Neural crest cell signaling pathways critical to cranial bone development and pathology. Exp Cell Res. 2014;325:138-147. [PMID: 24509233 DOI: 10.1016/j.yexcr.2014.01.019]

Aplasia Cutis Congenita Pathomechanisms Reveal Key Regulators of Skin and Skin Appendage Morphogenesis

Aplasia cutis congenita (ACC) manifests at birth as a defect of the scalp skin. New findings answer 2 longstanding questions: why ACC forms and why it affects mainly the midline scalp skin. Dominant-negative mutations in the genes KCTD1 or KCTD15 cause ACC owing to loss of function of KCTD1/KCTD15 complexes in cranial neural crest cells (NCCs), which normally form midline cranial suture mesenchymal cells that express keratinocyte growth factors. Loss of KCTD1/KCTD15 function in NCCs impairs the formation of normal midline cranial sutures and, consequently, the overlying skin, resulting in ACC. Moreover, KCTD1/KCTD15 complexes in keratinocytes regulate skin appendage morphogenesis.

Craniofacial chondrogenesis in organoids from human stem cell-derived neural crest cells

Knowledge of cell signaling pathways that drive human neural crest differentiation into craniofacial chondrocytes is incomplete, yet essential for using stem cells to regenerate craniomaxillofacial structures. To accelerate translational progress, we developed a differentiation protocol that generated self-organizing craniofacial cartilage organoids from human embryonic stem cell-derived neural crest stem cells. Histological staining of cartilage organoids revealed tissue architecture and staining typical of elastic cartilage. Protein and post-translational modification (PTM) mass spectrometry and snRNA-seq data showed that chondrocyte organoids expressed robust levels of cartilage extracellular matrix (ECM) components: many collagens, aggrecan, perlecan, proteoglycans, and elastic fibers. We identified two populations of chondroprogenitor cells, mesenchyme cells and nascent chondrocytes, and the growth factors involved in paracrine signaling between them. We show that ECM components secreted by chondrocytes not only create a structurally resilient matrix that defines cartilage, but also play a pivotal autocrine cell signaling role in determining chondrocyte fate.

Synergistic Effect of Electrical and Biochemical Stimulation on Human iPSC-Derived Neural Differentiation in a Microfluidic Electrode Array Chip

Neural differentiation is crucial for advancing our understanding of the nervous system and developing treatments for neurological disorders. The advanced methods and the ability to manipulate the alignment, proliferation, and differentiation of stem cells are essential for studying neuronal development and synaptic interactions. However, the utilization of human induced pluripotent stem cells (iPSCs) for disease modeling of neurodegenerative conditions may be constrained by the prolonged duration and uncontrolled cell differentiation required for functional neural cell differentiation. Here, we developed a microfluidic chip to enhance the differentiation and maturation of specific neural lineages by placing aligned microelectrodes on the glass surface to regulate the neural differentiation of human iPSCs. The utilization of electrical stimulation (ES) in conjunction with neurotrophic factors (NF) significantly enhanced the efficiency in generating functional neurons from human iPSCs. We also observed that the simultaneous application of NF and ES to human iPSCs promoted their differentiation and maturation into functional neurons while increasing synaptic interactions. Our research demonstrated the effect of combining NF and ES on human iPSC-derived neural differentiation.

Pth1r in Neural Crest Cells Regulates Nasal Cartilage Differentiation

Neural crest cells (NCC) arise from the dorsal margin of the neural plate border and comprise a unique cell population that migrates to and creates the craniofacial region. Although factors including Shh, Fgf8, and bone morphogenetic proteins have been shown to regulate these biological events, the role of parathyroid hormone 1 receptor (Pth1r) has been less studied. We generated an NCC-specific mouse model for Pth1r and researched gene expression, function, and interaction focusing on nasal cartilage framework and midfacial development. Wnt1-Cre;Pth1rfl/fl;Tomatofl/+ mice had perinatal lethality, but we observed short snout and jaws, tongue protrusion, reduced NCC-derived cranial length, increased mineralization in nasal septum and hyoid bones, and less bone mineralization at interfrontal suture in mutants at E18.5. Importantly, the mutant nasal septum and turbinate cartilage histologically revealed gradual, premature accelerated hypertrophic differentiation. We then studied the underlying molecular mechanisms by performing RNA seq analysis and unexpectedly found that expression of Ihh and related signaling molecules was enhanced in mutant nasomaxillary tissues. To see if Pth1r and Ihh signaling are associated, we generated a Wnt1-Cre; Ihhfl/fl;Pth1rfl/fl;Tomatofl/+ (DKO) mouse and compared the phenotypes to those of each single knockout mouse: Wnt1-Cre; Ihhfl/fl;Pth1rfl/+;Tomatofl/+ (Ihh-CKO) and Wnt1-Cre;Ihhfl/+;Pth1rfl/fl;Tomatofl/+ (Pth1r-CKO). Ihh-CKO mice displayed a milder effect. Of note, the excessive hypertrophic conversion of the nasal cartilage framework observed in Pth1r-CKO was somewhat rescued DKO embryos. Further, a half cAMP responsive element and the 4 similar sequences containing 2 mismatches were identified from the promoter to the first intron in Ihh gene. Gli1-CreERT2;Pth1rfl/fl;Tomatofl/+, a Pth1r-deficient model targeted in hedgehog responsive cells, demonstrated the enlarged hypertrophic layer and significantly more Tomato-positive chondrocytes accumulated in the nasal septum and ethmoidal endochondral ossification. Collectively, the data suggest a relevant Pth1r/Ihh interaction. Our findings obtained from novel mouse models for Pth1r signaling illuminate previously unknown aspects in craniofacial biology and development.

KCTD1/KCTD15 complexes control ectodermal and neural crest cell functions, and their impairment causes aplasia cutis

Aplasia cutis congenita (ACC) is a congenital epidermal defect of the midline scalp and has been proposed to be due to a primary keratinocyte abnormality. Why it forms mainly at this anatomic site has remained a long-standing enigma. KCTD1 mutations cause ACC, ectodermal abnormalities, and kidney fibrosis, whereas KCTD15 mutations cause ACC and cardiac outflow tract abnormalities. Here, we found that KCTD1 and KCTD15 can form multimeric complexes and can compensate for each other's loss and that disease mutations are dominant negative, resulting in lack of KCTD1/KCTD15 function. We demonstrated that KCTD15 is critical for cardiac outflow tract development, whereas KCTD1 regulates distal nephron function. Combined inactivation of KCTD1/KCTD15 in keratinocytes resulted in abnormal skin appendages but not in ACC. Instead, KCTD1/KCTD15 inactivation in neural crest cells resulted in ACC linked to midline skull defects, demonstrating that ACC is not caused by a primary defect in keratinocytes but is a secondary consequence of impaired cranial neural crest cells, giving rise to midline cranial suture cells that express keratinocyte-promoting growth factors. Our findings explain the clinical observations in patients with KCTD1 versus KCTD15 mutations, establish KCTD1/KCTD15 complexes as critical regulators of ectodermal and neural crest cell functions, and define ACC as a neurocristopathy.

Subdural osteoma in an adolescent patient with epilepsy: an unusual case report and literature review

OBJECTIVE

Subdural osteoma (SO) is a rarely reported benign tumor, and there is no report of SO manifested with epileptic seizures. We aim to further the understanding of SO-related epilepsy.

METHODS

Here, we report a meaningful case of epilepsy secondary to SO. A systematic review of the literature about SO using the electronic database PubMed and Web of science up to December 2022 was conducted.

