Visualizing canonical Wnt signaling during mouse craniofacial development

Single-Nucleotide Polymorphisms in WNT Genes in Patients with Non-Syndromic Orofacial Clefts in a Polish Population

Non-syndromic orofacial cleft (OFC) is the most common facial developmental defect in the global population. The etiology of these birth defects is complex and multifactorial, involving both genetic and environmental factors. This study aimed to determine if SNPs in the WNT gene family (rs1533767, rs708111, rs3809857, rs7207916, rs12452064) are associated with OFCs in a Polish population. The study included 627 individuals: 209 children with OFCs and 418 healthy controls. DNA was extracted from saliva for the study group and from umbilical cord blood for the control group. Polymorphism genotyping was conducted using quantitative PCR. No statistically significant association was found between four variants and clefts, with odds ratios for rs708111 being 1.13 (CC genotype) and 0.99 (CT genotype), for rs3809857 being 1.05 (GT genotype) and 0.95 (TT genotype), for rs7207916 being 0.86 (AA genotype) and 1.29 (AG genotype) and for rs12452064 being 0.97 (AA genotype) and 1.24 (AG genotype). However, the rs1533767 polymorphism in WNT showed a statistically significant increase in OFC risk for the GG genotype (OR = 1.76, p < 0.001). This research shows that the rs1533767 polymorphism in the WNT gene is an important risk marker for OFC in the Polish population.

E-cadherin variants associated with oral facial clefts trigger aberrant cell motility in a REG1A-dependent manner

BACKGROUND

Germline mutations of E-cadherin contribute to hereditary diffuse gastric cancer (HDGC) and congenital malformations, such as oral facial clefts (OFC). However, the molecular mechanisms through which E-cadherin loss-of-function triggers distinct clinical outcomes remain unknown. We postulate that E-cadherin-mediated disorders result from abnormal interactions with the extracellular matrix and consequent aberrant intracellular signalling, affecting the coordination of cell migration.

METHODS

Herein, we developed in vivo and in vitro models of E-cadherin mutants associated with either OFC or HDGC. Using a Drosophila approach, we addressed the impact of the different variants in cell morphology and migration ability. By combining gap closure migration assays and time-lapse microscopy, we further investigated the migration pattern of cells expressing OFC or HDGC variants. The adhesion profile of the variants was evaluated using high-throughput ECM arrays, whereas RNA sequencing technology was explored for identification of genes involved in aberrant cell motility.

RESULTS

We have demonstrated that cells expressing OFC variants exhibit an excessive motility performance and irregular leading edges, which prevent the coordinated movement of the epithelial monolayer. Importantly, we found that OFC variants promote cell adhesion to a wider variety of extracellular matrices than HDGC variants, suggesting higher plasticity in response to different microenvironments. We unveiled a distinct transcriptomic profile in the OFC setting and pinpointed REG1A as a putative regulator of this outcome. Consistent with this, specific RNAi-mediated inhibition of REG1A shifted the migration pattern of OFC expressing cells, leading to slower wound closure with coordinated leading edges.

CONCLUSIONS

We provide evidence that E-cadherin variants associated with OFC activate aberrant signalling pathways that support dynamic rearrangements of cells towards improved adaptability to the microenvironment. This proficiency results in abnormal tissue shaping and movement, possibly underlying the development of orofacial malformations.

The presence and distribution of various genes in postnatal CLP-affected palatine tissue

BACKGROUND

Worldwide cleft lip with or without a cleft palate (CL/P) is the most common craniofacial birth defect. Apart from changes in facial appearance, additionally affected individuals often suffer from various associated comorbidities requiring complex multidisciplinary treatment with overall high expenses. Understanding the complete pathogenetic mechanisms of CL/P might aid in developing new preventative strategies and therapeutic approaches, help with genetic counselling, and improve quality of life. Many genes have been associated with the development of orofacial clefts; however, the majority require further research. Based on the role of PAX7, PAX9, SHH, SOX3, WNT3A, and WNT9B in orofacial development, the intention was to use chromogenic in situ hybridization to detect the six genes in postnatal CLP-affected palatine tissue and compare their distribution within the tissue samples.

RESULTS

Statistically significant differences in the distribution of PAX7, PAX9, WNT3A, and WNT9B were observed. In total, 19 pairs of moderate to very strong positive correlations were noted.

CONCLUSIONS

Changes in the cleft-affected palatine epithelium primarily seem to be associated with the PAX7 gene; however, PAX9, WNT3A, WNT9B, and SOX3 role seems to be more limited. Whilst connective tissue changes seem to depend on PAX7 only, SHH seems to participate individually and indistinctly. Numerous positive correlations reflect the complicating interactions of the pathways and their components in the orofacial cleft morphopathogenesis.

Identification of copy neutral loss of heterozygosity on chromosomes 1p, 1q, and 6p among nonsyndromic cleft lip and/or without cleft palate with hypodontia

BACKGROUND

Nonsyndromic cleft lip and/or without cleft palate (NSCL/P) with or without hypodontia is a common developmental aberration in humans and animals. This study aimed to identify the loss of heterozygosity (LOH) involved in hypodontia and NSCL/P pathogenesis.

METHODS

This is a cross-sectional study that conducted genome-wide copy number analysis using CytoScan 750K array on salivary samples from Malay subjects with NSCL/P with or without hypodontia aged 7-13 years. To confirm the significant results, simple logistic regression was employed to conduct statistical data analysis using SPSS software.

RESULTS

The results indicated the most common recurrent copy neutral LOH (cnLOH) observed at 1p33-1p32.3, 1q32.2-1q42.13 and 6p12.1-6p11.1 loci in 8 (13%), 4 (7%), and 3 (5%) of the NSCL/P subjects, respectively. The cnLOHs at 1p33-1p32.3 (D1S197), 1q32.2-1q42.13 (D1S160), and 6p12.1-6p11.1 (D1S1661) were identified observed in NSCL/P and noncleft children using microsatellite analysis markers as a validation analysis. The regions affected by the cnLOHs at 1p33-1p32.3, 1q32.2-1q42.13, and 6p12.1-6p11.1 loci contained selected genes, namely FAF1, WNT3A and BMP5, respectively. There was a significant association between the D1S197 (1p33-32.3) markers containing the FAF1 gene among NSCL/P subjects with or without hypodontia compared with the noncleft subjects (p-value = 0.023).

CONCLUSION

The results supported the finding that the genetic aberration on 1p33-32.3 significantly contributed to the development of NSCL/P with or without hypodontia. These results have an exciting prospect in the promising field of individualized preventive oral health care.

Wnt/β-Catenin Signaling Pathway Is Necessary for the Specification but Not the Maintenance of the Mouse Retinal Pigment Epithelium

β-Catenin (Ctnnb1) has been shown to play critical roles in the development and maintenance of epithelial cells, including the retinal pigment epithelium (RPE). Ctnnb1 is not only a component of intercellular junctions in the epithelium, it also functions as a transcriptional regulator in the Wnt signaling pathway. To identify which of its functional modalities is critically involved in mouse RPE development and maintenance, we varied Ctnnb1 gene content and activity in mouse RPE lineage cells and tested their impacts on mouse eye development. We found that a Ctnnb1 double mutant (Ctnnb1dm), which exhibits impaired transcriptional activity, could not replace Ctnnb1 in the RPE, whereas Ctnnb1Y654E, which has reduced affinity for the junctions, could do so. Expression of the constitutively active Ctnnb1∆ex3 mutant also suppressed the development of RPE, instead facilitating a ciliary cell fate. However, the post-mitotic or mature RPE was insensitive to the loss, inactivation, or constitutive activation of Ctnnb1. Collectively, our results suggest that Ctnnb1 should be maintained within an optimal range to specify RPE through transcriptional regulation of Wnt target genes in the optic neuroepithelium.

