Mandible and Tongue Development

Macrophage is crucial for tongue development by regulating myogenesis and vascularization

BACKGROUND

Abnormal tongue development is a craniofacial deformity that affects dental-maxillofacial esthetics and function. Recent evidence has identified macrophages as multi-functional immune cells crucial for heart and brain development. However, it is still unknown whether macrophages affect tongue development. Therefore, this study aims to assess the distribution, phenotype, and roles of macrophages in the developing tongue.

METHODS

In this study, immunohistochemical (IHC) and multiplex immunofluorescence (mIF) staining were conducted on C57BL/6 mice at embryonic day (E) 13.5, E14.5, E16.5, and E18.5 to analyze the distribution and phenotype of macrophages. Hematoxylin-Eosin (HE), IHC, IF, and mIF staining were also performed on embryonic CX3 CR1-CreERT2; Rosa-DTA conditional macrophage-depleted mice to investigate the effects on fetal tongue development and elucidate mechanisms from myogenesis, vascularization, and cell apoptosis. Statistical significance between the two groups was determined using unpaired two-tailed Student's t-tests. For comparisons involving three or more groups, one-way analysis of variance (ANOVA) followed by Tukey's multiple comparison tests was utilized. A significance level of P < 0.05 was set for statistical significance.

RESULTS

Macrophages were present in the developing tongue from E13.5 to E18.5, with a majority being of the M2 phenotype. Depletion of macrophages resulted in abnormal tongue morphology, decreased tongue height, width, and size, as well as reduced and disorganized muscle fibers. Depletion of macrophages also increased apoptosis. Vascular morphogenesis was impacted, with reductions in the luminal and vascular wall cross-sectional areas of the lingual artery. Vascular endothelial cells were reduced and disorganized with decreased expression of VEGFA and TGF-β1. Moreover, macrophages were located near vascular endothelial cells and secreted pro-angiogenic factors, suggesting their involvement in promoting vascularization.

CONCLUSIONS

Our findings indicate that macrophages play crucial roles in fetal tongue development by affecting myogenesis, cell apoptosis, and vascular growth.

Embryonic exposure to Smoothened Agonist disrupts tongue development in mice

The tongue is an important muscular organ for chewing and speech, and its development is regulated by multiple molecular signaling pathways, such as the hedgehog and TGF pathways. These pathways are particularly crucial in muscle patterning, which determines the structural and functional integrity of the tongue. Proper hedgehog signaling is essential for craniofacial tissue development, influencing muscle arrangement and differentiation critical for normal tongue morphology. In this study, we administered the Smoothened Agonist (SAG) 25 mg/kg to pregnant mice via intraperitoneal injection at E10.5 to further investigate the regulatory role of overexpressed hedgehog signaling in the early developmental process of the tongue. The intraperitoneal injection of SAG at E10.5 resulted in reduced tongue height and abnormal muscle development. Consequently, these alterations led to a midline cleft. Detection of cell proliferation using PHH3 and Ki67 showed that cell proliferation was significantly inhibited in the experimental group, while apoptosis showed no significant difference compared to the control group. At E11.5, the expression levels of downstream markers of hedgehog signaling, including Gli1, Ptch1, Foxf1, and Foxf2, were significantly elevated in the experimental group compared to the control group, whereas TGF-β2 mRNA expression was significantly downregulated(P < 0.05). Thus, overexpression of hedgehog signaling, induced by SAG, disrupts normal cellular processes by inhibiting proliferation and downregulating TGF-β2, ultimately leading to cleft tongue malformations.

A Comprehensive Approach to Robin Sequence

Robin sequence is a congenital condition characterized by micrognathia, glossoptosis, and airway obstruction with or without cleft palate. The condition is best managed by a multidisciplinary team proficient in treating the complex pediatric airway, including pediatricians, speech and feeding specialists, and surgeons. Conservative treatment includes prone positioning, nasopharyngeal airways, supplemental oxygen, and feeding support to maintain a patent airway and promote infant growth. For infants requiring further intervention, the tongue may be repositioned anteriorly through surgical tongue-lip adhesion or nonsurgical techniques including the orthodontic airway plate. Mandibular distraction osteogenesis is used in severe cases with the goal to avoid tracheostomy.

An atlas of early human mandibular endochondral and osteogenic paracrine signaling regions of Meckel's cartilage

The mandible, also known as the lower jaw, is the only bone in the skull that can move and is essential for speaking and chewing. Meckel's cartilage (MC) is a temporary structure that supports the formation of the mandible, but how MC is involved in the ossification of the mandible is poorly understood. Through the use of single-cell RNA sequencing and single-cell spatial transcriptomics analyses, a spatiotemporal atlas of MC in human fetuses from 7 to 15 wk postconception was established, highlighting the role of MC in the ossification of the mandible. Importantly, we revealed that two populations of MC contributed to mandibular ossification through different mechanisms. The anterior MC can differentiate into osteolineage cells, as shown in an in vivo lineage tracing mouse model. The intermediate MC facilitates intramembranous ossification through cell-cell communications, possibly through signaling ligands like BMP5, BMP7, SEMA3A, PDGFC, and FGF7. This study suggests that MC plays a crucial role in mediating mandibular ossification through distinct mechanisms, providing valuable insights for understanding oral and craniofacial diseases and disorders in the future.

Light and scanning electron microscope characterization of mandibular symphysis tissue as a functional adaptation in the mandible development of human fetuses

When developing, the mandible presents great plasticity and contains condensed mesenchymal cells that develops into Meckel's cartilage, of which the anterior part forms the mandibular symphysis. Mandible human development studies focus on investigating whether the beginning of mandibular fusion in fetal period is related to symphysis ossification and the tensions imposed on it, considering that tongue movements, mouth opening, and closing can be seen in fetuses. This research analyses tissue modifications during human mandibular symphysis growth using light and scanning electron microscopy to relate them to its functional structure. The study sample consisted of 12 human fetuses distributed into two groups: Group I (GI) of 10-14 weeks old and Group II (GII) of 20-24 weeks old. Fragments of mandibular symphysis were removed en bloc together with the surrounding tissues to preserve the relation with adjacent structures. Decalcified specimens were prepared in semi-serial coronal sections 5-μm-thick and stained with hematoxylin and eosin, Masson՚s trichrome, Verhoeff, and Sirius red for histological analysis with light microscopy. Collagen fibers Type I or III and elastic fibers were quantified by volume fraction (Vv). Coronal sections of the GI and GII symphyseal region were submitted to scanning electron microscopy. Comparison between groups used independent t-test. Our study presents the different endochondral ossification stages in the anterior part of Meckel's cartilage in GI. Both groups showed abundantly vascularized mesenchymal tissue with intense cellular activity forming the mandibular symphysis, such as a source of new osteoblasts adjacent to the newly deposited bone matrix. Scanning electron microscopy analysis revealed an invasion of the bony trabecula in the transverse direction from the hemimandible, rectilinear in GI and sinuous in GII due to interdigitating bone process, promoting its ossification. In collagen Vv analysis was verified a prevalence of type I in GII and type III in GI, indicating a proportional relation between maturation and tissue arrangement. Functionally, the collagen and elastic fibers in the mandibular symphysis were arranged in a pantographic network, and the fibrillar interconnectivity clearly contributes to resilience capacity and efficiency of the force transfer. This study inferred the functional significance of the knowledge about the tissue composition of mandibular symphysis, and the importance of this tissue for surrounding structures. The mesenchymal tissue of mandibular symphysis participates in bone growth process, revealing an adaptation mechanism of mandibular symphysis in the fetal period investigated.

