Cranial Suture Biology

Comparing cranial suture interdigitation in humans and non-human primates: unearthing links to osteopathic cranial concept

CONTEXT

Since William Garner Sutherland's inception of osteopathic cranial manipulative medicine (OCMM), osteopathic physicians have practiced with the knowledge that cranial sutures exhibit motion. We hypothesize that the complexity of suture interdigitation in humans may provide clues to elucidate the concept of OCMM.

OBJECTIVES

We compared the interdigitation of sagittal, coronal (left and right), and lambdoid (left and right) sutures in computed tomography (CT) scans of humans and five nonhuman primate species (Gorilla gorilla, Pongo pygmaeus, Pan troglodytes, Hylobates lar, and Nasalis larvatus).

METHODS

Human ages are evenly distributed between 10 and 65 years of age, with an equal number of males (n=16) and females (n=16) in the sample. Nonhuman primates are all females, and the sample includes juveniles (n=6) and adults (n=34). Sutures were evaluated on a scale ranging from 0 to 3 (0: fused sutures; 1: no interdigitation; 2: low complexity; and 3: representing the highest degree of interdigitation and complexity).

RESULTS

Based on ordinary least squares linear regression, we found no significant relationship between suture interdigitation and age in humans. Chi-square tests were utilized to assess sex differences within humans, species-level differences, and differences between humans and nonhuman primates across all five sutures. Humans exhibited a statistically significant greater degree of suture complexity than all five nonhuman species across all five sutures.

CONCLUSIONS

These findings indicate that human suture interdigitation is more complex than their closest living relatives (African apes) and other primates (Asian monkeys and apes). We theorize that this would enable subtle movement and serve to transmit forces at the cranial sutures from dietary or ethological behaviors, similar to the pattern observed in other mammals. While humans have a softer diet compared to other living primates, the uniqueness of human craniofacial growth and extended developmental period could contribute to the necessity for complex cranial sutures. More studies are needed to understand variation in human and nonhuman sutural complexity and its relationship to cranial motion.

Craniosynostosis: orofacial and oral health perspectives with masticatory insights

BACKGROUND

Craniosynostosis (CS), premature fusion of one or more cranial sutures, leads to abnormal skull development, impacting both facial esthetics and oral function. This study aimed to evaluate the specific orofacial and oral health characteristics, including masticatory performance, in Thai patients with CS.

METHODS

A comparative study was conducted with Thai CS patients aged 6-17 years and a control group of healthy individuals with similar age distribution. Assessments included craniofacial morphology, oral health status, and masticatory performance. Intergroup comparisons utilized appropriate statistical tests.

RESULTS

The study included 24 CS patients with a mean age of 10.11 ± 2.98 years and 30 controls. CS patients exhibited a significantly higher prevalence of various oral conditions compared to controls: cleft palate (20.8%), anterior open bite (41.7%), anterior crossbite (54.2%), posterior crossbite (50%), combined anterior-posterior crossbite (45.8%), dental crowding in both maxilla and mandible (50% and 45.8% respectively), congenitally missing teeth (50%), supernumerary teeth (12.5%), and eruption failure (54.2%). Furthermore, CS patients exhibited significantly higher caries prevalence and susceptibility, alongside poorer oral hygiene, compared to controls. Regarding jaw relationships, CS patients exhibited a significantly higher proportion of Angle's Class III malocclusion (50%) compared to the control group, where Class I malocclusion was predominant (50%). Masticatory performance, assessed using the two-color gum mixing ability test, showed significantly higher hue variance in CS patients (0.12 ± 0.07) compared to the control group, indicating reduced chewing performance.

CONCLUSION

This study underscores the significant orofacial and oral health challenges faced by children with CS, including a high prevalence of malocclusions, dental anomalies, elevated caries experience, and compromised masticatory function. These findings emphasize the importance of tailored interventions and comprehensive oral healthcare strategies to address the unique needs of this population and improve their overall quality of life.

Distraction force promotes the osteogenic differentiation of Gli1+ cells in facial sutures via primary cilia-mediated Hedgehog signaling pathway

BACKGROUND

Trans-sutural distraction osteogenesis (TSDO) involves the application of distraction force to facial sutures to stimulate osteogenesis. Gli1+ cells in the cranial sutures play an important role in bone growth. However, whether Gli1+ cells in facial sutures differentiate into bone under distraction force is unknown.

METHODS

4-week-old Gli1ER/Td and C57BL/6 mice were used to establish a TSDO model to explore osteogenesis of zygomaticomaxillary sutures. A Gli1+ cell lineage tracing model was used to observe the distribution of Gli1+ cells and explore the role of Gli1+ cells in facial bone remodeling.

RESULTS

Distraction force promoted bone remodeling during TSDO. Fluorescence and two-photon scanning images revealed the distribution of Gli1+ cells. Under distraction force, Gli1-lineage cells proliferated significantly and co-localized with Runx2+ cells. Hedgehog signaling was upregulated in Gli1+ cells. Inhibition of Hedgehog signaling suppresses the proliferation and osteogenesis of Gli1+ cells induced by distraction force. Subsequently, the stem cell characteristics of Gli1+ cells were identified. Cell-stretching experiments verified that mechanical force promoted the osteogenic differentiation of Gli1+ cells through Hh signaling. Furthermore, immunofluorescence staining and RT-qPCR experiments demonstrated that the primary cilia in Gli1+ cells exhibit Hedgehog-independent mechanosensitivity, which was required for the osteogenic differentiation induced by mechanical force.

CONCLUSIONS

Our study indicates that the primary cilia of Gli1+ cells sense mechanical stimuli, mediate Hedgehog signaling activation, and promote the osteogenic differentiation of Gli1+ cells in zygomaticomaxillary sutures.

Transcriptomic and cellular decoding of scaffolds-induced suture mesenchyme regeneration

Precise orchestration of cell fate determination underlies the success of scaffold-based skeletal regeneration. Despite extensive studies on mineralized parenchymal tissue rebuilding, regenerating and maintaining undifferentiated mesenchyme within calvarial bone remain very challenging with limited advances yet. Current knowledge has evidenced the indispensability of rebuilding suture mesenchymal stem cell niches to avoid severe brain or even systematic damage. But to date, the absence of promising therapeutic biomaterials/scaffolds remains. The reason lies in the shortage of fundamental knowledge and methodological evidence to understand the cellular fate regulations of scaffolds. To address these issues, in this study, we systematically investigated the cellular fate determinations and transcriptomic mechanisms by distinct types of commonly used calvarial scaffolds. Our data elucidated the natural processes without scaffold transplantation and demonstrated how different scaffolds altered in vivo cellular responses. A feasible scaffold, polylactic acid electrospinning membrane (PLA), was next identified to precisely control mesenchymal ingrowth and self-renewal to rebuild non-osteogenic suture-like tissue at the defect center, meanwhile supporting proper osteointegration with defect bony edges. Especially, transcriptome analysis and cellular mechanisms underlying the well-orchestrated cell fate determination of PLA were deciphered. This study for the first time cellularly decoded the fate regulations of scaffolds in suture-bony composite defect healing, offering clinicians potential choices for regenerating such complicated injuries.

