechanisms

Non-progressive mandibular changes in children with Type I and II craniofacial microsomia

OBJECTIVE

To describe the mandibular growth of craniofacial microsomia (CFM) patients during early childhood to adolescence with attention to symmetry.

MATERIALS AND METHODS

Altogether 61 CFM patients were studied at the Cleft Palate and Craniofacial Center, Helsinki University Hospital between 1986 and 2006. In this cohort study, we measured and analysed 293 radiographs (posteroanterior, panoramic and lateral); 165 radiographs of 40 patients met the final inclusion criteria. The vertical height of the ramus in anteroposterior and panoramic radiographs, the length of the mandible in anteroposterior radiographs and the maxillary protrusion and mandibular retrognathia in lateral cephalograms were measured in four different age groups.

RESULTS

A statistical difference existed between the groups in the vertical height of the ramus and in the mandibular length. The vertical height of the ramus measured from the panoramic radiograph grew on both sides, and the ratios remained unchanged. In the sagittal dimension, the maxilla and mandible grew forward, but no significant differences emerged between the groups.

CONCLUSIONS

Results suggest that mild-type CFM is not progressive in nature. During growth, mandibular asymmetry measured in the horizontal, vertical and sagittal planes did not increase.

Characteristics of Factors Influencing the Occurrence of Cleft Lip and/or Palate: A Case Analysis and Literature Review

INTRODUCTION

Cleft lip with or without cleft palate (CL/P) stands as the most common congenital facial anomaly, stemming from multifactorial causes.

OBJECTIVE

Our study aimed to ascertain the prevalence and characteristics of cleft palates, identify associated risk factors to inform prevention and prenatal detection for early intervention, and assess postoperative rehabilitation protocols for cleft palates.

DESIGN

This study employs a retrospective descriptive and clinical approach.

PATIENTS

The study includes 103 children with cleft palates treated at the Department of Head and Neck Surgery Clinic for Children and Young Adults, Department of Clinical Pediatrics, University of Warmia and Mazury.

METHODS

We conducted a thorough evaluation of records, considering variables such as sex, cleft type, maternal occupation, parental education, and family history of clefts. Data analysis was carried out using R software version GPL-3 and ordinal logistic regression analyses.

RESULTS

Notably, children born to mothers who experienced significant stress during pregnancy exhibited a 9.4-fold increase in the odds of having bilateral cleft palates. Conversely, no substantial evidence was found to support the influence of the child's sex, birth order, body mass, maternal exposure to workplace toxins, infections, or drug toxicity on the dependent variable.

CONCLUSIONS

Our findings suggest that children with parents who have a history of clefts and those with less educated mothers are more likely to develop bilateral cleft palates. Additionally, children born to mothers experiencing stress during pregnancy face an increased risk of bilateral cleft palates. It is important to note that there is a paucity of literature on rehabilitation following various cleft palate surgical techniques in children.

De novo variants implicate chromatin modification, transcriptional regulation, and retinoic acid signaling in syndromic craniosynostosis

Craniosynostosis (CS) is the most common congenital cranial anomaly. Several Mendelian forms of syndromic CS are well described, but a genetic etiology remains elusive in a substantial fraction of probands. Analysis of exome sequence data from 526 proband-parent trios with syndromic CS identified a marked excess (observed 98, expected 33, p = 4.83 × 10-20) of damaging de novo variants (DNVs) in genes highly intolerant to loss-of-function variation (probability of LoF intolerance > 0.9). 30 probands harbored damaging DNVs in 21 genes that were not previously implicated in CS but are involved in chromatin modification and remodeling (4.7-fold enrichment, p = 1.1 × 10-11). 17 genes had multiple damaging DNVs, and 13 genes (CDK13, NFIX, ADNP, KMT5B, SON, ARID1B, CASK, CHD7, MED13L, PSMD12, POLR2A, CHD3, and SETBP1) surpassed thresholds for genome-wide significance. A recurrent gain-of-function DNV in the retinoic acid receptor alpha (RARA; c.865G>A [p.Gly289Arg]) was identified in two probands with similar CS phenotypes. CS risk genes overlap with those identified for autism and other neurodevelopmental disorders, are highly expressed in cranial neural crest cells, and converge in networks that regulate chromatin modification, gene transcription, and osteoblast differentiation. Our results identify several CS loci and have major implications for genetic testing and counseling.

Orthognathic Surgery in Goldenhar Syndrome With a Rare Course of the IAN

Although there are multiple variations of accessory foramina described in the literature, to our knowledge there is only 1 report of an isolated mandibular foramen and inferior alveolar neurovascular bundle that courses through the lateral ramus, particularly in those with branchial arch syndromes. Goldenhar syndrome, of the oculo-auriculo-vertebral spectrum, is a rare congenital condition, which most characteristically presents with hemifacial microsomia. Depending on the severity of hemifacial microsomia, there are predictable treatment modalities to correct the consequent facial asymmetry. We report on a patient with Goldenhar syndrome who was found to have a unique course of the inferior alveolar nerve during orthognathic surgery work-up and treatment.

PECULIARITIES OF THE HUMAN MAXILLA MORPHOGENESIS

OBJECTIVE

The aim: To find out the sources of formation and the chronological sequence of the morphogenesis of the maxilla at the early stages of human ontogenesis.

PATIENTS AND METHODS

Materials and methods: 14 series of consecutive histological specimens of human embryos and prefetuses (4,0-66,0 mm of parietal-coccygeal length) aged from 4 to 11 weeks of intrauterine development with the use of a complex of modern morphological methods of investigation (anthropometry, morphometry, microscopy, and 3D computer reconstruction) were studied.

RESULTS

Results: On the basis of a complex of morphological research methods, data were obtained that made it possible to establish the general patterns of development of the human maxilla: separation of the pharyngeal apparatus (4th week), convergence and fusion of the jaw processes (5-8th weeks), formation of tooth buds (7-8th weeks), which allows considering the specified periods as critical in the formation of possible anomalies in the facial part of the skull. At the same time, a tendency of heterochrony of morphological transformations in the maxilla and maxilla was revealed.