Assessing the relationship between single nucleotide polymorphisms in Wingless signaling pathway genes and sella turcica morphology

Sella turcica development involves molecular factors and genes responsible for ossification. It is possible that single nucleotide polymorphisms (SNPs) in key genes are involved in morphological variation of sella turcica. Genes belonging to the WNT signaling pathway are involved in the ossification process and are candidates of sella turcica morphology. This study aimed to evaluate if SNPs in WNT6 (rs6754599) and WNT10A (rs10177996 and rs3806557) genes are associated with the calcification and patterns of the sella turcica. Nonsyndromic individuals were included in the research. Cephalometric radiographs were examined and the sella calcification was evaluated and classified according to the calcification of the interclinoid ligament (no calcification, partial calcification, and incomplete calcification) and sella turcica pattern (normal sella turcica, bridge type A-ribbon-like fusion, bridge type B-extension of the clinoid processes, incomplete bridge, hypertrophic posterior clinoid process, hypotrophic posterior clinoid process, irregularity in the posterior part, pyramidal shape of the dorsum, double contour of the floor, oblique anterior wall, and oblique contour of the floor). DNA samples were used to evaluate SNPs in the WNT genes (rs6754599, rs10177996, and rs3806557) using real-time PCR. Chi-square test or Fisher's exact test were used to compare the allele and genotype distributions according to sella turcica phenotypes. The alpha was set as 5% for all comparisons. A total of 169 individuals were included, 133 (78.7%) present sella turcica partially or completely calcified. Sella turcica anomalies were found in 131 individuals (77.5%). Sella turcica bridge type A (27.8%), posterior hypertrophic clinoid process (17.1%), and sella turcica bridge type B (11.2%) were the most prevalent morphological patterns observed. Individuals carrying the TT genotype in rs10177996 (TT vs. CT + CC) had higher chance to present a partially calcified sella turcica (p = 0.047; Odds ratio = 2.27, Confidence Interval 95% 1.01-5.13). In conclusion, the SNP in WNT10A is associated with the calcification phenotype of the sella turcica, the pleiotropic effect of this gene should be taken into consideration in future studies.

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

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

[Association study between haplotypes of WNT signaling pathway genes and nonsyndromic oral clefts among Chinese Han populations]

OBJECTIVE

To explore whether WNT signaling pathway genes were associated with non-syndromic oral clefts (NSOC) based on haplotypes analyses among 1 008 Chinese NSOC case-parent trios.

METHODS

The genome-wide association study (GWAS) data of 806 Chinese non-syndromic cleft lip with or without cleft palate (NSCL/P) trios and 202 Chinese non-syndromic cleft palate (NSCP) case-parent trios were drawn from the International Consortium to Identify Genes and Interactions Controlling Oral Clefts (ICOCs) study GWAS data set, whose Chinese study population were recruited from four provinces in China, namely Taiwan, Shandong, Hubei, and Sichuan provinces. The process of DNA genotyping was conducted by the Center for Inherited Disease Research in the Johns Hopkins University, using Illumina Human610-Quad v.1_B Bead Chip. The method of sliding windows was used to determine the haplotypes for analyses, including 2 SNPs haplotypes and 3 SNPs haplotypes. Haplotypes with a frequency lower than 1% were excluded for further analyses. To further assess the association between haplotypes and NSOC risks, and the transmission disequilibrium test (TDT) was performed. The Bonferroni method was adopted to correct multiple tests in the study, with which the threshold of statistical significance level was set as P < 0.05 divided by the number of tests, e.g P < 3.47×10^-4 in the current stu-dy. All the statistical analyses were performed by using plink (v1.07).

RESULTS

After quality control, a total of 144 single nucleotide polymorphisms (SNPs) mapped in seven genes in WNT signaling pathway were included for the analyses among the 806 Chinese NSCL/P trios and 202 Chinese NSCP trios. A total of 1 042 haplotypes with frequency higher than 1% were included for NSCL/P analyses and another 1 057 haplotypes with frequency higher than 1% were included for NSCP analyses. Results from the TDT analyses showed that a total of 69 haplotypes were nominally associated with the NSCL/P risk among Chinese (P < 0.05). Another 34 haplotypes showed nominal significant association with the NSCP risk among Chinese (P < 0.05). However, none of these haplotypes reached pre-defined statistical significance level after Bonferroni correction (P>3.47×10^-4).

CONCLUSION

This study failed to observe any statistically significant associations between haplotypes of seven WNT signaling pathway genes and the risk of NSOC among Chinese. Further studies are warranted to replicate the findings here.

Relationship between non-syndromic oral clefts and cancer: a systematic review and meta-analysis

OBJECTIVE

To summarize the clinical evidence on the relationship between cancer and non-syndromic oral cleft (NSOC).

METHODS

The review was reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses checklist, and a literature search was conducted in six databases and gray literature. Studies published in any language mentioning cancer in patients with NSOC and their relatives and NSOC in patients with cancer and their relatives were included. Risk of bias was assessed using the Joanna Briggs Institute appraisal tool. The certainty of the evidence was evaluated using the GRADE (Grading of Recommendation, Assessment, Development, and Evaluation) assessment. After a 2-step selection process, 33 studies were included: 17 case-control studies, 13 cross-sectional studies, and 3 case reports.

RESULTS

The study evaluated 206,096 patients from 20 countries. Of these, 0.35% of patients with cancer (95% CI: 0.0% to 1.1%; I² = 86%), 3.0% of relatives of patients with cancer (95% CI: 1.19% to 5.46%; I² = 55%), and 0.26% of controls (95% CI: 0.0% to 0.83%; I² = 87%) had NSOC. Among the studies that examined the prevalence of cancer, 2.4% (95% CI: 0.0% to 19.3%; I² = 99%) of patients with NSOC, 15.4% of relatives of patients with NSOC (95% CI: 2.0% to 37.6%; I² = 99%), and 5.3% of controls (95% CI: 0.0% to 22.8%; I² = 99%) had cancer. Although no relationship was observed between the risk of cancer in patients with NSOC and the risk of NSOC in patients with cancer, there was an association for an increased risk of cancer in relatives of patients with NSOC (OR: 9.96, 95% CI: 1.55 to 63.99; P = 0.01) and a significant association for the NSOC risk in relatives of patients with leukemia (OR: 9.31; 95% CI: 1.13 to 76.67; P = 0.03).

CONCLUSION

Our findings demonstrate an increased risk of cancer in relatives of patients with NSOC and that relatives of patients with leukemia were more frequently affected by NSOC. Together, these findings can help guide cancer screening in patients with NSOC and their relatives and shed light on the risk of NSOC in families with a history of cancer.