Dissecting calvarial bones and sutures at single-cell resolution

Cranial bones constitute a protective shield for the vulnerable brain tissue, bound together as a rigid entity by unique immovable joints known as sutures. Cranial sutures serve as major growth centres for calvarial morphogenesis and have been identified as a niche for mesenchymal stem cells (MSCs) and/or skeletal stem cells (SSCs) in the craniofacial skeleton. Despite the established dogma of cranial bone and suture biology, technological advancements now allow us to investigate these tissues and structures at unprecedented resolution and embrace multiple novel biological insights. For instance, a decrease or imbalance of representation of SSCs within sutures might underlie craniosynostosis; dural sinuses enable neuroimmune crosstalk and are newly defined as immune hubs; skull bone marrow acts as a myeloid cell reservoir for the meninges and central nervous system (CNS) parenchyma in mediating immune surveillance, etc. In this review, we revisit a growing body of recent studies that explored cranial bone and suture biology using cutting-edge techniques and have expanded our current understanding of this research field, especially from the perspective of development, homeostasis, injury repair, resident MSCs/SSCs, immunosurveillance at the brain's border, and beyond.

A roadmap of craniofacial growth modification for children with sleep-disordered breathing: a multidisciplinary proposal

Craniofacial modification by orthodontic techniques is increasingly incorporated into the multidisciplinary management of sleep-disordered breathing in children and adolescents. With increasing application of orthodontics to this clinical population it is important for healthcare providers, families, and patients to understand the wide range of available treatments. Orthodontists can guide craniofacial growth depending on age; therefore, it is important to work with other providers for a team-based approach to sleep-disordered breathing. From infancy to adulthood the dentition and craniofacial complex change with growth patterns that can be intercepted and targeted at critical time points. This article proposes a clinical guideline for application of multidisciplinary care with emphasis on dentofacial interventions that target variable growth patterns. We also highlight how these guidelines serve as a roadmap for the key questions that will influence future research directions. Ultimately the appropriate application of these orthodontic techniques will not only provide an important therapeutic option for children and adolescents with symptomatic sleep-disordered breathing but may help also mitigate or prevent its onset.

FGF signaling in cranial suture development and related diseases

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

Mechanical isolation of neonatal and adult mouse dura leukocytes for flow cytometry analysis

The meninges, consisting of the pia, arachnoid, and dura layers, provide immunosurveillance of the central nervous system with both innate and adaptive immune cells. Here we present an optimized protocol for isolating dura leukocytes from neonatal and adult mice. We describe steps for harvesting the skull cap, extracting the dura mater, mechanical isolation of dura leukocytes, and flow cytometry analysis. Unlike the time-consuming enzymatic digestion isolation which makes dura hematopoietic stem cells (HSCs) undetectable, this rapid and simplified technique permits dura HSC identification. For complete details on the use and execution of this protocol, please refer to Niu et al. (2022).¹.

Bone structure and composition in a hyperglycemic, obese, and leptin receptor-deficient rat: Microscale characterization of femur and calvarium

Metabolic abnormalities, such as diabetes mellitus and obesity, can impact bone quantity and/or bone quality. In this work, we characterize bone material properties, in terms of structure and composition, in a novel rat model with congenic leptin receptor (LepR) deficiency, severe obesity, and hyperglycemia (type 2 diabetes-like condition). Femurs and calvaria (parietal region) from 20-week-old male rats are examined to probe bones formed both by endochondral and intramembranous ossification. Compared to the healthy controls, the LepR-deficient animals display significant alterations in femur microarchitecture and in calvarium morphology when analyzed by micro-computed X-ray tomography (micro-CT). In particular, shorter femurs with reduced bone volume, combined with thinner parietal bones and shorter sagittal suture, point towards a delay in the skeletal development of the LepR-deficient rodents. On the other hand, LepR-deficient animals and healthy controls display analogous bone matrix composition, which is assessed in terms of tissue mineral density by micro-CT, degree of mineralization by quantitative backscattered electron imaging, and various metrics extrapolated from Raman hyperspectral images. Some specific microstructural features, i.e., mineralized cartilage islands in the femurs and hyper-mineralized areas in the parietal bones, also show comparable distribution and characteristics in both groups. Overall, the altered bone microarchitecture in the LepR-deficient animals indicates compromised bone quality, despite the normal bone matrix composition. The delayed development is also consistent with observations in humans with congenic Lep/LepR deficiency, making this animal model a suitable candidate for translational research.

Stuck on you: Meninges cellular crosstalk in development

The spatial and temporal development of the brain, overlying meninges (fibroblasts, vasculature and immune cells) and calvarium are highly coordinated. In particular, the timing of meningeal fibroblasts into molecularly distinct pia, arachnoid and dura subtypes coincides with key developmental events in the brain and calvarium. Further, the meninges are positioned to influence development of adjacent structures and do so via depositing basement membrane and producing molecular cues to regulate brain and calvarial development. Here, we review the current knowledge of how meninges development aligns with events in the brain and calvarium and meningeal fibroblast "crosstalk" with these structures. We summarize outstanding questions and how the use of non-mammalian models to study the meninges will substantially advance the field of meninges biology.

Skeletal stem cells: a game changer of skeletal biology and regenerative medicine?

Skeletal stem cells (SSCs) were originally discovered in the bone marrow stroma. They are capable of self-renewal and multilineage differentiation into osteoblasts, chondrocytes, adipocytes, and stromal cells. Importantly, these bone marrow SSCs localize in the perivascular region and highly express hematopoietic growth factors to create the hematopoietic stem cell (HSC) niche. Thus, bone marrow SSCs play pivotal roles in orchestrating osteogenesis and hematopoiesis. Besides the bone marrow, recent studies have uncovered diverse SSC populations in the growth plate, perichondrium, periosteum, and calvarial suture at different developmental stages, which exhibit distinct differentiation potential under homeostatic and stress conditions. Therefore, the current consensus is that a panel of region-specific SSCs collaborate to regulate skeletal development, maintenance, and regeneration. Here, we will summarize recent advances of SSCs in long bones and calvaria, with a special emphasis on the evolving concept and methodology in the field. We will also look into the future of this fascinating research area that may ultimately lead to effective treatment of skeletal disorders.

Diploic vein morphology in normal and craniosynostotic adult human skulls

Diploic veins (DV) run within the cranial diploe, where they leave channels that can be studied in osteological samples. This study investigates overall DV variability in human adults and the effects of sex, age, cranial dimensions, and dysmorphogenesis associated with craniosynostosis (CS). The morphology of macroscopic diploic channels was analyzed in a set of the qualitative and quantitative variables in computed tomography-images of crania of anatomically normal and craniosynostotic adult individuals. Macroscopic diploic channels occur most frequently in the frontal and parietal bones, often with a bilaterally symmetrical pattern. DV-features (especially DV-pattern) are characterized by high individual diversity. On average, there are 5.4 ± 3.5 large macroscopic channels (with diameters >1 mm) per individual, with a mean diameter of 1.7 ± 0.4 mm. Age and sex have minor effects on DV, and cranial proportions significantly influence DV only in CS skulls. CS is associated with changes in the DV numbers, distributions, and diameters. Craniosynostotic skulls, especially brachycephalic skulls, generally present smaller DV diameters, and dolichocephalic skulls display increased number of frontal DV. CS, associated with altered cranial dimensions, suture imbalance, increased intracranial pressure, and with changes of the endocranial craniovascular system, significantly also affects the macroscopic morphology of DV in adults, in terms of both structural (topological redistribution) and functional factors. The research on craniovascular morphology and CS may be of interest in biological anthropology, paleopathology, medicine (e.g., surgical planning), but also in zoology and paleontology.

