Conditional inactivation of Tgfbr2 in cranial neural crest causes cleft palate and calvaria defects

Advance in candidate genes in mandibular retrognathism: A systematic review

OBJECTIVE

This research aims to dissect the polygenic nature of non-syndromic mandibular retrognathism (MR) and to better understand the genetic underpinnings of MR, with a particular focus on the role of ethnic diversity in influencing genetic predispositions.

METHODS

A comprehensive systematic review was conducted on MR. Electronic databases such as PubMed and Google Scholar were employed, utilizing terms like 'mandibular', 'retrognathism', 'gene', and 'genetic'. This study strictly adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) framework.

RESULTS

Ten genetic studies were identified that satisfied the eligibility criteria, involving 1010 participants. Variations in candidate genes were reported across different populations, including myosin 1 H (MYO1H), matrilin 1 (MATN1), a disintegrin and metalloproteinase with thrombospondin motifs 9 (ADAMTS9), bone morphogenetic protein 2 (BMP2), parathyroid hormone (PTH), the vitamin-D related genes: vitamin D receptor (VDR), cytochrome P450 family 24 subfamily A member 1 (CYP24A1), and cytochrome P450 family 27 subfamily B member 1 (CYP27B1), collagen type II alpha 1 chain (COL2A1), transforming growth factor-β (TGF-β), TGF-β receptor 2 (TGFBR2), epidermal growth factor (EGF), and EGF receptor gene (EGFR).

CONCLUSION

These findings shed light on the role of genetic factors in MR. Future studies should adopt a multicentric approach to expand sample sizes and enhance the analysis of genetic variants associated with MR.

Smooth muscle cells and fibroblasts in the ascending aorta exhibit minor differences between embryonic origins in angiotensin II-driven transcriptional alterations

Thoracic aortopathy is influenced by angiotensin II (AngII) and exhibits regional heterogeneity with the ascending aorta being particularly susceptible. In this region, smooth muscle cells (SMCs) and selected fibroblasts originate from the second heart field (SHF) and cardiac neural crest (CNC). While our previous study revealed a critical role of SHF-derived cells in AngII-mediated aortopathy, the contribution of CNC-derived cells remains unclear. To investigate lineage-specific responses to AngII, Mef2c-Cre R26RmT/mG mice were infused with AngII. Ascending aortas were harvested at baseline or after 3 days of infusion, representing the prepathological phase. Cells were sorted based on their embryonic origins and single-cell RNA sequencing was performed. Transcriptomic analysis revealed significant changes in both SHF- and nSHF-derived SMCs following short-term AngII infusion, although differences between the origins were modest. Similarly, fibroblast transcriptomes exhibited notable changes, yet lineage-specific differences remained modest, except for a newly identified fibroblast subpopulation where extracellular matrix-related genes such as Eln and Col3a1 were downregulated in SHF-derived fibroblasts compared to nSHF-derived fibroblasts. These findings suggest that while fibroblasts in the new subcluster exhibit lineage-specific extracellular matrix-related differences, overall transcriptomic variations between SHF- and nSHF-derived cells in response to AngII remain modest during the prepathological phase of AngII-induced thoracic aortopathy.

The mediating mechanism of Oct4 in the process of cleft palate induced by 2, 3, 7, 8-tetrachlorodibenz-p-dioxin (TCDD) and all-trans retinoic acid

2, 3, 7, 8-tetrachlorodiphenyl-p-dioxin (TCDD) and all-trans retinoic acid (atRA) have been shown to be inducers of cleft palate (CP). Relevant studies have shown that Oct transcription factor 4 (Oct4) can regulate the expression of the aromatic hydrocarbon receptor (AhR), a target gene of TCDD, as well as influence the retinoic acid signaling pathway. However, the mechanism of Oct4 regulating the interaction between TCDD and atRA in CP pathogenesis remains unclear. In order to solve the above problems, mouse embryonic palatal mesenchymal (MEPM) cells were used for further study. The results show that, TCDD and atRA induce a similar pattern of CP in vivo and significantly inhibit the proliferation of MEPM cells. In vitro, TCDD exposure led to up-regulation of AhR and cytochrome P450 1A1 (CYP1A1) expression and down-regulation of cellular retinoic acid binding protein 2 (CRABP2) and retinoic acid receptor-alpha (RARA) expression in MEPM cells. In addition, atRA exposure resulted in decreased expression of AhR and CYP1A1, and increased protein levels of RARA and CRABP2. When Oct4 was overexpressed, the down-regulation of CRABP2 and RARA by TCDD and the down-regulation of AhR by RA were reversed. The cross results of mass spectrometry and Biogrid database show that HSP90AB1 can bind to Oct4 and AhR. Co-immunoprecipitation (Co-IP) results showed that Oct4 and CRABP2 were combined, which further suggested the mediating effects of Oct4 in CP development. In summary, we hypothesize that AhR-HSP90AB1-Oct4-CRABP2 axis may play the key role mediating the interaction between TCDD and atRA in CP pathogenesis.

Exploring polymorphisms in genes encoding growth factors associated with non-syndromic cleft lip with or without cleft palate and tooth agenesis

OBJECTIVE

To evaluate the association between non-syndromic cleft lip with or without cleft palate (NSCL±P) and tooth agenesis (TA), as well as the association of both conditions with polymorphisms in genes encoding growth factors.

METHODOLOGY

This cross-sectional study included children with NSCL±P and a control group of children without NSCL±P. Permanent teeth TA (excluding third molars) was evaluated using panoramic radiographs by a trained examiner. Only TA located outside the cleft was considered in the NSCL±P group. Genetic polymorphisms in Transforming Growth Factor Beta 1 (TGFB1)-rs1800470 and rs4803455-Transforming Growth Factor Beta Receptor 2 (TGFBR2)-rs3087465 and rs764522-Epidermal Growth Factor (EGF)-rs4444903 and rs2237051-and Epidermal Growth Factor Receptor (EGFR)-rs2227983- were genotyped by real-time PCR allele discrimination from buccal cell samples. Associations were tested by uni and multivariable Poisson regression models (5% significance level).

RESULTS

A total of 243 children-127 with NSCL±P (mean age = 8.80±2.14 years) and 116 without NSCL±P (mean age = 8.58±2.03 years) were included. TA was more frequent in the NSCL±P group (23.8%) than in the control group (6.2%) (p<0.01). The EGF rs2237051 was significantly associated with NSCL±P, independently of the other variables (PRa=1.41; p=0.042). Regarding TA, only the cleft presence was associated with a higher prevalence of TA regardless of different variables (PRa=3.70; p=0.001). There was no association between TA and the investigated genetic polymorphisms. When TA and NSCL±P were considered together, a borderline association was observed with rs1800470 in TGFB1 (p=0.06).

CONCLUSION

NSCL±P is associated with TA outside the cleft area. The EGF rs2237051 was associated with NSCL±P. Polymorphisms in genes encoding growth factors are not associated with TA.

Molecular Regulation of Palatogenesis and Clefting: An Integrative Analysis of Genetic, Epigenetic Networks, and Environmental Interactions

Palatogenesis is a complex developmental process requiring temporospatially coordinated cellular and molecular events. The following review focuses on genetic, epigenetic, and environmental aspects directing palatal formation and their implication in orofacial clefting genesis. Essential for palatal shelf development and elevation (TGF-β, BMP, FGF, and WNT), the subsequent processes of fusion (SHH) and proliferation, migration, differentiation, and apoptosis of neural crest-derived cells are controlled through signaling pathways. Interruptions to these processes may result in the birth defect cleft lip and/or palate (CL/P), which happens in approximately 1 in every 700 live births worldwide. Recent progress has emphasized epigenetic regulations via the class of non-coding RNAs with microRNAs based on critically important biological processes, such as proliferation, apoptosis, and epithelial-mesenchymal transition. These environmental risks (maternal smoking, alcohol, retinoic acid, and folate deficiency) interact with genetic and epigenetic factors during palatogenesis, while teratogens like dexamethasone and TCDD inhibit palatal fusion. In orofacial cleft, genetic, epigenetic, and environmental impact on the complex epidemiology. This is an extensive review, offering current perspectives on gene-environment interactions, as well as non-coding RNAs, in palatogenesis and emphasizing open questions regarding these interactions in palatal development.

A novel TGFBR2 mutation causes Loeys-Dietz syndrome in a Chinese infant: A case report

Introduction

Loeys-Dietz syndrome (LDS) is a rare autosomal dominant disorder with extensive connective tissue involvement. The diagnosis of this disease is mainly based on clinical features combined with the detection of pathogenic gene mutations, mainly mutations in the transforming growth factor-beta (TGF-β) signaling pathway.

