Expression of Fgf signalling pathway related genes during palatal rugae development in the mouse

Advances in research of biological functions of Isthmin-1

Isthmin-1 (ISM1) was initially thought to be a brain secretory factor, but with the development of technical means of research and the refinement of animal models, numerous studies have shown that this molecule is expressed in multiple tissues, suggesting that it may have multiple biological functions. As a factor that regulates growth and development, ISM1 is expressed in different animals with spatial and temporal variability and can coordinate the normal development of multiple organs. Recent studies have found that under the dependence of a non-insulin pathway, ISM1 can lower blood glucose, inhibit insulin-regulated lipid synthesis, promote protein synthesis, and affect the body's glucolipid and protein metabolism. In addition, ISM1 plays an important role in cancer development by promoting apoptosis and anti-angiogenesis, and by regulating multiple inflammatory pathways to influence the body's immune response. The purpose of this paper is to summarize relevant research results from recent years and to describe the key features of the biological functions of ISM1. We aimed to provide a theoretical basis for the study of ISM1 related diseases, and potential therapeutic strategies. The main biological functions of ISM1. Current studies on the biological functions of ISM1 focus on growth and development, metabolism, and anticancer treatment. During embryonic development, ISM1 is dynamically expressed in the zebrafish, African clawed frog, chick, mouse, and human, is associated with craniofacial malformations, abnormal heart localization, and hematopoietic dysfunction. ISM1 plays an important role in regulating glucose metabolism, lipid metabolism, and protein metabolism in the body. ISM1 affects cancer development by regulating cellular autophagy, angiogenesis, and the immune microenvironment.

Cleft Palate in Apert Syndrome

Apert syndrome is a rare genetic disorder characterized by craniosynostosis, midface retrusion, and limb anomalies. Cleft palate occurs in a subset of Apert syndrome patients. Although the genetic causes underlying Apert syndrome have been identified, the downstream signaling pathways and cellular mechanisms responsible for cleft palate are still elusive. To find clues for the pathogenic mechanisms of palatal defects in Apert syndrome, we review the clinical characteristics of the palate in cases of Apert syndrome, the palatal phenotypes in mouse models, and the potential signaling mechanisms involved in palatal defects. In Apert syndrome patients, cleft of the soft palate is more frequent than of the hard palate. The length of the hard palate is decreased. Cleft palate is associated most commonly with the S252W variant of FGFR2. In addition to cleft palate, high-arched palate, lateral palatal swelling, or bifid uvula are common in Apert syndrome patients. Mouse models of Apert syndrome display palatal defects, providing valuable tools to understand the underlying mechanisms. The mutations in FGFR2 causing Apert syndrome may change a signaling network in epithelial–mesenchymal interactions during palatogenesis. Understanding the pathogenic mechanisms of palatal defects in Apert syndrome may shed light on potential novel therapeutic solutions.

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.

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.

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.

DNA hypermethylation of Fgf16 and Tbx22 associated with cleft palate during palatal fusion

OBJECTIVE

Cleft palate (CP) is a congenital birth defect caused by the failure of palatal fusion. Little is known about the potential role of DNA methylation in the pathogenesis of CP. This study aimed to explore the potential role of DNA methylation in the mechanism of CP.

METHODOLOGY

We established an all-trans retinoic acid (ATRA)-induced CP model in C57BL/6J mice and used methylation-dependent restriction enzymes (MethylRAD, FspEI) combined with high-throughput sequencing (HiSeq X Ten) to compare genome-wide DNA methylation profiles of embryonic mouse palatal tissues, between embryos from ATRA-treated vs. untreated mice, at embryonic gestation day 14.5 (E14.5) (n=3 per group). To confirm differentially methylated levels of susceptible genes, real-time quantitative PCR (qPCR) was used to correlate expression of differentially methylated genes related to CP.