Bioinspired artificial antioxidases for efficient redox homeostasis and maxillofacial bone regeneration

Reconstructing large, inflammatory maxillofacial defects using stem cell-based therapy faces challenges from adverse microenvironments, including high levels of reactive oxygen species (ROS), inadequate oxygen, and intensive inflammation. Here, inspired by the reaction mechanisms of intracellular antioxidant defense systems, we propose the de novo design of an artificial antioxidase using Ru-doped layered double hydroxide (Ru-hydroxide) for efficient redox homeostasis and maxillofacial bone regeneration. Our studies demonstrate that Ru-hydroxide consists hydroxyls-synergistic monoatomic Ru centers, which efficiently react with oxygen species and collaborate with hydroxyls for rapid proton and electron transfer, thus exhibiting efficient, broad-spectrum, and robust ROS scavenging performance. Moreover, Ru-hydroxide can effectively sustain stem cell viability and osteogenic differentiation in elevated ROS environments, modulating the inflammatory microenvironment during bone tissue regeneration in male mice. We believe this Ru-hydroxide development offers a promising avenue for designing antioxidase-like materials to treat various inflammation-associated disorders, including arthritis, diabetic wounds, enteritis, and bone fractures.

Comprehensive three-dimensional microCT and signaling analysis reveal the teratogenic effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on craniofacial bone development in mice

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in utero can result in osteogenic defect during palatogenesis, but the effects on other craniofacial bones and underlying mechanisms remain to be characterized. By treating pregnant mice with TCDD (40 μg/kg) at the vital craniofacial patterning stages (embryonic day 8.5, 10.5 and 12.5), and scanning and reconstructing the skulls at embryonic day 18.5 using microCT, we found that TCDD exposure at the earlier and later patterning stages induced variable craniofacial malformations, including premature fusion of metopic and coronal sutures, truncated palatal processes of maxillary and palatine bones, as well as opening oriented pterygoid processes. Further in vitro determination of the underlying mechanisms using human fetal palatal mesenchymal cells (hFPMCs) revealed that TCDD suppressed a wide variety of osteogenic genes responsible for osteoblast commitment and bone matrix synthesis and mineralization, through activating aryl hydrocarbon receptor (AhR) signaling and subsequently inhibiting estrogen signaling. The attenuation of AhR signaling significantly blocked the osteogenic toxicity, and partly restored the expressing level of estrogen receptor α (ERα). Additional treatment with ERα agonist (PPT) significantly relieved the activation of AhR and rescued the impairment of osteogenesis caused by TCDD. Together, our findings demonstrated that TCDD was teratogenic in numerous cranial neural crest cell-derived craniofacial bone development, and disrupted multiple genes for osteogenic differentiation via the TCDD-mediated AhR/ ERα signaling cross-talk.

Identification of human cranio-maxillofacial skeletal stem cells for mandibular development

Compared with long bone that arises from the mesoderm, the major portion of the maxillofacial bones and the front bone of the skull are derived from cranial neural crest cells and undergo intramembranous ossification. Human skeletal stem cells have been identified in embryonic and fetal long bones. Here, we describe a single-cell atlas of the human embryonic mandible and identify a population of cranio-maxillofacial skeletal stem cells (CMSSCs). These CMSSCs are marked by interferon-induced transmembrane protein 5 (IFITM5) and are specifically located around the periosteum of the jawbone and frontal bone. Additionally, these CMSSCs exhibit strong self-renewal and osteogenic differentiation capacities but lower chondrogenic differentiation potency, mediating intramembranous bone formation without cartilage formation. IFITM5+ cells are also observed in the adult jawbone and exhibit functions similar to those of embryonic CMSSCs. Thus, this study identifies CMSSCs that orchestrate the intramembranous ossification of cranio-maxillofacial bones, providing a deeper understanding of cranio-maxillofacial skeletal development and promising seed cells for bone repair.

The role of sonic hedgehog signaling in the oropharyngeal epithelium during jaw development

Sonic hedgehog (Shh) is expressed in the oropharyngeal epithelium, including the frontonasal ectodermal zone (FEZ), which is defined as the boundary between Shh and Fgf8 expression domains in the frontonasal epithelium. To investigate the role of SHH signaling from the oropharyngeal epithelium, we generated mice in which Shh expression is specifically deleted in the oropharyngeal epithelium (Isl1-Cre; Shhf/f). In the mutant mouse, Shh expression was excised in the oropharyngeal epithelium as well as FEZ and ventral forebrain, consistent with the expression pattern of Isl1. Isl1-Cre; Shhf/f mice exhibited a complete loss of lower jaw components and a malformed upper jaw with defects in the cranial base and secondary palate. Massive cell death was observed in the mandibular process at embryonic day (E) 9.5 and E10.5, while mild cell death was observed in the lambdoidal region (the fusion area in the maxillary, lateral nasal, and medial nasal processes) at E10.5. An RNA-seq analysis revealed that Satb2, a gene involved in cell survival during jaw formation, was downregulated in the lambdoidal region in Isl1-Cre; Shhf/f mice. These results suggest that Shh expression in the FEZ is required for cell survival and skeletogenesis in the lambdoidal region during the development of the upper jaw and that the developmental control governed by SHH signaling is different between upper and lower jaws.

Craniofacial Effects of Zoledronic Acid on the Osteogenesis Imperfecta Mouse (-/-) Model of Severe Osteogenesis Imperfecta

Background: Osteogenesis imperfecta (OI) is a rare genetic disorder affecting mainly type I collagen, which leads to bone fragility and deformities. OI patients also present craniofacial abnormalities such as macrocephaly and malocclusion. Recently, craniofacial dysmorphism was highlighted in the osteogenesis imperfecta mouse (oim), a validated model of the most severe form of OI. This study explores the impact of zoledronic acid (ZA), commonly administered to OI patients to increase bone mass and mechanical strength, on oim craniofacial structure. Methods: Fifteen oim received a single intravenous ZA injection (100 µg/kg) at 5 weeks (ZA group), while fifteen remained untreated (control). Before euthanasia at 14 weeks, in vivo computed tomography provided craniometric data. Post-euthanasia, heads underwent peripheral Quantitative Computed Tomography (pQCT); coronal decalcified sections through temporomandibular joints were analyzed (n = 6/mouse) after Masson's trichrome staining (3 sections) or under polarized light to study collagen birefringence (3 sections). Results: In vivo craniometry highlighted the positive effect on vertical growth in ZA oim models as compared to untreated ones, with significant increases in mandibular length and incisor height and without any change in transversal dimensions. The pQCT scans showed the significantly higher total mineral density and cortical mineral density of the mandibular ramus in the ZA than the untreated group. Via microscopic analysis, the cranial vault was thicker and the collagen birefringence was higher in the ZA group than in the untreated group, but differences were not significant. Conclusion: To conclude, ZA had some beneficial effects on craniofacial vertical height and ramus density and, to a lower extent, on vault thickness, while transversal dimensions did not seem to be influenced by ZA intake. These data emphasize the need to consider the whole skeleton when treating OI patients.

Influence of bite force and implant elastic modulus on mandibular reconstruction with particulate-cancellous bone marrow grafts healing: An in silico investigation

This study aims to investigate tissue differentiation during mandibular reconstruction with particulate cancellous bone marrow (PCBM) graft healing using biphasic mechanoregulation theory under four bite force magnitudes and four implant elastic moduli to examine its implications on healing rate, implant stress distribution, new bone elastic modulus, mandible equivalent stiffness, and load-sharing progression. The finite element model of a half Canis lupus mandible, symmetrical about the midsagittal plane, with two marginal defects filled by PCBM graft and stabilized by porous implants, was simulated for 12 weeks. Eight different scenarios, which consist of four bite force magnitudes and four implant elastic moduli, were tested. It was found that the tissue differentiation pattern corroborates the experimental findings, where the new bone propagates from the superior side and the buccal and lingual sides in contact with the native bone, starting from the outer regions and progressing inward. Faster healing and quicker development of bone graft elastic modulus and mandible equivalent stiffness were observed in the variants with lower bite force magnitude and or larger implant elastic modulus. A load-sharing condition was found as the healing progressed, with M3 (Ti6Al4V) being better than M4 (stainless steel), indicating the higher stress shielding potentials of M4 in the long term. This study has implications for a better understanding of mandibular reconstruction mechanobiology and demonstrated a novel in silico framework that can be used for post-operative planning, failure prevention, and implant design in a better way.

