The inductive role of Wnt-β-Catenin signaling in the formation of oral apparatus

Epithelial-mesenchymal crosstalk: the scriptwriter of craniofacial morphogenesis

Epithelial-mesenchymal interactions (EMI) are fundamental mechanisms in regulating development and organogenesis. Here we summarized the signaling mechanisms involved in EMI in the major developmental events during craniofacial morphogenesis, including neural crest cell induction, facial primordial growth as well as fusion processes. Regional specificity/polarity are demonstrated in the expression of most signaling molecules that usually act in a mutually synergistic/antagonistic manner. The underlying mechanisms of pathogenesis due to disrupted EMI was also discussed in this review.

LAMA5: A new pathogenic gene for non-syndromic cleft lip with or without cleft palate

BACKGROUND

This study aimed to investigate the effect of LAMA5 on palatal development in mice.

METHODS

The palatine process of C57BL/6 J fetal mice on the embryonic day 13.5 (E13.5) was cultured in vitro via the rotating culture method. The LAMA5-shRNA adenovirus vector was constructed, then transfected into the palatal process of E13.5 for 48 h in vitro. A fluorescence microscope was used to visualize the fusion of palates. The expression of LAMA5 was also detected. The expression of ki67, cyclin D1, caspase 3, E-cadherin, vimentin and SHH signaling pathway-related signaling factors in the blank control group, the negative control group, and the LAMA5 interference group were detected after virus transfection.

RESULTS

The bilateral palates in the LAMA5 interference group were not fused after virus transfection. PCR and WB showed that the mRNA and protein expressions of LAMA5 were decreased in the LAMA5 interference group. Furthermore, the mRNA and protein expressions of ki67, cyclin D1 and gli1 were decreased in the LAMA5 interference group, while the mRNA and protein expressions of caspase 3 were increased. However, the mRNA and protein expression of E-cadherin, vimentin, Shh and ptch1 did not significantly change in the LAMA5 interference group.

CONCLUSIONS

LAMA5 silencing causes cleft palate by inhibiting the proliferation of mouse palatal cells and promoting apoptosis, which may not be involved in EMT. LAMA5 silencing can also cause cleft palate by interfering with the SHH signaling pathway.

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.

Sonic hedgehog signaling in craniofacial development

Mutations in SHH and several other genes encoding components of the Hedgehog signaling pathway have been associated with holoprosencephaly syndromes, with craniofacial anomalies ranging in severity from cyclopia to facial cleft to midfacial and mandibular hypoplasia. Studies in animal models have revealed that SHH signaling plays crucial roles at multiple stages of craniofacial morphogenesis, from cranial neural crest cell survival to growth and patterning of the facial primordia to organogenesis of the palate, mandible, tongue, tooth, and taste bud formation and homeostasis. This article provides a summary of the major findings in studies of the roles of SHH signaling in craniofacial development, with emphasis on recent advances in the understanding of the molecular and cellular mechanisms regulating the SHH signaling pathway activity and those involving SHH signaling in the formation and patterning of craniofacial structures.

Canonical Wnt signaling is not required for Tgfb3 expression in the basal medial edge epithelium during palatogenesis

The secondary palate forms from two lateral primordia called the palatal shelves which form a contact in the midline, become adherent at the fusing interface (medial edge epithelia, MEE) and subsequently fuse. The gene encoding transforming growth factor-ß3 (Tgfb3) is strongly and specifically expressed in MEE cells. Our previous study suggested that Tgfb3 expression is controlled via upstream cis-regulatory elements in and around the neighboring Ift43 gene. Another study suggested that the canonical Wnt signaling via ß-Catenin is responsible for the MEE-specific Tgfb3 gene expression, since deletion of the Ctnnb1 gene by a commonly used Keratin 14-Cre (K14Cre) mouse line almost completely abolished Tgfb3 expression in the MEE resulting in cleft palate. Here, we wanted to analyze whether Tcf/Lef consensus binding sites located in the previously identified regions of the Ift43 gene are responsible for the spatiotemporal control of Tgfb3 expression during palatogenesis. We show that contrary to the previous report, deletion of the Ctnnb1 gene in basal MEE cells by the K14Cre driver (the same K14Cre mouse line was used as in the previous study referenced above) does not affect the MEE-specific Tgfb3 expression or TGFß3-dependent palatal epithelial fusion. All mutant embryos showed a lack of palatal rugae accompanied by other craniofacial defects, e.g., a narrow snout and a small upper lip, while only a small subset (<5%) of Ctnnb1 mutants displayed a cleft palate. Moreover, the K14Cre:Ctnnb1 embryos showed reduced levels and altered patterns of Shh expression. Our present data imply that epithelial ß-catenin may not be required for MEE-specific Tgfb3 expression or palatal epithelial fusion.

ISL1/SHH/CXCL12 signaling regulates myogenic cell migration during mouse tongue development

Migration of myoblasts derived from the occipital somites is essential for tongue morphogenesis. However, the molecular mechanisms of myoblast migration remain elusive. In this study, we report that deletion of Isl1 in the mouse mandibular epithelium leads to aglossia due to myoblast migration defects. Isl1 regulates the expression pattern of chemokine ligand 12 (Cxcl12) in the first branchial arch through the Shh/Wnt5a cascade. Cxcl12+ mesenchymal cells in Isl1ShhCre embryos were unable to migrate to the distal region, but instead clustered in a relatively small proximal domain of the mandible. CXCL12 serves as a bidirectional cue for myoblasts expressing its receptor CXCR4 in a concentration-dependent manner, attracting Cxcr4+ myoblast invasion at low concentrations but repelling at high concentrations. The accumulation of Cxcl12+ mesenchymal cells resulted in high local concentrations of CXCL12, which prevented Cxcr4+ myoblast invasion. Furthermore, transgenic activation of Ihh alleviated defects in tongue development and rescued myoblast migration, confirming the functional involvement of Hedgehog signaling in tongue development. In summary, this study provides the first line of genetic evidence that the ISL1/SHH/CXCL12 axis regulates myoblast migration during tongue development.

Macroglossia and less advanced dystrophic change in the tongue muscle of the Duchenne muscular dystrophy rat

Background

Duchenne muscular dystrophy (DMD) is an X-linked muscle disease caused by a complete lack of dystrophin, which stabilizes the plasma membrane of myofibers. The orofacial function is affected in an advanced stage of DMD and this often leads to an eating disorder such as dysphagia. Dysphagia is caused by multiple etiologies including decreased mastication and swallowing. Therefore, preventing the functional declines of mastication and swallowing in DMD is important to improve the patient’s quality of life. In the present study, using a rat model of DMD we generated previously, we performed analyses on the masseter and tongue muscles, both are required for proper eating function.

Methods

Age-related changes of the masseter and tongue muscle of DMD rats were analyzed morphometrically, histologically, and immunohistochemically. Also, transcription of cellular senescent markers, and utrophin (Utrn), a functional analog of dystrophin, was examined.