CONCLUSION

Conclusions: 1. At the beginning of the 4th week of intrauterine development, 3 pairs of pharyngeal arches are formed. Detachment of the mandibular and maxillary processes of the mandibular pharyngeal arch is planned. 2. During the 7th week of intrauterine development, the maximum convergence of the maxillary processes with the lateral and medial nasals occurs, and in embryos of 20.0 mm PCL grow with the frontal process, forming the maxilla and upper lip. During the 8th week of intrauterine development, the bone base of the jaws is modeled as a result of the increase in the size of osteogenic islands and their fusion, alveolar processes are formed. 3. During the 9-10th weeks of intrauterine development, the primary palate is formed as a result of the fusion of the palatine processes. 4. At the 11th week of intrauterine development, the bone base models both jaws. Due to the processes of histogenesis of the soft tissues of the maxillofacial apparatus, the face acquires anthropomorphic definitive human features.

E-liquids and vanillin flavoring disrupts retinoic acid signaling and causes craniofacial defects in Xenopus embryos

Environmental teratogens such as smoking are known risk factors for developmental disorders such as cleft palate. While smoking rates have declined, a new type of smoking, called vaping is on the rise. Vaping is the use of e-cigarettes to vaporize and inhale an e-liquid containing nicotine and food-like flavors. There is the potential that, like smoking, vaping could also pose a danger to the developing human. Rather than waiting for epidemiological and mammalian studies, we have turned to an aquatic developmental model, Xenopus laevis, to more quickly assess whether e-liquids contain teratogens that could lead to craniofacial malformations. Xenopus, like zebrafish, has the benefit of being a well-established developmental model and has also been effective in predicting whether a chemical could be a teratogen. We have determined that embryonic exposure to dessert flavored e-liquids can cause craniofacial abnormalities, including an orofacial cleft in Xenopus. To better understand the underlying mechanisms contributing to these defects, transcriptomic analysis of the facial tissues of embryos exposed to a representative dessert flavored e-liquid vapor extract was performed. Analysis of differentially expressed genes in these embryos revealed several genes associated with retinoic acid metabolism or the signaling pathway. Consistently, retinoic acid receptor inhibition phenocopied the craniofacial defects as those embryos exposed to the vapor extract of the e-liquid. Such malformations also correlated with a group of common differentially expressed genes, two of which are associated with midface birth defects in humans. Further, e-liquid exposure sensitized embryos to forming craniofacial malformations when they already had depressed retinoic acid signaling. Moreover, 13-cis-retinoic acid treatment could significantly reduce the e-liquid induced malformation in the midface. Such results suggest the possibility of an interaction between retinoic acid signaling and e-liquid exposure. One of the most popular and concentrated flavoring chemicals in dessert flavored e-liquids is vanillin. Xenopus embryos exposed to this chemical closely resembled embryos exposed to dessert-like e-liquids and a retinoic acid receptor antagonist. In summary, we determined that e-liquid chemicals, in particular vanillin, can cause craniofacial defects potentially by dysregulating retinoic acid signaling. This work warrants the evaluation of vanillin and other such flavoring additives in e-liquids on mammalian development.

Using an aquatic model, Xenopus laevis, to uncover the role of chromodomain 1 in craniofacial disorders

The chromodomain family member chromodomain 1 (CHD1) has been shown to have numerous critical molecular functions including transcriptional regulation, splicing, and DNA repair. Complete loss of function of this gene is not compatible with life. On the other hand, missense and copy number variants of CHD1 can result in intellectual disabilities and craniofacial malformations in human patients including cleft palate and Pilarowski-Bjornsson Syndrome. We have used the aquatic developmental model organism Xenopus laevis, to determine a specific role for Chd1 in such cranioafcial disorders. Protein and gene knockdown techniques in Xenopus, including antisense oligos and mosaic Crispr/Cas9-mediated mutagenesis, recapitulated the craniofacial defects observed in humans. Further analysis indicated that embryos deficient in Chd1 had defects in cranial neural crest development and jaw cartilage morphology. Additionally, flow cytometry and immunohistochemistry revealed that decreased Chd1 resulted in increased in apoptosis in the developing head. Together, these experiments demonstrate that Chd1 is critical for fundamental processes and cell survival in craniofacial development. We also presented evidence that Chd1 is regulated by retinoic acid signaling during craniofacial development. Expression levels of chd1 mRNA, specifically in the head, were increased by RAR agonist exposure and decreased upon antagonist treatment. Subphenotypic levels of an RAR antagonist and Chd1 morpholinos synergized to result in orofacial defects. Further, RAR DNA binding sequences (RAREs) were detected in chd1 regulatory regions by bioinformatic analysis. In summary, by combining human genetics and experiments in an aquatic model we now have a better understanding of the role of CHD1 in craniofacial disorders.

Craniofacial malformations and their association with brain development: the importance of a multidisciplinary approach for treatment

The craniofacial complex develops mainly in the first trimester of pregnancy, but its final shaping and the development of the teeth extend into the second and third trimesters. It is intimately connected with the development of the brain because of the crucial role the cranial neural crest cells play and the fact that many signals which control craniofacial development originate in the brain and vice versa. As a result, malformations of one organ may affect the development of the other. Similarly, there are developmental connections between the craniofacial complex and the teeth. Craniofacial anomalies are either isolated, resulting from abnormal development of the first two embryonic pharyngeal arches, or part of multiple malformation syndromes affecting many other organs. They may stem from gene mutations, chromosomal aberrations or from environmental causes induced by teratogens. The craniofacial morphologic changes are generally cosmetic, but they often interfere with important functions such as chewing, swallowing and respiration. In addition, they may cause hearing or visual impairment. In this review we discussed only a small number of craniofacial malformations and barely touched upon related anomalies of dentition. Following a brief description of the craniofacial development, we discussed oral clefts, craniofacial microsomia, teratogens that may interfere with craniofacial development resulting in different malformations, the genetically determined craniosynostoses syndromes and few other relatively common syndromes that, in addition to the craniofacial complex, also affect other organs. The understanding of these malformations is important in dentistry as dentists play an integral role in their diagnosis and multidisciplinary treatment.