RESULTS

A 15-year-old girl presented with epileptic seizures for 8 years. Magnetic resonance imaging revealed an irregular lesion with heterogeneous signal in the right frontal convexity. Right frontal craniotomy was performed to remove the lesion. The pathological diagnosis was SO. Histological analysis revealed that the mechanosensitive ion channels Piezo 1/2 were upregulated in the brain tissue compressed by the osteoma, compared with the levels in the osteoma-free region. Seizure freedom was obtained during the 6-month follow-up after the surgery. We identified 24 cases of SO in 23 articles. With our case, a total of 25 cases with 32 SOs was included. Of 25 cases, 24 are adults, and 1 is a child. Seizure has been reported only in our case. Frontal osteoma was found in 76% of the patients. Symptoms were cured in 56% of the patients after surgery.

CONCLUSION

Surgery is a safe and effective approach to the treatment of symptomatic osteoma. Mechanical compression on cerebral cortex may be a predisposing factor of the epileptogenesis caused by the SO.

Cranial Neural Crest Specific Deletion of Alpl (TNAP) via P0-Cre Causes Abnormal Chondrocyte Maturation and Deficient Cranial Base Growth

Bone growth plate abnormalities and skull shape defects are seen in hypophosphatasia, a heritable disorder in humans that occurs due to the deficiency of tissue nonspecific alkaline phosphatase (TNAP, Alpl) enzyme activity. The abnormal development of the cranial base growth plates (synchondroses) and abnormal skull shapes have also been demonstrated in global Alpl-/- mice. To distinguish local vs. systemic effects of TNAP on skull development, we utilized P0-Cre to knockout Alpl only in cranial neural crest-derived tissues using Alpl flox mice. Here, we show that Alpl deficiency using P0-Cre in cranial neural crest leads to skull shape defects and the deficient growth of the intersphenoid synchondrosis (ISS). ISS chondrocyte abnormalities included increased proliferation in resting and proliferative zones with decreased apoptosis in hypertrophic zones. ColX expression was increased, which is indicative of premature differentiation in the absence of Alpl. Sox9 expression was increased in both the resting and prehypertrophic zones of mutant mice. The expression of Parathyroid hormone related protein (PTHrP) and Indian hedgehog homolog (IHH) were also increased. Finally, cranial base organ culture revealed that inorganic phosphate (Pi) and pyrophosphate (PPi) have specific effects on cell signaling and phenotype changes in the ISS. Together, these results demonstrate that the TNAP expression downstream of Alpl in growth plate chondrocytes is essential for normal development, and that the mechanism likely involves Sox9, PTHrP, IHH and PPi.

BMP signaling during craniofacial development: new insights into pathological mechanisms leading to craniofacial anomalies

Cranial neural crest cells (NCCs) are the origin of the anterior part of the face and the head. Cranial NCCs are multipotent cells giving rise to bones, cartilage, adipose-tissues in the face, and neural cells, melanocytes, and others. The behavior of cranial NCCs (proliferation, cell death, migration, differentiation, and cell fate specification) are well regulated by several signaling pathways; abnormalities in their behavior are often reported as causative reasons for craniofacial anomalies (CFAs), which occur in 1 in 100 newborns in the United States. Understanding the pathological mechanisms of CFAs would facilitate strategies for identifying, preventing, and treating CFAs. Bone morphogenetic protein (BMP) signaling plays a pleiotropic role in many cellular processes during embryonic development. We and others have reported that abnormalities in BMP signaling in cranial NCCs develop CFAs in mice. Abnormal levels of BMP signaling cause miscorrelation with other signaling pathways such as Wnt signaling and FGF signaling, which mutations in the signaling pathways are known to develop CFAs in mice and humans. Recent Genome-Wide Association Studies and exome sequencing demonstrated that some patients with CFAs presented single nucleotide polymorphisms (SNPs), missense mutations, and duplication of genes related to BMP signaling activities, suggesting that defects in abnormal BMP signaling in human embryos develop CFAs. There are still a few cases of BMP-related patients with CFAs. One speculation is that human embryos with mutations in coding regions of BMP-related genes undergo embryonic lethality before developing the craniofacial region as well as mice development; however, no reports are available that show embryonic lethality caused by BMP mutations in humans. In this review, we will summarize the recent advances in the understanding of BMP signaling during craniofacial development in mice and describe how we can translate the knowledge from the transgenic mice to CFAs in humans.

Leite T, Gustafson J, Wilk K, Yozgatian J, Garakani S, Bassir SH, Cunningham ML, Lin CP, Intini G. Expansion of the sagittal suture induces proliferation of skeletal stem cells and sustains endogenous calvarial bone regeneration

In newborn humans, and up to approximately 2 y of age, calvarial bone defects can naturally regenerate. This remarkable regeneration potential is also found in newborn mice and is absent in adult mice. Since previous studies showed that the mouse calvarial sutures are reservoirs of calvarial skeletal stem cells (cSSCs), which are the cells responsible for calvarial bone regeneration, here we hypothesized that the regenerative potential of the newborn mouse calvaria is due to a significant amount of cSSCs present in the newborn expanding sutures. Thus, we tested whether such regenerative potential can be reverse engineered in adult mice by artificially inducing an increase of the cSSCs resident within the adult calvarial sutures. First, we analyzed the cellular composition of the calvarial sutures in newborn and in older mice, up to 14-mo-old mice, showing that the sutures of the younger mice are enriched in cSSCs. Then, we demonstrated that a controlled mechanical expansion of the functionally closed sagittal sutures of adult mice induces a significant increase of the cSSCs. Finally, we showed that if a calvarial critical size bone defect is created simultaneously to the mechanical expansion of the sagittal suture, it fully regenerates without the need for additional therapeutic aids. Using a genetic blockade system, we further demonstrate that this endogenous regeneration is mediated by the canonical Wnt signaling. This study shows that controlled mechanical forces can harness the cSSCs and induce calvarial bone regeneration. Similar harnessing strategies may be used to develop novel and more effective bone regeneration autotherapies.

Augmentation of bone morphogenetic protein signaling in cranial neural crest cells in mice deforms skull base due to premature fusion of intersphenoidal synchondrosis

Craniofacial anomalies (CFAs) are a diverse group of disorders affecting the shapes of the face and the head. Malformation of the cranial base in humans leads CFAs, such as midfacial hypoplasia and craniosynostosis. These patients have significant burdens associated with breathing, speaking, and chewing. Invasive surgical intervention is the current primary option to correct these structural deficiencies. Understanding molecular cellular mechanism for craniofacial development would provide novel therapeutic options for CFAs. In this study, we found that enhanced bone morphogenetic protein (BMP) signaling in cranial neural crest cells (NCCs) (P0-Cre;caBmpr1a mice) causes premature fusion of intersphenoid synchondrosis (ISS) resulting in leading to short snouts and hypertelorism. Histological analyses revealed reduction of proliferation and higher cell death in ISS at postnatal day 3. We demonstrated to prevent the premature fusion of ISS in P0-Cre;caBmpr1a mice by injecting a p53 inhibitor Pifithrin-α to the pregnant mother from E15.5 to E18.5, resulting in rescue from short snouts and hypertelorism. We further demonstrated to prevent premature fusion of cranial sutures in P0-Cre;caBmpr1a mice by injecting Pifithrin-α through E8.5 to E18.5. These results suggested that enhanced BMP-p53-induced cell death in cranial NCCs causes premature fusion of ISS and sutures in time-dependent manner.