Methods

The molecular pathogenesis of a LDS syndrome proband and his family members was analyzed using whole exome sequencing and validated using Sanger sequencing. Molecular dynamics simulations and in vitro cell experiments further analyzed the structural changes and functional abnormalities of the variation.

Results

This study describes the case of a 6-month-old infant diagnosed with LDS with typical craniofacial abnormalities, developmental delay, and a dilated aortic sinus (19 mm; Z-score 3.5). Genetic analysis showed the patient carried a novel de novo TGF-β receptor 2 (TGFBR2) mutation (NM_003242: c.1005_1007delGTA (p.Glu335_Tyr336delinsAsp)). Molecular dynamics simulation showed that the TGFBR2 c.1005_1007delGTA mutation changed the protein conformation, making the protein conformation more stable. The p.Glu335_Tyr336delinsAsp mutation significantly reduced TGF-β-induced gene transcription and phosphorylation of SMAD Family Member 2 (SMAD2) in vitro.

Conclusions

Our comprehensive genetic analysis suggested that the p.Glu335_Tyr336delinsAsp variant of TGFBR2 caused aberrant TGF-β signaling and contributed to LDS in the patient.

Smooth Muscle Cells and Fibroblasts in the Proximal Thoracic Aorta Exhibit Minor Differences Between Embryonic Origins in Angiotensin II-driven Transcriptional Alterations

Background

Thoracic aortopathy is influenced by angiotensin II (AngII) and exhibits regional heterogeneity with the proximal region of the thoracic aorta being susceptible. Smooth muscle cells (SMCs) and selected fibroblasts in this region are derived from two embryonic origins: second heart field (SHF) and cardiac neural crest (CNC). While our previous study revealed a critical role of SHF-derived cells in AngII-mediated aortopathy formation, the contribution of CNC-derived cells remains unclear.

Methods

Mef2c-Cre R26R mT/mG mice were infused with AngII (1,000 ng/kg/min). Proximal thoracic aortas were harvested at baseline or after 3 days of infusion, representing the prepathological phase. Cells were sorted by origins using mGFP (SHF-derived) and mTomato (other origins, nSHF-derived) signals, respectively. After sorting cells by origin, single-cell RNA sequencing was performed and analyzed.

Results

Short-term AngII infusion induced significant transcriptomic changes in both SHF- and nSHF-derived SMCs, but differences between origins were modest. Fibroblast transcriptomes also underwent notable changes by AngII infusion, but differences between SHF and nSHF origins remained modest. Interestingly, AngII infusion resulted in the emergence of a new fibroblast sub-population. Several molecules related to the extracellular matrix, such as Eln and Col3a1 , were downregulated in SHF-derived fibroblasts compared to nSHF-derived fibroblasts in the new subcluster.

Conclusion

Fibroblasts in the new subcluster exhibited lineage-specific differences in extracellular matrix-related genes; however, overall transcriptomic differences between origins in SMCs and fibroblasts in response to AngII were modest in the pre-pathological phase of AngII-induced thoracic aortopathy.

GRAPHIC ABSTRACT

Experimental study on the preventive effect of Anemarrhena rhizome on pregnancy loss and the incidence rate of cleft palate in A/J mice

Pregnancy loss is a significant concern worldwide, encompassing miscarriage and stillbirth. Miscarriage, defined as the loss of a baby before 28 weeks of gestation, accounts for approximately 15% of pregnancies. Stillbirth, occurring at or after 28 weeks of gestation, affects nearly 2.0 million pregnancies annually, predominantly in low- and middle-income regions. This study aims to investigate the potential of Anemarrhena rhizome (AR) herbal medicine in mitigating pregnancy loss and reducing the incidence of cleft palate in A/J mice models. A total of 390 6-week-old A/J mice were used for the study. Three different dosages of dried AR (6, 12, and 18 g) were boiled to prepare water extracts. The mice were divided into experimental groups receiving these extracts and a control group. Pregnancy outcomes, including fetal mortality rates and incidence of cleft palate, were assessed. The experimental groups receiving AR herbal medicine demonstrated significantly lower fetal mortality rates compared to the control group. Additionally, the incidence of cleft palate was notably reduced in the experimental groups, with the AR 6 g and AR 12 g groups showing significant reductions compared to the control group. AR herbal medicine shows promise in mitigating pregnancy loss and reducing the incidence of cleft palate in A/J mice models. These findings suggest the potential of AR as a therapeutic agent for improving fetal health outcomes. Further research is warranted to elucidate the underlying mechanisms and optimize dosage strategies for maximizing its therapeutic benefits in pregnancy-related complications.

The duct of von Ebner's glands is a source of Sox10 + taste bud progenitors and susceptible to pathogen infections

Introduction

We have recently demonstrated that Sox10-expressing (Sox10 +) cells give rise to mainly type-III neuronal taste bud cells that are responsible for sour and salt taste. The two tissue compartments containing Sox10 + cells in the surrounding of taste buds include the connective tissue core of taste papillae and von Ebner's glands (vEGs) that are connected to the trench of circumvallate and foliate papillae.

Methods

In this study, we performed single cell RNA-sequencing of the epithelium of Sox10-Cre/tdT mouse circumvallate/vEG complex and used inducible Cre mouse models to map the cell lineages of vEGs and/or connective tissue (including stromal and Schwann cells).

Results

Transcriptomic analysis indicated that Sox10 expression was enriched in the cell clusters of vEG ducts that contained abundant proliferating cells, while Sox10-Cre/tdT expression was enriched in type-III taste bud cells and vEG ductal cells. In vivo lineage mapping showed that the traced cells were distributed in circumvallate taste buds concurrently with those in the vEGs, but not in the connective tissue. Moreover, multiple genes encoding pathogen receptors were enriched in the vEG ducts hosting Sox10 + cells.

Discussion

Our data supports that it is the vEGs, not connective tissue core, that serve as the niche of Sox10 + taste bud progenitors. If this is also true in humans, our data indicates that vEG duct is a source of Sox10 + taste bud progenitors and susceptible to pathogen infections.

A novel perspective of calvarial development: the cranial morphogenesis and differentiation regulated by dura mater

There are lasting concerns on calvarial development because cranium not only accommodates the growing brain, but also safeguards it from exogenous strikes. In the past decades, most studies attributed the dynamic expansion and remodeling of cranium to the proliferation of osteoprecursors in cranial primordium, and the proliferation of osteoprogenitors at the osteogenic front of cranial suture mesenchyme. Further investigations identified series genes expressed in suture mesenchymal cells as the markers of the progenitors, precursors and postnatal stem cells in cranium. However, similar to many other organs, it is suggested that the reciprocal interactions among different tissues also play essential roles in calvarial development. Actually, there are increasing evidence indicating that dura mater (DM) is indispensable for the calvarial morphogenesis and osteogenesis by secreting multiple growth factors, cytokines and extracellular matrix (ECM). Thus, in this review, we first briefly introduce the development of cranium, suture and DM, and then, comprehensively summarize the latest studies exploring the involvement of ECM in DM and cranium development. Eventually, we discussed the reciprocal interactions between calvarium and DM in calvarial development. Actually, our review provides a novel perspective for cranium development by integrating previous classical researches with a spotlight on the mutual interplay between the developing DM and cranium.

Histology Atlas of the Developing Mouse Respiratory System From Prenatal Day 9.0 Through Postnatal Day 30

Respiratory diseases are one of the leading causes of death and disability around the world. Mice are commonly used as models of human respiratory disease. Phenotypic analysis of mice with spontaneous, congenital, inherited, or treatment-related respiratory tract abnormalities requires investigators to discriminate normal anatomic features of the respiratory system from those that have been altered by disease. Many publications describe individual aspects of normal respiratory tract development, primarily focusing on morphogenesis of the trachea and lung. However, a single reference providing detailed low- and high-magnification, high-resolution images of routine hematoxylin and eosin (H&E)-stained sections depicting all major structures of the entire developing murine respiratory system does not exist. The purpose of this atlas is to correct this deficiency by establishing one concise reference of high-resolution color photomicrographs from whole-slide scans of H&E-stained tissue sections. The atlas has detailed descriptions and well-annotated images of the developing mouse upper and lower respiratory tracts emphasizing embryonic days (E) 9.0 to 18.5 and major early postnatal events. The selected images illustrate the main structures and events at key developmental stages and thus should help investigators both confirm the chronological age of mouse embryos and distinguish normal morphology as well as structural (cellular and organ) abnormalities.