Craniofacial Microsomia

Clinicians use different diagnostic terms for patients with underdevelopment of facial features arising from the embryonic first and second pharyngeal arches, including first and second branchial arch syndrome, otomandibular dysostosis, oculoauriculovertebral syndrome, and hemifacial microsomia. Craniofacial microsomia has become the preferred term. Although no diagnostic criteria for craniofacial microsomia exist, most patients have a degree of underdevelopment of the mandible, maxilla, ear, orbit, facial soft tissue, and/or facial nerve. These anomalies can affect feeding, compromise the airway, alter facial movement, disrupt hearing, and alter facial appearance.

The ectodomain of cadherin-11 binds to erbB2 and stimulates Akt phosphorylation to promote cranial neural crest cell migration

During development, a multi-potent group of cells known as the cranial neural crest (CNC) migrate to form craniofacial structures. Proper migration of these cells requires proteolysis of cell adhesion molecules, such as cadherins. In Xenopus laevis, preventing extracellular cleavage of cadherin-11 impairs CNC migration. However, overexpression of the soluble cleavage product (EC1-3) is capable of rescuing this phenotype. The mechanism by which EC1-3 promotes CNC migration has not been investigated until now. Here we show that EC1-3 stimulates phosphorylation of Akt, a target of PI3K, in X.laevis CNC. Through immunoprecipitation experiments, we determined that EC1-3 interacts with all ErbB receptors, PDGFRα, and FGFR1. Of these receptors, only ErbB2 was able to produce an increase in Akt phosphorylation upon treatment with a recombinant EC1-3. This increase was abrogated by mubritinib, an inhibitor of ErbB2. We were able to recapitulate this decrease in Akt phosphorylation in vivo by knocking down ErbB2 in CNC cells. Knockdown of the receptor also significantly reduced CNC migration in vivo. We confirmed the importance of ErbB2 and ErbB receptor signaling in CNC migration using mubritinib and canertinib, respectively. Mubritinib and the PI3K inhibitor LY294002 significantly decreased cell migration while canertinib nearly prevented it altogether. These data show that ErbB2 and Akt are important for CNC migration and implicate other ErbB receptors and Akt-independent signaling pathways. Our findings provide the first example of a functional interaction between the extracellular domain of a type II classical cadherin and growth factor receptors.

Characterizing the skull base in craniofacial microsomia using principal component analysis

The aim of this study was to compare the anatomical differences in the skull base between the affected and non-affected side in patients with craniofacial microsomia (CFM), and to compare the affected and non-affected sides with measurements from a normal population. Three-dimensional computed tomography scans of 13 patients with unilateral CFM and 19 normal patients (age range 7-12 years) were marked manually with reliable homologous landmarks. Principal component analysis (PCA), as part of a point distribution model (PDM), was used to analyse the variability within the normal and preoperative CFM patient groups. Through analysis of the differences in the principal components calculated for the two groups, a model was created to describe the differences between CFM patients and normal age-matched controls. The PDMs were also used to describe the shape changes in the skull base between the cohorts and validated this model. Using thin-plate splines as a means of interpolation, videos were created to visualize the transformation from CFM skull to normal skull, and to display the variability in shape changes within the groups themselves. In CFM cases, the skull base showed significant asymmetry. Anatomical areas around the glenoid fossa and mastoid process showed the most asymmetry and restriction of growth, suggesting a pathology involving the first and second pharyngeal arches.

Three-dimensional Planning and Reconstruction of the Mandible in Children with Craniofacial Microsomia Type III Using Costochondral Grafts

Background:

In craniofacial microsomia (CFM) Type III patients, autogenous costochondral grafts (CCG) are conventionally used for the reconstruction of the ramus and condyle. The aim of this study was to describe the use of CCG in children with CFM in terms of outcomes, growth patterns, and complications.

Materials and Methods:

This is a retrospective study of nine, aged 4–12 years, patients with CFM Type III, who underwent reconstruction of the mandibular ramus condyle unit by CCG. Seven patients had right-sided CFM and two had left-sided CFM. The rationale for this choice was to utilize the potential growth of the CCG, providing length to the ramus, and the joint by acting as a growth center; to control the repositioning of the chin center; and to improve child compliance by undergoing only one operation. The surgical treatment plan was determined preoperatively, based on measurements of mandibular vertical and horizontal deficiency and analysis of the mandibular posterior and anterior angulation. The mandibular planes and axis were defined by a three-dimensional simulation software program to perform a “mock surgery”, by creating a prototype model. Clinical follow-up included measurements of the maximal opening, observation of the facial symmetry, and recording of complications, such as reankylosis.

Results:

There were no serious postoperative complications, infections, or graft rejections. Successful postoperative occlusal cants were noted and measured in five patients and acceptable results were obtained in three patients. In one case, the CCG underwent distraction osteogenesis to improve the facial symmetry. In one patient, the graft continued to grow and the chin started to deviate into the opposite side. Measuring and calculating the ratio of the ramus height on the panoramic X-ray revealed a good relation between the healthy contralateral and the reconstructed ipsilateral ramus. Postoperative mean mouth opening was 34.3 mm, with minimal midline deviation of 2.6 mm in occlusion. Mean follow-up was 51.7 months. The mean postoperative occlusal cant analysis for eight patients was 3.66°.

Conclusion:

CCG is useful in treating CFM Type III. The growth potential of the CCG makes it the ideal choice for children. The advantages of this graft are its biological compatibility, workability, functional adaptability, and minimal additional detriment to the patient. The use of a stereolithographic model preoperatively improved intraoperative precision by clearly displaying detailed anatomy of the patient undergoing craniofacial surgery. The surgeon can plan the length of the CCG before surgery and use the printed template while harvesting without waiting for the exact measurements to be provided by the facial surgical team.

