Symmetry and fluctuation of cell movements in neural crest-derived facial mesenchyme

Downstream branches of receptor tyrosine kinase signaling act interdependently to shape the face

BACKGROUND

Previously we found that increasing fibroblast growth factor (FGF) signaling in the neural crest cells within the frontonasal process (FNP) of the chicken embryo caused dysmorphology that was correlated with reduced proliferation, disrupted cellular orientation, and lower MAPK activation but no change in PLCγ and PI3K activation. This suggests RTK signaling may drive craniofacial morphogenesis through specific downstream effectors that affect cellular activities. In this study we inhibited three downstream branches of RTK signaling to determine their role in regulating cellular activities and how these changes affect morphogenesis of the FNP.

RESULTS

Small molecule inhibitors of MEK1/2, PI3K, and PLCγ were delivered individually and in tandem to the right FNP of chicken embryos. All treatments caused asymmetric proximodistal truncation on the treated side and a mild expansion on the untreated side compared to DMSO control treated FNPs. Inhibiting each pathway caused similar decreased proliferation and disrupted cellular orientation, and only mildly increased apoptosis.

CONCLUSIONS

Since RTK signaling is a ubiquitous and tightly regulated biochemical system, we conclude that the downstream pathways are robust to developmental perturbation through redundant signaling systems.

Downstream branches of receptor tyrosine kinase signaling act interdependently to shape the face

Background –

Previously we found that increasing fibroblast growth factor (FGF) signaling in the neural crest cells within the frontonasal process (FNP) of the chicken embryo caused dysmorphology that was correlated with reduced proliferation, disrupted cellular orientation, and lower MAPK activation but no change in PLCy and PI3K activation. This suggests RTK signaling may drive craniofacial morphogenesis through specific downstream effectors that affect cellular activities. In this study we inhibited three downstream branches of RTK signaling to determine their role in regulating cellular activities and how these changes affect morphogenesis of the FNP.

Results –

Small molecule inhibitors of MEK1/2, PI3K, and PLCy were delivered individually and in tandem to the right FNP of chicken embryos. All treatments caused asymmetric proximodistal truncation on the treated side and a mild expansion on the untreated side compared to DMSO control treated FNPs. Inhibiting each pathway caused similar decreased proliferation and disrupted cellular orientation, but did not affect apoptosis.

Conclusions –

Since RTK signaling is a ubiquitous and tightly regulated biochemical system we conclude that the downstream pathways are robust to developmental perturbation through redundant signaling systems.

Craniofacial studies in chicken embryos confirm the pathogenicity of human FZD2 variants associated with Robinow syndrome

Robinow syndrome is a rare disease caused by variants of seven WNT pathway genes. Craniofacial features include widening of the nasal bridge and jaw hypoplasia. We used the chicken embryo to test whether two missense human FZD2 variants (1301G>T, p.Gly434Val; 425C>T, p.Pro142Lys) were sufficient to change frontonasal mass development. In vivo, the overexpression of retroviruses with wild-type or variant human FZD2 inhibited upper beak ossification. In primary cultures, wild-type and variant human FZD2 significantly inhibited chondrogenesis, with the 425C>T variant significantly decreasing activity of a SOX9 luciferase reporter compared to that for the wild type or 1301G>T. Both variants also increased nuclear shuttling of β-catenin (CTNNB1) and increased the expression of TWIST1, which are inhibitory to chondrogenesis. In canonical WNT luciferase assays using frontonasal mass cells, the variants had dominant-negative effects on wild-type FZD2. In non-canonical assays, the 425C>T variant failed to activate the reporter above control levels and was unresponsive to exogenous WNT5A. This is the first single amino acid change to selectively alter ligand binding in a FZD receptor. Therefore, FZD2 missense variants are pathogenic and could lead to the altered craniofacial morphogenesis seen in Robinow syndrome.