Cardiac Neural Crest and Cardiac Regeneration

Neural crest cells (NCCs) are a vertebrate-specific, multipotent stem cell population that have the ability to migrate and differentiate into various cell populations throughout the embryo during embryogenesis. The heart is a muscular and complex organ whose primary function is to pump blood and nutrients throughout the body. Mammalian hearts, such as those of humans, lose their regenerative ability shortly after birth. However, a few vertebrate species, such as zebrafish, have the ability to self-repair/regenerate after cardiac damage. Recent research has discovered the potential functional ability and contribution of cardiac NCCs to cardiac regeneration through the use of various vertebrate species and pluripotent stem cell-derived NCCs. Here, we review the neural crest's regenerative capacity in various tissues and organs, and in particular, we summarize the characteristics of cardiac NCCs between species and their roles in cardiac regeneration. We further discuss emerging and future work to determine the potential contributions of NCCs for disease treatment.

Cranial shape variation in domestication: A pilot study on the case of rabbits

Domestication leads to phenotypic characteristics that have been described to be similar across species. However, this "domestication syndrome" has been subject to debate, related to a lack of evidence for certain characteristics in many species. Here we review diverse literature and provide new data on cranial shape changes due to domestication in the European rabbit (Oryctolagus cuniculus) as a preliminary case study, thus contributing novel evidence to the debate. We quantified cranial shape of 30 wild and domestic rabbits using micro-computed tomography scans and three-dimensional geometric morphometrics. The goal was to test (1) if the domesticates exhibit shorter and broader snouts, smaller teeth, and smaller braincases than their wild counterparts; (2) to what extent allometric scaling is responsible for cranial shape variation; (3) if there is evidence for more variation in the neural crest-derived parts of the cranium compared with those derived of the mesoderm, in accordance with the "neural crest hypothesis." Our own data are consistent with older literature records, suggesting that although there is evidence for some cranial characteristics of the "domestication syndrome" in rabbits, facial length is not reduced. In accordance with the "neural crest hypothesis," we found more shape variation in neural crest versus mesoderm-derived parts of the cranium. Within the domestic group, allometric scaling relationships of the snout, the braincase, and the teeth shed new light on ubiquitous patterns among related taxa. This study-albeit preliminary due to the limited sample size-adds to the growing evidence concerning nonuniform patterns associated with domestication.

Enhanced BMP signaling through ALK2 attenuates keratinocyte differentiation

Accumulated studies have suggested that bone morphogenetic proteins (BMPs) are critical for skin development. However, it remains elusive how BMP signaling via ALK2 (aka ACVR1), one of the important BMP type I receptors, regulates keratinocyte differentiation. To address this question, we utilized a genetic system that enhances BMP signaling via ALK2 in an epidermis-specific manner in mice (hereafter ca-Alk2:K14-Cre). Ca-Alk2:K14-Cre mice displayed a sticky and hairless skin phenotype with a thinner epidermis incapable of differentiating. Although cellular proliferation and survival were comparable between wild-type and ca-Alk2:K14-Cre mice, skin differentiation was severely hampered in ca-Alk2:K14-Cre mice. To uncover the mechanism of altered keratinocyte differentiation, we performed a transcriptome analysis. As a result, we found that the expression levels of cell cycle inhibitor p21 were increased in ca-Alk2:K14-Cre mice. Our findings suggest that aberrant BMP signaling via ALK2 positively regulates p21 expression that attenuates keratinocyte differentiation, and further highlights the critical role of BMP signaling in skin development.

Variant analyses of candidate genes in orofacial clefts in multi-ethnic populations

OBJECTIVES

Cleft lip with/without cleft palate and cleft palate only is congenital birth defects where the upper lip and/or palate fail to fuse properly during embryonic facial development. Affecting ~1.2/1000 live births worldwide, these orofacial clefts impose significant social and financial burdens on affected individuals and their families. Orofacial clefts have a complex etiology resulting from genetic variants combined with environmental covariates. Recent genome-wide association studies and whole-exome sequencing for orofacial clefts identified significant genetic associations and variants in several genes. Of these, we investigated the role of common/rare variants in SHH, RORA, MRPL53, ACVR1, and GDF11.

MATERIALS AND METHODS

We sequenced these five genes in 1255 multi-ethnic cleft lip with/without palate and cleft palate only samples in order to find variants that may provide potential explanations for the missing heritability of orofacial clefts. Rare and novel variants were further analyzed using in silico predictive tools.

RESULTS

Ninteen total variants of interest were found, with variant types including stop-gain, missense, synonymous, intronic, and splice-site variants. Of these, 3 novel missense variants were found, one in SHH, one in RORA, and one in GDF11.

CONCLUSION

This study provides evidence that variants in SHH, RORA, MRPL53, ACVR1, and GDF11 may contribute to risk of orofacial clefts in various populations.

Roles of osteoclasts in alveolar bone remodeling

Osteoclasts are large multinucleated cells from hematopoietic origin and are responsible for bone resorption. A balance between osteoclastic bone resorption and osteoblastic bone formation is critical to maintain bone homeostasis. The alveolar bone, also called the alveolar process, is the part of the jawbone that holds the teeth and supports oral functions. It differs from other skeletal bones in several aspects: its embryonic cellular origin, the form of ossification, and the presence of teeth and periodontal tissues; hence, understanding the unique characteristic of the alveolar bone remodeling is important to maintain oral homeostasis. Excessive osteoclastic bone resorption is one of the prominent features of bone diseases in the jaw such as periodontitis. Therefore, inhibiting osteoclast formation and bone resorptive process has been the target of therapeutic intervention. Understanding the mechanisms of osteoclastic bone resorption is critical for the effective treatment of bone diseases in the jaw. In this review, we discuss basic principles of alveolar bone remodeling with a specific focus on the osteoclastic bone resorptive process and its unique functions in the alveolar bone. Lastly, we provide perspectives on osteoclast-targeted therapies and regenerative approaches associated with bone diseases in the jaw.

Developmental principles informing human pluripotent stem cell differentiation to cartilage and bone

Human pluripotent stem cells can differentiate into any cell type given appropriate signals and hence have been used to research early human development of many tissues and diseases. Here, we review the major biological factors that regulate cartilage and bone development through the three main routes of neural crest, lateral plate mesoderm and paraxial mesoderm. We examine how these routes have been used in differentiation protocols that replicate skeletal development using human pluripotent stem cells and how these methods have been refined and improved over time. Finally, we discuss how pluripotent stem cells can be employed to understand human skeletal genetic diseases with a developmental origin and phenotype, and how developmental protocols have been applied to gain a better understanding of these conditions.

Isolation and Culture of Cranial Neural Crest Cells from the First Branchial Arch of Mice

Craniofacial anomalies (CFA) are a diverse group of deformities, which affect the growth of the head and face. Dysregulation of cranial neural crest cell (NCC) migration, proliferation, differentiation, and/or cell fate specification have been reported to contribute to CFA. Understanding of the mechanisms through which cranial NCCs contribute for craniofacial development may lead to identifying meaningful clinical targets for the prevention and treatment of CFA. Isolation and culture of cranial NCCs in vitro facilitates screening and analyses of molecular cellular mechanisms of cranial NCCs implicated in craniofacial development. Here, we present a method for the isolation and culture of cranial NCCs harvested from the first branchial arch at early embryonic stages. Morphology of isolated cranial NCCs was similar to O9-1 cells, a cell line for neural crest stem cells. Moreover, cranial NCCs isolated from a transgenic mouse line with enhanced bone morphogenetic protein (BMP) signaling in NCCs showed an increase in their chondrogenic differentiation capacity, suggesting maintenance of their in vivo differentiation potentials observed in vitro. Taken together, our established method is useful to visualize cellular behaviors of cranial NCCs.