An additional whole-exome sequencing study in 102 panel-undiagnosed patients: A retrospective study in a Chinese craniosynostosis cohort

Craniosynostosis (CRS) is a disease with prematurely fused cranial sutures. In the last decade, the whole-exome sequencing (WES) was widely used in Caucasian populations. The WES largely contributed in genetic diagnosis and exploration on new genetic mechanisms of CRS. In this study, we enrolled 264 CRS patients in China. After a 17-gene-panel sequencing designed in the previous study, 139 patients were identified with pathogenic/likely pathogenic (P/LP) variants according to the ACMG guideline as positive genetic diagnosis. WES was then performed on 102 patients with negative genetic diagnosis by panel. Ten P/LP variants were additionally identified in ten patients, increasing the genetic diagnostic yield by 3.8% (10/264). The novel variants in ANKH, H1-4, EIF5A, SOX6, and ARID1B expanded the mutation spectra of CRS. Then we designed a compatible research pipeline (RP) for further exploration. The RP could detect all seven P/LP SNVs and InDels identified above, in addition to 15 candidate variants found in 13 patients with worthy of further study. In sum, the 17-gene panel and WES identified positive genetic diagnosis for 56.4% patients (149/264) in 16 genes. At last, in our estimation, the genetic testing strategy of “Panel-first” saves 24.3% of the cost compared with “WES only”, suggesting the “Panel-first” is an economical strategy.

Epidemiology, Genetics, and Pathophysiology of Craniosynostosis

Craniosynostosis, the premature fusion of the infant cranial skulls, can be recognized by characteristic head shape differences that worsen with head growth. Craniosynostosis can be syndromic or nonsyndromic and can involve one suture or multiple sutures. Timely cranial vault surgery is recommended to expand and reshape the skull, with a goal of preventing increased intracranial pressure and providing sufficient space for brain growth. Several gene variants and environmental exposures are known to increase the risk of single suture craniosynostosis (SSC), including in utero constraint, exposure to specific toxins and medications, and medical conditions such as thyroid dysregulation and metabolic bone disorders.

Harnessing a Feasible and Versatile ex vivo Calvarial Suture 2-D Culture System to Study Suture Biology

As a basic science, craniofacial research embraces multiple facets spanning from molecular regulation of craniofacial development, cell biology/signaling and ultimately translational craniofacial biology. Calvarial sutures coordinate development of the skull, and the premature fusion of one or more, leads to craniosynostosis. Animal models provide significant contributions toward craniofacial biology and clinical/surgical treatments of patients with craniofacial disorders. Studies employing mouse models are costly and time consuming for housing/breeding. Herein, we present the establishment of a calvarial suture explant 2-D culture method that has been proven to be a reliable system showing fidelity with the in vivo harvesting procedure to isolate high yields of skeletal stem/progenitor cells from small number of mice. Moreover, this method allows the opportunity to phenocopying models of craniosynostosis and in vitro tamoxifen-induction of ActincreERT2;R26Rainbow suture explants to trace clonal expansion. This versatile method tackles needs of large number of mice to perform calvarial suture research.

Morphology of the Occipital Bones and Foramen Magnum Resulting From Premature Minor Suture Fusion in Crouzon Syndrome

To identify skull-base growth patterns in Crouzon syndrome, we hypothesized premature minor suture fusion restricts occipital bone development, secondarily limiting foramen magnum expansion.

Skull-base suture closure degree and cephalometric measurements were retrospectively studied using preoperative computed tomography (CT) scans and multiple linear regression analysis.

Evaluation of multi-institutional CT images and 3D reconstructions from Wake Forest's Craniofacial Imaging Database (WFCID).

Sixty preoperative patients with Crouzon syndrome under 12 years-old were selected from WFCID. The control group included 60 age- and sex-matched patients without craniosynostosis or prior craniofacial surgery.

None.

2D and 3D cephalometric measurements.

3D volumetric evaluation of the basioccipital, exo-occipital, and supraoccipital bones revealed decreased growth in Crouzon syndrome, attributed solely to premature minor suture fusion. Spheno-occipital (β = -398.75; P < .05) and petrous-occipital (β = -727.5; P < .001) suture fusion reduced growth of the basioccipital bone; lambdoid suture (β = -14 723.1; P < .001) and occipitomastoid synchondrosis (β = -16 419.3; P < .001) fusion reduced growth of the supraoccipital bone; and petrous-occipital suture (β = -673.3; P < .001), anterior intraoccipital synchondrosis (β = -368.47; P < .05), and posterior intraoccipital synchondrosis (β = -6261.42; P < .01) fusion reduced growth of the exo-occipital bone. Foramen magnum morphology is restricted in Crouzon syndrome but not directly caused by early suture fusion.

Premature minor suture fusion restricts the volume of developing occipital bones providing a plausible mechanism for observed foramen magnum anomalies.

Craniovascular traits and braincase morphology in craniosynostotic human skulls

Middle meningeal vessels, dural venous sinuses, and emissary veins leave imprints and canals in the endocranium, and thus provide evidence of vascular patterns in osteological samples. This paper investigates whether craniovascular morphology undergoes changes in craniosynostotic human skulls, and if specific alterations may reflect structural and functional relationships in the cranium. The analyzed osteological sample consists of adult individuals with craniosynostoses generally associated with dolichocephalic or brachycephalic proportions, and a control sample of anatomically normal adult skulls. The pattern and dominance of the middle meningeal artery, the morphology of the confluence of the sinuses, and the size and number of the emissary foramina were evaluated. Craniovascular morphology was more diverse in craniosynostotic skulls than in anatomically normal skulls. The craniosynostotic skulls often displayed enlarged occipito-marginal sinuses and more numerous emissary foramina. The craniosynostotic skulls associated with more brachycephalic morphology often presented enlarged emissary foramina, while the craniosynostotic skulls associated with dolichocephalic effects frequently displayed more developed posterior branches of the middle meningeal artery. The course and morphology of the middle meningeal vessels, dural venous sinuses, and emissary veins in craniosynostotic skulls can be related to the redistribution of growth forces, higher intracranial pressure, venous hypertension, or thermal constraints. These functional and structural changes are of interest in both anthropology and medicine, involving epigenetic traits that concern the functional and ontogenetic balance between soft and hard tissues.

Spatial transcriptomics reveals a role for sensory nerves in preserving cranial suture patency through modulation of BMP/TGF-β signaling

The patterning and ossification of the mammalian skeleton requires the coordinated actions of both intrinsic bone morphogens and extrinsic neurovascular signals, which function in a temporal and spatial fashion to control mesenchymal progenitor cell (MPC) fate. Here, we show the genetic inhibition of tropomyosin receptor kinase A (TrkA) sensory nerve innervation of the developing cranium results in premature calvarial suture closure, associated with a decrease in suture MPC proliferation and increased mineralization. In vitro, axons from peripheral afferent neurons derived from dorsal root ganglions (DRGs) of wild-type mice induce MPC proliferation in a spatially restricted manner via a soluble factor when cocultured in microfluidic chambers. Comparative spatial transcriptomic analysis of the cranial sutures in vivo confirmed a positive association between sensory axons and proliferative MPCs. SpatialTime analysis across the developing suture revealed regional-specific alterations in bone morphogenetic protein (BMP) and TGF-β signaling pathway transcripts in response to TrkA inhibition. RNA sequencing of DRG cell bodies, following direct, axonal coculture with MPCs, confirmed the alterations in BMP/TGF-β signaling pathway transcripts. Among these, the BMP inhibitor follistatin-like 1 (FSTL1) replicated key features of the neural-to-bone influence, including mitogenic and anti-osteogenic effects via the inhibition of BMP/TGF-β signaling. Taken together, our results demonstrate that sensory nerve-derived signals, including FSTL1, function to coordinate cranial bone patterning by regulating MPC proliferation and differentiation in the suture mesenchyme.