Effects of In Utero Thyroxine Exposure on Murine Cranial Suture Growth

Large scale surveillance studies, case studies, as well as cohort studies have identified the influence of thyroid hormones on calvarial growth and development. Surveillance data suggests maternal thyroid disorders (hyperthyroidism, hypothyroidism with pharmacological replacement, and Maternal Graves Disease) are linked to as much as a 2.5 fold increased risk for craniosynostosis. Craniosynostosis is the premature fusion of one or more calvarial growth sites (sutures) prior to the completion of brain expansion. Thyroid hormones maintain proper bone mineral densities by interacting with growth hormone and aiding in the regulation of insulin like growth factors (IGFs). Disruption of this hormonal control of bone physiology may lead to altered bone dynamics thereby increasing the risk for craniosynostosis. In order to elucidate the effect of exogenous thyroxine exposure on cranial suture growth and morphology, wild type C57BL6 mouse litters were exposed to thyroxine in utero (control = no treatment; low ~167 ng per day; high ~667 ng per day). Thyroxine exposed mice demonstrated craniofacial dysmorphology (brachycranic). High dose exposed mice showed diminished area of the coronal and widening of the sagittal sutures indicative of premature fusion and compensatory growth. Presence of thyroid receptors was confirmed for the murine cranial suture and markers of proliferation and osteogenesis were increased in sutures from exposed mice. Increased Htra1 and Igf1 gene expression were found in sutures from high dose exposed individuals. Pathways related to the HTRA1/IGF axis, specifically Akt and Wnt, demonstrated evidence of increased activity. Overall our data suggest that maternal exogenous thyroxine exposure can drive calvarial growth alterations and altered suture morphology.

Review of the Genetic Basis of Jaw Malformations

Genetic etiologies for congenital anomalies of the facial skeleton, namely, the maxilla and mandible, are important to understand and recognize. Malocclusions occur when there exist any significant deviation from what is considered a normal relationship between the upper jaw (maxilla) and the lower jaw (mandible). They may be the result of anomalies of the teeth alone, the bones alone, or both. A number of genes play a role in the facial skeletal development and are regulated by a host of additional regulatory molecules. As such, numerous craniofacial syndromes specifically affect the development of the jaws. The following review discusses several genetic anomalies that specifically affect the bones of the craniofacial skeleton and lead to malocclusion.

Genetic Advances in the Understanding of Microtia

Microtia is a genetic condition affecting the external ears and presents clinically along a wide spectrum: minimally affected ears are small with minor shape abnormalities; extremely affected ears lack all identifiable structures, with the most extreme being absence of the entire external ear. Multiple genetic causes have been linked to microtia in both animal models and humans, which are improving our understanding of the condition and may lead to the identification of a unified cause for the condition. Microtia is also a prominent feature of several genetic syndromes, the study of which has provided further insight into the possible causes and genetic mechanisms of the condition. This article reviews our current understanding of microtia including epidemiological characteristics, classification systems, environmental and genetic causative factors leading to microtia. Despite our increased understanding of the genetics of microtia, we do not have a means of preventing the condition and still rely on complex staged, surgical correction.

Effects of thyroxine exposure on the Twist 1 +/- phenotype: A test of gene-environment interaction modeling for craniosynostosis

BACKGROUND

Craniosynostosis, the premature fusion of one or more of the cranial sutures, is estimated to occur in 1:1800 to 2500 births. Genetic murine models of craniosynostosis exist, but often imperfectly model human patients. Case, cohort, and surveillance studies have identified excess thyroid hormone as an agent that can either cause or exacerbate human cases of craniosynostosis.

METHODS

Here we investigate the influence of in utero and in vitro exogenous thyroid hormone exposure on a murine model of craniosynostosis, Twist 1 +/-.

RESULTS

By 15 days post-natal, there was evidence of coronal suture fusion in the Twist 1 +/- model, regardless of exposure. With the exception of craniofacial width, there were no significant effects of exposure; however, the Twist 1 +/- phenotype was significantly different from the wild-type control. Twist 1 +/- cranial suture cells did not respond to thyroxine treatment as measured by proliferation, osteogenic differentiation, and gene expression of osteogenic markers. However, treatment of these cells did result in modulation of thyroid associated gene expression.

CONCLUSION

Our findings suggest the phenotypic effects of the genetic mutation largely outweighed the effects of thyroxine exposure in the Twist 1 +/- model. These results highlight difficultly in experimentally modeling gene-environment interactions for craniosynostotic phenotypes. Birth Defects Research (Part A) 106:803-813, 2016. © 2016 Wiley Periodicals, Inc.

Molecular mechanisms of midfacial developmental defects

The morphogenesis of midfacial processes requires the coordination of a variety of cellular functions of both mesenchymal and epithelial cells to develop complex structures. Any failure or delay in midfacial development as well as any abnormal fusion of the medial and lateral nasal and maxillary prominences will result in developmental defects in the midface with a varying degree of severity, including cleft, hypoplasia, and midline expansion. Despite the advances in human genome sequencing technology, the causes of nearly 70% of all birth defects, which include midfacial development defects, remain unknown. Recent studies in animal models have highlighted the importance of specific signaling cascades and genetic-environmental interactions in the development of the midfacial region. This review will summarize the current understanding of the morphogenetic processes and molecular mechanisms underlying midfacial birth defects based on mouse models with midfacial developmental abnormalities.

Microtia in the Netherlands: clinical characteristics and associated anomalies

BACKGROUND

In Europe there have been few detailed reports on the clinical characteristics of microtia patient populations. The objective of the present study is to contribute to our insight of microtia in Europe by examining the Dutch microtia population treated in the University Medical Center Utrecht (UMCU) with regards to its clinical features and associated anomalies. In addition, an overview of the literature is provided for thorough comparison.

