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Arl4c is involved in tooth germ development through osteoblastic differentiation

ABSTRACT: Murine tooth germ development proceeds in continuous and sequential steps with reciprocal interactions between the odontogenic epithelium and the adjacent mesenchyme, and several growth factor signaling and their activation are required for tooth germ development. The expression of ADP-ribosylation factor (Arf)-like 4c (Arl4c) has been shown to induce cell proliferation, thereby involving in epithelial morphogenesis and tumorigenesis. However, other functions of Arl4c except for cellular growth are largely unknown. Although we recently demonstrated the involvement of the upregulated expression of Arl4c in cell proliferation of ameloblastoma, which has the same origin as odontogenic epithelium, its effect on tooth germ development remains unclear. Herein, single-cell RNA sequencing (scRNA-seq) analysis revealed that the expression of Arl4c, among 17 members of the Arf-family members, was specifically detected in odontogenic epithelial cells, such as stratum intermedium, stella reticulum and outer enamel epithelium, of postnatal day 1 (P1) mouse molar. In addition, scRNA-seq analysis showed higher expression of Arl4c in non-ameloblast and inner enamel epithelium, which include immature cells. In the mouse tooth germ rudiments culture, treatment with SecinH3 (an inhibitor of ARNO/Arf6 pathway) reduced the size, width and cusp height and the thickness of eosinophilic layer, which would involve the synthesis of dentin and enamel matrix organization. In addition, loss-of-function experiments using siRNAs and shRNA revealed that Arl4c expression was involved in cell proliferation and osteoblastic cytodifferentiation in odontogenic epithelial cells. Finally, RNA-seq analysis with gene set enrichment analyses (GSEA) and Gene Ontology (GO) analysis showed that osteoblastic differentiation-related gene set and/or GO terms were downregulated in shArl4c expressing odontogenic epithelial cells. These results suggest that the Arl4c-ARNO/Arf6 pathway axis contributes to tooth germ development through osteoblastic differentiation.

ORGANISM(S): Mus musculus

PROVIDER: GSE235460 | GEO | 2023/07/01

REPOSITORIES: GEO

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Project description:The tooth is a convenient experimental model for the study of the basic mechanisms of organ development, including differentiation, cellular interaction, morphogenesis, and production and mineralization of extracellular matrices. The rodent incisor teeth grow continuously and exhibit all stages of tooth development at any time. This characteristic makes them convenient models for the study of enamel formation, which occurs in several distinct stages along the tooth axis. The distribution and structure of mouse incisor enamel resemble that of the rat. The enamel covers only the labial aspect of the tooth, and can be divided into four layers: a thin inner prism-free layer, inner enamel with prism decussation, i.e. transverse rows of prisms with prisms inclined medially and laterally in alternate rows, outer enamel with parallel prisms inclined incisally and a thin superficial prism-free layer. Recently, we have described how this elaborate organization of the enamel is established in the initial enamel formed on the unerupted and unworn incisal tip of the incisors. The very first enamel formed, i.e. the most incisally situated enamel, is always prism-free, corresponding to the superficial layer in fully established enamel, although thicker. Going in apical direction, i.e. in the direction of initiation of new enamel formation, isolated prisms appear among the crystals continuous with the prism-free zone crystals. These initial prisms are in general inclined incisally, corresponding to the prisms in the outer enamel layer in the fully established enamel. Inner enamel with the characteristic decussation pattern is added somewhat further apically and increases in thickness with increasing enamel thickness. Based on the structure of the enamel that they produce, the ameloblasts producing the initial, thin, prism-free enamel at the incisal tip of the unworn mouse incisor are probably differently configured (e.g. lacking Tomes' processes), probably differently organized (e.g. not organized in transverse rows moving sideways in opposite directions), and probably have a shorter life-span than the more apically situated ameloblasts which produce thicker enamel with the full four-layered configuration of mouse incisor enamel. For this reason it would be of interest to compare the gene expression profile of the incisal tip segment where prism-free enamel is being formed with the profile of the immediately adjacent segment where enamel with all four layers is being formed. As long as the incisor is unworn enamel formation and gene expression in these segments will likely reflect mechanistic differences between these segments as regards enamel biosynthesis. MicroRNAs (miRNA) are a class of non-coding RNAs that regulate gene expression at a post-transcriptional level, and are considered as important regulatory molecules during foetal development. By binding to target mRNA, miRNA induce mRNA decay or translation repression. Recent bioinformatic predictions of miRNA targets in vertebrates indicate that hundreds of miRNAs are responsible for regulating the expression of up to 30% of the human protein-coding genes, and miRNAs have recently also been shown to regulate expression of hundreds of mRNAs in cultured cells. Recently, miRNA expression profiles of the developing murine molar tooth germ and submandibular salivary gland have been established. We here report expression profiling of miRNAs present in the two adjacent segments of the incisor tooth germ on which we also have carried out mRNA expression profiling. The results suggest that also miRNAs are abundantly, and differentially, expressed during development of the incisor tooth germ in mouse. By analogy with the mRNA data also miRNA expression is dynamic, with respect to both the two incisor segments investigated and to the developmental stage of the incisor.

