FGF signalling in craniofacial development and developmental disorders

Genetic factors underlying Mandibular prognathism: insights from recent human and animal studies

This review aims to provide an updated overview of the genetic etiology of mandibular prognathism (MP), focusing on recent research efforts, to summarize the findings from human studies utilizing genome-wide association studies (GWAS), candidate gene analyses, whole exome sequencing (WES) and single-nucleotide polymorphisms (SNPs) in relation to MP. Additionally, insights from animal studies are incorporated to understand the molecular mechanisms underlying mandibular development and the pathogenesis of MP. A comprehensive literature search was conducted to identify relevant studies on the genetic basis of MP. Human studies employing GWAS, candidate gene analyses, and SNPs investigations were reviewed. Animal studies, including European seabass, zebrafish, transgenic mouse and miniature horse were also examined to provide additional insights into mandibular development and MP's pathogenesis using GWAS, WES, transgenic techniques, morpholino antisense oligos and homozygote. Human studies have identified multiple loci and genes potentially associated with MP through GWAS, candidate gene analyses, and SNP investigations. Animal models have contributed valuable information about the molecular mechanisms involved in mandibular development and the development of MP. Recent research efforts have enhanced our understanding of the genetic etiology of MP. Integration of genetic studies with functional analyses has shed light on key signaling pathways and gene regulatory networks implicated in MP.

Understanding the Role of MicroRNAs in Congenital Tooth Agenesis: A Multi-omics Integration

This study employs a comprehensive multi-omics approach to investigate the regulatory roles of specific microRNAs (miRNAs) in Congenital Tooth Agenesis (CTA). A total of 58 miRNAs associated with tooth diseases, cancer, and bone development were initially identified through a literature review and analyzed using bioinformatics. Based on target prediction and network analysis, eight miRNAs with strong connectivity and common target genes were shortlisted for further investigation. Blood samples from 10 CTA patients and 5 healthy controls were analyzed for miRNA expression using stem-loop RT-PCR. Four miRNAs-hsa-miR-218-5p, hsa-miR-15b-5p, hsa-miR-200b-3p, and hsa-let-7a-3p-were identified as significantly differentially expressed, marking their first reported involvement in CTA. Notably, hsa-miR-218-5p and hsa-let-7a-3p emerged as novel regulators with no prior associations with CTA or tooth development. To address the limitations of a small sample size, a multi-omics strategy was employed to validate these findings, integrating miRNA expression data with whole exome sequencing (WES), gene expression panels, and metabolomic profiling. The analysis confirmed the association of these four miRNAs with CTA and highlighted their involvement in critical biological pathways such as Wnt signaling, FGF signaling, and PI3 kinase pathways, which are essential for cellular proliferation, differentiation, and tissue morphogenesis. Importantly, the identification of these miRNAs in blood samples, rather than traditional dental tissues, highlights a minimally invasive approach that could aid in the early detection, therapeutic targeting, and personalized management of dental anomalies.

Polymorphisms in SOX2/FGFR1 are associated with skeletal class III maxillary and mandibular dimensions: A preliminary study

Objectives

The aim of the present study was to assess the association between class III malocclusion and genetic polymorphisms in two genes: SOX2 (rs4434184) and FGFR1 (rs881301).

Methods

A total of 60 patients, 30 with skeletal class I and 30 with skeletal class III malocclusion, were included in this study. Salivary DNA samples were collected and analyzed with Sanger sequencing. Digital tracing was performed on lateral cephalometric radiographs loaded into AutoCAD software (Version 2017) to assess the anteroposterior and vertical relationships of the maxillary and mandibular arches. Genotype distribution was compared between groups with the chi-square test to assess Hardy-Weinberg equilibrium. Multiple logistic regression analysis was conducted.

Results

The SOX2 rs4434184 polymorphism was associated with longer mandibular length. In contrast, shorter maxillary length, longer mandibular length, and hypodivergent face were correlated with the rs881301 polymorphism in FGFR1. New polymorphisms, including FGFR1 rs881300, rs881299, and rs7829058, have been identified in association with various phenotypes. Notably, rs881300 and rs7829058 displayed a substantial association with skeletal class III, whereas rs881299 revealed a significant association with a hypodivergent face and longer mandibular anteroposterior length.

Conclusions

A potential association was observed between class III skeletal malocclusion-related traits and polymorphisms of SOX2 (rs4434184) and FGFR1 (rs881301, rs881300, rs881299, and rs7829058). This finding holds promise for enhancing skeletal prediction and informing orthodontic treatment planning.

Immobile Integrin Signaling Transit and Relay Nodes Organize Mechanosignaling through Force-Dependent Phosphorylation in Focal Adhesions

Transmembrane signaling receptors, such as integrins, organize as nanoclusters that provide several advantages, including increasing avidity, sensitivity (increasing the signal-to-noise ratio), and robustness (signaling threshold) of the signal in contrast to signaling by single receptors. Furthermore, compared to large micron-sized clusters, nanoclusters offer the advantage of rapid turnover for the disassembly of the signal. However, whether nanoclusters function as signaling hubs remains poorly understood. Here, we employ fluorescence nanoscopy combined with photoactivation and photobleaching at subdiffraction limited resolution of ∼100 nm length scale within a focal adhesion to examine the dynamics of diverse focal adhesion proteins. We show that (i) subregions of focal adhesions are enriched in an immobile population of integrin β3 organized as nanoclusters, which (ii) in turn serve to organize nanoclusters of associated key adhesome proteins-vinculin, focal adhesion kinase (FAK) and paxillin, demonstrating that signaling proceeds by formation of nanoclusters rather than through individual proteins. (iii) Distinct focal adhesion protein nanoclusters exhibit distinct protein dynamics, which is closely correlated to their function in signaling. (iv) Long-lived nanoclusters function as signaling hubs─wherein immobile integrin nanoclusters organize phosphorylated FAK to form stable nanoclusters in close proximity to them, which are disassembled in response to inactivation signal by removal of force and in turn activation of phosphatase PTPN12. (v) Signaling takes place in response to external signals such as force or geometric arrangement of the nanoclusters and when the signal is removed, these nanoclusters disassemble. We term these functional nanoclusters as integrin signaling transit and relay nodes (STARnodes). Taken together, these results demonstrate that integrin STARnodes seed signaling downstream of the integrin receptors by organizing hubs of signaling proteins (FAK, paxillin, vinculin) to relay the incoming signal intracellularly and bring about robust function.

Effects of FGFR2b-ligand signaling on pancreatic branching morphogenesis and postnatal islet function

Pancreatic development is a complex process vital for maintaining metabolic balance, requiring intricate interactions among different cell types and signaling pathways. Fibroblast growth factor receptors 2b (FGFR2b)-ligands signaling from adjacent mesenchymal cells is crucial in initiating pancreatic development and differentiating exocrine and endocrine cells through a paracrine mechanism. However, the precise critical time window that affects pancreatic development remains unclear. To explore the roles of FGFR2b-ligands and identify the narrow window of time during which FGFR2b-ligand signaling affects pancreatic development, we used an inducible mouse model to control the expression of soluble dominant-negative FGFR2b (sFGFR2b) at various stages of pancreatic development. Our findings revealed a significant effect of FGFR2b-ligand signaling on epithelial morphology, lumen formation, and pancreatic branching during primary and secondary transition stages. Additionally, sFGFR2b expression reduced the number of Pdx1+ progenitor cells and altered the pancreatic islet structure. Furthermore, we examined the effect of mutation in FGF10, an FGFR2b ligand, on embryonic pancreatic β-cell function. FGF10 null mutant embryos exhibited reduced pancreatic size and a decrease number of islet-like structure. Although neonatal mice with haploinsufficiency for FGF10 exhibited abnormal glucose tolerance test results, indicating a potential diabetes predisposition, these abnormalities normalized with age, aligning with observations in wild type mice. Our study underscores the critical role of FGFR2b-ligand signaling in pancreatic development and postnatal islet function, offering insights into potential therapeutic targets for pancreatic disorders.

Downstream branches of receptor tyrosine kinase signaling act interdependently to shape the face

Background –

Previously we found that increasing fibroblast growth factor (FGF) signaling in the neural crest cells within the frontonasal process (FNP) of the chicken embryo caused dysmorphology that was correlated with reduced proliferation, disrupted cellular orientation, and lower MAPK activation but no change in PLCy and PI3K activation. This suggests RTK signaling may drive craniofacial morphogenesis through specific downstream effectors that affect cellular activities. In this study we inhibited three downstream branches of RTK signaling to determine their role in regulating cellular activities and how these changes affect morphogenesis of the FNP.

