Sonic hedgehog signaling in craniofacial development

Regulation of Skeletogenic Pathways by m6A RNA Modification: A Comprehensive Review

In the complex process of skeletal development, the significance of m6A RNA methylation-a predominant form of RNA modification-has not been fully explored. This review discuss how m6A RNA methylation plays an important, though not yet fully understood, role in regulating skeletal formation. It examines how m6A influences key signaling pathways essential for skeletal development and homeostasis, suggesting various possible interactions between m6A methylation and these critical pathways. While the exact mechanisms for many of these interactions remain to be elucidated, m6A RNA methylation is anticipated to be a key emerging regulator in skeletal structure development across vertebrates. Highlighting the need for further research, this overview provides an in-depth look at the potential regulatory interactions of m6A RNA methylation within skeletal system. Uniquely, this review is the most comprehensive compilation of evidence linking components of m6A RNA methylation to signaling pathways involved in skeletogenesis.

p75 neurotrophin receptor regulates craniofacial growth and morphology in postnatal development

Craniofacial abnormalities are among the most prevalent congenital defects, significantly affecting appearance, function, and quality of life. While the role of genetic mutations in craniofacial malformations is recognized, the underlying molecular mechanisms remain poorly understood. In this study, we investigate the role of p75 neurotrophin receptor (p75NTR) in craniofacial development by comparing wild-type (p75NTR+/+) mice against p75NTR-deficient (p75NTR-/-) knockout mice. We employed histology, micro-CT surface distance, volumetric analysis, and geometric morphometric analysis to assess craniofacial development and growth. On postnatal day 7 (P7), p75NTR-/- mice exhibited reduced skull length compared to wild-type controls. By P28, micro-CT analysis revealed significant reductions in calvarial bone volume and trabecular bone thickness in p75NTR-/- mice. Geometric morphometric analysis identified significant shape alterations in the nasal, parietal, and occipital regions, with p75NTR-/- mice showing a shortened cranium and tapered nasal bone morphology. These findings highlight the critical role of p75NTR in regulating postnatal craniofacial development. Disruption of p75NTR signaling impairs both the growth and morphological integrity of craniofacial structures, which may contribute to the pathogenesis of congenital craniofacial abnormalities. In the future, a better understanding of the molecular mechanisms through which p75NTR mediates craniofacial development may offer valuable insights for future targeted therapeutic strategies for craniofacial defects.

The primary cilium gene CPLANE1 is required for peripheral nervous system development

Ciliopathies are a group of neurodevelopmental disorders characterized by the dysfunction of the primary cilium. This small protrusion from most cells of our body serves as a signaling hub for cell-to-cell communication during development. Cell proliferation, differentiation, migration, and neural circuit formation have been demonstrated to depend on functional primary cilia. In the context of ciliopathies, the focus has been on the development of the central nervous system, while the peripheral nervous system has not been studied in depth. In line with phenotypes seen in patients, the absence of a functional primary cilium was shown to affect the migration of cranial and vagal neural crest cells, which contribute to the development of craniofacial features and the heart, respectively. We show here that the ciliopathy gene Cplane1 is required for the development of the peripheral nervous system. Loss of Cplane1 function in chicken embryos induces defects in dorsal root ganglia, which vary in size and fail to localize symmetrically along the spinal cord. These defects may help to understand the alteration in somatosensory perceptions described in some ciliopathy patients.

Single Cell Spatial Transcriptomics of the Murine Embryonic Palate Links Pax9 to Patterning and Organization of Extracellular Matrix Components

Despite advances in understanding the morphological disruptions that lead to defects in palate formation, the precise perturbations within the signaling microenvironment of palatal clefts remain poorly understood. To explore in greater depth the genomic basis of palatal clefts, we designed and implemented the first single cell spatial RNA-sequencing study in a cleft palate model, utilizing the Pax9 -/- murine model at multiple developmental timepoints, which exhibits a consistent cleft palate defect. Visium HD, an emerging platform for true single-cell resolution spatially resolved transcriptomics, was employed using custom bins of 2×2 μm spatial gene expression data. Validation of spatial gene expression was then validated using custom designed Xenium In Situ mRNA spatial profiling and RNAscope Multiplex assays. Functional enrichment analysis revealed a palate cell-specific perturbation in Wnt signaling effector function in tandem with disrupted expression of extracellular matrix genes in developing mesenchyme. As a key step toward laying the framework for identifying key molecular targets these data can be used for translational studies aimed at developing effective therapies for human palatal clefts.

New approach methodologies to confirm developmental toxicity of pharmaceuticals based on weight of evidence

The aim of embryo-fetal developmental toxicity assessments for pharmaceuticals is to inform potential risk of adverse pregnancy outcome, which has traditionally relied on studies in pregnant animals. Recent updates to international safety guidelines (ICH S5R3) have incorporated information on how to use weight of evidence and alternative assays to reduce animal use while still informing risk of fetal harm. Uptake of these alternative approaches has been slow due to limitations in understanding how alternative assays translate to in vivo effects and then relevance to human exposure. To understand the predictivity of new approach methodologies for developmental toxicity (DevTox NAMs), we used two pharmaceutical examples (glasdegib and lorlatinib) to illustrate the value of DevTox NAMs to complement weight of evidence (WoE) assessments while considering the relationship of concentration-effect levels in NAMs to in vivo studies. The in vitro results generated in a battery of assays (mEST, rWEC, zebrafish, and human based stem cells) confirmed the WoE based on literature and further confirmed by preliminary embryo-fetal development data. The data generated for these two compounds supports integrating DevTox NAMs into the developmental toxicity assessment for advanced cancer indications.

