Mouse models for the study of cranial base growth and anomalies

Impact of Sonic Hedgehog-dependent sphenoid bone defect on craniofacial growth

OBJECTIVES

The main objective of this study was to evaluate how an apparently minor anomaly of the sphenoid bone, observed in a haploinsufficient mouse model for Sonic Hedgehog (Shh), affects the growth of the adult craniofacial region. This study aims to provide valuable information to orthodontists when making decisions regarding individuals carrying SHH mutation.

MATERIALS AND METHODS

The skulls of embryonic, juvenile and adult mice of two genotypes (Shh heterozygous and wild type) were examined and measured using landmark-based linear dimensions. Additionally, we analysed the clinical characteristics of a group of patients and their relatives with SHH gene mutations.

RESULTS

In the viable Shh+/ - mouse model, bred on a C57BL/6J background, we noted the presence of a persistent foramen at the midline of the basisphenoid bone. This particular anomaly was attributed to the existence of an ectopic pituitary gland. We discovered that this anomaly led to premature closure of the intrasphenoidal synchondrosis and contributed to craniofacial deformities in adult mice, including a longitudinally shortened skull base. This developmental anomaly is reminiscent of that commonly observed in human holoprosencephaly, a disorder resulting from a deficiency in SHH activity. However, sphenoid morphogenesis is not currently monitored in individuals carrying SHH mutations.

CONCLUSION

Haploinsufficiency of Shh leads to isolated craniofacial skeletal hypoplasia in adult mouse. This finding highlights the importance of radiographic monitoring of the skull base in all individuals with SHH gene mutations.

The application of zebrafish model in the study of cleft lip and palate development: A systematic review

Objective

Craniofacial growth and development are more than a scientific curiosity; it is of tremendous interest to clinicians. Insights into the genetic etiology of cleft lip and palate development are essential for improving diagnosis and treatment planning. The purpose of this systematic review was to utilize a zebrafish model to highlight the role of the IRF6 gene in cleft lip and palate development in humans.

Data

This review adhered to the guidelines outlined in the PRISMA statement. Nine studies were included in the analysis.

Sources

This study used major scientific databases such as MEDLINE, EMBASE, Web of Science, and the Zebrafish Information Network and yielded 1275 articles. Two reviewers performed the screening using COVIDENCE™ independently, and a third reviewer resolved any conflicts.

Study selection

After applying the inclusion and exclusion criteria and screening, nine studies were included in the analysis. The Systematic Review Center for Laboratory Animal Experimentation's (SYRCLE's) risk-of-bias tool was used to assess the quality of the included studies.

Results

The main outcome supports the role of the IRF6 gene in zebrafish periderm development and embryogenesis, and IRF6 variations result in cleft lip and palate development. The overall SYRCLE risk of bias was low-medium.

Conclusion

In conclusion, this review indicated the critical role of the IRF6 gene and its downstream genes (GRHL3, KLF17, and ESRP1/2) in the development of cleft lip and palate in zebrafish models. Genetic mutation zebrafish models provide a high level of insights into zebrafish craniofacial development.

Clinical relevance

this review provides a productive avenue for understanding the powerful and conserved zebrafish model for investigating the pathogenesis of human cleft lip and palate.

Radiographic Imaging for the Diagnosis and Treatment of Patients with Skeletal Class III Malocclusion

Skeletal Class III malocclusion is one type of dentofacial deformity that significantly affects patients' facial aesthetics and oral health. The orthodontic treatment of skeletal Class III malocclusion presents challenges due to uncertainties surrounding mandibular growth patterns and treatment outcomes. In recent years, disease-specific radiographic features have garnered interest from researchers in various fields including orthodontics, for their exceptional performance in enhancing diagnostic precision and treatment effect predictability. The aim of this narrative review is to provide an overview of the valuable radiographic features in the diagnosis and management of skeletal Class III malocclusion. Based on the existing literature, a series of analyses on lateral cephalograms have been concluded to identify the significant variables related to facial type classification, growth prediction, and decision-making for tooth extractions and orthognathic surgery in patients with skeletal Class III malocclusion. Furthermore, we summarize the parameters regarding the inter-maxillary relationship, as well as different anatomical structures including the maxilla, mandible, craniofacial base, and soft tissues from conventional and machine learning statistical models. Several distinct radiographic features for Class III malocclusion have also been preliminarily observed using cone beam computed tomography (CBCT) and magnetic resonance imaging (MRI).