Results –

Small molecule inhibitors of MEK1/2, PI3K, and PLCy were delivered individually and in tandem to the right FNP of chicken embryos. All treatments caused asymmetric proximodistal truncation on the treated side and a mild expansion on the untreated side compared to DMSO control treated FNPs. Inhibiting each pathway caused similar decreased proliferation and disrupted cellular orientation, but did not affect apoptosis.

Conclusions –

Since RTK signaling is a ubiquitous and tightly regulated biochemical system we conclude that the downstream pathways are robust to developmental perturbation through redundant signaling systems.

Mandible development under gestational protein restriction: cellular and molecular mechanisms

Insufficient evidence regarding how maternal undernutrition affects craniofacial bone development persists. With its unique focus on the impact of gestational protein restriction on calvaria and mandible osteogenesis, this study aims to fill, at least in part, this gap. Female mice were mated and randomized into NP (normal protein) or LP (low protein) groups. On the 18th gestational day (GD), male embryos were collected and submitted to microtomography (µCT), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), PCR, and autophagy dynamic analyses. The study shows that the LP offspring exhibited lower body mass than the NP group, with µCT analysis revealing no volumetric differences in fetus's head. EDS analysis showed lower calcium and higher phosphorus percentages in mandibles and calvaria. SEM assessment evidenced higher hydroxyapatite crystal-like (HC) deposition on the calvaria surface in LP fetus. Conversely, lower HC deposition was observed on the mandible surface, suggesting delayed matrix mineralization in LP fetuses with a higher percentage of collagen fibers in the mandible bone. The autophagy process was reduced in the mesenchyme of LP fetuses. PCR array analysis of 84 genes revealed 27 genes with differential expression in the LP progeny-moreover, increased mRNA levels of Akt1, Mtor, Nfkb, and Smad1 in the LP offspring. In conclusion, the results suggest that gestational protein restriction anticipated bone differentiation in utero, before 18GD, where this process is reduced compared to the control, leading to the reduction in bone area at 15 postnatal day previously observed. These findings provide insights into the molecular and cellular mechanisms of mandible development and suggest potential implications for the Developmental Origins of Health and Disease (DOHaD).

Lacrimal Obstruction in Craniosynostosis: Anatomical and Genetic Risk Factors

PURPOSE

To investigate whether patients with craniosynostosis exhibit higher rates of nasolacrimal duct obstruction (NLDO) and to explore potential risk factors.

METHODS

Retrospective review including all craniosynostosis patients treated at both the Divisions of Ophthalmology and Plastic, Reconstructive, and Oral Surgery at The Children's Hospital of Philadelphia between 2009 and 2020 was conducted. Synostosis characteristics, lacrimal disorders, and genetic data were collected. Main outcome measures were the rate of NLDO and associations with anatomical and syndromic/genetic risk factors.

RESULTS

The total of 767 participants had a mean age of 2.8 ± 3.8 years, 465 (60.6%) were males, 485 (63.2%) had no syndromic association; 631 (82.3%) had one major suture involved, 128 (17%) had involvement of 2 to 4 major sutures, and 429 (55.9%) underwent craniofacial surgery. Forty-eight (6.2%) patients had NLDO, which more prevalent in the genetic/syndromic group (11.0% vs. 3.5%, respectively, p < 0.001), with the highest prevalence observed in patients with Apert syndrome (n = 4, 30.8%). The genetic variants most associated with NLDO were EFNB1 (n = 1, 100%) and FGFR2 (n = 6, 19.4%). There was no association between NLDO and the number or types of sutures involved or a history of craniofacial surgery.

CONCLUSIONS

Nasolacrimal duct obstruction is more common in patients with craniosynostosis compared to the general population. Having a putative syndrome or a putative genetic variant and female sex were risk factors for NLDO. Ophthalmic evaluations for all craniosynostosis patients and careful assessments of any symptoms of tearing are recommended.

Skeletal dysmorphology and mineralization defects in Fgf20 KO mice

Introduction

Fibroblast growth factor 20 (Fgf20), a member of the Fgf9 subfamily, was identified as an important regulator of bone differentiation and homeostasis processes. However, the role of Fgf20 in bone physiology has not been approached yet. Here we present a comprehensive bone phenotype analysis of mice with functional ablation of Fgf20.

Methods

The study conducts an extensive analysis of Fgf20 knockout mice compared to controls, incorporating microCT scanning, volumetric analysis, Fgf9 subfamily expression and stimulation experiment and histological evaluation.

Results

The bone phenotype could be detected especially in the area of​ the lumbar and caudal part of the spine and in fingers. Regarding the spine, Fgf20-/- mice exhibited adhesions of the transverse process of the sixth lumbar vertebra to the pelvis as well as malformations in the distal part of their tails. Preaxial polydactyly and polysyndactyly in varying degrees of severity were also detected. High resolution microCT analysis of distal femurs and the fourth lumbar vertebra showed significant differences in structure and mineralization in both cortical and trabecular bone. These findings were histologically validated and may be associated with the expression of Fgf20 in chondrocytes and their progenitors. Moreover, histological sections demonstrated increased bone tissue formation, disruption of Fgf20-/- femur cartilage, and cellular-level alterations, particularly in osteoclasts. We also observed molar dysmorphology, including root taurodontism, and described variations in mineralization and dentin thickness.

Discussion

Our analysis provides evidence that Fgf20, together with other members of the Fgf9 subfamily, plays a crucial regulatory role in skeletal development and bone homeostasis.

FGF signaling modulates mechanotransduction/WNT signaling in progenitors during tooth root development

Stem/progenitor cells differentiate into different cell lineages during organ development and morphogenesis. Signaling pathway networks and mechanotransduction are important factors to guide the lineage commitment of stem/progenitor cells during craniofacial tissue morphogenesis. Here, we used tooth root development as a model to explore the roles of FGF signaling and mechanotransduction as well as their interaction in regulating the progenitor cell fate decision. We show that Fgfr1 is expressed in the mesenchymal progenitor cells and their progeny during tooth root development. Loss of Fgfr1 in Gli1+ progenitors leads to hyperproliferation and differentiation, which causes narrowed periodontal ligament (PDL) space with abnormal cementum/bone formation leading to ankylosis. We further show that aberrant activation of WNT signaling and mechanosensitive channel Piezo2 occurs after loss of FGF signaling in Gli1-CreER;Fgfr1fl/fl mice. Overexpression of Piezo2 leads to increased osteoblastic differentiation and decreased Piezo2 leads to downregulation of WNT signaling. Mechanistically, an FGF/PIEZO2/WNT signaling cascade plays a crucial role in modulating the fate of progenitors during root morphogenesis. Downregulation of WNT signaling rescues tooth ankylosis in Fgfr1 mutant mice. Collectively, our findings uncover the mechanism by which FGF signaling regulates the fate decisions of stem/progenitor cells, and the interactions among signaling pathways and mechanotransduction during tooth root development, providing insights for future tooth root regeneration.

Nano-clusters of ligand-activated integrins organize immobile, signalling active, nano-clusters of phosphorylated FAK required for mechanosignaling in focal adhesions

Transmembrane signalling receptors, such as integrins, organise as nanoclusters that are thought to provide several advantages including, increasing avidity, sensitivity (increasing the signal-to-noise ratio) and robustness (signalling above a threshold rather than activation by a single receptor) of the signal compared to signalling by single receptors. Compared to large micron-sized clusters, nanoclusters offer the advantage of rapid turnover for the disassembly of the signal. However, if nanoclusters function as signalling hubs remains poorly understood. Here, we employ fluorescence nanoscopy combined with photoactivation and photobleaching at sub-diffraction limited resolution of ~100nm length scale within a focal adhesion to examine the dynamics of diverse focal adhesion proteins. We show that (i) subregions of focal adhesions are enriched in immobile population of integrin β3 organised as nanoclusters, which (ii) in turn serve to organise nanoclusters of associated key adhesome proteins- vinculin, focal adhesion kinase (FAK) and paxillin, demonstrating that signalling proceeds by formation of nanoclusters rather than through individual proteins. (iii) Distinct focal adhesion protein nanoclusters exhibit distinct dynamics dependent on function. (iv) long-lived nanoclusters function as signalling hubs- wherein phosphorylated FAK and paxillin formed stable nanoclusters in close proximity to immobile integrin nanoclusters which are disassembled in response to inactivation signal by phosphatase PTPN12 (v) signalling takes place in response to an external signal such as force or geometric arrangement of the nanoclusters and when the signal is removed, these nanoclusters disassemble. Taken together, these results demonstrate that signalling downstream of transmembrane receptors is organised as hubs of signalling proteins (FAK, paxillin, vinculin) seeded by nanoclusters of the transmembrane receptor (integrin).