On the association between Chiari malformation type 1, bone mineral density and bone related genes

Background

Chiari malformation type 1 (C1M) is a neurological disease characterized by herniation of the cerebellar tonsils below the foramen magnum. Cranial bone constriction is suspected to be its main cause. To date, genes related to bone development (e.g. DKK1 or COL1A2) have been associated with C1M, while some bone diseases (e.g. Paget) have been found to cosegregate with C1M. Nevertheless, the association between bone mineral density (BMD) and C1M has not been investigated, yet. Here, we systematically investigate the association between C1M and BMD, and between bone related genes and C1M.

Methods

We have recruited a small cohort of C1M patients (12 unrelated patients) in whom we have performed targeted sequencing of an in-house bone-related gene panel and BMD determination through non-invasive DXA.

Results

In the search for association between the bone related genes and C1M we have found variants in more than one C1M patient in WNT16, CRTAP, MYO7A and NOTCH2. These genes have been either associated with craniofacial development in different ways, or previously associated with C1M (MYO7A). Regarding the potential link between BMD and C1M, we have found three osteoporotic patients and one patient who had high BMD, very close to the HBM phenotype values, although most patients had normal BMD.

Conclusions

Variants in bone related genes have been repeatedly found in some C1M cases. The relationship of bone genes with C1M deserves further study, to get a clearer estimate of their contribution to its etiology. No direct correlation between BMD and C1M was observed.

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We used an in-house bone gene panel to investigate a small cohort of C1M patients.

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Variants in WNT16, CRTAP, MYO7A and NOTCH2 were found in more than one C1M patient.

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No clear relationship was found between C1M and BMD in this small C1M cohort.

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.

Disruption of Trip11 in cranial neural crest cells is associated with increased ER and Golgi stress contributing to skull defects in mice

BACKGROUND

Absence of Golgi microtubule-associated protein 210 (GMAP210), encoded by the TRIP11 gene, results in achondrogenesis. Although TRIP11 is thought to be specifically required for chondrogenesis, human fetuses with the mutation of TRIP11 also display bony skull defects where chondrocytes are usually not present. This raises an important question of how TRIP11 functions in bony skull development.

RESULTS

We disrupted Trip11 in neural crest-derived cell populations, which are critical for developing skull in mice. In Trip11 mutant skulls, expression levels of ER stress markers were increased compared to controls. Morphological analysis of electron microscopy data revealed swollen ER in Trip11 mutant skulls. Unexpectedly, we also found that Golgi stress increased in Trip11 mutant skulls, suggesting that both ER and Golgi stress-induced cell death may lead to osteopenia-like phenotypes in Trip11 mutant skulls. These data suggest that Trip11 plays pivotal roles in the regulation of ER and Golgi stress, which are critical for osteogenic cell survival.

CONCLUSION

We have recently reported that the molecular complex of ciliary protein and GMAP210 is required for collagen trafficking. In this paper, we further characterized the important role of Trip11 being possibly involved in the regulation of ER and Golgi stress during skull development. This article is protected by copyright. All rights reserved.

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 Osr2^Cre;Tgfbr1^fl/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 Osr2^Cre;Tgfbr1^fl/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.

Modularity patterns in mammalian domestication: Assessing developmental hypotheses for diversification

The neural crest hypothesis posits that selection for tameness resulted in mild alterations to neural crest cells during embryonic development, which directly or indirectly caused the appearance of traits associated with the "domestication syndrome" (DS). Although representing an appealing unitary explanation for the generation of domestic phenotypes, support for this hypothesis from morphological data and for the validity of the DS remains a topic of debate. This study used the frameworks of morphological integration and modularity to assess patterns that concern the embryonic origin of the skull and issues around the neural crest hypothesis. Geometric morphometric landmarks were used to quantify cranial trait interactions between six pairs of wild and domestic mammals, comprising representatives that express between five and 17 of the traits included in the DS, and examples from each of the pathways by which animals entered into relationships with humans. We predicted the presence of neural crest vs mesoderm modular structure to the cranium, and that elements in the neural crest module would show lower magnitudes of integration and higher disparity in domestic forms compared to wild forms. Our findings support modular structuring based on tissue origin (neural crest, mesoderm) modules, along with low module integration magnitudes for neural crest cell derived cranial elements, suggesting differential capacity for evolutionary response among those elements. Covariation between the neural crest and mesoderm modules accounted for major components of shape variation for most domestic/wild pairs. Contra to our predictions, however, we find domesticates share similar integration magnitudes to their wild progenitors, indicating that higher disparity in domesticates is not associated with magnitude changes to integration among either neural crest or mesoderm derived elements. Differences in integration magnitude among neural crest and mesoderm elements across species suggest that developmental evolution preserves a framework that promotes flexibility under the selection regimes of domestication.

Cranial Suture Mesenchymal Stem Cells: Insights and Advances

The cranial bones constitute the protective structures of the skull, which surround and protect the brain. Due to the limited repair capacity, the reconstruction and regeneration of skull defects are considered as an unmet clinical need and challenge. Previously, it has been proposed that the periosteum and dura mater provide reparative progenitors for cranial bones homeostasis and injury repair. In addition, it has also been speculated that the cranial mesenchymal stem cells reside in the perivascular niche of the diploe, namely, the soft spongy cancellous bone between the interior and exterior layers of cortical bone of the skull, which resembles the skeletal stem cells’ distribution pattern of the long bone within the bone marrow. Not until recent years have several studies unraveled and validated that the major mesenchymal stem cell population of the cranial region is primarily located within the suture mesenchyme of the skull, and hence, they are termed suture mesenchymal stem cells (SuSCs). Here, we summarized the characteristics of SuSCs, this newly discovered stem cell population of cranial bones, including the temporospatial distribution pattern, self-renewal, and multipotent properties, contribution to injury repair, as well as the signaling pathways and molecular mechanisms associated with the regulation of SuSCs.

Comparisons of Neurotrophic Effects of Mesenchymal Stem Cells Derived from Different Tissues on Chronic Spinal Cord Injury Rats

Cell-based therapies with mesenchymal stem cells (MSCs) are considered as promising strategies for spinal cord injury (SCI). MSCs have unique characteristics due to differences in the derived tissues. However, relatively few studies have focused on differences in the therapeutic effects of MSCs derived from different tissues. In this study, the therapeutic effects of adipose tissue-derived MSCs, bone marrow-derived MSCs, and cranial bone-derived MSCs (cMSCs) on chronic SCI model rats were compared. MSCs were established from the collected adipose tissue, bone marrow, and cranial bone. Neurotrophic factor expression of each MSC type was analyzed by real-time PCR. SCI rats were established using the weight-drop method and transplanted intravenously with MSCs at 4 weeks after SCI. Hindlimb motor function was evaluated from before injury to 4 weeks after transplantation. Endogenous neurotrophic factor and neural repair factor expression in spinal cord (SC) tissue were examined by real-time PCR and western blot analyses. Although there were no differences in the expression levels of cell surface markers and multipotency, expression of Bdnf, Ngf, and Sort1 (Nt-3) was relatively higher in cMSCs. Transplantation of cMSCs improved motor function of chronic SCI model rats. Although there was no difference in the degree of engraftment of transplanted cells in the injured SC tissue, transplantation of cMSCs enhanced Bdnf, TrkB, and Gap-43 messenger RNA expression and synaptophysin protein expression in injured SC tissue. As compared with MSCs derived other tissues, cMSCs highly express many neurotrophic factors, which improved motor function in chronic SCI model rats by promoting endogenous neurotrophic and neural plasticity factors. These results demonstrate the efficacy of cMSCs in cell-based therapy for chronic SCI.