Genetic and Epigenetic Studies in Nonsyndromic Oral Clefts

The etiology of non-syndromic oral clefts (NSOFC) is complex with genetics, genomics, epigenetics and stochastics factors playing a role. Several approaches have been applied to understand the etiology of non-syndromic oral clefts. These include linkage, candidate gene association studies, genome-wide association studies, whole genome sequencing, copy number variations and epigenetics. In this review we shared these approaches, genes and loci reported in some studies.

Cleft Candidate Genes and Their Products in Human Unilateral Cleft Lip Tissue

Cleft lip and palate are common congenital pathologies that affect the human population worldwide. The formation of cleft lip is associated with multiple genes and their coded proteins, which regulate the development of craniofacial region, but the exact role of these factors is not always clear. The use of morphological studies for evaluation of human cleft-affected tissue has been limited because of insufficiency of available pathological material. The aim of this study was to detect and compare the immunohistochemical expression of cleft candidate gene coded proteins (DLX4, MSX2, HOXB3, SHH, PAX7, SOX3, WNT3A, and FOXE1) in the non-syndromic unilateral cleft lip patient tissue and control group tissue. A semiquantitative counting method was used to evaluate the tissue in biotin-streptavidin-stained slides. Statistically significant differences between the patient and control groups were found for the number of immunoreactive structures for SHH (p = 0.019) and FOXE1 (p = 0.011) in the connective tissue and SOX3 (p = 0.012) in the epithelium. Multiple statistically significant very strong and strong correlations were found between the immunoreactives in cleft-affected tissue. These significant differences and various correlations indicate that multiple morphopathogenetic pathways are possibly involved in unilateral cleft lip pathogenesis. Therefore, we further discuss these possible interactions.

Wnt Signaling Drives Correlated Changes in Facial Morphology and Brain Shape

Canonical Wnt signaling plays multiple roles critical to normal craniofacial development while its dysregulation is known to be involved in structural birth defects of the face. However, when and how Wnt signaling influences phenotypic variation, including those associated with disease, remains unclear. One potential mechanism is via Wnt signaling’s role in the patterning of an early facial signaling center, the frontonasal ectodermal zone (FEZ), and its subsequent regulation of early facial morphogenesis. For example, Wnt signaling may directly alter the shape and/or magnitude of expression of the sonic hedgehog (SHH) domain in the FEZ. To test this idea, we used a replication-competent avian sarcoma retrovirus (RCAS) encoding Wnt3a to modulate its expression in the facial mesenchyme. We then quantified and compared ontogenetic changes in treated to untreated embryos in the three-dimensional (3D) shape of both the SHH expression domain of the FEZ, and the morphology of the facial primordia and brain using iodine-contrast microcomputed tomography imaging and 3D geometric morphometrics (3DGM). We found that increased Wnt3a expression in early stages of head development produces correlated variation in shape between both structural and signaling levels of analysis. In addition, altered Wnt3a activation disrupted the integration between the forebrain and other neural tube derivatives. These results show that activation of Wnt signaling influences facial shape through its impact on the forebrain and SHH expression in the FEZ, and highlights the close relationship between morphogenesis of the forebrain and midface.

Craniofacial Development: Neural Crest in Molecular Embryology

Craniofacial development, one of the most complex sequences of developmental events in embryology, features a uniquely transient, pluripotent stem cell-like population known as the neural crest (NC). Neural crest cells (NCCs) originate from the dorsal aspect of the neural tube and migrate along pre-determined routes into the developing branchial arches and frontonasal plate. The exceptional rates of proliferation and migration of NCCs enable their diverse contribution to a wide variety of craniofacial structures. Subsequent differentiation of these cells gives rise to cartilage, bones, and a number of mesenchymally-derived tissues. Deficiencies in any stage of differentiation can result in facial clefts and abnormalities associated with craniofacial syndromes. A small number of conserved signaling pathways are involved in controlling NC differentiation and craniofacial development. They are used in a reiterated fashion to help define precise temporospatial cell and tissue formation. Although many aspects of their cellular and molecular control have yet to be described, it is clear that together they form intricately integrated signaling networks required for spatial orientation and developmental stability and plasticity, which are hallmarks of craniofacial development. Mutations that affect the functions of these signaling pathways are often directly or indirectly identified in congenital syndromes. Clinical applications of NC-derived mesenchymal stem/progenitor cells, persistent into adulthood, hold great promise for tissue repair and regeneration. Realization of NCC potential for regenerative therapies motivates understanding of the intricacies of cell communication and differentiation that underlie the complexities of NC-derived tissues.

Potential interactions among single nucleotide polymorphisms in bone- and cartilage-related genes in skeletal malocclusions

OBJECTIVE

To investigate SNPs in bone- and cartilage-related genes and their interaction in the aetiology of sagittal and vertical skeletal malocclusions.

SETTINGS AND SAMPLE POPULATION

This study included 143 patients and classified as follows: skeletal class I (n = 77), class II (n = 47) and class III (n = 19); maxillary retrusion (n = 39), protrusion (n = 52) and well-positioned maxilla (n = 52); mandibular retrognathism (n = 50), prognathism (n = 50) and well-positioned mandible (n = 43); normofacial (n = 72), dolichofacial (n = 55) and brachyfacial (n = 16).

MATERIALS AND METHODS

Steiner's ANB, SNA, SNB angles and Ricketts' NBa-PtGn angle were measured to determine the skeletal malocclusion and the vertical pattern. Nine SNPs in BMP2, BMP4, SMAD6, RUNX2, WNT3A and WNT11 were genotyped. Chi-squared test was used to compare genotypes among the groups. Multifactor dimensionality reduction (MDR) and binary logistic regression analysis, both using gender and age as co-variables, were also used. We performed Bonferroni correction for multiple testing.

RESULTS

Significant associations at P < .05 were observed for SNPs rs1005464 (P = .042) and rs235768 (P = .021) in BMP2 with mandibular retrognathism and for rs59983488 (RUNX2) with maxillary protrusion (P = .04) as well as for rs708111 (WNT3A) with skeletal class III (P = .02; dominant model), rs1533767 (WNT11) with a brachyfacial skeletal pattern (P = .01, OR = 0.10; dominant model) and for rs3934908 (SMAD6) with prognathism (P = .02; recessive model). After the Bonferroni correction, none of the SNPs remained associated. The MDR predicted some interaction for skeletal class II, dolichofacial and brachyfacial phenotypes.

CONCLUSION

Our results suggest that SNPs in BMP2, BMP4, SMAD6, RUNX2, WNT3A and WNT11 could be involved in the aetiology of sagittal and vertical malocclusions.

[Evaluating the effect of WNT pathway genes considering interactions on the risk of non-syndromic oral clefts among Chinese populations]

OBJECTIVE

In this study, we used genome-wide association study (GWAS) data to explore whether WNT pathway genes were associated with non-syndromic oral clefts (NSOC) considering gene-gene interaction and gene-environment interaction.

METHODS

We conducted the analysis using 806 non-syndromic cleft lip with or without cleft palate (NSCL/P) case-parent trios and 202 non-syndromic cleft palate (NSCP) case-parent trios among Chinese populations selected from an international consortium established for a GWAS of non-syndromic oral clefts. Genotype data and maternal environmental exposures were collected through DNA samples and questionnaires. Conditional Logistic regression models were adopted to explore gene-gene interaction and gene-environment in teraction using trio package in R software. The threshold of significance level was set as 3.47×10^-4 using Bonferroni correction.