Mapping Human Immunity and the Education of Waldeyer's Ring

The development and deployment of single-cell genomic technologies have driven a resolution revolution in our understanding of the immune system, providing unprecedented insight into the diversity of immune cells present throughout the body and their function in health and disease. Waldeyer's ring is the collective name for the lymphoid tissue aggregations of the upper aerodigestive tract, comprising the palatine, pharyngeal (adenoids), lingual, and tubal tonsils. These tonsils are the first immune sentinels encountered by ingested and inhaled antigens and are responsible for mounting the first wave of adaptive immune response. An effective mucosal immune response is critical to neutralizing infection in the upper airway and preventing systemic spread, and dysfunctional immune responses can result in ear, nose, and throat pathologies. This review uses Waldeyer's ring to demonstrate how single-cell technologies are being applied to advance our understanding of the immune system and highlight directions for future research.

Distinct expression patterns of Hedgehog signaling components in mouse gustatory system during postnatal tongue development and adult homeostasis

The Hedgehog (HH) pathway regulates embryonic development of anterior tongue taste fungiform papilla (FP) and the posterior circumvallate (CVP) and foliate (FOP) taste papillae. HH signaling also mediates taste organ maintenance and regeneration in adults. However, there are knowledge gaps in HH pathway component expression during postnatal taste organ differentiation and maturation. Importantly, the HH transcriptional effectors GLI1, GLI2 and GLI3 have not been investigated in early postnatal stages; the HH receptors PTCH1, GAS1, CDON and HHIP, required to either drive HH pathway activation or antagonism, also remain unexplored. Using lacZ reporter mouse models, we mapped expression of the HH ligand SHH, HH receptors, and GLI transcription factors in FP, CVP and FOP in early and late postnatal and adult stages. In adults we also studied the soft palate, and the geniculate and trigeminal ganglia, which extend afferent fibers to the anterior tongue. Shh and Gas1 are the only components that were consistently expressed within taste buds of all three papillae and the soft palate. In the first postnatal week, we observed broad expression of HH signaling components in FP and adjacent, non-taste filiform (FILIF) papillae in epithelium or stroma and tongue muscles. Notably, we observed elimination of Gli1 in FILIF and Gas1 in muscles, and downregulation of Ptch1 in lingual epithelium and of Cdon, Gas1 and Hhip in stroma from late postnatal stages. Further, HH receptor expression patterns in CVP and FOP epithelium differed from anterior FP. Among all the components, only known positive regulators of HH signaling, SHH, Ptch1, Gli1 and Gli2, were expressed in the ganglia. Our studies emphasize differential regulation of HH signaling in distinct postnatal developmental periods and in anterior versus posterior taste organs, and lay the foundation for functional studies to understand the roles of numerous HH signaling components in postnatal tongue development.

The Contribution of Meckel's Cartilage-Derived Type II Collagen-Positive Cells to the Jawbone Development and Repair

Jawbones and long bones, despite their shared skeletal lineage, frequently exhibit distinct origins and developmental pathways. Identifying specific progenitor subsets for mandibular osteogenesis remains challenging. Type II collagen is conventionally associated with cartilaginous structures, yet our investigation has identified the presence of type II collagen positive (Col2+) cells within the jawbone development and regeneration. The role of Col2+ cells in jawbone morphogenesis and repair has remained enigmatic. In this study, we analyze single-cell RNA sequencing data from mice jawbone at embryonic day 10.5. Through fate-mapping experiments, we have elucidated that Col2+ cells and their progeny are instrumental in mandibular osteogenesis across both fetal and postnatal stages. Furthermore, lineage tracing with a tamoxifen-inducible CreER system has established the pivotal role of Col2+ cells, marked by Col2-CreER and originating from the primordial Meckel's cartilage, in jawbone formation. Moreover, our research explored models simulating jawbone defects and tooth extraction, which underscored the osteogenic differentiation capabilities of postnatal Col2+ cells during repair. This finding not only highlights the regenerative potential of Col2+ cells but also suggests their versatility in contributing to skeletal healing and regeneration. In conclusion, our findings position Col2+ cells as essential in orchestrating osteogenesis throughout the continuum of mandibular development and repair.

Regulatory role of primary cilia in oral and maxillofacial development and disease

Primary cilia have versatile functions, such as receiving signals from the extracellular microenvironment, mediating signaling transduction, and transporting ciliary substances, in tissue and organ development and clinical disease pathogenesis. During early development (embryos within 10 weeks) in the oral and maxillofacial region, defects in the structure and function of primary cilia can result in severe craniofacial malformations. For example, mice with mutations in the cilia-related genes Kif3a and IFT88 exhibit midline expansion and cleft lip/palate, which occur due to abnormalities in the fusion of the single frontonasal prominence and maxillary prominences. In the subsequent development of the oral and maxillofacial region, we discussed the regulatory role of primary cilia in the development of the maxilla, mandible, Meckel cartilage, condylar cartilage, lip, tongue, and tooth, among others. Moreover, primary cilia are promising regulators in some oral and maxillofacial diseases, such as tumors and malocclusion. We also summarize the regulatory mechanisms of primary cilia in oral and maxillofacial development and related diseases, including their role in various signaling transduction pathways. For example, aplasia of submandibular glands in the Kif3a mutant mice is associated with a decrease in SHH signaling within the glands. This review summarizes the similarities and specificities of the role of primary cilia in tissue and organ development and disease progression in the oral and maxillofacial region, which is expected to contribute several ideas for the treatment of primary cilia-related diseases.

Menopause-Associated Changes in Mandibular Bone Microarchitecture Are Site-Specific

BACKGROUND

There are conflicting reports on the effects of decreased estrogen levels on mandibular bone microarchitecture. Whether these effects are consistent throughout the mandible is unclear and may have important implications for treatment planning.

PURPOSE

The goal of this study was to evaluate trabecular and cortical bone microstructure in the mandibular condyle and the mandibular basal bone and compare these sites between premenopausal and postmenopausal women.

STUDY DESIGN, SETTING, SAMPLE

Participants were recruited for a cross-sectional cohort study at Columbia University Irving Medical Center. Each participant had cone-beam computed tomography taken of their mandibular condyles and the basal bone. Exclusion criteria for the population included a) current chemotherapy or immunotherapy; b) history of bisphosphonate or other osteoporosis therapy; and c) currently pregnant, nursing, or on hormonal birth control.

INDEPENDENT VARIABLE

The predictor variables are menopausal status (before or after menopause) and mandibular region of interest (condyle/basal bone).

MAIN OUTCOME VARIABLE

Parameters of interest included the following indicators of bone quality: trabecular bone volume fraction, trabecular thickness, trabecular number, trabecular separation, cortical bone volume fraction, cortical thickness, and cortical porosity.

COVARIATES

Covariates included demographic variables such as age, estrogen levels, and ethnicity.

ANALYSES

Quantitative microstructure analyses were conducted on cone-beam computed tomography images, and differences between groups for continuous measures (including age) were assessed with an unpaired t-test, and demographic variables were assessed by χ2. Statistical significance was recorded at P < .05.

RESULTS

The premenopausal and postmenopausal groups each had 31 participants, with the following average age: premenopausal = 43.9 ± 6.9 versus postmenopausal = 57.5 ± 7.6 years old; P < .001, and estrogen levels: premenopausal = 91.77 ± 80.13 pg/ml versus postmenopausal = 41.44 ± 61.62 pg/ml; P < .01). Postmenopausal women had significantly greater condylar trabecular separation (0.61 ± 0.18 vs 0.47 ± 0.11 mm; P < .001) and lower trabecular number (1.03 ± 0.18 vs 1.21 ± 0.19 mm-1; P < .001) compared to premenopausal women. There were no significant differences in the basal bone microarchitectural parameters between the menopausal groups.

CONCLUSION AND RELEVANCE

Menopause is associated with mandibular condylar trabecular bone loss but has minimal effects on the mandibular basal bone. This may have important ramifications for treatment planning in advanced-age individuals.

A new classification of mandible defects and condyle changed after mandible reconstruction with FFF

Objectives

To explore a new classification of mandibular defects and changes in the preserved condyle after mandibular reconstruction with free fibular flap(FFF).