METHODS

A retrospective chart review was performed for all microtia patients referred to the UMCU for reconstructive surgery of the auricle over the period 1990-2012. Previous studies were identified by a systematic search of the electronic literature databases PubMed and Embase. In a subsequent meta-analysis the results from the literature review were pooled by geographical region to facilitate comparison.

RESULTS

A total of 204 microtia patients were referred for reconstructive surgery during 1990-2012. This group was characterized by a male predominance of 60.8%. Unilateral disease was observed in 91.7% of patients, affecting the right auricle in 66.3%. In unilateral patients lobule type microtia was seen in 59.9%, (small) concha type in 34.4% and anotia in 5.7%. The more frequent anomalies associated with microtia were atresia of the acoustic meatus (76.0%), preauricular skin tags (30.5%), hemifacial microsomia (27.5%), facial nerve paralysis (8.3%) and congenital heart disease (2.5%). Familial occurrence of microtia was reported for 2.0% of UMCU patients and for 10.0% of patients in the literature.

CONCLUSION

The clinical characteristics of microtia in the Netherlands correspond to those reported for other patient populations in the literature. Most congenital anomalies associated with microtia in Dutch patients belong to the Oculo-Auriculo-Vertebral Spectrum. The considerable degree of familial microtia observed in the literature points to a substantial genetic component in the etiology of the condition.

Oral epithelial stem cells in tissue maintenance and disease: the first steps in a long journey

The identification and characterization of stem cells is a major focus of developmental biology and regenerative medicine. The advent of genetic inducible fate mapping techniques has made it possible to precisely label specific cell populations and to follow their progeny over time. When combined with advanced mathematical and statistical methods, stem cell division dynamics can be studied in new and exciting ways. Despite advances in a number of tissues, relatively little attention has been paid to stem cells in the oral epithelium. This review will focus on current knowledge about adult oral epithelial stem cells, paradigms in other epithelial stem cell systems that could facilitate new discoveries in this area and the potential roles of epithelial stem cells in oral disease.

Tbx1 regulates oral epithelial adhesion and palatal development

Cleft palate, the most frequent congenital craniofacial birth defect, is a multifactorial condition induced by the interaction of genetic and environmental factors. In addition to complete cleft palate, a large number of human cases involve soft palate cleft and submucosal cleft palate. However, the etiology of these forms of cleft palate has not been well understood. T-box transcriptional factor (Tbx) family of transcriptional factors has distinct roles in a wide range of embryonic differentiation or response pathways. Here, we show that genetic disruption of Tbx1, a major candidate gene for the human congenital disorder 22q11.2 deletion syndrome (Velo-cardio-facial/DiGeorge syndrome), led to abnormal epithelial adhesion between the palate and mandible in mouse, resulting in various forms of cleft palate similar to human conditions. We found that hyperproliferative epithelium failed to undergo complete differentiation in Tbx1-null mice (Tbx1(-/-)). Inactivation of Tbx1 specifically in the keratinocyte lineage (Tbx1(KCKO)) resulted in an incomplete cleft palate confined to the anterior region of the palate. Interestingly, Tbx1 overexpression resulted in decreased cell growth and promoted cell-cycle arrest in MCF7 epithelial cells. These findings suggest that Tbx1 regulates the balance between proliferation and differentiation of keratinocytes and is essential for palatal fusion and oral mucosal differentiation. The impaired adhesion separation of the oral epithelium together with compromised palatal mesenchymal growth is an underlying cause for various forms of cleft palate phenotypes in Tbx1(-/-) mice. Our present study reveals new pathogenesis of incomplete and submucous cleft palate during mammalian palatogenesis.

The nasopharynx in infants with cleft lip and palate

OBJECTIVE

The purpose of this study was to use three-dimensional computed tomography data and computer imaging technology to assess the skeletal components of the naso-pharyngeal area in patients with cleft lip and palate and to quantify anatomical variations.

METHODS

CT scans were obtained from 29 patients of Malay origin with cleft lip and palate aged between 0 and 12 months and 12 noncleft patients in the same age group, using a GE Lightspeed Plus Scanner housed in Hospital Universiti Sains Malaysia. Measurements were obtained using the 'Persona' three-dimensional software package, developed at Australian Craniofacial Unit, Adelaide.

RESULTS

The results of the present study show that there is an increased nasopharyngeal space in cleft lip and palate that may lead to compression of the nasopharyngeal structures, including the Eustachian tube. Alterations of the medial pterygoid plate and the hamulus may lead to an alteration in the origin and orientation of the tensor veli palatini muscle leading to alteration in its function.

CONCLUSIONS

These anatomical variations may compromise the dilatory mechanism of the Eustachian tube, thus leading to recurrent middle ear infections in cleft children and subsequent loss of hearing.

miR-200b regulates cell migration via Zeb family during mouse palate development

Palate development requires coordinating proper cellular and molecular events in palatogenesis, including the epithelial-mesenchymal transition (EMT), apoptosis, cell proliferation, and cell migration. Zeb1 and Zeb2 regulate epithelial cadherin (E-cadherin) and EMT during organogenesis. While microRNA 200b (miR-200b) is known to be a negative regulator of Zeb1 and Zeb2 in cancer progression, its regulatory effects on Zeb1 and Zeb2 in palatogenesis have not yet been clarified. The aim of this study is to investigate the relationship between the regulators of palatal development, specifically, miR-200b and the Zeb family. Expression of both Zeb1 and Zeb2 was detected in the mesenchyme of the mouse palate, while miR-200b was expressed in the medial edge epithelium. After contact with the palatal shelves, miR-200b was expressed in the palatal epithelial lining and epithelial island around the fusion region but not in the palatal mesenchyme. The function of miR-200b was examined by overexpression via a lentiviral vector in the palatal shelves. Ectopic expression of miR-200b resulted in suppression of the Zeb family, upregulation of E-cadherin, and changes in cell migration and palatal fusion. These results suggest that miR-200b plays crucial roles in cell migration and palatal fusion by regulating Zeb1 and Zeb2 as a noncoding RNA during palate development.