RESULTS

A total of 144 single nucleotide polymorphisms (SNPs) in seven genes passed the quality control process in NSCL/P trios and NSCP trios, respectively. Totally six pairs of SNPs interactions showed statistically significant SNP-SNP interaction (P < 3.47×10^-4) after Bonferroni correction, which were rs7618735 (WNT5A) and rs10848543 (WNT5B), rs631948 (WNT11) and rs556874 (WNT5A), and rs631948 (WNT11) and rs472631 (WNT5A) among NSCL/P trios; rs589149 (WNT11) and rs4765834 (WNT5B), rs1402704 (WNT11) and rs358792 (WNT5A), and rs1402704 (WNT11) and rs358793 (WNT5A) among NSCP trios, respectively. In addition, no significant result was found for gene-environment interaction analysis in both of the NSCL/P trios and NSCP trios.

CONCLUSION

Though this study failed to detect significant association based on gene-environment interactions of seven WNT pathway genes and the risk of NSOC, WNT pathway genes may influence the risk of NSOC through potential gene-gene interaction.

PBX-WNT-P63-IRF6 pathway in nonsyndromic cleft lip and palate

Nonsyndromic cleft lip and palate (NSCLP) is one of the most common craniofacial anomalies in humans, affecting more than 135,000 newborns worldwide. NSCLP has a multifactorial etiology with more than 50 genes postulated to play an etiologic role. The genetic pathway comprised of Pbx-Wnt-p63-Irf6 genes was shown to control facial morphogenesis in mice and proposed as a regulatory pathway for NSCLP. Based on these findings, we investigated whether variation in PBX1, PBX2, and TP63, and their proposed interactions were associated with NSCLP. Fourteen single nucleotide variants (SNVs) in/nearby PBX1, PBX2, and TP63 were genotyped in 780 NSCLP families of nonHispanic white (NHW) and Hispanic ethnicities. Family-based association tests were performed for individual SNVs stratified by ethnicity and family history of NSCLP. Gene-gene interactions were also tested. A significant association was found for PBX2 rs3131300 and NSCLP in combined Hispanic families (p = .003) while nominal association was found for TP63 rs9332461 in multiplex Hispanic families (p = .005). Significant haplotype associations were observed for PBX2 in NHW (p = .0002) and Hispanic families (p = .003), and for TP63 in multiplex Hispanic families (.003). An independent case-control group was used to validate findings, and significant associations were found with PBX1 rs6426870 (p = .007) and TP63 rs9332461 (p = .03). Gene-gene interactions were detected between PBX1/PBX2/TP63 with IRF6 in NHW families, and between PBX1 with WNT9B in both NHW and Hispanic families (p < .0018). This study provides the first evidence for a role of PBX1 and PBX2, additional evidence for the role of TP63, and support for the proposed PBX-WNT-TP63-IRF6 regulatory pathway in the etiology of NSCLP.

Wnt signaling in orofacial clefts: crosstalk, pathogenesis and models

Diverse signaling cues and attendant proteins work together during organogenesis, including craniofacial development. Lip and palate formation starts as early as the fourth week of gestation in humans or embryonic day 9.5 in mice. Disruptions in these early events may cause serious consequences, such as orofacial clefts, mainly cleft lip and/or cleft palate. Morphogenetic Wnt signaling, along with other signaling pathways and transcription regulation mechanisms, plays crucial roles during embryonic development, yet the signaling mechanisms and interactions in lip and palate formation and fusion remain poorly understood. Various Wnt signaling and related genes have been associated with orofacial clefts. This Review discusses the role of Wnt signaling and its crosstalk with cell adhesion molecules, transcription factors, epigenetic regulators and other morphogenetic signaling pathways, including the Bmp, Fgf, Tgfβ, Shh and retinoic acid pathways, in orofacial clefts in humans and animal models, which may provide a better understanding of these disorders and could be applied towards prevention and treatments.

Wnt/β-catenin signaling in the mouse embryonic cranial mesenchyme is required to sustain the emerging differentiated meningeal layers

Cranial neural crest cells (CNCCs) give rise to cranial mesenchyme (CM) that differentiates into the forebrain meningeal progenitors in the basolateral and apical regions of the head. This occurs in close proximity to the other CNCC-CM-derivatives, such as calvarial bone and dermal progenitors. We found active Wnt signaling transduction in the forebrain meningeal progenitors in basolateral and apical populations and in the non-meningeal CM preceding meningeal differentiation. Here, we dissect the source of Wnt ligand secretion and requirement of Wnt/β-catenin signaling for the lineage selection and early differentiation of the forebrain meninges. We find persistent canonical Wnt/β-catenin signal transduction in the meningeal progenitors in the absence of Wnt ligand secretion in the CM or surface ectoderm, suggesting additional sources of Wnts. Conditional mutants for Wntless and β-catenin in the CM showed that Wnt ligand secretion and Wnt/β-catenin signaling were dispensable for specification and proliferation of early meningeal progenitors. In the absence of β-catenin in the CM, we found diminished laminin matrix and meningeal hypoplasia, indicating a structural and trophic role of mesenchymal β-catenin signaling. This study shows that β-catenin signaling is required in the CM for maintenance and organization of the differentiated meningeal layers in the basolateral and apical populations of embryonic meninges.

FGF20-Expressing, Wnt-Responsive Olfactory Epithelial Progenitors Regulate Underlying Turbinate Growth to Optimize Surface Area

The olfactory epithelium (OE) is a neurosensory organ required for the sense of smell. Turbinates, bony projections from the nasal cavity wall, increase the surface area within the nasal cavity lined by the OE. Here, we use engineered fibroblast growth factor 20 (Fgf20) knockin alleles to identify a population of OE progenitor cells that expand horizontally during development to populate all lineages of the mature OE. We show that these Fgf20-positive epithelium-spanning progenitor (FEP) cells are responsive to Wnt/β-Catenin signaling. Wnt signaling suppresses FEP cell differentiation into OE basal progenitors and their progeny and positively regulates Fgf20 expression. We further show that FGF20 signals to the underlying mesenchyme to regulate the growth of turbinates. These studies thus identify a population of OE progenitor cells that function to scale OE surface area with the underlying turbinates.

Association of the WNT3 Variations and the Risk of Non-Syndromic Cleft Lip and Palate in a Population of Iranian Infants

BACKGROUND

Nonsyndromic cleft lip and/or palate (NSCL/P) is the most common orofacial birth defect, often attributed to ethnic and environmental differences. Up to now, linkage analyses and genome-wide association studies have identified several genomic susceptibility regions for NSCL/P. The WNT genes including WNT3 are strong candidates for NSCL/P, since they are involved in regulating mid-face development and upper lip fusion. This study tested association of the WNT3 polymorphisms, rs-3809857 G/T and rs9890413 G/A, with the risk of NSCL/P in a population of Iranian infants.

METHODS

The allelic and genotypic frequencies for each participant were determined in 113 unrelated Iranian subjects with NSCL/P and 220 control subjects using PCR and restriction fragment length polymorphism (RFLP) methods. A p-value of ≤0.05 was considered statistically significant.