Craniofacial anomalies in a murine model of heterozygous fibroblast growth factor 10 gene mutation

OBJECTIVE

Dysregulation of Fibroblast Growth Factor 10 (FGF10), a member of the family of Fibroblast Growth Factor (FGF) proteins, has been implicated in craniofacial and dental anomalies, including craniosynostosis, cleft palate, and Lacrimo-Auriculo-Dento-Digital Syndrome. The aim of this murine study was to assess the craniofacial and dental phenotypes associated with a heterozygous FGF10 gene (FGF10+/- ) mutation at skeletal maturity.

METHODS

Skulls of 40 skeletally mature mice, comprising two genotypes (heterozygous FGF10+/- mutation, n = 22; wildtype, n = 18) and two sexes (male, n = 23; female, n = 17), were subjected to micro-computed tomography. Landmark-based linear dimensions were measured for the cranial vault, maxilla, mandible, and first molar teeth. Multivariate analysis of variance was performed to assess whether there were significant differences in the craniofacial and dental structures between genotypes and sexes.

RESULTS

The craniomaxillary skeleton and the first molar teeth were smaller in the FGF10+/- mice (P < .05), but the mandible was unaffected. Sex did not have a significant effect on these structures (P > .05). Cranial sutural defects were noted in 5/22 (22.7%) mutant versus 2/18 (11.1%) wildtype mice, and cleft palate in only one (4.5%) mutant mouse. None of the mice displayed craniosynostosis, expansive bony lesions, bifid condyles, or impacted teeth.

CONCLUSION

The FGF10+/- mutation was associated with craniomaxillary skeletal hypoplasia that probably arose from deficient (delayed) intramembranous ossification of the sutured bones. Overall, the skeletal and dental data suggest that the FGF10 gene plays an important role in the aetiology of craniofacial dysmorphology and malocclusion.

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.

FGF signaling in cranial suture development and related diseases

Suture mesenchymal stem cells (SMSCs) are a heterogeneous stem cell population with the ability to self-renew and differentiate into multiple cell lineages. The cranial suture provides a niche for SMSCs to maintain suture patency, allowing for cranial bone repair and regeneration. In addition, the cranial suture functions as an intramembranous bone growth site during craniofacial bone development. Defects in suture development have been implicated in various congenital diseases, such as sutural agenesis and craniosynostosis. However, it remains largely unknown how intricate signaling pathways orchestrate suture and SMSC function in craniofacial bone development, homeostasis, repair and diseases. Studies in patients with syndromic craniosynostosis identified fibroblast growth factor (FGF) signaling as an important signaling pathway that regulates cranial vault development. A series of in vitro and in vivo studies have since revealed the critical roles of FGF signaling in SMSCs, cranial suture and cranial skeleton development, and the pathogenesis of related diseases. Here, we summarize the characteristics of cranial sutures and SMSCs, and the important functions of the FGF signaling pathway in SMSC and cranial suture development as well as diseases caused by suture dysfunction. We also discuss emerging current and future studies of signaling regulation in SMSCs.

FGF signaling regulates salivary gland branching morphogenesis by modulating cell adhesion

Loss of FGF signaling leads to defects in salivary gland branching, but the mechanisms underlying this phenotype remain largely unknown. We disrupted expression of Fgfr1 and Fgfr2 in salivary gland epithelial cells and found that both receptors function coordinately in regulating branching. Strikingly, branching morphogenesis in double knockouts is restored by Fgfr1 and Fgfr2 (Fgfr1/2) knock-in alleles incapable of engaging canonical RTK signaling, suggesting that additional FGF-dependent mechanisms play a role in salivary gland branching. Fgfr1/2 conditional null mutants showed defective cell-cell and cell-matrix adhesion, both of which have been shown to play instructive roles in salivary gland branching. Loss of FGF signaling led to disordered cell-basement membrane interactions in vivo as well as in organ culture. This was partially restored upon introducing Fgfr1/2 wild-type or signaling alleles that are incapable of eliciting canonical intracellular signaling. Together, our results identify non-canonical FGF signaling mechanisms that regulate branching morphogenesis through cell-adhesion processes.

TGF-β signaling and Creb5 cooperatively regulate Fgf18 to control pharyngeal muscle development

The communication between myogenic cells and their surrounding connective tissues is indispensable for muscle morphogenesis. During late embryonic development in mice, myogenic progenitors migrate to discrete sites to form individual muscles. The detailed mechanism of this process remains unclear. Using mouse levator veli palatini (LVP) development as a model, we systematically investigated how a distinct connective tissue subpopulation, perimysial fibroblasts, communicates with myogenic cells to regulate mouse pharyngeal myogenesis. Using single-cell RNAseq data analysis, we identified that TGF-β signaling is a key regulator for the perimysial fibroblasts. Loss of TGF-β signaling in the neural crest-derived palatal mesenchyme leads to defects in perimysial fibroblasts and muscle malformation in the soft palate in Osr2Cre;Tgfbr1fl/fl mice. In particular, Creb5, a transcription factor expressed in the perimysial fibroblasts, cooperates with TGF-β signaling to activate expression of Fgf18. Moreover, Fgf18 supports pharyngeal muscle development in vivo and exogenous Fgf18 can partially rescue myogenic cell numbers in Osr2Cre;Tgfbr1fl/fl samples, illustrating that TGF-β-regulated Fgf18 signaling is required for LVP development. Collectively, our findings reveal the mechanism by which TGF-β signaling achieves its functional specificity in defining the perimysial-to-myogenic signals for pharyngeal myogenesis.

Targeting fibroblast growth factor receptors causes severe craniofacial malformations in zebrafish larvae

Background and Objective

A key pathway controlling skeletal development is fibroblast growth factor (FGF) and FGF receptor (FGFR) signaling. Major regulatory functions of FGF signaling are chondrogenesis, endochondral and intramembranous bone development. In this study we focus on fgfr2, as mutations in this gene are found in patients with craniofacial malformations. The high degree of conservation between FGF signaling of human and zebrafish (Danio rerio) tempted us to investigate effects of the mutated fgfr2 ^sa10729 allele in zebrafish on cartilage and bone formation.

Methods

We stained cartilage and bone in 5 days post fertilization (dpf) zebrafish larvae and compared mutants with wildtypes. We also determined the expression of genes related to these processes. We further investigated whether pharmacological blocking of all FGFRs with the inhibitor BGJ398, during 0-12 and 24-36 h post fertilization (hpf), affected craniofacial structure development at 5 dpf.

Results

We found only subtle differences in craniofacial morphology between wildtypes and mutants, likely because of receptor redundancy. After exposure to BGJ398, we found dose-dependent cartilage and bone malformations, with more severe defects in fish exposed during 0-12 hpf. These results suggest impairment of cranial neural crest cell survival and/or differentiation by FGFR inhibition. Compensatory reactions by upregulation of fgfr1a, fgfr1b, fgfr4, sp7 and dlx2a were found in the 0-12 hpf group, while in the 24-36 hpf group only upregulation of fgf3 was found together with downregulation of fgfr1a and fgfr2.

Conclusions

Pharmacological targeting of FGFR1-4 kinase signaling causes severe craniofacial malformations, whereas abrogation of FGFR2 kinase signaling alone does not induce craniofacial skeletal abnormalities. These findings enhance our understanding of the role of FGFRs in the etiology of craniofacial malformations.

Keratinocyte Growth Factor Stimulates Growth of p75+ Neural Crest Lineage Cells During Middle Ear Cholesteatoma Formation in Mice

During development, cranial neural crest (NC) cells display a striking transition from collective to single-cell migration and undergo a mesenchymal-to-epithelial transformation to form a part of the middle ear epithelial cells (MEECs). While MEECs derived from NC are known to control homeostasis of the epithelium and repair from otitis media, paracrine action of keratinocyte growth factor (KGF) promotes the growth of MEECs and induces middle ear cholesteatoma (cholesteatoma). The animal model of cholesteatoma was previously established by transfecting a human KGF-expression vector. Herein, KGF-inducing cholesteatoma was studied in Wnt1-Cre/Floxed-enhanced green fluorescent protein (EGFP) mice that conditionally express EGFP in the NC lineages. The cytokeratin 14-positive NC lineage expanded into the middle ear and formed cholesteatoma. Moreover, the green fluorescent protein-positive NC lineages comprising the cholesteatoma tissue expressed p75, an NC marker, with high proliferative activity. Similarly, a large number of p75-positive cells were observed in human cholesteatoma tissues. Injections of the immunotoxin murine p75-saporin induced depletion of the p75-positive NC lineages, resulting in the reduction of cholesteatoma in vivo. The p75 knockout in the MEECs had low proliferative activity with or without KGF protein in vitro. Controlling p75 signaling may reduce the proliferation of NC lineages and may represent a new therapeutic target for cholesteatoma.