Results

The masseter muscle of DMD rats showed progressive dystrophic changes as observed in their hindlimb muscle, accompanied by increased transcription of p16 and p19. On the other hand, the tongue of DMD rats showed macroglossia due to hypertrophy of myofibers with less dystrophic changes. Proliferative activity was preserved in the satellite cells from the tongue muscle but was perturbed severely in those from the masseter muscle. While Utrn transcription was increased in the masseter muscle of DMD rats compared to WT rats, probably due to a compensatory mechanism, its level in the tongue muscle was comparable between WT and DMD rats and was similar to that in the masseter muscle of DMD rats.

Conclusions

Muscular dystrophy is less advanced in the tongue muscle compared to the masseter muscle in the DMD rat.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13395-022-00307-7.

SP1-Mediated Upregulation of Long Noncoding RNA ZFAS1 Involved in Non-syndromic Cleft Lip and Palate via Inactivating WNT/β-Catenin Signaling Pathway

Non-syndromic cleft lip and palate (NSCLP) is one of the most common congenital malformations with multifactorial etiology. Although long non-coding RNAs (lncRNAs) have been implicated in the development of lip and palate, their roles in NSCLP are not fully elucidated. This study aimed to investigate how dysregulated lncRNAs contribute to NSCLP. Using lncRNA sequencing, bioinformatics analysis, and clinical tissue sample detection, we identified that lncRNA ZFAS1 was significantly upregulated in NSCLP. The upregulation of ZFAS1 mediated by SP1 transcription factor (SP1) inhibited expression levels of Wnt family member 4 (WNT4) through the binding with CCCTC-binding factor (CTCF), subsequently inactivating the WNT/β-catenin signaling pathway, which has been reported to play a significant role on the development of lip and palate. Moreover, in vitro, the overexpression of ZFAS1 inhibited cell proliferation and migration in human oral keratinocytes and human umbilical cord mesenchymal stem cells (HUC-MSCs) and also repressed chondrogenic differentiation of HUC-MSCs. In vivo, ZFAS1 suppressed cell proliferation and numbers of chondrocyte in the zebrafish ethmoid plate. In summary, these results indicated that ZFAS1 may be involved in NSCLP by affecting cell proliferation, migration, and chondrogenic differentiation through inactivating the WNT/β-catenin signaling pathway.

Oral biosciences: The annual review 2020

BACKGROUND

The Journal of Oral Biosciences is devoted to the advancement and dissemination of fundamental knowledge concerning every aspect of oral biosciences.

HIGHLIGHT

This review featured the review articles in the fields of "Microbiology," "Palate," "Stem Cells," "Mucosal Diseases," "Bone Cell Biology," "MicroRNAs," "TRPV1 Cation Channels," and "Interleukins" in addition to the review article by prize-winners of the "Rising Members Award" ("DKK3 expression and function in head and neck squamous cell carcinoma and other cancers"), presented by the Japanese Association for Oral Biology.

CONCLUSION

These reviews in the Journal of Oral Biosciences have inspired the readers of the journal to broaden their knowledge regarding the various aspects of oral biosciences. The current editorial review introduces these exciting review articles.

Gene-Environment Interplay and MicroRNAs in Cleft Lip and Cleft Palate

Cleft lip (CL) with/without cleft palate (CP) (hereafter CL/P) is the second most common congenital birth defect, affecting 7.94 to 9.92 children per 10,000 live births worldwide, followed by Down syndrome. An increasing number of genes have been identified as affecting susceptibility and/or as causative genes for CL/P in mouse genetic and chemically-induced CL and CP studies, as well as in human genome-wide association studies and linkage analysis. While marked progress has been made in the identification of genetic and environmental risk factors for CL/P, the interplays between these factors are not yet fully understood. This review aims to summarize our current knowledge of CL and CP from genetically engineered mouse models and environmental factors that have been studied in mice. Understanding the regulatory mechanism(s) of craniofacial development may not only advance our understanding of craniofacial developmental biology, but could also provide approaches for the prevention of birth defects and for tissue engineering in craniofacial tissue regeneration.

Palatal rugae morphology is associated with variation in tooth number

This observational study compared palatal rugae morphology in adolescent subjects with normal tooth number and tooth agenesis. Maxillary dental study casts were used to compare rugae number, length and shape. Each study group contained 60 subjects (30 females and 30 males) mean age 13.4 (SD, 1.55) in control and 13.56 (SD, 1.54) years in tooth agenesis groups (p = 0.576). Mean number of missing tooth units in the tooth agenesis group was 2.1. Mean number of primary rugae in the whole sample was 4.35 (SD, 0.98) on the right and 4.33 (SD, 0.92) on the left with no significant differences (p = 0.236 and p = 0.404, respectively). However, the number of secondary rugae on the left (p = 0.006) and fragmentary rugae on the right (p = 0.004) was significantly increased in the tooth agenesis group. The shape of left primary rugae 2 and 3 also differed between groups, tending towards a wavy pattern in the control group and curved in the tooth agenesis group (p = 0.012 and p = 0.004, respectively). In addition, primary rugae 3 was more convergent (p = 0.008) whilst left primary rugae 3 and 5 were orientated in an antero-posterior direction (p = 0.04 for both rugae) in the tooth agenesis group. Subgroup analysis also identified significant associations between patterns of tooth agenesis and rugae number, in addition to shape of primary rugae. The identification of significant differences in rugae pattern between subjects with normal tooth number and agenesis suggests potential commonality in signal pathway disruption during establishment of these structures.

Genetics and signaling mechanisms of orofacial clefts

Craniofacial development involves several complex tissue movements including several fusion processes to form the frontonasal and maxillary structures, including the upper lip and palate. Each of these movements are controlled by many different factors that are tightly regulated by several integral morphogenetic signaling pathways. Subject to both genetic and environmental influences, interruption at nearly any stage can disrupt lip, nasal, or palate fusion and result in a cleft. Here, we discuss many of the genetic risk factors that may contribute to the presentation of orofacial clefts in patients, and several of the key signaling pathways and underlying cellular mechanisms that control lip and palate formation, as identified primarily through investigating equivalent processes in animal models, are examined.

Perturbation analysis of a multi-morphogen Turing reaction-diffusion stripe patterning system reveals key regulatory interactions

Periodic patterning is widespread in development and can be modelled by reaction-diffusion (RD) processes. However, minimal two-component RD descriptions are vastly simpler than the multi-molecular events that actually occur and are often hard to relate to real interactions measured experimentally. Addressing these issues, we investigated the periodic striped patterning of the rugae (transverse ridges) in the mammalian oral palate, focusing on multiple previously implicated pathways: FGF, Hh, Wnt and BMP. For each, we experimentally identified spatial patterns of activity and distinct responses of the system to inhibition. Through numerical and analytical approaches, we were able to constrain substantially the number of network structures consistent with the data. Determination of the dynamics of pattern appearance further revealed its initiation by 'activators' FGF and Wnt, and 'inhibitor' Hh, whereas BMP and mesenchyme-specific-FGF signalling were incorporated once stripes were formed. This further limited the number of possible networks. Experimental constraint thus limited the number of possible minimal networks to 154, just 0.004% of the number of possible diffusion-driven instability networks. Together, these studies articulate the principles of multi-morphogen RD patterning and demonstrate the utility of perturbation analysis for constraining RD systems.This article has an associated 'The people behind the papers' interview.