RESULTS

The WNT3 rs3809857 GT genotype was significantly lower (p=0.039, OR=0.55, 95% CI=0.30-0.97) in the NSCL/P (21.2%) than the control group (30.42%). For the WNT3 rs9890413 G/A polymorphism, neither genotype nor allele frequencies were significantly different between the case and control groups.

CONCLUSION

Our results indicated that the WNT3 rs3809857 GT genotype may have a protective effect against NSCL/P in Iranian population.

Developmental pathway genes and neural plasticity underlying emotional learning and stress-related disorders

The manipulation of neural plasticity as a means of intervening in the onset and progression of stress-related disorders retains its appeal for many researchers, despite our limited success in translating such interventions from the laboratory to the clinic. Given the challenges of identifying individual genetic variants that confer increased risk for illnesses like depression and post-traumatic stress disorder, some have turned their attention instead to focusing on so-called "master regulators" of plasticity that may provide a means of controlling these potentially impaired processes in psychiatric illnesses. The mammalian homolog of Tailless (TLX), Wnt, and the homeoprotein Otx2 have all been proposed to constitute master regulators of different forms of plasticity which have, in turn, each been implicated in learning and stress-related disorders. In the present review, we provide an overview of the changing distribution of these genes and their roles both during development and in the adult brain. We further discuss how their distinct expression profiles provide clues as to their function, and may inform their suitability as candidate drug targets in the treatment of psychiatric disorders.

Exome sequencing of two Italian pedigrees with non-isolated Chiari malformation type I reveals candidate genes for cranio-facial development

Chiari malformation type I (CMI) is a congenital abnormality of the cranio-cerebral junction with an estimated incidence of 1 in 1280. CMI is characterized by underdevelopment of the occipital bone and posterior fossa (PF) and consequent cerebellar tonsil herniation. The presence for a genetic basis to CMI is supported by many lines of evidence. The cellular and molecular mechanisms leading to CM1 are poorly understood. The occipital bone formation is dependent on complex interactions between genes and molecules with pathologies resulting from disruption of this delicate process. Whole-exome sequencing of affected and not affected individuals from two Italian families with non-isolated CMI was undertaken. Single-nucleotide and short insertion-deletion variants were prioritized using KGGSeq knowledge-based platform. We identified three heterozygous missense variants: DKK1 c.121G>A (p.(A41T)) in the first family, and the LRP4 c.2552C>G (p.(T851R)) and BMP1 c.941G>A (p.(R314H)) in the second family. The variants were located at highly conserved residues, segregated with the disease, but they were not observed in 100 unaffected in-house controls. DKK1 encodes for a potent soluble WNT inhibitor that binds to LRP5 and LRP6, and is itself regulated by bone morphogenetic proteins (BMPs). DKK1 is required for embryonic head development and patterning. LRP4 is a novel osteoblast expressed receptor for DKK1 and a WNT and BMP 4 pathways integrator. Screening of DKK1 in a cohort of 65 CMI sporadic patients identified another missense variant, the c.359G>T (p.(R120L)), in two unrelated patients. These findings implicated the WNT signaling in the correct development of the cranial mesenchyme originating the PF.

Clinical relevance of breast and gastric cancer-associated polymorphisms as potential susceptibility markers for oral clefts in the Brazilian population

BACKGROUND

Epidemiological studies have indicated a higher incidence of breast and gastric cancer in patients with nonsyndromic cleft lip with or without cleft palate (NSCL ± P) and their relatives, which can be based on similar genetic triggers segregated within family with NSCL ± P.

METHODS

This multicenter study evaluated the association of 9 single nucleotide polymorphisms (SNP) in AXIN2 and CDH1, representing genes consistently altered in breast and gastric tumors, with NSCL ± P in 223 trios (father, mother and patient with NSCL ± P) by transmission disequilibrium test (TDT).

RESULTS

Our results showed that the minor A allele of rs7210356 (p = 0.01) and the T-G-G-A-G haplotype formed by rs7591, rs7210356, rs4791171, rs11079571 and rs3923087 SNPs (p = 0.03) in AXIN2 were significantly under-transmitted to patients with NSCL ± P. In CDH1 gene, the C-G-A-A and A-G-A-G haplotypes composed by rs16260, rs9929218, rs7186053 and rs4783573 polymorphisms were respectively over-transmitted (p = 0.01) and under-transmitted (p = 0.008) from parents to the children with NSCL ± P.

CONCLUSIONS

The results suggest that polymorphic variants in AXIN2 and CDH1 may be associated with NSCL ± P susceptibility, and reinforce the putative link between cancer and oral clefts.

Postnatal Calvarial Skeletal Stem Cells Expressing PRX1 Reside Exclusively in the Calvarial Sutures and Are Required for Bone Regeneration

Post-natal skeletal stem cells expressing PRX1 (pnPRX1+) have been identified in the calvaria and in the axial skeleton. Here we characterize the location and functional capacity of the calvarial pnPRX1⁺ cells. We found that pnPRX1⁺ reside exclusively in the calvarial suture niche and decrease in number with age. They are distinct from preosteoblasts and osteoblasts of the sutures, respond to WNT signaling in vitro and in vivo by differentiating into osteoblasts, and, upon heterotopic transplantation, are able to regenerate bone. Diphtheria toxin A (DTA)-mediated lineage ablation of pnPRX1⁺ cells and suturectomy perturb regeneration of calvarial bone defects and confirm that pnPRX1⁺ cells of the sutures are required for bone regeneration. Orthotopic transplantation of sutures with traceable pnPRX1⁺ cells into wild-type animals shows that pnPRX1⁺ cells of the suture contribute to calvarial bone defect regeneration. DTA-mediated lineage ablation of pnPRX1⁺ does not, however, interfere with calvarial development.

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The suture is the exclusive niche of the calvarial PRX1-expressing cells

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Postnatal PRX1-expressing cells of the calvaria are required for bone regeneration

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Postnatal Prx1-expressing cells of the calvaria are dispensable for development

Molecular mechanisms of midfacial developmental defects

The morphogenesis of midfacial processes requires the coordination of a variety of cellular functions of both mesenchymal and epithelial cells to develop complex structures. Any failure or delay in midfacial development as well as any abnormal fusion of the medial and lateral nasal and maxillary prominences will result in developmental defects in the midface with a varying degree of severity, including cleft, hypoplasia, and midline expansion. Despite the advances in human genome sequencing technology, the causes of nearly 70% of all birth defects, which include midfacial development defects, remain unknown. Recent studies in animal models have highlighted the importance of specific signaling cascades and genetic-environmental interactions in the development of the midfacial region. This review will summarize the current understanding of the morphogenetic processes and molecular mechanisms underlying midfacial birth defects based on mouse models with midfacial developmental abnormalities.