Craniosynostosis: current conceptions and misconceptions

Cranial bones articulate in areas called sutures that must remain patent until skull growth is complete. Craniosynostosis is the condition that results from premature closure of one or more of the cranial vault sutures, generating facial deformities and more importantly, skull growth restrictions with the ability to severely affect brain growth. Typically, craniosynostosis can be expressed as an isolated event, or as part of syndromic phenotypes. Multiple signaling mechanisms interact during developmental stages to ensure proper and timely suture fusion. Clinical outcome is often a product of craniosynostosis subtypes, number of affected sutures and timing of premature suture fusion. The present work aimed to review the different aspects involved in the establishment of craniosynostosis, providing a close view of the cellular, molecular and genetic background of these malformations.

Macropore design of tissue engineering scaffolds regulates mesenchymal stem cell differentiation fate

Craniosynostosis is a debilitating birth defect characterized by the premature fusion of cranial bones resulting from premature loss of stem cells located in suture tissue between growing bones. Mesenchymal stromal cells in long bone and the cranial suture are known to be multipotent cell sources in the appendicular skeleton and cranium, respectively. We are developing biomaterial constructs to maintain stemness of the cranial suture cell population towards an ultimate goal of diminishing craniosynostosis patient morbidity. Recent evidence suggests that physical features of synthetic tissue engineering scaffolds modulate cell and tissue fate. In this study, macroporous tissue engineering scaffolds with well-controlled spherical pores were fabricated by a sugar porogen template method. Cell-scaffold constructs were implanted subcutaneously in mice for up to eight weeks then assayed for mineralization, vascularization, extracellular matrix composition, and gene expression. Pore size differentially regulates cell fate, where sufficiently large pores provide an osteogenic niche adequate for bone formation, while sufficiently small pores (<125 μm in diameter) maintain stemness and prevent differentiation. Cell-scaffold constructs cultured in vitro followed the same pore size-controlled differentiation fate. We therefore attribute the differential cell and tissue fate to scaffold pore geometry. Scaffold pore size regulates mesenchymal cell fate, providing a novel design motif to control tissue regenerative processes and develop mesenchymal stem cell niches in vivo and in vitro through biophysical features.

Intradural osteomas: Report of two cases

BACKGROUND

Intradural osteoma is very rarely located in the subdural or subarachnoid space. Unfortunately, intradural osteoma lacks specificity in clinical manifestations and imaging features and there is currently no consensus on its diagnosis method or treatment strategy. Moreover, the pathogenesis of osteoma without skull structure involvement remains unclear.

CASE SUMMARY

We describe two cases of intradural osteomas located in the subdural and subarachnoid spaces, respectively. The first case involved a 47-year-old woman who presented with a 3-year history of intermittent headache and dizziness. Intraoperatively, a bony hard mass was found in the left frontal area, attached to the inner surface of the dura mater and compressing the underlying arachnoid membrane and brain. The second case involved a 56-year-old woman who had an intracranial high-density lesion isolated under the right greater wing of the sphenoid. Intraoperatively, an arachnoid-covered bony tumor was found in the sylvian fissure. The pathological diagnosis for both patients was osteoma.

CONCLUSION

Surgery and pathological examination are required for diagnosis of intradural osteomas, and craniotomy is a safe and effective treatment.

Trio cooperates with Myh9 to regulate neural crest-derived craniofacial development

Trio is a unique member of the Rho-GEF family that has three catalytic domains and is vital for various cellular processes in both physiological and developmental settings. TRIO mutations in humans are involved in craniofacial abnormalities, in which patients present with mandibular retrusion. However, little is known about the molecular mechanisms of Trio in neural crest cell (NCC)-derived craniofacial development, and there is still a lack of direct evidence to assign a functional role to Trio in NCC-induced craniofacial abnormalities. Methods: In vivo, we used zebrafish and NCC-specific knockout mouse models to investigate the phenotype and dynamics of NCC development in Trio morphants. In vitro, iTRAQ, GST pull-down assays, and proximity ligation assay (PLA) were used to explore the role of Trio and its potential downstream mediators in NCC migration and differentiation. Results: In zebrafish and mouse models, disruption of Trio elicited a migration deficit and impaired the differentiation of NCC derivatives, leading to craniofacial growth deficiency and mandibular retrusion. Moreover, Trio positively regulated Myh9 expression and directly interacted with Myh9 to coregulate downstream cellular signaling in NCCs. We further demonstrated that disruption of Trio or Myh9 inhibited Rac1 and Cdc42 activity, specifically affecting the nuclear export of β-catenin and NCC polarization. Remarkably, craniofacial abnormalities caused by trio deficiency in zebrafish could be partially rescued by the injection of mRNA encoding myh9, ca-Rac1, or ca-Cdc42. Conclusions: Here, we identified that Trio, interacting mostly with Myh9, acts as a key regulator of NCC migration and differentiation during craniofacial development. Our results indicate that trio morphant zebrafish and Wnt1-cre;Trio^fl/fl mice offer potential model systems to facilitate the study of the pathogenic mechanisms of Trio mutations causing craniofacial abnormalities.

JAGGED1 stimulates cranial neural crest cell osteoblast commitment pathways and bone regeneration independent of canonical NOTCH signaling

Craniofacial bone loss is a complex clinical problem with limited regenerative solutions. Currently, BMP2 is used as a bone-regenerative therapy in adults, but in pediatric cases of bone loss, it is not FDA-approved due to concerns of life-threatening inflammation and cancer. Development of a bone-regenerative therapy for children will transform our ability to reduce the morbidity associated with current autologous bone grafting techniques. We discovered that JAGGED1 (JAG1) induces cranial neural crest (CNC) cell osteoblast commitment during craniofacial intramembranous ossification, suggesting that exogenous JAG1 delivery is a potential craniofacial bone-regenerative approach. In this study, we found that JAG1 delivery using synthetic hydrogels containing O9-1 cells, a CNC cell line, into critical-sized calvarial defects in C57BL/6 mice provided robust bone-regeneration. Since JAG1 signals through canonical (Hes1/Hey1) and non-canonical (JAK2) NOTCH pathways in CNC cells, we used RNAseq to analyze transcriptional pathways activated in CNC cells treated with JAG1 ± DAPT, a NOTCH-canonical pathway inhibitor. JAG1 upregulated expression of multiple NOTCH canonical pathway genes (Hes1), which were downregulated in the presence of DAPT. JAG1 also induced bone chemokines (Cxcl1), regulators of cytoskeletal organization and cell migration (Rhou), signaling targets (STAT5), promoters of early osteoblast cell proliferation (Prl2c2, Smurf1 and Esrra), and, inhibitors of osteoclasts (Id1). In the presence of DAPT, expression levels of Hes1 and Cxcl1 were decreased, whereas, Prl2c2, Smurf1, Esrra, Rhou and Id1 remain elevated, suggesting that JAG1 induces osteoblast proliferation through these non-canonical genes. Pathway analysis of JAG1 + DAPT-treated CNC cells revealed significant upregulation of multiple non-canonical pathways, including the cell cycle, tubulin pathway, regulators of Runx2 initiation and phosphorylation of STAT5 pathway. In total, our data show that JAG1 upregulates multiple pathways involved in osteogenesis, independent of the NOTCH canonical pathway. Moreover, our findings suggest that JAG1 delivery using a synthetic hydrogel, is a bone-regenerative approach with powerful translational potential.