Identification of rare variants in PTCH2 associated with non-syndromic orofacial clefts

Orofacial clefts (OFCs) represent the most prevalent congenital craniofacial anomalies, significantly impacting patients' appearance, oral function, and psychological well-being. Among these, non-syndromic OFCs (NSOFCs) are the most predominant type, with the etiology attributed to a combination of genetic and environmental factors. Rare variants of key genes involved in craniofacial development-related signaling pathway are crucial in the occurrence of NSOFCs, and our recent studies have identified PTCH1, a receptor-coding gene in the Hedgehog signaling pathway, as a causative gene for NSOFCs. However, the role of PTCH2, the paralog of PTCH1, in pathogenesis of NSOFCs remains unclear. Here, we perform whole-exome sequencing to explore the genetic basis of 144 sporadic NSOFC patients. We identify five heterozygous variants of PTCH2 in four patients: p.L104P, p.A131G, p.R557H, p.I927S, and p.V978D, with the latter two co-occurring in a single patient. These variants, all proven to be rare through multiple genomic databases, with p.I927S and p.V978D being novel variants and previously unreported. Sequence alignment suggests that these affected amino acids are evolutionarily conserved across vertebrates. Utilizing predictive structural modeling tools such as AlphaFold and SWISS-MODEL, we propose that these variants may disrupt the protein's structure and function. In summary, our findings suggest that PTCH2 may be a novel candidate gene predicted to be associated with NSOFCs, thereby broadening the spectrum of causative genes implicated in the craniofacial anomalies.

A male fetus with cyclopia was discovered after miscarriage: A rare case report from Syria

Key Clinical Message

This case of alobar holoprosencephaly and cyclopia emphasizes the value of prenatal check-ups, particularly in low-income countries. Early ultrasound diagnosis leads to early gestational termination, preventing psychological trauma for the parents.

Abstract

Alobar holoprosencephaly is a rare-occurrence malformation with a bad prognosis linked to cyclopia, the most severe cranial feature. Prenatal examinations are essential for identifying these deformities and preventing parental mental health damage.

Cardiovascular anomalies in patients with Tessier syndrome: a systematic review

Tessier clefts are skeletal and soft tissue abnormalities of a neonate's facial structures. They could be classified as syndromic and non-syndromic clefts, which can be attributed to disruptions in fetal development and genetic mutations, respectively. Reported cases of these clefts typically document the presence of additional abnormalities associated with these clefts. In this systematic review, we analyzed reports of Tessier clefts accompanied by cardiovascular anomalies, as one of the commonly encountered anomalies. We systematically searched PubMed (MEDLINE), Scopus, Web of Science, Science Direct, and Google Scholar. We selected and included case reports, case series, and case reviews on patients with Tessier cleft and cardiovascular anomalies. The critical appraisal of the included studies was performed by two independent investigators using the Consensus-based Clinical Case Reporting Guideline Development (CARE) checklist. Overall, 20 reports (18 case reports and 2 case series) were eligible for inclusion in this review. Tessier clefts 3 and 30 were the most commonly observed. In addition, the most prevalent cardiovascular anomalies consisted of the ventricular septal defect (VSD), double-outlet right ventricle, and atrial septal defect (ASD). Most of the patients received cosmetic and cardiovascular surgeries. However, some were not proper candidates for cardiovascular surgery because of their unstable condition and therefore did not survive.   Conclusion: Regardless of the focus placed on the cleft and subsequent plastic surgery procedures in these cases, it is important to prioritize other abnormalities that may be associated with mortality. A complete cardiovascular system and associated disorders assessment should be performed before facial cosmetic surgeries. What is Known: • Tessier clefts are congenital defects in the soft tissues and bones of the face and like many other congenital defects, they are accompanied by defects in other parts of the body. • In the current literature, the emphasis is on clefts and the cosmetic issues rather than the coinciding defects, particularly cardiovascular anomalies. What is New: • Review the cardiovascular anomalies that are commonly encountered in patients with Tessier clefts.

Cyclopia in a newborn rhesus macaque born to a dam infected with SIV and receiving antiretroviral therapy during pregnancy

Cyclopia, a rare genetic anomaly and birth defect, was recently observed in our nonhuman primate study. A newborn rhesus macaque, delivered via cesarean section, exhibited facial abnormalities, including a single eye in the middle of the forehead. This macaque was born to a dam who had been inoculated with SIV in the first trimester and received antiretroviral therapy (ART) in the early third trimester of pregnancy. Prenatal ultrasound detected fetal defects, including the fusion of the thalami and absence of third ventricle during the third trimester of fetal development. Remarkably, the newborn macaque was diagnosed with severe alobar holoprosencephaly, characterized by a single eye located on the facial midline and proboscises positioned above and below the eye. This condition was accompanied by the absence of a nose, mouth, mandible, maxilla, nasal and oral cavities, tongue, as well as the esophagus. Subsequent genetic screening identified a significant down-regulation of craniofacial development-associated genes, although genetic mutations in the sonic hedgehog gene (SHH) were not present. As the fetal defects were identified prior to the initiation of antiretroviral therapy, it is possible that other environmental factors may have contributed to the development of cyclopia in this rhesus case. However, the etiology of this congenital HPE case remains essentially unknown.