The main duct of von Ebner's glands is a source of Sox10 + taste bud progenitors and susceptible to pathogen infections

We have recently demonstrated that Sox10 -expressing ( Sox10 + ) cells give rise to mainly type-III neuronal taste bud cells that are responsible for sour and salt taste. The two tissue compartments containing Sox10 + cells in the surrounding of taste buds include the connective tissue core of taste papillae and von Ebner's glands (vEGs) that are connected to the trench of circumvallate and foliate papillae. In this study, we used inducible Cre mouse models to map the cell lineages of connective tissue (including stromal and Schwann cells) and vEGs and performed single cell RNA-sequencing of the epithelium of Sox10-Cre/tdT mouse circumvallate/vEG complex. In vivo lineage mapping showed that the distribution of traced cells in circumvallate taste buds was closely linked with that in the vEGs, but not in the connective tissue. Sox10 , but not the known stem cells marker Lgr5 , expression was enriched in the cell clusters of main ducts of vEGs that contained abundant proliferating cells, while Sox10-Cre/tdT expression was enriched in type-III taste bud cells and excretory ductal cells. Moreover, multiple genes encoding pathogen receptors are enriched in the vEG main ducts. Our data indicate that the main duct of vEGs is a source of Sox10 + taste bud progenitors and susceptible to pathogen infections.

From Bedside to Bench and Back: Advancing Our Understanding of the Pathophysiology of Cleft Palate and Implications for the Future

OBJECTIVE

To provide a comprehensive understanding of the pathophysiology of cleft palate (CP) and future perspectives.

DESIGN

Literature review.

SETTING

Setting varied across studies by level of care and geographical locations.

INTERVENTIONS

No interventions were performed.

MAIN OUTCOME MEASURE(S)

Primary outcome measures were to summarize our current understanding of palatogenesis in humans and animal models, the pathophysiology of CP, and potential future treatment modalities.

RESULTS

Animal research has provided considerable insight into the pathophysiology, molecular and cellular mechanisms of CP that have allowed for the development of novel treatment strategies. However, much work has yet to be done to connect our mouse model investigations and discoveries to CP in humans. The success of innovative strategies for tissue regeneration in mice provides promise for an exciting new avenue for improved and more targeted management of cleft care with precision medicine in patients. However, significant barriers to clinical translation remain. Among the most notable challenges include the differences in some aspects of palatogenesis and tissue repair between mice and humans, suggesting that potential therapies that have worked in animal models may not provide similar benefits to humans.

CONCLUSIONS

Increased translation of pathophysiological and tissue regeneration studies to clinical trials will bridge a wide gap in knowledge between animal models and human disease. By enhancing interaction between basic scientists and clinicians, and employing our animal model findings of disease mechanisms in concert with what we glean in the clinic, we can generate a more targeted and improved treatment algorithm for patients with CP.

Genetic Analysis and Functional Assessment of a TGFBR2 Variant in Micrognathia and Cleft Palate

Cleft lip and cleft palate are among the most common congenital anomalies and are the result of incomplete fusion of embryonic craniofacial processes or palatal shelves, respectively. We know that genetics play a large role in these anomalies but the list of known causal genes is far from complete. As part of a larger sequencing effort of patients with micrognathia and cleft palate we identified a candidate variant in transforming growth factor beta receptor 2 (TGFBR2) which is rare, changing a highly conserved amino acid, and predicted to be pathogenic by a number of metrics. The family history and population genetics would suggest this specific variant would be incompletely penetrant, but this gene has been convincingly implicated in craniofacial development. In order to test the hypothesis this might be a causal variant, we used genome editing to create the orthologous variant in a new mouse model. Surprisingly, Tgfbr2V387M mice did not exhibit craniofacial anomalies or have reduced survival suggesting this is, in fact, not a causal variant for cleft palate/ micrognathia. The discrepancy between in silico predictions and mouse phenotypes highlights the complexity of translating human genetic findings to mouse models. We expect these findings will aid in interpretation of future variants seen in TGFBR2 from ongoing sequencing of patients with congenital craniofacial anomalies.

Gene Regulatory Networks and Signaling Pathways in Palatogenesis and Cleft Palate: A Comprehensive Review

Palatogenesis is a complex and intricate process involving the formation of the palate through various morphogenetic events highly dependent on the surrounding context. These events comprise outgrowth of palatal shelves from embryonic maxillary prominences, their elevation from a vertical to a horizontal position above the tongue, and their subsequent adhesion and fusion at the midline to separate oral and nasal cavities. Disruptions in any of these processes can result in cleft palate, a common congenital abnormality that significantly affects patient's quality of life, despite surgical intervention. Although many genes involved in palatogenesis have been identified through studies on genetically modified mice and human genetics, the precise roles of these genes and their products in signaling networks that regulate palatogenesis remain elusive. Recent investigations have revealed that palatal shelf growth, patterning, adhesion, and fusion are intricately regulated by numerous transcription factors and signaling pathways, including Sonic hedgehog (Shh), bone morphogenetic protein (Bmp), fibroblast growth factor (Fgf), transforming growth factor beta (Tgf-β), Wnt signaling, and others. These studies have also identified a significant number of genes that are essential for palate development. Integrated information from these studies offers novel insights into gene regulatory networks and dynamic cellular processes underlying palatal shelf elevation, contact, and fusion, deepening our understanding of palatogenesis, and facilitating the development of more efficacious treatments for cleft palate.

Urinary phthalate metabolites and small non-coding RNAs from seminal plasma extracellular vesicles among men undergoing infertility treatment

Non-coding RNA (ncRNA) cargo of extracellular vesicles (EVs) in the male reproductive tract play critical roles in semen quality and emerging evidence suggests their susceptibility to environmental factors. Male phthalate exposures have been linked to poor semen quality, sperm DNA methylation profiles and embryo development; however, there is limited evidence on their potential impact on EV ncRNAs profiles. We evaluated the association between urinary phthalate metabolites and small ncRNAs (sncRNAs) of seminal plasma EVs (spEV) among men receiving clinical infertility care. We conducted sncRNA sequencing of EVs in 96 seminal plasma samples collected from the Sperm Environmental Epigenetics and Development Study (SEEDS). Sequencing reads were mapped to human transcriptome databases using STAR. Urinary metabolite concentrations of thirteen phthalates and two DiNCH, a phthalate alternative, were measured via tandem mass spectrometry. Associations with normalized counts were assessed using EdgeR (FDR<0.05) adjusting for urinary dilution via specific gravity, age, BMI, batch, and biotype-specific total counts. Select metabolites, MEOHP, MECPP, ∑DEHP, MCPP, MCNP, MCOP, were negatively (p < 0.05) correlated with miRNA relative abundance. Similarly, nine metabolites including MEOHP, MECPP, MEHP, MCPP, MHBP, MHiNCH, MiBP, MEHHP, MCOP and ∑DEHP were associated (q < 0.05) with normalized counts from 23 unique ncRNA transcripts (7 miRNAs (pre & mature); 6 tRFs; and 10 piRNAs), most (78%) of which displayed increased expression patterns. miRNA and tRFs gene targets were enriched in vesicle-mediated transport and developmental-related ontology terms, such as tyrosine kinase, head development, and cell morphogenesis. Six genes (MAPK1, BMPR1A/2, PTEN, TGFBR2, TP53 and APP) were present in all the ontology terms and predicted to form protein association networks. piRNAs were annotated to pseudogenes of genes important in EV cargo transfer and embryonic development. This is the first study to associate phthalate exposures to altered spEV sncRNA profiles. Future studies are needed to determine their impact on reproductive outcomes.

The Emerging Roles of the Cephalic Neural Crest in Brain Development and Developmental Encephalopathies

The neural crest, a unique cell population originating from the primitive neural field, has a multi-systemic and structural contribution to vertebrate development. At the cephalic level, the neural crest generates most of the skeletal tissues encasing the developing forebrain and provides the prosencephalon with functional vasculature and meninges. Over the last decade, we have demonstrated that the cephalic neural crest (CNC) exerts an autonomous and prominent control on the development of the forebrain and sense organs. The present paper reviews the primary mechanisms by which CNC can orchestrate vertebrate encephalization. Demonstrating the role of the CNC as an exogenous source of patterning for the forebrain provides a novel conceptual framework with profound implications for understanding neurodevelopment. From a biomedical standpoint, these data suggest that the spectrum of neurocristopathies is broader than expected and that some neurological disorders may stem from CNC dysfunctions.