Augmented BMP signaling commits cranial neural crest cells to a chondrogenic fate by suppressing autophagic β-catenin degradation

Cranial neural crest cells (CNCCs) are a population of multipotent stem cells that give rise to craniofacial bone and cartilage during development. Bone morphogenetic protein (BMP) signaling and autophagy have been individually implicated in stem cell homeostasis. Mutations that cause constitutive activation of the BMP type I receptor ACVR1 cause the congenital disorder fibrodysplasia ossificans progressiva (FOP), which is characterized by ectopic cartilage and bone in connective tissues in the trunk and sometimes includes ectopic craniofacial bones. Here, we showed that enhanced BMP signaling through the constitutively activated ACVR1 (ca-ACVR1) in CNCCs in mice induced ectopic cartilage formation in the craniofacial region through an autophagy-dependent mechanism. Enhanced BMP signaling suppressed autophagy by activating mTORC1, thus blocking the autophagic degradation of β-catenin, which, in turn, caused CNCCs to adopt a chondrogenic identity. Transient blockade of mTORC1, reactivation of autophagy, or suppression of Wnt-β-catenin signaling reduced ectopic cartilages in ca-Acvr1 mutants. Our results suggest that BMP signaling and autophagy coordinately regulate β-catenin activity to direct the fate of CNCCs during craniofacial development. These findings may also explain why some patients with FOP develop ectopic bones through endochondral ossification in craniofacial regions.

Molecular and Cellular Pathogenesis of Ellis-van Creveld Syndrome: Lessons from Targeted and Natural Mutations in Animal Models

Ellis-van Creveld syndrome (EVC; MIM ID #225500) is a rare congenital disease with an occurrence of 1 in 60,000. It is characterized by remarkable skeletal dysplasia, such as short limbs, ribs and polydactyly, and orofacial anomalies. With two of three patients first noted as being offspring of consanguineous marriage, this autosomal recessive disease results from mutations in one of two causative genes: EVC or EVC2/LIMBIN. The recent identification and manipulation of genetic homologs in animals has deepened our understanding beyond human case studies and provided critical insight into disease pathogenesis. This review highlights the utility of animal-based studies of EVC by summarizing: (1) molecular biology of EVC and EVC2/LIMBIN, (2) human disease signs, (3) dysplastic limb development, (4) craniofacial anomalies, (5) tooth anomalies, (6) tracheal cartilage abnormalities, and (7) EVC-like disorders in non-human species.

BMP Signaling in the Development and Regeneration of Cranium Bones and Maintenance of Calvarial Stem Cells

The bone morphogenetic protein (BMP) signaling pathway is highly conserved across many species, and its importance for the patterning of the skeletal system has been demonstrated. A disrupted BMP signaling pathway results in severe skeletal defects. Murine calvaria has been identified to have dual-tissue lineages, namely, the cranial neural-crest cells and the paraxial mesoderm. Modulations of the BMP signaling pathway have been demonstrated to be significant in determining calvarial osteogenic potentials and ossification in vitro and in vivo. More importantly, the BMP signaling pathway plays a role in the maintenance of the homeostasis of the calvarial stem cells, indicating a potential clinic significance in calvarial bone and in expediting regeneration. Following the inherent evidence of BMP signaling in craniofacial biology, we summarize recent discoveries relating to BMP signaling in the development of calvarial structures, functions of the suture stem cells and their niche and regeneration. This review will not only provide a better understanding of BMP signaling in cranial biology, but also exhibit the molecular targets of BMP signaling that possess clinical potential for tissue regeneration.

Role of thyroid hormones in craniofacial development

The development of the craniofacial skeleton relies on complex temporospatial organization of diverse cell types by key signalling molecules. Even minor disruptions to these processes can result in deleterious consequences for the structure and function of the skull. Thyroid hormone deficiency causes delayed craniofacial and tooth development, dysplastic facial features and delayed development of the ossicles in the middle ear. Thyroid hormone excess, by contrast, accelerates development of the skull and, in severe cases, might lead to craniosynostosis with neurological sequelae and facial hypoplasia. The pathogenesis of these important abnormalities remains poorly understood and underinvestigated. The orchestration of craniofacial development and regulation of suture and synchondrosis growth is dependent on several critical signalling pathways. The underlying mechanisms by which these key pathways regulate craniofacial growth and maturation are largely unclear, but studies of single-gene disorders resulting in craniofacial malformations have identified a number of critical signalling molecules and receptors. The craniofacial consequences resulting from gain-of-function and loss-of-function mutations affecting insulin-like growth factor 1, fibroblast growth factor receptor and WNT signalling are similar to the effects of altered thyroid status and mutations affecting thyroid hormone action, suggesting that these critical pathways interact in the regulation of craniofacial development.

ROCK-TAZ signaling axis regulates mechanical tension-induced osteogenic differentiation of rat cranial sagittal suture mesenchymal stem cells

Mechanical force across sutures is able to promote suture osteogenesis. Orthodontic clinics often use this biological characteristic of sutures to treat congenital cranio-maxillofacial malformations. However, the underlying mechanisms still remain poorly understood. Craniofacial sutures provide a special growth source and support primary sites of osteogenesis. Here, we isolated rat sagittal suture cells (rSAGs), which had mesenchymal stem cell characteristics and differentiating abilities. Cells were then subjected to mechanical tension (5% elongation, 0.5 Hz; sinusoidal waveforms) showing that mechanical tension could enhance osteogenic differentiation but hardly affect proliferation of rSAGs. Besides, mechanical tension could increase Rho-associated kinase (ROCK) expression and enhance transcriptional coactivator with PDZ-binding motif (TAZ) nuclear translocation. Inhibiting ROCK expression could suppress tension-induced osteogenesis and block tension-induced upregulation of nuclear TAZ. In addition, our results indicated that TAZ had direct combination sites with runt-related transcription factor 2 (Runx2) in rSAGs, and knock-downed TAZ simultaneously decreased the expression of Runx2 no matter with or without mechanical tension. In summary, our findings demonstrated that the multipotency of rSAGs in vitro could give rise to early osteogenic differentiation under mechanical tension, which was mediated by ROCK-TAZ signal axis.

The role of teratogens in neural crest development

The neural crest (NC), discovered by Wilhelm His 150 years ago, gives rise to a multipotent migratory embryonic cell population that generates a remarkably diverse and important array of cell types during the development of the vertebrate embryo. These cells originate in the neural plate border (NPB), which is the ectoderm between the neural plate and the epidermis. They give rise to the neurons and glia of the peripheral nervous system, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others. Neurocristopathies are a class of congenital diseases resulting from the abnormal induction, specification, migration, differentiation or death of NC cells (NCCs) during embryonic development and have an important medical and societal impact. In general, congenital defects affect an appreciable percentage of newborns worldwide. Some of these defects are caused by teratogens, which are agents that negatively impact the formation of tissues and organs during development. In this review, we will discuss the teratogens linked to the development of many birth defects, with a strong focus on those that specifically affect the development of the NC, thereby producing neurocristopathies. Although increasing attention is being paid to the effect of teratogens on embryonic development in general, there is a strong need to critically evaluate the specific role of these agents in NC development. Therefore, increased understanding of the role of these factors in NC development will contribute to the planning of strategies aimed at the prevention and treatment of human neurocristopathies, whose etiology was previously not considered.