Decoding the Human Face: Progress and Challenges in Understanding the Genetics of Craniofacial Morphology

Variations in the form of the human face, which plays a role in our individual identities and societal interactions, have fascinated scientists and artists alike. Here, we review our current understanding of the genetics underlying variation in craniofacial morphology and disease-associated dysmorphology, synthesizing decades of progress on Mendelian syndromes in addition to more recent results from genome-wide association studies of human facial shape and disease risk. We also discuss the various approaches used to phenotype and quantify facial shape, which are of particular importance due to the complex, multipartite nature of the craniofacial form. We close by discussing how experimental studies have contributed and will further contribute to our understanding of human genetic variation and then proposing future directions and applications for the field.

COL1A1 and FGFR2 Single-Nucleotide Polymorphisms Found in Class II and Class III Skeletal Malocclusions in Javanese Population

OBJECTIVE

 The aim of this article is to analyze and compare the presence of single-nucleotide polymorphisms (SNPs) of COL1A1 and FGFR2 in class II and class III Javanese populations.

MATERIALS AND METHODS

 Cephalometric radiographs from total 63 patients of class II and III were analyzed. SNP analysis was performed based on both COL1A1 and FGFR2 sequences amplified from total DNA of patients' fresh blood. Principal component analysis was done to calculate the data and find the correlation of the cephalometric indicators influenced by each mutation. t-test and Mann-Whitney analysis were performed to check the significance of differences occurred in each studied parameter (p < 0.05).

RESULT

 There were three COL1A1 SNPs found in class II and only two in class III, while three FGFR2 SNPs found in both classes. Class II phenotype seemed to be strongly influenced by Y-axis and mandibular plane angle, while class III by lower gonial angle and mandibular plane angle.

CONCLUSION

 Based on this study, we suggest that rs2249492 of COL1A1 and rs2981582 of FGFR2 play important roles in class III, while rs2277632 of COL1A1 and rs2981582 of FGFR2 play important role in class II skeletal malocclusion in Javanese population.

Comprehensive Genetic Evaluation of Bulgarian Children with Syndromic Craniosynostosis

Syndromic craniosynostosis (SC) is a genetically determined premature closure of one or more of the cranial sutures, which may result in severe dysmorphism, increased intracranial pressure along with many other clinical manifestations. The considerable risk of complications along with their significant incidence makes these cranial deformations an important medical problem. Aiming to elucidate the complex genetic etiology of syndromic craniosynostosis, we investigated 39 children, screened systematically with a combination of conventional cytogenetic analysis, multiplex ligation-dependent probe amplification (MLPA) and array-based comparative genomic hybridisation (aCGH). Pathological findings were established in 15.3% (6/39) of the cases using aCGH, in 7.7% (3/39) using MLPA and 2.5% (1/39) using conventional karyotyping. About 12.8% (5/39) of the patients with normal karyotype carried submicroscopic chromosomal rearrangements. Duplications were found to be more common than deletions. Conclusion: The systematic genetic evaluation of children with SC revealed a high prevalence of submicrosopic chromosomal rearrangements (most commonly duplications). This suggests the leading role of those defects in the pathogenesis of syndromic craniosynostosis. The genetic complexity of SC was reaffirmed by the dis Bulgaria covery of pathological findings in various chromosomal regions. Certain genes were discussed in conjunction with craniosynostosis.

Evaluation of dental maturity in Muenke syndrome, Saethre-Chotzen syndrome, and TCF12-related craniosynostosis

OBJECTIVES

To determine whether dental maturity (dental development) was delayed in patients with Muenke syndrome, Saethre-Chotzen syndrome, and TCF12-related craniosynostosis, compared with a Dutch control group without syndromes.

MATERIALS AND METHODS

This study included 60 patients (38 patients with Muenke syndrome, 17 patients with Saethre-Chotzen syndrome, and 5 with TCF12-related craniosynostosis), aged 5.8-16.8 years that were treated at the Department of Oral Maxillofacial Surgery, Special Dental Care, and Orthodontics, in Sophia Children's Hospital, Erasmus University Medical Center, Rotterdam, the Netherlands. Dental age was calculated according to Demirjian's index of dental maturity. The control group included 451 children without a syndrome.

RESULTS

Compared with the control group, dental development was delayed by an average of one year in 5- to 8-year-old patients with Muenke syndrome (P = 0.007) and in 8- to 10-year-old patients with Saethre-Chotzen syndrome (P = 0.044), but not in patients with TCF12-related craniosynostosis.

CONCLUSIONS

Our results indicated that dental development was delayed by one year, on average, in patients with Muenke syndrome and Saethre-Chotzen syndrome, compared with a Dutch control group without syndromes.

IMPLICATIONS

Our findings have improved the understanding of dental development in patients with Muenke and Saethre-Chotzen syndrome. These results can provide guidance on whether the orthodontist needs to consider growth disturbances related to dental development.

Spatiotemporal Expression Patterns of Critical Genes Involved in FGF Signaling During Morphogenesis and Odontogenesis of Deciduous Molars in Miniature Pigs

The fibroblast growth factor (FGF) pathway plays an important role in epithelial-mesenchymal interactions during tooth development. Nevertheless, how the ligands, receptors, and antagonists of the FGF pathway are involved in epithelial-mesenchymal interactions remains largely unknown. Miniature pigs exhibit tooth anatomy and replacement patterns like those in humans and hence can serve as large animal models. The present study investigated the spatiotemporal expression patterns of critical genes encoding FGF ligands (FGF3, FGF4, FGF7, and FGF9), antagonists (SPRY2 and SPRY4) and receptors (FGFR1, FGFR2, and FGFR3) in the third deciduous molars of miniature pigs at the cap (embryonic day 40, E40), early bell (E50), and late bell (E60) stages. The results of in situ hybridization (ISH) with tyramide signal amplification and of qRT-PCR analysis revealed increased expression of FGF7, FGFR1, FGFR2, and SPRY4 in dental epithelium and of FGF7 and FGFR1 in mesenchyme from E40 to E50. In contrast, the results revealed decreased expression of FGF3, FGF4, FGF9, and FGFR3 in dental epithelium and of FGF4, FGF9, FGFR2, and FGFR3 in the mesenchyme from E40 to E60. Mesenchyme signals of FGF3, FGF4, FGF7, SPRY2, FGFR2, and FGFR3 were concentrated in the odontoblast layer from E50 to E60. The distinct expression patterns of these molecules indicated elaborate regulation during dental morphogenesis. Our results provide a foundation for further investigation into fine-tuning dental morphogenesis and odontogenesis by controlling interactions between dental epithelium and mesenchyme, thus promoting tooth regeneration in large mammals.

Expression pattern of Ptch2 in mouse embryonic maxillofacial development

Embryogenesis is modulated by numerous complex signaling cascades, which are essential for normal development. The Hedgehog (Hh) signaling pathway is part of these central cascades. As a homolog of Patched (Ptch)-1, Ptch2 initially did not appear to be as important as Ptch1. Recent reports have revealed that Ptch2 plays a crucial role in ligand-dependent feedback inhibition of Hh signaling in vertebrates. The role of Ptch2 in facial development remains unclear. Here, we investigated the detailed expression pattern of Ptch2 during craniofacial development in murine embryos based on in situ hybridization (ISH) studies of whole-mounts and sections, immunohistochemistry (IHC), and quantitative real-time PCR. We found that both Ptch2 mRNA and protein expression increased in a dynamic pattern in the facial development at mouse embryonic days 11-14.5. Moreover, distinct expression of Ptch2 was observed in the structures of the facial region, such as the tooth germ, Meckel's cartilage, and the follicles of vibrissae. These data, combined with our work in the macrostomia family, suggest that Ptch2 may play a critical role in facial development.

Does the association between abnormal anatomy of the skull base and cerebellar tonsillar position also exist in syndromic craniosynostosis?

PURPOSE

Cerebellar tonsillar herniation (TH) occurs frequently in syndromic craniosynostosis; however, the exact pathogenesis is unknown. This study evaluates the association between skull base deformities and TH in syndromic craniosynostosis.

METHODS

Retrospective study MRI study comparing syndromic craniosynostosis to controls. Measured parameters included clivus length, skull base angle, Boogard's angle, foramen magnum area, and cerebellar tonsillar position (TP). The association between skull base parameters and TP was evaluated with linear mixed models, correcting for age and risk factors for TH in craniosynostosis (hydrocephalus, intracranial hypertension, craniocerebral disproportion, and lambdoid synostosis).

RESULTS

Two hundred and eighty-two scans in 145 patients were included, and 146 scans in 146 controls. The clivus was smaller at birth, and its growth was retarded in all syndromes. The skull base angle was smaller at birth in Apert and Crouzon syndromes, and the evolution through time was normal. Boogard's angle was smaller at birth in Apert syndrome, and its evolution was disturbed in Apert and Saethre-Chotzen syndromes. The foramen magnum was smaller at birth in Crouzon and Saethre-Chotzen syndromes, and its growth was disturbed in Apert, Crouzon, and Saethre-Chotzen syndromes. TP was higher at birth in Apert syndrome, but lowered faster. In Crouzon syndrome, TP was lower at birth and throughout life. A smaller clivus and larger foramen magnum were associated with a lower TP in controls (p<0.001, p=0.007), and in Crouzon syndrome, this applied to only foramen magnum size (p=0.004).