Emergence of a left-right symmetric body plan in vertebrate embryos

External bilateral symmetry is a prevalent feature in vertebrates, which emerges during early embryonic development. To begin with, vertebrate embryos are largely radially symmetric before transitioning to bilaterally symmetry, after which, morphogenesis of various bilateral tissues (e.g somites, otic vesicle, limb bud), and structures (e.g palate, jaw) ensue. While a significant amount of work has probed the mechanisms behind symmetry breaking in the left-right axis leading to asymmetric positioning of internal organs, little is known about how bilateral tissues emerge at the same time with the same shape and size and at the same position on the two sides of the embryo. By discussing emergence of symmetry in many bilateral tissues and structures across vertebrate model systems, we highlight that understanding symmetry establishment is largely an open field, which will provide deep insights into fundamental problems in developmental biology for decades to come.

High throughput miRNA sequencing and bioinformatics analysis identify the mesenchymal cell proliferation and apoptosis related miRNAs during fetal mice palate development

BACKGROUND

Palatogenesis requires a precise spatiotemporal regulation of gene expression. Recent studies indicate that microRNAs (miRNAs) are key factors in normal palatogenesis. The present study aimed to explain the regulatory mechanisms of miRNAs during palate development.

METHODS

Pregnant ICR mice were choose at embryonic day 10.5 (E10.5). Hemotoxylin and eosin (H&E) staining was used to observe the morphological changes during the development of palatal process at embryonic day (E)13.5, E14.0, E14.5, E15.0 and E15.5. The fetal palatal tissues were collected at E13.5, E14.0, E14.5 and E15.0 to explore miRNA expression and function by high throughput sequencing and bioinformatic analysis. Mfuzz cluster analysis was used to look for miRNAs related to the fetal mice palate formation. The target genes of miRNAs were predicted by miRWalk. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis was performed base on target genes. The mesenchymal cell proliferation and apoptosis related miRNAs-genes networks were predicted and constructed using miRWalk and Cytoscape software. The expression of mesenchymal cell proliferation and apoptosis related miRNAs at the E13.5, E14.0, E14.5, and E15.0 was detected by a quantitative real-time PCR (RT-qPCR) assay.

RESULTS

H&E staining found that the palatal process grows vertically along the sides of the tongue at E13.5, the position of the tongue begins to descend and the bilateral palatal processes rise above the tongue at E14.0, the palatal process grows horizontally at E14.5, there is palatal contact fusion at E15.0, and the palatal suture disappeared at E15.5. Nine clusters of miRNA expression changes were identified in the fetal mice palate formation progression, including two reducing trends, two rising trends and five disordered trends. Next, the heatmap showed the miRNA expression from Clusters 4, 6, 9, 12 in the E13.5, E14.0, E14.5 and E15.0 groups. GO functional and KEGG pathway enrichment analysis found target genes of miRNAs in clusters involved in regulation of mesenchymal phenotype and the mitogen-activated protein kinase (MAPK) signaling pathway. Next, mesenchymal phenotype related miRNA-genes networks were constructed. The heatmap showing that the mesenchymal phenotype related miRNA expression of Clusters 4, 6, 9 and 12 at E13.5, E14.0, E14.5 and E15.0. Furthermore, the mesenchymal cell proliferation and apoptosis related miRNA-gene networks were identified in Clusters 6 and 12, including mmu-miR-504-3p-Hnf1b, etc. The expression level of mesenchymal cell proliferation and apoptosis related miRNAs at the E13.5, E14.0, E14.5, and E15.0 was verified by a RT-qPCR assay.

CONCLUSIONS

For the first time, we identified that clear dynamic miRNA expression during palate development. Furthermore, we demonstrated that mesenchymal cell proliferation and apoptosis related miRNAs, genes and the MAPK signaling pathway are important during fetal mice palate development.

Gene-environment interactions in the pathogenesis of common craniofacial anomalies

Craniofacial anomalies often exhibit phenotype variability and non-mendelian inheritance due to their multifactorial origin, involving both genetic and environmental factors. A combination of epidemiologic studies, genome-wide association, and analysis of animal models have provided insight into the effects of gene-environment interactions on craniofacial and brain development and the pathogenesis of congenital disorders. In this chapter, we briefly summarize the etiology and pathogenesis of common craniofacial anomalies, focusing on orofacial clefts, hemifacial microsomia, and microcephaly. We then discuss how environmental risk factors interact with genes to modulate the incidence and phenotype severity of craniofacial anomalies. Identifying environmental risk factors and dissecting their interaction with different genes and modifiers is central to improved strategies for preventing craniofacial anomalies.