Study design

We reviewed patients who underwent mandibular reconstruction with FFF from 2015 to 2021 and classified the mandibular defects into five categories: classⅠ(unilateral-mandibular excluding condyle), classⅡ(unilateral-mandibular including condyle), classⅢ(bilateral-mandibular excluding condyle), classⅣ(bilateral-mandibular including one condyle), and classⅤ(bilateral-mandibular including both condyles). Cone Beam Computed Tomography (CBCT) data were collected preoperatively(T0), at 7-10 postoperative days(T1), 6 postoperative months(T2), and 1 postoperative year(T3). We calculated the condylar surface area, volume, and displacement.

Results

62 cases were collected. The condylar surface areas and volumes in T2 and T3 values were lower than those of T0 and T1(P < 0.01) The condylar displacement was the lowest in ClassI and the largest in ClassⅣ(P < 0.01), while no significant differences in classesⅠ-Ⅲ(P < 0.05). Displacement during T1-T0 was greater than that during T2-T0 and T3-T0(P < 0.05).

Conclusion

Mandibular reconstruction with FFF results in displacement and alteration of the condyle within a time interval, and this alteration stabilizes after 6 months. Mandibular defects that do not reach the midline, surgical alteration to preserve the condyle are not required. However, when the defects cross the midline, the condyle should be preserved as much as possible.

Tongue and Mandibular Disorders of the Pediatric Patient

Robin sequence, macroglossia, and ankyloglossia are disorders affecting the tongue and mandible in the pediatric population. Each of these can have a significant impact on breathing, feeding, speech, dentition, and craniofacial growth. This review discusses the interdependent and coordinated development of both the tongue and mandible, the functional impacts of these disorders, and appropriate management strategies.

Different Sources of Bone Marrow Mesenchymal Stem Cells: A Comparison of Subchondral, Mandibular, and Tibia Bone-derived Mesenchymal Stem Cells

BACKGROUND

Stem cell properties vary considerably based on the source and tissue site of mesenchymal stem cells (MSCs). The mandibular condyle is a unique kind of craniofacial bone with a special structure and a relatively high remodeling rate. MSCs here may also be unique to address specific physical needs.

OBJECTIVE

The aim of this study was to compare the proliferation and multidirectional differentiation potential among MSCs derived from the tibia (TMSCs), mandibular ramus marrow (MMSCs), and condylar subchondral bone (SMSCs) of rats in vitro.

METHODS

Cell proliferation and migration were assessed by CCK-8, laser confocal, and cell scratch assays. Histochemical staining and real-time PCR were used to evaluate the multidirectional differentiation potential and DNA methylation and histone deacetylation levels.

RESULTS

The proliferation rate and self-renewal capacity of SMSCs were significantly higher than those of MMSCs and TMSCs. Moreover, SMSCs possessed significantly higher mineralization and osteogenic differentiation potential. Dnmt2, Dnmt3b, Hdac6, Hdac7, Hdac9, and Hdac10 may be instrumental in the osteogenesis of SMSCs. In addition, SMSCs are distinct from MMSCs and TMSCs with lower adipogenic differentiation and chondrogenic differentiation potential. The multidirectional differentiation capacities of TMSCs were exactly the opposite of those of SMSCs, and the results of MMSCs were intermediate.

CONCLUSION

This research offers a new paradigm in which SMSCs could be a useful source of stem cells for further application in stem cell-based medical therapies due to their strong cell renewal and osteogenic capacity.

The Evolution of Robin Sequence Treatment Based on the Biomimetic Interdisciplinary Approach: A Historical Review

The Robin sequence is a congenital anomaly characterized by a triad of features: micrognathia, glossoptosis, and airway obstruction. This comprehensive historical review maps the evolution of approaches and appliances for its treatment from the past to the current modern possibilities of an interdisciplinary combination of modern engineering, medicine, materials, and computer science combined approach with emphasis on designing appliances inspired by nature and individual human anatomy. Current biomimetic designs are clinically applied, resulting in appliances that are more efficient, comfortable, sustainable, and safer than legacy traditional designs. This review maps the treatment modalities that have been used for patients with a Robin sequence over the years. Early management of the Robin sequence focused primarily on airway maintenance and feeding support, while current management strategies involve both nonsurgical and surgical interventions and biomimetic biocompatible personalized appliances. The goal of this paper was to provide a review of the evolution of management strategies for patients with the Robin sequence that led to the current interdisciplinary biomimetic approaches impacting the future of Robin Sequence treatment with biomimetics at the forefront.

ESCRT-dependent control of craniofacial morphogenesis with concomitant perturbation of NOTCH signaling

Craniofacial development is orchestrated by transcription factor-driven regulatory networks, epigenetic modifications, and signaling pathways. Signaling molecules and their receptors rely on endo-lysosomal trafficking to prevent accumulation on the plasma membrane. ESCRT (Endosomal Sorting Complexes Required for Transport) machinery is recruited to endosomal membranes enabling degradation of such endosomal cargoes. Studies in vitro and in invertebrate models established the requirements of the ESCRT machinery in membrane remodeling, endosomal trafficking, and lysosomal degradation of activated membrane receptors. However, investigations during vertebrate development have been scarce. By ENU-induced mutagenesis, we isolated a mouse line, Vps25ENU/ENU, carrying a hypomorphic allele of the ESCRT-II component Vps25, with craniofacial anomalies resembling features of human congenital syndromes. Here, we assessed the spatiotemporal dynamics of Vps25 and additional ESCRT-encoding genes during murine development. We show that these genes are ubiquitously expressed although enriched in discrete domains of the craniofacial complex, heart, and limbs. ESCRT-encoding genes, including Vps25, are expressed in both cranial neural crest-derived mesenchyme and epithelium. Unlike constitutive ESCRT mutants, Vps25ENU/ENU embryos display late lethality. They exhibit hypoplastic lower jaw, stunted snout, dysmorphic ear pinnae, and secondary palate clefting. Thus, we provide the first evidence for critical roles of ESCRT-II in craniofacial morphogenesis and report perturbation of NOTCH signaling in craniofacial domains of Vps25ENU/ENU embryos. Given the known roles of NOTCH signaling in the developing cranium, and notably the lower jaw, we propose that the NOTCH pathway partly mediates the craniofacial defects of Vps25ENU/ENU mouse embryos.

Quantitative and Qualitative Correlation of Mandibular Lingual Bone with Risk Factors for Third Molar Using Cone Beam Computed Tomography

Background

Lingual plate thickness, density, and proximity to the tooth are linked as risk factors for various complications associated with third molar extraction. The present study aimed to assess the lingual plate thickness, and density in the mandibular third molar region using cone beam computed tomography and to estimate its correlation with type and level of impaction, number of roots, age, and gender as the risk factors.

Methods

This was a retrospective study on CBCT images of 648 mandibular third molars. The lingual plate thickness at three different root levels - cervical, mid-root, and apex along with the position of the tooth, number of roots, density of lingual plate, age, and gender were evaluated. The measurements were done on Invivo 5-Anatomage software. Statistical comparison of the categorical variables was done by Chi-square test, and Fisher's exact test, and univariate and multivariate analysis were done using binomial logistic regression.

Results

Lingual plate thickness of the third molars at the cervical, mid root, and apex were 1.28 mm, 1.42 mm and .01 mm (mean). A significantly higher proportion of subjects with thin lingual plates at mid-root (p-value=0.01) and apex (p-value=0.05) were in the 21-30 age group. Lingual bone density was significantly associated with the thickness of the lingual plate at the mid-root. A significantly higher proportion of thinner lingual plates at the mid-root level were associated with mesioangularly placed third molars (p-value=0.002).

Conclusion

Our study presented that lingual plate thickness has a strong association with age, angulation, and the number of roots. Knowledge about these risk factors is imperative during the management of third molar impactions.

