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AmeloD regulates cell proliferation and differentiation process of ameloblasts through modulation of Sonic hedgehog (Shh) signaling pathway

ABSTRACT: Tooth morphogenesis is regulated by various molecules, with the enamel knot playing a particularly important role as a signaling center during early development. AmeloD, a basic-helix-loop-helix transcription factor, is expressed in the enamel knot. Cell proliferation was suppressed in AmeloD-overexpressing SF2 cells, consistent with its function in the cell proliferation arrest region of the enamel knot. RNA sequencing analysis also revealed decreased expression of proliferation-related molecules, such as Mki67, in AmeloD-overexpressing cells. Shh is also known to be expressed in the enamel knot, and AmeloD-overexpressing cells showed increased expression of ameloblastin and Sox21 upon shh stimulation. Indeed, AmeloD-deficient mice exhibited reduced tooth cusp distance, reduced mesio-distal and buccal-lingual tooth diameters, and enamel hypoplasia. To clarify how AmeloD functions in cells, we used a yeast two-hybrid system to identify AmeloD-binding proteins. Odam, Selenof, Kct2, and TCF4 were identified as AmeloD-binding molecules. AmeloD and Odam were expressed in similar regions in mouse postnatal day 1 molar tooth germs, and their expression was confirmed in SF2 cells. To clarify the mechanism by which Odam regulates AmeloD, we transfected AmeloD-overexpressing cells with the Odam gene, and found that AmeloD-mediated cell growth inhibition was reversed. Furthermore, cell scratch assays showed enhanced migration, which was suppressed by overexpression of AmeloD. These results suggest that AmeloD enhances cell arrest at the enamel knot and the stimulation of Shh signaling, and that Odam binds to AmeloD, regulating AmeloD function through these interactions.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE305871 | GEO | 2025/08/26

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.

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AmeloD regulates cell proliferation and differentiation process of ameloblasts through modulation of Sonic hedgehog (Shh) signaling pathway

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