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.

Skeletal stem and progenitor cells maintain cranial suture patency and prevent craniosynostosis

Cranial sutures are major growth centers for the calvarial vault, and their premature fusion leads to a pathologic condition called craniosynostosis. This study investigates whether skeletal stem/progenitor cells are resident in the cranial sutures. Prospective isolation by FACS identifies this population with a significant difference in spatio-temporal representation between fusing versus patent sutures. Transcriptomic analysis highlights a distinct signature in cells derived from the physiological closing PF suture, and scRNA sequencing identifies transcriptional heterogeneity among sutures. Wnt-signaling activation increases skeletal stem/progenitor cells in sutures, whereas its inhibition decreases. Crossing Axin2LacZ/+ mouse, endowing enhanced Wnt activation, to a Twist1+/- mouse model of coronal craniosynostosis enriches skeletal stem/progenitor cells in sutures restoring patency. Co-transplantation of these cells with Wnt3a prevents resynostosis following suturectomy in Twist1+/- mice. Our study reveals that decrease and/or imbalance of skeletal stem/progenitor cells representation within sutures may underlie craniosynostosis. These findings have translational implications toward therapeutic approaches for craniosynostosis.

Elevated Cranial Sutural Complexity in Burrowing Dicynodonts

Relationships between the complexity of the cranial sutures and the inferred ecology of dicynodont synapsids are explored. Simple complexity indices based on degree of sutural interdigitation were calculated for 70 anomodont species and indicate that the naso-frontal sutures of Cistecephalidae, a clade inferred to be dedicated fossors based on aspects of postcranial morphology, are substantially more complex than those of other dicynodonts. The elevated complexity of the naso-frontal suture in this clade is interpreted as being related to compressive forces sustained during burrowing, paralleling the condition in some other fossorial vertebrate groups (e.g., amphisbaenians). The most highly interdigitated sutures in the cistecephalid skull are those oriented transversely to its long axis, which would experience the greatest longitudinal stresses from contact with the substrate. Although it is uncertain to what degree cistecephalid burrowing was based on scratch vs. head-lift digging, it is argued that the head played an important role during locomotion in this group. Increased sutural complexity, rather than cranial fusion, as an adaptation to resisting compressive forces during burrowing may be related to indeterminate growth in dicynodonts.

Ciliary Signalling and Mechanotransduction in the Pathophysiology of Craniosynostosis

Craniosynostosis (CS) is the second most prevalent inborn craniofacial malformation; it results from the premature fusion of cranial sutures and leads to dimorphisms of variable severity. CS is clinically heterogeneous, as it can be either a sporadic isolated defect, more frequently, or part of a syndromic phenotype with mendelian inheritance. The genetic basis of CS is also extremely heterogeneous, with nearly a hundred genes associated so far, mostly mutated in syndromic forms. Several genes can be categorised within partially overlapping pathways, including those causing defects of the primary cilium. The primary cilium is a cellular antenna serving as a signalling hub implicated in mechanotransduction, housing key molecular signals expressed on the ciliary membrane and in the cilioplasm. This mechanical property mediated by the primary cilium may also represent a cue to understand the pathophysiology of non-syndromic CS. In this review, we aimed to highlight the implication of the primary cilium components and active signalling in CS pathophysiology, dissecting their biological functions in craniofacial development and in suture biomechanics. Through an in-depth revision of the literature and computational annotation of disease-associated genes we categorised 18 ciliary genes involved in CS aetiology. Interestingly, a prevalent implication of midline sutures is observed in CS ciliopathies, possibly explained by the specific neural crest origin of the frontal bone.

A Neurotrophic Mechanism Directs Sensory Nerve Transit in Cranial Bone

The flat bones of the skull are densely innervated during development, but little is known regarding their role during repair. We describe a neurotrophic mechanism that directs sensory nerve transit in the mouse calvaria. Patent cranial suture mesenchyme represents an NGF (nerve growth factor)-rich domain, in which sensory nerves transit. Experimental calvarial injury upregulates Ngf in an IL-1β/TNF-α-rich defect niche, with consequent axonal ingrowth. In calvarial osteoblasts, IL-1β and TNF-α stimulate Ngf and downstream NF-κB signaling. Locoregional deletion of Ngf delays defect site re-innervation and blunted repair. Genetic disruption of Ngf among LysM-expressing macrophages phenocopies these observations, whereas conditional knockout of Ngf among Pdgfra-expressing cells does not. Finally, inhibition of TrkA catalytic activity similarly delays re-innervation and repair. These results demonstrate an essential role of NGF-TrkA signaling in bone healing and implicate macrophage-derived NGF-induced ingrowth of skeletal sensory nerves as an important mediator of this repair.

The Intertwined Evolution and Development of Sutures and Cranial Morphology

Phenotypic variation across mammals is extensive and reflects their ecological diversification into a remarkable range of habitats on every continent and in every ocean. The skull performs many functions to enable each species to thrive within its unique ecological niche, from prey acquisition, feeding, sensory capture (supporting vision and hearing) to brain protection. Diversity of skull function is reflected by its complex and highly variable morphology. Cranial morphology can be quantified using geometric morphometric techniques to offer invaluable insights into evolutionary patterns, ecomorphology, development, taxonomy, and phylogenetics. Therefore, the skull is one of the best suited skeletal elements for developmental and evolutionary analyses. In contrast, less attention is dedicated to the fibrous sutural joints separating the cranial bones. Throughout postnatal craniofacial development, sutures function as sites of bone growth, accommodating expansion of a growing brain. As growth frontiers, cranial sutures are actively responsible for the size and shape of the cranial bones, with overall skull shape being altered by changes to both the level and time period of activity of a given cranial suture. In keeping with this, pathological premature closure of sutures postnatally causes profound misshaping of the skull (craniosynostosis). Beyond this crucial role, sutures also function postnatally to provide locomotive shock absorption, allow joint mobility during feeding, and, in later postnatal stages, suture fusion acts to protect the developed brain. All these sutural functions have a clear impact on overall cranial function, development and morphology, and highlight the importance that patterns of suture development have in shaping the diversity of cranial morphology across taxa. Here we focus on the mammalian cranial system and review the intrinsic relationship between suture development and morphology and cranial shape from an evolutionary developmental biology perspective, with a view to understanding the influence of sutures on evolutionary diversity. Future work integrating suture development into a comparative evolutionary framework will be instrumental to understanding how developmental mechanisms shaping sutures ultimately influence evolutionary diversity.