Sox2 Controls Periderm and Rugae Development to Inhibit Oral Adhesions

In humans, ankyloglossia and cleft palate are common congenital craniofacial anomalies, and these are regulated by a complex gene regulatory network. Understanding the genetic underpinnings of ankyloglossia and cleft palate will be an important step toward rational treatment of these complex anomalies. We inactivated the Sry (sex-determining region Y)-box 2 (Sox2) gene in the developing oral epithelium, including the periderm, a transient structure that prevents abnormal oral adhesions during development. This resulted in ankyloglossia and cleft palate with 100% penetrance in embryos examined after embryonic day 14.5. In Sox2 conditional knockout embryos, the oral epithelium failed to differentiate, as demonstrated by the lack of keratin 6, a marker of the periderm. Further examination revealed that the adhesion of the tongue and mandible expressed the epithelial markers E-Cad and P63. The expanded epithelia are Sox9-, Pitx2-, and Tbx1-positive cells, which are markers of the dental epithelium; thus, the dental epithelium contributes to the development of oral adhesions. Furthermore, we found that Sox2 is required for palatal shelf extension, as well as for the formation of palatal rugae, which are signaling centers that regulate palatogenesis. In conclusion, the deletion of Sox2 in oral epithelium disrupts palatal shelf extension, palatal rugae formation, tooth development, and periderm formation. The periderm is required to inhibit oral adhesions and ankyloglossia, which is regulated by Sox2. In addition, oral adhesions occur through an expanded dental epithelial layer that inhibits epithelial invagination and incisor development. This process may contribute to dental anomalies due to ankyloglossia.

Wnt/β-Catenin Signaling in Oral Carcinogenesis

Oral carcinogenesis is a complex and multifactorial process that involves cumulative genetic and molecular alterations, leading to uncontrolled cell proliferation, impaired DNA repair and defective cell death. At the early stages, the onset of potentially malignant lesions in the oral mucosa, or oral dysplasia, is associated with higher rates of malignant progression towards carcinoma in situ and invasive carcinoma. Efforts have been made to get insights about signaling pathways that are deregulated in oral dysplasia, as these could be translated into novel markers and might represent promising therapeutic targets. In this context, recent evidence underscored the relevance of the Wnt/β-catenin signaling pathway in oral dysplasia, as this pathway is progressively "switched on" through the different grades of dysplasia (mild, moderate and severe dysplasia), with the consequent nuclear translocation of β-catenin and expression of target genes associated with the maintenance of representative traits of oral dysplasia, namely cell proliferation and viability. Intriguingly, recent studies provide an unanticipated connection between active β-catenin signaling and deregulated endosome trafficking in oral dysplasia, highlighting the relevance of endocytic components in oral carcinogenesis. This review summarizes evidence about the role of the Wnt/β-catenin signaling pathway and the underlying mechanisms that account for its aberrant activation in oral carcinogenesis.

Left-right asymmetry in palatal rugae is associated with genetic variants in WNT signaling pathway

OBJECTIVE

The present study evaluated the association between genetic variants in WNT3A and WNT11, and palatal rugae phenotypes.

DESIGN

Eighty-five biological unrelated orthodontic patients were included. Dental casts were assessed and data regarding the length, shape, direction and unification of rugae were recorded. The individuals were subsequently classified for each of the following rugae traits: total amount of rugae; bilateral symmetry in the amount, length and shape of the rugae; presence of secondary or fragmentary rugae; presence of unifications; predominant shape; and, direction of the rugae. Genetic variants in WNT3A (rs708111) and WNT11 (rs1533767) were genotyped by real-time PCR. Genotype and allele distributions were compared with an established alpha of 5 %.

RESULTS

The wavy and curve rugae were the most common. Genotype/phenotype analyses identified that the presence of the rs708111 A allele (OR = 2.2, 95 % CI: 1.1-4.4, p = 0.01) and the rs1533767 G allele (OR = 2.3, 95 % CI: 1.0-5.3, p = 0.05) increased in more than two times the chance of having bilateral asymmetry in the amount of the rugae. In the recessive model, individuals carrying two risk alleles (AA) of WNT3A rs708111 had a higher risk of presenting this phenotype. SNP-SNP interaction analysis revealed that individuals carrying one rs708111 A allele and rs1533767 G allele showed even a higher chance of having bilateral asymmetry in the amount of rugae (OR = 5.6, 95 % CI: 1.1-28.8, p = 0.03). No associations were identified for other rugae phenotype (p > 0.05).

CONCLUSION

Genetic variants in WNT3A and WNT11 were associated with the left-right asymmetry in the amount of palatal rugae.

Temporospatial sonic hedgehog signalling is essential for neural crest-dependent patterning of the intrinsic tongue musculature

The tongue is a highly specialised muscular organ with a complex anatomy required for normal function. We have utilised multiple genetic approaches to investigate local temporospatial requirements for sonic hedgehog (SHH) signalling during tongue development. Mice lacking a Shh cis-enhancer, MFCS4 (ShhMFCS4/-), with reduced SHH in dorsal tongue epithelium have perturbed lingual septum tendon formation and disrupted intrinsic muscle patterning, with these defects reproduced following global Shh deletion from E10.5 in pCag-CreERTM; Shhflox/flox embryos. SHH responsiveness was diminished in local cranial neural crest cell (CNCC) populations in both mutants, with SHH targeting these cells through the primary cilium. CNCC-specific deletion of orofaciodigital syndrome 1 (Ofd1), which encodes a ciliary protein, in Wnt1-Cre; Ofdfl/Y mice led to a complete loss of normal myotube arrangement and hypoglossia. In contrast, mesoderm-specific deletion of Ofd1 in Mesp1-Cre; Ofdfl/Y embryos resulted in normal intrinsic muscle arrangement. Collectively, these findings suggest key temporospatial requirements for local SHH signalling in tongue development (specifically, lingual tendon differentiation and intrinsic muscle patterning through signalling to CNCCs) and provide further mechanistic insight into the tongue anomalies seen in patients with disrupted hedgehog signalling.