Taste papilla cell differentiation requires the regulation of secretory protein production by ALK3-BMP signaling in the tongue mesenchyme

Taste papillae are specialized organs, each of which comprises an epithelial wall hosting taste buds and a core of mesenchymal tissue. In the present study, we report that during early taste papilla development in mouse embryos, bone morphogenetic protein (BMP) signaling mediated by type 1 receptor ALK3 in the tongue mesenchyme is required for epithelial Wnt/β-catenin activity and taste papilla differentiation. Mesenchyme-specific knockout (cKO) of Alk3 using Wnt1-Cre and Sox10-Cre resulted in an absence of taste papillae at E12.0. Biochemical and cell differentiation analyses demonstrated that mesenchymal ALK3-BMP signaling governed the production of previously unappreciated secretory proteins, i.e. it suppressed those that inhibit and facilitated those that promote taste papilla differentiation. Bulk RNA-sequencing analysis revealed many more differentially expressed genes (DEGs) in the tongue epithelium than in the mesenchyme in Alk3 cKO versus control. Moreover, we detected downregulated epithelial Wnt/β-catenin signaling and found that taste papilla development in the Alk3 cKO was rescued by the GSK3β inhibitor LiCl, but not by Wnt3a. Our findings demonstrate for the first time the requirement of tongue mesenchyme in taste papilla cell differentiation.

The Role of Gli1+ Mesenchymal Stem Cells in Osteogenesis of Craniofacial Bone

Glioma-associated oncogene homolog 1 (Gli1) is a transcriptional activator of hedgehog (Hh) signaling that regulates target gene expression and several cellular biological processes. Cell lineage tracing techniques have highlighted Gli1 as an ideal marker for mesenchymal stem cells (MSCs) in vivo. Gli1+ MSCs are critical for the osteogenesis of the craniofacial bone; however, the regulatory mechanism by which Gli1+ MSCs mediate the bone development and tissue regeneration of craniofacial bone has not been systematically outlined. This review comprehensively elucidates the specific roles of Gli1+ MSCs in craniofacial bone osteogenesis. In addition to governing craniofacial bone development, Gli1+ MSCs are associated with the tissue repair of craniofacial bone under pathological conditions. Gli1+ MSCs promote intramembranous and endochondral ossification of the craniofacial bones, and assist the osteogenesis of the craniofacial bone by improving angiopoiesis. This review summarizes the novel role of Gli1+ MSCs in bone development and tissue repair in craniofacial bones, which offers new insights into bone regeneration therapy.

Sonic hedgehog signaling in craniofacial development

Mutations in SHH and several other genes encoding components of the Hedgehog signaling pathway have been associated with holoprosencephaly syndromes, with craniofacial anomalies ranging in severity from cyclopia to facial cleft to midfacial and mandibular hypoplasia. Studies in animal models have revealed that SHH signaling plays crucial roles at multiple stages of craniofacial morphogenesis, from cranial neural crest cell survival to growth and patterning of the facial primordia to organogenesis of the palate, mandible, tongue, tooth, and taste bud formation and homeostasis. This article provides a summary of the major findings in studies of the roles of SHH signaling in craniofacial development, with emphasis on recent advances in the understanding of the molecular and cellular mechanisms regulating the SHH signaling pathway activity and those involving SHH signaling in the formation and patterning of craniofacial structures.

Identification of distinct subpopulations of Gli1-lineage cells in the mouse mandible

The Hedgehog pathway gene Gli1 has been proposed to mark a subpopulation of skeletal stem cells (SSCs) in craniofacial bone. Skeletal stem cells (SSCs) are multi-potent cells crucial for the development and homeostasis of bone. Recent studies on long bones have suggested that skeletal stem cells in endochondral or intramembranous ossification sites have different differentiation capacities. However, this has not been well-defined in neural crest derived bones. Generally, the long bones are derived from mesoderm and follow an endochondral ossification model, while most of the cranial bones are neural crest (NC) in origin and follow an intramembranous ossification model. The mandible is unique: It is derived from the neural crest lineage but makes use of both modes of ossification. Early in fetal development, the mandibular body is generated by intramembranous ossification with subsequent endochondral ossification forming the condyle. The identities and properties for SSCs in these two sites remain unknown. Here, we use genetic lineage tracing in mouse to identify cells expressing the Hedgehog responsive gene Gli1, which is thought to mark the tissue resident SSCs. We track the Gli1+ cells, comparing cells within the perichondrium to those in the periosteum covering the mandibular body. In juvenile mice, these have distinct differentiation and proliferative potential. We also assess the presence of Sox10+ cells, thought to mark neural crest stem cells, but find no substantial population associated with the mandibular skeleton, suggesting that Sox10+ cells have limited contribution to maintaining postnatal mandibular bone. All together, our study indicates that the Gli1+ cells display distinct and limited differentiation capacity dependent on their regional associations.

An Absent Lingual Frenulum in a Non-syndromic Premature Infant

The lingual frenulum (LF) is a fold of tissue that connects the tongue to the oral cavity's floor. Abnormal frenula are associated with speech alterations. The absence of the LF is associated with Ehler's Danlos syndrome (EDS). In this case report, we present a premature infant incidentally found to have an absent lingual frenulum, with recurrent desaturations during feeding. The desaturations were believed to be due to the absent lingual frenulum, but they resolved after one month without treatment and were then attributed to apnea of prematurity. Whole exome sequence showed no genetic disorders. The infant is now doing well with no interventions. An absent lingual frenulum warrants molecular genetic testing for EDS. However, it does not warrant any treatment; special considerations are only required during intubation.

Missense polymorphisms potentially involved in mandibular prognathism

Objective

The current study aimed to identify and analyze missense single nucleotide polymorphisms (SNPs) that can potentially cause mandibular prognathism.

Methods

After reviewing the articles, 56 genes associated with mandibular prognathism were identified and their missense SNPs were retrieved from the NCBI website. Several web-based tools including CADD, PolyPhen-2, PROVEAN, SNAP2, PANTHER, FATHMM, and PON-P2 were used to filter out harmful SNPs. Additionally, ConSurf determined the level of evolutionary conservation at positions where SNPs occur. I-Mutant2 and MUpro predicted the effect of SNPs on protein stability. Furthermore, to investigate the structural and functional changes of proteins, HOPE and LOMETS tools were utilized.

Results

Based on predictions in at least four web-based tools, the results indicated that PLXNA2-rs4844658, DUSP6-rs2279574, and FBN3-rs33967815 are harmful. These SNPs are located at positions with variable or average conservation and have the potential to reduce the stability of their respective proteins. Moreover, they may impair protein activity by causing structural and functional changes.

Conclusions

In this study, we identified PLXNA2-rs4844658, DUSP6-rs2279574, and FBN3-rs33967815 as potential risk factors for mandibular prognathism using several web-based tools. According to the possible roles of PLXNA2, DUSP6, and FBN3 proteins in ossification pathways, we recommend that these SNPs be investigated further in experimental research. Through such studies, we hope to gain a better understanding of the molecular mechanisms involved in mandible formation.

Tri-lobed Tongue: Rare Manifestation Accompany With Pierre Robin Sequence

BACKGROUND

The tongue is an essential organ accounted for proper deglutition and articulation. Surgical repair should be planned soon after diagnosis of any structural abnormality to prevent later speech and swallowing disorders. The lobulated tongue could be isolated (sporadic) or in association with other disorders. Pierre Robin Sequence (PRS) consists of the clinical trial of congenital micrognathia, glossoptosis, and airway obstruction with variable inclusion of a cleft palate. We present the case of a rare congenital tri-lobed tongue with Pierre Robin sequence and its surgical management in our hospital setting.

CASE PRESENTATION

Six-month-old boy presented with severe retrognathia, high arch, complete isolated cleft palate, and a bizarre mass in the oral cavity instead of his tongue that led to disruption of his swallowing. The mass (deformed tongue) check clearly, and the normal shape of the tongue was restored through multiple local randomized flaps. Dramatic improvement in swallowing was noticed 6 months after surgery during postoperative follow-up.

DISCUSSION

We present the case of a patient with a tri-lobed tongue with Pierre Robin sequence characterized by severe retrognathia, high arch, and complete isolated cleft palate. This seems to be the first reported case of this particular craniofacial anomaly.