Pharmacological targeting of KDM6A and KDM6B, as a novel therapeutic strategy for treating craniosynostosis in Saethre-Chotzen syndrome

BACKGROUND

During development, excessive osteogenic differentiation of mesenchymal progenitor cells (MPC) within the cranial sutures can lead to premature suture fusion or craniosynostosis, leading to craniofacial and cognitive issues. Saethre-Chotzen syndrome (SCS) is a common form of craniosynostosis, caused by TWIST-1 gene mutations. Currently, the only treatment option for craniosynostosis involves multiple invasive cranial surgeries, which can lead to serious complications.

METHODS

The present study utilized Twist-1 haploinsufficient (Twist-1^del/+) mice as SCS mouse model to investigate the inhibition of Kdm6a and Kdm6b activity using the pharmacological inhibitor, GSK-J4, on calvarial cell osteogenic potential.

RESULTS

This study showed that the histone methyltransferase EZH2, an osteogenesis inhibitor, is downregulated in calvarial cells derived from Twist-1^del/+ mice, whereas the counter histone demethylases, Kdm6a and Kdm6b, known promoters of osteogenesis, were upregulated. In vitro studies confirmed that siRNA-mediated inhibition of Kdm6a and Kdm6b expression suppressed osteogenic differentiation of Twist-1^del/+ calvarial cells. Moreover, pharmacological targeting of Kdm6a and Kdm6b activity, with the inhibitor, GSK-J4, caused a dose-dependent suppression of osteogenic differentiation by Twist-1^del/+ calvarial cells in vitro and reduced mineralized bone formation in Twist-1^del/+ calvarial explant cultures. Chromatin immunoprecipitation and Western blot analyses found that GSK-J4 treatment elevated the levels of the Kdm6a and Kdm6b epigenetic target, the repressive mark of tri-methylated lysine 27 on histone 3, on osteogenic genes leading to repression of Runx2 and Alkaline Phosphatase expression. Pre-clinical in vivo studies showed that local administration of GSK-J4 to the calvaria of Twist-1^del/+ mice prevented premature suture fusion and kept the sutures open up to postnatal day 20.

CONCLUSION

The inhibition of Kdm6a and Kdm6b activity by GSK-J4 could be used as a potential non-invasive therapeutic strategy for preventing craniosynostosis in children with SCS. Pharmacological targeting of Kdm6a/b activity can alleviate craniosynostosis in Saethre-Chotzen syndrome. Aberrant osteogenesis by Twist-1 mutant cranial suture mesenchymal progenitor cells occurs via deregulation of epigenetic modifiers Ezh2 and Kdm6a/Kdm6b. Suppression of Kdm6a- and Kdm6b-mediated osteogenesis with GSK-J4 inhibitor can prevent prefusion of cranial sutures.

Glycosylation of DMP1 maintains cranial sutures in mice

Craniosynostosis, a severe craniofacial developmental disease, can only be treated with surgery currently. Recent studies have shown that proteoglycans are involved in the suture development. For the bone matrix protein, dentin matrix protein 1 (DMP1), glycosylation on the N-terminal of it could generate a functional proteoglycan form of DMP1 during osteogenesis. We identified that the proteoglycan form of DMP1 (DMP1-PG) is highly expressed in mineralisation front of suture. But, the potential role of DMP1-PG in suture fusion remain unclear. To investigate the role of DMP1-PG in cranial suture fusion and craniofacial bone development. By using a DMP1 glycosylation site mutation mouse model, DMP1-S89G mice, we compared the suture development in it with control mice. We compared the suture phenotypes, bone formation rate, expression levels of bone formation markers in vivo between DMP1-S89G mice and wild-type mice. Meanwhile, cell culture and organ culture were performed to detect the differences in cell differentiation and suture fusion in vitro. Finally, chondroitin sulphate (CHS), as functional component of DMP1-PG, was employed to test whether it could delay the premature suture fusion and the abnormal differentiation of bone mesenchymal stem cells (BMSCs) of DMP1-PG mice. DMP1-S89G mice had premature closure of suture and shorter skull size. Lack of DMP1-PG accelerated bone formation in cranial suture. DMP1-PG maintained the essential stemness of BMSCs in suture through blocking the premature differentiation of BMSCs to osteoblasts. Finally, chondroitin sulphate, a major component of DMP1-PG, successfully delayed the premature suture fusion by organ culture of skull in vitro. DMP1-PG could inhibit premature fusion of cranial suture and maintain the suture through regulating the osteogenic differentiation of BMSCs.

A Novel Frameshift Mutation in KAT6A Is Associated with Pancraniosynostosis

De novo heterozygous mutations in the KAT6A gene give rise to a distinct intellectual disability syndrome, with features including speech delay, cardiac anomalies, craniofacial dysmorphisms, and craniosynostosis. Here, we reported a 16-year-old girl with a novel pathogenic variant of the KAT6A gene. She is the first case to possess pancraniosynostosis, a rare suture fusion pattern, affecting all her major cranial sutures. The diagnosis of KAT6A syndrome is established via recognition of its inherent phenotypic features and the utilization of whole exome sequencing. Thorough craniofacial evaluation is imperative, craniosynostosis may require operative intervention, the delay of which may be detrimental.

Craniofacial Growth: Current Theories and Influence on Management

Craniofacial development is a highly coordinated process under a tight genetic control and environmental influence. Understanding the core concepts of growth and development of the craniofacial skeleton and the impact of treatment on growth potential is vital to successful patient management. To maximize outcomes and minimize iatrogenic consequences, proper sequencing and timing of interventions are critical. The development of the craniofacial skeleton occurs as a result of a sequence of normal developmental events: brain growth and development, optic pathway development, speech and swallowing development, airway and pharyngeal development, muscle development, and tooth development and eruption.

Two pediatric cases of epidural hematoma in the posterior fossa with extension along the sigmoid sinus groove: MR evaluation

To discuss the computed tomography (CT) and magnetic resonance (MR) findings of posterior fossa epidural hematoma (PFEDH) mimicking sinus thrombosis, we present two pediatric cases with the PFEDH extending along the sigmoid sinus groove evaluated by MR imaging (MRI) and MR venography (MRV). T2-weighted coronal MRI can diagnose both patency of the sigmoid sinus and epidural hematoma extending along the sinus groove. Phase-contrast MRV (PC-MRV) is also useful to evaluate the flow state in the dural sinuses but it should be diagnosed carefully whether low visualization of the dural sinus means only functional flow impairment or organized occlusion due to thrombus. To avoid an unnecessary anticoagulant therapy that may worsen epidural hematoma, it is important to recognize the pitfall that PFEDH extending along the sinus groove is easy to misdiagnose for a dural sinus thrombosis.

A review of the management of single-suture craniosynostosis, past, present, and future

BACKGROUND

Craniosynostosis is a condition in which 2 or more of the skull bones fuse prematurely. The spectrum of the disorder most commonly involves the closure of a single suture in the skull, but it can also involve syndromic diagnoses in which multiple skull bones and/or bones outside of the cranium are affected. Craniosynostosis can result in cosmetic deformity as well as potential limitations in brain growth and development, and the neurocognitive impact of the condition is just starting to be studied more thoroughly. Our knowledge regarding the genetics of this condition has also evolved substantially. In this review, the authors explore the medical and surgical advancements in understanding and treating this condition over the past century, with a focus on how the diagnosis and treatment have evolved.

METHODS

In this review article, the authors, who are the leaders of a craniofacial team at a major academic pediatric hospital, focus on single-suture craniosynostosis (SSC) affecting the 6 major cranial sutures and discuss the evolution of the treatment of SSC from its early history in modern medicine through the current state of the art and future trends. This discussion is based on the authors' broad experience and a comprehensive review of the literature.