RESULTS

We identified 196 differentially methylated genes, including 17,298 differentially methylated CCGG sites between ATRA-treated vs. untreated embryonic mouse palatal tissues (P<0.05, log2FC>1). The CP-related genes Fgf16 (P=0.008, log2FC=1.13) and Tbx22 (P=0.011, log2FC=1.64,) were hypermethylated. Analysis of Fgf16 and Tbx22, using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG), identified 3 GO terms and 1 KEGG pathway functionally related to palatal fusion. The qPCR showed that changes in expression level negatively correlated with methylation levels.

CONCLUSIONS

Taken together, these results suggest that hypermethylation of Fgf16 and Tbx22 is associated with decreased gene expression, which might be responsible for developmental failure of palatal fusion, eventually resulting in the formation of CP.

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.

Evolutionary aspects of the development of teeth and baleen in the bowhead whale

In utero, baleen whales initiate the development of several dozens of teeth in upper and lower jaws. These tooth germs reach the bell stage and are sometimes mineralized, but toward the end of prenatal life they are resorbed and no trace remains after birth. Around the time that the germs disappear, the keratinous baleen plates start to form in the upper jaw, and these form the food-collecting mechanism. Baleen whale ancestors had two generations of teeth and never developed baleen, and the prenatal teeth of modern fetuses are usually interpreted as an evolutionary leftover. We investigated the development of teeth and baleen in bowhead whale fetuses using histological and immunohistochemical evidence. We found that upper and lower dentition initially follow similar developmental pathways. As development proceeds, upper and lower tooth germs diverge developmentally. Lower tooth germs differ along the length of the jaw, reminiscent of a heterodont dentition of cetacean ancestors, and lingual processes of the dental lamina represent initiation of tooth bud formation of replacement teeth. Upper tooth germs remain homodont and there is no evidence of a secondary dentition. After these germs disappear, the oral epithelium thickens to form the baleen plates, and the protein FGF-4 displays a signaling pattern reminiscent of baleen plates. In laboratory mammals, FGF-4 is not involved in the formation of hair or palatal rugae, but it is involved in tooth development. This leads us to propose that the signaling cascade that forms teeth in most mammals has been exapted to be involved in baleen plate ontogeny in mysticetes.

Systematic analysis of copy number variants of a large cohort of orofacial cleft patients identifies candidate genes for orofacial clefts

Orofacial clefts (OFCs) represent a large fraction of human birth defects and are one of the most common phenotypes affected by large copy number variants (CNVs). Due to the limited number of CNV patients in individual centers, CNV analyses of a large number of OFC patients are challenging. The present study analyzed 249 genomic deletions and 226 duplications from a cohort of 312 OFC patients reported in two publicly accessible databases of chromosome imbalance and phenotype in humans, DECIPHER and ECARUCA. Genomic regions deleted or duplicated in multiple patients were identified, and genes in these overlapping CNVs were prioritized based on the number of genes encompassed by the region and gene expression in embryonic mouse palate. Our analyses of these overlapping CNVs identified two genes known to be causative for human OFCs, SATB2 and MEIS2, and 12 genes (DGCR6, FGF2, FRZB, LETM1, MAPK3, SPRY1, THBS1, TSHZ1, TTC28, TULP4, WHSC1, WHSC2) that are associated with OFC or orofacial development. Additionally, we report 34 deleted and 24 duplicated genes that have not previously been associated with OFCs but are associated with the BMP, MAPK and RAC1 pathways. Statistical analyses show that the high number of overlapping CNVs is not due to random occurrence. The identified genes are not located in highly variable genomic regions in healthy populations and are significantly enriched for genes that are involved in orofacial development. In summary, we report a CNV analysis pipeline of a large cohort of OFC patients and identify novel candidate OFC genes.