Dynamic activation of Wnt, Fgf, and Hh signaling during soft palate development

The soft palate is a key component of the oropharyngeal complex that is critical for swallowing, breathing, hearing and speech. However, complete functional restoration in patients with cleft soft palate remains a challenging task. New insights into the molecular signaling network governing the development of soft palate will help to overcome these clinical challenges. In this study, we investigated whether key signaling pathways required for hard palate development are also involved in soft palate development in mice. We described the dynamic expression patterns of signaling molecules from well-known pathways, such as Wnt, Hh, and Fgf, during the development of the soft palate. We found that Wnt signaling is active throughout the development of soft palate myogenic sites, predominantly in cells of cranial neural crest (CNC) origin neighboring the myogenic cells, suggesting that Wnt signaling may play a significant role in CNC-myogenic cell-cell communication during myogenic differentiation in the soft palate. Hh signaling is abundantly active in early palatal epithelium, some myogenic cells, and the CNC-derived cells adjacent to the myogenic cells. Hh signaling gradually diminishes during the later stages of soft palate development, indicating its involvement mainly in early embryonic soft palate development. Fgf signaling is expressed most prominently in CNC-derived cells in the myogenic sites and persists until later stages of embryonic soft palate development. Collectively, our results highlight a network of Wnt, Hh, and Fgf signaling that may be involved in the development of the soft palate, particularly soft palate myogenesis. These findings provide a foundation for future studies on the functional significance of these signaling pathways individually and collectively in regulating soft palate development.

Primary cilia in murine palatal rugae development

Periodic patterning of iterative structures is a fundamental process during embryonic development, since these structures are diverse across the animal kingdom. Therefore, elucidating the molecular mechanisms in the formation of these structures promotes understanding of the process of organogenesis. Periodically patterned ridges, palatal rugae (situated on the hard palate of mammals), are an excellent experimental model to clarify the molecular mechanisms involved in the formation of periodic patterning of iterative structures. Primary cilia are involved in many biological events, including the regulation of signaling pathways such as Shh and non-canonical Wnt signaling. However, the role of primary cilia in the development of palatal rugae remains unclear. We found that primary cilia were localized to the oral cavity side of the interplacode epithelium of the palatal rugae, whereas restricted localization of primary cilia could not be detected in other regions. Next, we generated mice with a placodal conditional deletion of the primary cilia protein Ift88, using ShhCre mice (Ift88^fl/fl;ShhCre). Highly disorganized palatal rugae were observed in Ift88^fl/fl;ShhCre mice. Furthermore, by comparative in situ hybridization analysis, many Shh and non-canonical Wnt signaling-related molecules showed spatiotemporal expression patterns during palatal rugae development, including restricted expression in the epithelium (placodes and interplacodes) and mesenchyme. Some of these expression were found to be altered in Ift88^fl/fl;ShhCre mice. Primary cilia is thus involved in development of palatal rugae.

The association between palatal rugae pattern and dental malocclusion

Introduction:

Palatal rugae complete its development during early intrauterine life, whereas dental malocclusions in permanent dentition establishes several years into the post-natal life.

Objective:

The objective of present study was to determine if there is an association between the palatal rugae pattern and Angle’s classes of malocclusion.

Methods:

A cross-sectional study was conducted on pretreatment dental casts of 184 patients. The sample was divided into the following groups: Class I, Class II div. 1, Class II div. 2, and Class III. The number of palatal rugae was recorded, bilaterally. The length, pattern and orientation of three anterior-most primary rugae on both sides were recorded.

Results:

The mean age of the study sample was 17.8 ± 5.4 years. The mean number of the palatal rugae was 11.18 ± 2.5, with significant differences among different malocclusion groups. The length of the first rugae on left side and third rugae on both sides varied significantly among the groups (p< 0.05). Similarly, the pattern of palatal rugae was also found to be significantly different among the malocclusion groups. The right sided rugae did not have any significant difference in the orientation in different malocclusion groups; however, the left sided rugae showed significant differences among the four malocclusion groups (p< 0.001).

Conclusions:

The current study showed subtle differences in the palatal rugae pattern among the Angle’s classes of malocclusion. Similarly, the length and orientation of some rugae were also found to be significantly different between malocclusion groups.

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.

Lrp4/Wise regulates palatal rugae development through Turing-type reaction-diffusion mechanisms

Periodic patterning of iterative structures is diverse across the animal kingdom. Clarifying the molecular mechanisms involved in the formation of these structure helps to elucidate the process of organogenesis. Turing-type reaction-diffusion mechanisms have been shown to play a critical role in regulating periodic patterning in organogenesis. Palatal rugae are periodically patterned ridges situated on the hard palate of mammals. We have previously shown that the palatal rugae develop by a Turing-type reaction-diffusion mechanism, which is reliant upon Shh (as an inhibitor) and Fgf (as an activator) signaling for appropriate organization of these structures. The disturbance of Shh and Fgf signaling lead to disorganized palatal rugae. However, the mechanism itself is not fully understood. Here we found that Lrp4 (transmembrane protein) was expressed in a complementary pattern to Wise (a secreted BMP antagonist and Wnt modulator) expression in palatal rugae development, representing Lrp4 expression in developing rugae and Wise in the inter-rugal epithelium. Highly disorganized palatal rugae was observed in both Wise and Lrp4 mutant mice, and these mutants also showed the downregulation of Shh signaling, which was accompanied with upregulation of Fgf signaling. Wise and Lrp4 are thus likely to control palatal rugae development by regulating reaction-diffusion mechanisms through Shh and Fgf signaling. We also found that Bmp and Wnt signaling were partially involved in this mechanism.

How to make a tongue: Cellular and molecular regulation of muscle and connective tissue formation during mammalian tongue development

The vertebrate tongue is a complex muscular organ situated in the oral cavity and involved in multiple functions including mastication, taste sensation, articulation and the maintenance of oral health. Although the gross embryological contributions to tongue formation have been known for many years, it is only relatively recently that the molecular pathways regulating these processes have begun to be discovered. In particular, there is now evidence that the Hedgehog, TGF-Beta, Wnt and Notch signaling pathways all play an important role in mediating appropriate signaling interactions between the epithelial, cranial neural crest and mesodermal cell populations that are required to form the tongue. In humans, a number of congenital abnormalities that affect gross morphology of the tongue have also been described, occurring in isolation or as part of a developmental syndrome, which can greatly impact on the health and well-being of affected individuals. These anomalies can range from an absence of tongue formation (aglossia) through to diminutive (microglossia), enlarged (macroglossia) or bifid tongue. Here, we present an overview of the gross anatomy and embryology of mammalian tongue development, focusing on the molecular processes underlying formation of the musculature and connective tissues within this organ. We also survey the clinical presentation of tongue anomalies seen in human populations, whilst considering their developmental and genetic etiology.