CONCLUSION

The skull base and its growth are significantly different in syndromic craniosynostosis compared to controls. However, only foramen magnum area is associated with TP in Crouzon syndrome.

Targeted sequencing of NOTCH signaling pathway genes and association analysis of variants correlated with mandibular prognathism

Introduction

The purpose of this study was to systematically identify variants in NOTCH signaling pathway genes that correlate with mandibular prognathism (MP) in the general Chinese population.

Methods

Targeted sequencing of NOTCH signaling pathway genes was conducted in 199 MP individuals and 197 class I malocclusion control individuals. The associations of common and rare variants with MP, cephalometric parameters, and continuous cephalometric phenotypes were analyzed by principal component (PC) analysis. The associations between rare variants and MP were tested for each gene.

Results

Six SNPs, including rs415929, rs520688, and rs423023 in an exonic region of NOTCH4; rs1044006 in an exonic region of NOTCH3; rs1051415 in an exonic region of JAG1; and rs75236173 in the 3′-untranslated region (3′-UTR) of NUMB were associated with MP (P < 0.05). One common variant, rs1051415, in an exonic region of JAG1 was significantly related to PC1 (P  = 3.608 × 10^− 4), which explained 24.3% of the overall phenotypic variation observed and corresponded to the sagittal mandibular position towards the maxilla, ranging from a posterior positioned mandible to an anterior positioned mandible. Additionally, 41 other variants were associated with PC1–5 (P  <  0.05). With respect to rare variant analysis, variants within the EP300, NCOR2, and PSEN2 gene showed an association with MP (t   < 0 .05).

Conclusions

An association between NOTCH signaling pathway genes and MP has been identified.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13005-021-00268-0.

Tissue interactions, cell signaling and transcriptional control in the cranial mesoderm during craniofacial development

The cranial neural crest and the cranial mesoderm are the source of tissues from which the bone and cartilage of the skull, face and jaws are constructed. The development of the cranial mesoderm is not well studied, which is inconsistent with its importance in craniofacial morphogenesis as a source of precursor tissue of the chondrocranium, muscles, vasculature and connective tissues, mechanical support for tissue morphogenesis, and the signaling activity that mediate interactions with the cranial neural crest. Phenotypic analysis of conditional knockout mouse mutants, complemented by the transcriptome analysis of differentially enriched genes in the cranial mesoderm and cranial neural crest, have identified signaling pathways that may mediate cross-talk between the two tissues. In the cranial mesenchyme, Bmp4 is expressed in the mesoderm cells while its signaling activity could impact on both the mesoderm and the neural crest cells. In contrast, Fgf8 is predominantly expressed in the cranial neural crest cells and it influences skeletal development and myogenesis in the cranial mesoderm. WNT signaling, which emanates from the cranial neural crest cells, interacts with BMP and FGF signaling in monitoring the switch between tissue progenitor expansion and differentiation. The transcription factor Twist1, a critical molecular regulator of many aspects of craniofacial development, coordinates the activity of the above pathways in cranial mesoderm and cranial neural crest tissue compartments.

Expression Analysis of FGF/FGFR and FOX Family Proteins in Mucosal Tissue Obtained from Orofacial Cleft-Affected Children

Orofacial clefts affect hundreds of thousands of children worldwide annually and are usually corrected by a series of surgeries extending to childhood. The underlying mechanisms that lead to clefts are still unknown, mainly because of the multifactorial etiology and the myriad of interactions between genes and environmental factors. In the present study, we investigated the role and expression of candidate genes belonging to the FGF/FGFR signaling pathway and FOX family in tissue material obtained from 12 pediatric patients undergoing cleft correction surgery. The expression was investigated using immunohistochemistry (IHC) and chromogenic in-situ hybridization (CISH) in three cell/tissue types-epithelial cells, connective tissue, and endothelial cells. We found elevated expression of FGFR1 in epithelial cells while no expression was observed in endothelial cells. Further, our results elucidate the potential pathogenetic role of FGFR1 in cellular proliferation, local site inflammation, and fibrosis in cleft patients. Along with bFGF (also called FGF2), FGFR1 could play a pro-inflammatory role in clefts. Over-amplification of FGFR2 in some patients, along with bFGF, could potentially suggest roles for these genes in angiogenesis. Additionally, increased expression of FOXE1 (also called TTF2) contributes to local site inflammation. Finally, zero to low amplification of FOXO1 could suggest its potential role in inducing oxidative stress in the endothelium along with reduced epithelial apoptosis.

Genetic variations at 10q26 regions near FGFR2 gene and its association with non-syndromic cleft lip with or without cleft palate

OBJECTIVES

In our study, we focussed on three SNPs in the non-coding regions near FGFR2 gene, as studies on non-coding variants in the genome are the novel trends to identify the susceptible loci for nonsyndromic cleft lip with or without cleft palate (NSCL/P). FGFR2 gene is selected as a candidate gene based on knock out animal models and the role played in syndromic forms of clefting. FGFR2 gene also plays an important role in FGF signaling pathway during craniofacial development.

METHODS

In the present study 148 case-parent triads were assessed for three SNPs rs10749408, rs11199874 and rs10788165 near FGFR2 gene by using TaqMan allelic discrimination method. Transmission disequilibrium test (TDT) was used to find the allelic association. Linkage disequilibrium (LD) between the markers was analysed using Haploview program 4.2. Haplotype transmission effects were estimated using FAMHAP package. The possible parent-of-origin effects were assessed by likelihood based approach.

RESULTS

TDT analysis of three SNPs failed to show significant transmission disortion from heterozygous parents to the affected child and are not associated with NSCL/P. Linkage disequilibrium analysis showed strong LD between rs11199874 and rs10788165 SNPs. In the haplotype TDT analysis, GG haplotype of rs11199874-rs10788165 showed significant undertransmission to affected child. No significant parent-of-origin effects were observed.

CONCLUSION

The present study on noncoding variants near FGFR2 gene is not associated with NSCL/P. As the numbers of triads included in the study are less, further studies are needed including large sample size to find association with NSCL/P.

The power of zebrafish models for understanding the co-occurrence of craniofacial and limb disorders

Craniofacial and limb defects are two of the most common congenital anomalies in the general population. Interestingly, these defects are not mutually exclusive. Many patients with craniofacial phenotypes, such as orofacial clefting and craniosynostosis, also present with limb defects, including polydactyly, syndactyly, brachydactyly, or ectrodactyly. The gene regulatory networks governing craniofacial and limb development initially seem distinct from one another, and yet these birth defects frequently occur together. Both developmental processes are highly conserved among vertebrates, and zebrafish have emerged as an advantageous model due to their high fecundity, relative ease of genetic manipulation, and transparency during development. Here we summarize studies that have used zebrafish models to study human syndromes that present with both craniofacial and limb phenotypes. We discuss the highly conserved processes of craniofacial and limb/fin development and describe recent zebrafish studies that have explored the function of genes associated with human syndromes with phenotypes in both structures. We attempt to identify commonalities between the two to help explain why craniofacial and limb anomalies often occur together.

First-Trimester Nonvisualization of the Parotid Gland and Aneuploidy in Fetuses With Increased Nuchal Translucency: A Prospective Cohort Study

OBJECTIVES

Aplasia and hypoplasia of the major salivary glands, particularly the parotid glands, were reported to be associated with trisomy 21. This study aimed to evaluate the value of first-trimester nonvisualization of the parotid gland in a high-risk population of fetuses with increased nuchal translucency (NT).

METHODS

A single-center prospective observational cohort study was conducted. The feasibility of imaging the parotid gland was assessed in 100 sequential cases of routine low-risk NT scans. In a 2-dimensional image in an axial plane at the level of the fetal mandible, the parotid glands appear as bilateral hyperechoic round areas. Cases referred for counseling for an NT measured above the 95th percentile for gestational age were evaluated for visualization of the parotid glands. Prenatal findings were correlated with fetal genetic analysis results.

RESULTS

Forty-two cases with increased NT constituted the final study group. Within the group with nonvisualization of the parotid gland, genetic testing revealed 9 cases of trisomy 21, 3 cases of trisomy 18, and 1 case of monosomy X. The sensitivity and specificity of nonvisualization of the parotid gland as a predictor of aneuploidy were 76% and 80%, respectively. The positive likelihood ratio, negative likelihood ratio, and relative risk were 3.82 (95% confidence interval [CI], 1.67-8.74), 0.29 (95% CI, 0.12-0.71), and 4.33 (95% CI, 1.69-11.09; P < .01). The negative predictive value was 95.14%.