Novel model of cortical-meningeal organoid co-culture system improves human cortical brain organoid cytoarchitecture

Human cortical organoids (hCOs), derived from human induced pluripotent stem cells (iPSCs), provide a platform to interrogate mechanisms of human brain development and diseases in complex three- dimensional tissues. However, current hCO development methods lack important non-neural tissues, such as the surrounding meningeal layer, that have been shown to be essential for normal corticogenesis and brain development. Here, we first generated hCOs from a single rosette to create more homogenous organoids with consistent size around 250 µm by day 5. We then took advantage of a 3D co-culture system to encapsulate brain organoids with a thin layer of meningeal cells from the very early stages of cortical development. Immunostaining analysis was performed to display different cortical layer markers during different stages of development. Real-time monitoring of organoid development using IncuCyte displayed enhanced morphology and increased growth rate over time. We found that meningeal-encapsulated organoids illustrated better laminar organization by exhibiting higher expression of REELIN by Cajal-Retzius neurons. Presence of meningeal cells resulted in a greater expansion of TBR2 intermediate progenitor cells (IPCs), the deep cortical layer (CTIP2) and upper cortical layer (BRN2). Finally, meningeal-encapsulated organoids enhanced outer radial glial and astrocyte formation illustrated by stronger expression of HOPX and GFAP markers, respectively. This study presents a novel 3D co-culture platform to more closely mimic the in vivo cortical brain structure and enable us to better investigating mechanisms underlying the neurodevelopmental disorders during embryonic development.

Periderm Fate during Palatogenesis: TGF-β and Periderm Dedifferentiation

Failure of palatogenesis results in cleft palate, one of the most common congenital disabilities in humans. During the final phases of palatogenesis, the protective function of the peridermal cell layer must be eliminated for the medial edge epithelia to adhere properly, which is a prerequisite for the successful fusion of the secondary palate. However, a deeper understanding of the role and fate of the periderm in palatal adherence and fusion has been hampered due to a lack of appropriate periderm-specific genetic tools to examine this cell type in vivo. Here we used the cytokeratin-6A (Krt-6a) locus to develop both constitutive (Krt6ai-Cre) and inducible (Krt6ai-CreERT2) periderm-specific Cre driver mouse lines. These novel lines allowed us to achieve both the spatial and temporal control needed to dissect the periderm fate on a cellular resolution during palatogenesis. Our studies suggest that, already before the opposing palatal shelves contact each other, at least some palatal periderm cells start to gradually lose their squamous periderm-like phenotype and dedifferentiate into cuboidal cells, reminiscent of the basal epithelial cells seen in the palatal midline seam. Moreover, we show that transforming growth factor-β (TGF-β) signaling plays a critical periderm-specific role in palatogenesis. Thirty-three percent of embryos lacking a gene encoding the TGF-β type I receptor (Tgfbr1) in the periderm display a complete cleft of the secondary palate. Our subsequent experiments demonstrated that Tgfbr1-deficient periderm fails to undergo appropriate dedifferentiation. These studies define the periderm cell fate during palatogenesis and reveal a novel, critical role for TGF-β signaling in periderm dedifferentiation, which is a prerequisite for appropriate palatal epithelial adhesion and fusion.

Creating morphological diversity in reptilian temporal skull region: A review of potential developmental mechanisms

Reptilian skull morphology is highly diverse and broadly categorized into three categories based on the number and position of the temporal fenestrations: anapsid, synapsid, and diapsid. According to recent phylogenetic analysis, temporal fenestrations evolved twice independently in amniotes, once in Synapsida and once in Diapsida. Although functional aspects underlying the evolution of tetrapod temporal fenestrations have been well investigated, few studies have investigated the developmental mechanisms responsible for differences in the pattern of temporal skull region. To determine what these mechanisms might be, we first examined how the five temporal bones develop by comparing embryonic cranial osteogenesis between representative extant reptilian species. The pattern of temporal skull region may depend on differences in temporal bone growth rate and growth direction during ontogeny. Next, we compared the histogenesis patterns and the expression of two key osteogenic genes, Runx2 and Msx2, in the temporal region of the representative reptilian embryos. Our comparative analyses suggest that the embryonic histological condition of the domain where temporal fenestrations would form predicts temporal skull morphology in adults and regulatory modifications of Runx2 and Msx2 expression in osteogenic mesenchymal precursor cells are likely involved in generating morphological diversity in the temporal skull region of reptiles.

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.

Cranium growth, patterning and homeostasis

Craniofacial development requires precise spatiotemporal regulation of multiple signaling pathways that crosstalk to coordinate the growth and patterning of the skull with surrounding tissues. Recent insights into these signaling pathways and previously uncharacterized progenitor cell populations have refined our understanding of skull patterning, bone mineralization and tissue homeostasis. Here, we touch upon classical studies and recent advances with an emphasis on developmental and signaling mechanisms that regulate the osteoblast lineage for the calvaria, which forms the roof of the skull. We highlight studies that illustrate the roles of osteoprogenitor cells and cranial suture-derived stem cells for proper calvarial growth and homeostasis. We also discuss genes and signaling pathways that control suture patency and highlight how perturbing the molecular regulation of these pathways leads to craniosynostosis. Finally, we discuss the recently discovered tissue and signaling interactions that integrate skull and cerebrovascular development, and the potential implications for both cerebrospinal fluid hydrodynamics and brain waste clearance in craniosynostosis.

Neuroimmune signaling at the brain borders

The central nervous system (CNS) has been viewed as an immunologically privileged site, but emerging works are uncovering a large array of neuroimmune interactions primarily occurring at its borders. CNS barriers sites host diverse population of both innate and adaptive immune cells capable of, directly and indirectly, influence the function of the residing cells of the brain parenchyma. These structures are only starting to reveal their role in controlling brain function under normal and pathological conditions and represent an underexplored therapeutic target for the treatment of brain disorders. This review will highlight the development of the CNS barriers to host neuro-immune interactions and emphasize their newly described roles in neurodevelopmental, neurological, and neurodegenerative disorders, particularly for the meninges.

Transforming Growth Factor Beta Receptor 2 (TGFBR2) Promoter Region Polymorphisms May Be Involved in Mandibular Retrognathism

Skeletal malocclusions are common phenotypes in humans and have a strong influence on genetic factors. Transforming growth factor beta (TGFβ) controls numerous functions of the human body, including cell proliferation, differentiation, and migration. Thus, this study is aimed at evaluating whether genetic polymorphisms in TGFB1 and its receptor TGFBR2 are associated with mandibular retrognathism in German children and adolescents. Children and teenagers older than 8 years in the mixed or permanent dentition were included in this study. Patients with syndromes and facial trauma and patients with congenital alterations were excluded. Digital cephalometric tracings were performed using the anatomical landmarks point A, point B, sella (S), and nasion (N). Patients that have a retrognathic mandible (SNB < 78°) were selected as case group, and the patients with an orthognathic mandible (SNB = 78°– 82°) were selected as the control group. Genomic deoxyribonucleic acid (DNA) from saliva was used to evaluate four genetic polymorphisms in TGFB1 (rs1800469 and rs4803455) and TGBR2 (rs3087465 and rs764522) using real-time PCR. Chi-square or Fisher exact tests were used to compare gender, genotype, and allele distribution among groups. Genotype distribution was calculated in an additive and recessive model. Haplotype analysis was also performed. The established alpha of this study was 5%. A total of 146 patients (age ranging from 8 to 18 years) were included in this epidemiological genetic study. The genetic polymorphism rs3087465 in TGFBR2 was associated with mandibular retrognathism. Carrying the AA genotype in the rs3087465 polymorphism decreased the chance of having mandibular retrognathism (odds ratio = 0.25, confidence interval 95% = 0.06 to 0.94, p = 0.045). None of the haplotypes was associated with mandibular retrognathism (p > 0.05). In conclusion, we found that the genetic polymorphism rs3087465 in the promoter region of the TGFBR2 was associated with mandibular retrognathism in Germans.

Species-specific sensitivity to TGFβ signaling and changes to the Mmp13 promoter underlie avian jaw development and evolution

Precise developmental control of jaw length is critical for survival, but underlying molecular mechanisms remain poorly understood. The jaw skeleton arises from neural crest mesenchyme (NCM), and we previously demonstrated that these progenitor cells express more bone-resorbing enzymes including Matrix metalloproteinase 13 (Mmp13) when they generate shorter jaws in quail embryos versus longer jaws in duck. Moreover, if we inhibit bone resorption or Mmp13, we can increase jaw length. In the current study, we uncover mechanisms establishing species-specific levels of Mmp13 and bone resorption. Quail show greater activation of and sensitivity to transforming growth factor beta (TGFβ) signaling than duck; where intracellular mediators like SMADs and targets like Runt-related transcription factor 2 (Runx2), which bind Mmp13, become elevated. Inhibiting TGFβ signaling decreases bone resorption, and overexpressing Mmp13 in NCM shortens the duck lower jaw. To elucidate the basis for this differential regulation, we examine the Mmp13 promoter. We discover a SMAD-binding element and single nucleotide polymorphisms (SNPs) near a RUNX2-binding element that distinguish quail from duck. Altering the SMAD site and switching the SNPs abolish TGFβ sensitivity in the quail Mmp13 promoter but make the duck promoter responsive. Thus, differential regulation of TGFβ signaling and Mmp13 promoter structure underlie avian jaw development and evolution.