SUMMARY

The management of SSC has evolved substantially over the past 100 years. There have been major advances in technology and medical knowledge that have allowed for safer treatment of this condition through the use of newer techniques and technologies in the fields of surgery, anesthesia, and critical care. The use of less invasive surgical techniques along with other innovations has led to improved outcomes in SSC patients. The future of SSC treatment will likely be guided by elucidation of the causes of neurocognitive delay in these children and assessment of how the timing and type of surgery can mitigate adverse outcomes.

The growth of the posterior cranial fossa in FGFR2-induced faciocraniosynostosis: A review

BACKGROUND

The growth of the posterior fossa in syndromic craniostenosis was studied in many papers. However, few studies described the pathophysiological growth mechanisms in non-operated infants with fibroblast growth factor receptor (FGFR) type 2 mutation (Crouzon, Apert or Pfeiffer syndrome), although these are essential to understanding cranial vault expansion and hydrocephalus treatment in these syndromes.

OBJECTIVE

A review of the medical literature was performed, to understand the physiological and pathological growth mechanisms of the posterior fossa in normal infants and infants with craniostenosis related to FGFR2 mutation.

DISCUSSION

Of the various techniques for measuring posterior fossa volume, direct slice-by-slice contouring is the most precise and sensitive. Posterior fossa growth follows a bi-phasic pattern due to opening of the petro-occipital, occipitomastoidal and spheno-occipital sutures. Some studies reported smaller posterior fossae in syndromic craniostenosis, whereas direct contouring studies reported no difference between normal and craniostenotic patients. In Crouzon syndrome, synchondrosis fusion occurs earlier than in normal subjects, and follows a precise pattern. This premature fusion in Crouzon syndrome leads to a stenotic foramen magnum and facial retrusion.

Pharmacological exposures may precipitate craniosynostosis through targeted stem cell depletion

The Centers for Disease Control and Prevention, National Birth Defects Study suggests that environmental exposures including maternal thyroid diseases, maternal nicotine use, and use of selective serotonin reuptake inhibitors (SSRIs) may exacerbate incidence and or severity of craniofacial abnormalities including craniosynostosis. Premature fusion of a suture(s) of the skull defines the birth defect craniosynostosis which occurs in 1:1800–2500 births. A proposed mechanism of craniosynostosis is the disruption of proliferation and differentiation of cells in the perisutural area. Here, we hypothesize that pharmacological exposures including excess thyroid hormone, nicotine, and SSRIs lead to an alteration of stem cells within the sutures resulting in premature fusion. In utero exposure to nicotine and citalopram (SSRI) increased the risk of premature suture fusion in a wild-type murine model. Gli1⁺ stem cells were reduced, stem cell populations were depleted, and homeostasis of the suture mesenchyme was altered with exposure. Thus, although these pharmacological exposures can deplete calvarial stem cell populations leading to craniosynostosis, depletion of stem cells is not a unifying mechanism for pharmacological exposure associated craniosynostosis.

Hedgehog Signaling and Embryonic Craniofacial Disorders

Since its initial discovery in a Drosophila mutagenesis screen, the Hedgehog pathway has been revealed to be instrumental in the proper development of the vertebrate face. Vertebrates possess three hedgehog paralogs: Sonic hedgehog (Shh), Indian hedgehog (Ihh), and Desert hedgehog (Dhh). Of the three, Shh has the broadest range of functions both in the face and elsewhere in the embryo, while Ihh and Dhh play more limited roles. The Hedgehog pathway is instrumental from the period of prechordal plate formation early in the embryo, until the fusion of the lip and secondary palate, which complete the major patterning events of the face. Disruption of Hedgehog signaling results in an array of developmental disorders in the face, ranging from minor alterations in the distance between the eyes to more serious conditions such as severe clefting of the lip and palate. Despite its critical role, Hedgehog signaling seems to be disrupted through a number of mechanisms that may either be direct, as in mutation of a downstream target of the Hedgehog ligand, or indirect, such as mutation in a ciliary protein that is otherwise seemingly unrelated to the Hedgehog pathway. A number of teratogens such as alcohol, statins and steroidal alkaloids also disrupt key aspects of Hedgehog signal transduction, leading to developmental defects that are similar, if not identical, to those of Hedgehog pathway mutations. The aim of this review is to highlight the variety of roles that Hedgehog signaling plays in developmental disorders of the vertebrate face.

Developmental biology of the meninges

The meninges are membranous layers surrounding the central nervous system. In the head, the meninges lie between the brain and the skull, and interact closely with both during development. The cranial meninges originate from a mesenchymal sheath on the surface of the developing brain, called primary meninx, and undergo differentiation into three layers with distinct histological characteristics: the dura mater, the arachnoid mater, and the pia mater. While genetic regulation of meningeal development is still poorly understood, mouse mutants and other models with meningeal defects have demonstrated the importance of the meninges to normal development of the calvaria and the brain. For the calvaria, the interactions with the meninges are necessary for the progression of calvarial osteogenesis during early development. In later stages, the meninges control the patterning of the skull and the fate of the sutures. For the brain, the meninges regulate diverse processes including cell survival, cell migration, generation of neurons from progenitors, and vascularization. Also, the meninges serve as a stem cell niche for the brain in the postnatal life. Given these important roles of the meninges, further investigation into the molecular mechanisms underlying meningeal development can provide novel insights into the coordinated development of the head.

Bone quality assessment of osteogenic cell cultures by Raman microscopy

The use of autologous stem/progenitor cells represents a promising approach to the repair of craniofacial bone defects. The calvarium is recognized as a viable source of stem/progenitor cells that can be transplanted in vitro to form bone. However, it is unclear if bone formed in cell culture is similar in quality to that found in native bone. In this study, the quality of bone mineral formed in osteogenic cell cultures were compared against calvarial bone from postnatal mice. Given the spectroscopic resemblance that exists between cell and collagen spectra, the feasibility of extracting information on cell activity and bone matrix quality were also examined. Stem/progenitor cells isolated from fetal mouse calvaria were cultured onto fused-quartz slides under osteogenic differentiation conditions for 28 days. At specific time intervals, slides were removed and analyzed by Raman microscopy and mineral staining techniques. We show that bone formed in culture at Day 28 resembled calvarial bone from 1-day-old postnatal mice with comparable mineralization, mineral crystallinity, and collagen crosslinks ratios. In contrast, bone formed at Day 28 contained a lower degree of ordered collagen fibrils compared with 1-day-old postnatal bone. Taken together, bone formed in osteogenic cell culture exhibited progressive matrix maturation and mineralization but could not fully replicate the high degree of collagen fibril order found in native bone.

The Etiology of Neuronal Development in Craniosynostosis: A Working Hypothesis

Craniosynostosis is one of the most common craniofacial conditions treated by neurologic and plastic surgeons. In addition to disfigurement, children with craniosynostosis experience significant cognitive dysfunction later in life. Surgery is performed in infancy to correct skull deformity; however, the field is at a crossroads regarding the best approach for correction. Since the cause of brain dysfunction in these patients has remained uncertain, the role and type of surgery might have in attenuating the later-observed cognitive deficits through impact on the brain has been unclear. Recently, however, advances in imaging such as event-related potentials, diffusion tensor imaging, and functional MRI, in conjunction with more robust clinical studies, are providing important insight into the potential etiologies of brain dysfunction in syndromic and nonsyndromic craniosynostosis patients. This review aims to outline the cause(s) of such brain dysfunction including the role extrinsic vault constriction might have on brain development and the current evidence for an intrinsic modular developmental error in brain development. Illuminating the cause of brain dysfunction will identify the role of surgery can play in improving observed functional deficits and thus direct optimal primary and adjuvant treatment.