Regulatory variant in FZD6 gene contributes to nonsyndromic cleft lip and palate in an African-American family

Nonsyndromic cleft lip with or without cleft palate (NSCLP) is a common birth defect affecting 135,000 newborns worldwide each year. While a multifactorial etiology has been suggested as the cause, despite decades of research, the genetic underpinnings of NSCLP remain largely unexplained. In our previous genome-wide linkage study of a large NSCLP African-American family, we identified a candidate locus at 8q21.3-24.12 (LOD = 2.98). This region contained four genes, Frizzled-6 (FZD6), Matrilin-2 (MATN2), Odd-skipped related 2 (OSR2) and Solute Carrier Family 25, Member 32 (SLC25A32). FZD6 was located under the maximum linkage peak. In this study, we sequenced the coding and noncoding regions of these genes in two affected family members, and identified a rare variant in intron 1 of FZD6 (rs138557689; c.-153 + 432A>C). The variant C allele segregated with NSCLP in this family, through affected and unaffected individuals, and was found in one other NSCLP African-American family. Functional assays showed that this allele creates an allele-specific protein-binding site and decreases promoter activity. We also observed that loss and gain of fzd6 in zebrafish contributes to craniofacial anomalies. FZD6 regulates the WNT signaling pathway, which is involved in craniofacial development, including midfacial formation and upper labial fusion. We hypothesize, therefore, that alteration in FZD6 expression contributes to NSCLP in this family by perturbing the WNT signaling pathway.

Expression characteristics of β-catenin in scallop Chlamys farreri gonads and its role as a potential upstream gene of Dax1 through canonical Wnt signalling pathway regulating the spermatogenesis

β-catenin is a key signaling molecule in the canonical Wnt pathway, which is involved in animal development. However, little information has been reported for β-catenin in bivalves. In the present study, we cloned a homolog of β-catenin from the scallop Chlamys farreri and determined its expression characteristics. The full-length cDNA of β-catenin was 3,353 bp, including a 2,511 bp open reading frame that encoded a predicted 836 amino acid protein. Level of the β-catenin mRNA increased significantly (P<0.05) with C. farreri gonadal development and presented a sexually dimorphic expression pattern in the gonads, which was significantly high in ovaries detected by quantitative real-time polymerase chain reaction (qRT-PCR). Immunohistochemical analysis revealed that the β-catenin was mainly located in germ cells of the gonads, with obvious positive immune signals in the oogonia and oocytes of ovaries as well as in the spermatogonia and spermatocytes of testes, implying β-catenin might be involved in the gametogenesis of C. farreri. Furthermore, when 0.1 µg/mL and 0.2 µg/mL DKK-1 (an inhibitor of the canonical Wnt pathway) were added in vitro to culture medium containing testis cells of C. farreri, the expression of β-catenin decreased significantly detected by qRT-PCR (P<0.05), suggesting the canonical Wnt signal pathway exists in the scallop testis. Similarly, when 50 µM and 100 µM quercetin (an inhibitor of β-catenin) were added in vitro to the culture system, Dax1 expression was significantly down-regulated compared with controls (P<0.05), implying the β-catenin is an upstream gene of Dax1 and is involved in the regulation of C. farreri spermatogenesis.

Wnt signaling interacts with bmp and edn1 to regulate dorsal-ventral patterning and growth of the craniofacial skeleton

Craniofacial development requires signals from epithelia to pattern skeletogenic neural crest (NC) cells, such as the subdivision of each pharyngeal arch into distinct dorsal (D) and ventral (V) elements. Wnt signaling has been implicated in many aspects of NC and craniofacial development, but its roles in D-V arch patterning remain unclear. To address this we blocked Wnt signaling in zebrafish embryos in a temporally-controlled manner, using transgenics to overexpress a dominant negative Tcf3, (dntcf3), (Tg(hsp70I:tcf3-GFP), or the canonical Wnt inhibitor dickkopf1 (dkk1), (Tg(hsp70i:dkk1-GFP) after NC migration. In dntcf3 transgenics, NC cells in the ventral arches of heat-shocked embryos show reduced proliferation, expression of ventral patterning genes (hand2, dlx3b, dlx5a, msxe), and ventral cartilage differentiation (e.g. lower jaws). These D-V patterning defects resemble the phenotypes of zebrafish embryos lacking Bmp or Edn1 signaling, and overexpression of dntcf3 dramatically reduces expression of a subset of Bmp receptors in the arches. Addition of ectopic BMP (or EDN1) protein partially rescues ventral development and expression of dlx3b, dlx5a, and msxe in Wnt signaling-deficient embryos, but surprisingly does not rescue hand2 expression. Thus Wnt signaling provides ventralizing patterning cues to arch NC cells, in part through regulation of Bmp and Edn1 signaling, but independently regulates hand2. Similarly, heat-shocked dkk1+ embryos exhibit ventral arch reductions, but also have mandibular clefts at the ventral midline not seen in dntcf3+ embryos. Dkk1 is expressed in pharyngeal endoderm, and cell transplantation experiments reveal that dntcf3 must be overexpressed in pharyngeal endoderm to disrupt D-V arch patterning, suggesting that distinct endodermal roles for Wnts and Wnt antagonists pattern the developing skeleton.

Craniofacial abnormalities are among the most common birth defects. Understanding the molecular mechanisms underlying craniofacial disorders is crucial for developing treatment strategies. Much of the craniofacial skeleton arises from specialized embryonic structures known as pharyngeal arches. Patterning of these arches requires precise spatial and temporal expression of multiple genes, which is coordinated between tissues by secreted signals. Wnts are secreted ligands expressed throughout the pharyngeal arches yet their role in craniofacial patterning remains unclear. In this study we examine the role of Wnts in craniofacial patterning using transgenic zebrafish to inhibit downstream Wnt signaling. We show that Wnt signaling deficient embryos have lower jaw specific defects, which strongly resembles loss-of-function phenotypes in both the Bmp and Edn1 signaling pathways. Through rescue experiments we find that Wnts are upstream regulators of both Bmp and Edn1 signaling. We thus have uncovered a crucial requirement for Wnt signaling in craniofacial patterning.

Distinct requirements for cranial ectoderm and mesenchyme-derived wnts in specification and differentiation of osteoblast and dermal progenitors

The cranial bones and dermis differentiate from mesenchyme beneath the surface ectoderm. Fate selection in cranial mesenchyme requires the canonical Wnt effector molecule β-catenin, but the relative contribution of Wnt ligand sources in this process remains unknown. Here we show Wnt ligands are expressed in cranial surface ectoderm and underlying supraorbital mesenchyme during dermal and osteoblast fate selection. Using conditional genetics, we eliminate secretion of all Wnt ligands from cranial surface ectoderm or undifferentiated mesenchyme, to uncover distinct roles for ectoderm- and mesenchyme-derived Wnts. Ectoderm Wnt ligands induce osteoblast and dermal fibroblast progenitor specification while initiating expression of a subset of mesenchymal Wnts. Mesenchyme Wnt ligands are subsequently essential during differentiation of dermal and osteoblast progenitors. Finally, ectoderm-derived Wnt ligands provide an inductive cue to the cranial mesenchyme for the fate selection of dermal fibroblast and osteoblast lineages. Thus two sources of Wnt ligands perform distinct functions during osteoblast and dermal fibroblast formation.

Craniofacial abnormalities are relatively common congenital birth defects, and the Wnt signaling pathway and its effectors have key roles in craniofacial development. Wntless/Gpr177 is required for the efficient secretion of all Wnt ligands and maps to a region that contains SNPs strongly associated with reduced bone mass, and heterozygous deletion is associated with facial dysmorphology. Here we test the role of specific sources of secreted Wnt proteins during early stages of craniofacial development and obtained dramatic craniofacial anomalies. We found that the overlying cranial surface ectoderm Wnts generate an instructive cue of Wnt signaling for skull bone and skin cell fate selection and transcription of additional Wnts in the underlying mesenchyme. Once initiated, mesenchymal Wnts may maintain Wnt signal transduction and function in an autocrine manner during differentiation of skull bones and skin. These results highlight how Wnt ligands from two specific tissue sources are integrated for normal craniofacial patterning and can contribute to complex craniofacial abnormalities.