Gene regulatory network from cranial neural crest cells to osteoblast differentiation and calvarial bone development

Calvarial bone is one of the most complex sequences of developmental events in embryology, featuring a uniquely transient, pluripotent stem cell-like population known as the cranial neural crest (CNC). The skull is formed through intramembranous ossification with distinct tissue lineages (e.g. neural crest derived frontal bone and mesoderm derived parietal bone). Due to CNC's vast cell fate potential, in response to a series of inductive secreted cues including BMP/TGF-β, Wnt, FGF, Notch, Hedgehog, Hippo and PDGF signaling, CNC enables generations of a diverse spectrum of differentiated cell types in vivo such as osteoblasts and chondrocytes at the craniofacial level. In recent years, since the studies from a genetic mouse model and single-cell sequencing, new discoveries are uncovered upon CNC patterning, differentiation, and the contribution to the development of cranial bones. In this review, we summarized the differences upon the potential gene regulatory network to regulate CNC derived osteogenic potential in mouse and human, and highlighted specific functions of genetic molecules from multiple signaling pathways and the crosstalk, transcription factors and epigenetic factors in orchestrating CNC commitment and differentiation into osteogenic mesenchyme and bone formation. Disorders in gene regulatory network in CNC patterning indicate highly close relevance to clinical birth defects and diseases, providing valuable transgenic mouse models for subsequent discoveries in delineating the underlying molecular mechanisms. We also emphasized the potential regenerative alternative through scientific discoveries from CNC patterning and genetic molecules in interfering with or alleviating clinical disorders or diseases, which will be beneficial for the molecular targets to be integrated for novel therapeutic strategies in the clinic.

Tgfbr2 in Dental Pulp Cells Guides Neurite Outgrowth in Developing Teeth

Transforming growth factor β (TGFβ) plays an important role in tooth morphogenesis and mineralization. During postnatal development, the dental pulp (DP) mesenchyme secretes neurotrophic factors that guide trigeminal nerve fibers into and throughout the DP. This process is tightly linked with dentin formation and mineralization. Our laboratory established a mouse model in which Tgfbr2 was conditionally deleted in DP mesenchyme using an Osterix promoter-driven Cre recombinase (Tgfbr2 ^cko ). These mice survived postnatally with significant defects in bones and teeth, including reduced mineralization and short roots. Hematoxylin and eosin staining revealed reduced axon-like structures in the mutant mice. Reporter imaging demonstrated that Osterix-Cre activity within the tooth was active in the DP and derivatives, but not in neuronal afferents. Immunofluorescence staining for β3 tubulin (neuronal marker) was performed on serial cryosections from control and mutant molars on postnatal days 7 and 24 (P7, P24). Confocal imaging and pixel quantification demonstrated reduced innervation in Tgfbr2 ^cko first molars at both stages compared to controls, indicating that signals necessary to promote neurite outgrowth were disrupted by Tgfbr2 deletion. We performed mRNA-Sequence (RNA-Seq) and gene onotology analyses using RNA from the DP of P7 control and mutant mice to investigate the pathways involved in Tgfbr2-mediated tooth development. These analyses identified downregulation of several mineralization-related and neuronal genes in the Tgfbr2 ^cko DP compared to controls. Select gene expression patterns were confirmed by quantitative real-time PCR and immunofluorescence imaging. Lastly, trigeminal neurons were co-cultured atop Transwell filters overlying primary Tgfbr2 ^f/f DP cells. Tgfbr2 in the DP was deleted via Adenovirus-expressed Cre recombinase. Confocal imaging of axons through the filter pores showed increased axonal sprouting from neurons cultured with Tgfbr2-positive DP cells compared to neurons cultured alone. Axon sprouting was reduced when Tgfbr2 was knocked down in the DP cells. Immunofluorescence of dentin sialophosphoprotein in co-cultured DP cells confirmed reduced mineralization potential in cells with Tgfbr2 deletion. Both our proteomics and RNA-Seq analyses indicate that axonal guidance cues, particularly semaphorin signaling, were disrupted by Tgfbr2 deletion. Thus, Tgfbr2 in the DP mesenchyme appears to regulate differentiation and the cells' ability to guide neurite outgrowth during tooth mineralization and innervation.

Second Heart Field-derived Cells Contribute to Angiotensin II-mediated Ascending Aortopathies

Background: The ascending aorta is a common location for aneurysm and dissection. This aortic region is populated by a mosaic of medial and adventitial cells that are embryonically derived from either the second heart field (SHF) or the cardiac neural crest. SHF-derived cells populate areas that coincide with the spatial specificity of thoracic aortopathies. The purpose of this study was to determine whether and how SHF-derived cells contribute to ascending aortopathies. Methods: Ascending aortic pathologies were examined in patients with sporadic thoracic aortopathies and angiotensin II (AngII)-infused mice. Ascending aortas without overt pathology from AngII-infused mice were subjected to mass spectrometry assisted proteomics, and molecular features of SHF-derived cells were determined by single cell transcriptomic analyses. Genetic deletion of either low-density lipoprotein receptor-related protein 1 (Lrp1) or transforming growth factor-β receptor 2 (Tgfbr2) in SHF-derived cells was conducted to examine the impact of SHF-derived cells on vascular integrity. Results: Pathologies in human ascending aortic aneurysmal tissues were predominant in outer medial layers and adventitia. This gradient was mimicked in mouse aortas following AngII infusion that was coincident with the distribution of SHF-derived cells. Proteomics indicated that brief AngII infusion, prior to overt pathology, evoked downregulation of SMC proteins and differential expression of extracellular matrix proteins, including several LRP1 ligands. LRP1 deletion in SHF-derived cells augmented AngII-induced ascending aortic aneurysm and rupture. Single cell transcriptomic analysis revealed that brief AngII infusion decreased Lrp1 and Tgfbr2 mRNA abundance in SHF-derived cells and induced a unique fibroblast population with low abundance of Tgfbr2 mRNA. SHF-specific Tgfbr2 deletion led to embryonic lethality at E12.5 with dilatation of the outflow tract and retroperitoneal hemorrhage. Integration of proteomic and single cell transcriptomics results identified plasminogen activator inhibitor 1 (PAI1) as the most increased protein in SHF-derived SMCs and fibroblasts during AngII infusion. Immunostaining revealed a transmural gradient of PAI1 in both ascending aortas of AngII-infused mice and human ascending aneurysmal aortas that mimicked the gradient of medial and adventitial pathologies. Conclusions: SHF-derived cells exert a critical role in maintaining vascular integrity through LRP1 and TGF-β signaling associated with increases of aortic PAI1.

Involvement of homeobox transcription factor Mohawk in palatogenesis

Palatogenesis is affected by many factors, including gene polymorphisms and exposure to toxic chemicals during sensitive developmental periods. Cleft palate is one of the most common congenital anomalies, and ongoing efforts to elucidate the molecular mechanisms underlying palatogenesis are providing useful insights to reduce the risk of this disorder. To identify novel potential regulators of palatogenesis, we analyzed public transcriptome datasets from a mouse model of cleft palate caused by selective deletion of transforming growth factor-β (TGFβ) receptor type 2 in cranial neural crest cells. We identified the homeobox transcription factor Mohawk (Mkx) as a gene downregulated in the maxilla of TGFβ knockout mice compared with wild-type mice. To examine the role of mkx in palatogenesis, we used CRISPR/Cas9 editing to generate zebrafish with impaired expression of mkxa and mkxb, the zebrafish homologs of Mkx. We found that mkx crispants expressed reduced levels of gli1, a critical transcription factor in the Sonic hedgehog (SHH) signaling pathway that plays an important role in the regulation of palatogenesis. Furthermore, we found that mkxa^-/- zebrafish were more susceptible than mkxa^+/+ zebrafish to the deleterious effects of cyclopamine, an inhibitor of SHH signaling, on upper jaw development. These results suggest that Mkx may be involved in palatogenesis regulated by TGFβ and SHH signaling, and that impairment in Mkx function may be related to the etiology of cleft palate.

The growth and expansion of meningeal lymphatic networks are affected in craniosynostosis

Skull malformations are associated with vascular anomalies that can impair fluid balance in the central nervous system. We previously reported that humans with craniosynostosis and mutations in TWIST1 have dural venous sinus malformations. It is still unknown whether meningeal lymphatic networks, which are patterned alongside the venous sinuses, are also affected. We now show that the growth and expansion of meningeal lymphatics are perturbed in Twist1 craniosynostosis models. Changes to the local meningeal environment, including hypoplastic dura and venous malformations, affect the ability of lymphatic networks to sprout and remodel. Dorsal networks along the transverse sinus are hypoplastic with reduced branching. By contrast, basal networks closer to the skull base are more variably affected, showing exuberant growth in some animals suggesting they are compensating for vessel loss in dorsal networks. Injecting a molecular tracer into cerebrospinal fluid reveals significantly less drainage to the deep cervical lymph nodes, indicative of impaired lymphatic function. Collectively, our results show that meningeal lymphatic networks are affected in craniosynostosis, suggesting the clearance of beta-amyloid and waste from the central nervous system may be impeded.