Dosage analysis of the 7q11.23 Williams region identifies BAZ1B as a major human gene patterning the modern human face and underlying self-domestication

We undertook a functional dissection of chromatin remodeler BAZ1B in neural crest (NC) stem cells (NCSCs) from a uniquely informative cohort of typical and atypical patients harboring 7q11.23 copy number variants. Our results reveal a key contribution of BAZ1B to NCSC in vitro induction and migration, coupled with a crucial involvement in NC-specific transcriptional circuits and distal regulation. By intersecting our experimental data with new paleogenetic analyses comparing modern and archaic humans, we found a modern-specific enrichment for regulatory changes both in BAZ1B and its experimentally defined downstream targets, thereby providing the first empirical validation of the human self-domestication hypothesis and positioning BAZ1B as a master regulator of the modern human face. In so doing, we provide experimental evidence that the craniofacial and cognitive/behavioral phenotypes caused by alterations of the Williams-Beuren syndrome critical region can serve as a powerful entry point into the evolution of the modern human face and prosociality.

From enhanceropathies to the epigenetic manifold underlying human cognition

A vast portion of intellectual disability and autism spectrum disorders is genetically caused by mutations in chromatin modulators. These proteins play key roles in development and are also highly expressed in the adult brain. Specifically, the pivotal role of chromatin regulation in transcription has placed enhancers at the core of neurodevelopmental disorders (NDDs) studies, ushering in the coining of the term enhanceropathies. The convergence of these disorders is multilayered, spanning from molecular causes to pathophysiological traits, including extensive overlaps between enhanceropathies and neurocristopathies. The reconstruction of epigenetic circuitries wiring development and underlying cognitive functions has gone hand in hand with the development of tools that increase the sensitivity of identifying regulatory regions and linking enhancers to their target genes. The available models, including loop extrusion and phase separation, have been bringing into relief complementary aspects to interpret gene regulation datasets, reinforcing the idea that enhancers are not all the same and that regulatory regions possess shades of enhancer-ness and promoter-ness. The current limits in enhancer definition, within the emerging broader understanding of chromatin dynamics in time and space, are now on the verge of being transformed by the possibility to interrogate developmentally relevant three-dimensional cellular models at single-cell resolution. Here we discuss the contours of how these technological advances, as well as the epistemic limitations they are set to overcome, may well usher in a change of paradigm for NDDs, moving the quest for convergence from enhancers to the four-dimensional (4D) genome.

Recent Advances in Craniosynostosis

Craniosynostosis is a pathologic craniofacial disorder and is defined as the premature fusion of one or more cranial (calvarial) sutures. Cranial sutures are fibrous joints consisting of nonossified mesenchymal cells that play an important role in the development of healthy craniofacial skeletons. Early fusion of these sutures results in incomplete brain development that may lead to complications of several severe medical conditions including seizures, brain damage, mental delay, complex deformities, strabismus, and visual and breathing problems. As a congenital disease, craniosynostosis has a heterogeneous origin that can be affected by genetic and epigenetic alterations, teratogens, and environmental factors and make the syndrome highly complex. To date, approximately 200 syndromes have been linked to craniosynostosis. In addition to being part of a syndrome, craniosynostosis can be nonsyndromic, formed without any additional anomalies. More than 50 nuclear genes that relate to craniosynostosis have been identified. Besides genetic factors, epigenetic factors like microRNAs and mechanical forces also play important roles in suture fusion. As craniosynostosis is a multifactorial disorder, evaluating the craniosynostosis syndrome requires and depends on all the information obtained from clinical findings, genetic analysis, epigenetic or environmental factors, or gene modulators. In this review, we will focus on embryologic and genetic studies, as well as epigenetic and environmental studies. We will discuss published studies and correlate the findings with unknown aspects of craniofacial disorders.

Regional difference in microRNA regulation in the skull vault

BACKGROUND

The murine calvaria has several membrane bones with different tissue origins (e.g., neural crest-derived frontal bone vs. mesoderm-derived parietal bone). Neural crest-derived frontal bone exhibits superior osteogenic activities and bone regeneration. MicroRNA (miRNA) has been emerged as a crucial regulator during organogenesis and is involved in a range of developmental processes. However, the underlying roles of miRNA regulation in frontal bone and parietal bone is unknown.

RESULTS

Total of 83 significantly expressed known miRNAs were identified in frontal bones versus parietal bones. The significantly enriched gene ontology and KEGG pathway that were predicted by the enrichment miRNAs were involved in several biological processes (cell differentiation, cell adhesion, and transcription), and multiple osteogenic pathways (e.g., focal adhesion, MAPK, VEGF, Wnt, and insulin signaling pathway. Focal adhesion and insulin signaling pathway were selected for target verification and functional analysis, and several genes were predicted to be targets genes by the differentially expressed miRNAs, and these targets genes were tested with significant expressions.

CONCLUSIONS

Our results revealed a novel pattern of miRNAs in murine calvaria with dual tissue origins, and explorations of these miRNAs will be valuable for the translational studies to enhance osteogenic potential and bone regeneration in the clinic.

Mutations in TFAP2B and previously unimplicated genes of the BMP, Wnt, and Hedgehog pathways in syndromic craniosynostosis

Craniosynostosis (CS) is a frequent congenital malformation featuring premature fusion of cranial sutures; 15% of these children have syndromic disease, often due to rare mutations with large effect. While many genes causing Mendelian forms of syndromic CS have been identified, clinical sequencing often fails to identify a likely causative mutation. We performed whole-exome sequencing of 12 case-parent trios with previously negative genetic evaluations. The results identified likely pathogenic mutations in TFAP2B, KAT6A, GLI2, SOX11, CTNNA1, and GPC4 in these families, adding several loci to those known to cause syndromic CS. The findings have implications for determining risk of disease in subsequent offspring and demonstrate that unexplained syndromic CS cases are a particularly rich vein for discovery of CS loci.

Craniosynostosis (CS) is a frequent congenital anomaly featuring the premature fusion of 1 or more sutures of the cranial vault. Syndromic cases, featuring additional congenital anomalies, make up 15% of CS. While many genes underlying syndromic CS have been identified, the cause of many syndromic cases remains unknown. We performed exome sequencing of 12 syndromic CS cases and their parents, in whom previous genetic evaluations were unrevealing. Damaging de novo or transmitted loss of function (LOF) mutations were found in 8 genes that are highly intolerant to LOF mutation (P = 4.0 × 10⁻⁸); additionally, a rare damaging mutation in SOX11, which has a lower level of intolerance, was identified. Four probands had rare damaging mutations (2 de novo) in TFAP2B, a transcription factor that orchestrates neural crest cell migration and differentiation; this mutation burden is highly significant (P = 8.2 × 10⁻¹²). Three probands had rare damaging mutations in GLI2, SOX11, or GPC4, which function in the Hedgehog, BMP, and Wnt signaling pathways; other genes in these pathways have previously been implicated in syndromic CS. Similarly, damaging de novo mutations were identified in genes encoding the chromatin modifier KAT6A, and CTNNA1, encoding catenin α-1. These findings establish TFAP2B as a CS gene, have implications for assessing risk to subsequent children in these families, and provide evidence implicating other genes in syndromic CS. This high yield indicates the value of performing exome sequencing of syndromic CS patients when sequencing of known disease loci is unrevealing.