The mesenchymal architecture of the cranial mesoderm of mouse embryos is disrupted by the loss of Twist1 function

The basic helix-loop-helix transcription factor Twist1 is a key regulator of craniofacial development. Twist1-null mouse embryos exhibit failure of cephalic neural tube closure and abnormal head development and die at E11.0. To dissect the function of Twist1 in the cranial mesoderm beyond mid-gestation, we used Mesp1-Cre to delete Twist1 in the anterior mesoderm, which includes the progenitors of the cranial mesoderm. Deletion of Twist1 in mesoderm cells resulted in loss and malformations of the cranial mesoderm-derived skeleton. Loss of Twist1 in the mesoderm also resulted in a failure to fully segregate the mesoderm and the neural crest cells, and the malformation of some cranial neural crest-derived tissues. The development of extraocular muscles was compromised whereas the differentiation of branchial arch muscles was not affected, indicating a differential requirement for Twist1 in these two types of craniofacial muscle. A striking effect of the loss of Twist1 was the inability of the mesodermal cells to maintain their mesenchymal characteristics, and the acquisition of an epithelial-like morphology. Our findings point to a role of Twist1 in maintaining the mesenchyme architecture and the progenitor state of the mesoderm, as well as mediating mesoderm-neural crest interactions in craniofacial development.

Tsukushi functions as a Wnt signaling inhibitor by competing with Wnt2b for binding to transmembrane protein Frizzled4

The Wnt signaling pathway is essential for the development of diverse tissues during embryogenesis. Signal transduction is activated by the binding of Wnt proteins to the type I receptor low-density lipoprotein receptor-related protein 5/6 and the seven-pass transmembrane protein Frizzled (Fzd), which contains a Wnt-binding site in the form of a cysteine-rich domain. Known extracellular antagonists of the Wnt signaling pathway can be subdivided into two broad classes depending on whether they bind primarily to Wnt or to low-density lipoprotein receptor-related protein 5/6. We show that the secreted protein Tsukushi (TSK) functions as a Wnt signaling inhibitor by binding directly to the cysteine-rich domain of Fzd4 with an affinity of 2.3 × 10(-10) M and competing with Wnt2b. In the developing chick eye, TSK is expressed in the ciliary/iris epithelium, whereas Wnt2b is expressed in the adjacent anterior rim of the optic vesicle, where it controls the differentiation of peripheral eye structures, such as the ciliary body and iris. TSK overexpression effectively antagonizes Wnt2b signaling in chicken embryonic retinal cells both in vivo and in vitro and represses Wnt-dependent specification of peripheral eye fates. Conversely, targeted inactivation of the TSK gene in mice causes expansion of the ciliary body and up-regulation of Wnt2b and Fzd4 expression in the developing peripheral eye. Thus, we uncover a crucial role for TSK as a Wnt signaling inhibitor that regulates peripheral eye formation.

Insights from studies with oral cleft genes suggest associations between WNT-pathway genes and risk of oral cancer

Oral squamous cell carcinoma (OSCC) accounts for more than 90% of the malignant neoplasms that arise in the mucosa of the upper aerodigestive tract. Recent studies of cleft lip/palate have shown the association of genes involved in cancer. WNT pathway genes have been associated with several types of cancer and recently with cleft lip/palate. To investigate if genes associated with cleft lip/palate were also associated with oral cancer, we genotyped 188 individuals with OSCC and 225 control individuals for markers in AXIN2, AXIN1, GSK3β, WNT3A, WNT5A, WNT8A, WNT11, WNT3, and WNT9B. Statistical analysis was performed with PLINK 1.06 software to test for differences in allele frequencies of each polymorphism between cases and controls. We found association of SNPs in GSK3B (p = 0.0008) and WNT11 (p = 0.03) with OSCC. We also found overtransmission of GSK3B haplotypes in OSCC cases. Expression analyses showed up-regulation of WNT3A, GSK3B, and AXIN1 and down-regulation of WNT11 in OSCC in comparison with control tissues (P < 0.001). Additional studies should focus on the identification of potentially functional variants in these genes as contributors to human clefting and oral cancer.

Epithelial Wnt/β-catenin signaling regulates palatal shelf fusion through regulation of Tgfβ3 expression

The canonical Wnt/β-catenin signaling plays essential role in development and diseases. Previous studies have implicated the canonical Wnt/β-catenin signaling in the regulation of normal palate development, but functional Wnt/β-catenin signaling and its tissue-specific activities remain to be accurately elucidated. In this study, we show that functional Wnt/β-catenin signaling operates primarily in the palate epithelium, particularly in the medial edge epithelium (MEE) of the developing mouse palatal shelves, consistent with the expression patterns of β-catenin and several Wnt ligands and receptors. Epithelial specific inactivation of β-catenin by the K14-Cre transgenic allele abolishes the canonical Wnt signaling activity in the palatal epithelium and leads to an abnormal persistence of the medial edge seam (MES), ultimately causing a cleft palate formation, a phenotype resembling that in Tgfβ3 mutant mice. Consistent with this phenotype is the down-regulation of Tgfβ3 and suppression of apoptosis in the MEE of the β-catenin mutant palatal shelves. Application of exogenous Tgfβ3 to the mutant palatal shelves in organ culture rescues the midline seam phenotype. On the other hand, expression of stabilized β-catenin in the palatal epithelium also disrupts normal palatogenesis by activating ectopic Tgfβ3 expression in the palatal epithelium and causing an aberrant fusion between the palate shelf and mandible in addition to severely deformed palatal shelves. Collectively, our results demonstrate an essential role for Wnt/β-catenin signaling in the epithelial component at the step of palate fusion during palate development by controlling the expression of Tgfβ3 in the MEE.

A sensitive and bright single-cell resolution live imaging reporter of Wnt/ß-catenin signaling in the mouse

BACKGROUND

Understanding the dynamic cellular behaviors and underlying molecular mechanisms that drive morphogenesis is an ongoing challenge in biology. Live imaging provides the necessary methodology to unravel the synergistic and stereotypical cell and molecular events that shape the embryo. Genetically-encoded reporters represent an essential tool for live imaging. Reporter strains can be engineered by placing cis-regulatory elements of interest to direct the expression of a desired reporter gene. In the case of canonical Wnt signaling, also referred to as Wnt/β-catenin signaling, since the downstream transcriptional response is well understood, reporters can be designed that reflect sites of active Wnt signaling, as opposed to sites of gene transcription, as is the case with many fluorescent reporters. However, even though several transgenic Wnt/β-catenin reporter strains have been generated, to date, none provides the single-cell resolution favored for live imaging studies.