Identification of Novel Single-Nucleotide Variants With Potential of Mediating Malfunction of MicroRNA in Congenital Heart Disease

Congenital heart defects (CHDs) represent the most common human birth defects. Our previous study indicates that the malfunction of microRNAs (miRNAs) in cardiac neural crest cells (NCCs), which contribute to the development of the heart and the connected great vessels, is likely linked to the pathogenesis of human CHDs. In this study, we attempt to further search for causative single-nucleotide variants (SNVs) from CHD patients that mediate the mis-regulating of miRNAs on their downstream target genes in the pathogenesis of CHDs. As a result, a total of 2,925 3'UTR SNVs were detected from a CHD cohort. In parallel, we profiled the expression of miRNAs in cardiac NCCs and found 201 expressed miRNAs. A combined analysis with these data further identified three 3'UTR SNVs, including NFATC1 c.^*654C>T, FGFRL1 c.^*414C>T, and CTNNB1 c.^*729_^*730insT, which result in the malfunction of miRNA-mediated gene regulation. The dysregulations were further validated experimentally. Therefore, our study indicates that miRNA-mediated gene dysregulation in cardiac NCCs could be an important etiology of congenital heart disease, which could lead to a new direction of diagnostic and therapeutic investigation on congenital heart disease.

Seq Your Destiny: Neural Crest Fate Determination in the Genomic Era

Neural crest stem/progenitor cells arise early during vertebrate embryogenesis at the border of the forming central nervous system. They subsequently migrate throughout the body, eventually differentiating into diverse cell types ranging from neurons and glia of the peripheral nervous system to bones of the face, portions of the heart, and pigmentation of the skin. Along the body axis, the neural crest is heterogeneous, with different subpopulations arising in the head, neck, trunk, and tail regions, each characterized by distinct migratory patterns and developmental potential. Modern genomic approaches like single-cell RNA- and ATAC-sequencing (seq) have greatly enhanced our understanding of cell lineage trajectories and gene regulatory circuitry underlying the developmental progression of neural crest cells. Here, we discuss how genomic approaches have provided new insights into old questions in neural crest biology by elucidating transcriptional and posttranscriptional mechanisms that govern neural crest formation and the establishment of axial level identity. Expected final online publication date for the Annual Review of Genetics, Volume 55 is November 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Quantification of three-dimensional morphology of craniofacial mineralized tissue defects in Tgfbr2/Osx-Cre mice

Craniofacial morphology is affected by the growth, development, and three-dimensional (3D) relationship of mineralized structures including the skull, jaws, and teeth. Despite fulfilling different purposes within this region, cranial bones and tooth dentin are derived from mesenchymal cells that are affected by perturbations within the TGF-β signaling pathway. TGFBR2 encodes a transmembrane receptor that is part of the canonical, SMAD-dependent TGF-β signaling pathway and mutations within this gene are associated with Loeys-Dietz syndrome, a condition which often presents with craniofacial signs including craniosynostosis and cleft palate. To investigate the role of Tgfbr2 in immature, but committed, mineralized tissue forming cells, we analyzed postnatal craniofacial morphology in mice with conditional Tgfbr2 deletion in Osx-expressing cells. Novel application of a 3D shape-based comparative technique revealed that Tgfbr2 in Osx-expressing cells results in impaired postnatal molar root and anterior cranial growth. These findings support those from studies using similar Tgfbr2 conditional knockout models, highlight the anomalous facial and dental regions/structures using tomographic imaging-based techniques, and provide insight into the role of Tgfbr2 during postnatal craniofacial development.

Case Report: Rare Presentation of Dentin Abnormalities in Loeys-Dietz Syndrome Type I

Loeys-Dietz syndrome type 1 (LDS1) is caused by a mutation in the transforming growth factor-beta receptor 1 (TGFBR1) gene. We previously characterized the oral and dental anomalies in a cohort of individuals diagnosed with LDS and showed that LDS1 had a high frequency of oral manifestations, and most affected individuals had enamel defects. However, dentin anomalies were not apparent in most patients in the cohort. In this cohort, we had identified dentin anomalies in a patient with LDS1, harboring mutation TGFBR1 c.1459C&gt;T (p.Arg487Trp), and in this report, we present clinical and radiographic findings to confirm the dentin anomaly. The proband had gray-brown discoloration of most teeth typical for dentinogenesis imperfecta (DI). A radiographic exam revealed obliterated or very narrow pulp canals, with maxillary anterior teeth being affected more than the posterior teeth. The son of the proband, who also has the same mutation variant, had a history of DI affecting the primary teeth; however, his permanent teeth were normal in appearance at the time of exam. TGFBR1 is expressed by odontoblasts throughout tooth development and deletion of TGFBR1 in mouse models is known to affect dentin development. In this report, we present a rare case of abnormal dentin in two individuals with LDS1. These dental anomalies may be the first obvious manifestation of a life-threatening systemic disease and demonstrate the variable and multi-organ phenotypic effects in rare diseases.

The Mandibular and Hyoid Arches-From Molecular Patterning to Shaping Bone and Cartilage

The mandibular and hyoid arches collectively make up the facial skeleton, also known as the viscerocranium. Although all three germ layers come together to assemble the pharyngeal arches, the majority of tissue within viscerocranial skeletal components differentiates from the neural crest. Since nearly one third of all birth defects in humans affect the craniofacial region, it is important to understand how signalling pathways and transcription factors govern the embryogenesis and skeletogenesis of the viscerocranium. This review focuses on mouse and zebrafish models of craniofacial development. We highlight gene regulatory networks directing the patterning and osteochondrogenesis of the mandibular and hyoid arches that are actually conserved among all gnathostomes. The first part of this review describes the anatomy and development of mandibular and hyoid arches in both species. The second part analyses cell signalling and transcription factors that ensure the specificity of individual structures along the anatomical axes. The third part discusses the genes and molecules that control the formation of bone and cartilage within mandibular and hyoid arches and how dysregulation of molecular signalling influences the development of skeletal components of the viscerocranium. In conclusion, we notice that mandibular malformations in humans and mice often co-occur with hyoid malformations and pinpoint the similar molecular machinery controlling the development of mandibular and hyoid arches.

Skeletal Deformities in Osterix-Cre;Tgfbr2f/f Mice May Cause Postnatal Death

Transforming growth factor β (TGFβ) signaling plays an important role in skeletal development. We previously demonstrated that the loss of TGFβ receptor II (Tgfbr2) in Osterix-Cre-expressing mesenchyme results in defects in bones and teeth due to reduced proliferation and differentiation in pre-osteoblasts and pre-odontoblasts. These Osterix-Cre;Tgfbr2^f/f mice typically die within approximately four weeks for unknown reasons. To investigate the cause of death, we performed extensive pathological analysis on Osterix-Cre- (Cre-), Osterix-Cre+;Tgfbr2^f/wt (HET), and Osterix-Cre+;Tgfbr2^f/f (CKO) mice. We also crossed Osterix-Cre mice with the ROSA26mTmG reporter line to identify potential off-target Cre expression. The findings recapitulated published skeletal and tooth abnormalities and revealed previously unreported osteochondral dysplasia throughout both the appendicular and axial skeletons in the CKO mice, including the calvaria. Alterations to the nasal area and teeth suggest a potentially reduced capacity to sense and process food, while off-target Cre expression in the gastrointestinal tract may indicate an inability to absorb nutrients. Additionally, altered nasal passages and unexplained changes in diaphragmatic muscle support the possibility of hypoxia. We conclude that these mice likely died due to a combination of breathing difficulties, malnutrition, and starvation resulting primarily from skeletal deformities that decreased their ability to sense, gather, and process food.

Loss of Wiz Function Affects Methylation Pattern in Palate Development and Leads to Cleft Palate

WIZ (Widely Interspaced Zinc Finger) is associated with the G9a-GLP protein complex, a key H3K9 methyltransferase suggesting a role in transcriptional repression. However, its role in embryonic development is poorly described. In order to assess the loss of function of WIZ, we generated CRISPR/Cas9 WIZ knockout mouse model with 32 nucleotide deletion. Observing the lethality status, we identified the WIZ knockouts to be subviable during embryonic development and non-viable after birth. Morphology of developing embryo was analyzed at E14.5 and E18.5 and our findings were supported by microCT scans. Wiz KO showed improper development in multiple aspects, specifically in the craniofacial area. In particular, shorter snout, cleft palate, and cleft eyelids were present in mutant embryos. Palatal shelves were hypomorphic and though elevated to a horizontal position on top of the tongue, they failed to make contact and fuse. By comparison of proliferation pattern and histone methylation in developing palatal shelves we brought new evidence of importance WIZ dependent G9a-GLP methylation complex in craniofacial development, especially in palate shelf fusion.