CONCLUSIONS

First-trimester nonvisualization of the parotid gland may constitute a potential method for detection of aneuploid fetuses within a high-risk population.

Why Does the Face Predict the Brain? Neural Crest Induction, Craniofacial Morphogenesis, and Neural Circuit Development

Mesenchephalic and rhombencephalic neural crest cells generate the craniofacial skeleton, special sensory organs, and subsets of cranial sensory receptor neurons. They do so while preserving the anterior-posterior (A-P) identity of their neural tube origins. This organizational principle is paralleled by central nervous system circuits that receive and process information from facial structures whose A-P identity is in register with that in the brain. Prior to morphogenesis of the face and its circuits, however, neural crest cells act as "inductive ambassadors" from distinct regions of the neural tube to induce differentiation of target craniofacial domains and establish an initial interface between the brain and face. At every site of bilateral, non-axial secondary induction, neural crest constitutes all or some of the mesenchymal compartment for non-axial mesenchymal/epithelial (M/E) interactions. Thus, for epithelial domains in the craniofacial primordia, aortic arches, limbs, the spinal cord, and the forebrain (Fb), neural crest-derived mesenchymal cells establish local sources of inductive signaling molecules that drive morphogenesis and cellular differentiation. This common mechanism for building brains, faces, limbs, and hearts, A-P axis specified, neural crest-mediated M/E induction, coordinates differentiation of distal structures, peripheral neurons that provide their sensory or autonomic innervation in some cases, and central neural circuits that regulate their behavioral functions. The essential role of this neural crest-mediated mechanism identifies it as a prime target for pathogenesis in a broad range of neurodevelopmental disorders. Thus, the face and the brain "predict" one another, and this mutual developmental relationship provides a key target for disruption by developmental pathology.

Association between craniofacial morphological patterns and tooth agenesis-related genes

Background

The aim of the present study was to assess if genetic polymorphisms in tooth agenesis (TA)-related genes are associated with craniofacial morphological patterns.

Methods

This cross-sectional, multi-center, genetic study evaluated 594 orthodontic Brazilians patients. The presence or absence of TA was determined by analysis of panoramic radiography. The patients were classified according to their skeletal malocclusion and facial growth pattern by means of digital cephalometric analysis. Genomic DNA was extracted from squamous epithelial cells of buccal mucosa and genetic polymorphisms in MSX1 (rs1042484), PAX9 (rs8004560), TGF-α (rs2902345), FGF3 (rs1893047), FGF10 (rs900379), and FGF13 (rs12838463, rs5931572, and rs5974804) were genotyped by polymerase chain reaction using TaqMan chemistry and end-point analysis.

Results

Genotypes (p = 0.038) and allele (p = 0.037) distributions for the FGF3 rs1893047 were significantly different according to the skeletal malocclusion. Carrying at least one G allele increased in more than two times the chance of presenting skeletal class III malocclusion (OR = 2.21, CI 95% = 1.14–4.32; p = 0.017). There was no association between another skeletal craniofacial pattern and some polymorphism assessed in the present study.

Conclusion

Our results suggest that the genetic polymorphism rs1893047 in FGF3 might contribute to variations in the craniofacial sagittal pattern.

Exogenous FGF8 signaling in osteocytes leads to mandibular hypoplasia in mice

OBJECTIVE

Fibroblast growth factor 8 (FGF8) signaling is essential in regulating craniofacial osteogenesis. This study aims to explore the effect of altered FGF8 signaling in maxillomandibular development during embryogenesis.

MATERIALS AND METHODS

Dmp1^Cre ;R26R^mTmG mice were generated to trace Dmp1⁺ cell lineage, and Dmp1^Cre ;R26R^Fgf8 mice were generated to explore the effects of augmented FGF8 signaling in Dmp1⁺ cells on osteogenesis with a focus on maxillomandibular development during embryogenesis, as assessed by whole mount skeletal staining, histology, and immunostaining. Additionally, cell proliferation rate and the expression of osteogenic genes were examined.

RESULTS

Osteocytes of maxillomandibular bones were found Dmp1-positive prenatally, and Fgf8 over-expression in Dmp1⁺ cells led to mandibular hypoplasia. While Dmp1^Cre allele functions in the osteocytes of the developing mandibular bone at as early as E13.5, and enhanced cell proliferation rate is observed in the bone forming region of the mandible in Dmp1^Cre ;R26R^Fgf8 mice at E14.5, histological examination showed that osteogenesis was initially impacted at E15.5, along with an inhibition of osteogenic differentiation markers.

CONCLUSIONS

Augmented FGF8 signaling in Dmp1⁺ cells lead to osteogenic deficiency in the mandibular bones, resulting in mandibular hypoplasia.

Extracellular Matrix Composition and Remodeling: Current Perspectives on Secondary Palate Formation, Cleft Lip/Palate, and Palatal Reconstruction

Craniofacial development comprises a complex process in humans in which failures or disturbances frequently lead to congenital anomalies. Cleft lip with/without palate (CL/P) is a common congenital anomaly that occurs due to variations in craniofacial development genes, and may occur as part of a syndrome, or more commonly in isolated forms (non-syndromic). The etiology of CL/P is multifactorial with genes, environmental factors, and their potential interactions contributing to the condition. Rehabilitation of CL/P patients requires a multidisciplinary team to perform the multiple surgical, dental, and psychological interventions required throughout the patient's life. Despite progress, lip/palatal reconstruction is still a major treatment challenge. Genetic mutations and polymorphisms in several genes, including extracellular matrix (ECM) genes, soluble factors, and enzymes responsible for ECM remodeling (e.g., metalloproteinases), have been suggested to play a role in the etiology of CL/P; hence, these may be considered likely targets for the development of new preventive and/or therapeutic strategies. In this context, investigations are being conducted on new therapeutic approaches based on tissue bioengineering, associating stem cells with biomaterials, signaling molecules, and innovative technologies. In this review, we discuss the role of genes involved in ECM composition and remodeling during secondary palate formation and pathogenesis and genetic etiology of CL/P. We also discuss potential therapeutic approaches using bioactive molecules and principles of tissue bioengineering for state-of-the-art CL/P repair and palatal reconstruction.

Chiari malformation type I: what information from the genetics?

PURPOSE

Chiari malformation type I (CMI), a rare disorder of the craniocerebral junction with an estimated incidence of 1 in 1280, is characterized by the downward herniation of the cerebellar tonsils of at least 5 mm through the foramen magnum, resulting in significant neurologic morbidity. Classical CMI is thought to be caused by an underdeveloped occipital bone, resulting in a posterior cranial fossa which is too small to accommodate the normal-sized cerebellum. In this review, we dissect the lines of evidence supporting a genetic contribution for this disorder.

METHODS

We present the results of two types of approaches: animal models and human studies encompassing different study designs such as whole genome linkage analysis, case-control association studies, and expression studies. The update of the literature also includes the most recent findings emerged by whole exome sequencing strategy.

RESULTS

Despite evidence for a genetic component, no major genes have been identified and the genetics of CMI is still very much unknown. One major challenge is the variability of clinical presentation within CMI patient population that reflects an underlying genetic heterogeneity.

CONCLUSIONS

The identification of the genes that contribute to the etiology of CMI will provide an important step to the understanding of the underlying pathology. The finding of a predisposing gene may lead to the development of simple and accurate diagnostic tests for better prognosis, counseling, and clinical management of patients and their relatives.

Fgf8a mutation affects craniofacial development and skeletal gene expression in zebrafish larvae

Craniofacial development is tightly regulated and therefore highly vulnerable to disturbance by genetic and environmental factors. Fibroblast growth factors (FGFs) direct migration, proliferation and survival of cranial neural crest cells (CNCCs) forming the human face. In this study, we analyzed bone and cartilage formation in the head of five dpf fgf8a^ti282 zebrafish larvae and assessed gene expression levels for 11 genes involved in these processes. In addition, in situ hybridization was performed on 8 and 24 hours post fertilization (hpf) larvae (fgf8a, dlx2a, runx2a, col2a1a). A significant size reduction of eight out of nine craniofacial cartilage structures was found in homozygous mutant (6–36%, P<0.01) and heterozygous (7–24%, P<0.01) larvae. Also, nine mineralized structures were not observed in all or part of the homozygous (0–71%, P<0.0001) and heterozygous (33–100%, P<0.0001) larvae. In homozygote mutants, runx2a and sp7 expression was upregulated compared to wild type, presumably to compensate for the reduced bone formation. Decreased col9a1b expression may compromise cartilage formation. Upregulated dlx2a in homozygotes indicates impaired CNCC function. Dlx2a expression was reduced in the first and second stream of CNCCs in homozygous mutants at 24 hpf, as shown by in situ hybridization. This indicates an impairment of CNCC migration and survival by fgf8 mutation.