RESULTS

We have placed six copies of a TCF/Lef responsive element and an hsp68 minimal promoter in front of a fluorescent protein fusion comprising human histone H2B to GFP and used it to generate a strain of mice that would report Wnt/β-catenin signaling activity. Characterization of developmental and adult stages of the resulting TCF/Lef:H2B-GFP strain revealed discrete and specific expression of the transgene at previously characterized sites of Wnt/β-catenin signaling. In support of the increased sensitivity of the TCF/Lef:H2B-GFP reporter, additional sites of Wnt/β-catenin signaling not documented with other reporters but identified through genetic and embryological analysis were observed. Furthermore, the sub-cellular localization of the reporter minimized reporter perdurance, and allowed visualization and tracking of individual cells within a cohort, so facilitating the detailed analysis of cell behaviors and signaling activity during morphogenesis.

CONCLUSION

By combining the Wnt activity read-out efficiency of multimerized TCF/Lef DNA binding sites, together with the high-resolution imaging afforded by subcellularly-localized fluorescent fusion proteins such as H2B-GFP, we have created a mouse transgenic line that faithfully recapitulates Wnt signaling activity at single-cell resolution. The TCF/Lef:H2B-GFP reporter represents a unique tool for live imaging the in vivo processes triggered by Wnt/β-catenin signaling, and thus should help the formulation of a high-resolution understanding of the serial events that define the morphogenetic process regulated by this signaling pathway.

Ectodermal Wnt/β-catenin signaling shapes the mouse face

The canonical Wnt/β-catenin pathway is an essential component of multiple developmental processes. To investigate the role of this pathway in the ectoderm during facial morphogenesis, we generated conditional β-catenin mouse mutants using a novel ectoderm-specific Cre recombinase transgenic line. Our results demonstrate that ablating or stabilizing β-catenin in the embryonic ectoderm causes dramatic changes in facial morphology. There are accompanying alterations in the expression of Fgf8 and Shh, key molecules that establish a signaling center critical for facial patterning, the frontonasal ectodermal zone (FEZ). These data indicate that Wnt/β-catenin signaling within the ectoderm is critical for facial development and further suggest that this pathway is an important mechanism for generating the diverse facial shapes of vertebrates during evolution.

Role of canonical Wnt signaling/ß-catenin via Dermo1 in cranial dermal cell development

Cranial dermis develops from cephalic mesoderm and neural crest cells, but what signal(s) specifies the dermal lineage is unclear. Using genetic tools to fate map and manipulate a cranial mesenchymal progenitor population in the supraorbital region, we show that the dermal progenitor cells beneath the surface ectoderm process canonical Wnt signaling at the time of specification. We show that Wnt signaling/β-catenin is absolutely required and sufficient for Dermo1 expression and dermal cell identity in the cranium. The absence of the Wnt signaling cue leads to formation of cartilage in craniofacial and ventral trunk regions at the expense of dermal and bone lineages. Dermo1 can be a direct transcription target and may mediate the functional role of Wnt signaling in dermal precursors. This study reveals a lineage-specific role of canonical Wnt signaling/β-catenin in promoting dermal cell fate in distinct precursor populations.

Studies with Wnt genes and nonsyndromic cleft lip and palate

BACKGROUND

Clefts of the lip and/or palate (cleft lip/palate) are notable for their complex etiology. The WNT pathway regulates multiple developmental processes including craniofacial development and may play a role in cleft lip/palate and other defects of craniofacial development such as tooth agenesis. Variations in WNT genes have been recently associated with cleft lip/palate in humans. In addition, two WNT genes, Wnt3 and Wnt9B, are located in the clf1 cleft locus in mice.

METHODS

We investigated 13 SNPs located in Wnt3A, Wnt5A, Wnt8A, Wnt11, Wnt3, and Wnt9B genes for association with cleft lip/palate subphenotypes in 463 cleft cases and 303 unrelated controls. Genotyping of selected polymorphisms was carried out using Taqman assays. PLINK 1.06 software was used to test for differences in allele frequencies of each polymorphism between affected and unaffected individuals. Haplotype analysis was also performed.

RESULTS

Individuals carrying variant alleles in WNT3 presented an increased risk for cleft lip/palate (p = 0.0003; OR, 1.61; 95% CI, 1.29-2.02) in the population studied.

CONCLUSION

Our results continue to support a role for WNT genes in the pathogenesis of cleft lip/palate. Although much remains to be learned about the function of individual WNT genes during craniofacial development, additional studies should focus on the identification of potentially functional variants in these genes as contributors to human clefting. Birth Defects Research (Part A), 2010. © 2010 Wiley-Liss, Inc.

Wnt/beta-catenin signaling in oral tissue development and disease

The Wnt/beta-catenin signaling pathway is one of several key conserved intercellular signaling pathways in animals, and plays fundamental roles in the proliferation, regeneration, differentiation, and function of many cell and tissue types. This pathway is activated in a dynamic manner during the morphogenesis of oral organs, including teeth, taste papillae, and taste buds, and is essential for these processes to occur normally. Conversely, forced activation of Wnt/beta-catenin signaling promotes the formation of ectopic teeth and taste papillae. In this review, we discuss our current understanding of the roles of Wnt/beta-catenin signaling in oral tissue development and in related human diseases, and the potential of manipulating this pathway for therapeutic purposes.

Adult rat bones maintain distinct regionalized expression of markers associated with their development

The incidence of limb bone fracture and subsequent morbidity and mortality due to excessive bone loss is increasing in the progressively ageing populations of both men and women. In contrast to bone loss in the weight-bearing limb, bone mass in the protective skull vault is maintained. One explanation for this could be anatomically diverse bone matrix characteristics generated by heterogeneous osteoblast populations. We have tested the hypothesis that adult bones demonstrate site-specific characteristics, and report differences at the organ, cell and transcriptome levels. Limb bones contain greater amounts of polysulphated glycosaminoglycan stained with Alcian Blue and have significantly higher osteocyte densities than skull bone. Site-specific patterns persist in cultured adult bone-derived cells both phenotypically (proliferation rate, response to estrogen and cell volumes), and at the level of specific gene expression (collagen triple helix repeat containing 1, reelin and ras-like and estrogen-regulated growth inhibitor). Based on genome-wide mRNA expression and cluster analysis, we demonstrate that bones and cultured adult bone-derived cells segregate according to site of derivation. We also find the differential expression of genes associated with embryological development (Skull: Zic, Dlx, Irx, Twist1 and Cart1; Limb: Hox, Shox2, and Tbx genes) in both adult bones and isolated adult bone-derived cells. Together, these site-specific differences support the view that, analogous to different muscle types (cardiac, smooth and skeletal), skull and limb bones represent separate classes of bone. We assign these differences, not to mode of primary ossification, but to the embryological cell lineage; the basis and implications of this division are discussed.

New directions in craniofacial morphogenesis

The vertebrate head is an extremely complicated structure: development of the head requires tissue-tissue interactions between derivates of all the germ layers and coordinated morphogenetic movements in three dimensions. In this review, we highlight a number of recent embryological studies, using chicken, frog, zebrafish and mouse, which have identified crucial signaling centers in the embryonic face. These studies demonstrate how small variations in growth factor signaling can lead to a diversity of phenotypic outcomes. We also discuss novel genetic studies, in human, mouse and zebrafish, which describe cell biological mechanisms fundamental to the growth and morphogenesis of the craniofacial skeleton. Together, these findings underscore the complex interactions leading to species-specific morphology. These and future studies will improve our understanding of the genetic and environmental influences underlying human craniofacial anomalies.