Microtia: epidemiology and genetics

Microtia is a congenital anomaly of the ear that ranges in severity from mild structural abnormalities to complete absence of the ear, and can occur as an isolated birth defect or as part of a spectrum of anomalies or a syndrome. Microtia is often associated with hearing loss and patients typically require treatment for hearing impairment and surgical ear reconstruction. The reported prevalence varies among regions, from 0.83 to 17.4 per 10,000 births, and the prevalence is considered to be higher in Hispanics, Asians, Native Americans, and Andeans. The etiology of microtia and the cause of this wide variability in prevalence are poorly understood. Strong evidence supports the role of environmental and genetic causes for microtia. Although some studies have identified candidate genetic variants for microtia, no causal genetic mutation has been confirmed. The application of novel strategies in developmental biology and genetics has facilitated elucidation of mechanisms controlling craniofacial development. In this paper we review current knowledge of the epidemiology and genetics of microtia, including potential candidate genes supported by evidence from human syndromes and animal models. We also discuss the possible etiopathogenesis in light of the hypotheses formulated to date: Neural crest cells disturbance, vascular disruption, and altitude.

MiR-200b is involved in Tgf-β signaling to regulate mammalian palate development

Various cellular and molecular events are involved in palatogenesis, including apoptosis, epithelial-mesenchymal transition (EMT), cell proliferation, and cell migration. Smad2 and Snail, which are well-known key mediators of the transforming growth factor beta (Tgf-β) pathway, play a crucial role in the regulation of palate development. Regulatory effects of microRNA 200b (miR-200b) on Smad2 and Snail in palatogenesis have not yet been elucidated. The aim of this study is to determine the relationship between palate development regulators miR-200b and Tgf-β-mediated genes. Expression of miR-200b, E-cadherin, Smad2, and Snail was detected in the mesenchyme of the mouse palate, while miR-200b was expressed in the medial edge epithelium (MEE) and palatal mesenchyme. After the contact of palatal shelves, miR-200b was no longer expressed in the mesenchyme around the fusion region. The binding activity of miR-200b to both Smad2 and Snail was examined using a luciferase assay. MiR-200b directly targeted Smad2 and Snail at both cellular and molecular levels. The function of miR-200b was determined by overexpression via a lentiviral vector in the palatal shelves. Ectopic expression of miR-200b resulted in suppression of these Tgf-β-mediated regulators and changes of apoptosis and cell proliferation in the palatal fusion region. These results suggest that miR-200b plays a crucial role in regulating the Smad2, Snail, and in apoptosis during palatogenesis by acting as a direct non-coding, influencing factor. Furthermore, the molecular interactions between miR-200b and Tgf-β signaling are important for proper palatogenesis and especially for palate fusion. Elucidating the mechanism of palatogenesis may aid the design of effective gene-based therapies for the treatment of congenital cleft palate.

Developmental patterns of Ki-67, bcl-2 and caspase-3 proteins expression in the human upper jaw

The distribution of the Ki-67, bcl-2 and caspase-3 proteins was immunohistochemically analyzed in the developing human upper jaw (5th-10th gestational weeks). During this period, proliferative activity gradually decreased from higher levels at the earliest stages (50-52%) to lower levels, both in the jaw ectomesenchyme and in the epithelium. The highest expression of bcl-2 protein was found in the epithelium and ectomesenchyme of areas displaying lower rates of cell proliferation. High levels of caspase-3 protein were detected during the earliest stages of jaw development, indicating an important role for apoptosis in morphogenesis of early derivatives of the maxillary prominences. The number of Ki-67, bcl-2 and caspase-3 positive cells changed in a temporally and spatially restricted manner, coincidently with upper jaw differentiation. While apoptosis might control cell number, bcl-2 could act in suppression of apoptosis and enhancement of cell differentiation. A fine balance between cell proliferation (Ki-67), death (caspase-3) and cell survival (bcl-2) characterized early human upper jaw development. A rise in the number of apoptotic cells always temporally coincided with the decrease in number of surviving bcl-2 positive cells within the palatal region. Therefore, the upper jaw development seems to be controlled by the precisely defined expression of genes for proliferation, apoptosis and cell survival.

Prevention of Retinoic Acid-Induced Early Craniofacial Abnormalities by Vitamin B12 in Mice

Objective

The purpose of the present study was to identify the potential effect of prenatal vitamin B12 administration on retinoic acid (RA)-induced early craniofacial abnormalities in mice and to investigate the possible mechanisms by which vitamin B12 reduces malformations.

Design

In our study, whole embryo culture was used to explore the effect of vitamin B12 on mouse embryos during the critical period of organogenesis. All embryos were exposed to 0.4 μM RA and different concentrations of vitamin B12 and scored for their growth in the branchial region at the end of a 48-hour culture period. The endothelin-1 (ET-1)/dHAND protein expression levels in the first branchial arch were investigated using an immunohistochemical method.

Results

In the whole embryo culture, 100 and 10 μM vitamin B12 dose-dependently prevented branchial region malformations and decreased craniofacial defects by 90.5% and 77.3%, respectively. ET-1 and dHAND protein levels were significantly increased in vitamin B12-supplemented embryos compared to the RA-exposed group in embryonic branchial region.

Conclusions

These results suggest that vitamin B12 may prevent RA-induced craniofacial abnormalities via prevention of an RA-induced decrease of ET-1 and dHAND protein levels in the branchial region during the organogenic period. This study may shed new light on preventing craniofacial abnormalities.