Spatio-Temporal Expression Pattern of Ki-67, pRB, MMP-9 and Bax in Human Secondary Palate Development

We analyzed the immunohistochemical expression of Ki-67, pRb, Bax, and MMP-9 during the human secondary palate formation (7th to 12th developmental weeks (DWs). The most significant proliferation was observed in the seventh DW with 32% of Ki-67-positive cells in the epithelium, while loose ectomesenchyme condensations (lec) and loose non-condensing ectomesenchyme (lnc) had only 18 and 11%, respectively (Kruskal–Wallis, p < 0.001), and diminished afterwards. Contrarily, pRb-positive cells were mostly located in the lnc (67%), with significant difference in comparison to epithelium and lec in all investigated periods (Kruskal–Wallis, p < 0.001). Ki-67- and pRb-positive cells co-expressed occasionally in all investigated periods. MMP-9 displayed a strong expression pattern with the highest number of positive cells during the seventh DW in the epithelium, with significant difference in comparison to lec and lnc (Kruskal–Wallis, p < 0.0001). The ninth DW is particularly important for the Bax expression, especially in the epithelium (84%), in comparison to lec (58%) and lnc (47%) (Kruskal–Wallis, p < 0.001). The co-expression of Bax and MMP-9 was seen only in the epithelium during seventh and ninth DWs. Our study indicates the parallel persistence of proliferation (Ki-67, pRb) and remodeling (MMP-9) that enables growth and apoptotic activity (Bax) that enable the removal of the epithelial cells at the fusion point during secondary palate formation.

FACEts of mechanical regulation in the morphogenesis of craniofacial structures

During embryonic development, organs undergo distinct and programmed morphological changes as they develop into their functional forms. While genetics and biochemical signals are well recognized regulators of morphogenesis, mechanical forces and the physical properties of tissues are now emerging as integral parts of this process as well. These physical factors drive coordinated cell movements and reorganizations, shape and size changes, proliferation and differentiation, as well as gene expression changes, and ultimately sculpt any developing structure by guiding correct cellular architectures and compositions. In this review we focus on several craniofacial structures, including the tooth, the mandible, the palate, and the cranium. We discuss the spatiotemporal regulation of different mechanical cues at both the cellular and tissue scales during craniofacial development and examine how tissue mechanics control various aspects of cell biology and signaling to shape a developing craniofacial organ.

MicroRNAs regulating TGFβ and BMP signaling in the osteoblast lineage

This review showcases miRNAs contributing to the regulation of bone forming osteoblasts through their effects on the TGFβ and BMP pathways, with a focus on ligands, receptors and SMAD-mediated signaling. The goal of this work is to provide a basis for broadly understanding the contribution of miRNAs to the modulation of TGFβ and BMP signaling in the osteoblast lineage, which may provide a rationale for potential therapeutic strategies. Therefore, the search strategy for this review was restricted to validated miRNA-target interactions within the canonical TGFβ and BMP signaling pathways; miRNA-target interactions based only bioinformatics are not presented. Specifically, this review discusses miRNAs targeting each of the TGFβ isoforms, as well as BMP2 and BMP7. Further, miRNAs targeting the signaling receptors TGFβR1 and TGFβR2, and those targeting the type 1 BMP receptors and BMPR2 are described. Lastly, miRNAs targeting the receptor SMADs, the common SMAD4 and the inhibitory SMAD7 are considered. Of these miRNAs, the miR-140 family plays a prominent role in inhibiting TGFβ signaling, targeting both ligand and receptor. Similarly, the miR-106 isoforms target both BMP2 and SMAD5 to inhibit osteoblastic differentiation. Many of the miRNAs targeting TGFβ and BMP signaling components are induced during fracture, mechanical unloading or estrogen deprivation. Localized delivery of miRNA-based therapeutics that modulate the BMP signaling pathway could promote bone formation.

Altered BMP-Smad4 signaling causes complete cleft palate by disturbing osteogenesis in palatal mesenchyme

As the major receptor mediated BMP signaling in craniofacial development, Bmpr1a expression was detected in the anterior palatal shelves from E13.5 and the posterior palatal shelves from E14.5. However, inactivating BMP receptor in the mesenchyme only leads to anterior cleft palate or submucous cleft palate. The role of BMP signaling in posterior palatal mesenchyme and palatal osteogenesis is still unknown. In this study, a secreted BMP antagonist, Noggin was over-expressed by Osr2-cre^KI to suppress BMP signaling intensively in mouse palatal mesenchyme, which made the newborn mouse displaying complete cleft palate, a phenotype much severer than the anterior or submucous cleft palate. Immunohistochemical analysis indicated that in the anterior and posterior palatal mesenchyme, the canonical BMP-Smad4 signaling was dramatically down-regulated, while the non-canonical BMP signaling pathways were altered little. Although cell proliferation was reduced only in the anterior palatal mesenchyme, the osteogenic condensation and Osterix distribution were remarkably repressed in the posterior palatal mesenchyme by Noggin over-expression. These findings suggested that BMP-Smad4 signaling was essential for the cell proliferation in the anterior palatal mesenchyme, and for the osteogenesis in the posterior palatal mesenchyme. Interestingly, the constitutive activation of Bmpr1a in palatal mesenchyme also caused the complete cleft palate, in which the enhanced BMP-Smad4 signaling resulted in the premature osteogenic differentiation in palatal mesenchyme. Moreover, neither the Noggin over-expression nor Bmpr1a activation disrupted the elevation of palatal shelves. Our study not only suggested that BMP signaling played the differential roles in the anterior and posterior palatal mesenchyme, but also indicated that BMP-Smad4 signaling was required to be finely tuned for the osteogenesis of palatal mesenchyme.

Non-syndromic Cleft Palate: An Overview on Human Genetic and Environmental Risk Factors

The epithelial and mesenchymal cells involved in early embryonic facial development are guided by complex regulatory mechanisms. Any factor perturbing the growth, approach and fusion of the frontonasal and maxillary processes could result in orofacial clefts that represent the most common craniofacial malformations in humans. The rarest and, probably for this reason, the least studied form of cleft involves only the secondary palate, which is posterior to the incisive foramen. The etiology of cleft palate only is multifactorial and involves both genetic and environmental risk factors. The intention of this review is to give the reader an overview of the efforts made by researchers to shed light on the underlying causes of this birth defect. Most of the scientific papers suggesting potential environmental and genetic causes of non-syndromic cleft palate are summarized in this review, including genome-wide association and gene–environment interaction studies.

How faithfully does intramembranous bone regeneration recapitulate embryonic skeletal development?

Postnatal intramembranous bone regeneration plays an important role during a wide variety of musculoskeletal regeneration processes such as fracture healing, joint replacement and dental implant surgery, distraction osteogenesis, stress fracture healing, and repair of skeletal defects caused by trauma or resection of tumors. The molecular basis of intramembranous bone regeneration has been interrogated using rodent models of most of these conditions. These studies reveal that signaling pathways such as Wnt, TGFβ/BMP, FGF, VEGF, and Notch are invoked, reminiscent of embryonic development of membranous bone. Discoveries of several skeletal stem cell/progenitor populations using mouse genetic models also reveal the potential sources of postnatal intramembranous bone regeneration. The purpose of this review is to compare the underlying molecular signals and progenitor cells that characterize embryonic development of membranous bone and postnatal intramembranous bone regeneration.

Cranial Neural Crest Cells and Their Role in the Pathogenesis of Craniofacial Anomalies and Coronal Craniosynostosis

Craniofacial anomalies are among the most common of birth defects. The pathogenesis of craniofacial anomalies frequently involves defects in the migration, proliferation, and fate of neural crest cells destined for the craniofacial skeleton. Genetic mutations causing deficient cranial neural crest migration and proliferation can result in Treacher Collins syndrome, Pierre Robin sequence, and cleft palate. Defects in post-migratory neural crest cells can result in pre- or post-ossification defects in the developing craniofacial skeleton and craniosynostosis (premature fusion of cranial bones/cranial sutures). The coronal suture is the most frequently fused suture in craniosynostosis syndromes. It exists as a biological boundary between the neural crest-derived frontal bone and paraxial mesoderm-derived parietal bone. The objective of this review is to frame our current understanding of neural crest cells in craniofacial development, craniofacial anomalies, and the pathogenesis of coronal craniosynostosis. We will also discuss novel approaches for advancing our knowledge and developing prevention and/or treatment strategies for craniofacial tissue regeneration and craniosynostosis.