Insights into the biology of fibrodysplasia ossificans progressiva using patient-derived induced pluripotent stem cells

The demand for development of new drugs remains on the upward trend because of the large number of patients suffering from intractable diseases for which effective treatment has not been established yet. Recently, several researchers have attempted to apply induced pluripotent stem cell (iPSC) technology as a powerful tool for studying the mechanisms underlying the onset of various diseases and for new drug screening. This technology has made an enormous breakthrough, since it permits us to recapitulate the disease phenotype in vitro, outside of the patient's body. Here, we discuss the latest findings that uncovered a mechanism underlying the pathology of a rare genetic musculoskeletal disease, fibrodysplasia ossificans progressiva (FOP), by modeling the phenotypes with FOP patient-derived iPSCs, and that discovered promising candidate drugs for FOP treatment. We also discussed future directions of FOP research.

Tissue Preparation and Immunostaining of Mouse Craniofacial Tissues and Undecalcified Bone

Tissue immunostaining provides highly specific and reliable detection of proteins of interest within a given tissue. Here we describe a complete and simple protocol to detect protein expression during craniofacial morphogenesis/pathogenesis using mouse craniofacial tissues as examples. The protocol consists of preparation and cryosectioning of tissues, indirect immunofluorescence, image acquisition, and quantification. In addition, a method for preparation and cryosectioning of undecalcified hard tissues for immunostaining is described, using craniofacial tissues and long bones as examples. Those methods are key to determine the protein expression and morphological/anatomical changes in various tissues during craniofacial morphogenesis/pathogenesis. They are also applicable to other tissues with appropriate modifications. Knowledge of the histology and high quality of sections are critical to draw scientific conclusions from experimental outcomes. Potential limitations of this methodology include but are not limited to specificity of antibodies and difficulties of quantification, which are also discussed here.

Rapamycin rescues BMP mediated midline craniosynostosis phenotype through reduction of mTOR signaling in a mouse model

Craniosynostosis is defined as congenital premature fusion of one or more cranial sutures. While the genetic basis for about 30% of cases is known, the causative genes for the diverse presentations of the remainder of cases are unknown. The recently discovered cranial suture stem cell population affords an opportunity to identify early signaling pathways that contribute to craniosynostosis. We previously demonstrated that enhanced BMP signaling in neural crest cells (caA3 mutants) leads to premature cranial suture fusion resulting in midline craniosynostosis. Since enhanced mTOR signaling in neural crest cells leads to craniofacial bone lesions, we investigated the extent to which mTOR signaling is involved in the pathogenesis of BMP-mediated craniosynostosis by affecting the suture stem cell population. Our results demonstrate a loss of suture stem cells in the caA3 mutant mice by the newborn stage. We have found increased activation of mTOR signaling in caA3 mutant mice during embryonic stages, but not at the newborn stage. Our study demonstrated that inhibition of mTOR signaling via rapamycin in a time specific manner partially rescued the loss of the suture stem cell population. This study provides insight into how enhanced BMP signaling regulates suture stem cells via mTOR activation.

Unraveling the Connection between Fibroblast Growth Factor and Bone Morphogenetic Protein Signaling

Ontogeny of higher organisms as well the regulation of tissue homeostasis in adult individuals requires a fine-balanced interplay of regulating factors that individually trigger the fate of particular cells to either stay undifferentiated or to differentiate towards distinct tissue specific lineages. In some cases, these factors act synergistically to promote certain cellular responses, whereas in other tissues the same factors antagonize each other. However, the molecular basis of this obvious dual signaling activity is still only poorly understood. Bone morphogenetic proteins (BMPs) and fibroblast growth factors (FGFs) are two major signal protein families that have a lot in common: They are both highly preserved between different species, involved in essential cellular functions, and their ligands vastly outnumber their receptors, making extensive signal regulation necessary. In this review we discuss where and how BMP and FGF signaling cross paths. The compiled data reflect that both factors synchronously act in many tissues, and that antagonism and synergism both exist in a context-dependent manner. Therefore, by challenging a generalization of the connection between these two pathways a new chapter in BMP FGF signaling research will be introduced.

Embryologic and Fetal Development of the Human Orbit

PURPOSE

To review the recent data about orbital development and sort out the controversies from the very early stages during embryonic life till final maturation of the orbit late in fetal life, and to appreciate the morphogenesis of all the definitive structures in the orbit in a methodical and timely fashion.

METHODS

The authors extensively review major studies detailing every aspect of human embryologic and fetal orbital morphogenesis including the development of extraocular muscles, orbital fat, vessels, nerves, and the supportive connective tissue framework as well as bone. These interdisciplinary studies span almost a century and a half, and include some significant controversial opposing points of view which the authors hopefully sort out. The authors also highlight a few of the most noteworthy molecular biologic studies regarding the multiple and interacting signaling pathways involved in regulating normal orbital morphogenesis.

RESULTS

Orbital morphogenesis involves a successive series of subtle yet tightly regulated morphogenetic events that could only be explained through the chronological narrative used by the authors. The processes that trigger and contribute to the formation of the orbits are complex and seem to be intricately regulated by multifaceted interactions and bidirectional cross-talk between a multitude of cellular building raw materials including the developing optic vesicles, neuroectoderm, cranial neural crest cells and mesoderm.

CONCLUSIONS

Development of the orbit is a collective enterprise necessitating interactions between, as well as contributions from different cell populations both within and beyond the realm of the orbit. A basic understanding of the processes underlying orbital ontogenesis is a crucial first step toward establishing a genetic basis or an embryologic link with orbital disease.

Reprogramming of Mouse Calvarial Osteoblasts into Induced Pluripotent Stem Cells

Previous studies have demonstrated the ability of reprogramming endochondral bone into induced pluripotent stem (iPS) cells, but whether similar phenomenon occurs in intramembranous bone remains to be determined. Here we adopted fluorescence-activated cell sorting-based strategy to isolate homogenous population of intramembranous calvarial osteoblasts from newborn transgenic mice carrying both Osx1-GFP::Cre and Oct4-EGFP transgenes. Following retroviral transduction of Yamanaka factors (Oct4, Sox2, Klf4, and c-Myc), enriched population of osteoblasts underwent silencing of Osx1-GFP::Cre expression at early stage of reprogramming followed by late activation of Oct4-EGFP expression in the resulting iPS cells. These osteoblast-derived iPS cells exhibited gene expression profiles akin to embryonic stem cells and were pluripotent as demonstrated by their ability to form teratomas comprising tissues from all germ layers and also contribute to tail tissue in chimera embryos. These data demonstrate that iPS cells can be generated from intramembranous osteoblasts.

A New Look at Etiological Factors of Idiopathic Scoliosis: Neural Crest Cells

Idiopathic scoliosis is one of the most common disabling pathologies of children and adolescents. Etiology and pathogenesis of idiopathic scoliosis remain unknown. To study the etiology of this disease we identified the cells' phenotypes in the vertebral body growth plates in patients with idiopathic scoliosis. Materials and methods: The cells were isolated from vertebral body growth plates of the convex and concave sides of the deformity harvested intraoperatively in 50 patients with scoliosis. Cells were cultured and identified by methods of common morphology, neuromorphology, electron microscopy, immunohistochemistry and PCR analysis. Results: Cultured cells of convex side of deformation were identified as chondroblasts. Cells isolated from the growth plates of the concave side of the deformation showed numerous features of neuro- and glioblasts. These cells formed synapses, contain neurofilaments, and expressed neural and glial proteins. Conclusion: For the first time we demonstrated the presence of cells with neural/glial phenotype in the concave side of the vertebral body growth plate in scoliotic deformity. We hypothesized that neural and glial cells observed in the growth plates of the vertebral bodies represent derivatives of neural crest cells deposited in somites due to alterations in their migratory pathway during embryogenesis. We also propose that ectopic localization of cells derived from neural crest in the growth plate of the vertebral bodies is the main etiological factor of the scoliotic disease.