CONCLUSION

The management of infants with the Pierre Robin sequence is complex, and much still needs to be learned and practiced. Congenital tri-lobed tongue with a cleft as part of the Pierre Robin sequence is a very rare malformation. Early repair of the tongue is important to assist the baby in adapting to speech and swallowing as they grow.

The Role of HIF-1α in Bone Regeneration: A New Direction and Challenge in Bone Tissue Engineering

The process of repairing significant bone defects requires the recruitment of a considerable number of cells for osteogenesis-related activities, which implies the consumption of a substantial amount of oxygen and nutrients. Therefore, the limited supply of nutrients and oxygen at the defect site is a vital constraint that affects the regenerative effect, which is closely related to the degree of a well-established vascular network. Hypoxia-inducible factor (HIF-1α), which is an essential transcription factor activated in hypoxic environments, plays a vital role in vascular network construction. HIF-1α, which plays a central role in regulating cartilage and bone formation, induces vascular invasion and differentiation of osteoprogenitor cells to promote and maintain extracellular matrix production by mediating the adaptive response of cells to changes in oxygen levels. However, the application of HIF-1α in bone tissue engineering is still controversial. As such, clarifying the function of HIF-1α in regulating the bone regeneration process is one of the urgent issues that need to be addressed. This review provides insight into the mechanisms of HIF-1α action in bone regeneration and related recent advances. It also describes current strategies for applying hypoxia induction and hypoxia mimicry in bone tissue engineering, providing theoretical support for the use of HIF-1α in establishing a novel and feasible bone repair strategy in clinical settings.

Physiology of the tongue with emphasis on taste transduction

The tongue is a complex multifunctional organ that interacts and senses both interoceptively and exteroceptively. Although it is easily visible to almost all of us, it is relatively understudied and what is in the literature is often contradictory or is not comprehensively reported. The tongue is both a motor and a sensory organ: motor in that it is required for speech and mastication, and sensory in that it receives information to be relayed to the central nervous system pertaining to the safety and quality of the contents of the oral cavity. Additionally, the tongue and its taste apparatus form part of an innate immune surveillance system. For example, loss or alteration in taste perception can be an early indication of infection as became evident during the present global SARS-CoV-2 pandemic. Here, we particularly emphasize the latest updates in the mechanisms of taste perception, taste bud formation and adult taste bud renewal, and the presence and effects of hormones on taste perception, review the understudied lingual immune system with specific reference to SARS-CoV-2, discuss nascent work on tongue microbiome, as well as address the effect of systemic disease on tongue structure and function, especially in relation to taste.

Oral alterations in children with microcephaly associated to congenital Zika syndrome: A systematic review and meta-analyses

AIMS

To synthesize the oral alterations observed in children with microcephaly associated with congenital Zika virus syndrome (CZS), and to compare the oral alterations of these children to a normotypic healthy controls.

METHODS AND RESULTS

A search was performed in six electronic databases. Observational studies published that reported oral alterations in children with CZS were selected. Two authors independently extracted data, assessed study quality, using the Joanna Briggs Institute Critical Appraisal Checklist tools, and the certainty of evidence, using Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. Twenty-one studies were included in this systematic review and meta-analysis. The pooled crude occurrence showed 88% of increased salivation (95%CI: 82%-94%), 83% of biofilm (95%CI: 75%-91%), and 73% of bruxism (95%CI: 52%-95%). Compared to normotypic controls, children with CZS-associated microcephaly had a higher chance to have difficulty in lip sealing (OR: 18.28; 95%CI: 1.42-235.91), inadequate lingual posture at rest (OR: 13.57; 95%CI: 4.24-43.44), and delayed eruption (OR: 12.92; 95%CI: 3.42-48.78), with very low certainty.

CONCLUSION

There are several oral alterations found among children with CZS-associated microcephaly. They are more prone to present some of these alterations, such as difficulty in lip sealing, although with very low certainty of evidence.

Nuclear factor 1 X-type-associated regulation of myogenesis in developing mouse tongue

OBJECTIVES

The tongue contains skeletal myofibers that differ from those in the trunk, limbs, and other orofacial muscles. However, the molecular basis of myogenic differentiation in the tongue muscles remains unclear. In this study, we conducted comprehensive gene expression profiling of the developing murine tongue.

METHODS

Tongue primordia were dissected from mouse embryos at embryonic day (E)10.5-E18.5, while myogenic markers were detected via microarray analysis and quantitative polymerase chain reaction (PCR). In addition to common myogenic regulatory factors such as Myf5, MyoD, myogenin, and Mrf4, we focused on Nfix, which acts as a unique molecular switch triggering the shift from embryonic to fetal myoblast lineage during limb myogenesis. Nfix inhibition was performed using a specific antisense oligonucleotide in the organ culture of tongue primordia.

RESULTS

Microarray and ingenuity pathway analyses confirmed the significant upregulation of myogenic signaling molecules, including Nfix, associated with the differentiation of myoblasts from myogenic progenitor cells during E10.5-E11.5. Quantitative PCR confirmed that Nfix expression started at E10.5 and peaked at E14.5. Fetal myoblast-specific genes, such as Mck and Myh8, were upregulated after E14.5, whereas embryonic myoblast-specific genes, such as Myh3 and Myh7, were downregulated. When Nfix was inhibited in the organ culture of tongue primordia, subtle morphological differences were noted in the tongue. Such an observation was only noted in the cultures of E10.5-derived tongue primordia.

CONCLUSIONS

These results reveal the contribution of Nfix to tongue myogenesis. Nfix expression during early tongue development may play a vital role in tongue muscle development.

Ectomesenchymal Six1 controls mandibular skeleton formation

Craniofacial development requires intricate cooperation between multiple transcription factors and signaling pathways. Six1 is a critical transcription factor regulating craniofacial development. However, the exact function of Six1 during craniofacial development remains elusive. In this study, we investigated the role of Six1 in mandible development using a Six1 knockout mouse model (Six1 ^-/- ) and a cranial neural crest-specific, Six1 conditional knockout mouse model (Six1 ^f/f ; Wnt1-Cre). The Six1 ^-/- mice exhibited multiple craniofacial deformities, including severe microsomia, high-arched palate, and uvula deformity. Notably, the Six1 ^f/f ; Wnt1-Cre mice recapitulate the microsomia phenotype of Six1 ^-/- mice, thus demonstrating that the expression of Six1 in ectomesenchyme is critical for mandible development. We further showed that the knockout of Six1 led to abnormal expression of osteogenic genes within the mandible. Moreover, the knockdown of Six1 in C3H10 T1/2 cells reduced their osteogenic capacity in vitro. Using RNA-seq, we showed that both the loss of Six1 in the E18.5 mandible and Six1 knockdown in C3H10 T1/2 led to the dysregulation of genes involved in embryonic skeletal development. In particular, we showed that Six1 binds to the promoter of Bmp4, Fat4, Fgf18, and Fgfr2, and promotes their transcription. Collectively, our results suggest that Six1 plays a critical role in regulating mandibular skeleton formation during mouse embryogenesis.

Quantitative structural analysis of hemifacial microsomia mandibles in different age groups

Introduction

This study aims to quantitively analyze mandibular ramus and body deformities, assessing the asymmetry and progression in different components.

Methods

This is a retrospective study on hemifacial microsomia children. They were divided into mild/severe groups by Pruzansky-Kaban classification and into three age groups (<1 year,1-5 years, 6-12 years old). Linear and volumetric measurements of the ramus and the body were collected via their preoperative imaging data to compare between the different sides and severities, using independent and paired tests, respectively. The progression of asymmetry was assessed by changes in affected/contralateral ratios with age using multi-group comparisons.

Results

Two hundred and ten unilateral cases were studied. Generally, the affected ramus and body were significantly smaller than those on the contralateral side. Linear measurements on the affected side were shorter in the severe group. Regarding affected/contralateral ratios, the body was less affected than the ramus. Progressively decreased affected/contralateral ratios of body length, dentate segment volume, and hemimandible volume were found.

Discussion

There were asymmetries in mandibular ramus and body regions, which involved the ramus more. A significant contribution to progressive asymmetry from the body suggests treatment focus in this region.