Narrating the Genetic Landscape of Human Class I Occlusion: A Perspective-Infused Review

This review examines a prevalent condition with multifaceted etiology encompassing genetic, environmental, and oral behavioral factors. It stands as a significant ailment impacting oral functionality, aesthetics, and quality of life. Longitudinal studies indicate that malocclusion in primary dentition may progress to permanent malocclusion. Recognizing and managing malocclusion in primary dentition is gaining prominence. The World Health Organization ranks malocclusions as the third most widespread oral health issue globally. Angle's classification system is widely used to categorize malocclusions, with Class I occlusion considered the norm. However, its prevalence varies across populations due to genetic and examination disparities. Genetic factors, including variants in genes like MSX1, PAX9, and AXIN2, have been associated with an increased risk of Class I occlusion. This review aims to provide a comprehensive overview of clinical strategies for managing Class I occlusion and consolidate genetic insights from both human and murine populations. Additionally, genomic relationships among craniofacial genes will be assessed in individuals with Class I occlusion, along with a murine model, shedding light on phenotype-genotype associations of clinical relevance. The prevalence of Class I occlusion, its impact, and treatment approaches will be discussed, emphasizing the importance of early intervention. Additionally, the role of RNA alterations in skeletal Class I occlusion will be explored, focusing on variations in expression or structure that influence craniofacial development. Mouse models will be highlighted as crucial tools for investigating mandible size and prognathism and conducting QTL analysis to gain deeper genetic insights. This review amalgamates cellular, molecular, and clinical trait data to unravel correlations between malocclusion and Class I phenotypes.

Chondrocyte Polarity During Endochondral Ossification Requires Protein-Protein Interactions Between Prickle1 and Dishevelled2/3

The expansion and growth of the endochondral skeleton requires organized cell behaviors that control chondrocyte maturation and oriented division. In other organs, these processes are accomplished through Wnt/planar cell polarity (Wnt/PCP) signaling pathway and require the protein-protein interactions of core components including Prickle1 (PK1) and Dishevelled (DVL). To determine the function of Wnt/PCP signaling in endochondral ossification of the cranial base and limb, we utilized the Prickle1^Beetlejuice (Pk1^Bj ) mouse line. The Pk1^Bj allele has a missense mutation in the PK1 LIM1 domain that results in a hypomorphic protein. Similar to human patients with Robinow syndrome, the Prickle1^Bj/Bj mouse mutants lack growth plate expansion resulting in shorter limbs and midfacial hypoplasia. Within the Prickle1^Bj/Bj limb and cranial base growth plates we observe precocious maturation of chondrocytes and stalling of terminal differentiation. Intriguingly, we observed that the growth plate chondrocytes have randomized polarity based on the location of the primary cilia and the location of PRICKLE1, DVL2, and DVL3 localization. Importantly, mutant PK1^Bj protein has decreased protein-protein interactions with both DVL2 and DVL3 in chondrocytes as revealed by in vivo co-immunoprecipitation and proximity ligation assays. Finally, we propose a model where the interaction between the Prickle1 LIM1 domain and DVL2 and DVL3 contributes to chondrocyte polarity and contributes to proximal-distal outgrowth of endochondral elements. © 2021 American Society for Bone and Mineral Research (ASBMR).

Selection for increased tibia length in mice alters skull shape through parallel changes in developmental mechanisms

Bones in the vertebrate cranial base and limb skeleton grow by endochondral ossification, under the control of growth plates. Mechanisms of endochondral ossification are conserved across growth plates, which increases covariation in size and shape among bones, and in turn may lead to correlated changes in skeletal traits not under direct selection. We used micro-CT and geometric morphometrics to characterize shape changes in the cranium of the Longshanks mouse, which was selectively bred for longer tibiae. We show that Longshanks skulls became longer, flatter, and narrower in a stepwise process. Moreover, we show that these morphological changes likely resulted from developmental changes in the growth plates of the Longshanks cranial base, mirroring changes observed in its tibia. Thus, indirect and non-adaptive morphological changes can occur due to developmental overlap among distant skeletal elements, with important implications for interpreting the evolutionary history of vertebrate skeletal form.

Defining the critical period of hedgehog pathway inhibitor-induced cranial base dysplasia in mice

BACKGROUND

The hedgehog signaling pathway is critical for developmental patterning of the limb, craniofacial and axial skeleton. Disruption of this pathway in mice leads to a series of structural malformations, but the exact role and critical period of the Hh pathway in the early development of the cranial base have been rarely described.