Chloroquine regulates the proliferation and apoptosis of palate development on mice embryo by activating P53 through blocking autophagy in vitro

Cleft lip and palate is one of the most frequent congenital developmental defects. Autophagy is a highly conserved process of cell self-degradation in eukaryotes, involving multiple biological processes in which chloroquine (CQ) is the most common inhibitor. However, whether CQ affects and how it affects palate development is unknown. Mouse embryonic palatal cells (MEPCs) were treated with CQ to observe cell viability, apoptosis, migration, osteogenic differentiation by cell proliferation assay, flow cytometric analysis, scratch assay, and alizarin red staining. PI staining was used to measure cell cycle distribution. Immunofluorescence (IF) assay and transmission electron microscopy were used to detect autophagosomes. The autophagy-related factors (LC3 and P62), apoptosis-related markers (P53, caspase-3 cleaved caspase-3, BAX, and BCL-2), and cell cycle-related proteins (P21, CDK2, CDK4, cyclin D1, and cyclin E) were all measured by western blot. CQ inhibited the proliferation of MEPCs by arresting the G0/G1 phase of the cell cycle in a concentration- and time-dependent manner with cell cycle-related proteins P21 upregulated and CDK2, CDK4, cyclin D1, and cyclin E downregulated. Then we detected CQ also induced cell apoptosis in a dose-dependent manner by decreasing the BCL-2/BAX ratio and increasing cleaved caspase-3. Next, it was investigated that migration and osteogenesis of MEPCs decreased with CQ treatment in a dose-dependent manner. Meanwhile, CQ blocked the autophagy pathway by upregulating LC3II and P62 expressions which activated the P53 pathway. CQ activates P53 which affects MEPC biological characteristics by changing the proliferation and apoptosis of MEPCs through inhibiting autophagy.

Evaluation of Mandibular Growth and Symmetry in Child with Congenital Zygomatic-Coronoid Ankylosis

Ankyloses in the area of the temporomandibular joint (TMJ) are mentioned as a potential etiological factor of mandibular growth disorders and facial asymmetry. The aim of this case study was to evaluate the changes in the mandible of a child with zygomatic-coronoid ankylosis during the first five years of life, in which two adhesion release procedures were performed. The adopted symmetrical approach is based on the assumption of symmetry of the structure of the stomatognathic system in relation to the sagittal median plane. However, the assessment of pathological changes in the structure of the skeletal system was performed using an asymmetrical approach. Computed tomography techniques and a system of computer-aided diagnosis (CAD) were used in the case study. During the child’s growth, linear and angular measurements were made thrice (at the age of 16, 25 and 54 months). The degree of asymmetry was estimated in the measurements made on the right and left sides of the three-dimensional mandible. Unilateral congenital hypoplasia of the articular process and zygomatic-coronoid adhesion caused asymmetrical growth of the mandible in the child along with shortening of the mandibular branch and body on the damaged side and a visible difference in the size of the mandibular angles. Removal of the adhesions during surgical procedures made it possible to reduce the asymmetry of the mandible and catch-up growth, although at the age of five, the mandible was still smaller than the mandible in healthy peers. It was shown that the early adhesion release procedures supported by the CAD analysis enabled the restoration of mandibular symmetry.

The people behind the papers – Adrian Danescu, Lisanne Rens and Joy Richman

During vertebrate face development, bilateral streams of neural crest cells migrate from the neural tube to give rise to the facial prominences. A new study in Development combines high-resolution live imaging of chick facial development with a mathematical examination of cell behaviour to understand the dynamics of facial symmetry. We caught up with Adrian Danescu, Lisanne Rens and corresponding author Joy Richman (Professor and Director of the Pediatric Dentistry Graduate Program in the University of British Columbia in Vancouver, Canada) to find out more about the work.