Controlled Release of Bone Morphogenetic Protein-2 Augments the Coupling of Angiogenesis and Osteogenesis for Accelerating Mandibular Defect Repair

Reconstruction of a mandibular defect is challenging, with high expectations for both functional and esthetic results. Bone morphogenetic protein-2 (BMP-2) is an essential growth factor in osteogenesis, but the efficacy of the BMP-2-based strategy on the bone regeneration of mandibular defects has not been well-investigated. In addition, the underlying mechanisms of BMP-2 that drives the bone formation in mandibular defects remain to be clarified. Here, we utilized BMP-2-loaded hydrogel to augment bone formation in a critical-size mandibular defect model in rats. We found that implantation of BMP-2-loaded hydrogel significantly promoted intramembranous ossification within the defect. The region with new bone triggered by BMP-2 harbored abundant CD31+ endomucin+ type H vessels and associated osterix (Osx)+ osteoprogenitor cells. Intriguingly, the new bone comprised large numbers of skeletal stem cells (SSCs) (CD51+ CD200+) and their multi-potent descendants (CD51+ CD105+), which were mainly distributed adjacent to the invaded blood vessels, after implantation of the BMP-2-loaded hydrogel. Meanwhile, BMP-2 further elevated the fraction of CD51+ CD105+ SSC descendants. Overall, the evidence indicates that BMP-2 may recapitulate a close interaction between functional vessels and SSCs. We conclude that BMP-2 augmented coupling of angiogenesis and osteogenesis in a novel and indispensable way to improve bone regeneration in mandibular defects, and warrants clinical investigation and application.

The transcription factors Foxf1 and Foxf2 integrate the SHH, HGF and TGFβ signaling pathways to drive tongue organogenesis

The tongue is a highly specialized muscular organ with diverse cellular origins, which provides an excellent model for understanding mechanisms controlling tissue-tissue interactions during organogenesis. Previous studies showed that SHH signaling is required for tongue morphogenesis and tongue muscle organization, but little is known about the underlying mechanisms. Here we demonstrate that the Foxf1/Foxf2 transcription factors act in the cranial neural crest cell (CNCC)-derived mandibular mesenchyme to control myoblast migration into the tongue primordium during tongue initiation, and thereafter continue to regulate intrinsic tongue muscle assembly and lingual tendon formation. We performed chromatin immunoprecipitation sequencing analysis and identified Hgf, Tgfb2 and Tgfb3 among the target genes of Foxf2 in the embryonic tongue. Through genetic analyses of mice with CNCC-specific inactivation of Smo or both Foxf1 and Foxf2, we show that Foxf1 and Foxf2 mediate hedgehog signaling-mediated regulation of myoblast migration during tongue initiation and intrinsic tongue muscle formation by regulating the activation of the HGF and TGFβ signaling pathways. These data uncover the molecular network integrating the SHH, HGF and TGFβ signaling pathways in regulating tongue organogenesis.

ISL1/SHH/CXCL12 signaling regulates myogenic cell migration during mouse tongue development

Migration of myoblasts derived from the occipital somites is essential for tongue morphogenesis. However, the molecular mechanisms of myoblast migration remain elusive. In this study, we report that deletion of Isl1 in the mouse mandibular epithelium leads to aglossia due to myoblast migration defects. Isl1 regulates the expression pattern of chemokine ligand 12 (Cxcl12) in the first branchial arch through the Shh/Wnt5a cascade. Cxcl12+ mesenchymal cells in Isl1ShhCre embryos were unable to migrate to the distal region, but instead clustered in a relatively small proximal domain of the mandible. CXCL12 serves as a bidirectional cue for myoblasts expressing its receptor CXCR4 in a concentration-dependent manner, attracting Cxcr4+ myoblast invasion at low concentrations but repelling at high concentrations. The accumulation of Cxcl12+ mesenchymal cells resulted in high local concentrations of CXCL12, which prevented Cxcr4+ myoblast invasion. Furthermore, transgenic activation of Ihh alleviated defects in tongue development and rescued myoblast migration, confirming the functional involvement of Hedgehog signaling in tongue development. In summary, this study provides the first line of genetic evidence that the ISL1/SHH/CXCL12 axis regulates myoblast migration during tongue development.

Disrupted tenogenesis in masseter as a potential cause of micrognathia

Micrognathia is a severe craniofacial deformity affecting appearance and survival. Previous studies revealed that multiple factors involved in the osteogenesis of mandibular bone have contributed to micrognathia, but concerned little on factors other than osteogenesis. In the current study, we found that ectopic activation of Fgf8 by Osr2-cre in the presumptive mesenchyme for masseter tendon in mice led to micrognathia, masseter regression, and the disrupted patterning and differentiation of masseter tendon. Since Myf5-cre;Rosa26R-Fgf8 mice exhibited the normal masseter and mandibular bone, the possibility that the micrognathia and masseter regression resulted directly from the over-expressed Fgf8 was excluded. Further investigation disclosed that a series of chondrogenic markers were ectopically activated in the developing Osr2-cre;Rosa26R-Fgf8 masseter tendon, while the mechanical sensing in the masseter and mandibular bone was obviously reduced. Thus, it suggested that the micrognathia in Osr2-cre;Rosa26R-Fgf8 mice resulted secondarily from the reduced mechanical force transmitted to mandibular bone. Consistently, when tenogenic or myogenic components were deleted from the developing mandibles, both the micrognathia and masseter degeneration took place with the decreased mechanical sensing in mandibular bone, which verified that the loss of mechanical force transmitted by masseter tendon could result in micrognathia. Furthermore, it appeared that the micrognathia resulting from the disrupted tenogenesis was attributed to the impaired osteogenic specification, instead of the differentiation in the periosteal progenitors. Our findings disclose a novel mechanism for mandibular morphogenesis, and shed light on the prevention and treatment for micrognathia.

Gene profiling in dorso-ventral patterning of mouse tongue development

BACKGROUND

The tongue is a muscular fleshy organ in the oral cavity that is anatomically divided into the dorsal, ventral, anterior, and posterior part. The intricate tissue organisation and diverse origins of the tongue make it a complex organ of the oral cavity.

OBJECTIVES

To reveal the signalling molecules involved in the formation of the dorsal and ventral parts of the tongue through microarray analysis.

METHODS

Dorsal and ventral tongue tissues were isolated from embryonic day 14 mice by micro-dissection. RNA was extracted from the dorsal and ventral tongue tissues separately for microarray analysis. Microarray data were confirmed by quantitative reverse transcription polymerase chain reaction and whole-mount in situ hybridisation.

RESULTS

Microarray analysis revealed expression of 33,793 genes. Of these, 931 genes were found to be equally expressed in both the dorsal and ventral parts of the tongue. On limiting the fold-change cut-off to over 1.5-fold, 725 genes were expressed over 1.5-fold in the ventral part and 1,672 in the dorsal part of the tongue. The qPCR and whole-mount in situ hybridisation revealed the expressions of angiopoietin 2 (Angpt2), fibroblast growth factor 18 (Fgf18), mesenchyme homeobox gene1 (Meox1), and SPARC-related modular calcium binding 2 (Smoc2) in the ventral part of the tongue.

CONCLUSIONS

Numerous signalling molecules can be selected from our microarray results to examine their roles in tongue development and disease model systems. In the near future, the selection of candidate genes and their functional evaluations will be performed through loss- and gain-of-function mutation studies.

Development and regeneration of periodontal supporting tissues

Periodontal tissues, including gingiva, cementum, periodontal ligament, and alveolar bone, play important roles in oral health. Under physiological conditions, periodontal tissues surround and support the teeth, maintaining the stability of the teeth and distributing the chewing forces. However, under pathological conditions, with the actions of various pathogenic factors, the periodontal tissues gradually undergo some irreversible changes, that is, gingival recession, periodontal ligament rupture, periodontal pocket formation, alveolar bone resorption, eventually leading to the loosening and even loss of the teeth. Currently, the regenerations of the periodontal tissues are still challenging. Therefore, it is necessary to study the development of the periodontal tissues, the principles and processes of which can be used to develop new strategies for the regeneration of periodontal tissues. This review summarizes the development of periodontal tissues and current strategies for periodontal healing and regeneration.