RESULTS

Embryos exposed to vismodegib from E7.5, E9.5, and E10.5 had a higher percentage of cranial base fenestra. The peak incidence of hypoplasia in sphenoid winglets and severe craniosynostosis in cranial base synchondroses was observed when vismodegib was administered between E9.5 and E10.5. Cranial base craniosynostosis results from accelerating terminal differentiation of chondrocytes and premature osteogenesis.

CONCLUSIONS

We define the critical periods for the induction of cranial base deformity by vismodegib administration at a meticulous temporal resolution. Our findings suggest that the Hh pathway may play a vital role in the early development of the cranial base. This research also establishes a novel and easy-to-establish mouse model of synostosis in the cranial base using a commercially available pathway-selective inhibitor.

The Skull's Girder: A Brief Review of the Cranial Base

The cranial base is a multifunctional bony platform within the core of the cranium, spanning rostral to caudal ends. This structure provides support for the brain and skull vault above, serves as a link between the head and the vertebral column below, and seamlessly integrates with the facial skeleton at its rostral end. Unique from the majority of the cranial skeleton, the cranial base develops from a cartilage intermediate-the chondrocranium-through the process of endochondral ossification. Owing to the intimate association of the cranial base with nearly all aspects of the head, congenital birth defects impacting these structures often coincide with anomalies of the cranial base. Despite this critical importance, studies investigating the genetic control of cranial base development and associated disorders lags in comparison to other craniofacial structures. Here, we highlight and review developmental and genetic aspects of the cranial base, including its transition from cartilage to bone, dual embryological origins, and vignettes of transcription factors controlling its formation.

Morphological consequences of artificial cranial deformation: Modularity and integration

The cranium is an anatomically complex structure. One source of its complexity is due to its modular organization. Cranial modules are distinct and partially independent units that interact substantially during ontogeny thus generating morphological integration. Artificial Cranial Deformation (ACD) occurs when the human skull is intentionally deformed, through the use of different deforming devices applied to the head while it is developing. Hence, ACD provides an interesting example to assess the degree to which biomechanical perturbations of the developing neurocranium impact on the degree of morphological integration in the skull as a whole. The main objective of this study was to assess how ACD affects the morphological integration of the skull. This was accomplished by comparing a sample of non-deformed crania and two sets of deformed crania (i.e. antero-posterior and oblique). Both developmental and static modularity and integration were assessed through Generalized Procrustes Analysis by considering the symmetric and asymmetric components of variation in adults, using 3D landmark coordinates as raw data. The presence of two developmental modules (i.e. viscero and neurocranium) in the skull was tested. Then, in order to understand how ACD affects morphological integration, the covariation pattern between the neuro and viscerocranium was examined in antero-posterior, oblique and non-deformed cranial categories using Partial Least-Squares. The main objective of this study was to assess how ACD affects the morphological integration of the skull. This was accomplished by comparing a sample of deformed (i.e. antero-posterior and oblique) and non-deformed crania. Hence, differences in integration patterns were compared between groups. The obtained results support the modular organization of the human skull in the two analyzed modules. The integration analyses show that the oblique ACD style differentially affects the static morphological integration of the skull by increasing the covariance between neuro and viscerocranium in a more constrained way than in antero-posterior and non-deformed skulls. In addition, the antero-posterior ACD style seems to affect the developmental integration of the skull by directing the covariation pattern in a more defined manner as compared to the other cranial categories.

Trans-pairing between osteoclasts and osteoblasts shapes the cranial base during development

Bone growth is linked to expansion of nearby organs, as is the case for the cranial base and the brain. Here, we focused on development of the mouse clivus, a sloping surface of the basioccipital bone, to define mechanisms underlying morphological changes in bone in response to brain enlargement. Histological analysis indicated that both endocranial and ectocranial cortical bone layers in the basioccipital carry the osteoclast surface dorsally and the osteoblast surface ventrally. Finite element analysis of mechanical stress on the clivus revealed that compressive and tensile stresses appeared mainly on respective dorsal and ventral surfaces of the basioccipital bone. Osteoclastic bone resorption occurred primarily in the compression area, whereas areas of bone formation largely coincided with the tension area. These data collectively suggest that compressive and tensile stresses govern respective localization of osteoclasts and osteoblasts. Developmental analysis of the basioccipital bone revealed the clivus to be angled in early postnatal wild-type mice, whereas its slope was less prominent in Tnfsf11^−/− mice, which lack osteoclasts. We propose that osteoclast-osteoblast “trans-pairing” across cortical bone is primarily induced by mechanical stress from growing organs and regulates shape and size of bones that encase the brain.