Anti-osteogenic function of a LIM-homeodomain transcription factor LMX1B is essential to early patterning of the calvaria

The calvaria (upper part of the skull) is made of plates of bone and fibrous joints (sutures and fontanelles), and the proper balance and organization of these components are crucial to normal development of the calvaria. In a mouse embryo, the calvaria develops from a layer of head mesenchyme that surrounds the brain from shortly after mid-gestation. The mesenchyme just above the eye (supra-orbital mesenchyme, SOM) generates ossification centers for the bones, which then grow toward the apex gradually. In contrast, the mesenchyme apical to SOM (early migrating mesenchyme, EMM), including the area at the vertex, does not generate an ossification center. As a result, the dorsal midline of the head is occupied by sutures and fontanelles at birth. To date, the molecular basis for this regional difference in developmental programs is unknown. The current study provides vital insights into the genetic regulation of calvarial patterning. First, we showed that osteogenic signals were active in both EMM and SOM during normal development, which suggested the presence of an anti-osteogenic factor in EMM to counter the effect of these signals. Subsequently, we identified Lmx1b as an anti-osteogenic gene that was expressed in EMM but not in SOM. Furthermore, head mesenchyme-specific deletion of Lmx1b resulted in heterotopic ossification from EMM at the vertex, and craniosynostosis affecting multiple sutures. Conversely, forced expression of Lmx1b in SOM was sufficient to inhibit osteogenic specification. Therefore, we conclude that Lmx1b plays a key role as an anti-osteogenic factor in patterning the head mesenchyme into areas with different osteogenic competence. In turn, this patterning event is crucial to generating the proper organization of the bones and soft tissue joints of the calvaria.

Role of Notch Signaling in the Physiological Patterning of Posterofrontal and Sagittal Cranial Sutures

BACKGROUND

The mutations in a Notch signaling ligand, jagged 1, are associated with unilateral coronal craniosynostosis in humans. However, the underlying mechanisms of Notch signaling in cranial suture biology still remain unclear.

METHODS

The temporal and spatial patterns of Notch signaling expression were examined in the posterofrontal and sagittal sutures of Sprague-Dawley rats by real-time quantitative reverse-transcription polymerase chain reaction at postnatal ages of 2, 15, and 25 days. The role of Notch signaling in the proliferation and differentiation of osteoblasts isolated from calvarial was examined in vitro by EdU incorporation assays and real-time quantitative reverse-transcription polymerase chain reaction after activating and inhibiting Notch signaling.

RESULTS

The mRNA levels of Notch family members (including Jagged 1, Delta 1, 3, 4, Notch 1-4, Hes 1, and Hes 5) decreased during the posterofrontal cranial suture fusion in rat. However, in the patent sagittal sutures, the mRNA levels of Notch family members (Jagged 2, Delta 1, Notch 1, Notch 3, Hes 5, and Hey 1) increased during suture development. The EdU incorporation assays revealed that the induction of Notch signaling in calvaria osteobalsts using Jagged 1 promoted the proliferation rates in those cells in vitro. Further studies showed that activation of Notch signaling calvaria osteobalsts using Jagged 1 led to the suppression of late osteogenetic markers such as type I collagen and osteocalcin.

CONCLUSIONS

The regulation of Notch signaling is of crucial importance during the physiological patterning of posterofrontal and sagittal cranial sutures. Thus, targeting this pathway may prove significant for the development of future therapeutic applications in craniosynostosis.

Human Foramen Magnum Area and Posterior Cranial Fossa Volume Growth in Relation to Cranial Base Synchondrosis Closure in the Course of Child Development

BACKGROUND

To date, no study has compared the evolution of the foramen magnum area (FMA) and the posterior cranial fossa volume (PCFV) with the degree of cranial base synchondrosis ossification.

OBJECTIVE

To illustrate these features in healthy children.

METHODS

The FMA, the PCFV, and the ossification of 12 synchondroses according to the Madeline and Elster scale were retrospectively analyzed in 235 healthy children using millimeter slices on a computed tomography scan.

RESULTS

The mean FMA of 6.49 cm in girls was significantly inferior to the FMA of 7.67 cm in boys (P < .001). In both sexes, the growth evolved in a 2-phase process, with a phase of rapid growth from birth to 3.75 years old (yo) followed by a phase of stabilization. In girls, the first phase was shorter (ending at 2.6 yo) than in boys (ending at 4.33 yo) and proceeded at a higher rate. PCFV was smaller in girls (P < .001) and displayed a biphasic pattern in the whole population, with a phase of rapid growth from birth to 3.58 yo followed by a phase of slow growth until 16 yo. In girls, the first phase was more active and shorter (ending at 2.67 yo) than in boys (ending at 4.5 yo). The posterior interoccipital synchondroses close first, followed by the anterior interoccipital and occipitomastoidal synchondroses, the lambdoid sutures simultaneously, then the petro-occipital and spheno-occipital synchondroses simultaneously.

CONCLUSION

The data provide a chronology of synchondrosis closure. We showed that FMA and PCFV are constitutionally smaller in girls at birth (P ≤ .02) and suggest that a sex-related difference in the FMA is related to earlier closure of anterior interoccipital synchondroses in girls (P = .01).

ABBREVIATIONS

AIOS, anterior interoccipital synchondrosesFMA, foramen magnum areaLS, lambdoid suturesOMS, occipitomastoidal synchondrosesPCFV, posterior cranial fossa volumePIOS, posterior interoccipital synchondrosesPOS, petro-occipital synchondrosesSOS, spheno-occipital synchondrosisyo, years old.

Dysregulated PDGFRα signaling alters coronal suture morphogenesis and leads to craniosynostosis through endochondral ossification

Craniosynostosis is a prevalent human birth defect characterized by premature fusion of calvarial bones. In this study, we show that tight regulation of endogenous PDGFRα activity is required for normal calvarium development in the mouse and that dysregulated PDGFRα activity causes craniosynostosis. Constitutive activation of PDGFRα leads to expansion of cartilage underlying the coronal sutures, which contribute to suture closure through endochondral ossification, in a process regulated in part by PI3K/AKT signaling. Our results thus identify a novel mechanism underlying calvarial development in craniosynostosis.