Summary: A function-blocking mutation in fgf8a causes craniofacial malformations in zebrafish larvae due to impaired cranial neural crest cell migration and survival.

Divergence in larval jaw gene expression reflects differential trophic adaptation in haplochromine cichlids prior to foraging

Background

Understanding how variation in gene expression contributes to morphological diversity is a major goal in evolutionary biology. Cichlid fishes from the East African Great lakes exhibit striking diversity in trophic adaptations predicated on the functional modularity of their two sets of jaws (oral and pharyngeal). However, the transcriptional basis of this modularity is not so well understood, as no studies thus far have directly compared the expression of genes in the oral and pharyngeal jaws. Nor is it well understood how gene expression may have contributed to the parallel evolution of trophic morphologies across the replicate cichlid adaptive radiations in Lake Tanganyika, Malawi and Victoria.

Results

We set out to investigate the role of gene expression divergence in cichlid fishes from these three lakes adapted to herbivorous and carnivorous trophic niches. We focused on the development stage prior to the onset of exogenous feeding that is critical for understanding patterns of gene expression after oral and pharyngeal jaw skeletogenesis, anticipating environmental cues. This framework permitted us for the first time to test for signatures of gene expression underlying jaw modularity in convergent eco-morphologies across three independent adaptive radiations. We validated a set of reference genes, with stable expression between the two jaw types and across species, which can be important for future studies of gene expression in cichlid jaws. Next we found evidence of modular and non-modular gene expression between the two jaws, across different trophic niches and lakes. For instance, prdm1a, a skeletogenic gene with modular anterior-posterior expression, displayed higher pharyngeal jaw expression and modular expression pattern only in carnivorous species. Furthermore, we found the expression of genes in cichlids jaws from the youngest Lake Victoria to exhibit low modularity compared to the older lakes.

Conclusion

Overall, our results provide cross-species transcriptional comparisons of modularly-regulated skeletogenic genes in the two jaw types, implicating expression differences which might contribute to the formation of divergent trophic morphologies at the stage of larval independence prior to foraging.

Electronic supplementary material

The online version of this article (10.1186/s12862-019-1483-3) contains supplementary material, which is available to authorized users.

Two novel genes TOX3 and COL21A1 in large extended Malay families with nonsyndromic cleft lip and/or palate

BACKGROUND

Nonsyndromic cleft lip and/or palate is one of the most common human birth defects worldwide that affects the lip and/or palate. The incidence of clefts varies among populations through ethnic, race, or geographical differences. The focus on Malay nonsyndromic cleft lip and/or palate (NSCL/P) is because of a scarce report on genetic study in relation to this deformity in Malaysia. We are interested to discuss about the genes that are susceptible to cause orofacial cleft formation in the family.

METHODS

Genome-wide linkage analysis was carried out on eight large extended families of NSCL/P with the total of 91 individuals among Malay population using microarray platform. Based on linkage analyses findings, copy number variation (CNV) of LPHN2, SATB2, PVRL3, COL21A1, and TOX3 were identified in four large extended families that showed linkage evidence using quantitative polymerase chain reaction (qPCR) as for a validation purpose. Copy number calculated (CNC) for each genes were determined with Applied Biosystems CopyCallerTM Software v2.0. Normal CNC of the target sequence expected was set at two.

RESULTS

Genome-wide linkage analysis had discovered several genes including TOX3 and COL21A1 in four different loci 4p15.2-p16.1, 6p11.2-p12.3, 14q13-q21, and 16q12.1. There was significant decreased, p < 0.05 of SATB2, COL21A1, and TOX3 copy number in extended families compared to the normal controls.

CONCLUSION

Novel linkage evidence and significant low copy number of COL21A1 and TOX3 in NSCLP family was confirmed. These genes increased the risks toward NSCLP formation in that family traits.

Network-based identification of critical regulators as putative drivers of human cleft lip

BACKGROUND

Cleft lip (CL) is one of the most common congenital birth defects with complex etiology. While genome-wide association studies (GWAS) have made significant advances in our understanding of mutations and their related genes with potential involvement in the etiology of CL, it remains unknown how these genes are functionally regulated and interact with each other in lip development. Currently, identifying the disease-causing genes in human CL is urgently needed. So far, the causative CL genes have been largely undiscovered, making it challenging to design experiments to validate the functional influence of the mutations identified from large genomic studies such as CL GWAS.

RESULTS

Transcription factors (TFs) and microRNAs (miRNAs) are two important regulators in cellular system. In this study, we aimed to investigate the genetic interactions among TFs, miRNAs and the CL genes curated from the previous studies. We constructed miRNA-TF co-regulatory networks, from which the critical regulators as putative drivers in CL were examined. Based on the constructed networks, we identified ten critical hub genes with prior evidence in CL. Furthermore, the analysis of partitioned regulatory modules highlighted a number of biological processes involved in the pathology of CL, including a novel pathway "Signaling pathway regulating pluripotency of stem cells". Our subnetwork analysis pinpointed two candidate miRNAs, hsa-mir-27b and hsa-mir-497, activating the Wnt pathway that was associated with CL. Our results were supported by an independent gene expression dataset in CL.

CONCLUSIONS

This study represents the first regulatory network analysis of CL genes. Our work presents a global view of the CL regulatory network and a novel approach on investigating critical miRNAs, TFs and genes via combinatory regulatory networks in craniofacial development. The top genes and miRNAs will be important candidates for future experimental validation of their functions in CL.

Neuron/Glial Antigen 2-Type VI Collagen Interactions During Murine Temporomandibular Joint Osteoarthritis

The degeneration of articular cartilage underscores the clinical pathology of temporomandibular joint osteoarthritis (TMJ-OA) and is promoted through dysfunctional biochemical or biophysical signaling. Transduction of these signals has a multifaceted regulation that includes important cell-matrix derived interactions. The matrix encapsulating the cells of the mandibular condylar cartilage (MCC) is rich in type VI collagen. Neuron/glia antigen 2 (NG2) is a type I transmembrane proteoglycan that binds with type VI collagen. This study defines the temporospatial dynamics of NG2-type VI collagen interactions during the progression of TMJ-OA. Membrane-bound NG2 is found to colocalize with pericellular type VI collagen in superficial layer cells in the MCC perichondrium but is present at high levels in the cytosol of chondroblastic and hypertrophic cells. When TMJ -OA is induced using a surgical instability model, localized disruptions of pericellular type VI collagen are observed on the central and medial MCC and are associated with significantly higher levels of cytosolic NG2. NG2 localized within the cytosol is found to be transported through clathrin and dynamin mediated endocytic pathways. These findings are consistent with NG2 behavior in other injury models and underscore the potential of NG2 as an entirely novel molecular mechanism of chondrocyte function contextually linked with TMJ-OA.

Roles of FGF8 subfamily in embryogenesis and oral‑maxillofacial diseases (Review)

Fibroblast growth factors (FGFs) are diffusible polypeptides released by a variety of cell types. FGF8 subfamily members regulate embryonic development processes through controlling progenitor cell growth and differentiation, and are also functional in adults in tissue repair to maintain tissue homeostasis. FGF8 family members exhibit unique binding affinities with FGF receptors and tissue distribution patterns. Increasing evidence suggests that, by regulating multiple cellular signaling pathways, alterations in the FGF8 subfamily are involved in craniofacial development, odontogenesis, tongue development and salivary gland branching morphogenesis. Aberrant FGF signaling transduction, caused by mutations as well as abnormal expression or isoform splicing, plays an important role in the development of oral diseases. Targeting FGF8 subfamily members provides a new promising strategy for the treatment of oral diseases. The aim of this review was to summarize the aberrant regulations of FGF8 subfamily members and their potential implications in oral‑maxillofacial diseases.

A tale of two cities: The genetic mechanisms governing calvarial bone development

The skull bones must grow in a coordinated, three-dimensional manner to coalesce and form the head and face. Mammalian skull bones have a dual embryonic origin from cranial neural crest cells (CNCC) and paraxial mesoderm (PM) and ossify through intramembranous ossification. The calvarial bones, the bones of the cranium which cover the brain, are derived from the supraorbital arch (SOA) region mesenchyme. The SOA is the site of frontal and parietal bone morphogenesis and primary center of ossification. The objective of this review is to frame our current in vivo understanding of the morphogenesis of the calvarial bones and the gene networks regulating calvarial bone initiation in the SOA mesenchyme.