A Wnt/Notch/Pax7 signaling network supports tissue integrity in tongue development

The tongue is one of the major structures involved in human food intake and speech. Tongue malformations such as aglossia, microglossia, and ankyloglossia are congenital birth defects, greatly affecting individuals' quality of life. However, the molecular basis of the tissue-tissue interactions that ensure tissue morphogenesis to form a functional tongue remains largely unknown. Here we show that Shh^Cre -mediated epithelial deletion of Wntless (Wls), the key regulator for intracellular Wnt trafficking, leads to lingual hypoplasia in mice. Disruption of epithelial Wnt production by Wls deletion in epithelial cells led to a failure in lingual epidermal stratification and loss of the lamina propria and the underlying superior longitudinal muscle in developing mouse tongues. These defective phenotypes resulted from a reduction in epithelial basal cells positive for the basal epidermal marker protein p63 and from impaired proliferation and differentiation in connective tissue and paired box 3 (Pax3)- and Pax7-positive muscle progenitor cells. We also found that epithelial Wnt production is required for activation of the Notch signaling pathway, which promotes proliferation of myogenic progenitor cells. Notch signaling in turn negatively regulated Wnt signaling during tongue morphogenesis. We further show that Pax7 is a direct Notch target gene in the embryonic tongue. In summary, our findings demonstrate a key role for the lingual epithelial signals in supporting the integrity of the lamina propria and muscular tissue during tongue development and that a Wnt/Notch/Pax7 genetic hierarchy is involved in this development.

Alteration of palatine ruga pattern in subjects with oligodontia: A pilot study

INTRODUCTION

The aim of this study was to compare the palatal ruga patterns in subjects with oligodontia and normal tooth numbers.

METHODS

An observational investigation was conducted by using maxillary dental study casts to compare ruga numbers, lengths, and shapes in subjects with diagnosed oligodontia or normal tooth numbers.

RESULTS

A total of 32 subjects comprised both the oligodontia (mean age, 14.0 years; SD, 5.0 years) and the control (mean age, 14.5 years; SD, 5.1 years) groups. The mean number of missing teeth in the oligodontia group was 8.7. The mean number of rugae in the whole sample was 7.36 (SD, 1.16), with no significant difference between the groups (P = 0.264). For ruga pattern, no differences were found for right-sided rugae; however, on the left side, a significant difference existed in shape frequency associated with ruga 2. Specifically, a curved shape was seen more frequently in ruga 2 of the oligodontia group (P = 0.01).

CONCLUSIONS

The identification of subtle differences in ruga patterns between subjects with oligodontia and normal tooth numbers suggests potentially shared pathways during the development of these oral structures. Further large-scale investigations are warranted.

A pilot study: Screening target miRNAs in tissue of nonsyndromic cleft lip with or without cleft palate

Nonsyndromic cleft lip with or without cleft palate (NSCLP) has been recognized as a condition resulting from a combination of environmental and genetic factors. Studies have demonstrated that microRNAs (miRNAs) are involved in embryonic development. However, few studies have focused on screening potential target miRNAs in human NSCLP tissue. Using microarray-based miRNA expression profiling, miRNA expression was compared in tissue samples from 4 NSCLP patients and 4 healthy control subjects. Two hundred and fifty-four miRNAs were found to be differentially expressed. Changes in Homo sapiens (hsa)-miR-24-3p, hsa-miR-27b-3p, hsa-miR-205-5p, hsa-miR-1260b and hsa-miR-720 were of particular interest with respect to Wnt signaling (fold-changes were 12.5, 12.2, 12.1, 12.3 and 10.5, respectively; P<0.005 for all). The levels of hsa-miR-24-3p, hsa-miR-1260b and hsa-miR-205-5p were higher in tissues from NSCLP patients than in those from controls according to PCR analysis. Hsa-miR-24-3p, hsa-miR-1260b and hsa-miR-205-5p may be candidate miRNAs involved in the etiology of NSCLP via Wnt signaling.

Bone morphogenetic protein-induced cell differentiation involves Atg7 and Wnt16 sequentially in human stem cell-derived osteoblastic cells

We established a differentiation method for homogeneous α7 integrin-positive human skeletal muscle stem cell (α7(+)hSMSC)-derived osteoblast-like cells with bone morphogenetic protein (BMP)-2. To explore the early signaling cascade for osteoblastic differentiation, we examined the upregulation of autophagy-related gene (Atg) and wingless/int1 (Wnt) signaling during BMP-2-mediated human osteoblastic differentiation. In a screening experiment, BMP-2 increased the mRNA and protein levels of Atg7, Wnt16, and Lrp5/Fzd2 (a Wnt receptor), but not microtubule-associated protein 1 light chain (LC3; a mammalian homolog of yeast Atg8), TFE3, Beclin1, Atg5, Atg12, Wnt3a, or Wnt5, together with the amounts of autophagosomes and autophagy fluxes. Treatment with siRNAs against Atg7 and Wnt16 individually suppressed the BMP-2-induced increase in osteoblastic differentiation. The osteoblastic phenotype, involving osteocalcin (BGLAP), osteopontin (SPP1), and osterix (SP7) expression, decreased when autophagy was inhibited by chloroquine (an autophagy inhibitor), but increased after treatment with rapamycin (an autophagy enhancer). Taken together with our previous findings, we have revealed a unique sequential cascade of BMP-2→Atg7→Wnt16→Lrp5/Fzd2→matrix metalloproteinase-13→osteoblastic differentiation. This cascade results in a potent increase in osteoblastic cell differentiation, indicating the unique involvement of Atg7, autophagy, and Wnt16 signaling in BMP-2-induced differentiation of α7(+)hSMSCs into osteoblast-like cells at a relatively early stage.

Hedgehog receptor function during craniofacial development

The Hedgehog signalling pathway plays a fundamental role in orchestrating normal craniofacial development in vertebrates. In particular, Sonic hedgehog (Shh) is produced in three key domains during the early formation of the head; neuroectoderm of the ventral forebrain, facial ectoderm and the pharyngeal endoderm; with signal transduction evident in both ectodermal and mesenchymal tissue compartments. Shh signalling from the prechordal plate and ventral midline of the diencephalon is required for appropriate division of the eyefield and forebrain, with mutation in a number of pathway components associated with Holoprosencephaly, a clinically heterogeneous developmental defect characterized by a failure of the early forebrain vesicle to divide into distinct halves. In addition, signalling from the pharyngeal endoderm and facial ectoderm plays an essential role during development of the face, influencing cranial neural crest cells that migrate into the early facial processes. In recent years, the complexity of Shh signalling has been highlighted by the identification of multiple novel proteins that are involved in regulating both the release and reception of this protein. Here, we review the contributions of Shh signalling during early craniofacial development, focusing on Hedgehog receptor function and describing the consequences of disruption for inherited anomalies of this region in both mouse models and human populations.