Genome-wide scanning reveals complex etiology of oculo-auriculo-vertebral spectrum

Oculo-auriculo-vertebral spectrum (OAVS) is a common developmental disorder involving first and second pharyngeal arches. Although some family cases and such patients showing chromosomal aberrations suggest that OAVS have a genetic basis, no consistent genetic defects have been recorded at present time. Thus, we conducted genetic studies of a three-generation family with five OAVS patients to identify a causative variant for OAVS. Cytogenetic studies revealed those family members had a normal karyotype and no causative mutations were founded in SALL1 and TCOF1, which known to be responsible for two other syndromes that have clinical overlapping with OAVS. Genotyping with commercially available BeadChips was performed on 13 individuals in the same family, showing no significant difference between the affected and normal members in terms of copy number variations (CNVs) in either number or size and no definitive causative CNV. A total of 8,224 informative autosomal SNPs that are evenly distributed throughout the genome were selected for both parametric and non-parametric linkage analysis. Significant negative LOD scores were obtained for the reported OAVS locus, providing further evidence for genetic heterogeneity of this complex disorder. The highest LOD score of 1.60 was noted on chromosome 15q26.2-q26.3 showing a potential linkage to this locus. The variable phenotypes of the affected members and the failure to identify a causative variant indicate that a complex etiology may be present even in a consanguineous family, which makes it more challenging to ascertain the cause of OAVS in further analysis.

Syndromes of the first and second pharyngeal arches: A review

Our aim in this review is to discuss currently known mechanisms associated with three important syndromes of the first and second pharyngeal arches: Treacher Collins syndrome (TCS), Oculo-auriculo-vertebral syndrome (AOVS) and Auriculo-Condylar syndrome (ACS) or question mark ear syndrome. TCS and ACS are autosomal dominant diseases, with nearly complete penetrance and wide spectrum of clinical variability. The phenotype of the latter has several overlapping features with OAVS, but OAVS may exist in both sporadic and autosomal dominant forms. Mutations in the TCOF1 gene are predicted to cause premature termination codons, leading to haploinsuficiency of the protein treacle and causing TCS. Low amount of treacle leads ultimately to a reduction in the number of cranial neural crest cells migrating to the first and second pharyngeal arches. Other than TCS, the genes associated with ACS and OAVS are still unknown. The first locus for ACS was mapped by our group to 1p21-23 but there is genetic heretogeneity. Genetic heterogeneity is also present in OAVS. Based on the molecular analysis of balanced translocation in an OAVS patient, it has been suggested that abnormal expression of BAPX1 possibly due to epigenetic disregulation might be involved with the etiology of OAVS. Involvement of environmental events has also been linked to the causation of OAVS. Identification of factors leading to these disorders are important for a comprehensive delineation of the molecular pathways underlying the craniofacial development from the first and the second pharyngeal arches, for genetic counseling and to open alternative strategies for patient treatment.

Abnormal mandibular growth and the condylar cartilage

Deviations in the growth of the mandibular condyle can affect both the functional occlusion and the aesthetic appearance of the face. The reasons for these growth deviations are numerous and often entail complex sequences of malfunction at the cellular level. The aim of this review is to summarize recent progress in the understanding of pathological alterations occurring during childhood and adolescence that affect the temporomandibular joint (TMJ) and, hence, result in disorders of mandibular growth. Pathological conditions taken into account are subdivided into (1) congenital malformations with associated growth disorders, (2) primary growth disorders, and (3) acquired diseases or trauma with associated growth disorders. Among the congenital malformations, hemifacial microsomia (HFM) appears to be the principal syndrome entailing severe growth disturbances, whereas growth abnormalities occurring in conjunction with other craniofacial dysplasias seem far less prominent than could be anticipated based on their often disfiguring nature. Hemimandibular hyperplasia and elongation undoubtedly constitute the most obscure conditions that are associated with prominent, often unilateral, abnormalities of condylar, and mandibular growth. Finally, disturbances of mandibular growth as a result of juvenile idiopathic arthritis (JIA) and condylar fractures seem to be direct consequences of inflammatory and/or mechanical damage to the condylar cartilage.

Prenatal exposure to drugs: effects on brain development and implications for policy and education

The effects of prenatal exposure to drugs on brain development are complex and are modulated by the timing, dose and route of drug exposure. It is difficult to assess these effects in clinical cohorts as these are beset with problems such as multiple exposures and difficulties in documenting use patterns. This can lead to misinterpretation of research findings by the general public, the media and policy makers, who may mistakenly assume that the legal status of a drug correlates with its biological impact on fetal brain development and long-term clinical outcomes. It is important to close the gap between what science tells us about the impact of prenatal drug exposure on the fetus and the mother and what we do programmatically with regard to at-risk populations.

Management of facial asymmetry

Asymmetries of the craniofacial region encompass a multitude of diverse and potentially complex abnormalities that may be the result of numerous causes. The expression and degree of asymmetry for a given condition, although a highly variable process, is the ultimate determinant of the nature of its treatment. This article highlights some of the key features and treatment strategies for various common facial asymmetries.

Abnormal maxillary trapezoid pattern in human fetal cleft lip and palate

OBJECTIVE

To elucidate abnormal growth patterns of human fetal maxillae with cleft lip and palate (CLP).

SUBJECT

A total of 71 fetal maxillae with CLP were obtained from aborted human fetuses.

METHOD

Dimensions of the maxillary trapezoid (MT), formed by the maxillary primary growth centers (MxPGC), were taken from radiographic images. The CLP dimensions were compared with maxillary trapezoid dimensions of normal fetuses from a previous study (Lee et al., 1992).

MAIN OUTCOME MEASURES

Cleft lip subjects without a cleft palate, unilateral cleft lip-alveolar cleft or cleft palate (UCL+A/UCLP), and bilateral cleft lip-alveolar cleft or cleft palate (BCL+A/BCLP) displayed abnormal MT patterns. MT abnormalities were most marked in the BCL+A/BCLP cohort.

RESULTS

The MT growth of prenatal CLP maxillae was severely arrested, resulting in abnormal MT shape on palatal radiograms. BCL+A/BCLP subjects had a more protruded nasal septum than subjects with other types of CLPs, while UCL+A/UCLP subjects showed severe deviation of the protruded nasal septum toward the noncleft side. Cleft lip-only subjects also exhibited abnormal MT growth.