Gingiva as a source of stem cells with therapeutic potential

Postnatal connective tissues contain phenotypically heterogeneous cells populations that include distinct fibroblast subpopulations, pericytes, myofibroblasts, fibrocytes, and tissue-specific mesenchymal stem cells (MSCs). These cells play key roles in tissue development, maintenance, and repair and contribute to various pathologies. Depending on the origin of tissue, connective tissue cells, including MSCs, have different phenotypes. Understanding the identity and specific functions of these distinct tissue-specific cell populations may allow researchers to develop better treatment modalities for tissue regeneration and find novel approaches to prevent pathological conditions. Interestingly, MSCs from adult oral mucosal gingiva possess distinct characteristics, including neural crest origin, multipotent differentiation capacity, fetal-like phenotype, and potent immunomodulatory properties. These characteristics and an easy, relatively noninvasive access to gingival tissue, and fast tissue regeneration after tissue biopsy make gingiva an attractive target for cell isolation for therapeutic purposes aiming to promote tissue regeneration and fast, scar-free wound healing. The purpose of this review is to discuss the identity, phenotypical heterogeneity, and function of gingival MSCs and summarize what is currently known about their properties, role in scar-free healing, and their future therapeutic potential.

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.

Cleft Lip and Palate in a Patient with 5q35.2-q35.3 Microdeletion: The Importance of Chromosomal Microarray Testing in the Craniofacial Clinic

We report on a 3½-year-old African American female with a 1.63 Mb microdeletion in 5q35.2-q35.3. This deletion includes NSD1, the gene that causes Sotos syndrome. The patient has unilateral cleft lip and palate (CLP) status postrepair, an unrepaired alveolar cleft, speech delay, global developmental delay, macrocephaly, mild cerebral palsy, and a patent ductus arteriosus status postrepair. Dysmorphic features include a prominent forehead and midface hypoplasia. This is one of the first cases of CLP associated with Sotos syndrome and emphasizes the utility of chromosomal microarray analysis in patients with more than isolated CLP in the Craniofacial Clinic.

Involvement of FGF9/16/20 subfamily in female germ cell development of the Nile tilapia, Oreochromis niloticus

Fibroblast growth factors (FGFs) have been proved to participate in a wide variety of processes, including growth, differentiation, cell proliferation, migration, sex determination and sex differentiation. The roles of FGF9/16/20 subfamily members in the gonadal development of teleost fish have not yet been reported. Three FGFs (16, 20a and 20b) of the FGF9/16/20 subfamily were cloned from the Nile tilapia by RT-PCR and RACE. Phylogenetic, bioinformatic and syntenic analyses demonstrated that these cloned FGFs are genuine FGF16, 20a and 20b. Our analyses further supported the non-existence of FGF9 ortholog and the existence of two FGF20 paralogs in teleost genomes. Tissue distribution analysis by RT-PCR demonstrated that FGF16 was expressed in a wide range of tissues including the testis and ovary, FGF20b in the brain, pituitary, intestine and ovary, but not in the testis, while FGF20a in the brain, pituitary and spleen, but not in the gonad. These results were consistent with the Northern blot analysis. The expression profiles of FGF16 and FGF20b during normal and sex reversed gonadal development were investigated by real-time PCR. Both showed much higher expression in the XX ovary and 17 beta-estradiol induced XY ovary compared with the XY testis and fadrozole and tamoxifen induced XX testis, with the highest in both sexes at 120 dah. Strong signals of FGF16 and FGF20b were detected in phase II oocytes by in situ hybridization. These data suggest that FGF9/16/20 subfamily is involved in the early oocyte development of the female.

Periodic stripe formation by a Turing mechanism operating at growth zones in the mammalian palate

We present direct evidence of an activator-inhibitor system in the generation of the regularly spaced transverse ridges of the palate. We show that new ridges, or rugae, marked by stripes of Sonic hedgehog (Shh) expression, appear at two growth zones where the space between previously laid-down rugae increases. However, inter-rugal growth is not absolutely required: new stripes still appear when growth is inhibited. Furthermore, when a ruga is excised new Shh expression appears, not at the cut edge but as bifurcating stripes branching from the neighbouring Shh stripe, diagnostic of a Turing-type reaction-diffusion mechanism. Genetic and inhibitor experiments identify Fibroblast Growth Factor (FGF) and Shh as an activator-inhibitor pair in this system. These findings demonstrate a reaction-diffusion mechanism likely to be widely relevant in vertebrate development.