Wnt16 Signaling Is Required for IL-1β-Induced Matrix Metalloproteinase-13-Regulated Proliferation of Human Stem Cell-Derived Osteoblastic Cells

We established a differentiation method for homogeneous α7 integrin-positive human skeletal muscle stem cell (α7⁺hSMSC)-derived osteoblast-like (α7⁺hSMSC-OB) cells, and found that interleukin (IL)-1β induces matrix metalloproteinase (MMP)-13-regulated proliferation of these cells. These data suggest that MMP-13 plays a potentially unique physiological role in the regeneration of osteoblast-like cells. Here, we examined whether up-regulation of MMP-13 activity by IL-1β was mediated by Wingless/int1 (Wnt) signaling and increased the proliferation of osteoblast-like cells. IL-1β increased the mRNA and protein levels of Wnt16 and the Wnt receptor Lrp5/Fzd2. Exogenous Wnt16 was found to increase MMP-13 mRNA, protein and activity, and interestingly, the proliferation rate of these cells. Treatment with small interfering RNAs against Wnt16 and Lrp5 suppressed the IL-1β-induced increase in cell proliferation. We revealed that a unique signaling cascade IL-1β→Wnt16→Lrp5→MMP-13, was intimately involved in the proliferation of osteoblast-like cells, and suggest that IL-1β-induced MMP-13 expression and changes in cell proliferation are regulated by Wnt16.

Autophagy-related gene 5 and Wnt5 signaling pathway requires differentiation of embryonic stem cells into odontoblast-like cells

We previously confirmed a unique and unanticipated role for an α2 integrin, extracellular matrix metalloproteinase inducer (Emmprin), and matrix metalloproteinase (MMP)-3-mediated signaling cascade, in driving the odontoblast-like differentiation of mouse embryonic stem (ES) cells in a collagen type-I scaffold (CS) combined with bone morphogenetic protein (BMP)-4 (CS/BMP-4). To explore the early signaling cascade for odontoblastic differentiation, we examined the upregulation of autophagy-related gene (Atg) and Wnt signaling by CS/BMP-4 mediated odontoblast differentiation. In a screening experiment, CS/BMP-4 increased the mRNA and protein levels of Atg5, Lrp5/Fzd9 (an Atg5 receptor), and Wnt5, but not microtubule-associated protein 1 light chain (LC3; a mammalian homolog of yeast Atg8), TFE3, Beclin1, and Atg12, together with the amount of autophagosomes and autophagy fluxes. Treatment with siRNAs against Atg5 and Wnt5 individually suppressed the CS/BMP-4-induced increase in odontoblast differentiation. The odontoblastic phenotype, involving dentin matrix protein-1 and dentin sialophosphoprotein expression, decreased when autophagy was inhibited by chloroquine, but increased after treatment with rapamycin (an autophagy enhancer). Taken together with our previous findings, we have revealed a unique sequential cascade involving Atg5, Wnt5a, α2 integrin, Emmprin, and MMP-3. This cascade results in a potent increase in odontoblastic cell differentiation, indicating the unique involvement of Atg5, autophagy and Wnt5 signaling in CS/BMP-4-induced differentiation of ES cells into odontoblast-like cells, at a relatively early stage.

Mandible and Tongue Development

The tongue and mandible have common origins. They arise simultaneously from the mandibular arch and are coordinated in their development and growth, which is evident from several clinical conditions such as Pierre Robin sequence. Here, we review in detail the molecular networks controlling both mandible and tongue development. We also discuss their mechanical relationship and evolution as well as the potential for stem cell-based therapies for disorders affecting these organs.

Embryonic tongue morphogenesis in an organ culture model of mouse mandibular arches: blocking Sonic hedgehog signaling leads to microglossia

Mouse tongue development is initiated with the formation of lateral lingual swellings just before fusion between the mediodorsal surfaces of the mandibular arches at around embryonic day 11.0. Here, we investigated the role of Sonic hedgehog (Shh) signaling in embryonic mouse tongue morphogenesis. For this, we used an organ culture model of the mandibular arches from mouse embryos at embryonic day 10.5. When the Shh signaling inhibitor jervine was added to the culture medium for 24-96 h, the formation of lateral lingual swellings and subsequent epithelial invagination into the mesenchyme were impaired markedly, leading to a hypoplastic tongue with an incomplete oral sulcus. Notably, jervine treatment reduced the proliferation of non-myogenic mesenchymal cells at the onset of forming the lateral lingual swellings, whereas it did not affect the proliferation and differentiation of a myogenic cell lineage, which created a cell community at the central circumferential region of the lateral lingual swellings as seen in vivo and in control cultures lacking the inhibitor. Thus, epithelium-derived Shh signaling stimulates the proliferation of non-myogenic mesenchymal cells essential for forming lateral lingual swellings and contributes to epithelial invagination into the mesenchyme during early tongue development.

Molecular basis of cleft palates in mice

Cleft palate, including complete or incomplete cleft palates, soft palate clefts, and submucosal cleft palates, is the most frequent congenital craniofacial anomaly in humans. Multifactorial conditions, including genetic and environmental factors, induce the formation of cleft palates. The process of palatogenesis is temporospatially regulated by transcription factors, growth factors, extracellular matrix proteins, and membranous molecules; a single ablation of these molecules can result in a cleft palate in vivo. Studies on knockout mice were reviewed in order to identify genetic errors that lead to cleft palates. In this review, we systematically describe these mutant mice and discuss the molecular mechanisms of palatogenesis.

Gpr177-mediated Wnt Signaling Is Required for Secondary Palate Development

Cleft palate represents one of the major congenital birth defects in humans. Despite the essential roles of ectodermal canonical Wnt and mesenchymal Wnt signaling in the secondary palate development, the function of mesenchymal canonical Wnt activity in secondary palate development remains elusive. Here we show that Gpr177, a highly conserved transmembrane protein essential for Wnt trafficking, is required for secondary palate development. Gpr177 is expressed in both epithelium and mesenchyme of palatal shelves during mouse development. Wnt1Cre-mediated deletion of Gpr177 in craniofacial neural crest cells leads to a complete cleft secondary palate, which is formed mainly due to aberrant cell proliferation and increased cell death in palatal shelves. By BATGAL staining, we reveal an intense canonical Wnt activity in the anterior palate mesenchyme of E12.5 wild-type embryos but not in Gpr177Wnt1-Cre embryos, suggesting that mesenchymal canonical Wnt signaling activated by Gpr177-mediated mesenchymal Wnts is critical for secondary palate development. Moreover, phosphorylation of JNK and c-Jun is impaired in the Gpr177Wnt1-Cre palate and is restored by implantation of Wnt5a-soaked beads in the in vitro palate explants, suggesting that Gpr177 probably regulates palate development via the Wnt5a-mediated noncanonical Wnt pathway in which c-Jun and JNK are involved. Importantly, certain cellular processes and the altered gene expression in palates lacking Gpr177 are distinct from that of the Wnt5a mutant, further demonstrating involvement of other mesenchymal Wnts in the process of palate development. Together, these results suggest that mesenchymal Gpr177 is required for secondary palate development by regulating and integrating mesenchymal canonical and noncanonical Wnt signals.