Neonatal Airway Abnormalities

Neonatal airway abnormalities are commonly encountered by the neonatologist, general pediatrician, maternal fetal medicine specialist, and otolaryngologist. This review article discusses common and rare anomalies that may be encountered, along with discussion of embryology, workup, and treatment. This article aims to provide a broad overview of neonatal airway anomalies to arm those caring for these children with a broad differential diagnosis and basic knowledge of how to manage basic and complex presentations.

A hierarchical vascularized engineered bone inspired by intramembranous ossification for mandibular regeneration

Mandibular defects caused by injuries, tumors, and infections are common and can severely affect mandibular function and the patient’s appearance. However, mandible reconstruction with a mandibular bionic structure remains challenging. Inspired by the process of intramembranous ossification in mandibular development, a hierarchical vascularized engineered bone consisting of angiogenesis and osteogenesis modules has been produced. Moreover, the hierarchical vascular network and bone structure generated by these hierarchical vascularized engineered bone modules match the particular anatomical structure of the mandible. The ultra-tough polyion complex has been used as the basic scaffold for hierarchical vascularized engineered bone for ensuring better reconstruction of mandible function. According to the results of in vivo experiments, the bone regenerated using hierarchical vascularized engineered bone is similar to the natural mandibular bone in terms of morphology and genomics. The sonic hedgehog signaling pathway is specifically activated in hierarchical vascularized engineered bone, indicating that the new bone in hierarchical vascularized engineered bone underwent a process of intramembranous ossification identical to that of mandible development. Thus, hierarchical vascularized engineered bone has a high potential for clinical application in mandibular defect reconstruction. Moreover, the concept based on developmental processes and bionic structures provides an effective strategy for tissue regeneration.

Micro-computed tomography assessment of bone structure in aging mice

High-resolution computed tomography (CT) is widely used to assess bone structure under physiological and pathological conditions. Although the analytic protocols and parameters for micro-CT (μCT) analyses in mice are standardized for long bones, vertebrae, and the palms in aging mice, they have not yet been established for craniofacial bones. In this study, we conducted a morphometric assessment of craniofacial bones, in comparison with long bones, in aging mice. Although age-related changes were observed in the microarchitecture of the femur, tibia, vertebra, and basisphenoid bone, and were more pronounced in females than in males, the microarchitecture of both the interparietal bone and body of the mandible, which develop by intramembranous ossification, was less affected by age and sex. By contrast, the condyle of the mandible was more affected by aging in males compared to females. Taken together, our results indicate that mouse craniofacial bones are uniquely affected by age and sex.

Type IA Oromandibular-Limb Hypogenesis Syndrome: A Case Report and A Case Update

Hypoglossia is a rare congenital anomaly resulting in a small rudimentary tongue. It is classified under the oromandibular-limb hypogenesis syndrome and can be found in isolation (Type IA) but is more often associated with other congenital disorders, such as limb defects. Isolated hypoglossia cases are rare, and while feeding disorders are common, in some cases, neonatal airway obstruction is the most problematic. In the present report, we discuss two cases of newborns presenting with hypoglossia without limb deformities or visceral anomalies: one new case and a 10-year update of a previously reported case. These two cases highlight the variability in presenting symptoms and the challenges in diagnosis and management of a rare clinical entity. We focus on the discussion of early diagnosis, multidisciplinary management, and shared decision-making, with emphasis on the current therapeutic strategies available to the clinician and their limitations during the neonatal period. Early surgical multivector mandibular distraction osteogenesis can be proposed with minimal short- and long-term morbidity, pending a consistent follow-up. This clinical entity will require multidisciplinary team care into adult years.

Hdac4 Regulates the Proliferation of Neural Crest-Derived Osteoblasts During Murine Craniofacial Development

Craniofacial development involves the regulation of a compendium of transcription factors, signaling molecules, and epigenetic regulators. Histone deacetylases (HDACs) are involved in the regulation of cell proliferation, differentiation, and homeostasis across a wide range of tissues, including the brain and the cardiovascular, muscular, and skeletal systems. However, the functional role of Hdac4 during craniofacial development remains unclear. In this study, we investigated the effects of knocking out Hdac4 on craniofacial skeletal development by conditionally disrupting the Hdac4 gene in cranial neural crest cells (CNCCs) using Cre-mediated recombination. Mice deficient for Hdac4 in CNCC-derived osteoblasts demonstrated a dramatic decrease in frontal bone formation. In vitro, pre-osteoblasts (MC3T3-E1 cells) lacking Hdac4 exhibited reduced proliferative activity in association with the dysregulation of cell cycle-related genes. These findings suggested that Hdac4 acts, at least in part, as a regulator of craniofacial skeletal development by positively regulating the proliferation of CNCC-derived osteoblasts.

Binder's phenotype with ankyloglossia: Report of a rare inherited association in an Indian female

Binder's syndrome, a rare congenital malformation of nasomaxillary complex, first described in 1962, has a hexad of characteristic clinical and radiographic features consisting of arhinoid face, intermaxillary hypoplasia with malocclusion, abnormal position of nasal bones, atrophy of nasal mucosa, reduced or absent anterior nasal spine and hypoplastic/absent frontal sinus. The typical facies due to mid-face hypoplasia may also be accompanied by other midline malformations such as cleft palate, spinal, skeletal and cardiac abnormalities. It is usually sporadic, of unknown etiology although various environmental and genetic mechanisms are implicated due to few familial cases predominantly in the Swedish population. A case of inherited Binder's syndrome is presented in an Indian female patient with an unusual finding of ankyloglossia (AG). The development of the anterior nasal spine and AG are chronologically related as they both occur during the 5^th–6^th weeks of gestation. The possible etiopathogenetic mechanisms for this rare association are reviewed.

Osteogenic and angiogenic profiles of the palatal process of the maxilla and the palatal process of the palatine bone

Hard palate consists anteriorly of the palatal process of the maxilla (ppmx) and posteriorly of the palatal process of the palatine (ppp). Currently, palatal osteogenesis is receiving increasing attention. This is the first study to provide an overview of the osteogenesis process of the mouse hard palate. We found that the period in which avascular mesenchymal condensation becomes a vascularized bone structure corresponds to embryonic day (E) 14.5 to E16.5 in the hard palate. The ppmx and ppp differ remarkably in morphology and molecular respects during osteogenesis. Osteoclasts in the ppmx and ppp are heterogeneous. There was a multinucleated giant osteoclast on the bone surface at the lateral-nasal side of the ppmx, while osteoclasts in the ppp were more abundant and adjacent to blood vessels but were smaller and had fewer nuclei. In addition, bone remodeling in the hard palate was asymmetric and exclusively occurred on the nasal side of the hard palate at E18.5. During angiogenesis, CD31-positive endothelial cells were initially localized in the surrounding of palatal mesenchymal condensation and then invaded the condensation in a sprouting fashion. At the transcriptome level, we found 78 differentially expressed genes related to osteogenesis and angiogenesis between the ppmx and ppp. Fifty-five related genes were up/downregulated from E14.5 to E16.5. Here, we described the morphogenesis and the heterogeneity in the osteogenic and angiogenic genes profiles of the ppmx and ppp, which are significant for subsequent studies of normal and abnormal subjects.

Comparison of Tendon Development Versus Tendon Healing and Regeneration

Tendon is a vital connective tissue in human skeletal muscle system, and tendon injury is very common and intractable in clinic. Tendon development and repair are two closely related but still not fully understood processes. Tendon development involves multiple germ layer, as well as the regulation of diversity transcription factors (Scx et al.), proteins (Tnmd et al.) and signaling pathways (TGFβ et al.). The nature process of tendon repair is roughly divided in three stages, which are dominated by various cells and cell factors. This review will describe the whole process of tendon development and compare it with the process of tendon repair, focusing on the understanding and recent advances in the regulation of tendon development and repair. The study and comparison of tendon development and repair process can thus provide references and guidelines for treatment of tendon injuries.