BMP9 induces osteogenesis and adipogenesis in the immortalized human cranial suture progenitors from the patent sutures of craniosynostosis patients

The cranial suture complex is a heterogeneous tissue consisting of osteogenic progenitor cells and mesenchymal stem cells (MSCs) from bone marrow and suture mesenchyme. The fusion of cranial sutures is a highly coordinated and tightly regulated process during development. Craniosynostosis is a congenital malformation caused by premature fusion of cranial sutures. While the progenitor cells derived from the cranial suture complex should prove valuable for studying the molecular mechanisms underlying suture development and pathogenic premature suture fusion, primary human cranial suture progenitors (SuPs) have limited life span and gradually lose osteoblastic ability over passages. To overcome technical challenges in maintaining sufficient and long-term culture of SuPs for suture biology studies, we establish and characterize the reversibly immortalized human cranial suture progenitors (iSuPs). Using a reversible immortalization system expressing SV40 T flanked with FRT sites, we demonstrate that primary human suture progenitor cells derived from the patent sutures of craniosynostosis patients can be efficiently immortalized. The iSuPs maintain long-term proliferative activity, express most of the consensus MSC markers and can differentiate into osteogenic and adipogenic lineages upon BMP9 stimulation in vitro and in vivo. The removal of SV40 T antigen by FLP recombinase results in a decrease in cell proliferation and an increase in the endogenous osteogenic and adipogenic capability in the iSuPs. Therefore, the iSuPs should be a valuable resource to study suture development, intramembranous ossification and the pathogenesis of craniosynostosis, as well as to explore cranial bone tissue engineering.

In vivo expression and regulation of genes associated with vascularization during early response of sutures to tensile force

Sutures are fibrous tissues that connect bones in craniofacial skeletal complexes. Cranio- and dentofacial skeletal deformities in infant and adolescent patients can be treated by applying tensile force to sutures to induce sutural bone formation. The early gene expression induced by mechanical stress is essential for bone formation in long bones; however, early gene expression during sutural bone formation induced by tensile force is poorly characterized. In vivo studies are essential to evaluate molecular responses to mechanical stresses in heterogeneous cell populations, such as sutures. In this paper we examined in vivo early gene expression and the underlying regulatory mechanism for this expression in tensile-force-applied cranial sutures, focusing on genes involved in vascularization. Tensile force upregulated expression of vascular factors, such as vascular endothelial growth factor (Vegf) and endothelial cell markers, in sutures within 3 h. The expression of connective tissue growth factor (Ctgf) and Rho-associated coiled-coil containing protein kinase 2 (Rock2) was also upregulated by tensile force. A CTGF-neutralizing antibody and the ROCK inhibitor, Y-27632, abolished tensile-force-induced Vegf expression. Moreover, tensile force activated extracellular signal-related kinase 1/2 (ERK1/2) signaling in sagittal sutures, and the ERK1/2 inhibitor, U0126, partially inhibited tensile-force-induced Ctgf expression. These results indicate that tensile force induces in vivo gene expression associated with vascularization early in tensile-force-induced sutural bone formation. Moreover, the early induction of Vegf gene expression is regulated by CTGF and ROCK2.

Neosuture formation after endoscope-assisted craniosynostosis repair

OBJECTIVE The goal of this study was to identify the rate of neosuture formation in patients with craniosynostosis treated with endoscope-assisted strip craniectomy and investigate whether neosuture formation in sagittal craniosynostosis has an effect on postoperative calvarial shape. METHODS The authors retrospectively reviewed 166 cases of nonsyndromic craniosynostosis that underwent endoscope-assisted repair between 2006 and 2014. Preoperative and 1-year postoperative head CT scans were evaluated, and the rate of neosuture formation was calculated. Three-dimensional reconstructions of the CT data were used to measure cephalic index (CI) (ratio of head width and length) of patients with sagittal synostosis. Regression analysis was used to calculate significant differences between patients with and without neosuture accounting for age at surgery and preoperative CI. RESULTS Review of 96 patients revealed that some degree of neosuture development occurred in 23 patients (23.9%): 16 sagittal, 2 bilateral coronal, 4 unilateral coronal, and 1 lambdoid synostosis. Complete neosuture formation was seen in 14 of those 23 patients (9 of 16 sagittal, 1 of 2 bilateral coronal, 3 of 4 unilateral coronal, and 1 of 1 lambdoid). Mean pre- and postoperative CI in the complete sagittal neosuture group was 67.4% and 75.5%, respectively, and in the non-neosuture group was 69.8% and 74.4%, respectively. There was no statistically significant difference in the CI between the neosuture and fused suture groups preoperatively or 17 months postoperatively in patients with sagittal synostosis. CONCLUSIONS Neosuture development can occur after endoscope-assisted strip craniectomy and molding helmet therapy for patients with craniosynostosis. Although the authors did not detect a significant difference in calvarial shape postoperatively in the group with sagittal synostosis, the relevance of neosuture formation remains to be determined. Further studies are required to discover long-term outcomes comparing patients with and without neosuture formation.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Understanding craniosynostosis as a growth disorder

Craniosynostosis is a condition of complex etiology that always involves the premature fusion of one or multiple cranial sutures and includes various anomalies of the soft and hard tissues of the head. Steady progress in the field has resulted in identifying gene mutations that recurrently cause craniosynostosis. There are now scores of mutations on many genes causally related to craniosynostosis syndromes, though the genetic basis for the majority of nonsyndromic cases is unknown. Identification of these genetic mutations has allowed significant progress in understanding the intrinsic properties of cranial sutures, including mechanisms responsible for normal suture patency and for pathogenesis of premature suture closure. An understanding of morphogenesis of cranial vault sutures is critical to understanding the pathophysiology of craniosynostosis conditions, but the field is now poised to recognize the repeated changes in additional skeletal and soft tissues of the head that typically accompany premature suture closure. We review the research that has brought an understanding of premature suture closure within our reach. We then enumerate the less well-studied, but equally challenging, nonsutural phenotypes of craniosynostosis conditions that are well characterized in available mouse models. We consider craniosynostosis as a complex growth disorder of multiple tissues of the developing head, whose growth is also targeted by identified mutations in ways that are poorly understood. Knowledge gained from studies of humans and mouse models for these conditions underscores the diverse, associated developmental anomalies of the head that contribute to the complex phenotypes of craniosynostosis conditions presenting novel challenges for future research. WIREs Dev Biol 2016, 5:429-459. doi: 10.1002/wdev.227 For further resources related to this article, please visit the WIREs website.

Craniosynostosis : Updates in Radiologic Diagnosis

The purpose of this article is to review imaging findings and to discuss the optimal imaging methods for craniosynostosis. The discussion of imaging findings are focused on ultrasonography, plain radiography, magnetic resonance imaging and computed tomography with 3-dimensional reconstruction. We suggest a strategy for imaging work-up for the diagnosis, treatment planning and follow-up to minimize or avoid ionized radiation exposure to children by reviewing the current literature.

Signaling mechanisms implicated in cranial sutures pathophysiology: Craniosynostosis

Normal extension and skull expansion is a synchronized process that prevails along the osteogenic intersections of the cranial sutures. Cranial sutures operate as bone growth sites allowing swift bone generation at the edges of the bone fronts while they remain patent. Premature fusion of one or more cranial sutures can trigger craniosynostosis, a birth defect characterized by dramatic manifestations in appearance and functional impairment. Up until today, surgical correction is the only restorative measure for craniosynostosis associated with considerable mortality. Clinical studies have identified several genes implicated in the pathogenesis of craniosynostosis syndromes with useful insights into the underlying molecular signaling events that determine suture fate. In this review, we exploit the intracellular signal transduction pathways implicated in suture pathobiology, in an attempt to identify key signaling molecules for therapeutic targeting.

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Cranial sutures operate as bone growth sites.

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Premature fusion of one or more cranial sutures can trigger craniosynostosis.

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Several genes are involved in the pathogenesis of craniosynostosis syndromes.

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An array of molecular signaling events determine suture fate.

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Herein, the signal transduction pathways implicated in suture pathobiology are discussed.