Dido mutations trigger perinatal death and generate brain abnormalities and behavioral alterations in surviving adult mice

Nearly all vertebrate cells have a single cilium protruding from their surface. This threadlike organelle, once considered vestigial, is now seen as a pivotal element for detection of extracellular signals that trigger crucial morphogenetic pathways. We recently proposed a role for Dido3, the main product of the death inducer-obliterator (dido) gene, in histone deacetylase 6 delivery to the primary cilium [Sánchez de Diego A, et al. (2014) Nat Commun 5:3500]. Here we used mice that express truncated forms of Dido proteins to determine the link with cilium-associated disorders. We describe dido mutant mice with high incidence of perinatal lethality and distinct neurodevelopmental, morphogenetic, and metabolic alterations. The anatomical abnormalities were related to brain and orofacial development, consistent with the known roles of primary cilia in brain patterning, hydrocephalus incidence, and cleft palate. Mutant mice that reached adulthood showed reduced life expectancy, brain malformations including hippocampus hypoplasia and agenesis of corpus callosum, as well as neuromuscular and behavioral alterations. These mice can be considered a model for the study of ciliopathies and provide information for assessing diagnosis and therapy of genetic disorders linked to the deregulation of primary cilia.

The formation of endoderm-derived taste sensory organs requires a Pax9-dependent expansion of embryonic taste bud progenitor cells

In mammals, taste buds develop in different regions of the oral cavity. Small epithelial protrusions form fungiform papillae on the ectoderm-derived dorsum of the tongue and contain one or few taste buds, while taste buds in the soft palate develop without distinct papilla structures. In contrast, the endoderm-derived circumvallate and foliate papillae located at the back of the tongue contain a large number of taste buds. These taste buds cluster in deep epithelial trenches, which are generated by intercalating a period of epithelial growth between initial placode formation and conversion of epithelial cells into sensory cells. How epithelial trench formation is genetically regulated during development is largely unknown. Here we show that Pax9 acts upstream of Pax1 and Sox9 in the expanding taste progenitor field of the mouse circumvallate papilla. While a reduced number of taste buds develop in a growth-retarded circumvallate papilla of Pax1 mutant mice, its development arrests completely in Pax9-deficient mice. In addition, the Pax9 mutant circumvallate papilla trenches lack expression of K8 and Prox1 in the taste bud progenitor cells, and gradually differentiate into an epidermal-like epithelium. We also demonstrate that taste placodes of the soft palate develop through a Pax9-dependent induction. Unexpectedly, Pax9 is dispensable for patterning, morphogenesis and maintenance of taste buds that develop in ectoderm-derived fungiform papillae. Collectively, our data reveal an endoderm-specific developmental program for the formation of taste buds and their associated papilla structures. In this pathway, Pax9 is essential to generate a pool of taste bud progenitors and to maintain their competence towards prosensory cell fate induction.

Gpr177-mediated Wnt Signaling is Required for Fungiform Placode Initiation

Fungiform papillae are formed as patterned rows on the surface of the anterior tongue at early organogenesis and contain one taste bud in each papilla to form one of the important sensory organs. Despite the essential role of Wnt/β-catenin signaling in controlling the development of fungiform taste papillae, the universal function of Wnt ligands in the initiation of the fungiform placode has not been completely elucidated. Here, by Shh (Cre) -mediated oral epithelial deletion of Wntless (Gpr177), a regulator essential for intracellular Wnt trafficking, we demonstrate that an overall function of Wnts is required for initiation of the fungiform placode. Multiple Wnts are expressed in the tongue epithelium at E11.5 before initiation of the fungiform placodes. Epithelial Gpr177 loss-of-function, associated with reduction of canonical Wnt signaling in lingual epithelium as exhibited by a loss of TopGal activity and Axin2 expression, results in the failure of fungiform placode initiation, as assessed by diminished expression of several taste placode molecular markers. Moreover, LiCl treatment of Gpr177 epithelial-deficient tongue explants at E11.5, but not at E12.5, restores tongue placode formation, demonstrating that Wnt ligands in the tongue surface prior to but not after fungiform placode initiation are responsible for fungiform papilla initiation. Epithelium-specific expression of an active β-catenin in the Gpr177-deficient tongue leads to fungiform papillae generation, suggesting that an intra-epithelial response to Wnts is required for placode initiation. Together, these results suggest that Gpr177 controls epithelial initiation of the fungiform placode through signaling via epithelial Wnt ligands.

Inhibition of Wnt/β-catenin pathway by Dickkopf-1 [corrected] affects midfacial morphogenesis in chick embryo

The development of the vertebrate face is regulated by complex interactions among several signaling pathways. Dickkopf-1 (Dkk-1), an inhibitor of the Wnt/β-catenin signaling pathway, can affect midfacial morphogenesis. The downstream target genes of the Wnt/β-catenin signaling pathway in morphogenesis of the developing upper jaw and lip remain unknown. To investigate the functional roles of Wnt/β-catenin signaling in facial development, we performed a loss-of-function experiment using local implantation of beads soaked with Dkk-1 during lip fusion at the maxillary prominence of chick embryos at stage 22(HH22). Antagonism of Wnt/β-catenin signaling by Dkk-1 induced deformities of the premaxilla and jugal bone, which are derived from the maxillary mesenchyme. Real-time and semi-quantitative RT-PCR analysis showed the significant reduction of Lhx8, Msx1 and Msx2 expression levels around the beads in the maxillary mesenchyme at 6 and 24 h after bead implantation. Time course experiments in the HH 22 embryos showed the effect of Dkk-1 on Lhx8, Msx1 and Msx2 expression was not significant after 48 h of the treatment. At HH 26 when the fusion of facial primordial started, Dkk-1 application did not exhibit any significant reduction of those genes. Our findings suggested that Dkk-1 regulates maxillary morphogenesis in chick embryos through Lhx8, Msx1 and Msx2 signals. Wnt/β-catenin signaling is responsible for intrinsic upper jaw development before the lip fusion.

Epigenetic regulation of Sox4 during palate development

AIM

Identification of genes that contribute to secondary palate development provide a better understanding of the etiology of palatal clefts. Gene-expression profiling of the murine palate from gestational days 12-14 (GD12-14), a critical period in palate development, identified Sox4 as a differentially expressed gene. In this study, we have examined if the differential expression of Sox4 in the palate is due to changes in DNA methylation.

MATERIALS & METHODS

In situ hybridization analysis was used to localize the expression of Sox4 in the developing murine secondary palate. CpG methylation profiling of a 1.8-kb upstream region of Sox4 in the secondary palate from GD12-14 and transfection analysis in murine embryonic maxillary mesenchymal cells using Sox4 deletion, mutant and in vitro methylated plasmid constructs were used to identify critical CpG residues regulating Sox4 expression in the palate.

RESULTS

Spatiotemporal analysis revealed that Sox4 is expressed in the medial edge epithelium and presumptive rugae-forming regions of the palate from GD12 to GD13. Following palatal shelf fusion on GD14, Sox4 was expressed exclusively in the epithelia of the palatal rugae, structures that serve as signaling centers for the anteroposterior extension of the palate, and that are thought to serve as neural stem cell niches. Methylation of a 1.8-kb region upstream of Sox4, containing the putative promoter, completely eliminated promoter activity. CpG methylation profiling of the 1.8-kb region identified a CpG-poor region (DMR4) that exhibited significant differential methylation during palate development, consistent with changes in Sox4 mRNA expression. Changes in the methylation of DMR4 were attributed primarily to CpGs 83 and 85.