Pak1ip1 Loss-of-Function Leads to Cell Cycle Arrest, Loss of Neural Crest Cells, and Craniofacial Abnormalities

Neural crest cells (NCCs) comprise a transient progenitor cell population of neuroepithelial origin that contributes to a variety of cell types throughout vertebrate embryos including most mesenchymal cells of the cranial and facial structures. Consequently, abnormal NCC development underlies a variety of craniofacial defects including orofacial clefts, which constitute some of the most common birth defects. We previously reported the generation of manta ray (mray) mice that carry a loss-of-function allele of the gene encoding the preribosomal factor Pak1ip1. Here we describe cranioskeletal abnormalities in homozygous mray mutants that arise from a loss of NCCs after their specification. Our results show that the localized loss of cranial NCCs in the developing frontonasal prominences is caused by cell cycle arrest and cell death. In addition, and consistent with deficits in ribosome biosynthesis, homozygous mray mutants display decreased protein biosynthesis, further linking Pak1ip1 to a role in ribosome biogenesis.

CXCL12-CXCR4 Interplay Facilitates Palatal Osteogenesis in Mice

Cranial neural crest cells (CNCCs), identified by expression of transcription factor Sox9, migrate to the first branchial arch and undergo proliferation and differentiation to form the cartilage and bone structures of the orofacial region, including the palatal bone. Sox9 promotes osteogenic differentiation and stimulates CXCL12-CXCR4 chemokine-receptor signaling, which elevates alkaline phosphatase (ALP)-activity in osteoblasts to initiate bone mineralization. Disintegration of the midline epithelial seam (MES) is crucial for palatal fusion. Since we earlier demonstrated chemokine-receptor mediated signaling by the MES, we hypothesized that chemokine CXCL12 is expressed by the disintegrating MES to promote the formation of an osteogenic center by CXCR4-positive osteoblasts. Disturbed migration of CNCCs by excess oxidative and inflammatory stress is associated with increased risk of cleft lip and palate (CLP). The cytoprotective heme oxygenase (HO) enzymes are powerful guardians harnessing injurious oxidative and inflammatory stressors and enhances osteogenic ALP-activity. By contrast, abrogation of HO-1 or HO-2 expression promotes pregnancy pathologies. We postulate that Sox9, CXCR4, and HO-1 are expressed in the ALP-activity positive osteogenic regions within the CNCCs-derived palatal mesenchyme. To investigate these hypotheses, we studied expression of Sox9, CXCL12, CXCR4, and HO-1 in relation to palatal osteogenesis between E15 and E16 using (immuno)histochemical staining of coronal palatal sections in wild-type (wt) mice. In addition, the effects of abrogated HO-2 expression in HO-2 KO mice and inhibited HO-1 and HO-2 activity by administrating HO-enzyme activity inhibitor SnMP at E11 in wt mice were investigated at E15 or E16 following palatal fusion. Overexpression of Sox9, CXCL12, CXCR4, and HO-1 was detected in the ALP-activity positive osteogenic regions within the palatal mesenchyme. Overexpression of Sox9 and CXCL12 by the disintegrating MES was detected. Neither palatal fusion nor MES disintegration seemed affected by either HO-2 abrogation or inhibition of HO-activity. Sox9 progenitors seem important to maintain the CXCR4-positive osteoblast pool to drive osteogenesis. Sox9 expression may facilitate MES disintegration and palatal fusion by promoting epithelial-to-mesenchymal transformation (EMT). CXCL12 expression by the MES and the palatal mesenchyme may promote osteogenic differentiation to create osteogenic centers. This study provides novel evidence that CXCL12-CXCR4 interplay facilitates palatal osteogenesis and palatal fusion in mice.

The development, patterning and evolution of neural crest cell differentiation into cartilage and bone

Neural crest cells are a vertebrate-specific migratory, multipotent cell population that give rise to a diverse array of cells and tissues during development. Cranial neural crest cells, in particular, generate cartilage, bone, tendons and connective tissue in the head and face as well as neurons, glia and melanocytes. In this review, we focus on the chondrogenic and osteogenic potential of cranial neural crest cells and discuss the roles of Sox9, Runx2 and Msx1/2 transcription factors and WNT, FGF and TGFβ signaling pathways in regulating neural crest cell differentiation into cartilage and bone. We also describe cranioskeletal defects and disorders arising from gain or loss-of-function of genes that are required for patterning and differentiation of cranial neural crest cells. Finally, we discuss the evolution of skeletogenic potential in neural crest cells and their function as a conduit for intraspecies and interspecies variation, and the evolution of craniofacial novelties.

Heme Oxygenase Protects against Placental Vascular Inflammation and Abortion by the Alarmin Heme in Mice

Both infectious as non-infectious inflammation can cause placental dysfunction and pregnancy complications. During the first trimester of human gestation, when palatogenesis takes place, intrauterine hematoma and hemorrhage are common phenomena, causing the release of large amounts of heme, a well-known alarmin. We postulated that exposure of pregnant mice to heme during palatogenesis would initiate oxidative and inflammatory stress, leading to pathological pregnancy, increasing the incidence of palatal clefting and abortion. Both heme oxygenase isoforms (HO-1 and HO-2) break down heme, thereby generating anti-oxidative and -inflammatory products. HO may thus counteract these heme-induced injurious stresses. To test this hypothesis, we administered heme to pregnant CD1 outbred mice at Day E12 by intraperitoneal injection in increasing doses: 30, 75 or 150 μmol/kg body weight (30H, 75H or 150H) in the presence or absence of HO-activity inhibitor SnMP from Day E11. Exposure to heme resulted in a dose-dependent increase in abortion. At 75H half of the fetuses where resorbed, while at 150H all fetuses were aborted. HO-activity protected against heme-induced abortion since inhibition of HO-activity aggravated heme-induced detrimental effects. The fetuses surviving heme administration demonstrated normal palatal fusion. Immunostainings at Day E16 demonstrated higher numbers of ICAM-1 positive blood vessels, macrophages and HO-1 positive cells in placenta after administration of 75H or SnMP + 30H. Summarizing, heme acts as an endogenous “alarmin” during pregnancy in a dose-dependent fashion, while HO-activity protects against heme-induced placental vascular inflammation and abortion.

Transforming Growth Factor-Beta and Sonic Hedgehog Signaling in Palatal Epithelium Regulate Tenascin-C Expression in Palatal Mesenchyme During Soft Palate Development

During palatogenesis, the palatal shelves first grow vertically on either side of the tongue before changing their direction of growth to horizontal. The extracellular matrix (ECM) plays an important role in these dynamic changes in palatal shelf morphology. Tenascin-C (TNC) is an ECM glycoprotein that shows unique expression in the posterior part of the palatal shelf, but little is known about the regulation of TNC expression. Since transforming growth factor-beta-3 (TGF-β3) and sonic hedgehog (SHH) signaling are known to play important roles in palatogenesis, we investigated whether TGF-β3 and SHH are involved in the regulation of TNC expression in the developing palate. TGF-β3 increased the expression of TNC mRNA and protein in primary mouse embryonic palatal mesenchymal cells (MEPM) obtained from palatal mesenchyme dissected at embryonic day 13.5-14.0. Interestingly, immunohistochemistry experiments revealed that TNC expression was diminished in K14-cre;Tgfbr2 ^fl/fl mice that lack the TGF-β type II receptor in palatal epithelial cells and exhibit cleft soft palate, whereas TNC expression was maintained in Wnt1-cre;Tgfbr2 ^fl/fl mice that lack the TGF-β type II receptor in palatal mesenchymal cells and exhibit a complete cleft palate. SHH also increased the expression of TNC mRNA and protein in MEPM cells. However, although TGF-β3 up-regulated TNC mRNA and protein expression in O9-1 cells (a cranial neural crest cell line), SHH did not. Furthermore, TGF-β inhibited the expression of osteoblastic differentiation markers (osterix and alkaline phosphatase) and induced the expression of fibroblastic markers (fibronectin and periostin) in O9-1 cells, whereas SHH did not affect the expression of osteoblastic and fibroblastic markers in O9-1 cells. However, immunohistochemistry experiments showed that TNC expression was diminished in the posterior palatal shelves of Shh^-/+ ;MFCS4 ^+/- mice, which have deficient SHH signaling in the posterior palatal epithelium. Taken together, our findings support the proposal that TGF-β and SHH signaling in palatal epithelium co-ordinate the expression of TNC in the posterior palatal mesenchyme through a paracrine mechanism. This signal cascade may work in the later stage of palatogenesis when cranial neural crest cells have differentiated into fibroblast-like cells. The spatiotemporal regulation of ECM-related proteins by TGF-β and SHH signaling may contribute not only to tissue construction but also to cell differentiation or determination along the anterior-posterior axis of the palatal shelves.