Project description:Embryologically the tooth is derived from both the ectoderm and neural crest (ectomesenchyme). It is often used as a model to study how epithelialmesenchymal interactions can control differentiation and morphogenesis. During early development organs of ectodermal origin share both a set of signalling molecules and exhibit common morphological features, subsequently proceeding along separate developmental programs. Tooth development is a continuous process that can be divided into the initiation -, bud -, cap -, and bell-stages. In mice, tooth development begins at embryonic day 11.5 (E11.5), by thickening of the dental epithelium, while mineralization of enamel and dentin in first molar starts at postnatal day 0 (P0) (5). A multistep and complex process of the gene expression are involved in the early stage of tooth development. So far expression of more than 1300 genes and/or proteins have been detected during tooth germ development by microarrays/immunocytochemistry/in situ hybridization. Studies with mutant mice have identified a number of genes that regulate tooth development and morphology. For example, deficiency of Lef-1 or P63 arrests tooth development at early stages. Deficiency of Msx1 or Pax9 results in arrest of tooth development at the bud stage , while deficiency of Runx2/Cbfa1 or Sp3 inhibits cyto-differentiation of ameloblasts and/or odontoblasts. Shh is required for normal growth and morphogenesis, but is not essential for cyto-differentiation of the ameloblast and odontoblast populations. Ameloblastin and amelogenin knock-out mice develop severe enamel hypoplasia with abnormal ameloblast differentiation. Recently, new connections between retinoid metabolism and PPAR responses have been identified. It has also been shown that endogenous retinoic acid is necessary for the initiation of odontogenesis , and that some of the genes that catalyze the oxidation of retinaldehyde into retinoic acid, exhibit distinct patterns of expression in developing murine teeth. Little is known about functions of PPAR-a as regards tooth germs or mature teeth. It is, however, likely that mitochondrial oxidative metabolism well as fatty acid metabolism is enhanced in late odontogenesis. These are metabolic activities which in other tissues are stimulated by PPAR-a agonists. For this reason it was of interest to carry out comparative gene expression profiling of the first molar tooth germs of PPAR-a knock-out mouse and of the corresponding wild-type mice. The results suggest marked differences in gene expression, parts of which may be associated with an observed hypomineralization of enamel in the mature PPAR-a knock-out murine tooth.

Project description:Previous studies have suggested that Bmp4 is a key Msx1-dependent mesenchymal odontogenic signal for driving tooth morphogenesis through the bud-to-cap transition. Whereas the bud stage tooth developmental arrest in Msx1-/- mutant mice was accompanied by reduction in mesenchymal Bmp4 mRNA expression, we show that depleting functional Bmp4 mRNAs in the tooth mesenchyme, through neural crest-specific gene inactivation in Bmp4f/f;Wnt1Cre mice, caused mandibular molar developmental arrest at the bud stage but allowed maxillary molars and incisors to develop to mineralized teeth. We show that the Wnt inhibitors Dkk2 and Wif1 were much more abundantly expressed in the mandibular than maxillary molar mesenchyme in wildtype embryos and that Dkk2 expression was significantly unregulated in the tooth mesenchyme in Bmp4f/f;Wnt1Cre embryos. In addition, expression of Osr2, which encodes a zinc finger protein that antagonizes Msx1-mediated activation of odontogenic mesenchyme, is significantly upregulated in the molar mesenchyme in Bmp4f/f;Wnt1Cre embryos. Msx1 heterozygosity enhanced maxillary molar developmental defects whereas Osr2 heterozygosity rescued mandibular first molar morphogenesis in Bmp4f/f;Wnt1Cre mice. Moreover, in contrast to complete lack of supernumerary tooth initiation in Msx1-/-Osr2-/- mutant mice, Osr2-/-Bmp4f/f;Wnt1Cre compound mutant mice exhibit formation and subsequent arrest of supernumerary tooth germs that correlated with down regulation of Msx1 expression in the tooth mesenchyme. Taken together, our data indicate that, while reduction in mesenchymal Bmp4 expression alone could not account for the tooth bud arrest phenotype in Msx1-/- mutant mice, Bmp4 signaling synergizes with Msx1 and antagonizes Osr2 to activate mesenchymal odontogenic activity to drive tooth morphogenesis and sequential tooth formation. E13.5 mouse embryos tooth germs were microdissected by laser capture microdissection (LCM), and the mandibular molar and maxillary molar were separated. 3 pairs of control and mutant samples were pooled for the RNA extraction.

Project description:Odontogenic tumors (OGTs), which originate from cells of odontogenic apparatus and their remnants, are rare entities. Primary intraosseous carcinoma, NOS (PIOC), is one of the OGTs, but it is even rarer and has a worse prognosis. The characteristics of PIOC, especially in immunohistochemical features and its pathogenesis, remain unclear. We characterized a case of PIOC arising from the left mandible, in which histopathological findings showed a transition between the odontogenic keratocyst and the carcinoma. The tumorous lesion of this PIOC exhibited malignant potentials with an invasive growth of carcinoma cells into the bone tissue, an elevated Ki-67 index, and lower signal for CK13 and higher signal for CK17 compared with the non-tumor region, histopathologically and immunohistopathologically. Further immunohistochemical analyses demonstrated increased expression of ADP-ribosylation factor (ARF)-like 4c (ARL4C) (accompanying expression of β-catenin in the nucleus) and yes-associated protein (YAP) in the tumorous lesion. On the other hand, YAP was expressed and the expression of ARL4C was hardly detected in the non-tumor region. In addition, quantitative RT-PCR analysis using RNAs and dot blot analysis using genomic DNA showed the activation of Wnt/β-catenin signaling and epigenetic alterations, such as an increase of 5mC levels and a decrease of 5hmC levels, in the tumorous lesion. A DNA microarray and gene ontology analysis demonstrated that numerous gene expression variations and signal activation, including Notch signaling, were altered in non-tumor and tumor lesions within this PIOC. Experiments with the GSK-3 inhibitor revealed that β-catenin pathway increased not only mRNA levels of ankyrin repeat domain1 (ANKRD1) but also protein levels of YAP and TAZ in oral squamous cell carcinoma cell lines. These results suggested that further activation of YAP signaling by Wnt/β-catenin signaling may be associated with the development of PIOC arising from odontogenic keratocyst in which YAP signaling is activated.

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Arl4c is involved in tooth germ development through osteoblastic differentiation

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