Autologous liquid platelet rich fibrin: A novel drug delivery system

There is currently widespread interest within the biomaterial field to locally deliver biomolecules for bone and cartilage regeneration. Substantial work to date has focused on the potential role of these biomolecules during the healing process, and the carrier system utilized is a key factor in their effectiveness. Platelet rich fibrin (PRF) is a naturally derived fibrin scaffold that is easily obtained from peripheral blood following centrifugation. Slower centrifugation speeds have led to the commercialization of a liquid formulation (liquid-PRF) resulting in an upper plasma layer composed of liquid fibrinogen/thrombin prior to clot formation that remains in its liquid phase for approximately 15 min until injected into bodily tissues. Herein, we introduce the use of liquid PRF as an advanced local delivery system for small and large biomolecules. Potential target molecules including large (growth factors/cytokines and morphogenetic/angiogenic factors), as well as small (antibiotics, peptides, gene therapy and anti-osteoporotic) molecules are considered potential candidates for enhanced bone/cartilage tissue regeneration. Furthermore, liquid-PRF is introduced as a potential carrier system for various cell types and nano-sized particles that are capable of limiting/by-passing the immune system and minimizing potential foreign body reactions within host tissues following injection.

STATEMENT OF SIGNIFICANCE

There is currently widespread interest within the biomaterial field to locally deliver biomolecules for bone and cartilage regeneration. This review article focuses on the use of a liquid version of platelet rich fibrin (PRF) composed of liquid fibrinogen/thrombin as a drug delivery system. Herein, we introduce the use of liquid PRF as an advanced local delivery system for small and large biomolecules including growth factors, cytokines and morphogenetic/angiogenic factors, as well as antibiotics, peptides, gene therapy and anti-osteoporotic molecules as potential candidates for enhanced bone/cartilage tissue regeneration.

Increased FGF8 signaling promotes chondrogenic rather than osteogenic development in the embryonic skull

The bones of the cranial vault are formed directly from mesenchymal cells through intramembranous ossification rather than via a cartilage intermediate. Formation and growth of the skull bones involves the interaction of multiple cell-cell signaling pathways, with fibroblast growth factors (FGFs) and their receptors exerting a prominent influence. Mutations within the FGF signaling pathway are the most frequent cause of craniosynostosis, which is a common human craniofacial developmental abnormality characterized by the premature fusion of the cranial sutures. Here, we have developed new mouse models to investigate how different levels of increased FGF signaling can affect the formation of the calvarial bones and associated sutures. Whereas moderate Fgf8 overexpression resulted in delayed ossification followed by craniosynostosis of the coronal suture, higher Fgf8 levels promoted a loss of ossification and favored cartilage over bone formation across the skull. By contrast, endochondral bones were still able to form and ossify in the presence of increased levels of Fgf8, although the growth and mineralization of these bones were affected to varying extents. Expression analysis demonstrated that abnormal skull chondrogenesis was accompanied by changes in the genes required for Wnt signaling. Moreover, further analysis indicated that the pathology was associated with decreased Wnt signaling, as the reduction in ossification could be partially rescued by halving Axin2 gene dosage. Taken together, these findings indicate that mesenchymal cells of the skull are not fated to form bone, but can be forced into a chondrogenic fate through the manipulation of FGF8 signaling. These results have implications for evolution of the different methods of ossification as well as for therapeutic intervention in craniosynostosis.

Analysis of Parent-of-Origin Effects on the X Chromosome in Asian and European Orofacial Cleft Triads Identifies Associations with DMD, FGF13, EGFL6, and Additional Loci at Xp22.2

Background: Although both the mother's and father's alleles are present in the offspring, they may not operate at the same level. These parent-of-origin (PoO) effects have not yet been explored on the X chromosome, which motivated us to develop new methods for detecting such effects. Orofacial clefts (OFCs) exhibit sex-specific differences in prevalence and are examples of traits where a search for various types of effects on the X chromosome might be relevant. Materials and Methods: We upgraded our R-package Haplin to enable genome-wide analyses of PoO effects, as well as power simulations for different statistical models. 14,486 X-chromosome SNPs in 1,291 Asian and 1,118 European case-parent triads of isolated OFCs were available from a previous GWAS. For each ethnicity, cleft lip with or without cleft palate (CL/P) and cleft palate only (CPO) were analyzed separately using two X-inactivation models and a sliding-window approach to haplotype analysis. In addition, we performed analyses restricted to female offspring. Results: Associations were identified in "Dystrophin" (DMD, Xp21.2-p21.1), "Fibroblast growth factor 13" (FGF13, Xq26.3-q27.1) and "EGF-like domain multiple 6" (EGFL6, Xp22.2), with biologically plausible links to OFCs. Unlike EGFL6, the other associations on chromosomal region Xp22.2 had no apparent connections to OFCs. However, the Xp22.2 region itself is of potential interest because it contains genes for clefting syndromes [for example, "Oral-facial-digital syndrome 1" (OFD1) and "Midline 1" (MID1)]. Overall, the identified associations were highly specific for ethnicity, cleft subtype and X-inactivation model, except for DMD in which associations were identified in both CPO and CL/P, in the model with X-inactivation and in Europeans only. Discussion/Conclusion: The specificity of the associations for ethnicity, cleft subtype and X-inactivation model underscores the utility of conducting subanalyses, despite the ensuing need to adjust for additional multiple testing. Further investigations are needed to confirm the associations with DMD, EGF16, and FGF13. Furthermore, chromosomal region Xp22.2 appears to be a hotspot for genes implicated in clefting syndromes and thus constitutes an exciting direction to pursue in future OFCs research. More generally, the new methods presented here are readily adaptable to the study of X-linked PoO effects in other outcomes that use a family-based design.

Head and Neck MRI Findings in CHARGE Syndrome

Coloboma of the eye, Heart defects, Atresia of the choanae, Retardation of growth and/or development, Genital and/or urinary abnormalities, and Ear abnormalities and deafness (CHARGE) syndrome is a disorder with multiple congenital anomalies seen on imaging. A retrospective review of 10 patients with CHARGE syndrome who underwent MR imaging of the brain as part of a preoperative evaluation for cochlear implantation was conducted. Structural abnormalities of the entire MR imaging of the head were evaluated, including the auditory system, olfactory system, face, skull base, and central nervous system. The most frequent MR imaging findings included dysplasias of the semicircular canals and hypoplasia of the frontal lobe olfactory sulci. Less frequent findings included cleft lip/palate and coloboma. Our study uncovered new findings of a J-shaped sella, dorsal angulation of the clivus, and absent/atrophic parotid glands, not previously described in patients with CHARGE. Our results emphasize the utility of MR imaging in the diagnosis and management of patients with CHARGE syndrome.

Biomaterials for Craniofacial Bone Regeneration

Functional reconstruction of craniofacial defects is a major clinical challenge in craniofacial sciences. The advent of biomaterials is a potential alternative to standard autologous/allogenic grafting procedures to achieve clinically successful bone regeneration. This article discusses various classes of biomaterials currently used in craniofacial reconstruction. Also reviewed are clinical applications of biomaterials as delivery agents for sustained release of stem cells, genes, and growth factors. Recent promising advancements in 3D printing and bioprinting techniques that seem to be promising for future clinical treatments for craniofacial reconstruction are covered. Relevant topics in the bone regeneration literature exemplifying the potential of biomaterials to repair bone defects are highlighted.

Targeted sequencing in FGF/FGFR genes and association analysis of variants for mandibular prognathism

To identify variants of the genes in fibroblast growth factors/fibroblast growth factor receptors (FGF/FGFR) signal pathway that predispose to mandibular prognathism (MP) in the general Chinese population systematically.Targeted sequencing of the FGF/FGFR genes was conducted in 176 MP individuals and 155 class I malocclusion controls. The associations of common and rare variants with MP as a categorical phenotype and also continuous malocclusion phenotypes generated by principal component (PC) analysis were analyzed.One common variant, rs372127537, located in the 3'-untranslated region of FGF7 gene, was significantly related to PC1 (P  =  4.22 × 10), which explained 23.23% of the overall phenotypic variation observed and corresponded to vertical discrepancies ranging from short anterior face height to long anterior face height, after Bonferroni correction. Also, 15 other variants were associated with PC1-4, although not significant after multiple corrections (P < .05). We also identified 3 variants: rs13317 in FGFR1, rs149242678 in FGF20, and rs79176051 FGF12 associated with MP (P < .05). With respect to rare variant analysis, variants within the FGF12 gene showed significant association with MP (P  =  .001).Association between FGF/FGFR signaling pathway and MP has been identified. We found a previously unreported SNP in FGF7 significantly related to increased facial height. Also, rare variants within the FGF12 were associated with MP. Our results provide new clues for genetic mechanisms of MP and shed light on strategies for evaluating rare variants that underlie complex traits. Future studies with larger sample sizes and more comprehensive genome coverage, and also in other population are required to replicate these findings.