CONCLUSION

MT is primarily involved in CLPs, so that the MT shape could be utilized as a sensitive indicator for the analysis of maxillary malformation in different types of CLPs.

X-chromosome inactivation patterns in monozygotic twins and sib pairs discordant for nonsyndromic cleft lip and/or palate

Nonsyndromic clefts of the lip and/or palate are common birth defects with a strong genetic component. Based on unequal gender ratios for clefting phenotypes, evidence for linkage to the X chromosome and the occurrence of several X-linked clefting syndromes, we investigated the role of skewed X chromosome inactivation (XCI) in orofacial clefts. Our samples consisted of female monozygotic (MZ) twins (n = 8) and sister pairs (n = 152) discordant for nonsyndromic clefting. We measured the XCI pattern in peripheral blood lymphocyte DNA using a methylation based androgen receptor gene assay. Skewing of XCI was defined as the deviation in inactivation pattern from a 50:50 ratio. Our analysis revealed no significant difference in the degree of skewing between twin pairs (P = 0.3). However, borderline significant differences were observed in the sister pairs (P = 0.02), with the cleft lip with cleft palate group showing the most significant result (P = 0.01). We did not find evidence for involvement of skewed XCI in the discordance for clefting in our sample of female MZ twins. However, results from the paired sister study suggest the potential contribution of skewed XCI to orofacial clefting, particularly cleft lip and palate.

The etiopathogenesis of cleft lip and cleft palate: usefulness and caveats of mouse models

Cleft lip and cleft palate are frequent human congenital malformations with a complex multifactorial etiology. These orofacial clefts can occur as part of a syndrome involving multiple organs or as isolated clefts without other detectable defects. Both forms of clefting constitute a heavy burden to the affected individuals and their next of kin. Human and mouse facial traits are utterly dissimilar. However, embryonic development of the lip and palate are strikingly similar in both species, making the mouse a model of choice to study their normal and abnormal development. Human epidemiological and genetic studies are clearly important for understanding the etiology of lip and palate clefting. However, our current knowledge about the etiopathogenesis of these malformations has mainly been gathered throughout the years from mouse models, including those with mutagen-, teratogen- and targeted mutation-induced clefts as well as from mice with spontaneous clefts. This review provides a comprehensive description of the numerous mouse models for cleft lip and/or cleft palate. Despite a few weak points, these models have revealed a high order of molecular complexity as well as the stringent spatiotemporal regulations and interactions between key factors which govern the development of these orofacial structures.

Development of the upper lip: morphogenetic and molecular mechanisms

The vertebrate upper lip forms from initially freely projecting maxillary, medial nasal, and lateral nasal prominences at the rostral and lateral boundaries of the primitive oral cavity. These facial prominences arise during early embryogenesis from ventrally migrating neural crest cells in combination with the head ectoderm and mesoderm and undergo directed growth and expansion around the nasal pits to actively fuse with each other. Initial fusion is between lateral and medial nasal processes and is followed by fusion between maxillary and medial nasal processes. Fusion between these prominences involves active epithelial filopodial and adhering interactions as well as programmed cell death. Slight defects in growth and patterning of the facial mesenchyme or epithelial fusion result in cleft lip with or without cleft palate, the most common and disfiguring craniofacial birth defect. Recent studies of craniofacial development in animal models have identified components of several major signaling pathways, including Bmp, Fgf, Shh, and Wnt signaling, that are critical for proper midfacial morphogenesis and/or lip fusion. There is also accumulating evidence that these signaling pathways cross-regulate genetically as well as crosstalk intracellularly to control cell proliferation and tissue patterning. This review will summarize the current understanding of the basic morphogenetic processes and molecular mechanisms underlying upper lip development and discuss the complex interactions of the various signaling pathways and challenges for understanding cleft lip pathogenesis.

Epithelial-mesenchymal transformation during craniofacial development

Epithelial to mesenchymal phenotype transition is a common phenomenon during embryonic development, wound healing, and tumor metastasis. This transition involves cellular changes in cytoskeleton architecture and protein expression. Specifically, this highly regulated biological event plays several important roles during craniofacial development. This review focuses on the regulation of epithelial-mesenchymal transformation (EMT) during neural crest cell migration, and fusion of the secondary palate and the upper lip.

Alteration of the sialylation pattern of the murine tooth germ after ethanol exposure

BACKGROUND

Ethanol consumption during pregnancy leads to changes in murine dental morphogenesis, dental size, cellular differentiation, enamel mineralization, and delayed eruption. It has been proposed that glycoproteins play a role during embryonic dental development that may determine the dental morphological pattern and extracellular matrix secretion. O-glycosylation and sialylation appear to actively participate in the differentiation and maturation processes. Because glycosylation may be affected by teratogens that can alter the maturation of several organisms, in this work we describe the main modifications of the sialylation pattern in prenatal day (PD) 18.5 murine tooth germs exposed to ethanol.

METHODS

Pregnant female mice were divided into groups that were given 15% or 20% ethanol solutions, or water as a control. The histochemistry of tooth germs from PD 18.5 fetuses was revealed with lectins specific for sialic acid (Neu5Ac), such as Sambucus nigra (SNA), Maackia amurensis (MAA), and Machrobrachium rosenbergii (MRL), and for sialylated-O-glycosidically linked glycans, such as Amaranthus leucocarpus (ALL).

RESULTS

The basement membrane, preameloblasts, inner-enamel epithelium, preodontoblasts, and subodontoblastic cells of the test groups showed changes in labeling according to the 4 lectins used. Intranuclear staining was observed with SNA (specific for Neu5Acalpha2,6Gal/GalNAc) in the control group, but this was reduced in the test groups. The nuclei of dental papillary cells under the experimental conditions were stained with MAA (Neu5Acalpha2,3Gal).

CONCLUSIONS

Dental development involves different types of sialylated O-glycosidically linked glycans that are likely to regulate cell-to-cell and cell-to-matrix interactions. Our results suggest that ethanol consumption during pregnancy alters the sialylation pattern during murine dental morphogenesis.