CONCLUSION

Our studies indicate that Sox4 is an epigenetically regulated gene that likely integrates multiple signaling systems for mediating palatal fusion, palatal extension and/or the maintenance of the neural stem cell niche in the rugae.

Inactivation of LAR family phosphatase genes Ptprs and Ptprf causes craniofacial malformations resembling Pierre-Robin sequence

Leukocyte antigen related (LAR) family receptor protein tyrosine phosphatases (RPTPs) regulate the fine balance between tyrosine phosphorylation and dephosphorylation that is crucial for cell signaling during development and tissue homeostasis. Here we show that LAR RPTPs are required for normal development of the mandibular and maxillary regions. Approximately half of the mouse embryos lacking both Ptprs (RPTPσ) and Ptprf (LAR) exhibit micrognathia (small lower jaw), cleft palate and microglossia/glossoptosis (small and deep tongue), a phenotype closely resembling Pierre-Robin sequence in humans. We show that jaw bone and cartilage patterning occurs aberrantly in LAR family phosphatase-deficient embryos and that the mandibular arch harbors a marked decrease in cell proliferation. Analysis of signal transduction in embryonic tissues and mouse embryonic fibroblast cultures identifies an increase in Bmp-Smad signaling and an abrogation of canonical Wnt signaling associated with loss of the LAR family phosphatases. A reactivation of β-catenin signaling by chemical inhibition of GSK3β successfully resensitizes LAR family phosphatase-deficient cells to Wnt induction, indicating that RPTPs are necessary for normal Wnt/β-catenin pathway activation. Together these results identify LAR RPTPs as important regulators of craniofacial morphogenesis and provide insight into the etiology of Pierre-Robin sequence.

Targeted mutations of genes reveal important roles in palatal development in mice

The process of palatal development is regulated by growth factors, extracellular matrix (ECM) protein, and cell adhesion molecules, of which disturbance may result in cleft palate. Knockout mice are important animal models for studying the role of genes during palatal development. Therefore, in this review, we will describe genes knockout in mice to reveal the biological mechanisms of these genes in the formation of the cleft palate.

Developmental profiles of the murine palatal methylome

BACKGROUND

Environmental factors contribute to the etiology of cleft palate (CP). Identification of genes that are methylated during development of the secondary palate will contribute to a better understanding of the gene-environment link contributing to CP.

METHODS

Genomic DNA fragments from secondary palate tissue from gestational days (GDs) 12 to 14 were subjected to Selective Enrichment of Methylated DNA (SEMD) and used to probe NimbleGen 2.1M mouse promoter arrays. Input (control) and SEMD samples were labeled with Cy3 and Cy5, respectively, and used for array hybridization (three arrays per GD). Data were analyzed using the Bioconductor package Ringo. Gene methylation was verified by pyrosequencing analysis and expression by quantitative real-time PCR.

RESULTS

A total of 5577 methylated genes were identified during palate development: (1) 74% of genes were methylated on all three GDs; (2) CpG islands accounted for only 30% of methylated regions of interest (MRIs); (3) location of MRIs was more often observed in gene bodies (73%) than in promoters; (4) evaluation of MRIs on GDs 12-14 revealed no significant differentially methylated regions; (5) DAVID analysis of MRIs revealed that the cadherin and Wnt signaling pathways, as well as pathways involved in proteoglycan synthesis, were significantly enriched for methylated genes.

CONCLUSIONS

Our prior studies identified differentially expressed mRNAs and microRNAs in the developing palate. The current study complements these studies by identifying genes whose expression may be altered as a result of DNA methylation.

Delineating a conserved genetic cassette promoting outgrowth of body appendages

The acquisition of the external genitalia allowed mammals to cope with terrestrial-specific reproductive needs for internal fertilization, and thus it represents one of the most fundamental steps in evolution towards a life on land. How genitalia evolved remains obscure, and the key to understanding this process may lie in the developmental genetics that underpins the early establishment of the genital primordium, the genital tubercle (GT). Development of the GT is similar to that of the limb, which requires precise regulation from a distal signaling epithelium. However, whether outgrowth of the GT and limbs is mediated by common instructive signals remains unknown. In this study, we used comprehensive genetic approaches to interrogate the signaling cascade involved in GT formation in comparison with limb formation. We demonstrate that the FGF ligand responsible for GT development is FGF8 expressed in the cloacal endoderm. We further showed that forced Fgf8 expression can rescue limb and GT reduction in embryos deficient in WNT signaling activity. Our studies show that the regulation of Fgf8 by the canonical WNT signaling pathway is mediated in part by the transcription factor SP8. Sp8 mutants elicit appendage defects mirroring WNT and FGF mutants, and abolishing Sp8 attenuates ectopic appendage development caused by a gain-of-function β-catenin mutation. These observations indicate that a conserved WNT-SP8-FGF8 genetic cassette is employed by both appendages for promoting outgrowth, and suggest a deep homology shared by the limb and external genitalia.

Mammalian limbs and external genitalia are body appendages specialized for locomotion and internal fertilization, respectively. Despite their marked anatomical and functional differences, development of the limb and external genitalia appears to involve similar genetic controls, and some have suggested that regulatory mechanisms common to both might be evolutionarily linked. One essential aspect for appendage development is the establishment and maintenance of a separated proximodistal developmental axis apart from the main body axis, which is often instructed by a distal signaling epithelium. Herein, we adopted comprehensive mouse genetic approaches to investigate regulatory mechanisms underlying the distal signaling center in the limb and the GT, and uncovered a conserved genetic cassette that is utilized by both paired and unpaired appendages to establish a distal signaling center in the epithelium that mediates subsequent proximodistal outgrowth. Our results further suggested that the evolution of the external genital organ involved co-option of the same genetic program underpinning limb development.

Molecular signaling along the anterior-posterior axis of early palate development

Cleft palate is a common congenital birth defect in humans. In mammals, the palatal tissue can be distinguished into anterior bony hard palate and posterior muscular soft palate that have specialized functions in occlusion, speech or swallowing. Regulation of palate development appears to be the result of distinct signaling and genetic networks in the anterior and posterior regions of the palate. Development and maintenance of expression of these region-specific genes is crucial for normal palate development. Numerous transcription factors and signaling pathways are now recognized as either anterior- (e.g., Msx1, Bmp4, Bmp2, Shh, Spry2, Fgf10, Fgf7, and Shox2) or posterior-specific (e.g., Meox2, Tbx22, and Barx1). Localized expression and function clearly highlight the importance of regional patterning and differentiation within the palate at the molecular level. Here, we review how these molecular pathways and networks regulate the anterior-posterior patterning and development of secondary palate. We hypothesize that the anterior palate acts as a signaling center in setting up development of the secondary palate.